Marcela Rizzotto

Oxidation of l-rhamnose and d-mannose by chromium(VI) in aqueous acetic acid

Abstract The oxidation of l -rhamnose and d -mannose by Cr(VI) in aqueous acetic acid follows the rate law: −d[Cr(VI)]/d t = ( k 2 + k 3 [H + ] [ aldose ] [Cr(VI)]/{1 + [H + ]/ K a + K 1 [H + ][ aldose ]}, where k 2 = 3.5 +- 0.8 × 10 −3 s −1 and 8.6 +- 1.0 × 10 −4 s −1 , K 3 = 6.8 ± 0.5 × 10 −3 M −1 s −1 and 5.1 ± 0.5 × 10 −3 M −1 s −1 , K a = 1–4 M and K 1 = 13∓_ 2 and 17±5 M −2 for l -rhamnose and d -mannose, respectively. This rate law corresponds to the reaction leading to the formation of l -1,4-rhamnonalactone and d -1,4-mannonalactone. No cleavage to carbon dioxide takes place when a 30-fold or higher excess of aldose over Cr(IV) is employed. The free radicals formed in the slow electron-transfer steps react with Cr(VI) to yield two intermediate Cr(V) complexes with EPR signals at g 1 = 1.978 and g 2 = 1.973. The mechanism and associated reactions kinetics are presented and discussed.

Chromic Oxidation of 2-Deoxy-d-Glucose. Comparative Study with Aldoses. I.

Abstract A rate law for the oxidation of 2-deoxy-d-glucose (2DG) by Cr(VI) in perchloric acid has been derived. This rate law corresponds to the reaction leading to the formation of 2-deoxy-d-gluconic acid (2DGA). No cleavage to carbon dioxide takes place when a twenty-fold or higher excess of aldose over Cr(VI) is employed. Kinetic constants are interpreted in terms of the absence of an hydroxyl group at C-2 on the stability of the chromic ester formed in the first reaction step. Free radicals formed during the reaction convert Cr(VI) to Cr(V). The latter species was detected by EPR measurements.

The interaction between mercury(II) and sulfathiazole

The interaction of mercury(II) with sulfathiazole has been analyzed. IR and NMR spectral studies suggest a coordination of Hg(II) with the Nthiazolic atom, unlike related Hg-sulfadrugs compounds. The complex was screened for its activity against Escherichia coli, showing an appreciable antimicrobial activity compared with the ligand.

Electron paramagnetic resonance and potentiometric studies of the interactions of Cr(VI) and Cr(V) with d-ribose 5-phosphate and nucleotides

Abstract Cr(VI) and Cr(V) interaction with d -ribose 5′-monophosphate (R5P), adenosine 5′-monophosphate (AMP), cytidine 5′-monophosphate (CMP) and 2′-deoxythymidine 5′-monophosphate (dTMP) was studied by electron paramagnetic resonance (EPR) spectroscopy (Cr(V)) and potentiometry (Cr(VI)) in aqueous solutions. The EPR spectra showed a narrow but composed signal. The Cr(V) signals showed experimental giso and 53Cr Aiso values that are typical of five-coordinate oxochromate(V) complexes. Potentiometric studies of CMP and AMP in the presence and absence of potassium dichromate allow us to suggest the presence of three species of S–Cr(VI), differing in their degree of protonation.

Comparative study of oxidation by chromium(V) and chromium(VI)

The kinetics and mechanism of the oxidation of 2-deoxy-D-glucose (dGlc) by CrVI which yields 2-deoxy-D-gluconic acid and CrIII as final products when a ten-fold or higher excess of sugar over CrVI is used, have been studied. The redox reactions occur through CrVI→ CrIV→ CrIII and CrVI→ CrV→ CrIII paths. The experimental data were fitted with a multilinear regression program. The complete rate law for the chromium(VI) oxidation reaction is expressed by –d[CrVI]/dt={c[H+]+(d+e[H+]+f[H+]2)[dGlc]}[CrVI], where c=(5 ± 1)× 10–4 dm3 mol–1 s–1, d=(3 ± 2)× 10–4 dm3 mol–1 s–1, e=(115 ± 13)× 10–4 dm6 mol–2 s–1 and f=(402 ± 17)× 10–4 dm9 mol–3 s–1, at 50 °C. Chromium(V) is formed in a rapid step by reaction of the radical dGlc and CrVI and CV reacts with dGlc faster than does CrVI. The chromium(V) oxidation of dGlc follows the rate low –dCrV/dt=(k1+k2[H+])[dGlc][CrV], where k1= 2.52 × 10–4 dm3 mol–1 s–1 and k2= 54.0 dm6 mol–2 s–1, at 25 °C. The EPR spectra show that three 1:1 CrV:dGlc intermediate complexes (g1= 1.9781, g2= 1.9752, g3= 1.9758) are formed in rapid pre-equilibria before the redox steps.

Synthesis, characterization, microbiological evaluation, genotoxicity and synergism tests of new nano silver complexes with sulfamoxole: X-ray diffraction of [Ag2(SMX)2]·DMSO

The synthesis and microbiological evaluation of two new Ag(I) complexes with sulfamoxole (SMX), [Ag2(SMX)2]·H2O and [Ag4(SCN)3(SMX)]·H2O are described. Both were characterized by elemental analysis, thermogravimetry, powder and single crystal X-ray diffraction, NMR, Raman and experimental and theoretical IR spectroscopies. Their antibacterial and antifungal properties were evaluated by agar and broth dilution assays, respectively. In addition, synergism tests for Pseudomonas aeruginosa were performed, and genotoxicity studies were carried out employing the Allium cepa test. Both complexes displayed good activity against Escherichia coli, Staphylococcus aureus, P. aeruginosa, and 10 fungi strains, with lower minimum inhibitory concentrations (MICs) than that of free SMX in all cases. The nanometrical crystallite particle size determined from XRPD, DLS and TEM might explain the good microbiological activity in spite of the low solubility of both complexes. The fractional inhibitory concentration (FIC) calculated from the P. aeruginosa test data indicated that the activity of the complexes is not due to synergism of the free components in the concentration ratios studied. Moreover, none of the complexes displayed cytotoxic effects on onions in the concentration range tested, and chromosome aberrations were not observed.

Antibacterial, Antifungal, Phytotoxic, and Genotoxic Properties of Two Complexes of AgI with Sulfachloropyridazine (SCP): X‐ray Diffraction of [Ag(SCP)]n

We report the synthesis, characterization, antibacterial and antifungal activities, phytotoxicity, and genotoxicity of two new complexes of silver(I) with sulfachloropyridazine (SCP), one of which is heteroleptic with SCP and SCN− ligands (Ag–SCP–SCN), the other of which is homoleptic (Ag–SCP); furthermore, the crystal structure of the homoleptic complex is disclosed. The heterocyclic N atom nearest to the Cl atom and the Nsulfonamide atom could be coordination sites for the silver ion in the Ag–SCP–SCN complex. The Ag–SCP complex is a polymeric compound with metal–metal bonds, and the heterocyclic and sulfonamide N atoms are points of coordination for AgI. Both complexes showed activity against all the tested bacteria, and in the cases of Escherichia coli and Pseudomonas aeruginosa, the action was better than that of SCP. In all cases, both silver–SCP complexes showed better antifungal activity than SCP, which was inactive against the tested fungi. Notably, the activity against P. aeruginosa, a nosocomial multidrug‐resistant pathogen, was better than that of the reference antibiotic cefotaxim. Both silver–sulfa complexes displayed moderate activity against the tested yeast, especially for C. neoformans, which is an important fact considering the incidence of cryptococcosis, mainly in immune‐deficient patients. No chromosomal aberrations were observed with the Allium cepa test, which is auspicious for further study of these complexes as potential drugs.

The interaction between sulfathiazole and cobalt(II): potentiometric studies

Potentiometric studies of sulfathiazole (HST) in the presence and absence of cobalt(II) were performed. Equilibrium constants for the formation of the detected species, [Co(ST)]+ and [Co(ST)(OH)], are reported. UV-Vis spectrophotometric measurements suggest that the coordination Co(II)-sulfathiazole might be through a N atom, which, in agreement with MO calculations, could be a thiazolic one. In spite of sulfonamides being better ligands at pH >7, [Co(ST)]+ was found at pH » 3.

Synthesis, characterization and antimicrobial properties of a Co(II)-phthalylsulfathiazolate complex

The reaction between phthalylsulfathiazole (H2PST), in alkaline aqueous solution, and cobalt(II) nitrate led to a pink solid, [Co(PST)(H2O)4] (1), which was characterized by elemental and thermogravimetric analysis; FT-IR, Raman and diffuse reflectance spectra. Spectroscopic data reveal that the ligand would be doubly deprotonated and that the Co(II) ion environment is a distorted octahedral one. (1) showed antibacterial activity similar to the ligand.

Redox and ligand-exchange chemistry of chromium(VI/V)-methyl glycoside systems

In order to establish a general pattern for the redox and coordination chemistry of glycosides with Cr(VI) and Cr(V), reactions of a series of methyl glycosides with Cr(VI) and Cr(V) have been studied at different acidities. Oxidations of methyl α- and β-D-glucopyranoside (Glc1Me), methyl α- and β-D-mannopyranoside (Man1Me), methyl α- and β-D-galactopyranoside (Gal1Me) and methyl α- and β-D-ribofuranoside (Rib1Me) by Cr(VI) proceed rapidly at pH ≤ 1, and yield Cr(III) and methyl glycofuranuronolactone as final products when an excess of methyl glycoside over Cr(VI) is used. At constant [H+], the reaction follows the rate law −d[Cr(VI)]/dt = kH [Gly1Me] [Cr(VI)]. Relative reactivities of methyl glycosides toward Cr(VI) reduction are: β-Rib1Me > α-Gal1Me > α-Rib1Me ≈ β-Gal1Me > β-Man1Me > α-Man1Me > α-Glc1Me > β-Glc1Me. This sequence is interpreted in terms of the degree of unfavorable steric interactions induced by the nonbonded 1,3-diaxial interactions in the respective Gly1Me-Cr(VI) monochelate, which is formed in rapid equilibrium that precedes the rate determining step. For all the glycosides, the oxidation rate decreases with an increase in pH value and becomes negligible at pH > 5. At pH 5.5 and 7.5, addition of an excess of α-Man1Me or α(β)-Gal1Me to an equimolar cysteine-Cr(VI) mixture, afforded two EPR triplets at giso1 1.9802 and giso2 1.9800/1 with Aiso 16.5(3) × 10−4 cm−1 in a 50 ∶ 50 giso1 ∶ giso2 ratio. The EPR spectral parameters and the superhyperfine pattern of the signal are consistent with the presence of two geometric isomers of the [CrVO(cis-O3,O4-Gal1Me)2]− and [CrVO(cis-O2,O3-Man1Me)2]− complexes. The same final spectral pattern is observed at pH 7.5 for the ligand-exchange reaction of Man1Me and Gal1Me with [CrVO(ehba)2]− (ehba = 2-ethyl-2-hydroxybutanoato(2−)). No EPR signal is observed when an excess of Xil1Me or Glc1Me is added to an equimolar cysteine-Cr(VI) mixture. In the ligand-exchange reactions of [CrVO(ehba)2]− at pH 7.5 with Xil1Me or Glc1Me, a very low intensity EPR singlet is observed at giso 1.9799. These results show that only glycosides with one cis-diolato group (such as Man1Me and Gal1Me) are effective for stabilizing Cr(V) at pH 5.5 and 7.5. The high redox reactivity of methyl glycosides with Cr(V) at high [H+] is attributed to the formation of [CrVO(O,O-glycoside)(OH2)3]+ species (giso 1.9716), which are not observed at pH 5.5–7.5, where only the five-coordinate bis-chelate oxochromate(V) species are observed.