Monolayer technique

Naturally, this section serves as only a very limited introduction to the present status of monolayer techniques. However, it should be... 

Lundquist and the Stenhagens concentrated their efforts on the physical aspects of monolayer chemistry and did not elaborate then-work much in the direction of structural variation of the surfactant molecules. Their results show clearly, however, that the response of chiral monolayers to changes in surface pressure and temperature is sharply dependent on both the molecular structure of the surfactant and the optical purity of the sample. The Stenhagens were keenly aware of the possible application of the monolayer technique to stereochemical and other structural problems (72) however, they failed to exploit the full potential suggested by their initial results and, instead, pursued the field of mass spectrometry, to which they made substantial contributions. 

Robb, l.D. Determination of the solubility of vinyl stearate in water by a monolayer technique. Colloid PoIym.ScI, 209 (2) 162-... 

In the present study, the monolayer technique is used to investigate the surface properties of octadecyldimethylamine oxide and sodium octadecyl sulfate, as single component films and in combination. The interpretation of the results provides a direct understanding of the mechanism of interaction between these two surface active agents. 

Cardiolipin Monolayers. Among various phospholipids studied by monolayer techniques, only cardiolipin (41) and phosphatidylserine (36) monolayers show significant condensation of their surface pressure-area curves in the presence of divalent as compared with monovalent cations in the subsolution. The condensation of cardiolipin is explained by the decrease in molecular area caused by the attraction between a divalent cation and the two phosphate groups in the molecule. This condensation is eliminated when the ratio of monovalent to divalent cations is greater than 5 to 1. At high surface pressures, the difference in the compressibility of cardiolipin monolayers correlates with the ionic radii of the metal ions (Mg2+ < Ca2+ < Sr2+ < Ba2+). 

Ringsdorf and coworkers used monolayer techniques for the creation of lipid functionalized streptavidin layers.252,253 In their pioneering work, a monolayer of biotinylated phospholipids initially created a two-dimensional docking matrix for the immobilization of streptavidin. In an effort to further expand this system while maintaining control over its structure, bis-biotinylated bifunctional linkers were employed. Addition of these linkers to concanavalin A created a new protein-based bidentate linker. Upon addition to the monolayer of the lipid-functionalized streptavidin a second biotilynated protein layer was created. Upon the further addition of streptavidin, they achieved in a step-by-step construction process well-defined alternating protein triple layers of streptavidin and concanavalin A (Figure 7.37b). A similar approach has more recently been used to crosslink... 

In addition to freeze-fracture electron microscopy, a combination of DSC, NMR, and the monolayer technique has been applied to study the various aspects of the interaction of the class IV calcium antagonist flunarizine [150] with a range of phospholipids. DSC shows only limited interaction of flunarizine with PC. The drug destabilizes the Lp-phase without stabilizing the La-phase. In contrast, flunarizine influences not only the onset of phase transition but also the phase transition temperature and the completion of the transition of phosphatidylserine (PS), indicating... 

The strong interaction with the solid surface sometimes compensates for a lack of self-assembling ability for some components (Fig. 4.36). Molecules whose structures are much different to those of typical amphiphiles can be used in this method. In addition, immobilizations of dyes, proteins and nucleic acid are possible using this self-assembled monolayer technique. These self-assembled monolayers have great potential for a wide range of applications. 

Several workers subsequently confirmed these observations. Stein et al. (1944) examined the hydrolytic products with the manometric methods developed by Van Slyke and co-workers (1941) and demonstrated that dipeptides represented the overwhelming proportion of the products formed when silk fibroin was hydrolyzed for 96 hr at 40°C in concentrated HCl. After 40 hr, the hydrolyzate contained about 25% free amino acids with the remainder of the residues existing as di- and tripeptides. Bull and Hahn (1948), using a spread monolayer technique for estimating molecular weights, examined partial acid hydrolysis of egg albumin. By this method, immediate cleavage of about fifty bonds was observed when egg albumin was dissolved in 7.6 N HCl at 60°C. The remainder of the bonds were hydrolyzed at much slower rates. 

In this section we address the measurement of interfacial tensions that are time dependent because the interface is not at equilibrium. Sometimes such tensions are called dynamic surface tensions but we prefer non-equilibrium surface tensions. Their measurement will be discussed in this section, particularly against the background of the techniques described so far. Most of the interpretation (in terms of surface rearrangements, transport to and from interfaces, etc.) and additional monolayer techniques (wave damping, for instance) will be deferred to chapters 3 and 4. 

F. MacRitchie, Chemistry at Interfaces. Academic Press (1990). (Emphasis on the real Interfacial chemistry, i.e. reactions, particularly in monolayers. In passing a variety of monolayer techniques and properties are reviewed. )... 

With conventional emulsified systems, it is not possible to control the interfacial qualit/ and to easily assess the distribution of soluble versus adsorbed amphiphilic molecules. This prompted us to use the monolayer technique, based upon surface pressure decrease due to lipid-film hydrolysis [55, 56]. This technique is applicable to those cases where the lipid forms a stable monomolecular fihn at the air/ water interface and where reaction products are freely soluble and diffuse away rapidly into the aqueous phase. 

The monolayer technique was also used to study the covalent inhibition of lipases using mixed monomolecular films of substrate containing amphiphilic inhibitor molecules and using a zero order trough with a reaction compartment containing the mixed substrate/inhibitor film whereas the reservoir compartment was covered with a film of pure substrate [44, 57]. 

Planar polymer films were recently mineralized with calcium phosphate [267], Using the Langmuir monolayer technique, it was possible to control the particle growth by the polymer film properties at the air-water interface and the subphase parameters (pH, ion strength). Small changes it the growth conditions resulted in various particle shapes and dimensions. Such examples of controlled biomimetic mineralization are indeed very motivating for further studies of crystallization processes in synthetic membranes. 

Monolayer techniques have been used with much success to study the interaction of proteins with surfactants (11, 12, 13), ions and lipids (14), and other proteins (15). This paper investigates, through well-established procedures, the surface chemistry of monolayers of a major component of heterogeneous wheat gluten protein, gliadin, and explores these interactions with various surface-active agents. 

Monolayer Techniques. Surface tension and surface potential were measured by a torsion balance with the Wilhelmy plate and a radioactive (226Ra) air electrode (5, 20). 

Monolayer techniques were used to characterize the interfacial properties of the resultant Fractions. Fraction I contained highly cohesive complexes that did not unfold at the interface and had an average diameter of 9.1 nm. These particles are thought to represent submicelles, previously identified in micelle formation. Fraction II showed interfacial properties that are characteristic of spread casein monomers, and contained mainly a -casein. The results are discussed in relation to casein interactions and micellar formation. Mixed monolayers of sodium caseinate/glyceride monostearate (NaCas/GMS) were also examined at different composition ratios. The results show that for low surface pressures (0-20 mNm ), there is a condensation ascribable to hydrophobic interactions in the mixed film. At high surface pressures, the hydrophobic interaction is modified and the protein is expelled from the monolayer into the subphase. These results are discussed in relation to emulsion stability. 

In the last few years, our research group evaluated the possibility of using monolayer techniques to caracterize caseins interactions. These techniques have allowed us to investigate the interfacial properties of milk caseins which are believed to be responsible for the interactions leading to micellar organization. Secondly, preparation of mixed films by these techniques provides relevant information about interactions between caseins and monoglycerides related to emulsion stability. 

Smdies involving complexes between PAA (43 kDa) and PC vesicles were conducted using fluorescence spectroscopy, calorimetry, and monolayer techniques. Using acenaphthylene dye-labeled PAA, it was shown that binding increased dramatically below pH 4.5 for EPC-LUVs. At pH 3.8, the saturation PAA content was 1.0 mg of PAA per 1.5 mg of phospholipid, or-4600 polymer chains per vesicle, or 7 acrylic acid monomer units per phospholipid assuming a numher of parameters including the fact that vesicles remained intact. DSC traces showed the for DPPC-MLVs shifted from 41.1 to 44.5 °C as the pH was lowered from 7.6 to 3.8. At pH = 4.6, there were two approximately equally sized transitions at 41.1 and 44.2 C. 

Geetha, B. Mandal, A. B. 2-Dimensional Surface Properties of w-Methoxy Poly(ethyleneglycol) Macromonomer in Absence and Presence of Stearic Acid and Its Interaction with SDS As a Fimction of Different Mole Compositions at Various Temperatures at Air-Water Interface Thermodynamic studies Using Langmuir Film Balance (Monolayer) Technique. Langmuir, 2000,16, 3957-3963. 

Conventional BLMs can also be formed by the L-B technique, [see Tien, 1974]. Essentially, it is a combination of the monolayer technique and the dipping method. A partition made from a sheet of Teflon (25-500-pm thick) with a hole (0.25-1 mm) at the center is placed between the two halves of a trough, with the hole above the aqueous phase. The trough is first filled with an aqueous solution. After the surface has been cleared, a monolayer of a suitable Kpid solution is spread in the surface in the usual manner. After evaporation of the solvent, the Teflon partition is then lowered slowly into the aqueous solution. A BLM is thus formed over the hole (see Fig. 4). Conversely, with the Teflon partition bearing a hole in place, the aqueous solution on either side is covered by a monolayer. Then, the levels of aqueous solutions are raised simultaneously above the... 

In 1995, Natan et al. reported that Au and Ag nanoparticles adsorbed onto an organosilane-polymer-modified Si substrate could be used as a SERS-active substrate [97]. Subsequently, in 2001 the same authors [98] proposed a novel approach based on the self-assembled monolayer technique which allows the preparation of regularly arranged monodispersed colloidal Au and Ag nanoparticles on functionalized metal or glass substrates. It is now possible to synthesize or fabricate metal nanostructures of various shapes and sizes with a narrow size distribution. Nanoparticles assembled on an electrically conductive substrate can significantly improve the surface uniformity of the EC-SERS substrate. Therefore, use of nanoparticle sols or assembled nanoparticles as SERS substrates has expanded very rapidly during recent years [92]. 

In order to determine the infants lung maturity and the necessity of surfactant therapy it is of great importance to substantiate the functionality of the alveolar surfactant, derived via invasive techniques [13], Several techniques and models have been largely used to investigate inteifacial physicochemical properties in vitro and to assess clinical efficiency of ES in vivo the Langmuir monolayer technique in combination with Wilhelmy plate method for surface tension measurements and black foam film method for determination of the ability of ES for stable film formation [14]. The pendant drop method combined with the Axisym-metric Drop Shape Analysis (ADSA) has been also used for similar purposes [4,15-18]. 

The monolayer technique is extremely significant and has numerous applications. With a system such as a monolayer, we have the realization of a simple molecular functional unit. In other words, it is a system whose properties are determined by an orderty arrangement of molecules, i.e., the molecules form a team and the stem behaves differently from an independoit molecule. Such functional systems are often encovmtered in biological structures, for example, the proteins interact with lipid, polysaccharides and with other interfaciaUy-boimd compoimds. In fact, the whole living body is a functional unit where varied molecules interact and cooperate with each other. 

Many Immunological and enzymatic reactions have been studied by surface film technique. In addition, various aspects of protein structure can be deduced by investigation of spread protein films, for example, the study of compressibility of a protein film permits the determination of the molecular weight of the protein molecules forming the film. Tumit in 1954 has described a method for obftiining protein diffusion coefficient (D) by monolayer technique which is less cumbersome and is speedy too. Lastly, surface films have also been used to study the effect of irradiation of proteins and the results supplement the infonnatlon obtained by more conventional methods. 

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