RECOVERY OF HAEMOPHILUS INFLUENZAE FROM ULTRAVIOLET AND X-RAY DAMAGE

Abstract— Results of experiments on reactivation of ultraviolet (u.v.)-irradiated Haemophilus influenzae and cellular reactivation of u.v.-damaged transforming deoxyribonucleic acid (DNA) and bacteriophage are reported. Liquid-holding recovery (LHR) is small for the u.v.-sensitive mutant BC100 which, relative to the wild type, also has greatly reduced host-cell reactivation (HCR) of u.v.-inactivated phage, and competent cultures show reduced competent cell reactivation (CCR) of u.v.-inactivated transforming DNA. BC100 cells can be transformed with DNA isolated from the wild type strain Rd to a u.v. resistance similar to that of Rd, and irradiation of the DNA reduces the transformation frequency for this marker (uvr). The u.v.-resistant mutant BC200 displays very little LHR under the usual conditions where reactivation occurs after plating. The colony-forming ability (cfa) of irradiated BC200 is greater than that of Rd, but HCR and CCR are the same on this mutant as on the wild type. The major difference between Rd and BC200 is the enhanced u.v. survival of cfa of the latter. It was determined that this difference reflects cell lysis of irradiated Rd and lack of lysis in BC200 cultures. That lysis is closely correlated with damage to the bacterial chromosome is suggested by the finding that the lytic response of Rd (as determined turbidimetrically) can be negated by the liquid-holding procedure, but lysis of BC100 (which lacks comparable DNA-repair ability) can be only partially inhibited by this procedure. LHR occurs when post-plating dark recovery is incomplete, is temperature-sensitive, and occurs unimpeded when post-u.v. protein synthesis is inhibited by chloramphenicol. It is suggested that enzymatically catalyzed reactivation of DNA occurs or is initiated during liquid-holding of u.v.-irradiated H. influenzae Rd and that the necessary enzyme(s) exists prior to appearance of u.v. lesions in the DNA. Results are reported for X-ray inactivation of transforming DNA as assayed on BC100, Rd and BC200 and of the cfa of the three strains.     

Liquid-holding effects in U.V.-irradiated phage T3

Abstract— Holding complexes of u.v.-irradiated (254 nm) T3 phage in E. coli B/r cells for several hours at 37°C in buffer, or broth with chloramphenicol, affects the phage survival in at least two different ways: (1) by enhancing excision repair, resulting under certain conditions in liquid-holding recovery (LHR), and (2) by destroying the phage (holding inactivation). LHR is most apparent in buffer containing 20 μg ml^-1 chloramphenicol (CAP). It is expressed by as much as a 10–fold increase in the fraction of complexes that display host-cell reactivation (resulting from excision repair), but the percentage of u.v. lesions repaired within repair-proficient complexes is slightly decreased. LHR is not observed if T3 infects the repair-deficient strain B_s-1. Holding inactivation is readily observed with unirradiated phage complexes in broth containing CAP. The response of irradiated-phage complexes to liquid-holding conditions is more complex: holding inactivation is less effective for irradiated than for unirradiated phage DNA (i.e. the irradiated DNA is to some extent ‘protected’), and processes leading to LHR are superimposed. Thus under certain holding conditions one observes the paradoxical phenomenon that the viable titer of irradiated phage is several times higher than that of unirradiated phage. The nature of holding inactivation is not known, nor is the mechanism by which irradiated DNA is partially protected against it. Holding inactivation does not require protein synthesis; it is rather enhanced at high CAP concentration and seems to be favored by otherwise active cell metabolism. At high CAP concentrations (200–400 μg ml^-1, as compared to 20 μg ml^-1) irradiated-phage complexes show neither LHR nor protection against holding inactivation. Likewise they fail to undergo some step by which the phage DNA becomes insensitive to repair inhibition by caffeine.     

REPAIR OF NEAR (365 nm)- AND FAR (254 nm)-UV DAMAGE TO BACTERIOPHAGE OF ESCHERICHIA COLI

Abstract: Intact bacteriophage have been irradiated at 365 nm or at 254 nm and then analysed for DNA photoproducts or injected into their bacterial host to test susceptibility of the damage to both phage and host-cell mediated repair systems. Both thymine dimers and single-strand breaks are induced in the phage DNA by 365 nm radiation. The dimers appear to be the major lethal lesion (approximately 2 dimers per lethal event) in both repair deficient bacteriophage T4 and bacteriophage λ. after irradiation with either 254 nm or 365 nm radiation. Damage induced in T4 by either wavelength is equally susceptible to x -gene reactivation (repair sector approximately 0.5). v -gene reactivation acts on a larger fraction of the near-UV damage (repair sector of 0.82 at 365 nm as against 0.66 at 254 nm). The host-cell mediated photoreactivation system is only slightly less effective for near-UV damage but host-cell reactivation (as measured by comparing survival of phage λ. on a uvr⁺ and a uvr^- host) is effective against a far smaller sector of near-UV damage (0.35) than far-UV damage (0.85). Weigle-reactivation (far-UV induced) of near-UV damage to phage λ is not observed. The results suggest that unless the near-UV damaged phage DNA is repaired immediately after injection. the lesions rapidly lose their susceptibility to repair with a consequent loss of activity of the phage particles.     

Photobiology of RNA bacteriophages. II. U.V.-irradiation of f2: effects on extracellular stages of infection and on early replication

Abstract— The effect of u.v. irradiation (2537 Å) on the RNA bacteriophage f2 has been studied with respect to the adsorption of f2 to E. coli K12 (male strain), the penetration of f2-RN A into the host cell and the conversion of the phage nucleic acid to the double-stranded replicative intermediate. The biological parameter most sensitive to u.v. was the plaque-forming ability of the phage. Its loss could be attributed to several factors. (1). A binding of capsid protein to phage nucleic acid interfering with host penetration by the f2-RNA. (2). Desorption of some irradiated phage at 37° from their attachment sites on the host. (3). Molecular alterations in the RNA preventing formation of the replicative intermediate within the host. The relationship of these factors to the lack of photoreactivability of irradiated f2 is discussed.     

OVERLAPPING ACTION OF HOSTCELL REACTIVATION AND PHOTOREACTIVATION IN BACTERIA

Abstract— The photoreactivation rate of U.V. irradiated phages is decreased in u.v. irradiated bacteria. In contrast, the normal photoreactivation rate is observed if the irradiated bacteria are photoreactivated before phage infection. The decrease of the photoreactivation ratc is understood as a competing effect of the u.v. lesions in the bacterial nucleic acids for the photoreactivation enzyme. This competitive inhibition can be diminished not only by photoreactivation of the bacteria before phage infection but also by hostcell reactivation of the u.v. lesions in the bacterium. The results provide strong evidence that hostcell reactivation and photoreactivation revert the same u.v. photoproducts in bacterial nucleic acids. The experiments show that the hostcell reactivation enzyme is not induced by phage infection or by irradiation, but is normally present in the bacterial cell.     

Properties of crystallized trans 1,4-polyisoprene

Stirrer crystallization of a trans-1,4-polyisoprene fraction(M?_n = 3 × 10⁵) was carried out from n-butyl acetate and from n-heptane solutions (2% w/v). Fibrous crystals in the ß form were obtained at temperatures of 46-48°C in the two solvents, respectively. At 36-46°C from n-butyl acetate and 25-35°C from n-heptane lamellar crystallization took place leading predominantly to the α form. Melting endotherms and densities for various samples were obtained. The maximum TENDO for α was 74°C and for ß 79°C and the maximum weight fraction crystallinity for ß was 0.78. The stability of performed α nuclei in n-butyl acetate and n-heptane using a fraction with M?_n = 2.5 × 10⁵ was monitored as a function of temperature. The dissolution temperature of fibrous ß-TPI with the maximum TENDO was measured in 13 liquids and the results analyzed in terms of the Flory-Huggins parameter. The heats of fusion for the α and ß forms, obtained by extrapolation of heat of fusion versus change in specific volume, were found to be 8.0 and 10 kJ mol^?1, respectively. The pressure coefficients of the melting temperature were calculated to be 38 and 43 K kbar^?1 and the fold-surface free energies recalculated to be 42 ± 1 and 53 ± 1 erg cm^?2 for the α and ß forms, respectively. The number of monomer units per average noncrystalline chain traverse for the most crystalline fibrous ß-TPI was estimated at 36.     

Radiation effects of paraffins as polymer model compounds—II. Crosslinking determination by liquid chromatography

The G-values of crosslinking and chain scission of normal paraffins (C₂₀H₄₂, C₂₁H₄₄, C₂₃H₄₈ and C₂₄H₅₀) and squalane (C₃₀H₆₂) as the model compounds of polymers were determined by the measurements with a liquid chromatography (LC) after Co-60 γ-rays irradiation in solid and in liquid phases at -77, 25 and 55°C. The crosslinking products as dimer, trimer and the more polymeric products were well resolved and the relative yield of polymeric products increased with increasing dose. The G(cross-linking) of n-paraffins was 1.0 in the crystalline at -77°C and 1.15 in the crystalline at 25°C, and 1.7–1.8 in the liquid phase at 55°C of irradiation temperature. The G(crosslinking) of squalane was 1.3 in the glassy phase at -77°C and 1.6 in the liquid phase at 25 and 55°C. However, the chain scission products were too small to detect by the LC measurement, that is, the yield was estimated to be less than 1/10 of the crosslinking products.The unsaturations which appeared in u.v. detector of LC spectrum were observed in monomer, dimer, trimer and the more polymeric products, and the relative concentration was the higher in the more polymeric products, especially in liquid phase. So the molecules with unsaturation would react preferentially with other molecules as monomer or dimer to produce the polymeric products including the unsaturation.     

Temperature dependence of radiation effects in polyethylene: Cross‐linking and gas evolution

High‐density polyethylene (HDPE) and low‐density polyethylene (LDPE) were irradiated in vacuo at 30–220 and 30–360°C, respectively, with γ‐rays at doses of 10–400 kGy. Temperature dependence of cross‐linking and gas evolution was investigated. It was found that cross‐linking was the predominant process up to 300°C and the gel point decreased smoothly with temperature. The increase of G(x) with temperature was likely attributed to the temperature effect on addition of radicals to the double bonds present in the polymer. Above 300°C, the gel fraction at a given dose decreased remarkably with temperature and turned to zero at 360°C. The molecular weight variation determined with gel permeation chromatography (GPC) indicated the enhanced degradation at 360°C by radiation. G‐values of H₂ increased with temperature and varied with dose. The compositions of the C₁–C₄ hydrocarbons evolved depended on the structures of side branches. Raising the temperature favored the formation of unsaturated hydrocarbons, and the yield of unsaturated relative to saturated hydrocarbons decreased with dose. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1541–1548, 1999     

Polymerization of α-amino acid N-carboxy anhydrides. III. Mechanism of polymerization of L- and DL-alanine NCA in acetonitrile

The polymerization of L - and DL -alanine NCA initiated with n-butylamine was carried out in acetonitrile which is a nonsolvent for polypeptide. The initiation reaction was completed within 60 min.; there was about 10% of conversion of monomer. The number-average degree of polymerization of the polymer obtained increased with the reaction period, and it was found to agree with value of W/I, where W is the weight of the monomer consumed by the polymerization and I is the weight of the initiator used. The initiation reaction of the polymerization was concluded as an attack of n-butylamine on the C₅ carbonyl carbon of NCA. The initiation, was followed by a propagation reaction, in which there was attack by an amino endgroup of the polymer on the C₅ carbonyl carbon of NCA. The rate of polymerization was observed by measuring the CO₂ evolved, and the activation energy was estimated as follows: 6.66 kcal./mole above 30°C. and 1.83 kcal./mole below 30°C. for L -alanine NCA; 15.43 kcal./mole above 30°C., 2.77 kcal./mole below 30°C. for DL -alanine NCA. The activation entropy was about ?43 cal./mole-°K. above 30°C. and ?59 cal./mole-°K. below 30°C. for L -alanine NCA; it was about ?14 cal./mole-°K. above 30°C. and ?56 cal./mole-°K. below 30°C. for DL -alanine NCA. From the polymerization parameters, x-ray diffraction diagrams, infrared spectra, and solubility in water of the polymer, the poly-DL -alanine obtained here at a low temperature was assumed to have a block copolymer structure rather than being a random copolymer of D - and L -alanine.     

Photoreactivation of killing in Streptomyces. II. Kinetics of formation and photolysis of pyrimidine dimers and adducts in S. coelicolor and S. griseus PHR-1

Abstract— A pyrimidine adduct, 6-4‘-[pyrimidine-2’-one] thymine (PO-T)?, observed in DNA hydrolysates of 254-nm ultraviolet (u.v.) irradiated conidia of Streptomyces coelicolor, increases linearly with u.v. dose up to 2 × 10⁵ ergs/mm². Yields of thymine dimer (T○) and uracil-thymine dimer (U○) level off at much lower doses. Initial relative rates of formation of these u.v. photoproducts are: 1:1.3:4.8 for PO-T, T○ and U○, respectively. Similar results were obtained with a Streptomyces griseus mutant, PHR-1. An equation is derived to estimate the ratio of the amount of PO-T to the total amount of thymine-derived photoproducts at low (biological) u.v. doses. The observed PO-T fractions compare well with the calculated values. Rapid photolysis of the precursor of PO-T was observed by post-u. v. treatment at 313 nm of conidia of S. coelicolor and of S. griseus PHR-1. The photolysis was much slower at 365 nm and did not occur at all at 405 nm. Pyrimidine dimers were not appreciably affected by post-u. v. treatment at the above wavelengths in these Streptomyces strains. Both of these strains are phenotypically photoreactivation-deficient, and the present results indicate that they do not possess active photoreactivating enzyme. In earlier papers[3,4,5], the pyrimidine adduct found in acid hydrolysates of DNA was loosely referred to as “uracil-thymine adduct (U-T adduct)”. Such terminology is not strictly correct. The pyrimidine adduct in acid hydrolysates is PO-T (sometimes called P₂B), which could theoretically result from removal of ammonia from a C-T adduct or removal of water from a U-T adduct (see [6]).     

Formation of free radicals in photoirradiated cellulose. VII. Radical decay

The ESR spectra of untreated and photosensitized celluloses irradiated with three different ultraviolet light sources, i.e., λ > 2537 Å, λ > 2800 Å, λ > 3400 Å, at 77°K under vacuum were studied. Based on the warm-up process, that is, warming the sample from 77°K to 273°K for a certain time and recorded at 77°K, the decay behavior of free radicals of celluloses was examined for changes of the pattern and the intensities of ESR spectra. For the untreated samples irradiated with light of λ > 2537 Å and λ > 2800 Å, beside the two doublet spectra originating from hydrogen atoms (508 gauss splitting) and formyl radicals (129 gauss splitting), the observed sevenline spectrum was resolved to be a superposition of a singlet (ΔH_msl = 16 gauss), a doublet (24 gauss splitting), a triplet (34 gauss splitting), and a quartet (overall width, 88 gauss) spectrum. For the photosensitized samples irradiated with light of λ > 3400 Å, the 1:1:1 three-line spectrum was resolved to be a superposition of a singlet (ΔH_msl = 27 gauss), a doublet (43 gauss splitting), and a triplet (34 gauss splitting) spectrum. The five-line spectra of the photosensitized samples irradiated with light of λ > 2537 Å and λ > 2800 Å were resolved to be a superposition of a singlet (ΔH_msl = 27 gauss), a doublet (43 gauss splitting), and a triplet (34 gauss splitting) spectrum. Based on these findings, the conclusion was drawn that at least six kinds of spectra, generated from six kinds of radical species, were formed in cellulose irradiated with ultraviolet light under appropriate experimental conditions.     

Acceleration of the cationic polymerization of an epoxy with hexanediol

Thin films of 3,4-epoxycyclohexylmethyl 3',4'-epoxycyclohexane carboxylate were UV irradiated (1.1 J cm^-2) under isothermal conditions ranging from 0 to 50°C. Under these conditions the polymerization advanced quickly but only to a conversion level of less than 10% before the reaction rate slowed by more than an order of magnitude. This drop off in rate was not caused by the glass transition temperature, T _g, reaching or exceeding the reaction temperature, T _rxn, since the epoxide's T _g remained at least 40°C below T _rxn. Raising the sample temperature above 60°C caused a sharp increase in the conversion level. At 100°C conversion exceeds 80% and the ultimate T _g approaches 190°C. The addition of 10 mass% 1,6-hexanediol, HD, to the epoxy caused the conversion at room temperature to quintuple over the level obtained without the alcohol present. The heat liberated from this alcohol epoxy blend during cure on a UV conveyor belt system caused the sample's temperature to increase by about 100°C above ambient whereas the epoxy alone under these conditions only experienced a modest temperature rise of about 26°C. If the amount of HD in the blend is increased above 10% the heat of reaction at 23°C decreases due to HD being trapped in a nonreactive crystalline phase. Boosting reaction temperatures above 50°C melts the HD crystals and yields significantly improved conversion ratios. As the level of alcohol blended with the epoxy is raised its ultimate T _g is lowered and when the concentration of alcohol in the blend nears 30 mass%T _g drops below room temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermophilic laccase from xerophyte species Opuntia vulgaris

Two laccase temperature isoforms capable of oxidizing phenolic compounds to quinones were isolated and purified to homogeneity from the cladodes of the xerophyte species Opuntia vulgaris. These catalytically active proteins exhibit apparent molecular masses of 137 and 90 kDa. Under reducing conditions, both isoforms yielded a subunit molecular mass of 43 kDa, suggesting that the enzyme is a multimer of the 43 kDa subunit. The 137 kDa isoform when heated at 80°C for 3min generated three polypeptide bands on activity stained polyacrylamide gels exhibiting 137, 90 and 43 kDa molecular forms. All isoforms of the enzyme exhibited an optimum pH of 10 when 2,6‐dimethoxyphenol was used as a substrate. The optimum temperature of the 137 kDa enzyme form was noted to be 80°C and that of the 90 kDa enzyme form was 70°C. Denaturation kinetics of both the laccase isoforms carried out at their respective optimum temperatures for 30 min exhibited enzyme activity in excess of their t_1/2 values throughout the assay period. The K_m for the 137 kDa form was determined to be 2.2 ± 0.3 mm and the V_max was 2.8 ± 0.2 IU/mL. These high temperature stable laccase isoforms having alkaline pH optima can find significant industrial use. Copyright © 2010 John Wiley & Sons, Ltd.     

Electron spin resonance study of ethylene–acrolein copolymer irradiated with ultraviolet light

When ethylene–acrolein copolymer was irradiated at ?196°C with ultraviolet light, a sharp singlet spectrum with a g value of about 2.001 was predominant. This spectrum is attributed to acyl radicals, which are produced by dissociation of a hydrogen atom from an aldehyde group. At the same time it is supposed that dissociation of formyl groups also took place to give alkyl radicals, CO, and H₂. The alkyl radicals reacted with CO molecules to give acyl radicals at ?78°C under vacuum. Peroxy radicals were produced when the sample irradiated at ?196°C in the presence of air was treated at ?78°C. The sample irradiated at ?196°C was warmed to near 0°C and an apparent singlet spectrum with a g value of about 2.004 was observed. This spectrum was tentatively assigned as due to free radicals of the type      

THE ROLE OF HOST-CELL REPAIR IN LIQUID-HOLDING RECOVERY OF U.V.-IRRADIATED ESCHERICHIA COLI

Abstract— The experiments reported give evidence that liquid-holding recovery (LHR) of u.v. irradiated E. coli cells involves basically the same type of dark repair which causes reactivation of phage and which results in much increased survival of the cells themselves [host-cell reactivation (HCR)]. LHR is very small in the two HCR(-) strains B syn^- and B_s-1, but occurs to larger but different extents in the three HCR(+) strains B, B/r, and B/r (Λ). LHR is inhibited if the liquid contains caffeine or acriflavine, both of which are known to inhibit HCR. The results indicate that most of the LHR effect, if not all, occurs during the liquid holding, rather than under growth conditions after liquid holding. It is assumed that the holding itself allows a prolonged time for, and therefore an enhancement of, HCR. It is thus implicit that LHR can be observed only where otherwise HCR of repairable u.v. damage would be incomplete, and that different extents of LHR, as observed in the three HCR(+) strains, reflect different extents of incompleteness of HCR. It is concluded that the repairable u.v. hits which are not fully repaired by HCR are predominantly those concerned with the extra u.v. sensitivity of the strains B and B/r (Λ), relative to B/r.     

Studies on the thermal decomposition kinetics of LiPF6 and LiBC4O8

Thermal decomposition of LiPF₆ and LiBC₄O₈ (lithium bis(oxalate)borate, abbreviated as LiBOB) were studied using TG (thermogravimetry)-DTG (derivative thermogravimetry) method with different heating rate β of 5, 10, 20 and 40°C min⁻¹ or at different constant temperature θ _C (109·80, 118·79, 148·41, 176·86°C for LiPF₆ and 278·51, 298·13, 317·65, 336·13 for LiBOB). From the non-isothermal kinetics we calculate that is 1·01, n _LiBOB is 1·04, is 91907·61 J/mol, and E _LiBOB is 205179·88 J/mol; from the isothermal kinetics we calculate that n for both LiPF6 and LiBOB are 1, E_LiPF6 is 91907·61 J/mol, E _LiBOB is 205179·88 J/mol, is 16·89 s⁻¹, and lnA_LiBOB is 31·96 s⁻¹. The results obtained from the two ways have minor differences and can validate each other.     

High Temperature Affects Photosynthetic and Molecular Processes in Field‐Cultivated Vitis vinifera L. × Vitis labrusca L.

High‐temperature stress markedly influences grape growth and development. However, how high‐temperature stress response differs between controlled and field‐cultivated grape is poorly understood. In this study, the effects of heat treatment on grapevines were studied for changes in photosystem II (PSII) activity and expression levels of heat‐responsive genes and heat shock protein HSP21. July 31st, 2015 was considered as the post high‐temperature treatment (“42°C”; temperatures above 40°C for a period of time each day ranging from 1–7 h) under field cultivation in our experiment. The recovery of chlorophyll fluorescence indicators and the increasing expression of heat‐responsive genes and the heat shock protein HSP21 suggested the development of heat tolerance in the form of acclimation in grape. Changes in various parameters of photosynthetic pigment fluorescence and of the electron transport chain (Fv/Fm, PI_ABS, W_k, RC_QA, Φ_Po, and Φ_Eo) between “42°C” and the 45°C treatment demonstrated that the donor side, reaction center, and acceptor side of PSII were influenced by a critical high temperature. Furthermore, the difference between the two cultivation conditions studied was attributed to other environmental factors and inherent tree vigor.     

Polyurethane elastomers based on amphiphilic poly(caprolactone)‐b‐poly(butadiene)‐b‐poly(caprolactone) triblockcopolyols

Hydroxyl‐terminated poly(butadiene) (HTPB; M_n = 2100 g mol⁻¹) was capped with 30 and 60 wt % of ɛ‐caprolactone to reach amphiphilic triblock copolymers in form of capped poly(butadiene) CPB. The former (CPB30; M_n = 3300 g/mol) is amorphous with a glass temperature of −56 °C. CPB60 (M_n = 4000 g mol⁻¹) is semi‐crystalline with a melting point of 50 °C and a glass transition at −47 °C. The CPBs, HTPB and polycaprolactone diol (M_n = 2000 g mol⁻¹) were used as soft segment components in the preparation of polyurethane elastomers (PUE), using a 1/1 mixture of an MDI prepolymer and uretonimine modified MDI, and hard phase components in form of 1,3‐propane diol, 1,4‐butane diol, and 1,5‐pentane diol. CPB‐based elastomers with 1,4 butane diol (8 wt %) show hard domains as fringed aggregates with a better connection to the continuous phase than the HTPB‐based PUE. The soft segment glass transition temperature (T_g) is at −28 °C for HTPB‐based PUE and at −43 °C for those of CPB. The tensile strength of the CPB30&60‐based PUE is found between 20 and 30 MPa at an elongation at break of 400% and 550%, respectively. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1162–1172     

Poly(p‐phenylene sulfide) nonisothermal cold‐crystallization

The poly(p‐phenylene sulfide) (PPS) nonisothermal cold‐crystallization behavior was investigated in a wide heating rate range. The techniques employed were the usual Differential Scanning Calorimetry (DSC), and the less conventional FT‐IR spectroscopy and Energy Dispersive X‐ray Diffraction (EDXD). The low heating rates (Φ) explored by EDXD (0.1 K min^?1) and FT‐IR (0.5–10 K min^?1) are contiguous and complementary to the DSC ones (5–30 K min^?1). The crystallization temperature changes from 95 °C at Φ = 0.05 K min^?1 to 130 °C at Φ = 30 K min^?1. In such a wide temperature range the Kissinger model failed. The model is based on an Arrhenius temperature dependence of the crystallization rate and is widely employed to evaluate the activation energy of the crystallization process. The experimental results were satisfactorily fit by replacing in the Kissinger model the Arrhenius equation with the Vogel–Fulcher–Tamann function and fixing U* = 6.28 k J mol^?1, the activation energy needed for the chains movements, according to Hoffmann. The temperature at which the polymer chains are motionless (T_∞ = 42 °C) was found by fitting the experimental data. It appears to be reasonable in the light of our previously reported isothermal crystallization results, which indicated T_∞ = 48 °C. Moreover, at the lower heating rate, mostly explored by FT‐IR, a secondary stepwise crystallization process was well evidenced. In first approximation, it contributes to about 17% of the crystallinity reached by the sample. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2725–2736, 2005     

ESR studies of some γ-irradiated organic crystals

Acrylamide, N-tert-butylacrylamide, and propionamide crystals were irradiated at ?196°C and the structures of radicals studied by ESR spectroscopy at various temperatures. The γ-irradiated acrylamide crystals show a five-line spectrum which is similar in shape to the signal obtained from the γ-irradiated propionamide crystals. Two types of radicals are produced in irradiated acrylamide and propionamide crystals at ?196°C. When the irradiated samples are kept at ?78°C the spectrum of propionamide remains the same, except in intensity. In contrast to this, the acrylamide spectrum changes to a triplet because of dimerization. Upon warming the irradiated acrylamide sample to between ?50 and ?30°C, some small new peaks become apparent on either side of the triplet. These new peaks disappear above ?20°C and the spectrum changes to a triplet because of polymerization. To observe the changes in the ESR spectra of γ-irradiated N-tert-butylacrylamide we kept the sample at various temperatures from ?196 to 100°C. From ?196°C to about room temperature the spectrum is a quintet. At and above 35°C, the spectrum changes to a triplet with shoulders on either side of the main peaks. With further warming above 80°C the spectrum changes to a broad triplet.