A naphthalene diimide dyad for fluorescence switch-on detection of G-quadruplexes.

A non-fluorescent naphthalene diimide (NDI) dimer, conjugating red and blue NDI dyes, becomes red/NIR emitting upon G-quadruplex binding. The fluorescence lifetime which is significantly different for the complexes, the G-quadruplex/dimer and the weakly emitting ds-DNA/dimer is the key feature for the development of new rationally engineered G-quadruplex sensors.

The crystallization of calcium carbonate on sodium cholate.

Recent studies in the bibliography showed that calcium carbonate was the major constituent (77.8%) in gall stones, and the polymorph calcite was at 62.5% of the cases examined. The kinetics of crystallization of calcite on sodium cholate has been studied using the constant composition technique. Analysis of the initial rates as a function of the solution supersaturation, according to the classical nucleation theory, yielded a value of 33mJm(-2) for the surface energy of the growing phase and a five-ion cluster, forming the critical nucleus. The apparent order for the calcite crystallization was found to be 4.5+/-0.7 indicative of a surface nucleation mechanism. The formation of calcite may be initiated through the interaction of Ca2+ ions with the negative end of the C=0 bond of the sodium cholate molecule.

The effect of sodium alginate on the crystal growth of calcium carbonate.

The effect of sodium alginate in supersaturated solutions of calcium carbonate was investigated under plethostatic conditions. The rates of crystal growth measured in the presence of sodium alginate at concentrations as low as 0.83 x 10(-7) mol dm(-3) were drastically reduced. Kinetic analysis according to a Langmuir-type adsorption isotherm led to the calculation of an affinity constant Kaff = 999.8 x 10(-4) mol dm(-3). The apparent order found from kinetic data was 3.0+/-0.2 suggesting a surface nucleation mechanism.