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1.
Cobalt(III) complexes with a thiolate or thioether ligand, t-[Co(mp)(tren)] + (2), t-[Co(mtp)(tren)] 2+ (1Me) and t-[Co(mta)(tren)] 2+ (2Me), (mp = 3-mercaptopropionate, MA = 3-(methylthio)propionate and MTA = 2-(methylthio)acetate) have been prepared in aqueous solutions. The crystal structures of 1, 2, 1Me and 2Me were determined by X-ray diffraction methods. The crystal data are as follows, t-[Co(mp)(tren)]ClO 4 (1CIO 4): monoclinic, P2 1/ n, A = 10.877(8), B = 11.570(4), c = 12.173(7) Å, β = 92.20(5)°, V = 1531(1) Å 3, Z = 4 and R = 0.060; t-[Co(ma)(tren)]Cl·3H 2O (2Cl·3H 2O): monoclinic, P2 1/ n, a = 7.7688(8), B = 27.128(2), C = 7.858(1) Å, β = 100.63(1)°, V = 1627.7(3) Å 3, Z = 4 and R = 0.066; (+) 465CD- t-[ Co( mtp)( tren)]( ClO4) 2 ((+) 465CD-1Me(ClO 4) 2): orthorhombic, P2 12 12 1, A = 10.6610(7), B = 11.746(1), C = 15.555(1) Å, V = 1947.9(3) Å 3, Z = 4 and R = 0.068; (+) 465CD- t-[Co(mta)(tren)](ClO 4) 2 ((+) 465CD-2Me(ClO 4) 2): orthorhombic, P2 12 12 1, a = 10.564(1), B = 11.375(1), C = 15.434(2) Å, V = 1854.7(4) Å 3, Z = 4 and R = 0.047. All central Co(III) atoms have approximately octahedral geometry, coordinated by four N, one O, and one S atoms. All of the complexes are only isomer, of which the sulfur atom in the didentate-O,S ligands are located at the trans position to the tertiary amine nitrogen atom of tren. 1 and 1Me contain six-membered chelate ring, and 2 and 2Me do five-membered chelate ring in the didentate ligand. The chirality of the asymmetric sulfur donor atom in (+) 465CD-1Me is the S configuration and that in (+) 465CD-2Me is the R one. The 1H NMR, 13C NMR and electronic absorption spectral behaviors and electrochemical properties of the present complexes are discussed in relation to their stereochemistries. 相似文献
2.
We have developed the economical and convenient biocatalytic process for the preparation of ( R)-1,3-butanediol (BDO) by stereo-specific microbial oxido-reduction on an industrial scale. ( R)-1,3-BDO is an important chiral synthon for the synthesis of various optically active compounds such as azetidinone derivatives lead to penem and carbapenem antibiotics. We studied on two approaches to obtain (R)-1,3-BDO. The first approach was based on enzyme-catalyzed asymmetric reduction of 4-hydroxy-2-butanone; the second approach was based on enantio-selective oxidation of the undesired (S)-1,3-BDO in the racemate. As a result of screening for yeasts, fungi and bacteria, the enzymatic resolution of racemic 1,3-BDO by the Candida parapsilosis IFO 1396, which showed differential rates of oxidation for two enantiomers, was found to be the most practical process to produce (R)-1,3-BDO with high enantiomeric excess and yield. We characterized the (S)-1,3-BDO dehydrogenase purified from a cell-free extract of C. parapsilosis. This enzyme was found to be a novel secondary alcohol dehydrogenase (CpSADH). We have attempted to clone and characterize the gene encoding CpSADH and express it in Escherichia coli. The CpSADH activity of a recombinant E. coli strain was more than two times higher than that of C. parapsilosis. The production yield of (R)-1,3-BDO from the racemate increased by using the recombinant E. coli strain. Interestingly, we found that the recombinant E. coli strain catalyzed the reduction of ethyl 4-chloro-3-oxo-butanoate to ethyl (R)-4-chloro-3-hyroxy-butanoate with high enantiomeric excess. 相似文献
3.
The preparation and structural characterization of dirhodium(II) tetrakis[ N,N-dimethyl-2-pyrrolidone-5( S)-carb- oxamide], Rh 2(5 S-DMAP) 4, a new sterically-demanding catalyst for enantioselective metal carbene transformations, is described. The pyrrolidone ligands are arrayed around the dirhodium(II) core with two oxygen and two nitrogen donor atoms, each oriented cis, bound to each octahedral rhodium. The crystal structure of this compound has been determined to be that of Rh 2(5 S-DMAP) 4(CH 3CN) 2·CH 3CN·6H 2O: space group P2 12 12 1 with cell constants a= 12.685(4), b=15.050(3), c=24.035(4) Å; V=4588.5(1.9) Å 3, Z=4, R=0.0316, Rh---Rh DISTANCE =2 4538(5) Å. Decreased activity for diazodecomposition catalyzed by Rh 2(5 S-DMAP) 4 is observed, and enantiocontrol for cyclopropanation and carbon-hydrogen insertion is lower than expected by analogy to the corresponding di- rhodium(II) tetrakis[methyl 2-pyrrolidone-5( S)-carboxylate], Rh 2(5 S-MEPY) 4 Electronic stabilization of the in- termediate metal carbene is absent in reactions catalyzed by Rh 2(5 S-DMAP) 4. 相似文献
4.
- erythro-5,6,7,8-Tetrahydrobiopterin (BH 4), which is the cofactor of aromatic amino acid hydroxylases, plays an important role in the biosyntheses of monoamine neurotransmitters. BH 4 exists as natural (6 R)- and unnatural (6 S)-isomers. In our previous reports, only (6 R)-isomer significantly stimulated cofactor activity for tyrosine, tryptophan and phenylalanine hydroxylases (TH, TPH, PAH) in whole animals or in tissue slices. In this study we have compared the in situ cofactor activity on TH between natural (6 R)- and unnatural (6 S)-isomers in clonal cells. We have transfected human TH type 2 cDNA into the normal rat kidney (NRK) fibroblasts. These cells expressed TH protein, but had neither DOPA decarboxylase (DDC) nor BH 4. Thus, TH activity was observed only in the presence of exogenous BH 4. We compared the difference in in situ DOPA formation by TH activity in the presence of (6 R)- or (6 S)-BH 4 in the human TH-transfected cells. The effect of exogenous BH 4 was also compared between (6 R)- and (6 S)-isomers in rat pheochromocytoma PC12h cells, which contained approximately 100 μM endogenous (6 R)-BH 4. The rate of uptake of both BH 4 isomers into these cells increased in proportion to the pterin cofactor concentrations in the incubation medium up to 400 μM but was nearly saturated at 1 mM BH 4. TH-transfected NRK fibroblasts formed DOPA only in the presence of exogenously added (6 R)- or (6 S)-BH 4 dose-dependently and released DOPA into the medium. At a saturating concentration of 1 mM, (6 R)-BH 4 was approximately three times as active as (6 S)-BH 4. In contrast, in PC12h cells which contained endogenous (6 R)-BH 4 (approximately 100 μM), exogenous (6 R)-BH 4 activated DOPA formation maximally at 500 μM about 10-fold, while (6 S)-BH 4 activated it only slightly, about 2.5-fold. These results suggest that (6 S)-isomer has lower cofactor activity with TH in the cells than (6 R)-isomer. This TH transfected fibroblasts should be useful to assess cofactor activities of tetrahydropteridines in the cell. 相似文献
5.
Rapid reactions occur between [Os VI(tpy)(Cl) 2(N)]X (X = PF 6−, Cl −, tpy = 2,2′:6′,2″-terpyridine) and aryl or alkyl phosphi nes (PPh 3, PPh 2Me, PPhMe 2, PMe 3 and PEt 3) in CH 2Cl 2 or CH 3CN to give [Os IV(tpy)(Cl) 2(NPPh 3)] + and its analogs. The reaction between trans-[Os VI(tpy)(Cl) 2(N)] + and PPh 3 in CH 3CN occurs with a 1:1 stoichiometry and a rate law first order in both PPh 3 and Os VI with k(CH 3CN, 25°C) = 1.36 ± 0.08 × 10 4 M − s −1. The products are best formulated as paramagnetic d 4 phosphoraniminato complexes of Os IV based on a room temperature magnetic moment of 1.8 μ B for trans-[Os IV(tpy)(Cl) 2(NPPh 3)](PF 6), contact shifted 1H NMR spectra and UV-Vis and near-IR spectra. In the crystal structures of trans-[Os IV(tpy)(Cl) 2( NPPh 3)](PF 6)·CH 3CN (monoclinic, P2 1/ n with a = 13.384(5) Å, b = 15.222(7) Å, c = 17.717(6) Å, β = 103.10(3)°, V = 3516(2) Å 3, Z = 4, Rw = 3.40, Rw = 3.50) and cis-[Os IV(tpy)(Cl) 2(NPPh 2Me)]-(PF 6)·CH 3CN (monoclinic, P2 1/ c, with a = 10.6348(2) Å, b = 15.146(9) ÅA, c = 20.876(6) Å, β = 97.47(1)°, V = 3334(2) Å 3, Z = 4, R = 4.00, Rw = 4.90), the long Os-N(P) bond lengths (2.093(5) and 2.061(6) Å), acute Os-N-P angles (132.4(3) and 132.2(4)°), and absence of a significant structural trans effect rule out significant Os-N multiple bonding. From cyclic voltammetric measurements, chemically reversible Os V/IV and Os IV/III couples occur for trans-[Os IV(tpy)(Cl) 2(NPPh 3)](PF 6) in CH 3CN at +0.92 V (Os V/IV) and −0.27 V (Os IV/III) versus SSCE. Chemical or electrochemical reduction of trans-[Os IV(tpy)(Cl) 2(NPPh 3)](PF 6) gives isolable trans-Os III(tpy)(Cl) 2(NPPh 3). One-electron oxidation to Os V followed by intermolecular disproportionation and PPh 3 group transfer gives [Os VI(tpy)Cl 2(N)] +, [OS III(tpy)(Cl) 2(CH 3CN)] + and [Ph 3=N=PPh 3] + (PPN +). trans-[Os IV(tpy)(Cl) 2(NPPh 3)](PF 6) undergoes reaction with a second phosphine under reflux to give PPN + derivatives and Os II(tpy)(Cl) 2(CH 3CN) in CH 3CN or Os II(tpy)(Cl) 2(PR 3) in CH 2Cl 2. This demonstrates that the Os VI nitrido complex can undergo a net four-electron change by a combination of atom and group transfers. 相似文献
6.
Four ergosterol derivatives (1–4) have been isolated for the first time from the fruiting bodies of a basidiomycete fungus, Lactarius hatsudake, through activity-guided fractionation. Their structures were determined, using spectroscopic analysis, as: (22 E,24 R)-ergosta-5,7,22-dien-3 β-ol (ergosterol, 1); 5 ,8 -epidioxy-(22 E,24 R)-ergosta-6,22-dien-3 β-ol (ergosterol peroxide, 2); 5 ,8 -epidioxy-(24 S)-ergosta-6-en-3 β-ol (3); and (22 E,24 R)-ergosta-7,22-dien-3 β,5 ,6 β-triol (cerevisterol, 4). Compounds 2 and 3 showed selective inhibitory activity against Crotalus adamenteus venom phospholipase A 2 (PLA 2) enzyme, but not against Apis mellifcra bee venom PLA 2. The antiphospholipase A 2 activity of compounds 2 and 3 are reported here for the first time. 相似文献
7.
Tricarbonyl(η 6-1-oxobenzocyclobutene)chromium(0) (1) can be transformed to tricarbonyl(η 6-1- endo-hydroxybenzocyclobutene) chromium(0) derivatives with substituents R (R=CH 3, CH=CH 2, (CH 2) 4CH=CH 2, (CH 2) 4OSi(Me) 2tBu) at Cl on the exo face of the complex. The relative configuration is proven by an X-ray crystal structure analysis of the trimethylsilyl ether 8 (C 16H 18CrO 4Si: a=8.693(1), b=9.490(1), c=11.063(1) Å, =97.51(1), β=110.32(1), γ=95.38(1)°, triclinic, space group P
(No.2), R=0.037, Rw=0.052 for 4609 observed reflections. Attempts directed at an intramolecular cycloaddition of the ortho-quinodimethane complex derived from 17 by anion promoted ring opening unexpectedly resulted in the formation of 12 as the product of an opening of the proximal bond of the anellated ring located between the hydroxy group and the coordinated aromatic ring in 16. The fact that the intermolecular cycloaddition reaction for 16 is possible in the presence of a dienophile is taken as evidence for an equilibrium between the alcoholate 17 and the two ring opened products 16 and 18. The proximal ring opening of 6 is not observed when the free organic ligand 21 is used as the educt. Ketone complexes 1 and 25 undergo proximal ring opening reaction when treated with alcoholate or primary amines. 相似文献
8.
[Fe(TIM)(CH 3CN) 2](PF 6) 2 (1) (TIM = 2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclodeca-1,3,8,10-tetraene) forms a complex with NO reversibly in CH 3CN (53±1% converted to the NO complex) or 60% CH 3OH/40% CH 3CN (81±1% conversion). Quantitative NO complexation occurs in H 2O or CH 3OH solvents. The EPR spectrum of [Fe(TIM)(solvent)NO] 2+ in frozen 60/40 CH 3OH/CH 3CN at 77 K shows a three line feature at g=2.01, 1.99 and 1.97 of an S=1/2FeNO 7 ground state. The middle line exhibits a three-line N-shf coupling of 24 G indicating a six-coordinate complex with either CH 3OH or CH 3CN as a ligand trans to NO. In H 2O [Fe(TIM)(H 2O) 2] 2+ undergoes a slow decomposition, liberating 2,3-butanedione, as detected by 1H NMR in D 2O, unless a π-acceptor axial ligand, L=CO, CH 3CN or NO is present. An equilibrium of 1 in water containing CH 3CN forms [Fe(TIM)(CH 3CN)(H 2O)] 2+ which has a formation constant KCH3CN=320 M −1. In water KNOKCH3CN since NO completely displaces CH 3CN. [Fe(TIM)(CH 3CN) 2] 2+ binds either CO or NO in CH 3CN with KNO/ KCO=0.46, sigificantly lower than the ratio for [Fe II(hemes)] of 1100 in various media. A steric influence due to bumping of β-CH 2 protons of the TIM macrocycle with a bent S=1/2 nitrosyl as opposed to much lessened steric factors for the linear Fe---CO unit is proposed to explain the lower KNO/ KCO ratio for the [Fe(TIM)(CH 3CN)] 2+ adducts of NO or CO. Estimates for formation constants with [Fe(TIM)] 2+ in CH 3CN of KNO=80.1 M −1 and KCO=173 M − are much lower than to hemoglobin (where KNO=2.5×10 10 M −1 and KCO=2.3×10 7) due to a reversal of steric factors and stronger π-backdonation from [Fe II(heme)] than from [Fe II(TIM)(CH 3CN)] 2+. 相似文献
9.
The reaction of RuCl 3(H 2O), with C 5Me 4CF 3J in refluxing EtOH gives [Ru 2(η 5-C 5Me 1CF 2) 2 (μ-Cl 2] (20 in 44% yield. Dimer 2 antiferromagnetic (−2 J=200 cm 1). The crystal structures of 2 (rhombohedral system, R3 space group, Z=9, R=0.0589) and [Rh 2(η 5-C 5Me 4CF 3( 2Cl 2(μ-Cl) 2] (3) (rhombohedral system.
space group, Z = 9, R = 0.0641) were solved; both complexes have dimeric structures with a trans arrangement of the η 5-C 5Me 4CF 4 rings. Comparison of the geometry of 2 and 3 with those of the corresponding η 5-C 5Me 5 complexes shows that lowering the ring symmetry causes significant distortion of the M 2(μ-Cl) 2 moiety. The analysis of the MCl 3 fragment conformations in 2 and 3 and in the η 5-C 5ME 5 analogues shows that they are correlated with the M---M distances. The Cl atoms are displaced by Br on reaction of 2 with KBr in MeOH to give the diamagnetic dimer [Ru 2(η 5-C 5Me 4CF 3) 2Br 2 (μ-Br 2] (4). Complex 2 reacts with O 2 in CH 2Cl 2 solution at ambient temperature to form a mixture of isomeric η 6-fulvene dimers [Ru 2(η 6-C 5Me 3CF 3 = CH 2) 2Cl 2(μ-Cl) 2] (5). Reactions of 5 with CO and allyl chloride give Ru(η 5-C 5Me 3CF 3CH 2Cl)(CO) 2Cl (6) and Ru(η 5-C 5Me 3CF 3CF 3CH 2Cl)(η 3-C 3H 5)Cl 2 (7) respectively. 相似文献
10.
The phosphinoalkenes Ph 2P(CH 2) nCH=CH 2 ( n= 1, 2, 3) and phosphinoalkynes Ph 2P(CH 2) n C≡CR (R = H, N = 2, 3; R = CH 3, N = 1) have been prepared and reacted with the dirhodium complex (η−C 5H 5) 2Rh 2(μ−CO) (μ−η 2−CF 3C 2CF 3). Six new complexes of the type (ν−C 5H 5) 2(Rh 2(CO) (μ−η 1:η 1−CF 3C 2CF 3)L, where L is a P-coordinated phosphinoalkene, or phosphinoalkyne have been isolated and fully characterized; the carbonyl and phosphine ligands are predominantly trans on the Rh---Rh bond, but there is spectroscopic evidence that a small amount of the cis-isomer is formed also. Treatment of the dirhodium-phosphinoalkene complexes with (η−CH 3C 5H 4)Mn(CO) 2thf resulted in coordination of the manganese to the alkene function. The Rh 2---Mn complex [(η−C 5H 5) 2Rh 2(CO) (μ−η 1:η 1−CF 3C 2CF 3) {Ph 2P(CH 2) 3CH=CH 2} (η−CH 3C 5H 4)Mn(CO) 2] was fully characterized. Simi treatment of the dirhodium-phosphinoalkyne complexes with Co 2(CO) 8 resulted in the coordination of Co 2(CO) 6 to the alkyne function. The Rh 2---Co 2 complex [(η−C 5H 5) 2Rh 2(CO) (μ−η 1:η 1−CF 3C 2CF 3) {Ph 2PCH 2C≡CCH 3}Co 2(CO) 2], C 37H 25Co 2F 6O 7PRh 2, was fully characteriz spectroscopically, and the molecular structure of this complex was determined by a single crystal X-ray diffraction study. It is triclinic, space group
( Ci1, No. 2) with a = 18.454(6), B = 11.418(3), C = 10.124(3) Å, = 112.16(2), β = 102.34(3), γ = 91.62(3)°, Z = 2. Conventional R on | F| was 0.052 fo observed ( I > 3σ( I)) reflections. The Rh 2 and Co 2 parts of the molecule are distinct, the carbonyl and phosphine are mutually trans on the Rh---Rh bond, and the orientations of the alkynes are parallel for Rh 2 and perpendicular for Co 2. Attempts to induce Rh 2Co 2 cluster formation were unsuccessful. 相似文献
11.
Chemical examination of the ethyl acetate solubles of the CH 3OH:CH 2Cl 2 (1:1) extract of the roots of Ceriops decandra collected from Kauvery estuary resulted in the isolation of four new diterpenoids, ceriopsins A–D (1–4). The structures of the new diterpenoids were elucidated by a study of their physical and spectral data as methyl 17-hydroxy-16-oxobeyeran-18-oate (1), methyl 16( R)-16,17-dihydroxybeyeran-18-oate (2), 1β,15( S)-isopimar-7-ene-1,15,16-triol (3), and 8,15( R)-epoxypimarane-1β,16-diol (4). 相似文献
12.
The chloro complexes trans-[Pt(Me)(Cl)(PPh 3) 2], after treatment with AgBF 4, react with 1-alkynes HC---C---R in the presence of NEt 3 to afford the corresponding acetylide derivatives trans-[Pt(Me) (C---C---R) (PPh 3) 2] (R = p-tolyl (1), Ph (2), C(CH 3) 3 (3)). These complexes, with the exception of the t-butylacetylide complex, react with the chloroalcohols HO(CH 2) nCl ( n = 2, 3) in the presence of 1 equiv. of HBF 4 to afford the alkyl(chloroalkoxy)carbene complexes trans-[Pt(Me) {C[O(CH 2) nCl](CH 2R) } (PPh 3) 2][BF 4] (R = p-tolyl, N = 2 (4), N = 3 (5); R=Ph, N = 2 (6)). A similar reaction of the bis(acetylide) complex trans-[Pt(C---C---Ph) 2(PMe 2Ph) 2] with 2 equiv. HBF 4 and 3-chloro-1-propanol affords trans-[Pt(C---CPh) {C(OCH 2CH 2CH 2Cl)(CH 2Ph) } (PMe 2Ph) 2][BF 4] (7). T alkyl(chloroalkoxy)-carbene complex trans-[Pt(Me) {C(OCH 2CH 2Cl)(CH 2Ph) } (PPh 3) 2][BF 4] (8) is formed by reaction of trans-[Pt(Me)(Cl)(PPh 3) 2], after treatment with AgBF 4 in HOCH 2CH 2Cl, with phenylacetylene in the presence of 1 equiv. of n-BuLi. The reaction of the dimer [Pt(Cl)(μ-Cl)(PMe 2Ph)] 2 with p-tolylacetylene and 3-chloro-1-propanol yields cis-[PtCl 2{C(OCH 2CH 2CH 2Cl)(CH 2C 6H 4- p-Me}(PMe 2Ph)] (9). The X-ray molecular structure of (8) has been determined. It crystallizes in the orthorhombic system, space group Pna2 1, with a = 11.785(2), B = 29.418(4), C = 15.409(3) Å, V = 4889(1) Å 3 and Z = 4. The carbene ligand is perpendicular to the Pt(II) coordination plane; the PtC(carbene) bond distance is 2.01(1) Å and the short C(carbene)-O bond distance of 1.30(1) Å suggests extensive electronic delocalization within the Pt---C(carbene)---O moietry. 相似文献
13.
Kinetic resolution of a chiral alcohol, 4-hydroxy-3-methyl-2-(2′-propenyl)-2-cyclopentenone (HMPC), a key intermediate for the production of prallethrin insecticides, was successfully carried out by enantioselective hydrolysis of ( RS)-HMPC acetate using calcium alginate gel-entrapped cells of a newly isolated esterase-producing bacterium Acinetobacter sp. CGMCC 0789. When the effect of different cosolvents was investigated, it was found that isopropanol could markedly enhance the activity and enantioselectivity of the immobilized cells. The optimum concentration of isopropanol was 10% (v/v) where immobilized cells still showed good operational stability. After 10 cycles of reaction, no significant decrease in the enzyme activity was observed. The catalytic specificity constants ( Vmax/ Km) for both enantiomers of the substrate were determined with partially purified enzyme, giving 0.0184 and 0.671 h −1 for the ( S)- and ( R)-ester, respectively. 相似文献
14.
采用便携式光合仪(Li-6400XT)对太行山南麓栓皮栎、刺槐2个树种叶片光合作用-CO 2响应曲线进行测定,利用直角双曲线模型(RH)、非直角双曲线模型(NRH)以及直角双曲线的修正模型—叶子飘模型(YZP)进行曲线拟合,并对3种光合模型的拟合参数(最大净光合能力 Amax、初始羧化速率 η、光呼吸速率 Rp、CO 2补偿点CCP和CO 2饱和点CSP)进行比较.结果表明: 与NRH和YZP模型相比,RH模型所得的 Amax、 η、 Rp和CCP较高,分别高出实测值59.8%、128.6%、133.4%和19.8%.与RH模型和YZP模型相比,NRH模型拟合得出的 Amax较大,高于实测值11.1%, η、 Rp和CCP接近于实测值.YZP模型能较好地模拟光合作用对CO 2的饱和现象,在 Amax和CSP的拟合效果上较好.栓皮栎阴叶的 Amax、 Rp和CCP比阳叶分别低31.3%、5.2%和14.3%.刺槐阴叶的 Amax、 Rp和CCP分别高出阳叶23.5%、11.0%和5.4%.栓皮栎、刺槐阴叶的 η分别比阳叶高6.9%和7.0%.刺槐叶片的 Rp和CCP与温度、光强均具有显著线性关系, η与气孔导度( gs)具有显著线性关系.栓皮栎叶片的 η与光强和气孔导度具有显著线性关系,CCP主要受温度和湿度影响.栓皮栎叶片的 Amax与相对湿度和 gs具有显著的正线性相关关系. 相似文献
15.
The ester cleavage of R- and S-isomers N-CBZ-leucine p-nitrophenyl ester intermolecularly catalyzed by R- (a) and S-stereoisomers (b) of the Pd(II) metallacycle [Pd(C 6H 4C *HMeNMe 2)Cl(py)] (3) follows the rate expression kobs = ko + kcat [3], where the rate constants kcat equal 25.8 ± 0.4 and 7.6 ± 0.5 dm 3 mol −1 s −1 for the S- and R-ester, respectively, in the case of 3a, but are 5.7 ± 0.6 and 26.7 ± 0.5 dm 3 mol −1 s −1 for the S- and R-ester, respectively, in the case of 3b (pH 6.23 and 25°C). Thus, the best catalysis occurs when the asymmetric carbons of the leucine ester and Pd(II) complex are R and S, or S and R configured, respectively. Molecular modeling suggests that the stereoselection results from the spatial interaction between the CH 2CHMe 2 radical of the ester and the -methyl group of 3. A hydrophobic/stacking contact between the leaving 4-nitrophenolate and the coordinated pyridine also seems to play a role. Less efficient intramolecular enantioselection was observed for the hydrolysis of N-t-BOC- S-metthionine p-nitrophenyl ester with R- and S-enantiomers of [Pd(C 6H 4C*HMeNMe 2)Cl] coordinated to sulfur. 相似文献
16.
The use of ( R)-specific enoyl-coenzyme A (CoA) hydratase (PhaJ) provides a powerful tool for polyhydroxyalkanoate (PHA) synthesis from fatty acids or plant oils in recombinant bacteria. PhaJ provides monomer units for PHA synthesis from the fatty acid ß-oxidation cycle. Previously, two phaJ genes ( phaJ1Pa and phaJ2Pa) were identified in Pseudomonas aeruginosa. This report identifies two new phaJ genes ( phaJ3Pa and phaJ4Pa) in P. aeruginosa through a genomic database search. The abilities of the four PhaJ Pa proteins and the ( R)-3-hydroxyacyl-acyl carrier protein [( R)-3HA-ACP] dehydrases, FabA Pa and FabZ Pa, to supply monomers from enoyl-CoA substrates for PHA synthesis were determined. The presence of either PhaJ1 Pa or PhaJ4 Pa in recombinant Escherichia coli led to the high levels of PHA accumulation (as high as 36–41 wt.% in dry cells) consisting of mainly short- (C4–C6) and medium-chain-length (C6–C10) 3HA units, respectively. Furthermore, detailed characterizations of PhaJ1 Pa and PhaJ4 Pa were performed using purified samples. Kinetic analysis revealed that only PhaJ4 Pa exhibits almost constant maximum reaction rates ( Vmax) irrespective of the chain length of the substrates. The assay for stereospecific hydration revealed that, unlike PhaJ1 Pa, PhaJ4 Pa has relatively low ( R)-specificity. These hydratases may be very useful as monomer-suppliers for the synthesis of designed PHAs in recombinant bacteria. 相似文献
17.
A series of dihydroxamic acid ligands of the formula [RN(OH)C(O)] 2(CH 2) n, ( n = 2, 4, 6, 7, 8; R = CH 3, H) has been studied in 2.0 M aqueous sodium perchlorate at 25.0 °C. These ligands may be considered as synthetic analogs to the siderophore rhodotorulic acid. Acid dissociation constants (p Ka) have been determined for the ligands and for N-methylacetohydroxamic acid (NMHA). The p Ka1 and p Ka2 values are: n = 2, R = CH 3 (8.72, 9.37); N = 4, R = CH 3 (8.79, 9.37); N = 6, R = CH 3; N = 7, R = CH 3 (8.95, 9.47); N = 8, R = CH 3 (8.93, 9.45); N = 8, R = H (9.05, 9.58). Equilibrium constants for the hydrolysis of coordinated water (log K) have been estimated for the 1:1 feeric complexes of the ligands n = 2, 4, 8; R = CH 3. The N = 8 ligand forms a monomeric complex with Fe(III) while the n = 2 and 4 ligands form dimeric complexes. For hydrolysis of the n = 8 monomeric complex, log K1 = −6.36 and log K2 = −9.84. Analysis of the spectrophotometric data for the dimeric complexes indicates deprotonation of all four coordinated waters. The successive hydrolysis constants, log K1–4, for the dimeric complexes are as follows: n = 2 (−6.37, −5.77, −10.73, −11.8); n = 4 (−5.54, −5.07, −11.57, −10.17). The log K2 values for the dimers are unexpectedly high, higher in fact than log K1, inconsistent with the formation of simple ternary hydroxo complexes. A scheme is proposed for the hydrolysis of the ferric dihydroxamate dimers, which includes the possible formation of μ-hydroxo and μ-oxo bridges. 相似文献
18.
The crystalline ion pair [Co 2{OOC---CCo 3(CO) 9} 5, C 10H 6(N(CH 3) 2) 2H] (1) presents unusual magnetic properties. The X-band EPR spectrum of 1 at room temperature presents two unresolved bands at g=1.98 and 4.55. At a low temperature (20 K), the cluster of clusters 1 presents a complicated spectrum with an intense signal at 1700 G. The magnetic susceptibility of 1 was fit to a two spin S1= S2=3/2 Heisenberg model, with J=11.2 cm −1 and a g value of 2.3. There is no field dependence of the magnetization, which suggests intramolecular coupling between the two tetrahedral centers of the cluster. Molecular orbital modeling indicates a sigma path of exchange between two topologically non-equivalent cobalt(II) centers. 相似文献
19.
A series of cationic nickel complexes [(η 3-methally)Ni(PP(O))]SbF 6 (1–4) [PP(O) = Ph 2P(CH 2)P(O)Ph 2 (dppmO) (1), Ph 2P(CH 2) 2P(O)Ph 2 (dppeO) (2), Ph 2P(CH 2) 3P(O)Ph 2 (dpppO) (3), pTol 2P(CH 2)P(O) pTol 2 (dtolpmO) (4)] has been synthesized in good yields by treatment of [(η 3-methally)NiBr] 2 with biphosphine monoxides and AgSbF 6. The ligands are coordinated in a bidentate way. Starting from [(η 3-all)PdI] 2 the cationic complexes [(η 3-all)PP(O))]Y (8–14). [PP(O) = dppmO, dppeO, dpppO, dtolpmO;Y = BF 4, SbF 6, CF 3SO 3, pTolSO 3] were synthesized in good yields. The coordination mode of the ligand is dependent on the backbone and the anion, revealing a monodentate coordination with dppmO for stronger coordinating anions. The intermediates [(η 3-all)Pd(I)(PP(O)-κ 1- P)] (5–7) [PP(O) = dppmO (5), dppeO (6), dtolpmO (7)] were isolated and characterized. Neutral methyl complexes [(Cl)(Me)Pd(PP(O))] (15–18). [PP(O) = dppmO (15), dppeO (16), dpppO (17), dtolpmO (18)] can easily be obtained in high yields starting from [(cod)PdCl 2]. For dppmO two different routes are presented. The structure of [(Me)(Cl)Pd{;Ph 2P(CH 2-P(O)Ph 2-κ 2- P, O};] · CH 2Cl 2 (15) with the chlorine atom trans to phosphorus was determined by X-ray diffraction. 相似文献
20.
The ligand 1,4,7-triazacyclononane-1,4,7-tris[2′( R)-2′-propionate](-3)(( R)-tacntp 3−), binds stereospecifically to transition metal ions. The structures of the complexes [Cr(( R)-tacntp)]·NaBr and [Fe(( R)-tacntp)]·H 2O have been determined by X-ray crystallography. Both complexes have the Λ-configuration but the conformation of the chelate rings in Λ-[Cr(( R)-tacntp)] is (λ,λ,λ) with a geometry close to octahedral while in Λ-[Fe(( R)-tacntp)] it is (δ,δ,δ) and the geometry is closer to that of a trigonal prism. Chiral induction in the electron transfer reactions of Λ-[Co(( R)-tacntp)], Λ-[Fe(( R)-tacntp)] and Λ-[Mn(( R)-tacntp)] with [Co(( RR,SS)-chxn) 3] 2+ has been investigated. All three reactions are outer-sphere and four isomeric [Co(( RR,SS)-chxn) 3] 3+ products are identified in each case. The oxidants Λ-[Fe(( R)-tacntp)] and Λ-[Mn(( R)-tacntp)] show very similar selectivities, quite different from those of Λ-[Co(( R)-tacntp)]. Reasons for this behavior are discussed. 相似文献
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