Analysis of the globins from fast human haemoglobins by isoelectrofocusing on polyacrylamide gel rods

The globins from all fast haemoglobin (Hb) components obtainable by Bio-Rex 70 cation-exchange chromatography were examined by isoelectrofocusing on polyacrylamide gel rods with 8.0 mol/l urea. From this analysis HbA1a1 and HbA1a2 seem to be very heterogeneous components. HbA1b is separable into two components, one of which is varied in both the beta chains. Between HbA1b2 and the well-known HbA1c components two chromatographic peaks are separated, one with a noticeable percentage of glucosylated beta chain and one that probably contains HbF. HbA1c has both beta chains glucosylated, while HbA1x seems to be a beta monoglucosylated Hb form. Finally, the early part of the HbAo peak has a large amount of glucosylation on both alpha and beta chains.     

Electron transfer-initiated Diels-Alder cycloadditions of 2'-hydroxychalcones

An efficient approach to cyclohexenyl chalcones employing highly electron rich 2'-hydroxychalcone dienophiles via electron transfer-initiated Diels-Alder cycloaddition is described. Using the methodology, the total synthesis of nicolaiodesin C has been accomplished.     

Studies of iron(II) and iron(III) complexes with fac-N2O, cis-N2O2 and N2O3 donor ligands: models for the 2-His 1-carboxylate motif of non-heme iron monooxygenases

Enzymes in the oxygen-activating class of mononuclear non-heme iron oxygenases (MNOs) contain a highly conserved iron center facially ligated by two histidine nitrogen atoms and one carboxylate oxygen atom that leave one face of the metal center (three binding sites) open for coordination to cofactor, substrate, and/or dioxygen. A comparative family of [Fe(II/III)(N(2)O(n))(L)(4-n))](±x), n = 1-3, L = solvent or Cl(-), model complexes, based on a ligand series that supports a facially ligated N,N,O core that is then modified to contain either one or two additional carboxylate chelate arms, has been structurally and spectroscopically characterized. EPR studies demonstrate that the high-spin d(5) Fe(III)g = 4.3 signal becomes more symmetrical as the number of carboxylate ligands decreases across the series Fe(N(2)O(3)), Fe(N(2)O(2)), and Fe(N(2)O(1)), reflecting an increase in the E/D strain of these complexes as the number of exchangeable/solvent coordination sites increases, paralleling the enhanced distribution of electronic structures that contribute to the spectral line shape. The observed systematic variations in the Fe(II)-Fe(III) oxidation-reduction potentials illustrate the fundamental influence of differential carboxylate ligation. The trend towards lower reduction potential for the iron center across the [Fe(III)(N(2)O(1))Cl(3)](-), [Fe(III)(N(2)O(2))Cl(2)](-) and [Fe(III)(N(2)O(3))Cl](-) series is consistent with replacement of the chloride anions with the more strongly donating anionic O-donor carboxylate ligands that are expected to stabilize the oxidized ferric state. This electrochemical trend parallels the observed dioxygen sensitivity of the three ferrous complexes (Fe(II)(N(2)O(1)) < Fe(II)(N(2)O(2)) < Fe(II)(N(2)O(3))), which form μ-oxo bridged ferric species upon exposure to air or oxygen atom donor (OAD) molecules. The observed oxygen sensitivity is particularly interesting and discussed in the context of α-ketoglutarate-dependent MNO enzyme mechanisms.     

The effect of varying carboxylate ligation on the electronic environment of N2O(x) (x = 1-3) nonheme iron: a DFT analysis

Mononuclear nonheme iron oxygenase (MNO) enzymes contain a subclass of metalloproteins capable of catalyzing the O(2)-dependent hydroxylation of unactivated substrates at a ferrous ion center coordinated to a highly conserved His-His-Glu/Asp motif. These enzymes, which utilize additional reducing equivalents obtained from the decarboxylation of a coordinated α-ketoglutarate (αKG) cofactor, do not readily interact with O(2) in the absence of αKG binding. Density functional theory calculations with the B3LYP functional were performed to gain insight into the electrochemical behavior of three sets of Fe(II/III) complexes containing a core N, N, O facial binding motif in which the number of carboxylate ligands was systematically altered, to provide one, two (cis) or three (fac) labile sites. The calculated trend in Fe(II/III) reduction potentials was observed to parallel that observed in cyclic voltammetry experiments, showing a decrease in potential (stabilized oxidized state) with increasing carboxylate ligation. This trend does not appear to be the result of differential charge on the metal complex. Changes in the redox-active molecular orbital (RAMO) energy due to covalent effects dominate across the series of complexes when chloride is modeled as the labile ligand, with the π anti-bonding nature of the RAMO being an important factor. With water molecules as the labile ligands, however, a much steeper redox dependence on the number of carboxylate ligands is observed and this effect seems to be largely electrostatic in origin. Differential relaxation of the occupied molecular orbitals in the ferric complexes appears to contribute to the redox trend as well. Finally, these observations are placed in the context of MNO enzyme mechanisms.