Babak Sanii

Shaken, Not Stirred: Collapsing a Peptoid Monolayer To Produce Free-Floating, Stable Nanosheets

Two-dimensional nanomaterials play a critical role in biology (e.g., lipid bilayers) and electronics (e.g., graphene) but are difficult to directly synthesize with a high level of precision. Peptoid nanosheet bilayers are a versatile synthetic platform for constructing multifunctional, precisely ordered two-dimensional nanostructures. Here we show that nanosheet formation occurs through an unusual monolayer intermediate at the air-water interface. Lateral compression of a self-assembled peptoid monolayer beyond a critical collapse pressure results in the irreversible production of nanosheets. An unusual thermodynamic cycle is employed on a preparative scale, where mechanical energy is used to buckle an intermediate monolayer into a more stable nanosheet. Detailed physical studies of the monolayer-compression mechanism revealed a simple preparative technique to produce nanosheets in 95% overall yield by cyclical monolayer compressions in a rotating closed vial. Compression of monolayers into stable, free-floating products may be a general and preparative approach to access 2D nanomaterials.

Antibody-Mimetic Peptoid Nanosheets for Molecular Recognition

The ability of antibodies to bind a wide variety of analytes with high specificity and high affinity make them ideal candidates as molecular recognition elements for chemical and biological sensors. However, their widespread use in sensing devices has been hampered by their poor stability and high production cost. Here we report the design and synthesis of a new class of antibody-mimetic materials based on functionalized peptoid nanosheets. A high density of conformationally constrained peptide and peptoid loops are displayed on the surface of free-floating nanosheets to generate an extended, multivalent two-dimensional material that is chemically and biologically stable. The nanosheet serves as a robust, high-surface area scaffold upon which to display a wide variety of functional loop sequences. The functionalized nanosheets were characterized by atomic force microscopy, X-ray diffraction, and X-ray reflectivity measurements, and were shown to serve as substrates for enzymes (protease and casein kinase II), as well as templates for the growth of defined inorganic materials (gold metal).

Bending membranes on demand: Fluid phospholipid bilayers on topographically deformable substrates

We combine hierarchical surface wrinkling of elastomers with lipid membrane deposition techniques to dynamically template complex three-dimensional topographies onto supported lipid bilayers. The real-time introduction of corresponding nano- to micrometer scale curvatures triggers spatially periodic, elastic bending of the bilayer, accompanied by molecular-level reorganizations. This ability to dynamically impose curvatures on supported bilayers and the ensuing re-equilibration promises fundamental material and biophysical investigations of curvature-dependent, static heterogeneities and dynamic reorganizations pervasive in biological membranes.

Protecting, patterning, and scaffolding supported lipid membranes using carbohydrate glasses

Disaccharides are known to protect sensitive biomolecules against stresses caused by dehydration, both in vivo and in vitro. Here we demonstrate how interfacial accumulation of trehalose can be used to (1) produce rugged supported lipid bilayers capable of near total dehydration; (2) enable spatial patterning of membrane micro-arrays; and (3) form stable bilayers on otherwise lipophobic substrates (e.g., metal transducers) thus affording protecting, patterning, and scaffolding of lipid bilayers.

Structure-determining step in the hierarchical assembly of peptoid nanosheets.

Organic two-dimensional nanomaterials are of growing importance, yet few general synthetic methods exist to produce them in high yields and to precisely functionalize them. We previously developed an efficient hierarchical supramolecular assembly route to peptoid bilayer nanosheets, where the organization of biomimetic polymer sequences is catalyzed by an air-water interface. Here we determine at which stages of assembly the nanoscale and atomic-scale order appear. We used X-ray scattering, grazing incidence X-ray scattering at the air-water interface, electron diffraction, and a recently developed computational coarse-grained peptoid model to probe the molecular ordering at various stages of assembly. We found that lateral packing and organization of the chains occurs during the formation of a peptoid monolayer, prior to its collapse into a bilayer. Identifying the structure-determining step enables strategies to influence nanosheet order, to predict and optimize production yields, and to further engineer this class of material. More generally, our results provide a guide for using fluid interfaces to catalytically assemble 2D nanomaterials.

A comparison of lateral diffusion in supported lipid monolayers and bilayers

Lipid monolayers and bilayers exist in distinct physical states differentiated by the differences in the manner in which translational fluidity relates to their phase transition and how cholesterol influences the two. Work presented here suggests that intra-leaflet diffusion and cholesterol interactions are modulated by the nature of inter-leaflet coupling. Our results also provide an important practical caveat in the comparisons of membrane physical properties deduced using the two, mono- and bilayer, model membrane configurations.

45-km horizontal path optical link demonstration

Observations made during a mountain-top-to-mountain-top horizontal optical link demonstration are described. The optical link spans a range of 46 Km at an average altitude of 2 Km above sea level. A multibeam beacon comprised of eight laser beams emerging from four multimode fiber coupled lasers (780 nm) is launched through a 0.6 m diameter telescope located at the JPL Table Mountain Facility (TMF) in Wrightwood, California. The multibeam beacon is received at Strawberry Peak located in the San Bernardino Mountains of California. The NASA, JPL developed optical communications demonstrator (OCD) receives the beacon, senses the atmospheric turbulence induced motion and using an upgraded fine steering loop actively points a communications laser beam (852 nm, 400 Mbps on-off key modulated, PN7 pseudo random bit sequence) to TMF. The eight-beam beacon allowed a four-fold reduction in normalized irradiance or scintillation index. This in turn was sufficient to eliminate beacon fades sensed by the OCD and enable performance evaluation of the fine steering loop. The residual tracking error was determined to be +/- 1.1 to +/- 1.7 (mu) rad compared to a model prediction of +/- 3.4 (mu) rad. The best link performance observed showed average bit error rates (BER) of 1E-5 over long durations (30 seconds); however, instantaneous BERs of at least 0.8E-6 over durations of 2 ms were observed. The paper also discusses results pertaining to atmospheric effects, link analysis, and overall performance.

3-Nitro-Tyrosine as an Internal Quencher of Autofluorescence Enhances the Compatibility of Fluorescence Based Screening of OBOC Combinatorial Libraries

In the one-bead-one-compound (OBOC) combinatorial method, compounds are constructed on bead resin via split-mix library synthesis such that multiple copies of the same compound are displayed on each bead. These libraries are rapidly screened with enzyme-linked colorimetric, fluorescent, radiometric, or whole-cell binding assays. While fluorescence-based probes are powerful tools in OBOC screening, their utility is greatly limited by the intrinsic fluorescence of many commonly used solid supports, (e.g. TentaGel), residual coupling reagents, and library compounds. To overcome this problem, we topologically partitioned TentaGel resin with a thin Fmoc-protected outer layer and an unprotected inner core. The inner core was derivatized with 3-nitro-tyrosine, followed by random peptide library construction. Spectral scans from a confocal microscope showed a dramatic decrease in the autofluorescence of blank beads and OBOC peptide libraries across a broad range of the optical spectrum. The quenching capacity of 3-nitro-tyrosine was also visualized in fluorescent micrographs. Using biotin/streptavidin as a model ligand/receptor system, we demonstrated a marked increase in visibility of three commercially available fluorescent probes binding to quenched beads, and increased feasibility of using a robust and efficient fluorescence-based, bead sorting platform known as COPAS. These data show that using 3-nitro-tyrosine as an internal quencher greatly enhances the compatibility of fluorescence-based applications and OBOC combinatorial screening.

Multi-gigabit data-rate optical communication depicting LEO-to-GEO and GEO-to-Ground links

Communication links with multi-giga-bits per sec (Gbps) data-rates depicting both LEO-GEO and GEO-to-Ground optical communications were characterized in the laboratory. A 5.4 Gbps link, with a capability of 7.5 Gbps, was demonstrated in the laboratory. The breadboard utilized a 13 cm diameter telescope as the transmit aperture that simulates the LEO terminal. The receiver is a 30-cm telescope that simulates the GEO terminal. The objective of the laboratory breadboard development is to validate the link analysis and to demonstrate a multi-gigabit link utilizing off-the-shelf or minimally modified commercially available components (optics and opto-electronics) and subsystems. For a bit-error-rate of 1E-7, the measured required received signal is within 1 to 2 dB of that predicted by the link analysis.

Calibrating surface weather observations to Atmospheric attenuation measurements

A correlation between near-IR atmospheric attenuation measurements made by the Atmospheric Visibility Monitor (AVM) at the Table Mountain Facility and airport surface weather observations at Edwards Air Force Base has been performed. High correlations (over 0.93) exist between the Edwards observed sky cover and the average AVM measured attenuations over the course of the 10 months analyzed. The statistical relationship between the data-sets allows the determination of coarse attenuation statistics from the surface observations, suggesting that such statistics may be extrapolated from any surface weather observation site. Furthermore, a superior technique for converting AVM images to attenuation values by way of MODTRAN predictions has been demonstrated.