Biliverdin is a useful component in various aspects of biochemistry and biosynthesis, but its synthetic preparation is often
long-winded. Micro-production (and subsequent isolation) by solar photolysis and gamma radiolysis of bilirubin provides rapid
in vitro generation. Both methods are competitive, and this article discusses their merits and limitations for application
in biosynthetic research. The investigation assumed a comparative study to evaluate the relative potential of the photolytic
and radiolytic phenomena in this respect. The calculated rate of incident energy in the case of solar photolysis was roughly30.4.10-2 W, and about 5.70.10-4 W during gamma-irradiation (from a 137Cs source). In both cases the bilirubin (40 µM) degradation was pronounced in the initial few minutes of exposure, producing
respective depletion rates of approximately 6.8 µM/min and 2.4 µM/min. Overall, both applications showed declining bilirubin
concentrations close to 90%, after about 30 minutes. However, the corresponding production of biliverdin was higher by about
50% in the photolytic application. To account for heat-up effects in the photolytic application, thermal effects were studied
up to 65 °C, and it was found that, as a result of this, a reduction in bilirubin concentration of about 40% was encountered.
The species of interest were monitored spectrophotometrically, and the composite results showed that regulated production
of biliverdin is possible under certain conditions.
Kinetics and concentration profile associated with the regulated radiodegradation of bilirubin in an organic solvent were
assessed. The pure unconjugated specimen was prepared in chloroform (40.0 µM). The depletion of bilirubin was almost linear
with dose, and complete degradation was accomplished with doses in excess of 100 Gy. The method was also evaluated for the
explicit production of the long-wavelength isomer of biliverdin, which was characterized spectrometrically by an absorbance
band in the region 600–650 nm. Results including differences in air, N2 and O2 purged samples are presented to identify the atmospheric medium for optimum production of biliverdin. The process was regulated
by controlling the dose. The general rate constant of the depletion process was estimated at a dose rate of 5.67·10−2Gy·s−1. The method is a convenient substitute for light illumination studies of bilirubin.
A bilirubin-chloroform solution was tested as a gamma-radiation dosimeter (SALPILL dosimeter) in the 0-100 Gy range, and at dose rates between 0.01 to 3.18 Gy . min-1, which displayed certain advantages over the conventional Fricke, TLD and diode dosimeters when examined under identical experimental conditions. The principle of operation involved gamma-irradiation of micro-molar quantities of the unconjugated specimen with a 137Cs source (662 keV gamma-rays), and measurement of the (degraded) bilirubin absorption at 453 nm. The relationship of bilirubin depletion and radiation dose was linear, which remained invariant with oxic and anoxic exposure, denoting excellent reproducibility under diverse experimental conditions. Further validation of performance was achieved by repeated in-air trials, which produced a reproducibility within ±2% (n = 5). Stringent comparative tests conducted against currently accepted gamma-radiation dosimeters favoured the SALPILL dosimeter in all the relevant areas. The merits of using chloroform as a solvent in place of water was considered. The SALPILL dosimeter has the following distinctive features: prolonged “shelf-life” (before and after irradiation), insensitive into oxygen, operational at relatively low dose rates, linear functionality at low doses (0-5 Gy), solvent stability, solute integrity, reliability, convenient and cost-effective. The drawbacks of SALPILL are minimal, which makes it a facile dosimeter for certain applications.
Authors:F. Doğan, M. Ulusoy, Ö. Öztürk, İ. Kaya, and B. Salih
The thermal decomposition kinetics of sterically hindered salen type ligand (L) and its metal complexes [M=Co(II), Ni(II), Cu(II)] were investigated by thermogravimetric analysis. A direct insertion probe-mass spectrometer (DIP-MS)
was used for the characterization of metal complexes of L and all fragmentations and stable ions were characterized. The thermogravimetry and differential thermogravimetry (TG-DTG)
plots of salen type salicylaldimine ligand and complexes showed a single step.
The kinetic analysis of thermogravimetric data was performed by using the invariant kinetic parameter method (IKP). The values
of the invariant activation energy, Einv and the invariant pre-exponential factor, Ainv, were calculated by using Coats-Redfern (CR) method. The thermal stabilities and activation energies of metal complexes of
sterically hindered salen type ligand (L) were found as Co(II)>Cu(II)>Ni(II)>L and ECu>ENi>ECo>L. Also, the probabilities of decomposition functions were investigated. The diffusion functions (Dn) are most probable for the thermal decomposition of all complexes.