The adsorption of water on a fully hydroxylated silica surface is studied by using density-functional total-energy and molecular dynamics calculations. The (100) surface of beta(alpha)-cristobalite covered by geminal hydroxyls has been taken as the substrate. A well-ordered and stable two-dimensional ice with quadrangular and octagonal patterns of hydrogen bond (H-bond) networks-an ice tessellation-is found on the surface for the first time. With the vibrational recognition, the four water molecules in the quadrangle are found to be bonded by strong H bonds while the quadrangles are connected to each other by weak H bonds. This configuration is the most stable, because all the water molecules are fully saturated with H bonds either to each other or to the surface hydroxyl groups.

The adsorption of water on Pt(111) surface has been studied with ab initio molecular dynamics simulation. Both the energetics and vibrational dynamics indicate the existence of a well-ordered molecular bilayer on this surface. This conclusion is in contrast to the recent result of water on Ru(0001) surface, but agrees with available experiments. In addition, our calculation identifies two different hydrogen bonds in the bilayer. Both can be directly recognized from the vibrational spectra of the OH stretch modes.

We present an ab initio investigation of water adsorption on ordered hydroxylated silica surfaces, using the density functional theory within the ultrasoft pseudopotentials and generalized-gradient approximation. The ͑100͒ and ͑111͒ surfaces of the hydroxylated cristobalite are used as substrates to adsorb water clusters and overlayers. Water adsorbs through hydrogen bonds formed between water and surface hydroxyl groups on the ␤͑␣͒-cristobalite ͑100͒ surface. A large enhancement of the hydrogen bonding in the adsorbed water dimer is observed, which can be inferred from the shortened hydrogen-bond ͑H bond͒ length, the vibrational spectra from the molecular dynamics simulation and the redistribution of electron density. At one monolayer ͑ML͒ coverage, a "tessellation ice," with characteristic quadrangular and octagonal hydrogen-bonded water rings, is formed. It has two types of H bonds and can exist on two different adsorption sites with two different OH orderings in a surface supercell. Our study is further extended to the ␤-cristobalite ͑111͒ surface. Based on these studies, we find that the water-silica bond, which comprises several H bonds, is usually stronger than other associative water-surface interactions. The H bonds between water and surface usually differ in strength-and hence, in vibrational spectra-from those between adsorbed water molecules. Because the ͑100͒ and ͑111͒ surfaces sustain different silanol groups ͑geminal and isolated silanols͒, a well-defined twodimensional tessellation ice phase can be observed only on the cristobalite ͑100͒ surface. On ␤-cristobalite ͑111͒ surface, however, isolated water molecules, hydrogen-bonded to the surface hydroxyls, are formed, even at 1 ML coverage.

Two new polycyclic tetramate macrolactams, lysobacteramides A (1) and B (2), together with HSAF (heat-stable antifungal factor, 3), 3-dehydroxy HSAF (4), and alteramide A (5) were isolated from a culture of Lysobacter enzymogenes C3 in nutrient yeast glycerol medium. Their structures were determined by MS and extensive NMR analysis. The absolute configurations of 1-5 were assigned by theoretical calculations of their ECD spectra. Although HSAF and analogues were reported from several microorganisms, their absolute configurations had not been established. The isolation and the absolute configurations of these compounds revealed new insights into the biosynthetic mechanism for formation of the polycycles. Compounds 1-4 exhibited cytotoxic activity against human carcinoma A549, HepG2, and MCF-7 cells with IC50 values ranging from 0.26 to 10.3 μM. Compounds 2 and 3 showed antifungal activity against Fusarium verticillioides with IC50 value of 47.9 and 6.90 μg/mL, respectively.