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We present the first scanning tunneling microscopy (STM) study of the deposition of mass-selected silver clusters (Agn,n=1, 2, 3) on a rutile TiO2(110)-1×1 surface at room temperature under hard-landing conditions. Under hard-landing conditions, only small features are observed on the surface in all cases without sintering or surface damage. This suggests that the high impact energy of the clusters mainly dissipates as thermal energy in the substrate, resulting in the recovery of any initial impact-induced surface damage and the formation of bound clusters on the surface near the impact point. STM images indicate that Ag1 binds on the bridging oxygen rows twice as often as on the Ti rows. Density-functional Theory (DFT) calculations are consistent with Ag1 binding at either bridging oxygen vacancies or with two adjacent bridging oxygen atoms in the same bridging oxygen row. STM images of Ag2 and Ag3 depositions indicate almost exclusive binding centered on the Ti-atom rows. DFT calculations suggest that the Ag2 and Ag3 clusters are bound between two bridging oxygen rows, which is consistent with the STM observations. [ABSTRACT FROM AUTHOR]

Mass-selected Agn+ (n=1,2,3) clusters with impact energy less than 2 eV per atom were deposited from the gas phase onto rutile titania (110)-(1×1) single crystal surfaces at room temperature and imaged using ultra-high vacuum scanning tunneling microscopy. Upon reaching the surface, Ag monomers sintered to form three-dimensional islands of approximately 50 atoms in size, with an average measured height of 7.5 Å and diameter of 42 Å. This suggests that the monomers are highly mobile on the titania surface at room temperature. Dimers also sintered to form large clusters upon deposition, approximately 30 atoms in size, with an average height of 6.2 Å and diameter of 33 Å. Clusters formed from monomer deposition appeared approximately three times more frequently at step edges than clusters formed from dimer deposition, indicating that the surface mobility of deposited monomers is higher than that of deposited dimers. In sharp contrast to the deposition of monomers and dimers, the deposition of trimers resulted in a high density of very small clusters on the order of a few atoms in size, indicative of intact trimers on the surface, implying that deposited trimers have very limited mobility on the surface at room temperature. [ABSTRACT FROM AUTHOR]

The structure of small carbon cluster anions, [C.sub.pi.sup-] (4 [lesser than] 20), was investigated with the use of ion chromatography. With this technique, both the existence and the relative amounts [...]

Ion mobility spectrometry-mass spectrometry (IMS-MS) is used to study the rigid rectangular, triangular, and prismatic supramolecular assemblies in the complexes of anthracene, phenanthrene and cyclobutadienecyclopentadienylcobalt based on dipyridyl ligands and square planar platinum coordination. The obtained results confirmed the utility of IMS-MS methods for characterization self-assembled complex structures when X-ray or other spectroscopic structures are not available.

Ion mobility spectrometry mass spectrometry (IMS-MS) is used to provide evidence for at least one very stable conformation of a truncated form of recombinant cellular prion protein (Pr[P.sup.C]) consisting of residues 90-231, which resists unfolding in the absence of solvent at high injection energies and at temperatures in excess of 600 K. The first absolute collision cross sections measured for recombinant Syrian hamster prion protein PrP(90-231) is also reported.

Combination of ion mobility spectrometry-mass spectrometry (IMS-MS) and replica exchange molecular dynamics (REMD) are used to examine the monomeric and oligomeric structures of normal prion protein PrP106-126 and two nonaggregating forms of the peptide. The data obtained suggested that the oligomerization observed only for the normal peptide and not for the oxidized peptide resulted from the association of ordered [beta]-hairpin monomers rather than disordered monomers.

The structural features of the human islet amyloid polypeptide (IAPP) monomer are probed by using a combination of ion mobility mass spectrometry (IMS-MS) and all-atom replica exchange molecular dynamics (REMD) simulations. The studies have provided evidence of a significant population of [beta]-hairpin conformers for the IAPP peptide.

The hydration of the protonated aromatic amino acids phenylalanine, tryptophan, and tyrosine are analyzed by using a mass spectrometer equipped with a drift cell to examine the sequential addition of individual water molecules. The studies have shown that both the ammonium and carboxyl groups have offered good water binding sites for the first water molecule, whereas subsequent water molecules are bound less strongly.

The combination of nanoelectrospray ionization mass spectrometry with ion mobility measurements were used to find evidence for a highly compact partially folded family of structures for [alpha]-synuclein protein implicated in Parkinson's disease (PD) and its disease-related A53T mutant with net charges of -6, -7, and -8. The mass spectral results showed that spermine complexation might induce oligomerization of [alpha]-syn by effectively binding to an extended conformation and rearrangement to more compact form by lowering the net charge from -10 to -6.

G-rich DNA sequences containing mixtures of linking bases was employed as model to predict the structure and stability of particular G-quadruplex forming sequences. The results revealed that when the loop length increases, the quadruplex conformations exhibited more intramolecular and antiparallel assemblies.

The interaction of the cyclic nonapeptide oxytocin (OT) with a number of alkaline earth and divalent transition metal ions ([X.sup.2+]) is examined by using mass spectrometry (MS) and ion mobility spectrometry (IMS) techniques. The studies have shown that under acidic conditions OT has displayed a strong affinity for all divalent metal ions resulting in strong [[OT + X].sup.2] peaks in the mass spectrum.

Different spectrometric methods were used to examine the intrinsic stabilization of folded G-quadruplexes and study different DNA sequences. It was found that G-quadruplex intramolecular folds are stabilized by N[H.sub.4.sup.+] cations and the ligands listed.

The intermolecular interactions in biochemical systems are examined by using mass spectrometric techniques. The interactions between biomolecules and solvent molecules, nucleic acid molecules are studied.

A mixture of islands and atomic features is observed at a landing energy of 20(plusmn)3.5eV, suggesting a critical energy above which pinning occurs. The observations suggest a mechanism in which high-energy collision leads to the annealing of any impact-created surface damage and the pinning of Au atoms to the surface.

Ion mobility mass spectrometry (IM-MS) is used to probe the structure of three metal complexes carrying pendant chromospheres, the copper(II) complex Cu(DAC)(super 2+), theN-nitrosylated ligand DAC-NO and the Roussin's red salt ester (PPIX-RSE). The Cu complex exists as a single conformer, DAC-NO has two conformations and the PPIX-RSE structure exhibits two bent conformations with the planes of the porphyrin and the Fe2S2 rings at different angles with respect to each other.

Ultrahigh vacuum (UHV) scanning tunneling microscopy (STM) is used to image the shape and size of the Au(sub n)(super +) clusters (n=1-8) deposited with low kinetic energy on a single crystal rutile TiO2(110)-(1*1) surface at room temperature. The importance of cluster-surface ligation is supported by the fact that the STM images observed were stable over several days and did not change with repeated scans by the STM tip.

The global structures of gas-phase silver cation clusters could be obtained from temperature-dependent equilibrium data that are consistent with theory. The method is sensitive to ligand-induced changes in bare cluster conformations, and results could be fine-tuned by changing ligands and, hence, ligand-binding energies.

The metal binding properties of the dinucleotide duplex, dCG.dCG, were analyzed in the gas phase with ion mobility mass spectrometry. It is shown that only Cu(super +), Ag(super +), Cu(super 2+), Zn(super 2+), Cd(super 2+), and Pt(super 2+) stabilize the Watson-Crick structure of dCG.dCG to form a globular structure.

Mass spectrometry and ion mobility is applied to the study of A(beta)42 and its Pro(super 19) alloform. Unfiltered solutions of A(beta)42 produce only monomers and large oligomers, whereas [Pro(super 19)]A(beta)42 solutions produce abundant monomers, dimers, trimers, and tetramers but no large oligomers.