In situ observation of single polymers adsorbed onto mica surfaces in water

The morphology of a cationic polymer of high molecular weight, poly[2-(acryloyloxy)ethyl(trimethyl)ammoniumchloride], adsorbed on to a mica surface in water was observed in situ using the tapping mode of an atomic force microscope with a high-resolution probe. It was found that the morphology of adsorbed polymers changes with time to be lumplike, floclike, and then fibril-like and that it takes surprisingly a long time for the polymers to relax completely in water, even though they are highly charged. Detailed structures of extended polymers are also discussed.     

Gapless spin liquid behavior in two-dimensional solid 3He

Direct demagnetization has been made for two-dimensional solid 3He in both the paramagnetic and the antiferromagnetic phases. The lowest temperature is about 10 microK, judging from the observed magnetization for the paramagnetic solid 3He. The magnetization of the antiferromagnetic solid 3He shows a gradual increase to about 10 microK for the 4/7 phase adsorbed on both one layer of 4He and two layers of HD preplated graphite. This strongly suggests that the triangular antiferromagnet with the higher order multiple exchange has a quantum spin liquid ground state with nearly zero or extremely small spin gap less than 10 microK.     

Digital phase-shifting interferometer with an electrically addressed liquid-crystal spatial light modulator

A digital phase-shifting interferometer with a liquid-crystal-display coupled, parallel aligned, nematic liquid-crystal spatial light modulator is developed. The optical phase shift in the Michelson-type polarization interferometer is achieved by a digital phase shift of a grating displayed on the spatial light modulator. Accurate experimental results of using the heterodyne system for pi/2 phase steps were demonstrated. A phase-shifting interferometer with no moving parts and no requirement for calibration of the value of the phase shift was achieved.     

Syntheses and properties of emissive iridium(III) complexes with tridentate benzimidazole derivatives

A series of novel emissive Ir(III) complexes having the coordination environments of [Ir(N--N--N)2]3+, [Ir(N--N--N)(N--N)Cl]2+, and [Ir(N--N--N)(N--C--N)]2+ with 2,6-bis(1-methyl-benzimidazol-2-yl)pyridine (L1, N--N--N), 1,3-bis(1-methyl-benzimidazol-2-yl)benzene (L2H, N--C--N), 4'-(4-methylphenyl)-2,2':6',2' '-terpyridine (ttpy, N--N--N), and 2,2'-bipyridine (bpy, N--N) have been synthesized and their photophysical and electrochemical properties studied. The Ir(III) complexes exhibited phosphorescent emissions in the 500-600 nm region, with lifetimes ranging from approximately 1-10 micros at 295 K. Analysis of the 0-0 energies and the redox potentials indicated that the lowest excited state of [Ir(L1)(L2)]2+ possessed the highest contribution of 3MLCT (MLCT = metal-to-ligand charge transfer) among the Ir(III) complexes, reflecting the sigma-donating ability of the tridentate ligand, ttpy < L1 < L2. The emission quantum yields (phi) of the Ir(III) complexes ranged from 0.037 to 0.19, and the highest phi value (0.19) was obtained for [Ir(L1)(bpy)Cl]2+. Radiative rate constants (k(r)) were 1.2 x 10(4) s(-1) for [Ir(ttpy)2]3+, 3.7 x 10(4) s(-1) for [Ir(L1)(bpy)Cl]2+, 3.8 x 10(4) s(-1) for [Ir(ttpy)(bpy)Cl]2+, 3.9 x 10(4) s(-1) for [Ir(L1)2]3+, and 6.6 x 10(4) s(-1) for [Ir(L1)(L2)]2+. The highest radiative rate for [Ir(L1)(L2)]2+ with the highest contribution of 3MLCT could be explained in terms of the singlet-triplet mixing induced by spin-orbit coupling of 5d electrons in the MLCT electronic configurations.     

Study on the surface density of surface-active substances through total-reflection X-ray absorption fine structure measurement

The total-reflection X-ray absorption fine structure (XAFS) method previously employed for the adsorption of dodecyltrimethylammonium bromide (DTAB) at the air/water interface was applied to that in the presence of NaBr. The surface concentration of the bromide ions Gamma(X)(B) of DTAB and NaBr was evaluated by using the Br K-edge absorption jump values of the total-reflection XAFS spectra and was compared to the corresponding value Gamma(H)(B) estimated from the dependence of surface tension on the bulk concentrations of DTAB m(1) and NaBr m(2). The Gamma(X)(B) values trace almost perfectly the Gamma(X)(B) versus m(1) curve up to a concentration near the critical micelle concentration (cmc) and deviate gradually above the concentration. This behavior is basically similar to that of the single DTAB system and ensures that the XAFS method is also applicable to the DTAB system, even in the presence of NaBr. In addition, this method was extended to the single nonionic amphiphile with covalently bonded bromine, and the surface concentrations of 6-bromo-1-hexanol (BrC6OH), Gamma(X)(1) and Gamma(H)(B), were evaluated and compared with each other. It was found that the Gamma(X)(1) value almost perfectly traces the Gamma(H)(1) versus m(1) curve, even at high surface concentrations. The excellent coincidence confirmed that the total-reflection XAFS method can be applied to the nonionic amphiphile system as well as a cationic surfactant with or without an added salt system. Finally, the difference between the Gamma(X)(B) and Gamma(H)(B) values observed in the DTAB with and without an added salt system is briefly described.     

Synthetic studies on oxindole spiro-lactones with thalliumd(III) trinitrate: A formal total synthesis of (±)-tryptoquivaline G

(±)-Tryptoquivaline G was formally synthesized through shortened steps from tryptophan, in which oxidation with thallium(III) trinitrate(TTN) was effected at the crucial stage. The present work also constitutes the first synthesis of oxindole lactones carrying 2-alkyl quinazolinones.     

Synthesis of tri- or tetrasubstituted pyrimidine derivatives through the [5+1] annulation of enamidines with either N,N-dimethylformamide dialkyl acetals or orthoesters and their application in a ring transformation of pyrimidines to pyrido[2,3-d]pyrimidin-5-one derivatives

The [5+1] annulation of enamidines, which were prepared from functionalized silanes, organolithium compounds and two nitriles, with N,N-dimethylformamide dialkyl acetals as the C1 unit is described, leading to the synthesis of tri- and tetrasubstituted pyrimidine derivatives under catalyst- and solvent-free reaction conditions. Furthermore, the [5+1] annulation of enamidines by using orthoesters as the C1 unit is described, in which catalytic amounts of ZnBr(2) catalyze the annulation to produce polysubstituted pyrimidines under toluene or xylene reflux conditions. Moreover, the combination of a reductive ring-opening reaction with [Mo(CO)(6)] and a subsequent intramolecular cyclization with tBuOK effectively causes a skeletal transformation from the pyrimidines containing an isoxazolyl and an ethoxy substituent to form pyrido[2,3-d]pyrimidin-5-one frameworks in excellent yield.