Mercury in organic chemistry. 20. Alkylation of organomercurials via organocopper reagents

Aryl-, alkenyl-, and alkylmercurials readily cross-couple with primary and secondary alkyl- and alkenylcuprate reagents to provide the first truly general method for the alkylation of a wide variety of organomercurials.     

Exponential Smoothing with an Adaptive Response Rate

A modification is proposed to forecasting systems employing exponential smoothing whereby the response rate is varied and made to depend on the value of a tracking signal. In a simple system, this is equivalent to varying α the smoothing constant according to the extent to which biased forecasts are being obtained. Such a system is shown to react much faster to, for example, step changes whilst still retaining the facility to filter out random noise.     

An integrable SIS model

We provide a demonstration of the integrability of a classical model of an infectious disease which neither kills nor induces autoimmunity by means of the Painlevé analysis and use the Lie theory of transformation groups to present an explicit solution.     

Solid angles 5. Chiral molecules and the case of face selectivity

In this paper we present the analytical algorithm to calculate the solid angle of a collection of spheres in a hemisphere and quadrant. The methodology is a reliable and useful measure of partial steric congestion and can readily be applied to chiral and pro-chiral molecules. This algorithm lays the foundation for the application of a steric measure to the prediction of diastereomeric and enantiomeric excess.     

Kinetic and electrochemical study of nitrile adducts of tetrachloro-bis (1,2-bis(diphenylphosphine)methane)dirhenium(II)

Summary The addition of two nitrile ligands to the complex Re₂Cl₄-(dppm)₂ (dppm= 1,2-bis(diphenylphosphine)methane)in CH₂Cl₂ solution has been investigated electrochemically. Upon addition of one equivalent of nitrile NCR (R = aromatic or aliphatic group) to the CH₂Cl₂/0.1m tetra-N-butylammonium hexafluorophosphate (TBAH) solution, Re₂Cl₄(dppm)₂(NCR) is formed immediately, without dissociation of chloride; electrochemical investigation indicates this nitrile addition is reversible upon oxidation of the dirhenium complex. On addition of two or more equivalents of nitrile, a slow ligand substitution takes place with addition of a second nitrile and concomitant loss of a chloride ion to form [Re₂Cl₃-(dppm)₂(NCR)₂]⁺. The rate of addition of nitrile to Re₂Cl₄(dppm)₂(NCR) appears to depend on the electrondonating or electron-withdrawing abilities of the ligand. The change from monoadduct to diadduct was followed with differential pulse voltammetry for various concentrations of added nitrile. The addition was found to be first order in nitrile.     

Intravascular delivery of hyperpolarized129Xenon forin vivo MRI

The nuclear polarization of¹²⁹Xe and³He can be enhanced by several orders of magnitude by using optical pumping techniques, thus allowing NMR detection of xenon and helium in very low concentrations. The benefits of optically enhanced magnetic resonance (MR) are already exploited in MR imaging of the lungs using optically polarized³He. The high solubility of xenon in blood and lipids suggests a variety ofin vivo MR applications, for instance perfusion measurements or functional MR studies. This article reviews some current work directed towards delivery of optically polarized xenon forin vivo MR applications.     

The application of Artificial Intelligence to the conformational analysis of strained molecules

An algorithm for predicting the conformations of strained molecules using Artificial Intelligence techniques is described and illustrated with some typical examples.     

The origins of noncovalent catalysis of intermolecular Diels-Alder reactions by cyclodextrins,self-assembling capsules,antibodies, and RNAses

The catalysis of Diels-Alder reactions by noncovalent binding by synthetic, protein, and nucleic acid hosts has been surveyed and compared. These catalysts consist of binding cavities that form complexes containing both the diene and the dienophile; the cycloaddition reaction occurs in the cavity. The binding requires no formation of covalent bonds and is driven principally by the hydrophobic (or solvophobic) effect. A molecular mechanics and dynamics study of the cyclodextrin catalysis of a Diels-Alder reaction is used to exemplify and probe this form of catalysis. Detailed kinetic data is available for catalysis by antibodies, RNA, cyclodextrins, and Rebek's tennis ball capsules. Some of these catalysts stabilize the reactants more than the transition state and consequently will only have catalytic effect under conditions of low substrate-to-catalyst ratios. None of the hosts achieve significant specific binding of transition states that is the hallmark of enzyme catalysis.     

Implementation of a system for reagent selection and library enumeration, profiling, and design

We describe an integrated suite of computational tools which are used to assist in the selection of compounds for biological assays and the design of combinatorial libraries. These functions are delivered in a platform-independent manner via a corporate intranet and are used by computational experts and nonexperts alike. While the system was primarily designed to be used prior to synthesis, it can also be used to provide structural information for library registration and for decoding beads in tagged libraries. We describe a simple statistical method for monomer selection and compare it to computationally more demanding approaches.     

Automated conformational analysis and structure generation: algorithms for molecular perception

Many methodologies for performing automated conformational analysis require some means of "perceiving" a molecule to determine features of interest. Algorithms for finding rings, bond orders, and stereocenters and detecting the presence of substructural fragments have been developed. These algorithms are described, emphasizing their importance in conformational analysis.