Surface-enhanced infrared ellipsometry of self-assembled undecanethiol and dodecanethiol monolayers on disordered gold nanoisland substrates.

Infrared spectroscopic ellipsometry (IRSE) is a powerful optical probe of various chemical and physical properties of molecules adsorbed onto solid surfaces. In particular, IRSE can be useful for detecting adsorption-induced changes in the IR spectra of self-assembled monolayers (SAMs), and unlike traditional IR absorption spectroscopies, IRSE provides useful information about the phase of the reflected radiation from the SAMs. However, in the standard IRSE experimental geometry using flat substrates for SAMs, the detectable signal containing these phase data is considerably weaker than the corresponding absorbance data. In our present work, we demonstrate that enhancing the local optical fields at the sample surface through the use of a disordered Au nanoisland substrate can substantially increase both these absorbance and phase signals. We also demonstrate how this surface-enhanced infrared spectroscopic ellipsometry (SEIRSE) can be utilized for straightforward analysis of absorption peak widths, as well as to obtain information about the orientation of the terminal methyl on adsorbed SAMs. As model SAMs for this study, we use undecanethiol (UDT) containing 10 CH(2) units and a terminal CH(3) group, as well as dodecanethiol (DDT) containing 11 CH(2) units with its terminal CH(3) at a different orientation than UDT. We show that surface-enhanced IRSE is sensitive to subtle vibrational signatures of the differently oriented terminal methyls of these two homologous alkanethiol SAMs.

Nanostructured gold hollow microspheres prepared on dissolvable ceramic hollow sphere templates.

Fifty and one-hundred micrometer diameter nanostructured gold hollow microspheres (GHSs), in >98% purity, have been prepared by using ceramic hollow spheres, CHSs, as templates. Tennanometer diameter gold nanoparticles were covalently linked to the thiol moiety of (3-mercaptopropyl)trimethoxysilane, which had been self-assembled onto the CHSs. Greater structural strength was obtained by the generation of additional gold nanoparticles, in situ on the gold nanoparticle coated CHSs (by immersing the gold nanoparticle coated CHSs into an aqueous mixture of hydroxylamine and gold chloride). GHSs were obtained by dissolving the CHSs templates. The sizes, shapes, surface areas (185.3 m2/g for CHSs and 182.9 m2/g for GHSs), pore diameters (7.7 nm for CHSs and 7.8 nm for GHSs), and pore volumes (0.41 cm3/g for CHSs and 0.36 cm3/g for GHSs) of GHSs were quite similar to their CHSs counterparts. Significantly, GHSs showed surface plasmon bands whose maximum (644 nm) shifted from that observed for the parent 10-nm gold nanoparticles (522 nm).

Action potentials pass severed earthworm MGA segments reconnected by laser and electric field pulses.

Active and passive electrical signals transmit across the earthworm (Lumbricus terrestris) medial giant axon (MGA) segment after reconnection induced by laser and electric field pulses. Laser pulses of 308 nm, 15 ns pulse duration, and pulse energy 5-50 microJ in the objective plane induced axon reconnection in 12 of 133 (9%) preparations. Electric field pulses of 200-800 V, 100 microseconds duration, induced axon reconnection in 15 of 188 (8%) preparations. Electrical continuity is possible after the reconnection of severed axons induced by laser and electric field pulses.

Electron and atomic force microscopic investigations of lead selenide crystals grown under monolayers.

Lead selenide (PbSe) particulate films, composed of highly oriented, equilateral triangular crystals, have been in situ generated by the exposure of arachidic-acid- (AA) monolayer-coated aqueous lead nitrate [Pb(NO32] solutions to hydrogen selenide (H2Se). The AA coated PbSe films, at different stages of their growth, were transferred to solid substrates and characterized by transmission electron microscopy (TEM), electron diffraction, and atomic force microscopy (AFM). The epitaxial growth of PbSe crystals has been rationalized in terms of matching the [111] plane of crystalline PbSe and the (100) plane of the hexagonally close-packed AA monolayer. The parallel alignment of the < or = 110 > and < or = 001 > axes and the perpendicular alignment of the < or = 110 > axis to the monolayer have been suggested to be responsible for the observed formation of rod-like PbSe particles. The presence of a negatively charged monolayer has been found to be an essential requirement for the oriented growth of PbSe crystals.

Electric-field-induced reconnection of severed axons.

We report the first successful axon reconnection in the earthworm (Lumbricus terrestris) medial giant axon (MGA) by electric fields generated by electrical pulses of 10-100 microseconds duration and 80-200 V amplitude. Reconnection was documented by light and electron microscopy, and by transport of Lucifer yellow dye across the reconnected MGA segments. Direct repair of a severed nerve axon promises the advantages of preserving axon viability and distal connections.

Laser-induced reconnection of severed axons.

After their axons have been severed, nerve cells can achieve functional recovery either by regrowth of the injured cells or by direct repair of the injured cell at the site of injury. Direct repair of a severed axon promises the advantages of preserving the viability and existing connections of the axon distal to the injury. We report here the first successful axon reconnection in the earthworm (Lumbricus terrestris) medial giant axon (MGA) in vitro system (1) by the application of well-focused 15 nsec, 5 to 50 muJ/pulse, 308 nm laser pulses. Axon reconnection is documented by light and electron microscopy, as well as by transfer of the iontophoretically injected fluorescent dye, Lucifer Yellow, across the reconnected MGA segments.

Retinylidene Schiff bases in alkylammonium carboxylate reversed micelles.

All-trans-retinal, incorporated into dodecylammonium propionate, dodecylammonium 3-chloropropionate and dodecylammonium trifluoroacetate reversed micelles in cyclohexane containing different amounts of solubilized water, gave all-trans-N-retinylidene-n-dodecylamine. Formation of all-trans-N-retinylidene-n-dodecylamine was complete within a few minutes when all-trans-retinal was solubilized along with L-lysine in reversed-micellar dodecylammonium propionate in cyclohexane as compared to the several hours required for the comparable reaction to occur in the absence of lysine. In situ formed all-trans-N-retinylidene-n-dodecylamine was not protonated by the acidic moiety (i.e., propionate, 3-chloropropionate or trifluoroacetate anions) of dodecylammonium propionate, dodecylammonium 3-chloropropionate or dodecylammonium trifluoroacetate reversed micelles. Addition of propionic or 3-chloropropionic acid did not cause observable protonation of the reversed-micelle-incorporated all-trans-N-retinylidene-n-dedecylamine. Addition of strong trifluoroacetic acid to reversed micellar solutions of all-trans-N-retinylidene-n-dodecylamine caused protonation as well as hydrolysis to retinal. Retinylidene Schiff bases are protected from protonation by strongly held surfactant-ion pairs which may model proton channels whose function is controlled by protein conformational changes.

Polymerized surfactant vesicles: novel membrane mimetic systems.

Vesicles formed from dialkyl surfactants containing vinyl, methacrylate, diacetylene, isocyano, and styrene groups have been stabilized by polymerization across their bilayers of head groups. Polymerized vesicles have shelf lives of many months and controllable permeabilities and sizes. The kinetics of surfactant vesicle photopolymerzation have been determined, and the mechanism of photopolymerization has been discussed as a two-dimensional surface process. Polymerized surfactant vesicles concentrate reagents in their aqueous interiors, in bilayers, and in their inner or outer surfaces. This, in turn, leads to altered reaction rates and sites. Polymerized surfactant vesicles also provide a good media for the generation, in situ, of small, uniform, and efficient colloidal catalysts.

Synthesis of amino acyl adenylates using the tert-butoxycarbonyl protecting group.

Alayl, [ 14c]-alanyl, phenylalanyl, and methionyl adenylates have been synthesized in high yields and relatively good purities. Elemental analysis 1H nmr and ir spectra have been utilized for the characterization of these extremely labile compounds. The present synthesis, which uses readily available N-tert-butoxycarbonyl amino acids, is compared with previous methods.

Pyranine as a sensitive pH probe for liposome interiors and surfaces. pH gradients across phospholipid vesicles.

Pyranine is shown to be a convenient and sensitive probe for reporting pH values, pHi, at the interior of anionic and at the outer surface of cationic liposomes. It is well shielded from the phospholipid headgroups by water molecules in the interior of anionic liposomes, but it is bound to the surface of cationic liposomes. Hydrogen ion concentrations outside the liposomes, 'bulk pH values', pHo, were measured by a combination electrode. While pHi = pHo for neutral, pHi less than pHo for anionic and pHi greater than pHo for cationic liposomes prepared in 5.0 . 10(-3) M phosphate buffers. pKa values for the ionization of pyranine were 7.22 +/- 0.04 and 6.00 +/- 0.05 in water and at the external surface of cationic liposomes. The surface potential for cationic liposomes containing dipalmitoyl-DL-alpha-phosphatidylcholine, cholesterol and octadecylamine in the molar ratio of 1.00 : 0.634 : 1.01, were calcuated to be +72.2 mV. Proton permeabilities were measured for single and multicompartment anionic liposomes. Transfer of anionic liposomes prepared at a given pH to a solution of different pH resulted in a pH gradient if sodium phosphate or borate were used as buffers. In the presence of sodium acetate proton equilibration is promptly established.

Partitioning of amino acids and nucleotides between water and micellar hexadecyltrimethylammonium halides. The prebiotic significance of cationic surfaces.

Using quantitative gel filtration techniques partition coefficients, Kp-values, have been determined between aqueous cationic micellar hexadecyltrimethylammonium bromide, CTAB, and several biomonomer. Kp-values for 5'-adenylic acid, 5'-cytidylic acid, 5'-guanylic acid, 5'-uridylic acid and 5'-thymidylic acid are 1,400 +/- 150. Nucleotides bind to CTAB micelles effectively, but nonselectively. Conversely, the binding of tRNAs to micellar CTAB is selective. Kp-values for glutamic acid II, tyrosine and phenylalanine tRNAs (in 1.0MNaCl) are 520, 3,100 and 5,600, respectively. Kp-values for the binding of alanine, arginine, aspartic acid, glutamic acid, glycine, histidine, phenylalanine, serine, threonine and tryptophan to micellar CTAB are less than 8. Conversion of unitless Kp-values for the binding of amino acids, nucleotides and nucleosides to both anionic and cationic micelles, to K (in 1/g) values allows the comparison of clays and micelles as prebiotic concentrating media. Using correlations between surface densities of the biomonomers and their binding constants, it is shown that aqueous micelles (at pH = 8) are a better concentrating media than are clays.

Differential partitioning of tRNAs between micellar and aqueous phases: a convenient gel filtration method for separation of tRNAs.

Partition coefficients (Kp) of phenylalanine, glutamic acid-II and tyrosine tRNAs between water and micellar cetyltrimethylammonium chloride (CTACl) have been determined to be 5600, 520 and 3100, respectively, by gel filtration on Sephadex G-100-120. Equations for obtaining Kp values from quantitative gel filtration have also been derived. The use of this method for the separation of tRNAs is demonstrated.

Novel prebiotic systems: nucleotide oligomerization in surfactant entrapped water pools.

Oligomerization of 5' -TMP in water pools entrapped by dodecyl-ammonium chloride surfactant aggregates in benzene: hexane in the presence of dicyanodiimide at temperatures ranging from 21 degree -72 degree resulted in the formation of linear and cyclic oligonucleotides containing up to pentamers. Effects of temperature, time and surfactants have been examined. Rate constants for the formation of oligomers have been determined at five different temperatures. These data afforded values of (formula: see text). Prebiotic significance of these results are discussed.