Coherent and incoherent components of a synchrotron radiation spot produced by separate capillaries.

We discuss soft-x-ray focusing properties of separate capillaries. It is shown that a nonnegligible fraction of the synchrotron radiation beam transmitted by the capillary is modal. Experimental and theoretical data are discussed to explain the superposition pattern of x rays in the focal plane due to the interference phenomena of electromagnetic radiation propagating through separate capillaries.

Observation of Interference Effects at the Focus of an X-ray Lens.

During an experiment on synchrotron radiation focusing with a capillary lens, an interference structure was observed at the focal spot of the lens, despite the fact that the lens capillary diameter is about a million times greater than the wavelength of the X-ray photons (600 mum and 8 A, respectively). The width of the central peak is close to the capillary diameter. At the same time the synchrotron radiation concentration increased by more than one hundred times. Analysis shows that the capillary lens acts in many respects as a macroscopic crystal. The observed effect is accounted for by wave theory. This phenomenon may have important practical effects in many fields.

Determination of fluorescent probes localization in membranes by nonradiative energy transfer.

One of the new methods of studying the structure and dimensions of biological membranes is based on the Förster's nonradiative energy transfer between special molecules, the so-called 'membrane fluorescent probes'. Further development of the approach is presented in this article. It consists of the combined use of the time-resolved and steady-state fluorescence data with subsequent computer simulation of the energy transfer in membranes. Anthracene as an energy donor, and 4-p-(dimethylamino)styryl-N-dodecylpyridinium (DSP-12) or 4-dimethylaminochalcone (DMC) as energy acceptors were bound with artificial phospholipid membrane vesicles ('liposomes'). The synchrotron radiation was used as an impulse source for the excitation light. The steady-state fluorescence data permit the area of possible probe localization in membranes to be distinguished, while the kinetic data allow them to be narrowed significantly. There is a good agreement between the obtained localization and our present-day knowledge of lipid bilayer structure. The accuracy of the method is ca. several Angströms.