Utility of π‐Acceptors in Alkaloid Assay

Abstract

The interaction of alkaloids with selected polyhaloquinone and polycyanoquinone n-acceptors was found to yield intensely coloured radical ions. This finding was developed into a sensitive spectrophotometric assay for alkaloids of general applicability and with adequate accuracy and precision. 7,7,8,8-Tetracyanoquinodimethane is used as the reagent. Anwendung von rr-Acceptoren zur quantitativen Analyse von AlkaloidenAkaloide geben mit rr-Acceptoren vom Typ der Polyhalogenchinone und Polycyanochinone intensiv gefirbte Radikal-Anionen. Auf Grund dieser Reaktion wurde eine allgemein anwendbare, empfindliche photometrische Bestimmungsmethode fur Alkaloide entwickelt, die auf der Umsetzung mit 7,7,8,8-Tetracyanochinondimethan beruht.n-Acceptors, such as tetracyanoethylene (TCNE), 7,7,8,8-tetracyanoquinodimethane (TCNQ), chloranil and 2,3-dichloro-5,6-dicyanoquinone (DDQ) are known to yield charge-transfer complexes and radical ions with a variety of electron donors which include amines' -'). This donor-acceptor interaction has not been investigated hitherto for alkaloids as a group of n-electron donors which were recently demonstrated to participate in charge-transfer complexation with iodine4-'). Furthermore, relatively few previous publications concerned the analytical applications of this interaction, and were mainly centered on indoles and aromatic amines with TCNE'-'').

Spectrophotometric methods based on charge transfer complexation reaction for the determination of some antifungal drugs in pure and dosage forms

“…The dissociation of the (D-A) complex was promoted by the high ionizing power of the polar solvent and the resulting peaks in the absorption spectra of D-acceptor reaction mixtures were similar to the maxima of the radical anions of the acceptors obtained by the iodide reduction method [22].…”

“…Polar solvents such as acetonitrile and alcohols were found to be unsuitable as their blanks with iodine gave high absorbance. It is obvious that, the rate of transformation of the outer complex to inner complex is in the order of 1,2-dichloroethane > dichloromethane > chloroform [22]. There is actually a considerable decrease in the energy of activation along with an increased dielectric constant ε r of the medium; in 1,2-dichloroehane (ε r = 10.2) the transformation of inner complex proceeds much faster than that in dichloromethane (ε r = 9.1) and chloroform (ε r = 4.8).…”

A novel analytical approach for reducing the consumption of organic solvents in the charge transfer-based spectrophotometric analysis: Application in the analysis of certain antihypertensive drugs

“…Dissociation of the (D-A) complex was promoted by the high ionizing power of the polar solvent and the resulting peaks in the absorption spectra of drug-acceptor reaction mixtures were similar to the maxima of radical anions of the acceptors obtained by the iodide reduction method (15). …”

“…Further support to this assignment was provided by the absorption maxima with those of the DDQ radical anion produced by the iodide reduction method (15). Dissociation of the (D-A) complex was promoted by the high ionizing power of the polar solvent and the resulting peaks in the absorption spectra of drug-acceptor reaction mixtures were similar to the maxima of radical anions of the acceptors obtained by the iodide reduction method (15).…”

High throughput microwell spectrophotometric assay for olmesartan medoxomil in tablets based on its charge-transfer reaction with DDQ

“…2). This band was attributed to the formation of the radical anion DDQ - (21), which was probably formed by the dissociation of an original donor-acceptor (D-A) complex: (19) demonstrated that the interaction of electron donors with DDQ in polar solvents (e.g., methanol and acetonitrile) produced CT complexes with molar absorptivity values higher than those produced in non-polar sol- vents (e.g., chloroform). Different polar solvents were tested to prepare the DDQ solution: methanol, ethanol, 1-propanol, 1-butanol, and acetonitrile.…”