Interaction of metal ions with 6-oxopurine nucleotides. Part 1. X-Ray structures of ternary cobalt(III) complexes with inosine 5'-monophosphate or guanosine 5'-monophosphate

The crystal structures of two ternary metal nucleotide complexes of cobalt, [Co(en)2(H2O)2]-[Co(5?-IMP)2(H2O)4]Cl2·4H2O (1) and [Co(en)2(H2O)2][Co(5?-GMP)2(H2O)4]Cl2·4H2O (2), have been analysed by X-ray diffraction (en = ethylenediamine, 5?-IMP = inosine 5?-monophosphate, and 5?-GMP = guanosine 5?-monophosphate). Both complexes crystallize in the orthorhombic space group C2221 with a= 8.725(1), b= 25.891(5), c= 21.212(5)Å, Z= 4 for (1) and a= 8.733(2), b= 26.169(4), c= 21.288(4)Å, Z= 4 for (2). The structure of (1) was solved by the heavy-atom method, while that of (2) was deduced from (1). The structures were refined to R values of 0.09 and 0.10 for 1 546 and 1 572 reflections for (1) and (2) respectively. The two structures are isomorphous. A novel feature is that the chelate ligand en and the nucleotide are not co-ordinated to the same metal ion. One of the metal ions lying on the two-fold a axis is octahedrally co-ordinated by two chelating en molecules and two water oxygens, while the other on the two-fold b axis is octahedrally co-ordinated by two N(7) atoms of symmetry-related nucleotides in a cis position and four water oxygens. The conformations of the nucleotides are C(2?)-endo, anti, and gauche�gauche. In both (1) and (2) the charge-neutralising chloride ions are disordered in the vacant space between the molecules. These structures bear similarities to the mode of nucleotide co-ordination to PtII complexes of 6-oxopurine nucleotides, which are the proposed models for intrastrand cross-linking in DNA by a metal complex.

Metallacarboranes: Toward Promising Hydrogen Storage Metal Organic Frameworks

Using first principles calculations, we show the high hydrogen storage capacity of metallacarboranes, where the transition metal (TM) atoms can bind up to 5 H-2-molecules. The average binding energy of similar to 0.3 eV/H favorably lies within the reversible adsorption range. Among the first row TM atoms, Sc and Ti are found to be the optimum in maximizing the H-2 storage (similar to 8 wt %) on the metallacarborane cluster. Being an integral part of the cage, TMs do not suffer from the aggregation problem, which has been the biggest hurdle for the success of TM-decorated graphitic materials for hydrogen storage. Furthermore, the presence of carbon atom in the cages permits linking the metallacarboranes to form metal organic frameworks, which are thus able to adsorb hydrogen via Kubas interaction, in addition to van der Waals physisorption.

Organometallic derivatives of diphosphazanes. 2. Seven-coordinated Group 6 metal tricarbonyl complexes of diphosphazane ligands. X-ray crystal structure of [WI2(CO)3{P(OPh)2}2NPh]

The reactions of the complexes [MI2(CO)3-(NCMe)2] (M = Mo, W) with the diphosphazane ligands RN{P(OPh)2}2 (R = Me, Ph) in CH2Cl2 at room temperature afford new seven-coordinated complexes of the type [MI2(CO)3{P(OPh)2}2NR]. The molybdenum complexes are sensitive to air oxidation even in the solid state, whereas the tungsten complexes are more stable in the solid state and in solution. The structure of the tungsten complex [WI2(CO)3{P(OPh)2}2NPh] has been determined by single-crystal X-ray diffraction. It crystallizes in the orthorhombic system with the space group Pna 2(1), a = 19.372 (2) angstrom, b = 11.511 (1) angstrom, c = 15.581 (1) angstrom, and Z = 4. Full-matrix least-squares refinement with 3548 reflections (I > 2.5-sigma-(I)) led to final R and R(w) values of 0.036 and 0.034, respectively. The complex adopts a slightly distorted pentagonal-bypyramidal geometry rarely observed for such a type of complexes; two phosphorus atoms of the diphosphazane ligand, two iodine atoms, and a carbonyl group occupy the equatorial plane, and the other two carbonyl groups, the apical positions.

Tuning the interfacial properties of supported metal nanoclusters

Nanoclusters are objects made up of several to thousands of atoms and form a transitional state of matter between single atoms and bulk materials. Due to their large surface-to-volume ratio, nanoclusters exhibit exciting and yet poorly studied size dependent properties. When deposited directly on bare metal surfaces, the interaction of the cluster with the substrate leads to alteration of the cluster properties, making it less or even non-functional. Surfaces modified with self-assembled monolayers (SAMs) were shown to form an interesting alternative platform, because of the possibility to control wettability by decreasing the surface reactivity and to add functionalities to pre-formed nanoclusters. In this thesis, the underlying size effects and the influence of the nanocluster environment are investigated. The emphasis is on the structural and magnetic properties of nanoclusters and their interaction with thiol SAMs. We report, for the first time, a ferromagnetic-like spin-glass behaviour of uncapped nanosized Au islands tens of nanometres in size. The flattening kinetics of the nanocluster deposition on thiol SAMs are shown to be mediated mainly by the thiol terminal group, as well as the deposition energy and the particle size distribution. On the other hand, a new mechanism for the penetration of the deposited nanoclusters through the monolayers is presented, which is fundamentally different from those reported for atom deposition on alkanethiols. The impinging cluster is shown to compress the thiol layer against the Au surface and subsequently intercalate at the thiol-Au interface. The compressed thiols try then to straighten and push the cluster away from the surface. Depending on the cluster size, this restoring force may or may not enable a covalent cluster-surface bond formation, giving rise to various cluster-surface binding patterns. Compression and straightening of the thiol molecules pinpoint the elastic nature of the SAMs, which has been investigated in this thesis using nanoindentation. The nanoindenation method has been applied to SAMs of varied tail groups, giving insight into the mechanical properties of thiol modified metal surfaces.

Singlet quenching of tetraphenylporphyrin and its metal derivatives by iron(III) coordination compounds

The quenching of fluorescence of the free-base tetraphenylporphyrin, H2TPP, and its metal derivatives, MgTPP and ZnTPP by diverse iron(III) complexes, [Fe(CN)6]3−, Fe(acac)3, [Fe(mnt)2]−, Fe(Salen)Cl, [Fe4S4(SPh)4]2−·, FeTPPCl and [Fe(Cp)2]+ has been studied both in homogeneous medium (CH3CN) and micellar media, SDS., CTAB and Triton X-100. The quenching efficiencies are analysed in terms of diffusional encounters and it has been possible to separate static quenching components. The quenching constants are dependent on the nature of the ligating atoms around iron(III) and also on the extent of π-conjugation of the ligands. The quenching mechanism has been investigated using steady-state irradiation experiments. Evidence for oxidative quenching by iron(III) complexes was obtained, though the spin multiplicities of the excited electronic states of iron(III) complexes permit both energy and electron transfer mechanisms for quenching of the singlet excited state of the porphyrins.

Group-VI metal-carbonyl-complexes of (amino)spirocyclic cyclotriphosphosphazenes

The reactions of (amino)spirocyclotriphosphazenes, N3P3(NMe2)4(NHCH2CH2NH) (1) and N3P3(NMe2)4(NHCH2CH2CH2NH) (2) with molybdenum- and tungsten-hexacarbonyls give complexes of the type [M(CO)4(L)] (L = 1 or 2) in which the phosphazenes act as bidentate chelating ligands via one of the phosphazene ring nitrogen atoms and one of the nitrogen atoms of the diaminoalkane moiety.

Studies of phosphazenes. Part 34. group 6 metal carbonyl complexes of bis(pyrazolyl)cyclotriphosphazenes

Reactions of the bis(3,5-dimethylpyrazol-1-yl)cyclotriphosphazenes gem-N3P3Ph4(C3HN2Me2)2 (L1) and N3P3(MeNCH2CH2O)2(C3HN2Me2)2 (L2) with [M(CO)6] (M = Mo or W) afford complexes of the type [M(CO)3L] (L = L1 or L2), which have been characterised by IR and NMR spectroscopic data. The structures of [Mo(CO)3L1], [W(CO)3L2] and the ligand L2 have been determined by single-crystal X-ray diffraction. The phosphazenes act as novel tridentate NNN-donor ligands with two pyrazolyl nitrogen atoms and one phosphazene ring nitrogen atom bonded to the metal atom

Synthesis, spectroscopic properties and biological evaluation of transition metal complexes of salicylhydrazone of anthranilhydrazide: X-ray crystal structure of copper complex

The transition metal complexes of salicylhydrazone of anthranilhydrazide (H2L) were synthesised. The structures of metal complexes were characterized by various spectroscopic [IR, NMR, UV-Vis, EPR], thermal and other physicochemical methods. The single-crystal X-ray diffraction study of [Cu(HL)Cl]center dot H2O reveal its orthorhombic system with space group P2(1)2(1)2 and Z=4. The copper center has a distorted square planar geometry with ONO and Cl as the donor atoms. The ligand and its metal chelates have been screened for their antimicrobial and anti-tubercular activities using serial dilution method. Metal complexes in general have exhibited better antibacterial and antifungal activity than the free ligand and in few cases better than the standard used. Among the bacterial strains used, the complexes are highly potent against Gram-positive strains compared to Gram-negative. Anti-tubercular activity exhibited by the Co(II) complex is comparable with the standard used. (C) 2011 Elsevier B. V. All rights reserved.

Stabilization of diborane(4) by transition metal fragments and a novel metal to pi Dewar-Chatt-Duncanson model of back donation

The feasibility of using transition metal fragments to stabilize B2H4 in planar configuration by donating 2 electrons to the boron moiety is investigated. Building upon the existing theoretical and experimental data and aided by the isolobal analogy, the model transition metal complexes Cr(CO)(4)B2H4 (6), Mn(CO)-CpB2H4 (7), Fe(CO)(3)B2H4 (8) and CoCpB2H4 (9) are chosen to illustrate this unique bonding feature bond strengthening with pi-back donation. Other possible types of complexes with B2H4 and the metal fragment are also explored and the energies are compared. One of the low energy isomers wherein the planar B2H4 interacts with the metal fragment in an in-plane fashion represents a unique case study for the Dewar-Chatt-Duncanson model. In this complex the back-donation from the metal fills the p bonding orbital between the two boron atoms thus forming a B=B double bond.

Performance analysis of boron nitride embedded armchair graphene nanoribbon metal-oxide-semiconductor field effect transistor with Stone Wales defects

We study the performance of a hybrid Graphene-Boron Nitride armchair nanoribbon (a-GNR-BN) n-MOSFET at its ballistic transport limit. We consider three geometric configurations 3p, 3p + 1, and 3p + 2 of a-GNR-BN with BN atoms embedded on either side (2, 4, and 6 BN) on the GNR. Material properties like band gap, effective mass, and density of states of these H-passivated structures are evaluated using the Density Functional Theory. Using these material parameters, self-consistent Poisson-Schrodinger simulations are carried out under the Non Equilibrium Green's Function formalism to calculate the ballistic n-MOSFET device characteristics. For a hybrid nanoribbon of width similar to 5 nm, the simulated ON current is found to be in the range of 265 mu A-280 mu A with an ON/OFF ratio 7.1 x 10(6)-7.4 x 10(6) for a V-DD = 0.68 V corresponding to 10 nm technology node. We further study the impact of randomly distributed Stone Wales (SW) defects in these hybrid structures and only 2.5% degradation of ON current is observed for SW defect density of 3.18%. (C) 2014 AIP Publishing LLC.

Syntheses and structural investigation of some alkali metal ion-mediated (LVO2-)-O-V (L2- = tridentate ONO ligands) species: DNA binding, photoinduced DNA cleavage and cytotoxic activities

Eight alkali metal ion-mediated dioxidovanadium(V), {(VO2L1-6)-O-V} A(H2O)n]proportional to, complexes for A = Li+, Na+, K+ and Cs+, containing tridentate aroylhydrazonate ligands coordinating via ONO donor atoms, are described. All the synthesised ligands and the metal complexes were successfully characterised by elemental analysis, IR, UV-Vis and NMR spectroscopy. X-ray crystallographic investigation of 3, 5-7 shows the presence of distorted NO4 coordination geometries for LVO2- in each case, and varying mu-oxido and/ or mu-aqua bridging with interesting variations correlated with the size of the alkali metal ions: with small Li+, no bridging-O is found but four ion aggregates are found with Na+, chains for K+ and finally, layers for Cs+. Two (5) or three-dimensional (3, 6 and 7) architectures are consolidated by hydrogen bonding. The dioxidovanadium(V) complexes were found to exhibit DNA binding activity due to their interaction with CT-DNA by the groove binding mode, with binding constants ranging from 10(3) to 10(4) M-1. Complexes 1-8 were also tested for DNA nuclease activity against pUC19 plasmid DNA which showed that 6 and 7 had the best DNA binding and photonuclease activity; these results support their good protein binding and cleavage activity with binding constants ranging from 104 to 105 M-1. Finally, the in vitro antiproliferative activity of all complexes was assayed against the HeLa cell line. Some of the complexes (2, 5, 6 and 7) show considerable activity compared to commonly used chemotherapeutic drugs. The variation in cytotoxicity of the complexes is influenced by the various functional groups attached to the aroylhydrazone derivative.

Physical Insights on the Ambiguous Metal-Graphene Interface and Proposal for Improved Contact Resistance

The ambiguous behavior of metal-graphene interface has been addressed in this paper using density functional theory and nonequilibrium Green's function formalism. For the first time, the fundamental chemistry of metal-graphene interface, in particular role of sp-hybridized and sp(2)-hybridized carbon atoms, has been emphasized and discussed in detail in this paper. It was discovered that the sp-hybridized sites at the edge of a graphene monolayer contribute to 40% of current conduction when compared with sp(2)-hybridized atom sites in the graphene-metal overlap region. Moreover, we highlighted the insignificance of an additional metal layer, i.e., sandwiched contact, due to lacking sp-hybridized carbon sites. A fundamental way of defining the contact resistance, while keeping chemical bonding in mind, has been proposed. The bonding insight has been further used to propose the novel ways of interfacing metal with graphene, which results in a 40% reduction in contact resistance.

Synthesis, structure, and photophysics of polypyridophenazine transition-metal complexes

The condensation of phenanthroline-5,6-dione (phendione) with polyamines is a versatile synthetic route to a wide variety of chelating ligands. Condensation with 2,3- napthalene diamine gives benzo[i]dipyrido[3,2-a:2',3'-c]phenazine (bdppz) a ligand containing weakly-coupled orbitals of benzophenazine (bpz) and 2,2' -bipyridinde(bpy) character. The bpy character gives Re and Ru complexes excited-state redox properties; intramolecular electron transfer (ET) takes place to the bpz portion of the ligand. The charge-separated state so produced has an extraordinarily-long 50 µs lifetime. The slow rate of charge recombination arises from a combination of extremely weak coupling between the metal center and the bpz acceptor orbital and Marcus "inverted region" behavior. Molecular orbital calculations show that only 3% the electron density in the lowest unoccupied molecular orbital lies on the bpy atoms of bdppz, effectively trapping the transferred electron on the bpz portion. The rate of charge recombination decreases with increasing driving force, showing that these rates lie in the inverted region. Comparison of forward and back ET rates shows that donor-acceptor coupling is four orders of magnitude greater for photoinduced electron transfer than it is for thermal charge recombination.

Condensation of phendione with itself or tetramines gives a series of binucleating tetrapyridophenazine ligands of incrementally-varying coordination-site separation. When a photoredox-active metal center is attached, excited-state energy and electron transfer to an acceptor metal center at the other coordination site can be studied as a function of distance. A variety of monometallic and homo- and heterodimetallic tetrapyridophenazine complexes has been synthesized. Electro- and magnetochemistry show that no ground-state interaction exists between the metals in bimetallic complexes. Excited-state energy and electron transfer, however, takes place at rates which are invariant with increasing donor-acceptor separation, indicating that a very efficient coupling mechanism is at work. Theory and experiment have suggested that such behavior might exist in extended π-systems like those presented by these ligands.

Condensation of three equivalents of 4,5-dimethyl-1,2-phenylenediamine with hexaketocyclohexane gives the trinucleating ligand hexaazahexamethyltrinapthalene (hhtn). Attaching two photredox-active metal centers and a third catalytic center to hhtn provides means by which multielectron photocatalyzed reactions might be carried out. The coordination properties of hhtn have been examined; X-ray crystallographic structure determination shows that the ligand's constricted coordination pocket leads to distorted geometries in its mono- and dimetallic derivatives.

Structure-, stereochemistry-, and metal-regulated DNA binding/cleaving molecules

In the cell, the binding of proteins to specific sequences of double helical DNA is essential for controlling the processes of protein synthesis (at the level of DNA transcription) and cell proliferation (at the level of DNA replication). In the laboratory, the sequence-specific DNA binding/cleaving properties of restriction endonuclease enzymes (secreted by microorganisms to protect them from foreign DNA molecules) have helped to fuel a revolution in molecular biology. The strength and specificity of a protein:DNA interaction depend upon structural features inherent to the protein and DNA sequences, but it is now appreciated that these features (and therefore protein:DNA complexation) may be altered (regulated) by other protein:DNA complexes, or by environmental factors such as temperature or the presence of specific organic molecules or inorganic ions. It is also now appreciated that molecules much smaller than proteins (including antibiotics of molecular weight less than 2000 and oligonucleotides) can bind to double-helical DNA in sequence-specific fashion. Elucidation of structural motifs and microscopic interactions responsible for the specific molecular recognition of DNA leads to greater understanding of natural processes and provides a basis for the design of novel sequence-specific DNA binding molecules. This thesis describes the synthesis and DNA binding/cleaving characteristics of molecules designed to probe structural, stereochemical, and environmental factors that regulate sequence-specific DNA recognition.

Chapter One introduces the DNA minor groove binding antibiotics Netropsin and Distamycin A, which are di- and tri(N-methylpyrrolecarboxamide) peptides, respectively. The method of DNA affinity cleaving, which has been employed to determine DNA binding properties of designed synthetic molecules is described. The design and synthesis of a series of Netropsin dimers linked in tail-to-tail fashion (by oxalic, malonic, succinic, or fumaric acid), or in head-to-tail fashion (by glycine, β-alanine, and γ-aminobutanoic acid (Gaba)) are presented. These Bis(Netropsin)s were appended with the iron-chelating functionality EDTA in order to make use of the technique of DNA affinity cleaving. Bis(Netropsin)-EDTA compounds are analogs of penta(N-methylpyrrolecarboxamide)-EDTA (P5E), which may be considered a head-to-tail Netropsin dimer linked by Nmethylpyrrolecarboxamide. Low- and high-resolution analysis of pBR322 DNA affinity cleaving by the iron complexes of these molecules indicated that small changes in the length and nature of the linker had significant effects on DNA binding/cleaving efficiency (a measure of DNA binding affinity). DNA binding/cleaving efficiency was found to decrease with changes in the linker in the order β-alanine > succinamide > fumaramide > N-methylpyrrolecarboxamide > malonamide >glycine, γ-aminobutanamide > oxalamide. In general, the Bis(Netropsin)-EDTA:Fe compounds retained the specificity for seven contiguous A:T base pairs characteristic of P5E:Fe binding. However, Bis(Netropsin)Oxalamide- EDTA:Fe exhibited decreased specificity for A:T base pairs, and Bis(Netropsin)-Gaba-EDT A:Fe exhibited some DNA binding sites of less than seven base pairs. Bis(Netropsin)s linked with diacids have C₂-symmmetrical DNA binding subunits and exhibited little DNA binding orientation preference. Bis(Netropsin)s linked with amino acids lack C₂-symmetrical DNA binding subunits and exhibited higher orientation preferences. A model for the high DNA binding orientation preferences observed with head-to-tail DNA minor groove binding molecules is presented.

Chapter Two describes the design, synthesis, and DNA binding properties of a series of chiral molecules: Bis(Netropsin)-EDTA compounds with linkers derived from (R,R)-, (S,S)-, and (RS,SR)-tartaric acids, (R,R)-, (S,S)-, and (RS,SR)-tartaric acid acetonides, (R)- and (S)-malic acids, N ,N-dimethylaminoaspartic acid, and (R)- and (S)-alanine, as well as three constitutional isomers in which an N-methylpyrrolecarboxamide (P1) subunit and a tri(N-methylpyrrolecarboxamide)-EDTA (P3-EDTA) subunit were linked by succinic acid, (R ,R)-, and (S ,S)-tartaric acids. DNA binding/cleaving efficiencies among this series of molecules and the Bis(Netropsin)s described in Chapter One were found to decrease with changes in the linker in the order β-alanine > succinamide > P1-succinamide-P3 > fumaramide > (S)-malicamide > N-methylpyrrolecarboxamide > (R)-malicamide > malonamide > N ,N-dimethylaminoaspanamide > glycine = Gaba = (S,S)-tartaramide = P1-(S,S)-tanaramide-P3 > oxalamide > (RS,SR)-tartaramide = P1- (R,R)-tanaramide-P3 > (R,R)-tartaramide (no sequence-specific DNA binding was detected for Bis(Netropsin)s linked by (R)- or (S)-alanine or by tartaric acid acetonides). The chiral molecules retained DNA binding specificity for seven contiguous A:T base pairs. From the DNA affinity cleaving data it could be determined that: 1) Addition of one or two substituents to the linker of Bis(Netropsin)-Succinamide resulted in stepwise decreases in DNA binding affinity; 2) molecules with single hydroxyl substituents bound DNA more strongly than molecules with single dimethylamino substituents; 3) hydroxyl-substituted molecules of (S) configuration bound more strongly to DNA than molecules of (R) configuration. This stereochemical regulation of DNA binding is proposed to arise from the inherent right-handed twist of (S)-enantiomeric Bis(Netropsin)s versus the inherent lefthanded twist of (R)-enantiomeric Bis(Netropsin)s, which makes the (S)-enantiomers more complementary to the right-handed twist of B form DNA.

Chapter Three describes the design and synthesis of molecules for the study of metalloregulated DNA binding phenomena. Among a series of Bis(Netropsin)-EDTA compounds linked by homologous tethers bearing four, five, or six oxygen atoms, the Bis(Netropsin) linked by a pentaether tether exhibited strongly enhanced DNA binding/cleaving in the presence of strontium or barium cations. The observed metallospecificity was consistent with the known affinities of metal cations for the cyclic hexaether 18-crown-6 in water. High-resolution DNA affinity cleaving analysis indicated that DNA binding by this molecule in the presence of strontium or barium was not only stronger but of different sequence-specificity than the (weak) binding observed in the absence of metal cations. The metalloregulated binding sites were consistent with A:T binding by the Netropsin subunits and G:C binding by a strontium or barium:pentaether complex. A model for the observed positive metalloregulation and novel sequence-specificity is presented. The effects of 44 different cations on DNA affinity cleaving by P5E:Fe were examined. A series of Bis(Netropsin)-EDTA compounds linked by tethers bearing two, three, four, or five amino groups was also synthesized. These molecules exhibited strong and specific binding to A:T rich regions of DNA. It was found that the iron complexes of these molecules bound and cleaved DNA most efficiently at pH 6.0-6.5, while P5E:Fe bound and cleaved most efficiently at pH 7.5-8.0. Incubating the Bis(Netropsin) Polyamine-EDTA:Fe molecules with K₂PdCl₄ abolished their DNA binding/cleaving activity. It is proposed that the observed negative metalloregulation arises from kinetically inert Bis(Netropsin) Polyamine:Pd(II) complexes or aggregates, which are sterically unsuitable for DNA complexation. Finally, attempts to produce a synthetic metalloregulated DNA binding protein are described. For this study, five derivatives of a synthetic 52 amino acid residue DNA binding/cleaving protein were produced. The synthetic mutant proteins carried a novel pentaether ionophoric amino acid residue at different positions within the primary sequence. The proteins did not exhibit significant DNA binding/cleaving activity, but they served to illustrate the potential for introducing novel amino acid residues within DNA binding protein sequences, and for the development of the tricyclohexyl ester of EDTA as a superior reagent for the introduction of EDT A into synthetic proteins.

Chapter Four describes the discovery and characterization of a new DNA binding/cleaving agent, [SalenMn(III)]OAc. This metal complex produces single- and double-strand cleavage of DNA, with specificity for A:T rich regions, in the presence of oxygen atom donors such as iodosyl benzene, hydrogen peroxide, or peracids. Maximal cleavage by [SalenMn(III)]OAc was produced at pH 6-7. A comparison of DNA singleand double-strand cleavage by [SalenMn(III)]⁺ and other small molecules (Methidiumpropyl-EDTA:Fe, Distamycin-EDTA:Fe, Neocarzinostatin, Bleomycin:Fe) is presented. It was found that DNA cleavage by [SalenMn(III)]⁺ did not require the presence of dioxygen, and that base treatment of DNA subsequent to cleavage by [SalenMn(III)]⁺ afforded greater cleavage and alterations in the cleavage patterns. Analysis of DNA products formed upon DNA cleavage by [SalenMn(III)] indicated that cleavage was due to oxidation of the sugar-phosphate backbone of DNA. Several mechanisms consistent with the observed products and reaction requirements are discussed.

Chapter Five describes progress on some additional studies. In one study, the DNA binding/cleaving specificities of Distamycin-EDTA derivatives bearing pyrrole N-isopropyl substituents were found to be the same as those of derivatives bearing pyrrole N-methyl substituents. In a second study, the design of and synthetic progress towards a series of nucleopeptide activators of transcription are presented. Five synthetic plasmids designed to test for activation of in vitro run-off transcription by DNA triple helix-forming oligonucleotides or nucleopeptides are described.

Chapter Six contains the experimental documentation of the thesis work.

Effects of chloride substitution on the chemical and physical properties and the crystallization behavior in heavy metal fluoride glasses

Effect of the substitutions of chloride for fluoride on the chemical and physical properties and the crystallization behavior in heavy metal fluoride glasses has been investigated. The characteristic temperature of the glass does not changed obviously when the fluoride was taken place by chloride. Compared with samples of being free of ErF3, the doping samples are more inclined to be surface crystallization. Optical basicity in the glass system increases with increasing the negative charge provided by the chloride atoms and the absorption peak red shifted is observed in absorption spectra. XRD measurements show that not a single crystalline phase appears in the heated glass samples, which indicate the substitutions of chloride for fluoride with a variety of crystalline precipitation trends. (c) 2007 Elsevier B.V All rights reserved.