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Measurements of electron transfer between singlet excited lipid-functionalized pyrene and alkyl-substituted dipyridinium cation have been carried out in the lipid-water interfacial region of both spread monolayers and vesicles. These studies have been conducted to evaluate the effects of limited dimensionality on the kinetics involved. It has been shown by monolayer compression studies that the rates of forward transfer in spread monolayers are sensitive to lipid organization and that the time-resolved quenching of pyrene fluorescence conforms well to Owen`s model for two-dimensional diffusion. The apparent dependence of the diffusion coefficient on surface pressure suggests some repositioning of CB{sup +} in the interfacial region at higher surface pressures. Flash photolysis measurements in vesicles demonstrate that electron transfer from the excited singlet state is more efficient than from the triplet. Further, the determination of back reaction shows both a short- and long-lived component for the reduced acceptor (CB) while the donor product cation (OPyPC{sup +}) disappears more quickly. This behavior indicates that the host lipid can act as a sacrificial donor for OPyPC{sup +}. 33 refs., 9 figs., 1 tab.

An optical spectrometer for the study of low level optical absorption and reflection of spread monolayers at the air‐water interface is described. This spectrometer is suitable for measurements at wavelengths from ∼350 to 800 nm and has a precision of ∼2×10−5 in terms of effective optical density. It employs a dual beam design utilizing fiber optic bundles to guide light and a multichannel photodiode array detection system. Instrumental control and data gathering are designed within Labwindows software. Representative spectral absorption data from chlorophyll a degradation kinetics are presented by way of illustration. Comparison of chlorophyll a reflection and absorption is also given.

Various methanofullerenes functionalized with either hydrophobic or polar groups have been synthesized. Studies of such compounds by surface pressure measurements and in situ UV-visible spectroscopy in Langmuir films show that these two types of functionalizations do not prevent the formation of aggregates at the nitrogen-water interface. Except for one compound studied in the present work, it appears that the aggregation occurs as soon as the spreading of the fullerenes solutions. However, the aggregates obtained appear to have different characteristics than those obtained with pure C{sub 60}. 26 refs., 9 figs., 2 tabs.

The 355 nm laser flash photolysis of argon-saturated pH 8 phosphate buffer solutions of the fluoroquinolone antibiotic flumequine produces a transient triplet state with a maximum absorbance at 575 nm where the molar absorptivity is 14,000 M(-1) cm(-1). The quantum yield of triplet formation is 0.9. The transient triplet state is quenched by various Type-1 photodynamic substrates such as tryptophan (TrpH), tyrosine, N-acetylcysteine and 2-deoxyguanosine leading to the formation of the semireduced flumequine species. This semireduced form has been readily identified by pulse radiolysis of argon-saturated pH 8 buffered aqueous solutions by reaction of the hydrated electrons and the CO2*- radicals with flumequine. The absorption maximum of the transient semireduced species is found at 570 nm with a molar absorptivity of 2,500 M(-1) cm(-1). In argon-saturated buffered solutions, the semireduced flumequine species formed by the reaction of the flumequine triplet with TrpH stoichiometrically reduces ferricytochrome C (Cyt Fe3+) under steady state irradiation with ultraviolet-A light. In the presence of oxygen, O2*- is formed but the photoreduction of Cyt Fe3+ by O2*- competes with an oxidizing pathway which involves photo-oxidation products of TrpH.

Various methanofullerenes functionalized with either hydrophobic or polar groups have been synthesized. Studies of such compounds by surface pressure measurements and in situ UV-visible spectroscopy in Langmuir films show that these two types of functionalizations do not prevent the formation of aggregates at the nitrogen-water interface. Except for one compound studied in the present work, it appears that the aggregation occurs as soon as the spreading of the fullerenes solutions. However, the aggregates obtained appear to have different characteristics than those obtained with pure C{sub 60}. 26 refs., 9 figs., 2 tabs.

A simple inexpensive device has been designed to measure the position of a flat surface to an accuracy of ±10 μm and has been applied to monitor water levels in studies of spread monolayers at the air‐water interface. This instrument provides for determination of surface location in a range intermediate between those accessible by physical methods and those requiring the much more expensive and difficult techniques of interferometry. This technique utilizes a sound transmitter operating at 45 kHz and simple microphones coupled to phase‐shift measurements via a phase‐to‐voltage converter.

The fluorescence and force-area behavior of chlorophyll a (Chl a) monomolecular films diluted with hydrocarbon on an aqueous subphase is reported. It is found that the diluent hexadecane, instead of conventional fatty alcohols, results in a substantial increase in the fluorescence yield of Chl a. The luminescence intensity varies nonmonotonically with respect to the intermolecular distance. A model for the mutual orientation of the chlorophyll pigments and the consequent energy transfer processes in terms of a Forster mechanism is proposed. For a random distribution of the Chl a molecules in the monolayer (k2 = 2/3) an average value of 43° is calculated for the angle between the molecular planes and the water surface. This model yields a value of 23 A for the Forster R0. Also, a value of 58° is derived for the angle between the Q-band transition moment and the line of intersection between the molecular plane and water surface. When a mixture of Chl a and Chl b in the monolayers is being excited at the absorption band of the latter pigment, typical fluorescence of Chl a is being detected. This sensitization process can also be interpreted in terms of the orientational model of the Chl molecules as presented in this work.

Etude des proprietes d'absorption et d'emission de 5 arylethylenes a groupes naphtyl-1, naphtyl-2 et phenyl en positions-1,2 dans des solutions aqueuses micellaires de laurylsulfate de sodium et de Triton X-100, ainsi que dans du methanol a temperature ambiante. Donnees sur la solubilisation dans les micelles

The fluorescence behavior of an amphiphatic oxacyanine dye and its thiacyanine analogue has been investigated in spread monolayers at the air-water interface. J-aggregate formation as a function of area/(dye molecule) was monitored by spectral changes in pure dye monolayers and in 1:1 mixtures of dye with various fatty acid coaggregates. Simultaneously, the thermodynamic behavior of these systems was characterized by the associated surface pressure-area isotherms. In all cases, J-aggregate formation may be related to a phase transition in the isotherm. The intensity of aggregate fluorescence is found to be inversely related to the work, ..delta..W, of compression of the monolayer through the transition. Inclusion of the fatty acid coaggregate was shown to facilitate J-aggregate formation in the order stearic > elaidic > oleic. Both fluorescence and thermodynamic data indicate more extensive aggregate formation in the thiacyanine systems. Aside from the paramount role played by the chromophore-chromophore interactions in determining J-aggregate phenomena, this study suggests important contributions from dispersion forces involving the long hydrocarbon moieties. 13 refs., 10 figs.

Ozone concentrations of 0.03 ppm are shown to initiate physical disruption of both oleic and linoleic acid spread monolayers in a few seconds. Approximately equal yields of water soluble products in nitrogen- and oxygencontaining environments as well as in the two acid systems suggest that the dominant reaction pathway involves direct attack on fatty acid double bonds and not oxidative chain reactions. A possible explanation for the observed loss of monolayer material is provided by the Criegee mechanism for ozonide rearrangement following ozone attachment to double bonds. In this scheme polar intermediates are generated which could pass into the aqueous subphase before recombination can occur. α-Tocopherol exhibits a protective effect only when present at a high fraction in the fatty acid monolayer (6 mole%). These systems provide an efficient elementary model for studying the physical effects of ozone on lipid membrane structure.

Oxidation of three closely related nickel (II) macrocyclic complexes Ni/sup II/(CR-2H), Ni/sup II/(CR), and Ni/sup II/(CR+4H) via anion radical reaction has been investigated by pulse radiolysis methods. While the initial oxidation products follow the form Ni/sup III/(L)(X/sup -/)(H/sub 2/O), in agreement with previous studies (L = macrocyclic ligand; X/sup -/ = Br/sup -/, SCN/sup -/), pH- and anion-concentration-dependent behavior provides evidence indicating subsequent formation of several other complexes Ni/sup III/(L)(X/sup -/)/sub 2/, Ni/sup III/(L)(OH/sup -/)(H/sub 2/O), Ni/sup III/(L)(OH/sup -/), and Ni/sup III/(L)(OH/sup -/)/sub 2/. The kinetics for interconversion among these species have been measured and are found in several cases to exhibit reversible behavior. In those cases the associated equilibrium constants have been determined. The formation of Ni/sup III/(L)(X/sup -/)/sub 2/ may be seen to depend on the degree of macrocyclic unsaturation and character of the anion. With the exception of the fully unsaturated CR-2H ligand, Ni/sup III/(L)(OH/sup -/) and Ni/sup III/(L)(OH/sup -/)(H/sub 2/O) and Ni/sup III/(L)(OH/sup -/)/sub 2/ decay via ligand radical formation at neutral pH and higher. Steady-state radiolysis results indicate introduction of an additional double bond into the ligand. At low pH, anion-substituted Ni(III) species return almost quantitatively to their parent Ni(II) complexes.

A laser photolysis study, on the nanosecond time scale, has been carried out on the major light-harvesting chlorophyll-protein complex of photosystem II (LHC II..beta..). The transient triplet absorption of the isolated LHC II..beta.. has been compared to those of its constituent chromophores in dilute micellar aqueous solutions, namely, chlorophyll a, chlorophyll b, chlorophyll a + chlorophyll b, and chlorophyll a + ..beta..-carotene. The results indicate that the carotenoid in the LHC II..beta.. is photosensitized by triplet chlorophyll a and that the decay of the transient triplet absorption exhibits two transients, one in the approx. 50-ns range and the other in the approx. 10..mu..s time scales. The former transient is light-intensity dependent and is attributed to an annihilation process between two triplets of chlorophyll a, while the latter is due to the decay of the triplet carotenoid to its ground state.

Oxidation of Ni(Me/sub 6/(14)-4,11-dieneN/sub 4/)/sup 2 +/, Ni(Me/sub 6/(14)aneN/sub 4/)/sup 2 +/, and Ni(Me/sub 6/(14)-1,4,8,11-tetraeneN/sub 4/)/sup 2 +/ by radiolytically generated OH,Cl/sub 2//sup -/,Br/sub 2//sup -/, and (NCS)/sub 2//sup -/ has been studied by spectral and chemical methods. In each case, oxidation produces intermediates characterized as Ni(III) complexes. Transient spectra of the intermediates formed by anion radical reaction strongly resemble spectra of Ni(III) analogues produced in nonpolar solvents with absorption bands in the region 300 to 400 nm. The decay rates of such intermediates depend on the anion radical used and may vary by 3 orders of magnitude (k approx. = 1-(3 x 10/sup 3/)s/sup -1/), indicating involvement of the associated anion in the intermediate oxidation product. Hydroxyl radical reactions with Ni(Me/sub 6/(14)-4,11-dieneN/sub 4/)/sup 2 +/ and Ni(Me/sub 6/(14)aneN/sub 4/)/sup 2 +/ generate intermediates with absorption peaks in the region 535 to 550 (epsilon approx. 10/sup 3/M/sup -1/cm/sup -1/). Decay of intermediates generated by anion radicals yields stable transients with spectra comparable to those produced directly via OH. These processes precede formation of final products. Mechanisms for product formation from Ni(III) intermediates suggest the involvement of base-assisted hydrolysis.

The emission spectrum of N-(5-(dimethylamino)naphthalene-1-sulfonyl)dihexadecylamine (dansyldihexadecylamine) in monolayers at the air-water interface has been studied. In some cases sudden shifts in the dansyl emission can be correlated with particular features of the surface pressure-area isotherms. These spectral shifts can be explained in terms of a change in the conformation of the head group on the surface and with aggregation of the dansyldihexadecylamine. In other cases the dansyl emission shows a blue shift with increasing compression that can be associated with reduced head-group hydration.

The three parameters, fluorescence polarization ( P ), relative quantum yield ( ϕ ), and lifetime ( T ) have been reinvestigated for solutions of chlorophyll b in lecithin as a function of concentration. All three show different concentration dependence, of which the depolarization only, may be described by a simple single step energy transfer. It is proposed that the self-quenching occurs when nonfluorescent pairs of molecules are excited directly, and that the reduction in lifetime is a result of energy transfer through the bulk solution to such 'pairs’ or other quencher. The origin of these ‘pairs’ of molecules may be shown to be purely statistical. The apparatus used for measurement of fluorescence lifetimes is described.

The effects of aggregation and of added radical scavengers on radiation-induced peroxidation in fatty acid soap solutions have been examined using linoleic, linolenic and arachidonic acids. Conjugate formation monitored by UV absorption at 232 nm was used as a measure of initial hydroperoxide formation. The dependence of hydroperoxide yield on soap concentration in these systems and yields in mixed micelles suggest that configuration of the unsaturate moieties may play a significant role in determining peroxidative reaction chain length. Evidence is given from several competition measurements and from effects of added S2O 8 2− that the predominant chain initiating radical in these systems is OH. Solubilization of alcohols, especially tert-butanol, by soap aggregates results in little reduction of conjugate diene formation indicating that alcohol radicals within the micellar pseudo-phase may initiate peroxidative processes. Introduction of α-tocopherol into linoleate aggregates sharply inhibits hydroperoxide yield even at molecular concentrations relative to soap of 1:104.

With pulse radiolysis techniques it is possible, on the nanosecond time scale, to generate a non-equilibrium distribution of transient species whose interactions with micellar media may be characterized in kinetic terms. Because of the wide variety of species that can be produced in this manner, such investigations have been shown useful in the study of (a) counterion-surface interactions, (b) monomer-micelle dynamics (c) substrate-micelle distributions. Further the effects of a heterogeneous environment on processes involving biologically important compounds have also been studied by pulse radiolysis in micelles. A brief review of this approach to micelle kinetics is given here.

The time resolved behavior of pyrenedecanoic acid excimers in spread phospholipid monolayers at the air-water interface is reported herein. Interactions of the pyrene-bearing probe, 1-pyrenedecanoic (PDecA) have been compared as functions of probe concentration and hydrocarbon structure of the host liquid to the character of the lipid environment. The time resolved fluorescence measurements of mixed PDecA-lipid monolayers exhibit two features at 480 nm: a very fast rise in excimer intensity and a dependence of the excimer decay on PDecA mole fraction in the layer. 9 references, 3 figures.

The radiosensitivity of the E. coli fatty acid auxotroph K-1060 has been shown to increase with the number of carbon-carbon double bonds in the fatty acid used in the growth medium. This increase applies to bacteria irradiated under both anoxic and oxic conditions. It is suggested that the primary mechanism underlying these observations may involve a slow postirradiation peroxidative process.