Interactions lipophilic

The concept of micelles consists of aggregation of amphiphilic molecules that contain polar and non-polar moieties, which associate in a manner that minimizes hydrophobic and lipophilic interactions. However, a cascade molecule consisting of an internal lipophilic framework and a external hydrophilic surface would effectively be a unimolecular micelle [59] capable of hosting molecular guest(s). 

As Table 20 shows, the yields of the Rh(II)-promoted reaction are temperature-dependent. Furthermore, competitive experiments between pairs of alkanes revealed a marked dependence on the alkoxy group of the diazoester and on the perfluoroalkyl carboxylate part of the catalyst. The observed relative selectivities have been taken as evidence for the importance of lipophilic interactions between carbenoid and alkane. 

Increasing the size of the ether substituent (5i) led to a further increase in potency and efficacy in vitro. However, this improvement in vitro, which might be accounted for by secondary lipophilic interactions, did not improve efficacy in vivo. Substitution at the 5-position of the indole nucleus by larger polar or lipophilic substituents (5j) abolished activity in vitro. 

Lipooligosaccharide (LOS) bacterial, 25 498 Lipophilic amphiphiles, 24 154-155 Lipophilic interaction dominated substrate recognition, 16 783-786 Lipophilic moieties, 8 706t Lipopolysaccharides (LPS), 4 706 11 47 BPI protein ability to neutralize, 18 257 peptide and protein binding affinity to, 18 256... 

First, it permitted the anion Nu to dissolve in an organic phase when the inorganic salt, M+Nu , proved insoluble. Second, since the principal mode of solvation in the organic phase is lipophilic-lipophilic interactions, the cation (Q+) is well solvated but the counteranion (Nu ) is not. The reactivity of Q+Nu is therefore greater than the reactivity of M+Nu although completely valid comparisons are limited by solubility. 

The technique of noncovalent derivatization employs the noncovalent intermolecular forces (hydrogen bonding, 7t-stacking, UpophUic-lipophilic interactions, and electrostatic interactions) to trap the molecular species in organized matrices. 

Another example of the separation of isotopomers was observed with deuterated benzoic acid, eluted with acidified 30% aqueous methanol. Deuteration, especially at meta and para positions, decreases retention.136 Ratios of retention times are presented in Table 9, where the IEs of monodeuterated benzoic acid or of benzoic-2,6-% acid are omitted because they are too small to produce resolvable peaks although they do lead to detectable peak broadening. Because the IEs are strongest at positions more distant from the carboxyl group, and because the elution conditions were sufficiently acidic that the benzoic acid was not ionized, an IE on the pKa was rejected as responsible. Instead some sort of lipophilic interaction was suggested, and deuteration at the ortho positions is less effective because the carboxyl group hinders those positions. However, it should be noted that the data in Tables 2 and 3 indicate that the IE on acidity does not fall off at meta and para positions.24,32... 

The chemical feature definitions described in the following sections are all categorized into hydrogen bond interactions, which are described as layer 3 features, and also into charge interactions and lipophilic interactions, which are represented as level 4 features. All current layer 4 features are represented as points with a tolerance radius forming a sphere, whereas layer 3 features are represented by vectors. The chemical feature definitions are specified in Daylight SMARTS notation [37] (listed in detail in Table 6.2) and directly imported into... 

Normal phase (NP) separations are comparatively rarely used in environmental analysis. Again, the reasons lie in the range of analytes amenable to this mode of separation, and in the limited compatibility of typical normal phase HPLC (NP-HPLC) mobile phases with mass spectrometric detection (this also applies to IC). Not only for this reason has interest recently grown in hydrophilic-lipophilic interaction chromatography (HILIC), which represents a viable alternative to the separation of very polar compounds with mobile phases that have a much better compatibility with MS detection, for example, acetonitrile/water with a low water content, typically below 10%, 32 Nonetheless, NP chromato-graphy retains its important role in sample preparation, particularly for the cleanup of complex environmental samples. In the off-line approach, fractions are collected and the relevant one is injected into the reversed phase HPLC (RP-HPLC) system, often after solvent exchange. 

In addition to the silica-based materials mentioned above, modem polymers are widely used for TTA and QTA sample preparation allowing SPE not impaired by undesirable silanol activities. HLB Oasis (Waters) is the tradename for a hydrophilic-lipophilic balance reversed-phase sorbent enabling lipophilic interaction to benzene moieties and hydrophilic interactions to pyrrolidone groups as present in the macroporous copolymer of poly(divinylbenzene-co-iV-vinylpyrrolidone). Elution of analytes is often performed with solvents containing MeOH or ACN. Applying this adsorbent TA such as atropine and scopolamine were extracted from human viscera [15], human serum [97-99], human urine [12] as well as from rat plasma and brain microdialysate [77], Furthermore, this hydrophilic-lipophilic balance phase was also suitable for extraction of the QTA trospium from human and rat plasma [77, 84] and methyl scopolamie from rat plasma [77] (Table 4). 

Hansch constant — A measure of the capability of a solute for hydrophobic (lipophilic) interaction (see - hydrophobic effect) based on the partition coefficient, P, for distribution of the solute between octan-l-ol and water. The most general way of applying P in correlation analysis, etc. is as logP, but the behavior of substituted benzene derivatives maybe quantified by a substituent constant scale, n, which is defined in a way analogous to the Hammett a scale. There are various n scales, depending on the substrate series used as reference. See also - hy-drophilicity. 

Jiang Xi-Kui (1988) Hydrophobic-lipophilic interactions. Aggregations and self-coiling of organic molecules. Accts Chem Res 21 362- 367... 

Figure 2 Role of water molecules in hydrogen bonds (upper part) and lipophilic interactions (lower part). In the unbound state (left side), the polar groups of the ligand and the protein form hydrogen bonds to water molecules. These water molecules are replaced upon complex formation. The hydrogen-bond inventory (total number of hydrogen bonds) does not change. In contrast, the formation of lipophilic contact increases the total number of hydrogen bonds due to the release of water molecules from the unfavorable lipophilic environment.

In agreement with the GRID findings, site-directed mutagenesis experiments demonstrated that lipophilic interactions are extremely important for binding to take place in the enzyme cavity CYP2C9. In turn, flexibility of sidechains modifies the physicochemical enviroment of the cavity, as well as the protein pharmacopho-ric pattern. 

Finally, so-called hydrophobic or lipophilic interactions are often mentioned as additional contribution to protein-ligand interactions. These term s are used to describe the preferential association of nonpolar groups in aqueous solution. It should be emphasized, however, that in contrast to what the name suggests, there is no special hydrophobic force. Instead, one should speak of a hydrophobic effect. As further mentioned below, according to the generally accepted view, it arises primarily from the entropically favorable replacement and release of water molecules (42, 43). The association between the nonpolar surfaces itself is simply based on weak London forces... 

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