Simple method of computing the partition coefficient

The values of log₁₀ P (partition coefficient, in octanol/water) were calculated for about 200 organic molecules of diverse structures and functionalities. The method involves a simple procedure and appears accurate enough for semiquantitative applications. Further, this method of calculating log₁₀ P values was shown to be successful in providing a better quantitative structure activity relationship (QSAR ) than the Hansch-type approach in the study of inhibitory activity of substituted phenols on Bacillus Subtilis spore germination.     

The electronic structure,spectra, and reactivity of nitrophenols

The all-valence-electron CNDO /2 calculations were performed for the three isomeric nitrophenols. Using the newly derived σ-core charges and subsequently revising the valence-state ionization potentials and one-center two-electron repulsion integrals, Pariser–Parr–Pople (PPP ) CI calculations were performed on the title compounds following the Nishimoto–Forster scheme. A better agreement between theory and experiment has been observed in spectral assignments compared to the conventional PPP approach. Information from the CNDO /2 calculations was used to obtain useful electronic structural parameters and to get a quantitative insight into the chemical reactivity of these molecules. All the results were compared with the basic compounds, phenol and nitrobenzene. The electronic spectra of these isomers were recorded in both polar and nonpolar solvents.     

A finite expansion method for the calculation and interpretation of molecular electrostatic potentials

Because it is useful to have the molecular electrostatic potential as an element in a complex scheme to assess the toxicity of large molecules, efficient and reliable methods are needed for the calculation and characterization of these potentials. A multicenter multipole expansion of the molecular electron charge density calculated with a limited Gaussian basis set is shown here to have only a finite number of nonzero terms from which the molecular electrostatic potential can be calculated. The discrete contributions to the electrostatic potentials from the terms of this expansion provide a physically meaningful decomposition of the potential and a means for its characterization. With pyrrole as an example, the electrostatic potential calculated from this finite expansion of the electron density is compared to that obtained from exact calculations from the same wave function. Good agreement is obtained at distances greater than 1.5 A from any atom in the molecule. In contrast, rearrangement of the terms into an expansion corresponding only to Mulliken atomic charges and dipoles yields a decomposition that produces electrostatic potentials which agree less well with the exact potential. This discrepancy is attributable to the neglect of terms due to higher moments.     

Expeditious oxidation of alcohols to carbonyl compounds using iron(III) nitrate

An efficient and solvent-free protocol for the oxidation of alcohols to corresponding carbonyl compounds using iron(III) nitrate nonahydrate has been developed.     

Cresols—An investigation into their electronic structure and spectra

The three isomeric cresols were subjected to the all-valence-electron CNDO/2 andPPP-CI calculations. Results from this study were used:

1. to compare the electronic structures of these isomers vis-à-vis parent compounds—phenol and toluene,
2. to obtain a quantitative picture of their chemical reactivities and electronic absorption spectra.

Using the σ-core charges derived from CNDO/2 calculations and subsequently revising the valence-state ionisation potential and one-center-two-electron repulsion integrals, thePPP-CI calculations were performed on the title compounds according toNishimoto andForster scheme. In these calculations the pseudo-unsaturated nature of the methyl group has been given due consideration. In spectral assignment, compared to the conventionalPPP approach, the CNDO/2-basedPPP-CI method gave a better agreement with the experimental data.     

Estimation of contact area of nanoparticles in chains using continuum elastic contact mechanics

In this research, we have studied the doping behaviors of eight transition metal ion dopants on the crystal phase, particle sizes, XRD patterns, adsorption spectra, anatase fraction, and photoreactivity of TiO₂ nanoparticles. The pristine and ion-doped TiO₂ nanoparticles of 15.91-25.47 nm were prepared using sol–gel method. Test metal ion concentrations ranged from 0.00002 to 0.2 at.%. The absorption spectra of the TiO₂ nanoparticles were characterized using UV-Visible spectrometer. The wavelength of the absorption edge of TiO₂ was estimated using the spectra derivative-tangent method. The photoreactivities of pristine and ion-doped TiO₂ nanoparticles under UV irradiation were quantified by the decoloring rate of methyl orange. XRD patterns were recorded using a Rigaku D/MAX-2500 V diffractometer with Cu Kα radiation (50 kV and 250 mA), and particle size and anatase fraction were calculated. Results reveal that different ion doping exhibited complex effects on the studied characteristics of TiO₂ nanoparticles. In general, red shift occurred to ion-doped TiO₂ nanoparticles, but still with higher TiO₂ photoreactivities when doped with Fe³⁺ and Ni²⁺ ions. Among the ions investigated, Ni-doped TiO₂ nanoparticles have shown highest photoreactivity at the concentration of 0.002 at.%, about 1.9 times that of the pristine TiO₂. Ion doping was shown to reduce the diameter and influence the fraction of anatase. Data also indicated that the combination of anatase diameter and ion radius might play an important role in the photoreactivity of TiO₂ nanoparticles. This investigation contributes to the understanding of complex ion doping effects on TiO₂ nanoparticles, and provides references for enhancing their environmental application.     

Surface-enhanced femtosecond CARS spectroscopy (SE-CARS) on pyridine

Surface-enhanced Raman scattering (SERS) has become an integral part of spectroscopy. The inelastic scattering process is enhanced by several orders of magnitude when molecules are in close contact to nano-structured coin metals. However, the use of surface enhancement in combination with nonlinear spectroscopy is by far not as common as in linear spectroscopy even though a more drastic effect could be expected. In our work, we report the observations we made from the preliminary studies on surface enhancement mechanisms in combination with coherent anti-Stokes Raman scattering (CARS) using femtosecond laser pulses. Silver colloids were used as enhancement medium. Molecules, which show conventional SERS were selected for the experiments. Femtosecond CARS was performed on these molecular systems in the presence and absence of silver colloids. The scattered CARS signal was collected both in the forward and sideward directions. From the analysis of the results general observations were made about the factors affecting the performance of SE-CARS.