Radiolysis of myoglobin concentrated gels by protons: specific changes in secondary structure and production of carbon monoxide.

While particle therapy has been used for decades for cancer treatment, there is still a lack of information on the molecular mechanisms of biomolecules radiolysis by accelerated ions. Here, we examine the effects of accelerated protons on highly concentrated native myoglobin, by means of Fourier transform infrared and UV-Visible spectroscopies. Upon irradiation, the secondary structure of the protein is drastically modified, from mostly alpha helices conformation to mostly beta elements at highest fluence. These changes are accompanied by significant production of carbon monoxide, which was shown to come from heme degradation under irradiation. The radiolytic yields of formation of denatured protein, carbon monoxide, and of heme degradation were determined, and found very close to each other: G+denatured Mb ≈ G+CO ≈ G-heme = 1.6 × 10-8 ± 0.1 × 10-8 mol/J = 0.16 ± 0.01 species/100 eV. The denaturation of the protein to a beta structure and the production of carbon monoxide under ion irradiation are phenomena that may play an important role in the biological effects of ionizing radiation.

Application of polyimide films as a nuclear track detector (2): A latent track structure study with Fourier transform infrared spectroscopy.

This paper reports the relation between latent track structure and the detection threshold of etch pits formation in UPILEX-S® and Kapton. At the similar stopping power value, effective track core radii and G values for heavier ions are lower than those of lighter ions. These results would be due to the difference of the radial dose distribution for low- and high-velocity ions. The G value starts more rapidly rising above 600 and 1000 keV/µm for Kapton and UPILEX-S®, respectively. The detection threshold of UPILEX-S is 4000 keV/µm for Ar ions, at which effective track core radii of all functional groups are larger than 2 nm. Since the length of a molecule unit of UPILEX-S® is about 1.4 nm, at least more than two molecule units have to be damaged for the etch pit formation. A similar discussion is applicable to Kapton, whose detection threshold is significantly lower than UPILEX-S®.

Application of polyimide films as a nuclear track detector (1): A systematic study of track registration sensitivity.

This paper reports the variation of track registration sensitivity as a function of the stopping power of heavy ions in UPILEX-S® films, which is known as the most radiation tolerant polyimide (PI). The detection thresholds in the stopping power for etch pit formation are determined as 4,000, 4,100, 4,800, and 5600 keV/µm for 40Ar, 84Kr, 132Xe and 238U ions, respectively. Furthermore, we investigate the latent track structure in two kinds of PI films (UPILEX-S® and Kapton) by means of FT-IR spectroscopy. At the similar stopping power value, the radiation chemical yields (G value) for heavier ions are lower than those of lighter ions. This is due to the difference of the radial dose distribution for low and high velocity ions.

Characterization of Functional Materials Using Coherence Scanning Interferometry and Environmental Chambers.

Functional materials are challenging to characterize because of the presence of small structures and inhomogeneous materials. If interference microscopy was initially developed for use for the optical profilometry of homogeneous, static surfaces, it has since been considerably improved in its capacity to measure a greater variety of samples and parameters. This review presents our own contributions to extending the usefulness of interference microscopy. For example, 4D microscopy allows real-time topographic measurement of moving or changing surfaces. High-resolution tomography can be used to characterize transparent layers; local spectroscopy allows the measurement of local optical properties; and glass microspheres improve the lateral resolution of measurements. Environmental chambers have been particularly useful in three specific applications. The first one controls the pressure, temperature, and humidity for measuring the mechanical properties of ultrathin polymer films; the second controls automatically the deposition of microdroplets for measuring the drying properties of polymers; and the third one employs an immersion system for studying changes in colloidal layers immersed in water in the presence of pollutants. The results of each system and technique demonstrate that interference microscopy can be used for more fully characterizing the small structures and inhomogeneous materials typically found in functional materials.

Methodological and Conceptual Progresses in Studies on the Latent Tracks in PADC.

Modified structure along latent tracks and track formation process have been investigated in poly (allyl diglycol carbonate), PADC, which is well recognized as a sensitive etched track detector. This knowledge is essential to develop novel detectors with improved track registration property. The track structures of protons and heavy ions (He, C, Ne, Ar, Fe, Kr and Xe) have been examined by means of FT-IR spectrometry, covering the stopping power region between 1.2 to 12,000 eV/nm. Through a set of experiments on low-LET radiations-such as gamma ray-, multi-step damage process by electron hits was confirmed in the radiation-sensitive parts of the PADC repeat-unit. From this result, we unveiled for the first-time the layered structure in tracks, in relation with the number of secondary electrons. We also proved that the etch pit was formed when at least two repeat-units were destroyed along the track radial direction. To evaluate the number of secondary electrons around the tracks, a series of numerical simulations were performed with Geant4-DNA. Therefore, we are proposing new physical criterions to describe the detection thresholds. Furthermore, we propose a present issue of the definition of detection threshold for semi-relativistic C ions. Additionally, as a possible chemical criterion, formation density of hydroxyl group is suggested to express the response of PADC.

Quantitative estimation of track segment yields of water radiolysis species under heavy ions around Bragg peak energies using Geant4-DNA.

We evaluate the track segment yield G' of typical water radiolysis products (eaq-, ·OH and H2O2) under heavy ions (He, C and Fe ions) using a Monte Carlo simulation code in the Geant4-DNA. Furthermore, we reproduce experimental results of ·OH of He and C ions around the Bragg peak energies (< 6 MeV/u). In the relatively high energy region (e.g., > 10 MeV/u), the simulation results using Geant4-DNA have agreed with experimental results. However, the G-values of water radiolysis species have not been properly evaluated around the Bragg peak energies, at which high ionizing density can be expected. Around the Bragg peak energy, dense continuous secondary products are generated, so that it is necessary to simulate the radical-radical reaction more accurately. To do so, we added the role of secondary products formed by irradiation. Consequently, our simulation results are in good agreement with experimental results and previous simulations not only in the high-energy region but also around the Bragg peak. Several future issues are also discussed regarding the roles of fragmentation and multi-ionization to realize more realistic simulations.

Single- and Double-Strand Breaks of Dry DNA Exposed to Protons at Bragg-Peak Energies.

Ultrathin layers (<20 nm) of pBR322 plasmid DNA were deposited onto 2.5 µm thick polyester films and exposed to proton Bragg-peak energies (90-3000 keV) at various fluences. A quantitative analysis of radio-induced DNA damage is reported here in terms of single- and double-strand breaks (SSB and DSB, respectively). The corresponding yields as well as G-values and the cross sections exhibit fairly good agreement with the rare available data, stemming from close experimental conditions, namely, based on α particle irradiation. SSB/DSB rates appear to be linear when plotted against linear energy transfer (LET) in the whole energy range studied. All the data present a maximum in the 150-200 keV energy range; as for LET, it peaks at 90 keV. We also show that fragmentation starts to be significant for proton fluences greater than 1 × 1011 cm-2 at the Bragg-peak energies. Finally, we determine the average proton track radial extension, rmax, corresponding to an occupation probability of 100% DSB in the Bragg-peak region. The rmax values determined are in excellent agreement with the radial extensions of proton tracks determined by simulation approaches in water. When plotted as a function of LET, both SSB and DSB cross sections bend back at high LETs.

TRLFS evidence for precipitation of uranyl phosphate on the surface of alumina: environmental implications.

We studied the ligand-enhanced sorption of uranyl ions (1-12 µM) on α-alumina colloids suspended in (and pre-equilibrated with) solutions at various concentrations of phosphate ions (P(T) = 0-900 µM). A highly sensitive technique, time resolved laser-induced fluorescence spectroscopy (TRLFS), was used to examine the chemical speciation of uranyl sorbed at trace concentrations (0.4-4 µmol U·g⁻¹). The suspensions with P(T) ≥ 100 µM exhibited high uranyl adsorption, and a very high intensity of fluorescence that increased with the sorbed amounts of phosphate and uranyl. These samples exhibited similar spectral and temporal characteristics of fluorescence emission, evidencing a uniform speciation pattern and a single coordination environment for sorbed U, despite large variation in parameters such as aqueous uranyl speciation, U loading, and extent of coverage of alumina by secondary Al phosphates precipitating on the surface. The results pointed formation of surface precipitates of uranyl phosphates, which are characterized by high quantum yield, peak maxima at positions similar to those of U(VI) phosphate minerals and four lifetimes indicating distortions, in-homogeneities or varying number of water molecules in the lattice. The findings have major implications for our understanding of the mechanisms of immobilization of U at trace levels on surfaces of oxides submitted to phosphated solutions in soils with low pH.

Mechanisms of uranyl and phosphate (co)sorption: complexation and precipitation at alpha-Al2O3 surfaces.

This study presents new in situ electrophoretic and ATR-FTIR data on the surface species controlling the cosorption of uranyl and phosphate ions in alpha-Al(2)O(3) suspensions at acidic pH (3.3). It was shown that the uranyl sorption (i) was promoted in the presence of phosphate, (ii) induced significant changes in zeta potential of P-loaded alumina, and (iii) was governed by two mechanisms, surface complexation and surface precipitation, with the predominant species being mainly dependent on phosphate surface coverage. Formation of surface precipitates of uranyl phosphate at high phosphate surface coverage was inferred from the high negative charges imparted to the surface by uranyl and phosphate (co)sorption, and from assignments of IR bands at 1107, 1024, and 971 cm(-1) to P-O-stretching vibrations for phosphate coordinated to uranyl, at the alumina surface. The ATR-FTIR study showed that the precipitates of uranyl phosphate formed at the surface of alpha-Al(2)O(3) for aqueous concentrations of uranyl at trace levels. It also evidenced that formation of surface precipitates of U(VI)-phosphate was occurring along with the transformation of alumina into secondary surface precipitates of Al-phosphate, at very high phosphate concentrations. These findings are relevant to the mechanisms of adsorption of trace uranyl on naturally occurring oxide surfaces, in soils with low pH where cosorption of phosphate and uranyl ions is known to play a crucial role in the long-term retention of U.

Surface reactivity of alpha-Al(2)O(3) and mechanisms of phosphate sorption: In situ ATR-FTIR spectroscopy and zeta potential studies.

We have investigated the effect of solution parameters on the adsorption of phosphate ions and on charges and structures, i.e., on the nature of species, at the alpha-Al(2)O(3) colloid/solution interface by using the batch method, zeta potential measurements, and in situ ATR-FTIR spectroscopy. The uptake of phosphate decreases with the extent of surface deprotonation (i.e., pH), imparts negative charges to the colloid surface, and induces IEP shifts showing chemical sorption. Use of complementary techniques provides evidence that phosphate is sorbed at low pH (3.3) by a combination of surface reactions of complexation and precipitation, whose relative contributions depend on phosphate loading. Surface complexation includes fast reactions of ligand exchange with single coordinated hydroxyls, and electrostatic attraction of H(2)PO(4)(-) ions at positively charged surface sites. This is supported by experiments at low coverage showing sharp and linear decrease of zeta potential (i.e., surface charge) with amount of phosphate sorbed. At high coverage, zeta potential values are low and independent of phosphate loading. Formation of surface precipitates of Al-phosphate is inferred from the assignment of the ATR-FTIR absorption band at 1137cm(-1), whose intensity increases with phosphate solution content and reaction time, to the P-O-stretching vibration mode for phosphate sorbed at high concentrations on alpha-Al(2)O(3). In situ ATR-FTIR spectroscopy reveals also structural reorganizations of surface hydroxyls with time, due to surface hydration and to surface precipitation continuing over extended periods along alumina dissolution.