Chitrani Medhi

Fertility Status of Soil in the Tea Garden Belts of Golaghat District, Assam, India

The increasing land use intensity without adequate and balanced use of chemical fertilizers and with little or no use of organic manure have caused severe fertility deterioration of our soils resulting in stagnating or even declining of crop productivity in Assam. The need of the hour is to achieve substantially higher crop yield than the present yield levels from our limited land resources on a sustainable basis. A study was carried out in the paddy fields of tea garden belts namely, Rungagora, Balijan, Banwaripur, Khomtai, Rungajaun, Lattakoojan, Borjan, Behora, Negheriting, and Borsapori of Golaghat district of Assam to investigate the fertility status of soil during 2008–2010. Results of the present study showed that soil solutions were acidic in nature in all seasons. Medium-to-high BD, medium SOM, medium-to-high available N and available phosphorous, and low availability of potash showed that soils were not sufficiently fertile for crop production. Depending on the SOM, available N, available P, and exchangeable K in soil, the study areas were grouped in to six fertility classes as MMML, MMHL, MMMM, MHHL, MHHM, and MMHM. Student t-test values of all the parameters with control sample showed statistically significant results for SOM, available N, and available P in both seasons (dry and wet) and EC in wet seasons and bulk density in dry season only.

Basicities of some 9-substituted acridine-4-carboxamides: A density functional theory (DFT) calculation

Acid-base properties of drugs are important in understanding the behaviour of these compounds under physiological condition. In order to understand such behaviour the proton affinities of acri-dine 4-carboxamides with substitution (R) at the 9-position are theoretically studied, and considered for the basic sites of both the heterocyclic ring as well as side chain nitrogens. In 9-amino acridine 4-carbox-amide, the -NH2 group is observed to be an additional basic site. The heterocyclic nitrogen of substituted carboxamides (R =-NH2, -O-methyl, -O-ethyl, and -O-phenyl) is more basic than the side chain nitrogen, however, side chain nitrogen corresponds to more basic site for some carboxamides (R = -OH and-Cl) and the -NH2 group represents the least basic site of 9-amino acridine 4-carboxamide. In addition to presenting the basicities of these drugs an indication of another hydrogen-bond between heterocyclic ring N and carboxamide chain O is observed. The difference of basicities with substituents at 9-position are very narrow and carboxamides with substituents at 9-position are found to be suitable for studying intramolecular H-bonds between the heterocyclic N and carboxamide O. The resultant stabilization of a configuration due to such H-bonding is determined

DENSITY FUNCTIONAL STUDY ON THE PROTON ASSISTED ISOMERIZATION OF 1H-IMIDAZO(4,5-b)PYRIDINE DERIVATIVES

The proton assisted isomerization reactions of 1H-imidazo(4,5-b)pyridine (IMP) derivatives have been studied by using B3LYP/6-31G + (d,p) calculations, and the transition states of the reactions are analyzed with B3LYP/6-31+G(d,p) opt=qst3 route. It has been found that the prototropic transformation could be the feasible pathway of isomerization, since the energy gaps between the various protonated isomers are found closer compared to free molecules. The conversion of IMP-a1 to IMP-b1 may pass through several protrotopic isomerization, since the activation energy as well as the relative energy levels of these isomers are not small compared to other pathways. However, the results suggest that some of the reactions may take place simultaneously through protrotopic transformation. The relative variations of energy gaps in the excited states are smaller than the ground states. The protrotropic transformation in the excited states may be more feasible than the ground state.

The models of proton assisted and the unassisted formation of CGC base triplets

The triple helix is formed by combining a double and a single strand DNAs in low pH and dissociates in high pH. Under such conditions, protonation of cytosine in the single strand is necessary for triplex formation where cytosine-guanine-cytosine (CGC+) base triplet stabilizes the triple helix. The mechanism of CGC+ triplet formation from guanine-cytosine (GC) and a protonated cytosine (C+) shows the importance of N3 proton. Similarly in the case of CGC (unprotonated) triplet, the donor acceptor H-bond at N3 hydrogen of the cytosine analog (C) initiates the interaction with GC. The correspondence between the two models of triplets, CGC+ and CGC, unambiguously assigned that protonation at N3 cytosine in low pH to be the first step in triplet formation, but a donor acceptor triplet (CGC) can be designed without involving a proton in the Hoogsteen H-bond. Further, the bases of cytosine analogue also show the capability of forming Watson Crick (WC) H-bonds with guanine.

EXFOLIATION OF GRAPHENE OXIDE NANOSHEETS FROM PENCIL LEAD AND IN SITU PREPARATION OF GOLD NANOPARTICLES ON GRAPHENE OXIDE NANOSHEETS

This work reports the low-cost exfoliation of graphene oxide (GO) from pencil lead using modified Hummers method. The gold nanoparticles (AuNPs) supported on GO is prepared via an in situ bio reduction of HAuCl4 by polyphenolic biomolecules present in young leaves of tea (Camellia sinensis) extracted in the presence of GO. The UV-Visible absorption spectrum of GO dispersion in water exhibits two bands at 228 nm and a shoulder at ~ 300 nm corresponding to π–π* transitions of aromatic C–C bonds and n–π* transitions of C=O bonds. In photoluminescence (PL) study, GO dispersion in water shows an emission band at 555 nm, when excited at 325 nm. When AuNPs are supported on GO nanosheets the bands at 228 nm and ~ 300 nm of GO disappears and two new UV-Visible bands at 229 nm for π–π* (for C=C) and 550 nm for transverse surface plasmon resonance (TSPR) of AuNPs appears. When AuNPs are supported on GO nanosheets, PL emission band at 555 nm disappears and two new PL emission bands appear at 431 nm and 658 nm. The physical and morphological characterizations are performed by Fourier-transform infrared (FT-IR), X-ray diffraction (XRD), High-resolution-transmission electron microscopy (HR-TEM) and BET surface area measurement. Morphological studies revealed that the GO nanosheets are well dispersed in water and AuNPs are supported on the GO nanosheets.

PROTON INDUCED STRUCTURAL REORGANIZATION OF A FEW CARBONYL MOLECULES IN THE GROUND AND EXCITED STATES

Quantum chemical valence parameters have been used to analyze the structural reorganization of carbonyl molecules like acrolein, glyoxal, propynal, and formamide after protonation. The effect of proton at the carbonyl oxygen is countable in the electronic configuration of the molecule as a whole. Structures in different electronic states are analyzed with respect to calculated values of bond orders and net charge densities on the atoms. Correlation has been made between the extent of structural changes in the protonated molecules and proton affinities of the molecules. Prominent structural reorganizations have been observed after protonation of the carbonyl molecules in comparison to the changes in the free molecules. The directionality of protonation and the π polarization of the CO bond is also observed to be dependent on the type of substituents attached to the carbonyl group.

Macroscopic solvent polarization‐induced reorganization of the electron density in different excited states: A study on formaldehyde molecule by a multiconfiguration self‐consistent reaction‐field method

A detailed study of the type and extent of electronic reorganization created by macroscopic solvation of a prototypical carbonyl solute is carried out within the framework of the semiempirical multiconfiguration self-consistent reaction-field model. The solvation causes additional polarization of the electronic charge density within the carbonyl group. Orbitalwise breakup of the electron densities on the key atoms throws light on such features as the polarity dependence of inversion barriers and out-of-plane bending. Macroscopic solvation is shown to cause a reverse π-polarization within the carbonyl group, affecting barrier heights on the inversion path.