Surface hydrophobic area

The lipophilicity (7 m value) and specific hydrophobic surface area of 1 ]/f-pyrido[2,]-fi]quinazolin-] 1-one and its isomeric 6//-pyrido[l, 2-u]qui-nazolin-6-one were determined by reversed-phase thin-layer chromatography (98MI4). 

Density functional theory study of aqueous-phase rate acceleration and endo/exo selectivity of the butadiene and acrolein Diels-Alder reaction72 shows that approximately 50% of the rate acceleration and endo/exo selectivity is attributed to hydrogen bonding and the remainder to bulk-phase effects, including enforced hydrophobic interactions and cosolvent effects. This appears to be supported by the experimental results of Engberts where a pseudothermodynamic analysis of the rate acceleration in water relative to 1-propanol and 1-propanol-water mixtures indicates that hydrogen-bond stabilization of the polarized activated complex and the decrease of the hydrophobic surface area of the reactants during the activation process are the two main causes of the rate enhancement in water.13... 

Lipophilicity and specific hydrophobic surface area were determined by using reversed-phase thin-layer chromatography for fused heterocyclic ring systems including five pyrido[2,iy][l,2,4]triazine derivatives <1998MI64>. 

Various Various organic compounds 8 x 10-5-3 x 10-2 Compilation of values determined for the transport of various organic compounds with low (8 — 15 x 10 5 s ) to high (0.2-3 x 10-2 s-1) hydrophobic surface areas [254]... 

The same RP-TLC investigations were carried out by using ethanol, THF and dioxane as organic modifiers. The parameters of regression analyses are compiled in Table 3.6. It was established that the type of organic modifier exerts a negligible effect on the lipophilicity but influences considerably the specific hydrophobic surface area of the dyes. 

The lipophilicity and specific hydrophobic surface area of 42 synthetic dyes were also measured on alumina-based RP-TLC layers as described above. The common and IUPAC names of the non-homologue series of synthetic dyes are compiled in Table 3.7. 

Fig. 3.6. Relationship between the lipophilicity (Rm) and specific hydrophobic surface area (b) of synthetic dyes (n = 41). Reprinted with permission from T. Cserhati et al. [87],...

T. Cserhati and G. Oros, Relationship between the lipophilicity and specific hydrophobic surface area on non-homologous series of synthetic dyes. Croat. Chem. Acta, 73 (2000) 293-303. 

HIC, like IEC, is performed under conditions that preserve protein shape and activity. It is used in preparative applications to obtain a selectivity complimentary to IEC and akin to RPLC but without the denaturing properties of the latter technique. Although HIC and RPLC share a mechanism based on hydro-phobic partitioning, the actual peak spacing and elution order of the two techniques can be different. This arises from the different hydrophobic contact points presented by the protein under native (HIC) and denaturing (RPLC) conditions. Although not widely used for analytical separations, HIC can be used to answer questions about accessible hydrophobic surface area that cannot be addressed by RPLC.44... 

B Hydrophobic suifiime area Hydrophobic surface area... 

C Charge type (C - Hydrophobic surface area (carten mimt>er) -t- charge type (C - Jfd... 

B/AC Hydrophobic surface area (carten number) Charge type... 

A polar surface area approximation can be calculated by summing the V, contribution of each polar atom in a molecule. A hydrophobic surface area approximation can be calculated by V) contribution of each hydrophobic atom in a molecule. More generally, for a given binary property Bt (such as is polar or is aromatic or is acceptor ) for each atom i in a molecule, an approximate surface-area based descriptor can be calculated with... 

Surface area descriptors van der Waals hydrophobic surface area 3D... 

Moreover, fluorine substitution reduces polarisability, increases the hydrophobic surface area and provides an enhanced driving force for desolvatation (estimated driving force 0.2-0.5 kcal/mol) [13]. 

The structure and function of enzymes is determined by both the amino acid sequence and the surrounding solvent. The overall stability of proteins is characterized by a subtle balance of into- and inter-molecular interactions. The basic principle of the structure (and of the stability) of the proteins is related to the nature of its normal enviromnent for (water) soluble globular proteins this is the minimization of the hydrophobic surface area, whereas the contrary is the case for membrane proteins (Jaenicke, 1991). 

This area is a development in the usage of NDDO models that emphasizes their utility for large-scale problems. Structure-activity relationships (SARs) are widely used in the pharmaceutical industry to understand how the various features of biologically active molecules contribute to their activity. SARs typically take the form of equations, often linear equations, that quantify activity as a function of variables associated with the molecules. The molecular variables could include, for instance, molecular weight, dipole moment, hydrophobic surface area, octanol-water partition coefficient, vapor pressure, various descriptors associated with molecular geometry, etc. For example, Cramer, Famini, and Lowrey (1993) found a strong correlation (r = 0.958) between various computed properties for 44 alkylammonium ions and their ability to act as acetylcholinesterase inhibitors according to the equation... 

For inorganic neutral salts, a is positive. Thus, for these salts, aFgay-j-ty is always negative if hydrophobic surface area is exposed upon solubilization (aA is positive). This term accounts for the salting out of proteins. 

The failure of the theory indicates that soy protein behavior is more complex than Melander and Horvath s (7, ) model. In deriving their simple theory, Melander and Horvath assumed that the changes in hydrophobic surface area, in the dipole moment, and in the net charge of the protein upon solubilization are invariant with respect to salt species or salt concentration. In other words, they assumed that the soluble proteins have the same thermodynamic state regardless of salt species or salt concentration. The results for soy proteins can be treated in the framework of the Melander and Horvath s theory if it is expanded to allow the exposed surface area, the dipole moment, and the net protein charge to be functions of the salt species and the salt concentration. 

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