Planar Supports Research Articles

Efficient synthesis of small molecule macroarrays: optimization of the macroarray synthesis platform and examination of microwave and conventional heating methods

We report a method for the efficient construction of small molecule macroarrays using microwave-assisted SPOT-synthesis. Macroarrays of 1,3-diphenylpropenones (chalcones) were synthesized rapidly and in high purity starting from robust, Wang-linker-derivatized planar supports. We have optimized the entire chalcone macroarray construction process and evaluated the efficiency and utility of microwave-assisted reactions in array synthesis. Microwave heating was found to be most beneficial for reactions that require temperatures greater than the boiling points of the solvents. These microwave-assisted conditions permitted straightforward access to macroarrays of 2,4,6-triarylpyridines derived from the original chalcone scaffold.

Discovery of Fluorescent Cyanopyridine and Deazalumazine Dyes Using Small Molecule Macroarrays

[structure: see text] Small molecule macroarrays of cyanopyridines and deazalumazines were generated in high purities via spatially addressed synthesis on planar cellulose supports. Examination of the spectral properties of the heterocycles both on and off of the planar support revealed a set of promising new fluorescent dyes that exhibit high quantum yields, low pH dependence, and high sensitivity to solvent polarity.

Nanoassembly of photoluminescent films containing rare earth complex nanoparticles on planar and microspherical supports

In this paper, we describe the fabrication of photoluminescent films containing rare earth complex nanoparticles on both planar and spherical supports by using the layer-by-layer (LBL) self-assembly technique. The rare earth complex nanoparticles are synthesized in aqueous solution, with trivalent europium as the metal center ion, dibenzoylmethane (DBM) as the ligand and poly(ethylenimine) (PEI) as the stabilizing agent. The particle size is about 2 nm as revealed by transmission electron microscopy (TEM) images. During the formation of Eu(DBM) 3 nanoparticles, PEI stabilize the nanoparticles and confer a well-defined positive surface, thus preventing the nanoparticles from aggregation and affording stable dispersion. These nanoparticles can be assembled to form ultrathin films by alternate deposition with poly(sodium 4-styrene sulfonate) (PSS) on planar supports. The resulting films show the same UV and fluorescence characteristics as the corresponding aqueous nanoparticle dispersion, which indicates that the deposition process is successful. In addition, atomic force microscopy (AFM) and TEM have been used to characterize the surface morphology of these films. Aggregations in the size range of 30–70 nm are found in the composite films. A strong and narrow emission peak at 612 nm can be found in the photoluminescence (PL) spectra of the LBL films, which is the characteristic emission of Eu 3+. We have also extended the substrate of LBL assembly to microspherical surface, and obtained composite fluorescent shells on silica microspheres.

Rapid synthesis of diketopiperazine macroarrays via Ugi four-component reactions on planar solid supports

Libraries of diketopiperazines have been generated in high purity using the small molecule macroarray synthesis platform.

Cell Membranes Suspended Across Nanoaperture Arrays

We present a method for spreading large (>100 microm(2)) cell membrane fragments across nanoapertures in planar supports. Electron-beam and focused-ion-beam lithography were used to fabricate arrays of 50-600 nm diameter holes in free-standing silicon nitride (SiN) solid films 100-500 nm thick. By pressing adhering live cells onto the nanostructured SiN surface and then removing them, planar cell membrane sheets (CMSs) were transferred in a well-defined orientation onto the SiN support. We demonstrate the accessibility to both extracellular and intracellular surfaces of CMSs by targeting membrane constituents side-specifically with fluorescent markers. Our approach is of interest for studying ligand-receptor interactions using optical, electrical, and scanning probe techniques at the single-molecule level.

Small Molecule Macroarray Construction via Ugi Four-Component Reactions

[reaction: see text] We report the construction of small molecule macroarrays via Ugi four-component reactions on planar cellulose supports. Array synthesis was enabled by the development of a high efficiency photocleavable linker system and the strategic use of both water- and microwave-assisted organic reactions.

DNA Multilayer Films on Planar and Colloidal Supports: Sequential Assembly of Like-Charged Polyelectrolytes

Multilayer films comprising solely negatively charged polyelectrolytes were sequentially assembled based on DNA hybridization. Films prepared from alternating layers of two-block homopolymeric nucleotides (polyA(20)G(20)/polyT(20)C(20)) grew linearly with increasing layer number, as verified by quartz crystal microgravimetry, UV-vis spectrophotometry and optical microscopy. Urea treatment of the films induced morphological changes, while exposure to low ionic strength solutions resulted in film disassembly. DNA multilayer films were also formed on silica particles, and DNA hollow capsules were obtained following dissolution of the template core.

Fabrication of Large Number Density Platinum Nanowire Arrays by Size Reduction Lithography and Nanoimprint Lithography

Large number density Pt nanowires with typical dimensions of 12 microm x 20 nm x 5 nm (length x width x height) are fabricated on planar oxide supports. First sub-20 nm single crystalline silicon nanowires are fabricated by size reduction lithography, and then the Si nanowire pattern is replicated to produce a large number of Pt nanowires by nanoimprint lithography. The width and height of the Pt nanowires are uniform and are controlled with nanometer precision. The nanowire number density is 4 x 10(4) cm(-1), resulting in a Pt surface area larger than 2 cm(2) on a 5 x 5 cm(2) oxide substrate. Bimodal nanowires with different width have been generated by using a Pt shadow deposition technique. Using this technique, alternating 10 and 19 nm wide nanowires are produced.

Metallurgy in a Beaker: Nanoparticle Toolkit for the Rapid Low-Temperature Solution Synthesis of Functional Multimetallic Solid-State Materials

Intermetallic compounds and alloys are traditionally synthesized by heating mixtures of metal powders to high temperatures for long periods of time. A low-temperature solution-based alternative has been developed, and this strategy exploits the enhanced reactivity of nanoparticles and the nanometer diffusion distances afforded by binary nanocomposite precursors. Prereduced metal nanoparticles are combined in known ratios, and they form nanomodulated composites that rapidly transform into intermetallics and alloys upon heating at low temperatures. The approach is general in terms of accessible compositions, structures, and morphologies. Multiple compounds in the same binary system can be readily accessed; e.g., AuCu, AuCu3, Au3Cu, and the AuCu-II superlattice are all accessible in the Au-Cu system. This concept can be extended to other binary systems, including the intermetallics FePt3, CoPt, CuPt, and Cu3Pt and the alloys Ag-Pt, Au-Pd, and Ni-Pt. The ternary intermetallic Ag2Pd3S can also be rapidly synthesized at low temperatures from a nanocomposite precursor comprised of Ag2S and Pd nanoparticles. Using this low-temperature solution-based approach, a variety of morphologically diverse nanomaterials are accessible: surface-confined thin films (planar and nonplanar supports), free-standing monoliths, nanomesh materials, inverse opals, and dense gram-scale nanocrystalline powders of intermetallic AuCu. Importantly, the multimetallic materials synthesized using this approach are functional, yielding a room-temperature Fe-Pt ferromagnet, a superconducting sample of Ag2Pd3S (Tc = 1.10 K), and a AuPd4 alloy that selectively catalyzes the formation of H2O2 from H2 and O2. Such flexibility in the synthesis and processing of functional intermetallic and alloy materials is unprecedented.

Copper‐Assisted Weak Polyelectrolyte Multilayer Formation on Microspheres and Subsequent Film Crosslinking

AbstractThe formation of weak polyelectrolyte films on planar and spherical supports has recently evoked major interest, as such coatings allow novel material properties to be tunable by pH and salt adjustment of the polyelectrolyte deposition conditions. We report on the build up of multilayers of the weak polyelectrolytes poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) on submicrometer‐sized polystyrene (PS) and silica colloid spheres (∼ 500 nm) with the aid of copper ion templating. The copper ions complex to the carboxylate groups of PAA, facilitating the formation of PAA/PAH multilayers on the particles. Regular growth of the layers on the colloid spheres with each polyelectrolyte deposition step was confirmed by microelectrophoresis, single‐particle light scattering (SPLS), and transmission electron microscopy (TEM), with an average bilayer thickness of ∼ 3 nm. The polyelectrolyte multilayer‐coated particles formed stable colloidal dispersions, with ζ‐potentials ranging from 30 mV (PAH outer layer) and –50 mV (PAA outer layer). Complementary quartz‐crystal microbalance and UV‐vis spectrophotometry studies on PAA/PAH multilayers formed on planar supports were performed to examine the film formation and the role of copper ion binding to the layers. PAA/PAH multilayers formed on colloid particles were also chemically crosslinked by using the activator 1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide (EDC). The degree of film crosslinking could be readily controlled by varying the concentration of EDC employed. Following solvent decomposition of the template particles coated with crosslinked PAA/PAH multilayers, intact hollow polymer capsules were obtained. These capsules were found to be impenetrable to polystyrene.

Out of the Oil Bath and into the Oven — Microwave‐Assisted Combinatorial Chemistry Heats up.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Surface-Modification of Polyelectrolyte Multilayer-Coated Particles for Biological Applications

Layer-by-layer multilayer films of poly(styrenesulfonate) (PSS) and 4th generation poly(amidoamine) dendrimer (4G PAMAM) assembled on particle supports were modified by a stepwise process involving (i) cross-linking of free amino groups of PSS/4G PAMAM multilayers using a bifunctional cross-linking agent, gluteraldehyde, which simultaneously chemically activates the surface, (ii) covalently linking the free aldehyde groups made available from the cross-linker with octadecylamine (fatty-acylation), and (iii) adsorbing a poly(ethylene glycol) (molecular weight ∼2000) derivative of distearylphosphatidylethanolamine (PEG2000-DSPE) on the fatty-acylated surface (PEGylation). Microelectrophoresis, confocal laser scanning microscopy, transmission electron microscopy, and differential scanning calorimetry were used to follow the modification of the PSS/4G PAMAM multilayer coatings on the particles. Analogous experiments were performed on planar supports (silicon, glass, and gold) to additionally quantify the process by Fourier transform infrared spectroscopy, atomic force microscopy, contact-angle, ellipsometry, and quartz crystal microbalance techniques. The experimental data from the colloid and planar supports were in mutual agreement, providing evidence for the stepwise surface modification of the multilayer films. Adsorption experiments involving biological cells or proteins and the surface-modified PSS/4G PAMAM multilayers were conducted to establish the surface biocompatibility of the modified films. Compared with the respective unmodified films, the surface-modified PSS/4G PAMAM multilayer-coated colloid particles showed reduced adhesion to the biological cell surfaces (macrophage cell line TPH-1), while the adsorbed amount of human serum albumin decreased upon exposure to the surface-modified PSS/4G PAMAM multilayer-coated planar substrates. This demonstrates the biocompatibility of the surface-modified multilayer films.

Out of the oil bath and into the oven--microwave-assisted combinatorial chemistry heats up.

The application of microwave irradiation to expedite solid-phase organic reactions could be the tool that allows combinatorial chemistry to deliver on its promise--providing rapid access to large collections of diverse small molecules. Herein, several different approaches to microwave (MW)-assisted solid-phase reactions and library synthesis are introduced, including the use of solid-supported reagents, multicomponent coupling reactions, solvent-free parallel library synthesis, and spatially addressable library synthesis on planar solid supports. The future impact of MW-assisted organic reactions on solid-phase and combinatorial chemistry could prove to be immense, and methods for further improvement of this strategic combination of technologies are highlighted.

Study of 2D Phase Transition of Polar Organic Dye Molecules at the Air-Water Interface by Using Granzing-Incidence X-Ray Diffraction

The grazing incidence X-ray diffraction from the 2D polar crystallites of organic dye molecules on an aqueous subphase was measured. The structure of the 2D crystallites shows a dependence on the subphase composition, and this dependence corresponds well to the results obtained from Langmuir-Blodgett films, which consist of the multilayer of the 2D crystallites deposited on the solid planar supports.

Nanofabrication of Planar Model Catalysts by Colloidal Lithography: Pt/Ceria and Pt/Alumina

We present a novel method, called colloidal lithography, to prepare well-defined model catalysts on planar supports. The method facilitates fabrication of monodisperse catalyst particles with variable, well-defined size, shape, and interparticle distance. The chemical and structural composition of the constituents (i.e., catalyst particles and support materials) may be independently varied. Large batches of model catalysts may be made in short processing times, with the dimensions of the samples only limited by the physical dimension of available support material, the processing vacuum systems, and so forth. Here we employed 2 in. Si wafers cut into 1 × 1 cm2 pieces as the primary lithography support, onto which the support (ceria and alumina) and active catalyst materials (Pt in this case) were deposited. A detailed chemical and structural characterization is presented of the individual steps in the fabrication process. The oxygen plasma used to remove the colloidal mask residues is shown to lead to substantial but reversible Pt oxidation. As a probe reaction, to validate the nanofabrication process, CO oxidation measurements were performed on 130 nm Pt particles on an alumina or a ceria support. The reactivity measurements are in good agreement with literature data and suggest a satisfactory performance of the colloidal lithography model catalysts.

Investigation of the Factors Influencing the Formation of Dendrimer/Polyanion Multilayer Films

Poly(amidoamine) dendrimer (PAMAM)/poly(styrenesulfonate) (PSS) multilayer films were prepared by an iterative electrostatic self-assembly process, viz., the layer-by-layer deposition of PAMAM and PSS onto planar supports. Multilayer film growth was monitored by UV−vis spectrophotometry, by use of a quartz crystal microbalance (QCM), and by ellipsometry and atomic force microscopy (AFM). The UV−vis data revealed an adsorption−desorption phenomenon that was sensitive to the pH and ionic strength of the PSS and dendrimer solutions, the dendrimer generation (2G, 3G, or 4G) and concentration, and the PSS molecular weight and concentration. This behavior was due to the different nature of interaction and complexation between the hierarchical (PAMAM) and linear (PSS) polyelectrolytes, both at the film−solution interface and in bulk solution. QCM experiments provided evidence for multilayer film growth, but the adsorption−desorption behavior precluded quantitative evaluation of the amount of polyelectrolyte depo...

Orientation selective immobilization of human erythrocyte membranes on ultrathin cellulose films

We report the orientation selective immobilization of human erythrocyte membranes on planar solid supports. The orientation of the immobilized membrane was identified with selective fluorescence labels. When the right-side-out (RSO) ghosts were incubated with planar glass cover slides, no adsorption or rupture of erythrocytes could be observed. To increase the interfacial attraction between cells and the surface, two types of hydrated polymer films were deposited on the glass cover slides; (a) physisorbed films of cationic polylysine, and (b) Langmuir–Blodgett (LB) films of cellulose derivatives. On polylysine films, patches of the ruptured membranes could be observed, but the surface coverage still remained poor. On the other hand, RSO ghosts were likely to coat the surface of cellulose films more continuously. The fluorescence labeling demonstrated that immobilized erythrocyte membranes selectively inverted their native orientation. Tentatively, we interpreted this larger surface coverage on the cellulose film in terms of the “wetting affinity” between the cell surface glycocalix and the polysaccharides. Such ultrathin (thickness 5–10 nm), biological polysaccharide films have a large potential to immobilize native cell membranes without denaturing their structure, membrane orientation, and functions.

Modeling heterogeneous catalysts: metal clusters on planar oxide supports

Model catalysts consisting of Au and Ag clusters of varying size have been prepared on single crystal TiO2(110) and ultra-thin films of TiO2, SiO2 and Al2O3. The morphology, electronic structure, and catalytic properties of these Au and Ag clusters have been investigated using low-energy ion scattering spectroscopy (LEIS), temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) and spectroscopy (STS) with emphasis on the unique properties of clusters <5.0 nm in size. Motivating this work is the recent literature report that gold supported on TiO2 is active for various reactions including low-temperature CO oxidation and the selective oxidation of propylene. These studies illustrate the novel and unique physical and chemical properties of nanosized supported metal clusters.

Models of metal catalysts: beyond single crystals

Because solid catalysts are typically complex in structure and composition, researchers have often used structurally simple models in attempts to identify catalytic sites and understand reaction mechanisms. Among models of metal catalysts, single crystals are the prototypes, but, because they cannot represent support effects or the smallest metal clusters and cannot easily be used in long-term catalyst testing, they are complemented by other types of model catalysts, including metal particles on well-defined planar supports and nearly molecular clusters of a few metal atoms each on metal oxide and zeolite supports. This account is a comparison of the various types of model metal catalysts and a summary of the advantages and limitations of each. Examples of rhodium and of platinum catalysts are given to illustrate the catalyst types and connections between them. More data are needed as a basis for comparisons of the performance of the various model catalysts.

Creating Spatially Addressed Arrays of Planar Supported Fluid Phospholipid Membranes

The use of planar supports for presenting large arrays of spatially addressed molecules is one of the most powerful and versatile methods for creating combinatorial libraries.1-3 These systems are starting to form the basis for a new generation of rapid screening assays and sensor devices in the biological and chemical sciences. Extending this approach to supported phospholipid bilayer membranes containing peptides, receptors, and integral membrane proteins is an especially valuable goal because of the ability of these systems to mimic many of the properties of native cell surfaces.4 Addressing biomembrane mimics on planar supports, however, presents unique challenges, as the twodimensional fluidity of the biomembrane must be preserved in many cases for it to function properly.5-7 The bilayer deposition process must take place in an aqueous environment, and the entire system must continue to remain submerged under water to preserve the planar supported structure. Because of this physical constraint as well as the inherent complexities of biomembrane materials, traditional technologies such as light-directed synthesis for addressing peptide or DNA sequences onto solid supports are inherently difficult to apply.1 We have, therefore, employed an alternate approach based upon depositing mesoscopic quantities of aqueous solution onto lithographically patterned hydrophilic surface well plates,8 followed by the immersion of the entire substrate into buffer. This is a general and flexible method for directing chemically distinct phospholipid membranes into individually addressable surface sectors. Previous studies have shown that patterned surfaces allow partitioning of one fluid lipid bilayer from the next.9,10 Molecules within an individual membrane are free to move within the confines of a single partition but do not cross over to a neighboring region. In the experiments presented here, planar borosilicate substrates were partitioned into arrays of micrometer-sized hydrophilic boxes using standard photolithography. Patterning was achieved by exposing the surface to ultraviolet light through a lithographic mask consisting of an array of square boxes. Developing the pattern and cleaning the substrate formed well plates of hydrophilic glass onto which picoliter-sized droplets of liposome solution were placed (Figure 1). The liposomes, which were small unilamellar vesicles (SUVs) of phospholipids, were present at 1 mg/mL concentration in a pH 7.0, 100 mM sodium phosphate buffer solution. Figure 2 shows the epifluorescence image of nine 50 μm × 50 μm well plates that have been addressed with three chemically