RESUMEN
The synthesis, photophysics, and photochemistry of a linked dyad ([Re]-[NiFe2]) containing an analogue ([NiFe2]) of the active site of [NiFe] hydrogenase, covalently bound to a Re-diimine photosensitizer ([Re]), are described. Following excitation, the mechanisms of electron transfer involving the [Re] and [NiFe2] centers and the resulting decomposition were investigated. Excitation of the [Re] center results in the population of a diimine-based metal-to-ligand charge transfer excited state. Reductive quenching by NEt3 produces the radically reduced form of [Re], [Re](-) (kq = 1.4 ± 0.1 × 10(7) M(-1) s(-1)). Once formed, [Re](-) reduces the [NiFe2] center to [NiFe2](-), and this reduction was followed using time-resolved infrared spectroscopy. The concentration dependence of the electron transfer rate constants suggests that both inter- and intramolecular electron transfer pathways are involved, and the rate constants for these processes have been estimated (kinter = 5.9 ± 0.7 × 10(8) M(-1) s(-1), kintra = 1.5 ± 0.1 × 10(5) s(-1)). For the analogous bimolecular system, only intermolecular electron transfer could be observed (kinter = 3.8 ± 0.5 × 10(9) M(-1) s(-1)). Fourier transform infrared spectroscopic studies confirms that decomposition of the dyad occurs upon prolonged photolysis, and this appears to be a major factor for the low activity of the system toward H2 production in acidic conditions.
Asunto(s)
Biomimética , Hidrogenasas/síntesis química , Fármacos Fotosensibilizantes/química , Renio/química , Aminas/química , Electroquímica , Hidrogenasas/química , Oxidación-Reducción , Espectrofotometría Infrarroja , Espectrofotometría UltravioletaRESUMEN
Enzyme models on the catwalk! A series of new model complexes of the active site of [Fe]-hydrogenase have been synthesized and characterized. These complexes are monomeric in solution, but dimeric in the solid state.
Asunto(s)
Hidrogenasas/síntesis química , Proteínas Hierro-Azufre/síntesis química , Modelos Moleculares , Compuestos de Sulfhidrilo/síntesis química , Dominio Catalítico , Hidrogenasas/química , Proteínas Hierro-Azufre/química , Estructura Molecular , Compuestos de Sulfhidrilo/químicaRESUMEN
The metal-sulphur active sites of hydrogenases catalyse hydrogen evolution or uptake at rapid rates. Understanding the structure and function of these active sites--through mechanistic studies of hydrogenases, synthetic assemblies and in silico models--will help guide the design of new materials for hydrogen production or uptake. Here we report the assembly of the iron-sulphur framework of the active site of iron-only hydrogenase (the H-cluster), and show that it functions as an electrocatalyst for proton reduction. Through linking of a di-iron subsite to a {4Fe4S} cluster, we achieve the first synthesis of a metallosulphur cluster core involved in small-molecule catalysis. In addition to advancing our understanding of the natural biological system, the availability of an active, free-standing analogue of the H-cluster may enable us to develop useful electrocatalytic materials for application in, for example, reversible hydrogen fuel cells. (Platinum is currently the preferred electrocatalyst for such applications, but is expensive, limited in availability and, in the long term, unsustainable.).
Asunto(s)
Materiales Biomiméticos/química , Materiales Biomiméticos/síntesis química , Hidrógeno/química , Hidrogenasas/química , Hidrogenasas/síntesis química , Hierro/química , Sitios de Unión , Catálisis , Clostridium/enzimología , Desulfovibrio desulfuricans/enzimología , Electroquímica , Proteínas Hierro-Azufre/síntesis química , Proteínas Hierro-Azufre/química , Modelos Moleculares , Oxidación-Reducción , Protones , Relación Estructura-Actividad , Azufre/químicaRESUMEN
This article is a short overview of some recent research activity in the Laboratory of Inorganic Synthesis and Catalysis (LSCI) at EPFL-ISIC. It summarizes the work on Ni-catalyzed cross-coupling reactions of non-activated alkyl halides. It then describes and discusses the work on the bio-mimetic chemistry of [Fe]-hydrogenase.
Asunto(s)
Materiales Biomiméticos , Biomimética/métodos , Hidrogenasas , Compuestos Organometálicos , Materiales Biomiméticos/síntesis química , Materiales Biomiméticos/química , Catálisis , Hidrogenasas/síntesis química , Hidrogenasas/química , Modelos Moleculares , Compuestos Organometálicos/síntesis química , Compuestos Organometálicos/químicaRESUMEN
Dithiolate bridging Ni-Fe complexes [(dppe)Ni(II)(mu-SEt)(2)Fe(II)(CN)(2)(CO)(2)](6) and [(dppe)Ni(II)(mu-pdt)Fe(II)(CN)(2)(CO)(2)] [dppe = 1,2-bis(diphenylphosphino)ethane and pdt = 1,3-propanedithiolate] have been synthesized and structurally characterized as structural analogues of the active site of Ni-Fe hydrogenase enzymes. The synthesis starts from key intermediate fac-[Fe(CN)(2)(CO)(3)I](-). [(dppe)Ni(II)(mu-SEt)(2)Fe(II)(CN)(2)(CO)(2)](6), which features a near-planar diethanethiolate-bridged Ni-Fe rhomb, and the arrangement of 2CN(-) ligands is cis to each other. In contrast, [(dppe)Ni(II)(mu-pdt)Fe(II)(CN)(2)(CO)(2)] shows a much more folded NiS(2)Fe rhomb, a short Ni-Fe distance, trans 2CN(-) ligands, and a semibridging CN(-) between Ni and Fe.
Asunto(s)
Hidrogenasas/síntesis química , Dominio Catalítico , Hidrogenasas/química , Modelos MolecularesRESUMEN
We report the assembly of the first electropolymeric materials incorporating catalytic diiron subsites related to those of the iron-only hydrogenases.
Asunto(s)
Electroquímica/métodos , Hidrogenasas/química , Compuestos Organometálicos/química , Polímeros/química , Pirroles/química , Cianuros/química , Ésteres/química , Hidrogenasas/síntesis química , Compuestos de Hierro/química , Compuestos Organometálicos/síntesis química , Polímeros/síntesis química , Pirroles/síntesis química , Azufre/químicaAsunto(s)
Materiales Biomiméticos/química , Materiales Biomiméticos/síntesis química , Hidrógeno/química , Hidrogenasas/química , Hidrogenasas/síntesis química , Hierro/química , Sitios de Unión , Catálisis , Electroquímica , Proteínas Hierro-Azufre/síntesis química , Proteínas Hierro-Azufre/química , Oxidación-Reducción , Protones , Relación Estructura-Actividad , Azufre/químicaRESUMEN
The 25 amino acid long subunit VhuU of the F420-non-reducing hydrogenase from Methanococcus voltae contains selenocysteine within the consensus sequence of known [NiFe] hydrogenases DP(C or U)CxxCxxH (U = selenocysteine). The sulfur-analogue VhuUc was chemically synthesized, purified and its metal binding capability, the catalytic properties, and structural features were investigated. The polypeptide was able to bind nickel, but did not catalyse the heterolytic activation of H2. 2D-NMR spectroscopy revealed an alpha-helical secondary structure for the 15 N-terminal amino acids in 50% TFE. Nickel only binds to the C-terminus, which contains the conserved amino acid motif. Structures derived from the NMR data are compatible with the participation of both sulfur atoms from the conserved cysteine residues in a metal ion binding. Structures obtained from the data sets for Ni.VhuUc as well as Zn.VhuUc showed no further ligands. The informational value for Ni.VhuUc was low due to paramagnetism.
Asunto(s)
Hidrogenasas/química , Hidrogenasas/metabolismo , Metales/metabolismo , Methanococcus/enzimología , Azufre , Secuencia de Aminoácidos , Sitios de Unión , Catálisis , Hidrógeno/metabolismo , Hidrogenasas/síntesis química , Espectroscopía de Resonancia Magnética , Datos de Secuencia Molecular , Estructura Molecular , Níquel/metabolismo , Estructura Secundaria de Proteína , Selenocisteína/análisis , Alineación de SecuenciaRESUMEN
Enzymatic catalysis and homogeneous catalysis offer complementary means to address synthetic challenges, both in chemistry and in biology. Despite its attractiveness, the implementation of concurrent cascade reactions that combine an organometallic catalyst with an enzyme has proven challenging because of the mutual inactivation of both catalysts. To address this, we show that incorporation of a d(6)-piano stool complex within a host protein affords an artificial transfer hydrogenase (ATHase) that is fully compatible with and complementary to natural enzymes, thus enabling efficient concurrent tandem catalysis. To illustrate the generality of the approach, the ATHase was combined with various NADH-, FAD- and haem-dependent enzymes, resulting in orthogonal redox cascades. Up to three enzymes were integrated in the cascade and combined with the ATHase with a view to achieving (i) a double stereoselective amine deracemization, (ii) a horseradish peroxidase-coupled readout of the transfer hydrogenase activity towards its genetic optimization, (iii) the formation of L-pipecolic acid from L-lysine and (iv) regeneration of NADH to promote a monooxygenase-catalysed oxyfunctionalization reaction.
Asunto(s)
Hidrogenasas/síntesis química , Hidrogenasas/metabolismo , Aminas/química , Aminoácido Oxidorreductasas/metabolismo , Catálisis , Colorimetría , Iminas/química , Modelos Moleculares , Biología Molecular , Estructura Molecular , Compuestos Organometálicos/química , Compuestos Organometálicos/metabolismo , Oxidación-Reducción , Isoformas de Proteínas , Proteínas/química , Proteínas/metabolismoRESUMEN
The purpose of the present study was to evaluate the use of a non-innocent ligand as a surrogate of the anchored [4Fe4S] cubane in a synthetic mimic of the [FeFe] hydrogenase active site. Reaction of 2,3-bis(diphenylphosphino) maleic anhydride (bma) with [Fe(2)(CO)(6)(mu-pdt)] (propanedithiolate, pdt=S(CH(2))(3)S) in the presence of Me(3)NO-2H(2)O afforded the monosubstituted derivative [Fe(2)(CO)(5)(Me(2)NCH(2)PPh(2))(mu-pdt)] (1). This results from the decomposition of the bma ligand and the apparent C-H bond cleavage in the released trimethylamine. Reaction under photolytic conditions afforded [Fe(2)(CO)(4)(bma)(mu-pdt)] (2). Compounds 1 and 2 were characterized by IR, NMR and X-ray diffraction. Voltammetric study indicated that the primary reduction of 2 is centered on the bma ligand.
Asunto(s)
Compuestos Férricos/química , Hidrogenasas/química , Proteínas Hierro-Azufre/química , Anhídridos Maleicos/química , Fosfinas/química , Compuestos de Sulfhidrilo/química , Materiales Biomiméticos/síntesis química , Materiales Biomiméticos/química , Dominio Catalítico , Técnicas Electroquímicas , Hidrogenasas/síntesis química , Proteínas Hierro-Azufre/síntesis química , Espectroscopía de Resonancia Magnética , Modelos Químicos , Estructura Molecular , Fotólisis , Difracción de Rayos XRESUMEN
Artificial metalloenzymes based on biotin-streptavidin technology, a "fusion" of chemistry and biology, illustrate how asymmetric catalysts can be improved and evolved using chemogenetic approaches.
Asunto(s)
Biotina/química , Hidrogenasas , Compuestos Organometálicos , Proteínas Recombinantes de Fusión/química , Rodio/química , Estreptavidina/química , Sitios de Unión , Biomimética , Biotina/genética , Catálisis , Hidrogenasas/síntesis química , Hidrogenasas/química , Hidrogenasas/genética , Ligandos , Modelos Moleculares , Mutagénesis , Compuestos Organometálicos/síntesis química , Compuestos Organometálicos/química , Ingeniería de Proteínas , Proteínas Recombinantes de Fusión/genética , Estereoisomerismo , Estreptavidina/genéticaRESUMEN
[NiFe] hydrogenase, the enzyme of which catalyzes the reversible oxidation of molecular hydrogen to protons and electrons, contains a unique heterodinuclear thiolate-bridged Ni-Fe complex in which the iron center is coordinated by CO and CN. We have synthesized dithiolate-bridged Ni-Fe complexes bearing CO and CN ligands to model the active center of [NiFe] hydrogenase. The Ni-Fe complexes containing a [(CN)2(CO)2Fe(mu-S2)NiS2] framework are the closest yet structural models of [NiFe] hydrogenase.
Asunto(s)
Hidrogenasas/química , Hierro/química , Modelos Químicos , Níquel/química , Compuestos Organometálicos/química , Sitios de Unión , Cristalografía por Rayos X , Hidrogenasas/síntesis química , Modelos Moleculares , Conformación Molecular , Compuestos Organometálicos/síntesis químicaRESUMEN
A dinuclear 2Fe2S mimic 6 of the active site of the Fe-only hydrogenases has been synthesized. Complex 6 contains a free amino group which enables linkage to a protein backbone or to a redox active species for the study of electron transfer processes in proteins or in supramolecular systems. The structures of the complex 6 and its Boc-protected precursor 5 could be verified by X-ray crystallography.
Asunto(s)
Aminas/química , Hidrogenasas/química , Hidrogenasas/síntesis química , Hierro/metabolismo , Imitación Molecular , Sitios de Unión , Hidrogenasas/metabolismo , Modelos Moleculares , Estructura Molecular , Oxidación-ReducciónRESUMEN
Uptake hydrogenase is an enzyme that is beneficial for nitrogen fixation in bacteria. Recent studies have shown that Frankia sp. has two sets of uptake hydrogenase genes, organized in synton 1 and synton 2. In the present study, phylogenetic analysis of the structural subunits of hydrogenase syntons 1 and 2 showed a distinct clustering pattern between the proteins of Frankia strains that were isolated from different host plants and non-Frankia organisms. The structural subunits of hydrogenase synton 1 of Frankia sp. CpI1, Frankia alni ACN14a, and F. alni AvCI1 were grouped together while those of Frankia spp. CcI3, KB5, UGL140104, and UGL011102 formed another group. The structural subunits of hydrogenase synton 2 of F. alni ACN14a and Frankia spp. CcI3 and BCU110501 grouped together, but those of Frankia spp. KB5 and CpI1, F. alni ArI3, and F. alniAvCI1 comprised a separate group. The structural subunits of hydrogenase syntons 1 and 2 of Frankia sp. EAN1pec were more closely related to those of non-Frankia bacteria, i.e., Streptomyces avermitilis and Anaeromyxobacter sp., respectively, than to those of other Frankia strains, suggesting the occurrence of lateral gene transfer between these organisms. In addition, the accessory Hyp proteins of hydrogenase syntons 1 and 2 of F. alni ACN14a and Frankia sp. CcI3 were shown to be phylogenetically more related to each other than to those of Frankia EAN1pec (AU)
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