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Structures and spectra are calculated for Sin and Sin−Gly (n = 3−5) complexes. Relative stability differences of Gly conformers are magnified by interactions with the Sin cluster, so that one conformer of Sin−Gly is stabilized. Significant charge transfer occurs from the amino group in Gly to a Si atom in the cluster. Interactions with Gly are predicted to shift the excitation energies of Sin significantly to the blue to 2.1−2.7 eV, although they are still lower than in a Si cluster passivated by hydrogen. [ABSTRACT FROM AUTHOR]

We present density functional theory (DFT) and time-dependent DFT (TD-DFT) study of the structures and electronic spectra of small CdSe nanocluster-adenine complexes CdnSen−adenine (n= 3, 6, 10, 13). We examine the changes in the geometries and excitation spectra of the nanoclusters induced by DNA base-binding. By comparing the results calculated for the bare (CdnSen), hydrogen-passivated (CdnSenH2n), as well as the corresponding adenine (Ade)-bound clusters (CdnSen−Ade, CdnSenH2n−Ade, CdnSenH2n−2−Ade), we find that binding with Ade slightly blue-shifts (up to 0.18 eV) the electronic excitations of bare nanoclusters but strongly red-shifts (<1.2 eV) those of hydrogen-passivated nanoclusters. Natural bond orbital analysis shows that the LUMO of CdnSenH2n−Ade is a π* orbital located on the purine ring. [ABSTRACT FROM AUTHOR]

We present density functional theory (DFT) structures and time-dependent DFT electronic excitation energies of several small CdSe nanoclusters with the composition CdnSen(n= 3, 6, 10, 13). We examine the effects on the geometries and excitation spectra of the nanoclusters induced by two chemical changes: peptide-binding and ligand passivation. We use cysteine (Cys) and cysteine-cysteine dipeptide (Cys−Cys) as model peptides and hydrogen atoms as surface-bound solvent ligands (or stabilizing agents). By comparing the results calculated for bare, hydrogen-passivated (CdnSenH2n), as well as the corresponding Cys- and Cys−Cys- bound clusters (CdnSen−, CdnSenH2n, −Cys, −Cys−Cys), we find that peptide-binding blue shifts the electronic excitations of bare nanoclusters, but red shifts those of hydrogen-passivated nanoclusters. The carboxyl oxygen and the sulfur atom tend to form a four-centered ring with adjacent two Cd atoms when the CdSe cluster forms covalent bonds with Cys or Cys−Cys. Further, this type of bonds may be distinguishable by significant red shifts of the excitation energies. [ABSTRACT FROM AUTHOR]