弱酸弱碱多元非线性回归电位返滴定

在被测弱酸或弱碱溶液中加入一定量过量ＮａＯＨ或ＨＣｌ标准溶液，再返滴入ＨＣｌ或ＮａＯＨ标准溶液若干次，依次测定ＰＨ玻璃电极在被测溶液中的电极电位。本方法的突优点是不需要活度与浓度的换算，不需要另行测定工作曲线。测定了ＮａＡｃ和（ＮＨ３）２ＳＯ４等弱酸弱碱，结果令人满意。     

微过氧化物酶-11修饰电极对O2和H2O2的电催化还原

运用电化学循环伏安法和旋转圆盘电极技术研究了Ｏ２和Ｈ２Ｏ２在Ｎａｆｉｏｎ膜固定的微过氧化物酶－１１修饰的玻磷（ＭＰ－１１＋Ｍａｆｉｏｎ／Ｇｃ）电极上的电化学还原,结果表明,饰电极 对Ｏ２和Ｈ２Ｏ２的还原均具电催化作用。测定和比较了Ｏ２和Ｈ２Ｏ２在ＭＰ－１１＋Ｎａｆｉｏｎ／ＧＣ的电极上电催化还原反应的一些动力学参数。发现Ｏ２在修饰电极上经历了四电子还原,且还原过程与溶液的ＰＨ值有关。     

电导法快速测定黑生料及煤中碳含量

本文利用碱熔液吸收ＣＯ２后电导率的变化值与吸收的ＣＯ２含量成正比这一关系来测定生料中的含碳量。５％ＫＯＨ溶液为最佳的吸收溶液。选择了最佳实验条件，在浓Ｈ２ＳＯ４介质中，煤或黑生料与氧化剂共热产生的ＣＯ２由ＫＯＨ溶液吸收。通过测定ＫＯＨ溶液吸收ＣＯ２前后电导率的变化值来确定含碳量。对标准煤样及黑生料进行了测定，得到了较为满意的结果。     

离子色谱法测定一元弱酸的离解常数

本文探索了抑制电导离子色谱法测定pK_a<7的一元弱酸的离解常数,对以HCl为标准测定HF、HNO_2的离解常数和以HF为标准测定乳酸、乙酸和甲酸的离解常数及测定方法的主要误差来源进行了讨论。     

电子激发态CH（C^2Σ^＋）自由基的猝灭速率常数的测定

用２６６ｎｍ激光光解ＣＨＢｒ３分子产生ＣＨ（Ｃ）态自由基，通过测量ＣＨ（Ｃ＾２Σ＾＋→Ｘ＾２Ⅱ）的总荧光信号强度来测定室温下Ｏ２、Ｎ２、ｎ－Ｃ５Ｈ１２、ｎ－Ｃ６Ｈ１４和ｎ－Ｃ７Ｈ１６对ＣＨ（Ｃ２Σ＾＋，ｖ′＝０）的猝灭常数。结果表明，这些碰撞伴侣（Ｏ２和Ｎ２例外）对ＣＨ（Ｘ、Ａ、Ｂ和Ｃ）的反应或猝灭速率常数ｋ存在下列关系：ｋ（Ｘ）〉ｋ（Ｂ）〉ｋ（Ａ）≈ｋ（Ｃ），且烷烃分子对ＣＨ（Ｃ）态的猝灭速率常     

硫电极法测定H_2S离解常数的研究

测定平衡常数多采用电导法、冻点法或反应速率法等。用离子选择电极测定平衡常数或离解常数多集中研究各种氟络合物。用硫电极测定平衡常数的工作仅见到测SnS_3~(2-)的平衡常数。我们在对硫电极研究的基础上,用pH玻璃电极测定溶液的pH值,用pS电极测定不同pH值溶液中的[S~(2-)]浓度,根据H_2S在溶液中的平衡理论及硫电极在溶液中的响应特性,找到一种推算H_2S离解常数的途径。     

难溶有机物在水中离解常数及其分配系数的测定

离解常数是弱酸、弱碱很重要的物理常数,特别是有机试剂,因其分析性能与离解常数有很大的关系,所以测定新试剂的离解常数尤为必要。离解常数的测定常用电位滴定法和光度法。就光度法来说,目前绝大多数报道的是测     

采用电位滴定法在DMSO／H2O混合溶剂体系中测定磺酰脲（ …

采用电位滴定法在ＤＭＳＯ／Ｈ２Ｏ（质量比８０：２０）混合体系中测定了横酰脲和三唑并嘧啶磺酰胺类除草剂的酸离解常数,进而采用回归分析方法探讨了测得的ｐＫ。值与化合物的前沿轨道能级以及取代基效应之间的相关性,结果较为满意,从而证明从该体系测得的ｐＫａ值用于构效关系分析是完全可行的。     

硫脲氧化的非线性动力学研究——H2O2—SC（NH2）2—Cu^2＋反应体系

研究了Ｈ２Ｏ２－ＳＣ（ＮＨ２）２－Ｃｕ＾２＋－Ｈ＾＋反应体系在封闭条件下以及在ＣＳＴＲ中的振荡行为，体系在封闭条件下出现单峰振荡行为，其振幅和诱导期与反应温度，（Ｈ２Ｏ２），（ＳＣ（ＮＨ２）２）等有关，在ＣＳＴＲ中体系的Ｐｔ电极电位，铜离子选择性电极电位以及ｐＨ值均显著稳定的周期性振荡，考察期振荡过程的流速序列，发现在低流速下的出现周期性复杂振荡，体系没有双稳态出现。     

氯化血红素模拟过氧化物酶高效液相色谱柱后衍生法测定过氧化氢和水溶性有机过氧化物

研究了氯化血红素（Ｈｅｍｉｎ）模拟辣根过氧化物酶（ＨＲＰ），对羟基苯乙酸（ＰＨＰＡＡ）作 底物，高效液相色谱（ＨＰＬＣ）柱后衍生荧光法测定Ｈ２Ｏ２和水溶性有机过氧化物的方法。采用 Ｈｅｍｉｎ作催化剂柱后衍生反应的最佳ｐＨ值约为１１，与荧光检测ｐＨ值一致，使得以往ＨＰＬＣ 柱后衍生方法所需的高压泵从３台减少到２台，而一些不能作为ＨＲＰ底物的羟烷基过氧化 物在ｐＨ值≥１０的溶液中迅速水解为Ｈ２Ｏ２从而得到测定。优化了测定Ｈ２Ｏ２和甲基过氧化 氢（ＣＨ３ ＯＯＨ， ＭＨＰ）的条件。最佳条件下 Ｈｅｍｉｎ方法测定 Ｈ２Ｏ２的检测限为 ９．０ × １０－９ ｍｏｌ／Ｌ， 测定 ＭＨＰ的检测限为 ２．０ × １０－７ ｍｏｌ／Ｌ。     

Hydrogen ion titration of alkyldimethylamine oxides by 13C and 1H NMR and conventional methods

In the hydrogen ion titration of micelles, the degree of ionization of the micelle at a given pH has to be evaluated to obtain a pKa value of micelles (Ka being the proton dissociation constant) at the pH. We compared the degree of ionization obtained from 13C and 1H NMR spectra with that obtained from the stoichiometric method. We used dodecyldimethylamine oxide (C12DMAO) and hexyldimethylamine oxide (C6DMAO) to examine the titration behavior of micelles and monomers, respectively. We determined pKa values of amine oxides both in H2O and D2O. As to the monomer (C6DMAO), the degree of ionization from NMR, alpha(NMR), coincided with that from the conventional stoichiometric method alpha. The difference of pK1 of amine oxide monomer between D2O and H2O was about 0.5: pK1(D) approximately pK1(H) + 0.5. The difference was about the same as that for carboxylic acids. As to the C12DMAO micelle, alphaNMR did not coincide with alpha over a considerable range of alpha. The NMR chemical shift might be influenced by micellar structure changes induced by the ionization, such as the sphere-to-rod transition. The intrinsic logarithmic dissociation constants of the micelle were 5.9+/-0.1 for H2O, and 6.5+/-0.1 for D2O.     

Thermodynamic, kinetic and pH studies on the reactions of NCS-, N3-, and CH3CO2- with Fusarium galactose oxidase

Thermodynamic and kinetic studies on the X- = NCS-, N3-, and CH3CO2- replacement of H2O/OH- at the CuII exogenous site of the tyrosyl-radical-containing enzyme galactose oxidase (GOaseox) from Fusarium (NRR 2903), have been studied by methods involving UV-vis spectrophotometry (25 degrees C), pH range 5.5-8.7, I = 0.100 M (NaCl). In the case of N3- and CH3CO2- previous X-ray structures have confirmed coordination at the exogenous H2O/OH- site. From the effect of pH on the UV-vis spectrum of GOaseox under buffer-free conditions, acid dissociation constants of 5.7 (pK1a; coordinated H2O) and 7.0 (pK2a; H+Tyr-495) have been determined. At pH 7.0 formation constants K(25 degrees C)/M-1 are NCS- (480), N3- (1.98 x 10(4)), and CH3CO2- (104), and from the variations in K with pH the same two pKa values are seen to apply. No pK1a is observed when X- is coordinated. From equilibration stopped-flow studies rate constants at pH 7.0 for the formation reaction kf(25 degrees C)/M-1 s-1 are NCS- (1.13 x 10(4)) and N3- (5.2 x 10(5)). Both K and kf decrease with increasing pH, consistent with the electrostatic effect of replacing H2O by OH-. In the case of the GOaseox Tyr495Phe variant pK1a is again 5.7, but no pK2a is observed, confirming the latter as acid dissociation of protonated Tyr-495. At pH 7.0, K for the reaction of four-coordinate GOaseox Tyr495Phe with NCS- (1.02 x 10(5) M-1) is more favorable than the value for GOaseox. Effects of H+Tyr-495 deprotonation on K are smaller than those for the H2O/OH- change. The pK1a for GOasesemi is very similar (5.6) to that for GOaseox (both at CuII), but pK2a is 8.0. At pH 7.0 values of K for GOasesemi are NCS- (270 M-1), N3- (4.9 x 10(3)), and CH3CO2- (107).     

The amide oxygen donor. Metal ion coordinating properties of the ligand nitrilotriacetamide. A thermodynamic and crystallographic study

The metal ion coordinating properties of ntam (nitrilotriacetamide) are reported. The protonation constant (pK) for ntam is 2.6 in 0.1 M NaClO(4) at 25 degrees C. Formation constants (log K(1)) in 0.1 M NaClO(4) at 25 degrees C, determined by (1)H NMR and UV-Vis spectroscopy are: Ca(II), 1.28; Mg(II), 0.4; La(III), 2.30; Pb(II), 3.69; Cd(II), 3.78; Ni(II), 2.38; Cu(II), 3.16. The measured log K(1) values for the ntam complexes are discussed in terms of the low basicity of the N-donor, as evidenced by the pK, and the effect of metal ion size on complex stability. The amide O-donors of ntam lead to the stabilization of complexes of large metal ions (Pb(II), Cd(II), La(III), Ca(II)) relative to log K1 for the NH3 complexes, while for small metal ions (Ni(II), Cu(II)) the amide O-donors lead to destabilization. This is discussed in terms of the role of chelate ring size in controlling metal ion size-based selectivity. The structures of [Pb(ntam)(NO3)2]2 (1) and [Ca2(ntam)3(H2O)2](ClO4)4.3H2O (2) are reported. For 1: triclinic, space group P1, a = 7.4411(16), b = 9.0455(19), c = 11.625(3) A, alpha = 69.976(4), beta = 79.591(4), gamma = 67.045(3) degrees, Z = 2, R = 0.0275. For 2: monoclinic, space group P2(1)/c, a = 10.485(2), b = 11.414(2), c = 38.059(8) A, beta = 92.05(3) degrees, Z = 4, R = 0.0634. Structure 1 is dimeric with two Pb atoms linked by bridging O-donors from the two ntam ligands. The coordination sphere consists of one N-donor and 3 O-donors from the ntam ligand, two O-donors from nitrates, and one bridging O-donor. The variation in bond length suggests a stereochemically active lone pair of electrons on the Pb. Structure 2 consists of two Ca(II) ions held together by 3 bridging O-donors from ntam groups. One Ca is 9-coordinate with two ntam ligands present, plus one bridging O-donor from the other Ca(II) ntam complex. The other Ca is 8-coordinate, with a single coordinated ntam, plus two coordinated H2O molecules, and two bridging O-donors from the other half of the complex. The role of M-O=C bond angles in controlling selectivity for metal ions on the basis of their size is discussed.     

Theoretical Calculations on Amphoteric Adsorptions of the Hydrogenated C(100)-2×1 Surface

In this work we study the adsorptions of some small molecules or group on the hydrogenated C(100)-2×1 surface using density functional theory method. The calculated results show that the ionization potential (IP) of the hydrogenated C(100)-2×1 surfaces after adsorption has amphoteric characteristics. From the weak basic NH3 molecule with small IP and negative electron affinity (EA), through the neutral H2O molecule, to the weak acid HF molecule and the OH group with large EA and IP, the IP values of the adsorbed diamond surfaces vary from decrease, through invariability, to slight increase for HF and obvious increase for OH. In all adsorption species, only the OH group makes the hydrogenated C(100)-2×1 surface change to the metal from the semiconductor with a wide-band gap, while the others only introduce impurity states into the electronic structures of the hydrogenated C(100)-2×1 surfaces.     

In situ synthesis of trisubstituted methanol ligands and their potential as one-pot generators of cubane-like metal complexes

Two different one pot routes to a variety of metal cubane compounds are reported; one route is based on an in situ benzilic acid type rearrangement and the other involves in situ nucleophilic attack at a ketone. Diketosuccinic acid in basic solution in the presence of certain divalent metal ions undergoes a benzilic acid type rearrangement to generate the carbon oxyanion, C(CO(2) (-))(3)O(-), which serves as a cubane-forming bridging ligand in a series of octanuclear complexes of composition [M(8){C(CO(2))(3)O}(4)](H(2)O)(12) (M=Mg, Mn, Fe, Co, Ni, Zn). At the heart of each of these highly symmetrical aggregates is an M(4)O(4) cubane core, each oxygen component of which is provided by the alkoxo centre of a C(CO(2) (-))(3)O(-) ligand. Reaction of 2,2'-pyridil, (2-C(5)H(4)N)COCO(2-C(5)H(4)N), and calcium nitrate in basic alcoholic solution, which proceeds by a similar benzilic acid type rearrangement, gives the cubane compounds, [Ca(4)L(4)(NO(3))(4)] in which L=(2-C(5)H(4)N)(2)C(COOR)O(-) (R=Me or Et). Nucleophilic attack by bisulfite ion at the carbonyl carbon atom of 2,2'-dipyridyl ketone in the presence of certain divalent metals generates the electrically neutral complexes, [{(C(5)H(4)N)(2)SO(3)C(OH)}(2)M] (M=Mn, Fe, Co, Ni, Zn and Cd). Cubane-like complexes [M(4){(C(5)H(4)N)(2)SO(3)C(O)}(4)] (M=Zn, Mn) can be obtained directly from 2,2'-dipyridyl ketone in one-pot reaction systems (sealed tube, 120 degrees C) if a base as weak as acetate ion is present to deprotonate the OH group of the initial [(C(5)H(4)N)(2)SO(3)C(OH)](-) bisulfite addition compound; the [(C(5)H(4)N)(2)SO(3)C(O)](2-) ligand in this case plays the same cubane-forming role as the ligands C(COO(-))(3)O(-) and (2-C(5)H(4)N)(2)C(COOR)O(-) above. When excess sodium sulfite is used in similar one-pot reaction mixtures, the monoanionic complexes, [M(3)Na{(C(5)H(4)N)(2)SO(3)C(O)}(4)](-) (M=Zn, Mn, Co) with an M(3)NaO(4) cubane core, are formed directly from 2,2'-dipyridyl ketone.     

Charge-driven fragmentation processes in diacyl glycerophosphatidic acids upon low-energy collisional activation. A mechanistic proposal

A mechanistic study of diacyl glycerophosphatidic acid (GPA) under low energy collisionally activated decomposition (CAD) with electrospray ionization tandem mass spectrometry is reported. The fragmentation pathways leading to the formation of carboxylate anions [RxCO2-], (x = 1, 2) and the formation of the ions representing neutral loss of fatty acid ([M-H-RxCO2H] ) and neutral loss of ketene ([M-H-R'xCH-C=O] ) (Rx=R'xCH2) are charge-driven processes that are governed by the gas-phase basicity and the steric configuration of the molecules. The preferential formation of the ions of [M-H-R2CO2H]- > [M-H-R1CO2H]- and [M-H-R'2CH=C=O]- > [M-H-R'1CH=C=O]- are attributed to the fact that loss of fatty acid and loss of ketene are sterically more favorable at sn-2. While the observation of the abundance of [M-H-RxCO2H]- > [M-H-R'xCH=C=O]- is attributed to the acidity of the gas phase ion of GPA, which undergoes a more facile neutral loss of acid than loss of ketene. The major pathway leading to the formation of RxCO2- ion under low energy CAD arises from further fragmentation of the [M-H-RxCO2H]- ions by neutral loss of 136, resulting in an abundance of R1CO2- > R2CO2-. The differential formation of the carboxylate anions permits accurate assignment of the regiospecificity of the fatty acid substituents of GPA molecules by tandem mass spectrometry.     

Schiff碱型和仲胺型双冠醚的合成和配位性能

由水杨醛与α,ω-二溴代烷或二(对-甲苯磺酸)三甘醇酯反应,制成相应的二醛化合物。再与4′-氨基苯并-15-冠-5反应生成5种Schiff碱型双冠醚,经LiAlH_4还原可生成5种仲胺型双冠醚。电导率测量结果表明可与KCl(Rb)盐生成2:1(冠醚单元:金属离子)的夹心型配合物。而与钠离子形成1:1配合物。用双冠醚制成PVC膜钾离子选择电极,并测量了电极的线性范围和选择系数。     

Water-exchange study revealed unexpected substitution behavior of [(CO)2(NO)Re(H2O)3]2+ in aqueous media

The pH-dependent water-exchange rates of [(CO)2(NO)Re(H2O(cis))2(H2O(trans))]2+ (1) in aqueous media were investigated by means of 17O NMR spectroscopy at 298 K. Because of the low pK(a) value found for 1 (pK(a) = 1.4 +/- 0.3), the water-exchange rate constant k(obs)(H2O(trans/cis)) was analyzed with a two-pathway model in which k(Re)(H2O(trans/cis)) and k(ReOH)(H2O)(trans/cis)) denote the water-exchange rate constants in trans or cis position to the nitrosyl ligand on 1 and on the monohydroxo species [(CO)2(NO)Re(H2O)2(OH)]+ (2), respectively. Whereas the rate constants k(ReOH)(H2O)(trans)) and k(ReOH)(H2O)(cis)) were determined as (4.2 +/- 2) x 10(-3) s(-1) and (5.8 +/- 2) x 10(-4) s(-1), respectively, k(Re)(H2O)(trans)) and k(Re)(H2O)(cis)) were too small to be determined in the presence of the much more reactive species 2. Apart from the water exchange, an unexpectedly fast C identical with 16O --> C identical withO exchange was also observed via NMR and IR spectroscopy. It was found to proceed through 1 and 2, with rate constants k(Re)(CO) and k(ReOH)(CO) of (19 +/- 4) x 10(-3) s(-1) and (4 +/- 3) x 10(-3) s(-1), respectively. On the other hand, N identical with 16O --> N identical with *O exchange was not observed.     

用氟钽酸根指示电位滴定钽的新方法

A new potentiometric titration method for the determination of tantalum in sulfuric acid and hydrofluoric acid media is described. EMF's were monitored with a double-junction reference electrode and a flurortantalate ion selective indicator electrode made in this laboratory previously. Five titrants have been evaluated for the precipitation titration. CPC, BDTAC and TPA yield the highest precision and largest potentiometric breaks, then rank CETAB and Hyamine 1622 in turn. CPC is considered to be the most satisfactory owing to the most sharp end-point break yielded when 10^-^4M of Ta is titrated with it. The concentration of H2SO4 suitable for the titration is 0.18 to 1.8M and that of HF is 0.23 to 1.7M. The method is suitable for Ta content in the range of 0.5 to 150 mg with a coefficient of variation of 0.15% (9 results) for 20 mg of Ta. HCl, H3PO4, tartaric acid and (NH4)2C2O4 as wellas a large amount of Fe^3^+, Ni^2^+, Cr^3^+, WO2^-^4, Zr^4^+, La^3^+, Al^3^+, MoO2^-^4 and Nb^5^+ do not interfere, while ClO^-^4, H2O2 and BF^-^4 must be avoided. The method has been found to be very useful for the determination of Ta in steels and crystalline lithium tantalate. The results obtained are in good agreement with those of comparable methods. This method is very simple and provides a fast determination process.     

Highly symmetric networks derived from cubane-related octametallic complexes of a new oxyanion of carbon, C4O7(4-), each molecule attached to eight neighbors by 24 equivalent hydrogen bonds

Aqueous reaction mixtures containing dihydroxyfumaric acid, M2+ (M = Zn, Co, Fe, and Mg) and acetate ion at room temperature give crystals, suitable for single-crystal X-ray diffraction studies, of composition [(MII)8(C4O7)4(H2O)12].24H2O, in which the C4O74- component is the alkoxide-tricarboxylate tetra-anionic species -OC(CO2-)3, a new oxyanion of carbon. All four compounds crystallize in the body-centered space group I3m with cell dimensions a approximately 15.0 A. Discrete electrically neutral [(MII)8(C4O7)4(H2O)12] molecules are present, with a cubane-like core consisting of four trigonal prismatic metal centers and four mu3-alkoxo bridges from separate -OC(CO2-)3 ligands. The octametallic molecule is highly symmetrical, with four fac tri-aqua octahedral metal centers tetrahedrally appended to the central cubane-based [(MII)8(C4O7)4 ]8- unit. The molecules assemble in the crystal in a body-centered cubic fashion, each being attached to its eight neighbors by 24 equivalent hydrogen bonds-an extreme example of self-complementarity.