Droplet interface bilayers (DIBs) provide a superior platform for the biophysical analysis of membrane proteins. The versatile DIBs can also form networks, with features that include built-in batteries and sensors.

The fragmentation dynamics of gas phase phenol molecules following excitation at many wavelengths in the range 279.145 > or = lambdaphot > or = 206.00 nm have been investigated by H Rydberg atom photofragment translational spectroscopy. Many of the total kinetic energy release (TKER) spectra so derived show structure, the analysis of which confirms the importance of O-H bond fission and reveals that the resulting phenoxyl cofragments are formed in a very limited subset of their available vibrational state density. Spectra recorded at lambdaphot > or = 248 nm show a feature centered at TKER approximately 6500 cm(-1). These H atom fragments, which show no recoil anisotropy, are rationalized in terms of initial S1<--S0 (pi*<--pi) excitation, and subsequent dissociation via two successive radiationless transitions: internal conversion to ground (S0) state levels carrying sufficient O-H stretch vibrational energy to allow efficient transfer towards, and passage around, the conical intersection (CI) between the S0 and S2(1pisigma*) potential energy surfaces (PESs) at larger R(O-H), en route to ground state phenoxyl products. The observed phenoxyl product vibrations indicate that parent modes nu16a and nu11 can both promote nonadiabatic coupling in the vicinity of the S0S2 CI. Spectra recorded at lambdaphot < or = 248 nm reveal a faster, anisotropic distribution of recoiling H atoms, centered at TKER approximately 12,000 cm(-1). These we attribute to H+phenoxyl products formed by direct coupling between the optically excited S1(1pi pi*) and repulsive S2(1pi sigma*) PESs. Parent mode nu16b is identified as the dominant coupling mode at the S1/S2 CI, and the resulting phenoxyl radical cofragments display a long progression in nu18b, the C-O in-plane wagging mode. Analysis of all structured TKER spectra yields D0(H-OC6H5) = 30,015 +/- 40 cm(-1). The present findings serve to emphasize two points of wider relevance in contemporary organic photochemistry: (i) The importance of 1) pi sigma* states in the fragmentation of gas phase heteroaromatic hydride molecules, even in cases where the 1pi sigma* state is optically dark. (ii) The probability of observing strikingly mode-specific product formation, even in "indirect" predissociations, if the fragmentation is driven by ultrafast nonadiabatic couplings via CIs between excited (and ground) state PESs.

High-resolution measurements of the kinetic energies of hydrogen atom fragments formed during ultraviolet photolysis of imidazole, pyrrole, and phenol in the gas phase confirm that N(O)-H bond fission is an important nonradiative decay process from their respective 1pisigma* excited states. The measurements also reveal that the respective cofragments (imidazolyl, pyrrolyl, and phenoxyl) are formed in very limited subsets of their available vibrational states. Identification of these product states yields uniquely detailed insights into the vibronic couplings involved in the photoinduced evolution from parent molecule to ultimate fragments.

The fragmentation dynamics of pyrrole molecules following excitation at many wavelengths in the range 193.3 o l phot o 254.0 nm have been investigated by H Rydberg atom photofragment translational spectroscopy. Excitation at the longer wavelengths within this range results in (vibronically induced) population of the 1 1 A 2 (ps*) excited state, but once l phot r 225 nm the electric dipole allowed 1 1 B 2 ' X 1 A 1 (p* ' p) transition becomes the dominant absorption. All of the total kinetic energy release (TKER) spectra so derived show a 'fast' peak, centred at TKER B7000 cm À1 . Analysis of the structure evident in this peak, particularly in spectra recorded at the longer excitation wavelengths, reveals selective population of specific vibrational levels of the pyrrolyl co-fragment. These have been assigned by comparison with calculated normal mode vibrational frequencies, leading to a precise determination of the N-H bond strength in pyrrole: D 0 ¼ 32850 AE 40 cm À1 , and the enthalpy of formation of the pyrrolyl radical: D f H 0 1(C 4 H 4 N) ¼ 301.9 AE 0.5 kJ mol À1 . The recoil anisotropy of the fast H atom photofragments formed following excitation to, and dissociation on, the 1 1 A 2 (ps*) potential energy surface (PES) is seen to depend upon the vibrational level of the pyrrolyl co-fragment. This observation, and the finding that the mean TKER associated with these fast H þ pyrrolyl fragments is essentially independent of l phot , can be explained by assuming that, upon N-H bond fission, the skeletal vibrational motions in pyrrole(1 1 A 2 ) molecules evolve adiabatically into the corresponding modes of the ground state pyrrolyl fragment. A second, 'slow' peak is increasingly evident in TKER spectra recorded at shorter photolysis wavelengths, and becomes the dominant feature once l phot r 218 nm. This component exhibits no recoil anisotropy; its TKER profile is reminiscent of that observed in many other dissociations that yield H atoms by 'statistical' decay of highly vibrationally excited ground state molecules. The form of the TKER spectra observed at these shorter excitation wavelengths is rationalised by assuming two possible decay routes for pyrrole molecules excited to the 1 B 2 (pp*) state. One involves fast 1 1 B 2 * 1 1 A 2 radiationless transfer and subsequent fragmentation on the 1 1 A 2 PES, yielding 'fast' H atoms (and pyrrolyl co-fragments)-reminiscent of behaviour seen at longer excitation wavelengths where the 1 1 A 2 PES is accessed directly. The second is assumed to involve radiationless transfer to the ground state, either by successive 1 1 B 2 * 1 1 A 2 * X 1 A 1 couplings mediated by conical intersections between the relevant PESs or, possibly, by an as yet unrecognised direct 1 1 B 2 * X 1 A 1 coupling, and subsequent unimolecular decay of the resulting highly vibrationally excited ground state molecules yielding 'slow' H atoms (together with, most probably, cyanoallyl co-fragments).

In cell membranes, the lipid compositions of the inner and outer leaflets differ. Therefore, a robust model system that enables single-channel electrical recording with asymmetric bilayers would be very useful. We and others recently developed the droplet interface bilayer (DIB), which is formed by connecting lipid monolayer-encased aqueous droplets submerged in an oil-lipid mixture. Here, we incorporate lipid vesicles of different compositions into aqueous droplets and immerse them in an oil bath to form asymmetric DIBs (a-DIBs). Both alpha-helical and beta-barrel membrane proteins insert readily into a-DIBs, and their activity can be measured by single-channel electrical recording. We show that the gating behavior of outer membrane protein G (OmpG) from Escherichia coli differs depending on the side of insertion in an asymmetric DIB with a positively charged leaflet opposing a negatively charged leaflet. The a-DIB system provides a general platform for studying the effects of bilayer leaflet composition on the behavior of ion channels and pores.