Studies on the supramolecular interaction between napropamide and β-cyclodextrin by spectrofluorimetry and its analytical application

Visible-light-mediated amidation from carboxylic acids and tertiary amines via C-N cleavage

In this communication, we report a photocatalyzed amidation strategy from carboxylic acids and tertiary amines through the C-N bond cleavage. A wide scope of structurally diverse carboxylic acids participates smoothly...

Inclusion of fluorophores in cyclodextrins: a closer look at the fluorometric determination of association constants by linear and nonlinear fitting procedures

The author discusses methods for the fluorometric determination of affinity constants by linear and nonlinear fitting methods. This is outlined in particular for the interaction between cyclodextrins and several anesthetic drugs including benzocaine. Special emphasis is given to the limitations of certain fits, and the impact of such studies on enzyme-substrate interactions are demonstrated. Both the experimental part and methods of analysis are well suited for students in an advanced lab.

Synthesis and Characterization of the Inclusion Complex of β-cyclodextrin and Azomethine

A β-cyclodextrin (β-Cyd) inclusion complex containing azomethine as a guest was prepared by kneading method with aliquot addition of ethanol. The product was characterized by Fourier Transform Infrared (FTIR) spectrometer, ¹H Nuclear Magnetic Resonance (¹H NMR) and Thermogravimetric Analyzer (TGA), which proves the formation of the inclusion complex where the benzyl part of azomethine has been encapsulated by the hydrophobic cavity of β-Cyd. The interaction of β-Cyd and azomethine was also analyzed by means of spectrometry by UV-Vis spectrophotometer to determine the formation constant. The formation constant was calculated by using a modified Benesi-Hildebrand equation at 25 °C. The apparent formation constant obtained was 1.29 × 10⁴ L/mol. Besides that, the stoichiometry ratio was also determined to be 1:1 for the inclusion complex of β-Cyd with azomethine.

Study on beta-cyclodextrin inclusion of Zn(II) aromatic complex and its analytical application

A new beta-cyclodextrin (beta-CD) inclusion compound Zn(2H1NA)(2)x 2beta-CD (2H1NA=2-hydroxy-1-naphthoic acid) was prepared. The structure was characterized by (1)H NMR, IR, the fluorescence spectra, thermogravimetric analysis (TG-DTA) and elementary analysis. Meanwhile, the mechanism of the formation of the supramolecular system (2H1NA:Zn(II):beta-CD) was studied and discussed by spectrofluorimetry. The results showed that the naphthalene rings of the Zn(II) aromatic complex Zn(2H1NA)(2) were encapsulated within the beta-CD's cavity to form a 2:1 stoichiometry host-guest compound. The inclusion constant calculated was 1.27 x 10(4)(L/mol)(2). A spectrofluorimetric method for the determination of 2H1NA in bulk aqueous solution in the presence of beta-CD was developed based on the great enhancement of the fluorescence intensity of 2H1NA. The linear relationship was obtained in the range of 9.00 x 10(-7) to 2.50 x 10(-5)mol/L and the detection limit was 8.00 x 10(-7)mol/L. The proposed method was successfully applied to determine 2H1NA in waste water with recoveries of 97-104%.

Acetylcholine detection at micromolar concentrations with the use of an artificial receptor-based fluorescence switch

An inclusion complex between water-soluble p-sulfocalix[n]arene (Cn, n=4, 6, 8) and the chromophore trans-4-[4-(dimethylamino)styryl]-1-methylpyridinium-p-toluenesulfonate (D) formed the basis for a highly sensitive sensor for the selective detection of neurotransmitter acetylcholine (ACh). Formation of the [Cn.D] complex (Ka=approximately 10(5) M(-1)) was accompanied by a drastic increase (up to 20-60-fold) in the chromophore relative quantum yield and by a large hypsochromic shift of the emission band maximum. The observed optical effects are fully reversible: ACh displaces the chromophore molecules from the calixarene cavity as shown by the reappearance of the free chromophore emission band. Formation and dissociation of the complex were studied by fluorescence, 1H NMR, and UV-vis absorption spectroscopies. The [Cn.D] complex is capable of sensing ACh selectively in solution at sub-micromolar concentrations. Immobilization of monocarboxyl p-sulfocalix[4]arene (C4m) on an oxide-containing silicon surface is in keeping with its properties, such as chromophore binding and the ability of the immobilized inclusion complex to detect ACh. The unique [Cn.D] complex optical switching paves the way for application in ACh imaging and optoelectronic sensing.

Simple determination of the herbicide napropamide in water and soil samples by room temperature phosphorescence

A new, simple, rapid and selective phosphorimetric method for determining napropamide is proposed which demonstrates the applicability of heavy-atom-induced room-temperature phosphorescence for analyzing pesticides in real samples. The phosphorescence signals are a consequence of intermolecular protection and are found exclusively with analytes in the presence of heavy atom salts. Sodium sulfite was used as an oxygen scavenger to minimize room-temperature phosphorescence quenching. The determination was performed in 1 M potassium iodide and 6 mM sodium sulfite at 20 degrees C. The phosphorescence intensity was measured at 520 nm with excitation at 290 nm. Phosphorescence was easily developed, with a linear relation to concentration between 3.2 and 600.0 ng ml(-1) and a detection limit of 3.2 ng ml(-1). The method has been successfully applied to the analysis of napropamide in water and soil samples and an exhaustive interference study was also carried out to display the selectivity of the proposed method.