Estimation of the time since death (postmortem interval, PMI) is one of the most difficult problems in forensic investigations and many methods currently are utilized to estimate the PMI. The aim of this study was to investigate the changes of Fourier transform infrared (FT-IR) spectra of rat kidney cortex from time zero to 168 h postmortem at molecular level. The spectra of rat kidney cortex displayed the prominent changes with increasing postmortem interval. (1) Significant increase in the intensity of the C-H stretching bands at 2958, 2925, 2871, 2852 cm −1 ,t he=C-H stretching band at 3012 cm −1 , the CO2 − symmetric stretching band at 1396 cm −1 and the N-H bend, C-N stretching at 1541 cm −1 ; (2) significant decrease in the intensity of the PO2 − stretching band at 1238, 1080 cm −1 ; (3) the intensity of at 3303, 1652 and 1170 cm −1 remained relatively stable. The linear regression analysis of the various absorption intensity and area ratios against the PMI shows a close correlation, maximum for A1541/A1396 ratio (R 2 = 0.95) and minimum for I1080/I1396 ratio (R 2 = 0.70). Our results indicate
Attenuated total reflection (ATR) Fourier transform infrared (FT-IR) spectroscopy has been applied to study the short and long term postmortem metabolic processes in rat and human kidney cortexes. The goals of this project were as follows: (1) to investigate the changes of ATR spectra in different rat and human tissues after death, (2) to explore the best mathematical model with different band absorption ratio changes to determine the postmortem interval (PMI), and (3) to establish a preliminary human postmortem ATR spectra database. There were three different types of metabolic changes after death based on the spectral results: (1) the intensities of some bands increased continuously (e. g., C–H stretching region), (2) the intensities of other bands decreased continuously (e.g., PO 2 − symmetric stretching), and (3) other bands remained relatively stable (e.g., C–OH bending, CO–O–C antisymmetric stretching). The band absorbance ratios for rats were found to display either a significant increase or decrease with increasing time after death. Of the absorbance ratios of the various bands investigated to find the best fit with the cubic model function in rats, the A 1652 / A 1396 ratio showed the strongest correlation ( R 2 = 0.937). Comparison of the rat kidney cortex spectra with selected human postmortem cases showed similar postmortem metabolic changes. In conclusion, ATR FT-IR spectroscopy was shown to be a convenient and reliable method of determining short and long term postmortem intervals by simultaneously monitoring several specific parameters, although these observations have yet to be applied at forensic scenes by further field studies.
Estimation of the time since death (postmortem interval, PMI) is one of the most difficult problems in forensic investigations and many methods currently are utilized to estimate the PMI. The aim of this study was to investigate the changes of Fourier transform infrared (FT-IR) spectra of rat kidney cortex from time zero to 168 h postmortem at molecular level. The spectra of rat kidney cortex displayed the prominent changes with increasing postmortem interval. (1) Significant increase in the intensity of the C–H stretching bands at 2958, 2925, 2871, 2852 cm –1 , the ═C–H stretching band at 3012 cm –1 , the CO 2 – symmetric stretching band at 1396 cm –1 and the N–H bend, C–N stretching at 1541 cm –1 ; (2) significant decrease in the intensity of the PO 2 – stretching band at 1238, 1080 cm –1 ; (3) the intensity of at 3303, 1652 and 1170 cm –1 remained relatively stable. The linear regression analysis of the various absorption intensity and area ratios against the PMI shows a close correlation, maximum for A 1541 / A 1396 ratio ( R 2 ═ 0.95) and minimum for I 1080 / I 1396 ratio ( R 2 ═ 0.70). Our results indicate that FT-IR spectroscopy may be a useful technique for estimating the short- and long-term PMI.
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