硫酸催化乙二醛气体相水化反应机理和速率常数理论计算研究

采用M06-2X和CCSD(T)高阶量化计算和传统过渡态理论研究硫酸催化乙二醛气体相水化反应.对HCOCHO+H₂O, HCOCHO+H₂O+H₂O, HCOCHO+H₂O+H₂O, HCOCHO+H₂O...H₂SO₄和HCOCHO+H₂O+H₂SO₄五个路径的反应机理和速率常数进行了研究.计算结果表明硫酸具有较强的催化能力,能显著减小乙二醛水化反应的能垒,在CCSD(T)/6-311++G(3df,3pd)//M06-2X/6-311++G(3df,3pd)理论水平,当硫酸分子参与乙二醛水化反应时,反应能垒从37.15 kcal/mol减少至7.08 kcal/mol.在室温条件下,硫酸催化乙二醛水化反应的反应速率1.34×10^-11 cm³/(molecule.s),是等量水分子参与乙二醛水化反应的速率的10¹²倍,大于乙二醛与OH自由基反应的反应速率1.10×10^-11 cm³/(molecule.s).这表明大气条件下,硫酸催化乙二醛水化反应可以发生,同乙二醛与OH自由基反应相竞争.     

The first total synthesis of (S)-clavulazine from d-mannitol

The first total synthesis of the marine natural product, (S)-clavulazine has been accomplished. d-Mannitol was used as a chiral starting material. Enantioselective zinc-mediated allylation, and ring-closing metathesis are the key steps in the synthesis. Subsequent condensation followed by dehydrogenation yielded the natural product, (S)-clavulazine.     

Efficient and direct solid phase synthesis of ketomethylenimino and ketomethylenamino peptides

The aim of this study is the synthesis of pseudopeptides on solid supports, in order to quickly obtain modified peptides. We report a convenient step-by-step synthesis of ketomethylenimino ψ[CO-CHN] and ketomethylenamino ψ[CO-CH₂-NH] peptides. The key is the reaction between the free amino terminus of the supported peptide and a glyoxal-modified amino acid, leading to a ketomethylenimino bond, which can be reduced to a ketomethylenamino bond.     

The structural modification of DNA nucleosides by nonenzymatic glycation: an <Emphasis Type="Italic">in vitro</Emphasis> study based on the reactions of glyoxal and methylglyoxal with 2′-deoxyguanosine

Methylglyoxal and glyoxal are generated from the oxidation of carbohydrates and lipids, and like d-glucose have been shown to nonenzymatically react with proteins to form advanced glycation end products (AGEs). AGEs can occur both in vitro and in vivo, and these compounds have been shown to exacerbate many of the long-term complications of diabetes. Earlier studies in our laboratory reported d-glucose, d-galactose, and d/l-glyceraldehyde formed AGEs with nucleosides. The objective of this study was to focus on purines and pyrimidines and to analyze these DNA nucleoside derived AGE adducts with glyoxal or methylglyoxal using a combination of analytical techniques. Studies using UV and fluorescence spectroscopy along with mass spectrometry provided for a thorough analysis of the nucleoside AGEs and demonstrated that methylglyoxal and glyoxal reacted with 2′-deoxyguanosine via the classic Amadori pathway, and did not react appreciably with 2′-deoxyadenosine, 2′-deoxythymidine, and 2′-deoxycytidine. Additional findings revealed that methylglyoxal was more reactive than glyoxal. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

固定床电解槽变电流成对电解合成乙醛酸

对电解氧化乙二醛合成乙醛酸过程 ,固定床电解槽和变电流电解效果明显优于平板型电解槽和恒电流电解效果 .当阳极液中乙二醛和盐酸初始质量分数 (WCHOCHO 和WHCI)分别等于7.0 %和 8.0 %、阴极液为始终饱和的草酸溶液和微量的添加剂时 ,采用平均电流密度 (i)为 15 35A/m2 的变电流方式电解 ,阳极电流效率 (CEa)为 85 .3%、乙醛酸选择性 (RSa)为 93.9% ;阴极电流效率 (CEc)为 86 .7% ,乙醛酸选择性 (RSc)为 94 .0 % .阳极初产品中WCHOCOOH∶WCHOCHO≥ 4 0∶3,克服了阳极产品中乙二醛难以除去的困难     

Ammonolysis of Glyoxal at the Air-Water Nanodroplet Interface

The reactions of glyoxal (CHO)₂) with amines in cloud processes contribute to the formation of brown carbon and oligomer particles in the atmosphere. However, their molecular mechanisms remain unknown. Herein, we investigate the ammonolysis mechanisms of glyoxal with amines at the air-water nanodroplet interface. We identified three and two distinct pathways for the ammonolysis of glyoxal with dimethylamine and methylamine by using metadynamics simulations at the air-water nanodroplet interface, respectively. Notably, the stepwise pathways mediated by the water dimer for the reactions of glyoxal with dimethylamine and methylamine display the lowest free energy barriers of 3.6 and 4.9 kcal ⋅ mol⁻¹, respectively. These results showed that the air-water nanodroplet ammonolysis reactions of glyoxal with dimethylamine and methylamine were more feasible and occurred at faster rates than the corresponding gas phase ammonolysis, the OH+(CHO)₂ reaction, and the aqueous phase reaction of glyoxal, leading to the dominant removal of glyoxal. Our results provide new and important insight into the reactions between carbonyl compounds and amines, which are crucial in forming nitrogen-containing aerosol particles.     

流动注射化学发光法测定湖水中2-硝基酚

在酸性介质下,KMnO4可以氧化2-硝基酚产生化学发光,乙二醛对该发光体系有增敏作用。结合流动注射技术,建立了测定2-硝基酚的流动注射化学发光新方法。该方法线性范围为8.0×10-10～5.0×10-6 mol/L,检出限为1.0×10-11mol/L,对1.0×10-7 mol/L的2-硝基酚平行测定11次,相对标准偏差为2.4%。该法已用于实际水样中2-硝基酚的测定。     

Temperature dependent near-UV molar absorptivities of glyoxal and gluteraldehyde in aqueous solution

Molar absorptivities have been determined for glyoxal and gluteraldehyde in aqueous solution. Absorptivities are reported at eight temperatures in the range 5-70 degrees C for wavelengths greater than 200 nm. For glyoxal the data indicate did less than 0.02% of the glyoxal molecules exist in the free dialdehyde form, and that at 25 degrees C approximately 98% of the molecules are hydrated at both carbonyl groups, results that are consistent with previous experiments. For gluteraldehyde hydration of the two carbonyl groups occurs in an independent manner. The following thermodynamic data are found for gluteraldehyde hydration: deltaH = - 35.8+/-1.3 kJ mole(-1), deltaS = 103+/-7 J (mole K)(-1), and K = 7.5+/-2.0. The results for gluteraldehyde are compared with previous results obtained for the hydration of aliphatic aldehydes.     

引发乙醛硝酸氧化合成乙二醛反应的研究

乙醛硝酸氧化合成乙二醛的反应需要引发才能发生，考察了不加引发剂和以ＮａＮＯ２、活性炭，ＳｅＯ２等为引发剂的反应情况和结果，并进行了添加金属离子以提高乙二醛选择的试验。     

AN EXPERIMENTAL STUDY ON THE SOL/GEL PHASE TRANSITION OF LINEAR POLYMER IN THE PRESENCE OF CROSSLINKERS

The sol/gel phase diagrams were studied for two systems: polyacrylamide/Cr (III) andpolyacrylamide/glyoxal. Sol or gel phase could be distinguished according to the concen-trations of polymer and crosslinker. The boundary polymer concentration did not de-pend on the types of gelation and decreased with increasing polymer dimension (molecularweight and conformation). The gelation, which is basically interchain bonding, requires theoccurrence of entanglement. The overlap concentration is thus considered as the minimumpolymer concentration required for gelation.