Structural Information on Supramolecular Copper(II) β-Diketonate Complexes from Atomic Force Microscopy and Analytical Ultracentrifugation

Supramolecular Cu(II) complexes were prepared from two trifunctional β-diketone ligands. The ligands (CH3Si(phacH)3 and CH3Si(phprH)3, represented by LH3) contain three aryl-β-diketone moieties joined by an organosilicon group. The complexes have the empirical formula Cu3L2, as expected for combinations of Cu2+ and L3-. Several metal-organic polyhedra (MOPs) [Cu3L2]n are possible (n = 1-10); a dodecahedron (Cu30L20; n = 10; estimated diameter of ca. 5 nm) should be the most stable because its internal bond angles would come closest to ideal values. Atomic force microscopy (AFM), performed on samples deposited from solution onto mica substrates, revealed a distribution of sample heights in the 0.5-3.0 nm range. The most commonly observed heights were 0.5-1.5 nm, corresponding to the smallest possible molecules (Cu3L2, i.e., n = 1). Some molecular cubes (Cu12L8; ca. 2.5 nm) or larger molecules or aggregates may be present as well. Equilibrium analytical ultracentrifugation (AUC) was also used to probe the compounds. A previously reported reference compound, the molecular square Cu4(m-pbhx)4 (M = 2241 g mol-1), behaved well in AUC experiments in four nonpolar organic solvents. AUC data for the new tris(β-diketonate) MOPs [Cu3L2]n in toluene and fluorobenzene did not agree well with the theoretical results for a single solute. The data were fit well by a two-solute model, but these results were not consistent in the two solvents used, and some run-to-run variability was noted even in the same solvent. Also, the calculated molecular weights differed significantly from those expected for [Cu3L2]n ([Cu3(CH3Si(phac)3)2]n, multiples of 1322 g mol-1; or [Cu3(CH3Si(phpr)3)2]n, multiples of 1490 g mol-1).

Reshaping sub-millimetre bubbles from spheres to tori

Shape-changing objects are prized for applications ranging from acoustics to robotics. We report sub-millimetre bubbles that reversibly and rapidly change not only their shape but also their topological class, from sphere to torus, when subjected to a simple pressure treatment. Stabilized by a solid-like film of nanoscopic protein "particles", the bubbles may persist in toroidal form for several days, most of them with the relative dimensions expected of Clifford tori. The ability to cross topological classes reversibly and quickly is enabled by the expulsion of protein from the strained surfaces in the form of submicron assemblies. Compared to structural modifications of liquid-filled vesicles, for example by slow changes in solution osmolality, the rapid inducement of shape changes in bubbles by application of pressure may hasten experimental investigations of surface mechanics, even as it suggests new routes to lightweight materials with high surface areas.

Molecular Dynamics Simulations of Nanostructures Formed by Hydrophobins and Oil in Seawater

Classical molecular dynamics simulations using the Martini coarse-grained force field were performed to study oil nanodroplets surrounded by fungal hydrophobin (HP) proteins in seawater. The class I EAS and the class II HFBII HPs were studied along with two model oils, namely, benzene and n-decane. Both HPs exhibit free energy minima at the oil-seawater interface, which is deeper in benzene compared to the n-decane systems. Larger constraint forces are required to keep both HPs within the n-decane phase compared to inside benzene, with HFBII being more affine to benzene compared to EAS. Smaller surface tensions are observed at benzene-seawater interfaces coated with HPs compared to their n-decane counterparts. In the latter the surface tension remains unchanged upon increases in the concentration of HPs, whereas in benzene systems adding more HPs lead to decreases in surface tension. EAS has a larger tendency to cluster together in the interface compared to HFBII, with both HPs having larger coordination numbers when surrounding benzene droplets compared to when they are around n-decane nanoblobs. The HP-oil nanostructures in seawater examined have radii of gyration ranging between 2 and 12 nm, where the n-decane structures are larger and have more irregular shapes compared to the benzene systems. The n-decane molecules within the nanostructures form a compact spherical core, with the HPs partially covering its surface and clustering together, conferring irregular shapes to the nanostructures. The EAS with n-decane structures are larger and have more irregular shapes compared to their HFBII counterparts. In contrast, in the HP-benzene structures both HPs tend to penetrate the oil part of the droplet. The HFBII-benzene structures having the larger oil/HP ratios examined tend to be more compact and spherical compared to their EAS counterparts; however, some of the HFBII-benzene systems that have smaller oil/HP ratios have a more elongated structure compared to their EAS counterparts. This simulation study provides insights into HP-oil nanostructures that are smaller than the oil droplets and gas bubbles recently studied in experiments and, thus, might be challenging to examine with experimental techniques.

Synergistic Reinforcement of Composite Hydrogels with Nanofiber Mixtures of Cellulose Nanocrystals and Chitin Nanofibers

Simultaneous incorporation of cellulose nanocrystals (CNCs) and chitin nanofibers (ChNFs) into a polyvinyl alcohol (PVA) matrix opens possibilities for customization of more environmentally friendly composite materials. When used in tricomponent composite hydrogels, the opposite surface charges on CNCs and ChNFs lead to the construction of beneficial nanofiber structures. In this work, composite hydrogels containing CNCs, ChNFs, or their mixtures are produced using cyclic freeze-thaw (FT) treatments. When considering different compositions and FT cycling, tricomponent composite hydrogels containing a specific ratio of CNCs/ChNFs are shown to have promising mechanical performance in comparison to other samples. These results together with results from water absorption, rheological, and light scattering studies suggest that the CNC/ChNF structures produced property improvement by concurrently accessing the stronger interfacial interactions between CNCs and PVA and the longer lengths of the ChNFs for load transfer. Overall, these results provide insight into using electrostatically driven nanofiber structures in nanocomposites.

Organophilic, Superparamagnetic, and Reversibly Thermoresponsive Silica-Polypeptide Core-Shell Particles

Particles with a superparamagnetic cobalt inner core, silica outer core, and covalently bound homopolypeptide shell were investigated under thermal and magnetic stimuli. The homopolypeptide was poly(ε-carbobenzyloxy-l-lysine), PCBL, which is known to exhibit a thermoreversible coil ⇔ helix transition when dissolved as a pure polymer in m-cresol. Tethering to a core particle did not prevent PCBL from undergoing this conformational transition, as confirmed by dynamic light scattering and optical rotation, but the transition was broadened compared to that of the untethered polymer. The Co@SiO₂-PCBL hybrid particles retained the superparamagnetic properties of the cobalt inner nougat. Indeed, some response remains even after aging for >5 years. The aged PCBL shell also preserved its responsiveness to temperature, although differences in the shape of the size vs temperature transition curve were observed compared to the freshly made particles. A reversible coil ⇔ helix transition for a particle-bound polypeptide in a pure organic solvent is rare. In addition to providing a convenient tool for characterizing coil ⇔ helix transitions for surface-bound polypeptides without interference from pH or the strong ionic forces that dominate behavior in aqueous systems, the Co@SiO₂-PCBL/m-cresol system may prove useful in studies of the effect of shell polymer conformation on colloid interactions. The stability of the magnetic core and polypeptide shell suggest a long shelf life for Co@SiO₂-PCBL, which can, in principle, be deprotected to yield positively charged Co@SiO₂-poly(l-lysine) particles for possible transfection or antimicrobial applications or chained magnetically to produce responsive poly(colloids).

Microbubbles and Oil Droplets Stabilized by a Class II Hydrophobin in Marinelike Environments

Hydrophobins are abundant amphipathic proteins produced by fungi. They have been interacting with oils in natural environments for millions of years; therefore, it is sensible to consider them as surfactants and dispersants for cleaning oil spills. To better understand the properties of these amphipathic proteins in seawater, a particular hydrophobin known as cerato-ulmin (CU; mass 7627 g/mol) was studied. CU is adept at forming strong membranes, as indicated by the capacity to stabilize gas-filled bubbles and oil-filled droplets with cylindrical and other nonspherical shapes. The limits of this unusual ability were tested using a wide variety of solvent conditions, including various salt solutions, alcohols, simple hydrocarbons (i.e., cyclohexane, dodecane), acids, and bases. CU concentrations ranged from 20 to 200 μg/mL. The bubbles and other structures made by CU in the presence of various gases span an enormous range of size, from nanometers to millimeters. After larger objects float to the surface, smaller structures remain, and these were found by light scattering to have a hydrodynamic diameter of ∼200 nm.

Condensation-Incompetent Ketosynthase Inhibits trans-Acyltransferase Activity

Nonelongating modules with condensation-incompetent ketosynthase (KS⁰) are frequently found in many trans-acyltransferase polyketide synthases ( trans-AT PKS). KS⁰ catalyzes translocation of carbon chain without decarboxylative condensation. Unlike typical elongating modules where malonylation of acyl carrier protein (ACP) precedes elongation, the malonylation of ACP downstream of KS⁰ is assumed to be prevented. In this study, the regulation mechanism(s) of ACP malonylation in a non-elongating module of difficidin biosynthase was investigated. In vitro reconstitution, protein mass spectrometry, and enzyme kinetics demonstrated that KS⁰ controls the pathway by inhibiting the trans-AT activity. Protein-protein interactions of the surrounding domains also contribute to the regulation. Enzyme kinetics further identified the DfnKS⁰5 as an allosteric inhibitor of trans-AT. The principle and knowledge discovered from this study will enhance the understanding of this unusual PKS system.

Diffusion of Rodlike Polymers: Pulsed Gradient Spin Echo NMR of Poly(γ-stearyl-α,l-glutamate) Solutions and the Importance of Helix Stability

Many natural and synthetic polymers and particles have a rodlike shape, leading to important and intriguing solution behavior, such as high intrinsic viscosities and liquid crystalline phases. Much of what is known about suspensions of rods has been learned by studying helical polypeptides, even though such molecules are not perfectly rigid, smooth cylinders. Previous optical tracer self-diffusion studies of poly(γ-benzyl-α,l-glutamate) (PBLG) revealed that the molecule initially resists topological constraints imposed by neighboring molecules, but diffusion strongly decreases as concentration rises beyond a certain number density. In contrast, the tracer self-diffusion coefficient of truly rigid tobacco mosaic virus begins decreasing immediately with concentration. We used pulsed gradient spin echo NMR to measure another polypeptide, poly(γ-stearyl-α,l-glutamate) (PSLG), to gain physical insight into the question of polypeptide diffusion in crowded isotropic solutions. The PSLG molecule, with long alkyl sidechains, is semiflexible like PBLG but does not exhibit the same ability to evade topological constraints. Instead, PSLG follows a simple exponential decay, D/ D_KR = A e^(-κν/ν*) + B, where D_KR is the Kirkwood-Riseman expectation for rod diffusion, ν is the number density of rods, ν* is the Onsager expectation for the number density at the onset of liquid crystal formation, A = 1 ± 0.1, B = 0.1 ± 0.01, and κ = 4.5 ± 0.5. The results emphasize the importance of helix stability when choosing rodlike polypeptides as model systems, particularly with regard to the chain ends.

Discovery of Novel Antimicrobial Peptides from Varanus komodoensis (Komodo Dragon) by Large-Scale Analyses and De-Novo-Assisted Sequencing Using Electron-Transfer Dissociation Mass Spectrometry

Komodo dragons are the largest living lizards and are the apex predators in their environs. They endure numerous strains of pathogenic bacteria in their saliva and recover from wounds inflicted by other dragons, reflecting the inherent robustness of their innate immune defense. We have employed a custom bioprospecting approach combining partial de novo peptide sequencing with transcriptome assembly to identify cationic antimicrobial peptides from Komodo dragon plasma. Through these analyses, we identified 48 novel potential cationic antimicrobial peptides. All but one of the identified peptides were derived from histone proteins. The antimicrobial effectiveness of eight of these peptides was evaluated against Pseudomonas aeruginosa (ATCC 9027) and Staphylococcus aureus (ATCC 25923), with seven peptides exhibiting antimicrobial activity against both microbes and one only showing significant potency against P. aeruginosa. This study demonstrates the power and promise of our bioprospecting approach to cationic antimicrobial peptide discovery, and it reveals the presence of a plethora of novel histone-derived antimicrobial peptides in the plasma of the Komodo dragon. These findings may have broader implications regarding the role that intact histones and histone-derived peptides play in defending the host from infection. Data are available via ProteomeXChange with identifier PXD005043.

Domed Silica Microcylinders Coated with Oleophilic Polypeptides and Their Behavior in Lyotropic Cholesteric Liquid Crystals of the Same Polypeptide

Liquid crystals can organize dispersed particles into useful and exotic structures. In the case of lyotropic cholesteric polypeptide liquid crystals, polypeptide-coated particles are appealing because the surface chemistry matches that of the polymeric mesogen, which permits a tighter focus on factors such as extended particle shape. The colloidal particles developed here consist of a magnetic and fluorescent cylindrically symmetric silica core with one rounded, almost hemispherical end. Functionalized with helical poly(γ-stearyl-l-glutamate) (PSLG), the particles were dispersed at different concentrations in cholesteric liquid crystals (ChLC) of the same polymer in tetrahydrofuran (THF). Defects introduced by the particles to the director field of the bulk PSLG/THF host led to a variety of phases. In fresh mixtures, the cholesteric mesophase of the PSLG matrix was distorted, as reflected in the absence of the characteristic fingerprint pattern. Over time, the fingerprint pattern returned, more quickly when the concentration of the PSLG-coated particles was low. At low particle concentration the particles were "guided" by the PSLG liquid crystal to organize into patterns similar to that of the re-formed bulk chiral nematic phase. When their concentration increased, the well-dispersed PSLG-coated particles seemed to map onto the distortions in the bulk host's local director field. The particles located near the glass vial-ChLC interfaces were stacked lengthwise into architectures with apparent two-dimensional hexagonal symmetry. The size of these "crystalline" structures increased with particle concentration. They displayed remarkable stability toward an external magnetic field; hydrophobic interactions between the PSLG polymers in the shell and those in the bulk LC matrix may be responsible. The results show that bio-inspired LCs can assemble suitable colloidal particles into soft crystalline structures.

Poly(colloid)s: "Polymerization" of Poly(l-tyrosine)-silica Composite Particles through the Photoinduced Cross-Linking of Unmodified Proteins Method

Photoinduced cross-linking of unmodified proteins, PICUP, was extended to core-shell silica-polypeptide composite particles to produce poly(colloid)s. Silica particles coated with poly(l-tyrosine), PTYR-SiO2, served as the monomer units. The PICUP reaction accomplished the formation of dityrosil linkages between the tyrosine units by illumination of photo-oxidizing ruthenium(II) bipyridyl catalyst under physiological conditions. The PICUP method was compared with an enzymatic route intermediated by horseradish peroxidase as catalyst. The PTYR-SiO2 particles feature high PTYR content in the shell, which facilitated the formation of heavily cross-linked but unstructured aggregates. After magnetic alignment of superparamagnetic PTYR-SiO2-cobalt composite particles, only the PICUP approach enabled the preparation of isolated chain-like poly(colloid)s. The cross-linking products were confirmed by FTIR. The native secondary structure of poly(l-tyrosine) is preserved in these poly(colloid)s. Because the PICUP reaction does not require the modification of the polypeptide structure, the cross-linked PTYR will retain its characteristic functions as a poly(amino acid). The PICUP method opens the door to a variety of PTYR-based poly(colloid) architectures.

Formation of a Rigid Hydrophobin Film and Disruption by an Anionic Surfactant at an Air/Water Interface

Hydrophobins are amphiphilic proteins produced by fungi. Cerato-ulmin (CU) is a hydrophobin that has been associated with Dutch elm disease. Like other hydrophobins, CU stabilizes air bubbles and oil droplets through the formation of a persistent protein film at the interface. The behavior of hydrophobins at surfaces has raised interest in their potential applications, including use in surface coatings, food foams, and emulsions and as dispersants. The practical use of hydrophobins requires an improved understanding of the interfacial behavior of these proteins, alone and in the presence of added surfactants. In this study, the adsorption behavior of CU at air/water interfaces is characterized by measuring the surface tension and interfacial rheology as a function of adsorption time. CU is found to adsorb irreversibly at air/water interfaces. The magnitude of the dilatational modulus increases with adsorption time and surface pressure until CU eventually forms a rigid film. The persistence of this film is tested through the sequential addition of strong surfactant sodium dodecyl sulfate (SDS) to the bulk liquid adjacent to the interface. SDS is found to coadsorb to interfaces precoated with a CU film. At high concentrations, the addition of SDS significantly decreases the dilatational modulus, indicating disruption and displacement of CU by SDS. Sequential adsorption results in mixed layers with properties not observed in interfaces generated from complexes formed in the bulk. These results lend insight to the complex interfacial interactions between hydrophobins and surfactants.

Preparation of Metalloporphyrin-Bound Superparamagnetic Silica Particles via "Click" Reaction

A facile approach using click chemistry is demonstrated for immobilization of metalloporphyrins onto the surface of silica-coated iron oxide particles. Oleic-acid stabilized iron oxide nanocrystals were prepared by thermal decomposition of iron(III) acetylacetonate. Their crystallinity, morphology, and superparamagnetism were determined using X-ray diffraction, transmission electron microscopy, and a superconducting quantum interference device. Monodisperse core-shell particles were produced in the silica-coating of iron oxide via microemulsion synthesis. Surface modification of these particles was performed in two steps, which included the reaction of silica-coated iron oxide particles with 3-bromopropyltrichlorosilane, followed by azido-functionalization with sodium azide. Monoalkylated porphyrins were prepared using the Williamson ether synthesis of commercially available tetra(4-hydroxyphenyl) porphyrin with propargyl bromide in the presence of a base. (1)H NMR and matrix-assisted laser desorption ionization confirmed the identity of the compounds. The prepared monoalkyne porphyrins were zinc-metalated prior to their introduction to azide-functionalized, silica-coated iron oxide particles in the click reaction. X-ray photoelectron spectroscopy, thermogravimetric analysis, and Fourier transform infrared spectroscopy were used to characterize the surface chemistry after each step in the reaction. In addition, particle size was determined using dynamic light scattering and microscopy. The presented methodology is versatile and can be extended to other photoreactive systems, such as phthalocyanines and boron-dipyrromethane, which may lead to new materials for optical, photonic, and biological applications.

Colorful Polyelectrolytes: An Atom Transfer Radical Polymerization Route to Fluorescent Polystyrene Sulfonate

A labeled green fluorescent polystyrene sulfonate (LNaPSS) has been synthesized using atom transfer radical polymerization of a styrene sulfonate monomer with a fluorescent co-monomer, fluorescein thiocyanate-vinyl aniline. As a result this 100 % sulfonated polymer contains no hydrophobic patches along the chain backbone besides the fluorescent marker itself. The concentration of the fluorescent monomer was kept low to maintain the characteristic properties of the anionic polyelectrolyte, LNaPSS. ATRP conditions facilitated the production of polymers spanning a range of molecular weights from 35,000 to 175,000 in gram-scale batches with polydispersity indices of 1.01-1.24. Molecular weight increased with the monomer to initiator ratio. Gel permeation chromatography results show a unimodal distribution, and the polymer structure was also confirmed by (1)H NMR and FT-IR spectroscopy. Fluorescence spectroscopy confirmed covalent bonding of fluorescein isothiocyanate to the polymer, indicating that the polymer is suitable as a probe in fluorescence microscopy. To demonstrate this ability, the polymer was used to locate structural features in salt crystals formed during drying, as in the evaporation of sea mist. A second application to probe diffusion studies is also demonstrated.

Sugar-Based Polyamides: Self-Organization in Strong Polar Organic Solvents

Periodic patterns resembling spirals were observed to form spontaneously upon unassisted cooling of d-glucaric acid- and d-galactaric acid-based polyamide solutions in N-methyl-N-morpholine oxide (NMMO) monohydrate. Similar observations were made in d-galactaric acid-based polyamide/ionic liquid (IL) solutions. The morphologies were investigated by optical, polarized light and confocal microscopy assays to reveal pattern details. Differential scanning calorimetry was used to monitor solution thermal behavior. Small- and wide-angle X-ray scattering data reflected the complex and heterogeneous nature of the self-organized patterns. Factors such as concentration and temperature were found to influence spiral dimensions and geometry. The distance between rings followed a first-order exponential decay as a function of polymer concentration. Fourier-Transform Infrared Microspectroscopy analysis of spirals pointed to H-bonding between the solvent and the pendant hydroxyl groups of the glucose units from the polymer backbone. Tests on self-organization into spirals of ketal-protected d-galactaric acid polyamides in NMMO monohydrate confirmed the importance of the monosaccharide's pendant free hydroxyl groups on the formation of these patterns. Rheology performed on d-galactaric-based polyamides at high concentration in NMMO monohydrate solution revealed the optimum conditions necessary to process these materials as fibers by spinning. The self-organization of these sugar-based polyamides mimics certain biological materials.

Separation and characterization of poly(tetrafluoroethylene) latex particles by asymmetric flow field flow fractionation with light-scattering detection

Poly(tetrafluoroethylene) (PTFE) latex particles have been analyzed and sorted according to size using asymmetric flow field flow fractionation (AF4) coupled with multiple-angle light scattering (MALS). Characterization of fractions by regular and depolarized dynamic light scattering confirmed that smaller particles elute prior to larger ones, as expected for field flow fractionation. The measured radii of the optically and geometrically anisotropic particles are consistent with those determined from transmission electron microscopy (TEM). A certain amount of heterogeneity remains in the fractions, but their uniformity for use as diffusion probes is improved. Full characterization of PTFE colloids will require a difficult assessment of the distribution, even within fractions, of the optical anisotropy. A general method to obtain number versus size distributions is presented. This approach is valid even when an online concentration detector is not available or ineffective. The procedure is adaptable to particles of almost any regular shape.

Reformulation of etoposide with solubility-enhancing rubusoside

Etoposide (ETO), a widely used anti-cancer drug, is constrained by its low aqueous solubility and by side effects from both the drug and its solubilizing excipients. In this study, a recently discovered natural solubilizer rubusoside (RUB) was used to achieve the solubilization of ETO. Dynamic light scattering and freeze-fracture transmission electron microscopy studies showed that ETO and RUB formed ETO-RUB nanoparticles (∼6 nm in diameter). The powder of ETO-RUB nanoparticles was completely reconstitutable in water and remained stable in this solution at 25 and 37°C for at least 24h. Under other physiologic conditions, ETO solution was clear and free of precipitation at 25°C, but underwent various structural transformations. In PBS and simulated intestinal fluid, RUB-solubilized ETO underwent epimerization and equilibrated to cis-ETO. In simulated gastric fluid, RUB-solubilized ETO degraded to 4'-demethylepipodophyllotoxin-beta-d-glucoside and 4'-demethylepipodophyllotoxin. Higher temperatures favored epimerization or degradation. Furthermore, a side-by-side comparison with DMSO-solubilized ETO confirmed that the RUB-solubilized ETO showed no significant differences in cytotoxicity in colon, breast and prostate cancer cell lines. RUB effectively solubilized and stabilized etoposide, which sets the stage for further toxicology, bioavailability, and efficacy investigations.

Synthesis and rapid characterization of amine-functionalized silica

Amine-functionalized colloidal silica finds use in a variety of applications and fundamental investigations. To explore convenient methods of synthesis and characterization of research-grade materials in relatively large quantities, nearly monodisperse colloidal silica particles were prepared by base-catalyzed hydrolysis of reagent-grade tetraethyl orthosilicate (TEOS) without the traditional time- and energy-consuming distillation step. Radius was varied reliably from 30 to 125 nm by changing the water/TEOS ratio. Asymmetric flow field flow fractionation (AF4) methods with online light scattering detection proved effective in assessing the uniformity of the various preparations. Even highly uniform commercial standards were resolved by AF4. The surface of the colloidal silica was decorated with amino groups using (3-aminopropyl) trimethoxysilane and spacer methyl groups from methyl-trimethoxysilane. The surface density of amino groups was quantified spectrophotometrically after reaction with ninhydrin; the nature of this analysis avoids interference from sample turbidity. As an alternative to the ninhydrin test, an empirical relationship between surface density of amino groups and zeta potential at low pH was found. The size of the colloidal silica was predictably decreased by etching with HF; this method will be effective for some preparations, despite a modest reduction in size uniformity.

Proteomic analysis of eccrine sweat: implications for the discovery of schizophrenia biomarker proteins

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) and multiple reaction monitoring mass spectrometry (MRM-MS) proteomics analyses were performed on eccrine sweat of healthy controls, and the results were compared with those from individuals diagnosed with schizophrenia (SZ). This is the first large scale study of the sweat proteome. First, we performed LC-MS/MS on pooled SZ samples and pooled control samples for global proteomics analysis. Results revealed a high abundance of diverse proteins and peptides in eccrine sweat. Most of the proteins identified from sweat samples were found to be different than the most abundant proteins from serum, which indicates that eccrine sweat is not simply a plasma transudate and may thereby be a source of unique disease-associated biomolecules. A second independent set of patient and control sweat samples were analyzed by LC-MS/MS and spectral counting to determine qualitative protein differential abundances between the control and disease groups. Differential abundances of selected proteins, initially determined by spectral counting, were verified by MRM-MS analyses. Seventeen proteins showed a differential abundance of approximately 2-fold or greater between the SZ pooled sample and the control pooled sample. This study demonstrates the utility of LC-MS/MS and MRM-MS as a viable strategy for the discovery and verification of potential sweat protein disease biomarkers.

Gelation of Rodlike Polymers

Some opportunities for utilizing gelation of rodlike polymers such as poly(p-phenylenebenzobisthiazole) for the production of new materials are described. Morphological studies concerning gels of poly(γ–benzyl–α,L–glutamate) in the solvents toluene, N,N-dimethylformamide and N,N-dimethylformamide/water are reviewed, newly interpreted and extended. A provisional diagram which maps out the gelling behavior in four distinct regions of concentration and temperature concludes the article.

A novel solubility-enhanced curcumin formulation showing stability and maintenance of anticancer activity

Curcumin (CUR) is an active food compound, but its insolubility and instability in water contributes to low bioavailability. In this study, the solubility of CUR was enhanced by utilizing the solubilizing properties of rubusoside (RUB). The solubility of CUR in water increased linearly from 61 μg/mL to 2.318 mg/mL in the presence of RUB ranging from 1% to 10% (w/v). Dynamic light scattering and transmission electron microscopy studies found that CUR and RUB formed CUR-RUB nanoparticle (∼8 nm) complexes. The RUB-solubilized CUR was stable in physiological conditions and did not precipitate when diluted or degrade when spray-dried to a completely reconstitutable powder. Furthermore, cell viability assays demonstrated the efficacy of RUB-solubilized CUR against human colon, breast, and pancreatic cancer cell lines. The development of this new solubilized, stable, and biologically active CUR formulation lays the foundation for future bioavailability improvement.

Silica-polypeptide composite particles: controlling shell growth

A method is presented for preparing core-shell silica-polypeptide composite particles with variable and controllable shell growth. The procedure is demonstrated using poly(carbobenzoxy-L-lysine) and poly(benzyl-L-glutamate); after deprotection, these can lead to the most common basic and acidic homopolypeptides, poly(L-lysine) and poly(L-glutamic acid). Control over shell thickness is made possible by sequential addition of N-carboxyanhydride peptide monomer to surfaces that have been functionalized with an amino initiator combined with a surface passivation agent. This results in a series of particles having different shell thicknesses. Variation of shell thickness was evident both in light scattering and in thermogravimetric assays. The shells were visible by transmission electron microscopy; these images along with light scattering measurements suggest the polymers in the shells are highly solvated.

Effect of type 2 diabetes on plasma kallikrein activity after physical exercise and its relationship to post-exercise hypotension

AIM

The present study was undertaken to determine the effects of type 2 diabetes (T2D) on plasma kallikrein activity (PKA) and postexercise hypotension (PEH).

METHODS

Ten T2D patients (age: 53.6±1.3 years; body mass index: 30.6±1.0kg/m(2); resting blood glucose: 157.8±40.2mgdL(-1)) and 10 non-diabetic (ND) volunteers (age: 47.5±1.0 years; body mass index: 28.3±0.9kg/m(2); resting blood glucose: 91.2±10.5mgdL(-1)) underwent two experimental sessions, consisting of 20min of rest plus 20min of exercise (EXE) at an intensity corresponding to 90% of their lactate threshold (90LT) and a non-exercise control (CON) session. Blood pressure (BP; Microlife BP 3AC1-1 monitor) and PKA were measured during rest and every 15min for 135min of the postexercise recovery period (RP).

RESULTS

During the RP, the ND individuals presented with PEH at 30, 45 and 120min (P<0.05) while, in the T2D patients, PEH was not observed at any time. PKA increased at 15min postexercise in the ND (P<0.05), but not in the T2D patients.

CONCLUSION

T2D individuals have a lower PKA response to exercise, which probably suppresses its hypotensive effect, thus reinforcing the possible role of PKA on PEH.

Reversibility of beta-amyloid self-assembly: effects of pH and added salts assessed by fluorescence photobleaching recovery

The 40-residue peptide isoform beta-amyloid (Abeta(1-40)) is associated with Alzheimer's disease. Although found in the tangles and fibrous mats that characterize the brain in advanced stages of the disease, the toxic form of Abeta is believed to be oligomers or "protofibrils". Characterization of these fairly small structures in solution, especially in the presence of the much larger assemblies they also form, is a daunting task. Additionally, little is known about the rate of Abeta assembly or whether it can be triggered easily. Perhaps most importantly, the conditions for reversing assembly are not fully understood. Fluorescence photobleaching with modulation detection of the recovery profile is a sensitive and materials-efficient way to measure diffusers over a wide range of hydrodynamic sizes. The method does require attachment of a fluorescent label. Experiments to validate the use of 5-carboxyfluorescein-labeled Abeta(1-40) as a representative of the unlabeled, naturally occurring material included variation of photobleaching time and mixture of labeled and unlabeled materials. A dialysis cell facilitated rapid in situ changes in pH and salt conditions. Multiple steps and complex protocols can be explored with relative ease. Oligomeric aggregates were found by fluorescence photobleaching recovery to respond readily to pH and salt conditions. Changing these external cues leads to formation or disassembly of aggregates smaller than 100 nm within minutes.

Surface properties of a series of amphiphilic dendrimers with short hydrophobic chains

A series of tree-shaped, amphiphilic dendrimers was synthesized. The products belong to the family of one-directional arborols of the form ([9]-n), where the notation signifies that each molecule has nine hydroxyl groups ([9]-) as the hydrophilic head and an alkyl chain as the hydrophobic moiety (n = 6, 8, or 10 carbon atoms). The surfactant character changes dramatically as the number of methylene groups increases. The critical micelle concentration of [9]-6 was determined, and pressure-area isotherms of the less soluble [9]-8 and [9]-10 were obtained. Large structures existed atop the spread layers. Large structures were also found in solutions of [9]-6.

Probe diffusion from dilute to concentrated in polyelectrolyte solution: Salt effect

The adsorption behaviors between a positively charged poly(allyamine) hydrochloride (PAH) matrix and negatively charged sulfate polystyrene (PS) particle probe were investigated using dynamic light scattering (DLS) and fluorescence photobleaching recovery (FPR) with reference to the matrix and salt concentration. The system experienced a steep decrease of diffusion (flocculation) under dilute conditions and a gradual decrease above semidilute concentrations. The fluorescence photobleaching recovery and viscometry experiments revealed that the probe behaviors in the polyelectrolyte solution were strongly affected by the coil overlap concentration (0.5 g/L poly(allyamine) hydrochloride). Near the coil overlap concentration, the hydrodynamic radius representing the entanglement dimension of the matrix was approximately 30 nm; however, at higher concentrations the radius gradually decreased, suggesting a transition toward a network structure. In this system, the salt performed two roles: (1) reinforcing the electrostatic interaction, and (2) preventing electrostatic interaction between the probe and the matrix.

Mesophase separation and probe dynamics in protein-polyelectrolyte coacervates

Protein-polyelectrolyte coacervates are self-assembling macroscopically monophasic biomacromolecular fluids whose unique properties arise from transient heterogeneities. The structures of coacervates formed at different conditions of pH and ionic strength from poly(dimethyldiallylammonium chloride) and bovine serum albumin (BSA), were probed using fluorescence recovery after photobleaching. Measurements of self-diffusion in coacervates were carried out using fluorescein-tagged BSA, and similarly tagged Ficoll, a non-interacting branched polysaccharide with the same size as BSA. The results are best explained by temporal and spatial heterogeneities, also inferred from static light scattering and cryo-TEM, which indicate heterogeneous scattering centers of several hundred nm. Taken together with previous dynamic light scattering and rheology studies, the results are consistent with the presence of extensive dilute domains in which are embedded partially interconnected 50-700 nm dense domains. At short length scales, protein mobility is unobstructed by these clusters. At intermediate length scales, proteins are slowed down due to tortuosity effects within the blind alleys of the dense domains, and to adsorption at dense/dilute domain interfaces. Finally, at long length scales, obstructed diffusion is alleviated by the break-up of dense domains. These findings are discussed in terms of previously suggested models for protein-polyelectrolyte coacervates. Possible explanations for the origin of mesophase separation are offered.

A detergent-like mechanism of action of the cytolytic toxin Cyt1A from Bacillus thuringiensis var. israelensis

The cytolytic delta-endotoxin Cyt1A from Bacillus thuringiensis var. israelensis is used in commercial preparations of environmentally safe insecticides. The current hypothesis on its mode of action is that the toxin self-assembles into well-defined cation-selective channels or pores, which results in colloid-osmotic lysis of the cell. Recently, a new hypothesis has been put forward suggesting that Cyt1A rather nonspecifically aggregates on the membrane surface and acts in a detergent-like manner. To distinguish between these two hypotheses, we investigated whether in the presence of lipid Cyt1A self-assembles into stoichiometric oligomers, which are characteristic of pores or channels, or aggregates into nonstoichiometric complexes, which would support the detergent-like model. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that in the presence of lipid Cyt1A forms protein aggregates with a broad range of molecular weights, some being too large to enter the gel. Cyt1A tryptophan (Trp) fluorescence in the presence of lipid exhibited a decrease in anisotropy and quantum yield, but an unchanged lifetime, which is consistent with the presence of toxin aggregates in the membrane. Electrostatic interactions between the charged amino acid residues and the lipid headgroups are responsible for bringing the protein to the membrane surface, while hydrophobic and/or van der Waals interactions make the membrane binding irreversible. Fluorescence photobleaching recovery, a technique that measures the diffusion coefficient of fluorescently labeled particles, and epifluorescence microscopy revealed that upon addition of Cyt1A lipid vesicles were broken into smaller, faster diffusing objects. Since no change in size or morphology of the vesicles is expected when pores are formed in the osmotically equilibrated membranes, our results support the detergent-like mode of action of Cyt1A.

Structural changes and aggregation of human influenza virus

The pH-induced change in the structure and aggregation state of the PR-8 and X-31 strains of intact human influenza virus has been studied in vitro. Reducing the pH from 7.4 to 5.0 produces a large increase in the intensity of light scattered to low angles. A modest increase in the polydispersity parameter from cumulants fits to the dynamic light scattering correlograms accompanies the increase, as does a change in how that parameter varies with scattering angle. These trends imply that the virus particles are not uniform, even at pH 7.4, and tend to aggregate as pH is reduced. The scattering profiles (angular dependence of intensity) never match those of isolated, spherical particles of uniform size, but the deviations from that simple model remain modest at pH 7.4. At pH 5.0, scattering profiles calculated for aggregates of uniformly sized spheres come much closer to matching the experimental data than those computed for isolated particles. Although these observations indicate that acid-induced aggregation develops over a period of minutes to hours after acidification, a nearly instantaneous increase in hydrodynamic size is the first response of intact virus particles to lower pH.

The human serum proteome: display of nearly 3700 chromatographically separated protein spots on two-dimensional electrophoresis gels and identification of 325 distinct proteins

Plasma, the soluble component of the human blood, is believed to harbor thousands of distinct proteins, which originate from a variety of cells and tissues through either active secretion or leakage from blood cells or tissues. The dynamic range of plasma protein concentrations comprises at least nine orders of magnitude. Proteins involved in coagulation, immune defense, small molecule transport, and protease inhibition, many of them present in high abundance in this body fluid, have been functionally characterized and associated with disease processes. For example, protein sequence mutations in coagulation factors cause various serious disease states. Diagnosing and monitoring such diseases in blood plasma of affected individuals has typically been conducted by use of enzyme-linked immunosorbent assays, which using a specific antibody quantitatively measure only the affected protein in the tested plasma samples. The discovery of protein biomarkers in plasma for diseases with no known correlations to genetic mutations is challenging. It requires a highly parallel display and quantitation strategy for proteins. We fractionated blood serum proteins prior to display on two-dimensional electrophoresis (2-DE) gels using immunoaffinity chromatography to remove the most abundant serum proteins, followed by sequential anion-exchange and size-exclusion chromatography. Serum proteins from 74 fractions were displayed on 2-DE gels. This approach succeeded in resolving approximately 3700 distinct protein spots, many of them post-translationally modified variants of plasma proteins. About 1800 distinct serum protein spots were identified by mass spectrometry. They collapsed into 325 distinct proteins, after sequence homology and similarity searches were carried out to eliminate redundant protein annotations. Although a relatively insensitive dye, Coomassie Brilliant Blue G-250, was used to visualize protein spots, several proteins known to be present in serum in < 10 ng/mL concentrations were identified such as interleukin-6, cathepsins, and peptide hormones. Considering that our strategy allows highly parallel protein quantitation on 2-DE gels, it holds promise to accelerate the discovery of novel serum protein biomarkers.