M. J. M. de Almeida

Local order in concentrated aqueous solutions of yttrium chloride and bromide

X-ray diffraction patterns of equimolecular concentrated aqueous solutions of yttrium chloride and bromide have been investigated from s=0.4 AA-1 up to s=15 AA-1. An assumed coordination of eight water molecules around each yttrium cation, at a distance of 2.36 AA, reproduces the intensity at high s values in agreement with the values obtained by some of the present authors from EXAFS experiments. Narrow interference maxima at s=(4 pi sin theta )/ lambda approximately=0.9 AA-1 may be interpreted as the existence of a local order of the hydrated yttrium cations surrounded by anions and free water molecules. Structural models with and without close packing of the hydrated cations were built to simulate that local order.

Charge densities of two rutile structures: NiF2 and CoF2

X-ray diffraction data were collected at room temperature for two rutile structures, NiF 2 and CoF 2 . Two different crystals of each compound have been used in the experiments. Atomic and thermal parameters were derived from least-squares refinements of high-angle data [(sinθ)λ≥0.6 A -1 ]. The results of Fourier inversion of the differences between observed and model structure factors are presented and discussed in terms of difference density maps

3β,5α,6β-Trihy­droxy­androstan-17-one

The title compound, C19H30O4, is an androstan-17-one derivative synthesized from the dehydroepiandrosterone through a sequential addition of an oxidant, followed by a trans-diaxial opening of the epoxide generated, with Bi(OTf)3 (OTf is trifluoromethanesulfonate). The six-membered rings have a slightly flattened chair conformation, while the five-membered ring adopts a 14-α envelope conformation. All rings are trans fused. In the crystal, the molecules are connected by O—H⋯O hydrogen bonds involving the hydroxyl and carbonyl groups, forming a three-dimensional network. A quantum mechanical ab initio Roothan Hartree–Fock calculation of the free molecule gives bond lengths, valency angles and ring torsion angles of the free molecule at equilibrium geometry (energy minimum) close to the experimental values.

A magnetic x-ray diffraction investigation of gadolinium selenide

A single-crystal synchrotron radiation study of gadolinium selenide has been made in the temperature range 15 - 100 K. GdSe has the rocksalt structure and becomes antiferromagnetic below a reported Neel temperature of 65 K. At 15 K, magnetic reflections are observed at with modulation wavevector propagating from reciprocal lattice point G. This is achieved by exploiting the resonant enhancement in the vicinity of the and edges. Similar enhancements are observed at the two edges, with the maximum effect occurring approximately 3 eV above the absorption edge. The temperature dependence of the intensity of the magnetic reflections indicates a Neel temperature of 63(1) K. These measurements, together with high-resolution studies of the fundamental reflections , contribute further evidence of magnetic or structural changes in the sample at 37(1) K. Our observations are discussed and compared with previous x-ray diffraction and magnetic susceptibility measurements.

3α,4β-Dihydroxy-5α-androstan-17-one

The crystal structure of the title compound, C 19 H 30 O 3 , is reported. This steroid was obtained as an intermediate in the synthesis of formestane. The molecules are held together by a network of hydrogen bonds involving the carbonyl and hydroxyl groups.

Androstane-3β,5α,6β,17β-tetrol tri-hydrate.

The title hydrated tetrol, C19H32O4·3H2O, was synthesized by stereoselective reduction of the compound 3β,5α,6β-trihydroxyandrostan-17-one. All rings are fused trans. The organic molecules are connected head-to-tail along the c axis via O—H⋯O hydrogen bonds. Layers of water molecules in the ab plane interconnect these chains. A quantum chemical ab initio Roothan Hartree–Fock calculation of the isolated molecule gives values for the molecular geometry close to experimentally determined ones, apart from the C—O bond lengths, whose calculated values are significantly smaller than the measured ones, probably a consequence of the involvement of the C—OH groups in the hydrogen-bonding network.

6-[(4-Fluorophenyl)(1H-imidazol-1-yl)methyl]-1,3-benzodioxol-5-ol and 6-[(4-methoxyphenyl)(1H-imidazol-1-yl)methyl]-1,3-benzodioxol-5-ol.

The title compounds, C(17)H(13)FN(2)O(3) and C(18)H(16)N(2)O(4), are new potent aromatase inhibitors combining the common features of second- and third-generation nonsteroid anti-aromatase compounds. The molecules have a propeller shape, with dihedral angles between adjacent planes in the range 49-86°. A quantum mechanical ab initio Roothaan-Hartree-Fock calculation for the isolated molecules shows values for these angles close to the ideal value of 90°. Docking studies of the molecules in the aromatase substrate show that their strong inhibitor potency can be attributed to molecular flexibility, hydrophobic interactions, heme Fe coordination and hydrogen bonding.

3α,4α-Ep­oxy-5α-androstan-17β-yl acetate

The title compound, C21H32O3, results from modifications of the A and D rings of the aromatase substrate androstenedione. Ring A adopts a conformation between 10β-sofa and 1α,10β half-chair. Rings B and C are in slightly flattened chair conformations. Ring D approaches a 13β-envelope conformation, probably due to the acetoxy substituent, and shows a very short Csp 3—Csp 3 bond next to the epoxide ring, which is characteristic of 3–4 epoxides. .

17-Oxo-5α-androstane-3α, 4β-diyl diacetate and 17-oxo-5β-androstane-3α, 4β-diyl diacetate

The title compounds, both C23H34O5, are the 5alpha and 5beta configurations of two diacetate epimers. The 5beta-diacetate crystallizes in an hexagonal structure, unusual for steroid molecules. The unit cell has an accessible solvent volume of 358 A(3), responsible for clathrate behaviour. The 5beta-epimer also features some shorter than average bond lengths in the 3alpha,4beta-acetoxy groups. The conformations of the molecules of both epimers are compared with those obtained through ab initio quantum chemistry calculations. Cohesion of the crystals can be attributed to van der Waals and weak molecular C-H...O interactions.

3α-Hydroxy-5α-androstane-4,17-dione

The asymmetric unit of the title compound, C 19 H 28 O 3 , contains two independent molecules with almost identical geometry. The molecules have a planar 5a configuration as a result of a trans-A/B junction of the rings. The compound crystallizes in a triclinic cell, which is unusual for steroids. The molecules are linked head-to-tail via hydrogen bonds between the ring A hydroxyl group and the ketone group of ring D, forming two independent chains running along the c axis.