二元羧酸的化学结构与其抑制草酸钙结晶能力研究

采用X射线衍射(XRD)、傅里叶红外光谱(FTIR)和扫描电镜(SEM)研究了相距3个C—C键长具有不同取代基的二元羧酸对草酸钙(CaOxa)晶体生长的影响。这些二元酸包括丁二酸、顺丁二烯酸、反丁二烯酸、苹果酸、天冬氨酸和酒石酸。它们均能抑制一水草酸钙(COM)晶体的聚集,减小COM比表面积,并诱导二水草酸钙(COD)生成,其能力随二元酸上取代的—OH或—NH₂基数量增加而增强。从二元羧酸化学结构讨论了其影响草酸钙结晶效果的分子机理,对COM生长具有最佳抑制效果的羧酸是含有HOOC—CH(R)—CH₂—COOH(ROH或NH₂)分子的化合物。实验结果可为临床上寻找新的防石药物提供参考。     

Experimental evidence of chiral crown ether complexation with aromatic amino acids

The complexation of L ‐ and D ‐enantiomers of phenylglycine, phenylalanine, and tryptophan with D ‐mannonaphto‐crown‐6‐ether in methanol solution was studied by NMR and isothermal titration calorimetry (ITC) at 298.15 K. The total heat effects attributed to the binding phenomena were measured in the range of 1.8 to 7.7 mJ, and the complexation was found stereo‐specific. The binding topologies were estimated basing on ¹H 2D‐ROESY experiments. The analysis of Job plots obtained from ¹H NMR‐monitored titrations proved the coexistence of 1:1 and 1:2 (crown ether:amino acids) complexes, which thermodynamic parameters, K_s, ΔG, ΔH°, and TΔS were determined with the aid of ITC. The 1:1 complexes were found enthalpically stabilized, generally by electrostatic interactions between the charged NH group of amino acid and crown ether macrocyclic moiety, while the binding of the second amino acid molecule was driven entropically due to solvatophobic effect. Strong enthalpy–entropy compensation points towards the uniform binding mode of all complexes studied. The mode of complex formation was found solvent dependent. For phenylalanine guest studied in various solvent systems, in contrast to the aqueous media, the noticeable chiral recognition is observed in methanol solution, and the complex stoichiometry (1:2 ether:Phe) differs from the 2:1 one, determined previously for the same host‐guest system in water (J. Thermal. Anal. Cal. 2006; 83: 575–578). Copyright © 2007 John Wiley & Sons, Ltd.     

Adsorption of dicarboxylic acids onto nano‐structured silver surfaces – surface‐enhanced Raman scattering studies of pH‐dependent adsorption geometries

Understanding and shaping adsorption orientations of molecular compounds on nano‐structured metallic surfaces is an important issue across many areas of contemporary research including the design of nano‐structured surfaces and catalytic processes. Here, we used surface‐enhanced Raman spectroscopy to study these orientations on nano‐structured silver surfaces using dicarboxylic acids (maleic acid and fumaric acid) as model substances. Results revealed a clear pH dependence of the observed adsorption geometries of dicarboxylic acids correlating well with the dissociation states of the two acidic groups. Our data demonstrate the potential of the technique and contribute to an improved understanding of adsorption orientations of molecules at the interface between nano‐structured metal surfaces and a liquid phase. Copyright © 2012 John Wiley & Sons, Ltd.     

红外光谱结合二维相关分析研究堆肥过程腐殖酸演化规律

堆肥材料中腐殖酸的组成和结构直接影响堆肥产品品质和腐熟度。为研究堆肥腐殖酸的组成和形成过程,进行了生活垃圾堆肥并提取了不同堆肥阶段样品中的胡敏酸和富里酸,采用红外光谱和二维相关分析,探讨了堆肥过程胡敏酸、富里酸的组成、结构及随时间演化规律。红外光谱结果显示,堆肥胡敏酸组成复杂,在2 917～2 924,2 844～2 852,2 549,1 662,1 566,1 454,1 398,1 351,990～1 063,839,711 cm-1均出现了吸收峰;相对于胡敏酸,堆肥富里酸结构简单,仅在1 725,1 637,990 cm-1出现了吸收峰。上述吸收峰的出现表明堆肥胡敏酸和富里酸均含有木质素来源的苯环和糖类结构,但胡敏酸还含有丰富的脂族和蛋白类结构,这些在富里酸中含量较低;堆肥过程糖类、脂类、蛋白类及木质素结构均发生了降解,但是在胡敏酸和富里酸中它们的降解优先顺序不同。二维相关光谱分析结果表明,胡敏酸中降解先后顺序为脂肪类—蛋白类—多糖类和木质素,而富里酸中为蛋白质—多糖和脂肪类,降解过程均生成了羧酸、酮类和酯类结构,其中羧酸类物质一部分在堆肥中形成了碳酸盐。研究结果表明,红外光谱结合二维相关分析不仅可以获得堆肥腐殖酸官能团组成,还可以揭示堆肥过程这些官能团降解顺序,确定堆肥腐殖酸合成机制和动力学过程。     

Microwave-assisted digestion with a single reaction chamber for mineral fertilizer analysis by inductively coupled plasma optical emission spectrometry

A systematic approach is proposed to evaluate microwave-assisted digestion in a single reaction chamber for the simultaneous determination of elements in the mineral fertilizer and raw material by inductively coupled plasma optical emission spectrometry. A reference material was digested using 12 acid mixtures containing nitric, hydrochloric, orthophosphoric, hydrofluoric or boric acid. Principal components analysis was applied for data treatment. Three digestion procedures based on diluted acids exhibited the most accurate results, with relative errors for reference values ranging from ?15% to +?9%. Limits of quantification were in the range of 0.2?mg cadmium kg^?1 up to 1000?mg aluminum kg^?1.     

Theoretical study of14N pure quadrupole resonance in amino acids

The theoretical hybridization model of Vega is adapted to the tetrahedral environment around the nitrogen nucleus in eleven amino acids to estimate the orbital occupation numbers using the experimental values of the quadrupole coupling constant and asymmetry parameter of¹⁴N quadrupole resonance and the results are discussed.     

几种N-取代马来酰胺酸辅酶模型的核磁共振研究

我们对8种N-取代马来酰胺酸辅酶模型与不同类型的亲核试剂反应后生成的产物进行了¹H、¹³C NMR的研究, 测得¹H、¹³C谱化学位移,研 究探讨其规律性, 并测试了IR谱和元素分析.     

15N/14N Analysis of Amino Acids with GC-C-IRMS - Methodical Investigations and Ecotoxicological Applications

Abstract

In order to perform the ¹⁵N/¹⁴N analysis of amino acids using a gas chromatograph and isotope ratio mass spectrometer linked up via a combustion interface (GC-C-IRMS), the amino acids must be derivatized. Tert-butyldimethylsilylation is examined using various techniques (direct conversion to nitrogen gas, ConFlo-IRMS [1], GC-C-IRMS [2]) and subsequently applied to isotopic characterization of amino acids from wheat protein hydrolyzate obtained from plants exposed to ozone. The method provides a reliable tool for studying ecotoxicological effects on plants at a molecular level in addition to the investigation of the natural variations of different N fractions.     

Relationship between experimental pKa values in aqueous solution and a gas phase bond length in bicyclo[2.2.2]octane and cubane carboxylic acids

Linear correlations were established between the calculated bond lengths and the pK_a or σ_I values for a series of 4‐substituted bicyclo[2.2.2]octane‐1‐carboxylic acid and 4‐cubane‐1‐carboxylic acid derivatives. The bond lengths have been calculated at a modest computational level, HF/6‐31G(d), both in the gas phase and with the continuum solvation model, polarisable continuum model (PCM). In general, the best correlations are obtained when the PCM model is taken into account, especially when neutral and charged molecules are considered together. The best models in each case show square correlation coefficients (R²) larger than 0.9 and indicate that they can be used as predictive tools. These results expand previous results that indicate the possibility of a relationship between gas phase bond length and pK_a values in aqueous solution and indicate that such relationships are more general than hitherto expected. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of halogen atom on electron spin polarization studied by CIDEP,using halogen substituted aromatic acyl compounds

The reaction and spin dynamics of the photocleavage reaction of 2-chloro-2′-acetylnaphthalene were studied by time-resolved FT-EPR and transient absorption (TA) spectroscopy. The photocleavage reaction from both singlet and triplet states was observed by TA and EPR experiments, although the radical cleavage reaction in the excited triplet state is energetically unfavourable. This feature has been explained by the ionic cleavage reaction due to the electro-negativity of the chlorine atoms. The time-resolved FT-EPR spectra were similar to those observed in the bromine substituted compound, 2-BAN, reported in a previous paper. The origin of the electron spin polarization was assigned to the radical triplet pair mechanism (RTPM) and free radical pair mechanism (F-pair RPM) from analysis of the time profiles of the spin polarization.