Use of Magic Angle Spinning ~1H NMR Spectroscopy to Monitor Reactions in Solid-Phase Synthesis

Proton NMR-spectra of Wang resin bound compounds were obtained using the magic angle spinning 1HNMR technique with standard equipment. It was possible to analyse the spectra to evaluate their utility in solid-phase chernistry. A typical example was presented, which could directly monitor solid-phase reactions

Monitoring the formation of oil–water emulsions with a fast spatially resolved NMR spectroscopy method

In the present study, a fast chemical shift imaging （CSI） method has been used to dynamically monitor the formation of oil-water emulsions and the phase separation process of the emulsion phase from the excessive water or oil phase on the molecular level. With signals sampled from series of small voxels simultaneously within a few seconds, high-resolution one-dimensional （1D） 1H nuclear magnetic resonance （NMR） spectra from different spatial positions for inhomogeneous emulsion systems induced by susceptibility differences among components can be obtained independently. On the basis of integrals from these ~H NMR spectra, profiles obtained explicitly demonstrate the spatial and temporal variations of oil concentrations. Furthermore, the phase separation time and the length of the oil-water emulsion phase are determined. In addition, effects of oil types and proportions of the emulsifier on the emulsification states are also inspected. Experimental results indicate that 1D PHASICS （Partial Homogeneity Assisted Inhomogeneity Correction Spectroscopy） provides a helpful and promising alternative to research on dynamic processes or chemical reactions.

Recent progress in fragment-based drug discovery facilitated by NMR spectroscopy

Considerable developments have been observed in fragment-based lead/drug discovery(FBLD/FBDD)recently,with four drugs approved and many others under investigation.Nuclear magnetic resonance(NMR)has gained increasing popularity in FBLD due to its intrinsic capability in characterizing protein-ligand interactions in a large dynamic range of affinity,from weak hits to highly potent drugs.Here,we summarize NMR applications in fragment-based hit-to-lead evolution,including the construction of a fragment library,screening methods,spectra processing,and the delineation of the protein-ligand binding modes.These state-of-the-art NMR techniques have been exemplified in the discovery of inhibitors against multiple targets over the past five years,and they are expected to continue to provide new insights in the future.

Effective assignment of positional isomers in dimeric shikonin and its analogs by ^(1)H NMR spectroscopy

An approach for distinguishing two types of positional isomers of dimeric shikonin and its analogs was explored with ^(4)JC,H long-range correlation by prolonging the acquisition time at ^(2,3)JC,H values of 2.0 and 8.0Hz.Furthermore,the ^(1)H(proton)nuclear magnetic resonance(NMR)pattern of phenolic hydroxyl protons was developed as a“diagnosis signal”to ascertain the relative location of each side chain in DMSO-d_(6) at sample concentrations of 0.022-0.034 mol/L.The chemical shift differences of 0.6ppm between OH-5' and OH-1 and between OH-8'and OH-4 are assigned to Type A and Type B,respectively.All reported ambiguous structures were corrected by this pattern.Additionally,the steric structures of isolated compounds were elucidated by quantum chemical calculations of electronic circular dichroism(ECD)spectra.

Postmortem ^(7)Li NMR analysis for assessing the reversibility of lithium metal electrodes in lithium metal batteries

Despite the proficiency of lithium(Li)-7 NMR spectroscopy in delineating the physical and chemical states of Li metal electrodes,challenges in specimen preparation and interpretation impede its progress.In this study,we conducted a comprehensive postmortem analysis utilizing ^(7)Li NMR,employing a stan-dard magic angle spinning probe to examine protective-layer coated Li metal electrodes and LiAg alloy electrodes against bare Li metal electrodes within Li metal batteries(LMBs).Our investigation explores the effects of sample burrs,alignment with the magnetic field,the existence of liquid electrolytes,and precycling on the ^(7)Li NMR signals.Through contrasting NMR spectra before and after cycling,we identi-fied alterations in Li^(0) and Li^(+) signals attributable to the degradation of the Li metal electrode.Our NMR analyses decisively demonstrate the efficacy of the protective layer in mitigating dendrite and solid elec-trolyte interphase formation.Moreover,we noted that Li*ions near the Li metal surface exhibit magnetic susceptibility anisotropy,revealing a novel approach to studying diamagnetic species on Li metal elec-trodes in LMBs.This study provides valuable insights and practical guidelines for characterizing distinct lithium states within LMBs.

Combination of NMR spectroscopy and X-ray crystallography offers unique advantages for elucidation of the structural basis of protein complex assembly

NMR spectroscopy and X-ray crystallography are two premium methods for determining the atomic structures of macro-biomolecular complexes.Each method has unique strengths and weaknesses.While the two techniques are highly complementary,they have generally been used separately to address the structure and functions of biomolecular complexes.In this review,we emphasize that the combination of NMR spectroscopy and X-ray crystallography offers unique power for elucidating the structures of complicated protein assemblies.We demonstrate,using several recent examples from our own laboratory,that the exquisite sensitivity of NMR spectroscopy in detecting the conformational properties of individual atoms in proteins and their complexes,without any prior knowledge of conformation,is highly valuable for obtaining the high quality crystals necessary for structure determination by X-ray crystallography.Thus NMR spectroscopy,in addition to answering many unique structural biology questions that can be addressed specifically by that technique,can be exceedingly powerful in modern structural biology when combined with other techniques including X-ray crystallography and cryo-electron microscopy.

STUDIES ON ORGANOPHOSPHORUS COMPOUNDS XXXV——SUBSTITUENT EFFECT OF ORGANOPHOSPHORUS COMPOUNDS ON ^(31)P NMR SPECTROSCOPY

The linear relationship between the chemical shift of the resenant nucleus and the localvan der Waals steric energy calculated by molecular mechanics with MM2 force field wasextended to various organophosphorus compounds including alkyl-phosphates, -phosphonates,-phosphinates as well as -phosphine oxides. The conformational equilibria of a series of alkylO,O-1,3--propylene-and O, O-1,4-butylenephosphonates were studied by the molecular mechanicscalculations and the dynamic ^(31)P NMR spectroscopic method. As shown by these experimentaldata, the former existed in a chair form, and the latter in a twist boat form with an equatorialalkyl group in both configurations, either in gaseous state or in non-polar solvent.

Study of native oil-bearing rocks of the Cuban basin by high resolution NMR spectroscopy

Application of high resolution^(13)C nuclear magnetic resonance(NMR)spectroscopy to characterize Cuba oil and oil-containing rock samples from Cuban basin was demonstrated.The chemical shifts of^(13)C NMR functional groups for later determination the composition of the oil and rock samples were determined.The different contribution of the studied samples in the aliphatic and aromatic areas was determined.Molar fractions of primary,secondary,quaternary,tertiary,aromatic groups,aromaticity factor and the mean length of hydrocarbon chain length of aliphatic hydrocarbons were estimated.Comparative analysis on the quantitative level for all major hydrocarbon components,the aromaticity factor and the mean length of the hydrocarbon chain were carried out.

Application of ammonia probe-assisted solid-state NMR technique in zeolites and catalysis

Solid-state NMR(ssNMR)spectroscopy is a powerful technique for characterizing the surface sites of solid acids and organic intermediates formed during the acid catalyzed reaction.As a very useful probe molecule,ammonia is often utilized to determine the density of solidacids’surface sites by ssNMR spectroscopy.The present mini-review summarizes some of the latest research developments on the quantitative characterization of the acid sites and carbenium ions during the zeolite catalytic reaction by ammonia probe-assisted ssNMR spectroscopy.

Novel Monomeric Phenanthroline - Thallium(III) Complexes Multinuclear NMR Characterization in Organic Solvents

A novel complex of monomeric thallium(III) with the nitrogen donor ligand phenanthroline (phen) has been prepared and characterized by multinuclear NMR (1H, 13C, 205Tl). The three complexes exist in equilibria in DMSO and acetonitrile solution, which was proved by the 205Tl NMR spectra. The 1H and 13C NMR spectra of tris-phen Tl(III) complex have been measured, where the spin-spin coupling between Tl (I = 1/2) and 13C or 1H signals were observed with the 1H and 13C NMR spectroscopy in acetonitrile. The coupling constants are presented and the chemical shifts of complexes are discussed in detail.

NMR SPECTROSCOPIC STUDY ON COPOLYMER OF ETHYLENE-NORBORNENE

A series of ethylene-norbornene copolymers were synthesized using VO (Oft) Cl-2/Al2Et3Cl3 catalytic system and their structure was characterized by H-1-NMR, H-1-H-1 COSY NMR and C-13-NMR. Assignments of NMR spectra were given and discussed in detail.

A SOLID NMR STUDY OF POLYETHERESTER-UREAS

The morphology of some polyetherester-ureas were studied by ^(13)C CP/MAS and ~1H wide-line NMR spectroscopy. It was found that the HDI and MDI based polymers have well crystallized hard segments, whereas the TDI and HMDI based ones have not. For HDI/MDI based polymers, the presented results suggest that the distribution of two kinds of hard segment units is mainly in a block form. The influences of the different hard segment and chain length on the mobility of the soft segment were also studied.

Characterization of humic acids extracted from the sediments of the various rivers and lakes in China

The humic acids (HAs) isolated from the sediments of the various rivers,lakes,and reservoirs in China were studied using elemental analyzer,fourier transform infrared (FT-IR),and CP/MAS 13C nuclear magnetic resonance (NMR) spectroscopy.The results showed that the HAs were characterized by some common chemical and physicochemical properties,but they also pose some differences in the C-containing functional groups.The C/N,C/H,O/C,and O/H ratios differ widely for the various HAs,showing that the elemental comp...

Reversible potassium storage in ultrafine CF_(x): A superior cathode material for potassium batteries and its mechanism

Current studies of cathodes for potassium batteries(PBs) mainly focus on the intercalation-type materials.The conversion-type materials that possess much higher theoretical capacities are rarely discussed in previous literatures.In this work,carbon fluoride(CF_x) is reported as a high capacity conversion-type cathode for PBs for the first time.The material delivers a remarkable discharge capacity of>250 mAh g^(-1) with mid-voltage of 2.6 V at 20 mA g^(-1).Moreover,a highly reversible capacity of around 95 mAh g^(-1) is achieved at 125 mA g^(-1) and maintained for 900 cycles,demonstrating its excellent cycling stability.The mechanism of this highly reversible conversion reaction is further investigated by nuclear magnetic resonance spectra,X-ray diffraction,and transmission electron microscopy studies.According to the analyses,the C-F bond in the cycled material is different from that in the pristine state,which presents relatively higher reversibility.This finding offers important insights for further improving the performance of the CF_x.This work not only demonstrates the CF_x as a high performance cathode for PBs,but also paves a new avenue of exploring conversion-type cathodes for high energy density PBs.

Structural Characterization and Antioxidant Activity of Lignin Extracted from Ficus Carica L.

The most abundant phenolic biopolymer in the biosphere is the lignin.This phenolic biopolymer commonly exists in combination with polysaccharides and other cell wall components.In this study,the solvent system dioxane-water is used to extract lignin,which is considered as unaltered native lignin.The dioxane lignin extracted from fig stems was characterized regarding to its structural feature,quantification of its functional groups,molecular weight,and evaluation of its thermal properties.Purity and molecular weight distribution of the studied lignin indicated that isolated lignin contained a low amount of sugar(c.a.19%)and had a high weight-average molecular weight(10068 g.mol-1).Lignin sample had approximately the same amounts of guaiacyl(G)and p-hydroxyphenyl(H)units with relatively fewer syringyl(S)units.The isolated lignin revealed good antioxidant properties.Therefore,it proved to have a high potential of application in new antioxidants formulations.

Changes in organic C stability within soil aggregates under different fertilization patterns in a greenhouse vegetable field

Knowledge of the stability of soil organic C(SOC)is vital for assessing SOC dynamics and cycling in agroecosystems.Studies have documented the regulatory effect of fertilization on SOC stability in bulk soils.However,how fertilization alters organic C stability at the aggregate scale in agroecosystems remains largely unclear.This study aimed to appraise the changes of organic C stability within soil aggregates after eight years of fertilization(chemical vs.organic fertilization)in a greenhouse vegetable field in Tianjin,China.Changes in the stability of organic C in soil aggregates were evaluated by four methods,i.e.,the modified Walkley-Black method(chemical method),13C NMR spectroscopy(spectroscopic method),extracellular enzyme assay(biological method),and thermogravimetric analysis(thermogravimetric method).The aggregates were isolated and separated by a wet-sieving method into four fractions:large macroaggregates(>2 mm),small macroaggregates(0.25–2 mm),microaggregates(0.053–0.25 mm),and silt/clay fractions(<0.053 mm).The results showed that organic amendments increased the organic C content and reduced the chemical,spectroscopic,thermogravimetric,and biological stability of organic C within soil aggregates relative to chemical fertilization alone.Within soil aggregates,the content of organic C was the highest in microaggregates and decreased in the order microaggregates>macroaggregates>silt/clay fractions.Meanwhile,organic C spectroscopic,thermogravimetric,and biological stability were the highest in silt/clay fractions,followed by macroaggregates and microaggregates.Moreover,the modified Walkley-Black method was not suitable for interpreting organic C stability at the aggregate scale due to the weak correlation between organic C chemical properties and other stability characteristics within the soil aggregates.These findings provide scientific insights at the aggregate scale into the changes of organic C properties under fertilization in greenhouse vegetable fields in China.

PRELIMINARY INVESTIGATION ON THE MISCIBILITY OF ISOTACTIC POLYPROPYLENE (iPP) AND SYNDIOTACTIC POLYPROPYLENE (sPP) BLENDS

Experimental miscibility studies were performed on different compositions of iPP/sPP blends, where sPP has a low syndiotacticity （[rrrr] = 81%）. Combining optical microscopy, rheology, and solid state NMR spectroscopy, the miscibility of the blends was investigated at different scales in the traditionally thought to be ＂immiscible＂ iPP/sPP blends. For the composition of iPP/sPP （90/10） blend, it shows to be miscible in the melt, and furthermore, the existence of intermolecular chain interactions between sPP and iPP components was detected in the solid state.

The origins of kinetics hysteresis and irreversibility of monoclinic Li_(3)V_(2)(PO_(4))_(3)

Monoclinic Li_(2)V_(2)(PO_(4))_(3);is a promising cathode material with complex charge–discharge behavior.Previous structural investigation of this compound mainly focuses on local environments;while the reaction kinetics and the driving force of irreversibility of this material remain unclear.To fully understand the above issues,both the equilibrium and the non-equilibrium reaction routes have been systematically investigated in this study.Multiple characterization techniques including X-ray diffraction,variable temperature(spinning rate)and ex/in situ ^(7)Li,^(31)P solid state NMR have been employed to provide comprehensive insights into kinetics,dynamics,framework structure evolution and charge ordering,which is essential to better design and application of lithium transition metal phosphate cathodes.Our results suggest that the kinetics process between the non-equilibrium and the quasi-equilibrium delithiation pathways from Li_(2)V_(2)(PO_(4))_(3);to V_(2)(PO_(4))_(3);is related with a slow relaxation from two-site to one-site delithiation.More importantly,it has been demonstrated that the irreversibility in this system is not solely affected by cation and/or charge ordering/disordering,but mainly driven by framework structure distortion.

Physicochemical Characterization and Antimicrobial Properties of Inulin Acetate Obtained by Microwave-Assisted Synthesis

Microwave-assisted irradiation was performed for esterification of chicory inulin with high degree of polymerization with acetic anhydride without a solvent only with a catalyst.The resulting esters were characterized by melting point,hydrophilic-lipophilic balance,thin-layer chromatography,ultraviolet spectroscopy,Fourier transform infrared spectroscopy(FTIR)and nuclear magnetic resonance(NMR)spectroscopy.Inulin acetate demonstrated a high degree of acetylation(2.5-3.0)and presented a white,water-insoluble substance with bitter taste.The FTIR and NMR spectra confirmed esterification and demonstrated the incorporation of hydrophobic residue to the water soluble inulin backbone.Swelling capacity,water holding,oil-holding capacities,the foamability,foam stability and emulsifying properties were also evaluated.Inulin acetate showed promising foam stability 52%for 60 min and formed stable emulsions at concentration 0.2 g/L with 50 and 80%oil phases.Its water holding capacity was lower than the oil holding capacity.In addition to this,for the first time,the antimicrobial potential of inulin acetate was tested against seventeen microorganisms(Gram-positive and Gram-negative bacteria,yeasts and fungi).Inulin acetate(10 mg/ml)inhibited the growth of Bacillus cereus,Escherichia coli ATCC 8739,Salmonella abony,Candida albicans and Penicillium sp.However,inulin acetate demonstrated antimicrobial activity at concentration 1 mg/ml against Listeria monocytogenes 863,Escherichia coli 3398,Candida albicans 8673,Fusarium oxysporum and Aspergillus niger.The current study demonstrated the applications of“green”synthesized inulin acetate as a foaming agent,oil-in-water emulsion stabilizer and antimicrobial substance in pharmaceutical,agricultural and cosmetic preparations.

Brown Algae (Phaeophyceae) from the Coast of Madagascar:preliminary Bioactivity Studies and Isolation of Natural Products

Eight species of brown algae(Phaeophyceae)from the coast of Madagascar have been investigated for their chemical constituents.Fucosterol(3)was obtained as the most abundant compound.The brown alga Sargassum ilicifolium was the source for the first isolation of the terpenoid C27-alcohol 1,10,2-trinorsqualenol(1)from marine sources.From S.incisifolium we isolated the highly unsaturated glycolipid 1-O-palmitoyl-2-O-stearidonoyl-3-O-β-D-galactopyranosylglycerol(4)and we report the first full assignment of its ^(1)H and ^(13)C NMR data.Apo-90-fucoxanthinone(8)along with 24-ketocholesterol(5),(22E)-3b-hydroxycholesta-5,22-dien-24-one(6),and saringosterol(7)were obtained from Turbinaria ornata.The crude extracts of all eight species of brown algae exhibited a pronounced antimicrobial activity against the Gram-positive bacteria Bacillus cereus,Staphylococcus aureus,and Streptococcus pneumoniae.