Transient Colloidal Stability Controls the Particle Formation of SBA-15

A hypothesis about (transient) colloidal stability as a controlling mechanism for particle formation in SBA-15 is presented. The hypothesis is based on results from both in situ and ex situ investigations, including cryogenic transmission electron microscopy (cryo-TEM), UV-vis spectroscopy, and dynamic light scattering (DLS). Cryo-TEM images show that particles grow via the formation of silica-Pluronic-water "flocs", which coalesce in a seemingly arbitrary manner. Despite this, the final material consists of well-defined particles with a small size distribution. We argue that the interface between the flocs and surrounding media is covered by Pluronic molecules, which provide steric stabilization. As the flocs grow, the coverage of polymers at the interface is increased until a stable size is reached, and that regulates the particle size. By targeting the characteristics of the Pluronic molecules, during the on-going synthesis, the hypothesis is tested. The results are consistent with the concept of (transient) colloidal stability.     

The degree of multivalued maps from manifolds to spheres

In this paper, for closed connected oriented manifolds M and N of the same dimension, we study the degree of a triple (??, p, q), where p is a Vietoris map from a compact space ?? to M and q is a continuous map from ?? to N. In particular, we have Borsuk?CUlam-type degree theorems on manifolds with involutions.     

Intrinsic transmission bandwidths of graded-index plastic optical fibers

We theoretically demonstrate that microscopic heterogeneous properties can enhance the transmission bandwidths of graded-index plastic optical fibers (POFs) for short-haul communication networks. The heterogeneities of the POF cores are quantitatively correlated with mode couplings by modifying the coupled power equation with consideration of the spatial correlation characteristics of the heterogeneities. Using the modified theory, we clarify that the larger fluctuation size and/or amplitude results in higher bandwidth because of greater forward scattering and/or higher scattering efficiency, respectively. This suggests that the multimode fiber bandwidths can depend on the macroscopically observed index profiles as well as on the microscopic material properties.     

Abnormalities of cerebral blood flow in multiple sclerosis: A pseudocontinuous arterial spin labeling MRI study

Arterial spin labeling (ASL) is a noninvasive technique that can measure cerebral blood flow (CBF). To our knowledge, there is no study that examined regional CBF of multiple sclerosis (MS) patients by using this technique. The present study assessed the relationship between clinical presentations and functional imaging data in MS using pseudocontinuous arterial spin labeling (pCASL). Twenty-seven patients with MS and 24 healthy volunteers underwent magnetic resonance imaging and pCASL to assess CBF. Differences in CBF between the two groups and the relationships of CBF values with the T2-hyperintense volume were evaluated. Compared to the healthy volunteers, reduced CBF was found in the bilateral thalami and right frontal region of the MS patients. The volume of the T2-hyperintense lesion was negatively correlated with regional CBF in some areas, such as both thalami. Our results suggest that demyelinated lesions in MS mainly have a remote effect on the thalamus and that the measurement of CBF using ASL could be an objective marker for monitoring disease activity in MS.     

Time-between-photons method for measuring fluorescence lifetimes

We have applied a time-between-photons (TBP) method to measure fluorescence lifetimes in a pulsed-light excitation scheme. The TBP method has been originally proposed by Rossi and his coworkers in the field of ion photon emission microscopy (IPEM) for measuring lifetimes of ion-luminescent materials [Nucl. Instrum. Methods Phys. Res., Sect. B 267 (2009) 2193]. The TBP method has an advantage in that no reference signal is required in the instrumental setup. In the present paper, we demonstrate, for the first time to our knowledge, that the TBP method is also applicable to measure conventional fluorescence lifetimes. The TBP method suits for measuring fluorescent samples whose lifetimes are sufficiently long (≥10 ns) and intensities are moderately high (≤4 × 10^?8 W): fluorescent samples with intermediate quantum yields for which the conventional time-correlated single-photon-counting (TC-SPC) method is somewhat difficult to employ as it is and the conventional analogue light-measurement method is still hard to use.     

Intelligent Sugar Complexes

Abstract

The structure of [Co(L-Rha)₃-mn)]Br₂.2CH₃OH, where (Rhah-tren is tris(N-rhamnosyl-2-aminoethyl)amine, was elucidated by X-ray crystallography, which confirmed the unprecedented configurational inversion of [Co((Rha)₃-tren)]²⁺, around the metal center reversibly by an addition and a removal of sulfate.     

Structure and dynamics of photogenerated triplet radical ion pairs in DNA hairpin conjugates with anthraquinone end caps

A series of DNA hairpins (AqGn) possessing a tethered anthraquinone (Aq) end-capping group were synthesized in which the distance between the Aq and a guanine-cytosine (G-C) base pair was systematically varied by changing the number (n - 1) of adenine-thymine (A-T) base pairs between them. The photophysics and photochemistry of these hairpins were investigated using nanosecond transient absorption and time-resolved electron paramagnetic resonance (TREPR) spectroscopy. Upon photoexcitation, (1*)Aq undergoes rapid intersystem crossing to yield (3*)Aq, which is capable of oxidizing purine nucleobases resulting in the formation of (3)(Aq(-?)Gn(+?)). All (3)(Aq(-?)Gn(+?)) radical ion pairs exhibit asymmetric TREPR spectra with an electron spin polarization phase pattern of absorption and enhanced emission (A/E) due to their different triplet spin sublevel populations, which are derived from the corresponding non-Boltzmann spin sublevel populations of the (3*)Aq precursor. The TREPR spectra of the (3)(Aq(-?)Gn(+?)) radical ion pairs depend strongly on their spin-spin dipolar interaction and weakly on their spin-spin exchange coupling. The anisotropy of (3)(Aq(-?)Gn(+?)) makes it possible to determine that the π systems of Aq(-?) and G(+?) within the radical ion pair are parallel to one another. Charge recombination of the long-lived (3)(Aq(-?)Gn(+?)) radical ion pair displays an unusual bimodal distance dependence that results from a change in the rate-determining step for charge recombination from radical pair intersystem crossing for n < 4 to coherent superexchange for n > 4.     

Colorimetric sensing of cyanide anion in aqueous media with a fluorescein–spiropyran conjugate

A fluorescein–spiropyran conjugate (2) behaves as a receptor for colorimetric sensing of cyanide anion (CN^?) in aqueous media under irradiation of UV light. The compound 2, which exists as a spirocycle-closed (SP) form in the dark condition, is isomerized to the spirocycle-opened merocyanine (MC) form upon irradiation of UV light and shows absorption bands at 467 and 568 nm. Addition of CN^? to the solution leads to a decrease in these bands and an appearance of new absorption band at 512 nm, via a nucleophilic interaction between CN^? and the spirocarbon of MC form. This absorption change occurs selectively with CN^? and enables ratiometric quantification of CN^? by absorption analysis.     

Catalytic Mannich-type reactions of α-aminoacetonitrile using fluorenylidene as a protecting and activating group

Catalytic Mannich-type reactions of 9-fluorenylidene-protected α-aminoacetonitrile with imines were investigated. The desired reactions proceeded smoothly to afford the Mannich-type adducts in high yields with high diastereoselectivities in the presence of a catalytic amount of 1,1,3,3-tetramethylguanidine (TMG). A chiral guanidine catalyzed the reaction with good enantioselectivity.     

Synthesis and electronic structure of highly electron-accepting radiaannulene and its reduced species

Highly electron-accepting radiaannulene (1) was synthesized. CV measurements revealed a high electron accepting ability and strong electronic coupling in the anionic species. Spectroelectrochemical analysis revealed a very low-energy absorption band in the spectra of 1⁻ and 1²⁻.