bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantum‐chemical simulation of the acid‐, base‐ and enzyme‐catalyzed isomerization of Δ5‐3‐keto steroids
Authors: Kooistra C. , Ae. Sluyterman L. A. , Buck H. M. 
Published: September 2010

AbstractΔ5‐3‐Keto steroids are isomerized to Δ4‐3‐keto steroids by acid, base and enzyme catalysis. The latter reaction occurs by a suprafacial [1,3] H shift from the 4β to the 6β position. These reactions have been simulated using propene and 3‐butenal as substrates. The catalytic effect of a number of bases, B, on the migrating H atom has been studied. The MINDO/3 proton affinities of a group of bases, relative to the affinity of NH3, correlated very well with values calculated using ab initio methods with a large basis set and with experimental gas‐phase data. The semi‐empirical MINDO/3 method has been used to study catalysis by H2O, NH3, formamidine, imidazole, HCOO− and OH− on the suprafacial [1,3] H shift in propene. Similar trends in barrier heights were found with STO‐3G and 4‐31G calculations. A linear dependence of activation enthalpy upon the relative proton affinity of the catalysts could be demonstrated. As a more realistic model for the enzymatic isomerization of 3‐keto steroids, the 3‐butenal → 2‐butenal rearrangement has been studied. Distinct co‐operation between proton acceptors, B, and proton donors, AH, interacting with the carbonyl group, could be established. Acid catalysis was simulated using AH = H3O+ and B = H2O, base catalysis in the absence of AH with B = OH− and enzyme catalysis using AH = imid · H+ and B = HCOO−, MINDO/3 calculated activation enthalpies were 28.0, 8.9 and ‐1.0 kcal · mol−1, respectively. These exhibit the same sequence as the experimental values of 14.0, 11.4 and 5.0 kcal · mol−1, found under the respective conditions. The electron distributions demonstrated that the reactions proceed more readily when the ionogenic component is more pronounced in the transition state. Almost complete deprotonation of the substrate occurs in the base‐catalyzed and the enzyme‐catalyzed reactions, giving rise to intermediates similar in structure to the dienol anion and the neutral dienol, respectively. When catalyzed, suprafacial shifts were favoured over the antarafacial shifts.
Trimethylacetic formic anhydride. Improved preparation and use as a highly efficient and selective N‐formylating reagent
Authors: Vlietstra Edward J. , Zwikker Jan W. , Nolte Roeland J. M. , Drenth Wiendelt 
Published: September 2010

AbstractThe title compound was prepared from trimethylacetyl chloride and sodium formate in the presence of 18‐crown‐6. The mixed anhydride proved to be a very useful reagent for the N‐formylation of amines. Even amines which are unstable when deprotonated can be formylated.
Bacteriorhodopsins with a chemically modified chromophore. The light‐driven proton pump action of [13‐demethyl‐11,14‐epoxy]‐, [9‐demethyl]‐, [13‐demethyl]‐ and [9,13‐bisdemethyl]‐bacteriorhodopsin
Authors: Muradin‐Szweykowska M. , Broek A. D. , Lugtenburg J. , van der Bend R. L. , van Dijck P. W. M. 
Published: September 2010

AbstractThe binding of the isomers of 13‐demethyl‐11,14‐epoxy‐, 9‐demethyl‐, 13‐demethyl‐and 9,13‐bisdemethylretinal to bacterioopsin has been studied. The bacteriorhodopsin analogues formed were incorporated into phospholipid vesicles and their light‐driven proton pump action examined.[9‐Demethyl]‐bacteriorhodopsin, with a similar light‐dark adaptation as the unmodified bacteriorhodopsin, shows 37% of the proton pumping ability of the native pigment.Interestingly, all‐trans‐13‐demethylretinal does not form [13‐demethyl]‐bacteriorhodopsin, whereas both the 11‐ and 13‐cis isomer form a dark‐adapted [13‐demethyl] pigment analogue. This [13‐demethyl]‐bacteriorhodopsin analogue neither shows light adaptation nor pumps protons, which is in agreement with the finding that only light‐adapted bacteriorhodopsin can exert such a function.The 13‐demethyl‐11,14‐epoxyretinal forms a light‐adapted bacteriorhodopsin analogue with a proton pump action. It does not show a dark‐adapted form.In the 9,13‐bisdemethylretinal, the perturbation at position 9 is considerably larger than in the previous cases. The specificity of the protein‐chromophore interaction no longer being present, all‐trans, 9‐cis, 11‐cis and 13‐cis isomers form the corresponding bacteriorhodopsin analogues with proton pump ability.These results indicate that the chromophore in light‐adapted bacteriorhodopsin can only occur in the 12‐s‐cis conformation. Furthermore, it would seem that isomerisation around the 13‐double bond is not as important in proton pumping as has generally been assumed.
Photoinduced electron transport in bi‐ and trichromophoric systems
Authors: Mes G. F. , van Ramesdonk H. J. , Verhoeven J. W. 
Published: September 2010

AbstractThe photophysical properties of a trichromophoric molecule (D2‐D1‐A) containing an electron acceptor (A) and two electron donors (D1,D2) are investigated. Photoinduced electron transport from D2 to A occurs effectively via D1,. If D1, is rendered inoperative by its selective protonation, the system switches to a mode of electron transport which involves direct transfer between the remote D2 and A chromophores.
Studies on polypeptides XXXVIII. An approach to the chemical semisynthesis of ribonuclease a analogues. Part II. Semisynthesis of alanyl‐Nϵ‐octaacetimidoyl‐S‐protein and Nϵ‐octaacetimidoyl‐ribonuclease(14–124)
Authors: Hoogerhout P. , Kerling K. E. T. 
Published: September 2010

AbstractThe semisynthesis of Alanyl‐Nϵ‐octaacetimidoyl‐S‐protein and Nϵ‐octaacetimidoyl‐ribonuclease(14‐124) is reported. The N‐hydroxysuccinimide esters of (tert‐butyloxycarbonyl)‐l‐alanine and of a partially protected ribonuclease heptapeptide(14‐20) were coupled with Nϵ‐octaacetimidoyl‐S‐protein. After reaction of the coupling products with trifluoroacetic acid, the N‐terminal unprotected proteins were obtained.
Photochemical reactions of some aromatic thiones with bis(tert‐butylthio)ethyne. Isolation and properties of thietes, the photochemical (2 + 2)‐cycloadducts and their isomeric α,β‐unsaturated dithioesters
Authors: Brouwer A. C. , George A. V. E. , Bos H. J. T. 
Published: September 2010

AbstractPhotochemical reaction of some aromatic thiones 2 with bis(tert‐butylthio)ethyne 1 affords the α,β‐unsaturated dithio esters 4 via a (2 + 2)‐cycloaddition reaction of the triplet‐excited thiones 2 with acetylene 1. In one case, a (2 + 2)‐cycloadduct, thiete 3o, was isolated. Spectroscopic investigations revealed that in solution there is an equilibrium between this thiete 3o and the isomeric α,β‐unsaturated dithio ester 4o. The generality of this equilibrium phenomenom is examined and discussed with respect to the substituents of the C=C‐C=S moiety of the α,β‐unsaturated dithio esters 4.
Chemistry of ketene acetals V. Catalyzed and non‐catalyzed (2 + 2)‐ and (4 + 2)‐cycloadditions between 1,2‐diketones and ketene acetals
Authors: Bakker C. G. , Scheeren J. W. , Nivard R. J. F. 
Published: September 2010

AbstractGenerally, 1,1‐dimethoxypropene [CH3CH=C(OMe)2, 1b] yields only (2 + 2)‐cycloadducts, viz. oxetanes (3) and bis‐oxetanes (4), in reactions with 1,2‐diketones; (4 + 2)‐cycloaddition products, viz. dihydrodioxins (5), are not formed because of their thermodynamic instability. In similar reactions of tetramethoxyethene [(MeO)2C=C(OMe)2, 1a], compounds 5, however, are obtained, when the (4 + 2)‐cycloaddition is accompanied by an increase in the stabilization energy of the diketone moiety. The difference between 1a and 1b can be ascribed to the low π‐bond energy of 1a.
On the total synthesis of the naloxones from 1‐benzylisoquinolines via 1‐bromo‐2‐(1‐phenyltetrazol‐5‐yloxy)dihydrocodeinone (Chemistry of Opium Alkaloids, Part XVII)
Authors: Crabbendam P. R. , Beyerman H. C. , Lie T. S. , Maat L. 
Published: September 2010

AbstractThe Delft total synthesis of morphinans starts from 1‐benzylisoquinolines (Scheme 2, 7) and gives both the morphinans with the natural (‐)‐morphine configuration and the corresponding enantiomers. This route has been used as a basis for an improved synthesis of (‐)‐naloxone and also provides the possibility of preparing (+ )‐naloxone, which is of interest in pharmacological research (Scheme 1, 6). We report here in particular on the conversion of 1‐(3,5‐dibenzyloxy‐4‐methoxybenzyl)‐1,2,3,4‐tetrahydro‐6‐methoxyisoquinoline (7) into dihydrocodeinone (2) via dihydrothebainone (1), the yield of which was raised from 6 to 17%. An improved procedure has been evolved for the conversion of noroxycodone (5) into naloxone (6).
Studies on polypeptides XXXIX. The role of the imidazole tele‐nitrogen atom of histidine‐12 in the catalytic action of RNase S′
Authors: Hoes C. , Kerling K. E. T. , Havinga E. 
Published: September 2010

AbstractOf three analogues of des(15‐20)‐RNase S′, in which the active site histidyl‐12 residue has been replaced by the 3‐(2‐pyridyl)‐l‐alanyl, the 3‐(3‐pyridyl)‐l‐alanyl and the 3‐(4‐pyridyl)‐l‐alanyl residue, respectively, the enzymatic activity, using various substrates as well as the capability to bind the inhibitor 2′(3′)‐(4‐thio)‐UMP, has been determined. Inhibitor binding is quite strong for the RNase S′ analogues with either a 4‐Pya or a 2‐Pya residue at position 12 but is significantly weaker for the 3‐Pya analogue. Appreciable activity, using RNA, pU>p and C>p as a substrate, is observed for the 4‐Pya analogue, demonstrating the feasibility of replacing an essential active‐site constituent by a structurally different group while retaining the enzymatic activity. The fact that the isomeric 3‐Pya and 2‐Pya analogues are inactive shows the delicate requirements which must be met if enzymatic activity is to be observed. Evidently, a properly orientated nitrogen atom having appropriate acid/base properties is required at position 12 in RNase A or S′. The results provide compelling evidence that the imidazolyl tele‐nitrogen atom of His‐12 in the native enzyme plays an essential role in the catalysis. The imidazolyl pros‐nitrogen atom of this residue, besides providing the tele‐nitrogen atom with the appropriate pKa value, may also contribute by favouring optimal juxtaposition during the catalytic reaction.
Dynamics of DNA. A quantumchemical study
Authors: VanLier Johan J. C. , Koole Leo H. , Buck Henk M. 
Published: September 2010

AbstractOn the basis of CNDO‐2 and MNDO quantumchemical calculations we suggest that direct generation of Pv trigonal bipyramidal (TBP) intermediates, in pC and pT fragments of ds DNA with repetitive purine‐pyrimidine sequences, results in the B → Z transition via a selective pathway. The calculations reveal that 5′‐d(GpC), 5′‐d(GpT), 5′‐d(ApC) and 5′‐d(ApT) fragments are selected to initiate the B → Z transition. We therefore suggest that the cooperative B → Z transition can only proceed in helices having repetitive GC, GT, AC or AT sequences.
On the configurational stability of allenes and butatrienes in the presence of organocopper(I) species
Authors: Westmijze H. , Nap I. , Meijer J. , Kleijn H. , Vermeer P. 
Published: September 2010

AbstractTwo epimeric steroidal allenes, 1 and 2, have been interconverted by reaction with Me2CuMgCl and Me2CuLi. MeCu could also be used, although in this case the isomerisation was much slower. The 1,4‐disubstituted butatrienes 6 and 8 have also been isomerised by means of Me2CuMgCl and MeCu, while the trisubstituted butatriene Z‐7 has been isomerised into its geometric isomer using Et2CuMgCl. The isomerisations are thought to proceed through radical anions. In the case of the butatriene series, it is assumed that the carbometallation of the inner double bond by the copper(I) reagents also proceeds through the proposed radical anion intermediates.
Trans‐substitution and equilibration of phenols. Part IV. The influence of various catalysts on the trans‐tert‐butylation reaction of phenols; mechanistic aspects
Authors: Willemse F. R. J. , Kooyman E. C. , van Lamoen H. B. , de Vos D. , Wolters J. 
Published: September 2010

AbstractThe trans‐tert‐butylation reaction by 2,6‐di‐tert‐butyl‐4‐methylphenol has been studied for a number of phenols in the presence of different catalysts. Equilibria, as well as reaction kinetics, have been investigated. The mechanism involves the intermediacy of a tert‐butyl ether. This mechanism is supported both by the kinetics and the initially high ortho/para ratio as well as by the reversed substituent effect.
Aromatic sulfonation 86. Sulfonation of pyrene, 1‐methylpyrene and perylene
Authors: Cerfontain Hans , Laali Khosrow , Lambrechts Hans J. A. 
Published: September 2010

AbstractThe mono‐ and di‐sulfonation of pyrene (1a), 1‐methylpyrene (1b) and perylene (2), with SO3 in nitromethane at 0°C, has been studied. The monosulfonation of 1a, 1b and 2 leads to the almost exclusive formation of the 1‐, the 6‐ + 8‐ and the 3‐sulfonic acid, respectively, which is in agreement with predictions based on the calculated localization energies for the various positions of the respective arenes. The sulfonation of pyrene‐1‐sulfonic acid yields the 1,3‐disulfonic acid as the main product while that of both 1‐methylpyrene‐6‐ and ‐8‐sulfonic acid mainly yields the 6,8‐disulfonic acid. Perylene‐3‐sulfonic acid yields almost exclusively the 3,9‐ and/or the 3,10‐disulfonic acid. The positional reactivity orders of the pyrenesulfonic acids are determined by the (electronic) directing effect of the sulfonic acid substituent, while that of perylene‐3‐sulfonic acid is determined by the localization energies of the parent arene.
Synthesis of 6H‐benzo[cd]pyren‐6‐one, a polar constituent of carbon black
Authors: Tintel C. , van der Brugge M. , Lugtenburg J. , Cornelisse J. 
Published: September 2010

Abstract6H‐Benzo[cd]pyren‐6‐one (6), a potentially carcinogenic constituent of carbon black, can be synthesized smoothly and in good overall yield (49%) from pyrene (1), by using the reactivity of the pyrene dianion.
The synthesis of precursors of labelled neuropeptides
Authors: van Nispen J. W. , Bijl W. A. A. J. , Hendrix A. M. M. , Greven H. M. 
Published: September 2010

AbstractModified amino acids which can serve as precursors in the synthesis of tritium‐labelled peptides were prepared and incorporated into biologically active peptides. Thus,p‐iodophenylalanine was incorporated at position 4 of H‐Met(O2)‐Glu‐His‐Phe‐D‐Lys‐Phe‐OH (Org 2766) and in des‐Tyr1‐γ‐endorphin. As a second labelling site, the precursor of L‐leucine, L‐methallylglycine, was incorporated in both des‐Tyr1‐γ‐endorphin and the shorter des‐enkephalin‐γ‐endorphin. Finally, the lysine residue in Org 2766 (D‐Lys) and des‐enkephalin‐γ‐endorphin (L‐Lys) was replaced by its analogue 2,6‐diamino‐4‐hexynoic acid. The precursor peptides were synthesized via the fragment condensation approach. With the exception of the methallylglycine‐containing des‐Tyr1‐γ‐endorphin, in which partial desulfurization of the methionine residue could not be prevented, these peptides could be converted by means of catalytic reduction into their respective parent compounds.
The use of immobilized enzymes in organic synthesis. Part 8. Oxidation of 1‐aryl‐3‐carbamoylpyridinium chlorides by rabbit liver aldehyde oxidase and bovine milk xanthine oxidase
Authors: Angelino S. A. G. F. , Buurman D. J. , van der Plas H. C. , Müller F. 
Published: September 2010

AbstractOxidation of 1‐aryl‐3‐carbamoylpyridinium chlorides with immobilized rabbit liver aldehyde oxidase gave predominantly 1‐aryl‐1,6‐dihydro‐6‐oxo‐3‐pyridinecarboxamides, together with the corresponding 1‐aryl‐1,4‐dihydro‐4‐oxo‐3‐pyridinecarboxamides.In general, the site of oxidation by this enzyme is determined by steric factors. The rate of oxidation by free aldehyde oxidase is very sensitive to electronic effects. A more electron‐withdrawing aryl substituent increases the reaction rate for oxidation to 6‐oxo product. Consequently, a positive ρ value of about 3.6 was calculated for free aldehyde oxidase. Oxidation of these compounds by bovine milk xanthine oxidase yielded mainly 4‐oxo products. Preparative‐scale reactions with both free and immobilized xanthine oxidase gave low product yields. The oxidation rate of free xanthine oxidase is only slightly affected by substituents in the aryl group.
A new chiral base derived from nicotinamide. Preparation and chiral stability ofN,N‐dimethyl‐2,4‐dimethyl‐3‐carbamoylpyridine in various solvents
Authors: van Lier P. M. , Meulendijks G. H. W. M. , Buck H. M. 
Published: September 2010

AbstractThe synthesis of enantiomerically pureN,N‐dimethyl‐2,4‐dimethyl‐3‐carbamoylpyridine is given. A model is outlined for its chiral stability in dependence of the solvent.
The palladium(0)‐catalysed formation of 3‐methoxy‐1,3‐butadienes from methoxypropadiene derivatives and organozinc compounds
Authors: Kleijn H. , Westmijze H. , Meijer J. , Vermeer P. 
Published: September 2010

AbstractThe smooth conversion of the readily available compounds, H2C=C(OMe)‐CR2′‐X (1; X = OC(O)Me or OS(O)Me), with R‐ZnCl reagents, using Pd[PPh3]4 as catalyst, is described. It is shown that via this route several 3‐methoxy‐1,3‐dienes H2C=C(R)‐C(O)Me)=CR2′ (2), in which the group R is 1‐alkenyl, aryl, 1,2‐alkadienyl or 1‐alkynyl, can be prepared. The results obtained with R‐Cu or R2CuM were generally inferior to those found with the zinc compounds.
Carbon‐carbon bond forming reactions of ω‐oxylactams in acid and neutral medium
Authors: Speckamp W. N. , de Boer J. J. J. 
Published: September 2010

Abstract1,3‐Dicarbonyl compounds and hydroxybenzenes condense under the influence of acid with ω‐hydroxylactams 1–7 in an intermolecular process, thereby affording ω‐alkylated lactams 8–13. The reactive intermediate in the carbon‐carbon bond forming step is a cyclic N‐acyliminium ion. The intramolecular variant affords keto ester 19. Upon activation of the ω‐hydroxylactam as a hexafluoroisopropoxy ester, condensations with cyanide in aprotic polar solvents under neutral conditions become possible.
t‐Butyldimethylsilyl (TBDMS) as protective group in carbohydrate chemistry migration of the tbdms group in trans‐diol systems
Authors: van Boeckel C. A. A. , van Aelst S. F. , Beetz T. 
Published: September 2010

AbstractIn the presence of base the t‐butyldimethylsilyl (TBDMS) protective group is able to migrate between trans‐diaxial hydroxyl functions of carbohydrates.
Etudes spectrales de la stéréoisomérie de dérivés de l'aldehyde malonique
Authors: Kirsch G. , Mieloszynski J. L. , Paquer D. , Andrieu C. G. 
Published: September 2010

AbstractA number of aromatic derivatives of malonaldehyde have been studied by NMR (13C, 1H) and IR. These techniques show that these compounds exist in solution as Z enol form magnified image. For nitrile derivatives magnified image, the Z as well as the E form has been identified. A detailed study of the 13C chemical shifts of these compounds is reported.
The amination of 3‐nitro‐1,5‐naphthyridines by liquid ammonia/potassium permanganate. A new and convenient amination method
Authors: Wozniak M. , van der Plas H. C. , Tomula M. , van Veldhuizen A. 
Published: September 2010

AbstractTreatment of a solution of 3‐nitro‐2‐X‐1,5‐naphthyridines (X = H, OC2H5, Cl, NH2, OH) in liquid ammonia with potassium permanganate gives the corresponding 4‐amino‐3‐nitro‐2‐X‐1,5‐naphthyridines in moderate to good yields.From 1H NMR spectroscopy, good evidence has been obtained for the intermediacy of 4‐amino‐1,4‐dihydro‐3‐nitro‐2‐X‐1,5‐naphthyridines in these amination reactions.
Lithiation of cyclopropane rings promoted by intramolecular alkoxy groups
Authors: Klumpp G. W. , Kool M. , Veefkind A. H. , Schakel M. , Schmitz R. F. 
Published: September 2010

AbstractCyclopropane C‐H separated from an alkoxy group by one, two or three carbon atoms can be lithiated if intramolecular coordination between Li and OR is possible in the reaction product.
Synthesis of arylsulfonimidoyl fluorides and their use in the preparation of (arylsulfonimidoyl)methyl isocyanides. Partial resolution of optically active S‐phenyl‐N‐tosylsulfonimidoyl fluoride
Authors: van Leusen Daan , van Leusen Albert M. 
Published: September 2010

AbstractN‐Tosyl‐ and N‐methyl‐substituted sulfonimidoyl fluorides (2) have been synthesized from the corresponding chlorides by displacement with fluoride ion. S‐Phenyl‐N‐tosylsulfonimidoyl fluoride (2a) is a stable (persistent) shelf compound, which has been used for the synthesis of (S‐phenyl‐N‐tosylsulfonimidoyl)methyl isocyanides (4). The latter compounds form a new class of derivatives of methyl isocyanides, which, much like tosylmethyl isocyanides, form azoles by baseinduced cycloadditions to unsaturated substrates. Fluoride 2a has been partially resolved into its enantiomers.
Base‐catalysed isomerization of 7‐(methoxycarbonyl)‐1,3,5‐cycloheptatriene
Authors: Zwaard A. W. , Prins M. D. , Kloosterziel H. 
Published: September 2010

AbstractIn basic alcohol, 7‐(methoxycarbonyl)‐1,3,5‐cycloheptatriene (7b) forms its 2‐, 3‐ and 1‐isomers (viz. 2b, 3b and 1b) in successive reactions. All isomers show specific hydrogen exchange in CD3ONa/CD3OD. For 3‐ and 1‐(methoxycarbonyl)‐1,3,5‐cycloheptatriene vinylic hydrogen atoms are exchanged rather than the “allylic” 7‐H atoms.
Bis[2‐(methylsulfonyl)ethyl] phosphochloridate, a new phosphorylating agent
Authors: Beld A. , Claesen C. A. A. , Roersma E. S. , Schippers W. J. M. , Keizer L. M. , Tesser G. I. 
Published: September 2010

AbstractThis communication describes the application of the 2‐(methylsulfonyl)ethyl group (Mse) as a base‐labile protecting group for the two hydroxyl functions in phosphoric acid monoesters. Due to its perfect stability towards acids, the Mse group can function as a stable protecting group in a phosphochloridate, providing a suitable phosphorylating agent. Some model phosphorylations are presented, and the reaction is applied to the synthesis of bis[2‐(methylsulfonyl)ethyl] tyrosine phosphate. Removal of the Mse functions is achieved effectively and extremely rapidly in alkaline media. The estimation of the minimum conditions necessary for the removal of one or both Mse functions from bis[2‐(methylsulfonyl)ethyl] p‐nitrophenyl phosphate and from a tyrosine derivative is described.
The reactivity of the anion of 2‐(diethylamino)‐5‐phenyl‐3H‐azepine. Synthesis of 3‐substituted 2‐(diethylamino)‐5‐phenyl‐3H‐azepines
Authors: Streef J. W. , van der Plas H. C. , van Veldhuizen A. , Goubits K. 
Published: September 2010

AbstractDeprotonation of 2‐(diethylamino)‐5‐phenyl‐3H‐azepine (1) with different base systems yields an anionic species, which, on treatment with appropriate electrophiles, gives the 3‐substituted derivatives of 1.
Reactivity of octachlorocyclotetraphosphazene towards alkyllithium reagents; formation of bi(cyclotetraphosphazenes)
Authors: Winter Herman , van de Grampel Johan C. 
Published: September 2010

AbstractReactions of octachlorocyclotetraphosphazene (NPCl2)4 with methyl lithium and isopropylalcohol or alkyl iodides afford hydrido‐phosphazenes and bi(cyclotetraphosphazenes). A reaction mechanism, based on an initial metal‐halogen exchange process, is proposed.
Electrochemical behaviour of horse‐heart cytochrome‐c
Authors: Schreurs J. , Veugelers P. , Wonders A. , Barendrecht E. 
Published: September 2010

AbstractA quasi‐reversible electrochemical behaviour of horse‐heart cytochrome‐c is obtained at gold and platinum electrodes in the presence of 4, 4′‐bipyridine. Transparent tin‐dioxide and glassy‐carbon electrodes, modified with pyridine groups, also give rise to a quasi‐reversible response of cytochrome‐c. From impedance measurements and from cyclic‐ and ac‐voltammetry at the gold an platinum electrodes, reaction rate constants (k0′) of 0.6·10−4 to 1.4·10−4 m·s−1 were determined for cytochrome‐c in the presence of 4, 4′‐bipyridine. In both cyclic‐ and ac‐voltammograms, an adsorption peak is observed at −0.2 V vs. SCE. This peak is ascribed to strong adsorption of both ferri‐ and ferrocytochrome‐c. The 4, 4′‐bipyridine molecule creates a suitable interface at the electrode surface. Although no interaction between 4, 4′‐bipyridine and cytochrome‐c could be detected in solution, a specific interaction is believed to be present between adsorbed 4, 4′‐bipyridine and cytochrome‐c.