Profiling the Active Site of a Copper Enzyme through Its Far-Infrared Fingerprint

Vibrations of the metal active site of the Cu,Zn-superoxide dismutase enzyme were analyzed by far-infrared difference spectroscopy and theoretical normal mode calculation. Both electrochemically triggered Cu(I) and Cu(II) redox states show well-defined infrared vibrational modes, notably modes of the histidine ligands, the Cu(II) -His(61) -Zn(II) bridge and of the water pseudo-ligand.     

Reduction of Transient Histidine Radicals by Tyrosine: Influence of the Protonation State of Reactants

The role of tyrosine radicals as mediators of electron transfer reactions in enzymes is well established, as is the involvement of histidine as a binding partner. But how environmental factors affect these reactions remains poorly explored. In the study presented here, kinetic data on the influence of the protonation state of the reactants on the reduction of transient histidine radicals by tyrosine were obtained in neutral and basic aqueous solution (pH 6–12) using time-resolved chemically induced dynamic nuclear polarization (CIDNP). The histidine radicals were generated in the photo-induced reaction with the photosensitizer 3,3′,4,4′-tetracarboxy benzophenone. From model simulations of the detected CIDNP kinetics, pH dependent second-order rate constants of the reduction of histidine radicals were obtained for four possible combinations of the amino acids and their N-acetyl derivatives, and also for the systems histidine-phenylalanine dipeptide/N-acetyl tyrosine, and N-acetyl histidine/tyrosine-glutamine dipeptide. The pH dependences of the rate constant of the reduction reaction are explained accounting for the protonation states of reactants, and also protonation state of the equilibrium form of the product - reduced form of histidine radical, which is histidine with neutral or a positively charged imidazole.     

Cobalt(III)‐Mediated Permanent and Stable Immobilization of Histidine‐Tagged Proteins on NTA‐Functionalized Surfaces

We present the cobalt(III)‐mediated interaction between polyhistidine (His)‐tagged proteins and nitrilotriacetic acid (NTA)‐modified surfaces as a general approach for a permanent, oriented, and specific protein immobilization. In this approach, we first form the well‐established Co²⁺‐mediated interaction between NTA and His‐tagged proteins and subsequently oxidize the Co²⁺ center in the complex to Co³⁺. Unlike conventionally used Ni²⁺‐ or Co²⁺‐mediated immobilization, the resulting Co³⁺‐mediated immobilization is resistant toward strong ligands, such as imidazole and ethylenediaminetetraacetic acid (EDTA), and washing off over time because of the high thermodynamic and kinetic stability of the Co³⁺ complex. This immobilization method is compatible with a wide variety of surface coatings, including silane self‐assembled monolayers (SAMs) on glass, thiol SAMs on gold surfaces, and supported lipid bilayers. Furthermore, once the cobalt center has been oxidized, it becomes inert toward reducing agents, specific and unspecific interactions, so that it can be used to orthogonally functionalize surfaces with multiple proteins. Overall, the large number of available His‐tagged proteins and materials with NTA groups make the Co³⁺‐mediated interaction an attractive and widely applicable platform for protein immobilization.     

Indirect reversed‐phase high‐performance liquid chromatographic and direct thin‐layer chromatographic enantioresolution of (R,S)‐Cinacalcet

Enantioresolution of the calcimimetic drug (R,S)‐Cinacalcet was achieved using both indirect and direct approaches. Six chiral variants of Marfey's reagent having l ‐Ala‐NH₂, l ‐Phe‐NH₂, l ‐Val‐NH₂, l ‐Leu‐NH₂, l ‐Met‐NH₂ and d ‐Phg‐NH₂ as chiral auxiliaries were used as derivatizing reagents under microwave irradiation. Derivatization conditions were optimized. Reversed‐phase high‐performance liquid chromatography was successful using binary mixtures of aqueous trifluoroacetic acid and acetonitrile for separation of diastereomeric pairs with detection at 340 nm. Thin silica gel layers impregnated with optically pure l ‐histidine and l ‐arginine were used for direct resolution of enantiomers. The limit of detection was found to be 60 pmol in HPLC while in TLC it was found to be in the range of 0.26–0.28 µg for each enantiomers. Copyright © 2010 John Wiley & Sons, Ltd.     

Nano‐sized metal complexes of azo L‐histidine: Synthesis,characterization and their application for catalytic oxidation of 2‐amino phenol

A novel azo dye ligand formed by the coupling of L‐histidine with 2‐hydroxy‐1‐naphthaldyhide(H₂L) and its Ru³⁺, Pd²⁺ and Ni²⁺ nano‐sized complexes were obtained and described by elemental analysis, TGA, magnetic moment measurements, molar conductance, UV‐Vis, ESR, X‐ray powder diffraction, IR, SEM, TEM, ¹H‐nmr, ¹³C‐nmr, and EI‐mass spectral studies. The analytical results and spectral studies detected that the H₂L ligand acts as dibasic tetradentate via aldehyde oxygen, azo nitrogen and deprotonated OH and COOH groups. The data showed the paramagnetic Ru³⁺ complex has octahedral geometry while Pd²⁺ and Ni²⁺ have square planar structures. The molar conductance measurements display all complexes are nonelectrolyte. The crystallinity, morphology and average particle size data revealed the prepared complexes were formed in the Nano scale. The average particle size as calculated from TEM images are found to be 13.72, 64.52 and 115.00 nm for Ru³⁺, Pd²⁺ and Ni²⁺ chelates, respectively. The catalytic activities of these compounds were checked for oxidation of 2‐amino phenol to 2‐amino‐3H phenoxazine‐3‐one as heterogeneous catalysts. A 96, 31 and 21% catalytic conversion are found when using Ru(III), Pd(II) and Ni(II) complexes respectively.     

SERS study of a tetrapeptide based on histidine and glycine residues,adsorbed on copper/silver colloidal nanoparticles

Surface‐enhanced Raman scattering has been employed to characterize the adsorption of an oligopeptide containing histidine residues on colloidal nanoparticles of metals as Ag and Cu obtained by laser ablation. The title molecule consists of two histidine and glycine residues alternating along the chain and terminating with an acetyl on one side and an amide group on the other. Histidine residues are found to act as docking sites of the molecule to the surface of the metal nanoparticles. Semiempirical parameterized model number 3 (PM3) calculations performed on molecule/metal model complexes suggest possible different adsorption geometries depending on the metallic substrate. This investigation could provide useful information to address the interaction of protein systems with metal ions, which is often related to fundamental biological process in living systems and can play an important role in different neuropathological diseases. Copyright © 2014 John Wiley & Sons, Ltd.     

An In Situ Generated Achiral Cu(II)‐Containing Polymer Complex Sensor for Enantioselective Recognition Induced from L‐/D‐Histidine Enantiomers

A novel achiral polymer P‐1 is synthesized by the polymerization of (2,5‐bis(octyloxy)‐1,4‐phenylene)diboronic acid ( M‐1 ) with pyridine‐2,6‐diylbis(methanylylidene)bis(4‐iodoaniline) ( M‐2 ) via Pd‐catalyzed Suzuki coupling reaction. The tridentate ligand in the main chain backbone can further coordinate with Cu²⁺ to afford the corresponding achiral copper‐containing polymer complex P‐2 , which selectively responds to L‐/D‐histidine with significant fluorescence enhancement over other amino acids. Interestingly, P‐2 exhibits obvious CD response toward L‐ or D‐histidine compared with its model compound MC , indicating that this kind Cu(II)‐containing polymer complex sensor can be used as an effective chemosensor for enantioselective recognition of histidine enantiomers by means of CD spectroscopy.

     

Involvement of histidines 11, 15 and 19 in the binding of zinc to the fusogenic H5WYG peptide

The histidine‐rich GLFHAIAHFIHGGWHGLIHGWYG peptide (H5WYG) coordinates a Zn²⁺ ion and forms a stable peptide–metal complex promoting membrane fusion at physiologic pH. In our previous article titled ‘Histidine‐rich peptide: evidence for a single zinc‐binding site on H5WYG peptide that promotes membrane fusion at neutral pH’ in Journal of Mass Spectrometry (2009, 44, 81–89), tandem mass spectrometry experiments have provided evidence for the binding of a single Zn²⁺ ion to H5WYG and suggested that this binding is shared between H¹¹, H¹⁹ and probably H¹⁵ residues. To clarify the involvement of these histidine residues in the binding to the Zn²⁺ ion and especially to remove the doubt about the implication of the H¹⁵ residue, here we have used three H5WYG mutants termed H5WYGH11A, H5WYGH15A and H5WYGH19A, whose H¹¹, H¹⁵ and H¹⁹ residues were replaced with an alanine residue. The novelty introduced by these new tandem mass spectrometry experiments performed with the mutants is the demonstration that H¹⁵ is involved in the binding of the single Zn²⁺ ion and that it may even favour the setting of another Zn²⁺ ion. Thus, the three histidines H¹¹, H¹⁵ and H¹⁹ could lead to a specific structuring of H5WYG that can promote membrane fusion upon the binding of zinc. Copyright © 2009 John Wiley & Sons, Ltd.     

Equilibria and kinetics for p H-dependent axial ligation of alkyl(aquo) cobaloximes with aromatic and aliphatic N-donor ligands

Equilibria and kinetics of the reaction of bromomethyl(aquo) cobaloxime with histamine, histidine, glycine and ethyl glycine ester and iodomethyl(aquo) cobaloxime with cyanide, imidazole and substituted imidazoles were studied as a function ofpH at 25°C, 10 M ionic strength (KCl) by spectrophotometry technique. The rate of substitution of H₂O varies with thepKa of the incoming ligand, thus establishing the existence of nucleophilic participation of the ligand in the transition state. Dissociation kinetic reactions were also studied as a function ofpH. Binding and kinetic data were interpreted based on the basicity, steric crowd of the entering ligand and HSAB principle. To compare the rate constants of the entering ligandspH independent second-order rate constants were calculated.