Dimension-Dependent Magnetic Behavior of Manganese-Cysteine Inorganic Complex Nanoparticles.

A cysteine-based complex of Mn2+ led to the formation of nanoparticles in aqueous medium under ambient conditions. The formation and evolution of the nanoparticles in the medium were followed by ultraviolet-visible light (UV-vis) spectroscopy, circular dichroism, and electron spin resonance spectroscopy that also revealed a first-order process. The magnetic properties of the nanoparticles isolated as solid powders exhibited strong crystallite and particle size dependence. At low crystallite size, as well as particle size, the complex nanoparticles showed superparamagnetic behavior similar to other magnetic inorganic nanoparticles. The magnetic nanoparticles were found to undergo a superparamagnetic to ferromagnetic transition, and then to paramagnetic transition with a gradual increase in either their crystallite size or particle size. The discovery of dimension-dependent magnetic property of inorganic complex nanoparticles may usher in a superior option for tuning the magnetic behavior of nanocrystals, depending on the component ligands and metal ions.

An ambient complexation reaction of zinc acetate and ascorbic acid leads to a new form of nanoscale particles with emergent optical properties.

We report the formation of nanoscale particles from the complexation reaction between zinc acetate and ascorbic acid under ambient conditions and in an aqueous medium. The reaction led to the formation of a molecular complex with the formula Zn x (AA) y (OAc) z (x, y, and z = possible smallest positive integer) with AA meaning ascorbate, based on the mass spectrometry results. Following this, the formation of luminescent nanoscale particles - the size of which increased with time - was observed. During 24 h of observation, the sizes increased to about 50 nm in the presence of different sizes at all times. Transmission electron microscopy results also indicated the formation of polycrystalline as well as amorphous nanoparticles in the medium. Further, the appearance of a UV absorption peak at 380 nm and photoluminescence peak at 473 nm marked the formation of the nanoparticles. The luminescence was also observed to be wavelength tuneable. FTIR and NMR spectroscopy results also supported the formation of a molecular complex with the above formula. The present work highlights the importance of emergent properties of nanoscale molecular materials for crystallization. Also, the present discovery is expected to contribute to the development of safe nanomaterials.

Zinc-Ion-Induced Aggregation of Gold Clusters for Visible-Light-Excitation-Based Fluorimetric Discrimination of Geometrical Isomers.

Herein, we report discrimination of dicarboxylic acids - fumaric acid (FA) and maleic acid (MA) - exhibiting geometrical isomerism, using nanoclusters based luminescent probe having excitation under broad day light. The luminescent probe was designed via complexation reaction between zinc ions and ligands (mercaptopropioinc acid; MPA) stabilizing the gold nanoclusters. This resulted in formation of nanoaggregates exhibiting bright green luminescence upon excitation at 450 nm capable of discriminating between FA and MA upto nanomolar level. The basis of discrimination has been attributed to deprotonation of FA and MA following interaction with MPA moieties present on the surface of the nanoaggregates and being governed by the stability of the respective conjugate base of the geometrical isomers of the dicarboxylic acids. As a consequence of different extent of deprotonation of FA and MA upon interaction with the cluster aggregates, different effect on the luminescence of the aggregates was observed, thus enabling discernible fluorimetric discrimination between FA and MA under visible light excitation.