Self-assembly of fluid-filled KHCO(3) microfibers

Self-assembly of KHCO(3) fibers is observed when glassy oligomerized films of poly[(aminopropyl)siloxane] containing K(+) ions, denoted K(+)/poly-APS, are exposed to CO(2) and H(2)O. The fibers are crystalline, narrow (0.4-3 microm diam), high aspect ratio (up to at least 300), and, on the basis of Raman spectroscopy, dominated by KHCO(3). The fibers contain fluid that is dominated by aqueous potassium formate (KOOCH). A multistep phenomenological model is proposed to account for the self-assembly.     

The EPR spectra of irradiated KHCO3 crystals

The EPR spectra of γ-irradiated KHCO₃ and KDCO₃ crystals were re-examined in the hope of identifying in them the species HOCO. This proved unsuccessful, but some anomalies in the results and conclusions of earlier workers concerning trapped CO^?₂ and CO^?₂ radicals are re-interpreted in the light of improved data.     

Photochemical oxidation of AmIII in KHCO3 + K2CO3 solutions containing XeO3

Russian Chemical Bulletin - The possibility of XeO3 photo-activation in KHCO3 + K2CO3 solutions at room temperature to oxidize AmIII was studied.     

Comparison of thermal properties and kinetics of decompositions of NaHCO3 and KHCO3

The thermodynamics and kinetics of the thermal decompositions of NaHCO₃ and KHCO₃ were studied by means of simultaneous TG-DSC. Analysis of the isothermal mass-change traces indicated that the thermal decompositions of NaHCO₃ and KHCO₃ follow an Avrami-Erofeyev A_1.5 law. The A_1.5 law was tentatively explained by assuming a combination of the A₁ and A₂ laws. It was illustrated that KHCO₃ is more stable than NaHCO₃ as concerns the thermodynamics and kinetics of the thermal decompositions. The apparent activation energies for the decompositions of the two hydrogencarbonates were a little larger than the corresponding enthalpy changes.     

Thiolated mucoadhesive and PEGylated nonmucoadhesive organosilica nanoparticles from 3-mercaptopropyltrimethoxysilane

A novel approach has been developed to synthesize thiolated sub-100 nm organosilica nanoparticles from 3-mercaptopropyltrimethoxysilane (MPTS) through its self-condensation in dimethylsulfoxide in contact with atmospheric oxygen. The formation of MPTS nanoparticles proceeds through the condensation of methoxysilane groups and simultaneous disulfide bridging caused by partial oxidation of thiol groups. These nanoparticles showed excellent colloidal stability in dilute aqueous dispersions but underwent further self-assembly into chains and necklaces at higher concentrations. They exhibited very good ability to adhere to ocular mucosal surfaces, which can find applications in drug delivery. The thiolated nanoparticles could also be easily modified through PEGylation resulting in a loss of their mucoadhesive properties.     

Layer-by-layer self-assembled polyelectrolyte multilayers with embedded liposomes: immobilized submicronic reactors for mineralization

The development of chemical reactions in nanospaces is of paramount importance for the development of active nanodevices, particularly in nanofluidics. It has been shown in a previous paper that phospholipid vesicles can be incorporated without spontaneous bilayer rupture into poly-L-glutamic acid/poly(allylamine) (PGA/PAH) multilayered polyelectrolyte films. The aim of the present study was to use such a system as an "embedded submicronic reactor" able to trigger precipitation of calcium phosphates within closed spaces through an enzymatic reaction, the enzyme also being encapsulated in the vesicle interior. To this aim, large unilamellar vesicles (LUVs) were produced containing calcium ions as active ions in the mineralization process, spermine as an activator of crystal growth, and alkaline phosphatase as a catalyst to convert phosphate esters into phosphates. After stabilization by adding a layer of poly-(D-lysine), these vesicles were embedded in a (PGA-PAH)n film. A paranitrophenyl phosphate containing solution was then put in contact with this film. It is shown by means of infrared spectroscopy in the attenuated total reflection mode that, consecutively to this contact, calcium phosphates are growing inside the embedded vesicles. By using scanning near-field fluorescence microscopy, it is demonstrated that the alkaline phosphatase enzymes are most probably located inside the vesicles after their embedding. In addition, atomic force microscopy was used to show, after chemical removal of the organic top layer of the film, that the inorganic platelets produced after the precipitation reaction are localized in volumes of similar size and shape as that of the vesicles into which the phosphate ester hydrolysis and subsequent precipitation reaction did occur.     

Highly ordered three-dimensional large-pore periodic mesoporous organosilica with Im3m symmetry

Highly ordered three-dimensional Im3m-type periodic mesoporous organosilica with a cavity size of 9.8 nm has been synthesized under strongly acidic media in the presence of inorganic salts using triblock copolymer F127 as the template and 1,2-bis(trimethoxysilyl)ethane as the organically bridged silica source.     

Synthesis of sorption materials based on dithiooxamidate aminopropyl polysiloxane

Reaction of reamidation of rubeanic acid with aminopropyl polysiloxane was systematically studied. It was found that the given type of transformations make it possible to obtain a derivative of aminopropyl polysiloxane with surface dithiooxamide groups in a concentration of up to 0.78 mmol g^?1 at a total degree of substitution of up to 0.25. The composition and structure of the derivatives obtained were characterized by elemental analysis, IR spectroscopy, thermogravimetry, and method of low-temperature adsorption of nitrogen. The sorption of Ni(II), Pd(II), and Pt(II) in a 0.2 M solution of hydrochloric acid was evaluated for the products obtained.     

3-methylthiophene self-assembled monolayers on planar and nanoparticle Au surfaces

In this article the adsorption of 3-methylthiophene on planar and nanoparticle Au surfaces is investigated. The resulting systems are compared with a benchmark system based on 1-decanethiol. The characterization data collected evidence the formation of a packed 3-methylthiophene SAM on the planar surface. In particular, spectroscopic investigations suggest that 3-methylthiophene aromatic system is not adsorbed on the surface through the pi-electron system but rather through the S atom alone. On the other hand, the behavior of 3-methylthiophene on nanoparticle surfaces is notably different from that of the alkanethiol. Only a limited fraction of the surface of Au nanoparticles results to be actually coated after purification; this notwithstanding, the nanoparticle growth seems to be strongly influenced by the presence of such a labile encapsulating agent.     

Mechanism of the Anionic Ring-Opening Oligomerization of Propylene Carbonate Initiated by the tert-Butylphenol/KHCO3 System

The ring-opening oligomerization reaction of propylene carbonate in the presence of the tert-butylphenol/KHCO₃ initiating system was studied by means of Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS) and Electrospray Ionization Time of Flight Mass Spectrometry (ESI-TOF MS). According to the MS spectra obtained, different series of peaks were identified. The MS spectra clearly showed that besides the chain-extension reaction yielding oligomers with all propylene oxide units, the formation of oligomers containing carbonate linkages in the chain, and condensation reaction between the latter two also took place. The structure of the oligomers carrying carbonate linkages was determined by the post-source decay (PSD) MALDI-TOF MS/MS method. Based on the MS results, a mechanism for the oligomerization reaction is proposed.     

Spectroelectrochemistry of type II cytochrome c3 on a glycosylated self-assembled monolayer

A modified silver electrode was prepared by the self-assembly of a thiol-derivatized neoglycoconjugate, forming a 2D surface with maltose functionality. This self-assembled-monolayer-modified electrode was utilized for adsorption and spectroelectrochemical studies of tetraheme-containing type II cytochrome c3. The glycosylated surface allowed for the determination of the hemes' redox potentials and demonstrated enhanced spectroelectrochemical performance, in comparison to the widely used self-assembled monolayer of 11-mercapto-undecanoic acid.     

Evidence of a phase transition of RbHCO3 from high-resolution solid-state 13C and 87Rb NMR by comparison with KHCO3

A variable-temperature high-resolution 13C and 87Rb solid-state NMR study of powder rubidium hydrogencarbonate, RbHCO3, is presented for the first time. At ambient temperature, RbHCO3 is formed by centrosymmetric dimers linked by hydrogen bonds, but almost no information is available on this compound concerning proton disorder and the low-temperature phase. However, potassium hydrogencarbonate, KHCO3, which has an isomorphic structure for the high temperature phase, was well studied: it undergoes a non-ferroic, non-ferroelectric phase transition at Tc = 318 K between two monoclinic structures. The protons are disordered in an asymmetric double-well potential in the low-temperature phase, and the double-well potential becomes symmetric in the high-temperature phase. By comparison with recent solid-state NMR experimental results on KHCO3, we show that RbHCO3 undergoes a phase transition at Tc approximately 245 K, and give evidence that the proton dynamic disorder in both compounds is very similar.     

Supramolecular structures of poly(γ-benzyl-L-glutamate) self-assembled on mica surface

This article reports the results of structural studies of poly (γ-benzyl-L -glutamate) (PBLG) layers self-assembled from dilute solutions in organic solvents on mica surface. Polarized dynamic light scattering and atomic force microscopy were used to study polymer properties in solutions and on the surface. The hierarchy of self-assembly from PBLG solutions in different solvents was investigated as a function of polymer concentration and solvent polarity. We show that the surface–polymer interaction is suppressed in polar solvents that is interpreted in terms of suppressed charge–dipole interaction. The transformation of the PBLG surface structure occurs upon addition of different amounts of trifluoroacetic acid to polymer solution in dioxane. Rigid-rod PBLG molecules experience rod–globular transition while assembling on nonmodified mica from the very dilute solutions. A scheme is proposed describing different stages of PBLG fibrogenesis on a charged surface. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1567–1577, 1998     

Film morphology and orientation of N‐cyclohexyl‐γ‐aminopropyl polydimethylsiloxane

A novel polysiloxane softener bearing N‐cyclohexyl‐γ‐aminopropyl side groups (ASO‐702) is synthesized by copolymerization of octamethylcyclotetrasiloxane with N‐cyclohexyl‐γ‐aminopropyl methyldimethoxylsilane and hexamethyldisiloxane. Chemical structure and film morphology of the synthesized polysiloxane are characterized and investigated by IR, ¹H NMR, ¹³C NMR, SEM and atomic force microscope (AFM). The results of the experiment indicate that ASO‐702 can form a hydrophobic film on both a cotton fiber and a silicon‐wafer surface. At scales > 100 nm, the ASO‐702 shows a relative smooth‐resin film on the treated fabric/fiber surface. But as the observation rule decreases to 2 nm, the molecular scale, the ASO‐702 film exhibits an inhomogeneous structure and uneven morphology in its AFM images. There are many low or high peaks in ASO‐702 topography. Consequently in 2 µm² scanning field, the root mean square roughness of ASO‐702 film is 0.246 nm, which is 3.05 times rougher as compared with that of polydimethylsiloxane (PDMS) film. Copyright © 2008 John Wiley & Sons, Ltd.     

Conglomerate crystallization on self-assembled monolayers

In this communication, we demonstrate that chiral self-assembled monolayers can be used for polymorphism control of chiral crystals. We studied the crystallization of DL-glutamic acid on chiral self-assembled monolayers and showed that crystallization of DL-glutamic acid on the chiral SAMs resulted in stabilization of the metastable conglomerate form.     

Micro-patterning of 3-aminopropyltrimethoxy- silane self-assembled monolayers with colloidal gold

This paper provides a new method to the micro-patterning of 3-aminopropyl-trimethoxysilane (ATS) self-assembled monolayers by colloidal Au. Photolithographing of ATS self-assembled monolayers on SiO₂-coated Si substrates and subsequent assembly of colloidal Au to the amino terminal groups in the unirradiated regions lead to the formation of Au microstructures. As revealed by scanning electron microscopy, the colloidal Au closely replicates the mask patterns on the unirradiated regions. The present approach may be applicable to fabrication of microelectronic circuits and microbiosensors.     

Micropatterning of Ni particles on a BaTiO3 green sheet using a self-assembled monolayer

We studied surface modification of ceramic BaTiO(3) green sheets including polyvinylbutyral (PVB) as an organic binder and successfully fabricated a patterned self-assembled monolayer (SAM) which has a region of amino groups and a region of silanol groups on the green sheet. The patterned SAM was then immersed in water containing Ni particles that show negative zeta potential in water. Ni particles were attracted to the amino groups of the patterned SAM that show positive zeta potential by attractive electrostatic interaction. Consequently, a micropattern of Ni particles was achieved using a SAM at room temperature in water. This process can be used to fabricate a thin uniform internal Ni electrode for miniaturized high-performance multilayer ceramic capacitors (MLCC).     

Controlled crystallization of CaCO(3) on hyperbranched polyglycerol adsorbed to self-assembled monolayers

The formation of biominerals by living organisms is governed by the cooperation of soluble and insoluble macromolecules with peculiar interfacial properties. To date, most of the studies on mineralization processes involve model systems that only account for the existence of one organic matrix and thus disregard the interaction between the soluble and insoluble organic components that is crucial for a better understanding of the processes taking place at the inorganic-organic interface. We have set up a model system composed of a matrix surface, namely, a self-assembled monolayer (SAM), and a soluble component, hyperbranched polyglycerol. The model mineral calcium carbonate displays diverse polymorphism. It could be demonstrated that the phase selection of calcium carbonate is controlled by the cooperative interaction of the SAM and hyperbranched polyglycerol of different molecular weights (M(n) = 500-6000 g/mol) adsorbed to the SAM. Our studies showed that hyperbranched polyglycerol is adsorbed to polar as well as to nonpolar SAMs. This effect can be related to its highly flexible structure and its amphiphilic character. The adsorption of hyperbranched polyglycerol to the SAMs with different surface polarities resulted in the formation of aragonite for alkyl-terminated SAMs and no phase selection for carboxylate-terminated SAMs.     

Synthesis of α-nitro derivatives of δ-oxocarboxylic and glutaric acids in heterogeneous catalytic system ionic liquid—KHCO3

An expedient method for the synthesis of α-nitro-δ-oxocarboxylic and α-nitroglutaric acid esters, including ones with isoprenoid substituents, by the solvent-free reaction of the corresponding alkyl α-nitrocarboxylates with activated olefins, assisted by heterogeneous catalytic system KHCO₃—1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]), was elaborated. The product yields remain stable even after eight recycles of the catalytic system. The synthesized dimethyl 2-(poly)prenyl-2-nitropentanedioates upon treatment with Fe in AcOH were reduced to 2-(poly)prenyl-5-oxopyrrolidine-2-carboxylates. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1431–1438, August, 2007.