Theoretical investigation of the apparently irregular behavior of pt-pt nuclear spin-spin coupling constants

One-bond Pt-Pt nuclear spin-spin coupling constants J(Pt-Pt) for closely related dinuclear Pt complexes can differ by an order of magnitude without any obvious correlation with Pt-Pt distances. As representative examples, the spin-spin couplings of the dinuclear Pt(I) complexes [Pt(2)(CO)(6)](2+) (1) and [Pt(2)(CO)(2)Cl(4)](2-) (2) have been computationally studied with a recently developed relativistic density functional method. The experimental values are (1)J((195)Pt-(195)Pt) = 5250 Hz for 2 but 551 Hz for 1. Many other examples are known in the literature. The experimental trends are well reproduced by the computations and can be explained based on the nature of the ligands that are coordinated to the Pt-Pt fragment. The difference for J(Pt-Pt) of an order of magnitude is caused by a sensitive interplay between the influence of different ligands on the Pt-Pt bond, and relativistic effects on metal-metal and metal-ligand bonds as well as on "atomic orbital contributions" to the nuclear spin-spin coupling constants. The results can be intuitively rationalized with the help of a simple qualitative molecular orbital diagram.     

Unexpected but Easy Synthesis of a Dihydrophosphadiazaazulene

Abstract

The title compound is the main product of the 2:1 reaction of DMAD with diazaphosphinines. The supposed mechanisms with intermediates and related products will be presented.     

Estimation of second order rate constants using chemometric methods with kinetic constraints

Several methods are described for determining rate constants for second order reactions of the form U + V --> W using chemometrics and hard modelling to analyse UV absorption spectroscopic data, where all species absorb with comparable concentrations and extinctions. An interesting feature of this type of reaction is that the number of steps in the reaction is less than the number of absorbing species, resulting in a rank-deficient response matrix. This can cause problems when using some of the methods described in the literature. The approaches discussed in the paper depend, in part, on what knowledge is available about the system, including the spectra of the reactants and product, the initial concentrations and the exact kinetics. Sometimes some of this information may not be available or may be hard to estimate. Five groups of methods are discussed, namely use of multiple linear regression to obtain concentration profiles and fit kinetics information, rank augmentation using multiple batch runs, difference spectra based approaches, mixed spectral approaches which treat the reaction as two independent pseudospecies, and principal components regression. Two datasets are simulated, one where the spectra are quite different and the other where the spectrum of one reactant and the product share a high degree of overlap. Three sources of error are considered, namely sampling error, instrumental noise and errors in initial concentrations. The relative merits of each method are discussed.     

Studies on the Anode/Electrolyte Interfacein Lithium Ion Batteries

Summary.  Rechargeable lithium ion cells operate at voltages of 3.5–4.5 V, which is far beyond the thermodynamic stability window of the battery electrolyte. Strong electrolyte reduction and anode corrosion has to be anticipated, leading to irreversible loss of electroactive material and electrolyte and thus strongly deteriorating cell performance. To minimize these reactions, anode and electrolyte components have to be combined that induce the electrolyte reduction products to form an effectively protecting film at the anode/electrolyte interface, which hinders further electrolyte decomposition reactions, but acts as membrane for the lithium cations, i.e. behaving as a solid electrolyte interphase (SEI). This paper focuses on important aspects of the SEI. By using key examples, the effects of film forming electrolyte additives and the change of the active anode material from carbons to lithium storage alloys are highlighted. Received May 30, 2000. Accepted June 14, 2000     

Assessment of the electronic structure of 2,2'-pyridylpyrrolides as ligands

The ligand class 2,2'-pyridylpyrrolide is surveyed, both for its structural features and its electronic structure, when attached to monovalent K, Cu, Ag, Au, and Rh. The influence of pyrrolide ring substituents is studied, as well as the question of push/pull interaction between the pyridyl and pyrrolide halves. The π donor ability of the pyrrolide is found to be less than that of an analogous phenyl. However, in contrast to the phenyl analog, the HOMO is pyrrolide π in character for pyridylpyrrolide complexes of copper and rhodium, while it is conventionally metal localized for planar, d(8) rhodium pyridylphenyl. Monovalent three-coordinate copper complexes show great deviations from Y-shaped toward T-shaped structures, including cases where the pyridyl ligand bonds only weakly.     

High throughput drug screening by direct RNA profiling on DNA sensors

The feasibility of DNA microarray sensor technology as a routine technique of molecular pharmacology to perform high throughput drug screening and the advantages of directly labeled RNA for a high throughput experiment are presented in this paper. A novel, single-step direct chemical labeling method for DNA microarray target samples has been developed to reduce the sample amount, cost, time and error of the experiment by eliminating the need for enzyme mediated labeling. Reproducibility of the data for high throughput drug screening is demonstrated by monitoring differential gene expression of a set of 45 gene targets involved in the genotoxic stress response pathways.     

Identification of acylated xanthone glycosides by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry in positive and negative modes from the lichen Umbilicaria proboscidea

The xanthoside composition of the crude extract of Umbilicaria proboscidea (L.) Schrader was characterized using LC-UV diode array detection and LC-atmospheric pressure chemical ionization (APCI) MS methods. The presence of acylated xanthone-O-glucosides was determined by both positive and negative ion LC-APCI-MS methods. Based on UV and MS spectral data and NMR spectroscopy, a total of 14 compounds (6-O-acylated umbilicaxanthosides A and B) were identified in U. proboscidea for the first time. In order to further develop the applicability of LC-MS techniques in phytochemical characterization, the effect of different ionization energy on fragmentation was studied using APCI. The optimal ionization conditions were achieved in positive ion APCI by using ammonium acetate buffer and in negative ion APCI by using formic acid (pH 4).     

One-pot two-step microwave-assisted reaction in constructing 4,5-disubstituted pyrazolopyrimidines

[reaction: see text] A microwave-assisted reaction was developed to facilitate the construction of 4,5-disubstituted pyrazolopyrimidines. This one-pot two-step process involves a sequential S(N)Ar displacement of the C4 chloro substituent with various anilines and amines, followed by a Suzuki coupling reaction with different boronic acids. Using microwave irradiation leads to high product conversion, low side product formation, and shorter reactions.