单宁酸与牛血红蛋白相互作用的光谱研究

利用荧光光谱技术研究了单宁酸与牛血红蛋白分子的相互作用。实验结果表明:单宁酸分子与BHb发生反应生成基态复合物,导致BHb内源荧光的猝灭,该猝灭属于静态猝灭。测定了不同温度下该反应的表观结合常数、结合位点数及结合热力学参数,热力学参数的变化表明上述作用过程是一个熵增加、自由能降低的自发分子间作用过程,单宁酸与BHb之间以疏水和氢键作用力为主;根据Frster能量转移理论,测得供体与受体间结合距离r和能量转移效率E;并用同步荧光光谱法探讨了单宁酸对BHb构象的影响。     

Thermoluminescence study of gamma irradiated BCNO nanophosphor

Boron carbon oxynitride (BCNO) is a low Z_eff (≈6.8), near tissue equivalent material. Nanocrystals of the BCNO:Dy and BCNO:Cu were synthesized by solid state reaction method using different concentrations of dopants. TL characteristics of the synthesized BCNO and BCNO:Dy material doped with 2500 ppm concentration of Dy were studied and compared with each other. It is observed that the doping of BCNO with Cu or Dy leads to the quenching of its TL properties. BCNO exhibits a linear response from 1×10² to 2×10³ Gy whereas BCNO:Dy exhibits a linear response from 1×10² to 1×10³ Gy of gamma radiations. Fading and reproducibility of phosphors are also studied and it is found that the undoped BCNO shows better TL results than that of Dy doped BCNO phosphor. The main disadvantages of this material are its low thermal stability and high fading, so further studies are needed for this material before concluding it as the best dosimeter for gamma doses.     

分子光谱法研究铝酞菁与牛血红蛋白的相互作用

利用紫外可见吸收光谱和荧光光谱研究了在生理pH条件下铝酞菁与牛血红蛋白(BHb)的相互作用.实验结果表明:铝酞菁分子与BHb发生反应生成基态复合物,导致BHb内源荧光的猝灭,该猝灭属于静态猝灭.测定了不同温度下该反应的表观结合常数、结合位点数及结合热力学参数,热力学参数的变化表明铝酞菁与BHb之间以静电和疏水作用力为主;根据Frster能量转移理论,测得供体与受体间结合距离r和能量转移效率E;并用同步荧光光谱法探讨了铝酞菁对BHb构象的影响.     

Dielectric relaxation study of gamma irradiated oriented low-density polyethylene

The influence of drawing, gamma irradiation and accelerated aging on the dielectric relaxation of low-density polyethylene has been studied using dielectric loss tangent measurements in the temperature range from 25 to 325 K and in the frequency range from 10³ to 10⁶ Hz. The intensity, position and activation energy of the γ- and β-dielectric relaxations were found to be strongly dependent upon the changes in the microstructure of the amorphous phase induced by uniaxial orientation, oxidation and crosslinking.     

ESR study of gamma irradiated 2-methyl nylon3

Gamma radiation-induced radicals of 2-methyl nylon3 (2mN3) have been investigated by electron spin resonance spectrometry. The type of radicals generated, conversion into other radicalic species and their room temperature stability were evaluated. Two types of radicals have been detected. Two different formation mechanisms have been proposed for each radical. As suggested in literature for commercial polyamides, in our system we also observed two different radicals (R1 and R2). Among these radicals, R1 is expected to convert to R2, which is a chemically favorable process.     

Spectroscopic analysis of irradiated erythrocytes

The aim of the present work is to study the effect of gamma radiation on the lipid part of the erythrocyte membrane, and to test the efficiency of lipoic acid as a radioprotector. This effect was evaluated using electron paramagnetic resonance (EPR), and Fourier transform infrared (FT-IR) spectroscopy. The results showed an increase in the number of spin density by 14%, 22% and 65% after exposure to 25, 50 and 100 Gy respectively; whereas there was a decline in the obtained density after incubation with lipoic acid by a factor of approximately 32%. The FT-IR spectra of the irradiated erythrocytes samples showed a marked decrease in the intensity of all characteristic peaks, which increased as the irradiation dose increased. The second-derivative of these spectra, allow the conformationally sensitive membrane acyl chain methylene stretching modes to be separated from the protein (mostly hemoglobin) vibrations that dominate the spectra of intact cells. The 2850 cm⁻¹ band showed changes in the band shape and position after exposure to 50 and 100 Gy. Therefore it can be concluded that the band at 2850 cm⁻¹ only is useful in monitoring the radiation effect of the lipids cell membrane intact cells.     

Physico-chemical changes taking place in gamma irradiated bovine globulins studied by thermal analysis

Structural transformations induced in gamma and alpha globulins under influence of gamma irradiation using doses of 2.5 and 24 kGy were studied by differential scanning calorimetry (DSC) and thermogravimetry (TG, DTG). Thermal decomposition of the globulins irradiated in water suspensions occurs at higher temperatures, in comparison to the reference non-irradiated samples. This was related to formation of covalent linkages in the irradiated proteins, apart to chemical changes induced in amino-acids. Essential modification of thermal decomposition was detected already after irradiation with a dose of 2.5 kGy performed for water suspensions. Irradiation of solid native proteins induces decrease in decomposition temperature and gives evidence of proteins degradation.     

Thermally stimulated currents depolarization study of gamma ray irradiated PMMA

We will investigate the effect of γ-irradiation on the polymethyl methacrylate (PMMA) properties. The Fourier transform infrared spectroscopy technique in attenuated total reflexion mode (FTIR-ATR) results allowed us to show that the irradiated PMMA undergoes a scission in its lateral chain combined to an oxidation phenomenon. In fact, a decrease in the carbonyl index, versus the radiation dose, is observed. The differential scanning calorimetry and the thermostimulated depolarization currents revealed that the scission in the lateral chain provides a better flexibility to the PMMA chain and an increase in the free volume of the material. The consequences of these phenomena appear in the decrease of the activation energy of PMMA and the appearance of a local order in the material at a temperature T_c which decreases versus the radiation dose.     

ESR study of free radicals in UHMW-PE fiber irradiated by gamma rays

ESR spectra of the trapped radicals in an ultra-high molecular weight polyethylene (UHMW-PE) fiber irradiated by gamma rays showed well-resolved hyperfine splitting at room temperature since the c-axis of the crystallites is aligned with the fiber direction and the radicals are trapped in crystallites. The alkyl radical (?CH₂?^?CH?CH₂?) was the major product after irradiation in vacuum and in air at room temperature. Some of the alkyl radicals converted to allyl radicals (?CH₂?^?CH?CH=CH?) and polyenyl radicals (?CH₂?^?CH?(CH=CH)_n?CH₂?) during storage in vacuum. Upon storage in air atmosphere, the alkyl radicals decayed by reaction with oxygen. Of particular interest is the very slow decay rate of the alkyl radical trapped in UHMW-PE fiber, the half-life is 26 days in vacuum, and 13 days in air at room temperature, which is about 1/30 and 1/100 of that reported for high density polyethylene (HDPE), respectively. The extremely long lifetime of the alkyl radical is supposed to be caused by the large size of crystallites in UHMW-PE fiber. The rate of radical decay was accelerated by annealing at elevated temperature.     

Wide and small-angle X-ray scattering study of isotactic polypropylene gamma irradiated in bulk

Gamma irradiated isotactic polypropylene (IPP) has been studied by means of wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS). The skin layer has been investigated by WAXS reflection mode while the core layer underwent WAXS studies by transmission mode. β-IPP has been found solely in the skin layer. An increase in the β-phase has been observed as result of the irradiation. A phase transitions and decrease of crystallite sizes have been also observed. All of the parameters show a sharp change at a critical dose of 100 kGy. At this point the system parameters reverse. Radiation processes proceeding up to 100 kGy called radiation annealing are related to the improved crystallite perfection and thus emphasize the phase boundary. The processes provoke at higher radiation doses, up to 2000 kGy, damage in both crystal and amorphous lamellar parts. The values of the crystal and amorphous densities get closer and the process is similar to the partial radiation melting.     

Spectroscopic study of conformation changes of bovine serum albumin in aqueous environment

The secondary structural changes of protein aqueous solutions with and without calcium cations were investigated by attenuated total reflection-Fourier transform infrared (ATR-FTIR) technology.     

Spectroscopic analysis of pindolol irradiated in the solid state

Pindolol ((2RS)-(1-(1H-indol-4-iloxy)-3- [(1-metyloetylo)amino]-2-propanol) in substantia was exposed to ionising radiation emitted by high energy electrons from an accelerator, in the standard sterilisation dose of 25 kGy and in higher doses from the range 50–400 kGy. The effects of irradiation were checked by spectrometric methods (UV, MS, FT-IR, EPR) and hyphenated methods (HPLC-MS) and the results were referred to those obtained for non-irradiated sample. EPR results indicated the presence of free radicals in irradiated samples, in the amount of 1.36 × 10¹⁶ spin g^?1 for 25 kGy and 3.70×10¹⁶ spin g^?1 for 400 kGy. The loss of pindolol content determined by HPLC was 1.34% after irradiation with 400 kGy, while the radiolytic yield of the total radiolysis for this dose of irradiation was 2.69×10⁷ mol J^?1. By means of HPLC-MS it was possible to separate and identify one product of radiolytic decomposition, which probably is 2-((R)-3-(1H-indol-4-yloxy)-2-hydroxypropylamino)propan-1-ol formed upon oxidation. In the range of sterilisation doses (25–50 kGy), pindolol was found to show high radiochemical stability and would probably be safely sterilised by the standard dose of 25 kGy.      

Chemometric characterization of gamma irradiated chestnuts from Turkey

Chestnut (Castanea sativa Miller) is a valuable natural resource, with high exportation levels. Due to their water content, chestnuts are susceptible to storage problems like dehydration or development of insects and microorganisms. Irradiation has been revealing interesting features to be considered as an alternative conservation technology, increasing food products shelf-life. Any conservation methodology should have a wide application range. Hence, and after evaluating Portuguese cultivars, the assessment of irradiation effects in foreign cultivars might act as an important indicator of the versatility of this technology. In this work, the effects of gamma irradiation (0.0, 0.5 and 3.0 kGy) on proximate composition, sugars, fatty acids (FA) and tocopherols composition of Turkish chestnuts stored at 4 °C for different periods (0, 15 and 30 days) were evaluated. Regarding proximate composition, the storage time (ST) had higher influence than the irradiation dose (ID), especially on fat, ash, carbohydrates and energetic value. Sucrose exhibited similar behavior in response to the assayed ST and ID. The prevalence of ST influence was also verified for FA, tocopherols and sucrose. Lauric, palmitoleic and linolenic acids were the only FA that underwent some differences with ID. Saturated, monounsaturated and polyunsaturated fatty acids levels were not affected either by storage or irradiation. α-Tocopherol was the only vitamer with significant differences among the assayed ST and ID. Overall, Turkish cultivars showed a compositional profile closely related with Portuguese cultivars, and seemed to confirm that gamma irradiation in the applied doses did not change chestnut chemical and nutritional composition.     

Thermal and crystallization behaviour of gamma irradiated PLLA

Structure, crystallization behaviour and some thermal properties of poly-l-lactide (PLLA), gamma irradiated up to 300 kGy, have been studied. Through differential scanning calorimetry measurements, radiation-induced changes were evident in the enthalpy of melting and cold crystallization, as well as in the degree of crystallinity. Decay of the glass transition, cold crystallization and melting temperatures with irradiation dose was observed in all cases. The annealing treatment, which can substantially reduce the concentration of free radicals, also had a great impact on thermal/crystallization behaviour of irradiated PLLA. Extensive chain scission, as a dominant effect of gamma irradiation, confirmed by gel permeation chromatography, has as a consequence a growth of new thin crystal lamellae and occurrence of the second low-temperature melting peak. Thermogravimetric analyses have shown that irradiation lowered the thermal stability of PLLA.     

A study of transcrystallinity in polypropylene in the presence of wood irradiated with gamma rays

The interest in lignocellulosic composites has been growing in recent years because of their specific properties. In this study, a new technique of wood treatment using γ-irradiation was used. This research focuses on the influence of the gamma irradiation on the chemical composition of wood and on the nucleation ability of polypropylene matrice. The inner morphology of the transcrystalline layer was investigated using hot stage optical microscopy. Differential scanning calorimetry was used to investigate the kinetic parameters of polypropylene crystallization in the presence of wood surface. The results showed that the gamma irradiation can decrease the content of the cellulose in the wood, but it has a slightly negative effect on the transcrystallization process of polypropylene. This treatment also affects the crystal conversion and the half-time of PP crystallization. These results suggested that the gamma irradiation of wood may play a useful role in changing the microstructure of the matrice near the wood. It was observed that the nucleation of the wood surface was selective, indicating that the chemical characteristics of the lignocellulosics might have influence on the polypropylene crystallization. A possible mechanism for the appearance of transcrystallinity involving chemical composition of lignocellulosic is also proposed.     

Temperature rising elution fractionation, infra red and rheology study on gamma irradiated HMSPP

It is well known that polypropylene undergoes simultaneous crosslinking and degradation under irradiation. However, there are speculations regarding the formation of branching under special conditions. It is also well known that the melt-strength property of a polymer increases with molecular weight and with long-chain branching due to the increase in the entanglement level. This study was a contribution to the understanding of the following points: the role of molecular weight, the role of structural modifications on nucleation properties; the structural changes on polypropylene.

The results showed that degradation was the major reaction in the initial step of irradiation, however, the largely modified molecules concentrated in the high molecular weight fraction. The results also confirm that the branching formation is likely to occur.     

尿素诱导牛血红蛋白变性的微量热和平衡渗析研究

应用恒温微量热技术和平衡渗析技术,对尿素与牛血红蛋白在30℃水溶液中的结合作用及造成牛血红蛋白变性的过程进行了研究,得到了尿素在牛血红蛋白上的平均结合数、二者之间的结合焓及每摩尔尿素与牛血红蛋白结合的焓效应,并根据简单结合模型,计算了它们之间的结合常数、结合自由能.对实验结果的热力学分析表明,尿素是通过直接和间接的两种作用造成牛血红蛋白变性的,它们之间的相互作用分为三个阶段:尿素浓度达到4molL-1之前为第一阶段,主要产生的是尿素与牛血红蛋白的直接结合作用,在弱酸性条件下这种作用较强;尿素浓度为4molL-1到6molL-1之间为第二阶段,主要通过尿素与溶剂水的作用造成牛血红蛋白周围水结构的变化,在尿素浓度达到6molL-1时两种作用的叠加造成牛血红蛋白结构的破坏,暴露出原来处于结构内部的基团;尿素浓度超过6molL-1之后为第三阶段,尿素分子继续与暴露出来的基团进行结合.牛血红蛋白次级结构的维系具有协作性,其结构的破坏不是渐进的,而是一次性全部打开,结构破坏产生的热效应并不太大.     

Spectroscopic studies of structural changes in irradiated LDPE and its blends

The low temperature glass transition occurring at low temperature in polyethylene samples was studied using Fourier transform infrared, FT‐Raman spectroscopic techniques, which are known to be sensitive to any structural changes in the investigated samples. Anomalous behavior was obtained in the temperature range (98 K → 383 K) indicating the existence of phase transition occurring at about 98 K and disappearing at about 323 K while heating for unirradiated virgin low density polyethylene (VPE) sample with or without crosslinking agent (trimethylol propane triacrylate, TMPTA). Addition of TMPTA monomer caused severe changes in the temperature dependence of both unirradiated and irradiated polyethylene samples. The results given indicated the occurrence of abnormal temperature dependence, which is thought to be related with low temperature structural change resulting from local crosslinking in scrapped polyethylene (SPE) sample already suffering from high degree of crosslinking. Differential scanning calorimetry (DSC) thermograms confirmed the observed new phase transition observed in both unirradiated and irradiated TMPTA loaded VPE/SPE (50/50 wt %) blend. Irradiation, addition of TMPTA as a crosslinking agent, and blending VPE with SPE were found to affect remarkably the variation of the vibration spectrum of LDPE and consequently the resulting structural changes. The experimental results obtained were discussed and correlated with reorientational disorders of the molecular segments (local crosslinking). © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 850–859, 2007     

Study on polytetrafluoroethylene aqueous dispersion irradiated by gamma ray

Gamma-radiation induced degradation of polytetrafluoroethylene (PTFE) in 60 wt.% dispersion was studied in the dose range of 20-200 kGy and the change in property of PTFE was characterized by differential scanning calorimetry (DSC), photon cross correlation spectroscopy (PCCS), X-ray diffraction (XRD), scanning electron microscopy (SEM), FT-IR spectroscopy and X-ray photoelectron spectroscope (XPS). It was found that the mean particle size of PTFE reduces from 250 nm of the control to 170 nm at 100 kGy, as confirmed by dynamic laser scattering and SEM. The crystallinity degree of PTFE increased at 20 kGy but remained unvaried at higher dose level. G-value of scission, G(s), was determined to be 0.46 μmol/J.