PM3-SM3: A general parameterization for including aqueous solvation effects in the PM3 molecular orbital model

Our recently proposed scheme for including aqueous solvation free energies in parameterized NDDO SCF models is extended to the Parameterized Model 3 semiempirical Hamiltonian. The solvation model takes accurate account of the hydrophobic effect for hydrocarbons, as well as electric polarization of the solvent, the free energy of cavitation, and dispersion interactions. Eight heteroatoms are included (along with H and C), and the new model is parameterized accurately for the water molecule itself, which allows meaningful treatments of specifically hydrogen bonded water molecules. The unphysical partial charges on nitrogen atoms predicted by the Parameterized Model 3 Hamiltonian limit the accuracy of the predicted solvation energies for some compounds containing nitrogen, but the model may be very useful for other systems, especially those for which PM3 is preferred over AM1 for the solute properties of the particular system under study. © 1992 by John Wiley & Sons, Inc.     

Simultaneous determination of trace concentrations of saturated and α,β-unsaturated carbonyl compounds in organic systems

A method for the simultaneous determination of trace concentrations of saturated and α,β-unsaturated carbonyl compounds in complex systems is presented. Carbonyl as the alkaline 2,4-dinitrophenylhydrazone is determined spectrophotometrically at 2 selected wavelengths of 480 and 426 nm. The apparent total carbonyl concentration is obtained from prepared calibration curves at the selected wavelengths based on known concentrations of n-heptaldehyde. From the observed relative response of known concentrations of n-heptaldehyde and 2-ethyl-2-hexenal, the true concentration for saturated and α,β-unsaturated carbonyl is obtained by a simple calculation. The method has been used extensively for alcohol systems ranging up to tetracontanol but is equally useful for hydrocarbons, aromatic oxygenates and hydrocarbons, petroleum distillates and kerosenes, organic acids and esters, and some ethers.     

Interaction of atrazine with Laurentian fulvic acid: binding and hydrolysis

Ultrafiltration fractionation and liquid chromatography (LC) have been applied to the study of the binding and hydrolysis of the polar herbicide atrazine on a stoichiometrically well characterized fulvic acid. Binding requires extensive carboxylate site protonation but the binding sites represent a very small fraction of total carboxylate. The data show that binding of atrazine is not competitive with binding of the hydrolytic product hydroxyatrazine. However, smaller molecular weight fractions of the fulvic acid mixture compete with atrazine for sites on the larger molecular weight fraction. Binding equilibrium is not rapid. A model of binding involving hydrogen bonding and/or charge-transfer complexing to specific sites created dynamically by the conformational equilibria of the higher molecular weight polymeric fulvic acid fractions is proposed as the best accommodation of the variety of observed facts.     

Novel one-dimensional structures and solution behaviour of copper(II) bromide and chloride complexes of a new pentapyridyldiamine ligand

Copper(II) bromide and chloride complexes of the new heptadentate ligand 2,6-bis(bis(2-pyridylmethyl)amino)methylpyridine (L) have been prepared. For the bromide complexes, chains of novel, approximately C2-symmetric, chiral [Cu2(L)Br2]2+ 'wedge-shaped' tectons are found. The links between the dicopper tectons and the overall chirality and packing of the chains are dictated by the bromide ion content, not the counter anion. In contrast, the chloride complexes exhibit linked asymmetric [Cu2(L)Cl3]+ tectons with distinct N3CuCl2 and N4CuCl2 centres in the solid. The overall structures of the dicopper bromide and chloride units persist in solution irrespective of the halide. The redox chemistry of the various species is also described.     

Improved syntheses of some monochloro- and monobromo-8-quinolinols

Summary Procedures were developed for the preparation of the 2-, 3-, 4-, and 6-monosubstituted chloro and bromo 8-quinolinols which afforded greater yields and/or reduced the number of steps in the preparation. 100 MHz¹H-NMR spectra for the 12 possible monochloro and monobromo analogues are given.

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Verbesserte Synthese von Monochlor- und Monobrom-8-chinolinolen

Zusammenfassung Es wurden Verfahren entwickelt, um 2-, 3-, 4- und 6-Chlor bzw. -Brom-8-chinolinole in besseren Ausbeuten und/oder bei reduzierter Anzahl von Synthesestufen herzustellen. Die¹H-NMR-Spektren der 12 möglichen Monochlor- und Monobromverbindungen werden angegeben.

     

On the calculation of induced electric and magnetic moments of atoms and molecules

We present a many-electron method for calculating first and second order perturbed wavefunctions due to external electric and magnetic fields, which identifies the important correlation effects for the response function a priori and calculates them variationally. It is accurate, economical and applicable to ground and excited states with the same ease. Thus, it presents a useful alternative to the well-known coupled Hartree-Fock methods. As an application of this method, we calculate the static electric dipole polarizability of the Be ground state. We find α_d = 5.49 ų in agreement with recent extensive calculations.     

Photolysis of (η5-C5H5)2V(CH3)2: II . Photo-induced formation of ethane

Photolysis of (η⁵-C₅H₅)₂V(CH₃)₂ results in the formation of methane and ethane. The percentage of ethane detected in the evolved gas can vary from a trace to 70%. The percentage of ethane formed is dependent on the solvent, the concentration of (η⁵-C₅H₅)₂V(CH₃)₂, time and temperature. The results of oxidation and reduction reactions involving (η⁵-C₅H₅)₂V(CH₃)₂ are also presented.     

Bioluminescent detection of insect pheromones using an enzyme-based flow injection analysis system

The combination of flow injection analysis with chemiluminescent detection is shown to provide extremely selective and sensitive detection of insect pheromones which possess an aldehyde moiety. The flow injection analysis system provides reproducible control of both the reaction chemistry and the sample introduction process. Microliter volume samples can be precisely handled and analyzed with this experimental configuration. The detection system is based on the luciferase-catalyzed oxidation of reduced flavin mononucleotide which occurs in the presence of aldehydes with carbon backbones of between 14 and 16 carbons. A limit of detection of 3 fmol of tetradecyl aldehyde is demonstrated and the system is shown to be insensitive to the presence of various organic solvents up to concentrations of approximately 10%. The key experimental variables which control sensitive detection of pheromone at the femtomole level with be investigated and discussed.     

Prediction of Complexation Properties of Crown Ethers Using Computational Neural Networks

A computational neural network method was used for the prediction of stability constants of simple crown ether complexes. The essence of the method lies in the ability of a computer neural network to recognize the structure-property relationships in these host-guest systems. Testing of the computational method has demonstrated that stability constants of alkali metal cation (Na+, K+, Cs+)-crown ether complexes in methanol at 25 °C can be predicted with an average error of ±0.3 log K units based on the chemical structure of the crown ethers alone. The computer model was then used for the preliminary analysis of trends in the stabilities of the above complexes.