PURPLE MEMBRANE ANALOGS SYNTHESIZED FROM C17 ALDEHYDE

Abstract— All- trans , 11- cis and 9- cis isomers of the C₁₇ aldehyde analogs of retinal bound with purple membrane apoprotein, probably through a Schiff base linkage at the normal retinal binding site. The complex formed from C₁₇ aldehyde and purple membrane apoprotein was slowly decomposed by 10m M hydroxylamine. The C₁₇ aldehyde competitively inhibited the regeneration of purple membrane from all- trans -retinal and purple membrane apoprotein. The differential ability of the different isomers to inhibit the regeneration suggests that purple membrane has a binding site for the side chain of retinal in addition to the Schiff base binding site.     

PREPARATION AND PHOTOPHYSICAL STUDIES OF PORPHYRIN-C60 DYADS

Abstract Porphyrin-C₆₀ dyads in which the two chromophores are linked by a bicyclic bridge have been synthesized using the Diels-Alder reaction. The porphyin singlet lifetimes of both the zinc (Pz_n-C₆₀) and free base (P-C₆₀) dyads, determined by time-resolved fluorescence measurements, are ≦17 ps in toluene. This substantial quenching is due to singlet-singlet energy transfer to C₆₀ The lifetime of Pzn-¹C₆₀ is -5 ps in toluene, whereas the singlet lifetime of an appropriate C₆₀ model compound is 1.2 ns. This quenching is attributed to electron transfer to yield P_zn^bull;+-C₆₀^bull;-. In toluene, P-¹C₆₀ is unquenched; the lack of electron transfer is due to unfavorable thermodynamics. In this solvent, a transient state with an absorption maximum at 700 ran and a lifetime of-10 μs was detected using transient absorption methods. This state was quenched by oxygen, and is assigned to the C₆₀ triplet. In the more polar benzonitrile, P-¹C₆₀ underoes photoinduced electron transfer to give P^•+-C₆₀^bull;-. The electron transfer rate constant is −2 × 10¹¹ s⁻¹.     

C4-CYCLODIMERS OF PSORALEN ENGAGING THE 4'',5''- DOUBLE BOND

Abstract— By irradiating psoralen (the parent linear furocoumarin) in thin solid film two new fluorescent photodimers. compounds I and II, have been isolated and characterized. Unlike previously isolated dimers of furocoumarins which showed a 'pyrone-pyrone' structure involving in the C₄-cycloaddition the 3,4-double bond of the furocoumarinic moiety, the new dimers show respectively a 'furan-furan' and a 'furan-pyrone' structure, involving therefore the 4',5'-double bond. By analogy with the photocycloaddition reactions between furocoumarins and pyrimidine bases of DNA, in this case too the 4',5'-double bond of the furocoumarin can be involved. The experimental conditions, however, in which irradiation is carried out play an important role.     

THE EFFECT OF DIFFERENT TYPES OF FLUORESCENT LIGHTING ON REPRODUCTION AND TUMOR DEVELOPMENT IN THE C3H MOUSE

Abstract— The effect of three different fluorescent lighting systems on the growth, reproduction, and lifespan of the C₃H/HeN(MTV) mouse has been investigated. The mice were born, weaned, and paired under luminaires containing daylight-simulating (DS; 425 μW/cm²), cool-white (CW; 425μW/cm²) or pink (PK; 234 μW/cm²) fluorescent lights. At the end of the study (19 months), 97% of the females in the DS and CW groups and 100% of females in the PK group had developed mammary tumors. The median times for mammary tumor development were 51 weeks (DS), 47 weeks (CW) and 42 weeks (PK) The median age of the dam at first litter and the median time between the first and second litters were not significantly different for the three lighting conditions. However, there was some evidence that the first litter was significantly delayed in both the CW and PK groups compared to the DS group. There were no significant differences in the total number of litters/dam, the total number of pups/dam, the neonatal mortality of the pups (at birth or weaning), the weights of the pups at weaning or the sex ratios among the three lighting groups. The growth of the male mice was the same under all three lighting conditions. The observed differences in tumor latency and reproduction, between female mice exposed to the DS and CW fluorescent lights, may be related to the different spectral energy distributions of these lighting systems since their irradiances were the same.     

THE PHOTOPHYSICAL PROPERTIES OF SOME C15 LUPINE ALKALOIDS:

Abstract Sparteine, the tetracyclic saturated amine alkaloid, is highly fluorescent in n-hexane solution (Φ_f= 0.64; ζ= 63 ns) and has a large Stokes shift [λ_max (abs) = 203 nm; λ_max (fluor) = 325 nm]. Its isomer, α-isosparteine, has similar properties: Φ_f= 0.55; ζ_f= 50 ns; λ_max (fluor) = 338 nm. Oxidized derivatives, such as lupanine, thermopsine, and α-diplospartyrine, are weakly fluorescent. Based on a comparison with spectroscopic and photophysical properties of the monoamine, quinolizidine, it is concluded that the excitation energy is delocalized over the two N-atoms in starteine and a-isosparteine. The self quenching rate constant for sparteine, ca. 1 times 10⁷M^-1 s^-1, is about 100 times smaller than that for quinolizidine, consistent with excited state derealization. The significant fluorescence quenching in lupanine is rationalized by the fact that N-methyl-2-piperidone mfe/molecularly quenches the fluorescence of quinolizidine at nearly the diffusion controlled rate in -hexane. Comparisons are made with the fluorescence properties of other diamines such as N, N'-dimethylbispidine and N, N'-disubstituted piperazines.     

TWENTY-TWO CARBON HOMOLOGUE OF 11-CIS RETINAL. PHOTOPHYSICAL AND PHOTOCHEMICAL PROPERTIES

Abstract— Results concerning absorption-emission spectra and fluorescence quantum yields at 77 and 298K. triplet absorption spectra, and quantum yields of intersystem crossing and photoisomerization at 298 K, are presented for 11- cis β-apo-14'-carotenal (C₂₂-Ald), the immediate higher homologue of 11- cis retinal. The absorption spectra are characterized by two band-systems with maxima at 390–400 and 270–280 nm, respectively. Upon cooling from 298 to 77 K, the intensities of these two band-systems undergo changes in opposite directions indicating 12-s- cis: 12- s-trans conformational changes. No intermediate band-system analogous to the one located at 270–310 nm in cis retinals is observed for 11- cis C₂₂-Ald. In nonpolar hydrocarbon solvents (e. g. cyclohexane) at room temperature, quantum yields of fluorescence (0.01), intersystem crossing (0.6) and photoisomerization (0.4) are all quite pronounced. The photophysical and photochemical properties of 11- cis C₂₂-Ald are discussed in the light of similarities and dissimilarities with those of all- trans C₂₂-Ald and 11- cis retinal under comparable conditions.     

AN 125I-LABELED N6-SUBSTITUTED AZIDO ANALOG OF NAD+ FOR THE PHOTOAFFINITY LABELING OF NAD+-LINKED ENZYMES

Abstract ¹²⁵I- N ⁶-(N-[6-N-{5-iodo-4-azidosalicyl}-aminohexyl]-aminocarbamoylmethyl)-nicotinamide adenine dinucleotide (¹²⁵I- N ⁶-I-ASA-AH-NAD⁺) was synthesized by coupling N ⁶ -([6-aminohexyl]-carbamoylmethyl)-NAD⁺ with 4-azidosalicylic acid N-hydroxysuccinimide ester followed by radioiodination. The utility of ¹²⁵I-N ⁶ -I-ASA-AH-NAD⁺ as an effective site-directed photoprobe was demonstrated by the photolabeling of both glutamate dehydro-genase and 15-hydroxyprostaglandin dehydrogenase. Both enzymes can be saturated with labeled probe with apparent dissociation constants comparable to those reported for NAD⁺. Photoincorporation of the probe into both enzymes was found to be protected specifically by NAD⁺. These results indicate that ¹²⁵I- N ⁶-I-ASA-AH-NAD⁺ can be a specific photoprobe for NAD⁺-linked enzymes.     

ELIMINATION OF THE EFFECT OF CONTAMINATING CO2 IN THE 18O-LABELING OF THE CO2 PRODUCED IN BIOLUMINESCENT REACTIONS

Abstract— Although the mechanism of bioluminescent reactions in various species, such as fireflies, ostracod crustaceans ( Cypridina ), sea pansies ( Renilla ), and the deep-sea shrimp Oplophorus , are thought to involve dioxetanone intermediates, studies reported in the past from different laboratories have included widely different experimental results, most likely due to various factors including the effects of contaminating CO₂. With the improved technique employed in the present study, bioluminescent reactions of the firefly and Cypridina in ¹⁸O₂ gas resulted in an incorporation of over 75% of ¹⁸O into one oxygen of the product CO₂. with a reproducibility within a few per cent. When ¹³CO₂. instead of the product CO₂ of the bioluminescent reaction, was studied in an H₂¹⁸O medium, the exchange of one oxygen of ¹³CO₂ with H₂O was 64%. and the effect of contaminant CO₂ amounted to 1418% of the total CO₂. These results suggest that every molecule of CO₂ formed in the bioluminescent reactions of the firefly and Cypridina had intially contained 1 oxygen atom derived from O₂.     

PHOTOCHEMISTRY OF trans-[Rh(BIS(DIPHENYLPHOSPHINO)ETHANE)2X2][PF6]: TRANSIENT ABSORBANCE KINETIC STUDIES OF METAL-HALOGEN BOND HOMOLYSIS

Abstract— Laser flash photolysis of trans -[Rh(dppe)₂X₂][PF₆] (X=Br and I; dppe=bis(diphenylphosphino)ethane) in CH₂Cl₂ or CH₃CN produces the d⁷ Rh(II) radicals, [Rh(dppe)₂X]⁺, and halogen atoms. The kinetics of the disappearance of [Rh(dppe)₂X]⁺ radicals in CH₂Cl₂ or CH₃CN were mixed order: H-atom abstraction from solvent to produce the rhodium hydrides, [RhH(dppe)₂X][PF₆], and Rh/X recombination. In the poor H-atom donor solvent, benzonitrile, Rh/Br recombination was observed to be uncomplicated by competing H-atom abstraction. The hydride complexes [RhH(dppe)²X][PF₆], formed by H-atom abstraction were completely characterized by ³¹P{¹H}-NMR, ¹H-NMR, and mass specrometry. Cyclohexene was used as an effective trap for photogenerated Br atoms and yielded bromocyclohexane and 3-bromocyclohexene in a relative yield, 1:9. The photochemical mechanism is discussed in light of the transient absorbance and trapping studies.     

PHOTOLYSIS OF AQUEOUS SOLUTIONS OF POTASSIUM CIS-DIAQUOBIS (OXALATO) CHROMATE (III)

Abstract— The photolysis of aqueous solutions of cis -[Cr(C₂O₄)₂(H₂O)₂]- at 254 nm and pH 4 produced CO₂ and H₂ in nearly equal yields. The quantum yield of hydrogen, φ², increased by 9% and the yield of carbon dioxide, φ, by 65% as the pH was lowered from 4 to I. The total gas yield, φ_gas, decreased in the presence of added oxalate or chromium (II) ions and when the light intensity was lowered. The gas yield in D₂O was appreciably higher than in H₂O. The variation of φ_gas with pH (D) and with added oxalate ion was roughly parallel in the two liquid media. The gas yield increased in the series:
A tentative mechanism is suggested to explain the results.     

THE GECKO OPSIN: RESPONSES TO GEOMETRIC ISOMERS OF RETINAL and 3-DEHYDRORETINAL

Abstract— The opsin of the visual pigment (P521) of the Tokay gecko rapidly regenerates four spectrally different photopigments with the 9-cis and 11-cis isomers of both the vitamin A,- and A₂-aldehydes. The opsin displays the classic stereospecificity for both A₁- and A₂-series of isomers. The two photopigments regenerated with 9-cis- and ll-cw-3-dehydroretinals respond to chloride and nitrate ions as do the comparable pigments formed with 9-cis- and 11-ris-retinal. The result is a family of pigments absorbing with spectral maxima ranging from 464 to 540 nm, a span of some 3000 cm^-1. The photosensitivity of all four pigments was determined and found to be in relative order: 100% (11-cis-A₂), 77% (11- cis -A₂), 36% (9- cis -A,) and 14% (9- cis -A₂).     

REEVALUATION OF THE SPECTRAL AND KINETIC PROPERTIES OF HO2 AND O2- FREE RADICALS

Abstract— The spectra and molar absorbances of the HO₂ and O₂^- free radicals have been redetermined in aqueous formate solutions by pulse and stopped-flow radiolysis as well as by ⁶⁰Co gamma-ray studies. The extinction coefficients at the corresponding maxima and 23°C are ²²⁵= 1400 ± 80 M ^-1 cm^-1 and ²²⁵= 2350 ± 120 M ^-1 cm^-1 respectively. Reevaluation of earlier published rate data in terms of the new extinction coefficients yielded the following rate constants for the spontaneous decay of HO₂ and O₂^-: K _Ho2+HO2= (8.60 ± 0.62) × 10⁵ M ^-1 s^-1; K _Ho2+O2-= (1.02 ± 0.49) × 10⁸ M ^-1 s^-1; K _Ho2+O2- < 0.35 M ^-1 s^-1. For the equilibrium HO₂→ O₂^-+ H⁺ the dissociation constant is K _Ho2= (2.05 ± 0.39) × 10^-5 M or p K _HO2= 4.69 ± 0.08. G (O₂^-) has been evaluated as a function of formate concentration.     

THE ABSOLUTE VALUE OF THE REACTION RATE CONSTANT OF BILIRUBIN WITH SINGLET OXYGEN IN D2O

Abstract— The chemical reaction rate constant of bilirubin with singlet oxygen in basic aqueous solution has been redetermined to be 3.5 × 10⁸ M^-1 s^-1 by a competitive technique using a 1,3-diphenylisobenzofuran in sodium dodecyl sulfate micelles. Bilirubin also physically quenches a singlet oxygen with a rate constant of 9 × 10⁸ M ^-1 s^-1. The lifetime of singlet oxygen in D₂O solution has been determined to be 35 μ s . The absorption cross-section for the molecular oxygen ³∑_g-→¹δ _g + 1 v electronic transition at 1.06μn in aqueous solution is unexpectedly larger than the gas paase cross-section.     

TRIPLET STATES AND cis-trans PHOTOISOMERIZATION PROCESSES IN THE SCHIFF BASES OF RETINAL ISOMERS

Abstract —The triplet states of the n -butyl-amine Schiff bases of 11- cis , 9- cis , 13- cis and all- trans retinal are produced via triplet-triplet energy transfer. Their absorption spectra, peaking around 435 nm, and their decay kinetics are recorded using pulsed-laser photolysis. Direct-excitation (φ^D_ISO) and triplet-sensitized (φ^T_ISO) photoisomerization yields, determined using steady irradiation methods, are found to be: φ^T_ISO (9- cis ) = 0.06, φ^T_ISO (11- cis ) = 045, φ^T_ISO (13- cis ) = 008, φ^T_ISO (all- trans ) = 0.02-0.05, φ^D_ISO (11- cis , = (4 ± 1) × 10^-3, φ^D_ISO (all- trans ) = (2 ± 1) × 10^-3. The possible role of the triplet state in the isomerization of rhodospin is discussed.     

PHOTOINACTIVATION OF A Chlamydomonas MUTANT(NL–11) IN THE PRESENCE OF METHIONINE: ROLES OF H2O2 and O-2

Abstract— A mutant of Chlamydomonas reinhardtii (NL–11) isolated from a wild type (137c+) was inactivated in the light in the presence of methionine at concentrations where the wild type was not inactivated. The inactivation was suppressed by either catalase or superoxide dismutase (SOD). Light-induced H₂O₂ formation and nitroblue tetrazolium (NBT) reduction inNL–11 were greater than those in the wild type. Methionine stimulated both the H₂O₂ formation and the NBT reduction inNL–11 as well as the wild type. The light-induced NBT reduction inNL–11 in the presence of methionine was partially suppressed by externally added SOD suggesting the participation of O^-₂. These results suggest that the hypersensitivity ofNL–11 to methionine in the light is due to stimulated formation of H₂O₂ and O^-₂.     

THE REACTION OF METHYLENE WITH HYDROGEN

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).     

SEARCH FOR SINGLET OXYGEN LUMINESCENCE IN THE DISPROPORTIONATION OF HO2/O2

Abstract— During the reaction HO₂+ HO₂ (or O₂^-) = H₂O₂+ O₂ in aqueous solution, no luminescence in the region 620–720 nm, expected if the product O₂ were formed in a singlet state, could be detected. If any singlet O₂ is formed, its yield must be less than 10%. Faint luminescence, sometimes found at shorter wavelengths, was shown to arise from reaction of HO₂ with impurities in the reagents present.     

THERMOLUMINESCENCE EVIDENCE FOR CHLORIDE REQUIREMENT IN THE S2→S3 TRANSITION OF THE WATER-SPLITTING SYSTEM

Abstract— The role of chloride in photosynthetic oxygen evolution was investigated by means of thermoluminescence measurements. It was found that chloride depletion in isolated chloroplasts almost completely abolished the B₁ thermoluminescence band (S₃Q_B⁻ recombination) but diminished only slightly the amplitude of the B₂ band (S₂Q_B⁻ recombination). The B₂ band could be excited to full intensity by the first flash of a flash series and subsequent flashes caused no further change in the amplitude of the band. These observations suggest a block in the S₂→S₃ transition of the water-splitting system in chloride-depleted chloroplasts. Readdition of chloride provided evidence that the inhibitory effect of chloride removal is reversible.     

THE ROLE OF O2- IN THE CHEMILUMINESCENCE OF LUMINOL*

Abstract— The chemiluminescence of luminol in buffered aqueous solutions is inhibited by superoxide dismutase. This occurs whether the luminescence is induced by ferricyanide, persulfate, hypochlorite, or by the action of xanthine oxidase on xanthine. Since superoxide dismutase inhibits reactions which involve O₂^-, we conclude that this radical is a constant factor in the chemiluminescence of luminol in aqueous solutions. The kinetics of light production are discussed in terms of hypothetical mechanisms that fit the available data. The strong luminescence of luminol in aprotic solvents or in aqueous systems containing relatively high concentrations of H₂O₂ could not be explored in this way, because superoxide dismutase is inactive under such conditions.     

CALCULATED RATES AND EQUILIBRIA OF THERMAL INTERCONVERSION OF TRIPLET (3g-) AND SINGLET (1Δg and g+) MOLECULAR OXYGEN

Abstract— From spectroscopic data and rate constants in the literature, equilibrium constants and rates of thermal formation of singlet oxygen (¹Δ_g and ¹Σ_g⁺) were calculated for a number of conditions. For the gas phase we estimate K _eq(¹Δ_g³Σ_g^-) = 1.67 exp(-94.31 KJ/RT) and K _eq(¹Σ_g⁺/³Σ_g^-) = 0.33 exp(-157.0 KJ/RT). The calculated rate constants for the ³Σ_g⁺→¹Δ_g transition of O₂ at 25°C varied from 2.5 × 10^-11 s^-1 in water to 4.8 × 10^-16 s^-1 in air, assuming equal solvent interactions with the ground and excited states. Physical quenchers for singlet oxygen are expected to be catalysts for its thermal formation. Equations are presented which allow one to estimate whether such catalysis by quenchers will result in a pro-oxidant effect.