In Situ AFM Studies on Self-Assembled Monolayers of Adsorbed Surfactant Molecules on Well-Defined H-Terminated Si(111) Surfaces in Aqueous Solutions

The formation of self-assembled monolayers (SAMs) of adsorbed cationic or anionic surfactant molecules on atomically flat H-terminated Si(111) surfaces in aqueous solutions was investigated by in situ AFM measurements, using octyl trimethylammonium chloride (C8TAC), dodecyl trimethylammonium chloride (C12TAC), octadecyl trimethylammonium chloride (C18TAC)) sodium dodecyl sulfate (STS), and sodium tetradecyl sulfate (SDS). The adsorbed surfactant layer with well-ordered molecular arrangement was formed when the Si(111) surface was in contact with 1.0 × 10-4 M C18TAC, whereas a slightly roughened layer was formed for 1.0 × 10-4 M C8TAC and C12TAC. On the other hand, the addition of alcohols to solutions of 1.0 × 10-4 M C8TAC, C12TAC, or SDS improved the molecular arrangement in the adsorbed surfactant layer. Similarly, the addition of a salt, KCl, also improved the molecular arrangement for both the cationic and anionic surfactant layers. Moreover, the adsorbed surfactant layer with a well-ordered structure was formed in a solution of mixed cationic (C12TAC) and anionic (SDS) surfactants, though each surfactant alone did not form the well-ordered layer. These results were all explained by taking into account electrostatic repulsion between ionic head groups of adsorbed surfactant molecules as well as hydrophobic interaction between their alkyl chains, which increases with the increasing chain length, together with the increase in the hydrophobic interaction or the decrease in the electrostatic repulsion by incorporating alcohol molecules into the adsorbed surfactant layer, the decrease in the electrostatic repulsion by increasing the concentration of counterions, and the decrease in the electrostatic repulsion by alternate arrangement of cationic and anionic surfactant molecules. The present results have revealed various factors to form the well-ordered adsorbed surfactant layers on the H−Si(111) surface, which have a possibility of realizing the third generation surfaces with flexible structures and functions easily adaptable to circumstances

Novel Solid-State Polymerization of Crystalline Monomer. Dehydrative Polycondensation of 1,3-Bis(hydroxyphenylmethyl)benzene

Novel Solid-State Polymerization of Crystalline Monomer. Dehydrative Polycondensation of 1,3-Bis(hydroxyphenylmethyl)benzen

Four Stereoisomeric Norbornadiene Dimers Containing a Cyclopropane Ring: ROMP, Polymer Properties, and Post-Polymerization Modification

The efficient and selective introduction of functional groups to hydrocarbon polymers enables facile access to new polymer materials with various physical properties. In the present study, we have focused on cyclopropane-containing norbornadiene dimers (NBDDs) as bifunctional monomers and post-polymerization modification (PPM) for the synthesis of functionalized cyclic olefin polymers (COPs). The ring-opening metathesis polymerization (ROMP) of the four NBDD stereoisomers (exo-exo, exo-endo, endo-exo, and endo-endo) and the subsequent hydrogenation proceeded selectively to give the corresponding COPs (H-poly­(NBDD)­s) with reactive cyclopropane moieties. There are distinct differences between the four isomers in terms of polymerization rate and the physical properties of the resultant polymers. The endo-exo- and endo-endo-NBDDs show lower ROMP reactivities than the exo-exo- and exo-endo-NBDDs due to steric hindrance. All of the polymers before and after hydrogenation are amorphous, regardless of annealing (with the exception for the unannealed H-poly­(exo-endo-NBDD)). Compared with the polymers of the exo-norbornenyl isomers, their endo-counterparts show lower solubilities, higher glass transition temperatures, sharper X-ray diffraction peaks, and larger d-spacings. The highly soluble H-poly­(exo-exo-NBDD) was employed for the PPM via protic acid-catalyzed cyclopropane ring-opening to produce six new COPs bearing acyloxy, alkoxy, or aryl groups. Although rearrangements occur during ring-opening presumably through nonclassical carbocations, the polymer structures were determined with reference to the reactions of their corresponding monomeric model compounds. The PPM with m-xylene, for example, proceeds regioselectively while maintaining a narrow molecular weight distribution to produce a xylyl-substituted COP with good solubility and high thermal stability

Cooperative N‑Heterocyclic Carbene/Brønsted Acid Catalysis for the Tail-to-Tail (Co)dimerization of Methacrylonitrile

The first tail-to-tail dimerization of methacrylonitrile (MAN) has been realized by the cooperative use of N-heterocyclic carbene (NHC) and Brønsted acid catalysts, producing 2,5-dimethylhex-2-enedinitrile with the <i>E/Z</i> ratio of 24:76. Although the NHC alone was not effective for the catalysis, the addition of alcohols resulted in the significant increase of the dimer yield up to 82% in the presence of 5 mol % NHC. Detailed experimental studies including the ESI-MS analysis of the intermediates, stoichiometric (co)­dimerizations, and deuterium-labeling experiments revealed the mechanistic aspects of the proton transfer, isomerization, umpolung, and rate-limiting steps, allowing us to observe several mechanistic differences between the dimerization of MAN and that of methyl methacrylate. The stoichiometric reactions in the presence and absence of an alcohol suggest that the alcohol additives play a role in promoting the intermolecular proton transfers from the deoxy-Breslow intermediate to the regenerated NHC in the second half of the catalytic cycle. In addition, the codimerizations of MAN with <i>n</i>-butyl methacrylate (<i>n</i>-BuMA) have been studied. While the dimerization of <i>n</i>-BuMA was sluggish in the presence of an alcohol, the catalytic activity for the codimerization was enhanced by the cooperative systems

Thiol-Mediated Controlled Ring-Opening Polymerization of Cysteine-Derived β‑Thiolactone and Unique Features of Product Polythioester

The controlled ring-opening polymerization of the β-thiolactone derived from <i>N</i>-Boc cysteine was achieved using <i>N</i>-Boc-<i>L</i>-cysteine methyl ester as the initiator in NMP at room temperature. The propagating end is the thiol group, which attacks the carbonyl to open the monomer ring by the C­(O)–S bond scission. A thiol–ene click reaction demonstrated the utility of the thiol group at the propagating terminal. The block copolymer was efficiently produced by the terminal coupling of the polythioester with the norbornene terminated PEG. As another interesting reaction, the polythioester underwent the main chain transformation to polycysteine through the intramolecular S-to-N acyl migration, triggered by the deprotection of the pendant Boc groups. The polythioester from <i>L-</i>cysteine showed Cotton effects between 200 and 300 nm in the circular dichroism (CD) spectrum. Although the CD pattern resembled that produced by the α-helix of polypeptide, it was ascribable not to the second structure but to the relative orientation of the thioester and carbamate carbonyls in the repeating unit

Negative Dielectrophoretic Patterning with Colloidal Particles and Encapsulation into a Hydrogel

Microparticle patterns have been fabricated on a nonconductive glass substrate and a conductive indium tin oxide (ITO) substrate using negative dielectrophoresis (n-DEP). The patterned microparticles on the substrate were immobilized by covalent bonding or embedded into polymer sheets or strings. The patterning device consisted of an ITO interdigitated microband array (IDA) electrode as the template, a glass or ITO substrate, and a polyester film (10-μm thickness) as the spacer. A suspension of 2-μm-diameter polystyrene particles was introduced into the device between the upper IDA and the bottom glass or ITO support. An ac electrical signal (typically 20 Vpp, 3 MHz) was then applied to the IDA, resulting in the formation of line patterns with low electric field gradient regions on the bottom support. When the glass substrate was used as the bottom support, the particles aligned under the microband electrodes of the IDA within 5 s because the aligned areas on the support were regions with the weakest electric field; however, for the ITO support, the particles were directed to the regions under the electrode gap and aligned on the support because these regions had the weakest electric field. The width of the particle lines could be roughly controlled by regulating the initial concentration of the suspended particles. The particles forming the line and grid patterns with single-particle widths were immobilized by using a cross-linking reaction between the amino groups on the aligned particles and N-hydroxysuccinimide-activated ester on the glass substrate activated by succinimidyl 4-(p-maleimidophenyl)-butyrate (SMPB). The patterned particles were also embedded in a photoreactive hydrogel polymer. A prepolymer solution of poly(ethylene glycol) diacrylate (PEG-DA) was used as the suspension medium to maintain the particle patterns in the polymerized hydrogel sheet and string following photopolymerization. The hydrogel sheets with particle patterns were fabricated by ultraviolet (UV) irradiation through the ITO-IDA template for 120 s. Hydrogel strings with the aligned particles were fabricated by using a conductive ITO support and a Pt-IDA template. Pt-IDA was used as a template as well as a photomask to block UV transmission. The present procedure affords extremely simple, rapid, and highly reproducible fabrication of particle arrays. The reusability of the template IDA electrode is also a substantial advantage over previous methods

Catalytic Enantioselective Synthesis of Key Intermediates for Triazole Antifungal Agents

A short-step synthesis of versatile chiral building blocks for triazole antifungal agents such as ZD0870 and Sch45450 was developed via catalytic enantioselective cyanosilylation of electron-deficient ketones as the key step. High enantioselectivity was produced using a catalyst prepared from Gd(HMDS)3 and ligand 5 in a 2:3 ratio. This new catalyst preparation method was superior to the previous method using Gd(OiPr)3 as a metal source. A rationale for the difference is proposed on the basis of structural studies of the catalyst complexes using ESI-MS

Negative Dielectrophoretic Patterning with Colloidal Particles and Encapsulation into a Hydrogel

Microparticle patterns have been fabricated on a nonconductive glass substrate and a conductive indium tin oxide (ITO) substrate using negative dielectrophoresis (n-DEP). The patterned microparticles on the substrate were immobilized by covalent bonding or embedded into polymer sheets or strings. The patterning device consisted of an ITO interdigitated microband array (IDA) electrode as the template, a glass or ITO substrate, and a polyester film (10-μm thickness) as the spacer. A suspension of 2-μm-diameter polystyrene particles was introduced into the device between the upper IDA and the bottom glass or ITO support. An ac electrical signal (typically 20 Vpp, 3 MHz) was then applied to the IDA, resulting in the formation of line patterns with low electric field gradient regions on the bottom support. When the glass substrate was used as the bottom support, the particles aligned under the microband electrodes of the IDA within 5 s because the aligned areas on the support were regions with the weakest electric field; however, for the ITO support, the particles were directed to the regions under the electrode gap and aligned on the support because these regions had the weakest electric field. The width of the particle lines could be roughly controlled by regulating the initial concentration of the suspended particles. The particles forming the line and grid patterns with single-particle widths were immobilized by using a cross-linking reaction between the amino groups on the aligned particles and N-hydroxysuccinimide-activated ester on the glass substrate activated by succinimidyl 4-(p-maleimidophenyl)-butyrate (SMPB). The patterned particles were also embedded in a photoreactive hydrogel polymer. A prepolymer solution of poly(ethylene glycol) diacrylate (PEG-DA) was used as the suspension medium to maintain the particle patterns in the polymerized hydrogel sheet and string following photopolymerization. The hydrogel sheets with particle patterns were fabricated by ultraviolet (UV) irradiation through the ITO-IDA template for 120 s. Hydrogel strings with the aligned particles were fabricated by using a conductive ITO support and a Pt-IDA template. Pt-IDA was used as a template as well as a photomask to block UV transmission. The present procedure affords extremely simple, rapid, and highly reproducible fabrication of particle arrays. The reusability of the template IDA electrode is also a substantial advantage over previous methods

Negative Dielectrophoretic Patterning with Colloidal Particles and Encapsulation into a Hydrogel

Microparticle patterns have been fabricated on a nonconductive glass substrate and a conductive indium tin oxide (ITO) substrate using negative dielectrophoresis (n-DEP). The patterned microparticles on the substrate were immobilized by covalent bonding or embedded into polymer sheets or strings. The patterning device consisted of an ITO interdigitated microband array (IDA) electrode as the template, a glass or ITO substrate, and a polyester film (10-μm thickness) as the spacer. A suspension of 2-μm-diameter polystyrene particles was introduced into the device between the upper IDA and the bottom glass or ITO support. An ac electrical signal (typically 20 Vpp, 3 MHz) was then applied to the IDA, resulting in the formation of line patterns with low electric field gradient regions on the bottom support. When the glass substrate was used as the bottom support, the particles aligned under the microband electrodes of the IDA within 5 s because the aligned areas on the support were regions with the weakest electric field; however, for the ITO support, the particles were directed to the regions under the electrode gap and aligned on the support because these regions had the weakest electric field. The width of the particle lines could be roughly controlled by regulating the initial concentration of the suspended particles. The particles forming the line and grid patterns with single-particle widths were immobilized by using a cross-linking reaction between the amino groups on the aligned particles and N-hydroxysuccinimide-activated ester on the glass substrate activated by succinimidyl 4-(p-maleimidophenyl)-butyrate (SMPB). The patterned particles were also embedded in a photoreactive hydrogel polymer. A prepolymer solution of poly(ethylene glycol) diacrylate (PEG-DA) was used as the suspension medium to maintain the particle patterns in the polymerized hydrogel sheet and string following photopolymerization. The hydrogel sheets with particle patterns were fabricated by ultraviolet (UV) irradiation through the ITO-IDA template for 120 s. Hydrogel strings with the aligned particles were fabricated by using a conductive ITO support and a Pt-IDA template. Pt-IDA was used as a template as well as a photomask to block UV transmission. The present procedure affords extremely simple, rapid, and highly reproducible fabrication of particle arrays. The reusability of the template IDA electrode is also a substantial advantage over previous methods

Negative Dielectrophoretic Patterning with Colloidal Particles and Encapsulation into a Hydrogel

Microparticle patterns have been fabricated on a nonconductive glass substrate and a conductive indium tin oxide (ITO) substrate using negative dielectrophoresis (n-DEP). The patterned microparticles on the substrate were immobilized by covalent bonding or embedded into polymer sheets or strings. The patterning device consisted of an ITO interdigitated microband array (IDA) electrode as the template, a glass or ITO substrate, and a polyester film (10-μm thickness) as the spacer. A suspension of 2-μm-diameter polystyrene particles was introduced into the device between the upper IDA and the bottom glass or ITO support. An ac electrical signal (typically 20 Vpp, 3 MHz) was then applied to the IDA, resulting in the formation of line patterns with low electric field gradient regions on the bottom support. When the glass substrate was used as the bottom support, the particles aligned under the microband electrodes of the IDA within 5 s because the aligned areas on the support were regions with the weakest electric field; however, for the ITO support, the particles were directed to the regions under the electrode gap and aligned on the support because these regions had the weakest electric field. The width of the particle lines could be roughly controlled by regulating the initial concentration of the suspended particles. The particles forming the line and grid patterns with single-particle widths were immobilized by using a cross-linking reaction between the amino groups on the aligned particles and N-hydroxysuccinimide-activated ester on the glass substrate activated by succinimidyl 4-(p-maleimidophenyl)-butyrate (SMPB). The patterned particles were also embedded in a photoreactive hydrogel polymer. A prepolymer solution of poly(ethylene glycol) diacrylate (PEG-DA) was used as the suspension medium to maintain the particle patterns in the polymerized hydrogel sheet and string following photopolymerization. The hydrogel sheets with particle patterns were fabricated by ultraviolet (UV) irradiation through the ITO-IDA template for 120 s. Hydrogel strings with the aligned particles were fabricated by using a conductive ITO support and a Pt-IDA template. Pt-IDA was used as a template as well as a photomask to block UV transmission. The present procedure affords extremely simple, rapid, and highly reproducible fabrication of particle arrays. The reusability of the template IDA electrode is also a substantial advantage over previous methods