The synthesis and characterisation of some MnLnX2 complexes (n = 1, L = pyridine, 4-pyrrolidinopyridine,X = Cl,Br, I,NCS; n = 1, L = EtOH,X = Cl,Br; n = 2, L = EtOH,X = I,NCS)

Mono-ligand complexes MnLX₂ (L = pyridine, 4-pyrrolidinopyridine, X = Cl, Br, I, NCS) have been prepared. The pyridine complexes contain only bridging halide and pseudohalide groups, whereas the 4-py complexes contain both bridging and terminal bound anions. Ethanol is coordinated in Mn(EtOH)X₂ (X=C1, Br) and Mn(EtOH)₂X₂ (X=I, NCS). Although the MnLX₂ complexes have the same stoichiometry as the Mn(PR₃)X₂complexes none show any activity towaxds binding dioxygen either in the solid state or in solution.     

Halide abstraction reactions of Sb(V) chloride: Synthesis and characterisation of hexachloroantimonate salts of M(II) M = Zn,Mg; M(III) M = Cr; and M(IV) M = Ti,Sn and related Cp2M(IV) M = Ti,Zr and Hf

Reactions of SbCl₅ with various covalent metal halides in MeCN have been studied as a convenient and direct route to metal hexachloroantimonate salts via Sb(V) halide abstraction. The isolation and characterization (Ir, Vis-UV, ¹H NMR spectroscopic and microanalytical) of the complexes [Zn(MeCN)₆][SbCl₆]₂, [CrCl₂(MeCN)₄][SbCl₆], [SnCl₃(MeCN)₃][SbCl₆], [TiCl₂(MeCN)₄][SbCl₆]₂, [Cp₂M(Cl)(MeCN)_x][SbCl₆] M = ti, x = 1; M = Zr, Hf, x = 2, and [Cp₂M(MeCN)_y][SbCl₆]₂ M = Ti, y = 2; M = Zr, Hf, y = 3, is described. The reaction of MgCl₂ with SbCl₅ was carried out in EtOAC as solvent and gave [Mg(EtOAc)₆][SbCl₆]₂. ¹²¹Sb NMR, IR and UV spectroscopic measurements provide positive identification of the SbCl_6⁻ anion.     

Synthesis, morphology and cytogenetics of Raphanofortii (TTRR, 2n = 38): a new amphidiploid of hybrid Brassica tournefortii (TT, 2n = 20) ×Raphanus caudatus (RR, 2n=18)

Amphidiploid Raphanofortii was synthesized by colchicinization of the F₁ hybrid Brassica tournefortii (TT, 2n = 20)×Raphanus caudatus (RR, 2n = 18). The crossability between these two species, and the cytomorphology of the F₁ plants and the amphidiploids were investigated. Intergeneric hybrids between the species were obtained only when B. tournefortii was involved as female parent. The hybrid plants were intermediate for most of the morphological attributes and showed very low pollen fertility compared to the parents. Although a majority of the pollen mother cells of the dihaploid hybrid (TR, 2n = 19) harboured univalents, a maximum of six bivalents were also observed. Of the 37 colchicine-treated F₁ plants analyzed cytologically, 21 were found to be true amphidiploids (2n = 38), whereas seven were mixoploids. Meiosis in the amphidiploids was characterized by the occurrence of 19 bivalents, though multivalents and univalents were also observed in a few cells. Most of the amphidiploid plants exhibited a fairly high pollen and seed fertility, which was further enhanced with the advancement of generations. Out of 69 plants investigated in the A₂ generation, 64 were euploids while the remaining five were aneuploids (2n = 36, 37, 39, 40 and 42). The newly synthesized Raphanofortii has great potential as a new commercial crop, as well as a bridge species for the transfer of economically important attributes of both the species to other Brassicas. Received: 2 November 1999 / Accepted: 26 March 2000     

Ciliary ultrastructure of neomeniomorphs (Mollusca, Neomeniomorpha = Solenogastres)

Abstract. The ultrastructure of the ciliary apparatus of multiciliated epidermal cells of the trochophore of Epimenia babai and the adult of Strophomenia scandens was studied. The trochal cirri of E. babai consists of long cilia with unspecialized tips. The surfaces between the trochs are sparsely covered with shorter cilia of similar structure except for length. In the adult of S. scandens , the foot is covered by a dense mat of cilia with blunt electron-dense tips. In both E. babai and S. scandens , all cilia have two perpendicularly orientated rootlets. This condition is similar to that of the Chaetodermomorpha (=Caudofoveata) and Polyplacophora. In other molluscs studied to date, the cilia of multiciliated epidermal cells have a single rootlet or a derivative thereof. The presence of two ciliary rootlets likely represents the basal plesiomorphic state for the Bilateria. The existence of this character in the Neomeniomorpha, Chaetodermomorpha, and Polyplacophora is congruent with the hypothesis of a basal position of these taxa within the Mollusca.     

Synthesis and reactions of [M(CO)4(Ph2PSiMe3)X] complexes (M = Mn,Re; X = Halogen)

The silylphosphine ligand Ph₂PSiMe₃ reacts readily with a slurry of [Re(CO)₅X] (X  Cl, Br) in polar and in non-polar solvents to yield soluble cis-[Re(CO)₄- (Ph₂PSiMe₃)X] (Ia, X  Cl;Ib, X  Br) via CO substitution. Compound I is readily hydrolyzed by water or silica gel to cis-[Re(CO)₄(Ph₂PH)X]. Compound Ib reacts with [Re(CO)₅Br] to yield [Re₂(CO)₈(μ-PPh₂)- (μ-Br)] (II), and with [Mn(CO)₅Br] to yield [MnRe- (CO)₈(μ-PPh₂)(μ-Br)] (III).The reaction of Ph₂PSiMe₃ with [Mn(CO)₅X] (X=Cl,Br,I) is highly dependent upon reaction conditions.In polar and in non-polar solvents, an excess of ligand gives mainly cis-[Mn(CO)₄(Ph₂PSiMe₃)X] (IVa, X  Cl;IVb, X  Br;IVc, X I). With ligand: [Mn(CO)₅X] reacting ratios in the range 0.5–1.0:1, the products from the three respective halomanganese complexes in THF were: (a) mainly [Mn₂(CO)₈(μ- PPh₂)(μ-Cl) (Va); (b) both [Mn(CO)₄(Ph₂PSiMe₃)Br] and [Mn₂(CO)₈(μ-PPh₂)(μ-Br)] (Vb); and (c) exclusively [Mn(CO)₄(Ph₂PSiMe₃)I]. The compounds IVa-c are stable in solution at ambient temperatures and are readily hydrolyzed by water or methanol to [Mn(CO)₄(Ph₂PH)X]. Compound IVb reacts at room temperature with [Mn(CO)₅Cl] to yield only [Mn₂- (CO)₈(μ-PPh₂)(μ-Br)] (Vb); compound IVc reacts in hot toluene with [Mn(CO)₅Cl] to yield mainly [Mn₂(CO)₈(μ-PPh₂)(μ-I)] (Vc), together with a small amount of the chloro-bridged analog.The dinuclear species II, III and Va-c appear to be formed mainly via an intermolecular elimination of Me₃SiX from the appropriate [M(CO)₄(Ph₂PSiMe₃)X] and metalpentacarbonylhalide (chloride or bromide) complexes.     

Dissociation of Aun (n = 3, 4) Microclusters

Abstract

The dissociation of Au₃ and Au₄ microclusters has been investigated using a molecular-dynamics computer simulation. The potential energy function used in the calculations includes two- and three-body interactions, which are represented by Lennard-Jones and Axilrod-Teller potentials, respectively. It has been found that dissociation starts for both clusters after 3000K.     

Durene-capped porphyrin complexes of iron(II). Binding of imidazoles, and spectroscopic trends within Fe(porp)B(L) species (B = imidazole base; L = RNC, CO, O2)

Solution equilibria are presented for in situ reactions of the type FeII(porp) + B----FeII(porp)B, where porp represents the dianion of some durene-capped porphyrins with variable length linking methylene straps, and B is 1-methyl, 1,2-dimethyl, or 1,5-dicyclohexylimidazole. Increasing distortion of the porphyrin skeleton has no effect on coordination of B at the unhindered side of the capped porphyrin. Increasing skeleton distortion gives rise to regular trends within the visible spectra of the free base porphyrins, the hemin (FeIII) chlorides, and six-coordinate FeII(porp)B(L) species (L = RNC, CO, O2), while the visible spectra of FeII(porp) and of FeII(porp)B species are independent of the nature of porp and B, which may be related to greater flexibility of the lower coordination number systems. v(CO) data for the FeII(porp)(CO)B species are discussed briefly.     

Thaptomys Thomas 1915 (Rodentia, Sigmodontinae, Akodontini) with karyotypes 2n = 50, FN = 48, and 2n = 52, FN = 52: Two monophyletic lineages recovered by molecular phylogeny

A novel karyotype with 2n = 50, FN = 48, was described for specimens of Thaptomys collected at Una, State of Bahia, Brazil, which are morphologically indistinguishable from Thaptomys nigrita, 2n = 52, FN = 52, found in other localities. It was hence proposed that the 2n = 50 karyotype could belong to a distinct species, cryptic of Thaptomys nigrita, once chromosomal rearrangements observed, along with the geographic distance, might represent a reproductive barrier between both forms. Phylogenetic analyses using maximum parsimony and maximum likelihood based on partial cytochrome b sequences with 1077 bp were performed, attempting to establish the relationships among the individuals with distinct karyotypes along the geographic distribution of the genus; the sample comprised 18 karyotyped specimens of Thaptomys, encompassing 15 haplotypes, from eight different localities of the Atlantic Rainforest. The intra-generic relationships corroborated the distinct diploid numbers, once both phylogenetic reconstructions recovered two monophyletic lineages, a northeastern clade grouping the 2n = 50 and a southeastern clade with three subclades, grouping the 2n = 52 karyotype. The sequence divergence observed between their individuals ranged from 1.9% to 3.5%.     

Architecture, electronic structure and stability of TM@Ge(n) (TM = Ti, Zr and Hf; n = 1-20) clusters: a density functional modeling

The present study reports the geometry, electronic structure and properties of neutral and anionic transition metal (TM = Ti, Zr and Hf)) doped germanium clusters containing 1 to 20 germanium atoms within the framework of linear combination of atomic orbitals density functional theory under spin polarized generalized gradient approximation. Different parameters, like, binding energy (BE), embedding energy (EE), energy gap between the highest occupied and lowest unoccupied molecular orbitals (HOMO-LUMO), ionization energy (IP), electron affinity (EA), chemical potential etc. of the energetically stable clusters (ground state cluster) in each size are calculated. From the variation of these parameters with the size of the clusters the most stable cluster within the range of calculation is identified. It is found that the clusters having 20 valence electrons turn out to be relatively more stable in both the neutral and the anionic series. The sharp drop in IP as the valence electron count increases from 20 to 21 in neutral cluster is in agreement with predictions of shell models. To study the vibrational nature of the clusters, IR and Raman spectrum of some selected TM@Ge_n (n = 15,16,17) clusters are also calculated and compared. In the end, relevance of calculated results to the design of Ge-based super-atoms is discussed.     

Comparative mapping of twenty-eight bovine loci in sheep (Ovis aries, 2n = 54) and river buffalo (Bubalus bubalis, 2n = 50) by FISH

Peripheral blood cell cultures were treated for late incorporation of both BrdU and Hoechst-33258 to obtain R-banding pattern preparations. Twenty-eight bovine cosmids from 19 bovine syntenic groups (U), three of which contain type I loci and 25 which contain microsatellite loci and have previously been assigned to cattle chromosomes, were comparatively FISH-mapped to sheep and river buffalo chromosomes according to the standard karyotypes (13 loci for the first time in the latter species). The results enrich the physical maps of both species with information relative to the following loci and to the corresponding syntenic groups: IDVGA35 and IDVGA53 (U6), IDVGA61 and IDVGA84 (U13), JAB10 (U5), IDVGA41 and IDVGA57 (U27), IDVGA87 (U11), IDVGA32 and IDVGA10 (U19), IDVGA49, IDVGA66 and IDVGA68 (U1), ZNF164 (U23), IDVGA74 and IDVGA70 (U9), IDVGA47, IDVGA46 and IDVGA58 (U21), MAP1B (U14), IDVGA79 (U4), CATHL (U12), IDVGA71 (U8), IDVGA59 (U26), IDVGA29 (U29), IDVGA7 (U7), IDVGA82 (X), IDVGA50 (Y). All mapped loci were localized on homoeologous chromosomes and chromosome regions of the two species, confirming the high degree of chromosome homoeologies between the subfamilies Bovinae and Caprinae.     

(Dien)M(II) (M=Pd, Pt) and (NH3)3Pt(II) complexes of 1-methylcytosine: Linkage and rotational isomerism, metal-promoted deamination, and pathways to dinuclear species

Despite their structural similarity, [Pt(dien)(1-MeC-N3)](2+) (1), [Pd(dien)(1-MeC-N3)](2+) (2), and [Pt(NH(3))(3)(1-MeC-N3)](2+) (3) (with dien=diethylenetriamine and 1-MeC=neutral 1-methylcytosine) behave in part markedly different at strongly alkaline pH (12-13) and at room temperature. While 1 and 2, yet not 3 show linkage isomerization from N3 to N4, deamination of the cytosine nucleobase to 1-methyluracilate occurs with 1 and 3, yet not with 2. Pathways leading to N3,N4-diplatinated 1-MeC(-) complexes (1-MeC(-)=1-methylcytosine, deprotonated at exocyclic amino group N4) have been studied at high pH by starting from 1 and 3, respectively, and adding (dien)Pt(II). It appears that initial migration of the metal entity from N3 to N4, followed by binding of the second metal to the available N3 site, is favored over sequential coordination to N3 and then N4. X-ray crystal data of 1-3 density functional theory (DFT) calculations, and NMR ((1)H, (195)Pt) data are presented.     

Theoretical study of structure, bonding, and electronic behavior of novel sandwich compounds M3(C6R6)2 (M = Ni, Pd, Pt; R = H, F)

The correlations between the structural and electronic properties of the monolayer clusters M(3) (where M = Ni, Pd, Pt) and the sandwich complexes M(3)(C(6)R(6))(2) (where M = Ni, Pd, Pt; R = H, F) were studied by performing quantum-chemical calculations. All of the sandwich complexes are strongly donating and backdonating metal-ligand bonding structures. The influence of the ligand as well as significant variations in the M-C, M-M, and C-C bond lengths and binding energies were examined to obtain a qualitative and quantitative picture of the intramolecular interactions in C(6)R(6)-M(3). Our theoretical investigations show that the binding energies of these sandwich complexes gradually decrease from Ni to Pt as well as from H to F, which can be explained via the frontier orbitals of the clusters M(3) and C(6)R(6).     

Tc(NX)Y3(Me2PhP)2 complexes (X = O or S; Y = Cl or Br). Preparation,characterization and EPR studies

The d⁵-‘low-spin’ Tc(II) complexes tribromonitrosyl-bis(dimethylphenylphosphine)technetium(II) and tribromo-thionitrosyl-bis(dimethylphenylphosphine)technetium(II) were prepared by ligand exchange starting from the analogous chloro compounds. The complexes were characterized chemically and IR, UVVis and EPR spectroscopically.In the room temperature EPR spectra a well-resolved ⁹⁹Tc hyperfine splitting is observed inidicating a ground state of the unpaired electron which is well separated from the other orbit states. The general features of the spectra at low temperatures are characteristic for an axially symmetric spin Hamiltonian. Analysis of the ⁹⁹Tc and ³¹P hfs (hfs = hyperfine splittings) shows a marked covalency of the Tcligand bonds. A comparison is given between the chloro and bromo, as well as between the nitrosyl and thionitrosyl complexes.     

Comparative studies on copper(I) complexes: synthesis, X-ray crystallography and electrochemical properties of [Cu(dafone)nX] complexes (dafone=4,5-diaza-fluoren-9-one, X=Br, I, SCN)

The synthesis, X-ray structures and electrochemical properties of stable five-coordinate, trigonal-bipyramidal Cu^I complexes of dafone (4,5-diaza-fluoren-9-one) [Cu(dafone)₂X] with X=Br (1) or I (2) as ancillary ligands are discussed. The thiocyanate-bridged polymeric Cu^I complex of dafone, [Cu(dafone)(SCN)]_n (3), forms two-dimensional sheets in the crystal, held together by weak interactions involving the dafone ketone group, while the phenanthroline complex, [Cu(phen)(SCN)]_n (4), a zigzag arrangement of the phen ligands leads to interchain π-stacking within the lattice. The electrochemical studies reveal that dafone stabilizes the Cu^I oxidation state more efficiently than phen due to its better π-acceptor ability as indicated by more positive redox potentials for the Cu^I/Cu^II couple.     

Photo-induced DNA scission by Cu(ii)-meso-tetrakis(n-N-methylpyridiniumyl)porphyrins (n = 2, 3, 4) and their binding modes to supercoiled DNA

The photo-induced cleavage of pGEM-7zf-NIS super-coiled DNA by Cu(ii)-meso-tetrakis(n-N-methylpyridiniumyl)porphyrins (n = 2, 3, 4 referred to as o-, m- and p-CuTMPyP, respectively) and their binding mode were investigated in this study. m-CuTMPyP was most efficient in cleavage than o- and p-CuTMPyP isomers. Cleavage was suppressed by N(2) bubbling, suggesting that the cleavage occurred by an oxidative cleavage mechanism. Sodium azide, an (1)O(2) quencher, and DMSO, a hydroxyl radical scavenger, inhibited cleavage, indicating that hydroxyl radicals and singlet oxygen were likely reactive species responsible for the cleavage. Reduced linear dichroism spectroscopy showed angles of o-CuTMPyP's electric transition moments, in which the periphery pyridinium ring was prevented from free rotation, of 59° and 61° with respect to the local DNA helix axis. The spectra of m- and p-CuTMPyP complexed with pGEM-7zf-NIS DNA were characterized by large signals in the Soret band, coincident with those of known intercalated porphyrins.     

Synthesis, characterization, DNA-binding and spectral properties of complexes [Ru(L)4(dppz)]2+ (L=Im and MeIm)

Two new Ru(II) complexes [Ru(L)(4)(dppz)](2+) (L=imidazole (Im), 1-methylimidazole (MeIm); dppz=dipyrido[3,2-a:2',3'-c]phenazine), have been synthesized and characterized in detail by elemental analysis, (1)H NMR, Electrospray ionization mass spectrometry (ESI-MS) and UV-visible (UV-Vis) spectroscopic techniques. The interaction of these complexes with calf thymus DNA (CT-DNA) has been explored by using electronic absorption titration, competitive binding experiment, circular dichroism (CD), thermal denaturation and viscosity measurements. The experimental results show that: both the two complexes can bind to DNA in an intercalation mode; the DNA-binding affinity of complex [Ru(Im)(4)(dppz)](2+)1 (K(b)=2.5 x 10(6)M(-1)) is greater than that of complex [Ru(MeIm)(4)(dppz)](2+)2 (K(b)=1.1 x 10(6)M(-1)). Moreover, it is very interesting to find that the circular dichroic spectrum of DNA-complex 1 adduct, in which both bands centered at 277 nm and 236 nm are all negative, is very different from those of DNA-complex 2 adduct and other Ru(II) complexes binding to DNA in general intercalation mode. It may be due to the hydrogen-bonding effect or the contribution of induced CD signals of complex 1. Another interesting finding is that the hypochromism of the complexes is not linear relation to their DNA-binding affinities. In order to deeply study these experimental phenomena and trends, the density functional theory (DFT) and time-dependent DFT (TDDFT) computations were carried out, and on the basis of the DFT/TDDFT results and the frontier molecular orbital theory, the trend in DNA-binding affinities, the spectral properties as well as the interesting phenomena of larger extent of hypochromism but relatively smaller K(b) values for the title complexes have been reasonably explained.     

Preparation and characterization of 6I,6n-di-O-(L-fucopyranosyl)-beta-cyclodextrin (n=II-IV) and investigation of their functions

Three positional isomers of 6(I),6(n)-di-O-(beta-L-fucopyranosyl)-cyclomaltoheptaose [6(I),6(n)-di-O-(beta-L-Fuc)-beta-cyclodextrin, -betaCD, n=II-IV] were chemically synthesized using the corresponding authentic compounds, 6(I),6(n)-di-O-(tert-butyldimethylsilyl)-betaCD (n=II-IV), as the fucosyl acceptors, and 2,3,4-tri-O-acetyl-L-fucopyranosyl trichloroacetimidate as the fucosyl donor. Their structures were analyzed by HPLC, MS, and NMR spectroscopy. The hemolytic activities of L-Fuc-betaCDs were lower than that of betaCD, while the solubilities of these branched CDs in water were much higher than that of betaCD. The molecular interaction between these compounds and the fucose-binding lectin Aleuria aurantia lectin (AAL) was investigated using an optical biosensor based on a surface plasmon resonance (SPR) technique. The order of binding affinity, as a function of the fucose-binding position, was 6(I),6(IV)->6(I),6(III)->6(I),6(II)-di-O-(beta-L-Fuc)-betaCD>6-O-(beta-L-Fuc)-betaCD.