Reversible pH-induced transformation of micellar aggregates between hemicylinders and laterally homogeneous layers at graphite-solution interfaces

pH-induced transformation between a hemicylindrical aggregate and a laterally homogeneous layer at the graphite-solution interface was demonstrated in micellar aggregates of dodecyldimethylamine oxide (C12DMAO) using atomic force microscopy (AFM). Nonionic C12DMAO (pH~8) and fully-ionized cationic C12DMAO (pH~1.5) both formed hemicylindrical aggregates on graphite, similar to aggregates formed by many other ionic (or nonionic) surfactants on graphite. However, a laterally homogeneous layer was observed in the case of nearly half-ionized C12DMAO around pH~4 (a 1:1 mixture of the nonionic and the cationic species). These results indicated that the surface curvature of the C12DMAO aggregates on graphite was the smallest around the degree of ionization =0.5, despite charging up the nonionic hemicylindrical aggregates. Using AFM images and the corresponding force curves, the transformation between the hemicylindrical aggregate and the laterally homogeneous layer was found to be reversible via a change in pH. The formation of the laterally homogeneous layer of nearly half-ionized C12DMAO is explained by hydrogen bond formation between the nonionic and the cationic headgroups.     

Micelle-vesicle transition of oleyldimethylamine oxide in water

We studied the effects of the degree of ionization() and the surfactant concentration (C_d) on the micelle–vesicle transition in salt-free oleyldimethylamine oxide (OlDMAO) aqueous solutions by the dynamic light scattering (DLS), the hydrogen ion titration, the small angle neutron scattering (SANS), the electrophoretic light scattering (ELS) and viscoelastic measurements. From the study of ionization effects, the micelle–vesicle transition was recognized as a change of aggregate size by the DLS measurement; however, the micelle–vesicle transition was not detected both in the ELS measurement and the hydrogen ion titration, suggesting that the electric properties of the worm-like micelles and the vesicles are very similar despite a large difference of shapes between them. From the results of the SANS, the DLS and the viscosity measurements, it was suggested that a concentration-dependent micelle–vesicle transition took place around C_p = 10 mmol kg⁻¹ for the solutions at = 0.5. In the concentration-range 10 mmol kg⁻¹ < C_d < 150 mmol kg⁻¹, the micelles and the vesicles coexisted. In the concentration region (C_d = 10–50 mmol kg⁻¹), the vesicle size increased with the surfactant concentration.     

Surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) of low molecular weight organic compounds and synthetic polymers using zinc oxide (ZnO) nanoparticles

We have developed surface-assisted laser desorption/ionization mass spectrometry using zinc oxide (ZnO) nanoparticles with anisotropic shapes (ZnO-SALDI-MS). The mass spectra showed low background noises in the low m/z, i.e. less than 500 u region. Thus, we succeeded in SALDI ionization on low molecular weight organic compounds, such as verapamil hydrochloride, testosterone, and polypropylene glycol (PPG) (average molecular weight 400) without using a liquid matrix or buffers such as citric acids. In addition, we found that ZnO-SALDI has advantages in post-source decay (PSD) analysis and produced a simple mass spectrum for phospholipids. The ZnO-SALDI spectra for synthetic polymers of polyethylene glycol (PEG), polystyrene (PS) and polymethylmethacrylate (PMMA) showed the sensitivity and molecular weight distribution to be comparable to matrix-assisted laser desorption/ionization (MALDI) spectra with a 2,5-dihydroxybenzoic acid (DHB) matrix. ZnO-SALDI shows good performance for synthetic polymers as well as low molecular weight organic compounds.     

Halohydrination of epoxy resins using sodium halides as cationizing agents in MALDI-MS and DIOS-MS

Halohydrination of epoxy resins using sodium halides as cationizing agents in matrix-assisted laser desorption/ionization (MALDI) and desorption ionization on porous silicon mass spectrometry (DIOS-MS) were investigated. Different mass spectra were observed when NaClO(4) and NaI were used as the cationizing agents at the highest concentration of 10.0 mM, which is much higher than that normally used in MALDI-MS. MALDI mass spectra of epoxy resins using NaI revealed iodohydrination to occur as epoxy functions of the polymers. The halohydrination also occurred using NaBr, but not NaCl, due to the differences in their nucleophilicities. On the basis of the results of experiments using deuterated CD(3)OD as the solvent, the hydrogen atom source was probably ambient water or residual solvent, rather than being derived from matrices. Halohydrination also occurred with DIOS-MS in which no organic matrix was used; in addition, reduction of epoxy functions was observed with DIOS. NaI is a useful cationizing agent for changing the chemical form of epoxy resins due to iodohydrination and, thus, for identifying the presence of epoxy functions.     

Characterization of polyether mixtures using thin-layer chromatography and matrix-assisted laser desorption/ionization mass spectrometry

Thin-layer chromatography (TLC) and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) were combined to achieve characterization of polyether mixtures. Three polyethers, polyethylene glycol (PEG), polypropylene glycol (PPG) and polytetramethylene glycol (PTMG), or mixtures of these compounds, were studied. One shortcoming of mixture analysis of synthetic polymers using MALDI-MS is that individual polymers in the mixture may display different detection sensitivities. For example, the MALDI mass spectrum of an equimolar mixture of PEG, PPG and PTMG displayed a high intensity of PPG ions, while no PTMG ions were detectable; however, PTMG ions were detected after the mixture had been separated by TLC. This combined TLC and MALDI-MS analysis of a PPG polymer bearing reactive epoxy groups showed that the polymer contained byproducts with different end-groups. These byproducts were identified as chloro-substituted polymers formed during polymer synthesis. Our study shows TLC to be a rapid and low-cost separation technique, and that it can be combined with MALDI-MS to achieve effective analysis of synthetic polymers.     

Photodynamic release of fullerenes from within carbon nanohorn

We have found that oxidized single-wall carbon nanohorns (SWNHox) can exhibit a near-infrared (NIR) laser-triggered accelerated release of encapsulated fullerenes (C₆₀) from within their inner nanospaces. After the NIR laser irradiation of an aqueous SWNHox encapsulating C₆₀ solution/toluene biphasic system, C₆₀ molecules are enriched in the toluene phase. NIR laser-driven SWNHs encapsulating substrates could initiate the development of a new range of drug-delivery systems.     

A new efficient synthetic strategy for N-(dialkylamino)azacycle as a tetrasubstituted hydrazine derivative using sodium triacyloxyborohydride

A new efficient and convergent method has been developed to construct a N-(dialkylamino)azacyclic system as a tetrasubstituted hydrazine via reductive alkylation of the corresponding hydrazone using sodium triacyloxyborohydride [NaBH(OCOR)₃], which is tolerant of various substituents (e.g., phenol, conjugated olefin, amide, and thioamide) on the substrate and useful for organization of the N-aminoazacycle array.     

Trapping of intact,singly-charged,bovine serum albumin ions injected from the atmosphere with a 10-cm diameter,frequency-adjusted linear quadrupole ion trap

High-resolution real-time particle mass measurements have not been achievable because the enormous amount of kinetic energy imparted to the particles upon expansion into vacuum competes with and overwhelms the forces applied to the charged particles within the mass spectrometer. It is possible to reduce the kinetic energy of a collimated particulate ion beam through collisions with a buffer gas while radially constraining their motion using a quadrupole guide or trap over a limited mass range. Controlling the pressure drop of the final expansion into a quadrupole trap permits a much broader mass range at the cost of sacrificing collimation. To achieve high-resolution mass analysis of massive particulate ions, an efficient trap with a large tolerance for radial divergence of the injected ions was developed that permits trapping a large range of ions for on-demand injection into an awaiting mass analyzer. The design specifications required that frequency of the trapping potential be adjustable to cover a large mass range and the trap radius be increased to increase the tolerance to divergent ion injection. The large-radius linear quadrupole ion trap was demonstrated by trapping singly-charged bovine serum albumin ions for on-demand injection into a mass analyzer. Additionally, this work demonstrates the ability to measure an electrophoretic mobility cross section (or ion mobility) of singly-charged intact proteins in the low-pressure regime. This work represents a large step toward the goal of high-resolution analysis of intact proteins, RNA, DNA, and viruses.     

A convenient C–H functionalization platform for pyrroloiminoquinone alkaloid synthesis

Pyrroloiminoquinone alkaloids represent a structurally intriguing class of natural products that display an array of useful biological properties. Here, we present a versatile and scalable platform for the synthesis of this diverse family – and in particular the antitumor discorhabdins – built upon sequential selective C–H functionalization of tryptamine. The utility of this strategy is showcased through short formal syntheses of damirones A–C, makaluvamines D and I, and discorhadbin E. Additionally, we describe efforts to develop the first catalytic asymmetric entry to the discorhabdin subclass.