Lipid-protein interactions in thylakoid membranes, and in the subthylakoid membrane fractions containing either photosystem 1 or photosystem 2, have been studied by using spin-labeled analogues of the thylakoid membrane lipid components, monogalactosyldiacylglycerol, phosphatidylglycerol, and phosphatidylcholine. The electron spin resonance spectra of the spin-labeled lipids all consist of two components, one corresponding to the fluid lipid environment in the membranes and the other to the motionally restricted membrane lipids interacting directly with the integral membrane proteins. Spectral subtraction has been used to quantitate the fraction of the membrane lipids in contact with the membrane proteins and to determine the selectivity between the different lipid classes for the lipid-protein interaction. The fractions of motionally restricted lipid in the thylakoid membrane are 0.36, 0.39, and 0.53, for the spin-labeled monogalactosyldiacylglycerol, phosphatidylcholine, and phosphatidylglycerol, respectively. Spin-labeled monogalactosyldiacylglycerol exhibits very little preferential interaction over phosphatidylcholine, which suggests that part of the role of monogalactosyldiacylglycerol in thylakoid membranes is structural, as is the case for phosphatidylcholine in mammalian membranes. Spin-labeled phosphatidylglycerol shows a preferential interaction over the corresponding monogalactosyldiacylglycerol and phosphatidylcholine analogues, in contrast to the common behavior of this lipid in mammalian systems. This pattern of lipid selectivity is preserved in both the photosystem 1 and photosystem 2 enriched subthylakoid membrane fractions.T e photosynthetic apparatus of green plants comprises a series of integral protein complexes embedded in the thylakoid membrane. The conversion of light energy into a chemically useful form takes place at two reaction centers, photosystem 1 (PSI)' and photosystem 2 (PS2), which consist of complexes of different integral proteins. In the thylakoids from the mesophyll cells of higher plants, the two reaction centers and associated protein complexes are separately located in the appressed (PS2) and nonappressed (PSI) membrane regions. The appressed membranes are arranged in stacks and are interconnected by the nonappressed membranes, which contain regions of high membrane curvature. Within the thylakoid,

We report the design, development, and implementation of an improved instrumentation approach for frequency-domain fluorescence lifetime (FDFL) optrodic sensing without a concurrent reference LED. FDFL traditionally uses a reference LED, at approximately the same wavelength as the sensor fluorophore emission, to measure phase shifts associated with changes in the fluorescence lifetime of fluorophore. For this work we used an oxygen optrode to design, develop, and test the reference-LED-free FDFL approach. Electronics and optics were optimized, and key system parameters, such as inherent system phase shifts, were determined to insure best performance. In our tests with the oxygen optrode, we observed that several key performance characteristics were improved by the implementation of the reference-LED-free instrumentation platform. This system can potentially be adapted to other analyte-selective fluorophores, which will enable scientists and researchers to expand the application of optrodic sensors as basic research tools in biology, medicine, and agriculture.

Saturation transfer ESR has been used to study the dynamic behaviour of iipids in the appressed regions of thylakoid membranes from pea seedlings. Four different phospno-and galacto-lipid spin labels (phosphatidylcholine labelled ~t the 12 or 14 C-atom positions of the m-2 chain, phosphatidylglycerol labelled .~t the 14-1msition nf !he sn2 chaiii, and monogalaetosyldiacylglycerol labelled at the 12-no¢itq_'e~ o, ¢ the m-2 chain) were ,~sed to probe the lipid environment in ?hot~ystem H-e~dched membranes prepared by detergent extraction. The ESR spectra show that the majarity of the lipid in these preparations is strongly motionally restricted. Values for the eifective rotational correlation times of the labelled chains were deduced from the lineheight ratios and integrals of the ~aturation transfer ESR spectra. The effective rotational correlation times were found to be in the i6 ~ s range, indicating a very low lipid chain mobility which correlates with the low lipid content of these preparations. Comparison of the effective rotational correlation times deduced from the different diagnostic regions of th.~ spectrum revealed little anisotropy in the chain mobility., indicating that the dominant motional mode was trans-gauche isomerization. The effective rotational correlation times deduced from the spectral integrals were similar to those deduced from the lineheight ratios, consistent with the absence of any appreciable fluid lipid component in these preparations. The results also indicate some selectivity, of interaction between the lipid species, with phosphatidylcholine exhibiting appreciably slower motion than either phosphatidylglycerol or monogalactosyldiac3 Iglycerol.

Three novel N-heteroacene molecules (SDNU-1, SDNU-2 and SDNU-3)b ased on tetraazachrysene units as cores have been designed, synthesized and fully characterized. Their photophysical, electrochemical and fluorescence properties were investigated, and they exhibited blue to green emission in the solid state. Interestingly, SDNU-2 exhibited high solid photoluminescence quantum efficiencies (75.3 %), which is the highest value of N-heteroacenes derivatives to date. Two-photon absorption studies have been conducted by using the open and close apertureZ -san tech-nique. SDNU-3 showed as ignificant enhancement in the two-photon absorption cross-section with magnitudes as high as about 700 GM (1 GM = 1 10 À50 cm 4 s/photon)w hen excited with 800 nm light, which is the largest value based on ah eteroacene system measured by using aZ -scan experiment so far.W ea ttribute the outcomet os ufficient electronic coupling between the strong charge transfer of quadrupolars ubstituents and the tetraazachrysenec ore. Our result would provide an ew guideline to design novel efficient two-photon materials based on N-heteroacene cores.

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