Overtone spectroscopy of some benzaldehyde derivatives

Overtone spectrum of o, m and p-nitrobenzaldehydes and p-chlorobenzaldehyde has been studied in 2000–12000 cm⁻¹ region. Vibrational frequencies and anharmonicity constants for aryl as well as alkyl CH stretch vibrations have been determined. We have also determined the internuclear distances for the aryl CH bond in the different molecules. The small variation observed in these distances is an indication of the substitution effect. It is observed that in the case of p-disubstituted benzens, the shift in aryl CH bond is proportional to sum of the Hammet σ of the substituents. However in the case of o-disubstituted benzenes it is only 80% of the para-substituted shift.     

A method for computing the solubility limit of solids: application to sodium chloride in water and alcohols

We present an adaptable method to compute the solubility limit of solids by molecular simulation, which avoids the difficulty of reference state calculations. In this way, the method is highly adaptable to molecules of complex topology. Results are shown for solubility calculations of sodium chloride in water and light alcohols at atmospheric conditions. The pseudosupercritical path integration method is used to calculate the free energy of the solid and gives results that are in good agreement with previous studies that reference the Einstein crystal. For the solution phase calculations, the self-adaptive Wang-Landau transition-matrix Monte Carlo method is used within the context of an expanded isothermal-isobaric ensemble. The method shows rapid convergence properties and the uncertainty in the calculated chemical potential was 1% or less for all cases. The present study underpredicts the solubility limit of sodium chloride in water, suggesting a shortcoming of the molecular models. Importantly, the proper trend for the chemical potential in various solvents was captured, suggesting that relative solubilities can be computed by the method.     

Time Resolved Microwave Interferometry Measurement of the Electron Density in a Pulsed 1,3-Butadiene Discharge

Pulsed plasmas containing organic precursors are becoming increasingly common for multiple applications. To understand the nature of such discharges, in-situ time resolved microwave interferometry measurements of the electron density in a 60 W pulsed inductively coupled 1,3-butadiene discharge have been made. Measurements were also made for continuous wave plasmas at 40, 50, 60 and 70 W power for comparison. The data shows that the time averaged electron densities are independent of pulse width at a particular duty cycle. In addition, time averaged values increase approximately linearly with increasing duty cycle. Such linearity in average density is tied to the ambipolar loss rate. This knowledge is important for understanding the growth kinetics of plasma polymerized films.     

The role of N dopant in inducing ferromagnetism in (ZnO)n clusters (n = 1-16)

The effect of nitrogen doping on the magnetic properties of (ZnO)(n) clusters (n = 1-16) has been investigated using spin polarized density functional theory. The total energy calculations suggest that N is more stable at the O site than at the Zn site in (ZnO)(n) clusters and induces a magnetic moment of 1 μ(B)/N atom. The N-Zn-N configuration is more stable than isolated N for 3D structures. The N dopants do not show any tendency for clustering. The binding energy is found to decrease with the increase in the number of N dopants. The magnetic moment increases gradually with the increase in the number of atoms with 1 μ(B)/N atom for n ≤ 4 and less than 1 μ(B)/N for n > 4. The local magnetic moment is mainly localized at the N site with a small magnetic moment induced at the O site. The presence of a Zn vacancy (V(Zn)) induced an additional magnetic moment of 2 μ(B) on the nearest O atoms. The N dopant prefers to form a N-V(Zn) pair. The combination of N and V(Zn) in 3D structures leads to a total magnetic moment of 3 μB. The Mulliken charge transfers from Zn to N and O in all N doped (ZnO)(n) clusters. The calculated results are consistent with existing experimental and theoretical results.     

Water coordination structures and the excess free energy of the liquid

We assess the contribution of each coordination state to the hydration free energy of a distinguished water molecule, the solute water. We define a coordination sphere, the inner-shell, and separate the hydration free energy into packing, outer-shell, and local, solute-specific (chemical) contributions. The coordination state is defined by the number of solvent water molecules within the coordination sphere. The packing term accounts for the free energy of creating a solute-free coordination sphere in the liquid. The outer-shell contribution accounts for the interaction of the solute with the fluid outside the coordination sphere and it is accurately described by a Gaussian model of hydration for coordination radii greater than the minimum of the oxygen-oxygen pair-correlation function: theory helps identify the length scale to parse chemical contributions from bulk, nonspecific contributions. The chemical contribution is recast as a sum over coordination states. The nth term in this sum is given by the probability p(n) of observing n water molecules inside the coordination sphere in the absence of the solute water times a factor accounting for the free energy, W(n), of forming an n-water cluster around the solute. The p(n) factors thus reflect the intrinsic properties of the solvent while W(n) accounts for the interaction between the solute and inner-shell solvent ligands. We monitor the chemical contribution to the hydration free energy by progressively adding solvent ligands to the inner-shell and find that four-water molecules are needed to fully account for the chemical term. For a chemically meaningful coordination radius, we find that W(4) ≈ W(1) and thus the interaction contribution is principally accounted for by the free energy for forming a one-water cluster, and intrinsic occupancy factors alone account for over half of the chemical contribution. Our study emphasizes the need to acknowledge the intrinsic solvent properties in interpreting the hydration structure of any solute, with particular care in cases where the solute-solvent interaction strength is similar to that between the solvent molecules.     

Consequential secondary structure alterations and aggregation during prolonged casein glycation

Non-enzymatic glycosylation (glycation) of casein is a process used not just to ameliorate the quality of dairy products but also to increase the shelf life of canned foods, including baby milk supplements. Incubation of κ-casein with reducing sugars for 15 days at physiological temperature showed the formation of a molten globule state at day 9 and 12 during fructation and glucation respectively. This state exhibits substantial secondary structure and maximum ANS binding. Later on, glycation resulted in the formation of aggregates at day 12 in presence of fructose and day 15 in presence of glucose. Aggregates possess extensive β-sheet structure as revealed by far-UV CD and FTIR. These aggregates showed altered tryptophan environment, decrease ANS binding relative to molten globule state and increase in Thioflavin T fluorescence. Aggregates were also accompanied by the accumulation of AGEs, indicative of structural damage to the protein and formation of potentially harmful species at the physiological level. Fructose was more reactive than glucose and thus caused early and significant changes in the protein. From our studies, we conclude that controlling the extent of the Maillard reaction in the food industry is essential to counter its negative effects and expand its safety spectrum.     

LC and LC-MS study on establishment of degradation pathway of glipizide under forced decomposition conditions

Forced degradation studies on glipizide are conducted under the conditions of hydrolysis, oxidation, photolysis, and dry heat. The solutions are subjected to liquid chromatographic (LC) investigations to establish the number of products formed in each condition. The degradation products are characterized through isolation and subsequent NMR, IR, and MS spectral analyses, or through LC-mass spectrometry (MS) fragmentation pattern study. The drug is shown to degrade in 0.1M HCl at 85 degrees C to two products: 5-methyl-N-[2-(4-sulphamoylphenyl)ethyl]pyrazine-2-carboxamide (II) and methyl N-[4-[2-{(5-methyl-2-pyrazinoyl)amino}ethyl] phenyl]sulfonyl carbamate (III). The latter, a methyl ester, is formed only in the presence of methanol (used as a solubilizer), and does not appear on use of acetonitrile. III is shown to convert to II on continued heating in acid. The drug degrades slowly in water at the same temperature, and both II and III could be seen in the chromatograms until the end of the study. The heating of the drug in alkali (0.1M NaOH) at 85 degrees C yields 5-methyl-2-pyrazinecarboxylic acid (IV), along with a small quantity of 4-(2-aminoethyl) benzenesulfonamide (I). On extended heating in the same condition, a new product, 4-(2-aminoethyl)-N,N-bis[(cyclohexylamino)carbonyl] benzenesulfonamide (VI) is formed in small quantities. At the lower temperature of 40 degrees C, the drug converts under each hydrolytic condition and in both the absence and presence of light to products II, III, or IV, along with a new product, 1-cyclohexyl-3-[[4-(2aminoethyl)phenyl] sulfonyl]urea (V). The light catalyzes formation of V, and it is formed until one or two weeks, after which its level decreases. The drug remains stable in 30% H2O2, except that products II and III appear as small peaks due to acidic character of the peroxide solution. Also, the drug remains unaffected in solid state under thermal and photolytic stress conditions. Based on the results, a more complete picture on degradation pathway of the drug is obtained, highlighting a clear advantage of the approach suggested by International Conference on Harmonization.     

Multiple ionization of argon in coincidence with projectile ions in 60–120 MeV Si q+-Ar collisions

A projectile ion-recoil ion coincidence technique has been employed to study the multiple ionization and the charge transfer processes in collisions of 60–120 MeV Si ^q+ (q = 4−14) ions with neutral argon atoms. The relative contribution of different ionization channels, namely; direct ionization, electron capture and electron loss leading to the production of slow moving multiply charged argon recoil ions have been investigated. The data reported on the present collision system result from a direct measurement in the considered impact energy for the first time. The total ionization cross-sections for the recoil ions are shown to scale as q ^1.7/E _p ^0.5 , where E _p is the energy in MeV of the projectile and q its charge state. The recoil fractions for the cases of total- and direct ionizations are found to decrease with increasing recoil charge state j. The total ionization fractions of the recoils are seen to depend on q and to show the presence of a ‘shell-effect’ of the target. Further, the fractions are found to vary as 1/j ² upto j = 8+. The average recoil charge state 〈j〉 increases slowly with q and with the number of lost or captured electrons from or into the projectile respectively. The projectile charge changing cross-sections σ _qq′ are found to decrease with increasing q for loss ionization and to increase with q for direct-and capture ionization processes respectively. The physics behind various scaling rules that are found to follow our data for different ionization processes is reviewed and discussed.