Elucidation of the Role of the Complex in Hydride Transfer Reaction between Methylene Blue and 1-Benzyl-1,4-dihydronictinamide by Effect of γ-Cyclodextrin

The kinetics of the hydride transfer reaction between Methylene Blue (MB⁺) and 1-benzyl-1,4-dihydronicotinamide (BNAH) were studied in 10% ethanol-90% water mixed solvents containing β- and γ-cyclodextrins (β-CD and γ-CD). The pseudo-first order rate constant shows kinetic saturation at high initial concentration of BNAH. This indicates the formation of a complex between MB⁺ and BNAH. The reaction was suppressed by addition of β-CD, but enhanced by addition of γ-CD. MB⁺ and BNAH were separately accommodated within the β-CD cavity and the cavity walls may protect the activity site of the reactants. On the other hand, in the MB⁺-BNAH-γ-CD system, the inclusion of the complex between MB⁺ and BNAH with γ-CD occurred. This effect of γ-CD can distinguish between the productive and non-productive nature of the complex.     

The role of metal cations in the homogeneous phase redox reaction of a NADH model compound

The catalytic activity of magnesium cations in the charge transfer between 1-benzyl-1,4-dihydronicotinamide (BNAH) and several aromatic compounds has been studied in acetonitrile by electrochemical techniques. Magnesium cations form complex compounds with both BNAH and the organic substrates studied. At the same time, magnesium forms ion-associates with negatively charged substrate molecules. Energetically, the effect of ion-pairing is much greater than the negative effect of complex formation. The rate of homogeneous phase reaction was also studied to show that the Michaelis-Menten type mechanism is operating.     

Mechanisms of electron-transfer oxidation of NADH analogues and chemiluminescence. Detection of the keto and enol radical cations

The radical cation of an NADH analogue (BNAH: 1-benzyl-1,4-dihydronicotinamide) has been successfully detected as the transient absorption and ESR spectra in the thermal electron transfer from BNAH to Fe(bpy)(3)(3+) (bpy = 2,2'-bipyridine) and Ru(bpy)(3)(3+). The ESR spectra of the radical cations of BNAH and the dideuterated compound (BNAH-4,4'-d(2)) indicate that the observed radical cation is the keto form rather than the enol form in the tautomerization. The deprotonation rate and the kinetic isotope effects of the keto form of BNAH(*)(+) were determined from the kinetic analysis of the electron-transfer reactions. In the case of electron transfer from BNAH to Ru(bpy)(3)(3+), the chemiluminescence due to Ru(bpy)(3)(2+) was observed in the second electron-transfer step from BNA(*), produced by the deprotonation of the keto form of BNAH(*)(+), to Ru(bpy)(3)(3+). The observation of chemiluminescence due to Ru(bpy)(3)(2+) provides compelling evidence that the Marcus inverted region is observed even for such an intermolecular electron-transfer reaction. When BNAH is replaced by 4-tert-butylated BNAH (4-t-BuBNAH), no chemiluminescence due to Ru(bpy)(3)(2+) has been observed in the electron transfer from 4-t-BuBNAH to Ru(bpy)(3)(3+). This is ascribed to the facile C-C bond cleavage in 4-t-BuBNAH(*)(+). In the laser flash photolysis of a deaerated MeCN solution of BNAH and CHBr(3), the transient absorption spectrum of the enol form of BNAH(*)(+) was detected instead of the keto form of BNAH(*)(+), and the enol form was tautomerized to the keto form. The rate of intramolecular proton transfer in the enol form to produce the keto form of BNAH(*)(+) was determined from the decay of the absorption band due to the enol form and the rise in the absorption band due to the keto form. The kinetic isotope effects were observed for the intramolecular proton-transfer process in the keto form to produce the enol form.     

A study on the reactions of NADH models with electron-deficient alkenes. A probe for the extreme of concerted electron-hydrogen atom transfer mechanism

The reactions of 9-fluorenylidenemalononitrile (FDCN) and 1,1-diphenyl-2,2-dicyanoethylene (DPCN) with Hantzsch ester (HEH), N-methyl Hantzsch ester (Me-HEH), and 1-benzyl-1,4-dihydronicotinamide (BNAH) in oxygen-saturated acetonitrile have been studied. The aerobic reactions with HEH give solely reduction products. However, reactions with Me-HEH and BNAH not only result in reduction products, but also give varying amounts of oxidation products. The amount of oxidation product appears to be related to the electronic character and bulkiness of reactants. We propose that all these reactions follow a general mechanism of concerted electron-hydrogen atom transfer mechanism. If the electron-transfer complex is very tight, only ‘concerted hydride transfer reaction’ occurs. However, if the electron-transfer complex is not so tight, oxygen can capture the radicaloid intermediate to result in oxidation products.     

Direct detection of radical cations of NADH analogues

The radical cation of an NADH analogue (BNAH: 1-benzyl-1,4-dihydronicotinamide) has been successfully detected as the transient absorption and ESR spectra in the thermal electron transfer from BNAH to Fe(bpy)33+ (bpy = 2,2'-bipyridine). The ESR spectra of the radical cations of BNAH and the dideuterated compound (BNAH-4,4'-d2) indicate that the observed radical cation is the keto form rather than the enol form in the tautomerization. The deprotonation rate and the kinetic isotope effects of the keto form of BNAH*+ were determined from the kinetic analysis of the electron-transfer reactions.     

Metal ion-catalyzed cycloaddition vs hydride transfer reactions of NADH analogues with p-benzoquinones

1-Benzyl-4-tert-butyl-1,4-dihydronicotinamide (t-BuBNAH) reacts efficiently with p-benzoquinone (Q) to yield a [2+3] cycloadduct (1) in the presence of Sc(OTf)(3) (OTf = OSO(2)CF(3)) in deaerated acetonitrile (MeCN) at room temperature, while no reaction occurs in the absence of Sc(3+). The crystal structure of 1 has been determined by the X-ray crystal analysis. When t-BuBNAH is replaced by 1-benzyl-1,4-dihydronicotinamide (BNAH), the Sc(3+)-catalyzed cycloaddition reaction of BNAH with Q also occurs to yield the [2+3] cycloadduct. Sc(3+) forms 1:4 complexes with t-BuBNAH and BNAH in MeCN, whereas there is no interaction between Sc(3+) and Q. The observed second-order rate constant (k(obs)) shows a first-order dependence on [Sc(3+)] at low concentrations and a second-order dependence at higher concentrations. The first-order and the second-order dependence of the rate constant (k(et)) on [Sc(3+)] was also observed for the Sc(3+)-promoted electron transfer from CoTPP (TPP = tetraphenylporphyrin dianion) to Q. Such dependence of k(et) on [Sc(3+)] is ascribed to formation of 1:1 and 1:2 complexes between Q(*)(-) and Sc(3+) at the low and high concentrations of Sc(3+), respectively, which results in acceleration of the rate of electron transfer. The formation constants for the 1:2 complex (K(2)) between the radical anions of a series of p-benzoquinone derivatives (X-Q(*)(-)) and Sc(3+) are determined from the dependence of k(et) on [Sc(3+)]. The K(2) values agree well with those determined from the dependence of k(obs) on [Sc(3+)] for the Sc(3+)-catalyzed addition reaction of t-BuBNAH and BNAH with X-Q. Such an agreement together with the absence of the deuterium kinetic isotope effects indicates that the addition proceeds via the Sc(3+)-promoted electron transfer from t-BuBNAH and BNAH to Q. When Sc(OTf)(3) is replaced by weaker Lewis acids such as Lu(OTf)(3), Y(OTf)(3), and Mg(ClO(4))(2), the hydride transfer reaction from BNAH to Q also occurs besides the cycloaddition reaction and the k(obs) value decreases with decreasing the Lewis acidity of the metal ion. Such a change in the type of reaction from a cycloaddition to a hydride transfer depending on the Lewis acidity of metal ions employed as a catalyst is well accommodated by the common reaction mechanism featuring the metal-ion promoted electron transfer from BNAH to Q.     

Reduction of diaryl disulfides with 1-benzyl-1,4-dihydronicotinamide

Reduction of diaryl disulfides with 1-benzyl-1,4-dihydronicotinamide (BNAH) proceeded through a radical chain reaction, while dialkyl disulfides were found to be inert to BNAH.     

On the question of one-electron transfer in the mechanism of reduction by nadh-models

The fluorescence of 1-benzyl-1,4-dihydronicotinamide (BNAH) is quenched by a variety of electron acceptors. The dependence of the rate constant of the quenching process on the electrochemical reduction potentials of the quenchers corresponds with that expected for quenching by an electron transfer mechanism in which BNAH acts as an electron donor with a one electron oxidation potential of 0.76 ± 0.02 V (in acetonitrile relative to the saturated calomel electrode).From this oxidation potential, and the reduction potentials of a number of substrates reported to be reduced by BNAH, the rates of thermal one-electron transfer from BNAH to these substrates were estimated via the Rehm-Weller relation for outersphere one-electron transfer. These calculated rates are many orders of magnitude lower than experimental rates reported for the overall reduction processes. This seems to exclude outersphere one-electron transfer as an intermediate step in such reductions.     

Transition metal complexes coordinated by an NAD(P)H model compound and their enhanced hydride-donating abilities in the presence of a base

The ruthenium(II) and rhenium(I) complexes containing an NAD(P)H model compound, 1-benzyl-1,4-dihydronicotinamide (BNAH), as ligand, [Ru(tpy)(bpy)(BNAH)]2+ (1 a) and [Re(bpy)(CO)3(BNAH)]+ (1 b), were quantitatively produced by the reaction of the corresponding metal hydrido complexes with BNA(+) (1-benzylnicotinamidium cation). In the presence of base with pK(a) = 8.9, 1 a and 1 b have much greater reducing power than "free" BNAH. The oxidation potentials of 1 a in the absence and the presence of triethylamine were 0.55 V and -0.04 V, respectively, versus Ag/AgNO(3), whereas that of "free" BNAH was 0.30 V. Spectroscopic results clearly showed that the base extracts a proton from the carbamoyl group on 1 a and 1 b to give the deprotonated BNAH coordinating to the transition-metal complexes [Ru(tpy)(bpy)(BNAH-H+)]+ (3 a) and [Re(bpy)(CO)3(BNAH-H+)] (3 b); this deprotonation underlies the enhancement in reducing ability. The deprotonated forms 3 a and 3 b can efficiently reduce other NAD(P) models to give the corresponding 1,4-dihydro form, resulting in the deprotonated BNA+ being coordinated to the metal complexes [Ru(tpy)(bpy)(BNA(+)-H+)]2+ (2 a) and [Re(bpy)(CO)3(BNA+-H+)]+ (2 b); "free" BNAH and the protonated adducts 1 a and 1 b cannot act in this way. X-ray crystallography was performed on the PF6- salt of 2 a, and showed that the deprotonated nitrogen atom on the carbamoyl group coordinates to the ruthenium(II) metal center with a bond length of 2.086(3) Angstroms. Infrared spectral data suggested that the deprotonated carbamoyl group on the reduced forms 3 a and 3 b is converted to the imido group, and that the oxygen atom coordinates to the metal center.     

Reaction of 1, 1-Di-p-methoxyphenyl-2, 2-dinitroethylene and 1, 1-Di-O-methoxyphenyl-2, 2-dinitroethylene with 1-Benzyl-1, 4-dihydronicotinamide： Evidence for Concerted Electron-hydrogen Atom Transfer Mechanism

1,1-Di-p-methoxyphenyl-2, 2-dinitroethylene reacts with 1-benzyl-1, 4-dihydronicotinamide (BNAH) in deaerated acetonitrile to give 1,1-di-p-methoxyphenyl-2, 2-dinitroethane,while 1,1-di-O-methoxyphenyl-2, 2-dinitroethylene fails to react with BNAH under the same conditions, which provides evidence for a concerted electron-hydrogen atom transfer mechanism.     

Polyelectrolytes containing dihydronicotinamide. III. Fluorescence quenching by nicotinamide-containing polymers in aqueous solution

Charge-transfer (CT) interaction of N-benzyl-1,4-dihydronicotinamide (BNAH) and poly(sodium styrene-p-sulfonate) containing 6 mol % of BNAH groups (PNAH) with several types of nicotinamide-containing polyelectrolytes in aqueous solution was investigated by fluorescence quenching. The experimental data were analyzed in terms of a kinetic model including both static and dynamic quenching. Hydrophobic association of BNAH with the polymers led to more effective quenching than the monomer [N-benzylnicotinamide (BNA)] system. Electrostatic attraction of PNAH and BNA also resulted in the remarkably large value of apparent quenching constant (K′ = 1.4 × 10⁴M^?1). Further, the fluorescence of PNAH was quenched far more effectively by poly[N-(p-vinylbenzyl)nicotinamide] (PBNA) and poly(acrylamide)s containing nicotinamide (NA) groups (PAm) due to the formation of a polyelectrolyte complex (PEC). In this case, the K′ value depended on the BNA content in the copolymer, suggesting the structural matching effect of the interacting pair on the intermacromolecular interaction.     

Mechanism of Reduction of 1,1-Dinitro-2,2-diphenylethylene by 1-Benzyl-1,4-dihydronicotinamide

1-Benzyl-1,4-dihydronicotinamide (BNAH) is widely used as a model to mimic coenzyme NAD(P)H reductions¹. The interest continues in distinguishing whether the formal hydride transfer from BNAH to the substrate takes place by a one-step hydride transfer or by an e-H⁺-e or e-H sequence^2,3.     

A Study on the Reaction of 1-（3-Pyridyl）-2,2-di-substituted Ethylenes with 1-Benzyl-1,4-dihydronicotinamide

The reaction of a series of 1-（3-pyridyl）-2,2-di-substituted ethylenes with 1-benzyl-1,4-dihydronicotinamide （BNAH） in deaerated acetonitrile produces the corresponding 1-（3-pyridyl）-2,2-di-substituted ethanes in contrast to benzylidenemalononitrile （BM） which does not react with BNAH under the same conditions.     

Reduction of methyl benzoylformate by reduced nicotinamide adenine dinucleotide model in the presence of rhodizonic acid

The reduction of rhodizonic acid(RA) with 1-benzyl-1,4-dihydronicotin-amide(BNAH; NADH model) was carried out at room temperature to obtain tetra-hydroxy-p-quinone(THQ) and hexahydroxybenzene(HHB) by two-electron and four-electron reductions, respectively. The reduction of methyl benzoylformate with BNAH proceeded smoothly in the presence of RA, although it could not be reduced at all without RA.     

Electron-transfer chain-substitution in hydrodemercuration of alkylmercury(II) compounds with n-benzyl-1,4-dihydronicotinamide

Reduction of alkylmercury(II) acetates with N-benzyl-1,4-dihydronicotinamide (BNAH) proceeds through electron-transfer chain-substitution mechanism. The rate constant of hydrogen transfer from BNAH to alkyl radical was estimated as in the order of 10⁵ 1/mol·sec.     

Magnetic nano-Fe3O4-supported 1-benzyl-1,4-dihydronicotinamide (BNAH): synthesis and application in the catalytic reduction of α,β-epoxy ketones

A novel magnetically recoverable organic hydride compound was successfully constructed by using silica-coated magnetic nanoparticles as a support. An as-prepared magnetic organic hydride compound, BNAH (1-benzyl-1,4-dihydronicotinamide), showed efficient activity in the catalytic reduction of α,β-epoxy ketones. After reaction, the magnetic nanoparticle-supported BNAH can be separated by simple magnetic separation which made the separation of the product easier.     

Catalytic hydrogenation of alpha,beta-epoxy ketones to form beta-hydroxy ketones mediated by an NADH coenzyme model

[reaction: see text] The hydrogenation of alpha,beta-epoxy ketones can be mediated by a catalytic amount of BNAH or BNA(+)Br(-) to form corresponding beta-hydroxy ketones in high yield. Na2S2O4 is used as the reducing agent to convert BNA(+)Br(-) to BNAH. A radical mechanism has been proposed to understand many observations of this catalytic reaction.     

NAD(P)H辅酶模型还原碳正离子反应的研究: 动力学、热力学及反应机理

本文对NAD(P)H模型物BNAH同xanthylium正离子反应的动力学进行了较为详尽的测定。同位素效应,自由基抑制剂对反应的影响以及对不同机理模式中各基元步骤的热力学趋动力的研究均表明,反应由决速的电子转移引发,随后通过快速的氢原子转移而形成产物。动力学活化参数的分析指出,电子转移前反应底物间首先形成一个预配合平衡。本文还对BNAH还原9-苯基xanthylium正离子和三苯甲烷正离子的机理进行了较合理的估测。     

Selective H2 and CO production with rhenium(I) biscarbonyl complexes as photocatalyst

Rhenium(I) biscarbonyl complexes with two phosphine ligands photocatalyzed not only CO₂ reduction under CO₂ atmosphere but also H₂ evolution under Ar. The reductant 1-benzyl-1,4-dihydronicotinamide (BNAH) worked only as a one-electron donor, and it was quantitatively converted to its corresponding oxidized dimer (BNA₂). The photocatalytic reactions required addition of a base such as triethanolamine, because deprotonation from the oxidized BNAH (BNAH^?+) is essential for the suppression of the back electron transfer from the reduced rhenium(I) complex to BNAH^?+. ¹H, ¹³C, and ³¹P NMR studies under vacuum or ¹³CO₂ atmosphere indicated that the rhenium(I) complex is relatively stable under the CO₂ reduction conditions, but it is converted to some other complexes under the H₂ evolution conditions.     

NAD(P)H辅酶模型在Mg2+离子催化条件下还原N-芳基芴亚胺反应的研究

对Hantzsch酯在Mg²⁺存在和不存在的情况下还原N-芳基芴亚胺的反应进行了研究, 并与BNAH的类似还原做了系统的比较.研究结果表明:Mg²⁺在该还原反应中起亲电催化剂的作用;还原能力较BNAH弱的Hantzsch酯在反应中所呈现的强的反应性是由于其3, 5-位两个极性谈基氧通过静电作用降低过渡态的能量的缘故;本文反应届H-一步转移机理.