Alanine films

Figure 15. Comparison of L- and D,L-A-stearoyl-alanine films enantiomeric discrimination is barely discernible. From Zeelen (84).

Other commercially radiochromic films are poly(methyl methacrylate) (PMMA), cellulose triacetate (CTA),i polyamide (nylon) films, poly(vinyl butyrate) with pararosaniline and p-nitrobenzoic acid, and alanine films. The CTA films are undyed PMMA films are available undyed and dyed (red and amber). ... 

Figure 17 shows the 11/A isotherms of racemic and enantiomeric films of the methyl esters of 7V-stearoyl-serine, -alanine, -tryptophan, and -tyrosine on clean water at 25°C. Although there appears to be little difference between the racemic and enantiomeric forms of the alanine surfactants, the N-stearoyl-tyrosine, -serine, and -tryptophan surfactants show clear enantiomeric discrimination in their WjA curves. This chiral molecular recognition is first evidenced in the lift-off areas of the curves for the racemic versus enantiomeric forms of the films (Table 2). As discussed previously, the lift-off area is the average molecular area at which a surface pressure above 0.1 dyn cm -1 is first registered. The packing order differences in these films, and hence their stereochemical differentiation, are apparently maintained throughout the compression/expansion cycles. 

The instability of these chiral monolayers may be a reflection of the relative stabilities of their bulk crystalline forms. When deposited on a clean water surface at 25°C, neither the racemic nor enantiomeric crystals of the tryptophan, tyrosine, or alanine methyl ester surfactants generate a detectable surface pressure, indicating that the most energetically favorable situation for the interfacial/crystal system is one in which the internal energy of the bulk crystal is lower than that of the film at the air-water interface. Only the racemic form of JV-stearoylserine methyl ester has a detectable equilibrium spreading pressure (2.6 0.3dyncm 1). Conversely, neither of its enantiomeric forms will spread spontaneously from the crystal at this temperature. 

Malcolm (1973, 1975) reported possible observable differences between the pressure-area curves of poly(L-alanine) mixed with poly(D-a-amino-n-butyric acid) and the corresponding mixture containing poly(D-alanine). Shafer (1974) observed differences in the film pressure between (/ )-phosphatidyl serine with poly-L-lysine and the corresponding film with poly-D-lysine injected under the film. 

The percent conversion of the monomer to the polypeptide can be estimated by the quantity 100 (Aq - At) / Aq, where Aq and At are the integrated intensities of the ester band at the start and time t, respectively. At 40 °C, it tended to saturate at about 30 % for the Y-type films of L-NaphAla-C-i s, and L-PyrAla-G 8, although the conversion for the LB film of long-chain ester of alanine (L-Ala- Ci s) reached to 90 % [52]. This difference is considered to be due to a larger steric hindrance of the aromatic rings. 

Alanine dosimeters are based on the ability of 1-a alanine (a crystalline amino acid) to form a very stable free radical when subjected to ionizing radiation. The alanine free radical yields an electron paramagnetic resonance (EPR) signal that is dose dependent, yet independent of the dose rate, energy type, and relatively insensitive to temperature and humidity. Alanine dosimeters are available in the form of pellets or films and can be used for doses ranging from 10 Gy to 200 kGy. A reference calibration service using the alanine EPR system was developed and the scans were sent to the service center by mail. Currently the available system allows transferring the EPR scan to a NIST server for a calibration certificate. This way the procedure has been shortened from days to hours. ... 

Electron beam damage effects followed the general rule that molecular groups in intimate contact with the metal substrate and aromatic groups appear relatively stable. Thus in the monolayer, alanine, with a methyl group likely sticking out from the surface, was the only molecule found to be unstable. In multilayer films, only tryptophan with the aromatic indole group to stabilize the molecule was found to yield multilayers stable under electron beam irradiation. 

Besides polymerization, another type of polyreaction can be used for stabilizing model membrane systems. Recently, Fukuda et al.28) described polyamide formation via polycondensation in monolayers at the gas/water interface (definition of mono-layers see Sect. 3.2). Long-chain esters of glycine and alanine were polycondensed to yield non-oriented polyamide films of polyglycine and polyalanine. 

A stretched fiber containing many poly-L-alanine molecules is suspended vertically and exposed to a collimated monochromatic beam of CuKa x-rays, as shown in figure 1(a). Only a small percentage of the x-ray beam is diffracted most of the beam travels through the specimen with no change in direction. A photographic film is held in back of the specimen. A hole in the center of the film allows the incident undiffracted beam to pass through. 

Alanine or Cysteine Grafting. The PP surface modified with y-aminopropyltrimethoxysilane and glutaraldehyde was incubated in a solution consisting of 1.0 g of alanine or cysteine dissolved in 10 ml of doubly distilled water for a period of 3 hours. The, the film was washed with water and methanol and dried. 

Ti(0 Bu)4 (100 mM) and carbobenzyloxy-L-alanine (Cbz-L-Ala, 25 mM) were mixed in toluene/ethanol and stirred at room temperature for more than 12 h. After addition of water and aging for several hours, the stock solution was diluted with toluene, and subjected to the surface sol-gel process. Uniform adsorption was observed up to 15 cycles with frequency shifts of 140-160 Hz per cycle. The template molecule, Cbz-L-Ala, was removed from the gel film by dipping in 1 wt % aqueous ammonia, as confirmed from the disappearance of characteristic peaks of the titanium-carboxylate complex and carbamate in reflection FT-IR spectra. 

Dosimeters that are sufficiently small, such as thin radiochromic films and alanine pellets, can readily be calibrated against the calorimeter, by irradiating in tandem (with a suitable radiation monitor) while encased in a phantom material that is identical in size, shape and substance to the calorimetric absorber. The main appreciable correction that is required is the ratio of mass energy-absorption coefficients of the two materials (in the case of photon irradiations) or the ratio of mass collision stopping powers of the two materials (in the case of electron beam irradiations) (McLaughlin et al., 1989). 

Figure 25. Circular dichroism spectra of the classical polypeptide conformations extended into the vacuum ultraviolet region. Solid curve, a-helical pattern averaged from poly-L-alanine and poly(y-methyl-L-glutamate) data. Dashed curve, antiparallel /5-pleated sheet CD pattern due to films of Boc-(l -Ala)7-OMe [78]. Dotted curve, parallel /S-pleated sheet patterns were calibrated by solution spectra. Dash-dot curve, disordered collagen to provide a measure of a random structure. Reproduced, with permission, from [79].

The monolayers chosen included cephalins and lecithins as examples of molecules expected to have a high polarizability normal to the interface (9, 26). Long chain sulfate and quaternary ammonium ions were studied as examples of monolayers with diffuse ionic double layers. Other experiments were made with protein films, with a long chain /5-alanine, and with monolayers of equimolar mixtures of long chain sulfates and quaternary ammonium ions. The various results can be explained by the effects illustrated below for long chain sulfates and lecithin. 

ZAGORSKI, Z.P., RAFALSKI, A., A thin alanine-polyethylene film dosimetry system with diffuse reflection spectrophotometric evaluation J.Radioanal.Nucl.Chem., Articles, 196(1995) 97-105. 

Figures 4.4 to 4.7 show the results obtained from an experiment conducted by varying the concentrations of complexing agent (alanine) and selechvity control agent (PAM) in aqueous slurry. Figure 4.4 shows the removal rate of Cu and TaN films versus the alanine concentration. The removal rate of Cu film increased with alanine concentrations. In addition, the removal rate of TaN film strongly suppressed and slightly increased with increasing alanine concentrahons in aqueous suspension. As with the removal rate of Cu film, the removal rate of TaN film drashcally decreased and was essentially saturated with a concentration of alanine beyond 0.5 wt%.

FIGURE 4.4 The removal rates of Cu and TaN films versus alanine concentration in slurry. 

Alanine could exist in aqueous solution in three different forms, namely, CHS CH(NH3+)COOH (cation), CHS CH(NH3+)COO- (zwitterions), and CHS CH(NH2)COO- (anion). These species are denofed as H2L+, HL, and L-, respectively, for brevify. The equilibrium befween fhese may be depicfed, as Babu ef al. (2005) previously reported, the dissolution and removal rate probability of fhe complexing agent, including phthalic acid, citric acid, glycine, oxalic acid, and carboxyl and/or amine functional group, which interact on the Cu film surface should strongly influence the removal rate. 

Figure 4.5 shows the electrokinetic behaviors of Cu film, TaN film, and colloidal silica slurries wifh alanine addition as a function of pH. The absolufe surface zeta potential of the Cu film was slighfly negatively charged above pH 5. The TaN film also exhibited a slightly negative charge at a pH above pH 5.3. Colloidal silica slurry with alanine exhibited a pHi p at pH 4.0. 

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