Spectra-structure correlations amino acids

Neural networks have been applied to IR spectrum interpreting systems in many variations and applications. Anand [108] introduced a neural network approach to analyze the presence of amino acids in protein molecules with a reliability of nearly 90%. Robb and Munk [109] used a linear neural network model for interpreting IR spectra for routine analysis purposes, with a similar performance. Ehrentreich et al. [110] used a counterpropagation network based on a strategy of Novic and Zupan [111] to model the correlation of structures and IR spectra. Penchev and co-workers [112] compared three types of spectral features derived from IR peak tables for their ability to be used in automatic classification of IR spectra. 

The authors expressed PKA consisting of 353 amino acids, of which eight are prolines. Resonances of 274 backbone amide peaks were visible in the spectrum, of which 191 were assigned. It was possible to assign resonances for the N- and C-terminal sequences, the majority of the N-lobe, including the glycine-rich loop, and most of the solvent-exposed residues of the C-lobe. This enabled a determination of the structure for the more flexible parts of the structure. However, many correlations were missing for the... 

Structural correlations on the basis of CD spectra provide good information about the stereochemistry of chiral molecules. The structure of (—)-tetrahydrobiopterin, the cofactor for hydroxyl-ations of aromatic amino acids, was determined by x-ray crystallographic analysis as (6R,l, 2 5)-6-(L -dihydroxypropyO-S J -tetrahydropterin (135). Its CD spectrum exhibits a negative Cotton... 

The application of proton-driven CSA correlation spectroscopy to amino-acid specifically carboxylic-labeled spider silk [63] is shown in Fig. 4.11. Spider silk is known to consist of alanine- and glycine-rich domains [64, 65] and is known to be semicrystalline. The assignment of alanine to the (crystalline) /3-sheet domains [66] is clearly supported by the chemical-shift correlation spectrum of Fig. 4.11. Because the tensors in a j8-sheet structure are almost parallel, or antiparallel, with the tensors in spatial proximity, a diagonal spin-diffusion spectrum is expected for that structure and is indeed found. In contrast, the glycine spectrum shows considerable off-diagonal intensity. Simulations have shown that the spectrum is compatible with a local 3i-helical structure [63]. 

Chapman and Morrison (1966) have found NMR evidence favoring a dipolar ionic form for the phosphatidyl ethanolamines. Also, their infrared spectra of chloroform solutions favor a dipolar ionic structure. The evidence was as follows if dioleoyl-phosphatidyl ethanolamines exist in chloroform in a nonionic form, then intense bands in the 3300 cm region should occur because of NH stretching frequencies. Bands were found at 3058, 2710, 2538, and a probable band at 3021 cm , which they correlated with vibrations of an NHj group. A comparison of the spectra of dioleoyl-phosphatidyl ethanolamine and a dipolar ionic amino acid, such as alanine, showed almost identical spectra in the 4000 to 2000 cm region. The spectrum of the non-ionized compound, OL-a-alanine methyl ester in chloroform shows intense absorption in the 3300 cm region characteristic of a free primary amino group. 

NMR spectrum of the dragline silk of the C/ N-proline-enriched Argiope aurantia spider, which is rich in MaSp2. However, extensive spectral overlap between Pro and other amino acids, with the exception of the Pro C(x, compromises the extraction of exact chemical shift values. Hence, 13c 13c correlation NMR with a medium 50 ms DARR recoupling period was utilized to exploit the connectivity within the Pro residue to yield precise chemical shifts. A chemical shift difference of 5.1 ppm was found, which was indicative of a type II P-tum structure. This structural assignment was further confirmed by using HETCOR experi-... 

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