Hydrophobic Template Research Articles

Patterning of Hybrid Metal Halide Perovskite via Printed Molecular Templates

AbstractPatterning metal halide perovskite thin films is a necessary pathway to expand their optoelectronic applications. However, developing a suitable patterning technique is challenging as conventional lithographic processes are either detrimental to the perovskite layer or lack compatibility with scalable fabrication processes used in the manufacturing of printed electronics. In this work, a complete bottom‐up patterning method is proposed based on de‐wetting from a hydrophobic molecular template, which constrains the perovskite ink to directly crystallize in selected hydrophilic regions. Octadecylphosphonic acid molecules are used as the hydrophobic template and are effectively transferred onto metal‐oxide substrates via micro‐contact printing. This allows for a low‐cost, rapid, and scalable micron‐scale patterning of perovskite thin films. Facile control over light transmittance is demonstrated by adjusting the amount of exposed area and the corresponding spectral shape changes shift the film's appearance toward being color‐neutral. Finally, the method's scalability and versatility are shown by fabricating 25 cm2 patterned films over rigid and flexible substrates.

Chaotropic and Kosmotropic Anions Regulate the Outcome of Enzyme-Mediated Dynamic Combinatorial Libraries of Cyclodextrins in Two Different Ways.

We demonstrate how different anions from across the Hofmeister series can influence the behavior of enzyme-mediated dynamic combinatorial libraries of cyclodextrins (CDs). Using cyclodextrin glucanotransferase to catalyze reversible transglycosylation, dynamic mixtures of interconverting cyclodextrins can be formed wherein the relative concentrations of α-CD, β-CD and γ-CD is determined by their intrinsic stabilities and any stabilizing influences of added template (guest) molecules. Here, we find that addition of high concentrations of kosmotropic anions can be used to enhance the effects of added hydrophobic templates, while chaotropic anions can themselves act as templates, causing predictable and significant changes in the cyclodextrin composition due to weak, but specific, binding interactions with α-CD.

Preparation of superhydrophobic flexible tubes with water and blood repellency based on template method

Superhydrophobic surfaces have been widely used in biology, medicine, aerospace and other fields due to their special surface wettability. The surface wettability of materials mainly depends on the surface chemical composition and surface morphology. Therefore, the wettability of materials can be effectively controlled by changing the surface chemical composition and surface morphology. In this paper, the hydrophobic templates with different wettability were obtained by controlling the laser etching distance of 6061 aluminium alloy tube surface. The superhydrophobic flexible tubes were further fabricated using prepared 6061 aluminum alloy tubes as the template and polydimethylsiloxane (PDMS) for replica. The contact angles of water and blood could reach 162.8°and 152.1° respectively. By using scanning electron microscopy (SEM) and fourier transform infrared spectroscopy (FTIR), it could be seen that there were micron-sized structures and hydrophobic groups on the surface. The free energy on the surface of superhydrophobic PDMS was 70.7% lower than that on smooth PDMS. In addition, the superhydrophobic flexible tube had excellent durability and abrasion resistance, and the prepared surface was also blood repellency. Blood droplets easily passed through the inclined flexible tube without contaminating the tube. And the superhydrophobic flexible tubes could be used in various fields requiring productivity extensively, such as medical catheters.

Self-Assembly and Ordering of Peptide-Based Cavitands in Water and DMSO: The Power of Hydrophobic Effects Combined with Neutral Hydrogen Bonds.

Directional self-assembly of uncharged molecules in water is a major challenge in supramolecular chemistry. Herein, it is demonstrated that peptide-based cavitands wrap around a hydrophobic core (fullerene C60 ) by a combination of the hydrophobic effect and hydrogen-bonding interactions to form highly ordered three-component complexes in water that resemble the molten-globule stage of protein folding. The complexes were characterized by DOSY NMR spectroscopy, small-angle X-ray scattering, and circular dichroism, and their structures were confirmed by X-ray crystallography. Enhancement of the CD signals by nearly one order of magnitude and increased hydrolytic stability of hydrazone bonds of the complexes relative to the nonassembled species were observed. In contrast, DMSO and DMSO/water mixtures were found to be highly disintegrative for these complexes. Interestingly, some cavitands can only be synthesized in the presence of the hydrophobic template followed by disassembly of the complexes.

Hydrophobic Cobalt-Ethylimidazolate Frameworks: Phase-Pure Syntheses and Possible Application in Cleaning of Contaminated Water.

Two highly porous Co-based metal-azolate frameworks (MAFs), MAF-5(Co) and MAF-6(Co), which are isostructural with MAF-5(Zn) and MAF-6(Zn), respectively, were first synthesized in high yield and purity at room temperature. The syntheses compared two mixing methods, slow and fast, using cobalt acetate as the metal ion (Co2+) source and 2-ethylimidazole as the ligand. Triethylamine was applied as an additive/promoter in aqueous/ethanol solutions, and benzene and cyclohexane were used as hydrophobic templates. Phase-pure MAF-5(Co) and MAF-6(Co) were obtained in high yield by optimizing the mixing speed, reactant composition, and solvent/template ratio. It was found that fast mixing of the reactant mixtures was effective for synthesizing MAF(Co) materials. MAF-5(Co) and MAF-6(Co) were found to be very hydrophobic, similar to the MAFs composed of Zn, suggesting possible applications in water purification. MAF-5(Co) and MAF-6(Co) were then applied to adsorb n-octane as a model oil and nonpolar adsorbate from water, and the obtained results were compared to those of related materials, i.e., MAF-4(Co and Zn), MAF-5(Zn), and MAF-6(Zn), as well as with Cu-BTC (Cu-benzenetricarboxylate) and a conventional adsorbent, activated carbon. Surprisingly, despite having low porosity, MAF-5(Co) showed remarkable competitiveness among the typical porous materials for n-octane removal. The results suggest that the framework structure such as cavity and aperture sizes rather than surface area plays a significant role in n-octane removal. Moreover, MAF-5(Co) can easily be regenerated by simple evacuation and reused, and thus it was found to be a potential adsorbent for the removal of spilled oil from water. Additionally, MAFs were applied in the adsorption of diclofenac sodium from water, showing the competitiveness of MAFs in water purification probably because of hydrophobicity.

Water-Soluble Molecularly Imprinted Nanoparticle Receptors with Hydrogen-Bond-Assisted Hydrophobic Binding.

Molecularly imprinted nanoparticles (MINPs) were prepared when surfactants with a tripropargylammonium headgroup and a methacrylate-functionalized hydrophobic tail were cross-linked in the micelle form on the surface and in the core in the presence of hydrophobic template molecules. With the surfactants containing an amide bond near the headgroup, the MINPs had a layer of hydrogen-bonding groups in the interior that strongly influenced their molecular recognition. Templates/guests with strong hydrogen-bonding groups in the midsection of the molecule benefited most, especially if the hydrophobe of the template could penetrate the amide layer to reach the hydrophobic core of the cross-linked micelles. The location and the orientation of the hydrophilic groups were also important, as they determined how the template interacted with the surfactant micelles and, ultimately, with the MINP receptors.

The Structural Role of Cholesterol in Cell Membranes: From Condensed Bilayers to Lipid Rafts

CONSPECTUS: Defining the two-dimensional structure of cell membranes represents one of the most daunting challenges currently facing chemists, biochemists, and biophysicists. In particular, the time-averaged lateral organization of the lipids and proteins that make up these natural enclosures has yet to be established. As the classic Singer-Nicolson model of cell membranes has evolved over the past 40 years, special attention has focused on the structural role played by cholesterol, a key component that represents ca. 30% of the total lipids that are present. Despite extensive studies with model membranes, two fundamental issues have remained a mystery: (i) the mechanism by which cholesterol condenses low-melting lipids by uncoiling their acyl chains and (ii) the thermodynamics of the interaction between cholesterol and high- and low-melting lipids. The latter bears directly on one of the most popular notions in modern cell biology, that is, the lipid raft hypothesis, whereby cholesterol is thought to combine with high-melting lipids to form "lipid rafts" that float in a "sea" of low-melting lipids. In this Account, we first describe a chemical approach that we have developed in our laboratories that has allowed us to quantify the interactions between exchangeable mimics of cholesterol and low- and high-melting lipids in model membranes. In essence, this "nearest-neighbor recognition" (NNR) method involves the synthesis of dimeric forms of these lipids that contain a disulfide moiety as a linker. By means of thiolate-disulfide interchange reactions, equilibrium mixtures of dimers are then formed. These exchange reactions are initiated either by adding dithiothreitol to a liposomal dispersion to generate a small amount of thiol monomer or by including a small amount of thiol monomer in the liposomes at pH 5.0 and then raising the pH to 7.4. We then show how such NNR measurements have allowed us to distinguish between two very different mechanisms that have been proposed for cholesterol's condensing effect: (i) an umbrella mechanism in which the acyl chains and cholesterol become more tightly packed as cholesterol content increases because they share limited space under phospholipid headgroups and (ii) a template mechanism whereby cholesterol functions as a planar hydrophobic template at the membrane surface, thereby maximizing hydrophobic interactions and the hydrophobic effect. Specifically, our NNR experiments rule out the umbrella mechanism and provide strong support for the template mechanism. Similar NNR measurements have also allowed us to address the question of whether the interactions between low-melting kinked phospholipids and cholesterol can play a significant role in the formation of lipid rafts. Specifically, these NNR measurements have led to our discovery of a new physical principle in the lipids and membranes area that must be operating in biological membranes, that is, a "push-pull" mechanism, whereby cholesterol is pushed away from low-melting phospholipids and pulled toward high-melting lipids. Thus, to the extent that lipid rafts play a role in the functioning of cell membranes, low-melting phospholipids must be active participants.

Exploring a Two-Step Adsorption of An Intrinsically Disordered Peptide at Model Templates

Biological processes offer several intriguing examples of directed self-assembly into higher order structures that influence human health and well-being. The aggregation of microtubule associating protein Tau, an intrinsically disordered soluble protein that forms neurofibrillar tangles in cells in Alzheimer's disease may be directed by the presence of hydrophobic templates. Using various lipid monolayers and lipid-free surfaces we monitor the adsorption and aggregation kinetics of Tau proteins to these model membranes. Monitoring the surface tension change shows a two-step adsorption process followed by these proteins. A novel microrheology and quartz crystal microbalance study shows that the first step is dominated by the N-terminus of peptide, while the second step is possibly due to an intermediate hair-pin structure. Our microrheology data also show that the viscoelastic properties of these proteins is dominated by the proteins propensity to aggregate.

Layer-by-Layer Assembly of Azulene-Based Supra-Amphiphiles: Reversible Encapsulation of Organic Molecules in Water by Charge-Transfer Interaction

Stable multilayer films have been fabricated on the basis of alternating layer-by-layer assembly of an azulene-based supra-amphiphile and a photoreactive polyanion. Moreover, one component of the supra-amphiphile, pyrene, can be removed from the multilayer films, generating functional surface-imprinted multilayer films. Uptake experiments show that the surface-imprinted films are capable of recognizing the hydrophobic template molecule in water. The reloading process increases with increasing of temperature. The loading capacity can be regulated by change of the layer pairs. In addition, the as-prepared multilayers are promising in purification of pyrene-polluted water.

Antimicrobial activity and mode of action of novel, N-terminal tagged tetra-peptidomimetics

We report herein, synthesis and mode of action of novel, cell selective, N-terminal tagged tetra-peptide conjugates. Analogues AP1 and AP2 with linoleic acid and p-terphenyl carboxylic acid tagging showed potent activity against Gram-positive and Gram-negative bacterial strains including the clinically relevant pathogen MRSA. For active analogues interaction studies with model bacterial mimic membranes revealed a direct correlation between activity and membrane perturbation. Further, active conjugates showed membrane depolarization and severe bacterial membrane disrupting ability. The hydrophobic–charge–hydrophobic template designed here can be useful in further optimizing end tagged peptidomimetics for therapeutic potential.

The encapsulation of an amphiphile into polystyrene microspheres of narrow size distribution

Encapsulation of compounds into nano- or microsized organic particles of narrow size distribution is of increasing importance in fields of advanced imaging and diagnostic techniques and drug delivery systems. The main technology currently used for encapsulation of molecules within uniform template particles while retaining their size distribution is based on particle swelling methodology, involving penetration of emulsion droplets into the particles. The swelling method, however, is efficient for encapsulation only of hydrophobic compounds within hydrophobic template particles. In order to be encapsulated, the molecules must favor the hydrophobic phase of an organic/aqueous biphasic system, which is not easily achieved for molecules of amphiphilic character.The following work overcomes this difficulty by presenting a new method for encapsulation of amphiphilic molecules within uniform hydrophobic particles. We use hydrogen bonding of acid and base, combined with a pseudo salting out effect, for the entrapment of the amphiphile in the organic phase of a biphasic system. Following the entrapment in the organic phase, we demonstrated, using fluorescein and (antibiotic) tetracycline as model molecules, that the swelling method usually used only for hydrophobes can be expanded and applied to amphiphilic molecules.

Hydrophobic Templates with Rough Patterns Fabricated by Laser Micromachining for Liquid Droplets Generation

This paper presents an approach to utilize high precision pulsed Nd:YAG laser to fabricate a rough array-pattern on a soda-lime glass plate by a laser-induced backside writing (LIBW) process, and a laser-induced plasma assisted ablation (LIPAA) technique. The current study investigates the effect of process parameters such as single-shot laser exposure time and number of passes on the material removal rate. After depositing 695 nm thick Teflon thin film on the glass plate, the surface of the laser micro-machined template becomes hydrophobic. The surface roughness, annular groove profile and surface micrograph were measured by an atomic force microscope, a profilometer, and a scanning electron microscope, respectively. A uniform liquid droplet by the sessile drop method is generated on the hydrophobic template. Droplet characteristics, such as contacted angle, size, and shape, are measured with a surface tension analyzer and microscope. This work also discusses the relationship between the formed droplets and the process recipe of the micro-machined template. The proposed approach can apply to future for uniform lens array formation.

Nucleation and Crystallization of Lysozyme: Role of Substrate Surface Chemistry and Topography

In an effort to better understand, direct and control the crystallization of molecular and macromolecular compounds, an approach using colloidal templates as substrates for heterogeneous nucleation was investigated. These templates combine both tuneable chemical functionalities and geometrical features, altering the crystal–substrate interactions. Colloidal templates were prepared from silica nanoparticles, where the surface chemistry was modified by silanization. Particle size varied from 30 to 700 nm, with silanols, NH2, CF3, phenyl, or dodecyl as surface functional groups. Here, we report on the template assisted crystallization of chicken egg white lysozyme (CEWL). Nucleation was dramatically affected by the surface chemistry and topography of the templates. Using 220 nm particles, hydrophobic templates generally produced fewer, larger crystals, while a larger number of small crystals were obtained on hydrophilic templates. The use of different particle sizes also affected the crystal size, the optimal for nucleation being 432 nm. Classical Nucleation Theory (CNT) can interpret surface chemistry effects but does not support the effect of particle size. This paper reports that the combined use of both geometrical and chemical interactions results in an increased ability to control the nucleation and growth of protein crystals.

Laser-assisted fabrication of submicron-structured hydrophilic/ hydrophobic templates for the directed self-assembly of alkylsiloxane monolayers into confined domains

A highly focused laser beam at a wavelength of 514 nm is used to pattern hydrophilic, surface-oxidized silicon substrates. Irradiation converts the affected surface areas from hydrophilic to hydrophobic and hence provides a means to prepare hydrophilic/hydrophobic patterns. The patterns are stable for weeks or longer, even if the samples are stored at ambient conditions. Contrary to ordinary avenues to hydrophilic/hydrophobic patterns no coating is required. This makes the procedure extremely simple and robust. Routine patterning can be carried out over large areas at fast writing speeds under ambient conditions. At a focal spot diameter of about 2.5 μm, hydrophobic lines with a width down to 0.4 μm are prepared indicating a highly superlinear dependence of the overall process on the laser intensity. The patterned substrates might be useful in a broad variety of applications. In particular, as shown here, they represent suitable templates for the directed self-assembly of organic monolayers.

Carbonised template molecular sieve silica membranes in fuel processing systems: permeation, hydrostability and regeneration

The permeation, hydrothermal stability (steam resilience) and regeneration behaviour of carbonised template molecular sieve silica (CTMSS) membranes were tested in this work for hydrogen purification in fuel cell fuel processing systems. A hydrostable CTMSS membrane was made using a novel surfactant templating procedure and compared with a standard non-templated molecular sieve silica (MSS) membrane. The MSS membrane H 2 permeance and H 2/CO permselectivity at 200 °C were in the order of 4.8 × 10 −8 mol m −2 s −1 Pa −1 and 16, respectively. The hydrostable CTMSS membrane compared quite closely at the same conditions, having a H 2 flux and H 2/CO permselectivity of 2.1 × 10 −8 mol m −2 s −1 Pa −1 and 13, respectively. When exposed to synthetic reformate gas, both membranes showed similar results to those obtained in pure gas streams. After steam was introduced at 34 mol%, the MSS membrane H 2/CO selectivity dropped to half its original value, while the hydrostable CTMSS membrane showed no major selectivity variation. Permeation decreased with time regardless of the membrane tested, indicating the effect of water on silica films. Upon regeneration, the CTMSS membrane H 2 permeance returned to its originally tested value, while the standard MSS membrane showed no improvement. As steam is present in gas reforming for fuel cells application, the hydrophobic template modifications are essential for stable membrane operation.

Micropatterned carbohydrate displays by self-assembly of glycoconjugate polymers on hydrophobic templates on silicon.

We report a novel strategy for micropatterned carbohydrate displays on Si substrates. This method exploited the hydrophobic-hydrophilic microfabrication by photolithography of ODS-SAM on Si substrates and the subsequent selective self-assembly of glycoconjugate polymers onto the hydrophobic regions. Protein micropatterning by molecular recognition on the carbohydrate substrates was also successful.

Photoinitiated Synthesis and Characterization of P(MMA/DPB) Polymer Nanoparticles Using Poly(N-isopropylacrylamide) in Aqueous Solutions as a Template

The photoinitiated polymerization of methyl methacrylate (MMA) using 2,3-diphenylbutadiene (DPB) as cross-linking agent and benzoin (BN), benzoin methyl ether (BME), and irgacure (IGC) as photoinitiators in the presence of poly(N-isopropylacrylamide) (PNIPAM) as a water-soluble, hydrophobic template polymer in H2O/DMF led to the formation of P(MMA/DPB) polymer latex particles. These particles were analyzed by using TEM in combination with the program IMAGE (NIH/USA). After purification by precipitation using THF/H2O, globular latex particles were found. Using BME as photoinitiator, “real nanoparticles” possessing a smaller diameter than 10 nm were formed among bigger particles (d > 20 nm). The CHN analysis of the P(MMA/DPB) polymers indicated that a smaller fraction of PNIPAM (4−10%) was incorporated into the latex particles.

Infrared Spectroscopic Characterization of Lipid−Alkylsiloxane Hybrid Bilayer Membranes at Oxide Substrates

Successive depositions of precompressed Langmuir monolayers have been shown to allow reproducible formation of air-stable, lipid−alkylsiloxane hybrid bimolecular architectures at oxidic supports. Specifically, prepolymerized Langmuir−Blodgett films of n-octadecylsiloxane (OTS) monolayers on oxided silicon substrates were used as the hydrophobic templates, upon which compressed monolayers of dipalmitoyl-sn1-glycerophosphatidylcholine (DPPC) and monosialogangliosides (Gm1) were deposited from a low-temperature air−water interface by the horizontal deposition method. Structural features of each leaflet of the resultant bimolecular architectures, namely DPPC/OTS/SiO2/Si and Gm1/OTS/SiO2/Si, were characterized using a combined application of infrared spectroscopy, null-ellipsometry, and surface wetting measurements. In both cases, the outer lipid leaflet (DPPC or Gm1) was found to be structurally decoupled with respect to the inner OTS layer. The inner silane layer was composed of essentially untilted (cant an...

In Situ Monitoring of Hydrogel Polymerization Using Speckle Interferometry

Electronic speckle pattern interferometry (ESPI) was proposed to study the polymerization kinetics of hydrogels in water. The potentials of the technique were demonstrated by studying the asymmetrical hydrogel formation between a hydrophobic template and a hydrophilic template. By ESPI, the spatial distribution of gelation was successfully followed in real time, and the concentration distribution of polymer gel was evaluated. By use of this technique, it was for the first time found that the gelation was suppressed at the hydrophobic surface and resulted in an inhomogeneous distribution of the polymer network density between two templates.

A new "hydrophobic template" method detects segments forming transmembrane α-helical bundles in ion channels

We present a “hydrophobic template” method enabling recognition of α-helix bundles in membrane channels from sequence analysis. Inspection of hydrophobic properties of pore-forming helices in proteins with known structure (A-B5 toxins) permits delineation of a common polarity motif: two hydrophobic surface stretches separated by polar areas. The bundles are stabilized by nonpolar interhelical contacts. A number of transmembrane segments were checked for presence of this motif, and it was detected for pore-forming helices of several ion transporters (segments M2 of acetylcholine and GABAA receptors, α5 peptide of δ-endotoxin), which reveal five α-helix bundle architecture. Applications of the method to modeling of membrane channels are discussed.