Comparison of AB2 and AB4 monomers in ferrocene-cored benzyl ether dendrimers

Ferrocene-cored unsymmetric and symmetric arylalkyl ether dendrimers based on an AB₂ monomer (3,5-dihydroxybenzyl alcohol) were prepared. Their electrochemical properties were compared with the unsymmetric and symmetric ferrocene-cored dendrimers based on a relatively rigid and three-dimensionally disposed AB₄ monomer. The thermodynamics and kinetics of heterogeneous electron transfer in these dendrimers show that G_2n of AB₂ dendrimers behave similar to G_n of AB₄ dendrimers. For example, the redox reaction shows significant irreversibility especially at higher scan rates in the case of G₄ didendron based on AB₂ monomer and G₂ didendron based on AB₄ monomer. Despite the fact that AB₄ building blocks are more rigid, the effective encapsulation in both these dendrimers are similar. This result is attributed to the three dimensional disposition of the branching points in the AB₄ monomer.     

Multicollinearity and some applications in biological chemistry

The relationship between various parameters characterizing a particular system are established using various techniques. In some specific cases, ordinary multiple regression is resorted to for relating one variable to various other variables. However, in such problems there is a high probability of an interrelationship among different variables giving rise to multicollinearity, thereby making it infeasible to place much reliability on ordinary regression techniques. This problem can be circumvented using ridge regression techniques. In this preent investigation an attempt has been made to study the multicollinear problems in biology.     

Vibrational spectra and potential energy distributions for 1‐benzyl‐1H‐imidazole by normal coordinate analysis

The Fourier‐transform (FT) Raman and infrared (IR) spectra of the crystallized novel pharmaceutical molecule 1‐benzyl‐1H‐imidazole (BI) were recorded and analyzed. The geometry, intermolecular hydrogen bond, and harmonic vibrational wavenumbers of BI were investigated with the help of B3PW91 density functional theory (DFT) methods. The detailed interpretation of the vibrational spectra was carried out with the aid of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). The aromaticities of the imidazole and phenyl rings were studied using the standard harmonic oscillator model of aromaticity (HOMA) index. Natural bond orbital (NBO) analysis on BI was carried out to demonstrate the various intramolecular interactions that are responsible for the stabilization of this molecule leading to its medicinal activity. The potential energy profile corresponding to the torsion around the bridge bonds connecting the two rings was drawn to explain the steric and/or electronic effects using potential energy surface (PES) scan studies. The pronounced double‐bond localization in the imidazole ring upon intermolecular H‐bonding appears to be the cause for its enhanced aromaticity. Copyright © 2008 John Wiley & Sons, Ltd.     

Highly diastereoselective multicomponent synthesis of unsymmetrical imidazolines

We report here a highly diastereoselective multicomponent synthesis of imidazolines. These low molecular weight scaffolds contain a four-point diversity applicable to alkyl, aryl, acyl, and hetereocyclic substitutions. [structure: see text]     

Enhanced hydrogen generation by particles during sonochemical decomposition of water

A novel effect of any oxide particle/intermetallics enhancing hydrogen generation from water as compared to water alone when subjected to ultrasonic irradiation is reported here. Addition of methanol to water or decrease in particle size also improved the hydrogen yield. Hydrogen generation from water was further enhanced by the presence of both methanol and particles in water.     

Ultrasonic and optical studies on charge transfer complexes of p-chloranil with certain aromatic hydrocarbons in DMSO at 303.15 K

Ultrasonic investigation has been carried out on six ternary systems to establish the complex formation between p-chloranil (acceptor) and six aromatic hydrocarbons (donors), namely, benzene, toluene, o-xylene, m-xylene, p-xylene and mesitylene in DMSO medium at 303.15 K and at atmospheric pressure. Studies were carried out in the concentration range of 0.002 to 0.02 M of acceptor and donor with equimolar concentration of the two components in solution. The trend in the acoustical parameters and magnitude of excess thermo acoustical parameters has been used to identify the existence of strong intermolecular interaction through charge transfer complex formation. The formation of 1:1 complex was also confirmed by UV-Visible spectroscopic method at 303.15 K in these systems. It may be pointed out that the formation constants of the charge transfer complexes determined by Benesi-Hildebrand (spectroscopic) and Kannappan (ultrasonic) methods show similar trend and well establish the influence of structural aspect of the donor aromatic compounds on the stability of charge transfer complexes.     

Quinine and chloroquine differentially perturb heme monomer-dimer equilibrium

Nuclear magnetic resonance (NMR) measurements of magnetic susceptibility have been utilized to study the equilibrium between two forms (high-spin monomer vs the antiferromagnetically coupled mu-oxo dimer) of ferriprotoporphyrin(IX) as a function of pH. The pH dependence of this equilibrium is significantly altered by the addition of either chloroquine or quinine. Chloroquine promotes the mu-oxo dimer whereas quinine promotes the monomer.     

Vibrational spectroscopic studies and ab initio calculations of Goniothalamin, a natural product

5,6-Dihydro-6-styryl-2-pyrone (Goniothalamin), is isolated from the leaves of Goniothalamus wightii and identified by spectral analysis and X-ray diffraction studies. FT-IR spectroscopy has also been used to characterize the vibrational bands. The vibrational wavenumbers and corresponding vibrational assignments are examined theoretically using the Gaussian03 set of quantum chemistry codes. Predicted IR and Raman intensities are reported.