用C-1 3核磁共振谱测定高聚物中微量异种结构单元的探讨

通过高低工作频率的高分辩率核磁共振谱仪（型号分别为GX-400和FX-90Q）对含有不同微量异种结构单元的聚乙烯样品作了^13C谱测量和比较分析;结果表明^13C谱在较高磁场频率（100.4MHz)条件下可检测灵敏度达到0.5个支化点/10000个碳原子（0.5/10000C);而较低磁场频率（22.5MHz)只达到1个支化点/1000个碳原子（1/1000C）以上;综合分析所得结果,指出在用电磁体系列（谱仪频率一般为90MHz或100MHz)核磁共振谱仪检测高分子量物质时,应注意有遗漏1/1000C以下浓度结构的可能性;分析了^13C谱可检测灵敏度与磁场强度等因素的关系,得到了可检测灵敏度S/N与磁场强度（H0）间比较适合的关系式。     

Elucidating the Germanium Distribution in ITQ-13 Zeolites by Density Functional Theory**

ITQ-13 is a medium-pore zeolite that can be prepared in all-silica form and as silicogermanate with Si/Ge ratios as low as 3. Usually synthesised in the presence of fluoride, ITQ-13 is among the very few systems containing fluoride anions in two distinct cage types, cube-like d4r units and [4 ⋅ 5⁶] cages. Here, dispersion-corrected density functional theory (DFT) calculations are used to investigate the energetically most favourable Ge distributions for Si/Ge ratios between 55 and 6. The calculations show Ge atoms are incorporated at both the corners of d4r cages and at the basal plane of the [4 ⋅ 5⁶] cages, in accordance with ¹⁹F NMR spectroscopy. Two Ge atoms at adjacent corners of [4 ⋅ 5⁶] cages are stable at the highest Ge content considered (Si/Ge=6). Such a local environment has not yet been considered in the experimental literature. A calculation of the corresponding ¹⁹F NMR resonance points to overlap with other resonances, which might preclude its clear identification. Additional calculations investigate the variation of the dynamic behaviour of the fluoride anions as a function of the local environment as well as the selective defluorination of the [4 ⋅ 5⁶] cages.     

Random isotopolog libraries for protein perturbation studies. 13C NMR studies on lumazine protein of Photobacterium leiognathi

[graph: see text] Lumazine proteins of luminescent bacteria are paralogs of riboflavin synthase which are devoid of catalytic activity but bind the riboflavin synthase substrate, 6,7-dimethyl-8-ribityllumazine, with high affinity and are believed to serve as optical transponders for bioluminescence emission. Lumazine protein of Photobacterium leiognathi was expressed in a recombinant Escherichia coli host and was reconstituted with mixtures (random libraries) of 13C-labeled isotopologs of 6,7-dimethyl-8-ribityllumazine or riboflavin that had been prepared by biotransformation of [U-(13)C6]-, [1-(13)C1]-, [2-(13)C1]-, and [3-(13)C1]glucose. 13C NMR analysis of the protein/ligand complexes afforded the assignments of the 13C NMR chemical shifts for all carbon atoms of the protein-bound ligands by isotopolog abundance editing. The carbon atoms of the ribityl groups of both ligands studied were shifted up to 6 ppm upon binding to the protein. Chemical shift modulation of the side chain and chromophore carbon atoms due to protein/ligand interaction is discussed on the basis of the sequence similarity between lumazine protein and riboflavin synthase.     

13Carbon nuclear magnetic resonance of ethylene–propylene–1‐decene terpolymers

Many studies have been reported on the ¹³C NMR characterization of ethylene–α‐olefin copolymers, but only a few have been reported on terpolymers. The incorporation of an α‐olefin into the polyethylene chain changes the structure and, consequently, the properties of the polymer obtained. Looking for new products, we obtained a series of ethylene–propylene–1‐decene terpolymers with the metallocenic system rac‐ethylene bisindenyl zirconium dichloride/methylaluminoxane. We performed a complete ¹³C NMR characterization of these terpolymers qualitatively and quantitatively. Here we present a detailed study of the ¹³C NMR chemical shifts, triad sequence distributions, monomer average sequence lengths, and reactivity ratios for these terpolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2531–2541, 2003     

Biosynthesis of aspergiolide A, a novel antitumor compound by a marine-derived fungus Aspergillus glaucus via the polyketide pathway

Aspergiolide A, a novel antitumor compound, was produced by a marine-derived filamentous fungus Aspergillus glaucus. The biosynthesis of it was unambiguously determined by feeding experiments using [l-¹³C]sodium acetate, [2-¹³C]sodium acetate, and [1,2-¹³C₂]sodium acetate precursors followed by ¹³C NMR spectroscopic investigation of the isolated products. Analysis of the patterns of ¹³C-enrichment revealed that all 25 carbon atoms in skeleton of aspergiolide A were derived from labeled acetate. And among them, 12 carbon atoms were labeled from the carboxylic group of acetate, while the other 13 carbon atoms were labeled from the methylic group of acetate. Besides, the labeling pattern of [1,2-¹³C₂]sodium acetate feeding experiment demonstrated that 12 intact acetate units were incorporated in aspergiolide A by polyketide pathway.     

~(13)C-NMR方法研究酚酞聚芳醚酮砜共聚物的序列结构

通过亲核共缩聚合成了一系列酚酞聚芳醚酮砜共聚物和嵌段共聚物 ,并利用1 3C NMR方法研究了共聚物的链结构 ,通过观察酚酞单元中三个位置的季碳原子的化学位移及其相应强度的变化 ,计算共聚物中不同链段的共聚物的组成、平均序列长度和无规度 .结果表明 ,除嵌段共聚物外 ,其它共聚物的无规度均接近 1 ,表明共聚物为无规共聚物 ,而且对三个位置的季碳原子分析均得出了相同的结果 .     

The azine bridge as a conjugation stopper: an NMR spectroscopic study of electron delocalization in acetophenone azines

Dipole parallel-alignment of organic molecular crystals of azines has been achieved with a design that was based on the hypothesis that the azine bridge is a conjugation stopper. This hypothesis has now been tested in detail, and (1)H and (13)C NMR spectroscopic data of symmetric and asymmetric acetophenone azines are presented in support of this design concept. Previous structural, ab initio, and electrochemical studies have shown that the azine bridge largely inhibits through-conjugation in molecules with the general structure DPhC(Me) [double bond] N [bond] N [double bond] C(Me)PhA, where D is a donor group and A is an acceptor group. NMR spectroscopy is an excellent tool to probe the degree of conjugation through the azine bridge. The NMR results reported here for nine symmetrical and 18 asymmetrical azines show in a compelling fashion that the hypothesis holds. Varying the donor group does not change the chemical shifts of the aromatic hydrogen and carbon atoms on the acceptor-substituted phenyl ring. Likewise, varying the acceptor group does not change the chemical shifts of the atoms in the donor-substituted phenyl ring.     

Chain transfer to polymer in emulsion copolymerizations

Chain transfer to polymer in emulsion copolymerizations of (i) vinyl acetate (VAc) with n‐butyl acrylate (BA) and (ii) BA/acrylic acid with (a) methyl methacrylate (MMA) and (b) styrene (S) has been studied using ¹³C NMR spectroscopy to quantify the level of branching in the copolymers produced. The results reveal synergistic effects in which the inclusion of a small amount of comonomer leads to disproportionate changes in the level of branching. The data from the VAc/BA copolymerizations show that radicals with VAc end units abstract hydrogen atoms from BA repeat units more frequently than from VAc repeat units and that radicals with VAc end units are more effective in abstracting hydrogen atoms from BA repeat units than are radicals with BA end units. These effects lead to higher levels of branching in VAc/BA copolymers than results from the corresponding homopolymerizations and are a consequence of the efficacy of hydrogen abstraction at BA backbone tertiary C‐H bonds by the highly‐reactive VAc‐ended chain radicals. In contrast, the effect of introducing MMA or S to an acrylate polymerization is to disproportionately reduce the level of branching, with S being more effective than MMA in moderating chain transfer to polymer. These effects arise because propagating radicals with MMA or S end‐groups have longer lifetimes compared to those with acrylate end groups and have a very much lower tendency to abstract hydrogen atoms from acrylate repeat units.     

Chain epimerization during propylene polymerization with metallocene catalysts: mechanistic studies using a doubly labeled propylene

The mechanisms of chain epimerization during propylene polymerization with methylaluminoxane-activated rac-(EBTHI)ZrCl(2) and rac-(EBI)ZrCl(2) catalysts (EBTHI = ethylenebis(eta(5)-tetrahydroindenyl); EBI = ethylenebis(eta(5)-indenyl)) have been studied using specifically isotopically labeled propylene: CH(2)=CD(13)CH(3). These isospecific catalysts provide predominantly the expected [mmmm] pentads with [minus signCH(2)CD(13)CH(3)(-)] repeating units ((13)C NMR). Under relatively low propylene concentrations at 50 and 75 degreesC, where stereoerrors attributable to chain epimerization are prevalent, (13)C NMR spectra reveal (13)C-labeled methylene groups along the polymer main chain, together with [CD(13)CH(3)] units in [mmmr], [mmrr], and [mrrm] pentads and [CH(13)CH(3)] units in [mmmmmm] and [mmmmmr] heptads, as well as [mrrm] pentads. The isotopomeric regiomisplacements and stereoerrors are consistent with a mechanism involving beta-D elimination, olefin rotation and enantiofacial interconversions, and insertion to a tertiary alkyl intermediate [Zr-C(CH(2)D)((13)CH(3))P] (P = polymer chain), followed by the reverse steps to yield two stereoisomers of [Zr-CHDCH((13)CH(3))P] and [Zr-(13)CH(2)CH(CH(2)D)P], as well as unrearranged [Zr-CH(2)CD((13)CH(3))P]. The absence of observable [-CH(2)CH(13)CH(2)D-] in the [mrrm] pentad region of the (13)C NMR spectra provides evidence that an allyl/dihydrogen complex does not mediate chain epimerization.     

Determination of the structural arrangements of ketene oligomers using NMR, FT-IR and ESI-MS

Oligomer of ketene was synthesized using glycine as the source material in presence of free electron rich carbon through free radical mechanism. The structure and the compositions were determined by using ¹³C{¹H} NMR and DEPT – 135 spectroscopy measurements. Two-dimensional heteronuclear (HETCOR) NMR spectroscopy was used to resolve the ¹H NMR spectrum of the polymer. The NMR spectra reveal that the oligomers were generated as oligoester (OE), oligoketene (OK) and oligoacetal (OA) structural units. ESI-MS and ATR-FTIR also support these types of structural units in the crude polymer.     

Mechanically linked polycarbonate

The synthesis, by solid-state copolymerization, and characterization of the first polycatenanes based on a commercial polymer are reported. Various amounts of a benzylic amide [2]catenane, the corresponding macrocycle, and a rigid bisphenol fluorene derivative have been quantitatively and homogeneously incorporated into bisphenol A polycarbonate. The resulting copolymers were characterized by size exclusion chromatography coupled with viscosimetry, (1)H NMR, differential scanning calorimetry, and dynamic mechanical analysis. The unexpectedly small influence of [2]catenane incorporation on the glass transition temperature of the copolymers points to remarkable internal mobility of the catenane comonomer rings. A new relaxation linked to the flexible catenane units is also observed. The studies represent a detailed structural characterization of a polymer containing small amounts of mechanical linkages in its backbone and demonstrate that significant effects can be induced by doping conventional polymers with small percentages (2-6% of repeat units) of flexible catenanes.     

Biosynthesis of citreothiolactone,citreopyrone and pyrenocine B

¹³C NMR spectroscopy using INADEQUATE pulse sequence method has been used to deduce the labelling patterns of the three metabolites of $\text{Penicillium citreo-viride}$ B. derived from [1,2-¹³C]acetate, indicating that their carbon skeletons consist of two different units [CH₃COCH₂COCH₂COS-Enzyme and CH₃COCH₂COS-Enzyme].     

Postmodification of poly(9‐alkyl‐9H‐carbazole‐2,7‐diyl)s as a route to new main‐chain‐functionalized carbazole polymers

The postmodification of poly[9‐(2‐hexyldecyl)‐9H‐carbazole‐2,7‐diyl] ( P1 ) upon its reaction with N‐bromosuccinimide affords exclusive and full bromination of the 3,6‐positions of the carbazole repeat units to yield poly[3,6‐dibromo‐9‐(2‐hexyldecyl)‐9H‐carbazole‐2,7‐diyl] ( P2 ). Brominated polymer P2 can be used as a precursor for further functionalization at the 3,6‐positions with the desired functional group to afford other useful polymers. Polymer P2 has hence been reacted with copper(I) cyanide to afford poly[3,6‐dicyano‐9‐(2‐hexyldecyl)‐9H‐carbazole‐2,7‐diyl] ( P3 ). Full substitution of the bromide groups with nitrile‐functional groups has been achieved. The preparation and structural characterization of polymers P2 and P3 are presented together with studies on their electronic conjugation and photoluminescence properties. Cyclic voltammetry studies on polymer P3 indicate that the new polymer is easier to reduce (n‐dope) but more difficult to oxidize than its unsubstituted counterpart ( P1 ) as a result of the introduction of the electron‐withdrawing nitrile‐functional groups at the 3,6‐positions on the carbazole repeat units on the polymer chains. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3336–3342, 2006     

测试温度对聚苯基缩水甘油醚的~(13)C-核磁共振谱的影响

^13C核磁共振谱（^13C－NMR）的化学位移对碳核所处的化学环境十分敏感,因此它是表征聚合物立构规整度的有效手段,常规^13C-NMR谱为质子噪声去偶谱,因各种碳核驰豫速率不同,谱线强度与碳原子数不成正比,为了使谱线强度与碳原子数成正比,以达到定量分析的目的,加大脉冲间隔是一种有效的方法。     

Recent Advances in MALDI Mass Spectrometry of Polymers

Matrix-Assisted Laser Desorption/Ionization (MALDI) allows the identification of repeat units and end groups, the structural analysis of linear and cyclic oligomers, and the estimate of composition and sequence for copolymers. MALDI has also been applied to the measurement of molar mass distributions in polymers and to the study of thermal and oxidative processes in polymers. This paper illustrates the detection of self-association in macromolecules made by coupling MALDI and Size Exclusion Chromatography (SEC), the investigation of polymer oxidation phenomena, and the characterization of copolymers formed in the processing of reactive polymer blends.     

Calix[n]arenes as components for the construction of micellar systems: synthesis and self-assembly properties of 5,11,17-Tris[(dimethylamino)methyl]-25-monoalkoxy-26,27,28-trihydroxycalix[4]arene derivatives

A series of mono-O-alkylated calix [4] arenes derivatives, with alkyl chain lengths of between 1 and 12 carbon atoms are reported. Monoalkylation is best achieved using potassium carbonate as the weak base and the respective alkyl iodide for chain lengths of one to three carbon atoms and using caesium fluoride as the base and the respective alkyl iodide for longer chain lengths. The mono-alkylated derivatives were converted into the tri-para-dimethylaminomethylene derivatives by the para-quinonemethide reaction in good yields. Surface tension measurements showed that at pH 2, 4, 6 and 8 all the tri-dimethylaminomethylene derivatives showed surfactant behaviour, and at pH 2 all show a Critical Micellar Concentration values. No correlation between Critical Micellar Concentration values and chain length is observed. Dynamic Light Scattering measurements showed that the CMC behaviour may be correlated with the observed aggregate sizes. The solid state structure of mono-O-ethoxy-calix[4]arene is described, in this structure a 1-D inclusion polymer is observed.     

13C nuclear magnetic resonance studies of the adducts of bis-(π-crotyl-D7-nickel iodide) and 2-alkylbutadienes as related to mechanism of polymerization

By ¹³C NMR spectroscopy, the structures of (C₄D₇Nil)₂ adducts with isoprene, 2-ethyl-, 2-isopropyl- and 2-tert. butylbutadienes have been investigated. The nature of the 2-alkyl substituent in the anti- and syn-1,2-disubstituted π-allylic complexes influences the character of electron charge densities distribution on the carbon atoms of a π-allylic ligand. Mutual arrangement of substituents in the π-allylic active sites has been shown to remain in the double bonds of elementary units of a polymer chain.     

Carbon nanotubes with small and tunable diameters from poly(ferrocenylsilane)-block-polysiloxane diblock copolymers

Iron-containing nanostructures produced from various self-assembled poly(ferrocenylsilane)-block-polysiloxane thin films are catalytically active for the initiation and growth of high density, small diameter carbon nanotubes (CNTs). Moreover, the tube diameter and density can be tuned by adjusting the chain lengths of the block copolymer. Iron-containing nanostructures from poly(ferrocenylmethylethylsilane)-b-poly(methylvinylsiloxane) polymer with 25 repeat units of an iron-containing segment and 265 repeat units of a non-iron-containing segment are able to produce CNTs with diameters around or less than 1 nm. Lithographically selective growth of CNTs across a large surface area has been demonstrated using this polymer system. Under the same growth condition, it has been found that the yield of defect-free CNTs varies with the size of the catalytically active nanostructures, which are dictated by the chain lengths of the two blocks. This result indicates that, for a specific-sized catalyst nanocluster, a unique set of growth conditions is required for synthesizing high yield, defect-free CNTs. This finding further addresses the importance of using uniform-sized catalyst-containing nanostructures for consistently achieving high-yield and high-quality CNTs with a minimum number of defects and amount of amorphous carbon.     

Carbon-13 nuclear magnetic resonance quantitative measurements of average sequence lengths of like stereochemical additions in polypropylene and polystyrene

Sequence lengths of stereochemical additions in vinyl polymers are described in terms of the number average lengths of like configurational placements. Under these circumstances, a pure syndiotactic polymer has a number average sequence length of 1.0; a polymer with 50:50 meso, racemic additions has a number average sequence length of 2.0 and polymers with more meso than racemic additions have number average sequence lengths greater than 2. Amorphous and crystalline polypropylenes and an amorphous polystyrene are examined using ¹³C NMR as examples of the applicability of the average sequence length method. The results appear to be accurate for amorphous and semicrystalline polymers but limitations are present when this method is applied to highly stereoregular vinyl polymers containing predominantly isotactic sequences.     

The synthesis of diene and of vinyl copolymers containing predetermined quantities of polynuclear hydrocarbon or heterocyclic adducts—V. Copolymers formed from styrene or α-methylstyrene,anthracene and alkyl dihalide

When a tetrahydrofuran solution of styrene or α-methylstyrene (M) and anthracene (A) is reacted with alkali metal, anionic species are produced which can be titrated with alkyl dibromides (RBr₂) to produce copolymers. These copolymers have been analysed structurally by NMR spectroscopy and by a model compound approach.With styrene as monomer, the copolymers have been shown to consist of two types of repeat units [AM_nAR] and [AR] linked together in a random manner: at equimolar styrene to anthracene ratios, n ～ 10 and 75 per cent of the anthracene is linked directly to the alkyl ligand as in the second repeat unit. When α-methylstyrene is used, the repeat units are predominantly [M_nR] and [AR] with n ～ 5. Production of copolymers of α-methylstyrene in particular is more efficient for decane dibromide than for butane dibromide, where formation of bridged anthracene derivatives by a cyclization and regeneration of anthracene competes with the copolymerization.The reasons for the structural differences between the copolymers of the two vinyl monomers are discussed.