Calorimetric methods are becoming important analytical tools in several areas of biochemical and biological research. In this work, a flow microcalorimetric method has been applied to the determination of dihydrofolate reductase (DHFR) activities in rat and human malignant tissue homogenates. In contrast to other commonly used DHFR analytical assays, the sensitivity of flow microcalorimetry allows direct measurements of this enzyme in crude tissue preparations. Our experimental data from rat tissue homogenates show that liver has the highest level of enzyme activity, while lung and brain have lower amounts of DHFR activity. The liver enzyme has a higher activity atpH 4.5, but the optimumpH for the lung and brain enzymes is 6.8. The substrate/cofactor molar ratio which gives the highest levels of DHFR activity is 1/1.5 for the liver and lung enzymes and 1/2.5 for brain DHFR. The DHFR in these rat tissue homogenates is activated by KCl or NaCl: in the presence of these salts (0.6M), the values of enzyme activity are 1.5–3 times higher than in their absence. Using flow microcalorimetry, very low levels of DHFR activity were also measured in human bone tumour homogenates, demonstrating the potential of the technique in the analysis of this enzyme in malignant tissues. 相似文献
The radiological accident that occurred in Goiania City, Brazil, in September 1987, led to the spreading of137Cs in the urban area. Even after the decontamination procedure, there was a reminiscence of137Cs activity in the soil of residential gardens. This activity was enough to conduct preliminary experiments for determination of soil to vegetable concentration ratios. Experiments were conducted for carrots, lettuce and radishes. Two types of experimental patterns were used to determine the concentration ratios: lysimeters cultivation under greenhouse condition and soil cultivation in open field plot. The concentration ratios measured for cultivation under greenhouse and field plot conditions are considerably higher than those mentioned in the International Union of Radioecologist (IUR) data bank for the same vegetables and cultivation condition. 相似文献
TMNO-activated reaction of the heteronuclear cluster Os3Ru(μ-H)2(CO)13 (1) with diphenylphosphine afforded the novel phosphido-bridged clusters Os3Ru(μ-PPh2)(μ-H)3(CO)11 (2), Os3Ru(μ-PPh2)2(μ-H)2(CO)10 (3), Os3Ru(μ-PPh2)2(μ-H)4(CO)9 (4), and Os3Ru(μ-PPh2)(μ-H)3(CO)11(PPh2H) (5). The formation of 2-5 proceeded via P-H bond cleavage in the adduct Os3Ru(μ-H)2(CO)12(PPh2H) (6). Reaction of 2 with PPh3 afforded the adduct Os3Ru(μ-PPh2)(μ-H)3(CO)11(PPh3) (7) and the substituted derivative Os3Ru(μ-PPh2)(μ-H)3(CO)10(PPh3) (8). 相似文献
The magnetic, electronic, and structural properties of the solid solutions LaxSr1−xRuO3 and LaxCa1−xRuO3 have been studied by 99Ru Mössbauer spectroscopy and other techniques. The LaxCa1−xRuO3 phases are reported for the first time and have been shown by powder X-ray diffraction measurements to be orthorhombically distorted perovskites. Electrical resistivity measurements on compacted powders show that all the phases are metallic with p 10−3, ohm-cm. Progressive substitution of Sr2+ by La3+ in ferromagnetic SrRuO3 leads to a rapid collapse of the magnetic hyper-fine splitting at 4.2°K. For x = 0.25 some ruthenium ions still experience a magnetic field but for 0.4 x 0.75 only single, narrow resonance lines are observed, consistent both with the complete removal of the ferromagnetism and with the presence of an averaged ruthenium oxidation state in each phase, i.e., Lax3+Sr1−x2+Ru(4−x)+O3 rather than Lax3+Sr1−x2+Rux3+Ru1−x4+O3. LaRuO3 and CaRuO3 both give essentially single-line spectra at 4.2°K, indicating that the ruthenium ions in these oxides are not involved in long-range antiferromagnetic order but are paramagnetic. The solid solutions LaxCa1−xRuO3 (0 < x 0.6) give sharp symmetrical singlets with chemical isomer shifts (relative to the Ru metal) which move progressively from the value characteristic of Ru4+ (−0.303 mm sec−1) toward the value for Ru3+ (−0.557 mm sec−1), consistent with the presence of intermediate ruthenium oxidation states in these phases also. 相似文献
Millions of tons of fruit waste are generated globally every year from agricultural residues, which makes it essential to find alternative uses to increase their aggregate value and reduce their environmental impact. The present study aimed to explore pineapple peel as an alternative source of cellulose by evaluating its chemical composition and physical properties, which are essential for applications. A sequence of chlorine-free treatments was applied to purify the cellulose by removing noncellulosic components in the fresh pineapple peels. The cellulosic pulp was characterized regarding its chemical composition and characterized by Nuclear Magnetic Resonance (13C NMR), X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis to determine crystallinity, structural properties, morphology, and thermal characteristics, respectively. The results revealed that the pineapple peel amorphous segments containing hemicelluloses and lignin were extensively removed with increasing chemical treatment steps, leading to increased purity, crystallinity index, and thermal stability of the extracted cellulose pulps. The maximum thermal degradation (150 °C) and crystallinity index (80.9%) were determined for the cellulosic material obtained from the second bleaching (2B) step. The cellulose content increased from 24% in the starting material (fresh pineapple peel) to 80.9% in the bleached cellulose (2B). These results indicate that the extracted cellulose from pineapple peel has characteristic for applications such as the production of cellulose nanocrystals due to the high crystallinity.
Acanthophora spicifera (M.Vahl) Børgesen is a macroalga of great economic importance. This study evaluated the antioxidant responses of two algal populations of A. spicifera adapted to different abiotic conditions when exposed to ultraviolet‐A+ultraviolet‐B radiation (UV‐A+UV‐B). Experiments were performed using the water at two collection points for 7 days of acclimatization and 7 days of exposure to UVR (3 h per day), followed by metabolic analyses. At point 1, water of 30 ± 1 practical salinity unit (psu) had concentrations of 1.06 ± 0.27 mm , 8.47 ± 0.01 mm , 0.17 ± 0.01 mm and pH 7.88. At point 2, water of 35 ± 1 psu had concentrations of 1.13 ± 0.05 mm , 3.73 ± 0.01 mm , 0.52 ± 0.01 mm and pH 8.55. Chlorophyll a, phycobiliproteins, carotenoids, mycosporins, polyphenolics and antioxidant enzymes (catalase, superoxide dismutase and guaiacol peroxidase) were evaluated. The present study demonstrates that ultraviolet radiation triggers antioxidant activity in the A. spicifera. However, such activation resulted in greater responses in samples of the point 1, with lower salinity and highest concentration of nutrients. 相似文献
The synthesis, characterization and photophysical properties of two perfluoroalkyl (5,10,15,20-tetrakis-[trifluoromethyl]- and [heptafluoropropyl]-porphyrin) and two perfluoroaryl (5,10,15,20-tetrakis-[2,6-difluorophenyl]- and [pentafluorophenyl]-porphyrin) are described, with reference to their potential in both photodynamic therapy (PDT) and in vivo imaging by fluorescence and 19F nuclear magnetic resonance spectroscopy. Absorption and fluorescence spectra, fluorescence lifetimes and triplet-singlet difference spectra are reported. Triplet yields have been obtained by flash photolysis and pulse radiolysis, whereas yields of sensitized singlet oxygen formation have been determined by time-resolved phosphorimetry. All four compounds show high yields of triplet formation and singlet oxygen sensitization. The spectral properties, stability and attractive solubility characteristics of the perfluoroalkyl derivatives make them particularly suitable candidates for future study for applications in PDT. 相似文献
Energy storage and conversion have become a prime area of research to address both the societal concerns regarding the environment and pragmatic applications such as the powering of an ever increasing cadre of portable electronic devices. This paper reviews the use of fluoride based electrode materials in energy storage devices. The majority of the energy storage and conversion applications for fluorine based materials resides in present and future lithium battery chemistries. The use of fluorides either as coatings or in the formation of oxyfluorides has resulted in a marked increase of the stability and morphological development of electrodes for use in nonaqueous lithium and lithium-ion batteries. Pure fluorides, despite their intrinsic insulative properties, have demonstrated the capability to exhibit exceptional energy densities and have the potential to open the door to future high energy lithium battery technology. 相似文献
The polymerization of methyl methacrylate initiated by Ce4+ methanol redox system was studied in aqueous solution of nitric acid at 15°C. The polymerization was initiated by primary radicals formed from Ce4+/alcohol complex. Poly(methyl methacrylate) chains containing the alcohol residue were obtained. Variations in the temperatuare and concentration of the components of the redox system allowed the control of the rate of polymerization and molecular weight of the polymer. The concentration of the hydroxyl end groups in the poly(methyl methacrylate) of low molecular weight was determined by titration and by spectrometric method. 相似文献