光固化聚氨酯丙烯酸酯杂化材料的核磁共振谱

光固化聚氨酯丙烯酸酯杂化材料的核磁共振谱;SiO2;溶胶-凝胶法     

Application of solid-state NMR (13C and 29Si CP/MAS NMR) spectroscopy to the characterization of alkenyltrialkoxysilane and trialkoxysilyl-terminated polyisoprene grafting onto silica microparticles

The solid-state Nuclear Magnetic Resonance (NMR) was used to characterize surfaces of silica gels chemically modified by alkenyltrialkoxysilanes and trialkoxysilyl terminated 1,4-polyisoprenes. The formation of covalent bonds created between alkoxy functional groups from alkenyltrialkoxysilane or trialkoxysilyl-terminated 1,4-polyisoprene and silanol groups on silica was clearly demonstrated by means of ¹³C and ²⁹Si CP/MAS NMR spectroscopy. Quantitative data, including calculation of the grafting yields in relation with the initial silanol concentrations, were also obtained by using solid-state ²⁹Si-NMR leading to a final well-defined characterization of the silica surfaces. A relatively good agreement was noticed between the grafting yields calculated from ²⁹Si-NMR spectra and those determined from other analytical techniques such as Wijs titration or elementary analysis. The reactivity of the various silica silanols towards each coupling agent was clearly characterized and estimated, as were the proportions of the various grafted structures formed at the silica surface. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36 : 437–453, 1998     

Structural characterization of monomeric and oligomeric arylamides by solution and solid‐state NMR spectroscopy

An extensive study of both liquid‐ and solid‐state NMR spectroscopy was undertaken in order to elucidate the structural features of a phenyleneterephthalamide oligomer (OPTA) and of some related diarylamides. 1D‐ and 2D‐COSY measurements allowed us to assign completely the proton signals of the title compounds in solution, while 1D‐, 2D‐HETCOR and 2D‐COLOC measurements were used to assign ¹³C resonances. Solid‐state ¹³C NMR experiments, by conventional cross‐polarization (CP) at different contact times and with the dipolar dephased CP technique, were used to characterize these molecules in the solid state. Such techniques allowed us to differentiate among different carbon atoms; in the resulting spectra it was then possible to observe the selective appearance of signals from protonated and quaternary carbon atoms. It was also ascertained that the limited structural mobility of the insoluble OPTA, existing as a single monophasic species, can be explained in terms of hydrogen‐type bonds present in the solid state. Copyright © 2002 John Wiley & Sons, Ltd.     

Characterization of polyphenols from plant materials through their silylation and 29Si NMR spectroscopy-line assignment through 29Si, 13C spin-spin couplings

The lines in (29)Si NMR spectra of silylated polyphenols and some other compounds are difficult to assign owing to the absence of couplings with protons outside the silyl group. The assignment can be derived through small (n)J((29)Si, (13)C) couplings (n > 1). Using a previously described method for measurements of these couplings, the assignment procedure is demonstrated here on three examples of trimethylsilylated phenols: 7-hydroxyflavone, ferulic acid, and quercetin. In some cases the procedure can be used to identify carbon atoms to which the siloxy groups are attached.     

Solid‐state NMR characterization of tri‐ethyleneglycol grafted polyisocyanopeptides

In aqueous media, ethylene glycol substituted polyisocyanopeptides (PICPs) change their state (undergo a sol‐to‐gel transition) as a response to temperature. This makes them promising materials for various biomedical applications, for instance, for controlled drug release and non‐damaging wound dressing. To utilize PICP in biomedical applications, understanding of the origin of the gelation process is needed, but this is experimentally difficult because of the notoriously low gelator concentration in combination with the slow polymer dynamics in the sample. This paper describes a detailed characterization of the dried state of PICPs by solid‐state NMR measurements. Both the ¹³C and the ¹H NMR resonances were assigned using a combination of 1D cross‐polarization magic angle spinning, 2D ¹³C–¹H heteronuclear correlation spectra and ¹H–¹H single quantum–double quantum experiments. In addition, the chemical groups involved in dipolar interaction with each other were used to discuss the dynamics and spatial conformation of the polymer. In contrast to other PICP polymers, two resonances for the backbone carbon are observed, which are present in equal amounts. The possible origin of these resonances is discussed in the last section of this work. The data obtained during the current studies will be further used in elucidating mechanisms of the bundling and gelation. A comprehensive picture will make it possible to tailor polymer properties to meet specific needs in different applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Novel Nafion®/ORMOSIL hybrids via in situ sol-gel reactions: 2. Probe of ORMOSIL phase nanostructure by 29Si solid state NMR spectroscopy

Perfluorosulfonic Acid (PFSA)]/[Organically-Modified Silicon Oxide (ORMOSIL)] hybrids were formulated via sol-gel reactions of mixtures of tetraethoxysilane (TEOS) and diethoxydimethylsilane (DEDMS) in the nanophase-separated morphology of a PFSA membrane (Nafion^®). The molecular structures of the ORMOSIL phases were investigated by ²⁹Si solid state NMR spectroscopy and the spectra compared with those of corresponding bulk ORMOSILs. PFSA-in situ ORMOSIL composition can be tailored by manipulating TEOS/DEDMS source solution composition and quantified by ²⁹Si solid state NMR spectroscopy. Copolymerization of TEOS and DEDMS monomers, rather than block formation, occurs within the PFSA as well as in the bulk. As DEDMS feed concentration increases, ORMOSIL nanostructures are more hydrophobic and more flexible. Dimethylsiloxane rings are dominant in PFSAs in which hydrolysis + condensation of pure DEDMS occurs.     

Fast measurement of heteronuclear relaxation: frequency-domain analysis of NMR accordion spectroscopy

NMR relaxation parameters are usually derived from series of 2D experiments. The whole procedure can be very time consuming, especially for the study of the relaxation of nuclei at natural abundance. Palmer and Mandel have proposed the use of accordion spectroscopy to determine one relaxation parameter using two experiments only. In this paper, we show that the experimental time can be further reduced, by recording only three experiments for the determination of both the longitudinal and transverse relaxation rates. The analysis of the experiments is performed in the frequency domain, the relaxation rates being deduced from the linewidth of the peaks of interest. A detailed statistical analysis of errors introduced by the line fitting procedure on derived relaxation parameters was used to derive guidelines for the choice of experimental parameters. This procedure was applied to the study of the Cα relaxation parameters of a six-residue unlabeled peptide. The results were compared with those obtained by classical accordion spectroscopy. Copyright © 2001 John Wiley & Sons, Ltd.     

NMR spectroscopy of citrate in solids: cross-polarization kinetics in weakly coupled systems

Solid-state NMR spectroscopy is a potentially powerful method for obtaining molecular level structural information crucial for understanding the specific relationship between calcite crystals and occluded organic molecules that are important in biomineralization and biomimetic materials. In this work, a method is developed based on cross-polarization/magic angle spinning (CP/MAS) NMR to measure the heteronuclear distances and obtain structural information for large intracrystalline citrate defects in a synthetic calcite/citrate composite. Using compounds with well-characterized crystal structures, Mg(II) citrate and Sr(II) citrate, a correlation is established between T(IS), the CP time, and M(2) (IS), the van Vleck heteronuclear dipolar second moment, which contains distance and structural information. This correlation is supported by peak assignments obtained from calculations of the (13)C chemical shifts for crystalline Mg(II) citrate. On the basis of T(IS) (-1) versus M(2) (IS) correlation, measurement of T(IS) for carbonate ions associated with citrate defects in a calcite((13)C-enriched)/citrate coprecipitate yields an estimate for the distance between citrate and the nearest carbonate carbon that indicates close spatial proximity and provides useful constraints for future computational study. The applicability of T(IS) (-1) versus M(2) (IS) correlations to other weakly coupled spin-1/2 systems is discussed in terms of the effects of (1)H homonuclear dipolar coupling, using the CP kinetics of Zn(II) dihydroxybenzoate and kaolinite for comparison. The results suggest a limited range of correlation constants and indicate that quantitative information can be obtained from CP/MAS kinetics obtained under similar experimental conditions.     

Secondary structure of peptides 16th. Characterization of proteins by means of13C NMR CP/MAS spectroscopy

50.3 or 75.4 MHz¹³C NMR cross-polarization/magic angle spinning spectra of human hair, horse hair, horse hoof, parrot feather, sperm whale myoglobin, and horse heart cytochrome C were measured. The spectra of human hair and horse hair indicate nearly equal mole fractions of-sheets and-helices and a low percentage of amorphous regions, whereas horse hoof contains a higher fraction of amorphous proteins. The parrot feathers contain a small-helix fraction (ca. 10±5 %) in additon to a large-sheet fraction whereas cytochrome C contains 70–90%-helices. The spectrum of myoglobin could not interpreted in terms of defined secondary structures. The usefulness of the¹³C NMR CP/MAS spectroscopy for the characterization of proteins is compared with that of IR spectroscopy and X-ray diffraction.     

Two synthesis routes of organometallic precursors for the elaboration of SiCNYO pre‐alloyed nanopowders

Two routes were simultaneously investigated to prepare organometallic precursors. They were characterized by NMR and FTIR techniques. In the first route, yttrium acetate was silylated by trimethylchlorosilane before its dissolution in hexamethydisilazane. That leads to a liquid precursor containing Si? C? N? Y? O? H elements. In the second route, a precursor with the same elements was elaborated by dissolution of an amminolysed yttrium compound in tetramethyldisiloxane. The amminolysed yttrium compound was obtained through the amminolysis of the yttrium trichloride by triethylamine [N(C₂H₅)₃]. Copyright © 2010 John Wiley & Sons, Ltd.     

NMR study of E/Z isomerism in N‐alkoxybenzoimidic acid derivatives

Well defined E/Z isomers of N‐methoxy‐p‐nitrobenzimidoyl chloride, N‐methoxybenzimidoyl chloride, methyl N‐methylbenzohydroximate and ethyl N‐hydroxybenzimidate were prepared in order to provide model data for studies of benzhydroximic acid derivatives and related compounds. NMR parameters [¹H, ¹³C and ¹⁵N chemical shifts and ¹J(¹³C, ¹³C) coupling constants] were determined. The results show that stereochemically most significant are the values of ¹J(¹³C, ¹³C) couplings between aromatic C_ipso and C?N carbons and that the relationship, |J_cis| > |J_trans|, known for this coupling from oximes, is not affected by electronegative substituents at the C?N carbon atom, but the values are. Copyright © 2002 John Wiley & Sons, Ltd.     

Structure determination of two new indole‐diterpenoids from Penicillium sp. CM‐7 by NMR spectroscopy

Two new indole‐diterpenoids 4b‐deoxy‐1′‐O‐acetylpaxilline (1) and 4b‐deoxypenijanthine A (2) were isolated from the fermentation broth and the mycelia of the soil fungus Penicillium sp. CM‐7, along with three known structurally related compounds, 1′‐O‐acetylpaxilline (3), paspaline (4) and 3‐deoxo‐4b‐deoxypaxilline (5). The structures of compounds 1 and 2 were elucidated by extensive spectroscopic methods, especially 2D NMR, and their absolute configurations were suggested on the basis of the circular dichroism spectral analysis and the NOESY data. Copyright © 2014 John Wiley & Sons, Ltd.     

Acetone‐induced polymerisation of 3‐aminopropyltrimethoxysilane (APTMS) as revealed by NMR spectroscopy

We followed the reactivity of acetone with 3‐aminopropyltrimethoxysilane, a potential organosilane coupling agent, by ¹H, ¹³C and ²⁹Si NMR spectroscopy. Selective 1D and 2D‐edited NMR experiments significantly contributed to simplify the spectral complexity of reaction solution and elucidated molecular structures within progressive reaction phases. The course of the 3‐aminopropyltrimethoxysilane reaction with acetone was shown by a progressive decrease of both reactants, and a concomitant appearance of water and methanol, due to formation of imine and hydrolysis of alkoxysilane groups, respectively. The occurrence of multiple siloxane linkages in a progressively larger cross‐linked macromolecular structure was revealed by DOSY‐NMR experiments and new signals in ²⁹Si‐NMR spectra at different reaction times. The NMR approach described here may be applied to investigate the reactivity of other γ‐aminopropylalkoxysilanes and contribute to define procedures for the preparation of silica‐based materials. Copyright © 2014 John Wiley & Sons, Ltd.     

Curing chemistry of phenylethynyl‐terminated imide oligomers: Synthesis of 13C‐labeled oligomers and solid‐state NMR studies

4‐(Phenylethynyl‐α,β‐¹³C)phthalic anhydride (PEPA) and ¹³C‐labeled phenylethynyl‐terminated imide (PETI) oligomers were synthesized, and solid‐state ¹³C nuclear magnetic resonance (NMR) spectroscopy was used to determine the structure of cured oligomers. Solid‐state ¹³C NMR spectra were collected before and after thermal curing. Using solid‐state ¹³C NMR difference spectroscopy, several cure products were identified. The observed ¹³C NMR resonances were assigned to four different classes of cure products: aromatics, products from backbone addition (substituted stilbenes and tetraphenylethanes), polyenes, and cyclobutadiene cyclodimers. The effects of postcuring and oligomer chain length on the structure of the cured resins were examined. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3486–3497, 2000     

NMR spectroscopy and MALDI-TOF MS characterisation of end-functionalised PVP oligomers prepared with different esters as chain transfer agents

Ester-functionalised poly(1-vinylpyrrolidin-2-one) (PVP) oligomers obtained by radical polymerisation in methyl propionate, diethyl malonate and diethyl 2-methylmalonate were characterised by NMR spectroscopy, and MALDI-TOF mass spectrometry. The chain-transfer constants were determined as 5.54 x 10(-4), 1.22 x 10(-3) and 1.70 x 10(-2), respectively, by measuring the variation of the number-average molecular weight on conversion. These values were compared with those of methyl isobutyrate (1.65 x 10(-3)) and ethyl lactate (1.03 x 10(-2)), which had been previously determined. A clear dependence was found on the reactivity of the mobile hydrogen atoms alpha with the ester group. All of the macromolecules carried a single ester function. Therefore, the re-initiation step by the CTA-derived radicals overwhelmingly prevailed over initiation by the primary radicals.     

Structure determination of two new trichothecenes from a halotolerant fungus Myrothecium sp. GS‐17 by NMR spectroscopy

Two new trichothecenes, named 8α‐hydroxyroridin H and myrothecin A, along with six known compounds, 8α‐acetoxy roridin H, isororidin K, verrucarin A, verrucarin J, verrucarin L and 8α‐acetoxy verrucarin L, were isolated from the fermentation broth of a halotolerant fungus Myrothecium sp. GS‐17, which was separated from the soil sample of a salina. Structure elucidation and NMR signal assignments were achieved on the basis of spectroscopy. In addition, compounds 1 and 2 were active against plant pathogenic fungi Rhizoctonia solani and Fusarium oxysporum. Copyright © 2012 John Wiley & Sons, Ltd.     

[60]富勒烯衍生物的对称性、碳笼结构与13C NMR谱

本文全面综述了多种[60]富勒烯衍生物的结构,阐述了(13)~C NMR谱在[60]富勒烯衍生物结构表征中的应用,重点讨论了不同对称性[60]富勒烯衍生物的(13)~C NMR谱图特征.通过[60]富勒烯部分(13)~C共振线的化学位移、数目和相对强度,可以确定[60]富勒烯衍生物的对称结构和加成方式.对于C_s、C_(2v)和C_(3v)对称性的[60]富勒烯衍生物,镜面上的碳原子的相对化学位移很大程度上取决于他们距加成位置的距离.因此,(13)~C NMR谱在碳笼具体结构的确定中具有不可替代的作用.     

A NMR Study on the Hydrolysis,Condensation and Epoxide Ring-Opening Reaction in Sols and Gels of the System Glycidoxypropyltrimethoxysilane-Water-Titaniumtetraethoxide

The examination of hydrolysis, homo- and hetero-condensation reactions, of the condensation degree and the extent of epoxide ring opening in the course of sol-gel process was carried out by means of liquid- and solid-state 29Si and 13C NMR in the system 3-glycidoxypropyltrimethoxysilane (GPTS)-titaniumtetraethoxide-water (molar ratio 1 : 1 : 1.5–14) which is frequently used for the synthesis of heterometal hybrid polymers. The monomeric silanol groups in the GPTS-prehydrolysate immediately co-condense with the Ti-tetraethoxide to Si–O–Ti bonds to an extent of about 50–60% which remain stable in sols and also in the corresponding gels at low amounts of free water (0.02 H2O/OR) in the sol. An increasing amount of free water in the sol (0.12 H2O/OR) leads to an increased hydrolytic cleavage of the heterometal bonds and to the formation of homo-condensed polysiloxanes. The condensation degree of RSiO1.5 units in the Ti-containing sols is with 30–60% relatively high in comparison to Ti-free GPTS sols (ca. 5%) whereas the condensation degree of GPTS derived gels (81%) was found to be similar to that of the Ti-containing gels (60–80%). Ti-tetraethoxide accelerates the ring opening reaction of the epoxide group in the sols in dependence on the water content. Up to 78% of the epoxide rings are opened after 24 h in the sol with the highest water content (2 H2O/OR). No epoxide rings can be detected in Ti-containing gels which derive from sols with an amount of free water of 0.12 H2O/OR. The results give a first insight into the different parallel reactions in this system and can contribute to more structure controlled syntheses of heterometal hybrid polymers.     

Stereochemical assignment of five new lignan glycosides from Viscum album by NMR study combined with CD spectroscopy

The chemical study of the leaves and twigs of Viscum album led to the isolation of five new lignan glycosides, namely, ligalbumosides A–E (2‐6) and one known lignan glycoside, alangilignoside C (1). The structures of five new lignan glycosides were determined to be (7R,8S,8'S)‐4,9,4'‐trihydroxy‐3,5,3',5'‐tetramethoxy‐7,9'‐epoxylignan 9‐O‐β‐D‐glucopyranoside (2), (7S,8S,7'S,8'R)‐4,9,4'‐trihydroxy‐3,5,3',5',7'‐pentamethoxy‐7,9'‐epoxylignan 9‐O‐β‐D‐glucopyranoside (3), (7R,8R,7'S,8'S)‐4,9,4'‐trihydroxy‐3,5,3',5',7'‐pentamethoxy‐7,9'‐epoxylignan 9‐O‐β‐D‐glucopyranoside (4), (7S,8R,7'S,8'R)‐4,9,4'‐trihydroxy‐3,5,3',5',7'‐pentamethoxy‐7,9'‐epoxylignan 9‐O‐β‐D‐glucopyranoside (5), and (7R,8S,7'R,8'S)‐4,9,4',7'‐tetrahydroxy‐3,5,3',5'‐tetramethoxy‐7,9'‐epoxylignan 9‐O‐β‐D‐glucopyranoside (6) using 1D‐, 2D‐NMR, and CD spectra, chemical methods, as well as comparing the results with those reported in the literature. Copyright © 2012 John Wiley & Sons, Ltd.