Synthesis, crystal structure and catalytic properties of (p-cymene)ruthenium(II) azophenol complexes: azophenyl to azophenol conversion by oxygen insertion to a ruthenium---carbon bond

Azophenol complexes of formulation [(η6-p-cymene)RuCl(Ln)] (1–6, n=1–6) were prepared by two synthetic methods involving either an oxygen insertion to the Ru---C bond in cycloruthenated precursors forming complexes 1 and 2 or from the reaction of [{(η6-p-cymene)RuCl}2(μ-Cl)2] with azophenol ligands (HL3–HL6) in the presence of sodium carbonate in CH2Cl2. The molecular structure of the 1-(phenylazo)-2-naphthol complex has been determined by X-ray crystallography. The complex has a η6-p-cymene group, a chloride and a bidentate N,O-donor azophenol ligand. The complexes have been characterized from NMR spectral data. The catalytic activity of the complexes has been studied for the conversion of acetophenone to the corresponding alcohol in the presence of KOH and isopropanol. Complexes 4 and 6 having a methoxy group attached to the ortho-position of the phenylazo moiety and 2 with a methyl group in the meta-position of the phenolic moiety show high percentage conversion (>84%).

Trans -> Cis isomerization of trans-[(dPPM)(2)Ru(H)(L)][BF4] (L = P(OR)(3)) Complexes: Preparation of cis-[(dppm)(2)Ru(eta(2)-H-2)(L)][BF4](2)

A series of new dicationic dihydrogen complexes of ruthenium of the type cis-[(dppm)(2)Ru(eta(2)-H-2)(L)][BF4](2) (dppm = Ph2PCH2PPh2; L = P(OMe)(3), P(OEt)(3), PF((OPr)-Pr-i)(2)) have been prepared by protonating the precursor hydride complexes cis-[(dppm)(2)Ru(H)(L)][BF4] (L = P(OMe)(3), P(OEt)(3), P((OPr)-Pr-i)(3)) using HBF4.Et2O. The cis-[(dppm)(2)Ru(H)(L)][BF4] complexes were obtained from the trans hydrides via an isomerization reaction that is acid-accelerated. This isomerization reaction gives mixtures of cis and trans hydride complexes, the ratios of which depend on the cone angles of the phosphite ligands: the greater the cone angle, the greater is the amount of the cis isomer. The eta(2)-H-2 ligand in the dihydrogen complexes is labile, and the loss of H-2 was found to be reversible. The protonation reactions of the starting hydrides with trans PMe3 or PMe2Ph yield mixtures of the cis and the trans hydride complexes; further addition of the acid, however, give trans-[(dPPM)(2)Ru(BF4)Cl]. The roles of the bite angles of the dppm ligand as well as the steric and the electronic properties of the monodentate phosphorus ligands in this series of complexes are discussed. X-ray crystal structures of trans-[(dppm)(2)Ru(H)(P(OMe)(3))][BF4], cis-[(dppm)(2)Ru-(H)(P(OMe)(3))][BF4], and cis-[(dppm)(2)Ru(H)(P((OPr)-Pr-i)(3))][BF4] complexes have been determined.

Ligand-modulated Parallel Mechanical Unfolding Pathways of Maltose-binding Proteins

Protein folding and unfolding are complex phenomena, and it is accepted that multidomain proteins generally follow multiple pathways. Maltose-binding protein (MBP) is a large (a two-domain, 370-amino acid residue) bacterial periplasmic protein involved in maltose uptake. Despite the large size, it has been shown to exhibit an apparent two-state equilibrium unfolding in bulk experiments. Single-molecule studies can uncover rare events that are masked by averaging in bulk studies. Here, we use single-molecule force spectroscopy to study the mechanical unfolding pathways of MBP and its precursor protein (preMBP) in the presence and absence of ligands. Our results show that MBP exhibits kinetic partitioning on mechanical stretching and unfolds via two parallel pathways: one of them involves a mechanically stable intermediate (path I) whereas the other is devoid of it (path II). The apoMBP unfolds via path I in 62% of the mechanical unfolding events, and the remaining 38% follow path II. In the case of maltose-bound MBP, the protein unfolds via the intermediate in 79% of the cases, the remaining 21% via path II. Similarly, on binding to maltotriose, a ligand whose binding strength with the polyprotein is similar to that of maltose, the occurrence of the intermediate is comparable (82% via path I) with that of maltose. The precursor protein preMBP also shows a similar behavior upon mechanical unfolding. The percentages of molecules unfolding via path I are 53% in the apo form and 68% and 72% upon binding to maltose and maltotriose, respectively, for preMBP. These observations demonstrate that ligand binding can modulate the mechanical unfolding pathways of proteins by a kinetic partitioning mechanism. This could be a general mechanism in the unfolding of other large two-domain ligand-binding proteins of the bacterial periplasmic space.

Synthesis and DNA binding studies of Ni(II), Co(II), Cu(II) and Zn(II) metal complexes of N(1),N(5)-bis[pyridine-2-methylene]-thiocarbohydrazone Schiff-base ligand

The thiocarbohydrazone Schiff-base ligand with a nitrogen and sulphur donor was synthesized through condensation of pyridine-2-carbaldehyde and thiocarbohydrazide. Schiff-base ligands have the ability to conjugate with metal salts. A series of metal complexes with a general formula [MCl(2)(H(2)L)]center dot nH(2)O (M=Ni, Co, Cu and Zn) were synthesized by forming complexes of the N(1),N5-bis[pyridine-2-methylene]thiocarbohydrazone (H2L) Schiff-base ligand. These metal complexes and ligand were characterized by using ultraviolet-visible (UV-Vis), Fourier Transform Infrared (FT-IR), (1)H and (13)C NMR spectroscopy and mass spectroscopy, physicochemical characterization, CHNS and conductivity. The biological activity of the synthesized ligand was investigated by using Escherichia coli DNA as target. The DNA interaction of the synthesized ligand and complexes on E. coli plasmid DNA was investigated in the aqueous medium by UV-Vis spectroscopy and the binding constant (K(b)) was calculated. The DNA binding studies showed that the metal complexes had an improved interaction due to trans-geometrical isomers of the complexes than ligand isomers in cis-positions. (C) 2011 Elsevier B.V. All rights reserved.

Conformational changes of the chaperone SecB upon binding to a model substrate - bovine pancreatic trypsin inhibitor (BPTI)

SecB is a homotetrameric cytosolic chaperone that forms part of the protein translocation machinery in E. coli. Due to SecB, nascent polypeptides are maintained in an unfolded translocation-competent state devoid of tertiary structure and thus are guided to the translocon. In vitro SecB rapidly binds to a variety of ligands in a non-native state. We have previously investigated the bound state conformation of the model substrate bovine pancreatic trypsin inhibitor (BPTI) as well as the conformation of SecB itself by using proximity relationships based on site-directed spin labeling and pyrene fluorescence methods. It was shown that SecB undergoes a conformational change during the process of substrate binding. Here, we generated SecB mutants containing but a single cysteine per subunit or an exposed highly reactive new cysteine after removal of the nearby intrinsic cysteines. Quantitative spin labeling was achieved with the methanethiosulfonate spin label (MTS) at positions C97 or E90C, respectively. Highfield (W-band) electron paramagnetic resonance (EPR) measurements revealed that with BPTI present the spin labels are exposed to a more polar/hydrophilic environment. Nanoscale distance measurements with double electron-electron resonance (DEER) were in excellent agreement with distances obtained by molecular modeling. Binding of BPTI also led to a slight change in distances between labels at C97 but not at E90C. While the shorter distance in the tetramer increased, the larger diagonal distance decreased. These findings can be explained by a widening of the tetrameric structure upon substrate binding much like the opening of two pairs of scissors.

Location and conformation of pantothenate and its derivatives in Mycobacterium tuberculosis pantothenate kinase: insights into enzyme action

Previous studies of complexes of Mycobacterium tuberculosis PanK (MtPanK) with nucleotide diphosphates and non-hydrolysable analogues of nucleoside triphosphates in the presence or the absence of pantothenate established that the enzyme has dual specificity for ATP and GTP, revealed the unusual movement of ligands during enzyme action and provided information on the effect of pantothenate on the location and conformation of the nucleotides at the beginning and the end of enzyme action. The X-ray analyses of the binary complexes of MtPanK with pantothenate, pantothenol and N-nonylpantothenamide reported here demonstrate that in the absence of nucleotide these ligands occupy, with a somewhat open conformation, a location similar to that occupied by phosphopantothenate in the `end' complexes, which differs distinctly from the location of pantothenate in the closed conformation in the ternary `initiation' complexes. The conformation and the location of the nucleotide were also different in the initiation and end complexes. An invariant arginine appears to play a critical role in the movement of ligands that takes place during enzyme action. The work presented here completes the description of the locations and conformations of nucleoside diphosphates and triphosphates and pantothenate in different binary and ternary complexes, and suggests a structural rationale for the movement of ligands during enzyme action. The present investigation also suggests that N-alkylpantothenamides could be phosphorylated by the enzyme in the same manner as pantothenate.

Complexes of rare-earth perchlorates with ditbutyl amides of di, tri and tetraglycolic acids

New complexes of lanthanide perchlorates with di-t-butyl amides of di, tri and tetraglycolic acids have been synthesised. The complexes have the general formula Ln(DiGA)3(ClO4)3; Ln(TriGA)2 (ClO4)3 and Ln(TetGA)2 (C1O4)3, where Ln = La-Yb and Y and DiGA = N,N′, di-t-butyl diglycolamide, TriGA N,N′, di-t-butyl triglycolamide and TetGA = N,N′ di-t-butyl tetraglycolamide, respectively. The complexes have been characterized by analysis, electrolytic conductance, infrared,1H and13C nuclear magnetic resonance and electronic spectral data.Infrared spectra indicate the coordination of all the available ether oxygens and the amide carbonyls in each of the ligands, to the metal ions. IR and conductance data show that the perchlorate groups in all the complexes are ionic.1H and13C NMR data support the IR data regarding the mode of coordination of ligands to the metal ions. Electronic spectral shapes have been interpreted in terms of nine, eight and ten coordination in DiGA, TriGA and TetGA complexes respectively.

Ferromagnetism Exhibited by Nanoparticles of Noble Metals

Gold nanoparticles with average diameters in the range 2.515 nm, prepared at the organic/aqueous interface by using tetrakis( hydroxymethyl) phosphonium chloride (THPC) as reducing agent, exhibit ferromagnetism whereby the saturation magnetization M(S) increases with decreasing diameter and varies linearly with the fraction of surface atoms. The value of M(S) is higher when the particles are present as a film instead of as a sol. Capping with strongly interacting ligands such as alkane thiols results in a higher M(S) value, which varies with the strength of the metal-sulfur bond. Ferromagnetism is also found in Pt and Ag nanoparticles prepared as sols, and the M(S) values vary as Pt > Au > Ag. A careful study of the temperature variation of the magnetization of Au nanoparticles, along with certain other observations, suggests that small bare nanoparticles of noble metals could indeed possess ferromagnetism, albeit weak, which is accentuated in the presence of capping agents, specially alkane thiols which form strong metal-sulfur bonds.

Impact of metal on the DNA photocleavage activity and cytotoxicity of ferrocenyl terpyridine 3d metal complexes

Ferrocenyl terpyridine 3d metal complexes and their analogues, viz. [M(Fc-tpy)(2)](ClO(4))(2) (1-4), [Zn(Ph-tpy)(2)](ClO(4))(2) (5) and [Zn(Fc-dpa)(2)]X(2) (X = ClO(4), 6; PF6, 6a), where M = Fe(II) in 1, Co(II) in 2, Cu(II) in 3 and Zn(II) in 4, Fc-tpy is 4'-ferrocenyl-2,2': 6', 2 `'-terpyridine, Ph-tpy is 4'-phenyl-2,2': 6', 2 `'-terpyridine and Fc-dpa is ferrocenyl-N,N-dipicolylmethanamine, are prepared and their DNA binding and photocleavage activity in visible light studied. Complexes 2, 4, 5 and 6a that are structurally characterized by X-ray crystallography show distorted octahedral geometry with the terpyridyl ligands binding to the metal in a meridional fashion, with Fc-dpa in 6a showing a facial binding mode. The Fc-tpy complexes display a charge transfer band in the visible region. The ferrocenyl (Fc) complexes show a quasi-reversible Fc(+)-Fc redox couple within 0.48 to 0.66 V vs. SCE in DMF-0.1 M TBAP. The DNA binding constants of the complexes are similar to 10(4) M(-1). Thermal denaturation and viscometric data suggest DNA surface binding through electrostatic interaction by the positively charged complexes. Barring the Cu(II) complex 3, the complexes do not show any chemical nuclease activity in the presence of glutathione. Complexes 1-4 exhibit significant plasmid DNA photocleavage activity in visible light via a photoredox pathway. Complex 5, without the Fc moiety, does not show any DNA photocleavage activity. The Zn(II) complex 4 shows a significant PDT effect in HeLa cancer cells giving an IC(50) value of 7.5 mu M in visible light, while being less toxic in the dark (IC(50) = 49 mu M).

Structural Annotation of Mycobacterium tuberculosis Proteome

Of the similar to 4000 ORFs identified through the genome sequence of Mycobacterium tuberculosis (TB) H37Rv, experimentally determined structures are available for 312. Since knowledge of protein structures is essential to obtain a high-resolution understanding of the underlying biology, we seek to obtain a structural annotation for the genome, using computational methods. Structural models were obtained and validated for similar to 2877 ORFs, covering similar to 70% of the genome. Functional annotation of each protein was based on fold-based functional assignments and a novel binding site based ligand association. New algorithms for binding site detection and genome scale binding site comparison at the structural level, recently reported from the laboratory, were utilized. Besides these, the annotation covers detection of various sequence and sub-structural motifs and quaternary structure predictions based on the corresponding templates. The study provides an opportunity to obtain a global perspective of the fold distribution in the genome. The annotation indicates that cellular metabolism can be achieved with only 219 folds. New insights about the folds that predominate in the genome, as well as the fold-combinations that make up multi-domain proteins are also obtained. 1728 binding pockets have been associated with ligands through binding site identification and sub-structure similarity analyses. The resource (http://proline.physics.iisc.ernet.in/Tbstructuralannotation), being one of the first to be based on structure-derived functional annotations at a genome scale, is expected to be useful for better understanding of TB and for application in drug discovery. The reported annotation pipeline is fairly generic and can be applied to other genomes as well.

Immunomodulation using agonists and antagonists: potential clinical applications

Introduction: Extensive studies have gone into understanding the differential role of the innate and adaptive arms of the immune system in the context of various diseases. Receptor-ligand interactions are responsible for mediating cross-talk between the innate and adaptive arms of the immune system, so as to effectively counter the pathogenic challenge. While TLRs remain the best studied innate immune receptor, many other receptor families are now coming to the fore for their role in various pathologies. Research has focused on the discovery of novel agonists and antagonists for these receptors as potential therapeutics. Areas covered: In this review, we present an overview of the recent advances in the discovery of drugs targeting important receptors such as G-protein coupled receptors, TRAIL-R, IL-1 beta receptor, PPARs, etc. All these receptors play a critical role in the modulation of the immune response. We focus on the recent paradigms applied for the generation of specific and effective therapeutics for these receptors and their status in clinical trials. Expert opinion: Non-specific activation by antagonist/agonist is a difficult problem to dodge. This demands innovation in ligand designing with the use of strategies such as allosterism and dual-specific ligands. Rigorous preclinical and clinical studies are required in transforming a compound to a therapeutic.

Design, synthesis and docking studies of new quinoline-3-carbohydrazide derivatives as antitubercular agents

Three new series of 4-hydroxy-8-trifluoromethyl-quinoline derivatives were synthesized through multi step reactions. All the newly synthesized compounds were characterized by spectral and elemental analyses. The structure of 5j was evidenced by X-ray crystallographic study. The newly synthesized title compounds were evaluated for their antimicrobial activities including antimycobacterial activity. Amongst the tested compounds, 5b, 5e, 5h, 5j, 6c and 7c displayed promising antimicrobial activity. The mode of action of these active compounds was carried out by docking of receptor enoyl-ACP reductase with newly synthesized candidate ligands, 5b, 5e, 5h, 5j and 6c. (C) 2011 Elsevier Masson SAS. All rights reserved.

A Monoclonal Antibody against Human Notch1 Ligand-Binding Domain Depletes Subpopulation of Putative Breast Cancer Stem-like Cells

Overexpression of Notch receptors and ligands has been associated with various cancers and developmental disorders, making Notch a potential therapeutic target. Here, we report characterization of Notch1 monoclonal antibodies (mAb) with therapeutic potential. The mAbs generated against epidermal growth factor (EGF) repeats 11 to 15 inhibited binding of Jagged1 and Delta-like4 and consequently, signaling in a dose-dependent manner, the antibodies against EGF repeats 11 to 12 being more effective than those against repeats 13 to 15. These data emphasize the role of EGF repeats 11 to 12 in ligand binding. One of the mAbs, 602.101, which specifically recognizes Notch1, inhibited ligand-dependent expression of downstream target genes of Notch such as HES-1, HES-5, and HEY-L in the breast cancer cell line MDA-MB-231. The mAb also decreased cell proliferation and induced apoptotic cell death. Furthermore, exposure to this antibody reduced CD44(Hi)/CD24(Low) subpopulation in MDA-MB-231 cells, suggesting a decrease in the cancer stem-like cell subpopulation. This was confirmed by showing that exposure to the antibody decreased the primary, secondary, and tertiary mammosphere formation efficiency of the cells. Interestingly, effect of the antibody on the putative stem-like cells appeared to be irreversible, because the mammosphere-forming efficiency could not be salvaged even after antibody removal during the secondary sphere formation. The antibody also modulated expression of genes associated with stemness and epithelial-mesenchymal transition. Thus, targeting individual Notch receptors by specific mAbs is a potential therapeutic strategy to reduce the potential breast cancer stem-like cell subpopulation. Mol Cancer Ther; 11(1); 77-86. (C) 2011 AACR.

DNA-binding and nuclease activity of1,10-phenanthroline-based thiocyanato, acetato, azido and benzoato bridged dinuclear copper(II) complexes

The mononuclear Cu(II) complex [Cu(phen)(H2O)(NO3)(2)] (1), obtained by the reaction of 1,10-phenanthroline with Cu(NO3)(2)center dot 3H(2)O in methanol solution, reacts with anionic ligands SCN-, AcO-, N-3(-) and PhCO2- in MeOH solution to form the stable binuclear complexes [Cu-2(H2O)(2)(phen)(2)(mu-X)(2)](2) (NO3)(2), where X = SCN- (2), AcO- (3), N-3(-) (4) or PhCO2- (5). The molecular structure of complex 3 was determined by single-crystal X-ray diffraction studies. These complexes were characterized by electronic, IR, ESR, magnetic moments and conductivity measurements. The electrochemical behaviour of the complexes was investigated by cyclic voltammetry. The interactions of these complexes with calf thymus DNA have been investigated using absorption spectrophotometry. Their DNA cleavage activity was studied on double-stranded pBR322 plasmid DNA using gel electrophoresis experiments in the absence and presence of H2O2 as oxidant.

DNA-binding and nuclease activity of 1,10-phenanthroline-based thiocyanato, acetato, azido and benzoato bridged dinuclear copper(II) complexes

The mononuclear Cu(II) complex [Cu(phen)(H2O)(NO3)(2)] (1), obtained by the reaction of 1,10-phenanthroline with Cu(NO3)(2)center dot 3H(2)O in methanol solution, reacts with anionic ligands SCN-, AcO-, N-3(-) and PhCO2- in MeOH solution to form the stable binuclear complexes [Cu-2(H2O)(2)(phen)(2)(mu-X)(2)](2) (NO3)(2), where X = SCN- (2), AcO- (3), N-3(-) (4) or PhCO2- (5). The molecular structure of complex 3 was determined by single-crystal X-ray diffraction studies. These complexes were characterized by electronic, IR, ESR, magnetic moments and conductivity measurements. The electrochemical behaviour of the complexes was investigated by cyclic voltammetry. The interactions of these complexes with calf thymus DNA have been investigated using absorption spectrophotometry. Their DNA cleavage activity was studied on double-stranded pBR322 plasmid DNA using gel electrophoresis experiments in the absence and presence of H2O2 as oxidant.