Showing papers by "Jan Reedijk published in 1992"

Sequence-dependent distortions induced in DNA by monofunctional platinum(II) binding.

Abstract: The effects on thermal stability and conformation of DNA produced by the monofunctional adducts of chlorodiethylenetriamineplatinum(II) chloride ([Pt(dien)Cl]Cl) have been investigated. Oligodeoxyribonucleotide duplexes of varying lengths (9-20 base pairs) and of varying central trinucleotide sequences were prepared and characterized that contained site-specific and unique N(7)-guanine adducts. Included are adducts at the sequences of d(AGC), d(AGT), d(CGA), d(TGA), d(TGC), and d(TGT). All these monofunctional adducts decrease the melting temperature (Tm) of the duplexes. This destabilization effect exhibits a sequence-dependent variability. The highest lowering of Tm is observed for the modified duplexes containing the central sequence of pyrimidine-guanine-pyrimidine. The destabilization effect is reduced with decreasing concentrations of Na+. Polarography, circular dichroism, phenanthroline-copper, and chemical probes reveal conformational distortions spreading over several base pairs around the adduct. The effects of monofunctional platinum(II) adducts on conformational distortions in DNA exhibit a sequence-dependent variability similar to those on thermal stability of DNA. The influence of the monofunctional adduct formed by cis-diamminemonoaquamonochloroplatinum(II) on the stability of the oligonucleotide duplex has been also studied. This lesion decreases thermal stability of DNA in the same way as does the adduct of [Pt(dien)Cl]Cl.

Spectroscopic analysis, coordination geometry, and x-ray structures of nickel(II) compounds with sterically demanding tris(pyrazolyl)borate ligands and azide or (thio)cyanate anions. Crystal and molecular structures of bis[(.mu.-thiocyanato-N,S)(hydrotris(3-isopropyl-4-bromopyrazol-1-yl)borato)nickel(II)]-3-heptane and (thiocyanato-N)(hydrotris(3-tert-butyl-5-methylpyrazol-1-yl)borato)nickel(II)

Abstract: Ligand-field spectra and infrared spectra of compounds with stoichiometry M(LLL)X, where X is one of the pseudohalides NCS - , NCO, and N 3 - , LLL - is a tridentate-substituted pyrazolylborate monoanionic ligand, and M=Ni (as well as a number of Co and Zn compounds for comparison), are described. [Ni{HB[N 2 C 3 H(Me)(C 4 H 9 )] 3 }(NCS)] crystallizes in P2 1 /n with a=9.594, b=17.429, c=17.933A, β=98.43°, Z=4. [Ni{HB[N 2 C 3 H(Br)(C 3 H 7 )] 3 }(NCS-μ-N,S)] 2 .3C 7 H 16 crystallizes in C2/c with a=21.301, b=12.740, c=30.198A, β=107.04°.

Electrochemical and photophysical properties of new triazole-bridged heterobimetallic ruthenium-rhodium and ruthenium-iridium complexes

Abstract: The synthesis, characterization, and the electrochemical and photophysical properties of ((bpy){sub 2}Ru{sup II}(bpt)Rh{sup III}(ppy){sub 2}){sup 2+}, ((bpy){sub 2}Ru{sup II}(bpt)Ir{sup III}(ppy){sub 2}){sup 2+}, ((Rh{sup III}(ppy){sub 2}){sub 2}(bpt)){sup +}, and ((Ir{sup III}(ppy){sub 2}){sub 2}(bpt)){sup +} are reported (Hppy = 2-phenylpyridine; bpy = 2,2{prime}-bipyridine, Hbpt = 3,5-bis(pyridin-2-yl)-1,2,4-triazole). The Ru(bpy){sub 2} moiety is bound via N1 of the triazole ring, while the M(ppy){sub 2} center (M = Rh or Ir) is coordinated via the N4 of the triazole ring. The electrochemical measurements show that in the mixed-metal complexes the first oxidized metal is Ru and the first reduced ligand is bpy. The homobimetallic Ir and Rh complexes exhibit a bpt{sup {minus}}-based reduction. The absorption spectra of the mixed-metal complexes exhibit both Ru {yields} bpy and M {yields} ppy{sup {minus}} transitions. The energies of these transitions are different from those of their homobimetallic analogs. The emission observed for ((Rh(ppy){sub 2}){sub 2}-(bpt)){sup +} at 77 K corresponds to a ligand-centered excited state, while for the analogous iridium complex a charge-transfer emission, which involves the bpt{sup {minus}} ligand, is observed. In the mixed-metal complexes efficient energy transfer occurs from higher energy excited states centered on the M(ppy){sub 2} component to the lowest energy excited state, which ismore » a metal-to-ligand charge transfer level localized on the Ru(bpy){sub 2} component.« less

Reactions of unsymmetrically substituted derivatives of cisplatin with short oligodeoxynucleotides containing a -GpG- sequence: H-bonding interactions in pGpG moieties cross-linked by an asymmetric platinum complex enhancing the formation of one geometrical isomer

Abstract: The interaction of unsymmetrically substituted cisplatin derivatives (general formula cis-Pt(LL'), L=NH 3 :L'=CH 3 NH 2 (Pt-mma); L'= CH 3 CH 2 NH 2 (Pt-mea); L'= NH(CH 3 ) 2 (Pt-dma)] with d(GpG), d(pGpG), and d(CpGpG) has been studied by 1 H and 31 P NMR spectroscopy.

Sulfur Vulcanization of Simple Model Olefins, Part I: Characterization of Vulcanization Products of 2,3-Dimethyl-2-Butene

Abstract: To study the mechanism of the sulfur vulcanization of rubber, 2,3-dimethyl-2-butene (C 612 ) was used as a simple, low-molecular-weight model alkene. Only equivalent allylic positions are present in this alkene. Treating C 6 H 12 with a mixture of Zn, S 8 , and the accelerator tetramethylthiuramdisulfide at 140°C yields a mixture of addition products (C 6 H 11 -S n -C 6 H 11 ). RP-HPLC in combination with MS and H-NMR shows that the products differ only in the length of the sulfur bridge. Small quantities of isomerized products have been found, in which a 1,3-shift of the double bonf has occured

Isolation of a Unique Hexanuclear [Bi6O4OH(cit)3(H2O)3]3− Cluster from the Bismuth-Containing Ulcer Healing Agent “Colloidal Bismuth Subcitrate (CBS)”

Abstract: An active ingredient of peptic ulcer healing agent “Colloidal Bismuth Subcitrate (CBS)” has been isolated by crystallization from a solution containing bismuth citrate and ammonia. The single-crystal X-ray structure analysis has demonstrated that it consists of unique anionic hexanuclear bismuth oxo-hydroxo-citrato clusters connected by ammonium ions and weak citrate bridges.

Synthesis, spectroscopy and magnetism of transition-metal complexes with pyridylmethylphosphonate ligands

Abstract: The compounds [ML2(H2O)2]X2[M = Co, Ni or Cu; L = diethyl 4-pyridylmethylphosphonate (4-pmpe) or diethyl 2-pyridylmethylphosphonate (2-pmpe); X = NO3 or ClO4] have been prepared. Two types of complexes, [M(4-pmpe)2(H2O)2]X2 with the N-bonded monodentate ligand and [M(2-pmpe)2(H2O)2]X2 where 2-pmpe acts as a didentate N,O-bonded chelate ligand, were obtained. The complexes of CoII and NiII are isomorphous. The new complexes were identified and characterized by elemental analysis, magnetic measurements and by infrared, electronic and some 1H NMR spectral studies. The crystal and molecular structure of [Co(4-pmpe)2(H2O)2][ClO4]2·2H2O has been determined: space group P, a= 8.159(1), b= 9.860(1), c= 11.262(1)A, α= 78.44(1), β= 75.11(1), γ= 84.30(1)°, Z= 2, R= 0.0485, R′= 0.0445, for 3078 reflections. The cobalt ion is octahedrally surrounded by two pyridine nitrogens with distances 2.133(3)A and two oxygens of the phosphoryl groups from two organic ligands at distances of 2.100(2)A. Two water molecules occupy the fifth and the sixth co-ordination sites trans with Co–O bond distances of 2.101(2)A. The ligand bridges the cobalt ions, thereby forming infinite chains (Co ⋯ Co 8.159 A). The spectroscopic and magnetic data are consistent with an octahedral geometry for all the studied complexes, e.g. mono- and poly-nuclear for the 2- and 4-pmpe ligands, respectively.

Co-ordination compounds with the N2S-donor ligand 1,5-bis(3,5-dimethylpyrazol-1-yl)-3-thiapentane

Abstract: With the ligand 1,5-bis(3,5-dimethylpyrazol-1-yl)-3-thiapentane (bdtp) the compounds [M(bdtp)-(NCS)2](M = Co or Zn), [Ni(bdtp)(NCS)2(H2O)], Cu(bdtp)(F)(BF4), M(bdtp)Cl2(M = Co or Cu), Zn(bdtp)Cl2·0.5EtOH, M(bdtp)(NO3)2(M = Co or Cu), Cu(bdtp)X (X = Br or Cl), [Cu(bdtp)]BF4·H2O and Ag(bdtp)(NO3) have been isolated. X-Ray single-crystal structures of [Co(bdtp)(NO3)2], Cu(bdtp)Br and Ag(bdtp)(NO3) were determined. The compound [Co(bdtp)(NO3)2] crystallizes in the monoclinic space group P21/n, with a= 8.984(2), b= 15.342(3), c= 14.888(3)A, β= 107.28(2)°, Z= 4 and R 0.038 for 2727 observed [F > 2σ(F)] reflections. The cobalt(II) atom is pseudo-octahedrally co-ordinated by three ligand donors, one mono- and one di-dentate. The Co–N [2.072(3) and 2.083(3)A] and Co–S bond lengths [2.584(1)A] are normal. The compound Cu(µ(bdtp)Br crystallizes in the monoclinic space group P21/n, with a= 9.017(2), b= 14.09(2), c= 13.660(3)A, β= 97.80(2)°, Z= 4 and R 0.040 for 1655 observed reflections. The pseudo-tetrahedral co-ordination environment of the copper(I) atom is made up by two pyrazole nitrogens [2.120(5) and 2.014(5)A], one thioether [2.461(2)A] and one bromide [2.432(1)A]. The ligand acts as a link between two successive copper centres, resulting in a polymeric compound structurally isomorphous to Cu(bdtp)Cl. The compound Ag(bdtp)(NO3) crystallizes in the monoclinic space group P21/n, with a= 18.710(4), b= 8.828(2), c= 11.162(5)A, β= 103.13(3)°, Z = 4 and R 0.038 for 2346 observed reflections. The structure, with bridging ligands, is similar to that of Cu(bdtp)Br. The silver(I) atoms are co-ordinated, in a very distorted-tetrahedral fashion, by two nitrogens [2.483(5) and 2.216(4)A], one thioether [2.571(2)A] and a monodentate nitrate anion [2.503(5)A].

Oxidative phenol coupling catalyzed by polymer‐bound copper‐imidazole complexes

Abstract: Polymer-bound imidazole-copper(II) complexes were investigated and applied as catalysts for oxidative coupling (polymerization) of 2,6-dialkylphenols. These polymeric catalysts were also immobilized on silica particles through adsorption, quaternization and grafting. Especially, the grafted catalysts showed interesting catalytic properties, e.g. good specificity for C-O coupling and very good stability during prolonged use in continuous processes. This stability furnished new information about the mechanism of the oxidative coupling polymerization. Finally, this reaction was optimized for the preparation of PPO-type telechelics.

Thermally and photochemically induced co-ordination change in ruthenium(II) bis(2,2′-bipyridine) complexes containing pyridyltriazole ligands

Abstract: A series of RuII(bipy)2 complexes (bipy = 2,2′-bipyridine) containing monodentate co-ordinated pyridyltriazole ligands has been prepared and characterised. The species are obtained by either thermal or photochemical methods. The co-ordination mode of the products obtained has been investigated using spectroscopic techniques. The molecular structure of one of the products, bis(2,2′-bipyridine)chloro-[3-methyl-1-(pyridin-2-yl)-1,2,4-triazole]ruthenium(II) hexafluorophosphate, has been determined. The compound crystallises in the triclinic space group P with unit-cell parameters a= 8.599(12), b= 13.503(16), c= 16.526(16)A, α= 89.88(9), β= 117.22(8), γ= 111.08(10)° and Z= 2. The pyridyltriazole is co-ordinated via the N4 nitrogen atom. In the compounds containing monodentate 4-methyl-3-(pyridin-2-yl)-1,2,4-triazole the ligand is most likely co-ordinated via the N1 atom. The conversion of the photoproduct acetonitrilebis(2,2′-bipyridine)[4-methyl-3-(pyridin-2-yl)-1,2,4-triazole]ruthenium(II) into the parent complex containing the chelating pyridyltriazole ligand by thermal as well as photochemical methods is reported.

Structure of bis[μ-4-amino-3,5-bis(aminomethyl)-1,2,4-triazole-N',N1,N2,N'']-bis[diaquacopper(II)] bis(sulfate) tetrahydrate

Abstract: [Cu(C 4 H 10 N 6 )(H 2 O) 2 ] 2 (SO 4 ) 2 4H 2 O cristallise dans C2/c avec a=19,009, b=11,273, c=13,144A, β=103,50°, Z=4; affinement jusqu'a R=0,0583 Ce compose est le premier complexe du cuivreponte par un triazole N1,N2 dans lequel l'anion n'est pas implique dans la coordination Les ions Cu(II) sont dans un environnement octaedrique deforme, avec quatre atomes N donneurs du coordinat triazole en positions equatoriales Deux molecules d'eau sont coordinees axialement Les anions sulfate ne sont pas coordines et sont fixes dans le reseau par un reseau etendu de liaisons hydrogene

First structurally characterized linkage isomers of two thiocyanatocopper(II) complexes

Abstract: Two linkage isomers of [Cu(aat)2(NCS)2](aat = 3-acetylamino-1,2,4-triazole), one with S- and one with N-bonded thiocyanate, have been prepared and characterized by spectroscopy and X-ray crystallography. These compounds are the first structurally characterized linkage isomers of a copper(II) thiocyanate complex. In both cases the copper atoms exhibit an elongated octahedral geometry with two axial thiocyanates and, in equatorial positions, two chelating aat ligands. The N-bonded isomer presents one of the smallest Cu–N–C angles [118.1(2)°] ever reported for thiocyanates and a quite long Cu–N(NCS) distance [2.521(3)A]. In the S-bonded isomer the Cu–S(NCS) distance is 2.864(2)A. As both compounds can be obtained from the same batch, packing differences must account for the isolation of the two different isomers. The different intermolecular hydrogen bonding between the ligands and anions exhibited by both crystal lattices is compared. ‘Ab-initio’ molecular orbital calculations have also been performed to study the theoretical stabilities of the isomers.

Crystal structures, electrical conductivity and band-structure calculations of three new [cation][Ni(C3S5)2]2 compounds

Abstract: The mixed-valence radical salts [smdt][Ni(C3S5)2]21, [dmp][Ni(C3S5)2]22 and [dmm][Ni(C3S5)2]23(C3S52–= 1,3-dithiole-2-thione-4,5-dithiolate, smdt =S-methyl-1,3-dithianium, dmp =N,N-dimethylpyrrolidinium and dmm =N,N-dimethylmorpholinium) have been obtained by electrochemical oxidation of the corresponding [cation][Ni(C3S5)2] complexes in acetonitrile. Single-crystal X-ray studies revealed that all three crystallise in essentially the same packing mode. Their structure consists of anionic diads stacked face-to-face along one direction. The stacks form layers of Ni(C3S5)2 units which are separated by the cations. In the structure of 3 two types of Ni(C3S5)2 layers exist, exhibiting different structural and electrical properties. The acceptor molecules neighbouring along the longest axis make an angle of 135 (1), 139 (2) and 152°(3) with each other, thereby forming a herringbone motif. In all three structures, short intermolecular S ⋯ S contacts can be found predominantly between Ni(C3S5)2 units lying side-by-side to each other, but also within the stacks in 3. At ambient pressure, all three Ni(C3S5)2 compounds have room-temperature conductivities ranging between 1 and 70 S cm–1. Their thermal behaviour is consistent with semiconductors having activation energies of about 0.14 eV. Band-structure calculations were carried out and found to be in agreement with the observed conductivities when some degree of electron correlation is taken into account. Calculation of molecular orbital overlaps indicated dimerisation of the anions, with a weak, essentially two-dimensional conduction pathway for salts 1 and 2. In the crystal lattice of 3 one Ni(C3S5)2 layer can be considered as conducting along the stacking direction, while in the second type of layer a two-dimensional conduction pathway appears to be present.

Mechanistic studies of the oxidative coupling polymerization of phenols. VI. Comparison of reactivities of DMP, PPO‐dimer, and ‐trimer in the copper‐catalyzed oxidative coupling polymerization

Abstract: In the oxidative coupling polymerization, catalyzed by copper-amine complexes, the oxidation rates of 2,6-dimethylphenol (DMP) and its C-O-coupled dimer [4-(2',6'-dimethylphenoxy)-2,6-dimethylphenol] and trimer [4-(-4'-(2",6"-dimethylphenoxy)-2',6'-dimethylphenoxy))-2,6-dimethylphenol] have been determined. The DMP concentration dependence shows a Michaelis-Menten-type behavior. On the other hand, the dimer and trimer showed a first-order rate-dependence in the respective phenol concentrations. This indicates that the slow reaction step, following an equilibrium complex formation between DMP and copper complex, is relatively fast for both the dimer and the trimer. Therefore, coordination of dimer or trimer to the copper complex appears to be rate-determining. Furthermore, the dimer and trimer gave overall reaction rates approximately eight times higher than found for DMP. Following the Flory principle of equal reactivity for functional groups of oligomers in polycondensations, all PPO oligomers can be assumed to have equally high oxidation rates as the dimer and trimer. The yield of undesired DPQ side product is strongly reduced when starting with the dimer (0.18%), or trimer (0.17%), compared to 3.3% for DMP. This is not unexpected, since DPQ can only be formed from two monomeric DMP residues. In fact, using a 1/10 molar mixture of dimer/DMP already results in a DPQ yield of only 1.7%. Furthermore, when starting from DMP, it has been observed that DPQ was predominantly formed during the first 30% conversion. Starting from dimer (or trimer) DPQ was formed at an almost constant very low rate during the whole course of the reaction. From these experiments it can be concluded that the most important polymerization reaction involves oxidation of copper-coordinated DMP anion to its corresponding cations, followed by coupling with a copper coordinated PPO chain.

The dinuclear complex [{trans-PtCl(NH3)2}2{µ-H2N(CH2)6NH2}]Cl2 forms a unique macrochelate intrastrand crosslink with d(GpG)

Abstract: Reaction of the dinuclear antitumour compound [{trans-PtCl(NH3)2}2{µ-H2N(CH2)6NH2}]Cl2 with d(GpG) results in the formation of the intrastrand macrochelate [{trans-Pt(NH3)2}2(µ-H2N(CH2)6NH2)](d(GpG–N7,N7).

The Relevance of Hydrogen Bonding in the Mechanism of Action of Platinum Antitumor Compounds

Abstract: A brief review is presented dealing with the mechanism of action of platinum antitumor drugs with the general formula cis-PtX2(NHR2)2 in which R can be almost any organic fragment, and X can be any leaving group, such as chloride, sulfate, or (chelating bis)carboxylate. Special emphasis is given on the role of hydrogen bonding in the several reactions taking place. It turns out that the NH group in the amine is important in determining the overall activity of the Pt compound. It is also likely to be responsible for the preferred ionic/dipolar interaction with nucleic acids, over proteins. Studies with single-stranded and double-stranded oligonucleotides have shown that the NH group also plays a role in discriminating between adenine and guanine. Finally the stabilization of the distorted DNA, after Pt binding, has been shown to originate from NH···Ophosphate interactions.

Structure of the dinuclear copper(II) compound of N,N,N',N'-tetrakis[2-(3,5-dimethyl-1-pyrazolyl)ethyl]-1,2-ethylenediamine (tped), [Cu2(tped)(H2O)2(NO3)2](NO3)2.2CH3OH

Abstract: [Cu 2 (C 30 H 48 N 10 ) 0.5 (H 2 O)(NO 3 )]NO 3 .CH 3 OH cristallise dans P2 1 /n avec a=12.683, b=10.374, c=19.229A, β=111.92°, Z=4; affinement jusqu'a R=0.036. L'ion Cu est entoure par deux atomes N du pyrazole a 1.993 et 2.013A, un atome N de l'amine a 2.303A, un atome O de l'un des anions nitrate a 2.063A et un atome O d'une molecule d'eau a 1.947A selon une pyramide carree deformee.