Amino acids, infrared spectra

FIGURE 3 The infrared spectrum of an amino acid, with the groups contributing to some ol the peaks identified. Notice that the spectrum displays the intensity of absorption. 

US patent 6,806,280, Polymorph of 5-[4-[2-( -methyl- (2-pyridyl)amino)ethoxy] benzyl]-thiazolidine-2,4-dione, maleic acid salt [117]. This invention discloses a polymorphic form of 5-[4-[2-(A-methyl-jV-(2-pyridyl)amino)cthoxy]benzyl]-thia-zolidine-2,4-dione, maleic acid salt. The polymorphic form is characterized by (i) an infrared spectrum containing peaks at 1763, 912, 856, and 709 cm-1 and/or... 

Pure SeMet may be distinguished from Met by its infrared spectrum (Shepherd and Huber, 1969). Identification of SeMet in protein hydrolysates is possible by means of standard amino acid analyzers (Sliwkowski, 1984). SeMet elutes near to, or with, leucine. Major factors affecting the resolution of these two amino acids are temperature and pH. 

Allonic acid, 5-amino-5-deoxy-DL-, 139 Allopyranoside, methyl 2-acetamido-4,6-0-benzylidene-2-deoxy-3-0-(methyl-sulfonyl)-a-D-, infrared spectrum, 255 —, methyl 2-acetamido-2-deoxy-3-0-... 

Infrared spectra were collected on a Perkin Elmer Spectrum 2000 infrared spectrometer equipped with an /-series IR microscope and controlled with Spectrum for Windows software (Perkin Elmer, Norwalk, CT). Spectra were coadded from 250 scans at a resolution of 8 cm with strong apodization. Reference spectra of CytC and individual amino acids were... 

Methods have been developed by which a single amino acid (or sometimes a di- or tripeptide) can be polymerized to yield polypeptides of high molecular weight. These products have been extremely useful as model compounds to show, for example, what kind of x-ray pattern or infrared spectrum is given by a peptide of known, comparatively simple structure. 

The infrared spectrum of cycloserine presented in Fig. 1 was taken in a KBr pellet. A spectrum of the same sample taken in a Nujol Mull is essentially identical to the one presented. Hidy- -, Kuehl, and Stammer showed that the solid state spectrum of cycloserine has two ionizable groups with pKa, equal to. A -. 5 and pKa2 equal to 7 Spectral bands typical of an amino acid zwitterion (2200 cm assigned to the -NH +) and a resonance stabilized hydroxamafe anion (1600 to 1500 cm-1) are in agreement with the peaks represented in Fig. 1. 

Dimethylformamide (DMF) has a much more complex structure than either acetonitrile or acetone, but it is interesting to compare its infrared spectrum with that of formamide. By replacing the two acidic protons on the amino group by methyl groups, one obtains an aprotic liquid. As can be seen by comparing figs 5.16 and 5.19, the infrared spectrum of DMF is much simpler than that of for-... 

Neural networks have been applied to infrared spectrum interpreting systems in many variations and applications. Anand introduced a neural network approach to analyze the presence of amino acids in protein molecules with a reliability of nearly 90% [37]. Robb used a linear neural network model for interpreting infrared spectra in routine analysis purposes with a similar performance [38]. Ehrentreich et al. used a counterpropagation (CPG) network based on a strategy of Novic and Zupan to model the correlation of structures and infrared spectra [39]. Penchev and colleagues compared three types of spectral features derived from infrared peak tables for their ability to be used in automatic classification of infrared spectra [40]. 

A rapid FTIR method for the direct determination of the casein/whey ratio in milk has also been developed [26]. This method is unique because it does not require any physical separation of the casein and whey fractions, but rather makes use of the information contained in the whole spectrum to differentiate between these proteins. Proteins exhibit three characteristic absorption bands in the mid-infrared spectrum, designated as the amide I (1695-1600 cm-i), amide II (1560-1520 cm-i) and amide III (1300-1230 cm >) bands, and the positions of these bands are sensitive to protein secondary structure. From a structural viewpoint, caseins and whey proteins differ substantially, as the whey proteins are globular proteins whereas the caseins have little secondary structure. These structural differences make it possible to differentiate these proteins by FTIR spectroscopy. In addition to their different conformations, other differences between caseins and whey proteins, such as their differences in amino acid compositions and the presence of phosphate ester linkages in caseins but not whey proteins, are also reflected in their FTIR spectra. These spectroscopic differences are illustrated in Figure 15, which shows the so-called fingerprint region in the FTIR spectra of sodium caseinate and whey protein concentrate. Thus, FTIR spectroscopy can provide a means for quantitative determination of casein and whey proteins in the presence of each other. 

Additional evidence was obtained for the structure (110) of the compound derived from D-mannose, ammonia, and ethyl acetoacetate. This substance, when suspended in water and kept at room temperature, is slowly hydrolyzed, giving di-n-mannosylamine, isolated in the crystalline state, and n-mannose, characterized as its phenylhydrazone. Acetylation gives a tetra-O-acetyl derivative (111). The infrared spectrum of this acetate shows bands at 3280 cm. , attributable to the presence of an intramolecularly bonded NH group, and at 1658 cm. S probably due to the carbonyl group of the /3-amino a, 8-unsaturated ester also involved in a hydrogen bond. Mild, acid hydrolysis of (111) gives 2,3,4,6-tetra-O-acetyl-D-mannose. 

An interesting fact, first noticed by Wright (1937, 1939) is that the infrared spectrum of the DL-form of an amino acid is usually markedly different from the spectrum of either the d- or the L-form of the same acid when each is examined in the solid state. Wright attributes this to compound formation between the d- and L-forms. Darmon et al. (1948) have confirmed this observation, which is extremely important if infrared methods are to be used for the analysis of mixtures of amino acids, e.g., the estimation of leucine iso-leucine ratios in protein hydrolysates. In this connection, Gore and Petersen (1949) have reported differences between the spectra of L-threonine and D-threonine when examined in the solid state. They point out that this might arise from a polarization effect in the spectrometer. 

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