Chromatic transition

Fig. 17.3 Chromatic transition of crystalline W03/CNT sheets, (a) Original state appear yellow colored states after applying -1.0 V for (b) 5 s, (c) 15 s and (d) 30 s. Reprinted with permission from [20], Copyright 2012, The Royal Society of Chemistry.

The chromatic transition was completely blocked by a-methyl sialoside, a soluble competitive inhibitor of the influenza virus, demonstrating that binding of the virus to the film was due to a specific carbohydrate-protein recognition event. This experiment demonstrated that the chromatic transition of the PDA backbone could be triggered by molecular recognition of a membrane surface ligand that was covalently attached to the polymerized lipid. 

Glycolipid incorporated liposomes have found extensive use as sensors for the detection of Escherichia coli bacteria. Liposomes prepared using a diacetylene and a glucosyl lipid underwent a chromatic transition upon the addition of E. coli (Ma et al. 1998). The chromatic transition is sensitive to the diyne and glycolipid stmc-ture (Ma et al. 2000). An optimized vesicle assembly, consisting of a maltotriosyl lipid, phospholipid, and diyne, detected E. coli at a concentration of 2x10 cells/mL... 

Liposomes prepared from diacetylene hydrazide 7 undergo chromatic transitions in response to pH changes (Jonas et al. 1999). Liposomes of 7, which form only in... 

Figure 12.9 Colorimetric bacterial fingerprinting. The color combination for each bacterium reflects the chromatic transitions (RCS) recorded 7 h after the start of growth at a bacterial concentration of 1 x lO /niL. The RCS color key is shown on the left (i) 1-a-dioleoylpho-sphatidylethanolamine (DOPE)/PDA (1 9 mole ratio), (ii) sphingomyelin/cholesterol/PDA (7 3 90), (iii) DMPC/PDA (1 9), and (iv) l-palmitoyl-2-oleoyl-j n-glycero-3-[phospho-rac-(l-glycerol)] (POPG)/PDA (1 9). Reprinted from Scindia et al. (2007). Copyright 2007 American Chemical Society. (See color insert.)...

Shim et al. 2004). When the NHS ester-containing liposomes are polymerized prior to immobilization on the glass, the blue liposomes turn red upon contact with the slide. However, if the liposomes are immobilized prior to polymerization and subsequently irradiated, the immobilized vesicles are blue and can undergo a subsequent chromatic transition in response to heat (Fig. 12.11). 

Polymers of thiophene carboxylic acids (9) undergo different chromatic transitions upon the addition of a variety of cations (McCullough et al. 1997). Although the acid form of the polymer was not water soluble, addition of various ammonium or metal... 

Polythiophenes functionalized with monosaccharides have been evaluated for their ability to detect the influenza virus and E. coli (Baek et al. 2000). Copolymers of thiophene acetic acid 10 and carbohydrate-modified thiophenes 11 have been prepared via iron(III) chloride mediated polymerization. Addition of influenza virus to a sialic acid containing copolymer resulted in a blue shift of the polymer absorption maximum, resulting in an orange to red chromatic transition. Mannose-containing polythiophenes underwent color changes upon the addition of the lectin ConA or E. coli cells that contain cell surface mannose-binding receptors. A similar biotinylated pol5hhiophene afforded a streptavidin responsive material (Paid and Leclerc 1996). 

Polythiophene binding to a sequence of DNA capable of forming a G-quartet was demonstrated (Ho and Leclerc 2004). Addition of polythiophene 12 to the single-stranded DNA resulted in a chromatic transition from yellow to pink/red. 

Cheng Q, Stevens RC. Charge-induced chromatic transition of amino acid-derivatized polydiacetylene liposomes. Langmuir 1998 14 1974-1976. 

Cheng Q, Yamamoto M, Stevens RC. Amino acid terminated polydiacetylene lipid microstmc-tures morphology and chromatic transition. Langmuir 2000 16 5333-5342. 

Geiger E, Hug P, Keller BA. Chromatic transitions in polydiacetylene Langmuir-Blodgett films due to molecular recognition at the film surface studied by spectroscopic methods and surface analysis. Macromol Chem Phys 2002 203 2422-2431. 

Song J, Cheng Q, Kopta S, Stevens RC. Modulating artificial membrane morphology pH-induced chromatic transition and nanostructural transformation of a bolaamphiphilic conjugated polymer from blue helical ribbons to red nanofibers. J Am Chem Soc... 

Summarizing, thermochromism only occurs above the glass temperature in amorphous polymer solids, and above the melting temperature for crystalline polymers [45], The crystallization of side chains, which may or may not occur, is not a necessary condition for the thermochromic transition. A more crucial requirement for thermochromism is that of the necessary level of regioregularity of the polymer. This will help define the local geometry of the polymer, which is crucial for the optical properties. Long-range order, like that found in crystalline phases, is not necessary for expression of the chromatic transitions. 

Electrochromism is a phenomenon displayed by some materials reversibly changing colors. Various materials can be used to construct electrochromic devices, such as transition metal oxides, liquid crystals, photonic crystals, and polymers (Booth and Casey, 2009 Nicoletta et al., 2005 Arsenault et al., 2007 Gamier et al., 1983). Here, we will focus on the electrochromic materials based on polymers. There are several mechanisms to explain the color changes of polymer electrochromic materials like electro-induced oxidation-reduction and electrothermal chromatic transition and so on. 

Another mechanism to realize electrochromism is electrothermal chromatic transition. Electricity is much easier to control compared to heat and most of the conductive materials, including many metals and conjugated polymers, can generate heat upon pass of electric current. Electrochromic device based on the electrothermal mechanism is generally composed of chromic and electrically conducting layers. 

On the other hand, despite interesting studies of visual titrations in acetic acid medium, in actual practice, crystal violet and methyl violet, which exhibit identical color changes, are by far the most widely used indicators. This is probably because their two chromatic transitions in acetic acid cover an unusually large potential range of 200 or 300 mV. However, in titrations of bases with pXb>6.8, the endpoint of crystal violet is assigned to a color that is not in agreement with the complete chromatic transition. Consequently, the visual endpoint location is difficult and depends on the base to be titrated and also on its concentration. 

Another critical aspect that must be considered for selection of a suitable indicator for an acid-base titration in a given solvent is the quality of color change of the indicator in this solvent. The quality of color change is related to the sharpness of the chromatic transition and to the sensitivity of the color change. 

Amino acid-terminated anq>hiphilic and bolaanq)hiphilic diacetylene lipids were synthesized and assembled to form microstructures of varied morphologies. UV irradiation of the assemblies leads to conjugated polymers with unique optical properties. Chromatic transition of polydiacetylene materials in response to pH and thermal effect and their morphological transformation upon lipid doping are discussed. 

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