Study Of The Structure And Vibrational Properties Of The Aromatic Amino Acids

The study of vibrational spectra of molecules is an important tool to explore the properties of molecules. Spectroscopic investigations of biological macromolecules, such as amino acid, the nucleic acid (NA) bases contained in non-interacting environments or their salvation may help clarify the role of these molecules in biological systems. There are many experimental and theoretical studies on some basic biological molecules, such as amino acid ,base pairs, their derivatives or compounds. IR and Raman vibrational spectra are the main two experimental methods, but it is difficult to assign the spectra of polyatomic molecules because of the complexity resulting from coupling of vibrational modes, molecular interactions, and other effects. So the theoretical calculation of vibrational spectra has an important meaning to comprehend the experiment result and to predict new spectra. There are many methods to describe the motions of the molecules, such as quantum chemical methods and empirical molecular dynamics simulation. The former mainly includes HF method, ab initio method, and so on.The contents of the paper are listed as following:(1)The structures of phenylalanine,tryptophan,tyrosine and phenylalanine,tryptophan,tyrosine in water solution have been constructed by using Gaussian 03 and a lots of the prodected vibration modes have been analyzded respectively. And then both the vibration types and the frequency of the isolated phenylalanine, tryptophan, tyrosine and the phenylalanine, tryptophan, tyrosine in water solution have been analyzed. It is found that the calculated frequencies are in good agreement with the experiment data and supplement the data which have not given in the experiment.(2)The amino acid is the basic component of the protein molecule. Except the proline is one kind ofα-sub-amino acid, all the others areα-amino acid. Most of the amino acids in the nature are L-aminophenol, besides the glycin constructed by the absence chirality carbon-atomic. Because of the amido and carboxyl, amino acid is ampholyte so that it exists as a sort of zwitterions or dipole ionic when it dissolves in the water or in crystal. Using Gaussian 3.0 the structures of L-tyrosine and its isomer D-tyrosine have been constructed and the 66 kinds of vibration modes have been analyzed. It shows that their vibration type and frequency for L-tyrosine and D-tyrosine are very similar,either for the Infrared spectra and Raman spectra. The calculations reproduce the spectra of L-tyrosine and D-tyrosine and supplement the data which have not given in the experiment.