Several biophysical properties of four synthetic archñal phospholipids [one polyprenyl macrocyclic lipid A and three polyprenyl double-chain lipids (B, C, D) bearing zero, one or four double bonds in each chain] were studied using differential scanning calorimetry, electron and optical microscopies, stopped-flow/light scattering and solidstate 2 H-NMR techniques. These phospholipids gave a variety of self-organized structures in water, in particular vesicles and tubules. These assemblies change in response to simple thermal convection. Some specific membrane properties of these archñal phospholipids were observed: They are in a liquidcrystalline state over a wide temperature range; the dynamics of their polyprenyl chains is higher than that of n-acyl chains; the water permeability of the membranes is lower than that of n-acyl phospholipid membranes. It was also found that macrocyclization remarkably improves the barrier properties to water and the membrane stability. This may be related to the adaptation of Methanococcus jannaschii to the extreme conditions of the deep-sea hydrothermal vents.

COMMUNICATIONSwhich allows structural information to be deduced from a measured vibrational spectrum. Strong hydrogen bonds with short 0-0 distances correlate with long, weakened 0 -H covalent bonds and low hydrogen stretching vibrations. If the 0-0 distance is increased. the length ofthe covalent bond approaches its unperturbed value approximately exponentially; the 0 -H stretching vibration increases almost linearly as the length of the covalent bond decreases. Aluminum-rich zeolites differ from their aluminum-poor counterparts both in their IR spectra and in their rea~tivity.'~. 16] In particular, the highest peak at 3500 cm-' seems to vanish as the Si:AI ratio approaches its lower limit of 1 ; 1. Therefore we investigated the interaction of methanol with two acid sites simultaneously. We find that the hydrogen bond between the methanol proton H, and an oxygen adjacent to another aluminum atom is shortened by about 5% and is therefore stronger than the hydrogen bond formed with an isolated acid site. Preliminary molecular dynamics simulations of I ps reveal a downward shift of the H,-0 vibration (located at 3500cm-' for the methanol hydroxyl group adsorbed on an isolated acid site) of roughly 400cm-', which could explain the disappearance of the former absorption band. However, it should be noted that aluminum-rich zeolites exhibit a substantially richer variety of structures for acid-site centers and adsorption complexes than aluminum-poor zeolites, a fact that has not yet been explored exhaustively.We studied sodalite to unravel processes that should also be relevant for the more complex zeolites actually used in technologically relevant processes. Therefore we should discuss to what extent our results apply to zeolites other than sodalite. We expect that the essential features of structure A are rather independent of the zeolite, as the tetrahedral angle on the Si and A1 atoms is largely conserved. Structure B, however, depends strongly on the local structure. Since it depends on the proximity of distant oxygen atoms, this structure can only occur in sufficiently small or highly deformed larger rings. Rings consisting of four atoms with tetrahedral coordination cannot be bridged, because the acid-site protons point outward. Since the structures A and B have similar vibrational patterns, we expect only quantitative changes in the IR spectra for zeolites that cannot form structure B. The largest deviations in the IR spectra will occur in the lower part (see Fig. 3), because this part is most sensitive to the strength of bond of the acid-site proton.Our computer experiments predicted adsorption structures of methanol in zeolites which, for the first time, are consistent with the available experimental data. This information forms the basis for the understanding of a large class of zeolite-catalyzed reactions. We have applied a theoretical approach t o zeolite chemistry, which allows us to study with a high level of accuracy dynamic behavior of molecules in zeolites at finite temperatures without the limitatio...

Several biophysical properties of four synthetic archaeal phospholipids [one polyprenyl macrocyclic lipid A and three polyprenyl double-chain lipids (B, C, D) bearing zero, one or four double bonds in each chain] were studied using differential scanning calorimetry, electron and optical microscopies, stopped-flow/light scattering and solid-state 2H-NMR techniques. These phospholipids gave a variety of self-organized structures in water, in particular vesicles and tubules. These assemblies change in response to simple thermal convection. Some specific membrane properties of these archaeal phospholipids were observed: They are in a liquid-crystalline state over a wide temperature range; the dynamics of their polyprenyl chains is higher than that of n-acyl chains; the water permeability of the membranes is lower than that of n-acyl phospholipid membranes. It was also found that macrocyclization remarkably improves the barrier properties to water and the membrane stability. This may be related to the adaptation of Methanococcus jannaschii to the extreme conditions of the deep-sea hydrothermal vents.

KEYWORDS:DNA structures´membranes´prebiotic chemistryś ingle molecules´vesicles Among the initial stages in the formation of proto-cells on Earth, the encapsulation of DNA molecules from the surrounding environment into closed systems appears to be essential, and several procedures for the encapsulation of DNA into liposomes have been described. [1] For example, Deamer and Barchfeld employed the dehydration/rehydration method to trap salmon sperm DNA (ca. 20 kb) into egg lecithin vesicles, [1a] Luisi's group studied the entrapment of a plasmid DNA (3.3 kb) by using the same method, the reverse-phase method and the freeze/thaw method, [1b] and Jay and Gilbert observed the enhancement of incorporation of DNA (1 kb) in the presence of a basic protein, lysozyme. [1c] DNA ± lipid complexes have also been considered to achieve transport of DNA into cells, in particular for gene transfer therapy. [2] However, conventional vesicles with a size of several tens of nanometers are too small to incorporate natural genomic DNA molecules containing 10 5 ± 10 8 bp (their full length being on the order of 100 mm ± 10 cm). In order to study DNA incorporation into model proto-cells, it is necessary to (1) prepare giant vesicles with a diameter of several micrometers, into which ªgiantº DNAs can be entrapped smoothly, and (2) monitor in real time individual DNA molecules entrapped within these giant vesicles. Recently, we have found that giant DNAs larger than 100 kb are entrapped spontaneously into giant vesicles of neutral phospholipids in the presence of magnesium ions. [3a] In this last study, we could not control the conformation of the entrapped DNAs. We now report two efficient methods for preparing a primitive cell model entrapping large DNA: natural swelling of polyprenyl phosphates in the presence of DNAs, and laser manipulation. We show that DNA and the DNA ± histone complex can be encapsulated into giant vesicles, where they assume ªelongated-coilº and ªfolded-compactº conformations, respectively. In this study, we have used as lipid membrane components the disodium and dicyclohexylammonium salts of geranylgeranyl phosphoric acid (1 a and 1 b, respectively), which we have postulated to be a ªprimitiveº membrane lipid. [4] O P O O O NH 3 1a : X = Na, 1b : X = 2 X We have prepared giant vesicles entrapping bacteriophage T4 DNA (166 kb, contour length 57 mm), [3] by spontaneous swelling of a dry lipid film in a solution containing the DNA.Figure 1 A exemplifies the fluorescence images of individualFigure 1. A: Fluorescence microscopic images of T4 DNA molecules with unfolded coil conformation (stained with DAPI) inside (left) and outside (right) of a giant vesicle of 1 a. The bar represents 5 mm. B: Dark-field microscopic image of giant vesicle of 1 a. In this case, DNA molecules are not visible by dark-field microscopy because of the weak light scattering of the coiled DNA. The bar represents 5 mm. C: Time series of fluorescence images of two coiled DNAs encapsulated in a vesicle: The images were obtained by an image ...