Surface structure of low-coveraged Cs on Si(0 0 1)-() system

Alkali metals (AM) on semiconductors have been investigated as a simple model system for the metal-semiconductor interfaces due to their simple electronic structures. Especially, cesium (Cs) on Si(0 0 1) surface has been studied with various experimental techniques. In this study, we investigated the atomic structure of initial Cs adsorption on Si(0 0 1)-(2×1) surface using coaxial impact collision ion scattering spectroscopy. When Cs atoms are adsorbed on Si(0 0 1)-(2×1) up to 0.2 ML at room temperature, the initial adsorption site is on-top T3 site with poor periodicity and the length of Si dimer is reserved as in the clean Si(0 0 1) surface. It is also found that Cs atoms adsorbed on Si(0 0 1) surface with a height of 2.83±0.05 Å from the second layer of Si(0 0 1) surface.     

Low valent tungsten reaction—Composition studies and reactions with sulfoxides and pyridine-N-oxides

Sulfoxides are converted to the corresponding sulfides in good yields by low valent tungsten agents derived from WCl₆—BuLi(1) and WCl₆—Zn (2). Pyridine-N-Oxides are also reduced easily with 1 to give the corresponding pyridines in almost quantitative yields. A yellow solid WCl₄ (THF)_n is isolated from the reaction of one mole of WCl₆ and two mole of n-BuLi in tetrahydrofuran (THF) at low temperature, and its composition is established by using ESCA. IR, ¹H and ¹²C NMR. Reaction of WCl₄ (THF)_n with excess of pyridine gives the known WCl₄(C₅H₅N)₂.     

Polyurethane cationomers. I. Structure-property relationships

Polyether polyurethane cationomers are prepared using poly (tetramethylene oxide) of molecular weight 2000 as soft segments, N-methyl-diethanolamine as chain extender, glycolic acid as quaternization agent, methyl ethyl ketone as solvent, and three different diisocyanates. The three diisocyanates are 4,4′-diphenylenemethylene diisocyanate (MDI), hexamethylene diisocyanate (HDI), and toluene diisocyanate (TDI). Properties of the films cast from solutions of the three series of ionomers are studied by infrared spectroscopy, dynamic mechanical analysis, thermogravimetric analysis, differential scanning calorimetry, wide angle x-ray diffraction, and tensile elongation testing. In the un-ionized and ionized systems, the hard segments exhibit disordered and ordered arrangements, respectively. Ionization disrupts the order and produces increased cohesion in the hard domains, which have opposing effects on the tensile elongation properties. In the MDI and TDI systems, cohesion is predominant, leading to an increased tensile strength and modulus and decreased elongation at break. But in the HDI system, the disruption of the order is predominant, leading to decreased tensile strength and only insignificant reduction in the elongation at break. In the TDI system, the tensile strength is rather low, which is attributed to the poor order in the hard domains resulting from the high content of the asymmetric 2,4-isomer of the urethane.     

Preparation and characterization of branched and linear sulfonated poly(ether ketone sulfone) proton exchange membranes for fuel cell applications

Branched sulfonated poly(ether ketone sulfone)s (Br‐SPEKS) were prepared with bisphenol A, bis(4‐fluorophenyl)sulfone, 3,3′‐disodiumsulfonyl‐4,4′‐difluorobenzophenone, and THPE (1,1,1‐tris‐p‐hydroxyphenylethane), respectively, at 180 °C using potassium carbonate in NMP (N‐methylpyrrolidinone). THPE, as a branching agent, was used with 0.4 mol % of bisphenol A to synthesize branched copolymers. Copolymers containing 10–50 mol % disulfonated units were cast from dimethylsulfoxide solutions to form films. Linear sulfonated poly(ether ketone sulfone)s (SPEKS) were also synthesized without THPE. The films were converted from the salt to acid forms with dilute hydrochloric acid. A series of copolymers were studied by Fourier transform infrared, ¹H‐NMR spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Sorption experiments were conducted to observe the interaction of sulfonated polymers with water and methanol. The ion‐exchange capacity (IEC), a measure of proton conductivity, was evaluated. The synthesized Br‐SPEKS and SPEKS membranes exhibit conductivities (25 °C) from 1.04 × 10^?3 to 4.32 × 10^?3 S/cm, water swell from 20.18 to 62.35%, IEC from 0.24 to 0.83 mequiv/g, and methanol diffusion coefficients from 3.2 × 10^?7 to 4.7 × 10^?7 cm²/S at 25 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1792–1799, 2008     

X-ray diffraction studies on cis- and trans-4'-cyanobiphenyl-4-yl 3-n-propylcyclobutane-1-carboxylate

X-ray diffraction has been used to study the nematic phases of the cis and trans isomers of an elongated molecule containing the cyclobutane group. It has been shown that these nematic phases consist of a mixture of single molecules and overlapping core dimers. It has been found that increasing the temperature of the cis isomer rapidly reduces the dimer population, whereas increasing the temperature of the trans isomer enhances the dimer population. This provides an explanation of the relatively high clearing temperature of the trans isomer. The different temperature dependences of the dimer population in the cis and trans isomers has been explained by a model involving inversion of the cylobutane group.     

Effect of aromatic substitution on phase behavior of blends of halogenated polystyrene and conventional polystyrene

Miscibility phase behavior in blends of poly(bromostyrene) with polystyrene (PS) has been investigated by means of time‐resolved light scattering, optical microscopy, and DSC. Cloud point phase diagrams of blends of conventional PS with poly‐(2‐bromostyrene) (P2BrS), poly‐(3‐bromostyrene), and poly‐(4‐bromostyrene) of comparable molecular weights were established by light scattering. Of particular interest is the fact that ortho, meta, and para substitutions in the styrenic aromatic rings of poly(bromostyrene) show profound effects on the composition–temperature phase diagrams of their blends with PS, exhibiting a lower critical‐solution temperature (LCST), an upper critical solution temperature (UCST), and combined LCST/UCST diagrams, respectively. Poly‐(2‐chlorostyrene) exhibits an LCST behavior very close to that of the P2BrS blend, suggesting that these types of halogen atoms may be inconsequential to phase behavior. A similar study has been extended to a PS blend containing commercial brominated PS (66 mol % bromine substitution) to determine what location of bromine substitution is crucial for miscibility enhancement in the flame‐retardant brominated PS blends. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1605–1615, 2001     

Synthesis of Nitrated Analogs of Distamycin and their DNA Cleaving and Protecting Activities under UV Irradiation

Two nitrated analogs of distamycin were synthesized by a novel haloform reaction and the DCC/HOBT coupling reaction in a convenient and effective way with out amino group protection. Our results have demonstrated that these polyamides show DNA cleaving activity under long UV (LUV 365 nm) irradiation. Furthermore, it is an unexpected discovery that these analogs can prevent DNA dam age under short UV (SUV 302 nm).     

Practical synthesis of (S)‐7‐(2‐isopropylamino)ethylcamptothecin hydrochloride,potent topoisomerase I inhibitor

A practical semi‐synthetic method of (S)‐7‐(2‐isopropylamino)ethylcamptothecin hydrochloride has been developed. The Mannich reaction of (S)‐7‐methylcamptothecin with isopropylamine hydrochloride in dimethyl sulfoxide as a formaldehyde source gave the desired product in moderate yield.     

Fast and low error color encrypted computer-generated hologram based on amplitude-phase modulation with a random mask for an identification tag application

A new APM computer-generated hologram algorithm for minimizing DC components and more effective data recovery is presented for the purpose of an ID tag application. In this method, a technique of randomization of the input data is introduced prior to the Fourier transform. As a result, DC components are localized at the center region, which is only 1 data cell, regardless of input data. The size of the tag pattern is reduced 2.25 times using a color encryption technique. Our experimental result through the image captured by a camera also shows that approximately 50% damaged APM-CGH tags can be reconstructed at a low error rate of about 1.8%.