Irradiated Frozen Aqueous Solutions Research Articles

Cryo-irradiation as a terminal method for the sterilization of drug aqueous solutions

The aim of this study is to evaluate the specificities of the irradiation of drugs in frozen aqueous solution. The structures of the degradation products were determined to gain insight into the radiolysis mechanisms occurring in frozen aqueous solutions. Metoclopramide hydrochloride and metoprolol tartrate were chosen as models. The frozen solutions were irradiated at dry ice temperature by high energy electrons at various doses. The drug purity (chemical potency) and the radiolysis products were quantified by HPLC-DAD. Characterization of the degradation products was performed by LC-APCI-MS-MS. The structures of the radiolysis products detected in irradiated frozen aqueous solutions were compared to those detected in solid-state and aqueous solutions (previous studies). For both metoclopramide and metoprolol, solute loss upon irradiation of frozen aqueous solutions was negligible. Five radiolysis products present in traces were identified in irradiated metoclopramide frozen solutions. Three of them were previously identified in solid-state irradiated metoclopramide crystals. The two others were formed following reactions with the hydroxyl radical (indirect effect). Only one fragmentation product was observed in irradiated metoprolol frozen solutions. For both drugs, radiosterilization of frozen solutions, even at high doses (25 kGy), was found to be possible.

Electron-spin-resonance spectra of irradiated frozen aqueous solutions

1. It was found by the methods of ESE and optical spectroscopy that Cd (I) and Hg(I) ions, arising in the γ irradiation of aqueous solutions of salts of Cd(II) and Hg(II) at 77°K, are characterized by several types of sites of stabilization. 2. The formation of dimer ions Cd23+ and Hg23+ in the process of heating of aqueous solutions of salts of Cd (II) and Hg(II) at 77°K, as a result of generalization of one electron on the σ-bond, was demonstrated.

Electron paramagnetic resonance spectra of irradiated frozen aqueous solutions. Communication 14. Solutions of acetic acid and potassium acetate

1. Free radicals inγ-irradiated acetic acid, its aqueous solutions, and aqueous solutions of potassium acetate at 77°K were studied by the methods of ESR and optical spectroscopy. The anion radicals CH3COOH− or CH3COO2− (in all systems), CH3 radicals (in solutions of CH3COOH and CH3COOK), and e capt − (in solutions of CH3COOK) were identified, and their yields were measured. 2. Thermal and photostimulated conversions of the free radicals in the indicated systems were investigated. 3. A mechanism was suggested for the origin of radicals in acetic acid and its aqueous solutions.

Electron paramagnetic resonance spectra of irradiated frozen aqueous solutions

Electron paramagnetic resonance spectra of irradiated frozen aqueous solutions

Electron paramagnetic resonance structure of irradiated frozen aqueous solutions

Electron paramagnetic resonance structure of irradiated frozen aqueous solutions

Epr spectra of irradiated frozen aqueous solutions

1. The formation of captured electrons (e−capt) in polyhydric alcohols (ethylene glycol, glycerin, etriol) and their aqueous solutions,γ-irradiated at 77°K, was investigated by the EPR method. 2. The characteristics of the optical spectra of e−capt in vitreous etriol and its aqueous solutions are cited. 3. The yields of e−capt in the indicated systems were measured. It was found that for vitreous matrices G(e−capt) is equal to ∼1.5, regardless of the nature of the alcohol and its content in the alcohol-water mixture. 4. The yields of organic free radicals in vitreous ethylene glycol and its aqueous solutions were determined. 5. A scheme of radiolysis of vitreous polyhydric alcohols was proposed, and the peculiarities of the radiation chemical behavior of alcohol-water mixtures were discussed.

Electron paramagnetic resonance spectra of irradiated frozen aqueous solutions

1. Free radicals in frozen aqueous solutions of formate, γ irradiated at -196°, were investigated by the methods of EPR and optical spectroscopy. 2. A captured electron (ecapt−) (its formation is the most characteristic in the case of vitreous solutions), CO2−, and\(\begin{gathered} O^{} \hfill \\ \hfill \\ H C \hfill \\ \hfill \\ O^{} \hfill \\ \end{gathered} \) were identified, and the mechanism of their formation was discussed. 3. The optical properties of captured electrons and CO2− radicals in formate “glasses” were studied. It was found that λmax ofcapt− in a 10 M solution of HCOONa in H2O and D2O lies at 555 and 535 mμ, respectively (the half-widths of the bands are equal to 0.93 and 0.72 eV), while CO2− is characterized by bands with maxima at 250, 270, and 350 mμ (its molar extinction coefficient at 250 m is equal to 2.4 · 103 liters per mole · cm). 4. It was discovered that in the photoannealing of ecapt− in alkaline “glasses,” containing HCOO−, CH3OH, and CO3−2, diamagnetic (ecapt−)2-centers are formed. The latter break down again into ecapt− as a result of heating at -140°.

Paramagnetic Relaxation of Trapped Hydrogen Atoms in Irradiated Frozen Aqueous Solutions

The paramagnetic relaxation characteristics of trapped hydrogen atoms in γ-irradiated acidic and oxyanion ices were studied by power-saturation techniques. Relaxation times were measured as a function of radiation dose, deuteration, phase, and solute. The EPR linewidth of the trapped hydrogen atom was measured under various conditions. The EPR lineshape and power-saturation response indicate that the linewidth is due to contributions from both homogeneous and inhomogeneous interactions. The changes in relaxation time with radiation dose indicate that hydrogen atoms are trapped with a uniform distribution near oxyanions in the ice and are not trapped within radiation-produced spurs. The presence of phase effects on relaxation times supports an interstitial-defect model for the hydrogen-atom trapping site and suggests that the trap potential energy well is shallower in the polycrystalline phase than in the glassy phase. In polycrystalline ices the coupling between trapped hydrogen atoms and lattice phonons is modified by the type of oxyanion.

Electron paramagnetic resonance spectra of irradiated frozen aqueous solutions

Electron paramagnetic resonance spectra of irradiated frozen aqueous solutions

Electron paramagnetic resonance spectra of irradiated frozen aqueous solutions Communication 2. Aqueous solutions of sodium nitrite

1. The EPR spectra of irradiated frozen aqueous solutions of sodium nitrite were investigated in acid, neutral, and alkaline media. 2. The EPR spectra of acid and neutral solutions are identical and are due to the NO2 radicals, while in alkaline medium two more radicals are formed: NO2−2 and O−. 3. The radical yields were measured at temperatures of −196 and −150‡ as a function of the concentration of NaNO2 and alkali. With increasing concentration of these substances, the radical yields increase. The possible causes of this phenomenon were discussed. 4. Thermal stability of the radical products formed during irradiation was studied, and it was found that under definite conditions the OH and O− radicals interact with the NO2− ions during unfreezing.

Transfer of Radiation Energy to Solute Molecules in Irradiated Frozen Aqueous Solutions

The effect of ionizing radiation on aqueous systems is in general considerably less when the systems are irradiated in the frozen state than when they are irradiated at temperatures above the freezing point (1). It has consequently been assumed that the contribution of the indirect effect is of little or no importance in the frozen state. However, several lines of evidence are available showing that an indirect effect operates also in the frozen state (2-10). Electron spin resonance (ESR) studies indicate that the same type of radicals is formed when ice and liquid water are irradiated (6, 7, 11-16). The decrease in the magnitude of the indirect effect at low temperatures has in part been explained by assuming that the yield of water radicals is considerably reduced at low temperatures (2, 3, 17, 18). When pure ice is irradiated at 77?K, water radicals are stabilized with a G value of about 1 (6, 7, 16). The purpose of the present investigation was to study the extent and the mechanism of the indirect effect in irradiated frozen aqueous solutions. ESR spectroscopy has been used, since it is possible with this method to study the formation and fate of free radicals without having to melt the system. The data indicate that the indirect effect occurring after irradiation at 77?K involves largely water radicals formed within a small sphere of water surrounding the solute molecules.

Electron paramagnetic resonance spectra of irradiated frozen aqueous solutions Communication 1. Solutions of alkalis

1. The radical products in irradiated frozen solutions of KOH in H2O and D2O were investigated by the electron paramagnetic resonance method at various concentrations and in the temperature range from −196 to −100°. 2. Stabilization of the hydrated electron and conversion of the OH radical to the ion radical O− · nH2O occur in alkaline medium. 3. H and D atoms were detected in irradiated concentrated frozen solutions of KOH in H2O and D2O at −196° 4. The thermal stability of the radical products in neutral water and in solutions of alkali of various concentrations was investigated. 5. The yields of radical products in alkaline medium were determined at temperatures of −196 and −150° as a function of the KOH concentration, and they were found to be increased in comparison with neutral frozen water.