| Fourier transform Raman(FT-Raman) spectroscopy is an important analytical technique for chemical and biological analysis due to the wealth of information on molecular structures, surface processes, and interface reaction that can be extracted from experimental data. The normal Raman signals is inherently weak, thus preventing the possibility of achieving low detection limit with normal Raman spectroscopy. In order to obtain Raman spectrum with higher quality and lower inerference, there should be used some kind of Raman enhanced effect such as resonance Raman Scattering(RRS) and surface enhanced Raman scattering(SERS).Surface Enhanced Raman Spectroscopy is based on that molecules are adsorbed on some rudely substrates (mostly are noble metals and their nanoparticles) surface which can produce the signal. The sensitivity of signal is higher 6-10 orders than normal Raman's. Since last century senventy age, SERS has been widely used in many different fields. Many agreements have been made on basic theory such as the preparation and choice of substrate, the enhanced mechanism.Amino acid is the basic constructed cell of protein. The protein is made of 20 amino acids (proteinic animo acids) in every organism. Furthermore, we can find animo acid in enzyme and other organisms. It widely goes in for lots of different chemitry and biology reaction. It also plays a very significant effect on the basic energy circle, the energy transfer and muscle movement in our body. For the growth of altitude life-form that contained in human beings, the amino acid can devide into essential amino acid and nonessential amino acid. The former must be ingested from food, which can ensure the body's health growth. There are 9 essential amino acids in proteinic animo acid. They are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. The amino acids in organism are allα-amino acids, and their optics isomers are all L type except alanine.This article studies a few representative amino acids in 20 proteinic amino acids by Raman spectroscopy and SERS. They are methionine, leucine, isoleucine, phenyllalanine and tryptophan. Their Raman spectra and SERS on two substrates are obtained. According to selective rules and mechanism of SERS, the adsorption on different substrates surface and the change at different concentration or different pH value are speculated. At last, the vibration of Boc-amino acid and Fmoc-amino acid are studied by Raman and infrared spectroscopy.1. FT-Raman and SERS on silver nanoparticles of amino acids1.1 FT-Raman and SERS of methionineFT-Raman and SERS of methionine in solid and in saturated liquid state are measured, the vibrationai peaks are assigned. SERS of methionine on silver nanoparticle are measured at different concentration and different pH value. According to the SERS mechanism, the adsorption of methionine on silver nanoparticle is confered. From the experimental result, we can know that the aminogen, carboxyl and sulfur atom in molecule all put up strong Raman vibrationai peaks in solid and liquid state. The best concentration scale of methionine's SERS is from 1×10-3 Mol·L to 1×10-4 Mol·L on silver nanoparticle. Methionine adsorbed better on silver nanoparticle when the system is alkalescence.1.2 FT-Raman and SERS of leucine and isoleucineLeucine and isoleucine is only a isomer in 20 proteinic amino acid. FT-Raman and SERS of leucine and isoleucine in solid and in saturated liquid state are measured, the vibrationai peaks are assigned. SERS of leucine and isoleucine on silver nanoparticle are measured at different concentration and different pH value. From the experimental result, Raman and SERS peaks of the isomer are different because the the different construction in the isomer.1.3 FT-Raman and SERS of phenyl amino acidFT-Raman and SERS on silver nanoparticle of phelylalanine and tryptophan in solid and in saturated liquid state are measured, the vibrationai peaks are assigned. And the adsorption model of phenylalanine and tryptophan on silver nanoparticle are confered. According to the experimental results, the benzene rings in phanalanine and tryptophan adsorbed on silver nanoparticle surface flat. Their adsorptional model is speculated.2. SERS of amino acid on Core-Shell Au/Ag nanoparticlesThe active-SERS substrate-core-shell Au/Ag nanoparticles and SERS of leucine and isoleucine on this substrate are abtained. According to the characteristic of core-shell Au/Ag nanoparticles and SERS mechanism, the adsorption mode of leucine and isoleucine are speculated. From the experimental result, we can know that the different adsorption model of leucine and isoleucine still caused by the different construction of the isomer. The other reason is the homogenization and high enhancement of core-shell Au/Ag nanoparticles.3. FTIR FT-Raman study of Fmoc-amino acidsFT-Raman and infrared spectra of Fmoc-leucine and Fmoc-isoleucine are gained, the vibrational peaks are assigned. The vibrational model of Fmoc-leucine and Fmoc-isoleucine are speculated, which could obtain the reference information of the mechanism and vibrational model after other amino acids are combined with the Fmoc group. |
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