Fluorescence zwitterions

It should be noted that no emission from the zwitterionic form of the proton-transferred tautomer was observed from any of the benzotriazoles studied in the present work. This implies that non-radiative relaxation processes from the excited state of this species are very efficient in all of the solvent and polymer environments studied. Thus no information is available on the effect of the medium polarity on the room-temperature photophysics of the zwitterionic form using fluorescence techniques. 

Aggregation of pseudoisocyanine (dye I, Fig. 3) and 5,5 -dichloro-3,3 -diethyl-9-phenylthiacarbocyanine chloride (dye II, Fig. 5) induced by the vesicles consisting of zwitterionic DMPC and anionic DCP (Fig. 6) lipids was studied in [28]. Both dyes were shown to form fluorescent J-aggregates upon addition of the vesicles formed of the mixture of DMPC and DCP with relative content equal to 1 1. At the same time, for both dyes pure DMPC vesicles did not induce the J-aggregation. Upon addition of the vesicles containing DMPC and DCP in the 4 1 ratio, as well as... 

Another photochemically driven proton transfer occurs in the system 46. This molecule on sublimation at low temperatures crystallizes in form 46a having infinite chains of intermolecular hydrogen bonds connecting zwitterionic molecules. Its fluorescence at such temperatures is essentially that of the acridinium ion. However, on prolonged UV irradiation, conversion to 46b occurs and the... 

The fluorescence decay parameters of tyrosine and several tyrosine analogues at neutral pH are listed in Table 1.2. Tyrosine zwitterion and analogues with an ionized a-carboxyl group exhibit monoexponential decay kinetics. Conversion of the a-carboxyl group to the corresponding amide results in a fluorescence intensity decay that requires at least a double exponential to fit the data. While not shown in Table 1.2, protonation of the carboxyl group also results in complex decay kinetics.(38)... 

Carbohydrate detection is important for applications such as glucose monitors these are arguably one of the most successful and relevant biosensors. An interesting fluorescence recovery-type saccharide sensor based on the reactivity of carbohydrates with boronic acids was reported in 2002 [36]. Specifically, modification of the cationic viologen-linked boronic acid derivative 40 to a zwitterionic species 41 upon covalent and reversible reaction of boronic acid with monosaccharides (Scheme 1) can cause the dissociation of the ion-pair in-... 

A number of studies on the fluorescence decay of tyrosine, tyrosine derivatives, and small tyrosyl peptides have been carried out. 36-38 Whereas the tyrosine zwitterion and tyrosine derivatives with an ionized a-carboxy group exhibited monoexponential fluorescence decay (x = 3.26-3.76 ns), double- or triple-exponential decay was observed in most other cases. As in the case of the tryptophan model compounds, the complex decay kinetics were again interpreted in terms of rotamer populations resulting from rotation around the C —Cp bond. There is evidence to indicate that the shorter fluorescence lifetimes may arise from rotamers in which the phenol ring is in close contact with a hydrated carbonyl group 36 37 and that a charge-transfer mechanism may be implicated in this quenching process. 39 ... 

Polyamide microcrystalline powders form measurable polymer-bound fluorescent reaction products with malonaldehyde from oxidizing lipids and with reducing sugars. The compounds form on the terminal amine groups which appear to exist in zwitterionic fields with carboxylate anions, as revealed by titration with acid, alkali, or benzoquinones. 

The interactions of TDZ (6) with model membranes composed of different phospholipids were also studied by the same group [78]. Calorimetric studies demonstrated that TDZ (6) altered the thermotropic properties of negatively charged DMPC membranes to a larger extent than of zwitterionic phospholipids (PC and PE). The character of the drug-induced changes of the transition parameters of all studied lipids indicated that TDZ (6), similarly to other phenothiazine derivatives, was likely to be localized close to the po-lar/apolar interface of the bilayers. Experiments in which fluorescent probe 1,6-diphenyl-1,3,5-hexatriene (DPH) was employed revealed that TDZ (6) reduced the mobility of lipid molecules in a concentration-dependent manner and thus decreased membrane fluidity. The influence of TDZ (6) on isolated... 

Zwitterionic cyclodextrins were designed and synthesized by Tabushi a long time ago as artificial receptors for amino acids in water [25]. Only a very low enantioselectivity was detected for Trp. Inoue also studied the complexation of two new P-cyclodextrin derivatives bearing m-toluidinyl and [(9-fluorenyl)-amino]alkylamino groups with various D/L-amino acids by fluorescence spectroscopy in buffered (pH=7.2) aqueous solution. An enantioselectivity as high as 33 was found for D/L-leucine and the former host [26]. 

In cases uncomplicated by quenching effects d)0 and d 0 values can be taken as the limiting value of the true fluorescence intensities at 2 or 3 pH units away from the half way point of the fluorescence change. The relative intensities (/0 and / 0) in the intermediate region can then be plotted against acidity. Figure 3 gives a plot of this type for the cation and zwitterion of 3-hydroxy quinoline... 

Figure 3. Acid dependence of 3-hydroxyquinoline fluorescence intensity cation (O) zwitterion ( ) (Haylock et al., 1963).

Ma, J. and Zimmt M.B., Equilibration between the fluorescent and zwitterionic phantom states in alkyl-substituted tetraphenylethylenes. J. Am. Chem.SOc. (1992) 114 9723-9724. 

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