De novo metallonucleases based on helix-loop-helix motifs

Three new 42-mer peptides (PR I-III) designed to fold into a hairpin helix-loop-helix motif have been prepared. In the peptide sequence two (PR II-III) or four (PR I) copies of an unnatural amino acid bearing a triazacyclononane metal-ion binding site (ATANP) have been inserted in appropriate positions to allow the ligand subunits to face each other either within the same helix or between the two helices of the hairpin motif. Circular dichroism (CD) studies in solution have shown that the apopeptides adopt a well-defined helix-loop-helix tertiary structure that dimerizes in solution at concentrations above 200 microM to form a four-helix bundle. However, the helical content is strongly dependent on pH and metal-ion binding. Both protonation of the amines of the triazacyclononane units present in the ATANP lateral arm and complexation with Zn(II) ions cause a significant decrease of the helical content of the sequences. The Zn(II) complexes of the three peptides catalyze the transesterification of the RNA model substrate 2-hydroxypropyl-p-nitrophenyl phosphate (HPNP) with different efficiency. The best catalyst appears to be PR I-4 Zn(II), that is, the peptide incorporating four ATANP units. Michaelis-Menten saturation kinetics allowed us to estimate that substrate fully bound to the catalyst reacts 380 times faster than in its absence. The kinetic evidence suggests cooperativity between (at least two) metal ions: one activating the nucleophilic species (directly or indirectly) and the other facilitating nucleophilic attack by coordination of the phosphate.     

Intercalation of α,ω-Alkanediamines in Layered Aluminium Dihydrogen Triphosphate Dihydrate

Intercalation of ,-alkanediamines, NH₂(CH₂) _n NH₂ (n = 3–10), into layered aluminium dihydrogen triphosphate dihydrate, AlH₂(P₃(O₁₀... 2H₂O, was investigated by XRD, DTA-TG, elemental analysis, and solid-state ³¹P, ¹³C and ²⁷Al NMR. ,-Alkanediamines are intercalated to form a monomolecular layer in the interlayer region, in which the alkanediamines incline at 57 ± 5° to the phosphate layers, whereas n-alkylamines form a bilayer structure with the same inclination angle. Two amino groups in an ,-alkanediamine molecule bridge the layered sheets of phosphates.     

Crystal Structures and Raman Spectra of cis‐[SnCl4(H2O)2]·2H2O,cis‐[SnCl4(H2O)2]·3H2O, [Sn2Cl6(OH)2(H2O)2]·4H2O,and [HL][SnCl5(H2O)]·2.5H2O (L=3‐acetyl‐5‐benzyl‐1‐phenyl‐4, 5‐dihydro‐1, 2, 4‐triazine‐6‐one oxime,C18H18N4O2)

The complexes cis‐[SnCl₄(H₂O)₂]·2H₂O ( 1 ), [Sn₂Cl₆(OH)₂(H₂O)₂]·4H₂O ( 3 ), and [HL][SnCl₅(H₂O)]·2.5H₂O ( 4 ) were isolated from a CH₂Cl₂ solution of equimolar amounts of SnCl₄ and the ligand L (L=3‐acetyl‐5‐benzyl‐1‐phenyl‐4, 5‐dihydro‐1, 2, 4‐triazine‐6‐one oxime, C₁₈H₁₈N₄O₂) in the presence of moisture. 1 crystallizes in the monoclinic space group Cc with a = 2402.5(1) pm, b = 672.80(4) pm, c = 1162.93(6) pm, β = 93.787(6)° and Z = 8. 4 was found to crystallize monoclinic in the space group P2₁, with lattice parameters a = 967.38(5) pm, b = 1101.03(6) pm, c = 1258.11(6) pm, β = 98.826(6)° and Z = 2. The cell data for the reinvestigated structures are: [SnCl₄(H₂O)₂]·3H₂O ( 2 ): a = 1227.0(2) pm, b = 994.8(1) pm, c = 864.0(1) pm, β = 103.86(1)°, with space group C2/c and Z = 4; 3 : a = 961.54(16) pm, b = 646.29(7) pm, c = 1248.25(20) pm, β = 92.75(1)°, space group P2₁/c and Z = 4.     

Na-Gd phosphate glasses

Summary The present paper deals with preparation, thermal properties and radioluminescence of Ce-doped Na-Gd phosphate glasses. Thanks to their high radioluminescence intensity, three times greater than that of BGO, these glasses are promising materials for the detection of neutrons, - and X-rays. The glasses with a Gd concentration up to 89 mol% were prepared by a rapid quenching technique in air. Their thermal properties were determined using DSC and temperatures of glass transition were measured in addition using TMA. Temperatures of glass transition, crystallization and melting depend on Gd concentration and they follow the liquidus line in a phase diagram of binary system in which two eutectics and a congruently melting compound exist. High glass-forming ability of this glass system was found evidenced. The glasses containing at least 30 mol% Gd were moisture resistant.     

Synthesis and Characterization of α‐Titanium Phosphate/Propylamine Intercalation Compounds Containing Transition‐Metal Ions

Polycrystalline intercalated TiM_xH_2−nx(PO₄)₂· yC₃H₇NH₂·wH₂O compounds with transition metal (TM) ions (Mⁿ⁺ = Co²⁺, Ni²⁺, Fe³⁺ or Cr³⁺) have been prepared by means of an indirect route and characterised using X-ray diffraction, scanning electron microscopy, chemical and thermal analysis, X-ray absorption and magnetic measurements. These novel pillared layered materials, which were obtained from the monoclinic (P2₁/c space group) α-Ti(HPO₄)₂·H₂O phase, lose its crystallinity after intercalation. However all the TM ions are octahedrally surrounded by 6 oxygen atoms, although the X-ray absorption spectra evidence a clear dependence on the temperature. Surprisingly, all the materials behave as paramagnetic down to 1.5 K, but they exhibit different colours, what means that they are optically active (Co²⁺: violet; Ni²⁺: pale green; Fe³⁺: yellow; Cr³⁺: dark green).     

二水草酸钙的热力学转化及海藻多糖的稳定作用

草酸钙结石的形成与尿液中草酸钙的存在形式密切相关，一水草酸钙(COM)促进尿石症形成，而二水草酸钙(COD)易随尿液排出体外。本文采用体外模拟方法，比较研究了COD晶体在水溶液、正常人尿液和结石患者尿液3个不同体系中的稳定性及海藻龙须菜多糖(SPS)对COD的稳定作用。在水溶液和患者尿液中，不但COD转化率高，而且得到的转化产物COM晶体聚集程度大；而在正常人尿液中，COD转化率低，转化产物聚集程度较小。COD在不同体系中转化的速度依次为：水溶液＞患者尿液＞正常人尿液。从海藻龙须菜中提取的硫酸多糖可以稳定COD的存在并减小COM的聚集，这有利于阻止草酸钙结石的形成，因此，海藻龙须菜多糖有可能用于防止草酸钙结石形成。     

Hydrothermal Synthesis and Structures of Two New Molybdenum Phosphate Compounds based on Keggin Cluster Units

Two new molybdenum phosphate complexes, [Cu₂(phen)₄(μ‐Cl)][PMo₁₂O₄₀]·H₂O (phen = 1,10‐phenanthroline) ( 1 ) and (Hbpy)[Cu^I(bpy)]₂[PMo^V₂Mo^VI₁₀O₃₉] (bpy = 4,4′‐bipyridine) ( 2 ), have been prepared under mild hydrothermal conditions and structurally characterized by single‐crystal X‐ray diffraction. Compounds 1 and 2 crystallize in triclinic system, space group , with a = 12.5458(7) Å, b = 13.4486(8) Å, c = 21.2406(12) Å, α = 99.7020(10)°, β = 94.2320(10)°, γ = 95.0890(10)°, V = 3504.2(3) ų and Z = 2 for 1 , and a = 10.7871(6) Å, b = 10.9016(6) Å, c = 12.7897(7) Å, α = 96.8500(10)°, β = 110.0850(10)°, γ = 103.5800(10)°, V = 1339.74(13) ų and Z = 1 for 2 . Compound 1 contains a [Cu₂(phen)₄(μ‐Cl)]³⁺ cation in which two similar [Cu(phen)₂] units are bridged by one chlorine atom. Compound 2 contains one‐dimensional straight chain of Keggin polyoxoanions [PMo^V₂Mo^VI₁₀O₃₉]_n^3? and two linear cationic chains of [Cu^I(bpy)]_nⁿ⁺. The molecular packing shows a two‐dimensional network, which is formed by the cross of the linear Keggin anions and Cu‐bpy cations.     

Thermal analysis of mechanoactivated mixtures of tunisia phosphorite and ammonium sulfate

The thermal behavior of Tunisia phosphorite and ammonium sulfate mixtures are examined by non-isothermal thermogravimetry in air atmosphere. It has been shown that the thermal stability of mixtures have different behavior after mechano-chemical treatment due to phase changes in the mixtures. New solid phases are confirmed by the stages and rate of mass changes and also by the heat effects observed. New phases are also confirmed by using X-ray diffraction method. Based on the data obtained by the mechanism of chemical transformations is proposed. The kinetics of mechano-activated mixtures decomposition is significantly influenced by the time of treatment and proceeds in few stages. Stage I is attributed to the effect of partially ammonia releasing, when the next stages are associated with the decomposition of apatite structures. Because of the interfacial interactions during mechano-chemical treatment insoluble phosphorous forms from apatite structures are transformed to the soluble forms suitable for plants nutrition. The results have shown that the soluble form can be controlled by the initial components ratio and conditions of treatment on the way to obtain slow releasing nutrition products. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of the organophosphate structure on the physical and flame‐retardant properties of an epoxy resin

2‐(6‐Oxido‐6H‐dibenzo〈c,e〉〈1,2〉oxa‐phosphorin‐6‐yl)1,4‐benzenediol (ODOPB) and bis(3‐dihydroxyphenyl) phenyl phosphate (BHPP) were successfully synthesized and used as reactive flame retardants in o‐cresol formaldehyde novolac epoxy resin. Because of the rigid, cyclic, side‐chain structure of ODOPB, the resultant phosphorus‐containing epoxy resin exhibited a higher glass‐transition temperature, better flame retardancy, higher modulus, and greater thermal stability than the regular bromine‐containing tetrabromobisphenol A epoxy resin and the linear, main‐chain, phosphorus‐containing BHPP epoxy resin. A UL‐94VO rating was achieved with a phosphorus content as low as 1.1% with ODOPB (comparable to a bromine content of 12% and a phosphorus content of 2.2% with BHPP) in the cured resins, and no fumes or toxic gas emissions were observed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 369–378, 2002     

Thin-Layer chromatography of inorganic ions on cellulose phosphate in sulfuric acid-organic solvent media

Summary Thin-layer chromatographic behavior of 49 inorganic ions on cellulose phosphate (P-cellulose) has systematically been surveyed with binary solvent mixtures consisting of sulfuric acid and an organic solvent such as methanol or acetone. The R_f values of many bivalent and monovalent ions as well as Te(VI) decrease on the P-cellulose layer with an increasing concentration of the organic solvent. Polyvalent ions which form strong phosphato-complexes and precipitate insoluble sulfate are strongly retained on P-cellulose. Oxy-anions, Au(III) and Pt(IV) are not adsorbed on the cellulose to any great extent. Feasibilities of the separation of multicomponent mixtures are demonstrated on the P-cellulose layer.