bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure and Electronic Properties of [Ni(dsdm){Fe(CO)3}2], an Unusual, Triangular Nickel Diiron Compound
Authors: Chalbot Marie‐Cécile , Mills Allison M. , Spek Anthony L. , Long Gary J. , Bouwman Elisabeth
Published: January 2003

Reaction of the low‐spin complex [Ni(dsdm)] with Fe2CO9 results in the unique trinuclear cluster [Ni(dsdm){Fe(CO)3}2]. NMR spectroscopy shows that the structure is diamagnetic, and, moreover, that the complex is stable in solution and C2‐symmetric. The X‐ray structure reveals short distances between the distorted octahedral nickel(II) ion and the two octahedral iron(0) centers. The observed diamagnetism is explained by the formation of a triangular metal core with three two‐electron two‐center bonds. The Mössbauer spectra, which are typical of iron(0), are composed of asymmetric quadrupole doublets as a result of the presence of two chemically similar, but crystallographically distinct, iron sites. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Co‐Condensation Reactions of Substituted Aromatic Compounds with Lithium Atoms at 77 K
Authors: Dunne John P. , Bockmeyer Matthias , Tacke Matthias
Published: January 2003

Lithium atoms were co‐condensed with +I‐substituted benzene derivatives like trimethyl(phenyl)silane and tert‐butylbenzene in the presence of THF at 77 K, which resulted in C−H bond activation, to produce the aryllithium compound as well as the coupling of the substituted phenyl radicals. Other +I‐substituted benzene derivatives like xylene and mesitylene failed to react with lithium atoms in the presence of THF. Oxygen and nitrogen donor substituted benzene derivatives (anisole, N,N‐dimethylaniline, and N,N‐dimethylbenzylamine) showed activation of the ortho C−H bond when co‐condensed with lithium atoms in the presence of THF. However, when thioanisole was co‐condensed with lithium atoms and THF, a C−S bond cleavage occurred instead. These results were interpreted with the aid of DFT calculations, which show π‐ and σ‐complexes between the lithium clusters and benzene derivatives as reactive intermediates. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Macrocyclic Complexes of [Ru(N‐N)2]2+ Units [N‐N = 1,10 Phenanthroline or 4‐(p‐Anisyl)‐1,10‐Phenanthroline]: Synthesis and Photochemical Expulsion Studies
Authors: Laemmel Anne‐Chantal , Collin Jean‐Paul , Sauvage Jean‐Pierre , Accorsi Gianluca , Armaroli Nicola
Published: January 2003

Two ruthenium complexes [Ru(phen)2(m‐36)]2+ and [Ru(aphen)2(m‐36)]2+, indicated as 1 and 2 respectively, which contain a 36‐membered macrocycle incorporating a sterically hindered bipyridine (m‐36), and two 1,10‐phenanthroline (phen) or 4‐(p‐anisyl)‐1,10‐phenanthroline (aphen) ligands, have been synthesised. Under light irradiation, as seen from the metal‐to‐ligand‐charge‐transfer (MLCT) bands of the visible spectral region, the [Ru(phen)]22+ core of 1 and 2 is selectively expelled from the macrocycle to give the corresponding bis‐acetonitrile derivative. This photochemical process was found to be notably less efficient than that observed in a simpler related complex [Ru(phen)2dmbp]2+ (dmbp = 6,6′dimethyl‐2,2′‐bipyridine), that lacks the macrocyclic motif. In the case of 1 thermal back reaction takes place quantitatively affording a completely reversible system. The isolation, by chromatographic techniques, of the axial‐axial cis‐[(a,a)Ru(aphen)2Cl2] isomer, where the two aphen ligands bear two p‐anisyl groups disposed trans to one another enabled the preparation of 2. This type of complex undergoes a more complicated photochemical process, in fact, following the expected photolabilisation of the [Ru(aphen)2]2+ unit, photoisomerisation of the primary photo‐product occurs and gives a statistical mixture of the three geometrical isomers: cis‐[(a,a)Ru(aphen)2(CH3CN)2](PF6)2, cis‐[(a,e)Ru(aphen)2(CH3CN)2](PF6)2 and cis‐[(e,e)Ru(aphen)2(CH3CN)2](PF6)2. This side‐reaction precludes its use as rotaxane precursor suggesting that, for this purpose, a bis‐phenanthroline ligand stabilising the ruthenium core is needed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Change in the Spin State of an FeIII Center upon One N‐to‐O Switch in the Coordination of a 2,6‐Pyridinedicarboxamido Unit: The Effect of Methyl Thioether and Methyl Ether Appendages at the Ligand Periphery
Authors: Harrop Todd C. , Tyler Laurie A. , Olmstead Marilyn M. , Mascharak Pradip K.
Published: January 2003

Two ligands bearing the 2,6‐pyridinedicarboxamide unit, namely PyPSMeH2 and PyPOMeH2, have been used to prepare complexes of FeIII which have been structurally characterised. The potentially pentadentate thioether ligand PyPSMeH2 affords only the bis complex (Et4N)[Fe(PyPSMe)2] (1), irrespective of the metal to ligand ratio, due to the weak affinity of the thioether groups for the FeIII center. In [Fe(PyPSMe)2]−, the two PyPSMe2− ligands bind to the iron center in a mer fashion and steric crowding among the pendant thioether groups forces one of the four deprotonated carboxamido moieties to bind to the FeIII center through the carbonyl oxygen, giving rise to an FeN5O chromophore. The tridentate ligand PyPOMeH2, in its deprotonated form, also gives rise to a bis complex, (Et4N)[Fe(PyPOMe)2] (2), in which the two PyPOMe2− ligands bind to the iron center in a mer fashion. In this case, however, less steric crowding among the smaller pendant ether groups allows binding of all four carboxamido nitrogens to the FeIII center in [Fe(PyPOMe)2]− giving rise to an FeN6 chromophore. This one N‐to‐O switch in donor atom makes the two complexes 1 and 2 very different. While complex 2 is low spin (g = 2.18, 1.94) much like the other reported FeIII bis complexes with two ligated 2,6‐pyridinedicarboxamido units, complex 1 is high spin (g = 4.3). The spin flip due to a switch in only one N or O donor atom in these two complexes is unprecedented. The two complexes also exhibit different stability towards water. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Studies on the Reduction of [(C5Me5)2Mo2O5] in Methanol/Water/Acetate Solutions by On‐Line Electrochemical Flowcell and Electrospray Mass Spectrometry
Authors: Gun Jenny , Modestov Alexandre , Lev Ovadia , Saurenz Dirk , Vorotyntsev Mikhail A. , Poli Rinaldo
Published: January 2003

The complex [Cp*2Mo2O5] (Cp* = η5‐C5Me5) and its electrochemical reduction products in acetic acid/acetate‐buffered (pH = 4.0) water/methanol solutions were investigated by combined electrochemical (EC) flowcell and on‐line electrospray ionization mass spectrometry (ESI‐MS). Mono‐, di‐, tri‐, and tetranuclear organometallic molybdenum oxides were identified in the starting solution. The effect of the relevant ESI‐MS parameters (ionic mode, heated capillary voltage, and heated capillary temperature) and of the concentration on the observed distribution of ions in the mass spectrometer was studied in order to minimize side reactions in the ESI chamber. It was verified that reduction in the ESI‐MS is undetectable under open‐circuit conditions. The on‐line electrochemical study revealed the potential‐dependent formation of previously unknown mono‐, di‐, tri‐, and tetranuclear MoV, MoIV, and mixed‐valence complexes. The compounds were identified by their characteristic isotope patterns and their ion trap MSn fragmentations. The observed formation potentials reflect the higher stability of the multinuclear species relative to the mononuclear ones with the same oxidation state. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Cover Picture
Authors: Zhang Xian‐Ming , Chen Xiao‐Ming
Published: January 2003

The cover picture shows a mixed‐valence copper(i,ii) coordination polymer [CuI2CuII(4,4′‐bpy)2(pydc)2]·4H2O (4,4′‐bpy = 4,4′‐bipyridine; pydc = pyridine‐2,4‐dicarboxylate) featuring the “metal‐complex ligands” [CuII(pydc)2]2− synthesized hydrothermally using Cu(MeCO2)2, pyridine‐2,4‐dicarboxylate, 4,4′‐bipyridine and NaOH. Single‐crystal structure analysis exhibits this compound to be the first porous 3‐D framework constructed from five‐fold parallel interpenetration of 2‐D (6,3) nets (right‐hand side). The one‐dimensional channels in the 3‐D framework (left‐hand side) occupying 17.4% of the crystal volume are occupied by guest water molecules. The porous network is stable after removal of the lattice water molecules, which may be attributed to the multiple entanglement of the 2‐D nets. Details are discussed in the article by X.‐M. Zhang and X.‐M. Chen on p. 413 ff.
New Monocyclopentadienyl Complexes of Tantalum(V) and Titanium(IV) with Chelating Pyrimidinethiolate and Oxypyridine Ligands − Molecular Structure of [Cp*TaCl3(SC6H7N2)]
Authors: Fandos Rosa , Hernández Carolina , Otero Antonio , Rodríguez Ana , Ruiz María José , Terreros Pilar
Published: January 2003

New monocyclopentadienyl species of TaV, [Cp*TaL3(XR)] (L = Cl, Me, X = O, S) bearing 4,6‐dimethyl‐2‐pyrimidinethiolate (SR = SC6H7N2) or 3‐cyano‐4,6‐dimethyloxypyridine (OR = OC8H7N2) ligands were prepared, namely [Cp*TaCl3(SC6H7N2)] (1), [Cp*TaCl3(OC8H7N2)] (2), [Cp*TaMe3(SC6H7N2)] (3). In addition, a bis(oxypyridine)titanium(IV) complex [Cp*TiMe2(OC8H7N2)2] was isolated. The X‐ray structure analysis of 1 revealed that the thiolate group is bonded to the metal center through the sulfur atom and one of the nitrogen atoms in an η2‐fashion. The reactivity of complex 3 with isocyanides (CNR), R = tBu, Xyl (Xyl = 2,6‐dimethylphenyl) was also studied showing differences depending on the nature of R group. The reaction with 2,6‐dimethylphenyl isocyanide gives the azatantalacyclobutane complex [Cp*TaMe{XylN=CC(Me2)NXyl}(SC6H7N2)] (5) as the final product, whereas in the reaction with tert‐butyl isocyanide the η2‐imine‐containing complex [Cp*Ta{tBuNC(Me2)}(SC6H7N2)] (6) is proposed to be formed. The dynamic behavior of [Cp*TaMe3(SC6H7N2)] (3) was also studied by variable‐temperature 1H NMR spectroscopy. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Efficient Asymmetric Synthesis of Δ‐ and Λ‐Enantiomers of (Bipyridyl)ruthenium Complexes and Crystallographic Analysis of Δ‐Bis(2,2′‐bipyridine)(2,2′‐bipyridine‐4,4′‐dicarboxylato)ruthenium: Diastereoselective Homo‐ and Heterochiral Ion Pairing Revisited
Authors: Caspar Régis , Amouri Hani , Gruselle Michel , Cordier Christine , Malézieux Bernard , Duval Raphäel , Leveque Hubert
Published: January 2003

Optically pure ruthenium complexes of the type Δ‐ or Λ‐[Ru(bpy)2(L−L)][PF6]2 [L−L = cmbpy = 4′‐methyl‐2,2′‐bipyridine‐4‐carboxylic acid (3a, b); L−L = dcbpy = 2,2′‐bipyridine‐4,4′‐dicarboxylic acid (4a, b)] were prepared and fully characterized. The RuII carboxylate complexes Δ‐ and Λ‐[Ru(bpy)2(dcabpy)] (5a, b) (dcabpy = 2,2′‐bipyridine‐4,4′‐dicarboxylate) were resolved efficiently by chiral column chromatography and isolated in good yields. The Δ‐[Ru(bpy)2(dcabpy)] (5a) enantiomer was crystallized and its X‐ray molecular structure determined. The enantiomeric nature and the absolute configuration of the tris(bipyridyl)ruthenium complexes were confirmed by NMR and circular dichroism studies. In addition, ion‐pairing interactions between Δ‐Trisphat (Δ‐1, D3 symmetry) and each enantiomer of the (monocarboxylic acid)RuII complex (3a and 3b, C1 symmetry) and the dicarboxylic acid complex (4a and 4b, C2 symmetry) were examined by NMR spectroscopy. (© Wiley‐VCH Verlag GmbH & Co KGaA, 69451 Weinheim, Germany, 2003)
In‐situ Energy‐Dispersive X‐ray Diffraction Studies of Crystal Growth and Compound Conversion Under Solvothermal Conditions
Authors: Engelke Lars , Schaefer Michael , Porsch Felix , Bensch Wolfgang
Published: January 2003

The results of in‐situ energy‐dispersive X‐ray diffraction under solvothermal conditions performed on isostructural, layered thioantimonates Mn2Sb2S5·L (L = amine) demonstrate the great potential of the method. When the synthesis was carried out at low temperatures with L being 1,3‐diaminopropane (DAP), two crystalline intermediate phases were detected which then grew and disappeared when product growth started. Surprisingly, when N‐methyl‐1,3‐diaminopropane (MDAP) was used, no crystalline intermediates could be detected and the induction time was significantly shorter than for DAP. For reactions up to 100 °C and for higher temperatures with α < 0.8 (α is the extent of reaction), the crystallisation is predominantly controlled by nucleation. Further progress of crystallisation (α > 0.8) leads to a change of the dominant process and a diffusion‐controlled mechanism is observed. During the reaction with diethylenetriamine (DIEN), three crystalline intermediates were detected prior to product growth. The induction time is longer than for the other two compounds. The crystallisation seems to be diffusion‐controlled and is faster than for the DAP and MDAP compounds. In a solution of DIEN, the crystalline phases Mn2Sb2S5·L (L = DAP or MDAP) are transformed into the DIEN product under solvothermal conditions, and a rigorous analysis of the intensities of the reflections suggests a partial dissolution of the crystalline starting materials followed by crystallisation of the DIEN material. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Formation of (σ‐Alkenyl)‐ and (μ‐Vinylidene)palladium and ‐platinum Complexes by Oxidative Addition of 4,4‐Dichloro‐1,1‐diphenyl‐2‐azabuta‐1,3‐diene − The Molecular Structure of an Unusual Asymmetric (μ‐Vinylidene)Pd−Pd Complex
Authors: Knorr Michael , Schmitt Gérard , Kubicki Marek M. , Vigier Estelle
Published: January 2003

4,4‐Dichloro‐1,1‐diphenyl‐2‐azabuta‐1,3‐diene (1) oxidatively adds to [Pd(PPh3)4] and [Pt(C2H4)(PPh3)2] giving rise to the σ‐alkenyl complexes trans‐[MCl{[C(Cl)=C(H)−N=CPh2]}(PPh3)2] (2a: M = Pd; 2b: M = Pt). When 1 is treated with [Pd(PPh3)4] in a 1:2 ratio in refluxing toluene, the dimetallic μ‐vinylidene complex [(PPh3)ClPd{μ‐[C=C(H)−N=CPh2]}PdCl(PPh3)2] (3) is formed. In this fluxional compound, a PPh3 ligands migrates in a reversible manner between the two Pd centers. Substitution of the PPh3 ligands of 3 by 2 equiv. of Ph2PCH2PPh2 affords the A‐frame complex [ClPd(μ‐dppm)2{μ‐[C=C(H)−N=CPh2]}PdCl] (4). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Coordination Modes in a Tridentate NNS (Thiosemicarbazonato)copper(II) System Containing Oxygen‐Donor Coligands − Structures of [{Cu(L)(X)}2] (X = Formato, Propionato, Nitrito)
Authors: Gómez‐Saiz Patricia , García‐Tojal Javier , Mendia Aránzazu , Donnadieu Bruno , Lezama Luis , Pizarro José Luis , Arriortua Maria Isabel , Rojo Teófilo
Published: January 2003

Complexes with the formula [{Cu(L)X}2] [X = HCOO− (1), CH3CH2COO− (2), NO2− (3)], where HL = C7H8N4S (pyridine‐2‐carbaldehyde thiosemicarbazone), have been synthesised and characterised. Single‐crystal X‐ray diffraction studies show that the structures of these compounds consist of centrosymmetric dimers containing distorted square‐pyramidal copper(II) ions. The metal centres are coordinated to the NNS atoms of the tridentate thiosemicarbazonato ligand and one oxygen atom of the X coligand in the basal position. These complexes mainly differ in the atom that occupies the apical position. The structures of compounds 1 and 3 are made up of {Cu2(μ−SL)2} entities in which the sulfur atom of the tridentate ligand acts as a bridge occupying the apical position. Compound 2 contains a {Cu2(μ‐OX)2} species bridged through the oxygen atoms from both propionato ligands. The results demonstrate the influence of the size of the coligand on the structure of these complexes. Structural and spectroscopic results suggest the presence of relevant ligand‐to‐metal charge transfers in these compounds. The EPR spectra exhibit rhombic symmetry. Magnetic measurements show antiferromagnetic couplings. The susceptibility data were fitted using the Bleaney−Bowers equation for copper(II) dimers. The J/k values obtained are −4.0, −4.8 and −4.9 K for compounds 1, 2 and 3, respectively. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
DNA Cleavage by Copper Complexes of 2‐ and 3‐Clip‐Phen Derivatives
Authors: Pitié Marguerite , Boldron Christophe , Gornitzka Heinz , Hemmert Catherine , Donnadieu Bruno , Meunier Bernard
Published: January 2003

The DNA cleavage activity of copper complexes of phenanthroline has been increased by the use of “2‐Clip‐Phen” and “3‐Clip‐Phen” ligands containing two phenanthroline entities linked by a serinol bridge. In order to optimize DNA cleavage activity, two series of new Clip‐Phen ligands (L) with two phenanthroline residues linked through their C‐2 or C‐3 carbon atoms by different bridges have been synthesized. The physicochemical properties and the DNA cleavage activities of the corresponding (Clip‐Phen)copper complexes were investigated in the presence of a reductant and air. X‐ray analyses of single crystals showed that the cupric complexes of Clip‐Phen were able adopt dimeric double‐helical geometries with L2Cu2 stoichiometries in the solid state. These complexes adopt different geometries and stoichiometries in solution, with monomeric LCu species predominant. The compounds with a bridge connected at C‐2 are less active as DNA cleavage agents than complexes with the bridge at the C‐3 positions. Copper complexes with a bridge containing three methylene units appear to give the best results in DNA cleavage experiments. This activity is increased in the case of 3‐Clip‐Phen·CuCl2 by the presence of the primary amine function of the serinol bridge. This amine function is probably coordinated to the copper atom in the case of 2‐Clip‐Phen·CuCl2, decreasing the reactivity toward DNA. (© Wiley‐VCH Verlag GmbH & Co KGaA, 69451 Weinheim, Germany, 2003)
Ground Spin State Variation in Carboxylate‐Bridged Tetranuclear [Fe2Mn2O2]8+ Cores and a Comparison with Their [Fe4O2]8+ and [Mn4O2]8+ Congeners
Authors: Chaudhuri Phalguni , Rentschler Eva , Birkelbach Frank , Krebs Carsten , Bill Eckhard , Weyhermüller Thomas , Flörke Ulrich
Published: January 2003

Syntheses of ten new tetranuclear complexes containing the [MA(μ3‐O)2MB]8+ butterfly core [MA = MB = FeIII (1 and 2), MA = MB = MnIII (3 and 4) and MA = FeIII, MB = MnIII (5−10)] using 1,4,7‐trimethyl‐1,4,7‐triazacyclononane (L) as the capping ligand, salicylaldoximato dianion (salox2−) and six different carboxylate anions as bridging ligands, are described. The crystal structures of [L2Fe2(μ3‐O)2(salox)2(diphenylglycolate)3Fe2](ClO4) (1), [L2Mn2(μ3‐O)2(salox)2(diphenylglycolate)3Mn2](ClO4) (3), [L2Fe2(μ3‐O)2(salox)2(acetate)3Mn2](ClO4) (5), [L2Fe2(μ3‐O)2(salox)2(diphenylglycolate)3Mn2](ClO4) (6), and [L2Fe2(μ3‐O)2(salox)2(benzoate)3Mn2](ClO4) (8) were determined by X‐ray crystallography. The complexes are isostructural, with MIII ions disposed in a butterfly core where bridging between the MIII ions occurs via two μ3‐oxo anions. In complexes 5, 6 and 8 the “wing‐tip” positions of the butterfly are occupied by the LFe3+ units, whereas the “body” metal ions are d4 high‐spin MnIII ions. Complexes 1−10 have been characterised by variable‐temperature (2−290 K) magnetic susceptibility measurements (1 T) and by Mössbauer spectroscopy. A “2J” model has been applied to simulate the experimental μeff vs. T plots. Overall exchange interactions are antiferromagnetic in nature. Complexes with the Fe4O2 core (1 and 2) and the Mn4O2 core (3 and 4) possess an St = 0 and St = 3 ground state, respectively, regardless of the nature of the bridging carboxylate ligand. In contrast, changing the bridging carboxylates in the [Fe2Mn2O2] core from acetate (5) to diphenylglycolate (6), triphenyl acetate (7), benzoate (8), chloroacetate (9) and propionate (10), results in a variation of the ground state from St = 1 to St = 3, due to spin frustration of the “body” manganese centres. The spin‐correlation diagram for the Fe2Mn2O2 butterfly arrangement clearly demonstrates the ground state variation as a function of the ratio of two competing coupling interactions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Chiral Complexes of RhI Containing Binaphthalene‐Core P,S‐Heterobidentate Ligands − Synthesis, Characterization, and Catalytic Activity in Asymmetric Hydrogenation of α,β‐Unsaturated Acids and Esters
Authors: Gladiali Serafino , Grepioni Fabrizia , Medici Serenella , Zucca Antonio , Berente Zoltán , Kollár László
Published: January 2003

The enantiopure complexes 3a and 3b [Rh(NBD)(P,S)]+BF4− [P,S = (S)‐2‐(diphenylphosphanyl)‐2′‐(methylthio)‐1,1′‐binaphthalene (a); (S)‐2‐(diphenylphosphanyl)‐2′‐(isopropylthio)‐1,1′‐binaphthalene (b)] have been prepared from [Rh(NBD)(THF)2]+BF4− by reaction with a stoichiometric amount of the appropriate P,S‐heterobidentate ligand. Single‐crystal X‐ray analysis of the S‐methyl derivative shows that the seven‐membered chelate ring is locked in a boat‐like conformation with the methyl group in the equatorial position. Variable‐temperature NMR measurements confirm that this conformation is maintained in solution and that the dynamic behaviour displayed by the complex is due to pseudo‐rotation of the diolefin. Complexes 3 have been tested in the asymmetric hydrogenation of α,β‐unsaturated acids and esters. Enantioselectivities of up to 60% ee have been recorded. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Activation of C−S Bonds in Organosulfur Compounds Containing α,β‐Unsaturated Ketone Systems by Carbonylruthenium and ‐iron Complexes
Authors: Alvarez‐Toledano Cecilio , Delgado Esther , Donnadieu Bruno , Gómez M. Angeles , Hernández Elisa , Martín Gema , Ortega‐Jiménez Fernando , Zamora Félix
Published: January 2003

Vinylidenetetraruthenium clusters have been obtained from the reactions between [Ru3(CO)12] and [CH3C(O)CH=C(SCH3)2] or [(C5H5)Fe{C5H4CH=CHC(O)CH=C(SCH2CH2S)}] by cleavage of the S−C sp2 bonds in these ligands. An excess of [CH3C(O)CH=C(SCH3)2] afforded the dinuclear complex [Ru2(CO)4(μ‐SCH3)2{η2:κ‐C,O‐C(SCH3)CHC(O)CH3}2], which was then converted into the vinylidene cluster [Ru4(CO)10(μ‐SCH3)2{μ4,η3:κ‐C,C,O‐C=CHC(O)CH3}] in the presence of more of the carbonylruthenium complex. However, the carbonyliron complex led to the formation of the dinuclear compounds [Fe2(CO)4(μ‐SCH3)2{η2:κ‐C,O‐C(SCH3)CHC(O)CH3}2] and [Fe2(CO)5{μ,η4:κ‐C,O,S,S‐(SCH2CH2S)C=CHC(O)CH=CHC5H4}Fe(C5H5)]. All of the new complexes exhibit a pentametallacycle group as a consequence of the rupture of the S−C bonds, as well as the presence of the C(O)R substituent in these ligands. The compounds have been characterised by analytical and spectroscopic data and the crystal structures of some of them have been solved by X‐ray diffraction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Short communication: Autoignition temperature of trichlorosilanes
Authors: Hshieh Fu‐Yu , Hirsch David B. , Williams James H.
Published: January 2003

Trichlorosilanes are important silicon intermediates used to manufacture silicone materials. Because they are produced and used in large quantities and some are very reactive, it is important to determine the autoignition temperature (AIT) of trichlorosilanes. This short communication reports the AIT of eight important trichlorosilanes and discusses the effect of substituted groups on the AIT. Copyright © 2002 John Wiley & Sons, Ltd.
Molecular cytogenetic characterization of Sézary syndrome
Authors: Mao Xin , Lillington Debra M. , Czepulkowski Barbara , Russell‐Jones Robin , Young Bryan D. , Whittaker Sean
Published: January 2003

Sézary syndrome (SS) is a rare form of erythrodermic cutaneous T‐cell lymphoma with hematological involvement and a poor prognosis. At present little is known about the molecular pathogenesis of this malignancy. To address this issue, we analyzed 28 SS cases through the use of molecular cytogenetic techniques. Conventional cytogenetic analysis showed 12 of 28 cases with clonal chromosome abnormalities (43%). Seven cases had aberrations affecting chromosomes 1 and 17; five demonstrated rearrangement of chromosomes 10 and 14; four presented with an abnormality of 6q. Multiplex‐fluorescence in situ hybridization (M‐FISH) revealed complex karyotypes in 6 of 17 cases (35%), and recurrent der(1)t(1;10)(p2;q2) and der(14)t(14;15)(q;q?) translocations were each identified in two cases, and confirmed by dual‐color FISH. There was an overall difference in the incidence of clonal abnormalities detected by G‐banded karyotyping and M‐FISH. In addition, comparative genomic hybridization studies revealed chromosome imbalances (CIs) in 9 of 20 cases (45%), with a mean DNA copy number change per sample of 1.95 ± 2.74, and losses (mean: 1.25 ± 1.77) more frequent than gains (mean: 0.7 ± 1.26). The most common CIs noted were loss of 1p, followed by losses of 10/10q, 17p, and 19, and gains of 17q and 18. Furthermore, in conjunction with this study a systematic literature review was conducted, which showed a high frequency and consistent pattern of chromosome changes in SS. These findings suggest that chromosomal instability is common in SS, although there are specific chromosomal abnormalities that appear to be characteristic, and the identification of two different recurrent chromosome translocations provides the basis for further studies. © 2003 Wiley‐Liss, Inc.
Multivariate and multilocus variance components method, based on structural relationships to assess quantitative trait linkage via SEGPATH
Authors: Province M.A. , Rice T.K. , Borecki I.B. , Gu C. , Kraja A. , Rao D.C.
Published: January 2003

A general‐purpose modeling framework for performing path and segregation analysis jointly, called SEGPATH (Province and Rao [1995] Stat. Med. 7:185–198), has been extended to cover “model‐free” robust, variance‐components linkage analysis, based on identity‐by‐descent (IBD) sharing. These extended models can be used to analyze linkage to a single marker or to perform multipoint linkage analysis, with a single phenotype or multivariate vector of phenotypes, in pedigrees. Within a single, consistent approach, SEGPATH models can perform segregation analysis, path analysis, linkage analysis, or combinations thereof. SEGPATH models can incorporate environmental or other measured covariate fixed effects (including measured genotypes), genotype‐specific covariate effects, population heterogeneity models, repeated‐measures models, longitudinal models, autoregressive models, developmental models, gene‐by‐environment interaction models, etc., with or without linkage components. The data analyzed can have any missing value structure (assumed missing at random), with entire individuals missing, or missing on one or more measurements. Corrections for ascertainment can be made on a vector of phenotypes and/or other measures. Because of the flexibility of the class of models, the SEGPATH approach can also be used in nongenetic applications where there is a hierarchical structure, such as longitudinal, repeated‐measures, time series, or nested models. A variety of specific models are provided, as well as some comparisons with other linkage analysis models. Particular applications demonstrate the importance of correctly accounting for the extraneous sources of familial resemblance, as can be done easily with these SEGPATH models, so as to give added power to detect linkage as well as to protect against spuriously inferring linkage. Genet Epidemiol 24:128–138, 2003. © 2003 Wiley‐Liss, Inc.
Three‐state frailty model for age at onset of dementia and death in Swedish twins
Authors: Ripatti Samuli , Gatz Margaret , Pedersen Nancy L. , Palmgren Juni
Published: January 2003

We present a frailty model to estimate the relative importance of genetic and environmental factors on age at onset of dementia in a twin design. We use modern survival methodology to define a model that accounts simultaneously for longitudinal aspects, e.g., left truncation and right censoring in data, and the multivariate nature of twin data. Additionally, we present a novel three‐state frailty model, with nondemented, demented, and dead states, describing variation in the onset of disease and mortality simultaneously in one model, while accounting for possible dependence for the two competing events. The frailty structure, i.e., the latent random effects structure, mimics the traditional twin model for continuous variables used in quantitative genetics, and as such describes within‐pair dependence. This in turn leads to estimates for intrapair correlations, as well as for additive genetic, and shared and nonshared environmental components of variance. A hierarchical Bayesian model formulation and Gibbs sampling are used to estimate posterior distributions of the parameters. The models are applied to Swedish Twin Registry data on the onset of dementia in elderly twins. Based on the three‐state frailty model, we estimate the intrapair correlations for dementia to be 0.87 [90% credible interval: 0.61,0.98] and 0.68[0.18,0.91] for MZ and DZ twins, respectively. Based on our model, we estimate that genetic effects account for about one third, and shared environmental effects for almost a half, of the variation in dementia hazards between individuals. More data, however, are needed to gain precision in these estimates.Genet Epidemiol24:139–149, 2003. © 2003 Wiley‐Liss, Inc.
Genetic association tests with age at onset
Authors: Hsu L.
Published: January 2003

Many diseases or traits exhibit a varying age at onset. Recent data examples of prostate cancer and childhood diabetes show that compared to simply treating the disease outcome as affected vs. unaffected, incorporation of age‐at‐onset information into the transmission/disequilibrium type of test (TDT) does not appear to change the results much. In this paper, we evaluate the power of TDT as a function of age at onset, and show that age‐at‐onset information is most useful when the disease is common, or the relative risk associated with the high‐risk genotype varies with age. Moreover, an extremely old unaffected subject can contribute substantially to the power of the TDT, sometimes as much as old‐onset subjects. We propose a modified test statistic for testing no association between the marker at the candidate locus and age at onset. The simulation study was conducted to evaluate the finite sample properties of proposed and the TDT test statistics under various sampling schemes for trios of parents and offspring, as well as for sibling clusters where unaffected siblings were used as controls.Genet Epidemiol24:118–127, 2003. © 2003 Wiley‐Liss, Inc.
Multipoint affected sibpair linkage methods for localizing susceptibility genes of complex diseases
Authors: Glidden David V. , Liang Kung‐Yee , Chiu Yen‐Feng , Pulver Ann E.
Published: January 2003

Recently, Liang et al. ([2001] Hum. Hered. 51:64–78) proposed a general multipoint linkage method for estimating the chromosomal position of a putative susceptibility locus. Their technique is computationally simple and does not require specification of penetrance or a mode of inheritance. In complex genetic diseases, covariate data may be available which reflect etiologic or locus heterogeneity. We developed approaches to incorporating covariates into the method of Liang et al. ([2001] Hum. Hered. 51:64–78) with particular attention to exploiting age‐at‐onset information. The results of simulation studies, and a worked data example using a family data set ascertained through probands with schizophrenia, suggest that utilizing covariate information can yield substantial efficiency gains in localizing susceptibility genes. Genet Epidemiol 24: 107–117, 2003. © 2003 Wiley‐Liss, Inc.
Power of multifactor dimensionality reduction for detecting gene‐gene interactions in the presence of genotyping error, missing data, phenocopy, and genetic heterogeneity
Authors: Ritchie Marylyn D. , Hahn Lance W. , Moore Jason H.
Published: January 2003

The identification and characterization of genes that influence the risk of common, complex multifactorial diseases, primarily through interactions with other genes and other environmental factors, remains a statistical and computational challenge in genetic epidemiology. This challenge is partly due to the limitations of parametric statistical methods for detecting genetic effects that are dependent solely or partially on interactions with other genes and environmental exposures. We previously introduced multifactor dimensionality reduction (MDR) as a method for reducing the dimensionality of multilocus genotype information to improve the identification of polymorphism combinations associated with disease risk. The MDR approach is nonparametric (i.e., no hypothesis about the value of a statistical parameter is made), is model‐free (i.e., assumes no particular inheritance model), and is directly applicable to case‐control and discordant sib‐pair study designs. Both empirical and theoretical studies suggest that MDR has excellent power for identifying high‐order gene‐gene interactions. However, the power of MDR for identifying gene‐gene interactions in the presence of common sources of noise is not currently known. The goal of this study was to evaluate the power of MDR for identifying gene‐gene interactions in the presence of noise due to genotyping error, missing data, phenocopy, and genetic or locus heterogeneity. Using simulated data, we show that MDR has high power to identify gene‐gene interactions in the presence of 5% genotyping error, 5% missing data, or a combination of both. However, MDR has reduced power for some models in the presence of 50% phenocopy, and very limited power in the presence of 50% genetic heterogeneity. Extending MDR to address genetic heterogeneity should be a priority for the continued methodological development of this new approach. Genet. Epidemiol. 24:150–154, 2003. © 2003 Wiley‐Liss, Inc.
Limits of fine‐mapping a quantitative trait
Authors: Atwood Larry D. , Heard‐Costa Nancy L.
Published: January 2003

Once a significant linkage is found, an important goal is reducing the error in the estimated location of the linked locus. A common approach to reducing location error, called fine‐mapping, is the genotyping of additional markers in the linked region to increase the genetic information. The utility of fine‐mapping for quantitative trait linkage analysis is largely unknown. To explore this issue, we performed a fine‐mapping simulation in which the region containing a significant linkage at a 10‐centiMorgan (cM) resolution was fine‐mapped at 2, 1, and 0.5 cM. We simulated six quantitative trait models in which the proportion of variation due to the quantitative trait locus (QTL) ranged from 0.20–0.90. We used four sampling designs that were all combinations of 100 and 200 families of sizes 5 and 7. Variance components linkage analysis (Genehunter) was performed until 1,000 replicates were found with a maximum lodscore greater than 3.0. For each of these 1,000 replications, we repeated the linkage analysis three times: once for each of the fine‐map resolutions. For the most realistic model, reduction in the average location error ranged from 3–15% for 2‐cM fine‐mapping and from 3–18% for 1‐cM fine‐mapping, depending on the number of families and family size. Fine‐mapping at 0.5 cM did not differ from the 1‐cM results. Thus, if the QTL accounts for a small proportion of the variation, as is the case for realistic traits, fine‐mapping has little value. Genet Epidemiol 24:99–106, 2003. © 2003 Wiley‐Liss, Inc.
Review of proteomics with applications to genetic epidemiology
Authors: Sellers Thomas A. , Yates John R.
Published: January 2003

Mapping of the human genome has the potential to transform the traditional methods of genetic epidemiology. The complete draft sequence of the 3.3 billion nucleotides comprising the genome is now available over the Internet, including the location and nearly complete sequence of the 26,000 to 31,000 protein‐encoding genes. However, aside from water, almost everything in the human body is either made of, or by, proteins. Although the DNA code provides the instructions for their amino acid sequence, there are an estimated 1.5 million proteins. Thus, the correlation between DNA sequence and protein is low, reflecting alternate splicing as well as post‐translational modification. The purpose of this article is to explore ways in which the emerging field of proteomics, the study of proteins in a cell, may inform our approach to gene mapping. This article reviews the various technical approaches currently available for proteomics. Technologies are available to quantify protein expression (and compare normal versus disease states), identify proteins through comparison with sequence information in databases or direct sequencing (which can then be mapped to chromosomal locations to ensure appropriate markers), elucidate protein‐protein interactions (which may underlie disease), determine localization of proteins within the cell (abnormal trafficking of proteins could have an inherited basis), and characterize modifications of proteins (which is relevant to modifier gene candidates). Several examples are presented to illustrate the potential application of proteomics to the field of genetic epidemiology, and we conclude with various considerations regarding design and analysis. Genet Epidemiol 24:83–98, 2003. © 2003 Wiley‐Liss, Inc.
Electrostatic component of solvation: Comparison of SCRF continuum models
Authors: Curutchet Carles , Cramer Christopher J. , Truhlar Donald G. , Ruiz‐López; Manuel F. , Rinaldi Daniel , Orozco Modesto , Luque F. Javier
Published: January 2003

We report a systematic comparison of the electrostatic contributions to the free energy of solvation from three different kinds of quantum mechanical self‐consistent reaction field (SCRF) methods. We also compare the liquid‐phase dipole moments as a measure of the solute's response to the reaction field of the solvent. In particular, we compare these quantities for the generalized Born model as implemented in the SM5.42R method, the multipolar expansion model developed at Nancy, and the MST version of the polarizable continuum model. All calculations are carried out at the HF/6‐31G(d) level. The effects of various choices of solute cavities and representations of the charge density are examined. The test set consists of 18 molecules containing prototypical polar groups, and three different values of the dielectric permittivity are considered. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 284–297, 2003
Ground and excited state CASPT2 geometry optimizations of small organic molecules
Authors: Page Christopher S. , Olivucci Massimo
Published: January 2003

A method for computing second‐order multiconfigurational perturbation theory (CASPT2) energy gradients numerically has been implemented and applied to a range of elementary organic chromophores, including 1,3 butadiene, acrolein, and two protonated Schiff bases. Geometries of ground and excited states—as well as conical intersections—are compared with the corresponding CASSCF structures, illustrating the effect of including the correction for dynamical electron correlation. It is shown that the differences between the two methods are not readily categorized, but that, while individual changes in bond lengths can be quite large (∼0.01–0.02 Å), the natures and CASPT2 energetics of the structures remain similar. Exceptions to this tend to be systems that have a strong ionic character and that are not well described at the CASSCF level. Basis set effects (double‐ vs. triple‐ζ) were examined for a limited number of examples, and found to be quite dramatic at both levels of theory. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 298–309, 2003
β‐Hairpins, α‐helices, and the intermediates among the secondary structures in the energy landscape of a peptide from a distal β‐hairpin of SH3 domain
Authors: Ikeda Kazuyoshi , Galzitskaya Oxana V. , Nakamura Haruki , Higo Junichi
Published: January 2003

Energy landscape of a peptide, extracted from a distal β‐hairpin of src SH3 domain, in explicit water was obtained with the multicanonical molecular dynamics. A variety of β‐hairpins with various strand–strand hydrogen bonds were found in the energy landscape at 300 K. There was no energy barrier between random‐coil and hairpins. Thus, the peptide conformation can easily change from the random‐coil to the hairpins in the thermal fluctuations at 300 K. The landscape also included two clusters of α‐helices, among which an energy barrier existed, and besides, these helix clusters were separated from the other conformations. Thus, the free‐energy barrier exists among the helices and the other conformations. Intermediate clusters were found between the helix and the hairpin clusters. The current study showed that the isolated state of this peptide in water fluctuates among random‐coil, β‐hairpin, and α‐helix. In SH3 domain, which has a topology of mainly β‐protein, the whole‐protein folding may proceed when the segment is folded in the β‐hairpin and the other parts of the protein are coupled with the β‐hairpin in an energetically or kinetically favorite way. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 310–318, 2003
Molecular mechanics (MM3) calculations on lithium amide compounds
Authors: Yoshida Takashi , Sakakibara Kazuhisa , Asami Masatoshi , Chen Kuo‐Hsiang , Lii Jenn‐Huei , Allinger Norman L.
Published: January 2003

The MM3 force field has been extended to deal with the lithium amide molecules that are widely used as efficient catalysts for stereoselective asymmetric synthesis. The MM3 force field parameters have been determined on the basis of the ab initio MP2/6‐31G* and/or DFT (B3LYP/6‐31G*, B3‐PW91/6‐31G*) geometry optimization calculations. To evaluate the electronic interactions specific to the lithium amides derived from the diamine molecules properly, the Lewis bonding potential term for the interaction between the lithium atom and the nonbonded adjacent electronegative atom such as nitrogen was introduced into the MM3 force field. The bond dipoles were evaluated correctly from the electronic charges on the atoms calculated by fitting to the electrostatic potential at points selected. The MM3 results on the molecular structures, conformational energies, and vibrational spectra show good agreement with those from the quantum mechanical calculations. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 319–327, 2003
Nonspecific interaction forces at water–membrane interface by forced molecular dynamics simulations
Authors: Lorenzo Alicia C. , Pascutti Pedro G. , Bisch Paulo M.
Published: January 2003

Nonspecific interactions are the main driving forces for the behavior of molecules with great affinity for biologic membranes. To investigate not only the molecular details of these interactions but to estimate their magnitude as well, the theoretical method of Forced Molecular Dynamics Simulations, based on the Atomic Force Spectroscopy experimental technique, was applied. In this approach, an additional one‐dimensional elastic force, representing the cantilever probe, was incorporated to the force field of a Molecular Dynamics computational program. This force represents a spring fixed on one end to a selected atom of the molecule; the other end of the spring is displaced at constant velocity to pull the molecule out of the membrane. The force experimented by the molecule due to the spring, is proportional to the spring elongation relative to its equilibrium position. This value is registered during the entire simulation, and its maximum value will determine the molecule–membrane interaction force. Nonexplicit medium simulations were carried out. Polar and apolar media were considered according to their polarizability degree and a specific dielectric constant value was assigned. In this approach, the membrane was considered as the apolar region limited by two flat surfaces with a polar aqueous medium. The potential energy discontinuity at the interfaces was smoothed by considering the polarization‐induced effects using the image method. The results of this methodology are presented using a small system, a single Alanine amino acid model, which enables extended simulations in a microsecond time scale. The confinement of this amino acid at the interface reduces its degrees of freedom and forces it to adopt one of the six defined conformations. A correlation between these stable structures at the water–membrane interface and the interaction force value was determined. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 328–339, 2003
A computationally inexpensive modification of the point dipole electrostatic polarization model for molecular simulations
Authors: Kaminski George A. , Friesner Richard A. , Zhou Ruhong
Published: January 2003

We present an approximation, which allows reduction of computational resources needed to explicitly incorporate electrostatic polarization into molecular simulations utilizing empirical force fields. The proposed method is employed to compute three‐body energies of molecular complexes with dipolar electrostatic probes, gas‐phase dimerization energies, and pure liquid properties for five systems that are important in biophysical and organic simulations—water, methanol, methylamine, methanethiol, and acetamide. In all the cases, the three‐body energies agreed with high level ab initio data within 0.07 kcal/mol, dimerization energies—within 0.43 kcal/mol (except for the special case of the CH3SH), and computed heats of vaporization and densities differed from the experimental results by less than 2%. Moreover, because the presented method allows a significant reduction in computational cost, we were able to carry out the liquid‐state calculations with Monte Carlo technique. Comparison with the full‐scale point dipole method showed that the computational time was reduced by 3.5 to more than 20 times, depending on the system in hand and on the desired level of the full‐scale model accuracy, while the difference in energetic results between the full‐scale and the presented approximate model was not great in the most cases. Comparison with the nonpolarizable OPLS‐AA force field for all the substances involved and with the polarizable POL3 and q90 models for water and methanol, respectively, demonstrates that the presented technique allows reduction of computational cost with no sacrifice of accuracy. We hope that the proposed method will be of benefit to research employing molecular modeling technique in the biophysical and physical organic chemistry areas. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 267–276, 2003
Correlation method for variance reduction of Monte Carlo integration in RS‐HDMR
Authors: Li Genyuan , Rabitz Herschel , Wang Sheng‐Wei , Georgopoulos Panos G.
Published: January 2003

The High Dimensional Model Representation (HDMR) technique is a procedure for efficiently representing high‐dimensional functions. A practical form of the technique, RS‐HDMR, is based on randomly sampling the overall function and utilizing orthonormal polynomial expansions. The determination of expansion coefficients employs Monte Carlo integration, which controls the accuracy of RS‐HDMR expansions. In this article, a correlation method is used to reduce the Monte Carlo integration error. The determination of the expansion coefficients becomes an iteration procedure, and the resultant RS‐HDMR expansion has much better accuracy than that achieved by direct Monte Carlo integration. For an illustration in four dimensions a few hundred random samples are sufficient to construct an RS‐HDMR expansion by the correlation method with an accuracy comparable to that obtained by direct Monte Carlo integration with thousands of samples. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 277–283, 2003