Cytochrome c interaction with the mitochondrial membrane: A spin label study

Horse-heart ferrocytochrome c has been labeled with N-(2,2,5,5-tetramethyl-3-pyrrolidinyl-1-oxyl) iodoacetamide at methionine-65. The paramagnetic resonance spectrum of labeled ferricytochrome c indicates a weak immobilization of the radical (τ_c = 9.3·10⁻¹⁰ sec) which becomes stronger upon binding of labeled cytochrome c to cytochrome c-depleted mitochondrial membranes (τ_c = 3.3·10⁻⁹ sec). The hyperfine coupling constant remains, however, unchanged (16.7 ± 0.1 gauss) indicating that the cytochrome c binding site is highly polar. The region where cytochrome c is bound to the membrane is insensitive to large variations of medium viscosity.     

Probing fluorescence induction in chloroplasts on a nanosecond time scale utilizing picosecond laser pulse pairs

The fluorescence induction and other fluorescence properties of spinach chloroplasts at room temperature were probed utilizing two 30-ps wide laser pulses (530 nm) spaced Δt (s) apart in time (Δt = 5–110 ns). The energy of the first pulse (P₁) was varied (10¹²–10¹⁶ photons · cm⁻²), while the energy of the second (probe) pulse (P₂) was held constant (5 · 10¹³ photons · cm⁻²). A gated (10 ns) optical multichannel analyzer-spectrograph system allowed for the detection of the fluorescence generated either by P₁ alone, or by P₂ alone (preceded by P₁). The dominant effect observed for the fluorescence yield generated by P₁ alone is the usual singlet-singlet exciton annihilation which gives rise to a decrease in the yield at high energies. However, when the fluorescence yield of dark-adapted chloroplasts is measured utilizing P₂ (preceded by pulse P₁) an increase in this yield is observed. The magnitude of this increase depends on Δt, and is characterized by a time constant of 28 ± 4 ns. This rise in the fluorescence yield is attributed to a reduction of the oxidized (by P₁) reaction center P-680⁺ by a primary donor. At high pulse energies (P₁ = 4 · 10¹⁴ photons · cm⁻²) the magnitude of this fluorescence induction is diminished by another quenching effect which is attributed to triplet excited states generated by intense P₁ pulses. Assuming that the P₁ pulse energy dependence of the fluorescence yield rise reflects the closing of the reaction centers, it is estimated that about 3–4 photon hits per reaction center are required to close completely the reaction centers, and that there are 185–210 chlorophyll molecules per Photosystem II reaction center.     

Alkene rotation in [Ru(η-C5H5) (L2) (η-alkene][CF3SO3] with L2 = iPr- or pTol-diazabutadiene. X-ray crystal structure of [Ru(η-C5H5(pTol-DAB) (η-ethene][CF3SO3]

Reaction of RuCl(η⁵-C₅H₅(pTol-DAB) with AgOTf (OTf = CF₃SO₃) in CH₂Cl₂ or THF and subsequent addition of L′ (L′ = ethene (a), dimethyl fumarate (b), fumaronitrile (c) or CO (d) led to the ionic complexes [Ru(η⁵-C₅H₅)(pTol-DAB)(L′)][OTf] 2a, 2b and 2d and [Ru(η⁵-C₅H₅)(pTol-DAB)(fumarontrile-N)][OTf] 5c. With the use of resonance Raman spectroscopy, the intense absorption bands of the complexes have been assigned to MLCT transitions to the iPr-DAB ligand. The X-ray structure determination of [Ru(η⁵-C₅H₅)(pTol-DAB)(η²-ethene)][CF₃SO₃] (2a) has been carried out. Crystal data for 2a: monoclinic, space group P2₁/n with A = 10.840(1), b = 16.639(1), C = 14.463(2) Å, β = 109.6(1)°, V = 2465.6(5) ų, Z = 4. Complex 2a has a piano stool structure, with the Cp ring η⁵-bonded, the pTol-DAB ligand σN, σN′ bonded (Ru-N distances 2.052(4) and 2.055(4) Å), and the ethene η²-bonded to the ruthenium center (Ru-C distances 2.217(9) and 2.206(8) Å). The C = C bond of the ethene is almost coplanar with the plane of the Cp ring, and the angle between the plane of the Cp ring and the double of the ethene is 1.8(0.2)°. The reaction of [RuCl(η⁵-C₅H₅)(PPh)₃ with AgOTf and ligands L′ = a and d led to [Ru(η⁵-C₅H₅)(PPh₃)₂(L′)]OTf] (3a) and (3d), respectively. By variable temperature NMR spectroscopy the rottional barrier of ethene (a), dimethyl fumarate (b and fumaronitrile (c) in complexes [Ru(η⁵-C₅H₅)(L₂)(η²-alkene][OTf] with L₂ = iPr-DAB (a, 1b, 1c), pTol-DAB (2a, 2b) and L = PPh₃ (3a) was determined. For 1a, 1b and 2b the barrier is 41.5±0.5, 62±1 and 59±1 kJ mol⁻¹, respectively. The intermediate exchange could not be reached for 1c, and the ΔG^# was estimated to be at least 61 kJ mol⁻. For 2a and 3a the slow exchange could not be reached. The rotational barrier for 2a was estimated to be 40 kJ mol⁻. The rotational barier for methyl propiolate (HC≡CC(O)OCH₃) (k) in complex [Ru(η⁵-C₅H₅)(iPr-DAB) η²-HC≡CC(O)OCH₃)][OTf] (1k) is 45.3±0.2 kJ mol⁻¹. The collected data show that the barrier of rotational of the alkene in complexes 1a, 2a, 1b, 2b and 1c does not correlate with the strength of the metal-alkene interaction in the ground state.     

Trapping, loss and annihilation of excitations in a photosynthetic system: II. Experiments with the purple bacteria Rhodospirillum rubrum and Rhodopseudomonas capsulata

In this paper a number of experiments with the purple bacteria Rhodospirillum rubrum and Rhodopseudomonas capsulata is described in which the total fluorescence yield and/or the total fraction of reaction centers closed after a picosecond laser pulse were measured as a function of the pulse intensity. The conditions were such that the reaction centers were either all in the open or all in the closed state before the pulse arrived. These experiments are analysed using the theoretical formalism discussed in the preceding paper (Den Hollander, W.T.F., Bakker J.G.C., and Van Grondelle, R., Biochim. Biophys. Acta 725, 492–507). From the experimental results the number of connected photosynthetic units, λ, the rate of energy transfer between neighboring antenna molecules, k_h, and the rate of trapping by an open reaction center, k^o_t, can be estimated. For R. rubrum it is found that λ = 14−17, k_h = (1−2)·10¹² s⁻¹ and k^o_t = (4−6)·10¹¹ s⁻¹, for Rps. capsulata λ ≈ 30, k_h ≈ 4·10¹¹ s⁻¹ and k^o_t ≈ 3·10¹¹ s⁻¹. The findings are discussed in terms of current models for the structure of the antenna and the kinetic properties of the decay processes occurring in these purple bacteria.     

Heterobimetallic aggregates of copper(I) with thiotungstates and thiomolybdates. Synthesis and characterization of polymeric (NEt4)3[Cu4(NCS)5WS4], (NEt4)2[(CuNCS)3WS4] and (NEt4)2[(CuNCS)4WS4], M = Mo, W

Reaction of (NEt₄)₂MS₄ (M = Mo, W) with CuCl and KSCN (or NH₄SCN) in acetone or acetonitrile affords a new set of mixed metal–sulfur compounds: infinite anionic chains Cu₄(NCS)₅MS_4³⁻ (1,2), (CuNCS)₃WS_4²⁻ (3) and two dimensional polymeric dianions (CuNCS)₄MS_4²⁻ (4,5). Crystal of 1 (M = W) and 3 are triclinic, space group P1(1:a = 10.356(2),b = 15.039(1),c = 17.356(2)Å, = 78.27(1)°, β = 88.89(2)° and γ = 88.60(1)°,Z = 2,R = 0.04 for 3915 independent data;3:a = 8.449(2),b = 14.622(4),c = 15.809(8)Å, = 61.84(3)°, β = 73.67(3)° and γ = 78.23(2)°,Z = 2,R = 0.029 for 6585 independent data). Crystals of 4 (M = W) and 5 (M = Mo) are monoclinic, space group P2₁/m,Z = 2 (4:a = 12.296(4),b = 14.794(4),c = 10.260(3)Åand β = 101.88(3)°,R = 0.034 for 4450 independent data;5:a = 12.306(2),b = 14.809(3),c = 10.257(2)Åand β = 101.99(3)°,R = 0.043 for 3078 independent data). The crystal structure determinations of 4 and 5 show that four edges of the tetrahedral MS_4²⁻ core are coordinated by copper atoms forming WS₄Cu₄ aggregates linked by eight-membered Cu(NCS)₂Cu rings. A two-dimensional network is thus formed in the diagonal (101) plane. The space between the anionic two-dimensional networks is filled with the NEt_4⁺ cations. Additional NCS groups lead to the [Cu₄(NCS)₅WS₄]³⁻ (1) trianion connected by NCS bridges forming pseudo-dimers. These latter are held together by weak CuS(NCS) interactions giving rise to infinite chains along a direction parallel to [100]. In contrast complex3 develops infinite chains from WS₄Cu₃ aggregates with the same Cu(NCS)₂Cu bridges as in 4 and 5. These chains are running along a direction parallel to [010]. The structural data of the different types of polymeric compounds containing MS_4²⁻ and CuNCS have been used to interpret vibrational spectroscopic data of the thiocyanate groups.     

The effects of in vivo and in vitro non-enzymatic glycosylation and glycoxidation on physico-chemical properties of haemoglobin in control and diabetic patients

The erythrocyte deformability, which is related to erythrocyte internal viscosity, was suggested to depend upon the physico-chemical properties of haemoglobin. In the present study we employed ESR spectroscopy in order to explore further the extent to which the in vivo or in vitro glycation and/or glycoxidation might affect haemoglobin structure and conformation. We revealed that under both in vivo and in vitro conditions the attachment of glucose induced a mobilization of thiol groups in the selected domains of haemoglobin molecules (the increased h₊₁/h₀ parameter of maleimide spin label, MSL; 0.377 ± 0.021 in diabetics vs 0.338 ± 0.017 in controls, n = 12, P < 0.0001). The relative rotational correlation time (τ_c) of two spin labels, TEMPONE and TEMPAMINE, respectively, in erythrocyte insides (5.22 ± 0.42 in diabetics, n = 21 vs 4.79 ± 0.38, n = 16 in controls, P < 0.005) and in the solutions of in vitro glycated haemoglobin, were increased. Neither oxidation nor crosslinking of thiol groups was evidenced in glycated and/or oxidized haemoglobin. In addition, erythrocyte deformability was found to be reduced in type 2 diabetic patients (6.71 ± 1.08, n = 28 vs 7.31 ± 0.96, n = 21, P < 0.015). In conclusion, these observations suggest that: the attachment of glucose to haemoglobin might have decreased the mobility of the Lys-adjacent Cys residues, thus leading to the increased h₊₁/h₀ parameter of MSL. Such structural changes in haemoglobin owing to non-enzymatic glycosylation may contribute to the increased viscosity of haemoglobin solutions (r = 0.497, P < 0.0035) and the enhanced internal viscosity of diabetic erythrocytes (r = 0.503, P < 0.003). We argue that such changes in haemoglobin, and consequently in red blood cells, might contribute to the handicapped oxygen release under tissue hypoxia in the diabetic state.     

Application of the hydro(solvo)thermal technique to the synthesis of metal carbonyl chalcogenide clusters Part 3. Synthesis, structural characterization, and spectroscopic studies of the clusters [{M(CO)4}n(MS4)] (M = Mo, W; N=1, 2)

The methanothermal reactions of M(CO)₆ (M = Mo, W) with Na₂S₂ gave a series of homonuclear clusters [{M(CO)₄}_n(MS₄)]²⁻ (M=Mo, W; N=1, 2), i.e. (Ph₄P)₂[(CO)₄Mo(MoS₄)] (I), (Ph₄P)₂[(CO)₄W(WS₄)] (II), (Ph₄P)₂[(CO)₄Mo(MoS₄)Mo(CO)₄] (III) and (Ph₄P)₂[(CO)₄W(WS₄)W(CO)₄] (IV). The two dimers, I and II, as well as the two trimers, III and IV, are isostructural to each other, respectively. All compounds crystallize in the triclinic space group with Z=2. The cell dimensions are: a=12.393(8), b=19.303(9), c=11.909(6) Å, =102.39(5), β=111.54(5), γ=73.61(5)°, V=2522(3) ų at T=23 °C for I; a=12.390(3), b=19.314(4), c=11.866(2) Å, =102.66(2), β=111.49(1), γ=73.40(2)°, V=2511(1) ų at T=23 °C for II; a=11.416(3), b=22.524(4), c=10.815(4) Å, =91.03(2), β=100.57(3), γ=88.96(2)°, V=2733(1) ų at T=−100 °C for III, a=11.498(1), b=22.600(4), c=10.864(3) Å, =90.92(2), β=100.85(1), γ=88.58(1)°, V=2771(2) ų at T=23 °C for IV. The dimers are each formed by the coordination of the tetrathiometalate as a bidentate chelating ligand to an M(CO)₄ fragment while addition of another M(CO)₄ fragment to the dimers results in the trimers. All compounds contain both tetrahedral and octahedral metal centers with the formal 6+ and 0 oxidation states, respectively.     

A hydrodynamic study of the depolymerisation of a high methoxy pectin at elevated temperatures

The hydrodynamic properties (intrinsic viscosity, [η]; infinite dilution sedimentation coefficient, s_20,w⁰; weight average molecular weight, M_w and translational frictional ratio, f/f₀) of a high methoxy pectin have been evaluated at various temperatures (20–60°C). A reduction in the value of all four hydrodynamic parameters is indicative of depolymerisation and is in agreement with an earlier study using viscometry [Axelos, M.A.V., & Branger, M., (1993). Food Hydrocolloids, 7, 91–102]. The apparent linearity of the Mark – Houwink plot of log[η] vs log M_w suggests that the conformation of the pectin molecule does not change significantly over the temperature range studied. The evaluation of the Mark–Houwink viscosity exponent (a=0.84) indicates a moderately extended structure. This then allows the calculation of the number of Kuhn statistical lengths per chain from the adapted ‘blob’ theory of Dondos [Dondos A. (2001). Polymer, 42, 897–901]. The weight average number of Kuhn statistical lengths per chain is reduced from (170±10) to (125±10) when the temperature is increased from 20–60°C. This may be of significance as many high methoxy pectins are exposed to high temperatures during processing in both the food and pharmaceutical industries.     

Peripheral insulin administration attenuates the increase in neuropeptide Y concentrations in the hypothalamic arcuate nucleus of fasted rats

Fasting increases neuropeptide Y (NPY) concentrations in the arcuate nucleus (ARC), its site of synthesis, and in other regions of the rat hypothalamus. Neuropeptide Y is a potent central orexigenic agent and may therefore stimulate appetite during fasting. We tested the hypothesis that low plasma insulin levels stimulate ARC levels of NPY in fasted rats. Compared with freely fed controls (n = 8), rats fasted for 72 h (n = 8) showed significantly lower plasma insulin levels (28.9 ± 1.6 vs. 52.6 ± 5.7 pmol/l; p < 0.001) and higher ARC NPY concentrations (14.2 ± 1.8 vs. 8.4 ± 2.2 fmol/μg protein; p < 0.001). Fasted rats treated with subcutaneous insulin (5 U/kg/day; n = 10), which nearly normalized plasma insulin (46.6 ± 2.8 pmol/l), showed intermediate ARC NPY levels (11.2 ± 1.4 fmol/μg protein; p < 0.01 vs. controls and untreated fasted rats). Insulin administered peripherally, therefore, attenuates fasting-induced NPY increases in the ARC, supporting the hypothesis that hypoinsulinemia stimulates hypothalamic NPY.     

Polynuclear copper(II) complexes with μ2-1,1-azide bridges. Structural and magnetic properties

Two novel, weakly antiferromagnetically coupled, tetranuclear copper(II) complexes [Cu₄(PAP)₂(μ₂-1,1-N₃)₂(μ₂-1,3-N₃)₂(μ₂-CH₃OH)₂(N₃)₄ (1) (PAP = 1,4-bis-(2′-pyridylamino)phthalazine) and [Cu₄(PAP3Me)₂ (μ₂-1,1-N₃)₂(μ₂-1,3-N₃)₂(H₂O)₂(NO₂)₂]- (NO₃)₂ (2) (PAP3Me = 1,4-bis-(3′-methyl-2′-pyridyl)aminophthalazine) contain a unique structural with two μ₂-1,1-azide intramolecular bridges, and two μ₂-1,3-azide intermolecular bridges linking pairs of copper(II) centers. Four terminal azide groups complete the five-coordinate structures in 1, while two terminal waters and two nitrates complete the coordination spheres in 2. The dinuclear complexes [Cu₂(PPD)(μ₂-1,1-N₃)(N₃)₂(CF₃SO₃)]CH₃OH) (3) and [Cu₂(PPD)(μ₂-1,1-N₃)(N₃)₂(H₂O)(ClO₄)] (4) (PPD = 3,6-bis-(1′-pyrazolyl)pyridazine) contain pairs of copper centers with intramolecular μ₂-1,1-azid and pyridazine bridges, and exhibit strong antiferromagnetic coupling. A one-dimensional chain structure in 3 occurs through intermolecular μ₂-1,1-azide bridging interactions. Intramolecular Cu-N₃-Cu bridge angles in 1 and 2 are small (107.9 and 109.4°, respectively), but very large in 3 and 4 (122.5 and 123.2°, respectively), in keeping with the magnetic properties. 2 crystallizes in the monoclinic system, space group C2/c with a = 26.71(1), b = 13.51(3), c = 16.84(1) Å, β = 117.35(3)° and R = 0.070, R_w = 0.050. 3 crystallizes in the monoclinic system, space group P2₁/c with a = 8.42(1), b = 20.808(9), c = 12.615(4) Å, β = 102.95(5)° and R = 0.045, R_w = 0.039. 4crystallizes in the triclinic system, space group P1, with a = 10.253(3), b = 12.338(5), c = 8.072(4) Å, = 100.65(4), β = 101.93(3), γ = 87.82(3)° and R = 0.038, R_w = 0.036 . The magnetic properties of 1 and 2 indicate the presence of weak net antiferromagnetic exchange, as indicated by the presence of a low temperature maximum in χ_m (80 K (1), 65 K (2)), but the data do not fit the Bleaney-Bowers equation unless the exchange integral is treated as a temperature dependent term. A similar situation has been observed for other related compounds, and various approaches to the problem will be discussed. Magnetically 3 and 4 are well described by the Bleaney-Bowers equation, exhibiting very strong antiferromagnetic exchange (− 2J = 768(24) cm⁻¹ (3); − 2J = 829(11) cm⁻¹ (4)).     

How are neuronal thermosensitivity and lack of thermoreception related in the duck's hypothalamus? A tentative answer

1. 1.|In 15 conscious Pekin ducks, 40 “warm sensitive” hypothalamic neurons were identified according to their discharge rates at 40°C T_hy (F₄₀), local temperature coefficients (Δ/ΔT) and Q₁₀.

2. 2.|Q₁₀ and either F₄₀ or ΔF/ΔT were little or not related.

3. 3.|A positive correlation between F₄₀ and ΔF/ΔT was observed which was particularly close (r = 0.94 and 0.96) when the neurons were classified according to their Q₁₀ of <2 and >2.

4. 4.|The results suggest that neurons with positive temperature coefficients in the duck's hypothalamus mostly exhibit linear to exponential temperature-discharge relationships.

5. 5.|This is an contrast to observations on mammalian hypothalamic thermosensitive neurons and may relate to the absence of the thermosensory function in the duck's rostral brainstem.

Molecular structure of the carbon-bound phosphorus ylide complex trans-dichlorobis(benzoyltri-n-butylphosphorane)palladium(II)

The molecular structure of trans-[Pd(PhC(O)CHP(n-C₄H₉)₃)₂Cl₂] has been determined via a single crystal X-ray diffraction study: triclinic,P1,a = 8.876(2),b = 10.908(3),c = 11.938(4)Å, = 97.06(2)°, β = 102.79(2)°, γ = 100.51(2)°,V= 1092.1(5)ų,Z = 1 and R(F) = 4.61%. The phosphorus ylide molecules are bound to the palladium atom through their methine carbon atoms, the overall coordination geometry about the palladium being square planar. The protons in the ortho-positions of the two phenyl group are poised above and below the palladium atom, suggesting that the complex is a precursor of the ortho-metalated complex [Pd(μ-Cl)(C₆H₄C(O)CHP(n-C₄H₉)₃)]₂ synthesized earlier in our laboratory.     

Synthesis and characterization of SrCu2(O2CR)3(bdmap)3 and Bi2(O2CCH3)4(bdmap)2(H2O) (R = CH3, CF3; bdmap = 1,3-bis(dimethylamino)-2-propanolato)

New mixed metal complexes SrCu₂(O₂CR)₃(bdmap)₃ (R = CF₃ (1a), CH₃ (1b)) and a new dinuclear bismuth complex Bi₂(O₂CCH₃)₄(bdmap)₂(H₂O) (2) have been synthesized. Their crystal structures have been determined by single-crystal X-ray diffraction analyses. Thermal decomposition behaviors of these complexes have been examined by TGA and X-ray powder diffraction analyses. While compound 1a decomposes to SrF₂ and CuO at about 380°C, compound 1b decomposes to the corresponding oxides above 800°C. Compound 2 decomposes cleanly to Bi₂O₃ at 330°C. The magnetism of 1a was examined by the measurement of susceptibility from 5–300 K. Theoretical fitting for the susceptibility data revealed that 1a is an antiferromagnetically coupled system with g = 2.012(7), −2J = 34.0(8) cm⁻¹. Crystal data for 1a: C₂₇H₅₁N₆O₉F₉Cu₂Sr/THF, monoclinic space group P2₁/m, A = 10.708(6), B = 15.20(1), C = 15.404(7) Å, β = 107.94(4)°, V = 2386(2) ų, Z = 2; for 1b: C₂₇H₆₀N₆O₉Cu₂Sr/THF, orthorhombic space group Pbcn, A = 19.164(9), B = 26.829(8), C = 17.240(9) Å, V = 8864(5) ų, Z = 8; for 2: C₂₂H₄₈O₁₁N₄Bi₂, monoclinic space group P2₁/c, A = 17.614(9), B = 10.741(3), C = 18.910(7) Å, β = 109.99(3)°, V = 3362(2) ų, Z = 4.     

Crystal and molecular structure of polymeric [MnCl2(bpy)]n

A crystal and molecular structure determination of MnCl₂(bpy) showed that it exists as polymeric octahedral [MnCl₂(bpy)]_n. [MnCl₂(bpy)_n crystallizes in the monoclinic space group I2/a with A = 7.007(1), B = 9.200(1), C = 16.495(1) Å, β = 91.313(5)° and Z = 4. On the basis of 979 unique observed reflections with I 2.5σ(I) the structure was refined to R = 0.032.     

Hydrodynamic properties of the fractions of mannan formed by Rhodotorula rubra yeast

Aqueous solutions of fractions of an extracellular linear mannan formed by Rhodotorula rubra yeast have been investigated by hydrodynamic methods (high-speed sedimentation, translation isothermic diffusion and viscometry). The molecular weight was determined according to Svedberg ( ) and the polydispersity parameters of the initial sample were also determined (M_w/M_n = 1·20 and M_z/M_w = 1·21). Relationships between the molecular weight (M) and s_o, D_o and [η] in the range were: [η] = 2·33 × 10⁻² M^0.75, D_o = 1·65 × 10⁻⁴ M^0·58, s_o = 2·24 × 10⁻¹⁵ M^0·43. The equilibrium rigidity and hydrodynamic diameter of chains representing mannan molecules were evaluated.     

Cortisol metabolism in vitro—III. Inhibition of microsomal 6β—hydroxylase and cytosolic 4-ene-reductase

The in vitro metabolism of cortisol in human liver fractions is highly complex and variable. Cytosolic metabolism proceeds predominantly via A-ring reduction (to give 3,5β-tetrahydrocortisol; 3,5β-THF), while microsomal incubations generate upto 7 metabolites, including 6β-hydroxycortisol (6β-OHF), and 6β-hydroxycortisone (6β-OHE), products of the cytochrome P450 (CYP) 3A subfamily. The aim of the present study was, therefore, to examine two of the main enzymes involved in cortisol metabolism, namely, microsomal 6β-hydroxylase and cytosolic 4-ene-reductase. In particular, we wished to assess the substrate specificity of these enzymes and identify compounds with inhibitory potential. Incubations for 30 min containing [³H]cortisol, potential inhibitors, microsomal or cytosolic protein (3 mg), and co-factors were followed by radiometric HPLC analysis. The K_m value for 6β-OHF and 6β-OHE formation was 15.2 ± 2.1 μM (mean ± SD; n = 4) and the V_max value 6.43 ± 0.45 pmol/min/mg microsomal protein. The most potent inhibitor of cortisol 6β-hydroxylase was ketoconazole (K_i = 0.9 ± 0.4 μM; N = 4), followed by gestodene (K_i = 5.6 ± 0.6 μM) and cyclosporine (K_i = 6.8 ± 1.4 μM). Both betamethasone and dexamethasone produced some inhibition (K_i = 31.3 and 54.5 μ, respectively). However, substrates for CYP2C (tolbutamide), CYP2D (quinidine), and CYP1A (theophylline) were essentially non-inhibitory. The K_m value for cortisol 4-ene-reductase was 26.5 ± 11.2 μM (n = 4) and the V_max value 107.7 ± 46.0 pmol/min/mg cytosolic protein. The most potent inhibitors were androstendione (K_i = 17.8 ± 3.3 μM) and gestodene (K_i = 23.8 ± 3.8 μM). Although both compounds have identical A-rings to cortisol, and undergo reduction, inhibition was non-competitive.     

The synthesis, fluctionality and structural characterization of ReMo3H4(CO)12

The reaction of ReH₉²⁻ with Mo(diglyme)(CO)₃ leads to the formation of the mixed metal cluster trianion, ReMo₃H₄(CO)₁₂³⁻. This species has been characterized analytically, spectroscopically and through X-ray diffraction analysis. A pseudo-tetrahedral arrangement of M(CO)₃ fragments is adopted, such that each set of three carbonyl ligands eclipses the adjacent three tetrahedral edges, an apparent result of the location of the hydride ligands on the tetrahedral faces. Variable temperature NMR studies revealed a fluctional process for some of the carbonyl ligands, but not for the hydrides. Crystal data for [Me₄N]₃[ReMo₃H₄(CO)₁₂]·THF; space group P2₁/n, a = 12.157(2), B = 21.480(4), C = 15.964(3) Å, β = 98.26(1)°, Z = 4, R = 0.067 and R_w = 0.076.     

Pyrazolonato complexes of lead. Crystal structures of bis(1-phenyl-3-methyl-4-acetyl pyrazolonato)lead(II) and bis(1-phenyl-3-methyl-4-butanoylpyrazolonato)lead(II)

The structures of the complexes [PbL₂], L = 1-phenyl-3-methyl-4-acylpyrazolonato, RCOC₁₀H₈N₂O, R = Me (2) or Pr (3), have been determined by X-ray diffraction studies. Compound 2 is monoclinic, space group P2₁, A = 11.285(4), B = 14.727(4), C = 20.749(5) Å, β = 95.83(3)°, R = 0.039 for 4486 reflections, and 3 is monoclinic, space group C2/c, A = 27.528(11), B = 7.245(11), C = 14.264(7) Å, β = 113.6(3)°, R = 0.021 for 2118 reflections. There are three different lead environments in 2 but only one in 3. In each case the lead atom makes four strong bonds to oxygen and two weaker bonds to either oxygen or nitrogen in adjacent molecules.     

The crystal and molecular structures of lithium trimethylenediaminetetraacetatoferrate(III) trihydrate Li[Fe(trdta)]·3H2O and sodium ethylenediamine-N,N′-diacetato-N,N′-di-3-propionatoferrate(II) pentahydrate Na[Fe(eddda)]·5H2O

The crystal structures of Li[Fe(trtda)]·3H₂O and Na[Fe(eddda)]·5H₂O (trtda = trimethylenediaminetetraacetate and eddda = ethylenediamine-N,N′-diacetate-N,N′-di-3-propionate) have been determined by single crystal X-ray diffraction techniques. The former crystal was monoclinic with the space group P2₁/n,a = 17.775(3),b = 10.261(1),c = 8.883(2)Å, β = 95.86(4)° and Z = 4. The latter was also monoclinic with the space group P2₁/n,a = 6.894(2),b = 20.710(6),c = 13.966(3)Å, β = 101.44(2)° and Z = 4. Both complex anions were found to adopt an octahedral six-coordinated structure with all of six ligand atoms of trdta⁴⁻ or eddda⁴⁻ coordinated to the Fe(III) ion, unlike the corresponding edta⁴⁻ complex which is usually seven-coordinate with the seventh coordination site occupied by H₂O. Of the three geometrical isomers possible for the eddda complex, the trans(O₅) isomer was actually found in the latter crystal. Factors determining the structural types of metal–edta complexes are discussed in detail.     

Differential scanning calorimetry and X-ray diffraction study of tendon collagen thermal denaturation

Differential scanning calorimetry, high and small angle X-ray diffraction analyses have been carried out on air-dried and rehydrated rat tail tendon collagen in order to test the reversibility of collagen thermal denaturation. The mean enthalpy values calculated for the denaturation process of air-dried and rehydrated samples are ΔH_D = 9.0 ± 0.8 cal/g and ΔH_D = 11.9 ±0.7 cal/g respectively, while the denaturation temperatures are T_D = 112 ± 1°C and T_D = 51 ± 1°C. Partial reversibility of the coiled coil—random coil process can be obtained by storing the samples in air or more rapidly by equilibration in water. After denaturation air-dried collagen fibres recover not only their molecular structure but also their characteristic fibrillar structure. The latter does not greatly influence the mean experimental enthalpy values.