Extraction of Cobalt(II) from Sulfate Medium with Substituted Salicylideneanilines

Russian Journal of Physical Chemistry A - The liquid-liquid extraction of cobalt(II) from sulfate media (Na2SO4) with substituted salicylideneanilines (SAN) is investigated. The stoichiometry of...     

Solvent Incorporation in Bromination of Alkynes With Tetrabutylammonium Tribromide in Methanol

ABSTRACT: The reaction of tetrabutylammonium tribromide (TBABr₃) with mono and disubstituted alkynes in methanol at 20°C leads to the formation of mainly the corresponding α,α-dibromo, β,β-dimethoxyalkane and the E-(α,β)-dibromoalkene. The additions are faster using sonication.     

Structure and mechanism of action of isopentenylpyrophosphate-dimethylallylpyrophosphate isomerase

We have obtained the three-dimensional X-ray crystallographic structure of a C67A mutant Escherichia coli isopentenylpyrophosphate-dimethylallylpyrophosphate isomerase (EC 5.3.3.2) complexed with the bromohydrin of isopentenylpyrophosphate, at 1.93 A resolution. The overall backbone fold is very similar to that obtained previously for the wild-type enzyme in the presence of a divalent metal cation (Mn2+ or Mg2+). However, in the new structure, there are two metal binding sites, not just one. The first metal binding site is occupied by Mn2+, coordinated to three histidine and two glutamate residues, while the second is occupied by Mg2+, coordinated to two bromohydrin-ligand phosphate oxygens, the carbonyl oxygen of A67, a carboxyl oxygen of E87, and two water molecules. The C3 hydroxyl group of the bromohydrin inhibitor is involved in a short hydrogen bond to the carboxyl group of E116, one of the two Mn-bound glutamates. The structure obtained is consistent with a mechanism of action of the enzyme in which the carboxyl group of E116 protonates the double bond in isopentenylpyrophosphate, forming a carbocation, followed by removal of a C2 proton by the thiolate of C67, in the wild-type enzyme. The inhibition of the enzyme by a wide variety of other potent inhibitors is also readily explained on the basis of the bromohydrin inhibitor structure.     

Positive solutions for nonlinear fractional differential equations

Positivity - We study the existence and uniqueness of positive solutions of the nonlinear fractional differential equation $$\begin{aligned} \left\{ \begin{array}{l} ^{C}D^{\alpha }x\left( t\right)...     

Preparation and characterization of the system NiMn2O4/TiO2 by sol–gel: application to the photodegradation of benzamide under visible light

Journal of Sol-Gel Science and Technology - Benzamide is successfully degraded on the novel heterosystem NiMn2O4/TiO2 under visible light. The nanosized spinel is synthesized by the sol–gel...     

A Facile Synthesis and Crystallographic Analysis of Seven Trityl Phosphorus Compounds and Two Nickel(II) Phosphine Side-Products

Abstract  The syntheses and X-ray analyses of triphenylmethyl (trityl=Tr) phosphorus compounds are reported and the structural similarities, differences and ³¹P chemical shifts compared. A series of seven trityl-substituted phosphorus-containing compounds have been characterized by single crystal X-ray diffraction. Ph₃CPPh₂, 1, a bulky P(III) compound crystallizes in the triclinic space group , a = 7.5624(6) ?, b = 9.5470(8) ?, c = 16.9722(14) ?, α = 83.4720(10)°, β = 80.541(2)°, γ = 68.1580(10)°, the borane complex of 1, 2, Ph₃CPPh₂(BH₃) crystallizes as monoclinic colorless crystals, P2₁/c, a = 10.0972(12) ?, b = 9.6955(12) ?, c = 25.197(3) ?, β = 90.258(2)°. The analogous methyl substituted, 3, Ph₃CPMe₂(BH₃) is monoclinic, C₂/c, a = 15.628(3) ?, b = 12.770(3) ?, c = 18.406(4) ?, β = 103.968(3)°. Compounds 4–7 are trityl substituted P(V) compounds: Ph₃CP(Ph)(O)(OH), 4, crystallizes in the triclinic space group , a = 8.9847(18) ?, b = 9.7443(19) ?, c = 12.786(3) ?, α = 72.045(3)°, β = 72.031(3)°, γ = 78.769(3)°. Esterification of 4 affords TrCP(O)(Ph)OBn 5, space group, P2₁/c, a = 7.9196(5) ?, b = 31.701(2) ?, c = 19.8062(13) ?, β = 99.7750(10)°. A phosphonate diester was also characterized, Ph₃CP(O)(OEt)₂, 6, triclinic, , a = 7.9521(17) ?, b = 9.2205(19) ?, c = 14.471(3) ?, α = 85.906(4)°, β = 83.031(4)°, γ = 68.283(4)°. Treatment of the trityl H-phosphinic acid, Ph₃CPO₂H_2, with elemental selenium yields yellow crystals of 7, [Ph₃CP(O)(OH)Se]_2, P2₁/c, a = 9.0603(4) ?, b = 22.3652(11) ?, c = 16.9134(7) ?, β = 107.035(2)°. In our efforts to isolate a nickel-phosphine complex, two Ni(II) complexes were crystallographically analyzed, [Ni(OP(H)Ph₂)₆]₂BF₄ ⁻ 8 and 9. Complex 8 with an uncoordinated BF₄ ⁻ ion crystallizes as yellow orthorhombic crystals, Pbca, a = 18.8247(12) ?, b = 18.5518(12) ?, c = 21.0976(14) ?, while crystals of 9 are trigonal, , a = b = 13.1545(12) ?, c = 68.461(9) ?. Graphical Abstract  The syntheses and X-ray analyses of triphenylmethyl (trityl=Tr) phosphorus compounds are reported and the structural similarities, differences and ³¹P chemical shifts compared.      

On Elliptic System Involving Critical Sobolev Exponent and Weights

This paper is devoted to the existence and nonexistence of positive solutions for a semilinear elliptic system involving critical Sobolev exponent and weights. We study the effect of the behavior of weights near their minima on the existence of solutions for the considered problem.     

A stability result of a Timoshenko system with a delay term in the internal feedback

In this paper, we consider a Timoshenko system with a delay term in the feedback and prove a stability result. The beam is clamped at the endpoints and has, in addition to an internal damping, a feedback with a delay.Under an appropriate assumption on the weights of the two feedbacks, we prove the well-posedness of the system and establish an exponential decay result for the case of equal-speed wave propagation.     

A crystallographic investigation of phosphoantigen binding to isopentenyl pyrophosphate/dimethylallyl pyrophosphate isomerase

We report the crystallographic structures of the potent phosphoantigens Phosphostim (the bromohydrin of isopentenyl pyrophosphate) and E-4-hydroxy-3-methyl-but-2-enyl pyrophosphate bound to the mevalonate pathway enzyme isopentenyl pyrophosphate/dimethylallyl pyrophosphate isomerase (IPPI). Racemic Phosphostim forms covalent complexes with IPPI: a 4-thioether with C67 and a 4-ester with E116. Only the E116 ester forms with the chiral species, S-Phosphostim, with the w.t. enzyme, while the C67 thioether forms with a mutant Y104F IPPI. The potent phosphoantigen HMBPP also binds to IPPI, but is only a weak ( approximately 50 muM) inhibitor. These results strongly support an SN2 reaction for inhibition of IPPI by Phosphostim, in contrast to the SN1 or concerted type of reaction found with epoxide inhibitors, which react at C-3, and are of general interest in the context of the development of novel mevalonate pathway inhibitors. They also provide clues as to the nature of the binding site of synthetic phosphoantigens in gammadelta T cell activation. In particular, both bromohydrin and epoxy phosphoantigens are potent, irreversible inhibitors of IPPI while HMBPP is only a weak inhibitor, ruling out an IPPI or IPPI-like target for HMBPP in gammadelta T cell activation.     

Borane complexes of the H3PO2 P(III) tautomer: useful phosphinate equivalents

The preparation and reactivity of novel (R¹O)(R²O)P(BH₃)H [R¹, R²=Et, TIPS] synthons is investigated. The direct alkylation of these compounds with lithium hexamethyldisilazide (LiHMDS) and various electrophiles, provided new series of phosphonite-borane complexes, which can be converted into H-phosphinates and boranophosphonates.