Androgens have similar structures with different biological activities. To identify molecular determinants responsible for the activity difference, we have docked six steroidal androgens to the binding site or the surface of androgen receptor by using molecular docking with computational investigation. The energy was calculated respectively based on the QM （quantum mechanics） and MM （molecular mechanics） methods. The result shows that the allosteric modulation of androgen receptor plays an important role in the binding process between androgens and receptor. The open state receptor is less stable than the close state one, but the latter is more favorable for binding with androgens. It is worthy of note that when the androgen receptors binding or without binding with androgen are in close state, they are difficult to return to their open state. This phenomenon is an exception of the well known two-state model theory in which the two states are reversible. Whether the internal of close state androgen receptor has a combination of androgen or not, the androgen receptor surface can be combined with another androgen, and their surface binding energies could be very close. The result is consistent with the experimental observations, but this phenomenon of continuous combination from open state is also an exception of the two-state model theory.
The quantitative structure-activity relationship （QSAR） of 14 phenoxybenzoic acid derivatives was studied by ab initio method at the HF/6-31G level using Guassian03 software. The optimized structures together with some characteristic and electric parameters of the title compounds were obtained; some stereo-parameters were calculated by HyperChem software. Stepwise multiple regression and principal component regression methods are adopted to establish multi-parametric models between biological activity and parameters. The results indicated that the lager Ehomo, M, V and LogP, the smaller Etumo and S, and the higher biological activity. A theoretical direction was provided to synthesize some compounds with high activity.
Steroid 5alpha-reductase of human is an enzyme in the biosynthetic pathway from testosterone （T） to dihydrotestosterone （DHT）. Up to now, no crystal structure of this enzyme has been reported. However, knowledge of the tertiary structure and possible active sites is essential for understanding the catalysis mechanism and for the design of inhibitors. A model with putative active sites has been created and evaluated by using homology modeling and molecular docking techniques based on the bioinformatics knowledge. The homology model is optimized in Swiss PDB Viewer with MM method and substrate structures before docking are also optimized on HF/6-31G. The active site for the docking of NADP, T, DHT and Finasteride is located near the N-terminus of enzyme. Four active amino acids in the active site are identified as Ala26, Arg53, Arg176 and Lys177. Reaction procedure, binding pattern of active sites, the types of weak interaction and so on are also discussed.
A new iodiplumbate polymer [（AOD）（Pb216）]n 1 （AOD = O-protonated 4-azonia-7- oxaspiro（4,5） decane quaternary ammonium） was synthesized by self-assembly reaction of AOD-I, Pb（NO3）2 and NaI, and structurally determined. Compound 1 crystallizes in the hexagonal system, space group P3, with a = 18.2704（8）, c = 8.1663（6） A, V= 2360.8（2） A3, Z = 3, De = 2.783 g/cm^3, F（000） = 1686, C8H17I6NOPb2, Mr = 1319.03, μ（MoKa） = 16.562 mm^-1, the final R = 0.0535 and wR = 0.1793 for 4943 observed reflections with I 〉 2σ（I）. In compound 1, three independent （PbEI6）^2-n infinite chains in each unit cell shape the sketch of compound 1 under the template of AOD-H^2＋ cation. Each （PbaI6）^2-n chain generates from the face-sharing of distorted PbI6 octahedra. （PbEI6）^2-n polyanions interact with AOD-H^2＋ cations by electrostatic interaction in the crystal to feature a so-called hybrid structure. Compound 1 was further characterized with IR, elemental analysis, fluorescence spectrum and thermal analysis. Based on the crystal structure data, DFT calculation was carried out to reveal the electronic structure of compound 1.
