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A systematic and comparative binding study between serum-albumins (SA) and a series of monomeric nickel(II)-Schiff-base-complexes (NSCs), which might be imperative to investigate the function of SA behind nickel allergy, has been carried out through docking and different spectroscopic techniques. The initial docking studies indicate structure-dependent selective hydrophobic and hydrophilic interactions. The pyridine and phenyl containing NSCs, which are more aromatic, show better π–π staking compared to pyrrole one. Again all the NSCs bind with BSA though amino acid residues of IB domain affecting local environment of the Trp-134 surrounded by both hydrophobic and hydrophilic residues instead of the hydrophobically buried Trp-212. In HSA the hydophobically buried Trp-214 is influenced by NSCs. The experimental results nicely support the docking outcomes. The changes in Gibbs free energy, binding affinity and the nature of hydrophilic/hydrophobic interactions of NSC–SA systems indicate greater accessibility of N2O2 donor set complex compared to N4 one towards SA. Quantum chemical structure optimizations support the better planarity of NSC with N2O2 which provides better binding. Therefore the structural variation of N2O2 donor set complexes becomes much more useful compared to N4 one to search out the most compatible NSC towards SAs.

The structural effects of different copper(II) and nickel(II) Schiff base complexes on hen egg white lysozyme (HEWL) have been investigated through steady state and time resolved absorption and fluorescence, and circular dichroism spectroscopy. The Schiff base ligands with N4 donor atoms show both hydrophobic and hydrophilic interactions, however hydrophilic interaction prevails with ligands having N2O2 donor atoms. Variation of metal ions from Cu2+ to Ni2+ with each type of Schiff base ligand increases the probability of hydrophilic over hydrophobic interactions, which supports their significance in regulating the binding affinity between HEWL and metal complexes. On photo-excitation the complexes comprising of Cu2+ ion instead of Ni2+ ion and ligands with N4 donor system rather than N2O2 donor system, increases the probability of intersystem crossing to populate the corresponding triplet state as observed from laser flash photolysis study. The better binding affinity of nickel complexes with different selectivities compared to copper complexes towards HEWL emphasizes the potentiality of less explored nickel complexes in drug–protein interactions.

Here we report a systematic and comparative study to define a correlation between the structure and function of a series of simple, biologically active small inorganic Schiff base copper complexes for the occurrence of charge transfer phenomenon in calf thymus DNA (CT-DNA) using transient absorption spectroscopy corroborated with magnetic field effect. Four copper(II) Schiff base complexes with differently substituted heterocyclic ligands with antioxidant activity have been used. The binding constants of the order of ∼104 support the moderate binding affinity of the complexes towards CT-DNA. The methyl-substituted pyrrole complex shows maximum binding affinity (Kb: 8.33 × 104) compared to others. The occurrence of photoinduced electron transfer (PET) from CT-DNA to pyrrole containing complexes has been confirmed by identifying the corresponding transient radical ions whereas the extent of PET with pyridine substituted complexes is too small to be observed. The increase of the yield of radical ions in presence of magnetic field depicts that the initial spin correlation in geminate radical ion pair is triplet. The difference between experimental and calculated B½ values, the measure of hyperfine interactions (HFI) present in the system, arises due to hole hopping through intrastrand and interstrand DNA bases. The unsubstituted pyrrole complexes cleave DNA much more than the methyl-substituted one. Therefore, the probability of intrastrand superexchange increases with methyl-substituted complexes, that reduces the rate of hole hopping and hence the B½ value.

It has been spectroscopically monitored that a mononuclear nickel(II)-Schiff base complex {[NiL]·CH(3)OH=NSC} exhibits greater binding affinity for bovine serum albumin (BSA) than that of its human counterpart (HSA). Moreover the modes of binding of NSC with the two serum albumins also differ significantly. Docking studies predict a relatively rare type of 'superficial binding' of NSC at domain IIB of HSA with certain mobility whereas for BSA such phenomena has not been detected. The mobile nature of NSC at domain IIB of HSA has been well correlated with the spectroscopic results. It is to be noted that thermodynamic parameters for the NSC interaction also differ for the two serum albumins. Occurrence of energy transfer between the donor (Trp of BSA and HSA) and acceptor (NSC) has been obtained by means of Förster resonance energy transfer (FRET). The protein stability on NSC binding has also been experimented by the GuHCl-induced protein unfolding studies. Interestingly it has been found that NSC-HSA interaction enhances the protein stability whereas NSC-BSA binding has no such impact. Such observations are indicative of the fact that the conformation of NSC is responsible in recognizing the two serum albumins and selectively enhancing protein stability.

International audience; Three new complexes of cobalt, manganese, and zinc have been synthesized using a hydrazone Schiff base ligand {(E)-N′-[1-(2-hydroxyphenyl)ethylidene]acetohydrazide} (LH2) produced by the 1:1 condensation of acetic hydrazide and 2-hydroxyacetophenone. The ligand has shown three different coordination modes in the three complexes: a monoanionic tridentate coordination mode with the CoII complex ([Co(LH)2]·CH3OH, 1), a dianionic tridentate coordination mode with the MnIV complex ([Mn(L)2], 2), and monoanionic μ2-phenoxo-bridged tridentate coordination mode with the ZnII complex ([Zn(LH)(OOCCF3)]2, 3). All three complexes show interesting supramolecular architectures, especially for 3 a nanoporous supramolecular (4, 4) grid 2D framework is formed. The ligand and the complexes are well characterized by elemental analysis, IR and UV–vis spectroscopy. The spin states of the CoII and MnIV metal ions and hence the coordination modes of the ligand in these complexes are in good agreement with the EPR spectroscopic data. The fluorescence emission spectra of LH2 and the zinc complex 3 are measured in acetonitrile solution as well as in solid state.

A dicyanoamide-bridged 2D polynuclear zinc(II) complex having formula [Zn2(L)(μ-dca-κN1κN5)2]n, 1 has been synthesized using the Schiff base ligand N,N′-bis(salicylidene)-1,3-diaminopentane, (H2L) ...

International audience; By slightly changing the synthetic conditions, we have prepared two closely related linear tetranuclear CuII complexes with the symmetrical ONNO donor tetradentate Schiff-base ligand [H2L = (OH)C6H4(CH3)Cdouble bond; length as m-dashN(CH2)3Ndouble bond; length as m-dashC(CH3)C6H4(OH)] and with azide ions. These two distinctly coloured crystalline products were characterized by elemental analysis, IR and UV–Vis spectroscopy, CV, EPR spectra and variable temperature magnetic measurements. Single crystal X-ray diffraction studies of the green [Cu4(μ-L)2(μ1,1-N3)2(N3)2] (1) and the red [Cu4(μ-L)2(μ1,1-N3)2(N3)2(H2O)2] (2) crystals show that the coordination environment of the two μ-phenoxo and μ1,1-azido bridged isomorphous tetranuclear CuII complexes are slightly different. Thus, both complexes are formed by very similar building units, although with a significant variation in the bridging Cu–O(phenoxo)–Cu and Cu–N(azido)–Cu bond angles. The consequences of these structural variations on the magnetic properties have been investigated from both the experimental and theoretical points of view by variable temperature magnetic measurements and DFT calculations.

Two terdentate NNO donor Schiff base ligands CH 3 C(OH) CHC(CH 3 ) NCH 2 C 5 H 4 N [ HL 1 ] and C 6 H 5 C(OH) CHC(CH 3 ) NCH 2 C 5 H 4 N [ HL 2 ] were used to synthesize two mononuclear square planar copper(II) complexes, [Cu L 1 (CF 3 COO)] ( 1 ) and [Cu L 2 (CF 3 COO)] ( 2 ). The complexes were characterized by elemental analyses, FT-IR, UV–vis spectral methods and their structures were established by single crystal X-ray diffraction study. The biochemical activity of the complexes towards DNA binding were performed using absorbance and fluorescence titration methods and their mode of binding with calf thymus DNA has been established by viscosity measurement technique.

A new tetradentate N 2 O 2 donor Schiff base ligand [OHC 6 H 4 CH NCH 2 CH 2 CH(CH 2 CH 3 )N CHC 6 H 4 OH = H 2 L ] was obtained by 1:2 condensation of 1,3-diaminopentane with salicylaldehyde and has been used to synthesise an unusual copper(II) complex whose asymmetric unit presents two structurally different almost linear trinuclear units [Cu 3 (μ- L ) 2 (ClO 4 ) 2 ] [Cu 3 (μ- L ) 2 (H 2 O)(ClO 4 ) 2 ] ( 1 ). The ligand and the complex were characterised by elemental analysis, FT-IR, 1 H NMR and UV–Vis spectroscopy in addition electrochemical and single crystal X-ray diffraction studies were performed for the complex. The magnetic properties of 1 reveal the presence of strong intra-trimer ( J 1 = −202(3) cm −1 and J 2 = −233(3) cm −1 ) as well as very weak inter-trimer ( zJ ′ = −0.11(1) cm −1 ) antiferromagnetic interactions.

Three new mono–di–trinuclear cobalt complexes of three different Schiff bases have been synthesised. In all the three complexes psuedohalides (NCO− and N3−) have been incorporated to generate structural variation. Of the three Schiff bases, HL1 and HL2 were obtained by selective condensation of two different 1,3-diamines with 2-hydroxyacetophenone and H2L3 resulted from non-selective condensation of 1,3-diamine with 2-hydroxyacetophenone. Only one –NH2 functionality of 1,3-diaminopropane and 1,3-diaminopentane was selectively condensed with 2-hydroxyacetophenone to generate Schiff bases HL1 and HL2, respectively. H2L3 was obtained by condensing both the amine functionality of 1,3-diaminopropane with 2-hydroxyacetophenone. Therefore HL1 and HL2 behave as a N2O donors, whereas H2L3 provides a N2O2 donor coordination environment for the cobalt ions in the respective complexes. In [Co(L1)2]2 [Co(NCO)4] (1) the asymmetric unit comprises of five mononuclear cobalt centers, [Co2(μ–N3)2(L2)2(N3)2] (2) is a dinuclear and [(H2O)2Co(μ–N3)2(μ–L3)2Co2(N3)1.25(CH3O)0.75] · H2O (3) is a trinuclear cobalt species. The three complexes have been characterised using IR, UV–Vis spectroscopy and cyclic voltammetry. Structural aspects of 1, 2 and 3 have been described by performing single crystal X-ray analysis. EPR analyses of 1 and 3, and DNA binding abilities of all three cobalt complexes have been studied in detail.

International audience; A new tridentate N2O donor Schiff base ligand [(C6H5C(OH)CHC(CH3)NCH2C5H4N)LH] was obtained by 1:1 condensation of benzoylacetone with 2-picolylamine and has been used to synthesise a mononuclear [CuLCl] (1) and an end-to-end dicyanamide bridged polynuclear {[Cu2(μ-L)2(μ2-1,5-(CN)2N)]ClO4}n (2) copper(II) complexes. The ligand, 1 and 2 were clearly characterised by elemental analysis, FT-IR, 1H NMR, UV–Vis spectral studies, electrochemical studies and in addition single crystal X-ray diffraction studies were performed for 1 and 2. The Schiff base ligand [LH] shows a significant variation in its coordination behaviour with copper(II) ion in absence and in presence of dicyanamide ion in 1 and 2 respectively. In absence of dicyanamide the deprotonated enolato oxygen of the tridentate Schiff base ligand [L]− coordinates the copper(II) ion in a monodentate fashion generating a mononuclear species (1) whereas in presence of the dicyanamide ion, the deprotonated enolato oxygen of [L]− bridges two adjacent [CuL(CN)2N] units through μ-OL bridges, forming dimers. The dimeric units are further linked to adjacent dimeric units through μ2-1,5-dicyanamide bridges to produce 1D polymeric chains in 2. Variable temperature magnetic susceptibility measurements for 2 in the temperature range 2-300 K reveal the presence of weak antiferromagnetic exchange interactions in the polymeric chain.

A novel hydroxo-bridged cyclic tetranuclear copper(II) complex with the guanazole ligand (3,5-diamino-1,2,4-triazole = Hdatrz), [Cu4(datrz)4(μ2-OH)2(NO3) (H2O)6] · (NO3) · 5(H2O) (1) has been synthesised and characterised by X-ray crystallography. In 1, the four copper(II) centres are linked by hydroxo bridges and the N1,N2-coordination of the deprotonated guanazole ligands. The core has considerably short Cu⋯Cu distances in the range of 3.3550(4)–3.3611(4) A. Thermal analysis of 1 reveals that the cyclic framework constructed with hydroxo and guanazole ligands is stable up to 285 °C.

International audience; Metal complexes of Schiff bases derived from an aromatic hydrazide are well characterised and have been reported several times. Single crystal structures of metal hydrazone complexes derived from an aliphatic hydrazide are very rare and still remain unexplored. In this paper we report two new end-on azido bridged dinuclear copper(II) and cobalt(III) hydrazone complexes derived from an aliphatic hydrazide. The Schiff base [LH = CH3C(O)NHNCHC5H4N] has resulted from the condensation of acetic hydrazide and pyridine-2-carboxaldehyde. The ligand and the complexes [Cu2(L)2(μ1,1-N3)2] (1) and [Co2(L)2(μ1,1-N3)2(N3)2] (2) are characterised by elemental analysis, IR and UV–Vis spectral studies and in addition mass spectroscopy has been also carried out for LH. The structures of 1 and 2 have been established by X-ray crystallography. Variable temperature magnetic susceptibility measurement studies of 1 indicate the χMT values remain constant in the whole range of temperature 10 to 300 K at a value close of 0.75 cm3 K mol−1, which is in good agreement with the one expected for two uncoupled copper(II) centers.

The effects of pseudohalides on the modes of binding of a hydrazone ligand are investigated and we report here four new hydrazone complexes [Co(L) 2 ] · ClO 4 ( 1 ), [Co(L) 2 ] 2 [Co(SCN) 4 ] ( 2 ), [Mn(L) 2 ] ( 3 ) and [Mn(N 3 ) 2 ( LH ) 2 ] · H 2 O ( 4 ) [where LH = condensation product of pyridine-2-carboxaldehyde and benzhydrazide]. The hydrazone ligand is quite diverse in its chelating ability and can act as a neutral or mononegative ligand and as a bidentate or tridentate unit. In this paper, we report structures showing different denticities of the ligand having different charges. The complexes are characterized by IR, UV–Vis spectroscopy and cyclic voltammetric studies and the structures are conclusively established by single crystal X-ray diffraction study. Of the complexes, 1 and 3 are purely metal hydrazone complexes whereas 2 and 4 incorporate coordinated pseudohalides in their crystal structures, and 4 shows different coordination modes of the hydrazone ligand.

Two new L–M–L type transition metal coordination polymers [M(C 6 H 12 N 4 )(NCO) 2 (H 2 O) 2 ] n , where M = Co(II) ( 1 ) and Ni(II) ( 2 ), have been synthesised under controlled hydrothermal condition and characterised spectroscopically and by thermal analyses. Here hmt or hexamethylenetetramine has behaved as a neutral organic bidentate spacer molecule. Both the complexes crystallise in the monoclinic system as confirmed from single crystal X-ray diffraction studies. Cryomagnetic susceptibility measurements over a wide range of temperature (2–300 K) under 0.5 T magnetic fields show a weak antiferromagnetic interaction of J = −0.65 cm −1 for 1 and −1.6 cm −1 for 2 . The values have been given a favorable support by weak covalent and H-bonding interactions between octahedral M(II) metal centers as revealed from X-ray structure determination. The high dimensionality of the structures is probably a manifestation of extensively weak covalent interactions and H-bondings.

A nickel(II) and a cobalt(III) complex of two different potentially tetradentate Schiff bases with different binding modes have been synthesised. The nickel(II) complex [NiL1] · CH3OH (1) was formed, on reacting the metal salt with a perfectly symmetrical N2O2 tetradentate Schiff base ligand H 2 L 1 , which is the 1:2 condensation product of 1,3-diamino propane and 2-hydroxyacetophenone. The cobalt(III) complex [Co(HL2)3] · (ClO4)3 · H2O (2) was synthesised using an asymmetric N2O2 tetradentate Schiff base ligand HL 2 on condensing N,N-dimethyl-1,3-diamino propane with o-vanillin in 1:1 mmol ratio. Although both Schiff bases are N2O2 functionalised, they showed variation in their coordinative property with nickel(II) and cobalt(III) ions. Both the complexes were characterised by IR spectroscopy and cyclic voltammetry and their single crystal structures clearly indicate that 1 is a mononuclear species whereas 2 is a hydrogen-bonded dimer.

Three new coordination complexes of Zn(II) and Mn(II) have been synthesised using two different tridentate N,N,O donor hydrazone ligands, Hpbh and Hacpbh respectively. The complexes [Zn(pbh)2] (1) and [Zn(acpbh)2] (2) have been synthesized by the treatment of ZnSO4 · 7H2O with Hpbh and Hacpbh hydrazone ligands, respectively. The Mn(II) complex [Mn(acpbh)2] (3) was obtained on reacting Mn(NO3)2 · 4H2O with the ligand Hacpbh. The ligands Hpbh and Hacpbh were prepared by condensing pyridine-2-carboxaldehyde and 2-acetylpyridine with benzhydrazide respectively. Inspite of varying the carbonyl functionality attached to the pyridine moiety present in the hydrazone ligands in both the Schiff bases, we obtained three mononuclear complexes 1, 2, and 3 which were clearly characterized from single crystal X-ray diffraction studies. Spectroscopic investigations like IR and UV/Vis have been carried out for 1, 2, and 3. Fluorescence studies have been performed for 1 and 2. For 3 cyclic voltammetry, room temperature magnetic study and EPR measurements have been recorded.

Three novel Schiff base Cd(II) trimeric complexes, [Cd3(L1)2(SCN)2(CF3COO)2] (1), [Cd3(L1)2(SCN)2(HCONMe2)] (2) and [Cd3(L2)2{N(CN)2}2] (3) have been prepared from two different symmetrical Schiff bases H2L1 and H2L2 (where H2L1 = N1,N3-bis(salicylideneimino)diethylenetriamine, a potentially pentadentate Schiff base with a N3O2 donor set, and H2L2 = N1,N3-bis(3-methoxysalicylideneimino)diethylenetriamine, a potentially heptadentate Schiff base with a N3O4 donor set). All the complexes have been synthesised under similar synthetic procedures and their crystal structures have been established by single crystal X-ray diffraction methods. The ligands and their metal complexes have been characterised by analytical and spectroscopic techniques. Among the three complexes, 1 and 3 are linear whereas 2 is a cyclic trimer. In 1 and 3, all the doubly phenoxo bridged Cd(II) metal centres are in a distorted octahedral environment. In complex 2, two of the three Cd(II) centres reside in a distorted octahedral environment and the remaining one enjoys a monocapped octahedral geometry. Altogether the variety in the bridging mode of two new salen-type ligands has been established through these complexes.

Three different ONO donor acetyl hydrazone Schiff bases have been synthesized from the condensation of acetic hydrazide with three different carbonyl compounds: salicylaldehyde (HL(1)), 2-hydroxyacetophenone (HL(2)), and 2, 3-dihydroxybenzaldehyde (HL(3)). These tridentate ligands are reacted with Ni(OOCCF(3))(2)·xH(2)O to yield three new Ni(II) complexes having distorted octahedral geometry at each Ni center: [Ni(L(1))(OOCCF(3))(CH(3)OH)](2) (1), [Ni(L(2))(OOCCF(3))(H(2)O)](2) (2), and [Ni(L(3))(L(3)H)](OOCCF(3))(H(2)O)(1.65)(CH(3)OH)(0.35) (3). The ligands and the complexes have been characterized by elemental analysis and IR and UV-vis spectroscopy, and the structures of the complexes have been established by single crystal X-ray diffraction (XRD) study. 1 and 2 are centrosymmetric dinuclear complexes and are structural isomers whereas 3 is a bis chelated cationic monomer coordinated by one neutral and one monoanionic ligand. O-H···O hydrogen bonds in 3 lead to the formation of a dimer. Slight steric and electronic modifications in the ligand backbone provoke differences in the supramolecular architectures of the complexes, leading to a variety of one, two, and three-dimensional hydrogen bonded networks in complexes 1-3 respectively. Variable temperature magnetic susceptibility measurements reveal that moderate antiferromagnetic interactions operate between phenoxo bridged Ni(II) dimers in 1 and 2 whereas very weak antiferromagnetic exchange occurs through hydrogen bonding and π-π stacking interactions in 3. All complexes are proved to be efficient catalysts for the epoxidation of alkenes by NaOCl under phase transfer condition. The efficiency of alkene epoxidation is dramatically enhanced by lowering the pH, and the reactions are supposed to involve high valent Ni(III)-OCl or Ni(III)-O· intermediates. 3 is the best epoxidation catalyst among the three complexes with 99% conversion and very high turnover number (TON, 396).

International audience; A tridentate NNO donor Schiff base ligand [(1Z,3E)-3-((pyridin-2-yl)methylimino)-1-phenylbut-1-en-1-ol = LH] in presence of azide ions coordinates with cobalt(II) and copper(II) ions giving rise to three new coordination complexes [Co2(L)2(μ1,1-N3)2(N3)2] (1), [Cu2(L)2(μ1,3-N3)]·ClO4 (2) and [(μ1,1-N3)2Cu5(μ-OL)2(μ1,1-N3)4(μ1,1,1-N3)2]n (3). The complexes have been characterized by elemental analysis, FT-IR, UV–Vis spectral studies, and single crystal X-ray diffraction studies. These complexes demonstrate that under different synthetic conditions the azide ions and the Schiff base ligand (LH) show different coordination modes with cobalt(II) and copper(II) ions, giving rise to unusual dinuclear and polynuclear species (1, 2 and 3) whose structural variations are discussed. Magneto-structural correlation for the very rare singly μ1,3-N3 bridged CuII–Schiff base dinuclear species (2) has been studied. In addition, the catalytic properties of 1 for alkene oxidation and the general catalase-like activity behavior of 2 have been discussed.

A novel family of homodinuclear complexes of the general formula [Ln(2)L(2)(X)(2)] (where Ln = Nd(3+), Pr(3+), Sm(3+) and Tb(3+) for 1, 2, 3 and 4, respectively and X, the coordinated NO(3)(-) or Cl(-) anion) has been synthesised from the corresponding lanthanide(III) salts with the pentadentate dianionic Schiff base ligand, H(2)L [N(1),N(3)-bis(salicylideneimino)diethylenetriamine], that exhibits a N(3)O(2) donor set. Single crystal X-ray diffraction studies evidenced the isostructurality of this family of centrosymmetric neutral dinuclear entities where the Ln(III) metal centres are coupled together by two phenolato oxygen atoms belonging to two units of ligand (H(2)L). Interestingly, the two other phenolato groups of H(2)L are mono-coordinated to the metal ions. Temperature dependence (2-300K) magnetic susceptibility studies suggest the presence of an antiferromagnetic interaction operating via double phenolato bridges. Photoluminescence activities of the complexes have been studied and compared with their precursor ligand. All the complexes have been characterised with microanalytical and several spectroscopic techniques.

International audience; Two new coordination complexes {[(L)Cu2('-L)(NO3)(CH3OH)0.3(H2O)0.7]·NO3}[Cu(L)(NO3)(CH3OH)] (1) and [Mn2(-L)2(H2O)(1-N3)2(CH3OH)] (2) derived from (E)-N-(2-hydroxy-3-methoxybenzylidene)acetohydrazide [LH] have been synthesized. The new potentially tetradentate ONOO donor hydrazone ligand [LH] has shown considerable metal ion selective phenoxo bridging in 1 and 2. It has coordinated copper(II) ions in its tridentate as well as in tetradentate fashion whereas for manganese(II) ions it solely showed its tetradentate character. In 1 the two adjacent pentacoordinate copper(II) centers are connected by a rare single phenoxo linkage of the hydrazone ligand whereas 2 is a doubly phenoxo-bridged heptacoordinated manganese(II) dinuclear species. The 3D supramolecular networks of 1 and 2 have resulted from extensive H-bonding interactions in the respective complexes. Structural variations observed for 1 and 2 have been described by performing single-crystal X-ray analysis. The ligand and the complexes are characterized by elemental analyses, IR, UV/Vis and 1H NMR spectroscopy. Cryomagnetic investigations, DFT studies and EPR analysis, of 1 and 2 have also been studied in detail.

The engineering of protein-small molecule interactions becomes imperative today to recognize the essential biochemical processes in living systems. Here we have investigated the interaction between hen egg white lysozyme (HEWL) and a newly synthesized small, simple nickel Schiff base complex (NSC) {(N(1)E,N(2)E)-N(1),N(2)-bis(pyridine-2-ylmethylene)propane-1,2-diaminenickel(II)} using different spectroscopic techniques. We attempted to determine the exact site of the interaction by crystallography. Absorption spectroscopy reveals that the interaction occurs through the ground state. The complex can quench the intrinsic fluorescence of HEWL through a static quenching method. The fluorescence quenching study along with the determination of thermodynamic parameters reveal that NSC binds HEWL spontaneously with moderate binding affinity. The results have also identified that the spontaneity of this enthalpy guided interaction is mainly governed by some H-bonding and hydrophobic interactions which are also indicated by the crystallographic analyses. Moreover, the crystallographic study shows that NSC makes its way into the active site enzyme cavity of HEWL forming a single covalent adduct between Ni(2+) and the oxygen of the active site Asp 52. The possibility of inhibiting the catalytic activity of HEWL by inclusion of NSC in the enzyme active site observed from crystallographic analyses has also been confirmed by enzyme kinetics experiments.

A new Na(I)/Cu(I-II) heterometallic coordination complex [Cu(2)L(2)Na(NCO)(2)Cu](n) (1) with an unusual architecture has been synthesised. In 1 cyclic Na-O-Cu-O-Cu cages constructed by the tetradentate N(2)O(2) donor Schiff base ligand (H(2)L = N, N'-bis(2-hydroxyacetophenone) propylenediimine) are interconnected to each other by a rare singly end-to-end bridged OCN-Cu(I)-NCO link generating 1D chain. The complex has been characterised by elemental, spectral and structural analysis. The cyclic voltammogram of 1 has been compared with the analogous complexes. Cryomagnetic susceptibility studies indicate the copper(II) centers in the cyclic Na-O-Cu-O-Cu cages are antiferromagnetically coupled with J = -13.8 cm(-1). Complex 1 is a new addition to a class of rare singly end-to-end cyanato bridged copper(I) species and interestingly the copper ions involved in OCN-Cu(I)-NCO links possess a linear 2-coordinate geometry. Density functional theory calculations have been carried out to gain additional insights into the metal and ligand orbitals participating in this unusual structure.