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At least 1,081 records · Page 60Linked to original sources
PubMed2000

Electron paramagnetic resonance for everybody--MICROspec-X--a new class of electron paramagnetic resonance spectrometer.

The electron paramagnetic resonance spectroscopy is the only method for detecting free radicals. Free radicals have an increased importance in our daily life. A small transportable EPR spectrometer is presented for the popularisation of the EPR method. The technical construction and some applications are illustrated which show the usability of the spectrometer.

Electron Spin Resonance Spectroscopy↗
PubMed2001

Rate constants in two dimensions of electron transfer between pyruvate oxidase, a membrane enzyme, and ubiquinone (coenzyme Q8), its water-insoluble electron carrier.

The functionality of the membrane-bound, ubiquinone-dependent pyruvate oxidase from the respiratory chain of Escherichia coli was reconstituted with a supported lipidic structure. The artificial structure was especially designed to allow the electrochemical control of the quinone pool through the lateral mobility of the ubiquinone (Q(8)) molecules. The kinetic coupling of the enzyme bound to the lipid structure with the quinone pool was ensured by the regeneration of the oxidized form of ubiquinone at the electrochemical interface. Such an experimental approach enabled us to carry out an unprecedented determination of the kinetic parameters controlling the reaction between the enzyme bound and the electron carrier under conditions taking rigorously into account the fact that the freedom of motion is restricted to two dimensions. The kinetic constants we found show that the activated enzyme can be efficiently regulated by the oxidation level of the quinone pool in natural membranes.

Carrier Proteins↗
PubMed2001

Thermodynamics of electron transfer in oxygenic photosynthetic reaction centers: volume change, enthalpy, and entropy of electron-transfer reactions in the intact cells of the cyanobacterium Synechocystis PCC 6803.

The volume and enthalpy changes for charge transfer in the 0.1-10 micros time window in photosynthetic reaction centers of the intact cells of Synechocystis PCC 6803 were determined using pulsed, time-resolved photoacoustics. This required invention of a method to correct for the cell artifact at the temperature of maximum density of water caused by the heterogeneous system. Cells grown under either white or red light had different PS I/PS II molar ratios, approximately 3 and approximately 1.7, respectively, but invariable action spectra and effective antenna sizes of the photosystems. In both cultures, the photoacoustic measurements revealed that their thermodynamic parameters differed strongly in the spectral regions of predominant excitation of PS I (680 nm) and PS II (625 nm). On correcting for contribution of the two photosystems at these wavelengths, the volume change was determined to be -27 +/- 3 and -2 +/- 3 A3 for PS I and PS II, respectively. The energy storage on the approximately 1 micros time scale was estimated to be 80 +/- 15% and 45 +/- 10% per trap in PS I and PS II, respectively. These correspond to enthalpies of -0.33 +/- 0.2 and -1 +/- 0.2 eV for the assumed formation of ion radical pairs P700+F(AB-) and Y(Z*)P680Q(A-), respectively. Taking the free energy of the above reactions as the differences of their redox potentials in situ, apparent entropy changes were estimated to be +0.4 +/- 0.2 and -0.2 +/- 0.2 eV for PS I and PS II, respectively. These values are similar to that obtained in vitro for the purified reaction center complexes on the microsecond time scale [Hou et al. (2001) Biochemistry 40, 7109-7116, 7117-7125]. The constancy of these thermodynamic values over a 2-fold change of the ratio of PS I/PS II is support for this method of in vivo analysis. Our pulsed PA method can correct the "cell" or heterogeneous artifact and thus opens a new route for studying the thermodynamics of electron transfer in vivo.

Calorimetry↗
PubMed2002

Chemically gated electron transfer. A means of accelerating and regulating rates of biological electron transfer.

Long-range protein electron transfer [ET] reactions may be relatively slow because of long ET distance and low driving force. It is possible to dramatically increase the rate of such nonadiabatic reactions by using an adiabatic chemical reaction to activate the system for rapid ET. Three such examples are discussed; nitrogenase, pyruvate:ferredoxin oxidoreductase, and the methylamine dehydrogenase-amicyanin complex. In each example, the faster activated ET reaction is gated (i.e., rate-limited) by the chemical reaction. However, the reaction rate is still orders of magnitude greater than that of the ungated true ET reaction in the absence of chemical activation. Models are presented to describe the mechanisms of activation in the context of ET theory, and the relevance of such chemically gated ET to the regulation of metabolism is discussed.

Bacterial Proteins↗
PubMed2002

A highly selective aerobic oxidation process catalyzed by electron-deficient nitroarenes via single electron transfer processes.

A versatile and simple method for aerobic oxidation of various aromatics containing an oxygen-functionalized benzylic carbon is reported. Results from oxidation experiments with methyl aryl ketones, benzaldehydes, benzylic alcohols, and mandelic acid are reported; all provide high yields of the corresponding aromatic carboxylic acids. By means of response surface methodology and mechanistic interpretation it is revealed that the oxidation process operates catalytically using electron-deficient nitroarenes, such as 1,3-dinitrobenzene, 1,2,3-trifluoro-4-nitrobenzene, and 2,4-difluoro-1-nitrobenzene, with molecular oxygen as the terminal oxidant. The reaction is carried out in a basic solution of potassium tert-butoxide in tert-butyl alcohol. Since the terminal oxidant is molecular oxygen and only 5-10 mol % of, e.g., 1,3-dinitrobenzene as catalyst is used, the new method represents an environmentally benign alternative to, for example, the well-known haloform reaction. The method is also a convincing alternative when transition metal free conditions are required.

Aerobiosis↗
PubMed2006

Direct detection of nucleotide radical cations produced by electron-transfer oxidation of DNA bases with electron-transfer state of 9-mesityl-10-methylacridinium ion and resulting efficient DNA cleavage without oxygen.

Photoinduced electron transfer of DNA as well as DNA bases with 9-mesityl-10-methylacridinium ion results in formation of all types of DNA base radical cations, which have been detected as the transient absorption spectra measurements, leading to efficient DNA cleavage in the absence of O2.

Acridines↗
PubMed1973

Electron carriers of cytochrome oxidase detectable by electron paramagnetic resonance and their relationship to those traditionally recognized in this enzyme.

On the basis of oxidoreductive rapid kinetic and titration experiments with purified cytochrome c oxidase (EC 1.9.3.1), monitored by electron paramagnetic resonance (EPR) at 13 degrees K and by spectrophotometry at 100 degrees K, a new assignment of EPR signals is proposed. The bulk of both the low-spin (g = 3.0; 2.2; 1.5) and highspin (g = 6; 2) signals is attributed to the component with the properties of traditional cytochrome a. It is further proposed that the absorption band at 655 nm represents the most unambiguous manifestation of the a(3) component.

Copper↗
PubMed1994

UV photoelectron and ab initio quantum mechanical characterization of valence electrons in Na(+)-water-2'-deoxyguanosine 5'-phosphate clusters: electronic influences on DNA alkylation by methylating and ethylating carcinogens.

UV photoelectron data for 1,9-dimethylguanine, 3-hydroxytetrahydrofuran, and water, and results from ab initio self-consistent field (SCF) and post-SCF molecular orbital calculations were employed to describe valence electrons in clusters of 2'-deoxyguanosine 5'-phosphate (5'-dGMP-) with four water molecules and a phosphate-bound sodium ion. Two clusters (A and B) were examined. In A, Na+ is coordinated to 5'-dGMP-. In B, Na+ and 5'-dGMP- are separated by water. In 5'-dGMP- clusters, the nucleotide valence ionization potentials (IPs) are different from those previously reported for isolated 5'-dGMP-. The smallest IP in isolated 5'-dGMP- (4.6 eV) arises from the phosphate group; the smallest IPs in A (8.2 eV) and B (7.9 eV) arise from the base. In the clusters, the IPs associated with the seven upper occupied base orbitals differ from corresponding IPs in 1,9-dimethylguanine by less than 0.4 eV. In A and B, the smaller IP of the base, compared with the phosphate group, is consistent with reactivity data indicating that DNA and RNA are subject to electrophilic SN2 attack by carcinogens such as N-methyl-N-nitrosourea, dimethyl and diethyl sulfate, and methyl and ethyl methanesulfonate, in which more than 75% of nucleotide alkylation occurs at the bases.

Alkylating Agents↗
PubMed2006

Intraoperative radiation therapy using a mobile electron linear accelerator: field matching for large-field electron irradiation.

Intraoperative radiation therapy (IORT) consists of delivering a large, single-fraction dose of radiation to a surgically exposed tumour or tumour bed at the time of surgery. With the availability of a mobile linear accelerator in the OR, IORT procedures have become more feasible for medical centres and more accessible to cancer patients. Often the area requiring irradiation is larger than what the treatment applicators will allow, and therefore, two or more adjoining fields are used. Unfortunately, the divergence and scattering of the electron beams may cause significant dose variations in the region of the field junction. Furthermore, because IORT treatments are delivered in a large single fraction, the effects of underdosing or overdosing could be more critical when compared to fractionated external beam therapy. Proper matching of the fields is therefore an important technical aspect of treatment delivery. We have studied the matching region using the largest flat applicator available for three different possibilities: abutting the fields, leaving a small gap or creating an overlap. Measurements were done using film dosimetry for the available energies of 4, 6, 9 and 12 MeV. Our results show the presence of clinically significant cold spots for the low-energy beams when the fields are either gapped or abutted, suggesting that the fields should be overlapped. No fields should be gapped. The results suggest that an optimal dose distribution may be obtained by overlapping the fields at 4 and 6 MeV and simply abutting the fields at 9 and 12 MeV. However, due to uncertainties in the placement of lead shields during treatment delivery, one may wish to consider overlapping the higher energy fields as well.

Electrons↗
PubMed1995

Histology and electron microscopy of fucosidosis of the skin. Subtle clues to diagnosis by electron microscopy.

Fucosidosis is an autosomal recessive inborn error of metabolism in which fucose-containing glycolipids, glycoproteins, and oligo- and polysaccharides accumulate in tissues as a consequence of alpha-L-fucosidase deficiency. Since the detection of this entity in 1966 several cases have been described, but until now investigations of clinically uninvolved skin have not been performed. In this study we have investigated clinically normal skin obtained from a patient with fucosidosis and his healthy sister, by light and electron microscopy, to determine whether normal skin in this condition yields clues that may have prognostic relevance. We found "empty"- appearing storage vesicles in melanocytes, endothelial cells, sweat glands, and fibroblasts in the skin.

Child, Preschool↗
PubMed1979

Early changes in the arterial endothelium under various pathological conditions: an electron histochemical study with visualization of altered permeability using electron microscopic tracers.

The authors have studied the endothelial changes in the aorta and the arteries of heart, kidney and other organs in cholesterol fed rabbits and endotoxin administrated rats through electron histochemical and vascular clearance methods. The vascular changes are variable presumably due to the functional and morphological difference of vessels. The administration of cholesterol and endotoxin may result in increased vascular permeability which is directly related to the qualitative increase and decrease of hydrolytic enzymes in the vascular wall. The permeability of high molecular substances was enhanced with the widening of the intercellular space in contraction of endothelium and the changing of molecular structure of plasma membrane accompanied with plasma lipid, platelets and hemodynamic stress. This fact was confirmed by use of horseradish peroxidase and dextran fesin as tracers of different molecular sizes. The authors emphasize that direct injury and subsequent abnormal contraction of the endothelial cell may initiate increased permeability of plasma protein and lipid in the medial layer and eventually may develop and enhance arteriosclerosis.

Acid Phosphatase↗
PubMed2005

The human bone-oxidized titanium implant interface: A light microscopic, scanning electron microscopic, back-scatter scanning electron microscopic, and energy-dispersive x-ray study of clinically retrieved dental implants.

BACKGROUND: Surface modification of titanium implants by anodic oxidation may lead to enhanced bone integration. For instance, in vivo studies have demonstrated formation of more bone contacts in less time than for turned control implants. In addition, oxidized implants have shown a higher resistance to torque forces, indicating a strong interlock between bone and the oxide layer. However, the structure of the oxidized titanium-bone interface in high resolution is not known. PURPOSE: The aim of the study was to analyze the human bone-oxidized titanium interface at a high-resolution level. Of particular interest was the relationship between bone tissue and the pores of the surface oxide. MATERIALS AND METHODS: Twelve clinically retrieved implants with an oxidized surface (TiUnite, Nobel Biocare AB, Göteborg, Sweden) were used. Seven were regular dental implants and five were experimental mini-implants and had been subjected to immediate, early, or no loading. They were retrieved after 5 to 9 months of healing and were processed and analyzed using light microscopy, scanning electron microscopy (SEM) in normal and back-scatter (BS-SEM) modes, and energy-dispersive x-ray (EDX) analysis techniques. RESULTS: Bone formation was observed to occur from adjacent bone structures toward the implant surface, and it was evident that bone formation had occurred at the implant surface. SEM, BS-SEM, and EDX revealed that mineralized bone had grown into the pores of the surface oxide layer, including pores with small diameters (< 2 microm). CONCLUSIONS: The clinically retrieved oxidized implants showed evidence of bone growth into the pores of the surface oxide layer. The findings indicate the establishment of a strong interlock between the bone and the oxidized titanium implant, which is suggested to be beneficial for clinical performance.

Coated Materials, Biocompatible↗
PubMed1991

Photoinitiated vectorial transmembrane electron transfer in bilayers sensitized by a face to face triporphyrin acting as a molecular electronic device. Amplification due to ionic coupling.

Under light excitation transmembrane electron transfer is observed when a stacked Zn-Cu-Zn triporphyrin is incorporated in a bilayer between aqueous redox phases. The electric polarization of the membrane due to the photoinduced transmembrane charge flux drives ion transport. This effect increases the net charge transfer across the system, giving rise to an amplification similar to a field effect transistor. Thus this system can be considered an organic phototransistor.

Electron Transport↗
PubMed1986

Electron probe analysis, X-ray mapping, and electron energy-loss spectroscopy of calcium, magnesium, and monovalent ions in log-phase and in dividing Escherichia coli B cells.

The elemental composition of individual cells of rapidly frozen and cryosectioned Escherichia coli B was measured with electron optical microanalytic methods. The Ca content was high (26.2 mmol/kg) in a 10-nm-wide region of the cell envelope. Amounts of cytoplasmic Ca in actively dividing cells were significantly higher (32.6 mmol/kg [dry weight]) than in the log-phase (1.5 mmol/kg) cells. Cellular Mg was 205 mmol/kg (dry weight) and it was uniformly distributed throughout the cell. Cells washed in distilled water before freezing lost monovalent ions (Na, Cl, and K), but the membrane-bound Ca and cellular Mg were not reduced, indicating that cellular Mg and membrane Ca are more tightly bound.

Calcium↗
PubMed1977

Localization of gold in synovial membrane of rheumatoid arthritis treated with sodium aurothiomalate. Studies by electron microscope and electron probe x-ray microanalysis.

The localization of gold in the synovial membrane of rheumatoid arthritis patients treated with sodium aurothiomalate was examined and quantitative analysis of epon-embedded sections was carried out with a wavelength dispersive x-ray microanalyser. Gold was only detected in the lysosomes of synovial lining type A cells and subsynovial mononuclear cells in the form of filamentous deposits and highly electron-dense granules, the latter being few in number. The concentration of gold within the lysosomes containing the characteristic deposits and granules was equivalent to that in epon-embedded standard specimens of freeze-dried albumin in which 2-0-87-4 mg/ml of gold was included. In addition, sulphur was detected in the lysosomes containing the filamentous deposits, but the S/Au x-ray signal ratio was not equal to that detected in sodium aurothiomalate. The significance of the coexistence of gold with sulphur in lysosomes is discussed.

Aged↗
PubMed1974

Diagnostic electron microscopy of faeces. I. The viral flora of the faeces as seen by electron microscopy.

A method is described for examining viruses in faeces by direct electron microscopy using negative staining. The particles found in a group of patients with gastroenteritis and a group with other conditions are compared. Small particles in the range of sizes covering parvoviruses and enteroviruses were found about as frequently in each group. Many of these were probably bacteriophages. Many bacteriophages with tails of various sizes and lengths were found. Adenoviruses were found in five of eight patients from whom they were isolated. Reovirus- (or orbivirus-) like particles were found associated with some gastroenteritis patients.

Adenoviridae↗
PubMed1975

Electron microscopy of vesicular-arbuscualr mycorrhizae of yellow poplar. I. Characterization of endophytic structures by scanning electron stereoscopy.

Vesicular-arbuscular mycorrhizae of yellow poplar (Liriodendron tulipifera L.) were examined by scanning electron microscopy. The morphology and spatial distribution of endophytic structures are illustrated. The use of stereoscopic techniques in conjunction with removal of host cytoplasm permits detection of subtle morphological alterations and progressive deterioration of the fungal component.

Cell Wall↗
PubMed1997

Repair of retinal pigment epithelium and choriocapillaries after laser photocoagulation: correlations between scanning electron, transmission electron and light microscopy.

Cell-to-cell interactions between retinal pigment epithelial (RPE) cells and vascular endothelium were examined by scanning electron microscopy, which demonstrates many facets of surface topography. The repair process after laser photocoagulation was characterized by a morphologically heterogeneous population of regenerated RPE cells, including normal-looking cells, macrophage-like cells and large elongated RPE cells. The macrophage-like and normal-looking RPE cells were predominantly seen adjacent to growing new choroidal vessels. Large cells appeared mainly in the vicinity of the extracellular matrix, where no viable new vessels were seen. The observed association between a specific phenotype of regenerated RPE cells and neovascularization may further support the hypothesis that regenerated RPE cells have a dual function, exerting both stimulatory and inhibitory effects on endothelial cells.

Animals↗