Hydrophobicity pyrene

Adsorption onto colloidal polystyrene results in very different behavior because of the hydrophobic nature of that surface. The addition of even a small amount of polystyrene particles to the polymer solution results in the complete disappearance of the excimer emission (Figure 6). In this case, the hydrophobic pyrene groups are strongly attracted to the polystyrene surface thus, the formation of excimers is precluded. A similar disappearance of the excimer was observed upon complexation with PMAA, a result indicating that the hydrophobic character of that polymer may hinder the formation of excimers by adsorbing the pyrene groups into a hydrophobic pocket. This observation is further supported by the fluorescence excitation spectra, presented in the next section. 

In 1993, Frdchet and coworkers demonstrated that den-drimers with hydrophilic surface groups were able to render hydrophobic pyrene molecules soluble in aqueous conditions by encapsulation. Related encapsulation phenomena have been observed for the inclusion of chromophores within hyperbranched polymers. ... 

A-(l-Phenylalanine)-4-(l-pyrene)butyramide, shown in Fig. 8, has been found able to recognize and bind to specific sites of proteins and to cleave the protein backbone by laser flash photolysis, reported by Kumar et al. [144]. This molecule is composed of the hydrophilic phenylalanine carboxyl group and the hydrophobic pyrene group as a consequence, this molecule appears to lodge only in the sites of a protein where a hydrophilic pocket is very close to a hydrophobic pocket. 

Despite the abundance of information retrieved about the behavior of the hydrophobic pyrene labels of Py-WSPs by monitoring the parameters /1//3, Tm, e/ m> Pa< e> Ae Me+ presented above, it is remarkable that all these... 

Associative Behavior of Pyrene Singly (Pyj-PEO) and Doubly (Py2-PEO) End-Labeled PEOs Due to their similarity to HEURs, namely a stretch of linear PEO terminated at both ends with a hydrophobe, the hydrophobic associations induced by pyrene doubly labeled PEOs have been under scientific scrutiny for more than three decades. In 1982, Winnik reported that an aqueous solution of a 9.6K PEO chain end capped with 1-pyrenebutyric acid yielded an unexpectedly high 7e//m ratio compared to the value obtained in 10 organic solvents [64]. This result represented a solid evidence that hydrophobic associations were taking place in water between the hydrophobic pyrene labels of Py2-PEO(9.6K). The demonstration that pyrene excimer fluorescence reflected the level of hydrophobic associations between the pyrene labels of Py2-PEO led to further and more detailed investigations. 

At salt concentrations lower than the the value of /1//3 depends on the nature of the modified polymer. For the polymer 3-C12 this value is very close to that measured in pure water, but decreases slightly for the 3-C14 and significantly for the 3-C18. It seems that the pyrene experiences a more hydro-phobic environment even before the onset of the hydrophobic aggregation. One can ascribe this result to the fact that the hydrophobic pyrene probe lies preferably close to the nonpolar alkyl chain than in the bulk solution. 

Hemoglobin is another heme-containing protein, which has been shown to be active towards PAH, oxidation in presence of peroxide [420], This protein was also modified via PEG and methyl esterification to obtain a more hydrophobic protein with altered activity and substrate specificity. The modified protein had four times the catalytic efficiency than that of the unmodified protein for pyrene oxidation. Several PAHs were also oxidized including acenaphthene, anthracene, azulene, benzo(a)pyrene, fluoranthene, fluorene, and phenanthrene however, no reaction was observed with chrysene and biphenyl. Modification of hemoglobin with p-nitrophenol and p-aminophenol has also been reported [425], The modification was reported to enhance the substrate affinity up to 30 times. Additionally, the solvent concentration at which the enzyme showed maximum activity was also higher. Both the effects were attributed to the increase in hydrophobicity of the active site. 

SCHEME 29. Syntheses of glycodendrons with hydrophobic and fluorescent pyrene head-groups for n—n... 

Pyrene was used as a fluorescent probe to sense various hydrophobic sites in the microheterogeneous architecture offered by PAMAM dendrimers, possessing an ammonia core and sodium carboxylated surface (Gn.5, n = 0-9) [17]. The IJIi ratio of pyrene in the presence of low generations (G0.5-G3.5) remained very similar to those in pure water. In the presence of higher generation dendrimers, however, pyrene sensed a more hydrophobic outer surface which was presum-... 

Because mirex is a very hydrophobic compound with a low vapor pressure, atmospheric transport is unlikely (Hoff et al. 1992). These authors reported detecting mirex in only 5 of 143 samples at a maximum and mean concentration of 22 pg/m and 0.35 pg/m, respectively. Based on a vapor pressure of <3x10 mm Hg at 25 °C, mirex is expected to exist mainly in the particulate phase with a small proportion existing in the vapor phase in the ambient atmosphere (IARC 1979c). A mass balance approach to the movement of mirex within Lake Ontario indicates that 5% of the total input of mirex to the lake can be attributed to atmospheric deposition compared with 72% of benzo(a)pyrene (Arimoto 1989). 

Fig. 1.5. Examples of hydrophobic, hydrophilic and amphiphilic probes. 1 pyrene. 2 8-hydroxypyrene-l,3,6-trisulfonic acid, trisodium salt (pyranine). 3 8-alkoxypyrene-l,3,6-trisulfonic acid, trisodium salt. 4 1-...

Vanderkoi J. M. and Callis J. B. (1974) Pyrene. A Probe of Lateral Diffusion in the Hydrophobic Region of Membrane, Biochemistry 13, 4000—4006. 

J. M. Vanderkooi and J. B. Callis, Pyrene. A probe of lateral diffusion in the hydrophobic region of membranes, Biochemistry 13, 4000-4007 (1974). 

H.-J. Galla and E. Sackmann, Lateral diffusion in the hydrophobic region of membranes Use of pyrene excimers as optical probes, Biochim. Biophys. Acta 339, 103-115 (1974). 

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