Nanodosimetry of Auger electrons: A case study from the decay of 125I and 0-18-eV electron stopping cross sections of cytosine.

Radiopharmaceuticals emitting Auger electrons are often injected into patients undergoing cancer treatment with targeted radionuclide therapy (TRT). In this type of radiotherapy, the radiation source is radial and most of the emitted primary particles are low-energy electrons (LEEs) having kinetic energies distributed mostly from zero to a few hundred electron volts with very short ranges in biological media. These LEEs generate a high density of energy deposits and clustered damage, thus offering a relative biological effectiveness comparable to that of alpha particles. In this paper, we present a simple model and corresponding measurements to assess the energy deposited near the site of the radiopharmaceuticals in TRT. As an example, a calculation is performed for the decay of a single 125I radionuclide surrounded by a 1-nm-radius spherical shell of cytosine molecules using the energy spectrum of LEEs emitted by 125I along with their stopping cross sections between 0 and 18 eV. The dose absorbed by the cytosine shell, which occupies a volume of 4 nm3, is extremely high. It amounts to 79 kGy per decay of which 3%, 39%, and 58% is attributed to vibrational excitations, electronic excitations, and ionization processes, respectively.

Absolute cross sections for vibrational excitations of cytosine by low energy electron impact.

The absolute cross sections (CSs) for vibrational excitations of cytosine by electron impact between 0.5 and 18 eV were measured by electron-energy loss (EEL) spectroscopy of the molecule deposited at monolayer coverage on an inert Ar substrate. The vibrational energies compare to those that have been reported from IR spectroscopy of cytosine isolated in Ar matrix, IR and Raman spectra of polycrystalline cytosine, and ab initio calculation. The CSs for the various H bending modes at 142 and 160 meV are both rising from their energy threshold up to 1.7 and 2.1 × 10(-17) cm(2) at about 4 eV, respectively, and then decrease moderately while maintaining some intensity at 18 eV. The latter trend is displayed as well for the CS assigned to the NH(2) scissor along with bending of all H at 179 meV. This overall behavior in electron-molecule collision is attributed to direct processes such as the dipole, quadrupole, and polarization contributions, etc. of the interaction of the incident electron with a molecule. The CSs for the ring deformation at 61 meV, the ring deformation with N-H symmetric wag at 77 meV, and the ring deformations with symmetric bending of all H at 119 meV exhibit common enhancement maxima at 1.5, 3.5, and 5.5 eV followed by a broad hump at about 12 eV, which are superimposed on the contribution due to the direct processes. At 3.5 eV, the CS values for the 61-, 77-, and 119-meV modes reach 4.0, 3.0, and 4.5 × 10(-17) cm(2), respectively. The CS for the C-C and C-O stretches at 202 meV, which dominates in the intermediate EEL region, rises sharply until 1.5 eV, reaches its maximum of 5.7 × 10(-17) cm(2) at 3.5 eV and then decreases toward 18 eV. The present vibrational enhancements, correspond to the features found around 1.5 and 4.5 eV in electron transmission spectroscopy (ETS) and those lying within 1.5-2.1 eV, 5.2-6.8 eV, and 9.5-10.9 eV range in dissociative electron attachment (DEA) experiments with cytosine in gas phase. While the ETS features are ascribed to shape resonances associated with the electron occupation of the second and third antibonding π-orbitals of the molecule in its ground state, the correspondence with DEA features suggests the existence of common precursor anion states decaying with certain probabilities into the vibrationally excited ground state.

Addition of clonidine to a continuous patient-controlled epidural infusion of low-concentration levobupivacaine plus sufentanil in primiparous women during labour.

We studied the potentiation of analgesia for labour by the addition of clonidine to epidural low-concentration levobupivacaine with sufentanil in a randomised, double-blinded study. We enrolled primiparous women who were in spontaneous labour. The study solutions, made of 100 ml levobupivacaine 0.0625% plus sufentanil 0.45 µg.ml(-1) and either 150 µg clonidine or no clonidine, were used for induction of analgesia, and for its maintenance with self-administered boluses and a continuous background infusion. The need for additional epidural boluses during labour was lower and analgesia and maternal satisfaction were better in the clonidine (n = 57) than in the control group (n = 58). Blood pressure was lower and the rate of instrumental delivery higher in the clonidine group. Clonidine (1.36 µg.ml(-1)) added to the epidural solution of low-concentration levobupivacaine improves the quality of analgesia. The relevance of the haemodynamic effects should be explored in larger validation studies.

[Post-partum haemorrhage in delivery room: anaesthetists' practioner in Auvergne]. / Hémorragie du post-partum en salle de naissance : pratique déclarée des anesthésistes en région Auvergne.

OBJECTIVE: To assess the management of post-partum haemorrhage (PPH) in delivery rooms by the anaesthetists of the Auvergne region. STUDY DESIGN: Cross sectional study. METHODS: An anonymous postal survey was sent to all the anaesthetists working in a public or private hospital with a maternity unit. RESULTS: The response rate was about 70 %. Eight percent of the respondents never practiced in obstetrics; others all declared to have managed PPH at least once. Only 66 % declared to know the right definition of PPH, 98 % declared to have guidelines in the delivery room, 87 % to use graduate blood receipt pockets, 85 % to work under midwives-directed delivery at expulsion, 88 % to have a HemoCue™ system. More than 80 % declared to use first oxytocin and to switch for prostaglandins in case of failure, to put two venous catheters and a urinary catheter, to administer broad-spectrum prophylactic antibiotic and to draw a blood sample for early biology. Packed red cells, platelets and fresh frozen plasma were accessible in less than 30 minutes for 98 %. Transfusion guidelines were applied. Only 27 % could have arterial radiologic embolisation on site. The knowledge about PPH and its consensual care tended to be poorer in practitioners from the university hospital, and younger under 40 also. CONCLUSION: This survey, with a good response rate, showed a practice generally fitting to the guidelines, although with some failures depending on the practioner's age and type of hospital.

Absolute cross sections for electronic excitations of cytosine by low energy electron impact.

The absolute cross sections (CSs) for electronic excitations of cytosine by electron impact between 5 and 18 eV were measured by electron-energy-loss (EEL) spectroscopy of the molecule deposited at low coverage on an inert Ar substrate. The lowest EEL features found at 3.55 and 4.02 eV are ascribed to transitions from the ground state to the two lowest triplet 1 (3)A(')(π→π(∗)) and 2 (3)A(')(π→π(∗)) valence states of the molecule. Their energy dependent CSs exhibit essentially a common maximum at about 6 eV with a value of 1.84×10(-17) cm(2) for the former and 4.94×10(-17) cm(2) for the latter. In contrast, the CS for the next EEL feature at 4.65 eV, which is ascribed to the optically allowed transition to the 2 (1)A(')(π→π(∗)) valence state, shows only a steep rise to about 1.04×10(-16) cm(2) followed by a monotonous decrease with the incident electron energy. The higher EEL features at 5.39, 6.18, 6.83, and 7.55 eV are assigned to the excitations of the 3 (3,1)A(')(π→π(∗)), 4 (1)A(')(π→π(∗)), 5 (1)A(')(π→π(∗)), and 6 (1)A(')(π→π(∗)) valence states, respectively. The CSs for the 3 (3,1)A(') and 4 (1)A(') states exhibit a common enhancement at about 10 eV superimposed on a more or less a steep rise, reaching, respectively, a maximum of 1.27 and 1.79×10(-16) cm(2), followed by a monotonous decrease. This latter enhancement and the maximum seen at about 6 eV in the lowest triplet states correspond to the core-excited electron resonances that have been found by dissociative electron attachment experiments with cytosine in the gas phase. The weak EEL feature found at 5.01 eV with a maximum CS of 3.8×10(-18) cm(2) near its excitation threshold is attributed to transitions from the ground state to the 1 (3,1)A(")(n→π(∗)) states. The monotonous rise of the EEL signal above 8 eV is attributed to the ionization of the molecule. It is partitioned into four excitation energy regions at about 8.55, 9.21, 9.83, and 11.53 eV, which correspond closely to the ionization energies of the four highest occupied molecular orbitals of cytosine. The sum of the ionization CS for these four excitation regions reaches a maximum of 8.1×10(-16) cm(2) at the incident energy of 13 eV.

Antimicrobial resistance of Listeria monocytogenes strains isolated from humans in France.

Susceptibility to antibiotics of 4,816 clinical L. monocytogenes strains isolated since 1926 was studied, and the temporal evolution of susceptibility to antibiotics was analyzed through several decades. The mechanisms of resistance in each resistant strain were studied. The prevalence of resistant strains was estimated at 1.27% among isolates from humans. Resistance to tetracyclines+ and fluoroquinolones was more common and has recently emerged. Although acquired resistance in clinical L. monocytogenes did not implicate clinically relevant antibiotics, the possibility of resistance gene transfers, the description of the first clinical isolate with high-level resistance to trimethoprim, and the recent increase in penicillin MICs up to 2 microg/ml reinforce the need for microbiological surveillance.

Electron induced dissociation in the condensed-phase nitromethane: II. Desorption of neutral fragments.

Low energy electron induced dissociation in multilayer films of nitromethane (CD3NO2) was investigated by high resolution electron energy loss spectroscopy (HREELS) and by the electron stimulated desorption (ESD) of neutral species. HREELS measurements show that the lowest electronic states of the condensed molecule are very similar to those seen in the gas phase. Desorbed neutrals were detected using combined non-resonant multi-photon ionization at 355 nm and time of flight mass spectrometry. The most intense signals detected were those of CD3 (+) and NO (+) and are attributed primarily to the desorption of CD3 and NO2 fragments following molecular dissociation via low-lying electronic excited states of nitromethane (the detected NO (+) being the result of the dissociative ionization of NO2). By varying the time delay between the incident electron pulse and the ionizing laser pulse, it is possible to measure the kinetic energy distributions of desorbing fragments. The kinetic energy distributions above ∼ 5 eV appear invariant with incident electron energy, indicating that the same desorption process (dissociation via low-lying electronic states) operates at all the studied incident energies. Nevertheless, measurements of neutral yields as functions of incident electron energy demonstrate that excitation of the dissociative electronic states also proceeds via previously identified transient negative ions. At energies less than ∼ 5 eV, contributions from dissociative electron attachment are also observed in the yield of CD3 and other neutral fragments.

Prevalence and reporting of near-point binocular convergence and acuity vision deficits in potential research participants.

Visual abilities at near-point distances of 200 self-reported normal vision college students were assessed. Results show that normal visual functioning with no deficits is the exception. The most common visual deficits observed involved binocular lateral posture and fusion convergence deficits. Binocular and monocular acuity deficits also had high prevalence rates, although not as prevalent as the binocular convergence deficits. In addition, 1,340 articles published in four major journals from the years 1997-2004 were examined to ascertain the extent to which authors report the visual capabilities of their participants. Reporting of research participant visual abilities by authors using visual stimuli in experiments appears to be lacking. The results are discussed in terms of the potential impact that visual deficits may have on results obtained in experiments in which visual stimuli are used and the importance of reporting the visual assessment tests and procedures used to assess the visual abilities of potential participants.

Ultraviolet-B-induced inactivation of human OGG1, the repair enzyme for removal of 8-oxoguanine in DNA.

The OGG1 proteins are DNA N-glycosylases-apurinic-apyrimidinic lyases that are responsible for the removal of 8-oxo-7,8-dihydroguanine (8-oxoG) base in DNA. The human enzyme (hOGG1) is a monomer of 345 amino acids containing 10 buried tryptophan (Trp) residues that are very sensitive to UVB irradiation. The photolysis quantum yield of these Trp residues is about 0.3 and 0.1 in argon- and air-saturated solutions, respectively. Matrix-assisted laser desorption-ionization-time-of-flight mass spectrometry shows that several cleavage sites are identical under aerobic and anaerobic photolysis of Trp residues; one of them includes the active site. Western blots and polyacrylamide gel electrophoresis indicate that fragments of high molecular size are also formed. In addition to common photochemical paths with argon-saturated solutions, specific reactions occur in air-saturated solutions of hOGG1. The photolysis rate is inhibited by more than 50% on binding of hOGG1 to a 34mer oligonucleotide containing a single 8-oxoG-C base pair. Binding to the oligonucleotide with 8-oxoG-C induced a 20% quenching of the hOGG1 fluorescence, suggesting interaction of nucleic acid bases with the Trp residue(s) responsible for the photolysis. Using 2,6-diamino-4-hydroxy-5-N-methylformamidopyrimidine (Me-FapyG) and 8-oxoG as substrates, it is shown that protein photolysis induces photoinactivation of the DNA N-glycosylase activities. The excision of 8-oxoG is more affected than that of Me-FapyG at the same dose of UVB irradiation under both air and argon conditions. Besides the role of Trp residues, the possible involvement of Cys 253 in the photoinactivation process of hOGG1 is discussed.

The impact of flow rate (simulated leaching) on plasmid transfer frequency between bacteria in a model rhizosphere system.

AIMS: To investigate the effect of flow rate and inoculation order on plasmid transfer frequency between bacteria in a model rhizosphere system. METHODS AND RESULTS: A physical model system was constructed and used to demonstrate that although flow rate did affect plasmid transfer frequency for an introduced strain, the flow rates necessary for a significant effect on an established population were much higher than typical water flow rates found through soil. Plasmid transfer frequency was highly sensitive to strain inoculation order. CONCLUSION: Flow rate may not have a significant effect on plasmid transfer frequency between established bacterial populations in the rhizosphere. SIGNIFICANCE AND IMPACT OF THE STUDY: This study contributes to the current debate over the release and spread of genetically modified organisms into the environment. It also demonstrates that model controlled systems may be used to rapidly obtain initial data about the potential behaviour of microorganisms, prior to more costly and lengthy glasshouse and field trials.

Interactions of superoxide anion with enzyme radicals: kinetics of reaction with lysozyme tryptophan radicals and corresponding effects on tyrosine electron transfer.

The kinetics of O2*- reaction with semi-oxidized tryptophan radicals in lysozyme, Trp*(Lyz) have been investigated at various pHs and conformational states by pulse radiolysis. The Trp*(Lyz) radicals were formed by Br2*- oxidation of the 3-4 exposed Trp residues in the protein. At pH lower than 6.2, the apparent bimolecular rate is about 2 x 10(8) M(-1) s(-1); but drops to 8 x 10(7) M(-1) s(-1) or less above pH 6.3 and in CTAC micelles. Similarly, the apparent bimolecular rate constant for the intermolecular Trp*(Lyz) + Trp*(Lyz) recombination reaction is about (4-7 x 10(6) M(-1) s(-1)) at/or below pH 6.2 then drops to 1.3-1.6 x 10(6) M(-1) s(-1) at higher pH or in micelles. This behavior suggests important conformational and/or microenvironmental rearrangement with pH, leading to less accessible semi-oxidized Trp* residues upon Br2*- reaction. The kinetics of Trp*(Lyz) with ascorbate, a reducing species rather larger than O2*- have been measured for comparison. The well-established long range intramolecular electron transfer from Tyr residues to Trp radicals--leading to the repair of the semi-oxidized Trp*(Lyz) and formation of the tyrosyl phenoxyl radical is inhibited by the Trp*(Lyz) + O2*- reaction, as is most of the Trp*(Lyz) + Trp*(Lyz) reaction. However, the kinetic behavior of Trp*(Lyz) suggests that not all oxidized Trp residues are involved in the intermolecular recombination or reaction with O2*-. As the kinetics are found to be quite pH sensitive, this study demonstrates the effect of the protein conformation on O2*- reactivity. To our knowledge, this is the first report on the kinetics of a protein-O2*- reaction not involving the detection of change in the redox state of a prosthetic group to probe the reactivity of the superoxide anion.

A laser flash photolysis and pulse radiolysis study of primary photochemical processes of flumequine.

The 355 nm laser flash photolysis of argon-saturated pH 8 phosphate buffer solutions of the fluoroquinolone antibiotic flumequine produces a transient triplet state with a maximum absorbance at 575 nm where the molar absorptivity is 14,000 M(-1) cm(-1). The quantum yield of triplet formation is 0.9. The transient triplet state is quenched by various Type-1 photodynamic substrates such as tryptophan (TrpH), tyrosine, N-acetylcysteine and 2-deoxyguanosine leading to the formation of the semireduced flumequine species. This semireduced form has been readily identified by pulse radiolysis of argon-saturated pH 8 buffered aqueous solutions by reaction of the hydrated electrons and the CO2*- radicals with flumequine. The absorption maximum of the transient semireduced species is found at 570 nm with a molar absorptivity of 2,500 M(-1) cm(-1). In argon-saturated buffered solutions, the semireduced flumequine species formed by the reaction of the flumequine triplet with TrpH stoichiometrically reduces ferricytochrome C (Cyt Fe3+) under steady state irradiation with ultraviolet-A light. In the presence of oxygen, O2*- is formed but the photoreduction of Cyt Fe3+ by O2*- competes with an oxidizing pathway which involves photo-oxidation products of TrpH.

Substrate Concentration and Plasmid Transfer Frequency between Bacteria in a Model Rhizosphere.

The influence of substrate concentration on plasmid transfer frequency in the rhizosphere was investigated using a physical model employing a hollow fiber membrane instead of a real root. The absolute number of transconjugants produced increased with increasing substrate (glucose) concentration, but the plasmid transfer frequency decreased exponentially with increasing substrate concentration from 4.4 × 10(-3) at 90 µg ml(-1) glucose to 1.35 × 10(-5) at 3600 µg ml(-1) glucose. These results were found to be heavily dependant on donor to recipient ratio and distribution of strains, but independent of initial donor and recipient inoculum density and regime. These observations also show that plasmid transfer frequency is reduced at high substrate concentrations, which suggests that plasmid transfer is either stimulated when growth limiting nutrient is scarce or inhibited when it is abundant.

[Vertebral osteomyelitis with epidural abscess in a child with sickle cell disease]. / Ostéomyélite vertébrale avec abcès épidural chez une enfant drépanocytaire.

A case of paraplegia due to a thoracic epidural abscess in a 6-year-old black girl with sickle cell anemia is reported. MRI and CT scan showed abnormalities involving T6 vertebra which were consistent with osteomyelitis. A laminotomy, associated to antibiotic administration, permitted rapid neurological improvement. Although cultures were negative, the infection was probably due to salmonellae. Salmonellosis is a well-known complication in children with sickle cell disease but spinal localization is unusual. Its pathogenesis is unclear but immunological abnormalities associated to vascular obstructions by abnormal blood red cells have been advocated. The underlying etiology of vertebral abnormalities in these children is difficult to determine, but early diagnosis with modern investigations, as CT scan and MRI, is crucial to promptly begin therapy for osteomyelitis, minimizing the risk of spinal cord compression.

EPIMART: prospective incidence study of epileptic seizures in newly referred patients in a French Carribean island (Martinique).

PURPOSE: To identify, in the population living in the island of Martinique, persons who had their first epileptic seizure or first came to medical attention because of an epileptic seizure. METHODS: Between May 1, 1994, and April 30, 1995, we collected all suspected cases of provoked and unprovoked epileptic seizures admitted to the hospitals or addressed to the private neurologists or pediatricians of the island. RESULTS: Three hundred nine cases were collected. Rate of initial diagnosis of provoked and nonprovoked seizures (standardized to the U.S. population): 77.7/100,000, with a bimodal distribution of the cases with age (86 in 0- to 10-year age group and 203 in patients older than 60 years). Sixty-three cases were classified as provoked seizures (incidence, 16.4/100,000). Alcohol consumption, stroke, and cranial trauma were the most frequent causes (30.1, 20.6, and 18.7%, respectively). Two hundred forty-six cases were classified as unprovoked seizures (incidence, 64.1): seizures with a stable condition, 74 cases (I, 19.3); seizures with an evolutive condition, 17 cases (I, 4.5); seizures of unknown etiology, 155 cases (I, 40.4). These figures must be considered as the minimal rate. CONCLUSIONS: The global incidence rate of newly referred persons with a diagnosis of epileptic seizures in this study is clearly higher than those observed in industrialized countries but lower than those in developing countries. The major risk factors are represented by alcohol consumption, followed by stroke, cranial trauma, and infectious diseases.

Lysosomes are sites of fluoroquinolone photosensitization in human skin fibroblasts: a microspectrofluorometric approach.

The fluoroquinolone antibiotics are widely used despite their strong phototoxicity under solar UV irradiation. Although they are known as good photodynamic photosensitizers, other factors than production of activated oxygen species may play a role in the effectiveness of the phototoxic effect. Subcellular localization is one of the important parameters that may determine this strength. Using microspectrofluorometry, it is shown that norfloxacin, ofloxacin, lomefloxacin, ciproflaxin and BAYy3118 are readily incorporated into lysosomes of HS68 human skin fibroblasts although weak staining of the whole cytoplasm also occurs especially with norfloxacin. Consistent with their photoinstability in solutions, the fluoroquinolones under study are readily photobleached by UVA in the HS68 fibroblasts. The BAYy3118 derivative that has the fastest bleaching rate also shows the strongest phototoxicity toward HS68 fibroblasts. Photosensitization with these fluoroquinolones induces lysosomal membrane damage as shown by the increased rate of leakage of the lysosomal probe lucifer yellow as compared to that observed with untreated cells.

Ultraviolet-B-induced damage to Escherichia coli Fpg protein.

We investigated the effect of UVB light (290 < or = lambda < or = 320 nm) on the structure and enzymatic activities of Escherichia coli Fpg protein (2,6-diamino-4-hydroxy-5N-methylformamidopyrimidine-DNA glycosylase), a DNA repair enzyme containing a zinc finger motif and five chromophoric Trp residues. Irradiation with UVB light of air-saturated pH 7.4 buffered aqueous solutions of Fpg induces the formation of polymers as shown by sodium dodecyl sulfate polyacrylamide gel electrophoretic analysis. In argon-saturated solutions, polymer formation produces a precipitate. The polymerization quantum yield is 0.07 +/- 0.01 and 0.15 +/- 0.02 in air- and argon-saturated solutions, respectively. In the polymerized Fpg protein, second-derivative absorption spectroscopy indicates that three and one Trp residues are destroyed in air- and argon-saturated solutions, respectively. Polymers are devoid of all three activities of the Fpg protein, whereas the unpolymerized protein retains full activities. Matrix-assisted laser desorption/ionization experiments demonstrate that polymer formation is accompanied by the formation of short polypeptides containing the first 32 or 33 residues of the N-terminal domain. Theses polypeptides are most probably formed by the photolytic cleavage of Fpg protein induced by light absorption by the adjacent Trp-34 residue.

[Epileptic seizures, epilepsy and risk factors. Experiences with an investigation in Martinique. Epimart Group]. / Crises épileptiques, épilepsies et facteurs de risque. Expérience d'une enquête en Martinique. Le Groupe Epimart.

A prospective incidence study was carried out in the French Caribbean island of Martinique between May 1st 1994 and April 31st 1995. incidence was 80.6 (77.7 when standardized with 1990 U.S. population). This incidence was higher than that observed in the Swiss canton of Geneva where the same methodology was used. The individualized risk factors of first provoked and unprovoked seizures in Martinique were alcoholism, head trauma and cerebro-vascular accidents.

Effect of single mutations on the structural dynamics of a DNA repair enzyme, the Escherichia coli formamidopyrimidine-DNA glycosylase--a fluorescence study using tryptophan residues as reporter groups.

The effects on the structure dynamics of the Escherichia coli wild-type formamidopyrimidine-DNA glycosylase (Fpg) protein of the single mutations Lys57-->Gly (FpgK57G), Pro2-->Gly (FpgP2G) and Pro2-->Glu (FpgP2E) were studied by fluorescence techniques, namely: lifetime measurements and acrylamide quenching of the fluorescence of Trp residues. The fluorescence decays of Fpg and its mutant forms were analysed by the maximum-entropy method and lifetime distributions in the range 200 ps to 9 ns were obtained. The lifetime distribution profiles of FpgK57G, FpgP2G and FpgP2E are different from that of wild-type Fpg. Both dynamic and static quenching by acrylamide were observed for all the proteins. At 20 degrees C, the bimolecular collisional quenching rate constant of the FpgP2E fluorescence by acrylamide was only 0.8 M(-1) s(-1) as compared to about 1.4 M(-1) s(-1) for the three other proteins. At 6 degrees C, all the spectroscopic properties of these four proteins are about the same. The analysis of experimental data demonstrates that all three mutations induce a structural reorganization of the Fpg protein. However, only the P2E mutation lead to a reduced accessibility of some Trp residues to acrylamide quenching. It is concluded that the single P2E replacement induces a conformational change leading to a more rigid globular structure as opposed to the wild type and K57G and P2G mutations. The influence of the single mutations on the enzyme activities of the Fpg protein is discussed.

[Mechanism of quenching of hematoporphyrin and mono-L-aspartyl chlorine e6 triplet states by metronidazole]. / O mekhanizme tusheniia tripletno-vozbuzhdennogo sostoianiia gematoporphirina i mono-L-aspartil khlorina e6 metronidazonom.

The quenching of the triplet state of hematopophyrin (3HP.) and mono-L-aspartyl chlorine e6, (3MACE.) by metrotlidazole (METRO) ground state, has been investigated in binary mixtures of water and aliphatic alcohol by means of 532 nm laser flash. In water, both 3HP. and 3MACE. quenched by METRO with at rate: kQw = 1.9 x 10(9) M-1.s-1. The quenching is accompanied by the appearance of a transient absorbance near 690 nm. This transient absorbance corresponds to the tetrapyrrole radical-cation formation in result of an electron transfer between 3HP. or 3MACE. and METRO. In neat alcohol, the electron transfer was not observed. In binary mixtures the quenching constant is reduced as the molar fraction of water is decreased. In water, the activation barrier of the quenching is 5.9 kcal/mol for HP and 3.9 kcal/mol for MACE. In going from water to water-alcohol mixtures the energy of activation is practically unchanged. Based on flash photolysis data, and analysis of absorption spectra of METRO we conclude that the electron-acceptor ability of metronidazole essentially depends on the intermolecular interaction with nearby solvent molecules. The mechanism of the quenching is discussed.