Solubilization of bilirubin by cholate micelles. Spectroscopic and gel permeation studies

The interactions of bilirubin with bile salts have been studied using fluorescence, circular dichroism and¹H NMR methods. Enhancement of bilirubin fluorescence and induction of optical activity in bilirubin in the presence of cholate has been observed. Fluorescence enhancement is pronounced above the critical micelle concentration, while induced CD bands are detectable even in the premicellar region. Dehydrocholate and deoxycholate did not cause a fluorescence increase, but induced CD bands were observed for bilirubin in these cases. Gel permeation chromatography on Sephadex G-50 yielded a single bilirubin-cholate species at alkaline pH, while two species were obtained at neutral pH.¹H NMR and CD spectral characterizations of these complexes are reported. A 4∶1 cholate-bilirubin mixture has been analysed by difference (nuclear Overhauser effect) NOE spectroscopy. Observation of strong, negative NOE, both intermolecular and intramolecular leads to the conclusion that specific methyl groups on bilirubin and cholate are proximal in the mixed micelle.     

Analysis of radiation induced degradation in FPC-461 fluoropolymers by variable temperature multinuclear NMR

Solid state nuclear magnetic resonance techniques have been used to investigate aging mechanisms in a vinyl chloride:chlorotrifluoroethylene copolymer, FPC-461, due to exposure to γ-radiation. Solid state ¹H MAS NMR spectra revealed structural changes in the polymer upon irradiation under both air and nitrogen atmospheres. Considerable degradation is seen with ¹H NMR in the vinyl chloride region of the polymer, particularly in the samples irradiated in air. ¹⁹F MAS NMR was used to investigate speciation in the chlorotrifluoroethylene blocks, though negligible changes were seen. ¹H and ¹⁹F NMR at elevated temperature revealed increased segmental mobility and decreased structural heterogeneity within the polymer, yielding significant resolution enhancement over room temperature solid state detection. The effects of multi-site exchange are manifested in both the ¹H and ¹⁹F NMR spectra as a line broadening and change in peak position as a function of temperature.     

Latex‐state NMR spectroscopy for quantitative analysis of epoxidized deproteinized natural rubber

Method of quantitative analysis through latex‐state ¹³C NMR spectroscopy was established for in situ determination of epoxy group content of epoxidized natural rubber in latex stage. The epoxidized natural rubber latex was prepared by epoxidation of deproteinized natural rubber with freshly prepared peracetic acid in latex stage. The resulting epoxidized deproteinized natural rubber (EDPNR) latex was characterized through latex‐state ¹³C NMR spectroscopy. Chemical shift values of signals of latex‐state ¹³C NMR spectrum for EDPNR were similar to those of solution‐state ¹³C NMR spectrum for EDPNR. Resolution of latex‐state ¹³C NMR spectrum was gradually improved as temperature for the nuclear magnetic resonance (NMR) measurement increased to 70°C. Signal‐to‐noise ratio of latex‐state ¹³C NMR measurement was similar to that of solution‐state ¹³C NMR measurement at temperature above 50°C. The epoxy group content determined through latex‐state NMR spectroscopy was proved to be the same as that determined through solution‐state NMR spectroscopy. Copyright © 2017 John Wiley & Sons, Ltd.     

Light absorption in solutions of cetyltrimethylammonium and cetylpyridinium bromides

Absorption of monochromatic light in solutions of cetyltrimethylammonium (CTAB) and cetylpyridinium (CPB) bromides has been studied in the wavelength λrange of 190–1000 nm. The investigation has been performed at 30°C and surfactant concentrations ranging from 5 × 10^?5 to 3.5 × 10^?3 M. Spectra of solutions of LiBr, KBr, and CTAB in the premicellar concentration region have been shown to coincide with each other. They are unimodal, and the heights of their maxima at λ_max ≈ 193 nm depend on Br^? concentration alone. In contrast to CTAB solutions, the UV spectra of CPB solutions are characterized by the presence of two absorption maxima near λ_max1 = 191 nm and λ_max2 = 259 nm, as well as a shoulder at 210–218 nm. Their existence is caused by the presence of both Br^? anions and CP⁺ cations in the solutions. The dependences of the integral absorption in the examined wavelength range on CPB concentration exhibit inflections both in the premicellar region and upon the transition to micellar solutions, with these inflections characterizing the critical dimerization and micellization concentrations, respectively. For CTAB, this regularity has only been observed at the critical micellization concentration. The data on the concentration dependence of the light absorption have resulted in the proposal of a method for determining the degree β of counterion binding by micelles of ionic surfactants. The β values calculated for CTAB and CPB are equal to 0.89 ±0 0.1.     

Effective self-diffusion coefficients of ions in sodium dodecyl sulfate micellar solutions

The effective self-diffusion coefficients of ions in premicellar and micellar solutions of sodium dodecyl sulfate are measured by the NMR self-diffusion method at 40°C. The obtained regularities are explained using a proposed model that takes into account the possible surface diffusion of counterions bound with micelles. This effect is shown to markedly influence the charge transfer in micellar solutions. Based on the results obtained, the self-diffusion coefficients of bound Na⁺ counterions are estimated and the causes and ranges of their variations are indicated.     

Quenching of Pyrene Fluorescence in Premiceljar Solutions

Abstract

The quenching of the fluorescence intensity of pyrene by KBr has been measured in premicellar solutions of cetyltrimethylammonium bromide (CTAB), sodium lauryl sulfate (SLS) and polyoxyethylene 23-lauryl ether (Brij 35). The association of pyrene with premicellar aggregates is thought to bring the bromide ion closer to the fluorophore and hence results in a greater quenching effect. In 1.0 × 10^?4 M CTAB solutions there is the beginning of “protective” premicellar aggregation. At this stage, 13 times more bromide ion is needed to effect the same degree of quenching as in pure water.     

Studies on the phase structure of ethylene‐vinyl acetate copolymers by solid‐state 1H and 13C NMR

The phase structure of a series of ethylene‐vinyl acetate copolymers has been investigated by solid‐state wide‐line ¹H NMR and solid‐state high‐resolution ¹³C NMR spectroscopy. Not only the degree of crystallinity but the relative contents of the monoclinic and orthorhombic crystals within the crystalline region varied with the vinyl acetate (VA) content. Biexponential ¹³C NMR spin–lattice relaxation behavior was observed for the crystalline region of all samples. The component with longer ¹³C NMR spin–lattice relaxation time (T₁) was attributed to the internal part of the crystalline region, whereas the component with shorter ¹³C NMR T₁ to the mobile crystalline component was located between the noncrystalline region and the internal part of the crystalline region. The content of the mobile crystalline component relative to the internal part of the crystalline region increased with the VA content, showing that the ¹³C NMR spin–lattice relaxation behavior is closely related to the crystalline structure of the copolymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2199–2207, 2002     

Structure and dynamics of room temperature ionic liquids with bromide anion: results from 81Br NMR spectroscopy

We report the results of a comprehensive ⁸¹Br NMR spectroscopic study of the structure and dynamics of two room temperature ionic liquids (RTILs), 1‐butyl‐3‐methylimidazolium bromide ([C₄mim]Br) and 1‐butyl‐2,3‐dimethylimidazolium bromide ([C₄C₁mim]Br), in both liquid and crystalline states. NMR parameters in the gas phase are also simulated for stable ion pairs using quantum chemical calculations. The combination of ⁸¹Br spin‐lattice and spin‐spin relaxation measurements in the motionally narrowed region of the stable liquid state provides information on the correlation time of the translational motion of the cation. ⁸¹Br quadrupolar coupling constants (C_Q) of the two RTILs were estimated to be 6.22 and 6.52 MHz in the crystalline state which were reduced by nearly 50% in the liquid state, although in the gas phase, the values are higher and span the range of 7–53 MHz depending on ion pair structure. The C_Q can be correlated with the distance between the cation–anion pairs in all the three states. The ⁸¹Br C_Q values of the bromide anion in the liquid state indicate the presence of some structural order in these RTILs, the degree of which decreases with increasing temperature. On the other hand, the ionicity of these RTILs is estimated from the combined knowledge of the isotropic chemical shift and the appropriate mean energy of the excited state. [C₄C₁mim]Br has higher ionicity than [C₄mim]Br in the gas phase, while the situation is reverse for the liquid and the crystalline states. Copyright © 2015 John Wiley & Sons, Ltd.     

13C‐TmDOTA as versatile thermometer compound for solid‐state NMR of hydrated lipid bilayer membranes

Recent advances in solid‐state nuclear magnetic resonance (NMR) techniques, such as magic angle spinning and high‐power decoupling, have dramatically increased the sensitivity and resolution of NMR. However, these NMR techniques generate extra heat, causing a temperature difference between the sample in the rotor and the variable temperature gas. This extra heating is a particularly crucial problem for hydrated lipid membrane samples. Thus, to develop an NMR thermometer that is suitable for hydrated lipid samples, thulium‐1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetate (TmDOTA) was synthesized and labeled with ¹³C (i.e., ¹³C‐TmDOTA) to increase the NMR sensitivity. The complex was mixed with a hydrated lipid membrane, and the system was subjected to solid‐state NMR and differential scanning calorimetric analyses. The physical properties of the lipid bilayer and the quality of the NMR spectra of the membrane were negligibly affected by the presence of ¹³C‐TmDOTA, and the ¹³C chemical shift of the complex exhibited a large‐temperature dependence. The results demonstrated that ¹³C‐TmDOTA could be successfully used as a thermometer to accurately monitor temperature changes induced by ¹H decoupling pulses and/or by magic angle spinning and the temperature distribution of the sample inside the rotor. Thus, ¹³C‐TmDOTA was shown to be a versatile thermometer for hydrated lipid assemblies. Copyright © 2015 John Wiley & Sons, Ltd.     

Sodium dodecyl sulfate self-diffusion in premicellar and low-concentrated micellar solutions in the presence of a background electrolyte

The Fourier transform pulsed field gradient NMR method is employed to investigate the self-diffusion of surface active sodium dodecyl sulfate ions in premicellar and low-concentrated micellar solutions at different NaCl concentrations in a system. The self-diffusion coefficient of the surfactant is found to markedly decrease in the premicellar region. An analysis of the experimental data carried out using a model implying the presence of sodium dodecyl sulfate monomers, dimers, and micelles in the system made it possible to determine the self-diffusion coefficients of the monomers and dimers, as well as the corresponding sizes of kinetic units.     

Phase diagram and phase structure of the sodium di-n-pentyl phosphate-water system.1H pulsed-gradient NMR self-diffusion,31P NMR and x-ray diffraction studies

Sodium di-n-pentylphos phate (DPP) has been synthesized, and the phase diagram of the DPP-water system consisting of five regions (I, II, III, IV, and V) has been determined. The phase structure has been investigated by¹H pulsed-gradient NMR self-diffusion,³¹P NMR and x-ray low angle diffraction methods. The results are summarized as follows. In region I, there exist two critical micelle concentrations (CMC), indicating that this region is in a monomer-micelle equilibrium and that variation in the aggregated state occurs at the second CMC. Region II is a two phase area in which regions I and IV coexist. In region III, hydrated crystals and an aqueous solution of DPP coexist. Region IV is a homogenous, transparent and fluid phase and the results of³¹P NMR spectra and x-ray diffraction patterns reveal the formation of a highly organized structure, similar to a lamellar-like structure. Region V is a homogenous, transparent and fluid phase and the self-diffusion coefficient value and³¹P NMR spectra show that its phase structure is very similar to that for the concentrated sample in region I.     

Dynamics in the crystalline polymorphic forms I and II and form III of isotactic poly‐1‐butene

Following an earlier study of the ¹H relaxation and NMR line shapes, we have carried out selective one‐dimensional and two‐dimensional ¹³C solid‐state NMR studies that yield to detailed interpretation of the dynamics in form I, II, and III polymorphs of isotactic poly‐1‐butene. A specific defect diffusion along the side group is proposed to account for the temperature dependence of the ¹³C spectra in form I. The backbone of the helix in forms II and III is shown to undergo large angle motions above the glass‐transition temperature. High‐resolution solid‐state ¹³C two‐dimensional exchange NMR under magic‐angle spinning with cross‐polarization techniques demonstrates the existence of slow rotational jumps of the helices in form III with typical jump rates of about 10 s⁻¹. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2611–2624, 2000     

Component analysis of proton NMR spectra of linear polyethylene in the α-transition temperature range and phase distribution

Broad-line ¹H NMR spectra of linear polyethylene at temperatures in the α-transition range can be analyzed in terms of contributions from the crystalline and noncrystalline components provided molecular motion in the crystalline region is adequately considered. The spectrum of solid n-C₃₂H₆₆ or n-C₄₄H₉₀ prior to melting is used to take account of the contribution of the crystalline region of the polymer to molecular motions. The temperature dependence of the component distribution in the polymer is briefly discussed for a wide range of temperatures, together with previously reported results at low temperatures. The noncrystalline component is in a rigid glassy state at very low temperatures but with rising temperature it transforms to a mobile glassy state with restricted molecular motion, and transforms partially to the rubbery state at high temperature. The crystalline component remains rigid at low temperature, but some molecular motion is associated with it at higher temperatures in the α-transition range.     

Probing the Double Bond and Phase Properties of Natural Lipid Dispersions by Cross Polarization/Magic Angle Spinning 13C NMR

Solid-state high resolution ¹³C NMR spectra of bovine brain sulfatide, egg sphingomyelin, egg phosphatidylcholine, and cholesterol/phosphatidylcholine dispersions were obtained by the cross-polarization/magic angle spinning (CP/MAS) method as functions of contact time, temperature and composition. Quantitative analysis of the chemical shift and linewidth data indicate that in the liquid-crystalline state the hydrocarbon chains of sulfatide are packed less orderly than those of sphingomyelin, and that there are two or more conformers for the ceramide residues of natural sphingolipids. The fatty acid double bond showed higher mobility than that of sphingosine as monitored by the signal intensity profiles as a function of contact time. The same approach was used to study the coexisting Lα (liquid-crystalline phase) and β (cholesterol-rich characterized phase) two-phase region of cholesterol/phosphatidylcholine mixtures. Without isotope enrichment, structural and phase properties of natural lipid dispersions can be obtained easily by monitoring the chemical shift, the signal intensity and the linewidth of ^l3C NMR spectra.     

Self‐Assembly of a Highly Organized,Hexameric Supramolecular Architecture: Formation,Structure and Properties

Two derivatives, ³ L and ⁹ L , of a ditopic, multiply hydrogen‐bonding molecule, known for more than a decade, have been found, in the solid state as well as in solvents of low polarity at room temperature, to exist not as monomers, but to undergo a remarkable self‐assembly into a complex supramolecular species. The solid‐state molecular structure of ³ L , determined by single‐crystal X‐ray crystallography, revealed that it forms a highly organized hexameric entity ³ L ₆ with a capsular shape, resulting from the interlocking of two sets of three monomolecular components, linked through hydrogen‐bonding interactions. The complicated ¹H NMR spectra observed in o‐dichlorobenzene (o‐DCB) for ³ L and ⁹ L are consistent with the presence of a hexamer of D₃ symmetry in both cases. DOSY measurements confirm the hexameric constitution in solution. In contrast, in a hydrogen‐bond‐disrupting solvent, such as DMSO, the ¹H NMR spectra are very simple and consistent with the presence of isolated monomers only. Extensive temperature‐dependent ¹H NMR studies in o‐DCB showed that the L ₆ species dissociated progressively into the monomeric unit on increasing th temperature, up to complete dissociation at about 90 °C. The coexistence of the hexamer and the monomer indicated that exchange was slow on the NMR timescale. Remarkably, no species other than hexamer and monomer were detected in the equilibrating mixtures. The relative amounts of each entity showed a reversible sigmoidal variation with temperature, indicating that the assembly proceeded with positive cooperativity. A full thermodynamic analysis has been applied to the data.     

Heating and temperature gradients of lipid bilayer samples induced by RF irradiation in MAS solid‐state NMR experiments

The MAS solid‐state NMR has been a powerful technique for studying membrane proteins within the native‐like lipid bilayer environment. In general, RF irradiation in MAS NMR experiments can heat and potentially destroy expensive membrane protein samples. However, under practical MAS NMR experimental conditions, detailed characterization of RF heating effect of lipid bilayer samples is still lacking. Herein, using ¹H chemical shift of water for temperature calibration, we systematically study the dependence of RF heating on hydration levels and salt concentrations of three lipids in MAS NMR experiments. Under practical ¹H decoupling conditions used in biological MAS NMR experiments, three lipids show different dependence of RF heating on hydration levels as well as salt concentrations, which are closely associated with the properties of lipids. The maximum temperature elevation of about 10 °C is similar for the three lipids containing 200% hydration, which is much lower than that in static solid‐state NMR experiments. The RF heating due to salt is observed to be less than that due to hydration, with a maximum temperature elevation of less than 4 °C in the hydrated samples containing 120 mmol l^?1 of salt. Upon RF irradiation, the temperature gradient across the sample is observed to be greatly increased up to 20 °C, as demonstrated by the remarkable broadening of ¹H signal of water. Based on detailed characterization of RF heating effect, we demonstrate that RF heating and temperature gradient can be significantly reduced by decreasing the hydration levels of lipid bilayer samples from 200% to 30%. Copyright © 2016 John Wiley & Sons, Ltd.     

NMR Crystallography Enhanced by Quantum Chemical Calculations and Liquid State NMR Spectroscopy for the Investigation of Se-NHC Adducts**

N-heterocyclic carbene ligands (NHC) are widely utilized in catalysis and material science. They are characterized by their steric and electronic properties. Steric properties are usually quantified on the basis of their static structure, which can be determined by X-ray diffraction. The electronic properties are estimated in the liquid state; for example, via the ⁷⁷Se liquid state NMR of Se-NHC adducts. We demonstrate that ⁷⁷Se NMR crystallography can contribute to the characterization of the structural and electronic properties of NHC in solid and liquid states. Selected Se-NHC adducts are investigated via ⁷⁷Se solid state NMR and X-ray crystallography, supported by quantum chemical calculations. This investigation reveals a correlation between the molecular structure of adducts and NMR parameters, including not only isotropic chemical shifts but also the other chemical shift tensor components. Afterwards, the liquid state ⁷⁷Se NMR data is presented and interpreted in terms of the quantum chemistry modelling. The discrepancy between the structural and electronic properties, and in particular the π-accepting abilities of adducts in the solid and liquid states is discussed. Finally, the ¹³C isotropic chemical shift from the liquid state NMR and the ¹³C tensor components are also discussed, and compared with their ⁷⁷Se counterparts. ⁷⁷Se NMR crystallography can deliver valuable information about NHC ligands, and together with liquid state ⁷⁷Se NMR can provide an in-depth outlook on the properties of NHC ligands.     

Hydrogels based on schiff base formation between an amino‐containing polyphosphazene and aldehyde functionalized‐dextrans

Hydrogels generated by the interaction of two different water‐soluble polymers offer access to a new group of soft materials. A prototype amino‐functionalized polyphosphazene with both tyramine and ferulic acid‐based side groups was coupled to aldehyde functionalized‐dextrans to form hydrogels crosslinked via Schiff base chemistry. Synthesis of the polyphosphazene was accomplished by macromolecular substitution and protection‐deprotection chemistry, with characterization by ¹H NMR, ³¹P NMR, solid state ¹³C NMR, and DSC techniques. Combination of the aqueous polyphosphazene and aldehyde functionalized‐dextran solutions at room temperature caused gelation with different gelation times and crosslink densities dependent on the aldehyde content of the dextran. The hydrogel properties were evaluated using rheology, thermal characterization, and cryo‐microscopy. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2984–2991     

In and F MAS NMR study of (NH4)3InF6 phases

This study presents for the first time an NMR spectroscopic characterization of the room and high temperature phases of (NH₄)₃InF₆ using ¹⁹F and ¹¹⁵In as probe nuclei. The reversible phase transition to the cubic phase at 353 K was followed by MAS NMR in situ. Static NMR experiments of the room temperature phase and MAS NMR experiments of the high temperature phase allowed the determination of the NMR parameters of both nuclei. Finally, the scalar In-F coupling, rarely observed in solid state NMR, is evidenced in both room and high temperature phases of (NH₄)₃InF₆, and measured in the high temperature phase.     

Premicellar aggregation of amphiphilic molecules

We revisit the problem of amphiphilic aggregation using a simple two-state (monomer-aggregate) thermodynamic model, which allows the study of metastable aggregates of variable size. A sequence of well separated concentrations emerge: c(1), where a metastable aggregated state appears; c(2), above which an appreciable amount of metastable aggregates forms; and c(3), where the aggregated state becomes stable. Of these, c(3) is shown to correspond to the critical micelle concentration (cmc) as commonly measured in macroscopic experiments. Thus, appreciable premicellar aggregation is predicted in the concentration range between c(2) and c(3). We show that, so long as the micelles are not too large, the extent of premicellar aggregation is much larger than that expected from mere finite-size effects. It stems from the variability of the micelle size and the small free energy difference between the metastable state, containing monomers and aggregates, and the pure monomeric one. The aggregate size is found to weakly change with concentration below and above the cmc. The existence of premicellar aggregates and their concentration-insensitive size are in agreement with a recent experiment.