Andrzej C. Skapski

Bio: Andrzej C. Skapski is an academic researcher from Imperial College London. The author has contributed to research in topics: Crystal structure & Molecule. The author has an hindex of 25, co-authored 112 publications receiving 2006 citations.

Refined crystal structure of tetra-µ-acetato-bisaquodicopper(II)

Abstract: The structure of the title compound has been refined from three-dimensional X-ray diffractometer data. Crystals are monoclinic, space group C2/c, with Z= 4 in a unit-cell of dimensions: a= 13·168(2), b= 8·564(2), c= 13·858(2)A, and β= 117·02(1)°, Full-matrix least-squares refinement, using 1280 independent reflections, has reached R 0·047.The refinement has, as expected, confirmed the original two-dimensional structure determination and much more accurate bond lengths and bond angles have been obtained: mean Cu–O(acetate) 1·969 A, Cu–O(water) 2·156, and Cu ⋯ Cu is 2·616 A. The geometry of the acetate bridges is planar and bond lengths and angles are as expected.

Studies on transition-metal peroxo complexes. Part 7. Molybdenum(VI) and tungsten(VI) carboxylato peroxo complexes, and the X-ray crystal structure of K2[MoO(O2)2(glyc)]·2H2O

Abstract: New complexes [MoO(O2)2L]2–[L = malate, tartrate (tart), tartronate, quinate, or glycolate (glyc)], [WO(O2)2L]2–(L = citrate, tartrate, malate, or glycolate), and [W2O2(O2)4(tart)]4– are reported, and modified preparations given for [MO(O2)2L]2– and [MO2(O2)L(H2O)]2–(M = Mo or W; L = oxalate). Raman and i.r. spectra of the solid complexes, and Raman, 13C and 95Mo n.m.r. spectra of their aqueous solutions, have been measured and are used to suggest the structures of the species in the solid state and solution. The X-ray crystal structure of K2[MoO(O2)2(glyc)]·2H2O has been determined: triclinic, space group P, with a= 7.222(4), b= 7.950(6), c= 10.450(5)A, α= 67.81(4), β= 73.72(7), γ= 64.84(4)° at 20 °C, and Z= 2; the structure has been refined to R= 0.035.

Crystal structure of dichlorotetra-µ-adenine-dicopper(II) chloride hexahydrate

Abstract: The structure of dichlorotetra-µ-adenine-dicopper(II) chloride hexahydrate, [Cu2(ade)4Cl2]Cl2,6H2O, has been determined by three-dimensional X-ray crystal structure analysis. The crystals are orthorhombic with unit-cell dimensions a= 23·92, b= 13·844, c= 11·262 A, Z= 4, space group Cmca. Full-matrix least-squares refinement, using 870 visually estimated reflections, has reached R 0·098.The structure contains the complex ion [Cu2(ade)4Cl2]2+, chloride ions and molecules of water of solvation. The complex ion, which has 2/m crystallographic symmetry, is dimeric with pairs of copper atoms held together by four bridging adenine ligans, co-ordinated via N(3) and N(9). The copper atoms have a square pyramidal co-ordination, with chlorine in the apical position at a distance of 2·429 A. The metal is 0·33 A above the plane of four nitrogen atoms, with Cu–N distances of 2·008 and 2·041 A. The Cu ⋯ Cu non-bonded separation is 3·066 A.The chloride ions together with the water molecules and all non-donor nitrogen atoms of adenine form an intricate network of hydrogen bonds in which linkages of the type O–H ⋯ N, N–H ⋯ O, and O–H ⋯ Cl– are involved.

Differentiation-inducing factor from the slime mould Dictyostelium discoideum and its analogues. Synthesis, structure and biological activity

Abstract: Previous work has led to the identification of a novel class of effector molecules [DIFs (differentiation-inducing factors) 1-3] released from the slime mould Dictyostelium discoideum. These substances induce stalk-cell differentiation in Dictyostelium discoideum and are thought to act as morphogens in the generation of the prestalk/prespore pattern during development. The DIFs are phenylalkan-1-ones, with chloro, hydroxy and methoxy substitution on the benzene ring. DIFs 1-3 and a number of their analogues have been synthesized by using a simple two-step procedure, and each analogue has been characterized by m.s., u.v. and n.m.r. spectroscopy. The crystal structure of synthetic DIF-1 [1-(3,5-dichloro-2,6-dihydroxy-4-methoxyphenyl)hexan-1-one, was investigated. The specific biological activity of each analogue was determined in a bioassay, where isolated Dictyostelium amoebae are induced to differentiate into stalk cells. The major biologically active substance, DIF-1, caused 50% stalk-cell differentiation at 1.8 x 10(-10) M; the C4 alkyl homologue (DIF-2) and C6 homologue possessed 40 and 16% of the activity of DIF-1 respectively. Further increase or decrease in the alkyl chain length resulted in a marked decrease in specific activity. The pattern of substitution on the benzene ring is a major determinant of bioactivity, since the specific activities of the 2,4-dihydroxy-6-methoxy and trihydroxy analogues were less than 1% of that of DIF-1. Substitution of bromine in DIF-1 had little effect on bioactivity; in contrast the activity of monochloro-DIF-1 (DIF-3) was diminished. There was no evidence for antagonism or synergy between DIF-1 and any of its analogues. This series of analogues will facilitate further studies in the biological effects and mode of action of DIF-1.

Secondary building units, nets and bonding in the chemistry of metal–organic frameworks

Abstract: This critical review presents a comprehensive study of transition-metal carboxylate clusters which may serve as secondary building units (SBUs) towards construction and synthesis of metal–organic frameworks (MOFs). We describe the geometries of 131 SBUs, their connectivity and composition. This contribution presents a comprehensive list of the wide variety of transition-metal carboxylate clusters which may serve as secondary building units (SBUs) in the construction and synthesis of metal–organic frameworks. The SBUs discussed here were obtained from a search of molecules and extended structures archived in the Cambridge Structure Database (CSD, version 5.28, January 2007) which included only crystals containing metal carboxylate linkages (241 references).

Generation of sulfate radical through heterogeneous catalysis for organic contaminants removal: Current development, challenges and prospects

Abstract: Sulfate radical-based advanced oxidation processes (SR-AOPs) employing heterogeneous catalysts to generate sulfate radical (SO4 −) from peroxymonosulfate (PMS) and persulfate (PS) have been extensively employed for organic contaminant removal in water. This article aims to provide a state–of–the–art review on the recent development in heterogeneous catalysts including single metal, mixed metal, and nonmetal carbon catalysts for organic contaminants removal, with particular focus on PMS activation. The hybrid heterogeneous catalyst/PMS systems integrated with other advanced oxidation technologies is also discussed. Several strategies for the identification of principal reactive radicals in SO4 −–oxidation systems are evaluated, namely (i) use of chemical probe or spin trapping agent coupled with analytical tools, and (ii) competitive kinetic approach using selective radical scavengers. The main challenges and mitigation strategies pertinent to the SR-AOPs are identified, which include (i) possible formation of oxyanions and disinfection byproducts, and (ii) dealing with sulfate produced and residual PMS. Potential future applications and research direction of SR-AOPs are proposed. These include (i) novel reactor design for heterogeneous catalytic system based on batch or continuous flow (e.g. completely mixed or plug flow) reactor configuration with catalyst recovery, and (ii) catalytic ceramic membrane incorporating SR-AOPs.