Micellar catalysis of the alkylation of mercuric ions by alkyl cobalt(III) complexes.

Anionic micelles of sodium lauryl sulfate, NaLS, catalyze the monoalkylation of Hg2+ in dilute acid by alkyl aquobis-(dimethyl glyoximato) cobalt (III), RCo(DH)2(H2O) degrees and the related propane derivatives RCo(DOH) DOpn (H2O)+, where R = Me, Et, n-C5H11. Nonionic micelles of Igepal do not catalyze the reaction. In the absence of micelles RCo(DH)2(H2O) degrees is considerably more reactive than RCo(DOH)DOpn(H2O)+, but this higher reactivity is offset in part by its higher basicity. Anionic micelles markedly increase the basicity of RCo(DOH)DOpn(H2O)+ and slightly increase that of RCo(DH)2(H2O) degrees. For reactions of the unprotonated Co(III) complexes the maximum rate enhancements by micelles of NaLS are: R = Me, 19(131); Et, 58 (65); n-C5H11, 46 (32). (The values in parentheses are for RCo(DOH)DOpn(H2O)+.)     

Olefin oxidation by cytochrome P-450: evidence for group migration in catalytic intermediates formed with vinylidene chloride and trans-1-phenyl-1-butene

Oxidation of the carcinogen vinylidene chloride (VDC) by rat liver cytochrome P-450 (P-450) in microsomal and purified enzyme systems produced both ClCH2CO2H and Cl2CHCHO with concomitant suicide inactivation of three of the eight P-450 isozymes examined. The proposed intermediary role of VDC oxide in ClCH2CO2H and Cl2CHCHO production was evaluated by using chemical and kinetic studies. Aqueous decomposition of authentic VDC oxide, prepared by m-chloroperoxybenzoic acid oxidation of VDC and characterized by nuclear magnetic resonance (NMR) and mass spectrometry, failed to produce Cl2CHCHO and yielded ClCH2CO2H only at pH less than 2. Moreover, kinetic studies of VDC oxide production in the iodosobenzene-supported oxidation of VDC by P-450 did not support its proposed role as an obligate intermediate in the formation of ClCH2CO2H and Cl2CHCHO. [2,2-2H2]VDC was synthesized and found to be oxidized to Cl2C2HCO2H by microsomes supplemented with aldehyde dehydrogenase and NAD+, indicating transfer of deuterium in the formation of the precursor Cl2C2HC2HO. To test the hypothesis that the heme Fe(III) of P-450 acts as a Lewis acid in catalyzing the rearrangement of a transient epoxide intermediate to Cl2CHCHO, the decomposition of VDC oxide in the presence of Fe(III) was studied. While FeBr3-saturated CHCl3 effected approximately 50% rearrangement of epoxide to Cl2CHCHO, neither an equivalent concentration of (meso-tetraphenylporphyrinato)iron(III) chloride in CHCl3 nor highly purified cytochrome P-450 in aqueous buffer produced Cl2CHCHO from VDC oxide. Parallel studies using trans-1-phenylbutene 1,2-oxide, a stable model epoxide, indicated that, although binding of epoxide to P-450 did occur, ferric P-450 did not catalyze epoxide degradation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Synthesis, characterization and anti-tumour testing of some platinum(II) amine complexes containing 1,1- and 1,2-cyclobutanedicarboxylate ligands

A series of new platinum(II) amine complexes containing 1,1- and 1,2-cyclobutanedicarboxylate ligands, cis-[PtA2(1,1-CBDCA)] (A = RNH2, where R = C2H5, n-C3H7, n-C4H9, n-C5H11, n-C6H13, c-C3H5, c-C5H9, c-C6H11; A2 = ethylenediamine, 1,3-diaminopropane), cis-[PtA2(1,2-CBDCA)] (A = NH3, RNH2 where R = CH3, C2H5, n-C3H7, n-C4H9, c-C3H5) and trans-[Pt(NH3)2(1,1-CBDCAH)2] (CBDCA, CBDCAH = dianion and monoanion of the dicarboxylic acid, respectively) have been synthesized by an improved route. These complexes are stable in aqueous solution and show good aqueous solubility. The [Pt(c-C3H5NH2)2(1,1-CBDCA)] can be isolated in white, grey and blue forms. The grey and blue forms exhibit ESR signals analogous to the so-called platinum blues. The existence of the blue form in aqueous solution is time and temperature dependent. Several of the complexes have been tested against leukaemia L1210 in male BDF mice and activity appears to decrease with the increase in length of the aliphatic chain (or increase in size of the alicyclic ring) of the primary amine. The Yoshida lymphoscarcoma screen, usually insensitive to platinum drugs, was found to respond well to [Pt(n-C4H9NH2)2(1,1-CBDCA)] in 5-day subcutaneously implanted tumours in female Wistar rats.     

Biomimetic oxidation of ibuprofen with hydrogen peroxide catalysed by horseradish peroxidase (HRP) and 5,10,15,20-tetrakis-(2',6'-dichloro-3'-sulphonatophenyl)porphyrinatoiro n(III) and manganese(III) hydrates in AOT reverse micelles

The oxidation of ibuprofen with H2O2 catalysed by Horseradish peroxidase (HRP), Cl8TPPS4Fe(III)(OH2)2 and Cl8TPPS4Mn(III)(OH2)2 in AOT reverse micelles gives 2-(4'-isobutyl-phenyl)ethanol (5) and p-isobutyl acetophenone (6) in moderate yields. The reaction of ibuprofen (2) with H2O2 catalysed by HRP form carbon radicals by the oxidative decarboxylation, which on reaction with molecular oxygen to form hydroperoxy intermediate, responsible for the formation of the products 5 and 6. The yields of different oxidation products depend on the pH, the water to surfactant ratio (Wo), concentration of Cl8TPPS4Fe(III)(OH2)2 and Cl8TPPS4Mn(III)(OH2)2 and amount of molecular oxygen present in AOT reverse micelles. The formation of 2-(4'-isobutyl phenyl)ethanol (5) may be explained by the hydrogen abstraction from ibuprofen by high valent oxo-manganese(IV) radical cation, followed by decarboxylation and subsequent recombination of either free hydroxy radical or hydroxy iron(III)/manganese(III) porphyrins. The over-oxidation of 5 with high valent oxo-manganese, Mn(IV)radical cation intermediate form 6 in AOT reverse micelles by abstraction and recombination mechanism.     

Synthesis and amphiphilic properties of glycosyl-1,4-benzodiazepin-2,5-diones

Glycosyl-1,4-benzodiazepin-2,5-diones were prepared by coupling polyhydroxylated groups at N-1 of the corresponding benzodiazepine. The groups include 1-deoxy-D,L-xylit-1-yl, 6-deoxy-D-glucopyranos-6-yl, and 6-deoxy-3-OR-D-glucopyranos-6-yl (R = n-CnH(2n +1); n = 8, 12, and 16). The structural variations of the sugar group allowed comparison of such amphiphilic data as water solubility (Sw), critical micelle concentration (CMC), and corresponding surface tension (gamma) values. At 25 degrees C, unsubstituted benzodiazepines have Sw values from 0.9 to 4.2 10(-3) mol L(-1), whereas xylit-1-yl and 6-deoxy-D-glucopyranos-6-yl derivatives are, respectively, 7.4-25 and 58-204 times more soluble. Also, compounds with R = n-C8H17 are more soluble than corresponding benzodiazepines (1.4-5.8 times) and give micelles with CMC from 2.7 to 5.6 10(-3) mol L(-1) and corresponding gamma from 29 to 37 mN m(-1). In contrast, compounds with R = n-C12H25 and n-C16H33 are not soluble enough to reach the critical micelle concentration.     

Coordination compounds derived from the interaction of streptomycin and cobalt, nickel, copper, and calcium salts characterized by 13C NMR and spectroscopic studies. Structure and bonding properties of the streptidine fraction

The coordination compounds of streptomycin (St), Co2(St)Cl4.13H2O (2), Co2(St)(NO3)4.7H2O (3), Ni2(St)Cl4.14H2O (4), Ni2(St)(NO3)4.14H2O (5), Cu2(St)Cl4.6H2O (6), and Ca(St)Cl2.8H2O (7) have been synthesized by the reaction of streptomycin sulfate (1) with three equivalents of the corresponding inorganic salt. The compounds (2)-(7) were characterized by electronic spectroscopy (in the solid state and in solution) by conductivity measurements and by 13C NMR in solution. The reaction of streptomycin with CuCl2 in water hydrolyzed the molecule giving the copper complex of the streptidine fraction (Std), Cu(Std)Cl.H2O (8). This compound was characterized by the same techniques. Detailed x-ray diffraction and 13C NMR studies of streptidine sulfate (9) were carried out.     

Vitamin C interaction with cobalt-ammine cations. Synthesis, spectroscopic and structural characterization of cobalt-pentammine and cobalt-tetrammine sugar complexes containing L-ascorbate anion

Interaction between [Co(NH3)5Cl]Cl2, [Co(NH3)4Cl2]Cl and L-ascorbic acid has been investigated in aqueous solution and solid complexes of the type [Co(NH3)5 ascorbate]Cl2 X H2O and [Co(NH3)4 ascorbate]Cl2 X H2O have been isolated and characterized by 13C-NMR, FT-IR and electron absorption spectroscopy. Spectroscopic and other evidence suggested that the sugar anion binds monodentately in the [Co(NH3)5 ascorbate]2+ cation via the ionized O3 oxygen atom and bidentately in [Co(NH3)4 ascorbate]2+ through the O1 and O4 oxygen atoms, resulting in a six-coordinate geometry around the Co(III) ion. The intermolecular sugar hydrogen-bonding network is perturbed upon sugar metalation and the sugar moiety shows a similar conformation to that of the sodium ascorbate compound in these series of cobalt-ammine complexes.     

Thermodynamics of hydrolysis of oligosaccharides

Microcalorimetry has been used to determine enthalpy changes for the hydrolysis of a series of oligosaccharides. High-pressure liquid chromatography was used to determine the extents of reaction and to check for any possible side reactions. The enzyme glucan 1,4-alpha-glucosidase was used to bring about the following hydrolysis reactions: (A) maltose(aq) + H2O(liq) = 2D-glucose(aq); (B) maltotriose(aq) + 2H2O(liq) = 3D-glucose(aq); (C) maltotetraose(aq) + 3H2O(liq) = 4D-glucose(aq); (D) maltopentaose(aq) + 4H2O(liq) = 5D-glucose(aq); (E) maltohexaose(aq) + 5H2O(liq) = 6D-glucose(aq); (F) maltoheptaose(aq) + 6H2O(liq) = 7D-glucose(aq); (G) amylose(aq) + nH2O(liq) = (n + 1) D-glucose(aq); and (H) panose(aq) + 2H2O(liq) = 3D-glucose(aq); (J) isomaltotriose(aq) + 2H2O(liq) = 3D-glucose(aq). The enzyme beta-fructofuranosidase was used for the reactions: (K) raffinose(aq) + H2O(liq) = alpha-D-melibiose(aq) + D-fructose(aq); and (L) stachyose(aq) + H2O(liq) = o-alpha-D-galactopyranosyl-(1----6)- alpha-o-D-galactopyranosyl-(1----6)-alpha-D-glucopyranose + D-fructose(aq). The results of the calorimetric measurements (298.15 K, 0.1 M sodium acetate buffer, pH 4.44-6.00) are: delta H0A = -4.55 +/- 0.10, delta H0B = -9.03 +/- 0.10, delta H0C = -13.79 +/- 0.15, delta H0D = -18.12 +/- 0.10, delta H0E = -22.40 +/- 0.15, delta H0F = -26.81 +/- 0.20, delta H0H = 1.46 +/- 0.40, delta H0J = 11.4 +/- 2.0, delta H0K = -15.25 +/- 0.20, and delta H0L = -14.93 +/- 0.20 kJ mol-1. The enthalpies of hydrolysis of two different samples of amylose were 1062 +/- 20 and 2719 +/- 100 kJ mol-1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of Igepal reverse micellar and micellar systems on activity and stability of heme peroxidases

The activities of horseradish peroxidase (HRP) and lactoperoxidase (LPO) entrapped in reverse micelles of Igepal CO-520 in cyclohexane were studied. When the molar ratio of water to surfactant, w ₀ was ≥13, the activity of HRP encapsulated in the water pool of the reverse micelle was comparable with that measured in buffer. For LPO, however, lower activity was observed after its incorporation into the same system.

The activity of the investigated peroxidases was also measured in an aqueous solution of Igepal CO-720 or after incubation with this surfactant. The enzymes became inactivated in an aqueous micellar solution of Igepal CO-720, although this process was reversible.

The stability of HRP and LPO at 37 or 50°C was lower in the micellar systems than in buffer with the exception for HRP in reverse micelles at 50°C.     

Synthetic, biologically active amphiphilic peptides

Amphiphilic peptides typically consist of a peptide portion that may be 5-25 (or more) amino acids in length. The hydrophobic portion may be a single fatty acid residue, but can also be more elaborate. The main focus of this article lies on the family of synthetic anion binders (SATs) of the general structure (R(1))(2)N-COCH(2)OCH(2)CO-(Aaa)(n)-OR(3). The most-common R(1) group is the octadecyl (C(18)H(37)) group. The most studied peptide sequence in this family is (Gly)(3)-Pro-(Gly)(3), although different sequences (and longer and shorter peptides) have been prepared as well. The C-terminal ester residue providing the most effective anion release from liposomes is heptyl (C(7)H(15)), although many others have been examined. The compound (C(18)H(37))(2)N-COCH(2)OCH(2)CO-(Gly)(3)-Pro-(Gly)(3)-OBn (Bn=benzyl) was found to mediate Cl(-) transport in mouse epithelial cells.     

Stopped-flow kinetic study of vitamin E regeneration reaction with biological hydroquinones (reduced forms of ubiquinone, vitamin K, and tocopherolquinone) in solution.

A kinetic study of the regeneration reaction of vitamin E (tocopherol) with eight biological hydroquinones (HQs) (ubiquinol-10 (Q10H2 1); ubiquinol-0 (Q0H2 2); vitamin K1 HQ (VK1H2 3); vitamin K3 HQ (VK3H2 4); alpha-, beta-, and gamma-tocopherol-HQs (alpha-, beta-, and gamma-TQH2 5-7); and 2,3,5-trimethyl-1,4-HQ (TMQH2 8)) in solution was performed. The second-order rate constants (k4) for the reaction of HQs 1-8 with alpha-tocopheroxyl and 5,7-diisopropyltocopheroxyl radicals in ethanol, benzene, and isopropyl alcohol/water (5:1, v/v) solutions were measured with a stopped-flow spectrophotometer. The order of magnitude of k4 values obtained for HQs is VK1H2 > VK3H2 > alpha-TQH2 > beta-TQH2 approximately gamma-TQH2 approximately TMQH2 > Q10H2 > Q0H2, being independent of the kinds of tocopheroxyl radicals and the polarity of the solvents. The log of the k4 values obtained for HQs was found to correlate with their peak oxidation potentials. Comparing the k2 value (2.68 x 10(6) M-1 s-1 obtained for the reaction of alpha-tocopheroxyl with vitamin C (sodium ascorbate) with those (k4 = 2.54 x 10(5) and 8.15 x 10(5) M-1 s-1) obtained for the reaction of alpha-tocopheroxyl with Q10H2 and alpha-TQH2 in isopropyl alcohol/water mixtures, the former is approximately 11 and 3 times as reactive as the latter, respectively. On the other hand, the k2 value obtained for sodium ascorbate is smaller than the k4 values obtained for VK1H2 and VK3H2. These results suggest that mixtures of vitamin E and these HQs (as well as those of vitamins E and C) may function synergistically as antioxidants in various tissues and mitochondria.     

Effects of equatorial ligand bulk on the orientation of axial ligands in methyl organocobalt B12 models assessed by X-ray and NMR methods

We prepared two new analogues of ([CH₃Co((DO)(DOH)pn)L]⁺) [(DO)(DOH)pn = N²,N^2′-propane-1,3-diylbis(2,3-butanedione-2-imine-3-oxime)] B₁₂ models but with an O-BF₂-O unit replacing the O-H?O unit as follows: [CH₃Co((DO)(DOBF₂)pn)L]PF₆ with L = pyridine (py) and 1,5,6-trimethylbenzimidazole (Me₃Bzm). Our goal was to compare the properties of these new O-BF₂-O complexes with the well-established O-H?O analogues. The Co-CH₃¹H NMR shifts indicate that the BF₂ group makes the Co(III) less electron rich. The X-ray crystal structures determined for the new compounds were compared to the one known structure with L = imidazole (Im). With increasing size of L, in the series Im < py < Me₃Bzm, the plane of L orients so as to avoid the bulky BF₂ group. This orientation effect becomes apparent in the L ¹H NMR shifts, which are not sensitive to Co(III) electronic properties. Thus, in the O-BF₂-O versus the O-H?O analogue, the Me₃Bzm H4 signal shifts 0.41 ppm upfield from the anisotropic effect of the equatorial ligand double bonds. We advance the concept (applicable to a broad series of complexes) that steric interactions between L and the equatorial ligands are alleviated by a combination of Co-N_ax bond elongation and opening of the N_eq-Co-N_ax angles.     

Isolation and characterization of an ornithine-containing lipid from Desulfovibrio gigas.

The isolation and characterization of an ornithine-containing lipid obtained from Desulfovibrio gigas are reported. The general structure for this aminolipid is represented by NH2-CH2-(CH)2-CHNH(CO-CH2CH(O-COR2)-R1)-COOH, where R1 represents 3-hydroxy palmitate linked through an amide bond to the alpha-amino group of ornithine, and R2 represents a complex variety of fatty acids esterified to the hydroxyl group of 3-hydroxy palmitate. Fatty acids characterized were n-C14:0 (21%), iso-C14:0 (14%) anteiso-C15:0 (43%), n-C16:0 (2%), n-C18:0 (8%), and n-C 18:1 (11%). The quantitative relationships between aminolipid and phospholipids showed the aminolipid to represent the major polar lipid. Isolation of the cytoplasmic and outer membranes of D. gigas showed the aminolipid to be evenly distributed between both membrane fractions, suggesting a compensatory role in phospholipid-deficient membranes.     

Synthesis, physico-chemical studies of manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) complexes with some p-substituted acetophenone benzoylhydrazones and their antimicrobial activity

Complexes of the type [M(pabh)(H2O)Cl], [M(pcbh)(H2O)Cl] and [M(Hpabh)(H2O)2 (SO4)] where, M = Mn(II), Co(II), Ni(II), Cu(II) and Zn(II); Hpabh = p-amino acetophenone benzoyl hydrazone and Hpcbh = p-chloro acetophenone benzoyl hydrazone have been synthesized and characterized with the help of elemental analyses, electrical conductance, magnetic susceptibility measurements, electronic, ESR and IR spectra, thermal (TGA & DTA) and X-ray diffraction studies. Co(II), Ni(II) and Cu(II) chloride complexes are square planar, whereas their sulfate complexes have spin-free octahedral geometry. ESR spectra of Cu(II) complexes with Hpabh are axial and suggest d(x(2)-y(2) as the ground state. The ligand is bidentate bonding through > C = N--and deprotonated enolate group in all the chloro complexes, whereas, >C = N and >C = O groups in all the sulfato complexes. Thermal studies (TGA & DTA) on [Cu(Hpabh)(H2O)2(SO4)] indicate a multistep decomposition pattern, which are both exothermic and endothermic in nature. X-ray powder diffraction parameters for [Co(pabh)(H2O)Cl] and [Ni(Hpabh)(H2O)2(SO4)] correspond to tetragonal and orthorhombic crystal lattices, respectively. The ligands as well as their complexes show a significant antifungal and antibacterial activity. The metal complexes are more active than the ligand.     

Reactions of peroxyl radicals with Fe(H(2)O)(6)(2+)

The reactions of RO(2)* radicals with Fe(H(2)O)(6)(2+) were studied, R[double bond]H; CH(3); CH(2)COOH; CH(2)CN; CH(2)C(CH(3))(2)OH; CH(2)OH; CHCl(2)/CCl(3). All these processes involve the following reactions: Fe(H(2)O)(6)(2+)+RO(2)*<==>(H(2)O)(5)Fe(III)[bond]OOR(2+) K(1) approximately 250 M(-1); (H(2)O)(5)Fe(III)[bond]OOR(2+)+H(3)O(+)/H(2)O-->Fe(H(2)O)(6)(3+)+ROOH+H(2)O/OH(-); (H(2)O)(5)Fe(III)[bond]OOR(2+)+2Fe(H(2)O)(6)(2+)-->3Fe(H(2)O)(6)(3+)+ROH; 2 RO(2)*-->Products; RO(2)*+(H(2)O)(5)Fe(III)[bond]OOR(2+)-->Fe(H(2)O)(6)(2+)+products. The values of k(1) and k(3) [reaction is clearly not an elementary reaction] approach the ligand exchange rate of Fe(H(2)O)(6)(2+), i.e. these reactions follow an inner sphere mechanism and the rate determining step is the ligand exchange step. The rate of reaction is several orders of magnitude faster than that of the Fenton reaction. Surprisingly enough the K(1) values are nearly independent of the redox potential of the radical and are considerably higher than calculated from the relevant redox potentials. These results indicate that the ROO(-) ligands considerably stabilise the Fe(III) complex, this stabilisation is smaller for radicals with electron withdrawing groups which raise the redox potential of the radical but decrease the basicity of the ROO(-) ligands, two effects which seem to nearly cancel each other. Finally, the results clearly indicate that reaction (5) is relatively fast and affects the nature of the final products. The contribution of these reactions to oxidation processes involving 'Fenton-like' processes is discussed.     

Methyl-transfer reaction to alkylthiol catalyzed by a simple vitamin B12 model complex using zinc powder

The catalytic methyl-transfer reaction from methyl tosylate to 1-octanethiol was carried out in the presence of a simple vitamin B₁₂ model complex, [Co(III){(C₂C₃)(DO)(DOH)pn}Br₂], with zinc powder as the reducing reagent at 50 °C. Such a catalytic reaction proceeded via the formation and dissociation of a cobalt-carbon bond in the simple vitamin B₁₂ model complex under non-enzymatic conditions. The mechanism for the methyl-transfer reaction was investigated by electronic and mass spectroscopies. The Co(I) species, which is generated from the reduction of the catalyst by the zinc powder, and its methylated CH₃-Co complex were found to be indispensable intermediates.     

Influence of Igepal reverse micellar and micellar systems on activity and stability of heme peroxidases

The activities of horseradish peroxidase (HRP) and lactoperoxidase (LPO) entrapped in reverse micelles of Igepal CO-520 in cyclohexane were studied. When the molar ratio of water to surfactant, w₀ was ≥13, the activity of HRP encapsulated in the water pool of the reverse micelle was comparable with that measured in buffer. For LPO, however, lower activity was observed after its incorporation into the same system.

The activity of the investigated peroxidases was also measured in an aqueous solution of Igepal CO-720 or after incubation with this surfactant. The enzymes became inactivated in an aqueous micellar solution of Igepal CO-720, although this process was reversible.

The stability of HRP and LPO at 37 or 50°C was lower in the micellar systems than in buffer with the exception for HRP in reverse micelles at 50°C.     

Antioxidant properties of rhenium cluster complexes with butyric acid derivatives in blood plasma and erythrocytes

The antioxidant action of rhenium cluster complexes with isobutiric and gamma-aminobutiric acids were studied in vitro. It was established that strong antiradical properties were found in the reaction with stable radical diphenylpycrylhydrazile Re2(i-C3H7COO)4Cl2, [Re2(GABA)2Cl5(H2O)]Cl.2H2O. The chemiluminescence investigation of antioxidant properties of both substances Re2(i-C3H7COO)4Cl2 and [Re2(GABA)2Cl5(H2O)]Cl.2H2O has established that these properties are realized in the blood plasma and erythrocytes, but to different extent.     

A new strategy for the study of oligomeric enzymes: gamma-glutamyltransferase in reversed micelles of surfactants in organic solvents

A heterodimeric enzyme (gamma-glutamyltransferase) was studied in the reversed micellar medium of Aerosol OT (AOT) in octane. As was shown earlier, the size (radius) of inner cavity of the AOT-reversed micelles is determined by their hydration degree, i.e., [H2O]/[AOT] molar ratio, in the system. Owing to this, the dependence of hydrolytic, transpeptidation and autotranspeptidation activities of the enzyme on the hydration degree was investigated using L- and D-isomers of gamma-glutamyl(3-carboxy-4-nitro)anilide and glycylglycine as substrates. For all of the reaction types, the observed dependences are curves with three optima. The optima are found at the hydration degrees, [H2O]/[AOT] = 11, 17 and 26 when the inner cavity radii of reversed micelles are equal to the size of light (Mr 21,000) and heavy (Mr 54,000) subunits of gamma-glutamyltransferase, and to their dimer (Mr 75,000), respectively. Ultracentrifugation experiments showed that a change of the hydration degree resulted in a reversible dissociation of the enzyme to light and heavy subunits. The separation of light and heavy subunits of gamma-glutamyltransferase formed in reversed micelles was carried out and their catalytic properties were studied. The two subunits catalyze hydrolysis and transpeptidation reactions; autotranspeptidation reaction is detected only in the case of the heavy subunit. These findings imply that the reversed micelles of surfactants in organic solvents function as the matrices with adjustable size permitting to regulate the supramolecular structure and the catalytic activity of oligomeric enzymes.     

Guest driven self-assembly of a rectangular box from methylaquacobaloxime and 4,4′-biphenyldiboronic acid

We described the guest-induced synthesis of a rectangular host derived from methylaquacobaloxime CH₃Co(dmgH)₂H₂O and 4,4′-biphenyldiboronic acid containing 4,4′-bipyridine (bipy) molecule as guest. The assembly, monitored by a time dependent ¹H NMR experiment, showed that the guest thermodynamically drives the organization of the host. The structural characterization of the complex evidenced a centrosymmetric rectangular box having two biphenyldiboronate units and a central 4,4′-bipyridine spacer connecting the cobaloxime units (1). The spacers have coplanar rings, being negligible the tilt angle around the central C-C bond. The molecular structure of 1 and of the dinuclear complex [CH₃Co(dmgH)₂]₂(bipy) indicates close comparable intermetallic distance for the rigid bipy bridge and a coplanar arrangement of the cobaloxime moieties that facilitates the formation of the molecular box. The other tested ditopic ligands L (α,α′-diamino-p-xylene and 1,6-diaminohexane) used in this study allowed only a partial assembly. These derivatives and the related dinuclear complexes [CH₃Co(dmgH)₂]₂(L), which were synthesized with the aim to obtain further insights about the formation of the molecular boxes, were also characterized by X-ray structural analysis. The structures of [CH₃Co(dmgH)₂]₂(L), beside the expected flexibility of L, indicate not facing cobaloxime moieties. CV measurements suggest the formation of dinuclear non organometallic Co(II) and Co(I) species after the first reduction for all the dinuclear compounds that are stable in solution. For 1 no electronic coupling is shown, in spite of coplanar conformation of the 4,4′-bipyridine rings.