bluuebunny/crossref_metadata_2025 huggingface dataset:
Cladistic analysis of the alderflies of America north of Mexico (Megaloptera: Sialidae)
Authors: WHITING MICHAEL F.
Published: January 2008

Abstract. A cladistic analysis of thirty‐five morphological characters is used to produce a cladogram for the twenty‐four American species of Sialis found north of Mexico, two European species, and three species of Protosialis. Three species groups (americana, califomica and infumata) proposed by Ross 1937 are shown to be monophyletic. Sialis, Protosialis, and the aequalis species group as currently constituted, are paraphyletic; S.nevadensis is nested within Protosialis and Protosialis is nested within Sialis. Character evolution is evaluated in the light of a phylogenetic hypothesis, and structural modifications are found to correlate with presumed functional constraints.
A revision of the family Rhachiberothidae Tjeder, 1959, stat.n. (Neuroptera)
Authors: ASPÖCK U. , MANSELL M. W.
Published: January 2008

Abstract. The subfamily Rhachiberothinae Tjeder, 1959, originally included in the Berothidae and recently transferred to the Mantispidae, is revised and elevated to family rank. A historical review and redescriptions of the family Rhachiberothidae stat.n. and of the genera Rhachiberotha Tjeder, 1959, and Mucroberotha Tjeder, 1959, are presented. Five new species, R.ingwe, R.sheilae, M.aethiopica, M.angolana and M.minted, are described and differentiated from the five hitherto‐known species. The hypothesis of a sister‐group relationship of the Rhachiberothidae to the Berothidae is re‐established. The phylogenetic position of the Dilaridae as an adelphotaxon of the monophyletic group ([Rhachiberothidae + Berothidae] + Mantispidae) is discussed.
A phylogenetic analysis of the fungus‐growing ants (Hymenoptera: Formicidae: Attini) based on morphological characters of the larvae
Authors: SCHULTZ TED R. , MEIER RUDOLF
Published: January 2008

A phylogenetic hypothesis of the fungus‐growing ants (subfamily Myrmicinae, tribe Attini) is proposed, based on a cladistic analysis utilizing forty‐four morphological characters (109 states) of the prepupal worker larva. The fifty‐one attine species analysed include representatives of eleven of the twelve currently recognized attine genera, excluding only the monotypic workerless parasitePseudoatta; the non‐attines include two outgroups (species of the basal myrmicine generaMyrmicaandPogonomyrmex), two myrmicine species presumed to be distantly related to the attines, and twelve species representing taxa that have been proposed by prior workers as possible sister groups of the Attini. There is strong character support for the monophyly of the Attini and for a sister‐group relationship of the Attini and the NeotropicalBlepharidatta brasiliensis.The Attini are divided into two distinct lineages, an ‘apterostigmoid’ clade (containingApterostigmaandMycocepurus)and an‘attoid’clade (containing all other attine genera exceptMyrmicocrypta).The attine genusMyrmicocryptaappears to be paraphyletic with respect to these two groups; the speciesM.buenzliiin particular retains many attine plesiomorphies.

These results indicate that the fungus‐growing behaviour had a single evolutionary origin in the ants. They also indicate that mycelium cultivation is plesiomorphic and that yeast cultivation is derived within the Attini, overturning the long‐standing assumption that the yeast‐growingCyphomyrmexspecies are the most primitive Attini. Behavioural and ecological investigations into the origin and evolution of the fungus‐growing behaviour might more profitably focus on species in the attine genusMyrmicocrypta, as well as those in the closely related non‐attine generaBlepharidattaandWasmannia.
STUDIES ON THE MECHANISM OF RADIATION INACTIVATION OF MICRO‐ORGANISMS—IX. MECHANISM OF THE ULTRAVIOLET‐INDUCED INACTIVATION OF TRANSFORMING DEOXYRIBONUCLEIC ACID
Authors: Stuy J. H.
Published: January 2008

Purified transforming DNA and whole cells of Haemophilus influenzae were exposed to ultraviolet radiation. The DNA and the cells carried three linked antibiotic‐resistant markers.

Inactivation of these markers, singly and in all possible combinations proceeded semilogarithmically with U.V. dose. The in vitro and in viva pictures were quite alike.

Experiments designed to test the possible integration of U.V. damaged DNA regions into the genome of recipient cells demonstrated that the bulk of these regions is rejected by the cells. The “inactivation” of genetic markers as scored by the transformation reaction is thus simply due to their location on such regions. They need not be damaged themselves.

U.V.‐induced DNA damage seemed to induce double recombination events in the transformation process.
CHLOROPLAST “DISAPPEARANCE” AS A TOOL FOR STUDYING SOME EFFECTS OF ULTRAVIOLET LIGHT ON PLANTS*
Authors: Chessin M. , Quinn G. H.
Published: January 2008

With certain precautions the “disappearance” of guard cell chloroplasts may serve as a quantitative measure of ultraviolet light damage to leaves.

Irradiated French bean leaves are still appreciably photoreactivable after 30–60 min in darkness, but eventually they cease to be. This critical time is the same as with irradiated viruses photoreactivated in their hosts.

Guard cells seem much less susceptible than other epidermal cells to damage by ultraviolet light because ultraviolet light doses 15 times as great as those that cause collapse of ordinary epidermal cells do not abolish reversible osmotic closure of stomata.
PHOTOLYSIS AND PHOTO‐OXIDATION OF AMINO ACIDS AND PEPTTDES—II. PHOTO‐DEGRADATION OF CYSTEINE AND RELATED AMINO ACIDS
Authors: Forbes W. F. , Savige W. E.
Published: January 2008

S‐methylcysteine (II) or lanthionine (III) in neutral aqueous solution is partly converted mainly to the corresponding sulphoxide (IV) on irradiation with sunlight or with a sunlamp; cysteine (I) affords cystine and/or products such as the acids (V—for example alaninethio‐sulphuric acid, V, X= SSO3H) shown to arise from photo‐degradation of cystine under similar conditiond(4). In dilute acid or alkaline solution, greater variations occur in the product patterns for cystine and lanthionine than for S‐methylcysteine. Cystine in dilute acid solution in the presence of air gives alaninesulphinic acid (V, X= SO2H) and cysteic acid (V, X= SO3H) but not the acids V (X= SSO3H, SSSO3H and X = SO2SH). In the solid state little photo‐degradation of the amino acids I, II, III or of cystine is detected.

Irradiation of each of the amino acids I, II, or III in solution with 2537Å light affords good yields of alanine and serine in addition to the same products as were obtained with the sunlamp; this behaviour contrasts with that of cystine, when only traces of alanine and serine are obtained on irradiation with 2537Å light unless air is excluded when alanine is the main product.

Alanine is also obtained from each of the three amino acids I, II, III or cystine on irradiation with 2537Å light in the solid state. In addition, irradiation of cysteine, cystine or lanthionine causes some interconversion. The main reactions of I, II and III with 2537Å light are compatible with homolytic fission of one of the bonds adjacent to the sulphur atom to yield the corresponding free radicals.

In conformity with the above type of fission the amino acids I, II, III and also cystine give characteristic ESR absorption spectra on irradiation with 2537Å light. On irradiation with the sunlamp, cystine but not the amino acids I, TI or 111, gives a strong ESR signal; however the free radical or radicals responsible do not appear to be identical with those produced by the action of 2537Å light.
PRIMARY REACTIONS IN BACTERIAL PHOTOSYNTHESIS—III. REACTIONS OF CAROTENOIDS AND CYTOCHROMES IN ILLUMINATED BACTERIAL CHROMATOPHORES
Authors: Clayton R. K.
Published: January 2008

Washed or air‐dried chromatophores of photosynthetic bacteria show a reversible light‐induced bleaching and red shift of the absorption bands of carotenoids. This change is sensitized by light absorbed by bacteriochlorophyll (BChl). The carotenoid reaction is abolished by exposure to deoxycholate. In dried preparations, the reaction is optimal in the presence of an extremely low water vapor concentration. All of the light‐induced absorbancy changes in chromatophores are suppressed reversibly by exhaustive desiccation.

Deoxycholate treatment and drying do not affect the efficiency of energy transfer from carotenoids to BChl in Rhodopseudomonas spheroides chromatophores, nor do these treatments affect the way in which carotenoids modify the absorption spectrum of BChl.

The carotenoid reaction in washed or dried chromatophores is interpreted as arising from the diffusion of electrons or holes from the neighborhood of a special BChl component (BChl,) to the carotenoid molecules.

Dark‐adapted Chromatium chromatophores show, in addition to the light‐induced alteration of BChl2 the reversible light‐induced oxidation of a cytochrome. Correspondingly, R. spheroides chromatophores show the oxidation of cytochrome c553. The cytochrome reaction occurs reversibly in dried films of Chromatium chromatophores; it is absent in dried chromatophores of R. spheroides.

In Chromatium the reactions of cytochrome and BChl, show a close kinetic relationship. It is inferred that BChl, is a photosynthetic reaction center that traps excitation energy and initiates the electron‐transfer processes of photosynthesis.
FLUORESCENT FILTERS TO INCREASE THE EFFICIENCY OF OPTICAL PUMPING: POTENTIAL USES IN FLASH PHOTOLYSIS AND LASER WORK
Authors: Holmström Bertil , Stening Börje
Published: January 2008

Abstract. Data are presented showing how fluorescent filters can be used to increase the efficiency of illumination processes, especially when using light sources with high colour temperature (as for instance flash lamps in flash photolysis or in LASER pumping).
SOME FACTORS AFFECTING THE THERMOCHEMILUMINESCENCE OF CHLOROPHYLL
Authors: Bellamy W.D.
Published: January 2008

Abstract— The therrnochemiluminescence of the chloroplasts from normal lettuce seedlings is enhanced by the addition of β carotene but not by chlorophyll a.The thermochemiluminescence of chloroplasts from etiolated seedlings is enhanced by neither β carotene nor chlorophyll a.A variety of electron donors were substituted for β carotene in the mixtures with chlorophyll a.The most active were squalene, β carotene, vitamin A, and nerolidol.

The isoprene structure (‐CH2‐CCH3=CH‐CH2‐) appears to be a necessary but not sufficient requirement for energy transfer during thermochemiluminescence.Changes in the absorption spectra indicate that both chlorophyll and carotene are destroyed during thermochemiluminescence.
A SOLUBLE PROTEIN‐CHLOROPHYLL COMPLEX FROM SPINACH CHLOROPLASTS 11. THE PHYSICAL AND PHOTOCHEMICAL PROPERTIES OF THE COMPLEX*
Authors: Kahn Joseph S. , Bannister Thomas T.
Published: January 2008

Abstract— Some physical and photochemical properties of a proteinxhlorophyll complex which can be extracted from spinach chloroplasts with dilute Triton X‐100, have been measured. The molar extinction coefficient at the red maximum (671 mμ) is 6.8 × 104. Solutions of the complex are weakly fluorescent, having a quantum yield of about 0.01. The complex undergoes photoautooxidation in the presence of oxygen with a quantum yield of about 0.2 × 10‐‐4, and sensitizes the autooxidation of p‐toluene‐diamine (quantum yield about 1×10‐‐3) and of ascorbic acid (quantum yield 0.25). The complex‐catalyzed reduction of ferricyanide, in the presence of a protein‐carotene complex, was confirmed; its quantum yield is about 8 × 10‐‐4. The protein‐chlorophyll complex does not undergo a Krasnovsky reaction, nor could sensitized reductions of dye by abscorbate be detected. When excess Triton is added to the protein‐chlorophyll complex, it is converted into a detergent colloid apparently identical to a previously described Tween colloid.

The properties of the protein‐chlorophyll complex are compared with those of other states of chlorophyll in vivo and in vitro.
PHOTOLYSIS OF SOME CYCLIC DISULFIDES*
Authors: Ramakrishnan V. , Thompson S.D. , McGlynn S. P.
Published: January 2008

Abstract— Photolysis of liquid pentarnethylene disuliide, liquid tetramethylene disulfide and liquid l, 4‐butanedithiol has been studied. Photolysis of the cyclic disulfides by irradiation in their lowest energy absorption band produces the corresponding dithiol; photolysis of alkali‐doped cyclic disulfide at the same irradiation wavelength as above produces the corresponding cyclic monosulfide. It is suggested that photolysis of undoped liquids proceeds via ‐S‐S‐ scission, whereas that of the doped liquids is supposed to involve initial ‐CS‐ scission. Photolysis of the dithiol produces the corresponding cyclic monosulfide, the rate of such production being considerably enhanced in the presence of alkali. Much of the above data and suggestions are rationalized using a simple MO formalism, which also involves an attempted interpretation of much of the electronic spectra of the various compounds. Product identification was made by study of the short wavelength absorption spectrum of the vapor in equilibrium with the photolysed material.
SPECTROSCOPIC STUDIES OF PURINE—II. PROPERTIES OF PURINE SUBSTITUTED AT THE SECOND AND SIXTH CARBONS*
Authors: Drobnik Jaroslav , Augenstein Leroy
Published: January 2008

Abstract— Substitution of an amino group at the C2 carbon of purine causes the two main components of the X absorption band to be separated by 200–500 Å: primarily this reflects the Occurrence of the lowest‐lying transition at much longer wavelengths than in purine since, except in deoxyguanosine, there is an appreciable absorption component at ˜ 2420 Å in these compounds. Unlike purine, the wavelength shifts produced by different solvents are not simply related to the dielectric constant or hydrogen bonding capacity of the solvents. In agreement with previous predictions thatπ‐π*states should be the lowest‐lying excited singlets, no phosphorescence is observed from 2–aminopurine—the fluorescence quantum yield is close to unity. Besides strong fluorescence very weak phosphoresence can be detected when another amino group is added at C6 and when an oxygen is attached to the sixth carbon (guanine) fluorescence and phosphorescence of comparable intensities are observed: the sum of the quantum yields for both types of emission is of the order of unity. Thus, the lowest‐lying singlet transition must be a π‐π*state. At room temperature themal quenching is the most important parameter in determining the fluorescence intensity of these molecules, however, at lower temperatures the intensity—similar to the wavelength—f this emission apparently also depends upon the ability of a given solvent to reorient and/or perturb Franck‐Condon surfaces. Discrepancies observed between absorption and excitation spectra in deoxyguanosine and azaguanine appear to reflect emission caused respectively by aggregation of molecules and by keto‐enol shifts.
ACTION SPECTRA FOR PHOTOREACTIVATION OF MUTATION TO PROTOTROPHY IN STRAINS OF ESCHERICHIA COLI POSSESSING AND LACKING PHOTOREACTIVATING‐ENZYME ACTIVITY*
Authors: Kondo S. , Jagger J.
Published: January 2008

Abstract— The action spectrum and dose‐rate dependence for photoreactivation of mutation to prototrophy in late‐lag‐phase cultures of Escherichia coli H3r30 (which lacks active photo‐reactivating enzyme) are roughly similar to those for photoprotection from killing in other strains. It is suggested that photoreactivation of this mutation in H/r30 is an indirect effect, similar in mechanism to photoprotection. The action spectrum and dose‐rate dependence for photoreactivation of mutation to prototrophy in late‐lag‐phase cultures of E. coli H3r30‐R (which possesses active photoreactivating enzyme) are roughly similar to those for photoreactivation of killing in most other strains. It is suggested that photoreactivation of this mutation in H/r30‐R is a direct effect at long wavelengths, but that there is an indirect component at short wavelengths. A quite different interpretation of these data is noted. Finally, it is found that, under the conditions of these experiments, indirect photoreactivation of killing in H/r30 and H/r30‐R is weak or nonexistent.
THYMINE DIMERIZATION IN L‐STRAIN MAMMALIAN CELLS AFTER IRRADIATION WITH ULTRAVIOLET LIGHT AND THE SEARCH FOR REPAIR MECHANISMS
Authors: Klímek Miroš
Published: January 2008

Abstract— The formation of thymine dimers in the DNA of L‐strain mammalian cells after irradiation with ultraviolet light has been demonstrated. The amount of dimer formed rises with the dose of u.v. light.

In the course of post‐irradiation incubation the thymine dimers remain in the TCA insoluble fraction and diminish as did the other thymidine‐H3 derivatives with increasing incubation time. The dimer is not found in the soluble fraction. Thus, dimer excision (i.e. its liberation into the soluble fraction) as an expression of repair of radiation damage analogous to dark repair in E. coli was not found in these experiments.
INVESTIGATION OF MAGNESIUM TETRABENZPORPHYRIN‐I.:ABSORPTION AND FLUORESCENCE IN ORGANIC SOLUTION AND AQUEOUS MEDIUM
Authors: Goedheer J. C. , Siero J. P. J.
Published: January 2008

Abstract Absorption and fluorescence properties of a magnesium containing porphyrin pigment are described which generally resemble those of the cholorophylls.

In organic solvents the absorption bands are appreciably sharper than those of the naturally occurring magnesium porphyrins, while the fluorescence yield is approximately equal. Dilution of alcoholic or other water miscible solvents with buffer or water results in the formation of non‐fluorescing “colloidal” pigment forms. Two are forms are evident which differ spectroscopically and photochemically. Addition of detergent prevents formation of such forms or may restore the “in solution” properties.
PHOTOLYSIS OF SOME ARYLALKYL THIOCYANATES, ISOTHIOCYANATES AND DISULFIDES IN RIGID GLASSES AT 77d̀K: FORMATION AND TRAPPING OF ARYLALKYL FREE RADICALS
Authors: Favaro G. , Mazzucato U.
Published: January 2008

Abstract Photolysis of benzyl and benzhydryl thiocyanates and of benzyl, benzhydryl and trityl isothiocyanates and disulfides has been studied in rigid glasses at liquid nitrogen temperature. Most intermediate and final products of photolysis have been identified by absorption and fluorescence spectroscopy. Evidence has been obtained for benzyl, diphenylmethyl and triphenylmethyl trapped radicals. A number of new luminescence bands of benzyl radical, in the 550–610 nm region, and the hitherto unknown lowest energy luminescence spectrum (doublet‐doublet) of diphenylmethyl radical, are reported.
CMPARISON OF THE ACTION SPECTRA AND QUANTUM REQUIREMENTS FOR PHOTOSYNTHESIS AND PHOTOREDUCTION OF SCENEDESMUS*
Authors: Bishop Norman I.
Published: January 2008

Abstract ‐The action spectrum and the quantum requirement of photoreduction (P.R) by hydrogen‐adapted Scenedesmus have been determined under conditions where photosystem II is inoperative. The action spectrum of P.R., when compared to that of photosynthesis, shows approximately a 20 nm shift in the long wavelength maxima and an apparent decreased utilization of light in the wavelength region 600–650 nm. The quantum requirement for P.R. is high at wavelengths below 650 nm and decreases to a minimum between 705–720 nm; the best value obtained was 10. These observations indicate that this process is exclusively a photosystem I reaction and furthermore offer additional evidence for a lack of appreciable transfer of excitation energy between the pigments of photosystems I and II. The relatively high requirement photophosphorylation or to the inadequacy of H2‐hydrogenase system as the electron donor mechanism for photosystem I.
SEMICONDUCTION AND PHOTOCONDUCTION ACTIVATION ENERGIES OF THE RETINALS
Authors: Rosenberg Barnett , Harder Horold C.
Published: January 2008

Abstract ‐The semiconduction and photoconduction currents through 1‐ml thick sandwich cells of all‐trans‐, 13‐cis‐, 11‐cis‐retinal‐, and 13‐cis‐retinal‐m‐nitroaniline‐hydrogen chloride were measured as a function of the temperature in both the crystalline and melted states. From the slopes of graphs of the log of the current against 1000/TGK, the activation energies for semiconduction and photoconduction were calculated using the conductivity equations for the band model. The results of the average semiconduction activation energy measurements fell into two categories: The first group has activation energies between 1.9 and 2.4 eV and includes crystalline all‐trans‐, 13‐cis‐,9cis‐retinal, and both crystalline and melted 13‐cis‐retinal‐m‐nitroanaline hydrogen chloride; the second group has activation energies between 3.1 and 3.6 eV and includes crystalline 11‐cis‐retinal samples shorted. The average photoconduction activation energy for crysalline 13‐cis‐ and 11‐cis‐retinal, being 0.25 and 0.24 eV respectively, were essentially identical within experimental error, whereas the same parameter for 13‐cis‐retinal‐m‐nitroaniline hydrogen chloride was considerably lower at 0.15 eV. All‐trans‐retinal was not measurably photoconductive and 9‐cis‐retinal was only slightly photoconductive.
SOLVENT DEPENDENCE OF THE QUANTUM YIELD OF TRIPLET STATE PRODUCTION OF 9‐PHENYLANTHRACENE
Authors: Horrocks A. R. , Medinger T. , Wilkinson F.
Published: January 2008

Abstract— Values of φT, the quantum yield of triplet state production of 9‐phenylanthracene, have been determined in four different solvents by measuring the effects which ‘heavy atom quenchers’ have on the fluorescence intensity and the triplet state absorption of the solute. A variety of quenchers have been used including organic and inorganic halides and the rare gas, Xenon. There is a converse solvent dependence of φF and φT, and for each of the four solvents used φF+φT has been found to be unity within experimental error.
PHOTOBIOLOGIE DU MÉSOCOTYLE D'AVOINE‐III. DOUBLE EFFET DE LA LUMIÈRE BLEUE
Authors: Sandmeier M. , Nitsch J. P.
Published: January 2008

Abstract— Using excise sections of oat first‐internodes, a dual effect of blue light can be demonstrated on elongation when the sections are first irradiated in distilled H2O, then incubated with gibberellic acid (GA). At low light energies (230 ergs/cm2 per sec, for 2 min), a pretreatment with blue light enhances the GA effect above the elongation it can produce in the dark. At high energies (650 ergs/cm2/sec for 45 min), the same wavelengths cause an inhibition of the GA‐induced elongation. An action spectrum for the two effects show a maximum near 435 mμ in both cases. Neither light effect is visible when indoyl‐3‐acetic acid is used instead of GA. Several physiological effects distinguish the two blue effects. The promotive effect is most marked in the young regions of the mesocotyl, whereas the maximum inhibitive effect is located in slightly older tissues. Time‐course experiments showed that the promotive effect is partly due to an extension of the duration of elongation. The inhibitory effect is only temporary and vanishes about 30 hr after the beginning of the experiment. The promotive effect of blue light resembles the effect of far‐red light, but the former can be observed with gibberellins A2, A4, A5, A6 and A7 which are practically inactive after an irradiation with far‐red light. The inhibitory effect of blue light is different from the red‐light effect as shown by the time‐course experiments.
ON THE LUMINESCENCE OF L‐TRYPTOPHANE AND l‐TYROSINE IN AQUEOUS SOLUTION AT 77dK INDUCED BY X‐RAYS AND U.V.‐LIGHT
Authors: STEEN H. B.
Published: January 2008

Abstract— The lumincscence arising from L‐tryptophane and L‐tyrosine in aqueous solutions at 77d̀K during irradiation with u.v.‐light and with X‐rays has been studied. The spectra obtained with the two types of radiation were largely similar, differing only in that the yields of phosphorescence relative to fluorescence were considerably enhanced in the case of X‐irradiation. The decay times observed for the exponentially decaying phosphorescence, being 6.6 sec and 2.7 sec for tryptophane and tyrosine respectively, were the same for both kinds of irradiation. The G‐value of the X‐ray induced luminescence was about 10 for both tryptophane and tyrosine. Thus, about 30 per cent of the total energy absorbed from X‐rays in these compounds was re‐emitted as light.

It was concluded that the X‐ray induced fluorescence and phosphorescence originate from the same levels as does the luminescence caused by u.v.‐light, i.e. the lowest excited singlet and the lowest triplet level of the aromatic structure of these compounds. In the case of X‐irradiation the enhanced ratios between the yields of phosphorescence and fluorescence indicated that some process other than excitation directly from the ground state contributed considerably to the luminescence yields. Assuming this process to be a recombination between the ionized molecule and its electron, it was calculated that the contribution to the luminescence yield from excitations directly from the ground state relative to that from ionizations, was negligible for both compounds.
THE VARIATION OF RADIATION SENSITIVITY OF BACTERIA FED TETRAHYMENA PYRIFORMIS DURING THE GROWTH CYCLE AND FACTORS RELATED TO ITS ORIGIN
Authors: Calkins J.
Published: January 2008

Abstract— Tetrahymena pyriformis shows a cyclic variation of sensitivity (for lethality) to u.v. light while the response to X‐rays is almost constant throughout the growth (division to division) cycle. It is demonstrated in this paper, and elsewhere, that survival of caffeine treated animals is higher after higher doses than after the lower doses of radiation; such a response indicates that the increased radiation dose induces a resistant state not existing at lower doses. Response of synchronized animals to postirradiation treatment with caffeine is interpreted as indicating that recovery from the lethal effect of radiation has two components as previously postulated: (1) a caffeine sensitive recovery system (termed the ‘N’ system) and, (2) an activated recovery capacity (termed the 'T’ system) which is less sensitive to caffeine.

The maximum activated (T) system repair capacity only equals the repair capacity of the (N) non‐activated system for X‐ray induced lesions and, since the N system does not seem to show a cyclic variation of effectiveness for X‐ray induced lesions, the X‐ray survival remains constant throughout the growth cycle.

The repair capacity of the activated (T) repair system is, throughout most of the cycle and especially during the S period, much greater than that of the N system for u.v. induced lesions. Thus the u.v. response vanes in a manner largely dependent upon the capacity of the activated system and the fraction of the population showing the activated response; in G2, a time when the activated repair system is rather ineffective, the non‐activated (N) system appears to become unusually efficient in the repair of u.v. induced lesions.
THE REACTION OF METHYLENE WITH HYDROGEN
Authors: Powell‐Wiffen J. W. , Wayne R. P.
Published: January 2008

Abstract— An investigation has been made of the reaction between methylene, formed by the photolysis of ketene, and hydrogen. Ethane, ethylene and methane are the major hydrocarbon products, and it has been shown that the formation of these products may be adequately described by the sequence of processes

CH2CO +hv→ CH2+ CO (1)

CH2+ H2→ CH3+H (2)

2CH3→ C2H6 (3)

CH3+ H2+ CH4+ H (4)

CH2+ CH2CO → C2H4+ CO (7)

In particular, the relative rates of ethane and methane formation are consistent with the known rate constants for reactions (3) and (4), and it is not therefore necessary to postulate the participation of an ‘insertion’ process

CH2+ H2→ CH4 (6) to account for the formation of methane.

Decrease of the energy possessed by the methylene, either by increase of the wavelength of ketene photolysis, or by increase of gas pressure, is shown to result in an increase in the reactivity of the methylene towards ketene relative to its reactivity towards hydrogen (i.e. the ratio k2/k2 increases).
DECREASED SURVIVAL RESULTING FROM LIQUID‐HOLDING OF U.V.‐IRRADIATED ESCHERICHIA COLI C AND SCHZZOSACCHAROMYCES POMBE
Authors: Harm W. , Haefner K.
Published: January 2008

Abstract— Ultraviolet‐irradiated cells of E. coli C and of haploid wild type yeast Schizosac‐charomyces pombe, held in buffer at 22°‐25°C for various periods of time prior to plating, show a lower survival than those plated immediately after irradiation. This ‘negative liquid‐holding effect’ (NLHE) contrasts ‘liquid‐holding recovery’ (LHR), found in a number of other E. coli strains and in Saccharomyces cerevisiae. NLHE was observed at all u.v. doses tested. The effect is maximal at holding temperatures in the range 25–30°C, it is very small at 5°C and (in E. coli C) at 44°C. NLHE and LHR resemble each other in several respects. In E. coli both effects are inhibitable by the dark repair inhibitors acriflavine, caffeine and potassium cyanide. They do not occur in nutrient broth, and they are much reduced if the irradiated cells were illuminated with photoreactivating light before holding. NLHE in S. pombe shows characteristics similar to those observed in E. coli C. Mutations leading to increased u.v. sensitivity in E. coli C and S. pombe can alter the liquid‐holding response so that LHR is observed. Tetrad analysis of crosses between u.v.‐sensitive and u.v.‐resistant S. pombe strains indicates that a single chromosome region can control both u.v. sensitivity and liquid‐holding response. Several possibilities explaining NLHE are discussed. From current knowledge about dark repair processes and from the similarities between NLHE and LHR in E. coli it seems likely that the two effects reflect slight changes in the efficiency of dark repair.
DONOR FLUORESCENCE AS A PROBE OF ENERGY TRANSFER*,†
Authors: Pearlstein Robert M.
Published: January 2008

Abstract— When a system of N similar molecules (the donors) gives its excitation energy rapidly enough to a dissimilar acceptor, the donor fluorescence rate equals the energy removal rate. Analysis of donor fluorescence decay then provides information about the N‐donor system even if the acceptor is chemically unidentified. The dependence of the removal rate on N in a linear polymer in the extreme limit of very strong interdonor coupling is compared with that of very weak interdonor coupling. The principal result is that removal can be slower in the strong coupling limit because standing‐wave excitons tend to avoid boundaries. Possible application of the concept of standing‐wave excitons to photosynthetic units is discussed. The theory of diffusive energy transfer (very weak coupling limit) is also discussed, and some of its basic formulas given in simple form.
PHOTOSENSITIZED OXIDATION THROUGH STEARATE MONOMOLECULAR FILMS*
Authors: Schnuriger B. , Bourdon J. , Bedu Miss J.
Published: January 2008

Abstract— The photosensitized oxidations of rubrene by methylene blue and of diphenylan‐thracene by eosin have been studied where the sensitizer and the oxidizable substrate are separated by oxygen permeable layers of barium or cadmium stearate monomolecular films. The rate of the photosensitized oxidation reaction was followed by measurements of the hydrocarbon fluorescence, as a function of the stearate layer thickness. It has been found that the sensitized reaction is observable for thickness up to 500 Å and depends only on the deactivation process of the excited species (singlet oxygen) diffusing through the layers. It has been found also that half of the excited oxygen molecules are deactivated after a diffusion path of 115 A. The starting hydrocarbon can be regenerated by heating the sample after the photoreaction to approximately 120°C showing the transannular peroxide nature of the oxidation product.
PHOTOPROCESSES AND MOLECULAR ASSOCIATIONS*
Authors: Leterrier F. , Douzou P.
Published: January 2008

Abstract— The progressive reduction in temperature of hydro‐alcoholic mixtures is a way of associating aromatic molecules. It is possible to test the solute association, both by absorption and fluorescence measurements, of ‘polymerizable dyes' and solutes of biological interest. It is also possible to test the solute association by electron spin resonance of stable radicals (Wür‐ster's blue). The application of this technique to the study of photoprocesses was performed with flavin mononucleotide (FMN) by electron spin resonance and absorption spectroscopy in order to analyze the mechanism of photoreduction, and the stability of photo‐induced free radicals.

The procedure of associating molecules by temperature effect in these solvents can be applied to the spectroscopic studies of the triplet state of aromatics in glassy solutions at 77°K.
THE CHEMILUMINESCENCE OF INDOLE DERIVATIVES IN DIMETHYL SULFOXIDE*
Authors: BERGER A. W. , DRISCOLL J. N. , DRISCOLL J. S. , PIROG J. A. , LINSCHITZ H.
Published: January 2008

The chemiluminescent autoxidation of over fifty indoles has been measured in dimethyl sulfoxide (DMSO). The 3‐alkylindole derivatives represent the brightest and most efficient members of this group.

The chemiluminescence yield (per mole) of skatole is (1·5 ± 0·6) × 10‐3. The chemiluminescence spectrum of skatole is identical with the fluorescence spectrum of o‐formamidoacetophenone in the same environment Similar results for 2,3‐dimethylindole lead to the identification of the acylamide anion as the emitter in indole chemiluminescence. A peroxide ring cleavage excitation mechanism is proposed.
TRIPLET BEHAVIOR OF ORGANIC COMPOUNDS
Authors: GRIFFIN R. N.
Published: January 2008

Abstract— The rates of phosphorescence decay of nine compounds in frozen glass were measured. Six of the nine compounds decay exponentially, indicating that previously reported non‐exponential decay of some of them may have resulted from impurities, probably in the solvent.

Three compounds – acetophenone, phenanthrene, and acridine orange–have unusual decay kinetics. Acetophenone has no wavelength–dependence of rate, but the decay is non‐exponential at all observed stages. The effect is believed due to a multiplicity of metastable excited states, all of which ultimately decay through a common lowest triplet. The delayed emission of phenanthrene in frozen glass consists of phosphorescence and a P‐type delayed fluorescence in the dimer band only. The ratio of the rates of decay of phosphorescence and delayed fluorescence is nearly the same in frozen glass as it is in liquid solution. It is suggested that excimers can be formed by molecules up to 100 A apart, and that the description ‘excited dimer’ is misleading. Finally, acridine orange has a P‐Type delayed fluorescence which decays initially with second‐order kinetics. The first‐order kinetics generally observed in P‐type delayed fluorescence are merely the result of the relative importance of competitive unimolecular reactions in depopulation of the triplet state.
PHOTOREACTIONS OF ISORHODOPSIN AT LOW TEMPERATURES
Authors: PRATT D. C.
Published: January 2008

Abstract— The photoreactions of isorhodopsin, a synthetic visual pigment containing 9‐cis retinal, were studied between –45° and –75°C using flash photolysis. Light‐induced absorbancy changes were observed which were indistinguishable from those caused by the photo‐production of prelumirhodopsin from the natural visual pigment rhodopsin. It is concluded that isorhodopsin is converted to prelumirhodopsin although less efficiently than is the natural pigment. Thermally unstable intennediates of bleaching are also converted to pre‐lumirhodop‐sin by light, possibly by way of rhodopsin or isorhodopsin.
REVERSIBLE EPR PHOTOSIGNALS IN CHARGE‐TRANSFER‐COMPLEXES
Authors: ILTEN D. F. , KRONENBERG M. E. , CALVIN M.
Published: January 2008

Abstract— Various organic solutions were irradiated in a search for rapidly reversible EPR photosignals. Using an averaging technique, the rise and decay of the photosignals of CT‐complexes formed between chloranil and organic solvents were shown to be of the order of tens of msec. However, the mechanism involved could not be fully elucidated without additional data such as those obtained from flash photolysis and other techniques.
STABILIZATION OF SEMIQUINONE INTERMEDIATES IN THE PHOTOREDUCTION OF PHENANTHRENEQUINONE BY COMPLEX FORMATION
Authors: Rennert J. , Mayer M. , Levy J. , Kaplan J.
Published: January 2008

Abstract— The yellow color of 9,10‐phenanthrenequinone in alcohol solution is bleached under the influence of exciting radiation in a band of wavelengths extending from the ultraviolet to the visible green. The bleaching is due to a photoreduction of the quinone yielding 9,10‐dihydroxyphenanthrene. In the presence of certain divalent metal ions, irradiation of the quinoid material results in a blue‐green long lived intermediate which may be further photo‐reduced to the colorless 9,10‐diol. The blue‐green photo‐intermediate is a cation‐semiquinone complex.
THYMINE‐DIMER AND ACTION‐SPECTRUM EVIDENCE FOR INDIRECT PHOTOREACTIVATION IN ESCHERICHIA COLI*
Authors: Jagger John , Stafford R. S. , Snow Jeanne M.
Published: January 2008

Abstract— Cells of Escherichia coli B and B phr‐ were labeled with tritiated thymidine, exposed to inactivating ultraviolet radiation at 254 nm, given photoreactivation (PR) treatment immediately thereafter, and then immediately hydrolyzed and assayed for thymine‐containing dimers. It was found that (1) PR treatment of strain B phr‐ does not split thymine dimers and (2) the amount of splitting of thymine dimers in strain B at 334 nm is only 45 per cent of the amount of splitting observed at 405 nm for the same amount of biological PR. These findings show that all of the PR in E. coli B phr‐, and part of the PR at 334 nm in E. coli B, is indirect (does not use PR enzyme) and is not due to thymine‐dimer splitting.

Action spectra for PR in Escherichia' coli strains Bs‐1 and B/r were obtained. At wavelengths below 366 nm (the indirect PR region), PR is relatively much more efficient in strain B/r in logarithmic phase than in strain B/r in stationary phase or in strain Bs‐l. This is consistent with the expectation that indirect PR would not be exhibited by strains, such as Bs‐1 that lack dark‐repair ability, or by certain strains in the stationary phase, such as B/r, which, upon plating, have a ‘built‐in’ growth delay that can permit optimal dark repair, but indirect PR would be exhibited by intermediate cases, such as in strain B (which is less resistant to u.v. than strain B/r) or in strain B/r in logarithmic phase. These findings support the hypothesis that indirect PR results from enhancement of dark repair.
STUDIES ON FLAVINS IN ORGANIC SOLVENTS — III. SPECTRAL BEHAVIOUR OF LUMIFLAVIN
Authors: Kozioł Jacek
Published: January 2008

Abstract— The absorption and fluorescence emission spectra of lumiflavin have been studied in nonaqueous solvents of different polarity. The corrected emission spectra show apparent mirror symmetry to the longest wavelength absorption maximum. In view of high molar extinction coefficient of the longest wavelength maximum in absorption spectra, constant polarization of fluorescence across it in dioxane and high values of quantum yields of Buorescence, τ→τ* character of corresponding electronic transition was proposed. Roughly linear correlation was found between transition energies and quantum yields of fluorescence on the one hand, and polarity of solvents expressed in Kosower's ‘Z’ values (excepting acetic acid) on the other.

In preliminary experiments it was found that lumiflavin in dioxane and in acetic acid is strongly photodecomposed by the monochromatic(436 nm) light.
PHOTOOXYDATION SENSIBILISEE DE COMPOSES APPARENTES AUX CAROTENOIDES
Authors: Mousseron‐Canet Magdeleine , Dalle Jean‐Paul , Mani Jean‐Claude
Published: January 2008

Abstract— The sensftized photooxidation of methyl β ionylidene acetates (I) in methanol was studied. After reduction three products were isolated and their structures determined: a peroxide (II) and two isomeric alcohols (III and IV). The formation of (IV) is particularly interesting, its allenic structure being closely related to those of several important carotenoids.
THE NATURE OF THE LOWEST TRIPLET CONFIGURATION OF FLAVINS†
Authors: Kurtin William E. , Song Pill‐Soon
Published: January 2008

Abstract— The phosphorescence spectrum of riboflavin has been reexamined at 77°K in an ethylene glycol: water matrix. The phosphorescence occurs at approximately the 605 nm (ca. 2‐·05 eV) region, in reasonable agreement with the theoretical calculations of 1·6–1·8 eV [21]. The emission was found to be negatively polarized, and to have a relatively long lifetime (0·56 sec). On the basis of this data and additional theoretical results, it is concluded that the lowest triplet of riboflavin is of 3(τ,τ*) type. Upon addition of potassium iodide, the phosphorescence emission is enhanced through spin‐orbit perturbation. The presence of oxygen (atmospheric pressure) in the frozen glass apparently has no effect on the emission. The phosphorescence spectra of alloxazine are also presented. Results of the present work have been applied to the photodephosphorylation of menadiol diphosphate in elucidating its mechan ism involving the riboflavin triplet and singlet oxygen.
ACTION SPECTRUM FOR INACTIVATION OF THE INFECTIVITY OF POTATO VIRUS X BY U.V. RADIATION
Authors: KLECZKOWSKI A. , GOVIER D. A.
Published: January 2008

Abstract— Quantum yields for inactivation of infectivity of potato virus X by monochromatic ultraviolet radiation of wavelengths ranging from 230 to 290 nm, were measured with reference to energy absorbed by (a) the whole virus and (b) the virus RNA. The yields depended on the wavelength, but those with reference to energy absorbed by the RNA varied much less (with extreme values of 10‐3 and 1.9 ± 10‐3 than those with reference to whole virus. Consequently the action spectrum for inactivation of a dilute solution of the virus resembled the shape of the absorption spectrum of the RNA, but not closely enough to allow coincidence by adjusting the scales. The amount of photoreactivation increased as the wavelength increased and also as the year progressed from May to July; the extreme values of the photoreactivable sector were 0.43 and 0.86.
PHOTOCHEMICAL STUDIES OF THYMINE IN ICE*
Authors: RAHN R. O. , HOSSZU J. L.
Published: January 2008

Abstract— Solutions containing various concentrations of thymine have been irradiated (254 nm) at — 196°, and the corresponding absorbance changes at 315 nm due to thymine‐thymine adduct formation have been followed as a function of dose. The maximum yield of the adduct is about 3–2 per cent. Additional irradiation leads to a reduction in the yield of adduct and to an increase in the yield of the proposed trimer, which shows a sigmoid dose response curve. Not more than 10 per cent of the thymine is converted to trimer. Irradiation of the trimer in solution converts it into adduct plus thymine. Fluorescence due to the adduct does not appear directly after irradiation at — 196°, but comes about upon annealing at elevated temperatures (T > ‐ 80°).
A VARIABLE TEMPERATURE, U.V. LUMINESCENCE SPECTROGRAPH FOR SMALL SAMPLES
Authors: EISINGER J.
Published: January 2008

Abstract— A variable temperature spectrometer suitable for recording phosphorescence, fluorescence and luminescence spectra is described. The instrument has been chiefly used for emission spectroscopy at temperatures between 80° and 370°K but may be used for excitation spectroscopy as well. The samples are contained in quartz tubes with inside diameters of 1.5 mm and are generally optically thick at the excitation wavelength. The sample volume can be as small as 10μl. Absolute quantum yields may be obtained with ease and the use of phase sensitive detection makes it possible to record in 30 sec a fluorescence spectrum with 30 Å resolution and a quantum yield of 10‐‐4 with a signal to noise ratio of 20. The instrument has also been useful for photochemical irradiations.
EXCITED STATES OF SIX‐MEMBERED N‐HETEROCYCLES. FLUORESCENCE, PHOSPHORESCENCE AND ACID—BASE EQUILIBRIA OF ELECTRONICALLY EXCITED PHENAZINE
Authors: GRABOWSKA A. , PAKUŁA B.
Published: January 2008

Abstract— An account of a systematic study of the acid‐base equilibria of phenazine in the two lowest excited (π,π) states is presented. Pure electronic levels of the free base and of both its protonated forms have been located by spectroscopic methods. Fluorescence, phosphorescence and corresponding absorption spectra have been measured. The O‐O energies of the free base, of the singly‐protonated species and of the doubly protonated form in the lowest triplet state (3Lα(π, π)) are: 15, 475 cm‐1, 14, 175 cm‐1 and about 9300cm‐1, respectively. This last value has been estimated from the experimentally determined S‐T splitting in the other two forms. Corresponding energies of the lowest singlet state (ILα(π,π)) are: 23,500 cm‐1, 21,250cm‐1 and 17,300 cm‐1. The fluorescence of the free base has been found in polar as well as in non‐polar solvents and has been checked by the fluorescence excitation spectrum. Fluorescence quantum yields for the free base have been measured: 8.6 times 10‐4 and 3.0 × 10‐5 in ethanol and hexane solutions, respectively. Emission in ethanol has been ascribed to (π,π), that in hexane —to (π, π). fluorescence.

The changes of pKα's under excitation, calculated from the Forster's cycle, are equal: δpKa1=+2.8±0.3; δpKa11≅+10±1.5 in the lowest (π, π) triplet state and δpKa1=+4.8±0.5; δpKa11=+8.4 ± 0.5 in the lowest (π,π) singlet state. The δpKa11 in the triplet state is at least as high as that in the 1La(π, π) state. P P P calculations of the electronic levels and of the molecular diagrams have been performed. The energies obtained exceed experimental values by not more than 0.5 eV. An increase of the net charge on nitrogen δp under excitation has been found to be +50, +70 and +19 per cent in the 1La, 1Lb and 3La states, respectively. A good correlation has been found between δpKa1 and δp in both excited states, which have been studied experimentally.
ENERGY TRANSFER IN PHENANTHRENE‐DOPED NAPHTHALENE CRYSTALS
Authors: HUNTER T. F.
Published: January 2008

Abstract— Measurements at 77°K and room temperature are described on naphthalene crystals containing varying concentrations of phenanthrene. The lowest excited singlet and triplet states of phenanthrene iie between the singlet and triplet exciton bands of the host crystal. Triplet‐triplet annihilation in the host was studied by absorbing radiation purely into the guest molecules; the absence of any phosphorescence or delayed naphthalene fluorescence allowed the radiationless processes out of the naphthalene triplet to be discussed. Singlet‐singlet energy transfer was studied using radiation absorbed by the naphthalene. Two separate mechanisms of transfer were observed: (A) free exciton motion in the naphthalene band till encounter with a phenanthrene trap, the last step having an activation energy of 65 cm‐1, and (B) defect traps in the naphthalene transferring energy by a resonance mechanism to the phenanthrene; the average depth of the defect traps was calculated at 200 cm‐1.