Redox-active antifungal cobalt(II) and copper(II) complexes with sterically hindered o-aminophenol derivatives

Co(II) complexes with 4,6-di(tert-butyl)-2-aminophenol (HL^I) and 2-anilino-4,6-di(tert-butyl)phenol (HL^II) have been synthesized and characterized by means of physico-chemical methods. The compounds HL^I and HL^II coordinate in their singly deprotonated forms and behave as bidentate O,N-coordinated ligands; their low-spin Co(II) complexes are characterized by CoN₂O₂ coordination modes and square planar geometry. Both the free ligands and their Co(II) and Cu(II) complexes (we have produced and characterized the latter before) exhibit a pronounced antifungal activity against Aspergillus niger, Fusarium spp., Mucor spp., Penicillium lividum, Botrytis cinerea, Alternaria alternata, Sclerotinia sclerotiorum, Monilia spp., which in a number of cases is comparable with that of Nystatin and Terbinafine or even higher. The reducing properties of the ligands and their metal(II) complexes, as well as their antifungal activities, were found to decrease in the order: Cu(L^I)₂ > Cu(L^II)₂ ? Co(L^I)₂ > Co(L^II)₂ > HL^I > HL^II.     

Synthesis and characterization of copper(II) and cobalt(II) complexes with two new potentially hexadentate Schiff base ligands. X-ray crystal structure determination of one copper(II) complex

Two new potentially hexadentate N₂O₄ Schiff base ligands 2-((z)-(2-(2-(2-((z)-3,5-di-tert-butyl-2-hydroxybenzylideneamino) phenoxy) phenoxy) phenylimino) methyl)-4,6-di-tert-butylphenol [H₂L¹] and 2-((z)-(2-(2-(2-((z)-3,5-di-tert-butyl-2-hydroxybenzylideneamino) phenoxy)-5-tert-butylphenoxy) phenylimino) methyl)-4,6-di-tert-butylphenol [H₂L²] were prepared from the reaction of 3,5-di-tert-butyl-2-hydroxy benzaldehyde with 1,2-bis(2′-aminophenoxy)benzene or 1,2-bis(2′-aminophenoxy)-4-t-butylbenzene, respectively. From the direct reaction of ligands [H₂L¹] and [H₂L²] with copper(II) and cobalt(II) salts in methanolic solution and in the presence of N(Et)₃ the neutral [CuL¹], [CuL²], [CoL¹] and [CoL²] complexes were prepared. All complexes were characterized by IR spectra, elemental analysis, magnetic susceptibility, mass spectra, molar conductance (Λ_m), UV-Vis spectra and in the case of [CuL²] with X-ray diffraction. X-ray crystal structure of [CuL²] showed that the complex contains copper(II) in a distorted square planar environment of N₂O₂ donors. Three CH/π interactions were observed in the molecular structure of latter complex.     

Some mixed-ligand palladium(II) complexes and comparison of their photosensitizing ability with analogous platinum(II) complexes

Three new palladium(II) complexes of formula [Pd(bipy)(XX)] [where bipy is 2,2′-bipyridine and XX are dianions of catechol (CAT), 4-tert-butylcatechol (BCAT) and 3,4-dimercaptotoluene (DMT)] have been prepared and characterized by physical methods. A ligand-ligand charge-transfer band in each complex was observed between 16–21 kK (ε_max = 1500–2200 1 mol^?1 cm^?1) which is negatively solvochromic. These palladium(II) complexes in dimethylformamide photosensitize the formation of singlet oxygen and their ability to photosensitize triplet oxygen (³O₂) to singlet oxygen (¹O₂) are compared with analogous platinum(II) complexes. In addition, 2,2′-bipyridine-platinum(II) complex of 3,4-dimercaptotoluene also undergoes self-sensitized photooxidation.     

Homogeneous and heterogeneous styrene epoxidation catalyzed by copper(II) and nickel(II) Schiff base complexes

Both monomeric Schiff base complexes and 1D helical polymeric complexes of Cu(II) and Ni(II) were synthesized and characterized by physicochemical and spectroscopic methods. X-ray single-crystal studies were made on [K₂(CuL)₂Ni(CN)₄]_n·0.5nEt₂O and [K₂(NiL)₂Ni(CN)₄]_n·0.5nEt₂O. The polymers were screened as heterogeneous catalysts for styrene epoxidation. For comparison, the catalytic properties of the homogeneous and heterogeneous catalysts were also examined under identical reaction conditions, and the influence of various solvents and oxidants was studied. The polymeric catalysts showed better activities in chloroform when using tert-butyl hydroperoxide as oxidant, suggesting that heterogenization increased the activity of the catalyst under this condition.     

Polymerization of acrylate monomers with MAO activated iron(II) and cobalt(II) complexes bearing tri- and tetradentate nitrogen ligands

Octahedral iron(II) and cobalt(II) based complexes, [N,N′-di(quinoline-2-methylene)-1,2-phenylenediimine]MCl₂, and [N,N′-di(quinoline-2-methylene)diiminocyclohexane]MCl₂ (M = Co and Fe), bearing tetradentate diimino nitrogen ligands were prepared and used in tert-butylacrylate (t-BA) polymerization after activation with methylaluminoxane (MAO). In general, polyacrylates with high molar mass and narrow molar mass distribution (MMD ≈ 2) were obtained. In order to understand the influence of the ligand on the polymerization process, polymerization behaviour of the hexacoordinated complexes was compared to pentacoordinated iron(II) and cobalt(II) complexes, 2,6-bis[1-(cyclohexylimido)ethyl]pyridine MCl₂ (M = Co and Fe), bearing tridentate diimine nitrogen ligands as well as to free iron(II) chloride. The ability of the MAO activated hexacoordinated complexes to polymerize methylacrylate (MA) and methyl methacrylate (MMA) was also considered, but reduced activities as well as lower molar mass polymers were obtained than in the experiments with t-BA.     

Syntheses,characterization, in vitro antiglycation and DPPH radical scavenging activities of isatin salicylhydrazidehydrazone and its Mn (II), Co (II), Ni (II), Cu (II), and Zn (II) metal complexes

2-Hydroxy salicylhydrazide isatin hydrazone (L) and its Mn (II), Co (II), Ni (II), Cu (II), and Zn (II), metal complexes were synthesized. ¹H NMR, UV–Vis, IR spectroscopy and elemental (CHN/S) analysis techniques were applied for characterization. TG/DTA techniques revealed that all the synthetic compounds are thermally stable up to 300 °C. They were found non-electrolytes in nature. Furthermore, all these complexes were evaluated for antiglycation and DPPH radical scavenging activities. They showed varying degree of activity with IC₅₀ values between 168.23 and 269.0 μM in antiglycation and 29.63–57.71 μM in DPPH radical scavenging activity. Mn (II), Co (II), Ni (II), Cu (II), and Zn (II), metal complexes showed good antiglycation as well as DPPH radical scavenging activity. The IC₅₀ values for antiglycation activity are 168.23 ± 2.37, 234.27 ± 4.33, 257.1 ± 6.43, 267.7 ± 8.43, 269.0 ± 8.56 Ni for Co, Zn, Mn, Cu, and Ni complexes, respectively, while IC₅₀ value were found to be 29.63 ± 2.76, 31.13 ± 1.41, 35.16 ± 2.45, 43.53 ± 3.12, 57.71 ± 2.61 μM for Cu, Zn, Mn, Co and Ni complexes, respectively, for DPPH radical scavenging activity. These synthesized metal complexes were found to be better active than standards Rutin (IC₅₀ = 294.46 μM) for anti-glycation, and tert-butyl-4-hydroxyanisole (IC₅₀ = 44.7 μM) for DPPH radical scavenging activity.     

Synthesis,characterization, and crystal structures of cobalt(II), copper(II), and zinc(II) complexes of a bidentate iminophenol

A bidentate iminophenol (HL = 2-((4-methoxyphenylimino)methyl)-4,6-di-tert-butylphenol derived from condensation of 4-methoxyaniline and 3,5-di-tert-butyl-2-hydroxybenzaldehyde) was mixed with divalent metal salts to form the corresponding mononuclear metal complexes [M^II(L)₂] (M = Co (1), Cu (2), and Zn (3)). The complexes are characterized by different spectroscopic and analytical tools. X-ray crystal structures of the complexes revealed homoleptic mononuclear complexes with MN₂O₂ coordination. The cobalt(II) (1) and zinc(II) (3) complexes display a pseudo-tetrahedral coordination geometry, whereas the copper(II) complex (2) exhibits a distorted square-planar coordination. The zinc(II) complex (3) emits at 460 nm with a twofold enhancement of emission with respect to the free iminophenol.     

Synthesis,structural, spectroscopic,biological and catalytic activity of Co(II), Ni(II) and Cu(II) complexes of benzilic hydrazide (BH)

Co(II), Ni(II) and Cu(II) chloro complexes of benzilic hydrazide (BH) have been synthesized. Also, reaction of the ligand (BH) with several copper(II) salts, including NO₃ ^?, AcO^?, and SO₄ ^? afforded metal complexes of the general formula [CuLX(H₂O) _n ]·nH₂O, where X is the anion and n = 0, 1 or 2. The newly synthesized complexes were characterized by elemental analysis, mass spectra, molar conductance, UV–vis, IR spectra, magnetic moment, and thermal analysis (TG/DTG). The physico-chemical studies support that the ligand acts as monobasic bidentate towards metal ion through the carbonyl and hydroxyl oxygen atoms. The spectral data revealed that the geometrical structure of the complexes is square planar for Cu (II) complexes and tetrahedral for Co(II) and Ni(II) complexes. Structural parameters of the ligand and its complexes have been calculated. The ligand and its metal complexes are screened for their antimicrobial activity. The catalytic activities of the metal chelates have been studied towards the oxidative decolorization of AB25, IC and AB92 dyes using H₂O₂. The catalytic activity is strongly dependent on the type of the metal ion and the anion of Cu(II) complexes.     

Complexation en solution aqueuse des ions magnesium(II), manganese(II), nickel(II), cuivre(II) et plomb(II) avec la s-carboxymethyl-l-cysteine: Complex formation of magnesium(II), manganese(II), nickel(II), copper(II) and lead(II) with S-carboxymethyl-L-cysteine in aqueous solution

Complex formation of magnesium(II), manganese(II), nickel(II), copper(II) and lead(II) with S-carboxymethyl-L-cysteine in aqueous solution.The complex formation between Mg(II), Mn(II), Ni(II). Cu(II), Pb(II) ions and S-carboxy-methyl-l-cysteine (H₂A) has been studied by measurement of pH at 25°C and constant ionic strength (1 M NaClO₄). Although no interaction occurs with Mg(II), this work provides evidence for a variety of complexes: MnA; CuHA⁺; CuA; CuA₂^2-; NiHA⁺; NiA; NiA₂^2-; PbHA⁺; PbA et PbA(OH)^-. The overall formation constants of all these species are computed and refined. The results allow the determination of the distribution of the complexes as a function of pH; some structural features of the metal complexes in solution are indicated.     

Synthesis and spectroscopic,magnetic and cyclic voltammetric characterization of some metal complexes of methionine: [(C5H10NO2S)2MII]; MII = Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II)

Some metal complexes of DL–methionine were prepared in aqueous medium and characterized by different physico-chemical methods. Methionine forms 1:2 complexes with metal, M(II). The general empirical formula of the complexes is proposed as [(C₅H₁₀NO₂S)₂M^II]; where M^II = Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II). All the complexes are extremely stable in light and air and optically inactive. Magnetic susceptibility data of the complexes demonstrate that they are high spin paramagnetic complex except Zn(II), Cd(II) and Hg(II) complexes. The bonding pattern in the complexes are similar to each other as indicated by electronic absorption spectra and FTIR spectral analysis. The current potential data, peak separation (AE) and the peak current ratio (i_pa/i_pc) of the (Mn, Cu and Cd) complexes indicate that the charge transfer processes are irreversible, the systems are diffusion controlled and also adsorptive controlled. The charge transfer rate constant of metals in their complexes are less than those in their metal salts at identical experimental conditions due to the coordination of metal with methionine.     

Synthesis,characterization and biological studies of Co(II), Ni(II), Cu(II) and Zn(II) complexes with pyrral-l-histidinate

The Schiff base ligand, pyrral-l-histidinate(L) and its Co(II), Ni(II), Cu(II) and Zn(II) complexes were synthesized and characterized by elemental analysis, mass, molar conductance, IR, electronic, magnetic measurements, EPR, redox properties, thermal studies, XRD and SEM. Conductance measurements indicate that the above complexes are 1:1 electrolytes. IR data show that the ligand is tridentate and the binding sites are azomethine nitrogen, imidazole nitrogen and carboxylato oxygen atoms. Electronic spectral and magnetic measurements indicate tetrahedral geometry for Co(II) and octahedral geometry for Ni(II) and Cu(II) complexes, respectively. The observed anisotropic g values indicate the presence of Cu(II) in a tetragonally distorted octahedral environment. The redox properties of the ligand and its complexes have been investigated by cyclic voltammetry. Thermal decomposition profiles are consistent with the proposed formulations. The powder XRD and SEM studies show that all the complexes are nanocrystalline. The in vitro biological screening effects of the synthesized compounds were tested against the bacterial species, Escherichia coli, Bacillus subtilis, Pseudomonas aeruginosa and Staphylococcus aureus; fungal species, Aspergillus niger, Aspergillus flavus and Candida albicans by the disc diffusion method. The results indicate that complexes exhibit more activity than the ligand. The nuclease activity of the ligand and its complexes were assayed on CT DNA using gel electrophoresis in the presence and absence of H₂O₂.     

Redox-active metal(II) complexes of sterically hindered phenolic ligands: Antibacterial activity and reduction of cytochrome c. Part II. Metal(II) complexes of o-diphenol derivatives of thioglycolic acid

The synthesis and physico-chemical characterization of Fe(II) and Mn(II) complexes of 2-[4,6-di(tert-butyl)-2,3-dihydroxyphenylsulfanyl]acetic acid (HL^I) and 2-[4,6-di(tert-butyl)-2,3-dihydroxyphenylsulfinyl]acetic acid (HL^II) were carried out. The investigation of the molecular and electronic structure of Cu(II), Ni(II), Zn(II), Fe(II) and Mn(II) complexes has been performed within the density functional theory (DFT) framework. The computed properties were compared to the experimental ones, and molecular structures of the compounds were proposed based on the array of spectral data and quantum chemical calculations. Antibacterial activity of the Fe(II) and Mn(II) complexes was evaluated in comparison with Cu(II), Co(II), Ni(II) and Zn(II) complexes and three standard antibiotics; it was found to follow the order: (1) Сu(L^I)₂ > Mn(L^I)₂ > HL^I > Ni(L^I)₂ > Zn(L^I)₂ > Fe(L^I)₂ > Co(H₂O)₂L^I; (2) Cu(L^II)₂ > Сo(L^II)₂ > Ni(L^II)₂ > Mn(H₂O)₂(L^II)₂ > Fe(L^II)₂ > HL^II > Zn(L^II)₂; their reducing ability (determined electrochemically) followed the same order. Spectrophotometric investigation was carried out in order to estimate the rate of the reduction of bovine heart сytochrome c with the ligands and their metal(II) complexes. The complexes Сu(L^I)₂, Mn(L^I)₂ and Co(L^II)₂ with the high reducing ability were found to be characterized by the highest rates of Cyt с reduction. NADPH:cytochrome P450-reductase had no substantial effect on the rate of сytochrome c reduction with HL^I and HL^II ligands.     

Bis[n(chlorophenyl)dithiocarbamato] complexes of Cu(II), Zn(II), Cd(II) and Sn(II)

Ammonium[N(o-chlorophenyl)dithiocarbamate], NH₄(OCD), ammonium [N(m-chlorophenyl)dithiocarbamate], NH₄(MCD) and ammonium [N(p-chlorophenyl)dithiocarbamate], NH₄(PCD) and their complexes with Cu(II), Zn(II), Cd(II) and Sn(II) have been synthesised. These complexes have been characterised on the basis of chemical analyses, molecular weight determinations, conductance measurements, electronic and IR spectral studies. Thermal behaviour of the compounds has been studied with the aid of TG and DTA techniques in static air atmosphere. Heats of reaction for different decomposition steps have been calculated from the DTA curves. The end products obtained after thermal decomposition of the complexes were identified by elemental analyses and IR spectral data.     

The thermal properties of the copper(II), nickel(II) and cobalt(II) glycinates

The thermal properties of the Ni(II), Co(II) and Cu(II) complexes of glycine were determined using TG, DTG and DSC techniques. The complexes, MGly₂·nH₂O (n = 1, 2), dehydrated in the temperature range of 75 to 200°C, followed by the decomposition of the anhydrous compounds in the temperature range of 200 to 400°C. The thermal stability of the complexes, as determined by procedural decomposition temperatures, was: Ni(II) >Co(II) >Cu(II).     

Thermogravimetry of heteroleptic zinc tri-tert-butoxysilanethiolates: synthesis and crystal structure of bis(tri-tert-butoxysilanethiolato)(pyridine) zinc(II)

Thermal behaviour of three silanethiolate zinc complexes i.e., bis(tri-tert-butoxysilanethiolato)bis(pyridine) zinc(II), bis(tri-tert-butoxysilanethiolato)bis(N-methylimidazole) zinc(II) and bis(tri-tert-butoxysilanethiolato) (2-methylpyridine) zinc(II) was studied. In order to determine the steps involved in thermal decay, decomposition intermediates were identified by means of IR spectroscopy and solid residues were analysed. Enthalpies of undergoing processes were estimated on the basis of DTA curves. The results of the study were applied to the synthesis of a new complex - bis(tri-tert-butoxysilanethiolato)(pyridine) zinc(II). NMR and IR spectra of this complex were measured and crystal and molecular structures were determined.     

Anion-selective receptors based on dinuclear copper(II) and nickel(II) cage complexes of bis-salicylaldimines

The selectivity, anion uptake and exchangeability of anion-binding by metal salt extractants of the form [M₂ L ₂]⁴⁺ have been assessed by the method of anion exchange chromatography in biphasic systems. The order of sulfate-, nitrate-, and chloride-uptake into the solid copper(II) complex as of the dioxime pro-ligand N,N??-dimethyl-N,N??-hexamethylenedi(3-hydroxyiminomethyl-2-hydroxy-5-tert-butylbenzylamine (L ¹ ) is 56, 42, and 16%, respectively, consistent with the relative magnitudes of formation constants for the inclusion complexes, [A?Cu₂ L ¹ ₂] ⁿ⁺ where A = anion, found in UV?Cvis titration studies in a single phase. X-ray structural determination of the bis-benzylimine pro-ligand, N,N??-dimethyl-N,N??-hexamethylenedi-(3-benzyliminomehyl-2-hydroxy-5-tert-butylbenzylamine), nickel(II) sulfato complex [SO₄?Ni₂ L ² ₂]SO₄ reveals the nickel atoms to have a significant tetrahedral distortion, providing more favourable sulfate-alkylammonium interactions within the cage.     

The thermal properties of cobalt(II), nickel(II) and copper(II) iminodiacetates

The thermal properties of the Cu(II), Ni(II) and Co(II) complexes of iminodiacetic acid (H₂IMDA) were determined using TG, DTG and DSC techniques. The complexes, of general formula, MIMDA-2H₂O evolved water of hydration from 50 to 150°C which was followed by the decomposition of the anhydrous complex in the 250 to 400°C temperature range. The thermal stability, as determined by procedural decomposition temperatures, was: Ni(II) >Co(II) >Cu(II). The thermal stability is discussed in terms of IR spectra, ΔH, and ΔS, as well as thermal data.     

Hexanuclear Zn(II) and Mononuclear Cu(II) Complexes containing imino phenol ligands: Exploitation of their Catalytic and Biological Perspectives

A unique hexanuclear zinc(II) ( 1 ) and two mononuclear copper(II) ( 2 and 3 ) complexes anchored with imino phenol ligand HL ¹ and HL ² were synthesized with good yield and purity (where HL ¹  = 4‐tert‐butyl‐2,6‐bis((mesitylimino)methylphenol and HL ²   =  5‐tert‐butyl‐2‐hydroxy‐3‐((mesitylimino)methyl)benzaldehyde). These complexes were characterized by utilizing various spectroscopic protocols like NMR, FTIR, UV as well as ESI‐Mass spectrometry, elemental analysis and single crystal X‐ray diffraction studies. Their potential to bind calf thymus DNA (CT‐DNA) was tested utilizing different techniques such as UV–visible and fluorescence spectroscopy. The experiment implies that they interact with CT‐DNA via non‐intercalative mode with moderate capabilities (K_b ~ 10⁴ M^?1). On the other hand, these complexes have high capabilities to quench the fluorescence of bovine serum albumin (BSA) following the static pathway. In addition, they are active catalysts for the oxidation reaction of 3,5‐di‐tert‐butylcatechol (3,5‐DTBC) to 3,5‐di‐tert‐butylquinone (3,5‐DTBQ) under aerobic condition. From the recorded EPR signals of all complexes, it has been concluded that the oxidation reaction proceeds via ligand oriented radical pathway instead of metal based redox participation. Kinetic studies using 1 – 3 indicate that it follows Michaelis–Menten type of equation with moderate to high turnover number (k_cat). Apart from these aspects, complexes 1 – 3 were screened for their cytotoxic behavior towards HeLa cells (human cervical carcinoma) and found quite active with comparable IC₅₀ values to cisplatin.     

Synthesis,characterization and catalytic activity of halo-methyl-bis(salicylaldehyde)ethylenediamine cobalt(II) complexes

The synthesis, characterization and catalytic activity of a series of tetra-halo-dimethyl salen and di-halo-tetramethyl-salen ligands are reported in this paper: α,α′-dimethyl-Salen (dMeSalen) (L¹); 3,3′,5,5′-tetrachloro-α,α′-dimethyl-Salen, (tCldMeSalen) (L²); 3,3′-dibromo-5,5′-dichloro-α,α′-dimethyl-Salen, (dCldBrdMeSalen) (L³); 3,3′,5,5′-tetrabromo-α,α′-dimethyl-Salen, (tBrdMeSalen) (L⁴); 3,3′,5,5′-tetraiodo-α,α′-dimethyl-salen, (tIdMeSalen) (L⁵); 3,3′-dichloro-5,5′,α,α′-tetramethyl-Salen (dCltMeSalen) (L⁶); 3,3′-dibromo-5,5′,α,α′-tetramethyl-Salen (dBrtMeSalen) (L⁷); and 3,3′-diiodo-5,5′,α,α′-tetramethyl-Salen (dItMeSalen) (L⁸) (Salen = bis(salicylaldehyde)ethylenediamine). Upon reaction with Co(II) ions, these ligands form complexes with square planar geometry that have been characterized by elemental analysis, cyclic voltammetry, UV–Vis, IR and EPR spectroscopies. In the presence of pyridine the obtained Co(II) complexes were found able to bind reversibly O₂, which was shown by EPR spectroscopy and cyclic voltammetry. They were also found able to catalyze the oxidation of 2,6-di-tert-butylphenol (DtBuP) (9) with formation of 2,6-di-tert-butyl-1,4-benzoquinone (DtBuQ) (10) and 2,6,2′,6′-tetra-tert-butyl-1,1′-diphenobenzoquinone (TtBuDQ) (11). These properties are first influenced by the coordination of pyridine in axial position of the Co(II) ion that causes an increase of the electronic density on the cobalt ion and as a consequence a decrease in the E_1/2 value and an increase of the reducing power of the Co(II) complex. It is noteworthy that, under those conditions the complexes also show a remarkable quasi-reversible behaviour. Second, complex properties are also influenced by the substituents (methyl and halogen) grafted on the aromatic ring and on the azomethynic groups. The donating methyl substituent on the azomethynic groups causes a decrease in the E_1/2 value, whereas the halogen substituents on the aromatic rings have two effects: a mesomeric donating effect that tends to lower the redox potential of the complex, and a steric effect that tends to decrease the conjugation of the ligand and then to increase the redox potential of the Co(II) complex. In pyridine, the steric effect predominates, which causes both an increase of the redox potential and a decrease of the selectivity of the oxidation of phenol 9. As a result of all these effects, it then appears that the best catalysts to realize the selective oxidation of 2,6-di-tert-butyl-phenol (9) by O₂ are the Co complexes of ligands bearing CH₃ donating substituents, Co(dMeSalen) 1 (2CH₃ substituents), and Co-di-halo-tetra-methyl-salen complexes 6, 7 and 8 (4CH₃ substituents), in the presence of pyridine.     

Redox-active metal(II) complexes of sterically hindered phenolic ligands: Antibacterial activity and reduction of cytochrome c

The synthesis and physico-chemical characterization of Fe(II) and Mn(II) complexes of 4,6-di-tert-butyl-3[(2-hydroxyethyl)sulphanyl]-1,2-dihydroxybenzene (HL^I) and 2-amino-4,6-di-tert-butylphenol (HL^II) were carried out. Antibacterial activity of the Co(II), Fe(II) and Mn(II) complexes was evaluated in comparison with Cu(II) complexes and three common antibiotics; it was found to follow the order: (1) Сu(L^I)₂ > Сo(L^I)₂ > Fe(L^I)₂ ? Mn(L^I)₂ > HL^I; (2) Сu(L^II)₂ > Сo(L^II)₂ > HL^II > Fe(L^II)₂ ? Mn(L^II)₂; and their reducing ability (determined electrochemically) followed the same order. Spectrophotometric investigation was carried out in order to estimate the rate of the reduction of bovine heart сytochrome c with the ligands and their metal(II) complexes. NADPH:cytochrome P450-reductase was found to increase the rate of сytochrome c reduction with HL^I and HL^II ligands, while adrenodoxin in couple with NAD(P)H: adrenodoxin reductase had no substantial effect thereon. It was shown that the reduction of сytochrome c with these compounds cannot be related solely to the facility of their oxidation оr ionization.