5096-13-9Relevant articles and documents
Macrocyclic Enzyme Model System. Kinetic Activity of Paracyclophane Bearing 1,4-Dihydronicotinamide and 2-Pyridinecarboxylic Acid Moieties as Effected by Zinc Ion
Murakami, Yukito,Aoyama, Yasuhiro,Kikuchi, Jun-ichi
, p. 2898 - 2901 (1982)
As regards the effect of zinc(II) ion on the reduction of hexachloroacetone, the kinetic activity of a paracyclophane (PCP) bearing 1,4-dihydronicotinamide (HNA) and 2-pyridinecarboxylic acid (Py) moieties, HNA-PCP-Py, has been investigated as an alcohol dehydrogenase model in reference to that of PCP-HNA in the light of their metal-coordination behavior.The reduction ability of PCP-HNA was significantly lowered as it underwent complex formation with zinc.On the other hand, HNA-PCP-Py showed an apparent rate maximum in a relatively lower concentration range of ZnCl2.The kinetic behavior was analyzed on the basis of the formation of two kinds of zinc complexes of HNA-PCP-Py: the 1:1 complex , in which both Py and HNA moieties are simultaneously coordinated to the same zinc ion, showed a decreased reactivity relative to metal-free HNA-PCP-Py; while the 2:1 complex (HNA-PCP-Py-ZnII-Py-PCP-HNA), in which HNA is free from metal-coordination, exercised a much enhanced activity, 7 times as reactive as metal-free HNA-PCP-Py.A plausible reaction mechanism for the enhanced reactivity has been discussed.
MECHANISM AND TRANSITION-STATE STRUCTURE OF HYDRIDE-TRANSFER REACTIONS MEDIATED BY NAD(P)H - MODELS
Verhoeven, J. W.,Gerresheim, W. van,Martens, F. M.,Kerk, S. M. van der
, p. 975 - 992 (1986)
The energy to transfer one electron from NAD(P)H and related 1,4-dihydropyridines to a series of substrates is calculated and compared with the experimental activation energy for transfer of a hydride equivalent between these species.It is concluded that single electron-transfer (SET) cannot occur as a primary step in the overall hydride-transfer process except for substrates with very strong one-electron oxidizing properties.A simple valence-bond configuration mixing (VBCM) model is presented, that rationalizes the general occurrence of concerted hydride transfer as the lowest energy reaction-pathway and furthermore explains why the activtion energy of such a concerted pathway is often linearly related to that of a -hypothetical- SET process.For one intramolecular and two related, intermolecular hydride-transfer reactions the temperature dependence of the primary kinetic isotope effect (TDKIE) was studied.For the intramolecular reaction, where a face to face orientation of the reactants is enforced, the TDKIE parameters suggest the occurence of a bent hydride-transfer pathway.For both intermolecular reactions, however, a linear transition-state geometry is indicated.MNDO calculations of the reaction profile for hydride transfer from a 1,4-dihydropyridine to either a positively charged substrate (i.e. the pyridinium-ion) or to a neutral substrate (i.e. 1,1-dicyanoethylene) confirm, that a linear transition-state geometry is favoured, unless the system is geometrically restrained to prevent such a geometry.The MNDO calculations furthermore indicate that in a linear transition-state almost unimpeded rotation can occur about the C...H...C axis.This rotation interconverts the relative orientation of the reactants between parallel-exo and tilted-endo, which may have important consequences for the interpretation of the stereochemical outcome of reactions involving (pro)chiral reactants.
Photocatalytic reduction of artificial and natural nucleotide co-factors with a chlorophyll-like tin-dihydroporphyrin sensitizer
Oppelt, Kerstin T.,W??, Eva,Stiftinger, Martin,Sch?fberger, Wolfgang,Buchberger, Wolfgang,Kn?r, Günther
supporting information, p. 11910 - 11922 (2013/11/19)
An efficient photocatalytic two-electron reduction and protonation of nicotine amide adenine dinucleotide (NAD+), as well as the synthetic nucleotide co-factor analogue N-benzyl-3-carbamoyl-pyridinium (BNAD +), powered by photons in the long-wavelength region of visible light (λirr > 610 nm), is demonstrated for the first time. This functional artificial photosynthetic counterpart of the complete energy-trapping and solar-to-fuel conversion primary processes occurring in natural photosystem I (PS I) is achieved with a robust water-soluble tin(IV) complex of meso-tetrakis(N-methylpyridinium)-chlorin acting as the light-harvesting sensitizer (threshold wavelength of λthr = 660 nm). In buffered aqueous solution, this chlorophyll-like compound photocatalytically recycles a rhodium hydride complex of the type [Cp*Rh(bpy)H]+, which is able to mediate regioselective hydride transfer processes. Different one- and two-electron donors are tested for the reductive quenching of the irradiated tin complex to initiate the secondary dark reactions leading to nucleotide co-factor reduction. Very promising conversion efficiencies, quantum yields, and excellent photosensitizer stabilities are observed. As an example of a catalytic dark reaction utilizing the reduction equivalents of accumulated NADH, an enzymatic process for the selective transformation of aldehydes with alcohol dehydrogenase (ADH) coupled to the primary photoreactions of the system is also demonstrated. A tentative reaction mechanism for the transfer of two electrons and one proton from the reductively quenched tin chlorin sensitizer to the rhodium co-catalyst, acting as a reversible hydride carrier, is proposed.
Synthesis of phenylene 1,3- and 1,4-bis(methylene)-3-carbamoylpyridinium bromides
Zhou, Feng,Wang, Chi-Hua,Warner, John C.
, p. 173 - 177 (2007/10/03)
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