Optimizing the sensitivity and radiological properties of the PRESAGE® dosimeter using metal compounds

The aim of this study is to investigate the radiation-modifying effects of incorporating commercially available bismuth-, tin- and zinc-based compounds in the composition of the PRESAGE^® dosimeter, and the feasibility of employing such compounds for radiation dose enhancement. Furthermore, we demonstrate that metal compounds can be included in the formulation to yield water-equivalent PRESAGE^® dosimeters with enhanced dose response. Various concentrations of the metal compounds were added to a newly developed PRESAGE^® formulation and the resulting dosimeters were irradiated with 100 kV and 6 MV photon beams. A comparison between sensitivity and radiological properties of the PRESAGE^® dosimeters with and without the addition of metal compounds was carried out. Optical density changes of the dosimeters before and after irradiation were measured using a spectrophotometer. In general, when metal compounds were incorporated in the composition of the PRESAGE^® dosimeter, the sensitivity of the dosimeters to radiation dose increased depending on the type and concentration of the metal compound, with the bismuth compound showing the highest dose enhancement factor. In addition, these metal compounds were also shown to improve the retention of the post-response absorption value of the PRESAGE^® dosimeter over a period of 2 weeks. Thus, incorporating 1–3 mM (ca. 0.2 wt%) of any of the three investigated metal compounds in the composition of the PRESAGE^® dosimeter is found to be an efficient way to enhance the sensitivity of the dosimeter to radiation dose and stabilize its post-response for longer times. Furthermore, the addition of small amounts of the metal compounds also accelerates the polymerization of the PRESAGE^® dosimeter precursors, significantly reducing the fabrication time. Finally, a novel water-equivalent PRESAGE^® dosimeter formula optimized with metal compounds is proposed for clinical use in both kilovoltage and megavoltage radiotherapy dosimetry.     

Sensitivity and stability of the Fricke–gelatin–xylenol orange gel dosimeter

Spectrophotometric measurements of the Fricke–gelatin–xylenol orange (FGX) gel dosimeter demonstrated reproducible linear dose response up to 25 Gy. However, oxidation processes continue post-irradiation, affecting the response of this dosimetry system. Additional oxygenation during preparation increases the sensitivity of the gel but does not improve the auto-oxidation stability of the dosimeter post-irradiation. A suitably stable gel composition that is recommended for radiotherapy dosimetry measurements contains 0.5 mM ferrous ammonium sulphate, 50 mM sulphuric acid, 0.15 mM xylenol orange and 3.0% by weight gelatin.     

“Living”/controlled radical copolymerization of N-phenylmaleimide and styrene using Fréchet-type dendritic initiators

Polyarylether dendrons as macroinitiators for the "living"/controlled free radical copoly-merization of N-phenylmaleimide (PhMI) and styrene (St) have been demonstrated. The copoly-merization was carried out in bulk or anisole with CuBr/bipy catalyst at 100-130℃. It is found that the resulting copolymers possess predetermined molecular weights and narrower polydispersities (1.18 < Mw/Mn<1.32). The effects of reaction temperature and monomer feed on the copolymeri-zation kinetics were investigated in detail. By using the Fineman-Ross method, the apparent monomer reactivity ratios for the atom transfer radical copolymerization of PhMI and St were determined to be rphM1 = 0.0207, and rst = 0.0484, respectively.     

Determination of the stability and magnetic properties of Fe–Pd nitride using the generalised gradient approximation (GGA)

In this study, an electronic structure calculation of the substituted nitride PdFe₃N was conducted, and a posterior understanding of its structural and magnetic properties was obtained. A first principle method was applied to study the lattice parameter variation in relation to the energy of solid formation. After the equilibrium parameter was found, some properties of the ground state, such as the magnetic moment and the bulk modulus, were calculated. Preliminary observations show that the material properties of γ′-Fe₄N vary significantly with the insertion of the palladium atom in the matrix as well as when the material is subjected to applied pressure. The density of states shows a strong interaction between the s states of nitrogen and, primarily, the s and p states of iron, presenting a weak interaction with the palladium atoms. The analysis of such properties illustrates why these nitrides have a promising future for use in technological applications.     

Effects of binders and graphite on the sensitivity of ε-HNIW

In order to optimize formulations of PBX based on Hexanitrohexaazaisowurtzitane (HNIW) and meet the application in mixed explosive, the mold powder of HNIW coated by varied binders was obtained by aqueous suspension technology. Several particle sizes of graphite were added as additive with a 0.5 % mass ratio. The experiment results showed that fluorine resin (FPM) was better than polyurethane and cis-butadiene rubber when the mass percentage of binders was fixed at 4 %. The characteristic height of HNIW/FPM (96/4) mold powder was at 28 cm (2.5 kg hammer), while that of the neat HNIW was at 15 cm merely, and the friction explosion probability fell from 100 to 70 %. The addition of flake graphite with proper grain size would reduce the mechanical sensitivity of HNIW and improved the fluxion property of HNIW-based mold powders. The thermal stability characteristic of HNIW FPM (96/4) and HNIW/FPM/G (96/4/0.5) were studied by thermogravimetric analysis (TG) at 10 °C min^?1, the peak decomposition temperatures were at 251 and 250 °C, which were closed to that of neat HNIW(249 °C) and also identified superior thermal stability of compound.     

Effect of acid catalysis on the direct electrophilic fluorination of ketones,ketals, and enamides using Selectfluor™

The fluorination of ketones, ketals, and enamides has been achieved using the electrophilic fluorinating reagent Selectfluor? (F-TEDA-BF₄). For the reactions of ketones and ketals the use of sulfuric acid (0.1 equiv) as an additive was found to facilitate the reaction leading to more rapid product formation. This behavior is analogous to the known effects of acid catalysis on the bromination of ketones. The reactions were generally quite selective leading to the formation of monofluorinated products, and could be accomplished on reaction scales up to 85 mmol using N-protected piperidone based substrates. Reactions in the presence of MeOH led to the formation of the corresponding fluoroketones or fluoroketals depending upon the substrate. The formation of the fluoroketals in this manner, as well as the fluorination of cyclic enamides are examples of multi-component coupling reactions.     

Computer simulation of the heat-resistant polyimides ULTEM™ and EXTEM™ with the use of GROMOS53a6 and AMBER99 force fields

An atomistic computer simulation was performed for the polyimides ULTEM? and EXTEM? via the molecular-dynamics method with the use of Gromos53a6 and Amber99 force fields. For parameterization of electrostatic interactions, the partial atomic charges were calculated through quantum-chemical methods. The temperature dependence of density and the thermal-expansion coefficients for the polyimides were obtained. The calculated density values of the polyimides at room temperature and their coefficients of thermal expansion in the glassy state are in agreement with available experimental data. It is shown that inclusion of electrostatic interactions is necessary for simulation of the thermophysical characteristics of the considered polyimides.     

Synthesis of (±)- and (−)-botryodiplodin using stereoselective radical cyclizations of acyclic esters and acetals

Three different routes for the stereoselective synthesis of botryodiplodin have been investigated. The intramolecular allylation of acetals proved to be unsatisfactory due to unstable intermediates and poor stereocontrol. Zard intramolecular radical allylation of a 2-iodopropionate derivative allows the development of an expeditious synthesis of racemic botryodiplodin. The relative configuration within the final product was corrected by a deprotonation–reprotonation step. The cyclization of allenyl bromoacetals was investigated next and proved to be satisfactory for the synthesis of racemic and enantiomerically pure botryodiplodin. Good stereocontrol was achieved by cyclizing a gem-dibromide followed by the stereoselective reduction of the thus formed cyclic monobromide.     

Monitoring the aggregation processes of amyloid-β using a spin-labeled, fluorescent nitroxyl radical

Amyloid nitroxyl radical (nitroxide) ligands were used to detect amyloid-β fibrils, the main constituents of senile plaques in Alzheimer's disease, using anisotropic ESR spectra, and were found to affect the aggregation process due to the radical functionality. These compounds have great potential as novel and multifunctional probes, combining spin labels, spin probes, and fluorescence probes.     

Effect of magnesium cations on the activity and stability of β-galactosidases

It was shown that the presence of magnesium cations in the reaction mixture increases, approximately twofold, the activity of bacterial Escherichia coli and yeast Kluyveromyces lactis β-galactosidases but does not affect the activity of bovine liver and fungous Penicillium canescens β-galactosidases. The catalytic constants for E. coli and yeast K. lactis β-galactosidases in the presence of 0.01 M and in the absence of Mg²⁺ cations were determined (490 and 220 s^?1 and 59.8 and 37.4 s^?1, respectively). It was shown that the Michaelis constants for these two enzymes are higher in the presence of Mg²⁺ cations, that the thermal stability of E. coli and K. Lactis β-galactosidases is higher in the presence of 0.01 M Mg²⁺, and that the effective rate constants of thermal inactivation of the enzymes are two-to eightfold lower, depending on conditions, in the presence of Mg²⁺ cations. The maximum stabilizing effect of magnesium cations was observed at weak alkaline pH values (7.5–8.5).     

Expression Optimization and Characterization of the Catalytic Domain of Human MT3-MMP

Introduction Matrixmetalloproteinases(MMPs)areafamilyof calciumandzincrequiringendoproteinasesthattogether candegradeallthemaincomponentsoftheextra cellu larmatrixandbasementmembranes[1].MMPsarein volvedinawiderangeofproteolyticevents,innormal andpatholog…     

A theoretical study of the stability and electronic properties of GenRu (n = 2–10) clusters and their sensitivity toward SO2 adsorption

Structural Chemistry - In this work, the stability and electronic properties of the Ru-doped germanium clusters were investigated with DFT calculations at the TPSS/SDD level. The adsorption of the...     

Oxidation of phenol in aqueous acid: characterization and reactions of radical cations vis-à-vis the phenoxyl radical

Aqueous sulfuric acid containing up to approximately 14 M acid (H0 > or = -7.0) was used as solvent in pulse radiolytic redox studies to characterize cationic transients of phenol (C6H5OH) and map their reactions. The primary radical yields were first measured to correlate the variation in various radical concentrations as a function of increasing acid fraction in the solvent. Compared to their respective values at pH 2, the G(Ox*) increased with almost a linear slope of approximately 0.024 micromol J(-1) for H0(-1) (or pH(-1)) up to H0 -6.0 (Ox* = *OH + SO4*-), whereas G(H*) increased with a slope of approximately 0.033 micromol J(-1) for H0(-1) (or pH(-1)) up to H0 -5.0. In the presence of > 10 M acid (H0 < -5.0), phenol was oxidized to its radical cation, C6H5OH*+, which further reacted with phenol and generated the secondary, dimeric radical cation, (C6H5OH)2*+, following an equilibrium reaction C6H5OH*+ + C6H5OH <==> (C6H5OH)2*+, with K(eq) = 315 +/- 15 M(-1). The two cationic radicals were characterized from their individual UV-vis absorption spectra and acidity. The C6H5OH*+ absorption peaks are centered at 276 and 419 nm, and it was found to be more acidic (pKa = -2.75 +/- 0.05) than (C6H5OH)2*+ (pKa = -1.98 +/- 0.02), having its major peak at 410 nm. On the other hand, in the presence of < 6.5 M acid the C6H5O* reactions followed the radical dimerization route, independent of the parent phenol concentration.     

Assessment of the oxidative stability of lubricant oil using fiber-coupled fluorescence excitation–emission matrix spectroscopy

The fluorescence of antioxidant additives in lubricant oil was used as an indicator of oxidative stability of the oil. It was found that the decrease in fluorescence intensities of phenyl-α-napthylamine, its dimer, and another unidentified antioxidant coincide with the formation of decomposition products of the oil base stock. Simple kinetic models were developed that were capable of describing antioxidant reactions as a pseudo first-order processes. It is shown that fluorescence excitation emission matrix (EEM) spectroscopy coupled with an optical fiber probe can provide real-time assessment of the oxidative stability of the lubricant. Parallel factor (PARAFAC) analysis was used to correlate the component scores to the oil breakdown number.     

Density functional and chemical model study of the competition between methyl and hydrogen scission of propane and ��-scission of the propyl radical

In this work, we study the competence between the reactions of hydrogen and methyl scission during thermal cracking and combustion of propane, the emergence of the two isomers of the propyl radical, n-propyl and i-propyl, and their subsequent ??-scission reaction to ethene and methyl radical. The purpose of the study was to analyze the accuracy of density functional (DFT) methods as applied on this relatively well-known subset of the reactions implied in the production of propylene oxide from propane and propene. Conventional (B3LYP, B3PW91) and state-of-the-art (PBE0, M06, BMK) DFT methods were employed, and their accuracy checked against experimental data and calculations performed using model chemistries (complete basis set CBS-4M, QB3, and APNO, and G4 methods) and ab initio methods (MP2, CCSD(T) with a large 6-311 ++G(3df,2pd) basis set). The results obtained at the BMK level for the thermodynamics of the reactions are closer to experimental data than those afforded by any other DFT method and very similar actually to CBS or CCSD(T) results, even if a medium size basis set is used. Activation energies determined using two- and three-parameter Arrhenius equations are also very good, but the preexponential factors are incorrect. Tunneling and internal rotation corrections must be applied to obtain semiquantitative results.     

Thermodynamic study of the influence of polyols and glucose on the thermal stability of holo-bovine α-lactalbumin

Thermal stability of bovine α-lactalbumin in buffer and dilute aqueous solutions of erythritol, xylitol, sorbitol, inositol and glucose was evaluated by fluorescence spectroscopy and circular dichroism. Results show that at the selected conditions, the transition is reversible and is well described by a two-state model. At low concentration the cosolutes do not show a structure stabilizing effect, and some of them even destabilize the protein. At higher concentration, all of them stabilize the native protein conformation; however, the extent of stabilization is lower than the effect shown with other proteins, presumably due to the lactalbumin incomplete unfolding.     

Synthesis of (−)-aphanorphine using a sulfur-directed aryl radical cyclization

Treatment of radical precursor 15a having a vinyl sulfide moiety with Bu₃SnH in the presence of AIBN in boiling benzene afforded exclusively the 6-exo cyclization product 16a, whereas similar treatment of the exo-methylene compound 15b gave a mixture of the 6-exo cyclization product 16b and the endo-olefin product 17 formed by a 1,5-hydrogen shift. Based on these findings, the synthesis of (−)-aphanorphine was achieved using a sulfur-directed 6-exo-selective aryl radical cyclization of 22.     

The fluoroformyloxyl radical geometry and ground-state rotational spectra of the free FC18O2· radical

The rotational spectra of the isotopically substituted free fluoroformyloxyl radical FC(18)O(2·) were measured using the Prague millimeter-wave high-resolution spectrometer. More than 110 rotational-fine-hyperfine transition lines were observed and assigned to appropriate quantum numbers in the frequency range of 235-270 GHz. The obtained transition frequencies were analyzed with standard effective Hamiltonians to acquire a set of precise rotational, centrifugal-distortion, fine, and hyperfine structure molecular constants. Merging the new FC(18)O(2·) isotopologue molecular parameters with those previously obtained for the ordinary FC(16)O(2)[middle dot] radical, the substitution molecular geometry in the ground vibronic state was evaluated. The molecular parameters for both radical isotopologues were also calculated by several quantum chemistry methods and their calculated mutual ratios are in remarkable agreement with the experimental FC(16)O(2·)/FC(18)O(2·) parameter ratios. The measurements, assignments of the 18-oxygen isotopologue FC(18)O(2·) radical millimeter-wave transitions, as well as the derivation of the fluoroformyloxyl radical ground-state geometry have been carried out for the first time.     

Group 4 initiators for the stereoselective ROP of rac-β-butyrolactone and its copolymerization with rac-lactide

In this paper we demonstrate the utility of Group 4 metals for the well-controlled and stereoselective (syndiotactic) ring opening polymerization (ROP) of rac-β-butyrolactone (BBL) and their ability to form copolymers.