Search

Metallobacitracins are complexes with an extensive antimicrobial and biological activity. In this work, we investigated the metal complexation of bacitracin with several divalent metal ions in aqueous solution. The binding constants of Zn(2+), Cd(2+), Hg(2+), Cu(2+), Ni(2+), Pd(2+), Fe(2+), Mn(2+) and Mg(2+) to bacitracin were measured by UV/Vis spectroscopy, isotermic titration calorimetry (ITC) and potentiometry while the complexes were studied by Circular Dichroism and Nuclear Magnetic Resonance (15N HSQC) for Zn(2+), Cd(2+) and Hg(2+) at different pH. By UV/Vis spectroscopy the affinity is in the range 104 to 105 M−1 at pH 6 and follows the order Ni(2+) > Cd(2+) > Hg(2+) > Zn(2+) > Fe(2+). By potentiometry, the binding constants were determined in the pH range 2–12. Microcalorimetry shows that the stoichiometry of metallobacitracins investigated is 1:1 with binding constants in the range 105–102 M−1 at pH 6 and with an order of stability of Ni(2+) > Cd(2+) > Zn(2+) > Hg(2+); ΔS, ΔH and ΔG parameters were also determined. NMR spectroscopy lets us establish the binding site of the metal ion when comparing 15N HSQC of free bacitracin and complex in natural abundance; these findings agree with calorimetric results. Chemical shift changes in complexes containing Zn(2+) and Cd(2+) exhibit a similar behavior despite pH differences. Conversely, there is not a significant change for Hg(2+) complex. The obtained data contribute to understand the mechanism of the biological activity of the metallobacitracins and give the guideline for the design of more powerful metalloantibiotics.

Two new chlorodiorganotin(IV) dithiocarbamate complexes with general formula {(R2SnCl)dtc} (dtc = R1R2NCS2−, R1 = Bn, R2 = naphtylimide; 3, R = n-Bu; 4, R = Ph) have been prepared from sodium N-[2-(benzylamino)ethyl]naphthalene-1,8-dicarboximide dithiocarbamate 2. The bis-dithiocarbamete 3d (R2Sn(dtc)2, R = n-Bu) was obtained as the thermodynamic product during the titration process (vide infra). All compounds were characterized by mass spectrometry, IR, 1H and 13C NMR spectroscopy. The chlorodiorganotin(IV) dithiocarbamate complexes 3–4 also were characterized by 119Sn NMR spectroscopy and single crystal X-ray diffraction analysis. The crystallographic study of these complexes showed the existence of C H…π, S…π and π…π intramolecular interactions, indicating that the naphthylimide aromatic fragment stabilized the complexes. Complexes 3 and 4 were studied as host for anions (CH3CO2−, F−, H2PO4−) in CDCl3 by UV–Vis and 119Sn NMR spectrometric titrations. The tested anions cause the displacement of the chloride ligand of the metallic centre. The excess of F− or H2PO4− induce the self-assembly of diorganotin(IV) dithiocarbamate to bis-dithiocarbamates R2Sn(dtc)2 (3d) instead of the breaking of the S Sn covalent bond. Quantum mechanical calculations at DFT level (B3LYP/def2-TZVP) were performed to obtain the thermodynamic parameters of the reactions involved in the anion addition to the complexes.

Phase relations in the pseudo-binary systems RFeO 3 -R 2 Ti 2 O 7 (R: Lu, Ho and Dy), RGaO 3 -R 2 Ti 2 O 7 (R: Lu and Er), LuAlO 3 -Lu 2 Ti 2 O 7 and RAO 3 -R 2 Ti 2 O 7 (R: Lu and Yb. A: Cr and Mn) at elevated temperatures in air were determined by means of a classic quenching method. There exist Lu(Fe 1−x Ti x )O 3+x/2 , R(Ga 1−x Ti x )O 3+x/2 (R: Lu and Er) and Lu(Al 1−x Ti x )O 3+x/2 (2/3≤ x≤3/4) having the Yb(Fe 1−x Ti x )O 3+x/2 -type of crystal structure (x=0.72, space group: R 3 m , a(A)=17.9773 and c(A)=16.978 as a hexagonal setting) in these pseudo binary systems. Eighteen compounds R(A 1−x Ti x )O 3+x/2 (R: Lu-Sm and Y, A: Fe, Ga and Al) were newly synthesized and their lattice constants as a hexagonal setting were measured by means of the X-ray powder diffraction method. The R occupies the octahedral site and both A and Ti does the trigonalbipyramidal one in these compounds. Relation between lattice constants for the rhombic R(A 1−x Ti x )O 3+x/2 and the monoclinic In(A 1−x Ti x )O 3+x/2 are as follows, a h ≈5 x b m , c h ≈3 x c m x sin β and a m =3 1/2 x b m , where a h and c h are the lattice constants as a hexagonal setting for R(A 1−x Ti x )O 3+x/2 and a m , b m , c m and β are those of the monoclinic In(A 1−x Ti x )O 3+x/2 . Crystal structural relationships among α-InGaO 3 (hexagonal, high pressure form, space group: P 63/ mmc ), InGaO 3 (rhombic, hypothetical), (RAO 3 ) n (BO) m and RAO 3 (ZnO) m (R: Lu-Ho, Y and In, A: Fe, Ga, and Al, B: divalent cation element, m, n: natural number), the orthorhombic-and monoclinic In(A 1−x Ti x )O 3+x/2 (A: Fe, Ga, Al, Cr and Mn) and the hexagonal-and rhombic R(A 1−x Ti x )O 3+x/2 (R: Lu-Sm and Y, A: Fe, Ga and Al) are schematically presented. We concluded that the crystal structures of both the α-InGaO 3 (high pressure form, hexagonal, space group: P 63/ mmc ) and the hypothetical InGaO 3 (rhombic) are the key structures for constructing the crystal structures of these compounds having the cations with CN=5.

The chlorodiphenyltin(IV) dithiocarbamate complexes 1–5 with general formula {(Ph2SnCl)dtc} (dtc = R1R2NCS2−; 1, R1 = Bn, R2 = 9-anthrylmethyl; 2, R1 = Bn, R2 = 9-phenanthrylmethyl; 3, R1 = Bn, R2 = 1-pyrenylmethyl; 4, R1 = 1-naphthylmethyl, R2 = 1-pyrenylmethyl; 5, R1 = R2 1-pyrenylmethyl) have been tested as host for anions and neutral amines in acetonitrile by spectrophotometric UV/Vis titrations. In addition, the titrations of the complexes 1 and 5 were studied in chloroform by 1H and 119Sn NMR spectroscopy. It was found that anions as acetate, benzoate, and dihydrogen phosphate cause a displacement of the dithiocarbamate ligands of metallic center independently of the aromatic nature of the substituents on the nitrogen atom functioning as chemodosimeters in which the indicator is displaced. However, some aliphatic amines and aromatic methylene amines and its aromatic analogs can act as guests with binding constants in the range of 103 to 106 M−1. Also, in these cases compound 5 functions as chemodosimeter without displacement of the indicator. According to 1H, 13C, 119Sn NMR data and using DFT (B3LYP) and Poisson–Boltzmann (PB) to model the solvent, structures of the complexes are proposed in which the hydrophobic and π–π interactions are suggested as the dominant interactions.

Four new homoditopic bis[chlorodiorganotin(IV) and triorganotin(IV) dithiocarbamate] complexes derived from naphthalene diimide (NDI) with general formula NDI-[(CH2)2-N(CH2Ph)(CS2SnR2X)]2, 3: R = n-Bu, X = Cl; 4: R = Me, X = Cl; 5: R = Ph, X = Cl; 6: R = X = Me; were prepared from triethylammonium ((1,3,6,8-tetraoxo-1,3,6,8-tetrahydrobenzo[lmn][3,8]phenanthroline-2,7-diyl)bis(ethane-2,1-diyl))bis(benzylcarbamodithioate) 2. All compounds were characterized by IR, as well as 1H and 13C NMR spectroscopy. The complexes 3–6 also were characterized by 119Sn NMR spectroscopy. In addition, complex 3 was further characterized by single-crystal X-ray diffraction analysis. The crystallographic study performed on complex 3 showed that the tin atom has a coordination geometry intermediate between square-pyramid and a trigonal-bipyramidal, with τ value of 0.69. In addition the presence of cooperative C H…π, C H…S, C H…O and S…π intramolecular interactions in the crystal structure of 3 was observed. The interaction of complexes 3–6 with anions (CH3CO2−, F−, H2PO4−) in CDCl3 was studied by UV/Vis, fluorescence and 119Sn NMR titrations. The addition of the foregoing anions to complexes 3-6 lead to the displacement of the chloride ligand at the tin(IV) atom. However, an the excess of F− or H2PO4− induced the self-assembly of complexes 3 and 5 in their corresponding binuclear metallomacrocycles.

Five new chlorodiorganotin(IV) complexes derived from dithiocarbamate ligands have been prepared and structurally characterized. The complexes 1–5 with the general formula {(Ph2SnCl)dtc} (dtc = R1R2NCS2−; 1, R1 = Bn, R2 = 9-anthrylmethyl; 2, R1 = Bn, R2 = 9-phenanthrylmethyl; 3, R1 = Bn, R2 = 1-pyrenylmethyl; 4, R1 = 1-naphthylmethyl, R2 = 1-pyrenylmethyl; 5, R1 = R2 = 1-pyrenylmethyl) have been obtained from Ph2SnCl2 and the sodium dithiocarbamate salts of benzyl(9-anthrylmethyl)amine, benzyl(9-phenanthrylmethyl)amine, benzyl(1-pyrenylmethyl)amine, 1-naphthylmethyl(1-pyrenylmethyl)amine and di(1-pyrenylmethyl)amine. Compounds 1–5 have been analyzed as far as possible by elemental analysis, FAB+ mass spectrometry, IR, UV–Vis, fluorescence and NMR (1H, 13C, 119Sn) spectroscopy, and single-crystal X-ray diffraction analysis (1–3). The solid-state and solution studies showed that the dtc ligands are coordinated to the tin atoms in the anisobidentate manner. In all cases the metal centers are five-coordinate. The coordination geometry is intermediate between square-pyramidal and trigonal-bipyramidal coordination polyhedra with τ-values in the range of 0.49–0.55. The crystal structures show the presence of C–H···Cl, C–H···S, C–H···π, offset π–π and S···π contacts. The stability of the (Ph2SnCl)dtc complexes in the presence of the acetate anion has been examined in acetonitrile solutions. For all of these organotin(IV) complexes the displacement of the coordinated ligands (i.e., chloride and dtc) by the acetate anion was observed. The lability, as well as their intrinsic fluorescent properties of the polyaromatic moieties in these (Ph2SnCl)dtc compounds make them interesting candidates to detect the presence of O-donor anions at very low concentrations by displacement of the metal-coordinated dtc.

Fluorescent responses and conformational changes against pH were studied on four new water-soluble 1-pyrene and 1-methylpyrene bichromophores, (ttha1py)H4, (edta1mpy)H2, (dtpa1mpy)H3 and (ttha1mpy)H4, with the objective of modifying pH–fluorescence profiles and other solution properties of 1-pyrene bichromophores, (edta1py)H2 and (dtpa1py)H3, developed previously by our group; the abbreviations with acidic protons stand for pyrenyl moieties interlinked by an EDTA, DTPA (diethylenetriaminepentacetic acid) or TTHA (triethylenetetraminehexaacetic acid) chain through amide linkages. The new derivatives exhibit emission bands of monomeric pyrene and an intense structureless excimer band; the latter responds to pH sensitively. The pH dependence of the emission intensity of the DTPA and TTHA derivatives is well correlated with species distribution determined by potentiometry. In every derivative, the completely deprotonated species Ln− is the most efficient for excimer emission, followed by the corresponding monoprotonated species LH(n−1)−. In the latter, the acidic hydrogen is located on the central amine, as confirmed by 1H NMR. The resulting hydrogen bond between amino nitrogen atoms makes the aliphatic chain rigid. Further protonation stretches the interlinking chain due to electrostatic repulsion. These conformational changes with protonation result in fluorescent on–off cycles against pH window. The switching cycles of the methylpyrene derivatives are reverse to those of the corresponding pyrene derivatives, as the CH2 spacer between the amide and aromatic groups defines the orientation of pyrene rings. The sensitiveness of amide group to environment leads to a sharp change in excimer emission above pH ∼11. The combined functions of amide and amino groups lead to the novel pH-responses.

A simplified method of synthesis and purification of Erbium-Tetraphenylporphyrin (ErTpp) complexes, and their incorporation within a silica gel by the sol–gel process, is presented. On the basis of optical spectroscopic measurements in the UV–VIS range it was found that in ErTpp complexes the tetraphenylporphyrin molecule served as a protective screen for erbium ions. The half-width of the erbium ion luminescence band for the 4 S 3/2 → 4 I 15/2 transition was narrower by a factor of 5–6 in the new material than the corresponding value in erbium doped glasses or glass ceramics. It was shown that the value of the nonlinear refraction coefficient in ErTpp gels could considerably exceed that of silica glasses.