Chemistry Reference
In-Depth Information
Studies with liposomes prepared using amino acid terminated diacetylenes indicate
that head-group rearrangements are capable of triggering lipid conformational changes,
which in turn perturb the conformation of the PDA backbone (Cheng and Stevens
1998). These amino acid terminated diacetylenes can also self-assemble into fibrous
structures under different conditions (Cheng et al. 2000). These fibers can be polymer-
ized to provide a blue colored material that undergoes chromatic transitions upon
changes in pH or temperature. The IR spectra of these materials indicate that different
mechanisms of chromatic transition may be operative in the thermochromatic and
pH-dependent responses.
12.2.1. Glycolipids
Despite the rich chemistry of the diacetylenes, their application in chemical and
biological sensing was not extensively explored before a seminal report in 1993
describing the use of solid-supported PDA monolayers for colorimetric detection
of the influenza virus (Charych et al. 1993; Fig. 12.2). A Langmuir-Blodgett
monolayer containing diyne acid 1 and sialolipid 2 was prepared on a glass slide
and subsequently irradiated to provide a blue film. The viral surface was coated
with a lectin (a carbohydrate-binding protein) that recognizes sialic acid residues.
Consequently, incubation of the coated slides in a solution of the X31 influenza A
virus resulted in a color change of the film from blue to red, as shown in
Figure 12.3a. The magnitude of this color change could be quantified by determining
the colorimetric response (CR value). The CR value is calculated from the ratio of the
Figure 12.2 Structures of glycolipids and other lipids used in polydiacetylene sensors.
