Influence of glycosidic linkage on the nature of carbohydrate binding in beta-prism I fold lectins: An X-ray and molecular dynamics investigation on banana lectin-carbohydrate complexes

The three crystal structures reported here provide details of the interactions of mannose and the mannosyl-alpha-1,3-mannose component of a pentamannose with banana lectin and evidence for the binding of glucosyl-alpha-1,2-glucose to the lectin. The known structures involving the lectin include a complex with glucosyl-beta-1,3-glucose. Modeling studies on the three disaccharide complexes with the reducing end and the nonreducing end at the primary binding site are also provided here. The results of the Xray and modeling studies show that the disaccharides with an alpha-1,3 linkage prefer to have the nonreducing end at the primary binding site, whereas the reducing end is preferred at the site when the linkage is beta-1,3 in mannose/glucose-specific beta-prism I fold lectins. In the corresponding galactose-specific lectins, however, alpha-1,3-linked disaccharides cannot bind the lectin with the nonreducing end at the primary binding site on account of steric clashes with an aromatic residue that occurs only when the lectin is galactose-specific. Molecular dynamics simulations based on the known structures involving banana lectin enrich the information on lectin-carbohydrate interactions obtained from crystal structures. They demonstrate that conformational selection as well as induced fit operate when carbohydrates bind to banana lectin.

Organometallic chemistry of diphosphazanes .13. Palladium complexes of unsymmetrical diphosphazanes Ph(2)PN(Pr-i)PYY'

Unsymmetrical diphosphazanes Ph(2)PN(Pr-i)PYY' [YY' = O2C12H8 (L(1)), O2C20H12 (L(2)); Y = Ph and Y' = OC6H4Br-4 (L(3)), OC(6)H(4)Me-4 (L(4)), OC(6)H(3)Me(2)-3,5 (L(5)), N(2)C(3)HMe(2)-3,5 (L(6))] react with cis-[PdCl2(COD)] (COD = cycloocta-1,5-diene) giving the chelate complexes of the type cis-[PdCl2{eta(2)-Ph(2)PN(Pr-i)PYY'}] [YY' = O2C12H8 (1), O2C20H12 (2), Y = Ph and Y' = OC6H4Br-4 (3), OC(6)H(4)Me-4 (4), OC(6)H(3)Me(2)-3,5 (5), N(2)C(3)HMe(2)-3,5 (6)]. The P-N bond in 3 and 5 undergoes a facile cleavage in methanol solution to give cis-[PdCl2{eta(1)Ph(2)P(OMe)}{eta(1)-PhP(NHPri)(Y')}] [Y' = OC6H4Br-4 (7), OC(6)H(3)Me(2)-3,5 (8)]. Reactions of Pd-2(dba)(3) . CHCl3 (dba = dibenzylideneacetone) with the diphosphazanes Ph(2)PN(Pr-i)PPhY' [Y' = OC(6)H(4)Me-4 (L(4)), N(2)C(3)HMe(2)-3,5 (L(6)), N2C3H3 (L(7))] in the presence of MeI yields cis-[PdI2{eta(2)-Ph(2)PN(Pr-i)PPhMe}] (9); the P-O or P-N(pyrazolyl) bond of the starting ligands is cleaved and a p-C(Me) bond is formed. An analogous oxidative addition reaction in the presence of Ph(2)PN(Pr-i)PPh(2) (L(8)) yields cis-[PdI(Me)(eta(2)-L(8))] (10) and cis-[PdI2(eta 2-L(8))] (11). The structures of 8 and 9 have been determined by X-ray diffraction. Copyright (C) 1996 Elsevier Science Ltd

Di- and tri-metallic complexes containing two bridging cyclodiphosphazane ligands: the crystal structure of [MO2(CO)8{µ-cis-[PhNP(OC6H4Me-p)]2}2]

The reactions of the mononuclear cyclodiphosphazane complexes, cis-[Mo(CO)(4){cis-[PhNP(OR)](2)}(2)] with [Mo(CO)(4)(nbd)] (nbd = norbornadiene). [Mo(CO)(4)(NHC5H10)(2)] or [MCl(2)(cod)] (cod = cycloocta-1,5-diene) afforded the homobimetallic complexes; [Mo-2(CO)(8){mu-cis-[PhNP(OR)](2)}(2)] (R = C(5)H(4)Me-p 5 or CH2CF3 6) or the heterobimetallic complexes. [Mo-2(CO)(8){mu-cis-[PhNP(OE)](2)}(2)MCl(2)] (R = C(6)H(4)Me-p; M = Pd 7 or Pt 8). In all the above complexes, the two metal moieties are bridged by two cyclodiphosphazane ligands. The reactions of the mononuclear complexes, cis-[M(CO)(4)(A){cis-[PhNP(OC(6)H(4)Me-p)](2)}] with (M'Cl-2(cod)] afforded the trinuclear complexes, cis-[M'Cl-2[M(CO)(4)(A){cis-[PhNP(OC(6)H(4)Me-p)](2)}](2)] (M' = Pd, M = Mo, A = P(OMe)(3) 10; M' = Pt, M = Mo. A = P(OMe)(3) 11; M' = Pd. M = W. A = NHC5H10 12; M' = Pt, M = W. A = NHC5H10 13). The structure of the complex 5 has been determined by single-crystal X-ray crystallography.

Photocytotoxicity and DNA photocleavage activity of La(III) and Gd(III) complexes of phenanthroline bases

Lanthanide(II) complexes La(B)(acac)(3)] (1-3) and Gd(B)(acac)(3)] (4-6), where B is a N,N-donor phenanthroline base, viz., 1,10-phenanthroline (phen in 1, 4), dipyrido3,2-d:2',3'-f]quinoxaline (dpq in 2, 5) and dipyrido3,2-a:2',3'-c]phenazine (dppz in 3, 6), have been prepared and characterized. The Gd(111) complexes 4 6 are structurally characterized by single crystal X-ray crystallography. The complexes display GdO6N2 coordination with the ligands showing bidentate chelating mode of bonding. The complexes are non-electrolytic in aqueous DMF and exhibit ligand-centered absorption bands in the UV region. The dppz complexes show a band at 380 nm in DMF. The La(111) complexes are diamagnetic. The Gd(III) complexes are paramagnetic with magnetic moment that corresponds to seven unpaired electrons. The Complexes are avid binders to calf thymus DNA giving K-b values in the range of 4.7 x 10(4) 6.1 x 10(5) M-1 with a relative binding order: 3, 6 (dppz) > 2, 5 (dpq) > 1, 4 (phen). The binding data suggest DNA surface and/or groove binding nature of the complexes. The dpq and dppz complexes efficiently cleave SC DNA to its nicked circular form in UV-A light of 365 nm via formation of both singlet oxygen (O-1(2)) and hydroxyl radical (HO center dot) species. The dppz complexes 3 and 6 exhibit significant PDT effect in He La cervical cancer cells giving respective IC50 value of 460(+/- 50) and 530(+/- 30) nM in UV-A light of 365 rim, and are essentially non-toxic in dark with an IC50 value of >100 mu M. The dppz ligand alone is cytotoxic in dark and UV-A light. A significant decrease in the dark toxicity of the dppz base is observed on binding to the Ln(III) ion while retaining its photocytotoxicity.

Systematic crystallographic investigation of hydrogen-bonded networks involving monohydrogen tartrate-amine complexes: Potential materials for nonlinear optics

Crystal structures of six binary salts involving aromatic amines as cations and hydrogen tartrates as anions are presented. The materials are 2,6-xylidinium-L-monohydrogen tartrate monohydrate, C12H18O6.5N, P22(1)2(1), a = 7.283(2) Angstrom, b = 17.030(2) Angstrom, c = 22.196(2) Angstrom, Z = 8; 2,6-xylidinium-D-dibenzoyl monohydrogen tartrate, C26H25O8N, P2(1), a = 7.906(1) Angstrom, b = 24.757(1) Angstrom, c = 13.166(1) Angstrom, beta = 105.01(1)degrees, Z = 4; 2,3-xylidinium-D-dibenzoyl monohydrogen tartrate monohydrate, C26H26O8.5N, P2(1), a = 7.837(1) Angstrom, b = 24.488(1) Angstrom, c = 13.763(1) Angstrom, beta = 105.69(1)degrees, Z = 4; 2-toluidinium-D-dibenzoyl monohydrogen tartrate, C25H23O8N, P2(1)2(1)2(1), a = 13.553(2) Angstrom, b = 15.869(3) Angstrom, c = 22.123(2) Angstrom, Z = 8; 3-toluidinium-D-dibenzoyl monohydrogen tartrate (1:1), C25H23O8N, P1, a = 7.916(3) Angstrom, b = 11.467(6) Angstrom, c = 14.203(8) Angstrom, alpha = 96.44(4)degrees, beta = 98.20(5)degrees, = 110.55(5)degrees, Z = 2; 3-toluidinium-D-dibenzoyl tartrate dihydrate (1:2), C32H36O10N, P1, a = 7.828(3) Angstrom, b = 8.233(1) Angstrom, c = 24.888(8) Angstrom, alpha = 93.98 degrees, beta = 94.58(3)degrees, = 89.99(2)degrees, Z = 2. An analysis of the hydrogen-bonding schemes in terms of crystal packing, stoichiometric variations, and substitutional variations in these materials provides insights to design hydrogen-bonded networks directed toward the engineering of crystalline nonlinear optical materials.

Tribridged diruthenium complexes: A new structural motif

Dinuclear complexes containing a (mu-oxo)bis(mu-carboxylato) diruthenium (III) core have been prepared by a novel synthetic route using metal-metal bonded diruthenium(II,III) tetracarboxylates as precursors. The complexes have been structurally characterized and they are redox active. The terminal ligands play an important role in tuning the electronic structure of the core. The stability of the core is found to be dependent on the size and pi-acidic nature of the terminal ligand cis- to the mu-oxo ligand. The chemistry of such tribridged complexes is relatively new. The rapid growth of this chemistry is based on the discovery of similar core structures in several non-heme iron- and manganese-containing metalloproteins. The tribridged core presents a new structural motif in coordination chemistry. The chemistry of diruthenium complexes with a [Ru-2(mu-O) (mu-O(2)CR)(2)(2+)] core has been reviewed.

Copper(I) complexes of modified nucleobases and vitamin B3 as potential chemotherapeutic agents: In vitro and in vivo studies

Three new complexes of Cu(I) have been synthesized using ancillary ligands like thiopyrimidine (tp) a modified nucleobase, and nicotinamide (nie) or vitamin B3, and characterized by spectroscopy and X-ray crystallography. In vitro cytotoxicity studies of the complexes on various human cancer cell lines such as Colo295, H226, HOP62, K562, MCF7 and T24 show that Cu(PPh3)(2)(tp)Cl] and Cu(PPh3)(2)(tp)ClO4 (2) have in vitro cytotoxicity comparable to cisplatin. Complex Cu(nic)(3)PPh3]ClO4 (3) is non-toxic and increases the life span by about 55 % in spontaneous breast tumor model. DNA binding and cleavage studies show that complex (3) binds to calf thymus DNA with an apparent binding constant of 5.9 x 10(5)M and completely cleaves super-coiled DNA at a concentration of 400 mu M, whereas complexes (1) and (2) do not bind DNA and do not show any cleavage even at 1200 mu M. Thus, complex (3) may exhibit cytotoxicity Via DNA cleavage whereas the mechanism of cytotoxicity of (1) and (2) probably involves a different pathway.

Structure, Spectra and Redox Behaviour of Copper(11) Complexes of Bis( benzimidazoly1)diamine Ligands

The linear quadridentate ligand N,N'-bis(benzimidazoI-2-ylethyl)ethane-l,2-diamine (L') and its 1 - methylbenzimidazole analogue (L2) and homologues form 1 : 1 complexes with Cu(CIO,),; L' also forms complexes of the types CuL'X, where X = NO,, PF,, Br or CI and CuL'(X)Y where X = CI or Br and Y = CIO, or Br. Deep blue CuL1Br,*2H20 crystallizes in the monoclinic space group C2/c with Z = 4, a = 9.91 9(2), b = 16.626(3), c = 14.1 02(3) le\ and p = 94.39(2)". The structure was solved by Patterson and Fourier difference methods and refined by the least-squares technique to R = 0.064 for 2195 independent reflections with / > 1.50(/). The molecule lies on a two-fold axis symmetrically around Cu". The co-ordination around Cu" is found to be square planar with two amino nitrogens and two benzimidazole nitrogens forming the equatorial plane [CU-N 1.983(3) and 2.037(4) A]. The bromides are at longer distances [3.349(1) A] in axial sites. Ligand field and EPR spectra indicate that one bromide or chloride ion is axially co-ordinated to Cu" in [CuL1l2+. This ion exhibits quasi-reversible redox behaviour. Electrochemical studies of the dihalides in methanol have established the presence of [CuL'X,], [CuL'(X)]+ and [CuL'I2+ in equilibrium. In complexes with 565 [CuL4I2+ [L4 = N,Nbis( benzimidazol-2-ylmethyl)ethane-l,2-diamine] and 555 [CuL3] [L3 = N,N'-bis(1 -methylbenzimidazol- 2-ylmethyl)propane-l,3-diamine] chelate rings, Cull does not seem to lie in the N, square plane, as revealed by their low A values and irreversible electrochemical behaviour. The Cu"-Cu' redox potentials in methanol are in the order [CuL1I2+ < [CuL3I2+ < [CuL4I2+; this illustrates that sixmembered chelate rings are suitable to stabilize Cu", when CU-N 0 interactions are favourable.

Synthesis, properties and crystal structures of diastereomeric areneruthenium(II) chiral Schiff-base complexes

Diastereomers (SRu,Sc)-1a and (RRu,Sc)-1b, in a ratio of 85: 15 and formulated as [Ru(η-MeC6H4Pri-p)Cl(L*)], have been prepared by treating [{Ru(η-MeC6H4Pri-p)Cl2}2] with the sodium salt of (S)-α-methylbenzylsalicylaldimine (HL*) in tetrahydrofuran at –70 °C. The reaction of 1(1a+1b) with AgClO4 in acetone followed by an addition of PPh3 or 4-methylpyridine (4Me-py) leads to the formation of adducts [Ru(η-MeC6H4Pri-p)(PPh3)(L*)]ClO42[(SRu,Sc)2a, (FRu,Sc)2b] and [Ru(η-MeC6H4Pri-p)(4Me-py)(L*)]ClO43[(SRu,Sc)3a, (RRu,Sc)3b] in the diastereomeric ratios (SRu,Sc) : (RRu,Sc) of 2 : 98 and 76 : 24, respectively. Complex 1 crystallises with equal numbers of 1a and 1b molecules in an asymmetric unit of monoclinic space group P21 with a= 10.854(1), b= 17.090(1), c= 12.808(4)Å, β= 110.51(1)°, and Z= 4. The structure was refined to R= 0.0552 and R′= 0.0530 with 2893 reflections having I[gt-or-equal] 1.5σ(I). The absolute configurations of the chiral centres in the optically pure single crystal of the PPh3 adduct have been obtained from an X-ray study. Crystals of formulation [Ru(η-MeC6H4Pri-p)-(PPh3)(L*)]2[ClO4][PF6]·1.5 CHCl3, obtained in presence of both ClO4 and PF6 anions, belong to the non-centric triclinic space group P1 with a= 10.852(2), b= 14.028(1), c= 15.950(2)Å, α= 91.51(1), β= 105.97(1), γ= 106.11(1)°, and Z= 2. The final residuals were R= 0.0713, R′= 0.0752 with 7283 reflections having I[gt-or-equal] 2.5σ(I). The crystal structures of 1a,1b, and the PPh3 adduct (2b,2b′) consist of a ruthenium(II) centre bonded to a η-p-cymene, a bidentate chelating Schiff base, and a unidentate ligand (Cl or PPh3). The chirooptical properties of the complexes have been studied using 1H NMR and CD spectral data. The presence of a low-energy barrier for the intermediate involved in these reactions, showing both retention as well as inversion of the metal configuration, is discussed.

Theoretical studies of the spin states of macrocyclic aza-amido binuclear copper (II) complexes

The spin and charge excitation gaps and charge and spin density distributions have been studied in macrocyclic binuclear aza-amido copper (II) complexes employing a model Hamiltonian. The spin gaps depend on the σ-orbital occupancies, and for small gaps, the exchange integral between the σ orbitals of the bridging oxygen atoms, KOO, which is sensitive to geometry, determines the low-lying spin excitations. The singlet—singlet gaps also depend upon the σ-orbital occupancy but are weakly dependent upon KOO.

Organometallic chemistry of diphosphazanes. Rhodium(I) complexes of RN(PX2)2 (R = C6H5; X = OC6H5, OC6H4Br?p, R = CH3; X = OC6H5)

Reactions of [Rh(COD)Cl](2) with the ligand RN(PX(2))(2) (1: R=C6H5; X=OC6H5) give mono- or disubstituted complexes of the type [Rh-2(COD)Cl-2{eta(2)-C6H5N(P(OC6H5)(2))(2)}-] or [RhCl{eta(2)-C6H5N(P(OC6H5)(2))(2)}](2), depending on the reaction conditions. Reaction of 1 with [Rh(CO)(2)Cl](2) gives the symmetric binuclear complex, [Rh(CO)Cl{mu-C6H5N(P(OC6H5)(2))(2)}], whereas the same reaction with 2 (R=CH3; X=OC6H5) leads to the formation of an asymmetric complex of the type [Rh(CO)(mu-CO)Cl{mu-CH3N(P(OC6H5)(2))(2)}] containing both terminal and bridging CO groups. Interestingly the reaction of 3 (R=C6H5, X = OC6H4Br-p) with either [Rh(COD)Cl](2) or [Rh(CO)(2)Cl](2) leads only to the formation of the chlorine bridged binuclear complex, [RhCl{eta(2)-C6H5N(P(OC6H4Br-p)(2))(2)}](2). The structural elucidation of the complexes was carried out by elemental analyses, IR and P-31 NMR spectroscopic data.

Short-bite chiral diphosphazanes derived from (S)-?-methyl benzyl amine and their Pd, Pt and Rh metal complexes

New chiral diphosphazane ligands of the type Ph(2)PN(S-*CHMePh)PYY' {YY'= Ph(2) (2), O2C6H4 (3); Y= Ph, Y'= Cl {4a (SS), 4b (SR)}, N(2)C(3)HMe(2)-3,5 {5a (SR), 5b (SS)} are synthesised starting from a chiral aminophosphine, Ph(2)PNH(S-*CHMePh) (1). The structure of one of the diastereomer 5a has been confirmed by single crystal X-ray diffraction {Orthorhombic system, P2(1)2(1)2(1); a=10.456 (4), b=15.362 (7), c=17.379 (6) Angstrom, Z=4}. Transition metal mononuclear complexes [Rh{eta(2)-(Ph(2)P)(2)N- (S-*CHMePh)}(2)](+)(BF4)(-) (6), [PdCl2{eta(2)-(Ph(2)P)(2)N(S-*CHMePh)}] (7) and [PtCl2{eta(2)-(Ph(2)P)(2)N- (S-*CHMePh)}] (8) have also been synthesised. The structure of the palladium complex 7 is solved by X-ray crystallography {Orthorhombic system, P2(1)2(1)2(1); a=8.746 (2), b=18.086 (2), c=20.811 (3) Angstrom, Z=4}. All these compounds are characterised by micro analyses, IR and NMR spectroscopic data.

Synthesis and studies on pyridinium chlorofluoro complexes of indium and bismuth

Pyridinium trichlorotrifluoroindate, (C5H5NH)(3)InCl3F3, and pyridinium trichlorofluorobismuthate, C5H5NHBiCl3F, have been synthesised by the reaction of pyridinium poly(hydrogen fluoride), PPHF, with InCI3 and BiCl3, respectively. These new complexes have been characterised by chemical and thermal analysis, NMR (H-1 and F-19) and infrared spectroscopy, and powder X-ray diffraction methods

Synthesis, structure and properties of monomeric complexes obtained from the cleavage of a (?-oxo)bis(?-carboxylato) diruthenium(III) core

Reaction of [Ru2O(O(2)CR)(2)(MeCN)(4)(PPh(3))(2)](ClO4)(2) (1) with 1,2-diaminoethane (en) in MeOH-H2O yielded a mixture of products from which a diamagnetic ruthenium(II) complex [Ru(MeCN)(en)(2)(PPh(3))](ClO4)(2) (2) and a paramagnetic ruthenium(III) species [Ru(O(2)CR)(en)(2)(PPh(3))](BPh(4))(2) (3) (R = Ph, a; C6H4-p-Me, b; C6H4-p-OMe, c) were isolated and characterized. The crystal structure of complex 2, obtained by X-ray diffraction analysis, shows a cis arrangement of the unidentate ligands in this octahedral complex. Complex 3 displays an axial EPR spectrum. Complex 2 undergoes two successive irreversible metal-centred one-electron oxidation processes at 1.13 and 1.33 V vs SCE in MeCN-0.1 M [NBu(4)(n)]ClO4 at 50 mV s(-1). The mechanistic aspects of the core cleavage reactions in 1 are discussed.