Structure in aqueous solution

Stillinger F 1973 Structure in aqueous solutions from the standpoint of scaled particle theory J. Solution Chem. 2 141 Widom B 1967 Intermolecular forces and the nature of the liquid state Sc/e/ ce 375 157 Longuet-Higgins H C and Widom B 1964 A rigid sphere model for the melting of argon Mol. Phys. 8 549... 

As has been described in Chapter 4, random copolymers of styrene (St) and 2-(acrylamido)-2-methylpropanesulfonic acid (AMPS) form a micelle-like microphase structure in aqueous solution [29]. The intramolecular hydrophobic aggregation of the St residues occurs when the St content in the copolymer is higher than ca. 50 mol%. When a small mole fraction of the phenanthrene (Phen) residues is covalently incorporated into such an amphiphilic polyelectrolyte, the Phen residues are hydrophobically encapsulated in the aggregate of the St residues. This kind of polymer system (poly(A/St/Phen), 29) can be prepared by free radical ter-polymerization of AMPS, St, and a small mole fraction of 9-vinylphenanthrene [119]. 

Fig. 2.14 Formulae of /5-peptides 81 and 82 forming stable 3,4-helical structures in aqueous solution and schematic representation of the position of the amino acid side-chains looking down the 3,4-helix axis [128, 165]...

Raman optical activity is an excellent technique for studying polypeptide and protein structure in aqueous solution since, as mentioned above, their ROA spectra are often dominated by bands originating in the peptide backbone that directly reflect the solution conformation. Furthermore, the special sensitivity of ROA to dynamic aspects of structure makes it a new source of information on order-disorder transitions. 

Most of the molecules introduced in this chapter are hydrophobic. Even those molecules that have been functionalized to improve water-solubility (for example, CCVJ and CCVJ triethyleneglycol ester 43, Fig. 14) contain large hydrophobic structures. In aqueous solutions that contain proteins or other macromolecules with hydrophobic regions, molecular rotors are attracted to these pockets and bind to the proteins. Noncovalent attraction to hydrophobic pockets is associated with restricted intramolecular rotation and consequently increased quantum yield. In this respect, molecular rotors are superior protein probes, because they do not only indicate the presence of proteins (similar to antibody-conjugated fluorescent markers), but they also report a constricted environment and can therefore be used to probe protein structure and assembly. 

Stillinger, F., Structure in aqueous solutions of nonpolar solutes from the standpoint of scaled-particle theory, J. Sol. Chem. 1973, 2, 141-158... 

Recently, many studies have focused on self-assembled biodegradable nanoparticles for biomedical and pharmaceutical applications. Nanoparticles fabricated by the self-assembly of amphiphilic block copolymers or hydrophobically modified polymers have been explored as drug carrier systems. In general, these amphiphilic copolymers consisting of hydrophilic and hydrophobic segments are capable of forming polymeric structures in aqueous solutions via hydrophobic interactions. These self-assembled nanoparticles are composed of an inner core of hydrophobic moieties and an outer shell of hydrophilic groups [35, 36]. 

Fig. 30 Types of nanocarriers for drug delivery, (a) Polymeric nanoparticles polymeric nanoparticles in which drugs are conjugated to or encapsulated in polymers, (b) Polymeric micelles amphiphilic block copolymers that form nanosized core-shell structures in aqueous solution. The hydrophobic core region serves as a reservoir for hydrophobic drugs, whereas hydrophilic shell region stabilizes the hydrophobic core and renders the polymer water-soluble.

Figure 1.26 Carbonyl groups and hydroxyls may react to form acetal or ketal products. Sugars naturally undergo these reactions to form ring structures in aqueous solution.

Proteins are fucntional only in the fluid membrane conditions, Tm of the lipids should be low, most preferebly below 0°C. First of all, the lipids should not inhibit protein functions and induce denaturation. For this we choose sugars as their headgroups, since sugars are empirically known to stabilize protein functions and structures in aqueous solution[29]. Moreover, rich variety of the carbohydrate chemistry can provide powerful means to control their aqueous phase structures. 

In aqueous solution both the tetramer and the pentamer have cyclical structures (Fig. 6) as shown by the narrow 51V NMR linewidths indicating high symmetry around vanadium (29). The relative amounts of the species are concentration dependent but under moderate concentrations the tetramer is the most important (Figs. 2 and 3). The hexamer [V60i8]6 is a very minor species under most conditions, but it becomes somewhat more prominent at high concentrations and high ionic strength (8, 10, 15, 32). Indications are that it has a cyclic structure in aqueous solution (10). 

On the other hand, basic myelin protein and monomeric melittin are proteins which, by many criteria, are devoid of ordered structure in aqueous solutions. This results in freedom of rotation of tryptophan residues which are exposed to the solvent. Such a situation may exist for peptides without regular structure and for denatured proteins. 

As previously stated, the use of templates such as DBSA, HDTMAB, and PEOPE allows the formation of well-defined micellar structures in aqueous solution when the template concentration is above its CMC. In a recent publication [38], the polymerization with a bifunctional sodium dodecyl diphenyloxide disulfonate (DODD) as template was proposed to proceed by a micellar mechanism in the same way (Scheme 2). In an aqueous acid solution of DODD and aniline, anilium ions locate at the micellar interface, with benzene parts penetrating into the hydrophobic core of the DODD micelle to form the complex (as illustrated in Scheme 3b). At the concentration of 0.055 mol a slight turbidity was observed in solution, indicating micellar aggregation. Once the micellar structure is formed and the enzyme is added to the aqueous medium, addition of H2O2 triggers the polymerization of anilinium ions around micelles (Scheme 3). 

The structures in aqueous solution of both AP-A [46] and AP-B [47] have been solved using high-resolution NMR data. Structures have also been determined for the Type 1 toxin ATX la [48] and the Type 2 toxin Sh I [49,50] from NMR data. The main secondary structure element in each of these structures is a... 

However, major drawbacks still limit the use of such materials on a large scale (1) the burning out of the expensive surfactant imposes both economical and ecological problems, (2) the stability of the MCM walls in hydrothermal conditions or thermal conditions needs to be improved and (3) incorporated and / or grafted transition metal ions leach out of the structure in aqueous solutions, rendering aqueous phase catalysis virtually impossible. 

Table 3. Major Non-Covalent Forces and Interactions Important in the Organization and Stabilization of Protein Structure in Aqueous Solutions 8 16-,7)... 

The polypeptide is shown as a zwitterion with charged NH3+ and C02 terminal groups. This is the favored structure in aqueous solution. A neutral tautomer with NH2 and C02H terminal groups is favored in the gas phase. See Chapter 16, Problem 5. 

An understanding of equilibrium phenomena in naturally occurring aqueous systems must, in the final analysis, involve understanding the interaction between solutes and water, both in bulk and in interfacial systems. To achieve this goal, it is reasonable to attempt to describe the structure of water, and when and if this can be achieved, to proceed to the problems of water structure in aqueous solutions and solvent-solute interactions for both electrolytes and nonelectrolytes. This paper is particularly concerned with two aspects of these problems—current views of the structure of water and solute-solvent interactions (primarily ion hydration). It is not possible here to give an exhaustive account of all the current structural models of water instead, we shall describe only those which may concern the nature of some reported thermal anomalies in the properties of water and aqueous solutions. Hence, the discussion begins with a brief presentation of these anomalies, followed by a review of current water structure models, and a discussion of some properties of aqueous electrolyte solutions. Finally, solute-solvent interactions in such solutions are discussed in terms of our present understanding of the structural properties of water. 

Ab Initio Modeling of Interface Structure in Aqueous Solutions... 

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