Radiation Chemical Methods Research Articles

Preparation of gold nanoparticles by photolysis and radiolysis in alcohol solutions of functional hyperbranched polyorganosiloxane/H[AuCl4]: Effect of irradiation mode on nanoparticle size and formation mechanism

Ethanol solutions of functional hyperbranched polyorganosiloxanes (0.2 vol%) with a molar ratio of NH2(CH2)2NH-/H[AuCl4]x3H2O of 8/1 were used as precursors for nanocomposite preparation using UV photolysis and X-ray radiolysis. It was shown that various irradiation modes provide the synthesis of gold nanoparticles (AuNPs) with tunable sizes and narrow size distributions. It was established that size distributions of AuNPs depend on the excitation wavelength. AuNPs with an average size of 3.5 nm were obtained by the direct excitation of gold ions using UV light with λmax = 365 nm. Meanwhile, the action of a higher energy light (λ = 254 nm) on the metal polymer complexes resulted in formation of ultra-small nanoparticles with an average size of 1.5 nm, presumably due to the increased efficiency of their nucleation process. In the case of radiolysis with X-rays, reduction of Au3+ ions occurs due to reactions with radicals produced from ethanol and leads to the formation of AuNPs of 2–3 nm. Thus, the size distribution of the prepared AuNPs may be controlled by the irradiation mode, which critically affects nanomaterial properties. Additionally nanoparticles obtained by photochemical or radiation-chemical methods are free of chemical impurities, which is important for the development of functional materials.

Gold nanoparticles in reverse micellar solutions: preparation, optical properties, and dimensional characteristics

Gold nanoparticles (NPs) were synthesized via chemical (Chem) and radiation-chemical (RadChem) methods for the reduction of ions in reverse micellar solutions (RMS). The gold NP have for the first time been obtained by self-organization (Self-assembly), and their optical properties were evaluated. The formation of Au NP (Chem, RadChem, and Self) was confirmed by the transmission electron microscopy. The spectral characteristics of optical absorption of gold NP in the RMS depend on the solubilization coefficient ω, the salt concentration, and the methods for initiating the primary steps of reduction reactions responsible for the formation of nanoscale structures.

Synthesis and Physicochemical Properties of Rhenium Nanoparticles

This work describes the physicochemical properties of stable rhenium nanoparticles (Re NPs) which were synthesized by the chemical and radiation–chemical methods in a reverse-micelle solution (RMS) of nanoparticles. The methods of UV-VIS spectrophotometry, fluorometry, atomic-force and transmission electron microscopies, and small-angle X-ray scattering were used. It was found that the sizes of Re NPs varied within the range from 1 to 18 nm depending on the synthesis conditions and procedures.

Radical Ions of a π-Bowl Sumanene: Effects of Strained Structure on the Electronic Transitions.

Strained polyaromatic carbon molecules exhibit interesting properties owing to enhanced interactions between p orbitals of sp2 carbons; sumanene (SUM) is one of these bowl-shaped π-conjugated molecules (π-bowls). In the present study, the radical cation and radical anion of SUM were characterized by radiation chemical methods, that is, pulse radiolysis and γ-ray radiolysis. Absorption spectra of the SUM radical cation and radical anion in a wide spectral region ranging from the visible to near-IR were successfully obtained. Absorption spectra of the SUM radical cation and radical anion are similar in shape to those of the corresponding species of triphenylene (TP), which possesses a planar structure and the same π-electron system as SUM. However, the SUM radical anion showed lower peak shifts than the TP radical anion. Theoretical calculations revealed that the MOs responsible for the electronic transitions of the SUM radical anion are different from those of the TP radical anion, in contrast to the radical cations. These results demonstrate that the strains in the molecular geometries affect the electronic transitions of radical ions.

Detection of Structural Changes upon One-Electron Oxidation and Reduction of Stilbene Derivatives by Time-Resolved Resonance Raman Spectroscopy during Pulse Radiolysis and Theoretical Calculations.

Stilbene (St) derivatives have been investigated for many years because of their interesting photochemical reactions such as cis-trans isomerization in the excited states and charged states and their relation to poly(p-phenylenevinylene)s. To clarify their charged state properties, structural information is indispensable. In the present study, radical cations and radical anions of St derivatives were investigated by radiation chemical methods. Absorption spectra of radical ion states were obtained by transient absorption measurements during pulse radiolysis; theoretical calculations that included the solvent effect afforded reasonable assignments. The variation in the peak position was explained by using HOMO and LUMO energy levels. Structural changes upon one-electron oxidation and reduction were detected by time-resolved resonance Raman measurements during pulse radiolysis. Significant downshifts were observed with the CC stretching mode of the ethylenic groups, indicative of the decrease in the bonding order. It was confirmed that the downshifts observed with reduction were larger than those with oxidation. On the other hand, the downshift caused by oxidation depends significantly on the electron-donating or electron-withdrawing nature of the substituents.

Radical Ions of Cyclopyrenylene: Comparison of Spectral Properties with Cycloparaphenylene

Hoop-shaped π-conjugated molecules have attracted much attention. In this study, the radical ions of [4]cyclo-2,7-pyrenylene ([4]CPY), a cyclic tetramer of pyrene, and [4]cyclo-4,5,9,10-tetrahydro-2,7-pyrenylene ([4]CHPY) were investigated using radiation chemical methods, namely, γ-ray radiolysis and pulse radiolysis. The absorption spectra of the radical ions of [4]CPY and [4]CHPY showed clear peaks in the near-IR and UV-vis regions similar to those of [8]cycloparaphenylene ([8]CPP). Theoretical calculations using time-dependent density functional theory provided reasonable assignments of the observed absorption bands. It was indicated that the C4-C5 and C9-C10 ethylene bonds of [4]CHPY do not contribute to the electronic transitions, resulting in absorption spectra similar to those of [8]CPP. On the other hand, it was confirmed that the allowed electronic transitions of the radical ions of [4]CPY are different from those of the radical ions of [4]CHPY and [8]CPP.

Radical Ions of Cycloparaphenylenes: Size Dependence Contrary to the Neutral Molecules.

Cycloparaphenylenes (CPPs) have attracted wide attention because of their interesting properties owing to distorted and strained aromatic systems and radially oriented p orbitals. For application of CPPs, information on their charged states (radical cation and radical anion) is essential. Here, we measured absorption spectra of the radical cations and the radical anions of CPPs with various ring sizes over a wide spectral region by means of radiation chemical methods. The peak position of the near-IR bands for both the radical cation and the radical anion shifted to lower energies with an increase in the ring size. This trend is contrary to what is observed for transitions between the HOMO and LUMO of the neutral CPP. The observed spectra of the CPP radical ions were reasonably assigned based on time-dependent density functional theory. These results indicate that the next HOMO and the next LUMO levels are important in the electronic transitions of radical ions.

Radical Cation of Star-Shaped Condensed Oligofluorenes Having Isotruxene as a Core: Importance of Rigid Planar Structure on Charge Delocalization

Because of their excellent optical and electronic properties, oligofluorenes and polyfluorenes have been investigated for years. Recently developed star-shaped oligomers bearing a truxene or isotruxene core are interesting two-dimensional oligomers. Since employment of a condensed ring system will be effective in further extension of π-conjugation system, we studied electronic and vibrational properties of radical cation of CITFn, star-shaped condensed oligomer with isotruxene core and fluorene unit, by means of the radiation chemical methods. Absorption spectra of radical cation of CITFn were measured in the wide spectral range, which revealed extended π-conjugation of CITFn. Furthermore, time-resolved resonance Raman spectra during pulse radiolysis revealed that the oxidation of CITFn induced structural change to enhance quinoidal character. The Raman data and theoretical calculation indicated that the rigid framework of the present star-shaped oligomer which makes the oligomer a planar structure is quite important in extension of the conjugation pathway.

HPLC in the study of radiation-chemical changes in the composition of wines

The study of radioprotective properties of wine related to their ability to regulate redox processes and resist oxidative stress caused by exposure to ionizing radiation and other factors in living systems is of cur� rent interest. Physicochemical approach, including th e use of such methods as chromatography for research on the effect of these factors is underdeveloped. In this paper, the HPLC method was used to identify products of γ�radiolysis of serotonin and other phenolic componen ts of wines and calculate the degrees of conversion of the starting compounds. These data are necessary for measuring the radiation resistance of biologically active compounds, including serotonin, since recently the radiationchemical methods of sterilization of medicinal preparations on their basis are widely used. Determination of products of radiationchemical reac� tions of bioactive compounds is important in the problem of studying the mechanism of the redox reactions in biological systems with different degrees of organization.

Recent Approach in Radiation Chemistry toward Material and Biological Science

In the present Perspective, a recent approach in radiation chemistry is summarized. By employing radiation chemical methods, such as γ-ray radiolysis and pulse radiolysis, powerful oxidative and reductive species can be generated to initiate various reactions. Thus, radiation chemical methods are applicable to various systems in a wide variety of fields and are not restricted to basic radical or radical ion chemistry. For example, our research group has employed radiation chemical methods to elucidate the mechanisms of various phenomena. Here, radiation chemical investigations on the charge delocalization process, excited radical ions, photocatalytic systems, emitting devices, and biological systems are introduced as examples of the wide applicability of radiation chemistry. Radiation chemical methods should be useful for a wide variety of researchers in the future as well.

ChemInform Abstract: The Elucidation of Peroxyl Radical Reactions in Aqueous Solution with Radiation-Chemical Methods

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Radiation and Quantum Chemical Studies of Chalcone Derivatives

The reactions of oxidizing radicals ((*)OH, Br(2)(*-), and SO(4)(*-)) with -OH-, -CH(3)-, or -NH(2)-substituted indole chalcones and hydroxy benzenoid chalcones were studied by radiation and quantum chemical methods. The (*)OH radical was found to react by addition at diffusion-controlled rates (k = 1.1-1.7 x 10(10) dm(3) mol(-1) s(-1)), but Br(2)(*-) radical reacted by 2 orders of magnitude lower. Quantum chemical calculations at the B3LYP/6-31+G(d,p) level of theory have shown that the (C2-OH)(*), (C11-OH)(*), and (C10-OH)(*) adducts of the indole chalcones and the (C7-OH)(*) and (C8-OH)(*) adducts of the hydroxy benzenoid chalcones are more stable with DeltaH = -39 to -28 kcal mol(-1) and DeltaG = -32 to -19 kcal mol(-1). This suggests that (*)OH addition to the alpha,beta-unsaturated bond is a major reaction channel in both types of chalcones and is barrierless. The stability and lack of dehydration of the (*)OH adducts arise from two factors: strong frontier orbital interaction due to the low energy gap between interacting orbitals and the negligible Coulombic repulsion due to small absolute values of Mulliken charges. The transient absorption spectrum measured in the (*)OH radical reaction with all the indole chalcone derivatives exhibited a maximum at 390 nm, which is in excellent agreement with the computed value (394 nm). The formation of three phenolic products under steady-state radiolysis is in line with the three stable (*)OH adducts predicted by theory. Independent of the substituent, identical spectra (lambda(max) = 330-360 and approximately 580 nm) were obtained on one-electron oxidation of the three indole chalcones. MO calculations predict the deprotonation from the -NH group is more efficient than from the substituent due to the larger electron density on the N1 atom forming the chalcone indolyl radical. Its reduction potential was determined to be 0.56 V from the ABTS(*-)/ABTS(2-) couple. In benzenoid chalcones, the (*)OH adduct spectrum is characterized by a peak at 270 nm and a broad maximum centered in the range 430-450 nm with an intense bleaching at 340 nm. The spectrum formed by electron transfer in these derivatives with lambda(max) = 280 and 380 nm (epsilon(280) = 5000 dm(3) mol(-1) cm(-1) and epsilon(380) = 700 dm(3) mol(-1) cm(-1)) was assigned to its phenoxyl radical. Our pulse radiolysis experiments in combination with quantum chemical calculations demonstrate that chalcones are efficient scavengers of damaging oxyl radicals.

Study of radiation chemical reactions of oxidising and reducing radicals with furazan derivatives

Reactions of OH, O−, N3 and SO4− and eaq− radicals with furazan and its dimethyl and diamino derivatives were studied by radiation chemical methods. The OH radical reaction is selective with the rates following the order furazan<3,4-dimethylfurazan (3,4-DMF)<3,4-diaminofurazan (3,4-DAF), the k values being <107, 3.5×108, 3.9×109dm3mol−1s−1, respectively. The transient absorption spectra measured in the OH radical reaction with 3,4-DMF and 3,4-DAF exhibited maxima at 270 and 290nm, respectively, which are assigned to the benzylic and anilino type radicals. The same intermediates are also formed in the O− reaction by H abstraction. All three derivatives showed lack of reactivity with N3 radical and was only 3,4-diaminofurazan found reactive with SO4− (k=3.6×109dm3mol−1s−1). The rates of eaq− with all the three derivatives are diffusion controlled k=(0.8–1.9)×1010dm3mol−1s−1 and its reaction mechanism involves very fast protonation of the initially formed radical anions by water (k≥107s−1) followed by tautomerisation of the N-atom protonated C-centred radical to the C-atom protonated N-centred radical. The transformation is catalysed by OH− and the rates for the spontaneous transformation in neutral solution are 5.4×104 and 1.5×105s−1 with furazan and 3,4-diaminofurazan, respectively.

ChemInform Abstract: Odd‐Electron Bonded Sulfur‐ and Selenium‐Centered Radical Cations as Studied by Radiation Chemical and Complementary Methods

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Glycine Decarboxylation: The Free Radical Mechanism

Radiation chemical methods were used to investigate the reactions of glycine anions, H2NCH2CO2- (Gly-), with •OH, (CH3)2C•OH, and •CH3 radicals. A major and most significant product from all of these processes is CO2. Pulse-radiolysis revealed that the initial step in the •OH-induced mechanism is oxidation of the amino group, producing +H2N•-CH2-CO2- and HN•-CH2-CO2- with yields of 63% and 37%, respectively. The amino radical cation, +H2N•-CH2-CO2-, suffers fast (≤100 ns) fragmentation into CO2 + •CH2NH2. The other primary radical, HN•-CH2-CO2-, can also be converted into the decarboxylating +H2N•-CH2-CO2- by reaction with proton donors such as phosphate (H2PO4-/k = 7.4 × 107 M-1 s-1, and HPO42-/k = 2.5 × 105 M-1 s-1) or the glycine zwitterion, Gly± (k = 3.9 × 105 M-1 s-1), but only on a much longer (typically μs to ms) time scale (k ≈ 4 × 105 M-1 s-1). Competitively, the HN•-CH2-CO2- transforms into a carbon-centered radical H2N-C•H-CO2- either by an intramolecular 1,2-H-atom shift (k = (1.2 ± 1.0) × 103 s-1) or by bimolecular reaction with Gly- (k = (3.0 ± 0.2) × 104 M-1 s-1). Both C-centered radicals, H2N-C•H-CO2- and •CH2NH2, are reductants as verified through their reactions with Fe(CN)63- and methyl viologen (MV2+) in pulse-radiolysis experiments (k ≈ 4 × 109 M-1 s-1). The eventual complete transformation of all primary radicals into H2N-C•H-CO2- and •CH2NH2 was further substantiated by γ-radiolytic reduction of Fe(CN)63-. In the presence of suitable electron donors, the HN•-CH2-CO2- radical acts as an oxidant. This was demonstrated through its reaction with hydroquinone (k = (7.4 ± 0.5) × 107 M-1 s-1). Although the C-centered H2N-C•H-CO2- radical is not generated in a direct H-atom abstraction by •OH, this radical appears to be the exclusive product in the reaction of Gly- with (CH3)2C•OH, •CH2NH2, and •CH3 (k ≈ 102 M-1 s-1). A most significant finding is that H2N-C•H-CO2- can be converted into the decarboxylating N-centered radical cation +H2N•-CH2-CO2- by reaction with proton donors such as Gly± (k ≈ 3 × 103 M-1 s-1) or phosphate and thus also becomes a source of CO2. The •CH2NH2-induced route establishes, in fact, a chain mechanism which could be proven through dose rate effect experiments and suppression of the chain upon addition of Fe(CN)63- or MV2+ as a scavenger for the reducing precursor radicals. The possible initiation of amino acid decarboxylation by C-centered radicals and the assistance of proton donors at various stages within the overall mechanism are considered to be of general significance and interest in chemical and biological systems.

Cobalt Porphyrin Catalyzed Reduction of CO2. Radiation Chemical, Photochemical, and Electrochemical Studies

Several cobalt porphyrins (CoP) have been reduced by radiation chemical, photochemical, and electrochemical methods, in aqueous and organic solvents. In aqueous solutions, the CoIP state is stable at high pH but is shorter lived in neutral and acidic solutions. Stable CoIP is also observed in organic solvents and is unreactive toward CO2. One-electron reduction of CoIP leads to formation of a species that is observed as a transient intermediate by pulse radiolysis in aqueous solutions and as a stable product following reduction by Na in tetrahydrofuran solutions. The spectrum of this species is not the characteristic spectrum of a metalloporphyrin π-radical anion and is ascribed to Co0P. This species binds and reduces CO2. Catalytic formation of CO and HCO2- is confirmed by photochemical experiments in acetonitrile solutions containing triethylamine as a reductive quencher. Catalytic reduction of CO2 is also confirmed by cyclic voltammetry in acetonitrile and butyronitrile solutions and is shown to occur ...

Iron Porphyrin-Catalyzed Reduction of CO2. Photochemical and Radiation Chemical Studies

Several iron porphyrins have been reduced by photochemical and radiation chemical methods, in organic solvents and in aqueous solutions, from FeIIIP to FeIIP to FeIP and beyond. In aqueous solutions, the FeIP state is relatively stable for the tetrakis(N-methyl-2-pyridyl)porphyrin at high pH but is shorter lived in neutral and acidic solutions. The FeIP state of tetrakis(N-methyl-3-pyridyl)porphyrin and tetrakis(N-methyl-4-pyridyl)porphyrin are short-lived at any pH. Decay of FeIP is accelerated by H+ and by CO2, probably via reaction with the Fe0P state formed upon disproportionation of FeIP. These reactions may lead to formation of H2 and CO, respectively, and to formation of the chlorin, FeIIPH2, as a side product. The FeIP state is also observed as a stable product in several organic solvents. This is observed by photolysis of iron tetraphenylporphyrin and several of its derivatives (e.g., trimethyl-, dichloro- and pentafluorophenyl), mainly in dimethylformamide and acetonitrile solutions, using triet...

Surface modification of fluoropolymers

COF groups are formed by electron irradiation of PTFE [poly(tetrafluoroethylene)] powders in air, especially at the surface and in near-surface regions which can be easily hydrolysed to carboxyl groups by air humidity. The application of special additives during irradiation leads to modified micropowders. Fourier transform infrared (FTIR) spectroscopy enables the detection of carboxyl and COF groups. γ-Irradiation of PTFE mainly causes degradation of the polymer; the concentration of carboxyl groups is much lower. Carboxylated micropowders created via radiation treatment retain the essential properties of PTFE. With increasing radiation dose, the increasing concentration of functional groups in the micropowders causes an increase in the surface free energy. This diminishes the strong water and oil repellency of PTFE in such a way that homogeneous incorporation into aqueous and organic liquids or other polymers is possible. So, the special properties of PTFE can be made effective in these media. Modified PTFE micropowders have been successfully tested in many application areas. The aim of our present work was to increase the concentration and vary the nature of functional groups by radiation-chemical methods or chemical conversion of COF groups (polymer-analogous reactions). A highly modified PTFE powder was used to reduce the repellent properties of PTFE diaphragms for application in brine electrolysis. The COF groups of the micropowders were modified by γ-aminopropyltriethoxysilane. The irradiation of FEP [poly(tetrafluoroethylene-co-hexafluoropropylene)] and PFA [poly(tetrafluoroethylene-co-perfluoroalkylvinylether)] yields products which contain a higher content of carboxyl groups than PTFE.

Radiation Chemistry Applied to Drug Design

Radiation chemistry can contribute to drug design by quantifying redox properties of drugs (useful parameters in quantitative structure-activity relationships), and where free radicals are suspected intermediates in drug action, radiation can be used to generate these putative species and help characterize relevant reactions. Steady radiolysis produces radicals at a readily-varied but quantified rate; pulse radiolysis with fast spectrophotometric and/or conductimetric detection enables the kinetic properties of radicals to be monitored directly. Using these methods, radical intermediates from drugs with specific cytotoxicity towards hypoxic cells have been shown to react rapidly with oxygen, a reaction probably responsible for the therapeutic differential. Radical oxidants from activated neutrophils include superoxide and hydroxyl radicals, and radiation-chemical methods have an important role to play in rational drug design to exploit such oxidative chemistry. Antioxidants can also be evaluated quantitatively by radiolysis methods; the conjugation reactions of thiyl radicals with thiolate and oxygen are now recognised to be major contributions of pulse radiolysis to thiol biochemistry.

Pulse radiolytically induced redox and alkylation processes of C70

Redox and alkylation (radical addition) reactions with C70 have been investigated by means of radiation chemical methods, particularly time-resolved pulse radiolysis measurements. All experiments were conducted in solutions (propan-2-ol, 2-methylpropan-2-ol and 1,2-dichloroethane) at room temperature. The differential spectrum obtained upon one-electron reduction of C70 by (CH3)2C(OH)˙(k= 8 × 108 dm3 mol–1 s–1) and attributable to the formation of C70˙– shows a relatively weak but still distinct absorption band in the IR at 880 nm. One-electron oxidation of C70 by the cation of 1,2-dichloroethane (1,2-DCE˙+) yields C70˙+ radical cations (k 2 × 1010 dm3 mol–1 s–1) with an even weaker but still noticable band at 925 nm. Compared with the IR-absorption bands of the analogue C60˙– and C60˙+(which exhibit relatively strong and characteristic bands at 1080 and 980 nm, respectively) those attributable to the C70-derived species are considerably less intense but not absent as might have been deduced from earlier experimental and theoretical studies. IR absorptions (with maxima around 960 nm) have also been observed for (C70–CH2CH2Cl)˙ and (C70–CH2C(CH3)2OH)˙ which are formed upon addition of ˙CH2CH2Cl (k= 1.9 × 109 dm3 mol–1 s–1) and ˙CH2C(CH3)2OH (k= 1.8 × 109 dm3 mol–1 s–1), respectively, to C70. The absolute rate constants are very similar to those measured for the corresponding radical reactions with C60. In conclusion, C70 exhibits rather similar features to those of C60 with respect to radical and one-electron redox initiated reactions with, however, some noticeable differences.