Photolysis of <Emphasis Type="Italic">o</Emphasis>-iodo- and <Emphasis Type="Italic">o</Emphasis>-bromophenols in aqueous solution of sodium sulfite and organic solvents

The photochemical reaction of o-iodo- and o-bromophenol in an aqueous sodium sulfite solution proceeds via both nonchain and chain mechanisms. The formation of the intermediate product, aromatic radical anion, was observed. The quantum yield of the photochemical reaction of o-iodophenol increases, when the electron donor diphenylamine is irradiated. In the photolysis of o-halophenols in organic solvents, free iodine is evolved in addition to aromatic products. The products of the photolysis of o-iodophenol in ethanol and carbon tetrachloride were identified by gas chromatography-mass spectrometry. These are phenol in the case of ethanol and a mixture of o-chlorophenol and hydroxychloro-substituted biphenyls in the case of carbon tetrachloride. The quantum yields were determined for all photochemical reactions studied.     

RED LIGHT INTERACTIONS WITH BLUE AND ULTRAVIOLET LIGHT IN POLAROTROPISM OF GERMLINGS OF A FERN AND A LIVERWORT

Abstract— In polarotropism of the chloronema of the fern Dryopteris filix-mas (L.) Schott and of the germ tube of the liverwort Sphaerocarpos donnellii Aust. a phytochrome action in blue and u.v. was presumed[1, 2]. In the present paper this assumption was tested by simultaneously irradiating with red and blue, and red and near u.v. Red energy is given to shift the phytochrome photoequilibrium in favour of high P _fr/ P ^total concentrations. The data obtained by simultaneous irradiation are consistent with the predictions made under the assumption of a phytochrome involvement in the blue- and u.v.-mediated polarotropic response.     

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.     

PRIMARY PRODUCTS IN THE FLASH PHOTOLYSIS OF TRYPTOPHAN*

There has been considerable interest in the photochemistry of tryptophan in connection with ultraviolet inactivation of enzymes. Earlier flash photolysis work has demonstrated that the hydrated electron (e^-_aq) is an initial product in the irradiation of indole derivatives, accompanied by a longer-lived transient absorption near 500 nm attributed to an aromatic radical species[1–5]. Similar transients were observed in a recent flash photolysis study of lysozyme[6] in which it was proposed that inactivation is a consequence of electron ejection from 1 to 2 essential tryptophan residues in the active center. However, there has been uncertainty concerning the tryptophan radical structure and its relationship to the triplet state and radical spectra reported for tryptophan photolysis in low-temperature rigid media. This note reports a flash photolysis investigation of L-tryptophan (Trp) and 1-Methyl-L-tryptophan (1-MeTrp) undertaken to clarify these points. The flash photolysis apparatus and methods employed are described in Ref. [6].     

Photodegradation of urethane model systems

The photo-oxidation products of ethyl N-phenyl-carbamate (EPC) were identified as ethyl o-aminobenzoate, ethyl p-aminobenzoate, aniline, water, carbon dioxide, azo compounds, and other colored material. The ethylaminobenzoates, formed by intramolecular rearrangement of EPC, were precursors of the azo and colored products. Diethyl 4,4′-azobenzenedicarboxylate was produced by the ultraviolet irradiation of the precursor, ethyl p-aminobenzoate, in the presence of oxygen. Benzophenone and anthraquinone, as the triplet donors, sensitized the photo-oxidation of EPC. Quantum yields of photolysis of EPC were measured. The photorearrangement reaction was inhibited by the polar solvent (ethanol). The presence of metal ions and phenyl isocyanate in EPC showed no effect on the oxygen consumption rate.     

Thermal decomposition of 4,4′-isopropylidene bis-2,6-dibromophenol (tetrabromobisphenol-A)

The thermal decomposition of tetrabromobisphenol-A (TBBPA) was found to proceed via an autocatalytic free-radical process. The major products of the decomposition are HBr; mono-, di- and tribromobisphenol-A; phenol; mono-, di-, and tribromophenol; and eventually, char. It was generally found that o- and p-halophenols are thermally unstable. In contrast, the m-bromophenol, 3,5-dibromo-2,4,6-trimethylphenol (dibromomesitol) was found to be quite stable. In addition, o- and p-halo-substituted phenols were found to react with LiI at 250°C to produce I₂, while m-halophenols did not. These results are explained by the formation from o- and p-halo-substituted phenols of a reactive halocyclohexadienone.     

Photolysis of pentacarbonyl(selenocarbonyl)chromium(0), Cr(CO)5(CSe), in an Argon matrix at 20 K

U. v. photolysis (254 and 366 nm) of Cr(CO)₅(CSe) isolated in an argon matrix at ca. 20 K produces a mixture of two isomeric forms of Cr(CO)₄(CSe), Cr(CO)₆ and molecular CO. The two Cr(CO)₄(CSe) isomers are assigned square pyramidal geometries (CSe group axial, C_4v symmetry; CSe group equatorial, C_s symmetry) by comparison with the results from a previous matrix isolation i.r. study of the products formed in the u.v. photolysis of the analogous thiocarbonyl complex, Cr(CO)₅(CS). On further irradiation of the Cr(CO)₄(CSe) species with visible light (λ > 425 nm), the parent Cr(CO)₅(CSe) molecule is regenerated.     

RETARDATION OF ULTRAVIOLET LIGHT ACCELERATED LEAF SENESCENCE BY A CYTOKININ: N6 BENZYLADENINE

O ne clear evidence of u.v. injury is the manifestation of chlorosis after leaf irradiation, and such chlorosis can be photorepaired by blue light[1]. We found that such u.v.-accelerated chlorosis could be prevented in the dark by applying N⁶ benzyladenine (BA), a synthetic cytokinin, either before or after u.v. irradiation. Cytokinins are known to retard natural senescence of detached leaves kept in the dark [2]. The present finding suggests that u.v. damage may accelerate the natural senescence process of detached leaves kept in the dark. N. glutinosa leaves were used in this experiment, because chlorosis develops quickly (within one week) when the mature leaves are detached and incubated in the dark. The plants were grown in a glasshouse without white-wash. The light intensity at noon often reached 9000 ft-c., and the temperature ranged from 19–35°C. The leaves shown in Fig. 1 were from mature plants, i.e. plants with the terminal growing point developed into a flower bud. The floral buds were cut off several days before the leaves were detached for exposure to u.v. light.     

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]).     

Magnetic field effects on photochemical reaction III. Mechanistic study of the photodecarboxylation of arylmethyl esters in micellar solutions

Photolysis of benzyl phenylacetate (ACO₂A), benzyl p-methylphenylacetate (BCO₂A) and 1-naphthyl phenylacetate (ACO₂Np) in homogeneous and micellar solutions results in products typical of radical coupling reactions and loss of carbon dioxide. The cage effects upon direct photolysis of these esters in acetonitrile are significantly greater than zero and those in SDS or HDTBr micellar solutions are even greater. In the triplet sensitization reaction of ACO₂Np in micellar solutions the cage effects are smaller than those obtained upon direct irradiation. However, the application of a 0.05 or 0.2 T external magnetic field in the photolysis in micellar solutions decreases the cage effects dramatically. All these results suggest that the photoextrusions of carbon dioxide from these esters proceed via radical intermediates, and upon direct photolysis the reactive states for the cleavage reaction involve both singlet and triplet excited states.     

The Photochemistry of Ketene the Reactions of Methylene with Toluene and P-Xylene in Vapor Phase (II)

In the photolysis of ketene with toluene in the vapor phase, ethylbenzene, xylenes, 2-methylcycloheptatriene-1, 3, 5, and three unidentified compounds are found as the products of the reactions of methylene with toluene. In the ketene-p-xylene system, p-ethyltoluene, 1,2,4-trimethylbenzene, 1,4-dimethylcyclohepatriene-1,3,5, and three unidentified compounds are obtained as the products of the reactions of methylene with p-xylene. The reaction mechanism is discussed.     

Characterization of the photodegradation products of metolachlor: structural elucidation,potential toxicity and persistence

Aqueous solutions of metolachlor and metolachlor‐d₆ were photolyzed with UV‐visible radiations. The structures of 15 by‐products of metolachlor were determined through gas chromatography‐mass spectrometry analyses using electron and chemical ionization combined with multistage mass spectrometry. The photolysis by‐products of metolachlor resulted mainly from dehalogenation and hydroxylation, in some cases accompanied by cyclization. In silico tests for toxicity prediction showed that the toxicity of some photolysis products is expected to be greater than that of metolachlor. Persistence studies showed that the by‐product relative abundances vary in large amounts with the irradiation time. The post‐photolysis evolution of the solution was also studied, in order to determine the persistence of the main by‐products. It allowed to establish that most of the by‐products can be found more than 12 h after the end of the photolysis, which is of a great concern as treated water is generally available for consumption only a few hours after treatment in most of industrial processes. Copyright © 2012 John Wiley & Sons, Ltd.     

Photolysis of <Emphasis Type="Italic">p</Emphasis>-benzoquinone and <Emphasis Type="Italic">p</Emphasis>-chloranil in aqueous sodium sulfite solution

Photosubstitution of the sulfo group for hydrogen (chlorine in chloranil) is observed under irradiation of sulfonated derivatives of hydroquinone formed upon dissolving of p-benzoquinone and p-chloranil in aqueous solutions of sodium sulfite. The quantum yield of the photochemical reaction is 0.18 ± 0.02 for p-benzoquinone. The rate constant of the thermal reaction of substitution is 5.5 × 10⁻⁴ l mol⁻¹ s⁻¹. The substitution reaction is sensitized by eosin upon irradiation with visible light. During the course of irradiation of sulfohydroquinones, the formation of a product with an absorption maximum at 235 nm was found. The product decays with a rate constant of 0.005 s⁻¹.     

PHOTOLYSIS AND RADIOLYSIS OF NITROMETHANE AND NITROETHANE

Abstract— Prolonged photolysis of nitromethane and nitroethane in liquid and vapour phases, with simultaneous photolysis of the nitrogen dioxide formed, was studied in the absence and presence of cupric oxide. A high-pressure quartz immersion lamp providing the full range of visible and u.v. spectrum, with a high output of radiation at 366 and 313 mμ, was employed as source of light. The products of photolysis were detected by microanalytical methods, infrared-absorption spectrum analysis and gas chromatography. Photolysis of liquid nitro-alkanes resulted in formation of many compounds; saturated hydrocarbons, and in the case of nitroethane, ethylene, were submitted to detailed examination. Photolysis in the vapour phase was carried out in a specially designed glass apparatus. The main products were nitrogen dioxide, aldehydes and polyaldehydes; hydrocarbons were not estimated.
Liquid nitromethane and nitroethane were also irradiated with γ-rays from a ⁶⁰Co source. The radiolysis products were similiar to those obtained on photolysis. The mechanism of photolytic decomposition of nitroalkanes is proposed and discussed.     

Investigation of the colour reaction of phenols with MBTH,II: Properties of the isolated products of the reaction with phenol, 2,6-dimethylphenol and 4-methylphenol

The following model compounds for the study of the oxidative coupling reactions of 2-hydrazono-3-methylbenzothiazoline (MBTH) with phenolic compounds were prepared: thep-coupling products of the reagent with phenol and 2,6-xylenol and theo-coupling product withp-cresol. The proposed structure of the dyes was confirmed. In strongly polar and ionic media the azobetaine form of the products predominates, and in non-polar media the azine structure. The principal physico-chemical properties of the products were determined and the results contributed to formulation of the course of the coupling reaction, and to optimization of the conditions for determination of small amounts of phenolic substances. The violeto-coupling product is less stable than the redp-coupling products, and intramolecularly hydrogen-bonded six-membered ring is assumed to exist in the structure. In acid medium the dyes are mainly monoprotonated, and partly diprotonated in concentrated sulphuric acid medium. The products are stable up to about pH 11. These properties make extraction into low-polarity solvents possible. The dye derived from 2,6-xylenol andp-cresol has not hitherto been prepared. The principal spectral characteristics, _max(), of the products in ethanol medium are: 499 nm (4.7 × 10⁴ 1·mole^–1 cm^–1) for the phenol derivative, 486 nm (5.0 × 10⁴) for the 2,6-xylenol product, and _max 540 nm for thep-cresol product.Part I: Mikrochim. Acta [Wien]1977,I, 241     

Structure of the Paramagnetic Products of Thiocyanate Photolysis at 77 K

Solid paramagnetic products of thiocyanate photolysis were studied at 77 K by EPR and diffuse reflectance spectroscopy. Ab initio calculations of the electronic structure of these products have been carried out. Direct UV irradiation can generate the SCN⁰ radical due to ionization of the thiocyanate ion. Interaction of the SCN⁰ radical with the neighboring thiocyanate ion forms another radical product of photolysis — (SCN)₂ ^- radical ion.     

CONCERNING THE PRODUCTION OF FREE RADICALS IN PROTEINS BY ULTRAVIOLET LIGHT

Abstract— Using electron paramagnetic resonance techniques, the response to u.v. light of several solid proteins and model compounds has been studied in vacuum and at low temperature. Emphasis has been placed on determining the response as a function of the wavelength (Λ 250 nm) and intensity of the incident radiation. Correlation of the parameters of radical production with sample luminescence, molecular amino-acid sequence and tertiary structure, light intensity and total irradiation time has allowed some insight into the mechanisms of free radical formation.
It is shown that the details of amino acid composition, sequence and the tertiary structure of a protein are important in determining both the rate of, and the mechanism for, radical production (two basic mechanisms are described), and in determining the conditions under which sulfur-type radicals can be produced. The results are related to enzyme inactivation and to the u.v. stability of proteins generally.     

SOME OBSERVATIONS ON THE LETHAL EFFECTS OF NEAR-ULTRAVIOLET LIGHT ON ESCHERICHIA COLI, COMPARED WITH THE LETHAL EFFECTS OF FAR-ULTRAVIOLET LIGHT

Abstract— Near-ultraviolet light (365.5 nm) reduces the ability of Escherichia coli B/r and B_8-1, to form colonies on nutrient agar after irradiation. This lethal effect is distinct from that obtained after far-u.v. irradiation (253.7 nm) because the far-u.v. sensitive and resistant strains are equally susceptible to near-u.v. Variation in susceptibility to ultraviolet light during growth is more marked for near-u.v. than for far-u.v. The number of survivors after near-u.v. irradiation of log phase cells is affected by several post-irradiation treatments; more cells survive if growth immediately after irradiation occurs at higher temperatures (unlike far-u.v.). Also, the presence of acriflavine and caffeine in the nutrient agar decreases the number of survivors (in common with far-u.v.).     

Photochemical properties of ferrocene,cobaltocene and nickelocene and their complexes with 2,2,2-trichloroethanol in liquid phase

Summary Photochemical changes in the solutions of ferrocene, cobaltocene, nickelocene and their complexes with 2,2,2-trichloroethanol exposed to near u.v. and argon laser (=514.5 nm) radiation were investigated. The solutions of cobaltocene, nickelocene and their complexes were found to undergo photolysis, whereas ferrocene solutions are not sensitive to this kind of irradiation and the ferrocene bound in a complex undergoes photooxidation to give the ferricenium cation. The activating effect of laser irradiation of ferrocene was revealed as a tendency to complex formation. The quantum yield of the investigated photoreactions, equilibrium constant of complex formation,K, and their molar extinction coefficients, _c, were determined.     

DEGRADATION OF THE DNA OF ESCHERICHIA COLI K12 REC- (JC1569b) AFTER IRRADIATION WITH ULTRAVIOLET LIGHT*

Abstract— Degradation of the DNA of a rec^- mutant of Escherichia coli K12 (JC1569 b) induced by u.v. light was investigated. The rate of degradation was much larger by growing bacteria than by stationary cells. When growing bacteria were starved for amino acids, their DNA became resistant to irradiation. The mode of u.v.-induced degradation was investigated by comparing the time course of release from the acid-insoluble fraction of the label for two growing cultures; the one was pulse-labeled with ³H-thymidine and the other was pulse-labeled and chased thereafter for 12 min. It was found that the label incorporated into the former culture begins to be lost from the acid-insoluble fraction prior to the loss of the label incorporated into the latter culture. It was concluded that breakdown of the replicating point precedes degradation of the bulk of the DNA. This result suggested that the replicating point is a sensitive site to irradiation and the u.v.-induced degradation of DNA seemed to be influenced by the state of chromosome at the time of irradiation. Experiments of centrifugation of lysed spheroplasts of bacteria uniformly labeled with ³H-thymidine in alkaline sucrose demonstrated that DNA of low molecular weight appeared after irradiation with only 5 ergs/ mm², and that the molecular weight could not be restored by post-irradiation incubation. Considering these results, an hypothesis is proposed concerning the initiation of induced degradation of the DNA of the rec^- mutant.