Several cobalt porphyrins (CoP) have been reduced by radiation chemical, photochemical, and electrochemical methods, in aqueous and organic solvents. In aqueous solutions, the CoIP state is stable at high pH but is shorter lived in neutral and acidic solutions. Stable CoIP is also observed in organic solvents and is unreactive toward CO2. One-electron reduction of CoIP leads to formation of a species that is observed as a transient intermediate by pulse radiolysis in aqueous solutions and as a stable product following reduction by Na in tetrahydrofuran solutions. The spectrum of this species is not the characteristic spectrum of a metalloporphyrin π-radical anion and is ascribed to Co0P. This species binds and reduces CO2. Catalytic formation of CO and HCO2 - is confirmed by photochemical experiments in acetonitrile solutions containing triethylamine as a reductive quencher. Catalytic reduction of CO2 is also confirmed by cyclic voltammetry in acetonitrile and butyronitrile solutions and is shown to occur at the potential at which CoIP is reduced to Co0P. As compared with CoTPP, fluorinated derivatives are reduced, and catalyze CO2 reduction, at less negative potentials.

A small library of emetine dithiocarbamate ester derivatives were synthesized in 25-86% yield via derivatization of the N2'- position of emetine. Anticancer evaluation of these compounds in androgen receptor positive LNCaP and androgen receptor negative PC3 and DU145 prostate cancer cell lines revealed time dependent and dose-dependent cytotoxicity. With the exception of compound 4c, all the dithiocarbamate ester analogs in this study showed appreciable potency in all the prostate cancer cell lines (regardless of whether it is androgen receptor positive or negative) with a cytotoxicity IC50 value ranging from 1.312 ± 0.032 μM to 5.201 ± 0.125 μM by day 7 of treatment. Compared to the sodium dithiocarbamate salt 1, all the dithiocarbamate ester analogs (2 and 4a-4 g) displayed lower cytotoxicity than compound 1 (PC3, IC50 = 0.087 ± 0.005 μM; DU145, IC50 = 0.079 ± 0.003 μM and LNCaP, IC50 = 0.079 ± 0.003 μM) on day 7 of treatment. Consequently, it appears that S-alkylation of compound 1 leads to a more stable dithiocarbamate ester derivative that resulted in lower anticancer activity in the prostate cancer cell lines.

The Raman spectra of the antitumor agent 6‐mercaptopurine (6MP) in the solid and solution state were recorded in the 600–1700 cm−1 spectral region. The normal modes of 6MP were calculated using a Urey–Bradley empirical force field (UBFF) and with the PM3 semi‐empirical method. Prior to performing the normal‐mode calculations on 6MP, similar calculations were performed on methanethiol and thiophenol. The force constant parameters obtained from these calculations were then transferred to the 6MP calculations. The results of the normal‐mode calculations were compared with the observed spectra and an assignment of the vibrational modes is proposed. Based on changes in the wavenumbers of the Raman spectra between the solution and solid form 6MP and on normal‐mode calculations, it is proposed that in the solid form 6MP crystallizes in the tautomer form whereas in solution the molecule ionizes by losing the hydrogen at the N‐1 position. Copyright © 2000 John Wiley & Sons, Ltd.

Electrochemical and surface spectroscopic techniques are used to investigate the reductive electrochemistry of the water-soluble manganese tetrasulfonatophenyl porphyrin. The electrocehmistry of MnTSPP at a Ag, Au, and Pt electrode and the normal Raman and surface-enhanced Raman scattering spectra of the two redox forms of MnTSPP were studied. Voltammetric studies indicate two reductive peaks at −0.45 and −0.85 V on an Ag electrode. Potential-dependent shifts in the 466 nm UV/vis absorbance band to 432 nm at −0.5 V on a gold minigrid electrode indicate that reduction of the porphyrin central metal from MnIII to MnII occurs at this potential. A 32 cm-1 downshift in the ν4 vibration from 1368 to 1336 cm-1 at −0.5 V is further evidence for the reduction of the metal from the MnIII to the MnII state. The reduction of the porphyrin macrocyclic ring to the radical anion is also observed at −0.8 V. The core-sensitive modes of aquo MnIIITSPP are in excellent agreement with that of a 6-coordinate species. Upon reduction to the MnIITSPP, the core size marker frequencies shift to those of a 5-coordinate species. Finally, Raman band frequencies for the solution and SERS spectra are systematically assigned, and normal Raman and surface-enhanced Raman spectra are presented for MnIIITSPP and its reduced MnIITSPP.

The reductive electrochemistry of manganese(III) protoporphyrin IX dimethyl ester, MnIII(PPDME), in an aprotic solvent was studied using cyclic voltammetry, surface-enhanced Raman scattering spectroscopy (SERS), and thin layer potential dependent UV/vis absorption spectroscopy. Good quality SERS spectra are reported for an electrochemically roughened silver electrode in contact with Mn(PPDME) dissolved in acetonitrile. A reversible one-electron reduction was observed at ca. −0.44 V/SCE in the cyclic voltammetric scans on silver, gold, and platinum electrodes. In thin layer UV/vis spectroelectrochemistry, the Soret band at 473 nm at 0.0 V undergoes a 36 nm blue shift to 437 nm when the electrode potential was stepped to −0.5 V. Resonance Raman and SERS spectral frequencies of Mn(PPDME) are assigned and tabulated. The shift of the Soret band along with the downshift in the ν4 oxidation state marker band from 1373 to 1360 cm-1 in the SERS spectra identify the process occurring at ca. −0.5 V to be the reduction of the porphyrin central metal ion from the MnIII to MnII state. Core sizes for MnIII(PPDME) and MnII(PPDME) adsorbed on an anodized silver electrode surface were calculated to be 1.993 and 2.072 Å, respectively. Both the MnII and MnIII complexes are adsorbed as high spin, five-coordinate species. On the basis of relative intensities of the SERS bands, the orientation of Mn(PPDME) adsorbed onto the silver electrode surface is proposed to be face-on.