Interactions between thiamine and large anions. Crystal structures of (H-thiamine)[Pt(SCN)4] · 3H2O and (H-thiamine)[Pt(SCN)6] · H2O

The reaction of thiamine with K₂Pt^IICl₄ and with Pt^IVCl₄ in the presence of excess NaSCN in aqueous solution gave thiamine salts, (H-thiamine)[Pt(SCN)₄] · 3H₂O (1) and (H-thiamine)[Pt(SCN)₆] · H₂O (2), respectively, structures of which have been determined by X-ray diffraction. The thiamine molecule adopts the usual F conformation in each salt. In 1, [Pt(SCN)₄]²⁻ ions act as large planar spacers in the crystal lattice and interact scarcely with thiamine, except for a hydrogen bonding with the terminal hydroxy O(5γ). Instead, water molecules form two types of host–guest-like interactions with the pyrimidine and the thiazolium moieties of a thiamine molecule, one being a C(2)–Hwaterpyrimidine bridge and the other being an N(4′)–Hwaterthiazolium bridge. In 2, despite the much larger ion size, octahedral [Pt(SCN)₆]²⁻ ions form a C(2)–Hanionpyrimidine bridge and an N(4′)–Hanionthiazolium bridge. An additional hydrogen bonding between the anion and the terminal O(5γ) of thiamine creates a hydrogen-bonded macrocyclic ring {thiaminium–[Pt(SCN)₆]²⁻}₂, a supramolecule.     

Studies on a thermal reaction associated with photosynthetic oxygen evolution

The modulated polarographic technique of O₂ detection was applied to Chlorella to study the rate-limiting thermal reaction between Photosystem II and O₂ evolution. From an analysis of the operation of the polarograph at different frequencies, it was concluded that a first order thermal reaction of rate constant 305±20 (S.E.) s⁻¹ was consistent with the results of 22 °C. When the algae were successively studied in solutions made up with ²H₂O and H₂O, a kinetic isotopic effect for the rate constant of 1.29±0.05 (S.E.) was found. This suggests that the rate limiting step does not involve the breaking of the O-H bond in water. A temperature study of the rate constant indicated an activation energy of 5.9±0.5 (S.E.) kcal·mole⁻¹ and an entropy of activation of −25 cal·degree⁻¹·mole⁻¹. The linearity of the Arrhenius plot between 8 and 42 °C demonstrated that only one reaction was rate-limiting over this temperature range.     

Structure and characterization of platinum(II) and platinum(IV) complexes with protonated nucleobase ligands

The reaction of H₂[PtCl₆] · 6H₂O and (H₃O)[PtCl₅(H₂O)] · 2(18C6) · 6H₂O (18C6 = 18-crown-6) with 9-methylguanine (MeGua) proceeded with the protonation of MeGua forming 9-methylguaninium hexachloroplatinate(IV) dihydrate (MeGuaH)₂[PtCl₆] · 2H₂O (1).The same compound was obtained from the reaction of Na₂[PtCl₆] with (MeGuaH)Cl.On the other hand, the reaction of guanosine (Guo) with (H₃O)[PtCl₅(H₂O)] · 2(18C6) · 6H₂O in methanol at 60 °C proceeded with the cleavage of the glycosidic linkage and with ligand substitution to give a guaninium complex of platinum(IV), [PtCl₅(GuaH)] · 1.5(18C6) · H₂O (2).Within several weeks in aqueous solution a slow reduction took place yielding the analogous guaninium platinum(II) complex, [PtCl₃(GuaH)] · (18C6) · 2Me₂CO (3).H₂[PtCl₆] · 6H₂O and guanosine was found to react in water, yielding (GuoH)₂[PtCl₆] (4) and in ethanol at 50 °C, yielding [PtCl₅(GuoH)] · 3H₂O (5).Dissolution of complexes 2 and 5 in DMSO resulted in the substitution of the guaninium and guanosinium ligands, respectively, by DMSO forming [PtCl₅(DMSO)]⁻.Reactions of 1-methylcytosine (MeCyt) and cytidine (Cyd) with H₂[PtCl₆] · 6H₂O and(H₃O)[PtCl₅(H₂O)] · 2(18C6) · 6H₂O resulted in the formation of hexachloroplatinates with N3 protonated pyrimidine bases as cation (MeCytH)₂[PtCl₆] · 2H₂O (6) and (CydH)₂[PtCl₆] (7), respectively. Identities of all complexes were confirmed by ¹H, ¹³C and ¹⁹⁵Pt NMR spectroscopic investigations, revealing coordination of GuoH⁺ in complex 5 through N7 whereas GuaH⁺ in complex 3 may be coordinated through N7 or through N9. Solid state structure of hexachloroplatinate 1 exhibited base pairing of the cations yielding (MeGuaH⁺)₂, whereas in complex 6 non-base-paired MeCytH⁺ cations were found. In both complexes, a network of hydrogen bonds including the water molecules was found. X-ray diffraction analysis of complex 3 exhibited a guaninium ligand that is coordinated through N9 to platinum and protonated at N1, N3 and N7. In the crystal, these NH groups form hydrogen bonds N–HO to oxygen atoms of crown ether molecules.     

The infrared absorption of amino acid side chains

Amino acid side chains play fundamental roles in stabilising protein structures and in catalysing enzymatic reactions. These fields are increasingly investigated by infrared spectroscopy at the molecular level. To help the interpretation of the spectra, a review of the infrared absorption of amino acid side chains in H₂O and ²H₂O is given. The spectral region of 2600–900 cm⁻¹ is covered.     

Resonance raman spectroscopy of chemically modified and isotopically labelled purple membranes. II. Kinetic studies

Kinetic resonance Raman spectra of native and isotopically labelled purple membranes are compared. Using these data and the assignments of the previous paper in this sequence, we have confirmed that the Schiff base is deprotonated at times that are short in comparison to M₄₁₂ evolution. In addition, by monitoring the kinetic resonance Raman spectra in ²H₂O with 488.0 nm excitation we have been able to characterize in more detail the vibrational features associated with this unprotonated intermediate that precedes M₄₁₂. Furthermore, the kinetic spectra of fully deuterated purple membranes in H₂O have allowed us to assign the 1465 cm⁻¹ band in these spectra to the C=C stretching frequency of BR₅₇₀ and the 1512 cm⁻¹ band to the C=C stretching frequency of M₄₁₂. These spectra have also provided an indication of a Raman spectral feature associated with O₆₄₀ and, finally, our kinetic spectra have provided evidence that there is a significant alteration in the rate constants for the evolution of the various intermediates when the non-exchangeable protons on the membrane are replaced by deuterons.     

Structural determinations, magnetic and EPR studies of complexes involving the Cr(OH)2Cr unit

Five heterometallic compounds with formulae [Ba(H₂O)₄Cr₂(μ-OH)₂(nta)₂] · 3H₂O (I), [M(bpy)₂(H₂O)₂] [Cr₂(OH)₂(nta)₂] · 7H₂O, where M²⁺ = Zn, (II); Ni, (III); Co, (IV) and [Mn(H₂O)₃(bpy)Cr₂(OH)₂(nta)₂] · (bpy) · 5H₂O (V); bpy = 2,2′-bipyridine, (nta = nitrilotriacetate ion) have been prepared by reaction of I with the corresponding M^II-sulfates in the presence of 2,2′-bipyridine. Substances I–V have been characterized by magnetic susceptibility measurements, EPR and X-ray determinations. I represents a 2D coordination polymer formed by coordination of centrosymmetrical dimeric chromium(III) units and Barium cations. The 10-coordinate Ba polyhedron is completed by four water molecules. Compounds II–IV are isostructural and consist of non-centrosymmetric dimeric anions [Cr₂(μ-OH)₂(nta)₂]²⁻, complex cations [M^II(bpy)₂(H₂O)₂]²⁺ and solvate water molecules. The octahedral coordination of chromium atoms implies four donor atoms of the nta³⁻ ligands and two bridging OH groups. Multiple hydrogen bonds of coordinated and solvate water molecules link anions and cations in a 3D network. A similar [Cr₂(μ-OH)₂(nta)₂]²⁻ unit is found in V. The bridging function is performed by a carboxylate oxygen atom of the nta ligand that leads to the formation of a trinuclear complex [Mn(bpy)(H₂O)₂Cr₂(μ-OH)₂(nta)₂]. Experimental and calculated frequency and temperature dependences of EPR spectra of these compounds are presented. The fine structure appearing on the EPR spectra of compound V is analyzed in detail at different temperatures. It is established that the main part of the EPR signals is due to the transitions in the spin states of a spin multiplet with S = 2. Analyses of experimental and calculated spectra confirm the absence of interaction between metal ions (M^II) and Cr-dimers in complexes III and IV and the presence of weak Mn–Cr interactions in V. The temperature dependence of magnetic susceptibilities for I–V was fitted on the basis of the expression derived from isotropic Hamiltonian including a bi-quadratic exchange term.     

Molecular structures of Fe(II) complexes with mono- and di-protonated ethylenediamine-N,N,N′,N′-tetraacetate (Hedta and H2edta), as determined by X-ray crystal analyses

The molecular structure of the title complexes [Fe(H₂O)₄][Fe(Hedta)(H₂O)]₂ · 4H₂O (I) and [Fe(H[₂edta)(H₂O)] · 2H₂O (II) have been determined by single-crystal X-ray analyses. The crystal data are as follows: I: monoclinic, P2₁/n, A = 11.794(2), B = 15.990(2), C = 9.206(2) Å, β = 90.33(1)°, V = 1736.1(5) ų, Z = 2 and R = 0.030; II: monoclinic, C2/c, A = 11.074(2), B = 9.856(2), C = 14.399(2) Å, β = 95.86(1)°, V = 1563.3(4) ų, Z = 4 and R = 0.025. I is found to be isomorphous with the Mn^II analog reported earlier and to contain a seven-coordinate and approximately pentagonal-bipyramidal (PB) [Fe^II(Hedta)(H₂O]⁻ unit in which Hedta acts as a hexadentate ligand. The [Fe^II(H₂edta)(H₂O)] unit in II has also a seven-coordinate PB structure with the two protonated equatorial glycine arms both remaining coordinated, and thus bears a structural resemblance to the seven-coordinate [Co^II(H₂edta)(H₂O)] reported previously.     

Two new multi-cobalt-containing heteropolyoxotungstates

Two new multi-cobalt-containing polyoxotungstates K₄Na₆Co₂(H₂O)₁₂{Co(H₂O)₄[Co₂(H₂O)₁₀Co₄(H₂O)₂(B--SiW₉O₃₄)₂]₂} · 40H₂O (1) and K₁₀Na₂[Co₄(H₂O)₂(GeW₉O₃₄)₂] · 20H₂O (2) have been obtained by the routine synthetic reactions in aqueous solution. The polyoxoanion framework of 1 consists of two sandwich-type polyoxoanions [Co₄(H₂O)₂(B--SiW₉O₃₄)₂]¹²⁻ connected together by a [CoO₂(H₂O)₄] cluster to constitute the sandwich dimer, and then, four isolated Co(H₂O)₅ cations coordinate to the dimer through four μ₂-O atoms. The polyoxoanion 2 is isomorphic to the sandwich-type polyoxoanion [Co₄(H₂O)₂(B--SiW₉O₃₄)₂]¹²⁻ in 1. The magnetic property of compound 1 has been studied by measuring its magnetic susceptibility in the temperature range 2.0–300.0 K, indicating the existence of intramolecular ferromagnetic Co–Co interactions, and, the electrochemical properties of 1 and 2 are detected in the pH 4 buffer solution.     

Effect of H2O on energy-dependent oxidoreduction of cytochrome b

The rate of oxidation of the long-wavelength cytochrome b (b₅₆₆) on addition of oligomycin to ATP-supplemented anaerobic rat-liver mitochondria was strongly inhibited when ²H₂O was substituted for medium water. This effect was dependent on added substrate, was reversed by uncoupling agents, and was absent in sub-mitochondrial particles. At the same phosphate potential, b₅₆₆ reduction was favoured in ²H₂O in comparison with H₂O medium. The redox state of b₅₆₆ may be controlled by the phosphate potential via an intramembrane acid-base equilibrium which is shifted by ²H₂O.     

Kinetics and equilibria of Ga(III)---thiocyanate complex formation. Mechanism of ligand substitution reactions of Ga(III) in aqueous solution

The kinetics and equilibria of complex formation by Ga(III) with NCS⁻ in aqueous solution have been measured over a range of acidities and temperatures, the contributing paths to the reaction resolved, and their rate constants and activation parameters determined. The hydrolysis equilibria required to carry out this resolution of kinetic behaviour have also been measured.

Unlike the other reported complexation reactions of Ga(III) in aqueous solution, the separate reaction pathways can be assigned with no ambiguity. At 25 °C and ionic strength 0.5 M, the observed forward rate constant for the complex formation is described by {k₁ + k₂K_1h/[H⁺] + k₃K_1hK_2h/[H⁺]²} M⁻¹ s⁻¹. For these conditions, the first and second successive hydrolysis constants of Ga(H₂O)₆³⁺ are given by pK_1h = 3.69 ± 0.01 and pK_2h = 3.74 ± 0.04. The rate constants corresponding to the reactions of the species Ga(H₂O)₆³⁺, Ga(H₂O)₅(OH)²⁺ and Ga(H₂O)₄(OH)₂⁺ with NCS⁻ are k₁ = 57 ± 4 M^{−1 −1}, k₂ = (1.08 ± 0.01) × 10⁵ M⁻¹ s⁻¹ and k₃ = 3 × 10⁶ M⁻¹ s⁻¹ respectively. The complexation equilibrium quotient [GaNCS²⁺]/([Ga³⁺][NCS⁻]) has been independently determined by spectrophotometric titration to be 20.8 ± 0.3 M⁻¹ at 25 °C and ionic strength 0.5 M.

These kinetic results lead to an interpretation of the data, and a reinterpretation of other data for aquo-Ga(III) complex formation kinetics from the literature which support the assignment of a dissociative interchange mechanism for these reactions rather than the associative activation mode sometimes proposed.     

Synthesis, structure, and heterogeneous catalytic activity of tungsten chalcogenide cubane cluster containing alkaline earth metal complex

A new compound containing a cubane tungsten chalcogenide cluster [W₄(μ₃-Te)₄(CN)₁₂]⁶⁻ and Ca²⁺ complex units has been prepared by the reaction of aqueous solution of K₆[W₄(μ₃-Te)₄(CN)₁₂] · 5H₂O with the solution of a Ca(NO₃)₂ and phen(1,10-phenanthroline) (1:2 molar ratio) in a solvent mixture of H₂O/EtOH. The structure of [{Ca(phen)₂(H₂O)}{Ca(phen)(H₂O)₄}{Ca(phen)₂(H₂O)₃}][W₄Te₄(CN)₁₂] · 5H₂O 1 has been determined by X-ray crystallography. Compound 1 contains [{Ca(phen)(H₂O)₄}{Ca(phen)₂(H₂O)₃}][W₄(μ₃- Te)₄(CN)₁₂] units bridged by {Ca(phen)₂(H₂O)}²⁺ units to form an one-dimensional zigzag chain structure. Interestingly, compound 1 showed a heterogeneous catalytic activity in the transesterification of a range of esters with methanol under the mild conditions. Moreover, it can be reused without any loss of activity through 10 runs with ester.     

The reaction of cytochrome c with [Fe(EDTA)(H2O)]

The interaction of horse ferricytochrome c with the reagents [Fe(EDTA)(H₂O)]⁻ and [Cr(CN)₆]³⁻ were studied at pH 7 and 25°C by ¹H-NMR spectroscopy. Two binding regions near to the heme crevice of cytochrome c were identified. Both regions bound both reagents but they exhibited different selectivities.

The relevance of this finding to the electron-transfer function of cytochrome c is discussed.     

An investigation of water splitting in the Kok scheme of photosynthetic oxygen evolution

The involvement of OH bond breaking in the 4 dark reactions of the Kok scheme of photosynthetic oxygen evolution was investigated using Chlorella and spinach chloroplasts. When the photosynthetic material was suspended in a ²H₂O based medium, the reaction rates in all 4 cases were only slightly reduced as compared to the rates observed in an H₂O based medium. This was evidence that these rate processes were probably not limited by the breaking of an OH bond. Observations were also made on the yields of O₂ from dark adapted Chlorella subjected to a sequence of brief saturating light flashes. The oscillating flash yield sequence observed with algae suspended in ²H₂O showed greater damping of the oscillations than when the algae were suspended in H₂O. A computer fit of the Kok model to these results revealed a slightly higher proportion of misses, (i.e. absorbed quanta that do not drive photochemistry) in the ²H₂O case.     

A convenient electrochemical preparation of reduced methyl viologen and a kinetic study of the reaction with oxygen using an anaerobic stopped-flow apparatus

1. Single reduced methyl viologen (MV^.+) acts as an electron donor in a number of enzyme systems. The large changes in extinction coefficient upon oxidation (λ_max 600 nm; MV^.+, = 1.3 · 10⁴ M⁻¹ · cm⁻¹; oxidised form of methyl viologen (MV²⁺), = 0.0) make it ideally suited to kinetic studies of electron transfer reactions using stopped-flow and standard spectrophotometric techniques.

2. A convenient electrochemical preparation of large amounts of MV^.+ has been developed.

3. A commercial stopped-flow apparatus was modified in order to obtain a high degree of anaerobicity.

4. The reaction of MV^.+ with O₂ produced H₂O₂ (k > 5 · 10⁶ M⁻¹ · s⁻¹, pH 7.5, 25 °C). H₂O₂ subsequently reacted with excess MV^.+ (k = 2.3 · 10³ M⁻¹ · s⁻¹, pH 7.5, 25 °C) to produce water. The kinetics of this reaction were complex and have only been interpreted over a limited range of concentrations.

5. The results support the theory that the herbicidal action of methyl viologen (Paraquat, Gramoxone) is due to H₂O₂ (or radicals derived from H₂O₂) induced damage of plant cell membrane.     

Influence of different site symmetries of Eu centers on the luminescence properties of Anderson-based compounds

Two compounds, [Eu(H₂O)₇][Al(OH)₆Mo₆O₁₈] · 4H₂O (1) and {(C₂H₅NO₂)₂[Eu(H₂O)₅]}[Al(OH)₆Mo₆O₁₈] · 10H₂O (2), have been synthesized by conventional solution method and determined by single-crystal X-ray diffraction. Compound 1 shows a 1D chain structure built up of alternating Anderson-type polyanions [Al(OH)₆Mo₆O₁₈]³⁻ and hydrated rare-earth ions Eu³⁺. Compound 2 displays a 3D supramolecular network structure containing 1D sandglass-like channels along c axis, which were occupied by repetitive array of (H₂O)₈ clusters. Extensive hydrogen bonds play an important role in the formation of the 3D structures of 1 and 2. Luminescence measurements reveal that 1 and 2 exhibit intense red and orange fluorescent emission at room temperature, respectively. Origin of the distinct emission can be assigned to the different site symmetries of Eu³⁺ centers in the two compounds. These results are consistent with the crystal structures of the two compounds.     

One-dimensional copper phosphonates containing μ-halide, μ-pyridyl N-oxide and phosphonate bridging ligands

This paper reports the syntheses and characterization of four copper phosphonates with chain structures based on (2-pyridyl-N-oxide)phosphonate, namely, [Cu₂X₂(C₅H₄NOPO₃)₂][Cu(H₂O)₆] · 2H₂O [X = Cl (1), Br (2)] and CuX(C₅H₄NOPO₃H) · H₂O [X = Cl (3), Br (4)]. Compounds 1 and 2 are isostructural and show a chain structure where Cu(1) and Cu(2) are triply bridged by halide, oxygen donor of the pyridyl N-oxide and O–P–O group. The [Cu(H₂O)₆]²⁺ serves as a charge-balancing cation and locate between the chains together with the water molecules. Compounds 3 and 4 are also isostructural. In these cases, one of the three phosphonate oxygen atoms is protonated, thus leading to a neutral chain structure which is very similar to the anionic chains in compounds 1 and 2. Magnetic studies of compounds 1–4 reveal that antiferromagnetic interactions are mediated between the copper ions.     

Pigment systems and electron transport in chloroplasts I. Quantum requirements for the two light reactions in spinach chloroplasts

From studies of electron-transport reactions of isolated spinach chloroplasts, we observe the following quantum requirements: (A) For the photoreduction of NADP⁺, measured both aerobically and anaerobically, in a 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU) poisoned system with ascorbate and reduced 2,6-dichlorophenolindophenol (DCIPH₂) present as electron donors, the quantum requirements are 1.0 ± 0.05 at wavelengths longer than 700 nm of actinic light, and 1.5–2.5 for wavelengths between 620 and 680 nm. (B) For the photoreduction of 2,6-dichlorophenolindophenol (DCIP) with water as the electron donor, the quantum requirements are 1.0 ± 0.05 in the range 630–660 nm. (C) For the photoreduction of NADP⁺ with water as the electron donor, the quantum requirements are 2.0 ± 0.1 in the wavelength range 640–678 nm of actinic light, increasing to 6 or greater at wavelengths beyond 700 nm. These results are shown to be inconsistent with the “separate package” model for the two pigment systems in higher plant photosynthetic electron transport. The evidence is most easily interpreted using a “controlled spillover” model, in which the transfer of electronic excitation energy from one pigment system to the other is under the control of incompletely identified factors in the reaction mixture.

At moderate light intensities the steady state rate of the [ascorbate + DCIPH₂ → NADP⁺] reaction (A) in the presence of DCMU and added ferredoxin can be increased more than 3 times when saturating amounts of plastocyanin and ferredoxin-NADP reductase are added to the chloroplasts. Similarly, the steady-state rate of the [H₂O → DCIP] Hill reaction (B) is increased about 3-fold by added MgCl₂ and plastocyanin, but added ferredoxin or ferredoxin-NADP reductase have no effect on this reaction. Plastocyanin appears to be the electron transport component which couples to DCIP, either in the oxidized or in the reduced form, in the reaction media. The steady-state rate of the [H₂O → NADP⁺] reaction (C) with saturating amounts of ferredoxin can be further increased more than 3-fold when MgCl₂, plastocyanin and ferredoxin-NADP reductase are added.     

Flash-induced absorption changes in Photosystem I,Radical pair or triplet state formation?

Absorption changes induced in chlorophyll protein (CP 1) particles by short laser flashes have been analyzed in order to decide whether a state lasting for a few microseconds at 21°C or 800 μs at 10 K corresponds to the biradical P-700⁺ ... A⁻₁ (A₁ being a chlorophyll a) or to a triplet state produced in a submicrosecond recombination of the preceding state. At 21°C the spectrum of the flash-induced ΔA (720–870 nm) presents a flat-topped band from 740 to 820 nm, clearly different from that of P-700⁺. A saturation curve (ΔA vs. laser energy), obtained with a 2 or 10 ns laser pulse, indicates that ΔA saturates at a value 2- or 3-times smaller than that expected on the basis of the chemical oxidation of P-700. At 21°C the size of flash-induced ΔA is slightly decreased (5–15%) when the sample is subjected to a 400 G magnetic field. The kinetics of decay are not affected; they are not affected either by the oxygen concentration. At 10 K the spectrum of the flash-induced ΔA has been measured between 650 and 1700 nm. Between 650 and 720 nm, the spectrum presents only one major negative peak at 702 nm; it is quite different from that due to the chemical oxidation of P-700 (which has additional peaks at 688 and 677 nm). Between 720 and 870 nm, the spectrum is identical to that obtained at 21°C. Above 870 nm, the spectrum includes a broad band around 1250 nm, which is absent in P-700⁺. A saturation curve leads to a maximum ΔA greater than that at 21°C and which is also greater with a 1 μs dye laser flash than with a 10 ns ruby laser flash. An analysis of the spectral data indicates that these do not fit correctly with the hypothesis of a contribution of P-700⁺ and of a chlorophyll a anion radical. They fit more closely with the hypothesis of a triplet state of P-700, a hypothesis which is discussed in relation to other experimental data.     

Investigations into the biosynthetic pathways for classical and ring B-unsaturated oestrogens in equine placental preparations and allantochorionic tissues

In on-going studies of ‘classical’ and ring B-unsaturated oestrogens in equine pregnancy, the products of metabolism of [2,2,4,6,6-²H₅]-testosterone and [16,16,17-²H₃]-5,7-androstadiene-3β,17β-diol with equine placental subcellular preparations and allantochorionic villi have been identified. Using mixtures of unlabelled and [²H]-labelled steroid substrates has allowed the unequivocal identification of metabolites by twin-ion monitoring in gas chromatography–mass spectrometry (GC–MS). Two types of incubation were used: (i) static in vitro and (ii) dynamic in vitro. The latter involved the use of the Oxycell™ cartridge (Integra Bioscience Systems, St Albans, UK) whereby the tissue preparation was continuously supplied with supporting medium plus appropriate cofactors in the presence of uniform oxygenation. [²H₅]-Testosterone was converted into [²H₄]-oestradiol-17β, [²H₄]-oestrone and [²H₃]-6-dehydro-oestradiol-17 in both placental and chorionic villi preparations, but to a greater extent in the latter, confirming the importance of the chorionic villi in oestrogen production in the horse.

On the basis of GC–MS characteristics (M⁺ m/z 477/482 (as O-methyl oxime-trimethyl silyl ether), evidence for 19-hydroxylation of testosterone was found in static incubations, while the presence of a 6-hydroxy-oestradiol-17 was recorded in dynamic incubations (twin peaks in the mass spectrum at m/z 504/507, the molecular ion M⁺). It was not possible to determine the configuration at C-6. The formation of small, but significant, quantities of [²H₄]-17β-dihydroequilin was also shown, and a biosynthetic pathway is proposed.

In static incubations of placental microsomal fractions, the 17β-dihydro forms of both equilin and equilenin were shown to be major metabolites of [²H₃]-5,7-androstadiene-3,17-diol. Using static incubations of chorionic villi, the deuterated substrate was converted into the 17β-dihydro forms of both equilin and equilenin, together with an unidentified metabolite (base peak, m/z 504/506). The isomeric 17-dihydroequilins were also obtained using the dynamic in vitro incubation of equine chorionic villi, together with the 17β-isomer of dihydroequilenin. Confirmation of the identity of 17β-dihydroequilin and 17β-dihydroequilenin was obtained by co-injection of the authentic unlabelled steroids with the phenolic fraction obtained from various incubations. Increases in the peak areas for the non-deuterated steroids (ions at m/z 414 (17β-dihydroequilin) and 412 (17β-dihydroequilenin) (both as bis-trimethyl silyl ether derivatives) were observed. Biosynthetic pathways for formation of the ring B-unsaturated oestrogens from 5,7-androstadiene-3β,17β-diol are proposed.     

Studies of the oxovanadium(IV)—oxalate system: syntheses and crystal structures of binuclear (Ph4P)2[(VO)2(H2O)2(C2O4)3]·4H2O and of the one-dimensional chain material, (Ph4P)[VOCl(C2O4)]

The hydrothermal reactions of (Ph₄P)[VO₂Cl₂] and H₂C₂O₄ at 150 and 125°C yield (Ph₄P)₂[V₂O₂(H₂O)₂(C₂O₄)₃]·4H₂O (1) and (Ph₄P)[VOCl(C₂O₄)] (2), respectively. The structure of the molecular anion of 1 consists of a binuclear unit of oxovanadium(IV) octahedra bridged by a bisbidentate oxalate group. The VO₆ coordination geometry at each vanadium site is defined by a terminal oxo group, an aquo ligand, and four oxygen donors — two from the bisbidentate bridging oxalate and two from the terminal bidentate oxalate. The structure of 2 consists of discrete Ph₄P⁺ cations occupying regions between [VOCl(C₂O₄)]⁻_∞ spiral chains. The structure of the one-dimensional anionic chain exhibits V(IV) octahedra bridged by bisbidentate oxalate groups. Crystal data: 1·4H₂O, monoclinic P2₁/n, A = 12.694(3), B = 12.531(3), C = 17.17(3) Å, β = 106.32(2)°, V = 2621.3(13) ų, Z = 2, D_calc = 1.501 g cm⁻³, structure solution and refinement converged at a conventional residual of 0.0518; 2, tetragonal P4₃, A = 12.145(2), C = 15.991(3) Å, V = 2358.7(12) ų, Z = 4, R = 0.0452.