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Cobalamin (Cbl, vitamin [B.sub.12]) serves for two essential cofactors in mammals. The pathway for its intestinal absorption, plasma transport, and cellular uptake uses cell surface receptors and three Cbl-transporting proteins, haptocorrin, intrinsic factor, and transcobalamin (TC). We present the structure determination of a member of the mammalian Cbl-transporter family. The crystal structures of recombinant human and bovine holo-TCs reveal a two-domain architecture, with an N-terminal [[alpha].sub.6]-[[alpha].sub.6] barrel and a smaller C-terminal domain. One Cbl molecule in base-on conformation is buried inside the domain interface. Structural data combined with previous binding assays indicate a domain motion in the first step of Cbl binding. In a second step, the weakly coordinated ligand [H.sub.2]O at the upper axial side of added [H.sub.2]O-Cbl is displaced by a histidine residue of the [[alpha].sub.6]-[[alpha].sub.6] barrel. Analysis of amino acid conservation on TC's surface in orthologous proteins suggests the location of the TC-receptor-recognition site in an extended region on the [[alpha].sub.6]-[[alpha].sub.6] barrel. The TC structure allows for the mapping of sites of amino acid variation due to polymorphisms of the human TC gene. Structural information is used to predict the overall fold of haptocorrin and intrinsic factor and permits a rational approach to the design of new Cbl-based bioconjugates for diagnostic or therapeutic drug delivery. cobalamin | crystal structure | P259R polymorphism | transport protein

The di-Mn(II) and di-Co(II) derivatives of variants of the DF1 metalloprotein exhibit an increased number and polarity of exogenous ligands with an increase in the size of the active site cavity. The geometric parameters defining the DF structures, which show significant helix tilting and sliding motions, are compared to natural diron proteins and it is seen that DF proteins have a restricted active site cavity, which imply substrate rocognition and chemical stability.

Research has been conducted on the alkyl-cobalt(III) complexes. The synthesis and characterization of these complexes have been carried out in investigating the role of the tridentate ligand in the alkylation reaction and the results are reported.

Research has been conducted on the dinuclear complexes with Me and H. The synthesis and the solution and solid-state characterization of the [MeCo-(DH)(DB(OMe)(4-Py))] (sub)2 compound which is a molecular box (the metal unit walls formed by a bifunctional ligand) have been investigated and discussed.

Research has been conducted on the organocobalt complexes. The X-ray structure and formation mechanisms of these complexes have been investigated and the results are reported.

Research has been conducted on the dinuclear copper(II) complexes with a new ligand. The reactivity of these complexes as models for tyrosinase has been examined.

Research has been conducted on the axial fragment in cobalamins that contain axial S ligand. The structural characterization of this fragment is presented.

A study is conducted on the crystals of chloro- and azidocobalamin containing LiCl, C62H103Cl3CoLi2N13O21.5P and C62H106.60Cl2CoLi2N16O23.3P to assess the interactions between corrin and ionic species. The crystals were prepared using the hanging-drop method of vapor diffusion while crystal structure was determined via the X-ray diffraction beamline of the Elettra Synchrotron. It is shown that the corrin functions as a molecular 'octopussy' which 'clutch' anions and cations through its amide side chains.

A study was conducted on the synthesis and characterization of the dicopper(II) complex derived from a triamino pentabenzimidazole ligand. The findings indicate that the ligand binds the two coppers nonsymmetrically and that Cu1 has distorted TBP geometry while Cu2 has distorted SP geometry. Voltammetric data reveal quasireversible reductions at the two copper centers with redox potential being higher for the CuN3 center and lower for the CuN5 center.

X-ray crystallographic determination of the molecular structure of trans-(NH3)2Pt(mu-1-MeC-)2Pd(NH3)Pd(NH3)4 0.5(NO3)3*3H2O shows that this compound crystallizes in the triclinic space group and has a square planar coordination of Pd and a square pyramidal coordination of Pt with Pd in the apical position. Extended studies have led to the formation of d8-d10 Pt(II)-Hg(II)13. The effect and correlation of the M-M' bond in d8-d8 dimers are discussed.

The sizes of the Me3Bzm ligand and py are compared to reveal the largeness of the ligand, though both have equal effective bulk. The two sides the lopsided ligand reveal more and less bulkiness compared to py. Stimulatory influences on shifts are presumed due to the stimulatory influences of Co on 13C shifts in cobaloximes. The process reveals the stimulatory abilities of simple metal ions on shifts over the potential of the proton. The ligand-responsive electronic characteristics of the metal core are calculated by epsilon.

Mixed-metal Pt-Hg complexes of the nucleobases 1-methylcytosine and 1,5-dimethylcytosine were described. It was shown that the heteronuclear compounds contain two bridging cytosyl ligands, binding Pt through N3 and Hg via deprotonated exocyclic amino groups of the nucleobases. 1H nuclear magnetic resonance spectra of the various Pt-Hg compounds show 195Pt and 199Hg coupling. Moreover, the mixed-metal Pt-Hg species, when reacted with a large variety of N and S donor ligands X, tend to decompose with formation of trans-(a2PtL2)2+ and HgX2.

The reaction of trans-(a2Pt(1-MeC-N3)2)(NO3)2 (a = NH3, CH3NH2; 1-MeC = 1- methylcytosine), K2PdCl4 and trans-(NH32Pd(H2O)2)(NO3)2 yielded trans-a2Pt((1-MeC- -N3,N4)PdCl)+,PtPdCl and trans-(a2Pt(1-MeC- -N3)), N42Pd(NH3)2+,PtPd(NH3). The PdPtY (Y = nucleobase) complexes consisted of large cations, nitrate anions and water molecules. Steric factors prevented the formation of trans-(a2Pt(1-MeC-)2PdY2)n+ (n = 2 or 0)-type compounds.

A novel slipped stack chains of either tri- or tetracationic copper porphyrins are detected crystallographicall using synchrotron X-ray diffraction data. Density functional theory calculations on the isolated porphyrins indicate HOMO orbitals with the correct topology to yield a bonding interaction among the stacked porphyrin units along the chain in the crystal.

The analysis of the electronic spectra of adenosylcobalamin (AdoCbl) and its derivative in which the trans axial base was replaced by a water molecule (AdoCbi–H2O) has been performed by means of time-dependent density functional theory (TDDFT). The latter corresponds to the situation encountered in strongly acidic conditions. The TDDFT electronic transitions and oscillator strengths were calculated at the optimized B3LYP and BP86 ground state equilibrium geometries. A comparison of the orbital energy diagrams obtained with the B3LYP and BP86 functionals reveals a different orbital order and composition of the highest occupied and lowest unoccupied molecular orbitals. In B3LYP the lowest-energy transitions are of π/d→π*, π/d→σ*, and π/d→d characters while in the case of BP86 they are mainly d/π→π* and d→π*. The long range charge transfer transitions involving excitations from adenine π orbitals to antibonding corrin π* orbital can be observed at low energies, especially in BP86 results. Calculated electronic excitations were used to simulate the absorption spectra for a direct comparison with the absorption spectra recorded for AdoCbl at different pH values. As previously found for methylcobalamin [see Andruniów et al., J. Chem. Phys. 129, 085101 (2008)] also for AdoCbl the two-parameter scaling technique is required to obtain a satisfactory agreement between theoretical and experimental spectra. Both functionals correctly predict the shifting of the lowest intense transition toward blue by approximately 13 nm upon changing pH from 7 to 1. [ABSTRACT FROM AUTHOR]

Time-dependent density functional theory (TDDFT) has been applied to the analysis of the electronic spectra of methylcobalamin (MeCbl) and its derivative in which the trans axial base was replaced by a water molecule (MeCbi[Single_Bond]H2O). The latter corresponds to the situation encountered in strongly acidic solutions. The study primarily focuses on the accuracy of two functionals, the hybrid B3LYP and the gradient corrected BP86, in dealing with the electronic excitations. The high resolution crystal structure of MeCbl was the source of the initial coordinates. To generate the initial structures, the full MeCbl was simplified by replacing the corrin side chains by H atoms. The vertical excitation energies, together with the corresponding oscillator strengths, were calculated at the optimized BP86 and B3LYP structures of the ground electronic state of the complexes. The NBO analysis shows that the B3LYP functional gives a bonding description of the ground state as a more polarized covalent bond compared to that given by BP86. The latter functional has more covalent bonding and is thus more appropriate for modeling the axial bonding properties. To validate the accuracy of the present TDDFT analysis, the computed excitations were directly compared to the absorption spectra of MeCbl. In order to obtain a reliable agreement between experiment and theory, the two-parameter scaling technique was introduced, which compensates differently the low-energy and high-energy excitations. Electronic excitations strongly depend on the choice of the functional. Transitions involving corrin π→π* excitations are better described by the B3LYP functional while transitions associated with metal-to-ligand (d/π→π*/d) excitations are better described by BP86. These differences can be associated with the different bonding descriptions obtained by B3LYP and BP86. [ABSTRACT FROM AUTHOR]

The reaction between H(AuCl4) and gly-L-his resulted in the formation of the binary complex, (Au gly-L-his Cl)Cl.3H2O. The complex contained a dipeptide structure attached to an Au(III) molecule which exhibited a strong polarizing activity. This property allowed the formation of the cyclic tetramer (Au gly-L-his3-)4.10H2O at pH six to seven. This identified Au(III) from Cu(II), Ni(II) and Pd(II) which required basic solutions to prepare cyclic tetramers.

Self-assembly of calixarene and porphyrin building blocks is used for obtaining a highly nanoporous material. The supramolecular zeolite-like structure is functionalized by diffusion and coordination of metal ions in order to form a new bifunctionalized nanoporous material containing a porphyrinic pigment together with a metal center.

The single-crystal X-ray diffraction analysis shows the arrangement of the four cavities bound to the C[H.sub.3][N.sup.+] groups of the porphyrin moiety and the four iodide anions nested between the phenethyl substituents of the hosts. HNMR investigations show that the structure is preserved in chloroform solution and underscore the affect of the counteranions.

The reaction of a cis beta folded organacobalt derivative, a racemeric compound of the delta and lambda enantiomers, with L-tyrosine afforded a mixture of two disastereoisomers delta and lambda. The successive isomerization reaction is negligible for L-trysine but goes practically to completion for trans-4 hydroxy-L-proline.

Research has been conducted on beta cis folded organocobalt derivatives with a salen-type ligand. The authors report the modification of equatorial ligand in organocobaloxime-type complexes.

Research has been conducted on 1,4-phenylenebisboronic acid and methylcobaloxime. The authors describe the guest-induced synthesis of the molecular box from these compounds with pyrazine as guest.

A catalytically active metalloenzyme is constructed by engineering an active site cavity into 'due-ferri-1' (DFI) with smaller residues. The experiments show that the dinuclear metal binding site of the diferric form of protein is accessible to azide-and carboxylate-containing molecules.