Size‐exclusion chromatographic NMR of polymer mixtures

The use of chromatographic stationary phases or solvent modifiers to modulate diffusion properties in NMR experiments is now well established. Their use can be to improve resolution in the diffusion domain or to provide an insight into analyte–modifier interactions and, hence, the chromatography process. Here, we extend previous work using size‐exclusion chromatographic stationary phases to the investigation of polymer mixtures. We demonstrate that similar diffusion modulation behaviour is observed with a size‐exclusion chromatographic stationary phase that can be understood in terms of size‐exclusion behaviour. Copyright © 2014 John Wiley & Sons, Ltd.     

一些高级NMR技术介绍

对一些二维NMR技术,例如^1H-^1H相关谱（^1H-^1H COSY),^1H-^13C杂核化学位移相关谱（^1H-C^13 COSY）,奥氏核效应交换相关谱（NOESY）作了介绍,列举了一些典型谱图。     

Interaction of curcumin with lipid monolayers and liposomal bilayers

Curcumin shows huge potential as an anticancer and anti-inflammatory agent. However, to achieve a satisfactory bioavailability and stability of this compound, its liposomal form is preferable. Our detailed studies on the curcumin interaction with lipid membranes are aimed to obtain better understanding of the mechanism and eventually to improve the efficiency of curcumin delivery to cells. Egg yolk phosphatidylcholine (EYPC) one-component monolayers and bilayers, as well as mixed systems containing additionally dihexadecyl phosphate (DHP) and cholesterol, were studied. Curcumin binding constant to EYPC liposomes was determined based on two different methods: UV/Vis absorption and fluorescence measurements to be 4.26 × 10⁴ M⁻¹ and 3.79 × 10⁴ M⁻¹, respectively. The fluorescence quenching experiment revealed that curcumin locates in the hydrophobic region of EYPC liposomal bilayer. It was shown that curcumin impacts the size and stability of the liposomal carriers significantly. Loaded into the EYPC/DPH/cholesterol liposomal bilayer curcumin stabilizes the system proportionally to its content, while the EYPC/DPH system is destabilized upon drug loading. The three-component lipid composition of the liposome seems to be the most promising system for curcumin delivery. An interaction of free and liposomal curcumin with EYPC and mixed monolayers was also studied using Langmuir balance measurements. Monolayer systems were treated as a simple model of cell membrane. Condensing effect of curcumin on EYPC and EYPC/DHP monolayers and loosening influence on EYPC/DHP/chol ones were observed. It was also demonstrated that curcumin-loaded EYPC liposomes are more stable upon interaction with the model lipid membrane than the unloaded ones.     

Taste sensing with polyacrylic acid grafted cellulose membrane

There are reports of fabrication of taste sensor by adsorbing lipids into Millipore filter paper, which improved the taste sensing efficiency of membrane remarkably. We have made an attempt to prepare taste sensor material by grafting polyacrylic acid (PAA) to cellulose. The research work covers polymer membrane preparation, morphology study, and structural characterization of the membrane and study of the taste sensing characteristics of this membrane for five different taste substances. FTIR spectroscopic analysis and SEM were done to get an idea about the structure and morphology of the PAA grafted cellulose membrane. Surface charge density of the membrane was estimated. The sensor characteristics like temporal stability, response stability, response to different taste substances, and reproducibility of sensing performance were studied using PAA grafted cellulose membrane. Sensor device prepared with this membrane has shown distinct response patterns for different taste substances in terms of membrane potential. Threshold concentrations of PAA grafted cellulose membrane for HCl, NaCl, quinine-hydrochloride (Q-HCl), sucrose and monosodium glutamate are 0.001 mM, 0.01 mM, 0.08 mM, 0.08 mM and 0.01 mM, respectively. The threshold concentrations except that in Q-HCl are below human threshold concentrations. Membranes also showed characteristic response patterns for organic acids like acetic acid, citric acid, formic acid, etc., mineral acids like HCl, H₂SO₄ and HNO₃, etc., salts, bitter substances, sweet substances and umami substances. Sensor device prepared with this membrane has excellent shelf life.     

Identification of modified natural porphyrin isomers: 1H and 13C NMR assignments by NOESY and reverse heteronuclear shift correlation

The efficiency of two-dimensional homonuclear ¹H ¹H NOE spectroscopy in characterizing and fully assigning the ¹H NMR spectra of several isomers of meso- or ring-substituted deuteroporphyrins is demonstrated. The carbon resonances of the skeleton and the substituents were fully assigned using two-dimensional reverse heteronuclear shift correlation spectroscopy.     

Interaction of surfactant with antistatic polymer thin layers

Thin layers made from three kinds of hydrophilic polymer were coated onto poly(ethylene terephthalate)(PET) fibers to study the interaction of an anionic surfactant, sodiumn-dodecyl benzenesulfonate, with the polymer layers. The coated layers include a) poly(vinyl alcohol) (PVA) crosslinked with glutaraldehyde [nonionic], b) crosslinked, sulfated PVA [anionic], and c) polyethyleneimine crosslinked with poly(ethyleneglycol diglycidylether) [cationic]. All of these coatings were found to reduce the electrostatic charging of the PET cloths, indicating that they were effectively coated with the hydrophilic polymers. The PET cloth coated with the thin layers was immersed in the aqueous solution of surfactant at 40°C for different durations and the electrostatic voltage as well as the weight change were determined after drying. When the cloth coated with the nonionic or the anionic layer was brought into contact with the surfactant, neither the electrostatic voltage nor the weight of PET changed. On the contrary, immersion in the surfactant solution brought about an increase in both the electrostatic voltage and the weight for the PET coated with the cationic layer. This suggested that the surfactant molecules were bound to the cationic layer, in contrast to the nonionic and the anionic layer. It was concluded that the binding was due to ion complexing between the cationic groups in the polymeric layer and the sulfate groups in the surfactant molecules.     

Interaction of metal ions with polypyrrole on polyacrylic acid matrix

The oxidative matrix polymerization of pyrrole (Py) by Fe(III), Cu(II), Ni(II), Co(II), and Zn(II) in the presence of polyacrylic acid (PAA) was studied and water‐soluble products along with insoluble products were obtained. The metal (Me) content of the insoluble part was determined by using atomic absorption spectroscopy (AAS). The effects of the oxidation potential of Me ions and ligands on the aggregation of polypyrrole (PPy) on the matrix polymer were measured by ultraviolet (UV)‐visible spectra. These findings also were checked by cyclic voltammetry (CV) measurements on PAA–Cu and PAA–PPy–Cu interactions. The conductometric titration results of PAA–PPy–Me ternary solutions were explained in the light of the interaction of Me ions with Py to polymerize on the PAA matrix resulting in some free carboxyl groups with a possibility of having Me–polymer complexes and a ternary complex (PAA–Me–PPy). The insoluble products were characterized by Fourier transform infrared (FTIR), elemental analysis, scanning electron microscopy (SEM), and four point probe conductivity measurements. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1115–1123, 1999     

NOESY,HOESY, T1 and solid‐state NMR studies on [RuH(η6‐toluene)(Binap)](CF3SO3): a molecule with a strongly distorted piano‐stool structure

Detailed solution‐NMR studies on the distorted ruthenium hydride complex [RuH(η⁶‐toluene)(Binap)](CF₃SO₃) (2) are reported. NOE‐spectroscopy, together with low‐temperature ¹H and ³¹P NMR data, reveals restricted rotation around a P—C bond for a specific axial P—phenyl ring with the activation energy determined via simulation. From ¹⁹F, ¹H HOESY data, the approach of the triflate anion relative to the hydride ligand is established. Comparison of the quadrupole coupling constant C_QF from both solution‐ and solid‐state MAS‐NMR on the deuteride [RuD(η⁶‐benzene)(Binap)](CF₃SO₃) (1‐D) provide information on the nature of the Ru—H bond. Copyright © 2003 John Wiley & Sons, Ltd.     

Gs-HSQC-NOESY versus gs-NOESY-HSQC experiments: signal attenuation due to diffusion; application to symmetrical molecules

Gradient-selected (gs) HSQC-NOESY type experiments are often applied in order to obtain NOE cross peaks in symmetrical molecules or in complex organic molecules, e.g. carbohydrates. Since the coherence-selecting gradients in these pulse sequences are separated by several delays, including the mixing time, the gs-HSQC-NOESY spectra exhibit severe signal attenuation due to diffusion effects. The respective NOE information unaffected by diffusion effects can be obtained by X-half-filtered gs-NOESY-HSQC spectra. In this paper, an X-half-filtered version of the gs-NOESY-HSQC experiment is presented and the NOE cross peak integrals of its spectra are compared with those of a standard gs-HSQC-NOESY experiment. With phenanthrene as an example of symmetrical molecules, it is shown that the relative signal attenuation of gs-HSQC-NOESY cross peaks versus gs-NOESY-HSQC cross peaks is caused by diffusion effects and follows the Stejskal-Tanner equation. In contrast, the X-half-filtered gs-NOESY-HSQC experiment provides NOE cross peaks with reasonable signal-to-noise ratios even for long-range interactions in the presence of quadrupolar relaxation. This is demonstrated by the spectra of lithium dimethylcuprate.     

Interaction of the antimalarial agents halofantrine and lumefantrine with lipid bilayers

The effects of antimalarial drugs halofantrine and lumefantrine on the fluoresence anisotropy of diphenylhexatriene (DPH)-containing phospholipid vesicles have been examined. Lumefantrine increases DPH anisotropy, indicating a condensing effect on bilayers of dipalmitoylphosphatidyl choline (DPPC), dioleoylphosphatidylcholine (DOPC), egg lecithin and mouse erythrocyte membranes (including membranes isolated from plasmodial-infected mice). Its condensing effect is more pronounced in bilayers of lower microviscosity. In contrast, increases or decreases in DPH anisotropy are observed with halofantrine, depending on the nature of the lipid. Decreases in anisotropy, which reflect a perturbing effect, are observed in bilayers of high microviscosity (for example, gel state of DPPC bilayers). Increases in anisotropy are observed in bilayers of low microviscosity (such as DOPC and egg lecithin bilayers). The perturbing effect of halofantrine is further confirmed by the increases in permeability of calcein-containing DPPC vesicles in the presence of the drug. However the perturbative effects of halofantrine are observed to the same magnitude in uninfected and plasmodial-infected erythrocyte membranes, and may not be relevant to the antimalarial action of the drug. In contrast, the condensing effect of lumefantrine is significantly greater in infected erythrocyte membranes and may contribute to its antimalarial action.     

Derivatives of pyrazinecarboxylic acid: 1H, 13C and 15N NMR spectroscopic investigations

NMR spectroscopic studies are undertaken with derivatives of 2‐pyrazinecarboxylic acid. Complete and unambiguous assignment of chemical shifts (¹H, ¹³C, ¹⁵N) and coupling constants (¹H,¹H; ¹³C,¹H; ¹⁵N,¹H) is achieved by combined application of various 1D and 2D NMR spectroscopic techniques. Unequivocal mapping of ¹³C,¹H spin coupling constants is accomplished by 2D (δ,J) long‐range INEPT spectra with selective excitation. Phenomena such as the tautomerism of 3‐hydroxy‐2‐pyrazinecarboxylic acid are discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Interaction of zervamicin IIB with lipid bilayers. Molecular dynamics study

In this work we have studied the interaction of zervamicin IIB (ZrvIIB) with the model membranes of eukaryotes and prokaryotes using all-atom molecular dynamics. In all our simulations zervamicin molecule interacted only with lipid headgroups but did not penetrate the hydrophobic core of the bilayers. During the interaction with the prokaryotic membrane zervamicin placed by its N-termini towards the lipids and rotated at an angle of 40° relatively to the bilayer surface. In the case of eukaryotic membrane zervamicin stayed in the water and located parallel to the membrane surface. We compared hydrogen bonds between peptide and lipids and concluded that interactions of ZrvIIB with prokaryotic membrane are stronger than those with eukaryotic one. Also it was shown that two zervamicin molecules formed dimer and penetrated deeper in the area of lipid headgroups.     

High-temperature degradation of polyacrylic acid in aqueous solution

Poly(acrylic acid) (PAA) was decarboxylated in aqueous solution as a function of pH and ionic strength in the temperature range 100–350°C. Degradation kinetics were first order with respect to acid functionality. The rate of decarboxylation at high pH (E_α = 51.1 kcal/mol) was much slower than that at low pH (E_α = 20.3 kcal/mol). At intermediate pH, the reactivity was found to depend on the degree of dissociation of PAA as a functions of ionic strength, pH, and temperature. No monomer was observed in the reaction product. © 1996 John Wiley & Sons, Inc.     

NMR-spectroscopic investigation of o-nitrosobenzoic acid

The synthesis of o-nitrosobenzoic acid 2 has been known for more than 100 years, and the photochemical preparation from o-nitrobenzaldehyde 1 became a textbook example for [1,5]-hydrogen shifts. However, neither the (1)H-NMR spectra nor the (13)C--{(1)H}-NMR of this compound have been reported so far. This fact can most likely be attributed to the monomer-dimer equilibrium of the nitrosobenzoic acid, which leads to rather complex, concentration-dependent NMR spectra. In this paper, we report a thorough investigation of these spectra. In the (13)C-{(1)H}-NMR spectra, all 21 lines could be assigned to the monomeric form, the E-dimer, and the Z-dimer.     

Parahydrogen induced polarization of barbituric acid derivatives: 1H hyperpolarization studies

Homogeneous hydrogenation of barbituric acid derivatives with parahydrogen yields a substantial increase of the (1)H NMR signals of the reaction products. These physiologically relevant compounds were hydrogenated at both ambient and elevated temperatures and pressures using a standard cationic rhodium catalyst. The resulting nonthermal nuclear spin polarization (hyperpolarization) is limited by the spin-lattice relaxation time T(1) of the corresponding nuclei in the products, being shorter than the time constant of the hydrogenation. The signal-to-noise ratio of the NMR spectra could be further increased upon signal averaging the antiphase PHIP signals of 25 successive scans following 30 degrees pulse experiments and a delay of 10 s.     

Solvent effect in polymer analysis by MALDI-TOF mass spectrometry

Solvent effect is one of the important factors in sample preparation which may affect matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectra of synthetic polymers. MALDI imaging, a useful imaging tool for discovering biomarkers in tissues, is applied here for better comprehension of solvent effect in polymer analysis by MALDI-TOF mass spectrometry. Nylon-6 was chosen as a model polymer for the study of solvent effect. Its MALDI mass spectra in different solvents were performed. MALDI imaging analysis was performed for studying the incorporation of analytes into matrix crystals in different solvent combinations. Specifically, the colocalization of matrix and analyte was obtained through Pearson’s correlation (PC) coefficient analysis of their MALDI images. The results demonstrated that satisfactory spectra were obtained in higher PC value conditions. PC decreased along with an increase in the ratio of poor solvent, which suggested that we should minimize the poor solvent ratio to obtain better MALDI spectra.     

Effect of phenyltin compounds on lipid bilayer organization

Phenyltin compounds are known to be biologically active. Their chemical structure suggests that they are likely to interact with the lipid fraction of cell membranes. Using fluorescence and NMR techniques, the effect of phenyltin compounds on selected regions of model lipid bilayers formed from phosphatidylcholine was studied. The polarization of N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) dipalmitoyl-L -phosphatidylethanolamine and desorption of praseodymium ions was used to probe the polar region, whereas the polarization of 1 - (4 - trimethylammoniumphenyl) - 6 - phenyl - 1,3,5-hexatriene p-toluenesulfonate measured the hydrophobic core of the membrane. In addition, changes in the N-(5-fluoresceinthiocarbanoly)dipalmitoyl - L - α - phosphatidyl - ethanolamine fluorescence intensity indicated the amount of charge introduced by organotin compounds to the membrane surface. There were no relevant changes of measured parameters when tetraphenyltin was introduced to the vesicle suspension. Diphenyltin chloride causes changes of the hydrophobic region, whereas the triphenyltin chloride seems to adsorb in the headgroup region of the lipid bilayer. When the hemolytic activity of phenyltin compounds was measured, triphenyltin chloride was the most effective whereas diphenyltin chloride was much less effective. Tetraphenyltin causes little damage. Based on the presented data, a correlation between activity of those compounds to hemolysis (and toxicity) and the location of the compound within the lipid bilayer could be proposed. In order to inflict damage on the plasma membrane, the compound has to penetrate the lipid bilayer. Tetraphenyltin does not partition into the lipid fraction; therefore its destructive effect is negligible. The partition of the compound into the lipid phase is not sufficient enough, by itself, to change the structure of the lipid bilayer to a biologically relevant degree. The hemolytic potency seems to be dependent on the location of the compound within the lipid bilayer. Triphenyltin chloride which adsorbs on the surface of the membrane, causes a high level of hemolysis, whereas diphenyltin chloride, which penetrates much deeper, seems to have only limited potency. © 1998 John Wiley & Sons, Ltd.     

Behavior of metal complexes of polyacrylic acid in solutions

Metal complexes of polyacrylic acid containing Li, Li, and Cu, or Li and Zn have been studied in saline aqueous solutions using molecular hydrodynamics and light scattering methods. Intrinsic viscosities, weight-average molar masses, hydrodynamic radii, and radii of gyration were obtained. It was shown that the macromolecules of polymetalloacrylates containing divalent metals form small and large supramolecular structures, their dimensions, and composition being dependent on the ionic strength of the solution.     

New tricyclic and tetracyclic pyranocoumarins with an unprecedented C‐4 substituent. Structure elucidation of tamanolide,tamanolide D and tamanolide P from Calophyllum inophyllum of French Polynesia

Three new pyranocoumarin derivatives, tamanolide (1), tamanolide D (2) and tamanolide P (3), were isolated from the almond seeds of Calophyllum inophyllum L. (Clusiaceae) grown in French Polynesia. These compounds, having an unprecedented C‐4 isobutyl substituent, have been characterized as a new class of pyranocoumarins called tamanolides. Their structures were elucidated on the basis of 1D and 2D NMR techniques (COSY, NOESY, HSQC and HMBC) in association with MS (HR‐ESI‐MS) data analysis. Copyright © 2009 John Wiley & Sons, Ltd.