Color Change Indicators for Molecules Using Methyl Red-Modified Cyclodextrins

Abstract

β-Cyclodextrin derivatives, MRCD and p-MRCD, which have a 4-(dimethylamino)azobenzene moiety with a carbonyl substituent at 2′ and 4′ positions, respectively, have been prepared as color change indicators for detecting organic compounds. In a 10% ethylene glycol solution, MRCD and p-MRCD form intramolecular self-complexes in which the pendant dye moiety is included in the cyclodextrin cavity with an orientation parallel and perpendicular to the cyclodextrin axisis, respectively. When guest molecules are added to the acidic solutions of MRCD (pH 1.60) and p-MRCD (pH 2.40), they exhibit color changes from yellow to red for MRCD and from orange to red for p-MRCD. These color changes, which arise from the structural change of the dye moieties from the azo form to the azonium one, are caused when MRCD and p-MRCD undergo a conformational change in which the dye moieties inserted in the cyclodextrin cavities are excluded to outside of the cavities upon guest accommodation. The extent of the guest-induced color changes of MRCD and p-MRCD depend on the shape, size, number, and position of the functional group of guest molecules. Selectivities between MRCD and p-MRCD in guest detection are roughly parallel and reflected in the host-guest binding constants. Among guest molecules examined, ursodeoxycholic acid and chenodeoxycholic acid were detected by MRCD and p-MRCD with high sensitivities. 1-Adamanetanecarboxylic acid and (-)borneol were also detected with high sensitivities. In neutral conditions, however, the selectivity in guest detection of p-MRCD is different from that in acidic conditions as shown by the fact that, for example, 1-adamantanol and 2-adamantanol were detected by p-MRCD with larger sensitivities than 1-adamanetanecarboxylic acid. The result indicates that the ionic nature of the guest molecules is an important factor for detection of the guest molecules. All these results demonstrate that MRCD and p-MRCD can be used as color change indicators for detecting various organic compounds in aqueous solution.

Substituent effects on absorption spectra of pH indicators: An experimental and computational study of sulfonphthaleine dyes

“…These values are compared to calculated vertical absorption energies E vert . The molecules of the test set ( Figure 1) can be divided into three types: those with electron donating substituents (2-5); with electron withdrawing substituents (6,7) and those with both electron donating and withdrawing groups (8)(9)(10). The UV/Vis spectra of dyes 2 and 6 are included in Figure 3 as examples of dyes with electron donating and electron withdrawing substituents, respectively.…”

“…[3] The most exploited chromic types are thermochromism and photochromism, [4,5] but halochromism (pH sensitivity) is also increasingly studied and put into practice. [6][7][8][9][10][11][12] Our main interest lies in the possible application of halochromic dyes in pH-responsive polymers, or more precisely intelligent textiles. This is part of a larger research field, namely functionalized polymers.…”

Aromatic Diamino-bridged Bis(β-cyclodextrin) as Fluorescent Sensor for the Molecular Recognition of Bile Salts

“…[1][2][3] The introduction of fluorophore sidearms to the CD framework not only provides additional binding sites but the sidearms are also capable of acting as fluorescent sensors with some optically silent guest molecules. [4][5][6] Possessing two appropriately located hydrophobic CD cavities in the same molecule, bis(β-CD)s feature very high binding ability and molecular selectivity for specific ditopic guests through the cooperative two-point recognition.…”

The Effect of the Electron Density Distribution of Guest on the Entropy Change During Complex Formation of Calix[]arene Hexasulfonate Host with ortho- and para-cresols as Guests

“…They show versatile recognition properties towards metallic or organic ions and neutral molecules [3][4][5]. Their thermodynamic [6] and redox properties [7], the extent of their metal ion binding character in solutions [8,9], and their wide applications in analytical and separation sciences have recently been reviewed [10][11][12].…”