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.

Nine mononuclear diorganotin(IV) dithiocarbamate complexes 1–9 with 19-, 20- and 21-membered macrocyclic structures were synthesized from dimethyl, di-n-butyl, and diphenyltin(IV) dichloride and three bis-dithiocarbamate ligands derived from secondary bis-amines having aromatic spacer groups. All compounds were characterized by elemental analysis, mass spectrometry, and spectroscopic methods (IR and 1H, 13C, and 119Sn NMR). Additionally, quantum chemical DFT calculations were performed for the dimethyltin(IV) derivatives in order to model the molecular structures. For one compound series the NMR spectra showed a concentration-dependent behavior in solution, which was analyzed in detail and permitted to postulate the existence of an equilibrium with the corresponding [2+2] macrocycles.

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.

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.

A condensation reaction between ethylenediaminetetraacetic dianhydride and p-xylenediamine gave a new chelating cyclophane, 3,10,21,28-tetraoxo-5,8,23,26-tetrakis(carboxymethyl)-2,5,8,11,20,23,26,29-octaaza[12.12]paracyclophane, abbreviated as (32edtaxan)H(4), which has three types of electron-donor groups, i.e., amine, carboxylate, and amide groups. The formation of the cyclophane has been confirmed by a single-crystal X-ray analysis of its Zn(2+) complex, [Zn(2)(32edtaxan)].7.5H(2)O, which crystallized in the monoclinic space group P2(1)/c with a = 19.818(1) Å, b = 13.169(1) Å, c = 18.134(1) Å, beta = 104.491(6) degrees, and Z = 4. Each cyclophane molecule coordinates two Zn(2+) ions and results in the formation of a binuclear chelate molecule. The coordination geometry around each metal ion is distorted octahedral, the donor atoms being two carboxylate oxygen atoms, two amine nitrogen atoms, and two amide oxygen atoms. The new cyclophane exhibited a well-defined fluorescence band at 290 nm with 210 nm excitation. The emission intensity was markedly increased in the Zn(2+) complex, in which the coordination of Zn(2+) ions increases the rigidity of the cyclophane leading to a high fluorescence quantum yield. When the cyclophane was coordinated to Cu(2+) ions, the molar absorptivity of a pi-pi transition band observed at 260 nm was increased by a factor of about 10. Such a large spectral change was not observed for the Zn(2+) and Ni(2+) complexes. In the Cu(2+) complex, the two phenyl rings of the cyclophane are expected to be brought closer, as a result of the coordination of deprotonated amide nitrogens to the central metal ion. This allosterism via ring contraction is responsible for the novel behavior of the absorption spectrum. The emission band of the cyclophane was weakened by coordination of copper and nickel as a result of fluorescence quenching caused by a photo-induced electron transfer.

Protonation of an aminoglycoside antibiotic kanamycin A sulfate was studied by potentiometric titrations at variable ionic strength, sulfate concentration and temperature. From these results the association constants of differently protonated forms of kanamycin A with sulfate and enthalpy changes for protonation of each amino group were determined. The protonation of all amino groups of kanamycin A is exothermic, but the protonation enthalpy does not correlate with basicity as in a case of simple polyamines. The sites of stepwise protonation of kanamycin A have been assigned by analysis of 1 H– 13 C–HSQC spectra at variable pH in D 2 O. Plots of chemical shifts for each H and C atom of kanamycin A vs. pH were fitted to the theoretical equation relating them to p K a values of ionogenic groups and it was observed that changes in chemical shifts of all atoms in ring C were controlled by ionization of a single amino group with p K a 7.98, in ring B by ionization of two amino groups with p K a 6.61 and 8.54, but in ring A all atoms felt ionization of one group with p K a 9.19 and some atoms felt ionization of a second group with p K a 6.51, which therefore should belong to amino group at C3 in ring B positioned closer to the ring A while higher p K a 8.54 can be assigned to the group at C1. This resolves the previously existed uncertainty in assignment of protonation sites in rings B and C.

The alkali metal (Na+, K+, Rb+, Cs+) bis-dithiocarbamate (bis-dtc) salts of N,N′-dibenzyl-1,2-ethylenediamine have been prepared from the reaction of N,N′-dibenzyl-1,2-ethylenediamine with carbon disulfide in the presence of two equivalents of the corresponding alkali metal hydroxide. Additionally, the analogous triethylammonium derivative has been obtained. The resulting compounds have been analyzed as far as possible by elemental analysis, FAB+ mass spectrometry, IR, UV-Vis and NMR (1H, 13C) spectroscopy, and single-crystal X-ray diffraction, showing that the composition of the metal salts can be described by the general formula [{[(H2O)xM-µ-(H2O)yM(H2O)x][bis-dtc]}n] (1, M = Na+, x = 3, y = 2; 2, M = K+, x = 1, y = 2; 3, M = Rb+, x = 0, y = 1; 4, M = Cs+, x = 0, y = 1; 5, M = Et3HN+, x = 0, y = 0). The solid-state and solution studies showed that all alkali metal ions participate in the formation of M–O and cation-π(arene) interactions, while M–S interactions are only observed for the larger alkali metals K+, Rb+ and Cs+. As expected, within the alkali metal group there is a clear tendency for a decreasing number of M–O bonds in favor of M–S and cation–π(arene) interactions, however, only K+ forms a semi-sandwich type complex with η6-coordination.

Kinetics of the cleavage of two phosphate diesters, bis(4-nitrophenyl) phosphate and 2-hydroxypropyl 4-nitrophenyl phosphate and a triester, 4-nitrophenyl diphenyl phosphate, in the presence of Mg(II), Ca(II) and Sr(II) were studied in 90% vol. DMSO at 37 degrees C. The alkaline hydrolysis of the triester was inhibited by all cations, but with both phosphodiesters strong catalytic effects were observed. Potentiometric titrations of metal perchlorates by Bu4N(OH) revealed formation of M2(OH)3+, M(OH)+, M(OH)2 and M2(OH)5- species. Rate constants for phosphodiester cleavage by individual species were obtained from analysis of rate-concentration profiles. Observed first-order rate constants in the presence of 1-2 mM Mg(II) or Ca(II) in neutral and weakly basic solutions were 10(8)-10(11) times higher than those for background hydrolysis at the same pH while in water additions of up to 50 mM metal produced100-fold accelerations. Possible structures of DMSO solvated catalyst-substrate complexes were modeled by DFT calculations with Mg(II). The increased catalytic activity in 90% DMSO is attributed to stronger association of hydroxide ions and anionic phosphodiesters with metal ions and to preferable solvation of cations by DMSO, which creates favorable for reaction anhydrous microenvironment in the coordination sphere of the catalyst.

A chelating cyclophane has been synthesized by cyclocondensation of two ethylenediaminetetraacetic (EDTA) units with two p-phenylenediamine units: the resulting cyclophane is 2,9,18,25-tetraoxo-4,7,20,23-tetrakis(carboxymethyl)-1,4,7,10,17,20,23,26-octaaza[10.10]paracyclophane, abbreviated as (bis-edtapdn)H(4). Cyclocondensation of two EDTA and two 1,5-diaminonaphthalene units has given the naphthalenophane, 2,9,22,29-tetraoxo-4,7,24,27-tetrakis(carboxymethyl)-1,4,7,10,21,24,27,30-octaaza[10.10](1,5)naphthalenophane, (bis-edtanap)H(4). Studies of electronic and EPR spectra have been carried out on the binuclear Cu(2+) complexes of these new ligands and of related chelating cyclophanes, 2,9,25,32-tetraoxo-4,7,27,30-tetrakis(carboxymethyl)-1,4,7,10,24,27,30,33-octaaza[10.1.10.1]paracyclophane, abbreviated as (bis-edtabpm)H(4), and 2,9,25,32-tetraoxo-4,7,27,30-tetrakis(carboxymethyl)-1,4,7,10,24,27,30,33-octaaza-17,40-dioxa[10.1.10.1]paracyclophane, abbreviated as (bis-edtabpe)H(4). Common features of these chelating cyclophanes are as follows: (1) amino, amide, and pendant carboxymethyl donor groups are substituents in the cyclophane ring, and (2) the amide groups are directly bound to the aromatic groups. These ligands formed neutral binuclear Cu(2+) chelates [Cu(2)L](0) that are water-insoluble. In alkaline solutions, these Cu(2+) complexes were converted to anionic chelates [Cu(2)(LH(-)(4))](4)(-) in which deprotonated amide nitrogens coordinated Cu(2+) ions. These anionic metal chelates of (bis-edtapdn)H(4), (bis-edtabpm)H(4), and (bis-edtabpe)H(4) exhibited three pi-pi transition bands in the spectral range 240-340 nm, in contrast to the uncoordinated cyclophanes, which showed a single band in this spectral range. The unusual pi-pi transition spectra of the [Cu(2)(LH(-)(4))](4)(-) complexes originate from the combined effect of metal-ligand charge transfer and proximity of the pi systems. The absorption and emission spectra of (bis-edtanap)H(4) were also influenced by coordination with copper. The EPR spectrum of [Cu(2)(bis-edtanapH(-)(4))](4)(-) in a methanol glass matrix showed a hyperfine structure due to the spin exchange between two Cu(2+) ions. These unusual spectral and magnetic properties arise from the strong coordination between Cu(2+) ions and deprotonated amide nitrogens that are bound to the pi systems.

Polyaniline salts of toluenesulfonate (TS) and sulfonated poly( p -vinylphenol) (SPVP) have been prepared. The polyaniline salt of TS exhibited a room-temperature electrical conductivity of 10 S cm −1 . The activation energy for electrical conduction was 0.02 eV, which was significantly smaller than the value 0.04 eV reported for other salts. The aromatic nature of the organic anion is expected to enhance the interchain diffusion of charge carriers. The electrical conductivity of the polyaniline salt of the polymer anion was of the order of 10 −4 S cm −1 . A polyaniline base derived from the SPVP salt was water-soluble in the presence of excess NaSPVP, due to complexation between the two polymers.