Kinetic Studies of the Ring-Opening Polymerization of 1-β-Cyanoethylazetidine

The ring-opening polymerization rate of 1-β-cyanoethylazetidine (CA) with 3-hydroxy-1-propanesulfonic acid sultone (HPSS) as an initiator has been investigated in acetonitrile. The polymerization of CA with HPSS proceeded by way of a zwitterion formed by the addition reaction of CA and HPSS. The course of polymerization involved, as an early stage, slow initiation due to the low reactivity of the zwitterion. The propagation constants were obtained as were the enthalpy of activation for propagation (ΔH_p? = 12 kcal/mol) and the entropy of activation for propagation (ΔS_p? = ?31 cal/K·mol).     

Studies on the Structure of Kansuinine A from Euphorbia kansui

Kansuinine A is a macrocyclic jatrophane diterpene that was isolated from Euphorbia kansui.Further investigation of the structure was revealed that the benzoyl group located at C-8 and the position of C-3 was the present of an acetyl group by means of HMQC,HMBC spectra.     

Three dimensional models of Cu(2+)-Aβ(1-16) complexes from computational approaches

Elucidation of the coordination of metal ions to Aβ is essential to understand their role in its aggregation and to rationally design new chelators with potential therapeutic applications in Alzheimer disease. Because of that, in the last 10 years several studies have focused their attention in determining the coordination properties of Cu(2+) interacting with Aβ. However, more important than characterizing the first coordination sphere of the metal is the determination of the whole Cu(2+)-Aβ structure. In this study, we combine homology modeling (HM) techniques with quantum mechanics based approaches (QM) to determine plausible three-dimensional models for Cu(2+)-Aβ(1-16) with three histidines in their coordination sphere. We considered both ε and δ coordination of histidines 6, 13, and 14 as well as the coordination of different possible candidates containing oxygen as fourth ligand (Asp1, Glu3, Asp7, Glu11, and CO(Ala2)). Among the 32 models that enclose COO(-), the lowest energy structures correspond to [O(E3),N(δ)(H6),N(ε)(H13),N(ε)(H14)] (1), [O(E3),N(δ)(H6),N(δ)(H13),N(δ)(H14)] (2), and [O(D7),N(ε)(H6),N(δ)(H13),N(δ)(H14)] (3). The most stable model containing CO(Ala2) as fourth ligand in the Cu(2+) coordination sphere is [O(c)(A2),N(ε)(H6),N(δ)(H13),N(ε)(H14)] (4). An estimation of the relative stability between Glu3 (1) and CO(Ala2) (4) coordinated complexes seems to indicate that the preference for the latter coordination may be due to solvent effects. The present results also show the relationship between the peptidic and metallic moieties in defining the overall geometry of the complex and illustrate that the final stability of the complexes results from a balance between the metal coordination site and amyloid folding upon complexation.     

Studies on the Fast Atom Bombardment Mass Spectrometry Fragmentation of Amino Sugars Using Synthetic Derivatives of the Trisaccharide Unit β-D-Glucopyranosyl-(1-3)-O-2-deoxy-2-amino-β-d-glucopyranosyl-(1-4)-O-d-glucopyranose

Abstract

N-Phthaloyl, N-acetyl, N-benzyl, N-acetyl-N-methyl, N,N-dimethyl, N-benzoyl, and N,N-dibenzoyl derivatives of the trisaccharide β-D-glucopyranosyl-(1-3)-O-(2-deoxy-2-amino-β-D-glucopyranosyl)-(1-4)-O-β-D-glucopyranose were synthesized and analyzed by FAB MS. The intensity ratios of the peaks resulting from cleavage of the anomeric bond of the glucosamine residue and the respective molecular ion peaks turned out to be high for the N-acyl derivatives and up to two orders of magnitude lower for the N-alkyl compounds. These results show that fragmentation at the anomeric carbon of the amino sugar may be assisted by the carbonyl group and the resulting cation is stabilized by delocalization of the positive charge.     

Structure of 1-β-d-xylofuranosyluracil in the crystal and in solution

The molecular and crystal structure of 1-β-d-xylofuranosyluracil hydrate was established by X-ray diffraction analysis. The mutual arrangement of the xylofuranose fragment and the nucleic base corresponds to the anti conformation. The furanose ring adopts a C-envelope conformation. The structure of the nucleoside in a DMSO-d₆ solution has been determined by¹H NMR spectroscopy. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1378–1380, July, 1998.     

Alignment effect of N2(A3Σu+) in the energy transfer reaction of aligned N2(A3Σu+) + NO(X2Π) → NO(A2Σ+) + N2(X1Σg+)

Steric effect in the energy transfer reaction of N(2)(A(3)Σ(u)(+)) + NO(X(2)Π) → NO(A(2)Σ(+)) + N(2)(X(1)Σ(g)(+)) has been studied under crossed beam conditions at a collision energy of ~0.07 eV by using an aligned N(2)(A(3)Σ(u)(+)) beam prepared by a magnetic hexapole. The emission intensity of NO(A(2)Σ(+)) has been measured as a function of the magnetic orientation field direction (i.e., alignment of N(2)(A(3)Σ(u)(+))) in the collision frame. A significant alignment effect on the energy transfer probability is observed. The shape of the steric opacity function turns out to be most reactive at the oblique configuration of N(2)(A(3)Σ(u)(+)) with an orientation angle of γ(v(R)) ~ 45° with respect to the relative velocity vector (v(R)), which has a good correlation with the spatial distribution of the 2pπ(g)* molecular orbital of N(2)(A(3)Σ(u)(+)). We propose the electron exchange mechanism in which the energy transfer probability is dominantly controlled by the orbital overlap between N(2)(2pπ(g)*) and NO(6σ).     

Time to Face the Fats: What Can Mass Spectrometry Reveal about the Structure of Lipids and Their Interactions with Proteins?

Since the 1950s, X-ray crystallography has been the mainstay of structural biology, providing detailed atomic-level structures that continue to revolutionize our understanding of protein function. From recent advances in this discipline, a picture has emerged of intimate and specific interactions between lipids and proteins that has driven renewed interest in the structure of lipids themselves and raised intriguing questions as to the specificity and stoichiometry in lipid-protein complexes. Herein we demonstrate some of the limitations of crystallography in resolving critical structural features of ligated lipids and thus determining how these motifs impact protein binding. As a consequence, mass spectrometry must play an important and complementary role in unraveling the complexities of lipid-protein interactions. We evaluate recent advances and highlight ongoing challenges towards the twin goals of (1) complete structure elucidation of low, abundant, and structurally diverse lipids by mass spectrometry alone, and (2) assignment of stoichiometry and specificity of lipid interactions within protein complexes.     

Crystal Structure of Nickel (Ⅱ) Complex with 3Hydroxy1-1, 5-diazacycloheptane

1INTRODUCT1ONMesocyclicdiamines(e.g.1,5-diazacyclooctane,1.4-diazacycloheptane)asversatilechelatingagentsoftenprovideastericeffectalongwithastrongligandfieldeffectE'jTheyeasilyformstablecomplexesinunusualgeometrieswiththetransitionmetalion.[2j.Forexample,thecrystalstructureoftheNiCl,complex,Ni(dach),Cl,(dach=1.4-diazacyclohepane),showsthattheNi(I)isplanarwithNi-Nbonddis-tancesof1.917(5)and1.921(6)Aandthetwodachligandsinthetransboat-boatco.fo.mation[3j'Inordertoextendfurtherthecomplexat…     

Studies on the Crystal Structure and Photoluminescence of a Mercury(Ⅱ)Complex Based on a Novel Pyridine Ligand

<正>A novel mercury(n)complex HgL_2Br_2 was prepared from HgBr_2 and the organic ligand 2-(N-methyl-N-(4-((E)-2-(pyridine-4-yl)vinyl)phenyl)amino)ethanol(L).The ligand was synthesized and then characterized by FT-IR spectroscopy,~1H NMR,mass spectrum and elemental analysis,while the single-crystal diffraction data of the complex were collected on a Siemens Smart CCD diffractometer.The complex crystallizes in triclinic space group P_1~-with a=5.367(5),b= 12.466(5),c=23.945(5)(?),α=90.812(5),β=96.318(4),γ=96.093(5)°,Z=2,D_c=1.817g·cm~(-3),μ=7.395 mm~(-1),S=0.825,and the final R=0.0396.The Hg(Ⅱ)ion in the distorted tetrahedral mercury(Ⅱ)complex C_(32)H_(36)HgBr_2N_4O_2 is coordinated by two N atoms from the two ligands together with two bromide ions.Solid-state emission of the ligand and its complex has been investigated at room temperature.     

Structure of the 1 : 1 Complex of Hexakis(2,3,6-tri- O-methyl) α-Cyclodextrin with ( R)-(-)-1,7-Dioxaspiro[5.5]undecane

The crystal structure of the 1 : 1 inclusion complex of hexakis(2,3,6-tri-O-methyl)- -cyclodextrin (TM CD) with 1,7-dioxaspiro[5.5]undecane (spiroacetal) is orthorhombic, space group C2221, with a = 24.002(2), b = 14.812(1), c = 21.792(2) Å V = 7747.3(11) Å3 and Z = 8. The molecular six-fold axis of TM CD coincides with the a two-fold crystallographic axis and the guest is located at the secondary methoxy group side, disordered over two positions related by that axis. The guest model used during the refinement is that of the (R)-enantiomer alone because trials to either refine a 1 : 1 mixture of (R)- and (S)-enantiomers or the (S)-enantiomer alone failed. The crystallographic evidence of enantioselectivity towards the (R)-enantiomer of spiroacetal was confirmed by independent experiments and may be attributed to numerous non bonding interactions between host and guest involving non conventional H-bonds.     

X-ray Structure of a 1:2 Complex of Hexakis (3-O-acetyl-2,6-di-O-methyl)-α-cyclodextrin with Butylacetate

Abstract

Crystal structure of a 1:2 complex of hexakis(3-O-acetyl-2,6-di-O-methyl)-α-cyclodextrin (ADMACD) with butylacetate was determined by the X-ray method. The space group of the crystal is P2₁2₁2₁ with Z = 4 and D _x = 1.293 g cm^?3, and the cell dimensions are a = 11.087(2), b = 23.543(3), and c = 31.739(6) Å. The structure was solved by the direct method and refined to the R-value of 0.123 for all the 4993 observed reflections with 1<0. The ADMACD molecule is in a round shape with the pseudo hexagonal symmetry. Methyl and acetyl groups point towards the outside of the molecule. Because of the acetyl groups attached to O3 and methyl groups attached to O6, the intramolecular cavity is ca. 3 Å deeper than the cavity of native α-CD. One butylacetate molecule is coaxially accommodated with its acetyl group at the O6 side in the host cavity while the other guest molecule is located in an intermolecular space between host molecules which are stacked to form a head-to-tail channel-type packing structure along the a axis.     

Synthesis of 2-Arylbenzofuran: Confirmation of the Structure of Gnetifolin A

GnethelinAu'asisolatedfromGnetumparvghlium(Warb.)C.Y.Chengb}'Lietal.'ItSstructUrextasproPosedpre\'iousl}'as2-(3.5allhydroxT4-methomphen}l)-3-methony-5-hydrox3-benLzofiiran(l).Aner9'nthesisofset1eralanalogsofStrUctUre(l),theStrUCtUrofGnetjfolinAseemstobenustakenanduasrerisedas2K3-5allhydrOny4-methomphenyl)4-methoxy-5-hvdrowtenzofuran(2).=Inordertoconfirmthisrer4ndmCtUranddevelopaversahlewtehcrouteforthe9-nthesisofGnetjfolinAandanalogs,2T-edSyl4-methoxy-5-hydrotwllZofuran(3)u'asselec…     

The electrostatic probe: a tool for the investigation of the Aβ(1-16) peptide deformations using the static modes

We investigate the conformational changes of the Amyloid β(1-16) peptide induced by moving Zn(2+) ions in the solvent, which we call the electrostatic probe. We use our recently developed approach of static modes which allows treating the flexibility of biological molecules at the atomic scale. Starting from an experimental apostructure, we find that several ion impacts allow the transition of the peptide toward its folded conformation, observed experimentally in the presence of Zn(2+) ions. This result shows the ability of our model and its associated software tool to describe properly the conformational changes and opens a new path toward the molecule/molecule docking problem.     

A Comparison in the Efficiency of Six Standard 2-Amino-2-Deoxy-Glucosyl Donors for the Synthesis of (2-Deoxy-2-Phthalimido-β-D-Glucopyranosyl) (1→ 4)-β-D-Glucopyranosides.

ABSTRACT

A systematic study is presented for the most common methods used for the preparation of the disaccharide benzyl O-(3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-β-D-glucopyranosyl)-(1→'4)-3,6-di-O-benzoyl-2-deoxy-2-phthalimido-β-D-glucopyranoside (9) from “standard 2-amino-2-deoxyglucopyranosyl donors” 1-6 and benzyl 3,6-di-O-benzoyl-2-deoxy-2-phthalimido-β-D-glucopyranoside (7) as an acceptor. It was found that the highest yield was obtained when the trichloroacetimidate derivative 1 was coupled to the 4 position of acceptor 7. In an analogous manner, the disaccharides allyl O-(3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-β-D-glucopyranosyl)-(1→'4)-3,6,-di-O-benzoyl-2-deoxy-2-phthalimido-β-D-glucopyranoside (10), benzyl O-(3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-β-D-glucopyranosyl)-(1→'4)-3,6-di-O-benzoyl-2-deoxy-2-phthalimido-β-D-galactopyranoside (12), and allyl O-(3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-β-D-glucopyranosyl)-(1→'3)-4,6-O-benzylidene-2-deoxy-2-phthalimido-β-D-glucopyranoside (14) were prepared.     

Synthesis,Crystal Structure and Catalytic Performance of the Trifluoro-substituted Mono(β-diiminato) Copper(Ⅱ) Complex

Two novel copper complexes with methyl or trifluoro-substituted mono-β-diiminato ligands and one acetoxyl anion were synthesized and characterized by IR spectroscopy and elemental analysis for the first time. The structure of complex 2 bearing trifluoro substituents was further confirmed by single-crystal X-ray diffraction. The crystal belongs to the triclinic system, space group P1 with a = 7.377(4), b = 11.727(6), c = 12.913(7) ?, α = 116.569(6), β = 98.829(7), γ = 96.520(6)°, V = 966.2(8) ?3, Z = 2, Mr = 479.86, Dc = 1.649 g/cm3, F(000) = 482, μ = 1.205 mm-1, the final R = 0.0370 and w R = 0.0903 for 3430 observed reflections with I 2σ(I). These mono-β-diiminato copper complexes can effectively catalyze methacrylate(MA) polymerization when activated by MMAO. The introduction of fluoro groups into the N-aryl ring of β-diiminato ligands can greatly increase the catalytic activity of copper complexes as well as the molecular weight of PMA.     

Nonadiabatic quantum reactive scattering of the OH(A 2Σ+) + D2

The seams of conical intersection exist between the ground (1 (2)A(')) and the first-excited (2 (2)A(')) electronic potential energy surfaces (PESs) of OH(A (2)Σ(+),X (2)Π) + H(2) system. This intersection induces the nonadiabatic quenching of OH(A (2)Σ(+)) by D(2). We present nonadiabatic quantum dynamics study for OH(A (2)Σ(+)) + D(2) on new five-dimensional coplanar PESs. The ab initio calculations of PESs are based on multireference configuration interaction (MRCI)/aug-cc-pVQZ level. A back-propagation neural network is utilized to fit the PESs and nonadiabatic coupling. High degrees of rotational excitation of quenched OH(X (2)Π) products are found in nonreactive quenching channel, and the quenched D(2) products are vibrationally excited up to quantum number v(2) (')=8. The theoretical results of nonadiabatic time-dependent wave-packet calculation are in good agreement with the existing experimental data.     

Study on the Crystal Structure of RS-1-(2-methoxyphenyl)-4-〔3-(1-naphthyloxy)-2-hydroxypropyl〕-piperazine

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