Geometrical parameters associated with N-H ... N types of hydrogen bonds have been analysed using crystal structure data on nucleic acids, amino acids and related compounds. Histograms depicting the frequency distribution of N-H ... N length (l) and H-N ... N angle (θ) have been drawn and conclusions on the favoured geometry of such bonds have been arrived at. The distribution ofl shows a pronounced maximum in the range between 2.9Å and 3.0Å with an overall average of 2.98 Å. The θ distribution shows a pronounced maximum for the hydrogen bond angle in the range 0°-10°, with a rapid fall-off in frequency for nonlinear hydrogen bonds. The frequency shows a cos⁶θ dependence as compared to cos²θ dependence term used earlier to predict the angular dependence of hydrogen bond potential energy in proteins and polypeptides.

A biochemical fuel cell is a device which converts chemical energy into electrical power. The catalysts used in this process can be either inorganic or organic type giving rise to ‘inorganic fuel cells’ or ‘biochemical fuel cells’, respectively. Biochemical fuel cells use either micro-organism or enzymes as active components to carry out electrochemical reactions. The efficiency of such a device theoretically can be as high as 90%. The difficulty in attaining these values arises due to sluggishness of electron transfer from active site to conducting electrode. This can be overcome by using mediators or by immobilizing active components on conducting electrode. We have immobilizedfad-glucose oxidase on a graphite electrode using a semiconducting chain as a bridge. At the present stage of development, such a device tacks high current densities, which is essential for commercial power generation but can be used in applications such as pacemakers and glucose sensors.

A biochemical fuel cell is an electrochemical power generation device that converts the chemical energy of a fuel (alcohol, glucose, hydrocarbons, etc) directly into electrical energy through enzyme-catalysed oxidation-reduction reactions. These systems possess several advantages over the conventional processes and are ideal for rural electrification in conjunction with biogas plants.

The major bottleneck in the design of such power sources is the electron transport from the substrate to the electrode. Biochemical systems which use coenzymes such asfad ornad seem to be the most promising in circumventing these difficulties. We have made systematic molecular orbital studies of the electron-flow diagrams of riboflavin during its oxidation-reduction cycle and it is possible to obtain very efficient electron transport from the coenzyme to the electrodes by immobilising flavin through semiconducting side chains, at certain selected positions, to electrodes such as graphite.

Based on these studies, we have immobilisedfad on graphite electrodes. The chemical steps involve creating active centres on graphite which are reacted withfad to form covalent linkages between the electrode and the coenzyme. Cyclic voltamograms of the modified electrode show thatfad is active and undergoes the expected redox cycles. We hope that such electrodes will form suitable bioanodes forfad-linked enzymatic reactions.