The Weierstrass semigroup of a pair and moduli inM 3

We classify all the Weierstrass semigroups of a pair of points on a curve of genus 3, by using its canonical model in the plane. Moreover, we count the dimension of the moduli of curves which have a pair of points with a specified Weierstrass semigroup.This work has been supported by the Japan Society for the Promotion of Science and the Korea Science and Engineering Foundation (Project No. 976-0100-001-2). Also the first author is partially supported by Korea Research Foundation Grant (KRF-99-005-D00003).     

Supramolecular assembly of biphenyl dicarboxylic acid on Au(1 1 1)

We investigate the structure of submonolayer film of 4,4′-biphenyl dicarboxylic acid (BDA) molecules on Au(1 1 1)-22 × √3 reconstructed surface with the use of scanning tunneling microscopy (STM). The BDA molecules form ordered structures on Au(1 1 1) surface which are commensurate with the substrate. We have concluded that the molecule-molecule interaction is mainly through hydrogen bonding formed by a straight dimer of BDA molecules. The straight dimer can be expressed as 4s + 2t or its six crystallographic equivalents using the unit vectors of the gold substrate of s and t. The length of hydrogen bonding (O-H-O) is estimated to be 0.31 nm assuming nearest neighbor distance of gold atoms of 0.275 nm. The ordering shows a clear contrast with the case of BDA on Cu(1 0 0) surface [S. Stepanow, N. Lin, F. Vidal, A. Landa, M. Ruben, J.V. Barth, K. Kern, Nanoletters 5 (2005) 901] in which a square type of ordering of molecules is observed by the formation of hydrogen bonding between a carboxylate (COO) and a benzene ring. The clear difference of the ordered structure on Cu(1 0 0) and Au(1 1 1) surface demonstrates that the absence (presence) of deprotonation of carboxyl group of BDA molecule on Au(1 1 1) (Cu(1 0 0)) switches the straight and square type ordering of BDA molecules.     

Intrinsic acid-base properties of purine derivatives in aqueous solution and comparison of the acidifying effects of platinum(II) coordinated to N1 or N7: acidifying effects are reciprocal and the proton "outruns" divalent metal ions

The effect of Pt(2+) coordination, in particular of (dien)Pt(2+) or cis-(NH(3))(2)Pt(2+), on the acid-base properties of the purine ligands 9-ethylguanine (9EtG), 9-methylhypoxanthine (9MeHx), inosine (Ino), 9-methyladenine (9MeA), and N6',N6',N9-trimethyladenine (TriMeA) is quantitatively evaluated. The corresponding acidity constants of the complexes are calculated by curve-fitting procedures using previously published (1)H NMR shift data which had been measured in aqueous solution (D(2)O) in dependence on pH (pD). Comparison of the pK(a) values of the ligands with those of the Pt(2+) complexes reveals the expected behavior for the (N7)-platinated complexes; i.e., the (N1)H(0/+) sites are acidified due to charge repulsion. However, Pt(2+) coordination at (N1)(-)(/0) sites leads to an (already previously observed) apparent increase in the basicity of the N7 sites for the guanine, hypoxanthine, and adenine residues; this is also the case if Pt(2+) is bound to N3. Coordination of Pt(2+) to both the (N1)(-) and N7 sites of 9EtG results apparently in an enhanced basicity of N3 if compared with the release of the proton from the (N3)H(+) site in H(2)(9EtG)(2+). For the former cases in aqueous solution (H(2)O) it is now proven for a comprehensive set of data (seven examples), by taking into account the intrinsic basicities of the various N7 sites via micro acidity constants, that the acidifications are reciprocal and identical. This means Pt(2+) coordinated to (N1)(-)(/0) sites in guanine, hypoxanthine, or adenine residues acidifies the (N7)H(+) unit to the same extent as (N7)-coordinated Pt(2+) acidifies the (N1)H(0/+) site. In other words, the apparently increased basicity of N7 upon Pt(2+) coordination at (N1)(-)(/0) sites disappears if the micro acidity constants of the appropriate isocharged tautomers of the ligand are properly taken into account. It is further proven, on the basis of the evaluations of the nucleotide analogue 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA), that these given conclusions are also valid for nucleotides. In addition, it is shown that the mentioned apparent basicity increase, which results from the use of macro acidity constants, has its origin in the fact that the proton-metal ion (Pt(2+)) interaction (the extent of which depends on the kind of metal ion involved) is less pronounced than the proton-proton interaction. Finally, the proven reciprocal behavior will now allow one to determine micro acidity constants of ligands by studying complexes formed with kinetically inert metal ions. A further result of interest is the proof that the competition of Pt(2+) (or Pd(2+)) with the proton for the (N1)(-) and N7 binding sites of inosinate results in the isomer where the metal ion is at N7 with the proton relegated to (N1)(-); this isomer is favored by a factor of about 2000 compared with the one having the metal ion at (N1)(-) and the proton at N7.     

Narrow photoemission peak at the Fermi level in Fe/Cu(111)

We have studied electronic states of Fe adatoms deposited on Cu(111) by photoemission spectroscopy and have found a narrow peak at the Fermi level in the Fe 3d spectral function. The Fe 3d spectral function would be consistent with the Anderson impurity model, which has been widely used for the interpretation of bulk Ce and Yb compounds. This result indicates a strong reduction of hybridization between the Fe 3d state and the conduction-band states and an enhancement of effective Coulomb interaction for the Fe 3d electrons in an Fe adatom on Cu(111).     

Theoretical investigation of the molecular structures and excitation spectra of triphenylamine and its derivatives

The molecular geometries, electronic structures, and excitation energies of NPh(3), NPh(2)Me, NPhMe(2), and NMe(3), were investigated using DFT and post-Hartree Fock methods. When the structural stabilities of these compounds were compared to results obtained by using MP4(SDQ) method, it was confirmed that the optimized geometries by using MP2 method were sufficiently reliable. The excited states with large oscillator strengths consisted of transition components from the HOMO. It should be noted that the orbitals of the nitrogen atom mix with the π-orbital of the phenyl group in an anti-bonding way in the HOMO, and the orbital energy increases with this mixing. The unoccupied orbitals are generated from bonding and anti-bonding type interactions between the π-orbitals of the phenyl groups; therefore, the number of phenyl groups strongly affects the energy diagram of the compounds studied. The differences in the energy diagram cause a spectral change in these compounds in the ultraviolet region.