The behavior of ferric protoporphyrin-IX in alkaline DMF

Induced-orientation of nitrogen monoxide and azide ion vibrations in human hemoglobin in bidistilled water solution under a static magnetic field

In this study, we report the effects of static magnetic fields (SMFs) at 200 mT on different hemoglobin aqueous solutions, in the absence and in the presence of sucrose and trehalose, studied by FTIR spectroscopic techniques. Significant decrease in intensity of Amide I and Amide II vibration bands was observed after 6 h exposure for hemoglobin in bidistilled water solution. Also, it was observed that the decrease in intensity of the Amide I band was larger than the Amide II after exposure. This result can be explained assuming that an SMF induces increase of hydrogen bonding in hemoglobin in bidistilled water solution. In particular, the use of second-derivative analysis highlighted two absorption peaks at 1907 and 2022 cm^-1 that can be attributed to nitrogen monoxide vibration and antisymmetric stretch of azide ion bound, respectively. These vibrations increased significantly after exposure to the SMF (P < 0.01). This result can be explained assuming that exposure to an SMF induces the orientation of nitrogen monoxide and azide ion ligands toward the direction of the field. Finally, it was observed that the addition of sucrose and trehalose in hemoglobin aqueous solution inhibited such alterations, suggesting that bioprotective effectiveness of these disaccharides occurs after exposure to an SMF. Bioelectromagnetics. 38:447-455, 2017. © 2017 Wiley Periodicals, Inc.

Quantum interference measurement of spin interactions in a bio-organic/semiconductor device structure

Quantum interference is used to measure the spin interactions between an InAs surface electron system and the iron center in the biomolecule hemin in nanometer proximity in a bio-organic/semiconductor device structure. The interference quantifies the influence of hemin on the spin decoherence properties of the surface electrons. The decoherence times of the electrons serve to characterize the biomolecule, in an electronic complement to the use of spin decoherence times in magnetic resonance. Hemin, prototypical for the heme group in hemoglobin, is used to demonstrate the method, as a representative biomolecule where the spin state of a metal ion affects biological functions. The electronic determination of spin decoherence properties relies on the quantum correction of antilocalization, a result of quantum interference in the electron system. Spin-flip scattering is found to increase with temperature due to hemin, signifying a spin exchange between the iron center and the electrons, thus implying interactions between a biomolecule and a solid-state system in the hemin/InAs hybrid structure. The results also indicate the feasibility of artificial bioinspired materials using tunable carrier systems to mediate interactions between biological entities.

Thermodynamic Profiles for CO Photodissociation from Heme Model Compounds: Effect of Proximal Ligands

Here we present a comprehensive study of the thermodynamic parameters (enthalpy, entropy, and volume changes) associated with carbon monoxide photodissociation and rebinding to Fe(II) microperoxidase-11 (Fe(II)MP11) and Fe(ll) tetrakis(4-sulfonatophenyl)porphine complex (FeII4SP) with water and 2-methylimidazole as proximal ligands. CO photodissociation from FeII4SP complexes is accompanied by a positive volume change of approximately 17 mL mol(-1). A smaller volume change of approximately 12 mL mol(-1) was observed for CO dissociation from Fe(II)MP-11. We attribute the positive volume change to cleavage of the Fe-CO covalent bond and to solvent reorganization due to the low-spin to high-spin transition. CO binding is an exothermic reaction with an enthalpy change of -17 kcal mol(-1) for the CO-FeII4SP complexes and -13 kcal mol(-1) for the CO-Fe(II)MP11 complex. In all cases, the ligand recombination occurs as a single-exponential process indicating that CO dissociation is followed by direct CO rebinding to a high-spin five-coordinate complex without concomitant dissociation of the proximal base. In addition, observed negative activation entropies and volumes for ligand binding to (2-Melm)FeII4SP and MP-11, respectively, suggest that CO rebinding can be described by an associative mechanism with bond formation being the rate-limiting step.

Volume and enthalpy profiles of CO binding to Fe(II) tetrakis-(4-sulfonatophenyl)porphyrin

The focus of this study is to examine volume and enthalpy profiles of ligand binding associated with CO-Fe(II) tetrakis-(4-sulfonato phenyl)-porphyrin (COFe(II)4SP) in aqueous solution. Temperature dependent photothermal beam deflection was employed to probe the overall enthalpy and volume changes associated with CO-photolysis and recombination. The analysis demonstrates that ligand recombination occurs with a pseudo first order rate constant of (2.5+/-0.2)x10(4) s(-1) (at 25 degrees C) with a corresponding volume decrease of 6+/-1 ml/mol. The activation enthalpy (DeltaH(double dagger)) and volume (DeltaV(double dagger)) change for CO recombination (determined from temperature/pressure dependent transient absorption spectroscopy) are found to be 3.9 kcal/mol and 8.2 ml/mol, respectively. These data are consistent with a mechanism in which photolysis yields a five-coordinate high spin (H(2)O)Fe(II)4SP complex that recombines in a single step to form the low spin (CO)(H(2)O)Fe(II)4SP complex. Base elimination, often associated with CO photolysis from hemes, is not observed in this system. The overall volume changes suggest a transition state with significant high spin character. Furthermore, these results demonstrate the utility of coupling photothermal techniques with variable pressure/temperature transient absorption spectroscopy to probe heme reaction dynamics.