Low frequency Raman scattering from acoustic phonons confined in ZnO nanoparticles

We report here the first observation of the low frequency Raman scattering from acoustic phonons in semiconducting zinc oxide (ZnO) nanoparticles without embedding in any solid matrix. ZnO nanoparticles (size 5-10 nm) with nearly spherical shape have been synthesized using a chemical route. A shift in the phonon peaks toward higher frequencies along with broadening was observed with a decrease in particle size. The size dependence of the acoustic phonons in ZnO nanoparticles is explained using Lamb's theory that predicts the vibrational frequencies of a homogeneous elastic body of spherical shape. Our results show that the observed low frequency Raman scattering originates from the spherical (l = 0) and quadrupolar vibrations (l = 2) of the spheroidal mode due to the confinement of acoustic vibrations in ZnO nanoparticles.     

Thio acid/azide amidation: an improved route to N-acyl sulfonamides

[STRUCTURE: SEE TEXT] A one-pot procedure for the conversion of carboxylic acids to N-acyl sulfonamides, via thio acid/azide amidation, is presented. The method is compatible with acid- and base-sensitive amino acid protection. N-Acyl sulfonamide synthesis on solid support, peptide thio acid/sulfonazide coupling, and N-alkyl amide synthesis via selective cleavage of sulfonyl from an N-alkyl-N-acyl sulfonamide are also reported.