Classification of the mode of inhibition of high-affinity choline uptake using capillary electrophoresis with electrochemical detection at an enzyme-modified microelectrode

Synthesis and characterization of luminescent cadmium selenide/zinc selenide/zinc sulfide cholinomimetic quantum dots

Luminescent quantum dots conjugated with highly selective molecular recognition ligands are widely used for targeting and imaging biological structures. In this paper, water soluble cholinomimetic cadmium selenide (core), zinc selenide/zinc sulfide (shell) quantum dots were synthesized for targeting cholinergic sites. Cholinomimetic specificity was incorporated by conjugation of the quantum dots to an aminated analogue of hemicholinium-15, a well known competitive inhibitor of the high affinity choline uptake transporter. Detailed evaluation of the nanocrystal synthesis and characterization of the final product was conducted by (1)H and (31)P NMR, absorption and emission spectroscopy, as well as transmission electron microscopy.

Combined use of chiral ionic liquid and CD for MEKC: Part II. Determination of binding constants

A competitive inhibition mechanism is proposed to investigate the interactions among 2,3,6-tri-O-methyl-beta-CD (TM-beta-CD), cationic ionic liquid type surfactants, N-undecenoxy-carbonyl-L-leucinol bromide (L-UCLB) and profens using affinity CE. The apparent binding constant of TM-beta-CD to L-UCLB was estimated by nonlinear and linear plotting methods. The binding constants of one representative profen (e.g. fenoprofen) to TM-beta-CD and L-UCLB were estimated by a secondary plotting approach. The R- and S-fenoprofens have different binding constant values, resulting in the enantioseparation due to the synergistic effect of the two chiral selectors, TM-beta-CD and L-UCLB.

Electrocatalytic microelectrode detectors for choline and acetylcholine following separation by capillary electrophoresis

Two electrocatalytic enzyme modified microelectrode systems were employed as end-column amperometric detectors of choline (Ch) and acetylcholine (ACh) following separation by capillary electrophoresis (CE). Horseradish peroxidase cross-linked in an osmium based redox polymer hydrogel (HRP-Os) was physically adsorbed on Au microelectrodes followed by chemical cross-linking of the enzymes acetylcholinesterase (AChE) and choline oxidase (ChO). An alternative approach utilized the deposition of the transition metal catalyst, Prussian Blue (PB), on Pt microelectrodes as the electrocatalyst. Utilizing butyrylcholine (BuCh) as an internal standard, the HRP-Os/AChE-ChO and PB/AChE-ChO electrodes exhibited excellent linear responses from 2-2000 microM and 10-2000 microM, respectively, for both Ch and ACh. Detection limits of 0.1 microM or 38 amol were determined for the HRP-Os/AChE-ChO electrode. The limit of detection for ACh and Ch at the PB/AChE-ChO electrode was 5 microM or 9.5 fmol. The electrodes were operated at potentials of +0.10 and -0.10 V vs Ag/AgCl (3 M NaCl), respectively, and thus minimized the potential response from oxidizable interferences. In addition, both electrocatalytic electrodes showed good operational stability for more than 70 h. The enhanced detection capability of the HRP-Os/AChE-ChO and PB/AChE-ChO electrodes in combination with efficient CE separation of Ch and ACh provides a new sensitive and selective strategy for monitoring and quantifying these cholinergic biomarkers in biological fluids.

Inhibition of choline transport by redox-active cholinomimetic bis-catechol reagents

Both N,N'-(2,3-dihydroxybenzyl)-N,N,N',N'-tetramethyl-1,6-hexanediamine dibromide (DTH, 6) and N,N'-(2,3-dihydroxybenzyl)-N,N,N',N'-tetramethyl-1,10-decanediamine dibromide (DTD, 7), which are symmetrical bis-catechol substituted hexamethonium and decamethonium analogues, respectively, were found to inhibit high-affinity choline transport in mouse brain synaptosomes. Inhibitory properties were evaluated using an extraordinarily sensitive capillary electrophoresis method employing electrochemical detection at an enzyme-modified microelectrode. Dose-response curves were generated for each inhibitor and IC(50) values were determined to be 76 microM for 6 and 21 microM for 7. Lineweaver-Burk analysis revealed that both molecules inhibit high-affinity choline uptake by a mixed inhibition mechanism. The K(I) values for 6 and 7 were determined to be 73+/-1 and 31+/-2 microM, respectively. The inhibition properties were further compared to a series of mono-catechol analogues, 3-[(trimethylammonio)methyl]catechol (1), N,N-dimethylepinephrine (4) and 6-hydroxy-N,N-dimethylepinephrine (5), as well as the well-characterized hemicholinium inhibitors, hemicholinium-15 (HC-15, 8) and hemicholinum-3 (HC-3, 9).