Parallel β-Sheet Structure and Structural Heterogeneity Detected within Q11 Self-Assembling Peptide Nanofibers

Q11 peptide nanofibers are used as a biomaterial for applications such as antigen presentation and tissue engineering, yet detailed knowledge of molecular-level structure has not been reported. The Q11 peptide sequence was designed using heuristics-based patterning of hydrophobic and polar amino acids with oppositely charged amino acids placed at opposite ends of the sequence to promote antiparallel β-sheet formation. In this work, we employed solid-state nuclear magnetic resonance spectroscopy (NMR) to evaluate whether the molecular organization within Q11 self-assembled peptide nanofibers is consistent with the expectations of the peptide designers. We discovered that Q11 forms a distribution of molecular structures. NMR data from two-dimensional (2D) 13C-13C dipolar-assisted rotational resonance indicate that the K3 and E9 residues between Q11 β-strands are spatially proximate (within ∼0.6 nm). Frequency-selective rotational echo double resonance (fsREDOR) on K3 Nζ and E9 Cδ-labeled sites showed that approximately 9% of the sites are close enough for salt bridge formation to occur. Surprisingly, dipolar recoupling measurements revealed that Q11 peptides do not assemble into antiparallel β-sheets as expected, and structural analysis using Fourier-transform infrared spectroscopy and 2D NMR alone can be misleading. 13C PITHIRDS-CT dipolar recoupling measurements showed that the most abundant structure consists of parallel β-sheets, in contrast to the expected antiparallel β-sheet structure. Structural heterogeneity was detected from 15N{13C} REDOR measurements, with approximately 22% of β-strands having antiparallel nearest neighbors. We cannot propose a complete structural model of Q11 nanofibers because of the complexity involved when examining structurally heterogeneous samples using NMR. Altogether, our results show that while heuristics-based patterning is effective in promoting β-sheet formation, designing a peptide sequence to form a targeted β-strand arrangement remains challenging.

Hierarchical ZIF-8 Materials via Acid Gas-Induced Defect Sites: Synthesis, Characterization, and Functional Properties

Microporous metal-organic frameworks (MOFs) have been widely studied for molecular separation and catalysis. The uniform micropores of MOFs (<2 nm) can introduce diffusion limitations and render the interiors of the crystal inaccessible to target molecules. The introduction of hierarchical porosity (interconnected micro and mesopores) can enhance intra-crystalline diffusion while maintaining the separation/catalytic selectivity. Conventional hierarchical MOF synthesis involves complex strategies such as elongated linkers, soft templating, and sacrificial templates. Here, we demonstrate a more general approach using our controlled acid gas-enabled degradation and reconstruction (Solvent-Assisted Crystal Redemption) strategy. Selective linker labilization of ZIF-8 is shown to generate a hierarchical pore structure with mesoporous cages (∼50 nm) while maintaining microporosity. Detailed structural and spectroscopic characterization of the controlled degradation, linker insertion, and subsequent linker thermolysis is presented to show the clustering of acid gas-induced defects and the generation of mesopores. These findings indicate the generality of controlled degradation and reconstruction as a means for linker insertion in a wider variety of MOFs and creating hierarchical porosity. Enhanced molecular diffusion and catalytic activity in the hierarchical ZIF-8 are demonstrated by the adsorption kinetics of 1-butanol and a Knoevenagel condensation reaction.

Understanding the Impacts of Support-Polymer Interactions on the Dynamics of Poly(ethyleneimine) Confined in Mesoporous SBA-15

Supported amines are a promising class of CO₂ sorbents offering large uptake capacities and fast uptake rates. Among supported amines, poly(ethyleneimine) (PEI) physically impregnated in the mesopores of SBA-15 silica is widely used. Within these composite materials, the chain dynamics and morphologies of PEI strongly influence the CO₂ capture performance, yet little is known about chain and macromolecule mobility in confined pores. Here, we probe the impact of the support-PEI interactions on the dynamics and structures of PEI at the support interface and the corresponding impact on CO₂ uptake performance, which yields critical structure-property relationships. The pore walls of the support are grafted with organosilanes with different chemical end groups to differentiate interaction modes (spanning from strong attraction to repulsion) between the pore surface and PEI. Combinations of techniques, such as quasi-elastic neutron scattering (QENS), ¹H T₁-T₂ relaxation correlation solid-state NMR, and molecular dynamics (MD) simulations, are used to comprehensively assess the physical properties of confined PEI. We hypothesized that PEI would have faster dynamics when subjected to less attractive or repulsive interactions. However, we discover that complex interfacial interactions resulted in complex structure-property relationships. Indeed, both the chain conformation of the surface-grafted chains and of the PEI around the surface influenced the chain mobility and CO₂ uptake performance. By coupling knowledge of the dynamics and distributions of PEI with CO₂ sorption performance and other characteristics, we determine that the macroscopic structures of the hybrid materials dictate the first rapid CO₂ uptake, and the rate of CO₂ sorption during the subsequent gradual uptake stage is determined by PEI chain motions that promote diffusive jumps of CO₂ through PEI-packed domains.

Single-walled zeolitic nanotubes

We report the synthesis and structure of single-walled aluminosilicate nanotubes with microporous zeolitic walls. This quasi-one-dimensional zeolite is assembled by a bolaform structure-directing agent (SDA) containing a central biphenyl group connected by C₁₀ alkyl chains to quinuclidinium end groups. High-resolution electron microscopy and diffraction, along with other supporting methods, revealed a unique wall structure that is a hybrid of characteristic building layers from two zeolite structure types, beta and MFI. This hybrid structure arises from minimization of strain energy during the formation of a curved nanotube wall. Nanotube formation involves the early appearance of a mesostructure due to self-assembly of the SDA molecules. The biphenyl core groups of the SDA molecules show evidence of π stacking, whereas the peripheral quinuclidinium groups direct the microporous wall structure.

Closed-loop trans-skull ultrasound hyperthermia leads to improved drug delivery from thermosensitive drugs and promotes changes in vascular transport dynamics in brain tumors

Effective drug delivery in brain tumors remains a major challenge in oncology. Although local hyperthermia and stimuli-responsive delivery systems, such as thermosensitive liposomes, represent promising strategies to locally enhance drug delivery in solid tumors and improve outcomes, their application in intracranial malignancies remains unexplored. We hypothesized that the combined abilities of closed-loop trans-skull Magnetic Resonance Imaging guided Focused Ultrasound (MRgFUS) hyperthermia with those of thermosensitive drugs can alleviate challenges in drug delivery and improve survival in gliomas.

Methods: To conduct our investigations, we first designed a closed loop MR-guided Focused Ultrasound (MRgFUS) system for localized trans-skull hyperthermia (ΔT < 0.5 °C) in rodents and established safety thresholds in healthy mice. To assess the abilities of the developed system and proposed therapeutic strategy for FUS-triggered chemotherapy release we employed thermosensitive liposomal Dox (TSL-Dox) and tested it in two different glioma tumor models (F98 in rats and GL261 in mice). To quantify Dox delivery and changes in the transvascular transport dynamics in the tumor microenvironment we combined fluorescent microscopy, dynamic contrast enhanced MRI (DCE-MRI), and physiologically based pharmacokinetic (PBPK) modeling. Lastly, to assess the therapeutic efficacy of the system and of the proposed therapeutic strategy we performed a survival study in the GL261 glioma bearing mice.

Results: The developed closed-loop trans-skull MRgFUS-hyperthermia system that operated at 1.7 MHz, a frequency that maximized the brain (FUS-focus) to skull temperature ratio in mice, was able to attain and maintain the desired focal temperature within a narrow range. Histological evidence (H&E and Nissl) suggests that focal temperature at 41.5 ± 0.5 °C for 10 min is below the threshold for tissue damage. Quantitative analysis of doxorubicin delivery from TSLs with MRgFUS-hyperthermia demonstrated 3.5-fold improvement in cellular uptake in GL261 glioma mouse tumors (p < 0.001) and 5-fold increase in delivery in F98 glioma rat tumors (p < 0.05), as compared to controls (TSL-Dox-only). Moreover, PBPK modeling of drug transport that was calibrated using the experimental data indicated that thermal stress could lead to significant improvement in the transvascular transport (2.3-fold increase in the vessel diffusion coefficient; P < 0.001), in addition to promoting targeted Dox release. Prospective experimental investigations with DCE-MRI during FUS-hyperthermia, supported these findings and provided evidence that moderate thermal stress (≈41 °C for up to 10 min) can promote acute changes in the vascular transport dynamics in the brain tumor microenvironment (K^trans value for control vs. FUS was 0.0097 and 0.0148 min^-1, respectively; p = 0.026). Crucially, survival analysis demonstrated significant improvement in the survival in the TSL-Dox-FUS group as compared to TSL-Dox-only group (p < 0.05), providing supporting evidence on the therapeutic potential of the proposed strategy.

Conclusions: Our investigations demonstrated that spatially controlled thermal stress can be attained and sustained in the mouse brain, using a trans-skull closed-loop MRgFUS system, and used to promote the effective delivery of chemotherapy in gliomas from thermosensitive drugs. This system also allowed us to conduct mechanistic investigations that resulted in the refinement of our understanding on the role of thermal stress in augmenting mass and drug transport in brain tumors. Overall, our study established a new paradigm for effective drug delivery in brain tumors based on closed-loop ultrasound-mediated thermal stress and thermosensitive drugs.

Multi-component T 2 ∗ relaxation modelling in human Achilles tendon: Quantifying chemical shift information in ultra-short echo time imaging

PURPOSE

To examine multi-component relaxation modelling for quantification of on- and off-resonance relaxation signals in multi-echo ultra-short echo time (UTE) data of human Achilles tendon (AT) and compare bias and dispersion errors of model parameters to that of the bi-component model.

THEORY AND METHODS

Multi-component modelling is demonstrated for quantitative multi-echo UTE analysis of AT and supported using a novel method for determining number of MR-visible off-resonance components, UTE data from six healthy volunteers, and analysis of proton NMR measurements from ex vivo bovine AT. Cramer-Rao lower bound expressions are presented for multi- and bi-component models and parameter estimate variances are compared. Bias error in bi-component estimates is characterized numerically.

RESULTS

Two off-resonance components were consistently detected in all six volunteers and in bovine AT data. Multi-component model exhibited superior quality of fit, with a marginal increase in estimate variance, when compared to the bi-component model. Bi-component estimates exhibited notable bias particularly in R 2 , 1 ∗ in the presence of off-resonance components.

CONCLUSION

Multi-component modelling more reliably quantifies tendon matrix water components while also providing quantitation of additional non-water matrix constituents. Further work is needed to interpret the origin of the observed off-resonance signals with preliminary assignments made to chemical groups in lipids and proteoglycans.

(4NPEA)2PbI4 (4NPEA = 4-Nitrophenylethylammonium): Structural, NMR, and Optical Properties of a 3 × 3 Corrugated 2D Hybrid Perovskite

(4NPEA)₂PbI₄ (4NPEA = 4-nitrophenylethylammonium) is the first 3 × 3 corrugated 2D organic-Pb/I perovskite. The nitro groups are involved in cation-cation and cation-iodide interactions. The structure contains both highly distorted and near-ideal PbI₆ octahedra, consistent with the observation of two ²⁰⁷Pb NMR resonances, while the optical properties resemble those of other 2D perovskites with distorted PbI₆ octahedra.

PIM-1 as a Solution-Processable "Molecular Basket" for CO2 Capture from Dilute Sources

Rising atmospheric CO₂ levels have triggered recent research into the science of amine materials supported on hard, porous materials such as mesoporous silica or alumina. While such materials can give high CO₂ uptakes and good sorption kinetics, they are difficult to utilize in practical applications due to difficulty in contacting large volumes of CO₂-laden gases with powder materials without significant pressure drops or sorbent attrition. Here, we describe a simple approach based on the impregnation of a permanently microporous polymer, PIM-1, with poly(ethylene imine) (PEI), removing the need for use of the hard oxide. PEI/PIM-1 composites demonstrate comparable performance to more traditionally studied oxide sorbents, with the benefit that PIM-1 is soluble in common solvents, making it eminently more viable for processing into morphologies that can facilitate heat and mass transfer and fabrication into low pressure drop contactors. In addition to adsorption studies performed on a variety of PEI/PIM-1 architectures, spin diffusion NMR studies were performed to suggest that PEI is well-dispersed within the PIM-1, allowing for rapid CO₂ adsorption.

Direct synthesis of single-walled aminoaluminosilicate nanotubes with enhanced molecular adsorption selectivity

Internal functionalization of single-walled nanotubes is an attractive, yet difficult challenge in nanotube materials chemistry. Here we report single-walled metal oxide nanotubes with covalently bonded primary amine moieties on their inner wall, synthesized through a one-step approach. Conclusive molecular-level structural information on the amine-functionalized nanotubes is obtained through multiple solid-state techniques. The amine-functionalized nanotubes maintain a high carbon dioxide adsorption capacity while significantly suppressing the adsorption of methane and nitrogen, thereby leading to a large enhancement in adsorption selectivity over unfunctionalized nanotubes (up to four-fold for carbon dioxide/methane and ten-fold for carbon dioxide/nitrogen). The successful synthesis of single-walled nanotubes with functional, covalently-bound organic moieties may open up possibilities for new nanotube-based applications that are currently inaccessible to carbon nanotubes and other related materials.

Understanding DABCO Nanorotor Dynamics in Isostructural Metal-Organic Frameworks

Flexible framework dynamics present in the subset of metal-organic frameworks known as soft porous crystals give rise to interesting structural properties that are unique to this class of materials. In this work, we use experiments and molecular simulation to understand the highly dynamic nanorotor behavior of the 1,4-diazabicyclo[2.2.2]octane (DABCO) ligand in the pillared Zn-DMOF and Zn-DMOF-TM (TM = tetramethyl) structures. While DABCO is known to be displaced in the presence of water in the parent Zn-DMOF structure, the Zn-DMOF-TM variation is highly stable even after adsorbing significant amounts of water vapor. The dynamics of DABCO in the presence of water guest molecules is therefore also explored in the Zn-DMOF-TM structure via in situ NMR and IR experiments. This analysis shows that the rotational motion of the DABCO linkers is dependent on water content, but not a likely source of water instability because the dynamics are fast and largely unaffected by the presence of methyl functional groups.

Aminosilanes grafted to basic alumina as CO2 adsorbents--role of grafting conditions on CO2 adsorption properties

Solid oxide-supported amine sorbents for CO2 capture are amongst the most rapidly developing classes of sorbent materials for CO2 capture. Herein, basic γ supports are used as hosts for amine sites through the grafting of 3-aminopropyltrimethoxysilane to the alumina surface under a variety of conditions, yielding the expected surface-grafted alkylamine groups, as demonstrated by FTIR spectroscopy and (29)Si and (13)C cross-polarization magic-angle spinning (CPMAS NMR) spectroscopy. Grafting amine sites on the surface in the presence of water leads to a high density of amine sites on the surface whereas simultaneously creating a unique type of aluminum species on the surface, as demonstrated by both 1D and 2D (27)Al MAS NMR spectroscopy. The thus prepared sorbents result in higher CO2 adsorption capacities and amine efficiencies compared to sorbents prepared in the absence of water or similar amine loading sorbents prepared using silica supports. In situ FTIR spectra of the sorbents exposed to CO2 at various pressures show no distinct difference in the nature of the adsorbed CO2 species on alumina- versus silica-supported amines, whereas water adsorption isotherms show that the improved performance of the amine-grafted alumina support is not a consequence of retained water on the more hydrophobic aminoalumina materials. The findings demonstrate that amine-grafted, basic alumina materials can be tuned to be more efficient than the corresponding silica-supported materials at comparable amine loadings, further demonstrating that the properties of amine sites can be tuned by controlling or adjusting the support surface properties.

Nanoparticle dispersion in polymer nanocomposites by spin-diffusion-averaged paramagnetic enhanced NMR relaxometry

We developed an analytical relationship between nuclear magnetic relaxation and interparticle spacings in polymer nanocomposites filled with paramagnetic-impurity-containing clay nanoparticles. Using (1)H NMR relaxometry, clay nanoparticle dispersion was quantified and agrees with interparticle spacing distributions determined from statistical analysis of TEM images. Some information on the overall quality of clay dispersion is revealed. This work offers a new approach and new insights into nanoparticle dispersion in polymer nanocomposites.

Nanoparticle dispersion in polymer nanocomposites by spin-diffusion-averaged paramagnetic enhanced NMR relaxometry: scaling relations and applications

Scaling relations were identified between NMR relaxometric observables and nanoparticle contents/spacings that enable predictions of clay dispersion in polymer nanocomposites.

Determination of porosity of lignocellulosic biomass before and after pretreatment by using Simons' stain and NMR techniques

To further investigate the effect of dilute acid pretreatment (DAP) and steam explosion pretreatment (SE) on the change in cellulose accessibility, several techniques were applied including a Simons' stain (SS) technique along with several NMR methods (i.e., NMR cryoporometry, (1)H spin-lattice (T1) and (1)H spin-spin (T2) relaxometry, and diffusometry). These methods were utilized to probe biomass porosity and thus assess cellulose accessibility on untreated and pretreated Populus. In general, these techniques indicate that pretreated Populus has larger pore size distributions and specific surface area (SSA) when compared to an untreated sample. The SS method revealed that DAP is more effective than SE in terms of the SSA increase, and that DAP increases SSA as a function of pretreatment severity. Relaxometry and diffusion measurements also suggest pore expansion occurs primarily in the first 10 min of DAP.

Biomarkers of whale shark health: a metabolomic approach

In a search for biomarkers of health in whale sharks and as exploration of metabolomics as a modern tool for understanding animal physiology, the metabolite composition of serum in six whale sharks (Rhincodon typus) from an aquarium collection was explored using (1)H nuclear magnetic resonance (NMR) spectroscopy and direct analysis in real time (DART) mass spectrometry (MS). Principal components analysis (PCA) of spectral data showed that individual animals could be resolved based on the metabolite composition of their serum and that two unhealthy individuals could be discriminated from the remaining healthy animals. The major difference between healthy and unhealthy individuals was the concentration of homarine, here reported for the first time in an elasmobranch, which was present at substantially lower concentrations in unhealthy whale sharks, suggesting that this metabolite may be a useful biomarker of health status in this species. The function(s) of homarine in sharks remain uncertain but it likely plays a significant role as an osmolyte. The presence of trimethylamine oxide (TMAO), another well-known protective osmolyte of elasmobranchs, at 0.1-0.3 mol L(-1) was also confirmed using both NMR and MS. Twenty-three additional potential biomarkers were identified based on significant differences in the frequency of their occurrence between samples from healthy and unhealthy animals, as detected by DART MS. Overall, NMR and MS provided complementary data that showed that metabolomics is a useful approach for biomarker prospecting in poorly studied species like elasmobranchs.

1H NMR T 1 Relaxation of Polymer/Montmorillonite Nanocomposites with Different Clay Contents and Degrees of Exfoliation: Magnetic Field Effects

The initial stage of the NMR 1H T 1 relaxation of well-defined polypropylene-montmorillonite nanocomposites was investigated at two different magnetic fields of 0.54 and 7.05 T. At 0.54 T, two periods can be distinguished during the first 30 ms after a saturation pulse train. Both periods scale linearly with the square root of the recovery time. The first period occurs during the first 1 ms and is attributed to direct dipolar relaxation of nuclei in immediate proximity to the clay. It is caused by paramagnetic impurities within the clay and is characterized by a magnetization recovery curve with a slope proportional to the concentration of these impurities. The second period occurs at 4 to 30 ms after saturation and is due to spin diffusion between the sink, formed by the initial relaxation at the clay surface, and the surrounding polymer matrix, which relaxes at a much slower rate. The second period is characterized by a magnetization recovery curve with a slope proportional to the effective surface area of the clay, from which a degree of exfoliation may be determined. At 7.05 T, only a single relaxation recovery period is observed. At this higher magnetic field, the direct relaxation is characterized by a substantially longer relaxation time so that it is not distinguished from the spin-diffusion process. As with the slope of the second period of the magnetization recovery at 0.54 T, the slope of the magnetization recovery curve at 7.05 T can be utilized to extract a degree of exfoliation.

Spatially resolved solid-state 1H NMR for evaluation of gradient-composition polymeric libraries

Polyurethane libraries consisting of films with composition gradients of aliphatic polyisocyanate and hydroxy-terminated polyacrylate resin were characterized using methods of (1)H NMR microimaging (i.e., magnetic resonance imaging, (MRI)) and solid-state NMR. Molecular mobilities and underlying structural information were extracted as a function of the relative content of each of the two components. Routine NMR microimaging using the spin-echo sequence only allows investigations of transverse relaxation of magnetization at echo times >2 ms. A single-exponential decay was found, which is likely due to free, noncross-linked polymer chains. The mobility of these chains decreases with increasing content of the aliphatic polyisocyanate. The concept of a 1D NMR profiler is introduced as a novel modality for library screening, which allows the convenient measurement of static solid-state NMR spectra as a function of spatial location along a library sample that is repositioned in the rf coil between experiments. With this setup the complete transverse relaxation function was measured using Bloch decays and spin echoes. For all positions within the gradient-composition film, relaxation data consisted of at least three components that were attributed to a rigid highly cross-linked resin, an intermediate cross-linked but mobile constituent, and the highly mobile free polymer chains (the latter is also detectable by MRI). Analysis of this overall relaxation function measured via Bloch decays and spin echoes revealed only minor changes in the mobilities of the individual fractions. Findings with respect to the most mobile components are consistent with the results obtained by NMR microimaging. The major effect is the significant increase in the rigid-component fraction with the addition of the hydroxy-terminated polyacrylate resin.

Control of microfluidic flow in amphiphilic fabrics

Woven textile fabrics were designed and constructed from hydrophilic and hydrophobic spun yarns to give planar substrates containing amphiphilic microchannels with defined orientations and locations. Polypropylene fibers were spun to give hydrophobic yarns, and the hydrophilic yarns were spun from a poly(ethylene terephthalate) copolyester. Water wicking rates into the fabrics were measured by video microscopy from single drops, relevant for point-of-care microfluidic diagnostic devices, and from reservoirs. intra-yarn microchannels in the hydrophilic polyester yarns were shown to selectively transport aqueous fluids, with the flow path governed by the placement of the hydrophilic yarns in the fabric. By comparing fluid transport in fabric constructions with systematic variations in the numbers of adjacent parallel and orthogonal hydrophilic yarns, it was found that inter-yarn microchannels significantly increased wicking rates. Simultaneous wicking of an aqueous and hydrocarbon fluid into the hydrophilic and hydrophobic microchannels of an amphiphilic fabric was successfully demonstrated. The high degree of interfacial contact and micrometer-scale diffusion lengths of such coflowing immiscible fluid streams inside amphiphilic fabrics suggest potential applications as highly scalable and affordable microcontactors for liquid-liquid extractions.

Removal and biosorption of C₆₀ from water by an aquatic plant, Ceratophyllum sp

The fate of fullerene water suspension (FWS) in an aquatic system of Ceratophyllum sp., a rootless submerged plant, under non-sterile sediment-free conditions was investigated. Fast removal of FWS from water by the plants was observed and irreversible adsorption of C(60) onto plants and increasing C(60) mass on the plant surface with prolonged exposure durations were confirmed. An intact plant extraction procedure was developed and the majority (>80%) of C(60) removed from water was extracted from the plants. C(60) remained aggregated after being associated with the plants, which was verified by (13)C NMR spectroscopy. Light micrographs showed association of FWS on and in the cuticle layers.

A permanent change in protein mechanical responses can be produced by thermally-induced microdomain mixing

Electrospinning was employed to fabricate 3-D fiber networks from a recombinant amphiphilic elastin-mimetic tri-block protein polymer and the effects of moderate thermal conditioning (60 degrees C, 4 h) on network mechanical responses investigated. Significantly, while cryo-high resolution scanning electron microscopy (cryo-HRSEM) revealed that the macroscopic and microscopic morphology of the network structure was unchanged, solid-state (1)H-NMR spectroscopy demonstrated enhanced interphase mixing of hydrophobic and hydrophilic blocks. Significantly, thermal annealing triggered permanent changes in network swelling behavior (28.75 +/- 2.80 non-annealed vs. 13.55 +/- 1.39 annealed; P < 0.05) and uniaxial mechanical responses, including Young's modulus (0.170 +/- 0.010 MPa non-annealed vs. 0.366 +/- 0.05 MPa annealed; P < 0.05) and ultimate tensile strength (0.079 +/- 0.008 MPa vs. 0.119 +/- 0.015 MPa; P < 0.05). To our knowledge, these investigations are the first to note that mechanical responses of protein polymers can be permanently altered through a temperature-induced change in microphase mixing.

Self-organization of water in lithium/nitrobenzene system

The effect of lithium ion on the ordering of water in water-saturated nitrobenzene has been probed by 2H NMR, diffusion ordered spectroscopy and neutron scattering. It was shown that increased water concentration in LiClO4/wet nitrobenzene results in the formation of a metastable solvatomer with mixed water and nitrobenzene character, Li+(W/NB). This species is shown to decay over hours to two solvatomers, one dominated by nitrobenzene Li+(NB) and the other dominated by water Li+(W). To confirm the assignment of these solvation states, diffusion ordered deuterium NMR spectroscopy has been used to elucidate the hydrodynamic radii of these solvatomers. Neutron scattering yields vibrational spectroscopy information that shows how addition of lithium to the nitrobenzene/water system results in relatively slow self-organization of the water environment (hours).

NMR study of lithium ion in nitrobenzene/water system

The goal of this project has been to elucidate the solvation states and kinetics involved in the transfer of Li ions between nitrobenzene and water. A large interface area has been realized by confining one phase in polymer beads and suspending them in the other phase. A 2D 7Li-NMR spectroscopic result of such a system obtained on a 400 MHz instrument has shown that the rate of the Li ion transfer exchange between nitrobenzene and water is too fast to resolve individual solvatomers. A pair of well-resolved 7Li-NMR peaks corresponding to different solvation environments of Li+ in "wet" nitrobenzene has been observed. The most surprising result is that the ratio of those two peaks and their separation changes over a period of days, but it can be reversibly changed by mechanical disturbance, such as ultrasonication. This effect is reproducible and suggests spontaneous but slow formation of metastable solvatomers of Li+. Another surprising observation has been slow and irreversible incorporation of lithium ion from wet nitrobenzene into the walls of the silica-containing vessels.

Sorption isotherm measurements by NMR

An experimental setup is described for the automated recording of sorption isotherms by NMR experiments at precisely defined levels of relative humidity (RH). Implementation is demonstrated for a cotton fabric; Bloch decays. T1 and T2* relaxation times were measured at predefined steps of increasing and decreasing relative humidities (RHs) so that a complete isotherm of NMR properties was obtained. Bloch decays were analyzed by fitting to relaxation functions consisting or a slow- and a fast-relaxing component. The fraction of slow-relaxing component was greater than the fraction of sorbed moisture determined from gravimetric sorption data. The excess slow-relaxing component was attributed to plasticized segments of the formerly rigid cellulose matrix. T1 and T2* sorption isotherms exhibit hysteresis similar to gravimetric sorption isotherms. However, correlating RH to moisture content (MC) reveals that both relaxation constants depend only on MC, and not on the history of moisture exposure.

1H NMR Relaxation Studies of Cured Natural Rubbers with Different Carbon Black Fillers

1H NMR relaxation data provide insight into the effects of carbon black fillers on the structure of polymer networks in products based on natural rubber so that accepted ideas concerning the interaction between elastomeric networks and active filling materials are confirmed. A new 1H NMR relaxation experiment allows the direct investigation of dangling chains within the polymeric network. In samples containing carbon black a motional anisotropy is observed for these chain ends, while dangling chains in samples without carbon black fillers show isotropic rotational motions. The parameter q′, quantifying the motional anisotropy, is suggested to be a measure of the physico-chemical interactions between elastomer and filler.

Response of phosphatidylcholine in the gel and liquid-crystalline states to membrane surface charges

The influence of membrane surface charge on the conformation of the choline head group of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) was investigated in the gel and liquid-crystalline states by using 2H NMR spectroscopy of specifically choline-deuterated DMPC. The surface charge was made progressively more negative through admixture of various proportions of 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG). All membrane compositions showed nearly identical gel- to liquid-crystalline-phase transitions centered about 24 degrees C. The gel-state 2H NMR spectra from all three choline head-group deutero-labeling positions (alpha, beta, and gamma) decreased in intensity and broadened relative to the liquid-crystalline-state spectra. These effects were not so severe that they masked the overriding influence of surface charge on the choline head-group conformation as reflected in the 2H NMR spectra. Thus, in both the liquid-crystalline and gel states, the presence of negative surface charge caused the quadrupole splitting from DMPC-alpha-d2 to increase while causing that from DMPC-beta-d2 and DMPC-gamma-d9 to decrease. These effects were progressive with increasing density of negative surface charge. Correlation plots of the quadrupole splittings obtained, under otherwise identical conditions, from different deutero-labeling positions were linear over most of the range of surface charge densities, in both the liquid-crystalline and gel states, for all three correlations (alpha-beta, beta-gamma, and alpha-gamma). At extreme surface charge densities, the alpha-beta and alpha-gamma correlations showed biphasic behavior in that, at high surface charge densities, the change in the quadrupole splittings from DMPC-alpha-d2 became less pronounced.(ABSTRACT TRUNCATED AT 250 WORDS)