SPECTROSCOPIC AND DYNAMIC CHARACTERIZATION OF FMN IN REVERSED MICELLES ENTRAPPED WATER POOLS

Abstract— The encapsulation of FMN in surfactant entrapped water pools resulted into specific interactions of FMN with the polar head groups, the entrapped water molecules and the outer apolar solvent. Two positively charged surfactant/solvent systems were employed: dodecyl ammonium propionate (DAP) in toluene and hexadecyltrimethylammonium bromide (CTAB) in chloroform/ n -octane (6:5, vol/vol). Also a surfactant with a negatively charged polar head group, sodium bis (2-ethylhexyl) sulfosuccinate (AOT) in n -octane, was used. In CTAB and especially DAP reversed micellar systems the light absorption spectra revealed the localization of the flavin in a more apolar environment, while in AOT reversed micelles FMN appeared to reside mainly in the core of the water pool. The fluorescence spectra showed unresolved bands, which were blue-shifted in DAP and CTAB reversed micelles as compared to the spectra of aqueous FMN solutions. The fluorescence decay kinetics of FMN in enclosed water droplets is non-exponential. The heterogeneity can be explained assuming incomplete relaxation of partly immobilized water molecules during the lifetime of the excited singlet state. The relatively high anisotropy of the fluorescence of FMN in encapsulated water indicated a higher viscosity than in bulk water. This was confirmed by anisotropy decay measurements of FMN in DAP and AOT entrapped water, for which the rotational correlation times were much longer than for FMN in plain water.     

EXCITED STATE PROPERTIES OF THE N-(DEOXYGUANOSIN-8-YL)-2-AMINOFLUORENE ADDUCTS

The spectroscopic characteristics of adducts derived from the covalent binding of the carcinogen 2-aminofluorene to the C8 position of deoxyguanosine [N-(deoxyguanosin-8-yl)-2-amino-fluorene, dGuo-C8-AF], and from an adduct of similar structure formed with the synthetic polynucleotide poly(dG-dC).poly(dG-dC), were investigated. At 77 K both adducts are characterized by well-defined and rather narrow fluorescence emission spectra with maxima at 370 and 390 nm characteristic of the aromatic, monomolecular 2-aminofluorene (AF) residue. In contrast, at room temperature, the fluorescence is characterized by a broad, structureless emission band with a maximum at 460 nm in aqueous mixtures, shifting to 415 nm in solvents of lower polarity (100% propanol); the maxima are located at intermediate wavelengths in solutions of different propanol/water compositions, and this emission is attributed to an excited state complex (exciplex). The fluorescence quantum yield decreases when either the solvent polarity or the temperature are increased, varying from 5.4% (100% propanol) to 0.04-0.05% (100% H2O). The fluorescence decay profiles of dGuo-C8-AF adducts (measured at the National Synchrotron Light Source facility at the Brookhaven National Laboratory) can be roughly, but not exactly, modeled in terms of two exponential decay components in the range of about 0.3-1.0 ns with the propanol concentration greater than 60%; at lower propanol concentrations, a single short lifetime is observed and in 100% water solutions its value is 0.08 ns. The shorter lifetime, favored in solvent mixtures of higher polarities, is attributed to an exciplex with significant charge-transfer character.(ABSTRACT TRUNCATED AT 250 WORDS)     

PHOTOREACTIVITY OF ISOLATED PHOTOSYSTEM I PARTICLES UPON COMBINATION WITH ARTIFICIAL LIPID MEMBRANES OR TRITON X-100 MICELLES*

Abstract— PS-I particles isolated according to Shiozawa et al. (1974) show increased rates of O₂-_- and H ⁺-uptake with ascorbate as electron donor upon combination with an artificial vesicular lipid membrane. The amount of increase varies depending on the reconstitution procedure used. Combination of PS-I particles with Triton X-100 micelles increases these photochemical activities even more. The observed proton uptake in PS-I lipid vesicles is not caused by the well-known proton gradient found in thylakoid membranes, since lipid vesicles containing extracted leaf Chl show the same activities and uncouplers have no effect. Because these phenomena are also caused by solubilized Chl, it is concluded that there is no obvious correlation with PS-I activity. Proton uptake most probably is caused by oxidation of ascorbate by either singlet oxygen, superoxide or OH-radicals formed in the light. Experimental results are obtained which indicate that Chl in lipid catalyzes formation of superoxide and singlet oxygen. However, it is not clear whether superoxide formation is caused by direct electron transport from excited Chl to oxygen or by a secondary reaction. Diphenylcarbazone disproportionation has been reported as a specific photosystem I reaction. However, PS-I lipid vesicles and Chl-lipid-Triton X-100 mixtures oxidize DPCN at comparable rates, showing that the reaction is not specific for PS-I. Cations stimulate DPCN disproportionation in Chl-lipid-Triton X-100 mixtures but do not affect the rate of P700 photooxidation at all. Therefore it is suggested that Gross and Greniers (1978) conclusion that cation regulation of PSI electron flow (studied by DPCN disproportionation of PS-I particles in Triton X-100 micelles) provides a fine tuning mechanism for energy transfer, has to be reevaluated.     

Quasi-linearization and the Identification of Parameters in Partial Differential Equations

The method of quasi-linearization has been adapted to the problemof identifying parameters in partial differential equations.Convective and radiative heat transfer coefficients are obtainedfrom an equation that models the transient heating of a bedof spheres.     

Predictor-corrector Methods with Improved Absolute Stability Regions

Generalized predictor-corrector methods with an extended regionof absolute stability are studied. Choosing an extrapolation-predictorand a backward-differentiation-corrector, methods of ordersup to 6 are constructed. The real stability boundaries of thesemethods are of magnitude m², where m is the number of right-handside evaluations per integration step. The coefficients of themethods can be generated during the computation for arbitraryvalues of m. The storage requirements are limited and are independentof m.     

The change in phase behaviour and orientational order of solid N2 at high pressure under the influence of Ar: a simulation study

We have studied the influence of Ar atoms on the high-pressure phase behaviour of N₂ by a Monte Carlo study of Ar _x (N₂)_1-x mixed solids. The results were obtained on the N₂ rich side (0 ≤ x ≤ 0.25), in the region where the ? and δ phases exist in pure N₂. The ??—δ? transition shifts rapidly to lower temperatures with x: it has vanished for x ? 0.05. For x ? 0.12, a cubic orientationally ordered phase appears. The transition from this phase to the δ? phases shifts to higher temperatures with increasing x. The temperature of the onset as well as the completion of the cascade process, responsible for the δ?_loc—δ?_rot transition, is independent of composition. This transition disappears in the x-region where the ordered phase is present for all temperatures below the transition to the δ?_rot phase. Therefore, the influence of the isotropic diluents on the orientational behaviour of the N₂ molecules is threefold. In the δ?_loc phase, the vibron frequencies show a splitting that shifts as a function of x, which might be related to the occurrence of a tetragonal modification of this phase.     

Ethnic Preferences and Residential Segregation: Theoretical Explorations Beyond Detroit

We are strongly supportive of Fossett's theoretical approach and modeling methodology, which uses computational methods to perform thought experiments that generate compelling insights into the enigma of persistent residential segregation in the U.S. We also agree with his theoretical results, which challenge the prevailing view among demographers that institutional discrimination is the essential cause. However, we think he did not go far enough. Fossett limited his analysis to a narrow region of the parameter space that corresponded to conditions observed in one city at one time. This precludes generalization to other times and places and exploration of theoretically motivated “what if” scenarios that trespass beyond the Detroit city limits. When we extended the parameter space, we noticed two interesting results. First, Fossett's “paradox of weak minority preferences” requires qualification. Disproportionate in-group preferences among minorities are indeed segregation-promoting, not integration-promoting, but they generally have less impact on segregation than the in-group preferences of the majority. Second, not only are exclusionary practices and institutional discrimination not necessary for segregation (as Fossett demonstrates), we show that in certain regions of the parameter space they are not even sufficient.     

MARINE PROTECTED AREAS IN THE HIGH SEAS AND THEIR IMPACT ON INTERNATIONAL FISHING AGREEMENTS

Abstract Marine protected areas (MPAs) are gaining momentum as tools within fisheries management. Although many studies have been conducted to their use and potential, only few authors have considered their use in the High Seas. In this paper, we investigate the effects of fish growth enhancing MPAs on the formation of regional fisheries management organisations (RFMOs) for highly migratory fish stocks. We argue that in absence of enforcement MPAs constitute a weakest‐link public good, which can only be realized if everyone agrees. We combine this notion with a game theoretic model of RFMO formation to derive potentially stable RFMOs with and without MPAs. We find that MPAs generally increase the parameter range over which RFMOs are stable, and that they increase stability in a number of cases as compared to the case without MPAs. They do not necessarily induce a fully cooperative solution among all fishing nations. In summary, results of this paper suggest a positive role for MPAs in the High Seas.     

Neurotransmitters in the gas phase: a computational and spectroscopic study of noradrenaline

The conformational structures of noradrenaline, isolated in the gas phase, have been explored through a combination of electronic structure computation (at the B3LYP/6-31 + G?, MP2/6-31 + G?, MP2/aug-cc-pVDZ and CIS/6-31 + G? levels of theory) and mass selected ultraviolet and infrared ion dip spectroscopy (following laser ablation of the neurotransmitter into a pulsed supersonic argon expansion). Despite the many possible low-lying conformational possibilities predicted by theory, almost the entire population of jet-cooled noradrenaline adopts the global minimum structure, associated with an extended, AG1a, ethanolamine side chain conformation. Intramolecular hydrogen bonds are formed between the neighbouring hydroxyl groups on the catechol ring and between the hydroxyl and amino groups on the side chain.     

Sub-weakly Embedded Singular and Degenerate Polar Spaces

We show that every sub-weak embedding of any singular (degenerate or not) orthogonal or unitary polar space of non-singular rank at least 3 in a projective space PG , a commutative field, is the projection of a full embedding in some subspace PG of PG , where PG contains PG and is a subfield of . The same result is proved in the symplectic case under the assumption that the field over which the polarity is defined is perfect if the characteristic is 2 and if each secant line of the embedded polar space contains exactly two points of . This completes the classification of all sub-weak embeddings of orthogonal, symplectic and unitary polar spaces (singular or not; degenerate or not) of non-singular rank at least 3 and defined over a commutative field , where in the characteristic 2 case is perfect if the polar space is symplectic and the degree of the embedding is 2.