Raman Spectroscopic Analysis Of Solid DNA Fiber Induced By He-Ne Laser Irradiation

In this thesis,using Raman spectroscope,after He-Ne laser irradiation of different power density treated calf thymus DNA in solid fiber at various time,the effect of He-Ne laser on calf thymus DNA molecular structure was studied.The DNA damage effect induced by He-Ne laser was analyzed from DNA phosphoric acid skeleton structure and conformation,desoxyribose and phosphoric acid-desoxyribose as well as basic group.The results of this research are helpful in understanding the interaction between He-Ne laser and DNA in molecular level,and will provide a certain value reference for breeding in the laser,laser medicine and laser biological genes.After repeated experiments,some results as the following were obtained.1,The conformation of the DNA solid fiber still is A-type after it was irradiated by low-power density He-Ne laser.But the conformation has the minor damage when the laser irradiation time lengthened.After laser irradiating of a short time,the experimental results proved that the laser irradiation bad hardly any effect on phosphoric acid skeleton structure and slightly damaged the hydrogen bonds and the bases.With the extended laser irradiation time,some of the di-phosphate ester key O-P-O and of the hydrogen boads were broken.Continued laser irradiation,the DNA damage induced by laser reduced firstly,then its damage was aggravated.But the time when extent of damage of phosphoric acid skeleton groups reduced is the earlier than the time when extent of damage of hydrogen bond reduced.The mechanism which the DNA damage reduced instead increased with laser irradiation for a longer time is not clear.First the laser destroyed the interaction of base-base which perpendicular with DNA for the majority of basic groups,then made hydrogen bonds of the base damaged and cut off.2,The damage to the DNA structure was very serious after it was irradiated by high-power density He-Ne laser.With laser irradiation for a short time,the intensity reduced rate of the bases was about 30%.With the extended irradiation time,the intensity reduced rate of the bases was about 60%to 80%.After a longer period of irradiation,its conformation still was A-type,but the conformation damage was aggravated with the extended laser irradiation time.At first a part of single and double strand broken;then DNA become disorderly;finally its configuration also changed. Lengthener along with the laser irradiation time,deoxyribose was damaged from minor to serious.Laser damaged all bases in some extent.The damage degrees of the base pairs in turn were guanine,adenine,thymine and cytosine.3,When the DNA solid fiber was irradiated by middle-power density He-Ne laser, the damage of phosphoric acid skeleton structure and of hydrogen bonds has got to the maximum in the very short irradiation time.By now not only had the di-phosphate ester key was broken,the hydrogen bond has also been broken.Along with irradiation time's extension,the DNA damage induced by the laser is first to reduce,then to aggravate again.First the effect of laser irradiation on the bases was intense Raman hypochromicity of the base peaks.Second Raman hypochromicity of the base peaks weakened gradually with laser irradiation time elongation;then the stronger Raman hyperchromicity of the base peaks emerged.The base peaks became weak again when the laser irradiation continued.The reasons for these phenomena may be that laser destroyed the stacking structure of base-base which perpendicular with DNA after it damaged bases,so resulted,in base peaks weakening first and strengthening subsequently.In this study,the damage effect of the laser on the DNA bases was tried to analyze at the bond level.After the laser irradiation on the DNA,the analytic results showed that the out-ring amino group numeration of the DNA pyridine component's cytosine C₄ site have reducing in the form of Raman hypochromicity.And Raman hypochromicity of the double bond of C₅C₆ maybe result from C₅C₆ electronic cloud density reducing, which also led the stretching vibrations of C₅C₄ single bond weakening.