Low-temperature radiation chemistry

An overview of studies on the radiation-initiated chemical reactions of polymerization, copolymerization, graft polymerization, telomerization, oxidation, cryoozonolysis, hydrobromination of olefins, and chlorination of paraffins occurring at low and ultralow temperatures has been presented. Particular attention has been paid to self-oscillating reactions.     

Chitosan and radiation chemistry

Chitosan as a raw material with special properties has drawn attention of scientists working in the field of radiation processing and natural polymer products development, and also of specialists working in the field of radiation protection and oncologists. Especially the applications concern reduced molecular weight chitosan which still retain its chemical structure; such form of the compound is fostering biological, physical and chemical reactivity of the product. Chitosan degrades into fragments under γ-ray or electron beam irradiation. Antibacterial properties of the product are applied in manufacturing hydrogel for wound dressing and additional healing properties can be achieved by incorporating in the hydrogel matrix chitosan bonded silver clusters. Another possible application of chitosan is in reducing radiation damage to the radiation workers or radiation cured patients. In the case of radioisotopes oral or respiratory chitosan-based materials can be applied as chelators. Applications of chitosan in oncology are also reported.     

Future perspectives of radiation chemistry

Future perspectives of radiation chemistry are discussed by the analysis of the related information in detail as obtained from our recent surveys of publications and scientific meetings in radiation chemistry and its neighboring research fields, giving some examples, and are summarized as follows. (1) Traditionally important core-parts of radiation chemistry should be activated more. The corresponding research programs are listed in detail. (2) Research fields of physics, chemistry, biology, medicine, and technology in radiation research should interact more among them with each other. (3) Basic research of radiation chemistry should interact more with its applied research. (4) Interface research fields with radiation chemistry should be produced more with mutually common viewpoints and research interests between the two. Interfaces are not only applied research but also basic one.     

Gas phase radiation chemistry of hexafluoroethane

The Co-60 gamma radiolysis of gaseous C₂F₆ was investigated at 50 Torr pressure, both pure and with 10% oxygen added. For the pure system, the radiolytic products and their respective C values were CF₄, 2.27; C₃F₈, 0.23; C₄F₁₀, 0.09; C₅F₁₂, 0.015; and C₆F₁₄, 0.009. All radiolysis products except for CF₄ (C = 0.61) were eliminated when 10% O₂ was added as scavenger. The results are discussed mainly in terms of the decomposition of excited C₂F₆ into free radicals, which can then combine. The unscavenged CF₄ is accounted for by the ion-molecule reaction CF₃⁺ + C₂F₆ → CF₄ + C₂F₅⁺.     

The growing applications of click chemistry

Click chemistry, the subject of this tutorial review, is a modular synthetic approach towards the assembly of new molecular entities. This powerful strategy relies mainly upon the construction of carbon-heteroatom bonds using spring-loaded reactants. Its growing number of applications are found in nearly all areas of modern chemistry from drug discovery to materials science. The copper(I)-catalysed 1,2,3-triazole forming reaction between azides and terminal alkynes has become the gold standard of click chemistry due to its reliability, specificity and biocompatibility.     

Viscosity study of radiation chemistry of polystyrene

The effects of γ-radiation on aqueous polystyrene emulsions were followed by measurements by intrinsic viscosities of soluble polymer in toluene. Estimates of incipient gel dose from intrinsic viscosity data do not coincide closely with those from measurements of gel content. This uncertainty and those in molecular weight averages make it difficult to assign a precise value to G(crosslink), even when the scission crosslinking ratio in the particular system is reliably known. The intrinsic viscosity of sol polymer in the postgel region decreases with increasing dose to an asymptotic value. The decrease is as expected if larger molecules are progressively linked into the gel network and the asymptote may be attributable to cyclization. Present theories of branching do not seem to be applicable for quantitative estimation of scission/crosslinking ratios caused by irradiation of polystyrene. This is probably connected with deficiencies in the theoretical connection between radius of gyration and intrinsic viscosity in good solvents. Diallyl fumarate and diallyl maleate increased crosslinking rates, but only at low doses. Chain scission was enhanced by addition of 1,2-dichloroethylene and 2,5-dimethylhexane-2,5-dihydroperoxide.     

Wavelet transform applications in analytical chemistry

The wavelet transform has been established with the Fourier transform as a data-processing method in analytical chemistry. The main fields of application in analytical chemistry are related to denoising, compression, variable reduction, and signal suppression. Analytical applications were selected showing prospects and limitations of the wavelet transform. An important aspect consists in showing the advantage of wavelet transform over Fourier transform with respect to dual localization of a signal in both the original and the transformed domain enabling principal new application fields in comparison with Fourier transform.     

Solitons in radiation chemistry and biology

Basic physical properties of highly nonlinear, collective soliton excitations in structured condensed matter are briefly formulated. Several mechanisms of microscopic soliton formation by the absorption of high energy radiation in biological matter are suggested. Soliton formation and reactions presumably may enhance the radiation sensitivity of living matter.Dedicated to Jií Teplý on the occassion of his 60th brithday.     

ESR application to radiation chemistry of polymers

Important results obtained in our group in the field of ESR application to the study of irradiated polymers are summarized. They are the analysis of the decay reaction of the free radicals, spur-like trapping of the free radicals and the related discussions. A diffusion controlled bimolecular reaction scheme was a good way of analyzing the data of the decay reaction. Power saturation phenomenon of ESR spectra of the free radicals showed a circumstance of the spur-like trapping of the free radicals in irradiated polyethylene. The phenomenon of spur-like trapping was quite consistent with the interpretation of the decay reaction of the free radicals.     

Practical synthesis and applications of benzoboroxoles

A convenient one-pot synthesis of benzoboroxoles has been developed via the reaction of o-bromobenzyl alcohols with NaH, ⁿBuLi, and B(OⁱPr)₃ followed by acidic hydrolysis. Applications of these benzoboroxoles have been demonstrated in Pd-catalyzed cross-coupling reactions and the protocol has been extended for the synthesis of a chiral benzoboroxole. Exceptionally short synthesis of a potent antifungal agent AN2690 and several of its analogs has also been realized.     

Electron localization and radiation chemistry of amides

Alkylamides (such as N,N'-dimethylformamide, N,N'-diethylformamide, and N,N'-dimethylacetamide) are aprotic solvents that are widely used in organic synthesis. These polar molecules have no electron affinity, and it is believed that irradiated liquid and solid amides stabilize excess electrons as cavity-type species analogous to hydrated and ammoniated electrons. In this study, we use isotope substitution and EPR spectroscopy to demonstrate that, in frozen amides, the suspected "cavity electron" is, in fact, a solvent-stabilized monomer anion. Our observations call into question other attributions of such features in the literature, both in low temperature solids and room temperature liquids. We also provide a general scheme describing amide radiolysis, as the related amides are used as metal ion extracting agents in nuclear separations.     

Graphene quantum dots from chemistry to applications

Graphene quantum dots (GQDs) have been widely studied in recent years due to its unique structure-related properties, such as optical, electrical and optoelectrical properties. GQDs are considered new kind of quantum dots (QDs), as they are chemically and physically stable because of its intrinsic inert carbon property. Furthermore, GQDs are environmentally friendly due to its non-toxic and biologically inert properties, which have attracted worldwide interests from academic and industry. In this review, a number of GQDs preparation methods, such as hydrothermal method, microwave-assisted hydrothermal method, soft-template method, liquid exfoliation method, metal-catalyzed method and electron beam lithography method etc., are summarized. Their structural, morphological, chemical composition, optical, electrical and optoelectrical properties have been characterized and studied. A variety of elemental dopant, such as nitrogen, sulphur, chlorine, fluorine and potassium etc., have been doped into GQDs to diversify the functions of the material. The control of its size and shape has been realized by means of preparation parameters, such as synthesis temperature, growth time, source concentration and catalyst etc. As far as energy level engineering is concerned, the elemental doping has shown an introduction of energy level in GQDs which may tune the optical, electrical and optoelectrical properties of the GQDs. The applications of GQDs in biological imaging, optoelectrical detectors, solar cells, light emitting diodes, fluorescent agent, photocatalysis, and lithium ion battery are described. GQD composites, having optimized contents and properties, are also discussed to extend the applications of GQDs. Basic physical and chemical parameters of GQDs are summarized by tables in this review, which will provide readers useful information.     

Multicollinearity and some applications in biological chemistry

The relationship between various parameters characterizing a particular system are established using various techniques. In some specific cases, ordinary multiple regression is resorted to for relating one variable to various other variables. However, in such problems there is a high probability of an interrelationship among different variables giving rise to multicollinearity, thereby making it infeasible to place much reliability on ordinary regression techniques. This problem can be circumvented using ridge regression techniques. In this preent investigation an attempt has been made to study the multicollinear problems in biology.     

Intramolecular tetrazine-acryloyl cycloaddition: chemistry and applications

An unprecedented intramolecular [4 + 2] tetrazine-olefin cycloaddition with α,β-unsaturated substrates was discovered. The reaction produces unique coumarin-dihydropyridazine heterocycles that exhibited strong fluorescence with large Stokes shifts and excellent photo- and pH-stability. This property can be used for reaction analysis. The rate of cycloaddition was found to be solvent dependent and was determined using experimental data with a kinetic modeling software (COPASI) as well as DFT calculations (k₁ = 0.64 ± 0.019 s⁻¹ and 4.1 s⁻¹, respectively). The effects of steric and electronic properties of both the tetrazine and α,β-unsaturated carbonyl on the reaction were studied and followed the known trends characteristic of the intermolecular reaction. Based on these results, we developed a “release-then-click” strategy for the ROS triggered release of methylselenenic acid (MeSeOH) and a fluorescent tracer. This strategy was demonstrated in HeLa cells via fluorescence imaging.

Tetrazines rapidly react with tethered acrylates/acrylamides to produce fused coumarin derivatives. This template can be used in prodrug designs by depleting toxic α,β-unsaturated byproducts while also producing an imaging agent.