Search

The bacteria Clostridium botulinum causing botulism. Botulism also known as botulinus intoxication is a rare but serious paralytic illness caused by botulinum toxin, which is produced by the bacterium Clostridium botulinum.CDP-diacylglycerol-serine O-phosphatidyltransferase is an enzyme that catalyzes the CDP-diacylglycerol, L-serine and produce Cytidine monophosphate (CMP), (3-snphosphatidyl)-L-serine in Clostridium botulinum. CMP is a nucleotide that is helpful in RNA synthesis in Clostridium botulinum.The objective of enzyme inhibition needs structural characterization from its 3-D structure in rational structure based drug design. Homology modeling can produce high-quality structural models when the target and templates are closely related. MODELLER is the program used for homology modeling which provides accurate and efficient models to build loops and side chains found non-identical in sequence. It implements comparative protein structure modeling by satisfaction of spatial restraints. The stereo chemical quality of a best model is validated by PROCHECK server with 86.2% residues under favored region from Ramachandran plot. The CASTp is used for locating, delineating and measuring concave surface regions on three-dimensional structures of proteins. The residues are identified in burial cavity of the best model as Leu (131,141,156), Ala (132), Ile (138,142), Asn (145), Thr (149,153), and Gly (151) with hydrophobic nature. These include pocket located on protein surfaces and voids buried in the interior of proteins that are frequently associated with binding events. Thus present studies of modeling of CDP-diacylglycerol-serine O-phosphatidyltransferas enzyme has brought future prospective to fight against botulism disease and provide better health standaaards for community.

In this paper, we have carried out thin film characterization of poly(3,4-propylenedioxythiophene)-sultone (PProDOT-S), a derivative of electrochromic poly(3,4-propylenedioxythiophene) (PProDOT). PProDOT-S was deposited onto transparent conducting oxide coated glass substrates by solution casting method. Single wavelength spectrophotometry is used to monitor the switching speed and contrast ratio at maximum wavelength (lambda (max)). The percentage transmittance at the lambda (max) of the neutral polymer is monitored as a function of time when the polymer film is repeatedly switched. This experiment gives a quantitative measure of the speed with which a film is able to switch between the two states i.e. the coloured and the bleached states. PProDOT-S films were switched at a voltage of 1 center dot 9 V with a switching speed of 2 s at lambda (max) of 565 nm and showed a contrast of similar to 37%. Cyclic voltammetry performed at different scan rates have shown the characteristic anodic and cathodic peaks. The structural investigations of PProDOT-S films by IR spectra were in good agreement with previously reported results. Raman spectra of PProDOT-S showed a strong Raman peak at 1509 cm (-aEuro parts per thousand 1) and a weak peak at 1410 cm (-aEuro parts per thousand 1) due to the C = C asymmetric and symmetric stretching vibrations of thiophene rings. The morphological investigations carried out by using scanning electron microscope (SEM) of polymer films have shown that these polymers are found to be arranged in dense packed clusters with non-uniform distribution having an average width and length of 95 nm and 160 nm, respectively.

Pressure shifts and collisional narrowing effects of the molecular hydrogen (H 2 ) 4-0 and 5-0 vibration rotation bands have been studied in greater detail than before. A high-resolution ring dye laser has been coupled to a multi-pass absorption cell with a base length of 22 m at Denison University in Granville, Ohio. Signal averaging periods of several hours, with an absorbing layer of 24 km-atm, were required to obtain acceptable measurements. A zero-density position and shift coefficient of 15 535.7441 ± 0.0036 cm −1 and −6.29 ± 1.29 × l0 −3 cm −1 /Amagat, respectively, have been determined for the 4-0 S (0) line. For the 4-0 S (1) line the corresponding values are 15 699.8011 ± 0.0010 cm −1 and −4.22 ± 0.36 × 10 −3 cm −1 /Amagat. The 5-0 S (1) line has been observed in the laboratory for the first time; its position has been located at 18 907.5160 ± 0.0200 cm −1 . Linestrengths were also determined in this study and the results are 2.31 ± 0.55 × l0 −5 cm −1 /(km Amagat) for the 4-0 S (0) line, 1.37 ± 0.17 × l0 −4 for the 4-0 S (1)line, and 1.76 ± 0.99 × 10 −5 for the 5-0 S (1) line. Collisional narrowing was clearly evident for the 4-0 S (0) and 4-0 S (1) lines.

The steady state creep behaviour of rapidly solidified and further processed Al-5 wt% Ti alloy has been studied in the temperature range 573–673 K. The experiememtald ata exhibited apparent stress exponents of 7–8 and an apparent activation energy of 240 kJ mol−1. The results are analyzed using the semi-empirical power law, the substructure invariant model and an exponential law. The semi-empirical power law with a threshold stress and a stress exponent of 5 is found to be the best representation for steady state creep of such alloys. By analyzing literature data on the metallic/ intermetallic dispersion strengthened aluminium alloys, a modification in the dimensionless constant, A = 8.3 × 103 exp[−104√(b/L)], is suggested to account for the influence of dispersion on creep kinetics. It is proposed that the attractive dislocation-particle interaction originates from the dissociation of lattice dislocations into interfacial dislocations when they enter the matrix-particle interface at high temperatures for climb by-pass.

The heteropolyacid salt inorganic exchanger triammonium dodecamolybdophosphate (AMP) was subjected to an electron dose up to 2 MGy to assess any possible radiation damage. The breakthrough and total exchange capacity of AMP for Cs+ from simulated fission product solutions were determined for both control and irradiated samples. The scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) were deployed to examine any marked microscopic changes taking place in this exchanger.

Precursor 2'-deoxythymidine 5'-monophosphate for DNA biosynthesis is supplied by thymidylate synthase (TS) (EC 2.1.1.45) through a de novo pathway and the enzyme levels are elevated in malignancy. TS is therefore a key target for cancer chemotherapy. Human leukocyte TS levels in patients with chronic myeloblastic leukemia (CML) and acute lymphoblastic leukemia (ALL) are highly elevated (66- and 33-fold, respectively) compared to the low baseline activity of normal healthy controls. Preliminary screening tests for the antitumor activity of the beta-carboline-benzoquinolizidine alkaloid deoxytubulosine (DTB) (isolated from the Indian medicinal plant Alanguim lamarckii) were performed employing in vitro inhibition studies on the leukemic leukocyte TS as the probe enzyme. Enzyme activity of the leukemic leukocytes was potently inhibited by DTB (IC50 = 50 microM) in both CML and ALL. The emetine alkaloid DTB was assessed for its biochemical and biological evaluation for the first time as a potential antileukemic agent.

The promotion of 7,12-dimethylbenzanthracene (DMBA) induced mammary cancer in Wistar rats by a 4% cholestyramine (CHST) diet was investigated. The rats, 50 days of age, were divided into six groups. First two groups were given an intragastric dose of 0.8 ml of corn oil whereas the remaining four groups were given a single intragastric dose of 5 mg of DMBA dissolved in 0.8 ml of corn oil. After 1 week on laboratory chow the first two groups and two groups treated with DMBA were fed a control diet and the two remaining groups treated with DMBA were fed a 4% CHST diet. Half the animals were killed at 100 days and the remainder at 200 days. A detailed histologic examination of grossly normal mammary tissue as well as any tumour mass was made for each rat. The serum lipids were extracted and the individual neutral lipid composition was determined. In rats treated with DMBA and fed a 4% CHST diet, the incidence of malignant tumours increased by 5 fold, and the tumour weight by 12 fold. In addition, the serum total lipids, cholesterol esters and triglycerides decreased significantly when compared with rats fed a control diet. These results suggest that CHST diet promotes DMBA induced mammary cancers in Wistar rats. Images Figure 1

The effect of surfactants on the absorption and emission properties of thionine (TH+) have been studied in detail. Among the various surfactants investigated sodium lauryl sulphate (SLS) has marked effect on these properties. Changes in the absorption spectrum and the decrease in fluorescence intensity at [SLS] below the critical micelle concentration (CMC) are attributed to the formation of a dye-surfactant complex. At [SLS] above CMC, the restoration of dye spectrum with increased extinction coefficient at the λmax and a small but definite red shift of the λmax are interpreted as due to the incorporation of the dye into the SLS micelle. The absorbance and spectral shift data suggest the thionine cation to be localized near the micelle Stern layer in the case of SLS micelles but completely outside the micelle in the aqueous environment in the case of CTABr. From the absorbance and fluorescence data, the association constant for the formation of the TH+-SLS complex in the premicellar region, and the binding constant for the incorporation of the dye into the micelle in the micellar region have been computed. The values of both these constants were found to increase markedly in the presence of electrolytes.

The regulation of cholesterol esterification during cell proliferation was studied. The serum free cholesterol, cholesterol esters and lecithin: cholesterol acyltransferase (LCAT) activity of nude mice with and without pancreatic acinar cell tumours and rats with proliferating tissues were determined. In addition, the apparent activity of acyl-CoA: cholesterol acyltransferase (ACAT) in homogenates of nude mouse tumours and proliferating rat tissues were determined and compared with those of normal nude mouse and rat tissues. Serum cholesterol ester levels were significantly lower in host nude mice with tumours and in rats with regenerating liver, and increased significantly in pregnant rats when compared with respective controls. Circulating LCAT activity levels decreased in host nude mice, in pregnant rats, and in rats with regenerating pancreas and regenerating liver. Apparent ACAT activity levels increased significantly in nude mouse tumours and in foetal and postnatal rat pancreata and also in postnatal liver. At the same time, apparent ACAT activity levels decreased in foetal and regenerating rat livers when compared with respective control tissues. These results suggest that serum cholesterol esters, circulating LCAT and cellular ACAT levels are modulated during cell proliferation.

The radiolytic decomposition of the B-group vitamins in neutral aqueous solutions has been studied under conditions such that these compounds undergo an initial one electron reduction. The radical intermediates so produced have been found to react very efficiently with H2O2 in the case of thiamine and nicotinamide, less so in the case of folic acid and not at all in the case of pyridoxin. The stable reduction products formed after radiolysis were unreactive towards H2O2 in all cases except riboflavin. In this case, both the radical intermediate and the stable leucoriboflavin were found to react with H2O2. In addition, the post-irradiation reaction of leucoriboflavin with O2” has been found to give H2O2 as a product.

Gamma-radiation initiated polymerisation of 4-vinyl pyridine has been studied at various dose rates and temperatures. The polymerisation is initiated by a free radical mechanism. The values (kp/kt1/2), energy of activation (EA) and chain transfer constant (ktrans/kP determined are 2.3 x 10-3, 11.0 kcal/mole and 1.5 x 10-2, respectively. An auto acceleration is observed at ∽10% conversion. Auto acceleration and the increase in molecular weight with conversion are explained as due to chain transfer to the monomer leading to an unsaturated terminal end group, which is being utilised for the polymer growth.

A cationic surfactant hexadecylpyridinium chloride (CPC) quenches the fluorescence emission from pyrene. Below the critical micellar concentration (CMC) of CPC, the quenching rate is diffusion controlled. Above the CMC, the quenching rate becomes faster and finally becomes independent of the surfactant concentrations. The observations were interpreted on the basis of partitioning of pyrene between the aqueous and micellar phases. For pyrene solubilized in the micellar core the estimated emission lifetime of 100 nanosec. Quenching of pyrene also was studied in the BRIJ-35-CPC mixed micelle system.

Phenyl acrylate was polymerised by γ-rays from Co-60 source and the kinetics of polymerisation were studied at various temperatures. The rate of polymerization was found proportional to I0.99 where I is the radiation intensity. The activation energy of polymerization reaction was found to be 8.5 kcal. The G-radical yield obtained by induction period method was 17.2. The rate of polymerization was high and the molecular weight was of the order of 2000. The low molecular weight has been explained as due to termination of the chain by degradative and nondegradative chain transfer.

A new steady state radiolysis method for the determination of the rate constants of reaction of H2O2 with solute radicals derived by reaction with radiation produced OH radicals is described. The values so obtained are comparable with the ones obtained by the method described by Soylemez and Balkas in the past. A method similar to the latter has been employed to determine the rate constant of reaction of H2O2 with solute radicals derived from e-aq reaction. In the case of the (CH3)2 COH radical which can be generated by either reaction of OH with isopropanol or e-aq with acetone, the three methods give values agreeing with each other within ± 15% (viz. 2.7 ± 0.4 × 105 dm3 mol-1 s-1). The reaction of the solute radicals with H2O2 is considered in the light of known one-electron redox potentials, and the limitations of the applicability of the methods described here are discussed.

One-electron reduction of thionine has been studied by using the technique of nanosecond pulse radiolysis and kinetic spectrophotometry. H,e aq − as well as radicals derived from methanol, ethanol, isopropanol, THF, dioxane andt-butanol by H atom abstraction were used as reductants. The rate constants for the transfer of electrons from these radicalts to thionine were directly determined from the pseudo first-order formation rates of the product, semithionine and the one-electron reduction potential of thionine estimated. The absorption spectrum of semithionine in its different conjugate acid-base forms was found to be in agreement with previously reported spectra and the decay of the species was second order. By monitoring transient absorbance changes as a function of pH, twopK a values were observed and, based on the effect of ionic strength on the second-order decay constants of the species were assigned to the equilibria described.

Riboflavin (RF) has been used as a standard for the determination of OH radical rate constants by the competition kinetic method. In oxygenated solutions its radiolytic decomposition was found to closely correspond to G(-RF) = (12)GOH. Its rate constant was first evaluated by employing ethanol as the standard and taking kOH+C2H5OH = 1.85 × 109 dm3mol-1s-1. The kOH+RF value was found to be constant (= 1.2 ± 0.05 × 1010dm3mol-1s-1) over the pH range 1–11. Using this value the rate constant for reaction of a number of other solutes have been determined and compared with literature values. The advantages of riboflavin over other standard solutes are discussed.

Radiation initiated post-polymerisation of trioxane has been studied by irradiating the super dry monomer at dry ice temperature and annealing them at higher temperatures. The mode of termination is presumed to be predominantly by chain transfer to the monomer. Kinetic expression has been derived for the same. Using the rate constant ratio k tr/k p from the data on in-source polymerisation the molecular weights were calculated to be of the order of 3.6 × 105. This was experimentally observed for various conversions.

A reliable method for the separation of amino coumarin dyes from associated impurities has been developed using reverse phase high performance liquid chromatography using an ODS-18 column and mixtures of methanol and water. Further, the relation between the retention times and structure of amino coumarines has also been studied.

Diallyl o-phthalate (DAP) was polymerized by $gamma$ radiation from a $sup 60$Co source and the kinetics of polymerization were studied at several dose rates and temperatures. The results show that the rate of polymerization was proportional to I$sup 0$.$sup 68$, where I is the radiation dose rate. The net activation energy of the polymerization reaction (E/sub p/-1/2E/sub t/) was 5.02 kcal/mole, where E/sub p/ and E/sub t/ are the activation energies for the propagation and termination steps, respectively. The radical yield G/sub R/ for DAP was measured by the loss of diphenyl picryl hydrazyl (DPPH) used as a radical scavenger. G/sub R/ in the solution after irradiation was 3.12. The ratio of the rate constants k$sup 2$/sub p//k/sub t/ was calculated to be 4.09 x 10$sup - 7$ at 25.8$sup 0$C and 15.0 x 10$sup -7$ at 55.4$sup 0$C. At room temperature, the ratio of degradative chain transfer constant to k/sub p/, i.e., k/sub u//k/ sub p/ was found to be 0.065 and k/sub tr//k/sub u/ as 0.032, where k/sub tr/ is the nondegradative chain-transfer constant. Molecular weights of these polymers as determined by vapor pressure osmometry showed that the degree of polymerization was between 8 and 10. Infrared spectramore » of the polymers indicated that intramolecular cyclization took place during polymerization. (auth)« less

Transient intermediates formed on γ-radiolysis of CHI 3 in 3-methylpentane glass at 77 K were characterized from the study of absorption spectra, changes induced by different scavengers, matrix viscosity, optical bleaching, photoionization of NNN'N'-tetramethyl-p-phenylenediamine, and identification of stable end products. Variation of stable products yields and intensity of absorption bands with solute concentration has been explained by solute aggregation at 77 K. It is concluded that the optical absorption bands at 450 and 600 nm are due to CHI + 3 and CHI 2 , respectively.

The γ-radiolysis of neutral aqueous solutions of thiamine (Thm+) has been studied employing the technique of differential pulse polarography to assay its concentration in the irradiated solutions. G(−Thm+) is dependent on [Thm+] reaching a maximum value of ∼ 11 at [Thm+] = 0.5 mol dm−3. This high value is shown to be not due to a direct effect on Thm+, but may be attributed either to spur scavenging or to secondary reactions of the initially produced thiamine radicals. In dilute solutions ([Thm+]

Gamma ray induced emulsion polymerization of vinylidene chloride has been carried out and the percent conversion of monomer to polymer and molecular weights of emulsion polymer were measured as a function of time and emulsifier concentration. Rp was found to be dependent on 0.3 power of emulsifier concentration whereas molecular weights increased with conversion and emulsifier concentration. The number of particles N also increased with conversion contrary to Smith Ewart's theory of emulsion polymerization. The results are discussed in the light of existing theories of emulsion polymerization.

The electrokinetic properties such as zeta potential, surface charge density, and surface conductivity of polyester fibers grafted with acrylic acid and acrylonitrile were measured when cationic dye solutions were streamed through. The presence of the cationic dyes on the surface of the fibers and their specific adsorption at the carboxylic groups in the acrylic acid graft copolymer produce lowering of zeta potential. The decrease in surface charge density as the percent graft increases is due to the decrease in surface area of the fibers due to the adsorption of the cationic dyes. The same trend is observed with acrylonitrile-grafted fibers. The surface conductivity of the acrylonitrile-grafted polyester fibers increases with increase in dye concentration of the streaming solution. The results for the 27.4% grafted sample differed from those of the 7.32% and 12.1% grafts, which is indicative of the formation of a three-dimensional network causing change in both the physical structure as well as the chemical nature of the surface of the substrate.

A procedure for the facile preparation of labelled carboxylic acids from labelled α-amino acids has been described. The reaction is attractive for the small scale synthesis of such compounds.

The extent of radiolytic decomposition of the B-group vitamins, riboflavin, pyridoxin, nicotinamide, thiamine and folic acid has been studied in aqueous media as a function of γ-dose up to 2.5 Mrad both in the absence and presence of glucose as a protective additive. In the absence of this additive, the γ-doses (in Mrad) resulting in more than 90% decomposition of the vitamins in a 10−4 M solution at pH 6.8 as judged by absorbance changes were riboflavin: 0.5, pyridoxin: 0.06, nicotinamide: 0.25, thiamine and folic acid: ∼1.5. In presence of 02 and 0.1 M glucose, the γ-dose for 90% decomposition was more than 2.5 Mrad in all cases. Other parameters whose effects on the radiolytic decomposition were investigated systematically are the concentrations of the vitamin and glucose, the ambient, pH and temperature of irradiation. Protective efficiencies of a few other additives, viz. ethanol, isopropanol, t-butanol, glycerol, thiourea, tryptophane and tyrosine have been evaluated and compared with that ...

Acrylic acid (AA) and acrylonitrile (AN) were used to carry out grafting on polyester (PE) fibers using the techniques of initiation by γ-radiation as well as benzoyl peroxide. The nature of the grafted fiber substance was found to be the same, irrespective of the grafting technique. Extent of grafting depended upon the time, concentration of the initiator, and the monomer as well as on the irradiation dose. The increase in the moisture regain was directly proportional to the amount of graft in the fiber. AA grafted fibers were rendered more hydrophilic than AN grafted fibers for equivalent amount of grafts. Considerable improvement in dyeability of the PE fibers was possible through grafting. About 50% to 100% improvement with disperse dyes was observed in case of PE fibers containing 22.4% and 9.0% graft of AA and AN, respectively. Intense fast dyeing with direct and basic (cationic) dyes was also possible, and the dye content was proportional to the extent of graft introduced in the fiber. The CN groups were reduced to NH2 groups in the AN graft on the fiber. In this way, deep, fast, and bright dyeing was obtained with reactive dyes. Electrokinetic studies were carried out on the grafted fibers. With the increased amount of AA graft, the maxima in the zeta potential curve shifted toward higher acidic pH as greater amounts of alkali was utilized by the COOH groups in the graft. In this respect, CN groups were less sensitive due to their lesser polarity as compared to the carboxylic groups. It was observed from surface charge density (S.C.D.) studies that the effective surface area of the fiber decreased with the increase in the amount of graft, particularly in case of AN graft. Surface conductivity (S.C.) studies revealed that with increase in the number of polar groups (COOH) on the surface of the fiber, the S.C. increased with the increase in the amount of AA graft. In case of AN grafts, the reduction in effective surface area of the fiber played a more important role than the contribution by the CN groups to surface conductivity.

Radiation initiated polymerisation of phenyl methacrylate has been studied at various dose rates and temperature. Predominant chain transfer to the monomer was observed and ktran/kp the chain transfer constant ratio was found to be 4 x 10 -2 · k p k t 1 2 value determined by the kinetic data and the molecular weight data were 0.0821 and 0.0198, respectively. IR studies of polymer at low conversion showed the presence of terminal unsaturation which disappeared at saturation conversion, thus showing its participation in the formation of a three dimensional network.

Transient intermediates formed on photolysis of CH2I2 and CHI3 in 3MP glass at 77 K have been characterized from their optical absorption and stable products analysis. Variation of stable products yields and intensity of absorption bands in presence of benzene, which is known to lessen solute clustering by molecular complex formation, has indirectly indicated solute aggregation at 77 K and formation of solute cations by energy transfer from excited solute molecules.

Thiamine and other vitamins of the B complex group are highly : ensitive to γ-radiation in aqueous solution owing to their high reactivity with the primary species formed by radiolysis of water, viz. hydrated electrons and hydroxyl radicals. In order to protect these compounds from radiolytic degradation, nitrous oxide and oxygen have been used as scavengers for the hydrated electrons and glucose for the hydroxyl radicals. By comparison of uv spectra it is shown that the above vitamins do not undergo radiolytic degradation in presence of nitrous oxide and glucose or oxygen and glucose. The importance of these results in connection with the sterilization of vitamin preparations is discussed.

Graft-copolymerization reactions of binary mixtures of vinyl monomers (acrylamide–acrylic acid and acrylonitrile–acrylic acid) with polyester fibers have been studied by chemical initiation technique using benzoyl peroxide as an initiator. The total graft add-on was determined gravimetrically, while the modified Kjeldahl's method for N-estimation was employed to determine acrylamide and acrylonitrile grafts in their mixtures with acrylic acid grafts. Synergism of very high order was noticed during the graft-copolymerization reactions. In the case of the acrylamide–acrylic acid system a very high order of synergism (129.15%) was noticed at equimolar proportions of the monomers in the grafting bath. Both acrylamide and acrylic acid showed synergistic influence over each other during graft-copolymerization reactions. In the case of the acrylonitrile–acrylic acid system, however, the presence of acrylonitrile reduced the graft yield of the acrylic acid component showing a negative synergism; but acrylic acid enhanced the acrylonitrile graft yield to a considerable extent. The results have been explained in terms of reactivity ratios of the monomers. The conductivity results of the monomer mixtures also supported the experimental results.

Cobalt-60 gamma ray induced polymerization of vinylidine chloride has been studied, as an example of precipitating type of polymers. The percentage conversion of the monomer was not linear with the absorbed dose but showed acceleration. By studying the initial part of the curve which was linear, the initial rates of polymerization have been determined for different temperatures and dose rates. The dose rate exponent was found to be 0.48, and the energy of activation was observed to be 7.4 kcal/mol. The radical yield was determined by competition reaction with a stable free radical DPPH using the induction period method and GR was found to be 21.0. The intrinsic viscosities of the polymers have been determined in o-dichlorobenzene at 120°C. The results show a maximum in molecular weight as the radiation dose is increased. These results as well as the results on the dose rate exponent, and energy of activation are discussed.

G -values for U(IV) formation in gamma-irradiated acid aqueous solutions of uranyl sulfate have been determined under various conditions. Whereas in the absence of a suitable OH radical scavenger, there is no net reduction of U(VI) to U(IV), reduction is observed in presence of OH radical scavengers such as the aliphatic alcohols, the limiting G U(IV) values being 3.6 (isopropanol), 3.2 (ethanol), 3 (methanol) and 1.3 (t-butanol). H 2 O 2 added prior to irradiation did not affect the G U(IV) value in the case of isopropanol, but decreased it to almost zero in the case of t-butanol as OH scavenger. These results are explained on the basis of the redox behaviour of the hydroxyalkyl radicals derived from the alcohols and the formation of OH radicals and U(V) as intermediates in the oxidation of U(IV) by H 2 O 2 .

Initiation and individual propagation rate constants for the first few steps are determined for e-aq, OH radical and H atom reactions with cyclohexyl methacrylate as the monomer using the technique of pulse radiolysis. Though the rate constants for initiation are higher, the propagation rate constants for the transient species formed by reaction of OH radical and H atom are lower compared to that by reaction of e-aq with the monomer. It is also observed that in the case of e-aq reaction the first propagation step is about an order of magnitude faster than the second propagation step and propagation through radical-anionic form is much faster than its radical counterpart.

The radiolytic decomposition of the B-group vitamins in 0.1 mM neutral aqueous solutions has been studied in oxygenated as well as N2O saturated solutions. In the former G(-Vit) and G(H2O2) values suggested the occurrence of reaction between the vitamin radioals and the H2O2 formed during radiolysis in the oase of pyridoxin, folic acid and cyanocobalamin. The occurrence of this reaction was directly confirmed in N2O saturated solutions initially containing hydrogen peroxide. In this case an increased vitamin decomposition and a parallel consumption of the H2O2 were observed. Reactivities of different types of radicals with H202 are discussed.

Radiation initiated in-source polymerisation of trioxane has been studied in super dry state. The dose rate exponent observed is 0.51 indicating the termination to be bimolecular i.e. neutralisation of cation with an anion or an electron. From the molecular weight data the rate constants k tr /k p and k t /k 2 p have been evaluated to be 2.5 × 10−4 and 13 respectively. The k tr is the rate constant for the chain transfer to the monomer and k p and k t are the rate constants for propagation and termination all expressed in M−1s−1. Assuming the neutralisation between the ions and k t value of isobutyl vinylether taken from the literature, the k p value was calculated to be 1.6 × 105. The G (total ions) was calculated to be equal to 9.1.

The polymerization of vinylidene chloride in benzene, chloroform and bromoform solvents has been carried out using γ-rays as initiator. Both rates of polymerizations and molecular weights of the resultant polymer in different systems have been determined. The rates of polymerizations Rp were found to follow the order Rp(bromoform) > Rp(chloroform) > Rp(benzene). The mechanism of polymerization seems to be bimolecular. The molecular weights ranged from 3000 to 7000 and followed the same order. M(bromoform) > M(chloroform) > M(benzene). The results are explained by the chain transfer mechanism to the solvent in the three systems studied.

The yields of various products formed in γ-irradiated nitrate ices, viz. NO2-, H2O2, O2 and H2, have been measured at different nitrate concentrations. Daniel's method of partition of yields has been employed to evaluate the direct and indirect effect contributions to the yields of the first three products. G(H2) is close to zero at all nitrate concentrations above ∽0.5 mol dm-3. The mechanism of product formation has been discussed in the light of various reactions put forth to explain the radiolysis of fluid aqueous nitrate solutions. The effect of various scavengers for the primary species on the product yields has also been investigated. From this it is inferred that nitrate is able to scavenge both the reducing species, viz. H and em- giving nitrate and possibly also the holes (hm+) giving O2, and excited water molecules (H2O∗) giving H2O2 and additional nitrite.

A study of the radiation induced decomposition of the B-group vitamins has been carried out in aqueous media at room temperature as well as in rigid matrices at low temperature. The detailed results on the effect of glucose and oxygen as protective additives at the different temperatures are presented in the case of Thiamine (Vitamin B1). Comparative data are given on the extent of decomposition of this and other vitamins of the B-group at room temperature and at 193 K. The importance of these results in connection with the radiation sterilization of pharmaceutical preparations is indicated.

The radiolytic degradation of thiamine in aqueous medium under reducing conditions has been employed to assess the extent of one electron transfer to this vitamin from various radicals of known reduction potential for oxidation. The graphical plot of these two quantities has the typical shape of redox titrational curves. Eo1 for the reduction of thiamine inferred from this plot is ∼−0.5 V. This is close to the Eo1 for the oxidation of reduced thiazole moiety of thiamine in cyclic voltammetric experiments. The reversible one electron redox potential of thiamine may therefore be taken as ∼−0.5 V.

Grafting of the mixture of acrylamide and acrylic acid onto polyester and polypropylene fibers and mixture of acrylic acid and methacrylic acid onto polypropylene by the radiation method are reported. It is observed that when pure acrylamide was used for grafting, the grafting extent was small, whereas when the mixture was used, the amount of acrylamide content in the copolymer was found to be more than the feed ratios. The results are explained on the basis of chain transfer mechanism. With methacrylic acid and acrylic acid mixtures, the rate of grafting decreased with the increase in the concentration of acrylic acid in the feed ratio, and this has been explained on the basis of the formation of either a 3-dimensional network structure or a highly branched structure involving backbone polymer molecules with acrylic acid, which prevents the diffusion of the monomer from the solution phase to the swollen phase.

Electrokinetic properties of methacrylic acid- and acrylonitrile-grafted polypropylene fibers measured in the presence of cationic dyes are reported. The zeta potential of polypropylene fibers decreases, and the surface charge density along with surface conductivity increases as the concentration of the dyes in the streaming solution increases. The zeta potential at pH 7 decreases as the amount of graft increases in case of both acrylonitrile- and methacrylic acid grafted fibers. Both surface charge density and surface conductivity increase with the increase in dye concentration for both acrylonitrile- and methacrylic acid-grafted fibers. The results are explained on the basis of the cationic dye adsorption on the grafted fiber in the case of methacrylic acid graft. In the case of acrylonitrile-grafted fibers, this could be due to the strong attraction of cationic dye to the nitrile group of the grafted fibers.