Lipophilic group part

Not all of the surfactants are capable of forming micelles. The appropriate ratio between the size of hydrophobic (hydrocarbon chains) and hydrophilic (polar group) parts of surfactant molecules, which determines their hydrophile-lipophile balance (HLB, see Chapter VIII, 3), is necessary for the formation of micelles to take place. Sodium and ammonium salts of C12 - C20 fatty acids, alkylsulfates, alkylbenzenesulfonates, and other synthetic ionic and nonionic surfactants are the examples of micelle-forming surface active substances. The true solubility, i.e. the concentration of dissolved substance in its molecular or ionic form, of such surfactants is rather low for ionic surfactants it is on the order of hundredths and thousandths of kmol m 3, while for nonionic ones it can be even lower by one or two orders of magnitude. 

Thus the analogue N-propyl-apomorphine is a more powerful dopaminergic agonist than the apomorphine itself. The creation of bulkiness is obviously not limited to cationic head groups and lipophilic groups can be attached to any other part of the molecule (Fig. 12.18). ... 

To efficiently cross the membrane, uncouplers must be reasonably lipophilic (generally log P > 2). However, this alone is not suffident. A key part of the action of a protonophoric uncoupler is the ability to cross the membrane in the anionic form, and this requires the negative charge to be extensively delocalized, or shielded from the lipid interior of the membrane in some way. For this reason, many of the most potent uncouplers combine bulky lipophilic groups adjacent to the ionizable proton with extended conjugated systems through which the charge can be spread. A typical example of this is malonoben (10), one of the most potent phenolic uncouplers known (Fig. 13.4.3) [100]. 

By serial replacement, it was found that the three active parts of the enkephalins are the —OH and —NH of the tyrosine fragment, and the lipophilic area in the phenylalanine residue (successfully replaceable by other lipophilic groups) (Gorin et al., 1980). Swiss workers who made stepwise changes to the molecule of Af enkephalin, produced FK 33-824 which is 1000 times as potent as morphine by intra-cerebroventricular injection in laboratory animals (Roemer et al., 1977), but has anaphylactoid side effects in Man. A French group then discovered thiorphan, an (artificial) dipeptide that... 

With regard to bioconcentration, it is important that surfactants are characterized by combining a lipophilic and a hydrophilic moiety in the same molecule. This is true for all four classes, namely anionic, nonionic, cationic and amphoteric surfactants. Although these classes possess quite different hydrophilic groups, the lipophilic part usually consists of an alkyl chain or alkyl chains of different lengths. There is some evidence that the lipophilic groups of surfactants are metabolized after uptake by aquatic invertebrate species (Daphnia and Chironomus) and fish. 

The word surfactant is an acronym for surface-active agents. It stands for molecules that tend to adsorb at interfaces when they are in solution. The molecular structure of surfactants is characterized by a polar group connected to a typically long nonpolar hydrocarbon chain. The polar group, frequently referred to as the head of the molecule, is also known as the hydrophilic group because it is compatible with water (hydro). The nonpolar part, frequently referred to as the tail of the molecule, is also known as the hydrophobic (water hating) or lipophilic group because it is compatible with lipids. The relative size of (balance between) the hydrophilic to the lipophilic (frequently abbreviated and known as HLB) determines whether a surfactant will be predominantly water soluble or oil soluble. 

Many types of substances act as surfactants, but all share the property of amphipathy the molecule is composed of a nonpolar hydrophobic portion and a polar hydrophilic portion, and is therefore partly hydrophilic and partly hydrophobic. Surfactants may be referred to as either amphiphilic or amphipathic the terms are synonymous. The polar, hydrophilic part of the molecule is called the hydrophilic or lipophobic group, and the nonpolar, hydrophobic part is called the hydrophobic or lipophilic group. Often the hydrophilic part of the molecule is simply called the head and the hydro-phobic part—usually including an elongated alkyl substituent—is called the tail. The presence of a hydrophilic group makes surfactants slightly soluble in aqueous media, and is central to the physicochemical properties of aqueous surfactant solutions. 

The binding of a dmg to a protein depends on the inter-molecular forces described in Chapter 1. Thus electrostatic, dipole-dipole, hydrogen bonding, k-k interaction and van der Waals interactions, and even covalent bonding all play a part. The strength of van der Waals interaction depends on the availability of lipophilic groups within the protein. The amino acids with high... 

Compare and contrast the electrostatic potential map of a typical detergent with that of a typical soap (stearate). Which part of each molecule will be most water soluble (hydrophilic) Draw a Lewis structure that describes each molecule s water-soluble group (make sure you indicate all necessary formal charges and lone pairs). Which part(s) of each molecule will be most grease soluble (lipophilic) What kinds of atoms and bonds are found in these groups ... 

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