Outbreak of Invasive Serratia marcescens among Persons Incarcerated in a State Prison, California, USA, March 2020-December 2022

Serratia marcescens is an environmental gram-negative bacterium that causes invasive disease in rare cases. During 2020-2022, an outbreak of 21 invasive Serratia infections occurred in a prison in California, USA. Most (95%) patients had a history of recent injection drug use (IDU). We performed whole-genome sequencing and found isolates from 8 patients and 2 pieces of IDU equipment were closely related. We also identified social interactions among patients. We recovered S. marcescens from multiple environmental samples throughout the prison, including personal containers storing Cell Block 64 (CB64), a quaternary ammonium disinfectant solution. CB64 preparation and storage conditions were suboptimal for S. marcescens disinfection. The outbreak was likely caused by contaminated CB64 and propagated by shared IDU equipment and social connections. Ensuring appropriate preparation, storage, and availability of disinfectants and enacting interventions to counteract disease spread through IDU can reduce risks for invasive Serratia infections in California prisons.

Large Community Outbreak of Legionnaires Disease Potentially Associated with a Cooling Tower - Napa County, California, 2022

Legionnaires disease is a serious infection acquired by inhalation of water droplets from human-made building water systems that contain Legionella bacteria. On July 11 and 12, 2022, Napa County Public Health (NCPH) in California received reports of three positive urinary antigen tests for Legionella pneumophila serogroup 1 in the town of Napa. By July 21, six Legionnaires disease cases had been confirmed among Napa County residents, compared with a baseline of one or two cases per year. NCPH requested assistance from the California Department of Public Health (CDPH) and CDC to aid in the investigations. Close temporal and geospatial clustering permitted a focused environmental sampling strategy of high-risk facilities which, coupled with whole genome sequencing results from samples and investigation of water system maintenance, facilitated potential linking of the outbreak with an environmental source. NCPH, with technical support from CDC and CDPH, instructed and monitored remediation practices for all environmental locations that tested positive for Legionella. The investigation response to this community outbreak illustrates the importance of interdisciplinary collaboration by public health agencies, laboratory support, timely communication with the public, and cooperation of managers of potentially implicated water systems. Timely identification of possible sources, sampling, and remediation of any facility testing positive for Legionella is crucial to interrupting further transmission.

Noncanonical Relationship between Heterogeneity and the Stokes-Einstein Breakdown in Deep Eutectic Solvents

The relationship between Stokes-Einstein breakdown (SEB) and dynamical heterogeneity (DH) is of paramount importance in the physical chemistry of complex fluids. In this work, we employ neutron scattering to probe the DH and SEB in a series of deep eutectic solvents (DESs) composed of acetamide and lithium salts. Quasielastic neutron scattering experiments reveal SEB in the jump diffusion of acetamide, represented by a fractional Stokes-Einstein relationship. Among these DESs, lithium perchlorate exhibits the most pronounced SEB while lithium bromide displays the weakest. Concurrently, elastic incoherent neutron scans identify that bromide DES is the most heterogeneous and perchlorate is the least. For the first time, our study unveils a counterintuitive incommensurate relationship between DH and SEB. Further, it reveals the intricate contrasting nature of the SEB-DH relationship when investigated in proximity to the glass-transition temperature and further away from it.

Serratia marcescens Outbreak at a Correctional Facility: Environmental Sampling, Laboratory Analyses and Genomic Characterization to Assess Sources and Persistence

Serratia marcescens is an environmental bacterium and clinical pathogen that can cause an array of infections. We describe an environmental sampling and comparative genomics approach used to investigate a multi-year outbreak of S. marcescens at a correctional facility. Whole genome sequencing analysis revealed a predominant cluster of clonally related S. marcescens from nine patient cases and items associated with illicit drug use. Closely related strains found among items associated with case-patient cells and diluted Cell Block 64 (CB64), a quaternary ammonium disinfectant, and Break Out (BO), a multipurpose cleaner, highlighted their role as environmental reservoirs for S. marcescens in this outbreak. Comparative genomic analysis suggested outbreak strains were both persistent (identical strains found over long periods and in multiple locations of the correctional facility) and diverse (strains clustered with multiple global samples from NCBI database). No correlation was found between antimicrobial resistance (AMR) genes of outbreak strains; NCBI strains have more AMR genes. Principal component analysis (PCA) of virulence factors associated with persistence and infectivity indicated variation based on phylogroups, including the predominant cluster; identifiable variations among environmental versus clinical strains were not observed. Identification of multiple distinct genetic groups highlights the importance of putting epidemiological genomic studies in a proper genetic context.

Discovery of a novel sub-lineage of multi-drug resistant Shigella flexneri in Southern California

Clustered outbreaks of multi-drug resistant (MDR) Shigella are on the rise among men who have sex with men (MSM). Identification of MDR sub-lineages is critical for clinical management and public health interventions. Here, we describe a novel MDR sub-lineage of Shigella flexneri isolated from an MSM patient without travel history in Southern California. Detailed genomic characterization of this novel strain would serve as a reference to aid monitoring and future outbreak investigation of MDR Shigella among MSM.

Salmonella Subpopulations Identified from Human Specimens Express Heterogenous Phenotypes That Are Relevant to Clinical Diagnosis

Clonal bacterial cells can give rise to functionally heterogeneous subpopulations. This diversification is considered an adaptation strategy that has been demonstrated for several bacterial species, including Salmonella enterica serovar Typhimurium. In previous studies on mouse models infected orally with pure Salmonella cultures, derived bacterial cells collected from animal tissues were found to express heterogenous phenotypes. Here, we show mixed Salmonella populations, apparently derived from the same progenitor, present in human specimens collected at a single disease time point, and in a long-term-infected patient, these Salmonella were no longer expressing surface-exposed antigen epitopes by isolates collected at earlier days of the disease. The subpopulations express different phenotypes related to cell surface antigen expression, motility, biofilm formation, biochemical metabolism, and antibiotic resistance, which can all contribute to pathogenicity. Some of the phenotypes correlate with single nucleotide polymorphisms or other sequence changes in bacterial genomes. These genetic variations can alter synthesis of cell membrane-associated molecules such as lipopolysaccharides and lipoproteins, leading to changes in bacterial surface structure and function. This study demonstrates the limitation of Salmonella diagnostic methods that are based on a single-cell population which may not represent the heterogenous bacterial community in infected humans. IMPORTANCE In animal model systems, heterogenous Salmonella phenotypes were found previously to regulate bacterial infections. We describe in this communication that different Salmonella phenotypes also exist in infected humans at a single disease time point and that their phenotypic and molecular traits are associated with different aspects of pathogenicity. Notably, variation in genes encoding antibiotic resistance and two-component systems were observed from the subpopulations of a patient suffering from persistent salmonellosis. Therefore, clinical and public health interventions of the disease that are based on diagnosis of a single-cell population may miss other subpopulations that can cause residual human infections.

179. Identification and Whole Genome Sequencing Analysis of an Oxacillinase (OXA)-48-like-producing Acinetobacter baumannii Outbreak in California, January-May 2021

Background

In January 2021, a California acute care hospital (ACH A), a sentinel site for Acinetobacter baumannii (AB) surveillance, identified OXA-48-like-carbapenemase producing (CP) AB in a patient admitted from a ventilator-equipped skilled nursing facility (vSNF A); OXA-48-like AB had not been previously reported in the United States.

Methods

Our investigation included onsite infection control (IC) assessments, contact tracing, and point prevalence surveys (PPS) at vSNF A. The Antibiotic Resistance (AR) Laboratory Network performed carbapenemase testing on AB isolates (including those from ACH A) and PPS swabs. A case was defined as a patient with an OXA-48-like AB isolate, or an epidemiologically-linked patient with an OXA-48-like gene detected via screening. We performed whole genome sequencing (WGS) of OXA-48-like AB and other CP organisms on the Illumina MiSeq and Oxford Nanopore MinION for short and long read sequencing, respectively.

Results

Since January 2021, we have identified five OXA-48-like AB cases (including the index), six OXA-48-like cases (no organism recovered), and six patients with other CP organisms at ACH A and vSNF A. Since August 2019, vSNF A has concurrently been experiencing an OXA-109 AB outbreak. A second vSNF A patient, Patient 2, who overlapped with the index patient, had OXA-48-like Klebsiella pneumoniae (KP) (November 2019) and OXA-109 AB (May 2020) isolates. WGS of the index patient’s AB and Patient 2’s KP isolates identified a rare OXA-48-like gene located on the AB chromosome and a KP plasmid. The OXA-48-like AB was also carrying an OXA-109 gene, and hqSNP analysis indicated it varied by 9-44 single-nucleotide polymorphisms (SNPs) from 14 OXA-109 AB isolates linked to that outbreak, and 0-3 SNPs from the other OXA-48-like AB case isolates.

Figure 1. Phylogenetic Tree Comparison of OXA-109 AB and OXA-48-like AB Isolates

Figure 2. Epidemic Curve of OXA-109 AB, OXA-48-like AB, and Other CP Organism Cases, 2019-2021

Conclusion

The first reported case of OXA-48-like AB in the US was identified through public health sentinel laboratory surveillance, allowing prompt response to contain spread of a novel multidrug-resistant organism (MDRO). WGS detected a rare OXA-48-like gene in AB and KP and provides evidence for possible interspecies transfer of this gene from KP to AB through plasmid transfer followed by chromosomal integration.

Disclosures

All Authors: No reported disclosures

802. Corynebacterium striatum Outbreak Among Ventilated COVID-19 Patients in an Acute Care Hospital – California, 2021

Background

Corynebacterium striatum (CS), a common human commensal colonizing the skin and nasopharynx, has been associated with nosocomial infections in immunocompromised and chronically ill patients. During the winter 2020-2021 COVID-19 surge, a 420-bed California hospital reported a marked increase in CS respiratory cultures among ventilated COVID-19 patients. We conducted a public health investigation to assess and mitigate nosocomial transmission and contributing infection prevention and control (IPC) practices.

Methods

A case was defined as a patient with CS in respiratory cultures from January 1, 2020 - February 28, 2021. We reviewed clinical characteristics on a subset of cases in 2021 and IPC practices in affected hospital locations. CS respiratory isolates collected on different dates and locations were assessed for relatedness by whole genome sequencing (WGS) on MiSeq.

Results

Eighty-three cases were identified, including 75 among COVID-19 patients (Figure 1). Among 62 patients identified in 2021, all were ventilated; 58 also had COVID-19, including 4 cases identified on point prevalence survey (PPS). The median time from admission to CS culture was 19 days (range, 0-60). Patients were critically ill; often it was unclear whether CS cultures represented colonization or infection. During the COVID-19 surge, two hospital wings (7W and 7S) were converted to negative-pressure COVID-19 units. Staff donned and doffed personal protective equipment in anterooms outside the units; extended use of gowns was practiced, and lapses in glove changes and hand hygiene (HH) between patients likely occurred. In response to the CS outbreak, patients were placed in Contact precautions and cohorted. Staff were re-educated on IPC for COVID-19 patients. Gowns were changed between CS patients. Subsequent PPS were negative. Two CS clusters were identified by WGS: cluster 1 (5 cases) in unit 7W, and cluster 2 (2 cases) in unit 7S (Figure 2).

Figure 1. Corynebacterium striatum Respiratory Cultures January 2020-February 2021

Conclusion

A surge in patients, extended use of gowns and lapses in core IPC practices including HH and environmental cleaning and disinfection during the winter 2020-2021 COVID-19 surge likely contributed to this CS outbreak. WGS provides supportive evidence for nosocomial CS transmission among critically ill COVID-19 patients.

Disclosures

All Authors: No reported disclosures

Diffusion of confined fluids in microporous zeolites and clay materials

Fluids exhibit remarkable variation in their structural and dynamic properties when they are confined at the nanoscopic scale. Various factors, including geometric restriction, the size and shape of the guest molecules, the topology of the host, and guest-host interactions, are responsible for the alterations in these properties. Due to their porous structures, aluminosilicates provide a suitable host system for studying the diffusion of sorbates in confinement. Zeolites and clays are two classes of the aluminosilicate family, comprising very ordered porous or layered structures. Zeolitic materials are important due to their high catalytic activity and molecular sieving properties. Guest molecules adsorbed by zeolites display many interesting features including unidimensional diffusion, non-isotropic rotation, preferred orientation and levitation effects, depending on the guest and host characteristics. These are useful for the separation of hydrocarbons which commonly exist as mixtures in nature. Similarly, clay materials have found application in catalysis, desalination, enhanced oil recovery, and isolation barriers used in radioactive waste disposal. It has been shown that the bonding interactions, level of hydration, interlayer spacing, and number of charge-balancing cations are the important factors that determine the nature of diffusion of water molecules in clays. Here, we present a review of the current status of the diffusion mechanisms of various adsorbed species in different microporous zeolites and clays, as investigated using quasielastic neutron scattering and classical molecular dynamics simulation techniques. It is impossible to write an exhaustive review of the subject matter, as it has been explored over several decades and involves many research topics. However, an effort is made to cover the relevant issues specific to the dynamics of different molecules in microporous zeolites and clay materials and to highlight a variety of interesting features that are important for both practical applications and fundamental aspects.

Foodborne Botulism Outbreak Associated With Commercial Nacho Cheese Sauce From a Gas Station Market

BACKGROUND

Botulism is a rare and potentially fatal paralytic disease caused by botulinum neurotoxin (BoNT). In April 2017, 4 California residents from 2 adjacent counties were hospitalized with suspected foodborne botulism, precipitating an investigation by state and local public health departments in California.

METHODS

We interviewed suspected botulism patients and their families, inspected the suspect establishment, and collected suspect food. We tested patient sera, stool, and gastric aspirates using mouse bioassay for BoNT and/or culture for Clostridium botulinum. We tested suspect food and environmental samples for BoNT and confirmed presumptive positives using direct mouse bioassay and culture. We performed whole-genome sequencing on food and clinical isolates.

RESULTS

From April 2017 through May 2017, 10 patients in the Sacramento area were hospitalized with laboratory-confirmed botulism; 7 required mechanical ventilation, and 1 died. Of 9 patients with information, all had visited Gas Station X before illness onset, where 8 reported consuming a commercial cheese sauce. BoNT/A and/or BoNT/A-producing C. botulinum were detected from each patient and from leftover cheese sauce. Clostridium botulinum isolates from 4 patients were closely related to cheese sauce isolates by whole-genome high-quality single-nucleotide polymorphism analysis. No other botulism cases associated with this cheese sauce were reported elsewhere in the United States.

CONCLUSIONS

This large foodborne botulism outbreak in California was caused by consumption of commercial cheese sauce dispensed at a gas station market. The epidemiologic and laboratory evidence confirmed the cheese sauce as the outbreak source. The cheese sauce was likely locally contaminated, although the mechanism is unclear.

Enhanced Microscopic Dynamics of a Liver Lipid Membrane in the Presence of an Ionic Liquid

Ionic liquids (ILs) are an important class of emerging compounds, owing to their widespread industrial applications in high-performance lubricants for food and cellulose processing, despite their toxicity to living organisms. It is believed that this toxicity is related to their actions on the cellular membrane. Hence, it is vital to understand the interaction of ILs with cell membranes. Here, we report on the effects of an imidazolium-based IL, 1-decyl-3-methylimidazolium tetrafluoroborate (DMIM[BF4]), on the microscopic dynamics of a membrane formed by liver extract lipid, using quasielastic neutron scattering (QENS). The presence of significant quasielastic broadening indicates that stochastic molecular motions of the lipids are active in the system. Two distinct molecular motions, (i) lateral motion of the lipid within the membrane leaflet and (ii) localized internal motions of the lipid, are found to contribute to the QENS broadening. While the lateral motion could be described assuming continuous diffusion, the internal motion is explained on the basis of localized translational diffusion. Incorporation of the IL into the liver lipid membrane is found to enhance the membrane dynamics by accelerating both lateral and internal motions of the lipids. This indicates that the IL induces disorder in the membrane and enhances the fluidity of lipids. This could be explained on the basis of its location in the lipid membrane. Results are compared with various other additives and we provide an indication of a possible correlation between the effects of guest molecules on the dynamics of the membrane and its location within the membrane.

Contrasting Behaviors of FA and MA Cations in APbBr3

It is known that the organic units in hybrid halide perovskites are free to rotate, but it is not clear if this freedom is of any relevance to the structure-property relationship of these compounds. We have employed quasi-elastic neutron scattering using two different spectrometers, thus providing a wide dynamic range to investigate the cation dynamics in methylammonium lead bromide (MAPbBr₃) and formamidinium lead bromide (FAPbBr₃) over a large temperature range covering all known crystallographic phases of these two compounds. Our results establish a plastic crystal-like phase forming above 30 K within the orthorhombic phase of MAPbBr₃ related to 3-fold rotations of MA units around the C-N axis with an activation energy, E_a, of ∼27 meV, which has no counterpart in the FA compound. MA exhibits an additional 4-fold orientational motion of the whole molecule via rotation of the C-N axis itself with an E_a of ∼68 meV common for the high-temperature tetragonal and cubic phases. In contrast, the FA compound exhibits only an isotropic orientational motion of the whole FA unit with E_a ≈ 106 meV within the orthorhombic phase and a substantially reduced common E_a of ∼62 meV for the high-temperature tetragonal and cubic phases. Our results suggest that the rotational dynamics of the organic units, crystallographic phases, and physical properties of these compounds are intimately connected.

Probing relaxation dynamics of a cationic lipid based non-viral carrier: a time-resolved fluorescence study

Lipid vesicles composed of cationic dioctadecyldimethylammonium bromide (DODAB) and neutral 1-monooleoyl-rac-glycerol (MO) are promising non-viral carriers of nucleic acids for delivery into cells. Among them, higher cell transfection efficiency was displayed by DODAB-rich vesicles than those enriched with MO. Structural relaxation of these mixed lipid vesicles plays a key role in their cell transfection efficiency because structural organization of the DODAB-rich vesicles are different from that of the MO-rich vesicles. Polarization-gated anisotropy in conjunction with picosecond resolved emission transients of a novel fluorophore 6-acetyl-(2-((4-hydroxycyclohexyl)(methyl)amino)naphthalene) (ACYMAN) has been employed to probe relaxation dynamics in pure DODAB vesicles, and in mixed vesicles of DODAB with varying content of MO. Both orientational relaxation of ACYMAN and relaxation dynamics of its local environment are retarded significantly in mixed lipid vesicles with increasing MO content, from a mole fraction (χ_MO) of 0.2 to that of 0.8 which is consistent with increased rigidity of the MO-rich (χ_MO > 0.5) vesicles relative to the DODAB-rich (χ_MO < 0.5) vesicles. Therefore, higher structural rigidity of the MO-rich vesicles (χ_MO > 0.5) gives rise to their lower cell transfection efficiency than the more flexible DODAB-rich (χ_MO < 0.5) vesicles as observed in previous in vivo studies (Biochim. Biophys. Acta, Biomembr., 2014, 1838, 2555–2567).

Lipid vesicles composed of cationic dioctadecyldimethylammonium bromide (DODAB) and neutral 1-monooleoyl-rac-glycerol (MO) are promising non-viral carriers of nucleic acids for delivery into cells.

1721. An Outbreak of Botulism Associated With Nacho Cheese Sauce From a Gas Station in California

Background

Foodborne botulism is rare with 0–6 cases reported annually in California. During April 24–28, 2017, 4 hospitalized patients with suspect foodborne botulism were reported to the California Department of Public Health (CDPH) from 2 adjacent California counties. In collaboration with local public and environmental health, CDPH conducted an investigation to determine the magnitude of the outbreak, identify potential sources, and implement control measures.

Methods

A case was defined as clinical botulism in a visitor to or resident of Sacramento County with illness onset during April 20 to May 5, 2017. Case-patients or their proxies were interviewed. Patient specimens and suspect food items were tested for the presence of botulinum toxin and toxin-producing Clostridium botulinum; C. botulinum isolates underwent whole genome sequencing (WGS) at the CDPH laboratory.

Results

In April–May 2017, a total of 10 patients were hospitalized with laboratory-confirmed botulism. Median age was 34 years (range 16–57); 7 were male, and 8 were Latino. All patients required intensive care, 7 required ventilator support, and 1 died. Nine patients confirmed visiting Gas Station A in the week before illness onset; 8 reported consuming nacho cheese sauce served from a dispenser there. Inspection of Gas Station A on May 5 indicated that the cheese in the dispenser had a best by date of April 11; the dispenser was removed that day, before all patients were identified. The remaining pouch of nacho cheese sauce was laboratory confirmed to have botulinum toxin type A and toxin-producing C. botulinum. C. botulinum isolates from 3 patients clustered with the cheese isolate by WGS.

Conclusion

Contaminated nacho cheese sauce served at a local gas station was the source of the largest outbreak of foodborne botulism reported to date in California. No other botulism cases associated with this commercial cheese sauce were identified elsewhere in the United States; although the mechanism of contamination is unclear, the cheese was likely contaminated locally. Intensive public health investigation and intervention, before all cases were identified and C. botulinum toxin was detected in the product, likely prevented additional cases and possible deaths

Disclosures

All authors: No reported disclosures.

Correction of Toe-Walking Gait in Children with Spastic Cerebral Palsy by using Electrical Stimulation Therapy

Toe-walking is a very common gait abnormality seen in children with Cerebral Palsy (CP). The present study aims to improvise the toe-walking gait by applying Electrical Stimulation (ES) therapy of the Tricep Surae (TS) muscles. The study was carried out on sixteen children with spastic CP with unilateral toe-walking gait problem, divided into the intervention group that received both ES therapy along with conventional physiotherapy treatment and the control group that received only conventional physiotherapy treatment. Both groups were treated for 60 (30 + 30) minutes per day, for 5 days a week, up to 12 weeks. The gait data were analyzed for spatiotemporal and parameters influencing the walking capacity. The results showed that those children who received the intervention had a significant increase in gait speed by 17.67 % (p = 0.019) and decrease in stride length by 10.25 % (p = 0.037), resulting in improvement of body balance. There was a significant percentage increase in initial contact (heel strike) of 85.71 % (p = 0.000) and flat foot position (loading response) of 49.2 % (p = 0.005), confirming reduction in toe-walking. There was also an increase in the swing power by 39.8 % (p = 0.028) and ground impact by 19.5 % (p = 0.003) suggesting a change in foot contact pattern. The results indicate that ES therapy on TS muscle along with conventional physiotherapy may correct the toe-walking gait in children with spastic hemiplegic CP.

Effects of NSAIDs on the Dynamics and Phase Behavior of DODAB Bilayers

Despite well-known side effects, nonsteroidal anti-inflammatory drugs (NSAIDs) are one of the most prescribed drugs worldwide for their anti-inflammatory and antipyretic properties. Here, we report the effects of two NSAIDs, aspirin and indomethacin, on the thermotropic phase behavior and the dynamics of a dioctadecyldimethylammonium bromide (DODAB) lipid bilayer as studied using neutron scattering techniques. Elastic fixed window scans showed that the addition of aspirin and indomethacin affects the phase behavior of a DODAB bilayer in both heating and cooling cycles. Upon heating, there is a change in the coagel- to fluid-phase transition temperature from 327 K for pure DODAB bilayer to 321 and 323 K in the presence of aspirin and indomethacin, respectively. More strikingly, upon cooling, the addition of NSAIDs suppresses the formation of the intermediate gel phase observed in pure DODAB. The suppression of the gel phase on addition of the NSAIDs evidences the synchronous ordering of a lipid headgroup and chain. Analysis of quasi-elastic neutron scattering data showed that only localized internal motion exists in the coagel phase, whereas both internal and lateral motions exist in the fluid phase. The internal motion is described by a fractional uniaxial rotational diffusion model in the coagel phase and by a localized translation diffusion model in the fluid phase. In the coagel phase, the rotational diffusion coefficient of DODAB is found to be almost twice for the addition of the drugs, whereas the mobility fraction did not change for indomethacin but becomes twice for aspirin. In the fluid phase, the lateral motion, described well by a continuous diffusion model, is found to be slower by about ∼30% for indomethacin but almost no change for aspirin. For the internal motion, addition of aspirin leads to enhancement of the internal motion, whereas indomethacin did not show significant effect. This study shows that the effect of different NSAIDs on the dynamics of the lipid membrane is not the same; hence, one must consider these NSAIDs individually while studying their action mechanism on the cell membrane.

EFFECT OF SILICA LOADING AND COUPLING AGENT ON WEAR AND FATIGUE PROPERTIES OF A TREAD COMPOUND

The effects of highly dispersible silica and the nature of silane in a tire tread cap compound were studied with particular reference to dynamic mechanical properties, abrasion resistance, side force coefficient, and fatigue crack growth (FCG) properties. The rubber matrix chosen was a blend of solution grade styrene butadiene rubber and polybutadiene rubber. Six different loadings of silica were used. Bistriethoxysilylpropyltetrasulfide (S) was taken as the coupling agent. In addition, the potential of two new generation silanes, 3-octanoylthio-1-propyltriethoxysilane (N) and 3-mercaptopropyl-di [tridecan-1-oxy-13-penta ethyleneoxideethoxysilane] (V) was also explored at 70 phr silica loading. Optimum properties were obtained at 50 phr loading of silica (S50). The tensile moduli for the compounds increased sharply with silica loading. Higher values of tan δ, indicating higher hysteresis, were obtained in compounds containing higher filler dosage. However, enhanced abrasion resistance and side force coefficient were observed at higher loadings of silica due to an increased reinforcement phenomenon. The crack growth exponent (β) was lowest for S50. Among the silanes tested, V showed a 22% drop in tan δ at 70 °C, 11% drop in abrasion loss, and an increase in FCG rate. N exhibited a lower FCG rate as compared with the silane S.

Modulation of Solvation and Molecular Recognition of a Lipid Bilayer under Dynamical Phase Transition

It is well accepted in contemporary biology that an ∼30 Å thick lipid bilayer film around living cells is a matter of life and death as the film typically delimits the environments that serve as a crucial margin. The dynamic organization of lipid molecules both across the lipid bilayer and in the lateral dimension are known to be crucial for cellular transport and molecular recognition by important biological macromolecules. Here, we study dilute (20 mM) Dioctadecyldimethylammonium bromide (DODAB) vesicles at different temperatures in aqueous dispersion with well-defined phases namely liquid crystalline, gel and subgel. The spectroscopic studies on two fluorescent probes 8-anilino-1-naphthalene sulfonic acid ammonium salt (ANS) and Coumarin 500 (C500), former in the head group region of the lipid-water interface and later located deeper in the lipid bilayer follow dynamics (solvation and fluidity) of their local environments in the vesicles. Binding of an anti-tuberculosis drug rifampicin has also been studied employing Förster resonance energy transfer (FRET) technique. The molecular insight concerning the effect of dynamical organization of the lipid molecules on the local dynamics of aqueous environments in different phases leading to molecular recognition becomes evident in our study.

Deciphering interactions of ionic liquids with biomembrane

Ionic liquids (ILs) are a special class of low-temperature (typically < 100 °C) molten salts, which have huge upsurge interest in the field of chemical synthesis, catalysis, electrochemistry, pharmacology, and biotechnology, mainly due to their highly tunable nature and exceptional properties. However, practical uses of ILs are restricted mainly due to their adverse actions on organisms. Understanding interactions of ILs with biomembrane is prerequisite to assimilate the actions of these ionic compounds on the organism. Here, we review different biophysical methods to characterize interactions between ILs and phospholipid membrane, a model biomembrane. All these studies indicate that ILs interact profoundly with the lipid bilayer and modulate the structure, microscopic dynamics, and phase behavior of the membrane, which could be the fundamental cause of the observed toxicity of ILs. Effects of ILs on the membrane are found to be strongly dependent on the lipophilicity of the IL and are found to increase with the alkyl chain length of IL. This can be correlated with the observed higher toxicity of IL with the longer alkyl chain length. These informations would be useful to tune the toxicity of IL which is required in designing environment-friendly nontoxic solvents of the so-called green chemistry for various practical applications.

Negative Differential Resistance Behavior of the Iron Storage Protein Ferritin

Realization of useful nanometer length scale devices in which metalloproteins are junction-confined in a distinct molecular arrangement for generating practical electronic signals (e.g., in bioelectronic switch configuration) is elusive till date. This is mostly due to difficulties in observing an electronically appropriate signal (i.e., reproducible and controllable), when studied under junction-assembled condition. A useful "ON"-"OFF" behavior, based on the negative differential resistance (NDR) peak characteristics in the current-voltage response curves, acquired using metal-insulator-metal (MIM) configuration, has been observed only in the case of a few proteins, namely, azurin, cytochrome c, bacteriorhodopsin, so far. The case of NDR in ferritin, an iron storage protein having a semiconducting iron core consisting of few thousands of iron atoms connected in an oxide network, has not been studied in the MIM configuration where single (or a few) molecule(s) are junction-trapped, for example, as in the case of local probe configuration of scanning probe microscopy. The present study by scanning tunneling microscopy (STM), using the naturally occurring iron-containing ferritin (human liver), as well as different iron-loaded ferritins, provides clear indication of the capability of ferritins to be NDR capable, at varying sweep conditions. As ferritin can be tailor-made in a structurally conserved manner, metal core-reconstituted ferritins, that is, Mn(III)-ferritin, Cu(II)-ferritin, and Ag-ferritin, were prepared. A correlation between the NDR peak signatures, as observed in the respective current-voltage response curves of these reconstituted ferritins, and the nature of the metal core is demonstrated. In support of our earlier proposition, here, we affirm that the ferritin protein behaves as a conductor-insulator (metal core-polypeptide shell) composite, where the overall electronic structure of the material can alter as a function of the nature of the conducting filler placed inside the insulated matrix.

Effects of ionic liquids on the nanoscopic dynamics and phase behaviour of a phosphatidylcholine membrane

Ionic liquids (ILs) are potential candidates for new antimicrobials due to their tunable antibacterial and antifungal properties that are required to keep pace with the growing challenge of bacterial resistance. To a great extent their antimicrobial actions are related to the interactions of ILs with cell membranes. Here, we report the effects of ILs on the nanoscopic dynamics and phase behaviour of a dimyristoylphosphatidylcholine (DMPC) membrane, a model cell membrane, as studied using neutron scattering techniques. Two prototypical imidazolium-based ILs 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM[BF4]) and 1-decyl-3-methylimidazolium tetrafluoroborate (DMIM[BF4]), which differ only in terms of the alkyl chain length of cations, have been used for the present study. Fixed Elastic Window Scan (FEWS) shows that the incorporation of ILs affects the phase behaviour of the phospholipid membrane significantly and the transition from a solid gel to a fluid phase shifts to lower temperature. This is found to be consistent with our differential scanning calorimetry measurements. DMIM[BF4], which has a longer alkyl chain cation, affects the phase behaviour more strongly in comparison to BMIM[BF4]. The pressure-area isotherms of the DMPC monolayer measured at the air-water interface show that in the presence of ILs, isotherms shift towards higher area-per lipid molecule. DMIM[BF4] is found to shift the isotherm to a greater extent compared to BMIM[BF4]. Quasielastic neutron scattering (QENS) data show that both ILs act as a plasticizer, which enhances the fluidity of the membrane. DMIM[BF4] is found to be a stronger plasticizing agent in comparison to BMIM[BF4] that has a cation with a shorter alkyl chain. The incorporation of DMIM[BF4] enhances not only the long range lateral motion but also the localised internal motion of the lipids. On the other hand, BMIM[BF4] acts weakly in comparison to DMIM[BF4] and mainly alters the localised internal motion of the lipids. Any subtle change in the dynamical properties of the membrane can profoundly affect the stability of the cell. Hence, the dominant effect of the IL with the longer chain length on the dynamics of the phospholipid membrane might be correlated with its cytotoxic activity. QENS data analysis has provided a quantitative description of the effects of the two imidazolium-based ILs on the dynamical and phase behaviour of the model cell membrane, which is essential for a detailed understanding of their action mechanism.

Effects of Hydrotropic Salt on the Nanoscopic Dynamics of DTAB Micelles

Effects of a hydrotropic salt, sodium salicylate (NaSal), on the dynamic behavior of cationic dodecyltrimethylammonium bromide (DTAB) micelles as studied using dynamic light scattering (DLS) and quasielastic neutron scattering (QENS) techniques are reported here. DLS study showed that the addition of NaSal leads to a decrease in the apparent diffusion coefficient of the whole micelle indicating micellar growth. QENS data analysis suggested that observed dynamics involves two distinct motions, lateral motion of the surfactant over the curved micellar surface and localized segmental motion of the surfactant. It is found that the addition of NaSal slows down the lateral motion of DTAB while the localized segmental motion of the DTAB chain is not affected much. An atomistic molecular dynamics (MD) simulation was performed to gain further insight into the underlying phenomena. MD simulation results are found to be consistent with the experimental observations. MD simulation revealed that location of the salicylate ions on the micellar surface and their strong electrostatic association with their oppositely charged surfactant headgroup are the major factors in slowing down the lateral motion of the DTAB molecule. In the present work, a quantitative description of the effects of NaSal on the nanoscopic dynamics of DTAB micelles and its correlation with the microstructure of the micelle is provided.

Discriminating Intercalative Effects of Threading Intercalator Nogalamycin, from Classical Intercalator Daunomycin, Using Single Molecule Atomic Force Spectroscopy

DNA threading intercalators are a unique class of intercalating agents, albeit little biophysical information is available on their intercalative actions. Herein, the intercalative effects of nogalamycin, which is a naturally-occurring DNA threading intercalator, have been investigated by high-resolution atomic force microscopy (AFM) and spectroscopy (AFS). The results have been compared with those of the well-known chemotherapeutic drug daunomycin, which is a non-threading classical intercalator bearing structural similarity to nogalamycin. A comparative AFM assessment revealed a greater increase in DNA contour length over the entire incubation period of 48 h for nogalamycin treatment, whereas the contour length increase manifested faster in case of daunomycin. The elastic response of single DNA molecules to an externally applied force was investigated by the single molecule AFS approach. Characteristic mechanical fingerprints in the overstretching behaviour clearly distinguished the nogalamycin/daunomycin-treated dsDNA from untreated dsDNA—the former appearing less elastic than the latter, and the nogalamycin-treated DNA distinguished from the daunomycin-treated DNA—the classically intercalated dsDNA appearing the least elastic. A single molecule AFS-based discrimination of threading intercalation from the classical type is being reported for the first time.

Enhancement of Lateral Diffusion in Catanionic Vesicles during Multilamellar-to-Unilamellar Transition

Catanionic vesicles are formed spontaneously by mixing cationic and anionic dispersions in aqueous solution in suitable conditions. Because of spontaneity in formation, long-term stability, and easy modulation of size and charge, they have numerous advantages over conventional lipid-based vesicles. The dynamics of such vesicles is of interest in the field of biomedicine, as they can be used to deliver drug molecules into the cell membrane. Dynamics of catanionic vesicles based on sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) have been studied using incoherent elastic and quasielastic neutron scattering (QENS) techniques. Neutron scattering experiments have been carried out on two backscattering spectrometers, IRIS and IN16B, which have different energy resolutions and energy transfer windows. An elastic fixed-window scan carried out using IN16B shows a phase transition at ∼307 K during the heating cycle, whereas on cooling the transition occurred at ∼294 K. DSC results are found to be in close agreement with the elastic scan data. This transition is ascribed to a structural rearrangement from a multilamellar to a unilamellar phase [ Andreozzi J. Phys. Chem. B 2010 , 114 , 8056 - 8060 ]. It is found that a model in which the surfactant molecules undergo both lateral and internal motions can describe the QENS data quite well. While the data from IRIS have contributions from both dynamical processes, the data from IN16B probe only lateral motions, as the internal motions are too fast for the energy window of the spectrometer. It is found that, through the transition, the fraction of surfactant molecules undergoing lateral motion increases of a factor of 2 from the multilamellar to the unilamellar phase, indicating an enhanced fluidity of the latter. The lateral motion is found to be Fickian in nature, while the internal motion has been described by a localized translational diffusion model. The results reported here could have direct interest for a number of applications, such as molecular transport, and the effect of specific drug molecules or hormones through the membrane.

Interactions of Histone Acetyltransferase p300 with the Nuclear Proteins Histone and HMGB1, As Revealed by Single Molecule Atomic Force Spectroscopy

One of the important properties of the transcriptional coactivator p300 is histone acetyltransferase (HAT) activity that enables p300 to influence chromatin action via histone modulation. p300 can exert its HAT action upon the other nuclear proteins too--one notable example being the transcription-factor-like protein HMGB1, which functions also as a cytokine, and whose accumulation in the cytoplasm, as a response to tissue damage, is triggered by its acetylation. Hitherto, no information on the structure and stability of the complexes between full-length p300 (p300FL) (300 kDa) and the histone/HMGB1 proteins are available, probably due to the presence of unstructured regions within p300FL that makes it difficult to be crystallized. Herein, we have adopted the high-resolution atomic force microscopy (AFM) approach, which allows molecularly resolved three-dimensional contour mapping of a protein molecule of any size and structure. From the off-rate and activation barrier values, obtained using single molecule dynamic force spectroscopy, the biochemical proposition of preferential binding of p300FL to histone H3, compared to the octameric histone, can be validated. Importantly, from the energy landscape of the dissociation events, a model for the p300-histone and the p300-HMGB1 dynamic complexes that HAT forms, can be proposed. The lower unbinding forces of the complexes observed in acetylating conditions, compared to those observed in non-acetylating conditions, indicate that upon acetylation, p300 tends to weakly associate, probably as an outcome of charge alterations on the histone/HMGB1 surface and/or acetylation-induced conformational changes. To our knowledge, for the first time, a single molecule level treatment of the interactions of HAT, where the full-length protein is considered, is being reported.

Allele-specific analysis of DNA replication origins in mammalian cells

The mechanisms that control the location and timing of firing of replication origins are poorly understood. Using a novel functional genomic approach based on the analysis of SNPs and indels in phased human genomes, we observe that replication asynchrony is associated with small cumulative variations in the initiation efficiency of multiple origins between the chromosome homologues, rather than with the activation of dormant origins. Allele-specific measurements demonstrate that the presence of G-quadruplex-forming sequences does not correlate with the efficiency of initiation. Sequence analysis reveals that the origins are highly enriched in sequences with profoundly asymmetric G/C and A/T nucleotide distributions and are almost completely depleted of antiparallel triplex-forming sequences. We therefore propose that although G4-forming sequences are abundant in replication origins, an asymmetry in nucleotide distribution, which increases the propensity of origins to unwind and adopt non-B DNA structure, rather than the ability to form G4, is directly associated with origin activity.

Direct Observation of Coupling between Structural Fluctuation and Ultrafast Hydration Dynamics of Fluorescent Probes in Anionic Micelles

The coupling of structural fluctuation and the dynamics of associated water molecules of biological macromolecules is vital for various biological activities. Although a number of molecular dynamics (MD) studies on proteins/DNA predicted the importance of such coupling, experimental evidence of variation of hydration dynamics with controlled structural fluctuation even in model macromolecule is sparse and raised controversies in the contemporary literature. Here, we have investigated dynamics of hydration at the surfaces of two similar anionic micelles sodium dodecyl sulfate (SDS) and sodium dodecylbenzenesulfonate (SDBS) as model macromolecules using coumarin 500 (C500) as spectroscopic probe with femtosecond to picosecond time resolution up to 20 ns time window. The constituting surfactants SDS and SDBS are structurally similar except one benzene moiety in the SDBS may offer additional rigidity to the SDBS micelles through π-stacking and added bulkiness. The structural integrity of the micelles in the aqueous medium is confirmed in dynamic light scattering (DLS) studies. A variety of studies including polarization gated fluorescence spectroscopy and quasielastic neutron scattering (QENS) have been used to confirm differential structural fluctuation of SDS and SDBS micelles. We have also employed femtosecond-resolved Förster resonance energy transfer (FRET) in order to study binding of a cationic organic ligand ethidium bromide (EtBr) salt at the micellar surfaces. The distance distribution of the donor (C500)-acceptor (EtBr) in the micellar media reveals the manifestation of the structural flexibility of the micelles. Our studies on dynamical coupling of the structural flexibility with surface hydration in the nanoscopic micellar media may find the relevance in the "master-slave" type water dynamics in biologically relevant macromolecules.

Structure and dynamics of ionic micelles: MD simulation and neutron scattering study

Fully atomistic molecular dynamics (MD) simulations have been carried out on sodium dodecyl sulfate (SDS), an anionic micelle, and three cationic (CnTAB; n = 12, 14, 16) micelles, investigating the effects of size, the form of the headgroup, and chain length. They have been used to analyze neutron scattering data. MD simulations confirm the dynamical model of global motion of the whole micelle, segmental motion (headgroup and alkyl chain), and fast torsional motion associated with the surfactants that is used to analyze the experimental data. It is found that the solvent surrounding the headgroups results in their significant mobility, which exceeds that of the tails on the nanosecond time scale. The middle of the chain is found to be least mobile, consolidating the micellar configuration. This dynamical feature is similar for all the ionic micelles investigated and therefore independent of headgroup form and charge and chain length. Diffusion constants for global and segmental motion of the different micelles are consistent with experimentally obtained values as well as known structural features. This work provides a more realistic model of micelle dynamics and offers new insight into the strongly fluctuating surface of micelles which is important in understanding micelle dispersion and related functionality, like drug delivery.

Therapeutic effects of functional electrical stimulation on motor cortex in children with spastic Cerebral Palsy

In the present study we have evaluated the electroencephalogram (EEG) signal recorded during ankle dorsal and plantar flexion in children with spastic Cerebral Palsy (CP) after Functional Electrical Stimulation (FES) of the Tibialis Anterior (TA) muscles. The intervention group had 10 children with spastic diaplegic/hemiplegic CP within the age group of 5 to 14 years of age who received both FES for 30 minutes and the conventional physiotherapy for 30 minutes a day, while the control group had 5 children who received only conventional physiotherapy for 60(30 + 30) minutes a day only. Both group were treated for 5 days a week, up to 12 weeks. The EEG data were analyzed for Peak Alpha Frequency (PAF), sensorimotor rhythm (SMR), mu wave suppression and power spectral density (PSD) of all the bands. The results showed a decrease in SMR and mu wave suppression in the intervention group as compared to the control group, indicating a positive/greater improvement in performance of motor activities. Therefore, from this study we could conclude that FES combined with conventional physiotherapy improves the motor activity in children with spastic CP.

Modified Pauwels’ intertrochanteric osteotomy in the management of nonunion of a femoral neck fracture following failed osteosynthesis

We report the outcome of 39 patients who underwent a modified Pauwels’ intertrochanteric osteotomy for nonunion of a femoral neck fracture following failed osteosynthesis. There were 31 men and eight women with a mean age of 47.2 years (34 to 59). By Pauwels’ classification, there were 11 Type II fractures and 28 Type III fractures. The mean follow-up was 7.9 years (2 to 19). In the 11 patients whose initial treatment had been osteotomy, union was achieved in nine (81.8%). In 28 patients whose initial treatment had been with a lag screw or a dynamic hip screw, union was achieved in 27 (96.4%). Limb lengths were equalised in 14 of 16 patients (87.5%) with pre-operative shortening. The mean neck-shaft angle improved significantly from 100.5° (80° to 120°) to 131.6° (120° to 155°) (p = 0.004). The mean modified Harris hip score was 85.6 points (70 to 97) and the mean modified Merle d’Aubigné score was 14.3 (11 to 18). Good to excellent functional outcomes were achieved in 32 patients (88.8%). A modified Pauwels’ intertrochanteric osteotomy is a reliable method of treating ununited fractures of the femoral neck following failed osteosynthesis: coxa vara and shortening can also simultaneously be addressed.

Cite this article: Bone Joint J 2014;96-B:1198–1201.

Allele-specific genome-wide profiling in human primary erythroblasts reveal replication program organization

We have developed a new approach to characterize allele-specific timing of DNA replication genome-wide in human primary basophilic erythroblasts. We show that the two chromosome homologs replicate at the same time in about 88% of the genome and that large structural variants are preferentially associated with asynchronous replication. We identified about 600 megabase-sized asynchronously replicated domains in two tested individuals. The longest asynchronously replicated domains are enriched in imprinted genes suggesting that structural variants and parental imprinting are two causes of replication asynchrony in the human genome. Biased chromosome X inactivation in one of the two individuals tested was another source of detectable replication asynchrony. Analysis of high-resolution TimEX profiles revealed small variations termed timing ripples, which were undetected in previous, lower resolution analyses. Timing ripples reflect highly reproducible, variations of the timing of replication in the 100 kb-range that exist within the well-characterized megabase-sized replication timing domains. These ripples correspond to clusters of origins of replication that we detected using novel nascent strands DNA profiling methods. Analysis of the distribution of replication origins revealed dramatic differences in initiation of replication frequencies during S phase and a strong association, in both synchronous and asynchronous regions, between origins of replication and three genomic features: G-quadruplexes, CpG Islands and transcription start sites. The frequency of initiation in asynchronous regions was similar in the two homologs. Asynchronous regions were richer in origins of replication than synchronous regions.

DNA replication in mammalian cells proceeds according to a distinct order. Genes that are expressed tend to replicate before genes that are not expressed. We report here that we have developed a method to measure the timing of replication of the maternal and paternal chromosomes separately. We found that the paternal and maternal chromosomes replicate at exactly the same time in the large majority of the genome and that the 12% of the genome that replicated asynchronously was enriched in imprinted genes and in structural variants. Previous experiments have shown that chromosomes could be divided into replication timing domains that are a few hundred thousand to a few megabases in size. We show here that these domains can be divided into sub-domains defined by ripples in the timing profile. These ripples corresponded to clusters of origins of replication. Finally, we show that the frequency of initiation in asynchronous regions was similar in the two homologs.

Identification of a BET family bromodomain/casein kinase II/TAF-containing complex as a regulator of mitotic condensin function

Condensin is a central regulator of mitotic genome structure with mutants showing poorly condensed chromosomes and profound segregation defects. Here, we identify NCT, a complex comprising the Nrc1 BET-family tandem bromodomain protein (SPAC631.02), casein kinase II (CKII), and several TAFs, as a regulator of condensin function. We show that NCT and condensin bind similar genomic regions but only briefly colocalize during the periods of chromosome condensation and decondensation. This pattern of NCT binding at the core centromere, the region of maximal condensin enrichment, tracks the abundance of acetylated histone H4, as regulated by the Hat1-Mis16 acetyltransferase complex and recognized by the first Nrc1 bromodomain. Strikingly, mutants in NCT or Hat1-Mis16 restore the formation of segregation-competent chromosomes in cells containing defective condensin. These results are consistent with a model where NCT targets CKII to chromatin in a cell-cycle-directed manner in order to modulate the activity of condensin during chromosome condensation and decondensation.

Dynamics of water in synthetic saponite clays: effect of trivalent ion substitution

Saponite clay belongs to the phyllosilicate family and is comprised of layers of Si(IV) tetrahedra and Al(III) or Mg(II) octahedra with definite interlayer spacing. In these systems, the trivalent ion substitutions in the tetrahedral layers lead to negative charge on the layers. Here we report the dynamics of water contained in [Si(6.97)Al(1.03)][Ni(6.00)]O(20)(OH)(4)[Na(1.03)]·28H(2)O (SAP-1) and [Si(7.13)Fe(0.86)][Ni(6.00)]O(20)(OH)(4)[Na(0.86)]·14H(2)O (SAP-2) saponite clays in the temperature range 200-310 K as studied by quasielastic neutron scattering technique. Particularly the effect of the ion substitution towards the dynamics of water is addressed here. Data analysis is carried out using the relaxing cage model. The existence of distribution in relaxation times indicated that the water molecules in saponite clay have a different local environment which leads to complex diffusion behavior. It is found that water exists in a supercooled state in the temperature range up to 235 K. However, some of the water molecules are found to be immobile in the temperature range 240-285 K. The fraction of immobile water decreases with increase in temperature. At higher temperatures, some of the water molecules in the hydration shells or those near the surface start participating in the diffusion process and at 293 K, almost all water molecules contribute to the dynamics. Diffusivity of water in both SAP-1 and SAP-2 are found to be lower in comparison to the bulk, and within the two samples of saponite clay diffusivity in SAP-1 is found to be lower compared to SAP-2; this has been explained on the basis of the charge on the tetrahedral layers and the charge balancing cations in the interlayer spacing.

Complete genome phasing of family quartet by combination of genetic, physical and population-based phasing analysis

Phased genome maps are important to understand genetic and epigenetic regulation and disease mechanisms, particularly parental imprinting defects. Phasing is also critical to assess the functional consequences of genetic variants, and to allow precise definition of haplotype blocks which is useful to understand gene-flow and genotype-phenotype association at the population level. Transmission phasing by analysis of a family quartet allows the phasing of 95% of all variants as the uniformly heterozygous positions cannot be phased. Here, we report a phasing method based on a combination of transmission analysis, physical phasing by pair-end sequencing of libraries of staggered sizes and population-based analysis. Sequencing of a healthy Caucasians quartet at 120x coverage and combination of physical and transmission phasing yielded the phased genotypes of about 99.8% of the SNPs, indels and structural variants present in the quartet, a phasing rate significantly higher than what can be achieved using any single phasing method. A false positive SNP error rate below 10*E-7 per genome and per base was obtained using a combination of filters. We provide a complete list of SNPs, indels and structural variants, an analysis of haplotype block sizes, and an analysis of the false positive and negative variant calling error rates. Improved genome phasing and family sequencing will increase the power of genome-wide sequencing as a clinical diagnosis tool and has myriad basic science applications.

Dynamics in anionic micelles: effect of phenyl ring

Micellar dynamics in sodium dodecyl benzene sulfonate (SDBS) is studied using quasi-elastic neutron scattering (QENS) technique. Results are compared with sodium dodecyl sulfate (SDS), a very similar surfactant except for the presence of a phenyl ring in SDBS. SDBS is a very important system for various industrial usages and variety of other applications. The aim here is to investigate the effect of molecular architecture of the surfactant molecule on micellar dynamics. Analysis of the QENS data showed that there exists two distinct motions in both of the micellar systems: whole micellar motion or global motion and the internal motion of the monomer within the micelles. The global diffusion associated with the whole micelle is found to be Fickian in nature. The diffusion coefficient corresponding to the global motion is found to be significantly lower for SDBS than SDS micelles. As far as internal motion is concerned, the structure factor indicates that the alkyl chains are more flexible in SDS compared with SDBS. Similar behavior is also reported in a recent molecular-dynamics simulation study. Detailed analysis showed that a localized translational diffusion model in which the hydrogen atoms undergo diffusion within a sphere could describe the internal motions in both the micelles. Diffusion coefficients corresponding to internal motions is found to be lower in the case of SDBS micelles compared with SDS micelles, implying that internal motions in SDBS micelles are relatively hindered vis-a-vis SDS micelles. This could be understood in terms of denser packing in SDBS micelles due to the presence of π-stacking.

Dynamical features in cationic micelles of varied chain length

Chain length is one of the parameters controlling the structural arrangement of micelle monomers, such that one can tailor the monomers for different applications, but the effect of chain length on the dynamical behavior of micelles is unknown. In this article, we report a study on the effect of varying chain length on the dynamical behavior of alkyltrimethylammonium bromide (C(n)TAB) micelles (n = 10, 12, 14, and 16) using incoherent quasielastic neutron scattering (QENS). The data analysis clearly shows the presence of two distinct motions: global motion of whole micelles and faster internal motions of the C(n)TAB monomers. The global diffusion is Fickian in nature, whereas the internal motions can be described with a model that considers the motions of the headgroup and the hydrophobic alkyl chain separately. Methyl groups in the headgroup undergo 3-fold jump rotations, and the hydrogen atoms belonging to the alkyl chain undergo localized translational diffusion. The hydrogen atoms belonging to the alkyl chain are confined within spherical volumes that increase linearly along the C(n)TAB chain: the hydrogen atoms closer to the headgroup move within smaller spheres with lower diffusion coefficients than those farther from the headgroup. The main result is that, with increasing chain length, the dynamics of the C(n)TAB monomer is greatly affected: diffusion is reduced and occurs in smaller spheres, and residence times are increased. Global motion is also hindered with increased chain length.

HYSTERESIS CHARACTERISTICS OF HIGH MODULUS LOW SHRINKAGE POLYESTER TIRE YARN AND CORD

Hysteresis characteristics of high modulus low shrinkage (HMLS) polyester tire yarn and cord were evaluated to determine “specific work loss,” which indicate its heat generation characteristics. Test parameters were selectively chosen, considering the service conditions of high-speed passenger radial tires in which HMLS polyester tire cords are predominantly used. Specific work loss was found to increase exponentially with the increase in extent of stress relief. Dynamic property of this yarn and cord was also studied to determine “loss tangent (tan δ),” which influences rolling resistance of tires in service. A good correlation has been found between specific work loss of hysteresis test (a slow speed test) and tan δ of dynamic test (a high-speed test). Dynamic property of polyester dipped cord was investigated for a wide range of temperatures (100–180 °C) and frequencies (5–25 Hz). Tan δ at 100 °C was found to be relatively low and its magnitude remained at the same level for a wide range of frequencies. This is a favorable condition for the high-speed passenger radial tires, made out of HMLS polyester tire yarn. Microstructure of HMLS polyester yarn was analyzed. Crystallinity is around 43% (measured by Wide angle x-ray scattering); crystal width and long period are 61 and 142 Å, respectively.

Diffusion of water in molecular magnet Cu(0.75)Mn(0.75)[Fe(CN)6]·7H2O

Here we report the dynamical behaviour of water in Prussian blue analogue (PBA) Cu(0.75)Mn(0.75)[Fe(CN)(6)]·7H(2)O molecular magnet in the temperature range 260-360 K as studied using the quasielastic neutron scattering technique. While significant quasielastic broadening is observed in the hydrated sample, no broadening was observed in the dehydrated one. Data analysis showed that the observed quasielastic broadening in Cu(0.75)Mn(0.75)[Fe(CN)(6)]·7H(2)O corresponds to the dynamics of the non-coordinated water molecules at the 32f site and the coordinated water molecules at the 24e site, existing in the cavities created by the absence of Fe(CN)(6) units. The non-coordinated water molecules at 8c interstitial sites do not contribute to the broadening, suggesting that they are immobile at least within the time window of the spectrometer used. Behaviour of the elastic incoherent structure factor is consistent with the model where the water molecules undergo translational diffusion localized within the cavity of 5.1 Å. While all the non-coordinated water molecules at the 32f site are dynamic over the entire range of temperatures, the coordinated ones at the 24e site become progressively dynamic with temperature. The water molecules were found to undergo hindered (~1.16 × 10(-5) cm(2) s(-1) at 300 K) diffusion compared to bulk water and the diffusivity followed Arrhenius behaviour within the measured temperature range with an activation energy of 1.26 kcal mol(-1).

An atomic force microscopy investigation on self-assembled peptide nucleic acid structures on gold(111) surface

Peptide Nucleic Acid (PNA) is an important alternative nucleic acid, which exhibits more effective DNA/RNA detection capabilities compared to DNA. Its potential utility in nucleic acid based detection technologies warrants detail understanding of it's self-assembly behavior on solid substrates, e.g., gold. In the present study, we have applied high-resolution Atomic Force Microscopy (AFM) for obtaining direct visual information on PNA adsorption and formation of a self-assembled monolayer of PNA on gold(111) surface. We show from the molecularly resolved AFM data that PNA molecules form a well-defined 1-dimensional molecule-by-molecule ordering, over a considerable length scale (few hundred nm), as well as 2-dimensional ordering over a wide area of about 10 μm×10 μm, due to parallel positioning of the 1-dimensional ordered arrangements. The way the parameters like PNA concentration, incubation time, incubation temperature and PNA deposition methods can affect the formation of such ordered self-assembled PNA structures has been investigated. Some of the primary observations are that the minimum PNA concentration and incubation time for large scale (10 μm ×10 μm) 2-dimensional order formation are 0.5 μM and 4h, respectively. Furthermore, a dense and well-ordered layer over a large area could be better formed in case of immersion method compared to the droplet contact and droplet deposition methods. From the Reflection Absorption Infra Red Spectroscopy (RAIRS) data, indications for PNA concentration-driven reorientation of the PNA backbone towards more upright configuration on gold(111) surface, were obtained.

Internal dynamics in SDS micelles: neutron scattering study

The molecular dynamics of sodium dodecyl sulfate (SDS) micelle has been investigated using high-resolution incoherent quasielastic neutron scattering technique. Data analysis clearly shows presence of two distinct motions: whole micellar motion or global diffusion and faster internal motion of the SDS monomer. The global diffusion associated with the whole micelle is found to be Fickian in nature, and the corresponding diffusion coefficients are found to be consistent with those obtained from dynamic light scattering measurements. The internal motion is described with a model consistent with the structure of the micelle and which accounts for the flexibility of the chains. The SDS monomer consists of a head group, which lies on the surface of the globular micelle, and a tail that hangs from the head toward the center of the globule. Considering various factors like conformational changes of the SDS chains, bending, stretching of the chemical bonds, etc., the dynamics of the SDS molecules is successfully described by a model in which the hydrogen atoms undergo localized translational motion confined within spherical volumes. This volume increases linearly along the SDS chain such that the hydrogen atoms closer to the head group move within smaller spheres with lower diffusion constant than the hydrogen atoms away from the head group. This model is found to be consistent with the data over the whole temperature and concentration range. Diffusivity and the volume of the spheres are also found to increase with temperature. The effect of lowering the SDS concentration is found to be similar to that of increasing the temperature.