Alpha-turn mimetics: short peptide alpha-helices composed of cyclic metallopentapeptide modules

Alpha-Helices are key structural components of proteins and important recognition motifs in biology. Short peptides (相似文献   

Automatic estimation of ring strain energies

A simple model has been developed which allows to estimate ring strain energies of monocyclic and bicyclic compounds. It can also be applied to polycyclic systems with reasonable accuracy. A computer program based on this model has been implemented which relies on a topological representation of molecular structures and performs the estimation of the effects of ring strain both on molecular energies and on reaction enthalpies.     

A cyclic hexamer of silver trifluoroacetate supported by four triphenylphosphine sulfide template molecules

Crystallization of silver trifluoroacetate from chloroform solutions containing triphenylphosphine sulfide affords a trigonal and a monoclinic form of a 6:4 complex {[CF3C(O)OAg]6(Ph3PS)4} of C2 symmetry with different amounts of chloroform in the crystals. With the Ph3PS components as template molecules, the CF3C(O)OAg units are assembled to form a 6-membered metallacycle codetermined by metallophilic bonding and enclosed by a 24-membered ring [AgOCO]6. A complex of the type [LAgOC(O)CF3]2, with L representing the isocyanide ligand pTolSO2CH2NC, has been shown to have a conventional bicyclic structure with three-coordinate silver atoms engaged in transannular metallophilic interactions.     

Solubility of methane in water: the significance of the methane-water interaction potential

The influence of the methane-water interaction potential on the value of the Henry constant obtained from molecular dynamics simulations was investigated. The SPC, SPC/E, MSPC/E, and TIP3P potentials were used to describe water and the OPLS-UA and TraPPE potentials for methane. Nonbonding interactions between unlike atoms were calculated both with one of four mixing rules and with our new methane-water interaction potential. The Henry constants obtained from simulations using any of the mixing rules differed significantly from the experimental ones. Good agreement between simulation and experiment was achieved with the new potential over the whole temperature range.     

Swollen poly(dimethylsiloxane) (PDMS) as a template for inorganic morphologies

We report a series of silica, titania, and zirconia microstructures synthesized within swollen poly(dimethylsiloxane) (PDMS). Voids created by solvent-swelling the polymer are used to template the product. The inorganic morphologies range from spheres to networks, depending upon the nature of the polymer, its degree of swelling, and the synthetic conditions. Organic solvents as well as pure metal alkoxide liquids have been used to swell the polymer. Once the alkoxide precursor is inside the swollen polymer, water is introduced to bring about hydrolysis and condensation polymerization. The product is a textured metal oxide within a PDMS matrix. Scanning electron microscopy (SEM), optical microscopy, nuclear magnetic resonance (NMR), and powder X-ray diffraction (PXRD) were used to characterize the products. Microstructures formed in this manner have potential use as an inexpensive route to catalysts, fillers, capsules, or membranes for separations.     

A new method for “ferrous iron” and “excess oxygen” in rocks, minerals, and oxides

A new method is given whereby oxygen excess or deficiency in many minerals and oxides may be simply determined. The method depends on the stability in phosphoric acid-pyrophosphate mixtures of both Mn^III and Mn^II. The sample is dissolved in a phosphoric acid mixture containing excess Mn^II, with or without the addition of standard oxidant, and Mn^III remaining in solution or produced by reaction with the sample is titrated with ferrous ammonium sulphate, using barium diphenylamine sulphate as indicator. The method is useful in many cases where existing methods are inapplicable or unsatisfactory. Accurate results can be obtained using relatively small samples.     

Implementation of a ”data filter” for the UK National Marine Monitoring Programme

The implementation of a strategy for the assessment of the validity of environmental monitoring data – a ”data filter”– is described. The approach was developed through the UK National Marine AQC Scheme for application to data collected during the UK National Marine Monitoring Programme. Data reported for the year 1999, by nine laboratories, for 74 determinand-matrix combinations were assessed on the basis of the completeness of their supporting quality assurance and quality control information. The approach to the establishment of criteria of acceptability for quality information is described. Received: 28 August 2001 Accepted: 29 November 2001     

Polysulfonylamine. LXXII [1]. Triphenylcarbenium- und Triphenylphosphonium-di(fluorsulfonyl)amid: Zwei Kristallstrukturen mit geordneten (FSO2)2N⊖-Lagen

Polysulfonyl Amines. LXXII. Triphenylcarbenium and Triphenylphosphonium Di(fluorosulfonyl)amides: Two Crystal Structures with Ordered (FSO₂)₂N^? Sites Treatment of HN(SO₂F)₂ in CH₂Cl₂ with Ph₃P, Ph₃PO or collidine (=B) affords the compounds Ph₃PH^⊕[(FSO₂)₂N]^? ( 3 ), Ph₃PO · HN(SO₂F)₂, and BH^⊕[(FSO₂)₂N]^? ( 7 ). The carbenium salt Ph₃C^⊕[(FSO₂)₂N]^? ( 5 ), obtained by metathesis of Ph₃CBr with [(C₆H₆)AgN(SO₂F)₂] in CH₂Cl₂, crystallizes from chloroform/petroleum ether as a monosolvate Ph₃C^⊕[(FSO₂)₂N]^? · CHCl₃ ( 6 ). In presence of a sterically hindered base, viz. collidine, 5 is a suitable reagent for the tritylation of molecules containing weakly activated H atoms (e. g.: MeCN → Ph₃CCH₂CN, acetone → tritylacetone; co-product: 7 ). The crystal structures of the ionic solids 3 (monoclinic, space group P2₁/n) and 6 (monoclinic, P2₁/c) were determined by X-ray diffraction at ?130°C; the structure refinements were not impaired by the notorious tendency of the (FSO₂)₂N moiety towards crystallographic disorder. As in the known structure of the tetraphenylarsonium salt, the anion of 3 and 6 adopts a staggered conformation of approximately C₂ symmetry (averages of all values: S? N? S 121.4°, N? S 156.2, S? O 141.6, S? F 156.6 pm). The crystal packing of 6 displays a three-centre C? H(…?O)₂ hydrogen bond between the CHCl₃ molecule and two oxygen atoms of a single anion, resulting in a six-membered ring [R₁²(6) pattern; H …? O 234 and 262 pm]. The crystal of 3 contains one-dimensional arrays of alternating cations and anions connected by a three-centre P? H(…?O)₂ bond [C(6) pattern; H …? O 237 and 254 pm]. The Ph₃C^⊕ cation of 6 is propeller-shaped, with three coplanar central bonds (mean C? C 144.5 pm) and interplanar angles of 52.7, 56.4 and 60.1° between the phenyl groups.     

Combination of HPLC and solid-phase binding assay for isolation and purification of MHC class I and associated peptides using a bladder tumour cell line

The major histocompatibility complex (MHC) class I molecules present processed self and non-self peptides to T lymphocytes. Given that the class I peptide complex plays a critical role in cell-mediated immunity, it is important to identify the nature of class I-associated peptides unique to malignant cells as a prelude to the development of vaccines. The aim of this study was to combine immuno-bead purification (using anti-class I antibody W6/32) technique, sequential ultra-filtration and high performance liquid chromatography (HPLC) to isolate class I antigens and associated peptides from an in-house established bladder tumour cell line (Fen) whose missing class I antigens had been restored by beta2-microglobulin (beta2-m) gene transfaction. The results were as follows: (a) class I antigens could be separated from tumour cell lysate but only from the class I positive Fen cells; (b) treatment of CNBr-W6/32 beads pre-exposed to class I positive Fen lysate and eluted with dissociation agent (mild acid) resulted in the release of more than 20 peptides at an approximate molecular weight of between 700 and 3000 Da based on SDS-PAGE and silver staining analysis; (c) purified and eluted peptides from class I antigens showed distinct peaks when analysed by HPLC. The data presented in this investigation demonstrated the feasibility of isolating class I antigens and associated peptides from a bladder tumour cell line. The extension of these approaches to isolate peptides from tissue tumour biopsies may help the future of vaccine therapy in cancer patients.