Metal-support interactions in systems of dispersed metals supported on thin-film silica surfaces were examined by x-ray photoelectron spectroscopy. Four metal-silica systems -Pt-, Pd-, Ag-and Au-SiO 2 -all indicated the formation of partially reduced Si(IV) species by the metal deposition. The extent of the reduction varied little with the kind or amount of deposited metal species. On the other hand, the amount of this newly formed Si(IV-d) indicated a strong metal species dependence.

The array structure of aqueous-phase-adsorbed cytosine, a DNA base, on a cleaved natural zeolite heulandite (010) surface was examined in situ by contact-mode atomic force microscopy (AFM). The adsorbed cytosine molecules formed a well-ordered two-dimensional sixfold array on the surface, with the rhombic unit cell dimension being 0.58 nm. Computer graphics representation of the adlayer molecules shows a possibility of the molecules being adsorbed with their pyrimidine ring plane tilted from the surface parallel.Atomic force microscopy (AFM) enables us to observe nonconductive solid surfaces under various environments, including liquid phases, with the resolution high enough to provide images of surface-adsorbed molecules. Here we used AFM to examine, in situ, the structure of a cytosine layer adsorbed from its aqueous solution on a cleaved (010) surface of a natural zeolite heulandite.Zeolites are naturally occurring crystalline aluminosilicate minerals that commonly consist of SiO 2 , Al 2 O 3 , H 2 O, Na 2 O, K 2 O, and CaO. They crystallize into various crystallographic structures, and hence there are numerous natural as well as synthetic zeolites. They are found to adsorb various chemical species and to catalyze various reactions, and are extensively used as adsorbents and catalysts in the chemical industry.Recently we successfully obtained atom-resolved AFM images of natural zeolite surfaces, stilbite(010) and heulandite(010), and in situ molecular images of liquid-phaseadsorbed pyridine and picolines (pyridine bases) on these surfaces [1][2][3][4]. From these AFM data we were able to determine the array and orientation structures of the adsorbed molecules. The present paper examines cytosine adsorption on a zeolite surface. The choice of cytosine as an adsorbate is a natural extension from our previous examinations of pyridine bases that contain one nitrogen atom in each of their rings, to pyrimidine ring systems that contain two N atoms each. Aqueous-phase adsorption and self-assembly of cytosine on a natural mineral surface are also interesting, because cytosine is one of the deoxyribonucleotides that constitute DNA chains. Several scanning probe microscopy (SPM) studies on DNA base molecule adsorption have been performed over different substrates. Allen et al. [5, 6] examined the adsorption of adenine and thymine on heated graphite surfaces by scanning tunneling microscopy (STM) and AFM under ambient conditions. Srinivasan et al. [7] examined electrochemically deposited adenine on HOPG with in situ STM. Freund et al. [8] examined molecular-beam-deposited adenine film on graphite surfaces with ultrahigh-vacuum (UHV) STM and force-field calculations. Tanaka et al. [9-11] examined adenine on Si(100)2 × 1, and four deoxyribonucleotides (adenine, guanine, thymine, and cytosine) on SrTiO 3 (100) and Pd(110) under UHV conditions.On the graphite surfaces those studies found ordered structures that consist of hydrogen-bonded dimers. Over Si and SrTiO 3 , adsorption of isolated molecules is indicated. In most of ...

For the first time the array structure of liquid-phase-adsorbed aromatics on a zeolite surface was determined, and the molecular orientation within the adsorbed phase was estimated. Pyridine molecules adsorbed on a cleaved heulandite(010) surface from an aqueous solution were imaged with a contact-mode atomic force microscope. The adsorbed pyridine molecules formed a well-ordered two-dimensional (2D) hexagonal array on the surface, with the rhombic unit cell dimension being 0.55 nm. The molecular plane is found to be tilted, with the estimated tilt angle being ca. 43°to the surface. The ring plane also makes an estimated angle of ca. 20°with respect to one of the 2D lattice vectors of the adsorbed pyridine unit cell.