Interaction of the neurotransmitter, neuropeptide Y, with phospholipid membranes: infrared spectroscopic characterization at the air/water interface.

The association of neuropeptide Y (NPY) at the air/water interface and with phospholipid monolayers on water as subphase has been investigated using external infrared reflection absorption spectroscopy (IRRAS). Studies of the conformation and orientation of NPY suggest that it adopts an alpha-helical structure and is oriented parallel to the air/water interface in neat peptide monolayers. Both secondary structure and orientation are preserved in mixed lipid/NPY monolayers.

Interaction of the neurotransmitter, neuropeptide Y, with phospholipid membranes: film balance and fluorescence microscopy studies.

The association of neuropeptide Y (NPY) with air-water interfaces and with phospholipid monolayers on water subphases and on physiological buffer has been investigated. Surface pressure (pi) versus molecular area (A) relations of the peptide at water surfaces depend on the concentration of the spreading solutions. Independent of that concentration, they show a transition from a low-density state to a high-density state at pi approximately 12 mN/m.

Headgroup organization and hydration of methylated phosphatidylethanolamines in Langmuir monolayers.

Subtle differences in the molecular conformation of fully hydrated phospholipids, and in their interaction with the water reservoir, were assessed as functions of headgroup methylation with surface-sensitive X-ray scattering. To achieve such a structural and functional comparison, diacylphosphatidylethanolamines (PEs) and their mono-, di- and trimethylated (diacylphosphatidylcholine, PC) derivatives in surface monolayers on water have been studied. While the molecular structures of these lipids are quite similar, their subtle distinctions lead to surprisingly large differences in their overall organization.

Measuring the number of independent emitters in single-molecule fluorescence images and trajectories using coincident photons.

A simple new approach is described and demonstrated for measuring the number of independent emitters along with the fluorescence intensity, lifetime, and emission wavelength for trajectories and images of single molecules and multichromophoric systems using a single PC plug-in card for time-correlated single-photon counting. The number of independent emitters present in the detection volume can be determined using the interphoton times in a manner similar to classical antibunching experiments. In contrast to traditional coincidence analysis based on pulsed laser excitation and direct measurement of coincident photon pairs using a time-to-amplitude converter, the interphoton distances are retrieved afterward by recording the absolute arrival time of each photon with nanosecond time resolution on two spectrally separated detectors.