Metal–Phenolic Supramolecular Gelation

Materials assembled by coordination interactions between naturally abundant polyphenols and metals are of interest for a wide range of applications, including crystallization, catalysis, and drug delivery. Such an interest has led to the development of thin films with tunable, dynamic properties, however, creating bulk materials remains a challenge. Reported here is a class of metallogels formed by direct gelation between inexpensive, naturally abundant tannic acid and group(IV) metal ions. The metallogels exhibit diverse properties, including self‐healing and transparency, and can be doped with various materials by in situ co‐gelation. The robustness and flexibility, combined with the ease, low cost, and scalability of the coordination‐driven assembly process make these metallogels potential candidates for chemical, biomedical, and environmental applications.     

Characterization of self-assembled monolayers of oligo(phenyleneethynylene) derivatives of varying shapes on gold: effect of laterally extended pi-systems

Fully conjugated organic molecules, such as the oligo(phenyleneethynylene) (OPE) systems, are of growing interest within the field of molecular electronics, as is the self-assembly of well-defined molecular thin films with predefined functions. The structure and function of such films are intimately related and governed by the structures of their molecular constituents, through the intermolecular interactions and the interactions between the molecules and the substrate, onto which the film is assembled. Here we report on the synthesis of a series of three OPE derivatives, with the general structure phenylethynylene-aryl-ethynylenephenylene-headgroup, and the structural investigation of the self-assembled monolayers (SAMs) formed from them on Au(111) surfaces. The SAMs were characterized by infrared reflection-absorption spectroscopy, spectroscopic ellipsometry, high-resolution X-ray photoemission spectroscopy, and near-edge X-ray absorption fine structure spectroscopy. The effective thickness of the SAMs was observed to decrease as the pi-system of the aryl moiety of the OPE adsorbate was extended perpendicular to its molecular long axis. Changing the aryl moiety from benzene to naphthalene to anthracene resulted in lower molecular surface densities and larger molecular inclination. The average tilt angles for the benzene, naphthalene, and anthracene SAMs were found to be about 30 degrees , 40 degrees , and 42 degrees from the surface normal, respectively. For the largest adsorbate, the anthracene derivative, there is spectroscopic evidence suggesting the existence of nonequivalent binding sites. The differences observed between the SAMs are rationalized in terms of the shape of the adsorbates and the strength of the pi-pi interactions between them.     

Acyl group migration and cleavage in selectively protected beta-d-galactopyranosides as studied by NMR spectroscopy and kinetic calculations

The migration of acetyl, pivaloyl, and benzoyl protective groups and their relative stabilities at variable pH for a series of beta- d-galactopyranoses were studied by NMR spectroscopy. The clockwise and counterclockwise migration rates for the different ester groups were accurately determined by use of a kinetic model. The results presented provide new insights into the acid and base stabilities of commonly used ester protecting groups and the phenomenon of acyl group migration and may prove useful in the planning of synthesis strategies.     

Automatic fitting procedures for EPR spectra of disordered systems: matrix diagonalization and perturbation methods applied to fluorocarbon radicals

Two types of automatic fitting procedures for EPR spectra of disordered systems have been developed, one based on matrix diagonalization of a general spin Hamiltonian, the other on 2nd order perturbation theory. The first program is based on a previous Fortran code complemented with a newly written interface in Java to provide user-friendly in and output. The second is intended for the special case of free radicals with several relatively weakly interacting nuclei, in which case the general method becomes slow. A least squares' fitting procedure utilizing analytical or numerical derivatives of the theoretically calculated spectrum with respect to the g- and hyperfine structure (hfs) tensors was used to refine those parameters in both cases. 'Rigid limit' ESR spectra from radicals in organic matrices and in polymers, previously studied experimentally at low temperature, were analyzed by both methods. Fluorocarbon anion radicals could be simulated, quite accurately with the exact method, whereas automatic fitting on, e.g. the c-C(4)F(8)(-) anion radical is only feasible with the 2nd order approximative treatment. Initial values for the (19)F hfs tensors estimated by DFT calculations were quite close to the final. For neutral radicals of the type XCF(2)CF(2)* the refinement of the hfs tensors by the exact method worked better than the approximate. The reasons are discussed. The ability of the fitting procedures to recover the correct magnetic parameters of disordered systems was investigated by fittings to synthetic spectra with known hfs tensors. The exact and the approximate methods are concluded to be complementary, one being general, but limited to relatively small systems, the other being a special treatment, suited for S=1/2 systems with several moderately large hfs.     

Efficient symmetry-based homonuclear dipolar recoupling of quadrupolar spins: double-quantum NMR correlations in amorphous solids

We report novel symmetry-based pulse sequences for exciting double-quantum (2Q) coherences between the central transitions of half-integer spin quadrupolar nuclei in the NMR of rotating solids. Compared to previous 2Q-recoupling techniques, numerical simulations and 23Na and 27Al NMR experiments on Na2SO4 and the open-framework aluminophosphate AlPO-CJ19 verify that the new dipolar recoupling schemes display higher robustness to both radio-frequency field inhomogeneity and to spreads in resonance frequencies. These advances allowed for the first demonstration of 2Q-recoupling in an amorphous solid for revealing its intermediate-range structural features, in the context of mapping 27Al-27Al connectivities between the aluminium polyhedra (AlO4, AlO5 and AlO6) of a lanthanum aluminate glass (La0.18Al0.82O1.5).     

Narrow linewidth, 100 W cw Yb3+-doped silica fiber laser with a point-by-point Bragg grating inscribed directly into the active core

We report on the power scaling to 103 W of a 1.1 microm continuous-wave Yb(3+)-doped silica fiber laser incorporating a point-by-point (PbP) fiber-Bragg grating inscribed directly into the active core using 800 nm femtosecond laser pulses. The spectrum of the laser exhibited a narrow linewidth that broadened to 260 pm at 103 W. The output was frequency doubled using an 11 mm long periodically poled MgO:LiNbO3 crystal to generate 2.1 W of green with an internal conversion efficiency of 10% at high power and 0.81%/W at low power.     

Boson Stars as Solitary Waves

We study the nonlinear equation