Deciphering the Distinct Role for the Metal Coordination Motif in the Catalytic Activity of Mycobacterium smegmatis Topoisomerase I

Mycobacterium smegmatis topoisomerase I (Mstopol) is distinct from typical type IA topoisomerases. The enzyme binds to both single- and double-stranded DNA with high affinity, making specific contacts. The enzyme comprises conserved regions similar to type IA topoisomerases from Escherichia coli and other eubacteria but lacks the typically found zinc fingers in the carboxy-terminal domain. The enzyme can perform DNA cleavage m the absence of Mg2+ but religation needs exogenously added Mg2+. One molecule of Mg2+ tightly bound to the enzyme has no role in DNA cleavage but is needed only for the religation reaction. The toprim. (topoisomerase-primase) domain in MstopoI comprising the Mg2+ binding pocket, conserved in both type IA and type II topoisomerases, was subjected to mutagenesis to understand the role of Mg2+, in different steps of the reaction. The residues D108, D110, and E112 of the enzyme, which form the acidic triad in the DXDXE motif, were changed to alanines. D108A mutation resulted in an enzyme that is Mg2+ dependent for DNA cleavage unlike Mstopol and exhibited enhanced DNA cleavage property and reduced religation activity. The mutant was toxic for cell growth, most likely due to the imbalance in cleavage-religation equilibrium. In contrast, the E112A mutant behaved like wild-type enzyme, cleaving DNA in a Mg2+-independent fashion, albeit to a reduced extent. Intra- and intermolecular religation assays indicated specific roles for D108 and E112 residues during the reaction. Together, these results indicate that the D108 residue has a major role during cleavage and religation, while E112 is important for enhancing the efficiency of cleavage. Thus, although architecturally and mechanistically similar to topoisomerase I from E. coli, the metal coordination pattern of the mycobacterial enzyme is distinct, opening up avenues to exploit the enzyme to develop inhibitors.

Novel 3-dimensional sixfold interpenetrating diamondoid networks of copper(I) coordination polymers of polypyridyl ligands - Syntheses,characterization and crystal structures

Two new coordination polymers [Cu(L-1)(2)](n)(ClO4)(n)center dot 2nH(2)O (1), [Cu(L-2)(2)](n)(ClO4)(n)center dot 2nH(2)O (2) of polydentate imine/pyridyl ligands, L-1 and L-2 with Cu(I) ion have been synthesized and characterized by single crystal X-ray diffraction studies, elemental analyses, IR' UV-vis and NMR spectroscopy. They represent 3-dimensional, sixfold interpenetrating diamondoid network structures having large pores of dimension, 35 x 21 angstrom(2) in 1 and 38 x 19 angstrom(2) in 2, respectively.

Coordination polymers and hybrid networks of different dimensionalities formed by metal sulfites

In our effort to explore the use of the sulfite ion to design hybrid and open-framework materials, we have been able to prepare, under hydrothermal conditions, zero-dimensional [Zn(C12H8N2)(SO3)]center dot 2H(2)O, I (a = 7.5737(5) angstrom, b = 10.3969(6) angstrom, c = 10.3986(6) angstrom, alpha = 64.172(1)degrees, beta = 69.395(1)degrees, gamma = 79.333(1)degrees, Z = 2, and space group P (1) over bar), one-dimensional [Zn-2(C12H8N2)(SO3)(2)(H2O)], II (a = 8.0247(3) angstrom, b = 9.4962(3) angstrom, c = 10.2740(2) A, alpha = 81.070(1)degrees, beta = 80.438(1)degrees, gamma = 75.66(5)degrees, Z = 2, and space group P (1) over bar), two-dimensional [Zn-2(C10H8N2)(SO3)(2)]center dot H2O, III (a = 16.6062(1) angstrom, b = 4.7935(1) angstrom, c = 19.2721(5) angstrom, beta = 100.674(2)degrees, Z = 4, and space group C2/c), and three-dimensional [Zn-4(C6H12N2)(SO3)(4)(H2O)(4)], IV (a = 11.0793(3) angstrom, c = 8.8246(3) angstrom, Z = 2, and space group P42nm), of which the last three are coordination polymers. A hybrid open-framework sulfite-sulfate of the composition [C2H10N2][Nd(SO3)(SO4)(H2O)](2), V (a = 9.0880(3) angstrom, b = 6.9429(2) angstrom, c = 13.0805(5) A, beta = 91.551(2)degrees, Z = 2, and space group P2(1)/c), with a layered structure containing metal-oxygen-metal bonds has also been described.

One-dimensional zig-zag type coordination polymers of Ni(II) and Cu(II) containing 1,3-benzenedicarboxylate and 1,3-diaminopropane: Structural, spectral and thermal studies

Two coordination polymers [Ni(ipt)(dap)(2)](n) (1) and [Cu(ipt)(dap)H2O](n) center dot nH(2)O (2) with an overall one-dimensional arrangement and having isophthalate (ipt) as bridging moieties and chelating 1,3-diaminopropane (dap) as structure modulating units have been prepared and characterized by crystallographic, spectroscopic and thermo-analytical studies. Both have an overall one-dimensional zig-zag nature but with a distorted octahedral NiN4O2 chromophore for 1 and a distorted square pyramidal CuN2O3 chromophore for 2. Even though the ipt units are acting as bridging units through mono-dentatively coordinating carboxylate functions in both polymers, compound 1 has the carboxylate oxygen linkages at the trans positions, while in 2 the oxygen linkages occur at the cis positions leading to a different type of zig-zag arrangement. Relevant spectral and bonding parameters also could be evaluated for the compounds using UV-Vis and EPR spectra. Thermal stability and possible structural modifications on thermal treatment of the compounds were also investigated and the relevant thermodynamic and kinetic parameters evaluated from the thermal data. (C) 2007 Elsevier B.V. All rights reserved.

Enhanced Ion Anisotropy by Nonconventional Coordination Geometry: Single-Chain Magnet Behavior for a [{(FeL)-L-II}(2){Nb-IV(CN)(8)}] Helical Chain Compound Designed with Heptacoordinate Fe-II

Nonconventional heptacoordination in combination with efficient magnetic exchange coupling is shown to yield a 1-D heteronuclear {(FeNbIV)-Nb-II} compound with remarkable magnetic features when compared to other Fe(II)-based single chain magnets (SCM). Cyano-bridged heterometallic {3d-4d} and {3d-5d} chains are formed upon assembling Fe(II) bearing a pentadentate macrocycle as the blocking ligand with octacyano metallates, [M(CN)(8)](4-) (M = Nb-IV, Mo-IV, W-IV.) X-ray diffraction (single-crystal and powder) measurements reveal that the [{(H2O)Fe(L-1)}{M(CN)(8)}{Fe(L-1)}](infinity) architectures consist of isomorphous 1-D polymeric structures based on the alternation of {Fe(L-1)}(2+) and {M(CN)(8)}(4-) units (L-1 stands for the pentadentate macrocycle). Analysis of the magnetic susceptibility behavior revealed cyano-bridged {Fe-Nb} exchange interaction to be antiferromagnetic with J = -20 cm(-1) deduced from fitting an Ising model taking into account the noncollinear spin arrangement. For this ferrimagnetic chain a slow relaxation of its magnetization is observed at low temperature revealing a SCM behavior with Delta/k(B) = 74 K and tau(0) = 4.6 x 10(-11) s. The M versus H behavior exhibits a hysteresis loop with a coercive field of 4 kOe at 1 K and reveals at 380 mK magnetic avalanche processes, i.e., abrupt reversals in magnetization as H is varied. The origin of these characteristics is attributed to the combination of efficient {Fe-Nb} exchange interaction and significant anisotropy of the {Fe(L-1)) unit. High field EPR and magnetization experiments have revealed for the parent compound [Fe(L-1)(H2O)(2)]Cl-2 a negative zero field splitting parameter of D approximate to -17 cm(-1). The crystal structure, magnetic behavior, and Mossbauer data for [Fe(L-1)(H2O)(2)]Cl-2 are also reported.

Enhanced Ion Anisotropy by Nonconventional Coordination Geometry: Single-Chain Magnet Behavior for a [{(FeL)-L-II}(2){Nb-IV(CN)(8)}] Helical Chain Compound Designed with Heptacoordinate Fe-II

Nonconventional heptacoordination in combination with efficient magnetic exchange coupling is shown to yield a 1-D heteronuclear {(FeNbIV)-Nb-II} compound with remarkable magnetic features when compared to other Fe(II)-based single chain magnets (SCM). Cyano-bridged heterometallic {3d-4d} and {3d-5d} chains are formed upon assembling Fe(II) bearing a pentadentate macrocycle as the blocking ligand with octacyano metallates, [M(CN)(8)](4-) (M = Nb-IV, Mo-IV, W-IV.) X-ray diffraction (single-crystal and powder) measurements reveal that the [{(H2O)Fe(L-1)}{M(CN)(8)}{Fe(L-1)}](infinity) architectures consist of isomorphous 1-D polymeric structures based on the alternation of {Fe(L-1)}(2+) and {M(CN)(8)}(4-) units (L-1 stands for the pentadentate macrocycle). Analysis of the magnetic susceptibility behavior revealed cyano-bridged {Fe-Nb} exchange interaction to be antiferromagnetic with J = -20 cm(-1) deduced from fitting an Ising model taking into account the noncollinear spin arrangement. For this ferrimagnetic chain a slow relaxation of its magnetization is observed at low temperature revealing a SCM behavior with Delta/k(B) = 74 K and tau(0) = 4.6 x 10(-11) s. The M versus H behavior exhibits a hysteresis loop with a coercive field of 4 kOe at 1 K and reveals at 380 mK magnetic avalanche processes, i.e., abrupt reversals in magnetization as H is varied. The origin of these characteristics is attributed to the combination of efficient {Fe-Nb} exchange interaction and significant anisotropy of the {Fe(L-1)) unit. High field EPR and magnetization experiments have revealed for the parent compound [Fe(L-1)(H2O)(2)]Cl-2 a negative zero field splitting parameter of D approximate to -17 cm(-1). The crystal structure, magnetic behavior, and Mossbauer data for [Fe(L-1)(H2O)(2)]Cl-2 are also reported.

Comparison of Multiclass SVM Classification Methods to Use in a Supportive System for Distance Relay Coordination

This paper aims at evaluating the methods of multiclass support vector machines (SVMs) for effective use in distance relay coordination. Also, it describes a strategy of supportive systems to aid the conventional protection philosophy in combating situations where protection systems have maloperated and/or information is missing and provide selective and secure coordinations. SVMs have considerable potential as zone classifiers of distance relay coordination. This typically requires a multiclass SVM classifier to effectively analyze/build the underlying concept between reach of different zones and the apparent impedance trajectory during fault. Several methods have been proposed for multiclass classification where typically several binary SVM classifiers are combined together. Some authors have extended binary SVM classification to one-step single optimization operation considering all classes at once. In this paper, one-step multiclass classification, one-against-all, and one-against-one multiclass methods are compared for their performance with respect to accuracy, number of iterations, number of support vectors, training, and testing time. The performance analysis of these three methods is presented on three data sets belonging to training and testing patterns of three supportive systems for a region and part of a network, which is an equivalent 526-bus system of the practical Indian Western grid.

Solution concepts in two-person multicriteria games

In this paper, we propose new solution concepts for multicriteria games and compare them with existing ones. The general setting is that of two-person finite games in normal form (matrix games) with pure and mixed strategy sets for the players. The notions of efficiency (Pareto optimality), security levels, and response strategies have all been used in defining solutions ranging from equilibrium points to Pareto saddle points. Methods for obtaining strategies that yield Pareto security levels to the players or Pareto saddle points to the game, when they exist, are presented. Finally, we study games with more than two qualitative outcomes such as combat games. Using the notion of guaranteed outcomes, we obtain saddle-point solutions in mixed strategies for a number of cases. Examples illustrating the concepts, methods, and solutions are included.

Multicriterion differential games with applications to combat problems

In this paper a theory for two-person zero sum multicriterion differential games is presented. Various solution concepts based upon the notions of Pareto optimality (efficiency), security and equilibrium are defined. These are shown to have interesting applications in the formulation and analysis of two target or combat differential games. The methods for obtaining outcome regions in the state space, feedback strategies for the players and the mode of play has been discussed in the framework of bicriterion zero sum differential games. The treatment is conceptual rather than rigorous.

Synthesis, crystal structures and magnetic behavior of two 3D coordination polymers using N-(4/3-arboxyphenyl)iminodiacetic acids as bridging ligands

Research on structure and magnetic properties of polynuclear metal complexes to understand the structural and chemical factors governing the electronic exchange coupling mediated by multi-atom bridging ligands is of growing interest. Hydrothermal treatment of Ni(NO3)(2)center dot 6H(2)O with N-(4-carboxyphenyl)iminodiacetic acid N-4(H(3)CPIDA)] at 150 degrees C yielded a 3D coordination polymer of general formula Ni-3{N-4( CPIDA)}(2)(H2O)(3)]center dot 6H(2)O (1). An analogous network of general formula Co-3{N-3(CPIDA)}(2)(H2O)(3)]center dot 3H(2)O (2) was synthesized using N-(3-carboxyphenyl) iminodiacetic acid N-3(H(3)CPIDA)] in combination with Co(NO3)(2)center dot 6H(2)O under identical reaction condition. Both the complexes contain trinuclear secondary building unit, and crystallized in monoclinic system with space groups C2/c (1) and P2(1)/c (2), respectively. Variable temperature magnetic characterization of these complexes in the temperature range of 2-300 K indicated the presence of overall ferromagnetic and antiferromagnetic behavior for 1 and 2, respectively. Density functional theory calculations (B3LYP functional) were performed for further insight on the trinuclear units to provide a qualitative theoretical interpretation on the overall magnetic behavior of the complexes 1 and 2. (C) 2010 Elsevier B.V. All rights reserved.