Spectroscopic Graphite Research Articles

高圧下におけるアモルファス炭素からのダイヤモンド合成

Formation of diamond from amorphous carbon was studied under static high pressure (10-18GPa) and high temperature (1120-2000°C) without any planned addition of catalysts. Diamond was formed upon heating amorphous carbon at fixed pressures higher than 10GPa, but was not formed below 8GPa. The formation of diamond occurred via crystallization of amorphous carbon into graphite. The graphitization was not, however, completed prior to the diamond formation. The temperature of diamond formation from amorphous carbon was markedly lower than those from glassy carbon or spectroscopic graphite, being strongly dependent on the temperature for preparing amorphous carbon. The results were interpreted from the two-species model of amorphous carbon.

Diamond synthesis by weak shock loading

A hexagonal polymorph of diamond has been synthesized by relatively weak shock loading (in a range of projectile velocity 0.655 to 1.88 km sec−1) with a recovery technique. Four mixtures of copper with spectroscopic graphite, amorphous carbon, glassy carbon and graphite fluoride, with densities of 4.8 to 7.8 g cm−3, were used to control the shock temperature rise and to quench efficiently. Spectroscopic graphite gave the maximum yield of diamond (8%). Chaoite was also observed in the shocked amorphous carbon and glassy carbon. A local temperature rise during shock was inferred from the temperature of some spherical particles, indicative of superheating of the particles to near or above the melting point.

Production of Graphite Targets by Deposition from CO/H2for Precision Accelerator14C Measurements

A method has been developed at the Arizona AMS facility for production of graphite directly from CO2by catalytic reduction of CO/H2mixtures. The method is a modification of procedures discussed by Vogelet al(1984). Currents of12C−from these targets vary considerably, but have a median value which is 70% of that achieved from spectroscopic graphite. Precisions of ±60 to 100 yr are routinely achieved for14C ages of 5000-yr-old samples containing one milligram of carbon. The yield of14C from “blank” targets is 0.6 ± 0.1% of that from modern material.

Effect of small concentrations of co on rate of gasification of spectroscopic graphite in o 2

The influence of CO on the steady state gasification rate of a spectroscopically pure graphite powder with ultra high purity O 2 was studied at 840 ± 3 K for CO levels up to about 3000 ppm. The behavior of low reactivity samples differed from that of high reactivity samples. The gasification rate of low reactivity samples, distinguished as those having higher CO/CO 2 product ratios and lower gasification rates with no added CO, was inhibited by CO beyond that expected from simple dilution. The gasification of high reactivity samples was inhibited for CO additions under about 100 ppm. For higher CO additions, the gasification rate of high reactivity samples was unaffected or slightly enhanced. The difference in behavior is thought to be due to different, trace amounts of impurities (catalysts) present and the inability of these trace levels of catalysts to dissipate effectively the heat of CO oxidation. Accessible catalysts are thought to originate, more or less, from dust particles and impurities within the graphite.

Electrochemical and enzymatic activity of flavin adenine dinucleotide and glucose oxidase immobilized by adsorption on carbon

Flavin adenine dinucleotide (FAD) and glucose oxidase were adsorbed on medium porosity spectroscopic graphite (SG) and on low porosity glassy carbon (GC) with retention of electrochemical activity, as measured by cyclic and differential pulse voltammetry. Adsorption on the SG was very strong, while that on GC was much weaker. Enzyme activity could be partially restored by the addition of the apoenzyme of glucose oxidase to the SG-adsorbed FAD preparation. The holoenzyme of glucose oxidase also was adsorbed on SG with retention of enzyme activity. The mechanism for the reconstitution of active enzyme from adsorbed FAD and soluble apoenzyme is not clear. The data suggest that the reconstituted enzyme stays adsorbed to the SG, but it is not clear whether the FAD or protein portions (or both) are adsorbed after reconstitution. The data also indicate that substrate mass transfer resistance may be important with the reconstituted-adsorbed enzyme.

Comparison of various sensors in the potentiometric microdetermination of nitroform and perchlorate with cetylpyridinium chloride

Various organic coatings on spectroscopic graphite as well as several types of uncoated graphite materials were examined as sensors in the precipitation titration of nitroform and perchlorate vs. cetylpyridinium chloride. The polymer used in the coatings was poly(vinyl chloride). The plasticizer of choice was di(ethylhexyl) phthalate (dioctylphthalate) because of its low toxicity and large endpoint breaks. Other plasticizers such as nitrobenzene, tricresyl-phosphate, and phthalates with an alkyl chain length between 4 and 8 carbon atoms are also suitable. The plastic-coated sensors yielded larger breaks than any of the uncoated graphite sensors. Of the latter materials, Poco AXF-9Q graphite yielded the largest breaks for both anions examined. Coated and uncoated graphite electrodes can be used as sensors in a variety of potentiometric titrations. While these electrodes are not selective per se, selectivity is governed by the analyte/titrant interaction.

The effect of netropsin on the electrochemical oxidation of DNA at a graphite electrode

The interaction of netropsin with calf thymus, Bacillus cereus and Micrococcus luteus DNAs and with the RNA of phage f2 was studied by means of differential pulse voltammetry at a paraffin-wax-impregnated spectroscopic graphite electrode. It was found that the oxidation voltammetric peaks of double-helical calf thymus and Bacillus cereus DNAs were lowered when netropsin was added to the DNA solution. The peak corresponding to electro-oxidation of adenine residues was lowered more than that corresponding to electro-oxidation of guanine residues. Under the same experimental conditions the oxidation peaks of double-helical Micrococcus luteus DNA, double-helical RNA and thermally denatured samples of all DNAs used were almost uninfluenced by the addition of netropsin. The results observed were explained by ( i) decreased flexibility of the segments to which netropsin was bound, and ( ii) the specific binding of netropsin to the segments of double-helical DNA rich in adenine.thymine pairs.

459—The effect of netropsin on the electrochemical oxidation of DNA at a graphite electrode

The interaction of netropsin with calf thymus, Bacillus cereus and Micrococcus luteus DNAs and with the RNA of phage f2 was studied by means of differential pulse voltammetry at a paraffin-wax-impregnated spectroscopic graphite electrode. It was found that the oxidation voltammetric peaks of double-helical calf thymus and Bacillus cereus DNAs were lowered when netropsin was added to the DNA solution. The peak corresponding to electro-oxidation of adenine residues was lowered more than that corresponding to electro-oxidation of guanine residues. Under the same experimental conditions the oxidation peaks of double-helical Micrococcus luteus DNA, double-helical RNA and thermally denatured samples of all DNAs used were almost uninfluenced by the addition of netropsin. The results observed were explained by ( i) decreased flexibility of the segments to which netropsin was bound, and ( ii) the specific binding of netropsin to the segments of double-helical DNA rich in adenine thymine pairs.

A Simple Sensor for Potentiometric Titrations

Abstract A sensor for potentiometric titrations was prepared by coating a spectroscopic graphite rod with a solution of poly(vinyl chloride) and dioctylphthalate in tetrahydrofuran. The reference was a Ag/AgCl single-junction electrode. The sensor was used in the following potentiometric titrations: 1. precipitation titrations 2. acid-base titrations, 3. compleximetric titrations, and 4. redox titrations. A survey of its use in such titrations is presented. Preparation of the coated-graphite sensor is simple and rapid. Moreover, it is quite inexpensive. A limitation is its applicability in aqueous media only, because organic solvents will dissolve the membrane.

434 — Electrochemical behaviour of proteins at graphite electrodes Part III. The effect of protein adsorption

Electrochemical oxidation of bovine serum albumin, ribonuclease (of bovine pancreas) and lysozyme (of hen egg white) at a paraffin-wax-impregnated spectroscopic graphite electrode was studied by means of linear sweep, cyclic and differential pulse voltammetry. It was found that the proteins studied are adsorbed at the graphite electrode in a broad region of negative and positive potentials including potentials of protein electro-oxidation. Adsorbability of proteins at the graphite electrode can be influenced by the pH of the background electrolyte and by the electrode potential. It was concluded that the adsorption of proteins at graphite electrodes can be stimulated by the electrostatic attractive forces between electric charges of the electrode and those of the protein molecule.

434 — Electrochemical behaviour of proteins at graphite electrodes: Part III. The effect of protein adsorption

Electrochemical oxidation of bovine serum albumin, ribonuclease (of bovine pancreas) and lysozyme (of hen egg white) at a paraffin0wax-impregnated spectroscopic graphite electrode was studied by means of linear sweep, cyclic and differential pulse voltammetry. It was found that the proteins studied are adsorbed at the graphite electrode in a broad region of negative and positive potentials including potentials of protein electro-oxidation. Adsorbability of proteins at the graphite electrode can be influenced by the pH of the background electrolyte and by the electrode potential. It was concluded that the adsorption of proteins at graphite electrodes can be stimulated by the electrostatic attractive forces between electric charges of the electrode and those of the protein molecule.

Relation between differential pulse voltammetric oxidation of polyriboinosinic acid and its structure

Electrooxidation of poly (I) at a paraffin wax-impregnated spectroscopic graphite electrode was studied by means of differential pulse voltammetry. It was found that the transition of single-stranded poly (I) to its multistranded form, induced by increasing the ionic strength of neutral medium, is accompanied by a lowering of the oxidation current of poly (I). The marked lowering of the oxidation current is also observable as a consequence of the formation of double-stranded complex of poly (I). poly (C). The voltammetry at carbon electrodes provides for the study of poly(I) structure in principle identical information as optical methods.

Electrochemical behaviour of proteins at graphite electrodes

Electrochemical oxidation of L,alpha-amino acids at a paraffin-wax impregnated spectroscopic graphite electrode (WISGE) was studied by means of linear sweep, cyclic, phase-sensitive alternating current and differential pulse voltammetric techniques. It was found that out of the amino acids usually occurring in proteins only tyrosine, tryptophan, histidine, cystine, cysteine and methionine were oxidized at the WISGE. At relatively low concentrations of amino acids (up to ca. 2 x 10(-4) M) the electrode process in which the amino acids are oxidized at the WISGE has the characteristics of an irreversible reaction controlled by diffusion. Coulometric measurements showed that oxidation of tyrosine and tryptophan at the WISGE, i.e. of amino acids which are responsible for the oxidizability of proteins at graphite electrodes, is a two-electron process. At higher concentrations of tyrosine-and tryptophan (above ca. 2 x 10(-4) M) adsorption of the oxidation product of these amino adds was demonstrated.

Electrochemical behaviour of proteins at graphite electrodes. I. Electrooxidation of proteins as a new probe of protein structure and reactions

Electrochemical oxidation of proteins at a paraffin-wax-impregnated spectroscopic graphite electrode was studied by means of linear sweep and differential pulse voltametric techniques. It was found that proteins at the graphite electrode yield an oxidation current in the vicinity of potentials of 0.7–0.8 V in the range of neutral pH values. This current has the characteristics of adsorption currents. It was shown that irreversible electrooxidation of tyrosine or tryptophan residues is responsible for the occurrence of these protein currents. This previously undescribed electrochemical activity of proteins was exploited for the demonstration of the influence of urea on the accessibility of both tyrosine and tryptophan residues in protein molecules for interaction with their environment. It was also demonstrated that voltammetry at graphite electrodes permits an electrochemical analysis of proteins that do not contain cystine or cysteine residues.

314 - Electrochemical oxidation of nucleic acids and proteins at graphite electrode. Qualitative aspects

The electrochemical oxidation of DNAs differing in the content of guanine plus cytosine (G+C) was investigated at a pyrolytic graphite electrode by means of differential pulse (DP) voltammetry. At pH 6.4 all samples of DNA studied yielded a peak G on DP voltammograms corresponding to the oxidation of the guanine residues, and a peak A corresponding to the oxidation of the adenine residues. The potentials of the peaks G and A were not influenced by the G+C content in DNA and differed by 0.28 V. It was found that the ratio of the heights of the peaks A and G was identical with great accuracy to the ratio of the contents (adenine+thymine) and (G+C). This fact was exploited for developing a new method for the determination of the G+C content in DNA. The electrochemical oxidation of proteins at a spectroscopic graphite electrode impregnated with paraffin wax (WISGE) was studied by means of linear sweep, cyclic, and DP voltammetry. It was found that proteins were electrochemically oxidizable at the WISGE. They yielded a faradaic peak on voltammograms in the vicinity of 0.7–0.8 V in a neutral medium. The voltammetric study of proteins, poly-(aminoacids), peptides of known aminoacid composition and free aminoacids revealed that the irreversible electrooxidation of tyrosine (and, contingently, of tryptophan) residues is responsible for the appearance of the protein peak at the WISGE. It is suggested that DP voltammetry at a graphite electrode might become another electrochemical method suitable for studies of conformational changes of proteins, and in particular of those not containing cystine or cysteine ( e.g. histones).

Electrochemical oxidation of nucleic acids and proteins at graphite electrode. Qualitative aspects

Summary The electrochemical oxidation of DNAs differing in the content of guanine plus cytosine (G+C) was investigated at a pyrolytic graphite electrode by means of differential pulse (DP) voltammetry. At pH 6.4 all samples of DNA studied yielded a peak G on DP voltammograms corresponding to the oxidation of the guanine residues, and a peak A corresponding to the oxidation of the adenine residues, and a peak A corresponding to the oxidation of the adenine residues. The potentials of the peaks G and A were not influenced by the G+C content in DNA and differed by 0.28 V. It was found that the ratio of the heights of the peaks A and G was identical with great accuracy to the ratio of the contents (adenine+thymine) and (G+C). This fact was exploited for developing a new method for the determination of the G+C content in DNA. The electrochemical oxidation of proteins at a spectroscopic graphite electrode impregnated with paraffin wax (WISGE) was studied by means of linear sweep, cyclic, and DP voltammetry. It was found that proteins were electrochemically oxidizable at the WISGE. They yielded a faradaic peak on voltammograms in the vicinity of 0.7–0.8 V in a neutral medium. The voltammetric study of proteins, poly-(aminoacids), peptides of known aminoacid composition and free aminoacids revealed that the irreversible electrooxidation of tyrosine (and, contingently, of tryptophan) residues is responsible for the appearance of the protein peak at the WISGE. It is suggested that DP voltammetry at a graphite electrode might become another electrochemical method suitable for studies of conformational changes of proteins, and in particular of those not containing cystine or cysteine (e.g. histones).

Interaction of nucleic acids with electrically charged surfaces

Adsorption and electrochemical oxidation of deoxyribonucleic acid (DNA) at a pyrolytic graphite electrode (PGE) and a paraffin wax-impregnated spectroscopic graphite electrode (WISGE) were studied using differential pulse voltammetry. DNA is adsorbed at the surface of the graphite electrodes in a broad range of potentials including the potentials of electrochemical oxidation of DNA. Both native and denatured DNAs yield two single, well-defined and separated peaks, G and A, on the differential pulse voltammograms at the PGE and WISGE. The more negative peak, G, corresponds to electrochemical oxidation of guanine residues, whereas the more positive peak, A, corresponds to electrochemical oxidation of adenine residues. Peaks G and A of native DNA occur at the same potentials as peaks G and A of denatured DNA. However, electrochemical oxidation of adenine and guanine residues at graphite electrodes is markedly suppressed in native DNA. The heights of the peaks G and A represent a sensitive indicator of the helix-coil transition of DNA. An analysis of the product of interaction of a sample of native DNA with a large pyrolytic graphite electrode in the presence of formaldehyde at approximately neutral pH did not prove changes in the secondary structure of native DNA due to its interaction with the graphite electrode. It is suggested that the decreased differential pulse-voltammetric activity of native DNA is connected with its decreased flexibility.

Combined sampling-analysis method for the determination of trace elements in atmospheric particulates.

A method is described in which spectroscopic graphite electrodes are used as filters for atmospheric particulates and are analyzed for several elements directly by an emission spectrographic method. The sampling system and the analysis method are described and an evaluation of the approach is presented. The results indicate that several elements can be accurately determined at atmospheric concentrations ranging down to the parts pcr billion level with minimal filter blank problems. (auth)

Combustion d'un carbone vitreux sous basses pressions d'oxygene

No fundamental difference is found in combustion kinetics of a non graphitizing vitreous carbon and of a spectroscopic graphite. After an initial degassing at high temperature, rates of combustion decrease in the same way; the relative rates of production of CO and CO 2 follow similar laws; apparent activation energies are for both approximately 50 kcal. mole −1. In agreement with other results, it was not possible to show any significant influence of the crystal structure on the carbon combustion.

The application of electron beam heating for the purification of spectroscopic graphite electrodes

The application of electron beam heating for the purification of spectroscopic graphite electrodes