Histamine metal complexes

High-spin/low-spin transitions bipyridyl metal complexes, 90 iron complexes, 94 polypyridyl metal complexes, 91 Histamine metal complexes, 82 Histidine copper complexes naturally occurring, 965 metal complexes, 746 naturally occurring, 966 reactivity, 756 stereoselectivity, 754 Schiff bases... 

Transient metal complexes. Carnosine and anserine are able to form complexes with transient metal ions Cu, Zn,Co, Va, Mn, Ni and Fe. Cu(II) complexes are better studied. Cu(II) and carnosine form both monodentate and bidentate complexes being in equilibrium with each other and interconverting depending on surrounding conditions under physiological conditions only monodentate complexes exist [28]. Stability constants, pKa at room temperature are 13.3 for Cu-Cam-H complex and 8.47 for Cu-Cam complex. Complex between Cu(I) and carnosine is also formed [29], which is characteristic of unpredictable low ability to interact with molecular oxygen contrary with that of similar complexes of histidine and histamine. 

Agonists - The existence of two receptor populations for histamine raises the interesting question of whether the chemical mechanism of histamine interaction differs between the two receptor types. Some indications of the chemical properties which may differentiate receptor action come from studies of histamine chemistry and from structure-activity considerations of congeners. Histamine in aqueous solution is a mixture of equilibrating species, viz. ionic forms, tautomers and conformers nmr studies confirm earlier pK work indicating a N -H N -H (structures 1 and 2) tautomer ratio of approximately 4 1 for histamine monocation, and a comparable ratio for histamine base. The latter result contrasts with crystal structure data and molecular orbital predictions, and may indicate an influence of solvent on tautomer stability. Recent studies of properties pertinent to consideration of ligand-receptor interactions are conformation (MO calculations and infra-red comparison of solid state and chloroform solutions of histamine base ), electronic charge distribution, metal complexation, and phospholipid inter-... 

Mn2+, D.F.P.-ase is further activated by cysteine, histidine, thiolhistidine, and serine, histamine and 2 2 -dipyridyl. Reagents reacting with metal ions, SH groups and carbonyl groups inhibit D.F.P.-ase activity. Work is proceeding on the further elucidation of such mechanisms.1 In a somewhat similar connexion attention is called to the fact that the non-enzymic hydrolysis of D.F.P. is accelerated by heavy metals and their complexes, in particular by copper chelates of ethylene diamine, o-phenanthroline, 2 2 -dipyridyl and histidine.2... 

Marchelli used the copper(II) complex of histamine-functionalized P-cy-clodextrin for chiral recognition and separation of amino acids [27]. The best results were obtained for aromatic amino acids (Trp). Enantioselective sensing of amino acids by copper(II) complexes of phenylalanine-based fluorescent P-cyclodextrin has been recently published by the same author [28, 29]. The host containing a metal-binding site and a dansyl fluorophore was shown to form copper(II) complexes with fluorescence quenching. Addition of d- or L-amino acids induced a switch on of the fluorescence, which was enantioselective for Pro, Phe, and Trp. This effect was used for the determination of the optical purity of proline. 

Zinc and other metal ions have been found to promote pyrrole hydrogen ionization in 2-(2 -pyridyl)imidazole.269 Complexation studies114 on the systems N-methyl-histamine and NN-dimethylhistamine with bivalent zinc, copper, cobalt, and nickel have shown that the stabilities of the complexes follow the Irving-Williams series. With respect to the variation of a ligand with the same metal ion, the stability decreases in the series histamine, N-methylhistamine, NN-dimethylhistamine, possibly as a result of steric hindrance. The complexes are assigned the structure (12). 

Leakage of metals from the column during elution can be the most significant problem due to their toxicity, but there are several ways to avoid this pitfall. Some references suggest the precaution of underloading IMAC columns (by as much as 20%) with the metal ion to begin with [8]. Another precaution is to add EDTA with imidazole, histidine, or histamine to the column fractions. EDTA competitively blocks formation of coordination complexes between protein... 

The complexation of the Group IIB metals by amino-acid and related derivatives continues to be a subject of interest stability constants reported include those for histidine and its derivatives, histamine, glycylhistamine, aspartic and glutamic acids, aspargine, glutamine, glycine, cysteine, and alanine. " ... 

We have previously found that solvophobic interactions between side chain moieties of two different ligands co-ordinated to die same metal ion favor mixed complex formation by means of a favorable enthalpy contribution [47-49]. In the CDhm systems the cavity seems to play the same role as a side chain moiety and stereoselectivity is seen to be enthalpy driven. The entropy change seems to be less favorable for the D-enantiomers, the side chains of which are most probably included in the cavity. This could also be interpreted as resulting from the loss of internal rotational freedom of the side chain which predominates over the effect of cavity desolvation due to inclusion. Thermodynamic stereoselectivity was also found in the copper(U) ternary complexes with 6-deoxy-6-[4-(2-aminoethyl)imidazolyl]-p-cyclodextrin 2 (CDmh) [29], an isomer of CDhm, where the histamine is linked by the imidazole nitrogen (Table IE). In this case the copper(II) mixed complex with the D-isomer of tryptophan is less stable than the complex with the L-isomer. 

Another means to modify the retention of proteins in MIC is the inclusion of a competing complexing agent such as imidazole [24,82], histidine [82], histamine [83], glycine [31,32,83], ammonia [12], glutamate [65], or phosphate [65] in the mobile phase. Protein retention decreases with increasing concentration of the additive because of competition for the metal chelate binding sites. Imidazole is... 

The complexes Ni(PIpip), where H2PIpip = pyridylbis[N(4)-(piperidyl)] thiosemi-carbazones, show vNiN at 461 cm and vNiS at 335 cm Metal-isotope and deuteriation experiments were used to assign skeletal modes for the nickel-histamine complexes Ni(hm)Cl2 (vNiNH2 401 cm ) and [Ni(hm)3] + (380... 

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