Water subphase

FIG. 11 Force profiles between poly(glutamic acid), 2C18PLGA(44), brushes in water (a) at pH = 3.0 (HNO3), (b) at pH 10 (KOH) 1/k represents the decay length of the double-layer force. The brush layers were deposited at tt = 40 mN/m from the water subphase at pH = 3.0 and 10, respectively. 

Figure 11a shows a force-distance profile measnred for poly(L-glutamic acid) brushes (2C18PLGA(44)) in water (pH = 3.0, 10 M HNO3) deposited at 40 mN/m from the water subphase at pH = 3.0. The majority of peptides are in the forms of an a-helix (38% determined from the amide I band) and a random coil. Two major regions are clearly seen in... 

Therefore, the following method was suggested and realized (the scheme is shown in Fig. 17). A 1.5 M solution of KCl or NaCl (the effect of preventing BR solubility of these salts is practically the same) was used as a subphase. A platinum electrode was placed in the subphase. A flat metal electrode, with an area of about 70% of the open barriered area, was placed about 1.5-2 mm above the subphase surface. A positive potential of +50 -60 V was applied to this electrode with respect to the platinum one. Then BR solution was injected with a syringe into the water subphase in dark conditions. The system was left in the same conditions for electric field-induced self-assembly of the membrane fragments for 1 hour. After this, the monolayer was compressed to 25 mN/m surface pressure and transferred onto the substrate (porous membrane). The residual salt was washed with water. The water was removed with a nitrogen jet. 

The second step, Figure 32b, consists of the covering of the styli with cadmium arachidate LB films. Monolayers of arachidic acid (in principle, it is also possible to use stearic or behenic acids with practically the same results) were spread over the surface of 10 " M CdCli water subphase in a Langmuir trough. The monolayer was compressed to a surface pressure of 27 mN/m and transfered onto styli by a vertical dipping technique. Up to six monolayers were deposited. 

It is also interesting to note that only a fraction of PS II membrane protein forms a stable monolayer structure and the rest of them fall into the water subphase. This can be seen directly by the naked eye during the compression. Furthermore, if we use the total amount of PS II membrane protein to calculate the average particle size from the n-A curve, we obtain an area of about 200 nm. This value is very small when compared with that of the PS II core complex (320 nm, as discussed in the subsequent section), which is a smaller subunit of the PS II membranes. A PS II membrane fragment contains PS II core complex and several LHC II proteins, and is much larger in size than a PS II core complex... 

However, one must also be careful when using a high concentration of salt to increase the density of the water subphase. Two disadvantages of using high-concentration salt solution as subphase are (1) high concentration of salt in the subphase can change the protein conformation at the air-water interface (2) the salt particles can be deposited... 

Fig. 5 Surface pressure/area isotherm for the compression cycle of dipalmitoylphos-phatidyl choline (dashed line) and l-palmitoyl-2-(l2-hydroxystearoyl)phosphatidyl choline (solid line) on a pure water subphase at 25°C. Reprinted with permission from Arnett et al., 1989. Copyright 1989 American Chemical Society.

Fig. 14 Compression/expansion hysteresis loops for monolayers of dipalmitoylphos-phatidyl choline at 25°C on pure water subphase. Rate of compression/expansion is 12.5 A2/molecule per minute.

Both the N- (a-methylbenzy 1) stearamide and phospholipid systems as detailed above proved to be difficult systems with which to work. The inability of N- a-methylbenzy 1)stearamide to form stable monolayers or even to spread from the crystal on anything but very acidic subphases presents a significant technical challenge despite the presence of a chiral headgroup that is unobstructed by other molecular features. On the other hand, the phospholipid surfactants that spread to form stable films both from solution and from their bulk crystals on pure water subphases at ambient temperatures displayed no discernible enantiomeric discrimination in any film property. The chiral functionality on these biomolecules is apparently shielded from intermolecular interactions with other chiral centers to the extent... 

Table 2 Lift-off areas per molecule for different chiral surfactants studied at 25°C on a pure water subphase.

Fig. 17 Surface pressure/area isotherms for the compression and expansion cycles of racemic (dashed line) and enantiomeric (solid line) stearoylserine (A), stearoyl-alanine (B), stearoyltryptophan (C), and stearoyltyrosine methyl esters (D) on a pure water subphase at 25°C carried out at a compression rate of 7.1 A2/molecule per minute. Arrows indicate the direction of compression and expansion.

Table 3 Stability results for the stearoylamino acid esters on pure water subphases at 25°C using Cadenhead s criterion for stability.

When spread from a benzene/hexane solution on to a slightly acidic water subphase, spread films of racemic and enantiomeric STy exhibit nearly the same IT/A isotherms (Fig. 22) and surface shear viscosities (Harvey et al., 1990). The shapes of these isotherms and the apparently small differences between the compression/expansion characteristics of these fluid homochiral and heterochiral monolayers is conserved throughout the... 

Fig. 24 Surface pressure/area isotherms for palmitic acid/stearoylserine methyl ester films at 25°C on a pure water subphase and compressed at 29.8 A2/molecules per minute. A, 16.7-33.3% B, 50% C, 66.6% D, 83.3% SSME.

Fig. 32 Surface pressure/area isotherms for the compression/expansion cycles of diastereomeric monolayers of (R or S)-iV-(a-methylbenzyl)stearamides mixed 1 1 with (R or S )-stearoylalanine methyl esters on a pure water subphase at 35°C. Dashed lines denote heterochiral pairs (R S or R S) and solid lines denote homochiral pairs (R R or S S ).

Table 11 Work of compression of the C-15 3,3, C-15 6,6, C-15 9,9, and C-15 12,12 ketodiacids on a pure water subphase at 25°C compressed at a rate of 19.24 A2/molecule per minute.

Arachidic acid monolayers were prepared from a benzene solution on the water subphase of pH5.8(pure water) and 12.6(adjusted by addition of NaOH) at Tsp of 303 K below Tm(=328 K) of the monolayer [31]. The ionic dissociation state of hydrophilic group was estimated on the basis of the stretching vibrations of carbonyl and carboxylate groups by Fourier transform-infrared attenuated total reflection, FT-IR ATR measurements. 70 arachidic acid monolayers were transferred on germanium ATR prism, resulting in the formation of the multi-layered film. Transfer on the prism was carried out at surface pressures of 25 or 28 mN-nr1. Infrared absorption measurements revealed that almost carboxylic groups of arachidic acid molecules did not dissociate on the water subphase of pH5.8, whereas all carboxylic groups dissociated as carboxylate ions on the water subphase of pH 12.6. 

We review useful usages of a quartz crystal-microbalnce (QCM) as tool of in situ characterization of Langmuir-Blodgett (LB) films transfer ratio and water incorporation during a transfer process, swelling behavior in water subphase, and detachment at the air-water interface. 

The incorporated amount of water (W2) seems to increase with decreasing the dipping speed. Since the W2 value may include both the really incorporated water and the swelling with water when the substrate exists in the water subphase, the effect of dipping speed on W2 values should be divided in two factors. We have already reported... 

On the other hand, in two-dimensional films, the state is much different. The amphiphile molecules are oriented at the interface such that the polar groups are pointed toward water (subphase), while the alkyl groups are oriented away from it. This orientation gives the minimum surface energy. The structure is stabilized through lateral interaction between... 

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