Insights into Plasmon-Induced Dimerization of Rhodanine-A Surface-Enhanced Raman Scattering Study.

Plasmon-mediated chemical reactions (PMCRs) have attracted considerable interest in recent times. The PMCR initiated by hot carriers is known to be influenced by the type of metals and the excitation wavelength. Herein, we have carried out the surface-enhanced Raman scattering (SERS) investigation of rhodanine (Rd), an important pharmacologically active heterocyclic compound, adsorbed on silver and gold nanoparticles (AgNP and AuNP) using 514.5 and 632.8 nm lasers. The prominent Raman band at 1566 cm-1 observed in the SERS spectra is attributed to the characteristic ν(C═C) stretching vibration of the Rd dimer and not of Rd tautomers. The chemical transformation of Rd to Rd dimer on metal surfaces is plausibly triggered by the indirect transfer of energetic hot electrons generated during the non-radiative decay of plasmon. The mechanism involved in the dimerization of Rd via the indirect transfer of hot electrons is also presented. The effect of wavelength on the dimerization of Rd is also observed on the AgNP surface, which indicates that the dimerization occurs more efficiently on the AgNP surface with excitation at 514.5 nm wavelength.

Hydrogen bonds and ionic forms versus polymerization of imidazole at high pressures.

Imidazole (C3H4N2) is an important biomaterial for material research and applications. Our high-pressure Raman spectroscopic investigations combined with ab initio calculations on crystalline imidazole suggest that C-H---X (X = N, π) and N-H---N intermolecular hydrogen bonding interactions largely influence the nature of its structural and polymeric transformations under pressure. At pressures around ∼10 GPa, the reduction in the N---N distances close to the symmetrization limit and the emergence of the spectral features of the cationic form indicate the onset of proton disorder. The pressure-induced strengthening of the "blue-shifting hydrogen bonds" C-H---X (X = N, π) in this compound is revealed by the Raman spectra and the ab initio calculations. No polymer phase was retrieved on release from the highest pressure of 20 GPa in this study.

DFT and surface-enhanced Raman scattering study of tryptophan-silver complex.

Surface-enhanced Raman scattering (SERS) study of tryptophan was carried out in silver hydrosol. The surface adsorption properties of tryptophan were investigated due to its biological importance. Tryptophan is an essential amino acid needed for the normal growth in infants and for nitrogen balance in adults. DFT calculations using B3LYP functional with LANL2DZ basis set was carried out to support the experimental Raman and SERS data. The strong enhancement of 1343 cm(-1) band, assigned to the CO(2) sym. stretching vibration in the SERS spectrum along with a red shift of 63 cm(-1), manifests that chemical mechanism contributes to the SERS activity. Moreover, the observed features in the SERS spectrum as well as theoretical calculations infer that tryptophan is chemisorbed to the silver surface directly through the oxygen and nitrogen atoms of the carboxylate and amino groups with an edge-on orientation with the indole ring lying nearly perpendicular to the silver surface. The SERS enhancement factors for various Raman vibrations of tryptophan were found to be of the order of 10(5)-10(6).

Ring-opening polymerization in carnosine under pressure.

Our high pressure Raman scattering experiments on carnosine, a dipeptide of L-histidine and ß-alanine, show pressure induced ring-opening polymerization involving the imidazole ring. While the onset of polymeric transformation is found to be at ∼2.8 GPa, a substantial fraction of the monomeric solid becomes polymerized by 12 GPa. On release to ambient conditions, the observed Raman spectra do not contain any of the Raman modes of the ambient phase.

Advising families on AD/HD: a multimodal approach.

Nurses who interact with families having children with attention deficit hyperactivity disorder (AD/HD) are perfectly poised to help them understand optimal AD/HD management. While medication can be important in managing AD/HD symptoms, many times it is not a sufficient treatment. A medical examination and a comprehensive neuropsychological or psycho-educational evaluation are important to establish the diagnosis and identify or rule out competing diagnoses and potential co-morbid conditions. A comprehensive evaluation will also lay the groundwork for planning accommodations in school and supports at home that will best facilitate an individual child's learning and development. Nurses can encourage comprehensive evaluations, educate parents about school advocacy, and assist families in understanding ways in which changes in parenting style and the home environment can benefit a child with AD/HD. Nurses can also educate families about the varied professionals and range of resources helpful in managing AD/HD and improving outcomes.

Studies on adsorption of mono- and multi-chromophoric hemicyanine dyes on silver nanoparticles by surface-enhanced resonance Raman and theoretical calculations.

Structural and vibrational properties of mono- and multichromophoric hemicyanine (HC) dyes in solution and adsorbed on silver-coated films have been investigated using optical absorption and resonance Raman scattering techniques, with interpretations aided by theoretical calculations. This is the first report on the Raman spectroscopic studies of multichromophoric HC derivatives. The structure of the monomer, N-propyl-4-(p-N,N-dimethylamino styryl)pyridinium bromide (HC3), and its charged and neutral silver complexes (HC3-Ag) in the ground electronic (S(0)) state were optimized using density functional calculations with the B3LYP method using the 6-31G(*) and LANL2DZ basis sets. The ground state structure of N-hexyl-4-(p-N,N-dimethylamino styryl)pyridinium bromide (HC6) and multichromophoric HC dyes were computed using the HF6-31G(*) method. The negligible shift or broadening observed in the electronic absorption and resonance Raman spectra in solution with increasing size of the HC chromophore suggests that the excitations are localized within individual monomer units in bis and tetra chromophores. However, in the tris chromophore, considerable redshift and broadening were observed, indicating a significant electronic interaction between the nonbonded electrons of the N atom and the aromatic pi-system that is supported by the calculated excitation energies using the time-dependent density functional theory method. The effect of HC dye concentration on the electronic absorption spectra of the silver-coated film showed significant broadening, which was attributed to the formation of H- and J-aggregates in addition to the formation of a metal-molecule complex. A considerable redshift along various vibrations observed in the surface-enhanced resonance Raman scattering (SERRS) spectra of the HC derivatives indicates that adsorption on the silver surface leads to a considerable interaction of the electron rich moiety of HC derivatives with the silver surface. The enhancement of various in-plane and out-of-plane vibrations, along with slight broadening and redshifts observed in the SERRS spectra, suggests that binding of the HC dyes to the silver surface occurs through the aromatic pi-system attached to the electron rich dimethylamino group, with the ring lying almost parallel to the silver surface. Theoretical results have further indicated adsorption via chemisorption for the charged HC3-Ag complexes and by physisorption for the neutral HC3-Ag complexes.