Peptide surfactants amino acid

The prevalence of the carboxylate moiety in both biogenic and man-made molecules of interest makes this functional group a popular target for anion host chemistry. Needless to say, carboxylates are a major constituent of proteins, peptides and amino acids, and the expansion of proteomics begets increasing requirements for means of specific detection of such biomolecules. Other relevant examples of carboxylates include fatty acids, while many small molecule di- and tricarboxylates are implicated in key metaboUc pathways such as the citric acid cycle (e.g. citrate, succinate, fumarate and malonate). Carboxylated anthropogenic molecules include trichloroacetic acids, anionic surfactants and S-lactam antibiotics. 

Protein-based surfactants are usually synthesized with amino acids/peptides and fatty acids as building blocks. They are mainly of two types peptide and amino acid surfactants. Both are interesting compounds that contain an amino or a peptide as the hydrophilic part and a long hydrocarbon chain as the hydrophobic portion. The hydrocarbon chain can be introduced through acyl, ester, amide, alkyl, or ether linkage. Protein-based surfactants are usually con-... 

Rl, R2, and R5 peptides, three amino acid sequences found in the sillp protein (Fig. 3), were used in vitro to study the silica formation. It was revealed that these polypeptides also form silica upon the addition of TMOS solution. Another investigation made use of arginine-based surfactants to synthesize mesoporous silica." ... 

Depicted in Fig. 2, microemulsion-based liquid liquid extraction (LLE) of biomolecules consists of the contacting of a biomolecule-containing aqueous solution with a surfactant-containing lipophilic phase. Upon contact, some of the water and biomolecules will transfer to the organic phase, depending on the phase equilibrium position, resulting in a biphasic Winsor II system (w/o-ME phase in equilibrium with an excess aqueous phase). Besides serving as a means to solubilize biomolecules in w/o-MEs, LLE has been frequently used to isolate and separate amino acids, peptides and proteins [4, and references therein]. In addition, LLE has recently been employed to isolate vitamins, antibiotics, and nucleotides [6,19,40,77-79]. Industrially relevant applications of LLE are listed in Table 2 [14,15,20,80-90]. 

Drugs, alkaloids, mycotoxins, amino acids, flavinoids, heterocyclic compounds, lipids, steroids, organic acids, terpenes, vitamins. Proteins, peptides, surfactants. 

In this chapter, we have surveyed a wide range of chiral molecules that self-assemble into helical structures. The molecules include aldonamides, cere-brosides, amino acid amphiphiles, peptides, phospholipids, gemini surfactants, and biological and synthetic biles. In all of these systems, researchers observe helical ribbons and tubules, often with helical markings. In certain cases, researchers also observe twisted ribbons, which are variations on helical ribbons with Gaussian rather than cylindrical curvature. These structures have a large-scale helicity which manifests the chirality of the constituent molecules. 

The peptide chain in globular proteins is folded into fairly compact conformations. Water-soluble enzymes are typical globular proteins which have most of the hydrophobic amino acid residues located in the interior and the hydrophilic residues located mainly at the surface in contact with solvent water. The average radii are 20-40 A (Boyer, 1970). It is clear that there are common morphological features between surfactant micelles and enzyme molecules. This fact has prompted many chemists to use micelles as enzyme models. However, it must be emphasized that micelles exist in dynamic equilibria with monomeric surfactant and their hydrophobic core is quite fluid, whereas enzyme molecules have precisely fixed three-dimensional structures. 

The positively charged amino acids promote the interaction between the peptide and the negatively charged head groups of the phosphatidylgly-cerol (123-125). The purpose of this particular property has been proposed to facilitate the transition of surfactant phospholipid membranes from the lamellar body to the alveolar spaces (123). 

Small ACTH fragments related to ACTH-(4-10) have also been investigated for the presence of ordered structure. CD of ACTH--(5-10) in TFE showed a random structure (50) as was found with H-NMR for fragment 4-10 (51). The addition of anionic or cationic surfactants to an aqueous solution of ACTH-(4-11) dit not promote any a-helix or 3-form in this peptide (CD experiments S2). When ACTH-(1-14) and 1-10 were measured by CD and NMR respectively, indications for a helical or ordered structure were found (90, ). Thus it seems that the addition of the non-helix "prone" fragment 1-3 or 1-4 can promote the formation of a helical structure in the adjacent sequence. Arguments in favour of this come from the theoretical work of Argos and Palau (53) on amino acid distribution in protein secondary structures. They found that Ser and Thr frequently occur at the N-terminal helical position (cf. Ser in ACTH) to provide stability the position adjacent to the helical C-terminus is often occupied by Gly or Pro (adjacent toTrp in ACTH we have Gly ) acidic amino acid residues are frequently found at the helix N-terminus (cf. Glu in ACTH) and/or basic residues at the C-terminus (cf. Arg ). 

Shea and colleagues [109-111] added an exciting contribution to this field They created molecular imprints for the peptide melittin, the main component of bee venom, in polymer nanoparticles, resulting in artificial antibody mimics that can be used for the in vivo capture and neutralization of melittin. Melittin is a peptide comprising 26 amino acids which is toxic because of its cytolytic activity. Shea and colleagues strategy was to synthesize cross-linked, acrylamide-based MIP nanoparticles by a process based on precipitation polymerization using a small amount of surfactant. To maximize the specificity and the affinity for melittin, a number of hydrophilic monomers were screened for complementarity with the template. The imprinted nanoparticles were able to bind selectively the peptide with an apparent dissociation constant of Ax>app > 1 nM [109]. 

A few years ago, we began a research program to develop methods of analysis which would involve the use of FAB and a high performance tandem mass spectrometer. The tandem instrument was the first triple sector mass spectrometer to be designed and built by a commercial instrument company (Kratos of Manchester, U.K.). The first mass spectrometer of the combination is a double focussing Kratos MS-50 which is coupled to a low resolution electrostatic analyzer, which serves as the second mass spectrometer U). This FAB MS-MS combination has been used to verify the structures of an unknown cyclic peptide (2), a new amino acid modified by diphtheria toxin (3), and an ornithine-containing lipid (4). A number of methods have also been worked out which rely on this instrumentation. They Include the structural determination of cyclic peptides (5), nucleosides and nucleotides (6), and unsaturated fatty acids (7) and the analysis of mixtures of both anionic (8) and cationic surfactants (9). 

While the aforementioned technologies focus either on bulk or on solid-phase assembly, a more recent innovation in peptide self-assembly has targeted the soft or fluid-fluid interface. Designer peptides of 7 amino acid "heptad repeats" can be reversibly triggered to fold into an a-helix conformation to organize both hydrophilic and hydrophobic faces, thus inducing surfactant-like structure. These peptide surfactants, however, interact with each other in the interfacial plane, through reversible metal-ion coordination... 

When peptides with subtle differences in hydrophobicity are being separated, nonionic surfactants may provide a better balance between the electrostatic and hydrophobic forces influencing the separation. Polyoxyethylene-10 (20 mM) has been found useful for separating two analogues of growth hormone-releasing peptide (composed of six amino acids) with the same mass-to-charge ratio. 

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