The effect of dose on light-sensitivity of radicals in alanine EPR dosimeters

In this work we present a study of light-induced effects on free radicals and their transformations in gamma-irradiated pure L-alanine and in commercially available alanine detectors: rods, pellets and films. Samples irradiated to doses from 2 Gy to 4000 kGy were exposed to light from a fluorescent lamp and to ordinary daylight. The observed changes in EPR spectra of the samples were analyzed with regard to their intensity and shape. The shape analysis was based on numerical decomposition of the measured spectra into model spectra reflecting contributions of R1, R2 and R3 radical populations in the samples. The illumination of alanine dosimeters resulted in significant decrease of the central EPR line and was accompanied by distinct variations in the shape of EPR spectra. The rate of light-induced decay in spectra amplitude was found to be dependent on dose of ionizing radiation--the sensitivity to light was decreasing with increase in dose in all detectors in the 2-5x10(5) Gy dose range. The exposure of gamma-irradiated (to 300 Gy) alanine to normal, diffused daylight resulted in decay of the signal amplitude at rate about 0.5% per week. It was shown that decay in the R1 component was responsible for the observed reduction of the spectra amplitude. The observed increase in R2 contributions in samples exposed to light confirmed a hypothesis of R-->R2 radical transformations promoted by visible light. The reported effects indicate a necessity of protection of irradiated dosimeters from their prolonged exposure to light.     

A new graphite calorimeter for calibrating thin-film and alanine dosimeters in electron beams

The design and experiments of a graphite absorbed-dose calorimeter in the operation of quasi- adiabatic mode is described which is used for measuring high dose and calibrating passive dosimeters in electron beam.     

A methodology for choosing parameters for ESR readout of alanine dosimeters for radiotherapy

Spectrometer settings for ESR readout of alanine dosimeters for radiotherapy have been investigated. Several ESR parameters were studied and determined. The main reason for this work is to choose the suitable parameters to increase signal-to-noise ratio and to reduce the uncertainty on ESR readout, which is one of the main components of uncertainty of alanine/ESR dosimetry system for radiotherapy. The new spectrometer settings have been applied for ESR readout of alanine dosimeters irradiated from 1 to 10 Gy. A higher signal-to-noise ratio has been achieved compared to our old spectrometer settings. The extended uncertainty (k=2) has been evaluated in the dose range 2–10 Gy (maximum uncertainty of 4.9% for 2 Gy, while minimum uncertainty of 1.4% for 10 Gy), which implies that the alanine/ESR dosimetry system can be applied to radiotherapy dose level that needs a global accuracy of 5%.     

LET effects following neutron irradiation of lithium formate EPR dosimeters

Lithium formate electron paramagnetic resonance (EPR) dosimeters were irradiated using 60Co gamma-rays or fast neutrons to doses ranging from 5 to 20 Gy and investigated by EPR spectroscopy. Using a polynomial fitting procedure in order to accurately analyze peak-to-peak line widths of first derivative EPR spectra, dosimeters irradiated with neutrons had on average 4.4+/-0.9% broader EPR resonance lines than gamma-irradiated dosimeters. The increase in line width was slightly asymmetrical. Computer simulated first derivative polycrystalline EPR spectra of a *CO2- radical gave very good reconstructions of experimental spectra of irradiated dosimeters. The spectrum simulations could then be used as a tool to investigate the line broadening observed following neutron irradiation. It was shown that an increase in the simulated Lorentzian line width could explain both the observed line broadening and the asymmetrical effect. The ratio of the peak-to-peak amplitude of first derivative EPR spectra obtained at two different microwave powers (20 and 0.5 mW) was 7.8+/-1.2% higher for dosimeters irradiated with neutrons. The dependence of the spectrum amplitude on the microwave power was extensively investigated by fitting observations to an analytical non-linear model incorporating, among others, the spin-lattice (T1) and spin-spin (T2) relaxation times as fitting parameters. Neutron irradiation resulted in a reduction in T(2) in comparison with gamma-irradiation, while a smaller difference in T1 was found. The effects observed indicate increased local radical density following irradiation using high linear energy transfer (LET) neutrons as compared to low LET gamma-irradiation. A fingerprint of the LET may thus be found either by an analysis of the line width or of the dependence of the spectrum amplitude on the microwave power. Lithium formate is therefore a promising material for EPR dosimetry of high LET radiation.     

EPR and ab-initio study on the solid state radiolysis of aliphatic and aromatic polyesters

Low temperature matrix EPR spectroscopy was employed to investigate the free radical intermediates in the solid state radiolysis of poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), poly(ethylene naphthalate) (PEN), poly(1,4-cyclohexanedimethylene terephthalate-co-ethylene terephthalate) (PCT-co-ET) and poly(ethylene adipate) (PEA). With PEA the species identified is consistent with the formation of carbon centred radicals stemming from electron capture, C–O scissions and H abstractions, the most abundant species at room temperature being the -ester radical, –CH₂–CH–COO–. The radiolysis of PEN is characterized by the predominance of radicals arising from the aromatic section, the preferred reaction being the H atom addition at a position adjacent to the ester unit, leading to the formation of cyclohexadienyl type radicals. In the copolymer, PET and PBT, the role played by the aliphatic and aromatic sections with respect to radical forming processes is of comparable importance. The cyclohexadienyl radicals arising from these latter polymers are reckoned with the prominent H addition at the sites adjacent to the esters groups which are also statistically favoured. The reactivity distribution in the aromatic rings with respect to the formation of cyclohexadienyls was analyzed in greater detail by comparing the experimental results with DFT B3LYP M.O. calculations. The DFT method has also been employed for assessing the EPR properties of the cyclohexadienyl and ion-radicals from PEN and PET models.     

Semiconductivity,optical properties,and EPR spectra of phenothiazine derivatives in the solid state

The optical, EPR, and electrical properties of phenothiazine derivatives have been investigated as a function of R₂ substituents. Diffuse reflectance spectra show a charge transfer complex transition between 600 and 1100 nm. The EPR spectra show the existence of the radical cation with an unpaired electron per molecule; also there can be seen a dependence of the bandwidth on the R₂ substituents. Measurements of electrical conductivity show a semiconductor behavior in the studied temperature range; the values show as well a dependence of conductivity on R₂. The estimation of the drift mobility of charge carriers seems to indicate a hopping mechanism for the charge conduction.     

Solvent free reactions in the solid state: solid state metathesis

Transition Metal Chemistry -     

Ternary hydrogen halide/base/benzene mixtures: A new generation of liquid clathrates

Liquid clathrates have been prepared via contact of excess hydrogen halide (chloride or bromide) with benzene solutions of various simple organic nitrogen containing bases. The liquid clathrates or solutions so formed have been characterized via¹H NMR and shown to be, as expected, ternary mixtures of hydrogen halide, benzene and salt.     

The triplet state of picene in p-terphenyl crystals by EPR

Spin-hamiltonian parameters of the triplet state of picene in p-terphenyl crystals are determined. Optical spin polarization and transient nutations are also observed using pulsed light sources.     

A new singlet state of Te2

The 4067 Å line of the krypton-ion laser covers two transitions in the BO⁺_u-X O⁺_g system of ¹³⁰Te₂, R(36) in the 16-0 band and R(172) in the 18-0 band. Subsequent fluorescence has been recorded by Fourier transform spectrometry in the range 5900 to 15000 cm⁻¹. Many transitions, with v' in the range 0 to 47, have been assigned to a new system, B O⁺_u-b¹ ∑⁺_g, and vibrational and rotational constants for the new state have been derived. The value of T_e for b ^I∑_g⁺ is about 9600.2 cm⁻¹.     

Fabrication of new solid state phosphate selective electrodes for environmental monitoring

A highly selective and sensitive phosphate sensor has been fabricated by constructing a crystal disk consisting of variable mixtures of aluminium powder (Al), aluminium phosphate (AlPO₄) and powdered copper (Cu). The membrane sensor exhibits linear potential response in the concentration range of 1.0 × 10⁻¹ to 1.0 × 10⁻⁶ mol L⁻¹. The proposed sensor also exhibits a fast response time of <60 s. Its detection limit is lower than 1.0 × 10⁻⁶ mol L⁻¹. The electrode has a long lifetime and can be stored in air when not in use. The selectivity of the sensor with respect to other common ions is excellent.     

Novel enzyme/DNA/inorganic nanomaterials: a new generation of biocatalysts

The design, synthesis and properties of a new class of enzyme/DNA/inorganic nanobiomaterials are described here. DNA has been used to stabilize the enzymes intercalated in the galleries of the inorganic solid, alpha-Zr(iv) phosphate (alpha-Zr(HPO(4))(2).H(2)O, abbreviated as alpha-ZrP). Interestingly, the presence of DNA improved the activity and stability of the bound enzymes. Key studies leading to the current strategy are presented initially, and these are followed by more recent developments. Several enzymes and proteins, including horseradish peroxidase, lysozyme, glucose oxidase, chymotrypsin, bovine serum albumin, cytochrome c, met-hemoglobin and met-myoglobin are successfully intercalated in the galleries of alpha-ZrP, under benign ambient conditions (aqueous buffered solutions, at room temperature and neutral pH). These novel materials are characterized by XRD, SEM and TEM as well as by biochemical, calorimetric and spectroscopic methods. Spectroscopic studies (circular dichroism, CD), for example, indicated that co-intercalation of DNA improved the retention of bound enzyme structure. The activity was enhanced markedly (five-fold) when DNA is co-intercalated, when compared to the activity in the absence of DNA. Addition of DNA to the sample, after enzyme intercalation, did not make any improvements. Our hypothesis is that enzyme-DNA supramolecular complex binds to the solid and the unfavorable interactions between the enzyme and the solid are minimized. These novel nanobiocomposite materials provide a simple method for packaging DNA and aid in engineering more effective synthetic materials for gene/RNA-delivery and drug delivery applications.     

Electrochemical generation of stable carbocation-tetrafluoroborate salts and the cation-anion interactions in their solid state structures

The electrochemical generation of stable carbocations, among other heterocyclic products, by a unique electrochemical process involving the anodic oxidation of aryl-substituted ketene imines is described. The electrochemical oxidation undergoes an unusual multiannulation process to form these types of products by intermolecular cyclization. The X-ray crystal structures of two carbocation tetrafluoroborate salts,4c and4d, of which the latter is solvated by CH₂Cl₂, are presented. We have observed that one of the B-F bonds in4c is relatively long with respect to the other three similar in length B-F bonds, while in the solvated salt (4d·CH₂Cl₂), one of the B-F bonds is particularly short relative to its congeners. In both cases, the exceptional B-F bonds are oriented toward the positive center of the carbocation. These phenomena are compared with other known X-ray structures of organic tetrafluoroborate salts and discussed.     

Theory of excluded volume equation of state: higher approximations and new generation of equations of state for entire density range

A novel theory of an equation of state based on excluded volume and formulated in two preceding papers for gases and gaseous mixtures is extended to the entire density range by considering higher (beginning from the third) approximations of the theory. The algorithm of constructing higher approximations is elaborated. Equations of state are deduced using the requirement of maximum simplicity and contain a single free parameter to be chosen by reason of convenience or simplicity or to be used as a fitting parameter with respect to the computer simulation database. In this way, precise equations of state are derived for the hard-sphere fluid in the entire density range. On the side, the theory reproduces most known earlier equations of state for hard spheres and determines their place in the hierarchy of approximations. Equations of state for van der Waals fluids are also presented, and their critical parameters are estimated.     

A theoretical model of solid state phase reactions: Hysteresis and kinetics

Hysteresis in the pressure-dependent solid state phase transition Pr₇O₁₂Pr₉O₁₆ is modeled using a thermodynamic formalism. The system is considered to be formed of a fixed number of domains, which are differentiated on the basis of size. The two cases of noninteracting and interacting domains are considered. The interacting domains model allows a better fit to experimental results. In each case, the model is applied to four different isothermal hysteresis curves for the Pr₇O₁₂Pr₉O₁₆ phase transition. The kinetics of the phase transition are studied for the case of noninteracting domains.     

A unique tetramer of 4:5 beta-cyclodextrin-ferrocene in the solid state

A single crystal of a unique 4:5 inclusion complex between beta-cyclodextrin and ferrocene was prepared and the structure was determined by X-ray crystallographic analysis, showing that four of the five ferrocenes were included in the cavities of four beta-cyclodextrins along the axial orientation of the tetramer, while another was co-included between two beta-cyclodextrins from the equatorial orientation.     

Preparation of a new solid state fluoride ion selective electrode and application

A new solid state fluoride ion selective electrode composed of 70% Ag₂S, 10% Cu₂S and 20% CaF₂ has been developed. An analytically useful potential change occurred, from 1 × 10⁻⁶ to 1 × 10⁻¹ M fluoride ion. The slope of the linear portion (1 × 10⁻¹-1 × 10⁻⁵ M) was about 26 ± 2 mV/10-fold concentration changes in fluoride. It was found that pH change between 1 and 8 had no effect on the potential of the electrode. There was no interference of most common cations such as K^+, Na⁺, Ca²⁺ and Mg²⁺ and anions such as Cl⁻, NO₃⁻, SO₄²⁻ and PO₄³⁻. The lifetime of the electrode was more than 2 years, when used at least 4-5 times a day, and the response time was about 60 s.The measurements were made at constant ionic strength (0.1 M NaNO₃) and at room temperature. This electrode has been used for the determination of fluoride ion in Ankara city tap water and in bottled spring water using standard addition method. The validation of the electrode has been made with a commercial fluoride ion selective electrode (Orion) and high consistency was obtained.     

Temperature study of a glycine radical in the solid state adopting a DFT periodic approach: vibrational analysis and comparison with EPR experiments

The major radiation-induced radical in crystalline glycine is examined using DFT calculations, in which both molecular environment and temperature are accounted for. This is achieved by molecular dynamics simulations of the radical embedded in a supercell under periodic boundary conditions. At 100 and 300 K, a vibrational analysis is performed based on Fourier transformation of the atomic velocity autocorrelation functions. By the use of a novel band-pass filtering approach, several vibrational modes are identified and associated with experimental infrared and Raman assignments. Decomposition of the calculated spectra in terms of radical motion reveals that several vibrational modes are unique to the radical, the most prominent one at 702 cm(-1) corresponding to out-of-plane motion of the paramagnetic center, inversely coupled with similar motion of the carboxyl carbon. A hybrid periodic/cluster scheme is used to evaluate the EPR properties of the glycine radical along the MD trajectories resulting in temperature dependent magnetic properties. These are compared with available experimental data conducted at 77 K and room temperature. Ground state or low temperature calculations yield very good agreement with 77 K experimental EPR properties. From the 300 K simulations, an important improvement is achieved on the isotropic hyperfine coupling of the (13)C tensor, which becomes closer to the value measured at room temperature. It is established that this is the result of a nonlinear relation between the planarity of the radical center and the isotropic couplings of the nuclei bound to it. Finally, a critical reevaluation of the experimental (14)N hyperfine tensor data strongly suggests that an erroneous tensor was reported in literature. It is convincingly shown that from the same experimental data set a different tensor can be derived, which is in substantially better agreement with all calculations.     

A new amidoimidomalonate zinc complex with a sedecameric solid state structure catalyzing the copolymerization of CO2 and cyclohexene oxide

A new amidoimidomalonate ligand was synthesized in a short and effective way and the zinc acetate complex thereof was prepared. XRD investigation revealed an unprecedented solid state structure, where the sedecameric complex [(lig)₂Zn₄(OAc)₄]₄ builds the edges of a square cavity. Each edge is made up by a similar unit [(lig)₂Zn₄(OAc)₄] with four zinc atoms. The complex is an active catalyst in the copolymerization of CO₂ and cyclohexene oxide and produces polyethercarbonates with broad molecular weight distributions.