Relative hydrophobicity

Cyclodextrins are macrocyclic compounds comprised of D-glucose bonded through 1,4-a-linkages and produced enzymatically from starch. The greek letter which proceeds the name indicates the number of glucose units incorporated in the CD (eg, a = 6, /5 = 7, 7 = 8, etc). Cyclodextrins are toroidal shaped molecules with a relatively hydrophobic internal cavity (Fig. 6). The exterior is relatively hydrophilic because of the presence of the primary and secondary hydroxyls. The primary C-6 hydroxyls are free to rotate and can partially block the CD cavity from one end. The mouth of the opposite end of the CD cavity is encircled by the C-2 and C-3 secondary hydroxyls. The restricted conformational freedom and orientation of these secondary hydroxyls is thought to be responsible for the chiral recognition inherent in these molecules (77). 

Ionophores constitute a large collection of structurally diverse substances that share the ability to complex cations and to assist in the translocation of cations through a lipophilic interface.1 Using numerous Lewis-basic heteroatoms, an ionophore organizes itself around a cationic species such as an inorganic metal ion. This arrangement maximizes favorable ion-dipole interactions, while simultaneously exposing a relatively hydrophobic (lipophilic) exterior. 

NCD-4 is a nonfluorescent carbodiimide derivative that forms a fluorescent adduct with the Ca -ATPase, accompanied by inhibition of ATPase activity and phos-phoenzyme formation [376-378]. Ca protected the enzyme against the inhibition by NCD-4 and reduced the extent of labeling, suggesting that the reaction may involve the Ca " " binding site. The stoichiometry of the Ca -protected labeling was i 2mole/mol ATPase. The fluorescence emission of the modified Ca -ATPase is consistent with the formation of a protein bound A-acylurea adduct in a relatively hydrophobic environment. After tryptic proteolysis of the NCD-4 labeled ATPase the fluorescence was associated with the A2 band of 24 kDa [376,379]. 

Relative hydrophobicity and lipophilicity of P-blockers and related compounds as measured by aqueous two-phase partitioning, octanol-buffer partitioning, and HPLG. Eur. J. Pharm. Sci. 2002, 17, 81-93. 

Zaslavsky, B., and Masimov, E. Methods of Analysis of the Relative Hydrophobicity of Biological Solutes. 146, 171-202(1988). 

Figure 2.1 Three types of fluorophenyl esters have been used for coupling to amine-containing molecules. The PFP and TFP esters are relatively hydrophobic and typically have better stability toward hydrolysis in aqueous solution than NHS esters. The STP ester is water-soluble due to the negatively charged sulfonate group, and it provides better solubility to associated crosslinkers or bioconjugation reagents similar to that of a sulfo-NHS ester group.

Dendrimers bearing certain fluorescent molecules attached on their periphery have been shown to be environmentally sensitive probes for the presence of certain metal ions or to changes in pH (Balzani et al., 2000 Paola et al., 2005). In addition, PAMAM dendrimers modified with the relatively hydrophobic dye Oregon Green 488 were shown to be a more effective transfection agent for anti-sense oligonucleotides than the dendrimer alone-plus the complex could be tracked within the cell due to the fluorescence of the dye (Yoo and Juliano, 2000). 

Uncharged oligos appear to enter the cell by passive diffusion, as well as possibly by endocytosis. However, elimination of the charges renders the resultant oligos relatively hydrophobic, thus generating additional difficulties with their synthesis and delivery. 

The hydrophilic SiO substrate)static water contact angle 0=3O°) was prepared by vapor-deposited SiO onto a Formvar substrate[4], with which an electron microscope grid(200-mesh) was covered. The relatively hydrophobic siliconized substrate(0=9O°) was also prepared by surface siliconized treatment a collodion-covered electron microscope grid was dipped into an aqueous solution of silane coupling agent. 

Measurements of the surface tension of aqueous solutions of various sulphonated and unsulphonated phenylazonaphthol dyes showed that the degree of surface activity (that is, the lowering of surface tension) tended to increase progressively with the degree of alkyl substitution in the series of dyes [7]. The surface-active behaviour of such alkylated dye ions ensures that they become more concentrated at the interface between the dyebath and the fibre surface, just as they do at the air-water interface of the dye solution. Foaming of dyebaths can be a serious practical problem with relatively hydrophobic dye structures solubilised by means of a single ionised group. 

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