Blackbody Infrared Radiative Dissociation of Protonated Oligosaccharides

The dissociation pathways, kinetics, and energetics of protonated oligosaccharides in the gas phase were investigated using blackbody infrared radiative dissociation (BIRD). Time-resolved BIRD measurements were performed on singly protonated ions of cellohexaose (Cel₆), which is composed of β-(1 → 4)-linked glucopyranose rings, and five malto-oligosaccharides (Mal_x, where x = 4–8), which are composed of α-(1 → 4)-linked glucopyranose units. At the temperatures investigated (85–160 °C), the oligosaccharides dissociate at the glycosidic linkages or by the loss of a water molecule to produce B- or Y-type ions. The Y ions dissociate to smaller Y or B ions, while the B ions yield exclusively smaller B ions. The sequential loss of water molecules from the smallest B ions (B₁ and B₂) also occurs. Rate constants for dissociation of the protonated oligosaccharides and the corresponding Arrhenius activation parameters (E_a and A) were determined. The E_a and A-factors measured for protonated Mal_x (x > 4) are indistinguishable within error (~19 kcal mol⁻¹, 10¹⁰ s⁻¹), which is consistent with the ions being in the rapid energy exchange limit. In contrast, the Arrhenius parameters for protonated Cel₆ (24 kcal mol⁻¹, 10¹² s⁻¹) are significantly larger. These results indicate that both the energy and entropy changes associated with the glycosidic bond cleavage are sensitive to the anomeric configuration. Based on the results of this study, it is proposed that formation of B and Y ions occurs through a common dissociation mechanism, with the position of the proton establishing whether a B or Y ion is formed upon glycosidic bond cleavage.     

Packing Structures of Thiophene Dimers and Their Effects on Excitation Energies of Thiophene Dimers

IntroductionPi(π) conjugated polymers have received exten-sive experimental and theoretical attention because oftheir fascinating electronic and optical properties[1—3].Recently, many new experiment results[4—6]have re-vealed that the inter-chain inter…     

Cooperative Hairpin Dimers for Recognition of DNA by Pyrrole–Imidazole Polyamides

A doubling of the length of binding site for the same size of ligand is achieved by the title compound by formation of a cooperative hairpin dimer on binding to DNA (depicted schematically below) . The binding affinity and selectivity are unaffected by this new binding pattern. Circles represent heterocyclic rings, and diamonds and curved lines represent β-alanine and (R)-2,4-diaminobutyric acid residues, respectively.     

EPA甲酯和DHA甲酯标准样品的制备和结构解析

从鱼油中分离制备得到二十碳五烯酸（EPA）甲酯和二十二碳六烯酸（DHA）甲酯,采用红外光谱、质谱、核磁共振波谱等手段对EPA甲酯和DHA甲酯的结构进行表征,提供了不饱和脂肪酸甲酯标准物质研制基础。样品的红外光谱（IR）、质谱（MS）、核磁共振谱图（1HNMR、13CNMR）所给出的结构信息与EPA甲酯和DHA甲酯的化学结构式相符,并通过DEPT谱和I3C-1H COSY化学位移相关谱（HMBC）对各共振峰进行了指认,样品的谱图数据与文献报道基本一致。     

Anionic Copolymerizations of Acrolein with Methyl Vinyl Ketone and Acrylamide by Imidazole

The anionic copolymerizations of acrolein (AL) with methyl vinyl ketone (MVK) and acrylamide (AAm) in the presence of imidazole (Im) as an initiator have been studied in tetrahydrofuran at 0°C. The AL-MVK copolymers were found to be composed of vinyl polymer with one Im group attached and having an aldehyde and a carbonyl side chain. The monomer reactivity ratio was determined from a Fineman-Ross plot as r₁ = 2.02 and r₂ = 0.06. On the other hand, the AL-AAm copolymer were found to be composed of polymer units of 1,2 and 1,4 addition polymerization of AAm. These observations might be explained by the intermolecular hydrogen transfer mechanism of AAm. The polymerization mechanisms were discussed on the basis of these copolymerization results.     

基于环糊精二聚体与紫精聚合物的包结作用制备超分子水凝胶

制备了对苯二甲酸连接的环糊精二聚体(α,α-CD Dimer)及紫精聚合物(VP), 利用α,α-CD Dimer与VP之间的主客体识别作用构筑了一种超分子水凝胶. ¹H NMR测定结果表明α,α-CD Dimer和VP的主客体相互作用是通过α-CD空腔和VP形成包结络合物进行的. 环糊精二聚体α,α-CD Dimer和聚合物VP凝胶体系的构筑受环糊精二聚体类型的影响, 同时该超分子水凝胶对有竞争作用的客体分子表现出响应性, 该超分子水凝胶在竞争性客体分子存在的条件下, 可发生小分子诱导的凝胶与溶胶转化行为. 此外, 该凝胶体系还具有良好的热稳定性.     

Proton Transfer Accounting for Anomalous Collision-Induced Dissociation of Proton-Bound Hoogsteen Base Pair of Cytosine and Guanine

To understand the anomalous collision-induced dissociation (CID) behavior of the proton-bound Hoogsteen base pair of cytosine (C) and guanine (G), C:H⁺???G, we investigated CID of a homologue series of proton-bound heterodimers of C, 1-methylcytosine, and 5-methylcytosine with G as a common base partner. The CID experiments were performed in an energy-resolved way (ER-CID) under both multiple and near-single collision conditions. The relative stabilities of the protonated complexes examined by ER-CID suggested that the proton-bound complexes produced by electrospray ionization in this study are proton-bound Hoogsteen base pairs. On the other hand, in contrast to the other base pairs, CID of C:H⁺???G exhibited more abundant productions of C:H⁺, the fragment protonated on the moiety with a smaller proton affinity, than that of G:H⁺. This appeared to contradict general prediction based on the kinetic method. However, further theoretical exploration of potential energy surfaces found that there can be facile proton transfers in the proton-bound Hoogsteen base pairs during the CID process, which makes the process accessible to an additional product state of O-protonated C for C:H⁺ fragments. The presence of an additional dissociation channel, which in other words corresponds to twofold degeneracy in the transition state leading to C:H⁺ fragments, effectively doubles the apparent reaction rate for production of C:H⁺. In this way, the process gives rise to the anomaly, the observed pronounced formation of C:H⁺ in the CID of the proton-bound Hoogsteen base pair, C:H⁺???G.

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基于环糊精二聚体与金刚烷修饰的温敏性聚合物的主客体识别构筑超分子水凝胶

利用环糊精二聚体(trans-Stilbene β-CD Dimer)与金刚烷修饰的温敏性聚合物(Pnipam-Ad)的主客体识别作用构筑了超分子水凝胶. 2D NMR 测定结果表明trans-Stilbene β-CD Dimer 和Pnipam-Ad 的主客体相互作用是通过β-CD 空腔和疏水体Ad 形成包结络合物进行的. 环糊精二聚体trans-Stilbene β-CD Dimer 和聚合物Pnipam-Ad 两者之间的缔合程度受trans-Stilbene β-CD Dimer 和Pnipam-Ad 的浓度以及trans-Stilbene β-CD Dimer 光异构的影响. 此外, 由于trans-Stilbene β-CD Dimer 对Pnipam-Ad 聚合物链的物理交联作用使两者混合溶液的最低临界溶解温度(LCST)低于纯聚异丙基丙烯酰胺(Pnipam)的LCST.     

对萘普生和萘普生甲酯的毛细管电泳手性分离

以磺化β－ＣＤ作为手性分离添加剂,分别对萘普生和萘普生甲酯进行了手性分离研究,当磺化β－ＣＤ的浓度为３．５％（Ｗ／Ｖ）时,萘普生和萘普生甲酯的手性分离度都可大于２,但萘普生与萘普生甲酯不能达到同时拆分。如果同时以磺化β－ＣＤ和ＨＰ－β－ＣＤ作为作为手性分离添加剂,则可对萘普生甲酯达到同时拆分,当磺化β－ＣＤ和ＨＰ－β－ＣＤ的浓度分别为３．５％和１．５％（Ｗ／Ｖ）时,对萘磺生和萘普生甲酯两种消旋体的     

脂肪酸甲酯乙氧基化物的气相色谱分析

用0.5 mol/L KOH乙醇溶液水解脂肪酸甲酯乙氧基化物(FMEO),酯键断裂,其疏水基甲 酯化、亲水基硅醚化后分别用气相色谱法测定其组成,并采用峰面积归一化法进行了组分的 定量。成功测定了各种FMEO样品的疏水基组成和环氧乙烷(EO)加成数分布,方法简单,重复性 好,尤其是对原料为混碳脂肪酸甲酯的FMEO更有意义。     

Kinetics of the Copolymerization of Methyl Vinyl Ketone and Acrylamide Initiated by the Adduct of Methyl Vinyl Ketone and Imidazole

N-(Butyl-3-one)imidazole acts as an initiating adduct which is formed in the anionic polymerization of methyl vinyl ketone (MVK) induced by imidazole (Im) and is directly formed from Im and the MVK monomer. The kinetics of the anionic homopolymerization of MVK and acrylamide (AAm) under argon in the presence of the adduct were investigated in tetrahydrofuran (THF). The rate of polymerization for the MVK system is expressed as R_p = k[Adduct] [MVK], where k = 3.1 × 10^?6 L/(mol·s)in THF at 30°C. The overall activation energy, E_a , was found to be 5.34 kcal/mol. The R_p for the AAm system is expressed as R_p = k[Adduct] [AAm], where k = 6.8 × 10^?6 L/(mol·s) in THF at 30°C, with E_a 7.78 kcal/mol. The mechanism of the polymerization induced by the initiator adduct is discussed on the basis of these results.     

手性咪唑酯类离子液体的合成及其物理性能

以咪唑,溴代烷烃及(-)-薄荷醇为原料合成了12个手性咪唑酯类离子液体,其结构经NMR和IR表征.物理性能研究结果表明,该类离子液体具有较好的热稳定性,且比旋光度存在一定的改变规律.     

The NMR Spectra of Styrene-Itaconate Ester Copolymers Obtained by Free Radical Mechanism

Styrene copolymerized with dimethyl itaconate and with methyl benzyl itaconate by use of a free radical initiator.

Monomer reactivity ratios for styrene (M₁)-dimethyl itaconate (M₂) co-polymerization were r₁ = 0.50 and r₂ = 0.06 and for styrene (M₁-methyl benzyl itaconate (M₂), r₁ = 0.42 and r₂ = 0.19. The nonconjugative methoxycarbonyl affected the monomer reactivity of itaconate toward polystyrene radical.

The NMR spectra of styrene-dimethyl itaconate copolymers were very complex and could not be interpreted because the two methoxy groups have similar chemical shifts.

The NMR spectra of styrene-itaconate copolymers were not so complex if methyl benzyl itaconate was used as comonomer instead of dimethyl itaconate. Methoxy and benzyloxy absorptions were sufficiently separated and “co-isotacticity” could be determined.

It is shown that the nonconjugative methoxycarbonyl group had little influence on the steric course of the cross-propagation reaction between styrene and itaconate.     

乙腈介质中S-NO键异裂能和均裂能的测定

近年来, 大量研究表明, 一氧化氮在许多生命过程(如免疫、神经传导和血管扩张等)中发挥着十分重要的作用[1～4]. 然而, 文献[5]的研究表明, NO在生命体内很少以游离形式存在, 绝大部分都是与生命体内活线性分子结合着, 其中NO与有机硫以S-NO键方式结合形成的NO蕴合物(Nitric oxide-generating agent)被认为是NO在生命体内贮存、 转移和释放最主要的分子源[5]. 因此, 系统研究各种类型硫键NO蕴合物中S-NO键的断裂能, 可以诠释和预测NO在生命体内的转移方向和转移机制. 由于这一原因, S-NO键断裂能的研究是当今许多键能化学家正致力于解决的最热门课题之一. 10多年来, 我们从事的化学键键能研究, 已为这一领域的深入研究奠定了基础. 前文[6～8]根据热力学循环利用滴定量热法成功地测得了多个系列的N-NO键的异裂能和均裂能. 最近, 我们在此工作的基础上, 通过改变热力学循环方式又成功地利用滴定量热法测得了12个S-亚硝基化合物中的S-NO键的异裂能和均裂能, 其中9个为芳香体系, 3个为脂肪体系, 分别模拟生命体系内芳香体系和脂肪体系中的S-NO键. 本文首次报道其实验结果, 并进行一些讨论.     

烯丙位化学键均裂离解能及其取代基效应

使用复合从头算方法系统地获得了一批精确的烯丙位化学键的均裂裂解能(BDE). 取代基效应的研究表明, C—H与Si—H的BDE表现出差的Hammett关系, 而N—H, O—H, P—H与S—H的BDE表现出好的Hammett关系. 进一步分析表明烯丙位BDE受共轭效应比诱导/场效应的影响更为明显. 并且还讨论了BDE的基态效应和自由基效应, 其结果与最近报道的有关苄位BDE的结果基本一致.     

Heterolytic and Homolytic N-NO Bond Dissociation Energies of N-Nitroso-benzenesulfonylmethylamines in Acetonitrile

Great interests have been accumulated in recent years in the chemistry and biochemistry of nitric oxide (NO) since the remarkable discoveries of its key roles in a wide range of human physiological processes. To elucidate the mechanistic details of NO migration from its donor to its acceptor, it is necessary to determine the Y-NO bind energy that registers the thermodynamic driving force for NO release and capture. In this paper the heterolytic and homolytic N-NO bond dissociation energies [ i. e., △Hhet(N-NO) and △Hhomo(N-NO)] for ten N-nitroso-p-substituted-benzensulfonyl methylamines in acetonitrile are offered, which were obtained from titration calorimetry and thermodynamic cycles, respectively (Scheme 1).     

The Importance of Methyl Positioning and Tautomeric Equilibria for Imidazole Nucleophilicity

Imidazole (IMZ) rings catalyze many biological dephosphorylation processes. The methyl positioning effect on IMZs reactivity has long intrigued scientists and its full understanding comprises a promising tool for designing highly efficient IMZ‐based catalysts. We evaluated all monosubstituted methylimidazoles (xMEI) in the reaction with diethyl 2,4‐dinitrophenyl phosphate by kinetics studies, NMR analysis and DFT calculations. All xMEI showed remarkable rate enhancements, up to 1.9×10⁵ fold, compared with spontaneous hydrolysis. Unexpectedly, the electron‐donating methyl group acts to decrease the reactivity of the xMEI compared to IMZ, except for 4(5)methylimidazole, (4(5)MEI). This behavior was attributed to both electronic and steric effects. Moreover, reaction intermediates were monitored by NMR and surprisingly, the reactivity of the two different 4(5)MEI tautomers was distinguished.     

短链羟基甲基咪唑离子液体的合成与电化学性能

通过2-(2-氯乙氧基)乙醇和2-溴乙醇分别与1-甲基咪唑反应,合成乙醇基甲基咪唑溴(EMIMBr)和乙氧基乙醇基甲基咪唑氯(EEMIMCl)2种羟基咪唑离子液体,用1H NMR和FT-IR表征结构,TG和DSC进行热性能测试,并研究了其电化学性能.结果表明,羟基类咪唑离子液体具有高的热稳定性,这种含醚氧键和羟基的短链离子液体有利于电导率的提高,导电机理符合Vogel-Tmman-Fulcher (VTF)方程.乙醇基甲基咪唑溴和乙氧基乙醇基甲基咪唑氯的室温电导率分别为1.2×10-4和1.7×10-4 S/cm.对于碳酸丙二醇酯、乙氧基乙醇基甲基咪唑氯和钾盐体系,室温电导率最高可达3.82×10-3 S/cm.乙氧基乙醇基甲基咪唑氯的电化学窗口为3.4V.     

Chiral Separation of N-Benzoyl Phenylalanine Methyl Ester by Nonaqueous Capillary Electrophoresis

Theseparationofopticalisomersisarapidlygrowingareaincapillaryelectrophoresis(CE),andmostchiralseparationbyCEhavebeenperformedinaqueousbackgroundelectrolyte.Organicsolventssuchasmethanolandacetonitrilehavebeenappliedasbuffermodifiersatconcentrationtypicallynothigherthan40%inordertoincreasehydrophobicanalytesolubilityandtoimproveselectivity,resolution,ortoaltertheelectroosmoticflow(EOF)andelectrophoreticmobilityofanalyte.Buttherehavebeenonlyafewreportsonthechiralseparationusingpurenonaqueousme…