Rm Aq Research Articles

UV-induced synthesis, characterization and formation mechanism of silver nanoparticles in alkalic carboxymethylated chitosan solution

The silver nanoparticles (AgNPs) were synthesized in an alkalic aqueous solution of silver nitrate (AgNO3)/carboxymethylated chitosan (CMCTS) with ultraviolet (UV) light irradiation. CMCTS, a water-soluble and biocompatible chitosan derivative, served simultaneously as a reducing agent for silver cation and a stabilizing agent for AgNPs in this method. UV–vis spectra and transmission electron microscopy (TEM) images analyses showed that the pH of AgNO3/CMCTS aqueous solutions, the concentrations of AgNO3 and CMCTS can affect on the size, amount of synthesized AgNPs. Further by polarized optical microscopy it was found that the CMCTS with a high molecular weight leads to a branch-like AgNPs/CMCTS composite morphology. The diameter range of the AgNPs was 2–8 nm and they can be dispersed stably in the alkalic CMCTS solution for more than 6 months. XRD pattern indicated that the AgNPs has cubic crystal structure. The spectra of laser photolysis of AgNO3/CMCTS aqueous solutions identified the early reduction processes of silver cations (Ag+) by hydrated electron \((\hbox{e}_{\rm aq}^{-})\) formed by photoionization of CMCTS. The rate constant of corresponding reduction reaction was 5.0 × 109 M−1 s−1.

Inactivation of a Single Eucaryotic Gene Irradiated in Vitro in Transcriptionally Active Chromatin Form.

The transcriptional activity of endogenous RNA polymerases has been used to study the inactivation of a single eucaryotic gene irradiated in chromatin form in aqueous solution. The gene codes for the ribosomal RNA precursor in Tetrahymena where it exists in multiple copies as free extrachromosomal molecules. The gene chromatin is isolated with intact RNA polymerases on the coding strand. Irradiation with 10-MeV electrons reduces the in vitro RNA synthesis on the isolated chromatin in a dose-dependent manner which allows the amount of DNA damage to be determined. Irradiation of the gene chromatin in dilute solution under various gas atmospheres demonstrates that OH radicals account for most of the inactivation. Under these conditions, $e_{{\rm aq}}^{-}$ is unimportant, while the results suggest that H may contribute to inactivation of gene transcription.

Reactions of Radicals with Lecithin Bilayers

The kinetics of reaction of •OH and $e{}_{{\rm aq}}{}^{-}$ with lecithin bilayers have been measured. The rate for •OH + lecithin is $5.1\pm 0.9\times 10^{8} M^{-1} {\rm sec}^{-1}$ while the $e{}_{{\rm aq}}{}^{-}$ + lecithin rate is very slow. When a solute such as pyrene is solubilized in the bilayer, •OH and $e{}_{{\rm aq}}{}^{-}$ may react with the solute; rates of $1.65\pm 0.12\times 10^{9} M^{-1} {\rm sec}^{-1}$ and $7\times 10^{7} M^{-1} {\rm sec}^{-1}$ have been measured for reaction of •OH and $e{}_{{\rm aq}}{}^{-}$ , respectively, with pyrene in lecithin. These rates are lower than those observed for similar reactions in homogeneous systems. This is explained in terms of (a) the protective effect of the bilayer, this being especially true for $e{}_{{\rm aq}}{}^{-}$ which does not readily leave the aqueous phase, and (b) in ter...

Pulse Radiolysis of Bilirubin in Aqueous Solution

A pulse radiolysis study of bilirubin, the breakdown product of heme, has been made. In aqueous solution at pH 12, short-lived transient spectra have been obtained for reaction of bilirubin with $e{}_{{\rm aq}}{}^{-}$ and OH. Bimolecular rate constants for these reactions have been measured, namely, $k_{{\rm BR}+e{}_{{\rm aq}}{}^{-}}=9.5\times 10^{9} M^{-1} {\rm sec}^{-1}$ and $k_{{\rm BR}+{\rm OH}}=3.45\times 10^{9} M^{-1} {\rm sec}^{-1}$ , and the spectrum of a long-lived product resulting from decay of the bilirubin-OH adduct has been obtained. In addition, solute destruction by OH has been investigated in detail. The transient absorption spectrum for reduction of bilirubin with the H atom at neutral pH has been measured. By measuring the rate of reaction with $e{}_{{\rm aq}}{}^{-}$ in the presence of bovine serum albumin (BSA), the mode of binding of bilirubin to this biologically important compound has been studied.

LET Dependence of Transient Yields in the Pulse Radiolysis of Aqueous Systems with Deuterons and α Particles

The variation of G ( $e{}_{{\rm aq}}{}^{-}$ ) with beam penetration depth, and hence, with LET, has been measured in water using 10-μsec pulses of 20-MeV deuterons and 40-MeV α p...

Repairable and Nonrepairable Inactivation of Irradiated Aqueous Papain: Effects of OH, O 2 - ,e aq - , and H 2 O 2

Repairable inactivation of papain irradiated in dilute aqueous solutions saturated with air or nitrous oxide is caused predominantly by reversible oxidation of $\text{Cys}_{25}{\rm SH}$ by H2 O2. The same process occurs in nitrogen-saturated solutions but the yield of repairable product decreases at higher doses, probably because of the consumption of H2 O2 by intermediates formed from $e{}_{{\rm aq}}{}^{-}$ and papain. The OH radical produces only nonrepairable damage, with the fraction of the OH radical causing nonrepairable inactivation $(f_{{\rm OH}}{}^{{\rm n.r.}})$ equal to 0.1 and this is accompanied by, if not solely due to, SH loss. The O2- radical with $f_{{\rm O}_{2}}{}^{-{\rm n.r.}}=0.4$ also causes nonrepairable damage resulting from or accompanied by SH loss. In addition, there is evidence that every O2- reacts with papain to produce a hydrogen peroxide molecule, thus causing a marked increase in the repairab...

Electron-Affinic Sensitization: VI. A Pulse Radiolysis and ESR Comparison of Some 2- and 5-Nitroimidazoles

The nitroimidazoles are effective radiosensitizers for both hypoxic bacterial and mammalian cells and are currently under clinical investigation as adjuncts in radiotherapy. It is known that the 2-nitroimidazoles are biologically more efficient than the 5-nitro derivatives. This paper reports on some aspects of the radiation chemistry of one biologically important example of each class, together with results obtained with other related derivatives. Metronidazole (a 5-nitroimidazole) and Ro-07-0582 (a 2-nitroimidazole) react rapidly with both $e{}_{{\rm aq}}{}^{-}$ and OH to produce transient absorbing species which decay by second-order kinetics. Both compounds accept electrons from the radical anion of thymine at near diffusion-controlled rates, but not from neutral thymine radicals formed by H and OH attack. From a study of one-electron transfer reactions involving p-nitroacetophenone as an electron acceptor it is shown that the electron affinity of the 2-nitroimidazole structure is...

Inactivation of Ribonuclease S-Peptide by the Primary Aqueous Radicals

The separate contributions of the primary radical species to changes in enzymatic activity, amino acid composition and molecular configuration of RNase S-peptide have been determined by γ-irradiation of dilute solutions in controlled environments. For H· and ·OH, approximately one out of two radicals is effective for the enzymatic inactivation of S-peptide; $e^{-}{}_{{\rm aq}}$ is much less effective, only one out of eight or more radicals causing loss of activity. Amino acid analyses of irradiated S-peptide show that only the single sulfur-containing residue, methionine, and the single aromatic residue, phenylalanine, are significantly destroyed. For H atom attack, loss of enzymatic activity correlates with the destruction of methionine; phenylalanine is much less affected and no new products are separated on gel filtration. Hydroxyl radicals cause a significant destruction of phenylalanine, as well as methionine, and gel filtration shows that a new product of higher molecular weight...

A Pulse Radiolysis Study of the Free Radical Intermediates in the Radiolysis of Uracil

The technique of pulse radiolysis has been utilized to study the absorption spectra of the transient free radical adducts which result from reactions of ·OH and $e_{{\rm aq}}{}^{-}$ with the pyrimidine, uracil. The ·OH attaches to the 5,6 bond of uracil to form an adduct (·UOH) which has peaks at 390 nm and ∼240 nm. Changes in the spectrum of ·UOH with pH have led us to the conclusion that at least one isomer of ·UOH has ${\rm pK}_{{\rm a}}\text{'}$s of ∼7 and 9.5. The ·UOH decays by a second order kinetics with rate constant, $2k=(1.1\pm 0.2)\times 10^{9} M^{-1} s^{-1}$ which is independent of ionic strength. There is a residual spectrum which remains after the decay of the ·UOH absorption. This residual spectrum is different at pH 5 and 8.5, and shows a similar pH dependence to that of ·UOH itself. The $e_{{\rm aq}}{}^{-}$ adds to uracil to form an adduct which has protonated ( $\cdot {\rm UH}_{1}$) and unprotonated ( $\cdot {\rm U}^{-}$) forms which are in equilibrium with a pK a of 7. The spectra of...

Electron Spin Resonance Study of Radicals Produced by One-Electron Reduction of Pyridines

Radicals produced in irradiated aqueous solutions of carboxy and N-methyl derivatives of pyridine have been studied by the in situ radiolysis steady-state ESR technique. All solutions contained other efficient OH scavengers so that only radicals produced by reaction of the pyridines with $e_{{\rm aq}}^{-}$ have been observed. The electron adducts initially produced were found to undergo protonation on the ring nitrogen (if not methylated) to produce pyridinyl radicals. Protonation occurred rapidly both in neutral and strongly alkaline solutions, which indicates that a molecule of water rather than H+ is involved in the process. The pK of the ring NH group of the pyridinyl radicals if above 13 in all cases examined. The ortho and para carboxy derivatives were found to produce pyridinyl radicals which are long-lived as compared to the unsubstituted or meta carboxy compounds. The higher stability is probably a result of increased conjugation in the case of ortho and para derivatives, whi...

Radiation Sensitization Reactions of N-Ethylmaleimide with Model Compounds

The reaction of $e_{{\rm aq}}^{-}$ , OH radicals and H atoms with N-ethylmaleimide (NEM) and N-ethylmaleamic acid (NEMA, which is produced from the hydrolysis of NEM at pH > 7) were investigated in aqueous solutions. The reaction rate constants, the transient optical absorption spectra and the decay kinetics of the resulting intermediates were obtained. The free radical sensitization reactions of NEM with model compounds were followed by pulse radiolysis. A number of organic free radicals were found to react with NEM by an electron transfer process (oxidation of free radicals) to produce $\cdot {\rm NEM}^{-}$ , and/or by addition to NEM. NEMA, being a poorer oxidizing agent, does not appear to undergo most of these reactions. Electron adducts (e.g., radical anions of pyrimidine bases) were shown to transfer an electron to NEM. Solutes with redox potentials higher than that of NEM, such as menadione and oxygen, were found to be good electron acceptors from ...

Radiation Chemical Studies of Hemocyanin in Oxygen-Free Media

The oxygen-carrying capacity of Busycon and Limulus hemocyanins is eliminated following irradiation of the protein with cobalt-60 γ-rays in neutral, oxygen-free media. The loss of oxygen-carrying capacity of the protein is measured from the change of the characteristic copper band at 340 nm, before and after irradiation. The limiting ${\rm G}(-{\rm O}_{2})$ values in the absence of scavengers are 0.026 and 0.044 for Busycon and Limulus hemocyanins, respectively. Radiation effects in oxygen-free media on Busycon and Limulus hemocyanins can either be enhanced or prevented by appropriate scavengers. The Busycon methemocyanin activity is restored by the hydrated electron, $e_{{\rm aq}}^{-}$, and the secondary ${\rm CO}_{2}{}^{-}$ radical. The loss of oxygen-carrying capacity of hemocyanin by γ irradiation is attributed, therefore, to the OH radical which oxidizes the protein-bound copper at the active site, thus forming methemocyanin. The restoration of the oxygen-carrying capacity of Busycon methemocyanin is...

Transient Radicals of DNA Bases by Pulse Radiolysis. Effects of Cysteine and Cysteamine as Radioprotectors

Transient radicals of nucleic acid components formed by ${\rm e}_{{\rm aq}}^{-}$ and OH reaction during pulse radiolysis have been observed using the electron paramagnetic resonance (EPR) technique. The effect of cysteamine and cysteine on the decay properties of the radical has been investigated. For the natural bases, the predominant mechanism of protection seems to be a competition reaction for the OH rather than a hydrogen transfer from the thiol to the organic radical; however, hydrogen transfer does occur for dihydrothymine. Rate constants are given for these reactions and for reactions with OH and O2.

Reductive Deamination of Oligopeptides by Solvated Electrons in Aqueous Solution

The reaction rate constants of the hydrated electron $({\rm e}_{({\rm aq})}^{-})$ have been determined, by pulse radiolysis, for a number of oligopeptides, including oligoglycines, the N-acetyl der...

Radiation Chemistry of Some Sulfonephthalein Dyes

Reactions of hydrated electrons $e_{{\rm aq}}^{-}$ with xylenol orange, thymol blue, cresol red, phenol red, and p-benzoquinone and of the OH radical with xylenol orange have been studied, using flash photolysis and gamma irradiation under conditions where the roles of $e_{{\rm aq}}^{-}$ and OH are emphasized. The rate constants of the reactions of $e_{{\rm aq}}^{-}$ with xylenol orange, cresol red, and p-benzoquinone at pH 11 are $5.2\times 10^{9} M^{-1} {\rm sec}^{-1},8.5\times 10^{9} M^{-1} {\rm sec}^{-1}$ , and $4.2\times 10^{9} M^{-1} {\rm sec}^{-1}$ , respectively; k(OH + xylenol orange) = $1.1\times 10^{10} M^{-1} {\rm sec}^{-1}$ . Although xylenol orange reacts rapidly with $e_{{\rm aq}}^{-}$ the principal decolorization reaction is by the OH radical. The decolorization yields of thymol blue, cresol red, and phenol red are very small compared to <t...

Factors Affecting the Rate of Hydrated Electron Attack on Polynucleotides

The rate constants for the attack of ${\rm e}_{{\rm aq}}^{-}$ on adenine, cytosine, and several derivatives were measured in the pH range 6-14. The rate constants at neutral pH are $0.9\times 10^{10} M^{-1}s^{-1}$ and $1.3\times 10^{10} M^{-1}s^{-1}$ for adenine and cytosine, respectively. The rate constants, per base, for the attack of ${\rm e}_{{\rm aq}}^{-}$ on polynucleotides are much lower. At pH 7 they are $7.5\times 10^{8} M^{-1}s^{-1}$, $2.5\times 10^{8} M^{-1}s^{-1}$, and $1.3\times 10^{8} M^{-1}s^{-1}$ for poly U, poly A, and poly (A + U), respectively. It is shown that the low overall reactivity of polynucleotides results from a lowered collision frequency with ${\rm e}_{{\rm aq}}^{-}$. Secondary structure is an important factor, responsible for the observed differences in the values of the rate constants for the polynucleotides studied. Poly (A + U), which has a double helical structure, is least reactive, and poly U, an unstacked random coil, is most reactive. The inherent reactivity of ...

Effects of γ-Irradiation on Sodium Sulphacetamide

The effects of γ-irradiation on sodium sulphacetamide in aqueous solutions and in the solid state have been studied. Pulse radiolysis and steady-state experiments demonstrate that hydrated electrons $({\rm e}_{{\rm aq}}^{-})$ and hydroxyl radicals (OH) are mainly responsible for the degradation between $10^{-4}-1.2 M$ solute concentrations. The reaction with ${\rm e}_{{\rm aq}}^{-}$ yields sulphanilic acid and an additional unidentified product. Hydroxyl radicals give two products which have tentatively been identified as monomeric and dimeric phenolic derivatives of sulphacetamide. Suitable ${\rm e}_{{\rm aq}}^{-}$ and OH scavengers selectively remove these products. G(-sulphacetamide) is a maximum of 4.8 in aqueous solution and < 0.01 for the solid. The implications of the results in the radiation sterilization of sulphacetamide formulations is discussed.

Chemical Effects of γ-Irradiation of Aqueous Solutions of Heparin and Keratan Sulphate

During γ-irradiation of dilute aqueous solutions of heparin and keratan sulphate, acid and reducing products are formed, mainly as a result of attack by OH radicals. Depolymerization to give lower dextrins also occurs without loss of sulphate groups, which results in a decrease in the dye binding ability of the polyanion. Pulse radiolysis was used to measure the rate constants for attack by OH radicals $(k_{2}=4.7\times 10^{8} M^{-1} {\rm sec}^{-1})$ and $e_{{\rm aq}}^{-} (k_{2}=3.0\times 10^{7} M^{-1} {\rm sec}^{-1})$. Oxygen exerts a protective effect which can be accounted for by the scavenging reaction $e_{{\rm aq}}^{-}+{\rm O}_{2}\rightarrow {\rm O}_{2}{}^{-}$.

Effects of Ionizing Radiations on Glucuronic Acid

The effects of radical scavengers and solute concentration indicate that the degradation of glucuronic acid by60 Co γ-irradiation is mainly due to OH radicals. Pulse radiolysis demonstrates no significant reaction of sodium glucuronate with $e_{{\rm aq}}^{-}(k_{2}\leq 10^{6} M^{-1} \text{second}^{-1})$, but a facile reaction with OH radicals ( $k_{2}\sim 10^{9} M^{-1} \text{second}^{-1}$). Moreover, a transient intermediate is produced, which appears to be the result of OH radical abstraction and decays by second-order kinetics ( $k_{2}\sim 10^{7} M^{-1} \text{second}^{-1}$). Beyond $7.5\times 10^{-3} M$ solute concentration additional processes lead to glucuronic acid degradation, which cannot be accounted for on the basis of direct action effects. When irradiated in the solid state -G (glucuronic acid) = 4, but this is considerably reduced due to energy transfer if the p-toluidine-ammonium complex is irradiated.

Radiation Chemistry of Gelatin Gels Containing Ferricyanide

The G value of the reduction of ferricyanide in gels containing up to 20% w/w gelatin increases with increasing protein concentration to a value corresponding approximately to the sum of the primary radicals, $G(e_{{\rm aq}}^{-}+{\rm H}+{\rm OH})$. In the presence of added $N_{2}{\rm O}$ a similar value is reached at lower gelatin concentrations. Added O2 reduces the yield but does not eliminate the reduction process. The results are interpreted in terms of a mechanism involving intermediate organic free radicals, and an attempt is made to correlate the results with radical diffusion in gels.