Colorimetric Detection of Aliphatic Alcohols in β-Cyclodextrin Solutions

Abstract

The sensitive, selective, and practical detection of aliphatic alcohols is a continuing technical challenge with significant impact in public health research and environmental remediation efforts. Reported herein is the use of a β-cyclodextrin derivative to promote proximity-induced interactions between aliphatic alcohol analytes and a brightly colored organic dye, which resulted in highly analyte-specific color changes that enabled accurate alcohol identification. Linear discriminant analysis of the color changes enabled 100% differentiation of the colorimetric signals obtained from methanol, ethanol, and isopropanol in combination with BODIPY and Rhodamine dyes. The resulting solution-state detection system has significant broad-based applicability because it uses only easily available materials to achieve such detection with moderate limits of detection obtained. Future research with this sensor system will focus on decreasing limits of detection as well as on optimizing the system for quantitative detection applications.

Figure 1

Structure of alcohol analytes (1–3) and highly colored dyes (4 and 5).

Figure 2

Generated arrays for the detection of ethanol, isopropanol, and methanol with each cyclodextrin supramolecular host using BODIPY (4): (A) β-cyclodextrin, (B) methyl-β-cyclodextrin, and (C) 2-hydroxypropyl-β-cyclodextrin.

Figure 3

Generated arrays for the detection of ethanol, isopropanol, and methanol with each cyclodextrin supramolecular host using Rhodamine (5): (A) β-cyclodextrin, (B) methyl-β-cyclodextrin, and (C) 2-hydroxypropyl-β-cyclodextrin.

Figure 4

Electrostatic potential maps of (A) methanol, (B) ethanol, and (C) isopropanol. Red areas indicate regions of negative electron density, and blue areas indicate regions of positive electron density. These computations were done using Spartan version 18 computational software.

Figure 5

Linear discriminant analysis results obtained at 3.0 M analyte concentration for (A) BODIPY (4) and (B) Rhodamine (5). All results were obtained using Systat version 13 and following the procedures detailed in the Experimental Section.

Figure 6

Linear discriminant analysis results generated at lower analyte concentrations. (A) BODIPY (4) at 0.5 M concentration of the analyte; (B) BODIPY (4) at 1.0 M concentration of the analyte; (C) BODIPY (4) at 2.0 M concentration of the analyte; (D) Rhodamine (5) at 0.5 M concentration of the analyte; (E) Rhodamine (5) at 1.0 M concentration of the analyte; and (F) Rhodamine (5) at 2.0 M concentration of the analyte. All results were obtained using Systat version 13 and following the procedures detailed in the Experimental Section.

Figure 7

Lowest energy conformations of BODIPY (4) and Rhodamine (5) in 2-HP-β-CD. (A) Side view of the complex with BODIPY (4). (B) Aerial view of the complex with BODIPY (4). (C) Side view of the complex with Rhodamine (5). (D) Aerial view of the complex with Rhodamine (5). Color coding: for the cyclodextrin host, the dark blue color represents the carbon atoms, the red color represents the oxygen atoms, and the gray color represents hydrogen atoms. For BODIPY, the purple color represents carbon atoms, gray represents hydrogen, blue represents nitrogen, orange represents boron, and green represents fluorine. For Rhodamine, the teal color represents carbon, gray represents hydrogen, red represents oxygen, and dark blue represents nitrogen.

Figure 8

Lowest energy conformations of BODIPY (4) in 2-HP-β-CD following the introduction of methanol. The methanol is modeled as teal stick figures, and the colors of the BODIPY and cyclodextrin are identical to the colors used in Figure 7.

Figure 9

Colorimetric array of the 60 samples from the trial using dye 4 and analyte 3. The concentration of the analyte increases from left to right.