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Heterodinuclear mixed valence [Zn(II) - Fe(III)] and the homodinuclear [Zn(II) - Zn(II)] and [Ni(II) - Ni(II)] complexes of a bicompartmental ligand containing a bridging phenoxy as a O - donor and four pyridyl moieties and two amine moieties as the N-donors exhibit phosphoester hydrolysis activity similar to the hydrolase family of enzymes. While the heterodinuclear [Zn(II)-Fe(III)] (2) complex was obtained by the sequential addition of Fe(NO3)(3).9H(2)O and Zn(OAc)(2).2H(2)O to the ligand 2,6-bis{[bis(2-pyridylmethyl)amino]methyl}-4-t-butylphenol (HL) (1) in moderate yield of 37%, the homodinuclear [Zn(II) - Zn(II)] (3) and [Ni(II) - Ni (II)] (4) complexes were obtained by the direct reaction of the ligand (1) with Zn(OAc)(2).2H(2)O and Ni (OAc)(2).2H(2)O respectively, in good to moderate yields (43-63%). Based on the spectrophotometric titration and the mass spectrometry studies, a monoaquated and dihydroxo species 2C, 3C and 4C has been identified as the catalytically active species responsible for the phosphodiester hydrolysis of the bis(2,4 - dinitrophenyl)phosphate (2,4 - BDNPP) substrate in the pH range 5.5-10.5. The kinetic studies further revealed that the homodinuclear [Ni(II) - Ni(II)] complexes (4) (k(cat) = 1.26 x 10(-2)s(-1)) is more active by 39 times than the homodinuclear [Zn(II) - Zn(II)] complexes (3) (k(cat) = 3.20 x 10(-4)s(-1)) and 27 times more active than the heterodinuclear [Zn(II) - Fe(III)] complex (2) (k(cat) = 4.62 x 10(-4)s(-1)) in the phosphodiester hydrolysis activity. Significantly enough, the catalyst - substrate adduct species (2E, 2F and 3F) containing a metal bound bis (2,4-dinitrophenyl)phosphate has been detected by mass spectrometry for the first time.

Reaction of a bulky Schiff base, 2,6-dibenzhydryl-N-4-((2,6 dibenzhydryl-4-methylphenyl)imino)pent-2-en-2-yl)-4-methylaniline (Ar(2)NacNacH (Ar = 2,6-dibenzhydryl-4-methylphenyl)) with PdCl2 in toluene under reflux condition affords dinuclear [(Ar(2)NacNac)Pd (mu-CI)](2) (1). Complex 1 upon crystallization from CH2Cl2-MeCN mixture affords mononuclear [(Ar(2)NacNac)Pd(NCMe)Cl] (2). On the other hand, the reaction of Ar(2)NacNacH with Pd(OAc)(2) in toluene under reflux condition or with Cu(OAc)(2)center dot H2O in CH2Cl-MeOH at room temperature affords mononuclear complexes [(Ar(2)NacNac)M(kappa(2)-OAc)] (M = Pd (3) and Cu (4)). The new complexes have been characterized by spectroscopic (IR, ESI-MS, NMR or EPR, UV-Vis), microanalytical (CHN) and thermogravimetric analysis (TGA) techniques, in addition to a single crystal X-ray diffraction study for 2-4. Complexes 1-3 have been employed in Suzuki coupling whereas complex 4 has been investigated for the oxidation of secondary alcohols and have been found to be highly efficient catalysts for the respective reactions. (C) 2018 Elsevier B.V. All rights reserved.

The reaction of [Fe2(CO)6(μ-toluene-3, 4-benzenedithiolate)] 1 and bidentate diphosphine, 1, 1′-bis(diphenylphosphino)ferrocene (dppf) has been studied. New complexes obtained have been characterized by various spectroscopic techniques as bioinspired models of the iron hydrogenase active site. The crystal structure of [Fe2(CO)5(κ 1-dppfO)(μ-toluene-3, 4-benzenedithiolate)] 4 is reported.

Molecular tunnels in enzyme systems possess variable architecture and are therefore difficult to predict. In this work, we design and apply an algorithm to resolve the pathway followed by ammonia using the bifunctional enzyme formylglycinamide ribonucleotide amidotransferase (FGAR-AT) as a model system. Though its crystal structure has been determined, an ammonia pathway connecting the glutaminase domain to the 30 angstrom distal FGAR/ATP binding site remains elusive. Crystallography suggested two purported paths: an N-terminal-adjacent path (path 1) and an auxiliary ADP-adjacent path (path 2). The algorithm presented here, RismPath, which enables fast and accurate determination of solvent distribution inside a protein channel, predicted path 2 as the preferred mode of ammonia transfer. Supporting experimental studies validate the identity of the path, and results lead to the conclusion that the residues in the middle of the channel do not partake in catalytic coupling and serve only as channel walls facilitating ammonia transfer.

Microwave irradiation of a toluene solution of the diyne FcC(2)C(2)Ph and Ru-3(CO)(12) yields the [Ru(CO)(3)(eta(4)-ruthenole)] derivatives 1a-f, which differ in relative positions of the uncoordinated alkyne group. Upon treatment with Pt(PPh3)(2)C2H4, the ruthenoles 1a-c, containing a single free C equivalent to C unit at the a position with respect to the ring Ru metal, yield the novel allene-coordinated, phosphido-bridged Ru2Pt clusters 3a-c along with their phosphine-substituted derivatives 4a-c. Under similar reaction conditions, isomers 1d,e, which are devoid of any free C equivalent to C unit at the alpha position, and If, having free C equivalent to C units at both alpha positions, form only their phosphine-substituted derivatives 4d-f. The formation of Ru2Pt clusters from ruthenole complexes involves cleavage of the P-C bond of the phosphine and migration of the resulting phenyl group onto the free alkyne, which leads to enyne to allene transformation.

Two coumarin derived alpha-dicarbonyls, HOCGO and DMACGO, are presented as pH, polarity and quencher sensitive fluorescent reporters for proteins that can be targeted at reactive arginines. Both inactivate a number of enzymes that feature functionally critical and chemically susceptible arginyls. Both are chemoselective in responding towards Arg side chain but not towards Cys or Lys side chains under suitably dilute conditions. With pK(app) approximate to 6.7, HOCGO can serve as a pH sensor, while with pK(app) much less than 4.0, DMACGO is better suited as a polarity sensor. A contrasting set of changes are manifest in the CGOs upon protein interaction that are either attributable to Arg modification or to the noncovalent probe associations with hydrophobic protein domains. DMACGO probes a single hydrophobic site on ovalbumin while HOCGO is largely unresponsive to this protein. Three to five arginyls are modified in HSA and BSA by HOCGO as well as DMACGO, while the latter also probes two hydrophobic sites on both these proteins. HOCGO modifies a single arginine in LDH active site, while its adducts with H-4 and M(4)LDH isozymes titrate to the apparent pK(a) of 7.8. Other proteins labeled with HOCGO or DMACGO reveal a number of variations that can furnish information about the microenvironment in the sites probed. The CGOs are thus potentially useful reporters of protein domains that feature reactive arginines. Suitable experimental condition are defined based on mechanistic considerations that may be used in applying the CGOs as Arg modifiers and as fluorescent probes.