Biomedical subjects

J R Kirchhoff

Publications and source records attributed to J R Kirchhoff.

6 recordsLinked to original sources

PubMed1996

6-Hydroxycatecholine, a choline-mimicking analogue of the selective neurotoxin, 6-hydroxydopamine.

The synthesis and properties of 6-hydroxy-N,N-dimethylepinephrine (6-hydroxy-catecholine) are reported. This agent is intended for use as a selective presynaptic cholinotoxin and is based on previously reported neurotoxins of the same type. 6-hydroxycatecholine is a close structural analogue of the catecholaminergic neurotoxin 6-hydroxydopamine, and is expected both to be selectively reactive at cholinergic sites and to undergo less vigorous and potentially more selective inactivating reactions. It is also possible that in specific dementia-inducing pathologies, 6-hydroxycatecholine could be formed endogenously.

Cholinergic Antagonists↗

PubMed1996

Dual-electrode detection for capillary electrophoresis/electrochemistry.

The extremely low sample volumes required for capillary electrophoresis and the high sensitivity and selectivity of electrochemical detection make capillary electrophoresis/electrochemistry (CEEC) a very useful method for bioanalysis. In this paper, two types of dual-electrode detectors for CEEC are described. The first employs a ring-disk microelectrode placed in a wall-jet configuration and is used for the selective detection of substances undergoing chemically reversible oxidations. Collection efficiencies obtained for catecholamines with this configuration were between 25 and 35%. The second electrode design consists of two adjacent carbon fibers embedded in an epoxy matrix and is analogous to the parallel dual-electrode configuration used in liquid chromatography/electrochemistry. This configuration can be used to confirm peak identity and purity by operating the electrodes at two different potentials. Alternatively, it is possible to perform simultaneous oxidative and reductive electrochemical detection.

Catecholamines↗

PubMed1995

Chemical vapor deposition fabrication and characterization of silica-coated carbon fiber ultramicroelectrodes.

Carbon fiber disk ultramicroelectrodes (UMEs) with well-defined geometries were prepared by chemical vapor deposition techniques. Transparent silica films with thicknesses from 1 to 600 microns were deposited on the cylindrical length of 5 and 10 microns carbon fibers from a SiCl4, H2, and O2 ternary precursor system at 850-1150 degrees C or sequential deposition from Si(OEt)4 as a single source precursor at 700 degrees C followed by the SiCl4, H2, and O2 precursor system. Film thickness, film adhesion to the fiber substrate, and the overall dimensions of the silica-coated carbon fiber were studied and found to be a function of the precursor system, precursor concentrations, fiber diameter, deposition time, and fiber temperature. The silica films were found to be free of microcracks and characterized by a quality seal between the carbon fiber and the coating. As a result, the silica-coated disk UME exhibits an excellent electrochemical response without the need to use an epoxy sealant at the electrode tip. Furthermore, the deposition of hard and inert ceramic materials imparts durability to fragile carbon fibers and facilitates the handling of UMEs in microenvironments. Finally, the advantage of concentric deposition about the fibers to produce a disk UME in the center of an insulating plane was used to examine the effect of the thickness of the insulating coating on the limiting current response.

Carbon↗

PubMed1995

High performance liquid chromatographic separation and pH-dependent electrochemical properties of pyrroloquinoline quinone and three closely related isomeric analogues.

Pyrroloquinoline quinone 1 (PQQ, methoxatin, 4,5-dihydro-4,5-dioxo-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid) is a novel coenzyme. Closely related isomeric analogues of PQQ may be formed in nature and may possess PQQ-like functions. Here, the electrochemical pH-dependent properties and the high performance liquid chromatographic (HPLC) separation protocols are reported for three major isomeric PQQ analogues likely to be formed in nature. The electrochemical data (cyclic voltammetry) provided the pKas of the five ionizable groups in each isomeric PQQ. The HPLC protocols provide the means of investigating the formation of PQQ and the PQQ isomers reported here during the normal turnover of eukaryotic amine oxidases containing integral topaquinone residues, as well as from direct enzyme-mediated reactions which remain to be characterized.

Chromatography, High Pressure Liquid↗

PubMed1995

Carbon ring-disk ultramicroelectrodes.

Novel ring-disk ultramicroelectrodes (RD-UMEs) with analytical tip diameters as small as 25-30 microns were fabricated. Carbon RD-UMEs were reproducibly prepared by the chemical vapor deposition of alternating concentric layers of silica and carbon on resistively heated 10 microns carbon fibers. High-quality films with excellent adhesion at the interfaces between the carbon and silica layers were shown by electrochemical and scanning electron microscopy measurements. Electrochemical measurements of a solution of 1.0 mM ferrocene with 200 mM LiClO4 in CH3CN were used to characterize the single- and dual-electrode response lf the RD-UME. The electrochemical responses of the ring and the disk are sigmoidal in shape and indicated that radial diffusion is the primary mode of mass transport at each electrode at slow scan rates. Diffusion-controlled generation-collection experiments showed that the concentric dual-electrode configuration exhibits high collection efficiencies at the ring electrode with a 2-5 microns separation between electrodes and a 2-4 microns ring thickness. Close proximity of the ring and disk electrodes led to enhanced detection sensitivity due to back diffusion of regenerated molecules of a reversible redox couple from the collector to the generator electrode.

Carbon↗

PubMed1994

Mechanism of action of the redox affinity reagent [(trimethylammonio)methyl]catechol.

The synthesis of 4- and 5-hydroxy-3-[(trimethylammonio)methyl]catechol (4- and 5-HTMC) was carried out to examine their proposed involvement as intermediates in the spontaneous redox-dependent half-of-sites inactivation of neurotoxin binding sites in the nicotinic acetylcholine receptor (nAcChR) mediated by the parent compound 3-[(trimethylammonio)methyl]catechol (TMC) [Nickoloff et al. (1985) Biochemistry 24, 999-1007]. Oxidation of 4- and 5-HTMC occurred with sodium periodate with facile conversion to the corresponding p-quinones which were intercepted with thiols and cyclopentadiene. Both 4- and 5-HTMC inactivated neurotoxin binding in the nAcChR in a time course and over a concentration range consistent with their involvement as intermediates in the TMC redox-dependent inactivation of neurotoxin ([125I]-alpha-bungarotoxin) binding sites. Rapid concentration-dependent inactivation of neurotoxin sites occurred over a 10-1000 microM range and was resistant to further inactivation after 50% loss of available toxin binding sites on the nAcChR. Both 4- and 5-HTMC inactivated nAcChR neurotoxin sites much more rapidly and efficiently than was observed previously with TMC. The apparent binding constants for 4- and 5-HTMC with the nAcChR, calculated from their concentration-dependent inactivation behavior toward toxin binding sites, were Kd = 224 +/- 98 and 39 +/- 17 microM, respectively. The observed results and the redox potentials (vs Ag/AgCl reference electrode) measured by cyclic voltammetry at pH 1.8 for TMC (719 mV) and the 4- and 5-HTMC derivatives (519 and 443 mV, respectively) supported the previously proposed mechanism for inactivation of the nAcChR by TMC.(ABSTRACT TRUNCATED AT 250 WORDS)

Benzalkonium Compounds↗