基于质子条件式的终点误差精确式

容量分析中,滴定终点的误差决定了该分析方法的可靠性。根据质子条件式,可推导出终点误差的精确式。该表达式用滴定开始前而不是终点时物质的浓度进行计算;用滴定终点时的p H进行计算,不需要计算化学计量点时的p H;所得出的精确式具有通用性,能有效降低学习与记忆的难度,提高计算结果的准确度。     

Computational characterization and design of SARS coronavirus receptor recognition and antibody neutralization

The sequential determination of crystal structures of the SARS coronavirus spike receptor-binding domain (RBD) in complex with its cellular receptor or neutralizing antibody opened a door for the design and development of antiviral competitive inhibitors. Based on those complex structures, we conduct computational characterization and design of RBD-mediated receptor recognition and antibody neutralization. The comparisons between computational predictions and experimental evidences validate our structural bioinformatics protocols. And the calculations predict a number of single substitutions on RBD, receptor or antibody that could remarkably elevate the binding affinities of those complexes. It is reasonable to anticipate our structure-based computation-derived hypotheses could be informative to the future biochemical and immunological tests.     

平头pH电极用于流动注射-电位滴定法测定碱溶液的浓度

以盐酸溶液为滴定剂,采用流动注射-平头pH电极测定强碱(如氢氧化钠溶液)及弱碱(如氨水)溶液的浓度。选择流动注射分析系统的工作参数为:①混合管长度40 cm;②载流盐酸溶液浓度1.027×10-3mol·L-1;③样品进样量310μL;④流速0.82 mL·min-1。结果表明:氢氧化钠和氨水的峰面积、峰高和半峰宽均与其浓度的对数值在一定的范围内呈线性关系。方法用于实际样品分析,滴定灵敏度比手工滴定方法的灵敏度高10倍,测定值的相对标准偏差(n=5)在1.1%~1.8%之间。     

Charging of a dust particle in a plasma with a nonextensive ion distribution function

The dust charge neutralization in a plasma with nonextensive ions is considered. The condition that the total current to a grain be zero is expressed in terms of the Lambert function. The fall-off of the net negative dust charge is then considered and a parameter study conducted, assuming hydrogen as well as argon plasma. Owing to ion nonextensivity, the dust charge reduction becomes much faster. Moreover, stronger is the ions correlation, more important is the involved electron depletion for a complete dust “decharging”.     

Novel long alkyl side chain benzo[a]phenoxazinium chlorides: synthesis, photophysical behaviour and DNA interaction

Several fluorescent benzo[a]phenoxazinium chlorides possessing a propyl-, octyl-, decyl-, dodecyl- or tetradecylamino at the 5-position of the heterocyclic moiety were efficiently synthesised. The absorption and emission maxima of all compounds lie in the range 627-638 nm and 654-678 nm, respectively, with good fluorescence quantum yields. Studies of their photophysical properties in ethanol allowed for the estimation of the acid-base dissociation constant, K_a, revealing an enhancement with the increase in the alkyl side-chain length. It is in the aqueous medium only that the acid form is observed as coexisting with H-aggregates. The solubility markedly decreased when the chain length increased. The residual ethanol (0.2% v/v) used to facilitate the solubilisation of the benzo[a]phenoxazinium dyes allow for the existence of the basic form in an aqueous solution, possibly through preferential solvation. Photophysical studies in the presence of DNA revealed that the compounds with an alkyl side chain of up to eight carbon atoms could intercalate between DNA nucleotides. Moreover, other forms of DNA binding were found to be operative, involving also the basic form of benzo[a]phenoxazinium dyes.     

Mutual recombination in slow Si^＋ ＋ H^- collisions

This paper studies the process of mutual neutralization of Si^＋ and H^- ions in slow collisions within the multichannel Landau-Zener model. All important ionic-covalent couplings in this collision system are included in the collision dynamics. The cross sections for population of specific final states of product Si atom are calculated in the CM energy range 0.05 e∨/u-5 ke∨/u. Both singlet and triplet states are considered. At collision energies below -10 e∨/u, the most populated singlet state is Si（3p4p, ^1S0）, while for energies above -150e∨/u it is the Si（3p, 4p, ^1P1） state. In the case of triplet states, the mixed 3p4p（^3S1 ＋^3P0） states are the most populated in the entire collision energy range investigated. The total cross section exhibits a broad maximum around 200 300e∨/u and for ECM ≤ 10e∨/u it monotonically increases with decreasing the collision energy, reaching a value of 8 × 10^-13 cm^2 at ECM = 0.05 e∨/u. The ion-pair formation process in Si（3p^2 ^3PJ）＋H（1s） collisions has also been considered and its cross section in the considered energy range is very small （smaller than 10^-20 cm^2 in the energy region below 1 ke∨/u）.     

Medium effects on the ionization constants of some pyridinecarboxylic acid derivatives

Summary The dissociation constants of 3-hydroxy-2-carboxypyridine (3H2CP), 2-hydroxy-3-carboxypyridine (2H3CP), and 2-mercapto-3-carboxypyridine (2M3CP) were determined by potentiometric titration in 20 mole% ethanol/water, dimethylsulfoxide/water, N,N-dimethylformamide/water, and dioxane/water mixtures at 25±0.1°C applying an empiricalpH correction for mixed aqueous solvents. ThepK _n values obtained are discussed with respect to the nature of the solvent and the ionic strength of the medium as well as the molecular structure. Linearization of the titrimetric data for the second equivalence point of3H2CP,2H3CP, and2M3CP was carried out using theGran method.

---

Einfluß des Mediums auf die Ionisationskonstanten einiger Pyridincarbonsäurederivate

Zusammenfassung Die Dissoziationskonstanten von 3-Hydroxy-2-carboxypyridine (3H2CP), 2-Hydroxy-3-carboxypyridin (2H3CP) und 2-Mercapto-3-carboxypyridin (2M3CP) wurden mittels potentiometrischer Titration in 20 mol% Ethanol/Wasser, Dimethylsulfoxid/Wasser, N,N-Dimethylformamid/Wasser und Dioxan/Wasser bei 25±0.1°C unter Verwendung einer empirischenpH-Korrektur für wässrige Lösungsmittelgemische bestimmt. Die erhaltenenpK _n-Werte werden im Zusammenhang mit Lösungsmitteleigenschaften, Ionenstärken und Molekülstruktur diskutiert. Die titrimetrischen Daten für die zweiten Äquivalenzpunkte von3H2CP,2H3CP und2M3CP wurden mit Hilfe derGranschen Methode linearisiert.

     

动态模拟法在酸碱滴定中的应用

本文建立了ＮａＯＨ滴定混合酸过程中〔Ｈ〕随滴定剂Ｖ变化的微分滴定方程，选用龙格－库塔算法求解上述微分方程，从而进行ｐＨ随△Ｖ变化的动态模拟计算。本文将离子的活度系数引入计算过程，因而获得了与实验值吻合的模拟计算结果。     

弱磁场下低温中和法制备亚微米非晶态δ-FeOOH的研究

利用XRD和SEM分别对在弱磁场下通过低温中和法制备的羟基铁氧化物进行相成分和颗粒形貌分析. 试验结果表明: 无磁场下, 产物是由部分球形和部分针状的α-FeOOH组成. 0.1 T磁场下, 产物是纺锤形的γ-FeOOH, 但是, 其粒度分布很不均匀. 0.3 T磁场下, 产物是球形的Fe_1.833(OH)_0.5O_0.25. 0.5 T磁场下, 产物是100 nm左右的球形的非晶态δ-FeOOH. Fe_1.833(OH)_0.5O_0.25是无磁场下制备的α-FeOOH向弱磁场下制备的δ-FeOOH转变的中间产物. 并且, 亚微米球形Fe_1.833(OH)_0.5O_0.25和亚微米非晶态球形δ-FeOOH的粒度分布都很均匀. 此外, 弱磁场影响羟基铁氧化物的结晶度.     

Study of acid-base properties of fulvic acids using fluorescence spectrometry and multivariate curve resolution methods

Samples of fulvic acids obtained from cultivated calcareous soils are analyzed using acid-base titrations with spectrofluorimetric detection. Observed changes in both synchronous and emission spectra of fulvic acids when pH is changed are explained in terms of a limited number of fluorescent contributions each defined by its specific fluorescent spectrum and a concentration profile (species distribution) recovered from the multivariate curve resolution analysis of experimental data. Information on equilibrium is estimated from concentrations of the acid-base species.