1.Linkage isomerism and spin frustration in heterometallic rings: synthesis, structural characterization, and magnetic and EPR spectroscopic studies of Cr(7)Ni, Cr(6)Ni(2), and Cr(7)Ni(2) rings templated about imidazolium cations.
Boeer AB1, Collison D, Muryn CA, Timco GA, Tuna F, Winpenny RE. Chemistry. 2009 Dec 7;15(47):13150-60. doi: 10.1002/chem.200901938.
The synthesis and structural characterization of three heterometallic rings templated about imidazolium cations is reported. The compounds are [2,4-DiMe-ImidH][Cr(7)Ni(II)F(8)(O(2)CtBu)(16)] 1 (2,4-DiMe-ImidH=the cation of 2,4-dimethylimidazole), [ImidH](2)[Cr(6)Ni(II) (2)F(8)(O(2)CCtBu)(16)] 2 (ImidH=the cation of imidazole), and [1-Bz-ImidH](2) [Cr(7)Ni(II) (2)F(9)(O(2)CtBu)(18)] 3 (1-Bz-ImidH=the cation of 1-benzylimidazole). The structures show the formation of octagonal arrays of metals for 1 and 2 and a nonagon of metal centers for 3. In all cases the edges of the polygon are bridged by a single fluoride and two pivalate ligands, and the position of the divalent metal centers cannot be distinguished by X-ray diffraction. Magnetic studies combined with EPR spectroscopy allow the characterization of the magnetic states of the compounds. In each case the exchange is antiferromagnetic with a magnetic exchange parameter J approximately -5.
2.Relative reactivity of ribosyl 2'-OH vs. 3'-OH in concentrated aqueous solutions of phosphoimidazolide activated nucleotides.
Kanavarioti A1, Lee LF, Gangopadhyay S. Orig Life Evol Biosph. 1999 Oct;29(5):473-87.
Phosphoimidazolide activated ribomononucleotides (*pN, see structure) are useful substrates for the non-enzymatic synthesis of oligonucleotides. In the presence of metal ions, aqueous solutions of *pN yield primarily the two internucleotide-linked (pN2' pN and pN3' pN) and the pyrophosphate-linked (N5' ppN) dimers. Small amounts of cyclic dimers and higher oligomers are also produced. In this study the relative reactivity of 2'-OH vs. 3'-OH was determined from the ratio of the yields of pN2' pN vs. pN3' pN. Experiments were performed at 23 degrees C in the range 7.2 < or = pH < or = 8.4 with substrates that differ in nucleobase (guanosine (G), cytidine (C), uridine (U), and adenosine (A)) and leaving group (imidazole (Im), 2-methylimidazole (2-MeIm) and 2,4-dimethylimidazole (2,4-diMeIm)). Two metal ions (Mg2+ or Mn2+) were employed as catalysts. The conditions used here, i.e. a substrate concentration in the range 0.1 M to 1.0 M and metal ion concentration in the range 0.
3.Time resolved velocity map imaging of H-atom elimination from photoexcited imidazole and its methyl substituted derivatives.
Hadden DJ1, Wells KL, Roberts GM, Bergendahl LT, Paterson MJ, Stavros VG. Phys Chem Chem Phys. 2011 Jun 7;13(21):10342-9. doi: 10.1039/c1cp20463g. Epub 2011 Apr 21.
The photoresistive properties of DNA bases, amino acids and corresponding subunits have received considerable attention through spectroscopic studies in recent years. One photoresistive property implicates the participation of (1)πσ* states, allowing electronically excited states to evolve either back to the electronic ground state or undergo direct dissociation along a heteroatom-hydride (X-H) coordinate. To this effect, time-resolved velocity map imaging (TR-VMI) studies of imidazole (a subunit of both adenine and histidine) and methylated derivatives thereof have been undertaken, with the goal of understanding the effects of increasing molecular complexity, through methylation, on the dynamics following photoexcitation at 200 nm. The results of these measurements clearly show that H-atom elimination along the N-H coordinate results in a bimodal distribution in the total kinetic energy release (TKER) spectra in both imidazole and it's methylated derivatives: 2-methyl, 4-methyl and 2,4-dimethylimidazole.
4.Uroporphyrinogen oxidation catalyzed by reconstituted cytochrome P450IA2.
Lambrecht RW1, Sinclair PR, Gorman N, Sinclair JF. Arch Biochem Biophys. 1992 May 1;294(2):504-10.
Previous work suggested that the oxidation of uroporphyrinogen to uroporphyrin is catalyzed by cytochrome P450IA2. Here we determined whether purified reconstituted mouse P450IA1 and IA2 oxidize uroporphyrinogen. Cytochromes P450IA1 and IA2 were purified from hepatic microsomes from 3-methylcholanthrene (MC)-treated C57BL/6 mice, using a combination of affinity chromatography and high performance liquid chromatography. Reconstituted P450IA1 was more active than P450IA2 in catalyzing ethoxyresorufin-O-deethylase (EROD) activity, whereas P450IA2 was more active than P450IA1 in catalyzing uroporphyrinogen oxidation (UROX). Both reactions required NADPH, NADPH-cytochrome P450 reductase, and either P450IA1 or IA2. Ketoconazole competitively inhibited both EROD and UROX activities, in microsomes from MC-treated mice. Ketoconazole also inhibited UROX catalyzed by reconstituted P450IA2. In contrast, ketoconazole did not inhibit UROX catalyzed by xanthine oxidase in the presence of iron-EDTA.