(S)-2-[(2-Hy-droxy-benz-yl)aza-nium-yl]-4-(methyl-sulfan-yl)butano-ate.

The zwitterionic title compound, C(12)H(17)NO(3)S, is a reduced Schiff base derived from (S)-N-(2-hy-droxy-benzyl-idene)methio-nine. An intra-molecular inter-action between the N-H and carboxyl-ate groups forms a roughly planar (r.m.s. deviation = 0.1405 Å) five-membered ring containing the H(N), N, Cα, C(carboxyl-ate) and O atoms in a penta-gonal conformation. In the crystal, a supra-molecular triangle-shaped motif is generated by mol-ecules held together by O-H⋯O and N-H⋯O hydrogen bonds.

7-Amino-2-methylsulfanyl-1,2,4-triazolo[1,5-a]pyrimidine-6-carboxylic acid as the dimethylformamide and water monosolvates at 293†K.

The molecular structure of 7-amino-2-methylsulfanyl-1,2,4-triazolo[1,5-a]pyrimidine-6-carboxylic acid is reported in two crystal environments, viz. as the dimethylformamide (DMF) monosolvate, C(7)H(7)N(5)O(2)S·C(3)H(7)NO, (I), and as the monohydrate, C(7)H(7)N(5)O(2)S·H(2)O, (II), both at 293 (2) K. The triazolo[1,5-a]pyrimidine molecule is of interest with respect to the possible biological activity of its coordination compounds. While the DMF solvate exhibits a layered structural arrangement through N...O hydrogen-bonding interactions, the monohydrate displays a network of intermolecular O...O and N...O hydrogen bonds assisted by cocrystallized water molecules and weak π-π stacking interactions, leading to a different three-dimensional supramolecular architecture. Based on results from topological analyses of the electron-density distribution in X-H...O (X = O, N and C) regions, hydrogen-bonding energies have been estimated from structural information only, enabling the characterization of hydrogen-bond graph energies.

The interaction of native DNA with Zn(II) and Cu(II) complexes of 5-triethyl ammonium methyl salicylidene orto-phenylendiimine.

The interaction of native calf thymus DNA with the Zn(II) and Cu(II) complexes of 5-triethyl ammonium methyl salicylidene orto-phenylendiimine (ZnL(2+) and CuL(2+)), in 1 mM Tris-HCl aqueous solutions at neutral pH, has been monitored as a function of the metal complex-DNA molar ratio by UV absorption spectrophotometry, circular dichroism (CD) and fluorescence spectroscopy. The results support for an intercalative interaction of both ZnL(2+) and CuL(2+) with DNA, showing CuL(2+) an affinity of approximately 10 times higher than ZnL(2+). In particular, the values of the binding constant, determined by UV spectrophotometric titration, equal to 7.3x10(4) and 1.3x10(6)M(-1), for ZnL(2+) and CuL(2+), respectively, indicate the occurrence of a marked interaction with a binding size of about 0.7 in base pairs. The temperature dependence of the absorbance at 258 nm suggests that both complexes strongly increase the DNA melting temperature (Tm) already at metal complex-DNA molar ratios equal to 0.1. As evidenced by the quenching of the fluorescence of ethidium bromide-DNA solutions in the presence of increasing amounts of metal complex, ZnL(2+) and CuL(2+) are able to displace the ethidium cation intercalated into DNA. A tight ZnL(2+)-DNA and CuL(2+)-DNA binding has been also proven by the appearance, in both metal complex-DNA solutions, of a broad induced CD band in the range 350-450 nm. In the case of the CuL(2+)-DNA system, the shape of the CD spectrum, at high CuL(2+) content, is similar to that observed for psi-DNA solutions. Such result allowed us to hypothesize that CuL(2+) induces the formation of supramolecular aggregates of DNA in aqueous solutions.

The dynamics of 57Fe nuclei in Fe(II)-DNA and [Fe(II)(1-methyl-2-mercaptoimidazole)2]-DNA condensates.

Alcoholic solutions of FeCl(2) and Fe(II)(Hmmi)(2)Cl(2) (Hmmi=1-methyl-2-mercaptoimidazole) induce calf thymus DNA condensation from aqueous solutions buffered at pH 7.4. A 1:1 Fe(II)-(DNA monomer) stoichiometry is assumed. The (57)Fe Mössbauer hyperfine parameters suggest an octahedral coordination environment, severely distorted, in both Fe(II)-(DNA monomer) and [Fe(II)(Hmmi)(2)]-(DNA monomer) condensates. The dynamic properties of iron nuclei in freeze-dried samples were investigated by means of variable temperature (57)Fe Mössbauer spectroscopy. Mean square displacements, (T), were calculated, such as the effective vibrating mass and the Mössbauer lattice temperature of the solids. increases linearly with the temperature in the whole temperature range explored; the absolute values are typical for lattice or solid-state vibrations. Very similar values for the effective vibrating masses were extracted, suggesting comparable covalency of the bonding interaction between the metal atom and its ligands, while the Mössbauer lattice temperatures show a softening of the lattice for [Fe(II)(Hmmi)(2)]-(DNA monomer) with respect to Fe(II)-(DNA monomer) condensate.

The interaction of native DNA with iron(III)- N ,N'-ethylene-bis(salicylideneiminato)-chloride.

The interaction between native calf thymus deoxyribonucleic acid (DNA) and Fe(III)- N ,N'-ethylene-bis (salicylideneiminato)-chloride, Fe(Salen)Cl, was investigated in aqueous solutions by UV-visible (UV-vis) absorption, circular dichroism (CD), thermal denaturation and viscosity measurements. The results obtained from CD, UV-vis and viscosity measurements exclude DNA intercalation and can be interpreted in terms of an electrostatic binding between the Fe(Salen)(+) cation and the phosphate groups of DNA. The trend of the UV-vis absorption band of the Fe(Salen)Cl complex at different ratios [DNA(phosphate)]/[Fe(Salen)Cl] and the large increase of the melting temperature of DNA in the presence of Fe(Salen)Cl, support the hypothesis of an external electrostatic interaction between the negatively charged DNA double helix and the axially stacked positively charged Fe(Salen)(+) moieties, analogously to what reported for a number of porphyrazines and metal-porphyrazine complexes interacting with DNA.

The dynamics of (57)Fe nuclei in Fe(III)-DNA condensates.

The dynamics of iron nuclei in the condensates obtained by interaction of Fe(III) with DNA, Fe(III)(DNA monomer)(2), have been investigated by variable temperature (57)Fe Mössbauer spectroscopy. Studies were effected on gel and freeze-dried samples, obtaining nearly coincident values of the parameters isomer shift and nuclear quadrupole splitting in T ranges 20-260 K. Functions ln(A(T)/A(77.3)) vs. T, here employed to investigate the dynamics of Fe nuclei, showed linear trends in the T ranges 20-150 and 150-260 K, respectively, the latter with larger slopes. Data coincided for gelled and freeze-dried specimens. No variation of delta or Delta E parameters occurred at the two T intervals, which suggests constancy of structure and bonding with the temperature changes. Functions (T) showed trends analogous to the corresponding functions determined for iron proteins, which were attributed to the occurrence of 'conformational substates'.

Synthesis, characterization, crystal structures and in vitro antistaphylococcal activity of organotin(IV) derivatives with 5,7-disubstituted-1,2,4-triazolo[1,5-a]pyrimidine.

New organotin(IV) complexes of 5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine (dbtp) and 5,7-diphenyl-1,2,4-triazolo[1,5-a]pyrimidine (dptp) with 1:1 and/or 1:2 stoichiometry were synthesized and investigated by X-ray diffraction, FT-IR and (119)Sn Mössbauer in the solid state and by (1)H and (13)C NMR spectroscopy, in solution. Moreover, the crystal and molecular structures of Et(2)SnCl(2)(dbtp)(2) and Ph(2)SnCl(2)(EtOH)(2)(dptp)(2) are reported. The complexes contain hexacoordinated tin atoms: in Et(2)SnCl(2)(dbtp)(2) two 5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine molecules coordinate classically the tin atom through N(3) atom and the coordination around the tin atom shows a skew trapezoidal structure with axial ethyl groups. In Ph(2)SnCl(2)(EtOH)(2)(dptp)(2) two ethanol molecules coordinate tin through the oxygen atom and the 5,7-diphenyl-1,2,4-triazolo[1,5-a]pyrimidine molecules are not directly bound to the metal center but strictly H-bonded, through N(3), to the OH group of the ethanol moieties; Ph(2)SnCl(2)(EtOH)(2)(dptp)(2) has an all-trans structure and the C-Sn-C fragment is linear. On the basis of Mössbauer data, the 1:2 diorganotin(IV) complexes are advanced to have the same structure of Et(2)SnCl(2)(dbtp)(2), while Me(2)SnCl(2)(dptp)(2) to have a regular all-trans octahedral structure. A distorted cis-R(2) trigonal bipyramidal structure is assigned to 1:1 diorganotin(IV) complexes. The in vitro antibacterial activities of the synthesized complexes have been tested against a group of reference pathogen micro-organisms and some of them resulted active with MIC values of 5µg/mL, most of all against staphylococcal strains, which shows their inhibitory effect.

DFT calculations of the electric field gradient at the tin nucleus as a support of structural interpretation by 119Sn Mössbauer spectroscopy.

DFT calculations, using an all-electron basis set and with full geometry optimization, were performed on 34 Sn(II) and Sn(IV) compounds of known structure and (119)Sn Mössbauer parameters, to obtain the theoretical values of the electric field gradient components, V(xx), V(yy), and V(zz), at the tin nucleus. These were used to determine the quantity V = V(zz)[1+ 1/3((V(xx) - V(yy))/((V(zz))(2)](1/2), for each investigated compound, which is related to the quadrupole splitting (DeltaE) parameter according to DeltaE = 1/2eQV, where e is the electronic charge and Q is the quadrupole moment of the tin nucleus. The linear fitting of the correlation plot of the experimental DeltaE, versus the corresponding calculated V values, produced a slope that is equal to 0.93 +/- 0.03 and a correlation coefficient R = 0.982. The value of Q obtained, 15.2 +/- 4.4 fm(2), is in agreement with that previously experimentally determined or calculated by analogous procedures. The calculation method is able to establish the sign of the electric field gradient component V(zz), in agreement with the sign of DeltaE determined experimentally by Mössbauer-Zeeman spectroscopy. The calculated structural parameters are in good agreement with the corresponding experimental data, determined by X-ray crystallography in the solid state, with average structural deviations of about 3 % for bond lengths and angles in the tin environment. Calculated values of DeltaE were obtained from the calibration fitting constant and from the values of V. By comparing experimental and calculated DeltaE parameters, the structure assignment of configurational isomers was successful in two test cases, in agreement with the experimental X-ray crystallographic structures. These results indicate that the method can be used as a tool to support the routine structure interpretation of tin compounds by (119)Sn Mössbauer spectroscopy.