Role of the Central Metal Ion and Ligand Charge in the DNA Binding and Modification by Metallosalen Complexes

Several metal complexes of three different functionalized salen derivatives have been synthesized. The salens differ in terms of the electrostatic character and the location of the charges. The interactions of such complexes with DNA were first investigated in detail by UV−vis absorption titrimetry. It appears that the DNA binding by most of these compounds is primarily due to a combination of electrostatic and other modes of interactions. The melting temperatures of DNA in the presence of various metal complexes were higher than that of the pure DNA. The presence of additional charge on the central metal ion core in the complex, however, alters the nature of binding. Bis-cationic salen complexes containing central Ni(II) or Mn(III) were found to induce DNA strand scission, especially in the presence of co-oxidant as revealed by plasmid DNA cleavage assay and also on the basis of the autoradiogram obtained from their respective high-resolution sequencing gels. Modest base selectivity was observed in the DNA cleavage reactions. Comparisons of the linearized and supercoiled forms of DNA in the metal complex-mediated cleavage reactions reveal that the supercoiled forms are more susceptible to DNA scission. Under suitable conditions, the DNA cleavage reactions can be induced either by preformed metal complexes or by in situ complexation of the ligand in the presence of the appropriate metal ion. Also revealed was the fact that the analogous complexes containing Cu(II) or Cr(III) did not effect any DNA strand scission under comparable conditions. Salens with pendant negative charges on either side of the precursor salicylaldehyde or ethylenediamine fragments did not bind with DNA. Similarly, metallosalen complexes with net anionic character also failed to induce any DNA modification activities.

A novel amino acid racemization in vitamin b6-amino acid schiff base copper complexes: crystal structures of aquo (5'-phosphopyridoxylidene-dl-tyrosinato) copper(II) 3.5H2O and aquo (5'-phosphopyridoxylidene-dl-phenylalaninato) copper(II) 2.5H2O

A novel racemization observed in the Vitamin B6-amino acid Schiff base complexes, aquo (5'-phosphopyridoxylidene-l-tyrosinato) copper(II) and aquo (5'-phosphopyridoxylidene-l-phenylalaninato) copper(II) is described. The racemization taking place in solution under mild acidic conditions (pH 5-6) was confirmed by CD studies and the products were characterized by single crystal X-ray diffraction. The structures of both complexes show almost parallel orientation of the aromatic side chain and the pyridoxal II-system. The activation of the αCsingle bondH group due to the intermolecular II- interaction is probably the reason for the unusual racemization observed.

X-ray studies on crystalline complexes involving amino acids and peptides. XXIII. Variability in ionization state, conformation and molecular aggregation in the complexes of succinic acid with DL- and L-lysine

Crystalline complexes of succinic acid with DL- and L-lysine have been prepared and analysed by X-ray diffraction. DL-Lysine complex: C6HIsN202 + 1 2- 1 ~C4H404 .~C4H604, Mr -- 264"2, PI, a = 5"506 (4), =8.070(2), c=14.089(2) A,, a=92.02(1), /3= 100"69 (3), y = 95"85 (3) ~>, Z = 2, Dx = 1"44 g cm -3, R = 0.059 for 2546 observed reflections. Form I of the e-lysine complex: C6HIsN20-, ~ .C4H504, Mr = 264.2, P1, a = 5" 125 (2), b = 8"087 (1), c = 8"689 (1) A,, a = 112.06 (1), /3 = 99.08 (2), y = 93"77(2) °, Z--l, D,,,=1"34(3), Dx=l"34gcm 3 R = 0.033 for 1475 observed reflections. Form II of + I 2- the e-lysine complex: C6H15N202 .,iC4H404 .- 1 I ") 4C4H604.4(C4HsO4""H'"CaH404)" , Mr = 264"2, P1, a = 10.143 (4), b = 10.256 (2), c = 12"916 (3) A,, a = 105.00 (2),/3 = 99-09 (3), y = 92"78 (3)::, Z = 4, Dm= 1"37(4), D,.= 1.38gcm 3, R=0.067 for 2809 observed reflections. The succinic acid molecules in the structures exhibit a variety of ionization states. Two of the lysine conformations found in the complexes have been observed for the first time in crystals containing lysine. Form II of the L-lysine complex is highly pseudosymmetric. In all the complexes, unlike molecules aggregate into separate alternating layers. The basic element of aggregation in the lysine layer in the complexes is an S2-type head-to-tail sequence. This element combines in different ways in the three structures. The basic element of aggre gation in the succinic acid layer in the complexes is a hydrogen-bonded ribbon. The ribbons are interconnected indirectly through amino groups in the lysine layer.

Stereospecific photodimerization of coumarins in crystalline inclusion complexes. Molecular and crystal structure of 1:2 complex of (S,S)-(-)-1,6-bis(o-chlorophenyl)-1,6-diphenyl-hexa-2,4-diyne-1,6-diol and coumarin

Proximity of molecules is a crucial factor in many solid- state photochemical processes.'S2 The biomolecular photodimerization reactions in the solid state depend on the relative geometry of reactant molecules in the crystal lattice with center-to-center distance of nearest neighbor double bonds of the order of ca. 4 A. This fact emanates from the incisive studies of Schmidt and Cohen.2 One of the two approaches to achieve this distance requirement is the so-called "Crystal-Engineering" of structures, which essentially involves the introduction of certain functional groups that display in-plane interstacking interactions (Cl...Cl, C-He-0, etc.) in the crystal The chloro group is by far the most successful in promoting the /3- packing m ~ d e ,th~o,u~gh recent studies have shown its limitations? Another approach involves the use of constrained media in which the reactants could hopefully be aligned.

4-Nitro and 4-chloro pyridine-N-oxide complexes of lanthanide perchlorates

Adducts of lanthanide perchlorates with 4-nitro and 4-chloro pyridine-Noxides (4-NPNO and 4-CPNO respectively) have been synthesised for the first time and characterised by analysis, electrolytic conductance, infrared, proton-NMR and electronic spectral data. The complexes are of the compositions Ln2(NPNO)15 (ClO4)6 (Ln = La, Pr, Nd and Gd), Tb(NPNO), (C1O4)6), Ln2(NPNO)13 (C1O4)6) (Ln = Dy, Ho, and Yb); Ln (CPNO)8 (C104)3) (Ln = La, Pr, Nd, Tb, Dy, Ho and Yb) and Ln(CPNO), (C1O4)3) (Ln = Sm and Gd). Conductivity and IR data provide evidence for the non-coordinated nature of the perchlorate groups. IR and NMR spectra suggest coordinationvia the oxygen of the N-oxide group. Electronic spectral shapes of the Nd+3 and Ho+3 complexes are interpreted in terms of eight-and seven-coordinate environments in the case of 4-NPNO complexes and eight-coordination in the case of 4-CPNO complexes. IR data indicate bridged structure in NPNO complexes of lanthanides other than Tb.

Metal-Nucleotide Interactions: Crystal Structures of Alkali (Li+, Na+, K+) and Alkaline Earth (Ca2+, Mg2+) Metal Complexes of Adenosine 2'-Monophosphate

Crystal structures of lithium, sodium, potassium, calcium and magnesium salts of adenosine 2'-monophosphate (2'-AMP) have been obtained at atomic resolution by X-ray crystallographic methods. 2'-AMP.Li belongs to the monoclinic space group P21 with a = 7.472(3)Å, b = 26.853(6) Å, c = 9.184(1)Å, b = 113.36(1)Å and Z= 4. 2'-AMP.Na and 2'-AMP.K crystallize in the trigonal space groups P31 and P3121 with a = 8.762(1)Å, c = 34.630(5)Å, Z= 6 and a = 8.931(4), Åc = 34.852(9)Å and Z= 6 respectively while 2'-AMP.Ca and 2'-AMP.Mg belong to space groups P6522 and P21 with cell parameters a = 9.487(2), c = 74.622(13), Z = 12 and a = 4.973(1), b = 10.023(2), c = 16.506(2), beta = 91.1(0) and Z = 2 respectively. All the structures were solved by direct methods and refined by full matrix least-squares to final R factors of 0.033, 0.028, 0.075, 0.069 and 0.030 for 2'-AMP.Li, 2'-AMP.Na, 2'- AMP.K, 2'-AMP.Ca and 2'-AMP.Mg, respectively. The neutral adenine bases in all the structures are in syn conformation stabilized by the O5'-N3 intramolecular hydrogen bond as in free acid and ammonium complex reported earlier. In striking contrast, the adenine base is in the anti geometry (cCN = -156.4(2)°) in 2'-AMP.Mg. Ribose moieties adopt C2'-endo puckering in 2'-AMP.Li and 2'-AMP.Ca, C2'-endo-C3'-exo twist puckering in 2'-AMP.Na and 2'-AMP.K and a C3'-endo-C2'-exo twist puckering in 2'-AMP.Mg structure. The conformation about the exocyclic C4'-C5' bond is the commonly observed gauche-gauche (g+) in all the structures except the gauche- trans (g-) conformation observed in 2'-AMP.Mg structure. Lithium ions coordinate with water, ribose and phosphate oxygens at distances 1.88 to 1.99Å. Na+ ions and K+ ions interact with phosphate and ribose oxygens directly and with N7 indirectly through a water oxygen. A distinct feature of 2'-AMP.Na and 2'-AMP.K structures is the involvement of ribose O4' in metal coordination. The calcium ion situated on a two-fold axis coordinates directly with three oxygens OW1, OW2 and O2 and their symmetry mates at distances 2.18 to 2.42Å forming an octahedron. A classic example of an exception to the existence of the O5'-N3 intramolecular hydorgen bond is the 2'-AMP.Mg strucure. Magnesium ion forms an octahedral coordination with three water and three phosphate oxygens at distances ranging from 2.02 to 2.11Å. A noteworthy feature of its coordination is the indirect link with N3 through OW3 oxygen resulting in macrochelation between the base and the phosphate group. Greater affnity of metal clays towards 5' compared to 2' and 3' nucleotides (J. Lawless, E. Edelson, and L. Manring, Am. Chem. Soc. Northwest Region Meeting, Seattle. 1978) due to macrochelation infered from solution studies (S. S. Massoud, H. Sigel, Eur. J. Biochem. 179, 451-458 (1989)) and interligand hydrogen bonding induced by metals postulated from metal-nucleotide structures in solid state (V. Swaminathan and M. Sundaralingam, CRC. Crit. Rev. Biochem. 6, 245-336 (1979)) are borne out by our structures also. The stacking patterns of adenine bases of both 2'-AMP.Na and 2'-AMP.K structures resemble the 2'-AMP.NH4 structure reported in the previous article. 2'-AMP.Li, 2'-AMP.Ca and 2'-AMP.Mg structures display base-ribose O4' stacking. An overview of interaction of monovalent and divalent cations with 2' and 5'-nucleotides has been presented.

Complexes of lanthanide perchlorates with N,N,N′,N′-tetramethyl-α-carboxamido-O-anisamide and N,N′-di-t-butyl-α-carboxamido-O-anisamide

A survey of the literature on lanthanide coordination compounds reveals that ligands involving ether oxygens as donor atoms have received very little attention [ 11. Only recently have the complexes of lanthanides with cyclic polyethers been characterized [l-3]. We report in this communication that interaction of rareearth perchlorates with two new ligands namely N,N,N’,N’-tetramethyl-u-carboxamido-Oanisamide (TMCA) and N,N’-di-t-butyl-crcarboxamido- 0-anisamide (DTBCA). The two ligands are potentially tridentate possessing two amide moieties and an ether linkage in between. The isolated complexes have been characterized by analysis, electrolytic conductance, infrared and electronic spectra. The ‘H and “C NMR spectra for the diamagnetic La3+ and Y3+ complexes are also discussed.

Lanthanide perchlorate complexes of picolinamide-N-oxide and 4-chloro pyridine 2-aldoxime-N-oxide

Abstract is not available.

Palladium(II) and platinum(II) complexes of beta-functionalized ethyl selenolates: Effect of substitution on synthesis, reactivity, spectroscopy, structures and thermal behavior

Sodium ethylselenolates with functional groups X (where X = -OH, -COOH, -COOMe and -COOEt) at beta-carbon were prepared in situ by reductive cleavage of corresponding diselenide with NaBH4 either in methanol or aqueous ammonia. Treatment of these selenolates with [M2Cl2(mu-Cl)(2)(PR'(3))(2)] (M = Pd or Pt; PR'(3) = PMePh2, PnPr(3)) in different stoichiometry yielded various bi- and tri-nuclear complexes. The homoleptic hexanuclear complexes [Pd(mu-SeCH2CH2X)(2)](6) (X = OH, COOH, COOEt), were obtained by reacting Na2PdCl4 with NaSeCH2CH2X. All these complexes have been fully characterized. Molecular structures of ethylselenolates containing hydroxyl and carboxylic acid groups revealed solid state associated structures through inter-molecular hydrogen bond interactions. Trinuclear complex, [Pd3Cl2(mu-SeCH2CH2COOH)(4)(PnPr(3))(2)] (3a), was disposed in a boat form unlike chair conformation observed for the corresponding methylester complex. The effect of beta-functionality in ethylselenolate ligands towards reactivity, structures and thermal properties of palladium and platinum complexes has been extensively Studied.

Ruthenium(II)-CO complexes of N-[(2-pyridyl)methyliden]-alpha(or beta)-aminonaphthalene: Synthesis, spectral studies, crystal structure, redox properties and DFT calculation

The characterization and properties of trans-(X)-[RuX2(CO)(2)(alpha/beta-NaiPy)] (1, 2) (alpha-NaiPy (a), beta-NaiPy (b); X = Cl (1), I (2)) are described in this work. The structures are confirmed by single crystal X-ray diffraction studies. Reaction of these compounds with Me3NO in MeCN has isolated monocarbonyl trans-(X)-RuX2(CO)(MeCN)(alpha/beta-NaiPy)] (3, 4). The complexes show intense emission properties. Quantum yields of 1 and 2 (phi= 0.02-0.08) are higher than 3 and 4 (phi = 0.006-0.015). Voltammogram shows higher Ru(III)/Ru(II) (1.3-1.5 V) potential of 1 and 2 than that of 3 and 4 (0.8-0.9 V) that may be due to coordination of two pi-acidic CO groups in former. The electronic spectra and redox properties of the complexes are compared with the results obtained by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) using polarizable continuum model (CPCM).

Co(II) and Cr(III) complexes of formate-formamide mixed ligands: synthesis, structures, single crystal-to-single crystal transformation and magnetic behaviour

Solvothermal treatment of an equimolar mixture of Co(NO3)(2)center dot 6H(2)O, HCONH2 and NaN3 in MeOH at 100 degrees C yielded a three-dimensional NaCl type network Co(HCOO)(2)(HCONH2)(2) center dot HCONH2 (1a) containing formamides in the pores of the structure. Solvated pink 1a undergoes single crystal-to-single crystal (SCSC) transformation at 215 degrees C to form the desolvated dark brown product Co(HCOO)(2)-( HCONH2)(2) (1b) with the retention of the original framework. Reversible single crystal-to-single crystal transformation of 1b (brown) to 1a (pink) in the presence of excess formamide was also established at room temperature. The coordination environment around Co(II) in both 1a and 1b is octahedral with a CoN2O4 coordination composition. A similar reaction replacing Co(II) by Cr(III) produced a heterometallic 3D extended network Na[Cr(HCOO)(4)(HCONH2)(2)]center dot 2H(2)O (2a) at 100 degrees C. An increase in reaction temperature to 150 degrees C produced a simple mononuclear complex Cr(HCOO)(3)(HCONH2)(3) center dot 3H(2)O (2b). Variable temperature magnetic studies revealed the presence of a canting phenomena in both 1a and 1b, and hysteresis loop in the field dependent magnetisation plot at 2 K whereas complex 2a is simply paramagnetic in nature.

Two highly unsymmetrical tetradentate (N3O) Schiff base copper(II) complexes: Template synthesis, structural characterization, magnetic and computational studies

Two new copper(II) complexes, [Cu-2(L-1)(2)](ClO4)(2) (1) and [Cu(L-2)(ClO4)] (2), of the highly unsymmetrical tetradentate (N3O) Schiff base ligands HL1 and HL2 (where HL1 = N-(2-hydroxyacetophenone)-bis-3-aminopropylamine and HL2 = N-(salicyldehydine)-bis-3-aminopropylamine) have been synthesised using a template method. Their single crystal X-ray structures show that in complex 1 two independent copper(II) centers are doubly bridged through sphenoxo-O atoms (O1A and O1B) of the two ligands and each copper atom is five-coordinated with a distorted square pyramidal geometry. The asymmetric unit of complex 2 consists of two crystallographically independe N-(salicylidene) bis(aminopropyl)amine-copper(II) molecules, A and B, with similar square pyramidal geometries. Cryomagnetic susceptibility measurements (5-300 K) on complex 1 reveal a distinct antiferromagnetic interaction with J=-23.6 cm(-1), which is substantiated by a DFT calculation (J=-27.6 cm(-1)) using the B3LYP functional. Complex 1, immobilized over highly ordered hexagonal mesoporous silica, shows moderate catalytic activity for the epoxidation of cyclohexene and styrene in the presence of TBHP as an oxidant.

Are Metallocene-Acetylene (M = Ti, Zr, Hf) Complexes Aromatic Metallacyclopropenes?

The bonding nature of metallocene acetylene complexes Cp2M(eta(2)-H3SiC2SiH3) 1M and CP2M (eta(2)- HC2H) 1M' (M = Ti, Zr, Hf) wits studied by density functional theory method. It is found that this acetylene complex has indeed it metallacyclopropene moiety with two in-plane M-C sigma-bonds and one out-of-plane pi-bond interacting with the metal center, resulting in the formation of it delocalized three-center and two-electron (3c-2e) system. Along with its delocalized out-of-plane bonding, this complex has been characterized its aromatic on the basis of the computed stabilizing energy and negative nucleus-independent chemical shifts (NICS). The aromatic stabilization increases from Ti to Zr and Hf, and this is because of the increased charge separation between the CP2M fragment and the H3SiC2SiH3 (also HC2H) unit. The decrease of the M-C bond length from Zr to Hf is ttributed to the increased s character of both M and C hybridization of the M-C a-bonds.

Cytotoxicity of half sandwich ruthenium(II) complexes with strong hydrogen bond acceptor ligands and their mechanism of action

Neutral and cationic organometallic ruthenium(II) piano stool complexes of the type [(eta(6)-cymene)R-uCl(X)(Y)] (complexes R1-R8) has been synthesized and characterized. In cationic complexes, X, Y is either a eta(2) phosphorus ligand such as 1,1-bis(diphenylphosphino)methane (DPPM) and 1,2-bis(diphenylphosphino)ethane (DPPE) or partially oxidized ligands such as 1,2-bis(diphenylphosphino)methane monooxide (DPPMO) and 1,2-bis(diphenylphosphino)ethane monooxide (DPPEO) which are strong hydrogen bond acceptors. In neutral complexes. X is chloride and Y is a monodentate phosphorous donor. Complexes with DPPM and DPPMO ligands ([(eta(6)-cymene)Ru(eta(2)-DPPM)Cl]PF6 (R2), [(eta(6)-cymene)Ru(eta(2)-DPPMO)Cl]PF6 (R3), [(eta(6)-cymene)Ru(eta(1)-DPPM)Cl-2] (R5) and [(eta(6)-cymene)Ru(eta(1)-DPPMO)Cl-2] (R6) show good cytotoxicity. Growth inhibition study of several human cancer cell lines by these complexes has been carried out. Mechanistic studies for R5 and R6 show that inhibition of cancer cell growth involves both cell cycle arrest and apoptosis induction. Using an apoptosis PCR array, we identified the sets of antiapoptotic genes that were down regulated and pro-apoptotic genes that were up regulated. These complexes were also found to be potent metastasis inhibitors as they prevented cell invasion through matrigel. The complexes were shown to bind DNA in a non intercalative fashion and cause unwinding of plasmid DNA in cell-free medium by competitive ethidium bromide binding, viscosity measurements, thermal denaturation and gel mobility shift assays.