Synthesis of the diastereoisomeric Yingzhaosu D

Yingzhaosu D (1), coexisting with Yingzhaosu A (2) which is an antimalarial principlein a traditional Chinese herbal medicine Yingzhao (Artabotrys uncinatus L. Merr.), has shownto be a new polyhydroxy sesquiterpene. We have previously reported the synthesis of Ying-zhaosu A (2) and shown that the configuration at C-4 is S. It is therefore reasonable to as-sume that the corresponding carbon atom in Yingzhaosu D has the same absolute configura-tion. Herein we report an effective method to prepare Yingzhaosu D and its three stereo-     

A Novel 2D→3D Network with the Coexistence of Polythreading and Inclined Polycatenation Constructed by the Tripodal Linker

A new cadmium(II) coordination polymer with unique structure was synthesized under diffusion process by employing triangular N-containing ligand tris(4-(pyridyl) phenyl) amine(Tppa). Complex 1 crystallizes in the space group Pbcn, with a = 28.906(3), b = 13.5294(14), c = 17.8727(18), V = 6989.7(12) 3, C66H48 Cd Cl2N8, Mr = 1136.42, Dc = 1.080 g/cm3, F(000) = 2328, μ = 0.428 mm-1 and Z = 4. Complex 1 features a 2D → 3D framework with the coexistence of inclined polycatenation and polythreading. In addition, the luminescent property of complex 1 was studied.     

To D or not to D? On estimating the microenvironment polarity of biomolecular cavities

Knowledge of the local polarity of specific cavities in biopolymers can facilitate the design of selective low MW ligands that impact the structure and function of macromolecules. The most common tools for interrogating local polarity are fluorescent probes that are sensitive to their microenvironment. Researchers often evaluate and express this local polarity using dielectric constants, a parameter that reflects an inherent bulk property. A more appropriate expression should take into account solvent-solute interactions at the molecular level. Reevaluation of commonly used fluorophores illustrates the improved correlation between observed Stokes shift changes and E(T)(30) values as compared to the corresponding dielectric constants.     

A New Method for the Synthesis of C/D Ring Synthon of Vitamin D

Inrecentyears,vitaminDresearchareahasbeenstimulatedbythediscoveriesthatIQ,25-dihydroxyvitaminD,,theactivemetaboliteofvitaminD,,inadditiontotheclassicalrolesofregulatingcalciumandphosphorusmetabolisms',hasamuchbroaderspectrumofactivitiesthanoriginallythought,suchaspromotingcelldifferelltiationandinhibitingcellproliferation"'.Thebiologicalsignificanceandmedicalneedshaveledeffortstowardthesearchforanaloguesofpotentcelldifferelltiationandantiproliferationactivitywithouttoxichypercalcemiaassociate…     

Infinite order sudden approximation treatment of the H + D2 → HD + D reaction

Results of a study of the H + D₂ → HD + D reaction within the quantum infinite order sudden approximation (RIOS) are reported here for the total energy range 1.0317 ⩽ E_t ⩽ 2.1417 eV. We present the vibrationally selected integral and total integral cross sections, and the latter are compared with both classical and experimental results. The RIOS results are in excellent agreement with the experimental results at 1.0317 eV and in reasonable agreement (≈ 20% high) at 2.1417 eV.     

Facile Construction of the 7,8‐Olefin Linkage in Vitamin D3: A Practical Synthesis Benefiting the Vitamin D3 Analog Study

Abstract

A facile procedure for construction of the 7,8‐olefin linkage in vitamin D₃ is described. Treatment of a mixture of A‐ring phosphine oxide and CD‐ring ketone in THF with lithium hexamethyldisilazide (LHMDS) at ?20°C followed by gradual heating to 50°C gives the key intermediate of vitamin D₃ analogs in excellent yield. This simplified procedure makes possible small‐scale synthesis benefiting the vitamin D₃ analog study.     

Mean potential statistical theory of the H+ + D2 → HD + D+ reaction

The reactive collision process H(+) + D(2)(ν = 0, j = 0) → HD + D(+) is theoretically analyzed for collision energies ranging from threshold up to 1.3 eV. It is assumed that the reaction takes place via formation of a collision complex. In calculations, a statistical theory is used, based on a mean isotropic potential deduced from a full potential energy surface. Calculated integral cross sections, opacity functions, and rotational distributions of the HD products are compared with recent statistical and quantum mechanical calculations performed using a full potential energy surface. Satisfactory agreement between the results obtained using the two statistical methods is found, both of which however overestimate the existing quantum mechanical predictions. The effects due to the presence of identical particles are also discussed.     

Hydrogen-bonded 1D and 2D Assemblies of Tetraiso-butyl-resorcin[4]arene in the Crystalline State

1 INTRODUCTION There is continuing interest in the assembly of molecular capsules based on concomitant formation of multiple hydrogen bonds between smaller mole- cular components[1]. A particularly attractive buil- ding block is calix[4]resorcinarenes with eight pen- dant hydroxyl functional groups[2]. In a crystal engi- neering design strategy for molecular self-assembly, cocrystallization of C-methylcalix[4]resorcinarenes with nitrogen-donor molecules such as pyridines in the presence …     

Fully analytical integration over the 3D volume bounded by the β sphere in topological atoms

Atomic properties of a topological atom are obtained by 3D integration over the volume of its atomic basin. Algorithms that compute atomic properties typically integrate over two subspaces: the volume bounded by the so-called β sphere, which is centered at the nucleus and completely contained within the atomic basin, and the volume of the remaining part of the basin. Here we show how the usual quadrature over the β sphere volume can be replaced by a fully analytical 3D integration leading to the atomic charge (monopole moment) for s, p, and d functions. Spherical tensor multipole moments have also been implemented and tested up to hexadecupole for s functions only, and up to quadrupole for s and p functions. The new algorithm is illustrated by operating on capped glycine (HF/6-31G, 35 molecular orbitals (MOs), 322 Gaussian primitives, 19 nuclei), the protein crambin (HF/3-21G, 1260 MOs, 5922 primitives and 642 nuclei), and tin (Z = 50) in Sn(2)(CH(3))(2) (B3LYP/cc-pVTZ and LANL2DZ, 59 MOs, 1352 primitives).     

Four New Isovalertatins M33, D13, D33, and D43, from the Culture Filtrate of Streptomyces luteogriseus

In a program of investigating the chemical constituents of the potentially α-amylase- inhibiting complex, WC670, extracted from the culture filtrate of Streptomyces luteogriseus, we found it contains the known aminooligosaccharides, isovalertatins M03, M…     

3D S-Wave Velocity Structure of the Crust and Upper Mantle

In this paper, 238 Rayleigh wave path data are selected and processed by the matched-filtering frequency-time analysis technique and the grid dispersion inversion method to obtain the 3D S-wave velocity structure of China mainland and its adjacent sea regions. The results show that the velocity structure relates to geotectonic division, Bouguer gravity anomaly is basically controlled by the relief of Moho discontinuity, the buried depth of LVL in upper mantle concerns the surface heat flow deeply. In this paper, authors indicate the main characteristics of the velocity structure in tectonic active and stable regions.     

The application of selected radionuclides for monitoring of the D–D reactions produced by dense plasma-focus device

The dense plasma focus (DPF) device—DPF-1000U which is operated at the Institute of Plasma Physics and Laser Microfusion is the largest that type plasma experiment in the world. The plasma that is formed in large plasma experiments is characterized by vast numbers of parameters. All of them need to be monitored. A neutron activation method occupies a high position among others plasma diagnostic methods. The above method is off-line, remote, and an integrated one. The plasma which has enough temperature to bring about nuclear fusion reactions is always a strong source of neutrons that leave the reactions area and take along energy and important information on plasma parameters and properties as well. Silver as activated material is used as an effective way of neutrons measurement, especially when they are emitted in the form of short pulses like as it happens from the plasma produced in Dense Plasma-Focus devices. Other elements such as beryllium and yttrium are newly introduced and currently tested at the Institute of Plasma Physics and Laser Microfusion to use them in suitable activation neutron detectors. Some specially designed massive indium samples have been recently adopted for angular neutrons distribution measurements (vertical and horizontal) and have been used in the recent plasma experiment conducted on the DPF-1000U device. This choice was substantiated by relatively long half-lives of the neutron induced isotopes and the threshold character of the ¹¹⁵In(n,n′)^115mIn nuclear reaction.     

Study and 3D modeling of the phase diagram of the Ag–Ge–Se system

In view of the contradictoriness of the literature data, phase equilibria in the Ag–Ge–Se system were restudied by differential thermal analysis and X-ray powder diffraction analysis. A number of polythermal sections and an isothermal section at room temperature of the phase diagram were constructed, and so was the projection of the liquidus surface. The primary crystallization fields of phases and the types and coordinates of in- and monovariant equilibria were determined. It was shown that, in the system, a single ternary compound, Ag₈GeSe₆, forms, which undergoes congruent melting at 1175 K and a polymorphic transformation at 321 K. The formation of the compounds Ag₂GeSe₃ and Ag₈GeSe₅, which was previously reported in the literature, was not confirmed. Based on the phase diagrams of boundary binary systems and the results of the differential thermal analysis of a number of samples of the ternary system, equations were obtained for calculation and 3D modeling of the liquidus and phase-separation surfaces.     

Experimental Study and 3D Modeling of the Phase Diagram of the Ag–Sn–Se System

In connection with the contradictoriness of literature data, phase equilibria in the Ag–Sn–Se system were restudied by differential thermal analysis and X-ray powder diffraction analysis. A number of polythermal sections and the isothermal section at room temperature of the phase diagram were constructed, and a projection of the liquidus surface was built. The primary crystallization fields of phases and the types and coordinates of in- and monovariant equilibria were determined. It was demonstrated that, in the system, two ternary compounds, Ag₈SnSe₆ and Ag_xSn_{2 – x}Se₂ (0.84 < x < 1.06), form. The former melts congruently at 1015 K and undergoes a polymorphic transformation at 355 K, and the latter melts with decomposition by a peritectic reaction at 860 K. The formation of the compound Ag₂SnSe₃, which was previously reported in the literature, was not confirmed. Based on the phase diagrams of boundary binary systems and the results of the differential thermal analysis of a limited number of samples of the ternary system, equations were obtained for calculation and 3D modeling of the liquidus and phase-separation surfaces.     

On the Photochemical Proton Expulsion Capability of Fringelite D – A Model of the Protist Photosensory Pigments of the Stentorin and Blepharismin Types

Summary.  Using simultaneous two-photon excitation of fringelite D and a fluorescence indicator embedded in a vesicle system it was demonstrated that after excitation a proton was transferred from the pigment to the indicator similarly as recently documented for hypericin. Semiempirical AM1 calculations were used to show that the radical species formed by electron transfer from the excited pigment state constitutes an acid which is therefore well suited for intermolecular proton transfer. Accordingly, this process constitutes a suited candidate for the primary photoprocess in the signal transduction cascade of the photosensory pigments of the stentorin and blepharismin type. Received April 26, 2000. Accepted May 16, 2000     

James D. Watson 88—the discovery of the double helix was an iconic event in structural chemistry

The ingenuity of James D. Watson and Francis Crick, the convergence of the advances in X-ray crystallography, the accumulated knowledge of structural chemistry, and the breakthroughs in chemical methods of analysis led to the discovery of the double helix structure of DNA. The discovery catapulted Watson to a career that helped DNA and the applications of the knowledge about its structure triumph in biomedical sciences. Watson’s eighty-eighth birthday is an occasion to have a look at his path to success, his personality, and assess his legacy.     

A perturbation theoretical method for determination of the dependence of the intramolecular X–H(D) potential on the hydrogen bond strength

A perturbation theoretical method is proposed that allows determination of the function describing the dependence of the intramolecular XH(D) potential on the hydrogen bond strength. Treating the XH(D) oscillators as mixed cubic–quartic oscillators in which the stretch–stretch couplings of the ν(X–H(D)) mode with the internal modes of the radical X may be neglected, and introducing the hydrogen bonding influence through the changes in the harmonic diagonal force constants (as proposed by Sceats and Rice [41]), it is possible to extract the analytical form of the function ) from the experimental versus correlations. The other parameters obtained by the empirical correlations, within this model, also have an exact physical meaning. The method is applicable to weak hydrogen bonds as well as to hydrogen bonds of intermediate strength, and, strictly speaking, to linear X– systems. However, extension to arbitrary geometry may be easily done. This revised version was published online in July 2006 with corrections to the Cover Date.     

EPR study on the photosensitized generation of reactive oxygen species by actinomycin D

Actinomycin D (AMD) is an anticancer antibiotic that can bind selectively to both double-stranded and single-stranded DNA, and this binding greatly enhances DNA photosensitization. Using electron paramagnetic resonance (EPR) in combination with spin trapping techniques, a systematic study was carried out on the reactive oxygen species generated in the photosensitization process of AMD. It was found that 1O2 and O2- are important reactive intermediates either insolution or in DNA complexes, and the generation of these species is in competition. This finding suggests that the photodynamic action of AMD proceeds via two pathways: energy transfer (type Ⅰ mechanism) and electron transfer (type Ⅱ mechanism). 1O2 is the main product formed via energy transfer reaction in solution while electron transfer between the excited states of AMD and DNA becomes the predominant pathway in DNA complexes.