Combined Monolayer Research Articles

ESTIMATION OF RBE VALUES FOR CARBON-ION BEAMS IN THE WIDE DOSE RANGE USING MULTICELLULAR SPHEROIDS.

Hypofractionated carbon-ion therapy has been applied to treatment of several tumours. In this case, relative biological effectiveness (RBE) at high dose region must be considered, however, the RBE calculated physically has been not verified biologically. In this study, spheroid technique was adopted to estimate RBE in wide dose range. Cells were irradiated with X-rays and heavy-ions with LET of 13, 35, 100 and 300 keV/μm with monolayer and spheroid condition. Surviving fractions in wide dose range (0-15 Gy) were obtained to combined monolayer with spheroid survival data. The linear-quadratic and multi-target single-hit equation fitted well in survival data at low dose, and high dose region, respectively. A multi-process equation showed best fitting for survival data in wide dose range. RBE values of heavy-ions could be estimated by combination of monolayer and spheroid data. The values converged at 1.1-1.4 and varied by LET values at high and low dose region, respectively.

A jack-of-all-trades: 2-mercaptosuccinic acid.

2-Mercaptosuccinic acid (MS) is an important and versatile substance for diverse fields of applications of which the most significant are surveyed in this article. Biological, chemical, and physical properties of MS as well as the knowledge of its synthesis and microbial degradation are illustrated. In addition, exemplary structural analogs of the organic sulfur compound are commented. The key application of MS in nanotechnology is discussed in detail with particular emphasis on quantum dots (nanocrystals) and self-assembled monolayers in combination with gold or silver. Furthermore, some medical and pharmaceutical applications are given, inter alia in bioimaging, as a nanocarrier, and with regard to the antimicrobial activity of MS-silver and MS-gold nanoparticles. Moreover, biological and chemical applications of MS are exemplified: the thiol compound can serve as an inhibitor for glutathione peroxidase, or the toxicity of substances can be increased due to the presence of MS in the respective cells or tissues. In the field of cosmetics, MS is widely utilized as a reducing agent for numerous products as explained in this article. Additionally, the microbial utilization of MS as a carbon and energy source for growth is elucidated in-depth, providing insight into different catabolic mechanisms.

Adaptability of monoglyceride-induced crystallization of K2SO4: effect of various anions and lipid chain splay.

Understanding the interaction of a surfactant assembly with surrounding ionic compositions is critical in controlling the nanostructure formed by amphiphilic systems. In this study, we investigated the influence of specific anions upon the character of the crystallization process of a model inorganic salt (K2SO4) in an aqueous microdroplet (10-100 μm) in the presence of monolayers of monoelaidin (ME), monovaccenin (MV), monoolein (MO), and monolinolein (ML) assembled at a water-decanol interface. In particular, control monolayers of each monoglyceride at the water-oil interface did not accelerate nucleation (i.e., act as a template) of the crystallization of K2SO4. However, in the presence of 1-10 mM exogenous anions, certain types of monoglycerides did induce nucleation. The influence of the anions was consistent with the Hofmeister series. Monoglyceride monolayers in combination with chaotropic anions, such as SCN(-), imparted a euhedral crystal habit with a relatively lower C(onset), while kosmotropic anions showed less notable changes in the crystallization characteristics. However, this specific anion effect was seen only for monolayers of ME, MV, and MO but not for ML. This enhancement of nucleation-inducing ability upon addition of chaotropic anions appears to be related to the degree of chain splay: the larger the chain splay, the less anion efficiency in enhancing the templating capability. Our findings indicate that the improved nucleation-enhancing capabilities may originate from mutual interactions between anions and the monolayer, allowing the monoglyceride monolayers to adapt to a modulated self-assembled structure resulting in the greatest degree of control over K2SO4 crystallization.

Modulation of dipalmitoylphosphatidylcholine monolayers by dimethyl sulfoxide.

The action of the penetration-enhancing agent, dimethyl sulfoxide (DMSO), on phospholipid monolayers was investigated at the air-water interface using a combination of experimental techniques and molecular dynamics simulations. Brewster angle microscopy revealed that DPPC monolayers remained laterally homogeneous at subphase concentrations up to a mole fraction of 0.1 DMSO. Neutron reflectometry of the monolayers in combination with isotopic substitution enabled the determination of solvent profiles as a function of distance perpendicular to the interface for the different DMSO subphase concentrations. These experimental results were compared to those obtained from molecular dynamic (MD) simulations of the corresponding monolayer systems. There was excellent agreement found between the MD-derived reflectivity curves and the measured data for all of the H/D contrast variations investigated. The MD provide a detailed description of the distribution of water and DMSO molecules around the phosphatidylcholine headgroup, and how this distribution changes with increasing DMSO concentrations. Significantly, the measurements and simulations that are reported here support the hypothesis that DMSO acts by dehydrating the phosphatidylcholine headgroup, and as such provide the first direct evidence that it does so primarily by displacing water molecules bound to the choline group.

Chemical vapor deposition processes for the fabrication of epitaxial Si-O superlattices

Band engineered Si/O superlattices are promising channel materials for ultimately scaled complementary metal oxide semiconductor devices. Theoretical calculations have indicated that insertion of O monolayers into Si lattice creates anisotropy in the Si band structure with an enhanced carrier mobility in the channel direction. However, the experimental demonstration of such superlattices is not straightforward, as it requires processes for the deposition of a monolayer of O on Si, and to continue the Si epitaxy thereon. In this work, we investigate processes for the fabrication of Si/O superlattices using the chemical vapor deposition technique. Ozone is used for the O deposition with control of the deposited O content at the monolayer level. The SiH4 based Si deposition is performed at low temperatures (500°C–550°C) in order to obtain a confined O monolayer in the Si superlattice. Si deposited on O layer of 1.2 O monolayers is completely amorphous. This indicates that this O layer is extremely uniform as it prevents any epitaxial ordering with the substrate. Reducing the O content to 0.9 O monolayers in combination with a slower Si deposition favors epitaxial ordering of Si on O/Si. Finally a defect free Si epitaxy is demonstrated on the O monolayer. Such ordering of epitaxial Si on the O layer provides a promising outlook for the growth of superlattices.

Pressure-Sensitive Microfluidic Gates Fabricated by Patterning Surface Free Energies Inside Microchannels

A series of pressure-sensitive microfluidic gates to regulate liquid flow have been successfully fabricated by patterning surface free energies inside microchannels using self-assembled monolayers in combination with either multistream laminar flow or photolithography. The designs are based on the principles of surface-directed liquid flow previously reported. Aqueous liquids, including protein solutions, are confined to the hydrophilic pathways (or the most hydrophilic pathway) under spontaneous flow conditions and flow into the hydrophobic regions or the less hydrophilic pathways when pressures exceed critical values. A programmable pressure-sensitive liquid delivery device is demonstrated. We have also investigated the initial rate of liquid flow in surface-patterned microchannels under spontaneous flow conditions from both analytical and experimental approaches. The methods described here provide an alternative to the conventional approaches to control liquid flow in the fast-developing field of micro...

Molecular Switching in Phospholipid and Azobenzene Mixed Monolayers Using Maxwell-Displacement-Current-Measuring Technique

Molecular switching in phospholipid and azobenzene mixed monolayers was examined by Maxwell-displacement-current (MDC) measurement in combination with the surface pressure measurement. It was found that the molecular aggregation of pure azobenzene monolayers was reduced by the introduction of phospholipids possessing unsaturated long alkyl chains (DOLPC) or saturated long alkyl chains (D-DPPC). The surface pressure change was detected from mixed monolayers over the entire range of molecular area with alternating irradiation of ultraviolet and visible light. On the one hand, MDC was generated from DOLPC-azobenzene mixed monolayers over the entire range of the molecular area, whereas the generation of MDC from D-DPPC-azobenzene mixed monolayers was limited in the molecular area. We discussed the generation of MDC from phospholipids-azobenzene mixed monolayers in combination with the surface pressure change measurement.

Adsorption of Viologen-Based Polyelectrolytes on Carboxylate-Terminated Self-Assembled Monolayers

The adsorption of viologen-containing polyelectrolytes on the surface of carboxylate-terminated, self-assembled monolayers was investigated by voltammetric methods. The two polyelectrolytes used had either butyl (VC4) or undecyl (VC11) linkages between the repeating viologen (4,4‘-bipyridinium) subunits. Both polyelectrolytes were found to adsorb at neutral pH on monolayers prepared by the self-assembly of either 3-mercaptopropionic (HSC2COOH) or 8-mercaptooctanoic (HSC7COOH) acids on gold. However, the adsorption was optimized by using the more hydrophobic polyelectrolyte (VC11) and the longer thiol (HSC7COOH). The gradual deprotonation of the HSC7COOH monolayer in the pH range 6−11 enhances the adsorption of the VC11 polyelectrolyte. From these data, an apparent pKa of ∼8 for the monolayer −COOH groups was obtained. The overall degree of packing of the viologen subunits at the monolayer−solution interface was found to be rather poor. The combined monolayer−polyelectrolyte interfacial structures did not ...