Ligand versus metal protonation of an iron hydrogenase active site mimic

The protonation behavior of the iron hydrogenase active-site mimic [Fe2(mu-adt)(CO)4(PMe3)2] (1; adt=N-benzyl-azadithiolate) has been investigated by spectroscopic, electrochemical, and computational methods. The combination of an adt bridge and electron-donating phosphine ligands allows protonation of either the adt nitrogen to give [Fe2(mu-Hadt)(CO)4(PMe3)2]+ ([1 H]+), the Fe-Fe bond to give [Fe2(mu-adt)(mu-H)(CO)4(PMe3)2]+ ([1 Hy]+), or both sites simultaneously to give [Fe2(mu-Hadt)(mu-H)(CO)4(PMe3)2]2+ ([1 HHy]2 +). Complex 1 and its protonation products have been characterized in acetonitrile solution by IR, (1)H, and (31)P NMR spectroscopy. The solution structures of all protonation states feature a basal/basal orientation of the phosphine ligands, which contrasts with the basal/apical structure of 1 in the solid state. Density functional calculations have been performed on all protonation states and a comparison between calculated and experimental spectra confirms the structural assignments. The ligand protonated complex [1 H]+ (pKa=12) is the initial, metastable protonation product while the hydride [1 Hy]+ (pKa=15) is the thermodynamically stable singly protonated form. Tautomerization of cation [1 H]+ to [1 Hy]+ does not occur spontaneously. However, it can be catalyzed by HCl (k=2.2 m(-1) s(-1)), which results in the selective formation of cation [1 Hy]+. The protonations of the two basic sites have strong mutual effects on their basicities such that the hydride (pK(a)=8) and the ammonium proton (pK(a)=5) of the doubly protonated cationic complex [1 HHy]2+ are considerably more acidic than in the singly protonated analogues. The formation of dication [1 HHy]2+ from cation [1 H]+ is exceptionally slow with perchloric or trifluoromethanesulfonic acid (k=0.15 m(-1) s(-1)), while the dication is formed substantially faster (k>10(2) m(-1) s(-1)) with hydrobromic acid. Electrochemically, 1 undergoes irreversible reduction at -2.2 V versus ferrocene, and this potential shifts to -1.6, -1.1, and -1.0 V for the cationic complexes [1 H]+, [1 Hy]+, and [1 HHy]2+, respectively, upon protonation. The doubly protonated form [1 HHy]2+ is reduced at less negative potential than all previously reported hydrogenase models, although catalytic proton reduction at this potential is characterized by slow turnover.     

Electronic spectroscopy, photophysical properties, and emission quenching studies of an oxidatively robust perfluorinated platinum porphyrin

The highly electron-deficient, beta-octafluorinated meso-tetrakis(pentafluorophenyl)-porphyrin (H(2)F(28)TPP) was metalated with platinum to afford the oxidatively robust luminophore [PtF(28)TPP], and its X-ray structure shows that the porphyrin core exists in a slightly saddle-shaped conformation. The absorption spectrum of [PtF(28)TPP] in CH(2)Cl(2) displays a near-UV Soret band (B) at 383 nm (epsilon = 2.85 x 10(5) dm(3) mol(-1) cm(-1)) and two visible Q(1,0) and Q(0,0) bands at 501 (epsilon = 1.45 x 10(4) dm(3) mol(-1) cm(-1)) and 533 (epsilon = 1.36 x 10(4) dm(3) mol(-1) cm(-1)) nm, respectively. These absorption bands of [PtF(28)TPP] are blue-shifted from those in [PtF(20)TPP] (390, 504, and 538 nm, respectively) and [PtTPP] (401, 509, and 539 nm, respectively). Excitation of [PtF(28)TPP] (complex concentration = 1.5 x 10(-6) mol dm(-3)) in dichloromethane at the Soret or Q(1,0) or Q(0,0) band gave a phosphorescence with peak maximum at 650 nm (lifetime = 5.8 micros) and a weak shoulder at 712 nm. Both the emission lifetime and quantum yield vary with solvent polarity, and plots of tau versus E(K) and Phi versus E(K) (where E(K) is the empirical solvent polarity parameter based on the hypsochromic shift of the longest wavelength absorption of the [Mo(CO)(4)[(C(5)H(4)N)HC[double bond]NCH(2)C(6)H(5)]] complex with increasing solvent polarity; see: Kamlet, M. J.; Abboud, J. L. M.; Taft, R. W. Prog. Phys. Org. Chem. 1981, 13, pp 485-630) show linear correlation, indicating that the emission is sensitive to the local environment/medium. Electrochemical studies on [PtF(28)TPP] by cyclic voltammetry showed no porphyrin-centered oxidation at potential < or = 1.5 V versus Ag/AgNO(3), demonstrating that [PtF(28)TPP] is more resistant toward oxidation than [PtF(20)TPP] (E(1/2) = 1.33 V) and [PtTPP] (E(1/2) = 0.97 V). The porphyrin-centered reduction of [PtF(28)TPP] occurs at -0.75 and -1.18 V, which is anodically shifted from those at -1.06 and -1.55 V in [PtF(20)TPP], and -1.51 V in [PtTPP], respectively. The excited-state reduction potential of [PtF(28)TPP] is estimated to be 1.49 V versus Ag/AgNO(3). Over 97% of the emission intensity of [PtF(28)TPP] was retained after irradiation with a high power mercury arc lamp (500 W) for 14 h, compared to 90% and 12% for [PtF(20)TPP] and [PtTPP], respectively; hence, [PtF(28)TPP] exhibits superior photostability. Quenching of the emission of [PtF(28)TPP] by oxygen, alcohol, catechol, and butylamine reveals that [PtF(28)TPP] is an oxidatively robust material with medium-sensitive photoluminescence properties.     

Dechlorination of beta-methylallyl chloride by electrogenerated [Co(I)(bipyridine)3]+: an electrochemical study in the presence of cationic surfactants

We have investigated the electrocatalytic dehalogenation of beta-methylallyl chloride (beta-mAC), widely used in the polymer industry, using [Co(I)(bpy)3]+ (where bpy=2,2'-bipyridine) electrochemically generated in situ from [Co(II)(bpy)3]2+ at a glassy carbon electrode in the presence of three different cationic surfactants in aqueous solution. Cetyltrimethylammonium bromide (CTAB), tetradecyltrimethylammonium bromide (TDTAB), and cetylbenzyldimethylammonium chloride (CBDAC) were employed in the present investigation. The [Co(II)(bpy)3]2+-cationic surfactant systems show excellent electrocatalytic activity toward dehalogenation of beta-mAC. The dependence of the catalytic current, the corresponding potential, and the current function on the potential scan rate has been analyzed to assess the nature of the catalytic reaction. The second-order rate constant, kchem, for the reaction between the beta-mAC substrate and the electrogenerated-micelle stabilized-Co(I) complex has been calculated by a cyclic voltammetry technique. The reduction products after 3 h of bulk electrolysis have been identified by GC/MS to be one nonchloro compound (2-methyl-1,5-hexadiene (IV)) and two chloro compounds (1-chloro-2,5-dimethyl-2,5-hexadiene (V) and spiro[1.2]cylopropyl-6-chloro-5-methyl-hex-4-ene (VI)). Based on the electrochemical results and the mass spectral data, a reaction scheme involving all the reduction products has been proposed. Finally, a good correlation between the catalytic efficiency and the structural features of the surfactant molecules is demonstrated. The present study emphasizes the need for further optimization work to achieve maximum yield of nonchloro compound (IV) to employ the present [Co(II)(bpy)3]2+-cationic surfactant systems with a high catalytic efficiency as promising for possible applications.     

A novel bornane synthesis by an old idea

Aiming at a synthesis of spiro[2.4]hepta-4,6-dienes with a carbon substituent at C-4, we investigated solvolysis reactions of the thiatricycle 2, obtained from spiro[2.4]hepta-4,6-diene (1) and thiophosgene by [4 + 2] cycloaddition. With methanol or ethanol a mixture of the esters 7 and 8 was formed. Desulfurization of the thionoesters 8 gave methyl and ethyl spiro[2.4]hepta-4,6-diene-4-carboxylate (10a,b). The corresponding alcohol (11) was prepared from 10b by LiAlH(4) reduction. Ethenetetracarbonitrile combined with the 4-substituted spiro[2.4]hepta-4,6-dienes to give the [4 + 2] cycloadducts 12a-c. Diels-Alder reaction between 11 and 2-chloroacrylonitrile afforded the spiro(bicyclo[2.2.1]hept-5-ene-7,1'-cyclopropane) derivative 14a that was transformed in three steps to rac-10-hydroxycamphor (17). This synthesis of a bornane derivative opens opportunity for variations and thus may find further applications.     

Introduction of an arylthio(trimethylsilyl)methyl group into arenes by friedel-crafts reaction: synthesis of arylmethyltrimethylsilanes

Friedel-crafts reactions of [arylthio(chloro)methyl]trimethylsilanes (1a,b) with arenes gave [aryl(arylthio)methyl]trimethylsilanes (2a,b), which were converted into arylmethyltrimethylsilanes (3) by reduction with raney nickel.     

Polymeric fullerene hydrides. Birch reduction of [60] fullerene polymers from solution-based photopolymerization and free radical polymerization reactions

Fullerene polymers represent a new class of carbon materials for potential hydrogen storage applications. Poly[60]fullerene polymers were obtained by covalently linking [60]fullerene molecules in photochemical reactions. [60]Fullerene polymers were also prepared in free radical reactions of [60]fullerene with radical initiator benzoyl peroxide. The polymeric [60]fullerene materials were hydrogenated under Birch reduction conditions. The hydrides, which contain ≈3.5% (wt/wt) of hydrogen, were characterized by use of gel permeation chromatography, NMR, FT-IR, and elemental analysis. The results are compared with those of monomeric [60]fullerene hydrides.     

Uranyl complexation by chloride ions. Formation of a tetrachlorouranium(VI) complex in room temperature ionic liquids [Bmim][Tf2N] and [MeBu3N][Tf2N

The tetrachlorouranium(VI) complex is formed in [Bmim][Tf2N] and [MeBu3N][Tf2N] from a uranium(VI) solution in the presence of a stoichiometric quantity of chloride ions. The [UVIO2Cl4]2- absorption and emission spectra show bands splitting in comparison with the [UVIO2]2+ spectra, as observed in the solid state, organic solvents, and chloroaluminate-based ionic liquids. The fluorescence lifetime of [UO2Cl4]2- in [MeBu3N][Tf2N] is 0.7 +/- 0.1 mus. The reduction potential of this complex is -1.44 and -1.8 V vs Ag/Ag+ respectively in [Bmim][Tf2N] and [MeBu3N][Tf2N] and does not depend on the chloride concentration. The mechanism proposed for the redox process is a monoelectronic reduction to form [UVO2Cl4]3-, followed by a chemical reaction. The tetrachlorouranium(V) complex seems more stable in [Bmim][Tf2N] than in [MeBu3N][Tf2N]. The electrochemical analysis put in evidence specific interactions of the ionic liquid cation with the uranium anionic species.     

Polynuclear heterocyclic compounds containing an indole fragment

Derivatives of 6,7,9,10,11,12-hexahydro-5H-indolo[3,2,1-d,e]phenazine and 1,2,3,4-tetrahydroindolo[1,2-a]quinoxaline were obtained by condensation of the sodium derivatives of 1-keto-1,2,3,4-tetrahydrocarbazoles and 2-aroylindoles, respectively, with-bromocyclohexanone dimethylketal. These compounds are converted to derivatives of indolo[1,2-a]-quinoxaline, 5,6-dihydroindolo[1,2-a]quinoxaline, and 8a,9,10,11,12,12a-hexahydro- and 5,6,7,7a,8a,9,10,11,12,12a-decahydro-8H-indolo[3,2,1-d,e]phenazine by dehydrogenation over a Raney nickel catalyst and reduction with sodium in alcohol.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1348–1352, October, 1970.     

An electroactive nickel containing polymeric film obtained by electrochemical reduction of an aryl-nickel derivative

The electrochemical reduction of [Ni(PPh₃)₂(p-C₆H₄Br)Br] in acetonitrile results in a polymeric coating of a nickel-containing poly-p-phenylene, formulated as [-Ni(p-C₆H₄)_n-] (n=6?7) on the basis of elemental analysis, IR, UV, MS and ESCA measurements. This coating is found to undergo a two-electron reversible reduction and a one-electron reversible oxidation with a large potential window (3.6 V), without the polymeric film being destroyed. Moreover, the polymer obtained is shown to be electroactive towards dissolved reactants via permeation or mediated electron transfer, depending on the molecular size of the electroactive species employed.     

Gold nanoparticles in organic capsules: a supramolecular assembly of gold nanoparticles and cucurbituril

Gold nanoparticles (相似文献   

Dinaphthotetraaza[14]annulene copper(II) complexes in the electrocatalytic reduction of carbon dioxide and bisulfite anion

A modified synthetic route for the complexes [Cu(II)5,7,12,14-tetramethyldinaphtho [b,i][1,4,8,11]tetraaza[14]annulene], [Cu(II)tmdnTAA], and [Cu(II) 5,7,12,14-tetramethyl-6,13-dichloro-dinaphtho[b,i][1,4,8,11]tetraaza[14]annulene], [Cu(II)dCltmdnTAA], is presented in this work. The electrochemical characterization of both complexes and their precursors, [bis(2,4-pentanedionato)copper(II)], [Cu(II)(acac)₂] and [bis(3-chloro-2,4-pentanedionato)copper(II)], [Cu(II)(3-Cl-acac)₂], respectively, under nitrogen and carbon dioxide is also presented. The voltammetric response of [Cu(II)(acac)₂] and [Cu(II)(3-Cl-acac)₂] are different compared to [Cu(II)tmdnTAA] and [Cu(II)dCltmdnTAA] under nitrogen. Precursors show the reduction of Cu(I) to Cu(0) and the tetraazadinaphtho[14]annulene complexes do not. The chlorine substituted complex has a lower reduction potential than the unsubstituted homologue under nitrogen atmosphere. However, the contrary response is obtained in the presence of carbon dioxide: the unsubstituted complex is more catalytic in terms of potential because the current discharge appears 270?mV shifted to the anodic region. These facts can be explained in terms of electronic and steric effects. The modified electrode obtained by oxidative electropolymerization of [Cu(II)tmdnTAA] over glassy carbon electrode presented a suitable amperometric response for the sulfite reduction in acidic medium (pH?=?2.7). A linear correlation was observed for the catalytic current and sulfite concentration between 0.6–6.0?mM range.     

Uranium halide complexes in ionic liquids: an electrochemical and structural study

The electrochemistry of the salts, [emim]2[UBr6] and [emim]2[UO2Br4] ([emim] = 1-ethyl-3-methylimidazolium), has been investigated in both a basic and an acidic bromoaluminate(III) ionic liquid. In the basic ionic liquid, the hexabromo salt undergoes a one-electron reversible reduction process at a stationary glassy carbon disc electrode, while the tetrabromodioxo salt was reduced to a uranium(IV) species by an irreversible two-electron process with the simultaneous transfer of oxide to the ionic liquid. On the other hand, dissolution of either of the salts in an acidic bromoaluminate(III) ionic liquid resulted in the formation of the same electroactive species. The solid state structures of the uranium chloride salts, [emim]2[UCl6] and [emim]2[UO2Cl4], have previously been reported, but have now been re-evaluated using a new statistical model developed in our group, to determine the presence or absence of weak hydrogen bonding interactions in the crystalline state.     

Synthesis and properties of a new kinetically stabilized digermyne: new insights for a germanium analogue of an alkyne

The reduction of an overcrowded (E)-1,2-dibromodigermene, Bbt(Br)Ge=Ge(Br)Bbt (2) [Bbt = 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl], with KC8 afforded a stable digermyne, BbtGe[triple bond]GeBbt (1). The Ge[triple bond]Ge triple-bond characters of 1 were revealed by the X-ray crystallographic analysis and spectroscopic studies (UV/vis and Raman spectra) together with theoretical calculations. The Ge[triple bond]Ge bond lengths of the two nonidentical molecules of 1 observed in the unit cell were shorter than that of the previously reported digermyne, Ar'Ge[triple bond]GeAr' (Ar' = 2,6-Dip2C6H3, Dip = 2,6-diisopropylphenyl).     

Electronic structure studies of oxomolybdenum tetrathiolate complexes: origin of reduction potential differences and relationship to cysteine-molybdenum bonding in sulfite oxidase

Electronic absorption, magnetic circular dichroism, and resonance Raman spectroscopies have been used to determine the nature of oxomolybdenum-thiolate bonding in (PPh4)[MoO(SPh)4] (SPh = phenylthiolate) and (HNEt3)[MoO(SPh-PhS)2] (SPh-PhS = biphenyl-2,2'-dithiolate). These compounds, like all oxomolybdenum tetraarylthiolate complexes previously reported, display an intense low-energy charge-transfer feature that we have now shown to be comprised of multiple S-->Mo dxy transitions. The integrated intensity of this low-energy band in [MoO(SPh)4]- is approximately twice that of [MoO(SPh-PhS)2]-, implying a greater covalent reduction of the effective nuclear charge localized on the molybdenum ion of the former and a concomitant negative shift in the Mo(V)/Mo(IV) reduction potential brought about by the differential S-->Mo dxy charge donation. However, this is not observed experimentally; the Mo(V)/Mo(IV) reduction potential of [MoO(SPh)4]- is approximately 120 mV more positive than that of [MoO(SPh-PhS)2]- (-783 vs -900 mV). Additional electronic factors as well as structural reorganizational factors appear to play a role in these reduction potential differences. Density functional theory calculations indicate that the electronic contribution results from a greater sigma-mediated charge donation to unfilled higher energy molybdenum acceptor orbitals, and this is reflected in the increased energies of the [MoO(SPh-PhS)2]- ligand-to-metal charge-transfer transitions relative to those of [MoO(SPh)4]-. The degree of S-Mo dxy covalency is a function of the O identical to Mo-S-C dihedral angle, with increasing charge donation to Mo dxy and increasing charge-transfer intensity occurring as the dihedral angle decreases from 90 to 0 degree. These results have implications regarding the role of the coordinated cysteine residue in sulfite oxidase. Although the O identical to Mo-S-C dihedral angles are either approximately 59 or approximately 121 degrees in these oxomolybdenum tetraarylthiolate complexes, the crystal structure of the enzyme reveals an O identical to Mo-SCys-C angle of approximately 90 degrees. Thus, a significant reduction in SCys-Mo dxy covalency is anticipated in sulfite oxidase. This is postulated to preclude the direct involvement of coordinated cysteine in coupling the active site into efficient superexchange pathways for electron transfer, provided the O identical to Mo-SCys-C angle is not dynamic during the course of catalysis. Therefore, we propose that a primary role for coordinated cysteine in sulfite oxidase is to statically poise the reduced molybdenum center at more negative reduction potentials in order to thermodynamically facilitate electron transfer from Mo(IV) to the endogenous b-type heme.     

银纳米颗粒的合成及用于抗癌药氟他胺的电化学检测（英文）

Ag nanoparticles were synthesized on the surface of a glassy carbon electrode modified with p‐tert‐butylcalix[4]arene and p‐tert‐butylcalix[6]arene by the deposition of Ag+ at an open circuit potential followed by the electrochemical reduction of the Ag+.The presence of the calixarene layer on the electrode surface controlled the particle size and prevented agglomeration.Cyclic voltam‐metry showed that the Ag nanoparticles on the modified glassy carbon electrode had good catalytic ability for the reduction of flutamide.The effects of calixarene concentration,potential applied for the reduction of Ag+,number of calixarene layers,and p H value on the electrocatalytic activity of the Ag nanoparticles were investigated.The modified electrode had a linear range in differential pulse voltammetry of 10-1000 μmol/L with a detection limit of 9.33 μmol/L for flutamide at an S/N = 3.The method was applied to the detection of flutamide in practical samples.     

Novel synthesis, properties, and NAD+-NADH type redox ability of 1,3-dimethylcyclohepta[4,5]pyrrolo[2,3-d]pyrimidine- 2,4(1,3h)-dionylium ions annulated with additional pyrrolo[2,3-d]pyrimidine-1,3(2,4h)-dione and furan analogue, and their hydride adducts

[reaction: see text] A convenient preparation of novel cations 11a,b+ x BF4(-) and 12a,b+ x BF4(-), which are derived from annulation of the 1,3-dimethylcyclohepta[4,5]pyrrolo[2,3-d]pyrimidine-2,4(1,3H)-dionylium ion with additional pyrrolo[2,3-d]pyrimidine-1,3(2,4H)-dione and a furan analogue, was accomplished by a novel oxidative cyclization of 1,7-dihydro-7-[1',3'-dimethyl-2',4'(1',3'H)-dioxo-6'-(phenylamino)-pyrimidin-5'-yl]-1,3-dimethyl-10-phenylcyclohepta[4,5]pyrrolo[2,3-d]pyrimidine-2,4(1,3H)-dione 9 and its furan-analogue by using DDQ or photoirradiation under aerobic conditions. Structural characteristics of 11a,b+ and 12a,b+ were clarified on inspection of the UV-vis and NMR spectral data as well as X-ray crystal analyses. The stability of cations 11a,b+ and 12a,b+ is expressed by the pK(R+) values that were determined spectrophotometrically to be 10.7-12.6. The electrochemical reduction of 11a,b+ x BF4(-) and 12a,b+ x BF4(-) exhibited reduction potential at -0.93 to -1.00 (V vs Ag/AgNO3). The first reduction potential of 11a+ was reversible due to steric hindrance of two phenyl groups. The photoinduced oxidation reaction of 11a,b+ x BF4(-) and 12a,b+ x BF4(-) toward some amines under aerobic conditions was carried out to give the corresponding imines (isolated by converting to the corresponding 2,4-dinitrophenylhydrazones) with the recycling numbers of 0.6-30.3. Furthermore, as an example of the NAD+-NADH models, the reduction of a pyruvate analogue and some carbonyl compounds with the hydride-adduct of 11a+ x BF4(-) was accomplished for the first time to give the corresponding alcohol derivatives.     

Electrochemical Study on the Interaction Betwwen Neutral Red and DNA

A voltammetric study of the interaction of neutral Red(NR) with DNA at a gold electrode in a phosphate buffer solution is described. After adding DNA in an NR solution, the reduction peak current of NR decreases. The binding mechahisms of NR to DNA in different pH ranges are different. The reduction peak potential of NR in a pH 7.0 phosphate buffer solution in the presence of DNA shifts positively, indicating that the binding of NR to DNA is intercalation action, but at pH=6.0 the reduction peak potential of NR shifts negatively, indicating that the binding of NR to DNA is electrostatic action. The formed complexes are DNA-NR when [NR]/[DNA]<0.18 and DNA-3NR when [NR]/[DNA]>0.35, respectively.     

Electrochemical Study on the Interaction Between Neutral Red and DNA

IntroductionDeoxyribonucleic acid( DNA) is the most im-portant germ plasma of most organisms.It playsan importantrole in the process ofstoring,copyingand transmitting germ messages.There have beenmany papers studying on the interaction betweensmall molecules and DNA since the1 960′s.Nowthe researches have become a field of common in-terest[1] .Those researches have contributed to theunderstanding of the way of the interaction be-tween DNA and protein.What is more,those re-searches are he…     

Synthesis of 3-substituted-4-phenyl-2-thioxo-1,2,3,4,5,6,7,8-octahydrobenzo[4,5]thieno[2,3-á]pyrimidines

The reactions between 3-benzoyl-2-isothiocyanato-4,5,6,7-tetrahydrobenzo[b]thiophene and hydrazine or primary amines have been studied. The products obtained were identified as derivatives of 4-phenyl-2-thioxo-2,3,5,6,7,8-hexahydrobenzo[4,5]thieno[2,3-d]pyrimidine. Their easy reduction with sodium borohydride provided a useful method for the synthesis of 3-substituted-4-phenyl-2-thioxo-1,2,3,4,5,6,7,8-octahydrobenzo[4,5]thieno[2,3-d]pyrimidines. Both kind of compounds were evaluated as potential analgesic, anti-inflammatory and anti-arthritic agents.     

Use of an ionic liquid in a two-phase system to improve an alcohol dehydrogenase catalysed reduction

Due to favourable partition coefficients the highly enantioselective reduction of 2-octanone, catalysed by an alcohol dehydrogenase from Lactobacillus brevis, is faster in a biphasic system containing buffer and the ionic liquid [BMIM][(CF(3)SO(2))(2)N] compared to the reduction in a biphasic system containing buffer and methyl tert-butyl ether.