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Michel Dupuis

Publications and source records attributed to Michel Dupuis.

15 recordsLinked to original sources
PubMed2006

Electronic coupling between heme electron-transfer centers and its decay with distance depends strongly on relative orientation.

A method for calculating the electron-transfer matrix element V(RP) using density functional theory Kohn-Sham orbitals is presented and applied to heme dimers of varying relative orientation. The electronic coupling decays with increased iron separation according to V(RP) = V(0)(RP)exp(-beta r/2) with a distance dependence parameter beta approximately 2 A(-1) for hemes with parallel porphyrins and either 1.1 or 4.0 A(-1) when the porphyrin planes are perpendicular, depending on the alignment of the iron d(pi) orbital. These findings are used to interpret the observed orientation of the hemes in tetraheme redox proteins such as Flavocytochrome c(3) fumarate reductase (Ifc(3), PDB code 1QJD) of Shewanella frigidimarina, another flavocytochrome from the same bacterium (Fcc(3), 1E39) and a small tetraheme cytochrome of Shewanella oneidensis strain MR1 (1M1P). Our results show that shifting and rotating the hemes controls the adiabaticity of the three electron hopping steps.

Computer Simulation↗
PubMed2006

The OH radical-H2O molecular interaction potential.

The OH radical is one of the most important oxidants in the atmosphere due to its high reactivity. The study of hydrogen-bonded complexes of OH with the water molecules is a topic of significant current interest. In this work, we present the development of a new analytical functional form for the interaction potential between the rigid OH radical and H(2)O molecules. To do this we fit a selected functional form to a set of high level ab initio data. Since there is a low-lying excited state for the H(2)O.OH complex, the impact of the excited state on the chemical behavior of the OH radical can be very important. We perform a potential energy surface scan using the CCSD(T)/aug-cc-pVTZ level of electronic structure theory for both excited and ground states. To model the physics of the unpaired electron in the OH radical, we develop a tensor polarizability generalization of the Thole-type all-atom polarizable rigid potential for the OH radical, which effectively describes the interaction of OH with H(2)O for both ground and excited states. The stationary points of (H(2)O)(n)OH clusters were identified as a benchmark of the potential.

Journal Article↗
PubMed2006

Evaluation of MRSA Select, a new chromogenic medium for the detection of nasal carriage of methicillin-resistant Staphylococcus aureus.

MRSA Select is a new chromogenic medium for the detection from clinical specimens of methicillin-resistant Staphylococcus aureus (MRSA) growing as pink colonies. Screening samples (n=666) taken from patients were spread onto MRSA Select, oxacillin resistance screening agar base (ORSAB), mannitol salt agar and an in-house medium containing tobramycin-colistin-fungizone (TCF). Ninety-nine samples were positive for MRSA on at least one selective medium. Sensitivity and specificity were >94% for all media provided that incubation was extended to 48 h for ORSAB and that a coagulase test was performed for ORSAB and TCF. By contrast, on the single criterion of the colour of colonies for MRSA positivity, the specificity and sensitivity of MRSA Select were high (99.8% and 99%, respectively).

Amphotericin B↗
PubMed2006

Activity of a new oral streptogramin, XRP2868, against gram-positive cocci harboring various mechanisms of resistance to streptogramins.

The antibacterial activity of XRP2868, a new oral streptogramin composed of a combination of RPR132552 (streptogramin A) and RPR202868 (streptogramin B), was evaluated against a collection of clinical gram-positive isolates with characterized phenotypes and genotypes of streptogramin resistance. The effects of genes for resistance to streptogramin A or B on the activity of XRP2868 and its components were also tested by cloning these genes individually or in various combinations in gram-positive recipient strains susceptible to quinupristin-dalfopristin. The species tested included Staphylococcus aureus, coagulase-negative staphylococci, Enterococcus faecalis, Enterococcus faecium, Streptococcus pneumoniae, and other species of streptococci. XRP2868 was generally fourfold more potent than quinupristin-dalfopristin against S. aureus, E. faecium, and streptococci and had activity against E. faecalis (MICs = 0.25 to 1 microg/ml). XRP2868 appeared to be affected by the same mechanisms of resistance as those to quinupristin-dalfopristin. Nevertheless, the strong activity of factor A of the oral streptogramin enabled the combination to be very potent against streptogramin-susceptible staphylococci, streptococci, and E. faecium (MICs = 0.03 to 0.25 microg/ml) and to retain low MICs against the strains harboring a mechanism of resistance to factor A or factor B of the streptogramin. However, the combination of mechanisms of resistance to factors A and B caused an increase in the MICs of XRP2868, which reached 1 to 4 mug/ml. As with the other streptogramins, there was a reduction in the bactericidal effect of XRPR2868 when the staphylococcal strains acquired a constitutively expressed erm gene.

Administration, Oral↗
PubMed2005

Ab initio electronic structure study of one-electron reduction of polychlorinated ethylenes.

Polychlorethylene radicals, anions, and radical anions are potential intermediates in the reduction of polychlorinated ethylenes (C(2)Cl(4), C(2)HCl(3), trans-C(2)H(2)Cl(2), cis-C(2)H(2)Cl(2), 1,1-C(2)H(2)Cl(2), C(2)H(3)Cl). Ab initio electronic structure methods were used to calculate the thermochemical properties, (298.15 K), S degrees (298.15 K,1 bar), and DeltaG(S)(298.15 K, 1 bar) of 37 different polychloroethylenyl radicals, anions, and radical anion complexes, C(2)H(y)Cl(3)(-)(y)(*), C(2)H(y)Cl(3)(-)(y)(-), and C(2)H(y))Cl(4)(-)(y)(*)(-) for y = 0-3, for the purpose of characterizing reduction mechanisms of polychlorinated ethylenes. In this study, 8 radicals, 7 anions, and 22 radical anions were found to have stable structures, i.e., minima on the potential energy surfaces. This multitude of isomers for C(2)H(y)Cl(4)(-)(y)(*)(-) radical anion complexes are pi*, sigma*, and -H...Cl(-) structures. Several stable pi* radical anionic structures were obtained for the first time through the use of restricted open-shell theories. On the basis of the calculated thermochemical estimates, the overall reaction energetics (in the gas phase and aqueous phase) for several mechanisms of the first electron reduction of the polychlorinated ethylenes were determined. In almost all of the gas-phase reactions, the thermodynamically most favorable pathways involve -H...Cl(-) complexes of the C(2)H(y)Cl(4)(-)(y)(*)(-) radical anion, in which a chloride ion is loosely bound to a hydrogen of a C(2)H(x)Cl(2)(-)(x))(*) radical. The exception is for C(2)Cl(4), in which the most favorable anionic structure is a loose sigma* radical anion complex, with a nearly iso-energetic pi* radical anion. Solvation significantly changes the product energetics with the thermodynamically most favorable pathway leading to C(2)H(y)Cl(3)(-)(y)(*) + Cl(-). The results suggest that a higher degree of chlorination favors reduction, and that reduction pathways involving the C(2)H(y)Cl(3)(-)(y)(-) anions are high energy pathways.

Journal Article↗
PubMed2005

Should plain X-rays be routinely performed after blunt knee trauma? A prospective analysis.

BACKGROUND: We tested the hypothesis that it was possible to decrease the number of performed x-rays after a knee trauma without delayed fracture diagnosis by using the Ottawa knee rules. METHODS: Patients had routine x-rays of the injured knee during the first stage of the study and selective x-rays during the second stage. All patients were followed up to 6 months after the trauma. RESULTS: 138 patients were included in the first stage; 57 had negative Ottawa criteria: no fracture was observed; following the Ottawa rules, 41% of the x-rays could have been avoided. 178 patients were included in the second stage; 63 patients had negative Ottawa criteria: no fracture was diagnosed during the whole follow-up; 35% of the x-rays have been avoided. CONCLUSIONS: Ottawa rules allowed decreasing the number of x-rays performed after a knee trauma by 35% with a sensitivity for a knee fracture detection of 100%.

Aged↗
PubMed2004

[Choice of a strategy for screening for methicillin-resistant Staphylococcus aureus on admission to rehabilitation units].

OBJECTIVE: To identify a strategy of MRSA screening (methicillin-resistant Staphylococcus aureus) on admission to geriatric rehabilitation units, which would lead to acceptable efficacy and cost compared with a reference maximaliste strategy combining all six sampling sites. Method MRSA screening was conducted prospectively for 3 months in all the patients admitted to a geriatric follow-up and rehabilitation unit, using samples from the nostrils, armpits, urine scars cutaneous ulcers and sores. Six strategies were defined combing different sampling sites. Their efficacy and cost were compared with those of a maximaliste strategy combining the 6 sampling sites. RESULTS: Combined screening of all six sites was the most effective but also the most expensive strategy. The least expensive strategy used only samples from ulcers and sores, but its efficacy was of only 45%. The strategy with the lowest loss of efficacy compared to the reference strategy combined the sampling of ulcers and sores and sampling from the nostrils: it was efficient in 91% and its cost was 2.5 fold lower than the cost of the reference strategy. DISCUSSION: A preliminary, short term study established an MRSA screening strategy adapted to the specificities of a geriatric rehabilitation unit and its recruitment. The ability to define the optimal strategy for MRSA screening in a geriatric rehabilitation and follow-up unit may be an important factor in controlling the diffusion of MRSA.

Aged↗
PubMed2004

Activation of the sulfhydryl group by Mo centers: kinetics of reaction of benzyl radical with a binuclear Mo(micro-SH)Mo complex and with arene and alkane thiols.

This paper provides evidence from kinetic experiments and electronic structure calculations of a significantly reduced S-H bond strength in the Mo(micro-SH)Mo function in the homogeneous catalyst model, CpMo(micro-S)(2)(micro-SH)(2)MoCp (1, Cp = eta(5)-cyclopentadienyl). The reactivity of 1 was explored by determination of a rate expression for hydrogen atom abstraction by benzyl radical from 1 (log(k(abs)/M(-)(1) s(-)(1)) = (9.07 +/- 0.38) - (3.62 +/- 0.58)/theta) for comparison with expressions for CH(3)(CH(2))(7)SH, log(k(abs)/M(-)(1) s(-)(1)) = (7.88 +/- 0.35) - (4.64 +/- 0.54)/theta, and for 2-mercaptonaphthalene, log(k(abs)/M(-)(1) s(-)(1)) = (8.21 +/- 0.17) - (4.24 +/- 0.26)/theta (theta = 2.303RT kcal/mol, 2sigma error). The rate constant for hydrogen atom abstraction at 298 K by benzyl radical from 1 is 2 orders of magnitude greater than that from 1-octanethiol, resulting from the predicted (DFT) S-H bond strength of 1 of 73 kcal/mol. The radical CpMo(micro-S)(3)(micro-SH)MoCp, 2, is revealed, from the properties of slow self-reaction, and exclusive cross-combination with reactive benzyl radical, to be a persistent free radical.

Journal Article↗
PubMed2004

Reorganization energy associated with small polaron mobility in iron oxide.

The reorganization energy is an important quantity controlling electron transfer rates. The internal contribution arising from the energy to reorganize donor/acceptor bonds can be evaluated by the "direct" and "4-point" methods. We examine how spatial separation leading to the noninteracting character of the donor and acceptor affects the reorganization energy. We show that the direct method captures contributions from interaction of the donor and acceptor while the 4-point method does not, and the two methods converge at large separation. Comparing reorganization energies determined by the two methods yields a measure of the degree of interaction between the initial and final states. The analysis is illustrated in the characterization of small polarons in iron oxides.

Journal Article↗
PubMed2004

Thermochemistry of aqueous hydroxyl radical from advances in photoacoustic calorimetry and ab initio continuum solvation theory.

Photoacoustic signals from dilute ( approximately 30 mM) solutions of H2O2 were measured over the temperature range from 10 to 45 degrees C to obtain the reaction enthalpy and volume change for H2O2(aq) --> 2 OH(aq) from which we ultimately determined DeltafG degrees , DeltafH degrees and partial molal volume, v degrees , of OH (aq). We find DeltarH = 46.8 +/- 1.4 kcal/mol, which is 4 kcal/mol smaller than the gas-phase bond energy, and DeltaVr = 6.5 +/- 0.4 mL/mol. The v degrees for OH in water is 14.4 +/- 0.4 mL/ml: smaller than the v degrees of water. Using ab intio continuum theory, the hydration free energy is calculated to be -3.9 +/- 0.3 kcal/mol (for standard states in number density concentration units) by a novel approach devised to capture in the definition of the solute cavity the strength and specific interactions of the solute with a water solvent molecule. The shape of the cavity is defined by "rolling" a three-dimensional electron density isocontour of water on the ab initio water-OH minimum interaction surface. The value of the contour is selected to reproduce the volume of OH in water. We obtain for OH(aq): DeltafH degrees = -0.2 +/- 1.4 and DeltafG degrees = 5.8 +/- 0.4 kcal/mol that are in agreement with literature values. The results provide confidence in the pulsed PAC technique for measuring aqueous thermochemistry of radicals and open the way to obtaining thermochemistry for most radicals that can be formed by reaction of OH with aqueous substrates while advancing the field of continuum solvation theory toward ab initio-defined solute cavities.

Journal Article↗
PubMed2004

Clinical trials in an emergency setting: implications from the fifth version of the Declaration of Helsinki.

Everybody agrees that research is crucial to improve the quality of emergency care. Consent of human subjects for participation in research requires that they fully understand their role and risk, not be coerced, and be allowed to withdraw at any time without penalty. In an emergency situation, informed consent is not always possible but the need for good research data is very high. Here is the ethical difficulty, and a real conflict of values: a population that might ultimately benefit from research cannot consent to the research and are thus excluded from the potential therapeutical advances. Patients at high risk of morbidity or death, with cardiac arrest, shock, head injury, or altered mental status, are evidently incapable of providing an adequate consent, but nevertheless are often in the greatest need of innovative therapy and might be willing to assume some risk for potential benefit. In an attempt to resolve this dilemma, the new version of the Declaration of Helsinki presents updated requirements for the waiver of informed consent and the protection of human subjects in emergency research.

Clinical Trials as Topic↗
PubMed2003

Dynamics-driven reaction pathway in an intramolecular rearrangement.

A critical role is traditionally assigned to transition states (TSs) and minimum energy pathways, or intrinsic reaction coordinates (IRCs), in interpreting organic reactivity. Such an interpretation, however, ignores vibrational and kinetic energy effects of finite temperature. Recently it has been shown that reactions do not necessarily follow the intermediates along the IRC. We report here molecular dynamics (MD) simulations that show that dynamics effects may alter chemical reactions even more. In the heterolysis rearrangement of protonated pinacolyl alcohol Me3C-CHMe-OH2+ (Me, methyl), the MD pathway involves a stepwise route with C-O bond cleavage followed by methyl group migration, whereas the IRC pathway suggests a concerted mechanism. Dynamics effects may lead to new interpretations of organic reactivity.

Journal Article↗
PubMed2003

Characterization of electronic structure and properties of a Bis(histidine) heme model complex.

Ferric and ferrous hemes, such as those present in electron transfer proteins, often have low-lying spin states that are very close in energy. To explore the relationship between spin state, geometry, and cytochrome electron transfer, we investigate, using density functional theory, the relative energies, electronic structure, and optimized geometries for a high- and low-spin ferric and ferrous heme model complex. Our model consists of an iron-porphyrin axially ligated by two imidazoles, which model the interaction of a heme with histidine residues. Using the B3LYP hybrid functional, we found that, in the ferric model heme complex, the doublet is lower in energy than the sextet by 8.4 kcal/mol and the singlet ferrous heme is 6.7 kcal/mol more stable than the quintet. The difference between the high-spin ferric and ferrous model heme energies yields an adiabatic electron affinity (AEA) of 5.24 eV, and the low-spin AEA is 5.17 eV. Both values are large enough to ensure electron trapping, and electronic structure analysis indicates that the iron d(pi) orbital is involved in the electron transfer between hemes. Mössbauer parameters calculated to verify the B3LYP electronic structure correlate very well with experimental values. Isotropic hyperfine coupling constants for the ligand nitrogen atoms were also evaluated. The optimized geometries of the ferric and ferrous hemes are consistent with structures from X-ray crystallography and reveal that the iron-imidazole distances are significantly longer in the high-spin hemes, which suggests that the protein environment, modeled here by the imidazoles, plays an important role in regulating the spin state. Iron-imidazole dissociation energies, force constants, and harmonic frequencies were calculated for the ferric and ferrous low-spin and high-spin hemes. In both the ferric and the ferrous cases, a single imidazole ligand is more easily dissociated from the high-spin hemes.

Hemeproteins↗
PubMed1997

Percutaneous Laser Photocoagulation of Osteoid Osteomas.

Osteoid osteoma is a painful benign bone tumor. The curative treatment of this tumor consists of complete surgical or percutaneous excision of the nidus with immediate and dramatic relief of symptoms. Interstitial laser photocoagulation (ILP) is a low-invasive percutaneous technique of thermal destruction (coagulation) of deep-seated tumors elsewhere in the body, using low-power laser energy. The aim of ILP is the local destruction of osteoid osteoma without bone weakening. Twenty-two patients with osteoid osteoma were treated with percutaneous ILP of the nidus under computed tomography guidance. The laser energy was provided by a high-power semiconductor diode laser (805 nm) with a 400-&mgr;m optical fiber. Complete pain relief was obtained in 21 patients. Percutaneous ILP of osteoid osteoma seems to be a promising, simple, precise, and minimally invasive technique as an alternative to traditional surgical and percutaneous ablations.

Journal Article↗