Microscopic solvation of a lithium atom in water-ammonia mixed clusters: solvent coordination and electron localization in presence of a counterion

The microsolvation structures and energetics of water-ammonia mixed clusters containing a lithium atom, i.e., Li(H(2)O)(n)(NH(3)), n = 1-5, are investigated by means of ab initio theoretical calculations. Several structural aspects such as the solvent coordination to the metal ion and binding motifs of the free valence electron of the metal are investigated. We also study the energetics aspects such as the dependence of vertical ionization energies on the cluster size, and all these structural and energetics aspects are compared to the corresponding results of previously studied anionic water-ammonia clusters without a metal ion. It is found that the Li-O and Li-N interactions play a very important role in stabilizing the lithium-water-ammonia clusters, and the presence of these metal ion-solvent interactions also affect the characteristics of electron solvation in these clusters. This is seen from the spatial distribution of the singly occupied molecular orbital (SOMO) which holds the ejected valence electron of the Li atom. For very small clusters, SOMO electron density is found to exist mainly at the vicinity of the Li atom, whereas for larger clusters, it is distributed outside the first solvation shell. The free dangling hydrogens of water and ammonia molecules are involved in capturing the SOMO electron density. In some of the conformers, OH{e}HO and OH{e}HN types of interactions are found to be present. The presence of the metal ion at the center of the cluster ensures that the ejected electron is solvated at a surface state only, whereas both surface and interiorlike states were found for the free electron in the corresponding anionic clusters without a metal ion. The vertical ionization energies of the present clusters are found to be higher than the vertical detachment energies of the corresponding anionic clusters which signify a relatively stronger binding of the free electron in the presence of the positive metal counterion. The shifts in different vibrational frequencies are also calculated for the larger clusters, and the results are discussed for some of the selective modes of water and ammonia molecules that are directly influenced by the location and hydrogen bonding state of these molecules in the clusters.     

Nitro-functionalization and luminescence quantum yield of Eu(III) and Tb(III) benzoic acid complexes

In our pursuit of luminescent lanthanide ion-based coordination polymers, we have isolated several complexes with nitrobenzoic acid ligands and characterized these by X-ray crystallography and luminescence spectroscopy. 2-Nitrobenzoic acid reacts with Eu(III) to form 1, which crystallizes in the P-1 space group, with a = 12.385(3), b = 12.912(3), c = 17.889(4) A, alpha = 97.49(3), beta = 109.64(3) and gamma = 101.99(3) degrees . 3-Nitrobenzoic acid forms a one-dimensional coordination polymer with Eu(III), 2, which crystallizes in the triclinic space group P-1 with a = 9.7100(19), b = 10.579(2), c = 13.361(3) A, alpha = 77.41(3), beta = 88.78(3) and gamma = 88.16(3) degrees. Structures 3 and 4 correspond to the isostructural one-dimensional coordination polymers of Eu(III) and Tb(III), respectively, with the 4-nitrobenzoato anion. These crystallize in the triclinic space group P-1 with a = 9.2242(18), b = 15.102(3), c = 18.587(4) A, alpha = 75.93(3), beta = 82.88(3) and gamma = 79.00(3) degrees for 3 and a = 9.2692(19), b = 15.369(3), c = 18.353(4) A, alpha = 75.37(3), beta = 81.32(3) and gamma = 78.15(3) degrees for 4. Potentiometry, absorption and NMR spectroscopy indicate that in solution only 1 : 1 species are present. All compounds are weakly luminescent as solids and the photophysics of solutions of ligands with Ln(III) in 1 : 1 stoichiometry were studied. Quantum yields around 1 and 3% for Eu(III)-and Tb(III)-containing methanolic solutions were measured.     

Electron solvation in water-ammonia mixed clusters: Structure, energetics, and the nature of localization states of the excess electron

The structure and energetics of water-ammonia mixed clusters with an excess electron, [(H2O)n(NH3)m]- with m=1, n=2-6 and m=2, n=2, and also the corresponding neutral clusters are investigated in detail by means of ab initio quantum chemical calculations. The authors focus on the localization structure of the excess electron with respect to its surface versus interiorlike states, its binding to ammonia versus water molecules, the spatial and orientational arrangement of solvent molecules around the excess electron, the changes of the overall hydrogen-bonded structure of the clusters as compared to those of the neutral ones and associated dipole moment changes, vertical detachment energies of the anionic clusters, and also the vertical attachment energies of the neutral clusters. It is found that the hydrogen-bonded structure of the anionic clusters are very different from those of the neutral clusters unlike the case of water-ammonia dimer anion, and these changes in structural arrangements lead to drastically different dipole moments of the anionic and the neutral clusters. The spatial distribution of the singly occupied molecular orbital holding the excess electron shows only surface states for the smaller clusters. However, for n=5 and 6, both surface and interiorlike binding states are found to exist for the excess electron. For the surface states, the excess electron can be bound to the dangling hydrogens of either an ammonia or a water molecule with different degrees of stability and vertical detachment energies. The interiorlike states, wherever they exist, are found to have a higher vertical detachment energy than any of the surface states of the same cluster. Also, for interiorlike states, the ammonia molecule with its dangling hydrogens is always found to stay on top or on a far side of the charge density of the excess electron without participating in the hydrogen bond network of the cluster; the intermolecular hydrogen bonds are formed by the water molecules only which add to the overall stability of these anionic clusters.     

Stable quasiperiodic icosahedral states

The discovery of icosahedral quasicrystals five years ago, has challenged the validity of the well-known conjecture that the ground state of a system of particles interacting via short-range forces is always crystalline at absolute zero. We have calculated the classical cohesive energies and pair distribution functions of a large class of monatomic icosahedral structures, interacting via the Lennard-Jones (LJ) and the Square-Well (SW) potentials. For the SW potential, we have found an icosahedral phase, with lower enthalpy than the BCC, FCC and HCP phases. The phase is robust with respect to small changes in the potential, pressure and even structure, and transforms to the BCC phase above a critical pressure. Our results suggest that icosahedral ground states may indeed be possible for a class of potentials with Friedel-like oscillations, whose extremal positions satisfy geometric constraints favoring icosahedral order.     

Determination of Heraclenin and Heraclenol in Heracleum candicans D.C. by TLC

A simple TLC method has been developed for the simultaneous determination of heraclenin and heraclenol in the roots of Heracleum candicans D.C. The analytes were separated on silica gel F₂₅₄ plates with toluene:ethyl acetate (7:3) and scanned using densitometry at 366 nm. The method was validated in terms of precision, repeatability and accuracy. The linear range for heraclenin was found to be 4 - 10 μg per spot with correlation coefficient of 0.997 while for heraclenol it was 1–5 μg per spot with a correlation coefficient of 0.985. The two compounds were quantified in different samples of H. candicans and were found to be present in the range of 1.02 – 1.36% and 0.29 – 0.43% w/w. The method was found to be very simple, accurate, precise and economical and can be used for routine quality control.     

A New,Convenient Method for Determination of Mangiferin,an Anti-Diabetic Compound,in Mangifera indica L.

JPC – Journal of Planar Chromatography – Modern TLC - A simple, precise, and rapid HPTLC method has been established for quantitative determination of the bioactive marker compound...     

Excess thermodynamic properties of binary liquid mixtures containing dimethylsulfoxide at 30°C

The exess volumes of mixing of dimethylsulfoxide with n-, sec- and tertbutylamine, n-pentylamine, n-hexylamine, n-heptylamine, n-octylamine and cyclohexylamine have been measured as a function of composition at 30°C by a dilatometric method. For all amines V^E values are negative over the entire mole fraction range. The results are attributed to the interaction between unlike molecules.     

Incorporation of biotransformed silver nanoparticles in plant polysaccarides resin and their effect on sustained drug release

The intension of current study was to determine antibacterial and drug releasing capacity of green synthesized silver nanoparticles (AgNps) with Moringa oleifera resin in the presence of Montelukast sodium and Ibuprofen. This plant gum is economic, easily available, biodegradable, safe and potential tablet binder. There was no significant study reported on the incorporation of green synthesized silver nanoparticle with plant resin in drug release. The aqueous extract of Clerodendron phlomoides was used for the bioreduction of silver nanoparticles as well as a capping agent. This green synthesized AgNps was observed in UV at 489 nm due to the SPR (Surface Plasmon Effect) effect, and the presence of protein and polyol compounds was identified by FTIR. The crystalline structure of AgNps was analyzed by XRD, elemental silver composition was measured by EDAX, morphological structure and size was revealed by SEM and TEM analysis. The antibacterial effect of green synthesized AgNps was analyzed by zone of inhibition method. Silver nanoparticles incorporated in M. oleifera plant resin and its functional groups and thermal degradation properties were characterized by FTIR and TGA, respectively. The drug release properties of the AgNps incorporated with plant resin were evaluated for the sustained release and compared with raw plant gum without AgNps consistency.     

Characterization and Enhanced Production of Prodigiosin from the Spoiled Coconut

Many bacterial secondary products are bioactive substances that play an important role in biotechnology and pharmacology (e.g., as antibiotics or antitumor agents). Over the past few years interest in prodigiosin has been increased due to its promising anti-cancer activity. Prodigiosin is also of potential clinical interest because it is reported to have anti-fungal, anti-bacterial, anti-protozoal/anti-malarial, and immunosuppressive activity. Thus there is a need to develop a high-throughput and cost-effective bioprocess for the production of prodigiosin. In the present study, Serratia rubidaea was isolated from colored portion of a spoiled coconut and further it was authenticated by MTCC, India. The various parameters like temperature, pH, salt concentration, and precursors were optimized for the production of prodigiosin. We now report that the pigment production was higher in our isolated strain than S. marcescens. It was observed that prodigiosin binds with plastic, paper, and fibers and thus in near future, it can also be used as a natural dye.