The Stabilities and Thermodynamic Properties of Manganese(II) and Nickel(II) Chelates of Trans-1,2-Diaminocyclohexane-N,N, N', N'-Tetraacetic Acid

The interaction between trans-1,2-diaminocyclohexane-N, N, N', N'-tetraacetic acid (H₁DCTA or H₄Z) and Mn(II) and Ni(II) ions has been investigated. The formation constants of the hydrogen chelates (MHZ^?), and of the normal chelates (MZ^2?), have been measured at 20, 30 and 40°C, and an ionic strength of 0.10 (KNO₃). The former was done by a titration technique and the latter by a mercury indicator electrode method. Enthalpy and entropy changes characterizing the formation of the normal chelates have been calculated at 25°C.     

Reduced Overlap Population Analysis for Triosmium Clusters

The use of reduced overlap population (ROP) analysis from EHMO calculations as a means to gauge the presence of metal–metal bonds in triosmium clusters is examined. A number of triosmium clusters containing bridging ligands have been used as test cases, including the bis-ethoxy bridged cluster Os₃(μ-OEt)₂(CO)₁₀, 1b, and some of its group 15 derivatives Os₃(μ-OEt)₂(CO)₉(EPh₃), 2. These latter clusters are newly synthesized and have been characterized completely, including by single-crystal X-ray crystallographic studies. In honour of Professor Dieter Fenske on his 65th birthday.     

Hydrogen–hydrogen bonding in biphenyl revisited

The evidence for the stabilizing nature of the H–H bonding in planar biphenyl is succinctly reviewed. The stabilizing nature of the H–H bonding is revealed through a comparison of the atomic energy of every atom in planar biphenyl with the same atom in the twisted equilibrium structure. It is shown that the barrier to rotation via the planar transition state is the net resultant of a stabilisation of the four ortho-hydrogen atoms (by 8 kcal/mol each), a stabilisation of the two para-carbon atoms (by 3 kcal/mol each) and by the dominant destabilisation of the two carbon atoms joining the two rings—the two junction carbon atoms—(by 22 kcal/mol each). The energetic stabilisation of the four ortho-hydrogen atoms is further shown to be in large proportion due to the formation of the hydrogen–hydrogen interatomic surface. Furthermore, neither the “bond order” between the two junction carbon atoms nor the total electron delocalisation between the two rings exhibit a significant change in going from the planar to the twisted equilibrium geometry. These findings are in contrast with the classical view of a balance between “steric non-bonded repulsion” and better electron delocalisation as a function of the twist dihedral angle. Similar conclusions have been recently reached by Pacios and Gómez through a study of the electrostatic potential at the position of the hydrogen nuclei. We dedicate this article to Professor TM Krygowski on the occasion of his 70th birthday wishing him a long and productive life.     

High-performance liquid chromatographic determination of 18 alpha-glycyrrhetinic acid and 18 beta-glycyrrhetinic acid in rat plasma: application to pharmacokinetic study.

A high-performance liquid chromatographic method for the separation and determination of 18 alpha-glycyrrhetinic acid and 18 beta-glycyrrhetinic acid has been developed. Indomethacin was used as an internal standard. The drugs were separated on a reversed-phase column and detected by UV detection at a wavelength of 254 nm. Methanol-water-perchloric acid-ammonia (80:20:0.4:0.4, v/v) was used as the mobile phase at pH of 7.0-7.5. The detection limit of both compounds was 0.1 microgram/ml in rat plasma. The method was applied to pharmacokinetic studies of glycyrrhetinic acids in rats. The results suggest that the pharmacokinetics appeared to be non-linear in nature.     

Electrochemical investigation of hymecromone at a multi-wall carbon nano-tube/cetyl pyridine bromine composite film electrode

A multi-wall carbon nanotube (MWNT)/cetyl pyridine bromine (CPB) composite film modified glassy carbon electrode (GCE) was developed for the electrochemical determination of hymecromone in phosphonate buffer. Electrochemical behaviour of hymecromone at the composite film electrode was investigated with voltammetry. Compared with an irreversible oxidation of hymecromone at the bare GCE, the oxidation peak current was enhanced greatly at the film electrode. Some parameters such as pH, scan rate, accumulation potential and accumulation time were optimized. Under optimal conditions, an oxidation peak at 0.82 V was employed to determine hymecromone electrochemically. A linearity between the oxidation peak current and the hymecromone concentration was obtained in the range of 3.0 × 10⁻⁷ − 2.0 × 10⁻⁵ mol 1⁻¹ with a detection limit of 8.0 × 10⁻⁸ mol 1⁻¹. The proposed procedure was successfully applied to assay hymecromone in pharmaceutical formulation with satisfactory results. The text was submitted by the authors in English.     

Synthesis and mechanism research of an ethylene glycol-based sol-gel method for preparing PZT nanopowders

Lead zirconate titanate nanopowders Pb(Zr_0.52Ti_0.48)O₃ (PZT) were prepared by modified sol-gel process in ethylene glycol system with zirconium nitrate as the zirconium source. The research showed that it was critical to add lead acetate after the reaction of zirconium nitrate and tetrabutyl titanate in ethylene glycol system for preparing PZT of exact titanium content. The reaction mechanisms of the sol synthesis, preparation of xerogel and agglutinating process were characterized through using FT-IR, NMR, TG-FTIR, and GC-MS. The experiment proved that ethylene glycol system did not rely on hydrolysis and condensation reactions in the process of the sol formation, but on the formation of chain or network large molecules from complexation of ethylene glycol and all Ti and minor Pd, Zr. In the preparation of xerogel, the complexation reaction was so completed that it formed large molecules network composed of metal and dioxyethyl. Bulk weight loss happened before 350°C in the process of sintering xerogel to prepare PZT nanopowders. Volatile matters and vapor phase decomposition resultants were primarily oxy-compounds including ethylene glycol, aldehyde-ketone compounds, carbon dioxide and nitrate radical conversion matters. After 350°C, primary vapor phase decomposition resultants were carbon dioxide and minor carbonyl compound.     

Two novel four-coordinated zinc(II) complexes [Zn(dmatrz)<Subscript>2</Subscript>Cl<Subscript>2</Subscript>] and [Zn(dmatrz)<Subscript>2</Subscript>(SCN)<Subscript>2</Subscript>] exhibiting strong blue fluorescent properties

Two novel complexes, [Zn(dmatrz)₂]Cl₂ (1) and [Zn(dmatrz)₂(SCN)₂] (2), have been prepared and characterized by X-ray crystallography, absorption and luminescence spectrometries (dmatrz=3,5-dimethy-4-amino-1,2,4-triazole). The coordination environment of the zinc(II) ions in (1) and (2) has a distorted tetrahedral geometry completed via two independent nitrogen atoms of two triazole ligands and two anions, respectively. Both (1) and (2) show strong blue luminescence properties. Furthermore, (1) displays stronger blue photoluminescence than (2) as the result of different anions (Cl^- and SCN^-) coordinated to the zinc(II) ions.     

Hydrogen peroxide oxidation of di(hydroxo)platinum(II) species in carboxylic acids

A facile procedure for synthesizing the mono(hydroxo)tris(carboxylato)platinum(IV) species has been achieved. The reaction of [Pt^II(OH)₂(dmpda)] (dmpda=2,2-dimethyl-1,3-propanediamine) with a 30% aqueous solution of H₂O₂ in the presence of a carboxylic acid produces a stable [Pt^IV(OOCR)₃(OH)(dmpda)] (R=Me, Et) complex in high yield. The crystal structures of [Pt^IV(OOCMe)₃(OH)(dmpda)] . H₂O (triclinic P1 bar, a=8.761(2) Å, b=9.245(3) Å, c=10.659(2) Å, =106.25(2)°, =93.90(2)°, =98.92(2)°, V=813.1(3) ų, Z=2, R= 0.0474) and [Pt^IV(OOCEt)₃(OH)(dmpda)] (monoclinic P2₁/c, a=12.777(4) Å, b=10.514(2) Å, c=14.971(3) Å, =107.40(2)°, V=1919.2(8) ų, Z=4, R=0.0611) show that the hydroxyl group has been selectively positioned at an axial site. The intramolecular hydrogen bond between the OH and C=O moiety exists (O(H)...=C, 2.83 Å for [Pt^IV(OOCMe)₃(OH)(dmpda)] · H₂O; 2.72 Å for [Pt^IV(OOCEt)₃(OH)(dmpda)]. Formation of the axial-mono(hydroxo)tris(carboxylato)platinum(IV) species may be ascribed to a combination of `reactive-equatorial effects' with `cis-addition' in the carboxylic acid.     

Study on multimers and their structures in molecular association mixture

Self-association system of(R)-1,3-butanediol in dilute carbon tetrachloride(CCl4)solution is studied as a model of molecular association mixture.Analysis methods including FSMWEFA(fixed-size moving window evolving factor analysis)combined with PCA(principal component analysis),SIMPLISMA (simple-to-use interactive self-modeling mixture analysis),and ITTFA(iterative target transformation factor analysis)are adopted to resolve infrared spectra of(R)-1,3-butanediol solution.Association number and equilibrium constant are computed.(R)-1,3-butanediol in dilute inert solution is determined as a monomer-trimer equilibrium system.Theoretical investigation of trimer structures is carried out with DFT(density functional theory),and structural factors are analyzed.     

<Emphasis Type="Italic">Brønsted</Emphasis> Acids in Ionic Liquids: Fundamentals,Organic Reactions,and Comparisons

Summary. A background for studying acids in various solvents is developed, emphasizing the importance of knowing to what extent a solvent conducts electricity and is therefore ionized, the dissociation equilibria of common molecular solvents and the acidic and basic species generated by solvent leveling. Acidity measurements in the atypical solvent water are discussed and the common method of expressing acidity in other systems – by Hammett values – is introduced. Representative examples of reactions involving Br?nsted acids in ionic liquids are presented and attention paid to the questions of speciation and acidity values. It is found that the gas phase proton affinity of a base is often a better guide to the acidity of its conjugate acid in an ionic liquid than is the dissociation constant of the said acid in water.