Structure and properties of molybdenum(IV,V) arenethiolates with a neighboring amide group. Significant contribution of NH.cntdot..cntdot..cntdot.S hydrogen bond to the positive shift of redox potential of Mo(V)/Mo(IV)

Ueyama, Norikazu; Okamura, Taka‐aki; Nakamura, Akira

doi:10.1021/ja00047a022

Cited by 91 publications

(145 citation statements)

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“…The effect of hydrogen bonding on the reduction potential in molybdenum complexes has been extensively studied (45Ϫ48). The NH ⅐⅐⅐ S hydrogen bond makes a significant contribution to the positive shift of the reduction potential of Mo V /Mo IV in monooxomolybdenum complexes with o-(acylamino)benzenethiolate ligands (48).…”

mentioning

confidence: 99%

Role of Conserved Tyrosine 343 in Intramolecular Electron Transfer in Human Sulfite Oxidase

Feng¹,

Wilson²,

Hurley³

et al. 2003

Journal of Biological Chemistry

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Tyrosine 343 in human sulfite oxidase (SO) is conserved in all SOs sequenced to date. Intramolecular electron transfer (IET) rates between reduced heme (Fe II ) and oxidized molybdenum (Mo VI ) in the recombinant wild-type and Y343F human SO were measured for the first time by flash photolysis. The IET rate in wild-type human SO at pH 7.4 is about 37% of that in chicken SO with a similar decrease in k cat . Steady-state kinetic analysis of the Y343F mutant showed an increase in K m sulfite and a decrease in k cat resulting in a 23-fold attenuation in the specificity constant k cat /K m sulfite at the optimum pH value of 8.25. This indicates that Tyr-343 is involved in the binding of the substrate and catalysis within the molybdenum active site. Furthermore, the IET rate constant in the mutant at pH 6.0 is only about one-tenth that of the wild-type enzyme, suggesting that the OH group of Tyr-343 is vital for efficient IET in SO. The pH dependences of IET rate constants in the wild-type and mutant SO are consistent with the previously proposed coupled electron-proton transfer mechanism.In vertebrates the molybdenum cofactor-containing enzyme sulfite oxidase (SO, 1 EC 1.8.3.1) catalyzes the oxidation of sulfite to sulfate with the reduction of two equivalents of ferricytochrome c (Equation 1) (1, 2), according to the following equation.This is the terminal reaction in the oxidative degradation of sulfur-containing compounds and is physiologically essential. The absence of SO activity in humans is characterized by dislocation of ocular lenses, mental retardation, and in severe cases, attenuated growth of the brain and early death. These severe neurological symptoms result from the inability to properly produce the molybdenum cofactor and also from point mutations in the SO protein itself (3). The x-ray crystal structure of the dimeric chicken liver SO has recently been reported (4). Each subunit consists of an N-terminal b 5 -type cytochrome domain and two larger segments that constitute the central molybdenum binding and C-terminal interface domains. The molybdenum center in SO has square pyramidal coordination geometry. Solvent access to the deeply buried active site is via a channel that opens onto the equatorial MoϪO group. As expected for binding an anionic substrate, the sulfite-binding pocket is very positively charged and consists of three arginines (Arg-138, Arg-190, and Arg-450), Trp-204, and Tyr-322. Tyr-322 is also in close proximity to the molybdenum coordination sphere (Fig. 1A).In the generally accepted catalytic cycle (Fig. 2 , followed by reduction of a second equivalent of cyt c ox , returns the enzyme to the fully oxidized resting state. We have previously shown that exogenous flavin radicals generated in situ with a laser pulse will rapidly reduce the heme center of SO by one electron (Fig. 2) and have used this unique technique to investigate IET between the molybdenum and iron centers as a function of pH values (10Ϫ12). Note that this process corresponds to the second IET step noted above. Comb...

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confidence: 99%

Role of Conserved Tyrosine 343 in Intramolecular Electron Transfer in Human Sulfite Oxidase

Feng¹,

Wilson²,

Hurley³

et al. 2003

Journal of Biological Chemistry

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“…76°) between two S-Mo-S angles indicates the distorted square-pyramidal MoOS 4 core toward trigonal-bipyramidal geometry as described in the literature. 5 The amide and benzene ring are found in almost the same plane and the S-C torsion angle is limited by the steric hindrance of the arene group. Thus the degree of the bending of S 4 plane as illustrated in Figure 7 is a predominant factor to determine the orientation of hydrocarbon chains adjacent to the amide plane.…”

Section: Supramolecular Structure In Solid Statementioning

confidence: 99%

“…Unfortunately, the poor intensity of the reflections resulted in the lack of satisfactory electron density, therefore we tried to refine the orientation of the fixed structure of 1' which was assumed to be similar to the reported structure of (PPh 4 )[Mo v O(S-2-CH3CONH C 6 H 4 ) 4 ]. 5 The cation and anions were located based on Patterson map (R= 34%). In this paper, a preliminary result of X-ray analysis using a model colmplex, (PPh 4 )[Mo vo(S-2-CH 3 CONHC 6 H 4 ) 4 ] is shown.…”

Section: Physical Measurementsmentioning

confidence: 99%

“…Because the solvent-dependent change of the relative intensity is also observed for [Mo vO(S-2-CH3CONHC6H4)4r, it is not caused by the abundance of the two isomers as found for [Mo vO(S-2-tBuCONHC6H4)4]-. 5 The difference of the absorption spectra between 1 and [Mo vO(S-2-CH 3 CONHC 6 H 4 ) 4 ]-and the spectral change depending on solvent suggest variation of environment around the metal ion, which is ascribed to hydrophobic circumstance made by the long hydrocarbon chains.…”

Section: Micellization and Stabilitymentioning

confidence: 99%

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Molecular Assembly and Micellization of Molybdenum(V, IV) Thiolate and Selenolate Complexes with Long Hydrocarbon Chains

Okamura

Taniuchi

Ueyama

et al. 1999

Polym J

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ABSTRACT:Molybdenum(IV, V) thiolate and selenolate complex with four long bundling hydrocarbon chains connected to the amide group, (Ph4 P)[MovO{S-2-CHiCH2) 10CO NHC6H4 } 4 ] and (NEt4h[Mo 1 vO{Se-2-CHiCH 2 ) 10 CONHC 6 H 4 } 4 ] were synthesized. The four chains are oriented toward the same direction in the solution as established by 1 H NMR. These complexes were soluble in an aqueous micellar solution and stabilized against hydrolysis in such aqueous media efficiently by the hydrocarbon chains. The preliminary results of X-ray analysis revealed the individual molecular assembly behavior which depends significantly on the oxidation state of metal ion and the kind of coordinated atom.KEY WORDS Micellization / Hydrocarbon Chain / Assembly / Molybdenum Complex / From a biological point of view, bundling polypeptides or hydrocarbon chains with the same orientation are interesting models for a protein folding, the active site of enzymes, and molecular recognition in biomembrane.1-4 Previously, we reported molybdenum(V) and molybdenum(IV) complexes containing oriented four acetylamino groups, (NEt 4 )[MovO(S-2-CH 3 CO NHC 6 H 4 ) 4 ] and (NEt 4 )i[Mo 1 vO(S-2-CH 3 CONHC 6 H 4 ) 4 ], whose structure allows unique opportunity to bundle four long hydrocarbon chains on the acetyl groups. 5 Replacement of sulfur by selenium gave isostructual molecule due to their similar chemical properties. The MoOQ 4 (Q = S, Se) core has a potential flexibility depending on the oxidation state of metal ion and a kind of Q which determines distance and character of the Mo-Q bonds. Furthermore some biological activities are considered to be supported in hydrophobic media. To simulate biological hydrophobic environment, ones have used hydrophobic solvents, e.g., chloroform, or aqueous micellar solution where the micelles exclude bulk water and hydrogen bond is supported inside of the hydrophobic micelles. 6 Our complexes with hydrocarbon chains can possess a good affinity to both hydrophobic solvents and micelles.On the other hand, three dimensional construction of molecules or supramolecular structure is one of the most noteworthy problems. Especially, supramolecules involving metal ion have been synthesized for their unique physical properties. An ordered orientation of layered molecules in the solid state leads to interesting electronic and magnetic properties. 7 -9 Many of the known such supramolecules exist as assemblies of molecules having two dimensional spread and/or long linear hydrocarbon chains perpendicular to a disk-shape molecule, e.g., porphyrin. 1 o-i 3 Some molecules having bent structure 14 or radial chains 15 have also been reported. Although many kinds of molecules have been known, these molecules have a rigid structure connecting hydrocarbon chains. We have tried to design novel molecules containing flexible basic structure for developing a new t To whom correspondence should be addressed. type of supramolecule.In this paper, the structures of molybdenum(V, IV) complexes containing long hydrocarbon chains with speci...

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“…Mononuclear metal-thiolate complexes including Cu(I) [49], Mo(IV) [50], Fe(II) [51] and Co(II) ions [10], exhibit shortening of the MÀS bond distances with NHÁ Á ÁS hydrogen bonding when compared with the corresponding thiophenolate complexes without hydrogen bonding. For example, a Co(II)-thiolate complex has a tetrahedral geometry with a strong intramolecular NHÁ Á ÁS hydrogen bond (Figure 27.8(c)).…”

Section: Regulation Of Thiolate and Phenolate Ligands In Metal Complementioning

confidence: 99%

Conformational Switching Between Acids and their Anions by Hydrogen Bonding

Okamura

Yamamoto

Ueyama

2010

Hydrogen Bonding and Transfer in the Excited State

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In general, pK a shifts for acids, such as thiols, carboxylic acids, phenols and phosphoric acid monoanions, are considered to occur under homogeneous conditions and change with dielectric constant. Theoretical calculations have been performed for homogeneous environments [1][2][3][4], and some improved theoretical studies have considered anisotropic and heterogeneous environments [4][5][6][7][8] to deal with the particularly large shift for thiols, phenols and carboxylic acids located inside proteins. This paper discusses pK a shifts for acids having neighbouring amide NHs.A relationship between the pK a shift and the formation constant is observed for metal complexes in hydrophobic environments. The influence of intramolecular NHÁ Á ÁX hydrogen bonds on the metal-X bond character is also observed for metal complexes. The presence of NHÁ Á ÁS hydrogen bonds in iron-sulfur proteins observed by crystallographic studies has been suggested by Adman and coworkers [9]. Various synthetic metal-thiolate complexes having chelating Cys-containing oligopeptides and synthetic simple intramolecularly NHÁ Á ÁS hydrogen-bonded thiolate ligands exist. NHÁ Á ÁS hydrogen bonds in metal-thiolate complexes play an important role in the following functions.Intramolecular hydrogen bonds contribute to the following: increase in the stabilization constant, e.g. Fe(II), Zn(II), Cd(II), Hg(II) and Ca(II) complexes; positive shift of the redox potential, e.g. Fe(II), Fe(III), Mo(IV) and W(IV) complexes; and increase in air stabilization, e.g. Fe(II) and Fe(III) complexes. In addition, the NHÁ Á ÁS hydrogen bond increases the formation constant for metal-sulfur complexes formed by substitution reaction between non-hydrogen-bonded and hydrogen-bonded thiolates [10]. The large formation constant is due not only to the pK a -lowering shift of thiol but also to a pp-dp interaction by the NHÁ Á ÁS hydrogen bond.

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Structure and properties of molybdenum(IV,V) arenethiolates with a neighboring amide group. Significant contribution of NH.cntdot..cntdot..cntdot.S hydrogen bond to the positive shift of redox potential of Mo(V)/Mo(IV)

Cited by 91 publications

References 1 publication

Role of Conserved Tyrosine 343 in Intramolecular Electron Transfer in Human Sulfite Oxidase

Role of Conserved Tyrosine 343 in Intramolecular Electron Transfer in Human Sulfite Oxidase

Molecular Assembly and Micellization of Molybdenum(V, IV) Thiolate and Selenolate Complexes with Long Hydrocarbon Chains

Conformational Switching Between Acids and their Anions by Hydrogen Bonding

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