Hydrophobic attractions

It can be seen from the figure that the electrostatic repulsive forces between the macrocations are overwhelmed, probably by hydrophobic attractive forces between their hydrophobic side groups. It should be noted that the complimentary base-base pairing is unimportant in the present case. If this is not the case, the mixtures of APVP and TPVP should show the largest hypochromicity. This, however, is not the case. The importance of the hydrophobic interactions between nucleic acid bases has been proposed by Ts o et al.I9 from thermodynamic parameters of various nucleic acid bases or nucleosides in aqueous media. 

The colloid probe technique was first applied to the investigation of surfactant adsorption by Rutland and Senden [83]. They investigated the effect of a nonionic surfactant petakis(oxyethylene) dodecyl ether at various concentrations for a silica-silica system. In the absence of surfactant they observed a repulsive interaction at small separation, which inhibited adhesive contact. For a concentration of 2 X 10 M they found a normalized adhesive force of 19 mN/m, which is small compared to similar measurements with SEA and is probably caused by sufactant adsorption s disrupting the hydration force. The adhesive force decreased with time, suggesting that the hydrophobic attraction was being screened by further surfactant adsorption. Thus the authors concluded that adsorption occurs through... 

The exponential dependence is indicative of hydrophobic attractive forces between the glycerol-air interface and the glycerol-mica interface. This potential gives a negative disjoining pressnre of 1 atm at z close to 0. The strength of the force appears to be 100 times lower than that typical for water between hydrophobic surfaces [6]. 

Attard P (2003) Nanobubbles and the hydrophobic attraction. Adv Colloid Interface Sci 104 75-91... 

The pseudophase model is often applied to reactions of hydrophobic ionic substrates, e.g. pyridinium ion in solutions of cationic micelles (Tables 3 and 4) with the hydrophobic attraction between micelle and substrate over-... 

The problems of the constancy of a and the site of reaction are closely linked. It is very convenient to assume that the charge on the micellar head groups is extensively neutralized by counterions which bind specifically to the micellar surface. In this way micellar stability is associated with a balance between hydrophobic attractions between apolar groups and coulombic repulsions of the ionic head groups which will be reduced by favorable interactions with the counterions in both the Stem and the diffuse Gouy-Chapman layers. It is the behavior of the counterions which is important in considerations of their chemical reactivity. 

Hydrophobic attractive interactions between a polymer and a small-molecule reactant often occur in reactions carried out in aqueous media [Imanishi, 1979 Morawetz, 1975 Overber-ger and Guterl, 1978, 1979]. Acid catalysis of ester hydrolysis by polysulfonic acids is most... 

Figure 21, Proposed model of adsorbed chiral selector (A-alkylproline)- Cu(U)-[free amino acid] mixed chelate complex, The lipophilized proline selector is held in position via intercalation of the alkyl chain. Case A the alkyl part of the mixed chelate complex is fixed by hydrophobic interactions with stationary phase (RP-J). Case B the complex formation is stabilized by other types of hydrophobic attraction. Chiral recognition and elution order is therefore not only dependent on the simple and isolatedly viewed chelate complex stability. In general, retention and chiral recognition in chiral LC is based on mixed-mode adsorption/dcsorption processes which act synergisticallv and also antagonistically with respect to the observed chiral resolution and intermolecular complex formation.

However, recently other intriguing facts have come to light, which makes it obvious that some other factors may also be involved in the enantioselectivity of the addition. When cyclo[(S)-Leu-(S)-His] is used as the catalyst for the same reaction, (S)-mandelonitrile is formed with 55% ee. The best solvent for this reaction was ether (better than toluene). Aliphatic aldehydes generally led to better enantioselectivities (60 to 80% ee). This perhaps suggests some hydrophobic attraction with the leucyl side chain (89CL2119). 

Nonspecific hydrophobic attractions are Important to the dissociative-associative reactions which Inltate the gelation process. These attractions could also be Involved In layering or thickening of the gel network strands upon cooling which results In Improved strength and stability. This thickening of gel network strands also results In Increased opacity (8). 

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