环丙沙星的光谱性质、质子化作用与荧光量子产率

研究了环丙沙星(ciprofloxacin, CIP)在不同pH条件下的荧光光谱、紫外吸收光谱和质子化作用,测量了CIP在中性条件下的荧光量子产率。在H+浓度大于1 mol·L-1的HCl介质中,CIP分子(简写为HL)可以结合3个质子而以H₄L3+形式存在,有微弱的荧光,最大荧光发射波长(λ_ｍａｘ)为456 nm。在pH 0～2的酸性条件下,CIP主要以H₃L2+形式存在,λ_ｍａｘ为450 nm,荧光较弱,荧光强度随pH的升高而上升。在pH 2～4时,CIP主要以H₂L+形式存在,具有强荧光,λ_ｍａｘ仍为450 nm。当pH＞4时,λ_ｍａｘ逐步蓝移到414 nm,荧光强度随pH的升高而稍有降低,同时紫外吸收光谱也有明显变化,表明H₂L+随pH升高而失去质子,以双极离子HL形式存在。当pH＞8时,荧光强度随pH升高而减弱至消失,表明HL逐步失去质子,转化为无荧光的阴离子L-。在分子形态变化过程中,最大荧光激发波长始终在275 nm附近,但最大荧光发射波长有较大变化。在pH 7.0的缓冲溶液中,以硫酸奎宁为参比,测得CIP在最大荧光激发波长275 nm处的荧光量子产率为0.12。     

三氟乙酸对无金属卟啉-苝酰亚胺分子阵列激发态衰变过程的影响

用紫外-可见吸收光谱和荧光光谱研究了CF₃COOH浓度变化对CHCl₃溶液中N-[p-5′-(m^-10′,15′,20′-三苯基卟啉)基]-N′-正十二烷基-3,4:9,10-四羧基二酰亚胺分子阵列(TrPP-MDPTCDI)的光致激发态衰变机理的影响,发现无论激发无金属卟啉还是酰亚胺基元,分子阵列均表现出质子化无金属卟啉生色团的特征荧光发射.对电子结构的分析说明质子化使[H₂²⁺TrPP^*-MDPTCDI]成为各种激发态中相对稳定的物种,因此,未质子化前占主导的从卟啉到酰亚胺基元的光致电子转移衰变途径在质子化后受到有效抑制,激发卟啉生色团(λ=439nm)直接得到[H₂²⁺TrPP-MDPTCDI^*],并以辐射衰变方式回到基态;激发酰亚胺生色团(λ=491nm)得到的[H₂²⁺TrPP^*-MDPTCDI]通过电荷分离态迅速弛豫到[H₂²⁺TrPP^*-MDPTCDI],并辐射荧光,同时伴随少量的从酰亚胺到质子化无金属卟啉生色团的能量转移.     

Theoretical Studies on Electronic Spectrum Property of 2—（2—Hydroxyphenyl）pyridine Via Time—Dependence Density Functional Theory Method

The geometrical structures of 2-(2-hydorxyphenyl) pyridine(PP) and its protonation states were optimized by means of the B3LYP/6-31G(d) method.For all the selected systems,the existence of H-bond is in favor of the stability of the systems.On the basis of the optimized geometrical structures,their electronic spectrum properties were studied by time-dependent density functional theory(TD-DFT)methosd via a hybrid runction of B3LYP and 6-31G(d) basis set.The TD-DFT calculation result predicts the absorption spectrum of PP at 324nm (3.82eV),which is in very good agreement with the experimental value of 322nm (3.85eV)determined in solvent chloroform.The absorption spectra of the two protoation states both exert a red shift in various pH media.     

Acidity and Lactonization of Xylonic Acid: A Nuclear Magnetic Resonance Study

In acidic aqueous solutions the xylonic acid/xylonate equilibrium is coupled with the formation of the γ- and δ-lactones. The γ-lactone is formed more readily, whereas the δ-lactone can only be observed in traces at very low pH values (<2.5). By means of ¹³C NMR, both the lactone hydrolization constant and the acid dissociation constant could be determined (K_L = 4.08, = 3.65 ± 0.34). Further, a second deprotonation of one of the hydroxyl groups could be observed at very high pH ( = 13.3 ± 0.76).     

A Proton Complex of p-tert-Butylcalix[4]arene-tetrakis(N,N-dimethylthioacetamide): NMR Evidence and Probable Structure

Using ¹H and ¹³C NMR together with density functional theoretical (DFT) calculations, it is shown that p-tert-butylcalix[4]arene-tetrakis(N,N-dimethylthioacetamide) (1) forms a stable equimolecular complex with proton in the form of hydroxonium ion in nitrobenzene-d ₅. Protons were offered by hydrogen bis(1,2-dicarbollyl) cobaltate (HDCC) and converted to hydroxonium ions by traces of water. The complex 1·H₃O⁺ adopts a slightly asymmetric but rapidly motionally averaged conformation, which is distinctly more cone-like than ligand 1. The hydroxonium ion H₃O⁺ is bound partly to thiocarbonyl sulphur atoms and partly to phenoxy oxygen atoms of 1 by strong hydrogen bonds and other electrostatic interactions.

     

Nanographene with a Nitrogen-Doped Cavity

Nitrogen-doped cavities are pervasive in graphenic materials, and represent key sites for catalytic and electrochemical activity. However, their structures are generally heterogeneous. In this study, we present the synthesis of a well-defined molecular cutout of graphene featuring N-doped cavity. The graphitization of a macrocyclic pyridinic precursor was achieved through photochemical cyclodehydrochlorination. In comparison to its counterpart with pyridinic nitrogen at the edges, the pyridinic nitrogen atoms in this nanographene cavity exhibit significantly reduced basicity and selective binding to Ag⁺ ion. Analysis of the protonation and coordination equilibria revealed that the tri-N-doped cavity binds three protons, but only one Ag⁺ ion. These distinct protonation and coordination behaviors clearly illustrate the space confinement effect imparted by the cavities.     

NorDATA: An original ligand based on the norbornane skeleton. Synthesis and thermodynamic characterization of metal complexes

An original diaminotetracarboxylic ligand based on the rigid bicyclic norbornane skeleton was synthesized in four steps. The stability of its metal complexes was measured in water by potentiometric titration and discussed.     

DFT and NBO theoretical study of protonation of tri-tert-butoxysilanethiol and its anion

Density functional theory (DFT) calculations of geometry optimization at the B3LYP/6-31+G(d) level have been made for the tri-tert-butoxysilanethiolato anion, i.e. (^tBuO)₃SiS⁻ [coded A], and its O- and S-protonated derivatives: (^tBuO)₃SiSH (B), (^tBuO⁺H)(^tBuO)₂SiS⁻ (C), (^tBuO)₃SiSH₂⁺ (D) and (^tBuO⁺H)(^tBuO)₂SiSH (E). Energy balances for the protonation of silanethiol B in vacuum and the aqueous phase (using the polarized continuum IPCM model) were considered. Based on theoretical calculations, it was found that protonation on the oxygen atom causes Si–S bond shortening, while protonation on the sulfur atoms results in elongation of the bond. Changeability of the Si–S and Si–O bond lengths was analyzed in terms of the natural bond orbital (NBO) method. Principal electronic delocalizations caused by anomeric effects of the sulfur and oxygen lone pairs interaction with the anti-bonding Si–O orbitals were confirmed by the correlation between the shortening of the Si–S bond length and the elongation of the Si–O bond within the structures of the species A–E.     

液/液界面电子转移研究苯甲酰吡啶-缩氨基硫脲的亲脂性

The ion transfer reaction of 2-benzoylpyridine-thiosemicarbazone (HL), which has antimicrobial and antifungal properties and anticancer activity, has been studied to determine its lipophilicity by cyclic voltammetry at the water/1,2-dichloroethane (1,2-DCE) interface. The physicochemical parameters such as standard partition coefficient (IgP1) and the standard Gibbs energy of transfer (△G0,w→otr,I) of the protonated form of the ligand were measured as a function of pH in aqueous phase. The protonated form of the ligand exhibited reversible or quasi-reversible voltammograms at the 1,2-DCE in the range of pH 1-5. The protonation constants of the ligand, pKal, and pK? were determined spectrophotometrically and were found to be 12.14 and 3.24, respectively. The standard Gibbs energy of transfer (△G0,w→otr,N) and the partition coefficient of neutral species (IgPN) were also determined by the shake-flask method. The standard Gibbs energy of transfer of this compound across the water/1,2-DCE interface was evaluated as the quantitative measure of its lipophilicity. The difference between lgP1 and lgPN was related to the degree of charge delocalization and was used to evaluate qualitatively the lipophilicity of the ligand.     

Investigation of the Lipophilicity of 2-Benzoylpyridine-Thiosemicarbazone Based on the Ion Transfer across the Liquid/Liquid Interface

The ion transfer reaction of 2-benzoylpyridine-thiosemicarbazone (HL), which has antimicrobial and antifungal properties and anticancer activity, has been studied to determine its lipophilicity by cyclic voltammetry at the water/1,2-dichloroethane (1,2-DCE) interface. The physicochemical parameters such as standard partition coefficient (lgP_I) and the standard Gibbs energy of transfer ( ) of the protonated form of the ligand were measured as a function of pH in aqueous phase. The protonated form of the ligand exhibited reversible or quasi-reversible voltammograms at the 1,2-DCE in the range of pH 1–5. The protonation constants of the ligand, pK_a1 and pK_a2, were determined spectrophotometrically and were found to be 12.14 and 3.24, respectively. The standard Gibbs energy of transfer ( ) and the partition coefficient of neutral species (lgP_N) were also determined by the shake-flask method. The standard Gibbs energy of transfer of this compound across the water/1,2-DCE interface was evaluated as the quantitative measure of its lipophilicity. The difference between lgP_I and lgP_N was related to the degree of charge delocalization and was used to evaluate qualitatively the lipophilicity of the ligand.