Triplet excited states of pyrene, phenanthrene, and naphthalene have been prepared in zeolite KY by pulsed laser excitation and the influence of coadsorbed water on quenching of these triplet states by ferrocene and the immobile ferrocene derivative ferrocenylmethytrimethylammonium cation (FcMN) has been studied by transient absorption spectroscopy. To make these measurements, probe loadings in KY have been kept deliberately low such that quenching involves migration of molecules from one supercage to another. In all cases, maxima in bimolecular triplet quenching rates versus the number of H 2 O per supercage (N sc ) were observed at N sc ≈ 4, a value which coincides with the number of H 2 O molecules that fill the sodalite cages. For pyrene quenching by FcMN, the effect of 4 H 2 O/sc was particularly dramatic, where the quenching rate increased by 3 orders of magnitude relative to dehydrated KY. Above N sc ) 4, further additions of H 2 O lowered the rate of quenching. The rate of triplet quenching by FcMN, where quenching results from motion of the aromatic probes in their triplet state to FcMN, generally followed the trend 3 Np* > 3 Ph* . 3 Py*. This trend, as well as the influence of coadsorbed H 2 O on quenching, have been explained by the effects of adsorption and molecular size on diffusion of these molecules in KY.

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Of current interest in our laboratory is the nature of photoinduced processes in the cavities of zeolites completely submerged in polar solvents, or polar-solvated zeolites (PSZ). The present study addresses the nature of electron trapping in PSZ with emphasis on the zeolites NaX and NaY. Free electrons were generated by two-photon, pulsed-laser excitation of either pyrene or naphthalene included in zeolite cavities. Trapped electrons were monitored by diffuse transmittance, transient absorption spectroscopy at visible wavelengths. In anhydrous alcohols, electron trapping by Na(4)(4+) ion clusters was observed in both NaX and NaY. The resulting trapped electrons decayed over the course of tens of milliseconds. No evidence for alcohol-solvated electrons was found. More varied results were observed in solvents containing water. In NaX submerged in CH(3)OH containing 5% or higher water, species having microsecond lifetimes characteristic of solvated electrons were observed. By contrast, a 2 h exposure of NaY to 95/5 CH(3)OH/H(2)O had no effect on electron trapping relative to anhydrous CH(3)OH. The difference between NaX and NaY was explained by how fast water migrates into the sodalite cage. Prolonged exposure to water at room temperature or exposure to water at elevated temperatures was necessary to place water in the sodalite cages of NaY and deactivate Na(4)(4+) as an electron trap. Additional studies in NaY revealed that solvent clusters eventually become lower energy traps than Na(4)(4+) as the water content in methanol increases. In acetonitrile-water mixtures, electron trapping by Na(4)(4+) was eliminated and no equivalent species characteristic of solvated electrons in methanol-water mixtures was observed. This result was explained by the formation of low energy solvated electrons which cannot be observed in the visible region of the spectrum. Measurements of the rate of O(2) quenching in anhydrous solvents revealed rate constants for the quenching of ion cluster trapped electrons that were 2-4 times higher than that for pyrene triplets. In NaX, the rate constant in methanol was 10(4) times smaller than that in cyclohexane, showing greater inhibition of O(2) reactivity in the medium of PSZ. The results of this study point out the conditions under which Na(4)(4+) is active as an electron trap in PSZ and that water must be present in the sodalite cage to produce solvated electrons in the supercage.

The interaction of bovine prothrombin with phospholipids was measured, using as the lipid source monolayers spread at the air-buffer interface. Fluorescence spectroscopy was implemented to determine the equilibrium concentration of free prothrombin in the aqueous subphase of the protein-monolayer suspensions, in a continuous assay system. The increase in surface pressure (pi) from the protein-monolayer adsorption was also measured and, with values of the adsorbed protein concentration (c[s]), was used to calculate dc(s)/d(pi). At a particular phosphatidylserine (PS) content of liquid-expanded (LE) phosphatidylcholine (PC)/PS monolayers, dc(s)/d(pi) was independent of the initial surface pressure (pi[i]), when this latter value exceeded 30 mN/m. However, dc(s)/d(pi) varied significantly with the relative PS content of the monolayer. Values of the equilibrium dissociation constants calculated from the concentration dependence of delta(pi) indicated that the affinity of prothrombin for LE monolayers was higher at higher PS contents and lower packing densities. The affinity of prothrombin for liquid-condensed (LC) PC/PS monolayers was found to be much weaker relative to LE monolayers of similar phospholipid composition. This approach, employing spread monolayers to study prothrombin-phospholipid binding, coupled with a simple and accurate method to determine the free protein concentration in protein-monolayer suspensions, offers significant advantages for the investigation of protein-membrane interaction. The equilibrium characteristics that describe the interaction of prothrombin with the different phospholipid monolayers under various conditions also provide support for previous results which indicated that hydrophobic interactions are involved in the adsorption of vitamin K-dependent coagulation and anticoagulation proteins to model membrane systems.

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The photoinduced generation of pyrene cation radicals (Py+·) has been examined as a function of oxygen pressure in the internal cavities of the zeolites NaX and NaY. Excitation of pyrene was carried out at ultraviolet wavelengths by utilizing either a pulsed laser or a steady-state arc lamp. For lamp-irradiated samples, the generation of long-lived Py+· was monitored during the course of irradiation by visible-wavelength absorption spectroscopy. In dehydrated NaX (dNaX), irradiation of pyrene in the presence of 0.01−1 bar O2 produced an approximately 10-fold increase in the yield of Py+· relative to samples irradiated under evacuated conditions. By contrast, when pyrene was irradiated in dehydrated NaY (dNaY), no increase in Py+· yield was observed at any O2 pressure relative to evacuated conditions. However, in hydrated NaY, O2-induced increases in Py+· yield were observed, while no similar increases were observed in hydrated NaX. Following laser excitation of samples, the yield, stability, and reactivity of Py+· were monitored by transient absorption spectroscopy. The transient studies revealed differences in the yield of Py+· that were in accord with the lamp studies, but only when the effects of O2 on two-photon ionization were properly accounted for. An efficient back-reaction of Py+· with superoxide (O2 - •) is postulated in hydrated NaX, to account for the absence of Py+· in the lamp studies. A direct excited-state electron-transfer mechanism (type I) is favored for the O2-induced generation of Py+· in zeolites, and it is supported by results which rule out mechanisms involving singlet oxygen and the reaction of O2 with trapped electrons that would otherwise recombine with Py+·. Comparisons of the fluorescence spectrum and lifetime of pyrene in dNaX and dNaY show that pyrene encounters a microenviroment of unusually high polarity in dNaY. It is suggested that the highly polar interaction is related to the electrophilicity of dNaY and is characteristic of a type of charge-transfer interaction that draws electron density from pyrene and prevents the excited state from donating an electron to O2. Such an interaction does not occur in dNaX, which is known to be less electrophilic or more electronegative than dNaY. In hydrated NaY, the presence of water weakens the strongly polar interaction and allows the electron transfer to occur. This study illustrates an important difference between zeolites that vary in electronegativity and how photoinduced charge separation involving neutral molecules is affected by hydration of the zeolite.

Spread phospholipid monolayers are particularly useful as model membranes in that changes in surface pressure (Deltapi) can be monitored in response to protein adsorption to the monolayer, thus providing a unique manner of assessing protein-membrane contact. In the present study, spread monolayers below their collapse pressures have been utilized to evaluate Ca2+-specific adsorption of several vitamin K-dependent coagulation proteins to monolayers that contain negatively charged phospholipid. From combined measurements of Deltapi and Gamma (the surface excess protein concentration), values of dGamma/dpi have been evaluated for different proteins with varying lipid composition of the monolayers. Using mixed, liquid-expanded monolayers at equivalent initial surface pressures (pii) and which contain different amounts of phosphatidylserine, phosphatidylcholine, and phosphatidylethanolamine, the dGamma/dpi of bovine prothrombin was shown to decrease monotonically with increasing protein affinity for the monolayer. For example, KD values of 7, 20, and 60 nM produced dGamma/dpi values of 14, 17, and 21 nmol m-1 mN-1, respectively. However, the trend in dGamma/dpi appears to originate from characteristics of the monolayer and not from those of the protein, since a much different adsorbate (i.e., a positively charged pyrene derivative) exhibited a similar trend in dGamma/dpi with monolayer composition. On the other hand, dGamma/dpi values of bovine prothrombin, human factor IX, human protein S, bovine protein C, and human protein C, determined using liquid-expanded phosphatidylserine monolayers, were essentially equivalent. Therefore, the five vitamin K-dependent proteins that were examined were equivalent in terms of the manner in which the gamma-carboxyglutamic acid (Gla) domain of each protein perturbed the surface pressure. This study shows that Ca2+-specific membrane contact sites in the Gla domain of the five proteins tested are similar despite the naturally occurring differences in the normal Gla domain sequence of these proteins.

Ultrathin films of polystyrene (PS) and poly(methyl methacrylate) (PMMA) coated on fused quartz plates (or slides) by dip coating are examined by using fluorescence spectroscopy. Cations of the pyrene derivative (4-(1-pyrenyl)butyl)trimethylammonium bromide (PBN) are adsorbed onto the quartz slides from aqueous solutions. The rate of dynamic quenching and prompt quenching by O2 of the PBN fluorescence on the slide in the presence of PMMA and PS films at varying degrees of coverage indicates that, at low coverage, PS films are patchy while PMMA films are continuous. These results are in agreement with published data from AFM studies of similar systems. The fluorescence of pyrene dissolved in ultrathin films on quartz and on hydrophobic (surface derivatized) quartz slides is also examined. As revealed by the trend in pyrene III/I and average fluorescence decay time with coverage, a fraction of the pyrene molecules in PS films diffuse to the polar quartz surface, where they become adsorbed. PMMA, on the other hand, blocks access of pyrene to adsorption sites on the quartz surface presumably by an interaction between carbonyl groups and quartz surface hydroxyls. This fluorescence technique thus provides additional information to AFM in the penetration of reactive species, such as O2, to the silica−polymer interface and in the polymer-mediated interaction of molecular dopants, such as pyrene, with the silica surface.