Beyond the Förster formulation for resonance energy transfer: the role of dark states.

Resonance Energy Transfer (RET) is investigated in pairs of charge-transfer (CT) chromophores. CT chromophores are an interesting class of π conjugated chromophores decorated with one or more electron-donor and acceptor groups in polar (D-π-A), quadrupolar (D-π-A-π-D or A-π-D-π-A) or octupolar (D(-π-A)(3) or A(-π-D)(3)) structures. Essential-state models accurately describe low-energy linear and nonlinear spectra of CT-chromophores and proved very useful to describe spectroscopic effects of electrostatic interchromophore interactions in multichromophoric assemblies. Here we apply the same approach to describe RET between CT-chromophores. The results are quantitatively validated by an extensive comparison with time-dependent density functional theory (TDDFT) calculations, confirming that essential-state models offer a simple and reliable approach for the calculation of electrostatic interchromophore interactions. This is an important result since it sets the basis for more refined treatments of RET: essential-state models are in fact easily extended to account for molecular vibrations in truly non-adiabatic approaches and to account for inhomogeneous broadening effects due to polar solvation. Optically forbidden (dark) states of quadrupolar and octupolar chromophores offer an interesting opportunity to verify the reliability of the dipolar approximation. In striking contrast with the dipolar approximation that strictly forbids RET towards or from dark states, our results demonstrate that dark states can take an active role in RET with interaction energies that, depending on the relative orientation of the chromophores, can be even larger than those relevant to allowed states. Essential-state models, whose predictions are quantitatively confirmed by TDDFT results, allow us to relate RET interaction energies towards allowed and dark states to the supramolecular symmetry of the RET-pair, offering reliable design strategies to optimize RET-interactions.

Skin cancers in chronic arsenic toxicity--a study of predictive value of some proliferative markers.

Prolonged exposure to arsenic contaminated water produces various clinical features, cutaneous features e.g. melanosis, keratosis and cancers being very common. Evaluation of such lesions by proliferative markers can provide useful information in regards to the biological behaviour of the lesions. Thus, cases with high proliferative status can be ominous sign for development of cancers. We studied skin biopsy of 42 cases. These were evaluated with AgNOR score and PCNA stain, in addition to H & E examination. Here, invasive cancer cases had mean AgNOR score of 3.56, those with severe dysplasia had 3.0, moderate and mild dysplasia scored 1.73, benign changes had mean score of 1.35 while normal control cases had 1.08. PCNA index in cancers was above 50, that of severe dysplasia 25-30, mild to moderate dysplasia 1.0-5.0, those with benign changes 0.5 -1.0 and normal control had LI of less than 0.5%. PCNA has the advantage of less chance of observer error over AgNOR stain.

Product development studies for stabilization of oral liquid enzyme preparations containing diastase and papain.

A product development study was undertaken with a view to stabilize acid sensitive amylolytic enzyme diastase and alkali sensitive proteolytic enzyme papain. An unique high technology method was adopted for both enzymes with enteric coating and non-enteric film forming materials respectively to achieve site specificity of action, better stability and to protect diastase from the adverse acid pH of the stomach. Feasibility of incorporating various excipients like thickening agents, surfactants, preservatives, etc., to produce stable elegant oral liquid suspension was also studied. Release studies of the enzymes both in simulated gastric and simulated intestinal juices showed steady and consistent release. The proteolytic and amylolytic activities were assessed by standard pharmacopoeial methods. The stability of the product during the studies was satisfactory. Reduction in addition of overages of costly enzymes met the project technically feasible and economically viable.