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e 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. e 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 �elds 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-tohigh 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 signi�cant 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.

The use of appropriate level of theories for studying weak interactions such as stacking of aromatic molecules has been an important aspect, since the high level methods have limitations for application to large molecules. The differences in the stacking energies of various structures are found significant for identifying the most favored stacked benzene rings and the pyridine rings. The most favored structure of benzene rings obtained from various methods are similar, and also comparable with that of reported accurate CCSD(T) method. The effect of basis set in the stacking energies of MP2 calculations is small. Thus the moderately accurate methods may be feasible for studying the stacking interactions as demonstrated for benzene and pyridine molecules.

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 acridine 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-carboxamide, the-NH 2 group is observed to be an additional basic site. The heterocyclic nitrogen of substituted carboxamides (R =-NH 2 ,-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-NH 2 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.

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The gas phase studies on the electronic stabilities and thermochemical properties of metastable AC mismatches have been performed and the results are analyzed to explain the features of experimentally available AC mismatches. The hydrogen bonding patterns observed in these mismatches are relevant to the formation of stable AC mismatches. In these AC pairs, the H migration mechanism to generate other tautomeric forms is not observed, which shows the compatibility of H bonding capacity of the sites involved in H bonds. The presence of hydrogen bond type –N[Formula: see text]H–N– may contribute to better AC pairing, hence cisA1-1cisC2, transA2-cisC1 and transA1-1cisC2 are found to be more favorable pairs compared to other AC pairs.

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) opt¼qst3 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.

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