En route to a carbohydrate-based vaccine against Burkholderia cepacia

We report a very high yielding first total synthesis of trisaccharide 5, alpha-D-Rhap-(1 --> 3)-alpha-D-Rhap-(1 --> 4)-alpha-D-Galp, corresponding to the repeating unit 1 of an O-polysaccharide present in the lipopolysaccharide of clinical isolate of Burkholderia cepacia. The approach included two successive glycosylations, based on D-rhamnosyl trichloroacetimidate donors 12 and 14. The oligosaccharide 5 has been further functionalized by photochemical coupling or cross-metathesis with non-natural amino acid derivatives. Trisaccharidylamino acids 16 and 17 are now available, with the aim of preparing a novel synthetic carbohydrate-based vaccine.     

Nano-structured proton exchange membranes molded by polymerizing bi-continuous microemulsion

A unique type of nano-structured proton exchange membrane (PEM) has been fabricated through photo-polymerizing a bicontinuous microemulsion. This microemulsion is constituted by a polymerizable zwitterionic surfimer 3-((11-acryloyloxyundecyl)imidazoyl)propyl sulfonate (AIPS), 3-sulfopropylmethacrylate, potassium salt (SPM), acrylonitrile and water. As the resulting colloidal system maintains quasi-homogeneous state throughout the polymerization course, the inherent bicontinuous microemulsion structure was successfully transferred to the matrix of the polymer membrane. Such membranes are therefore composed of dual phase channels with ca. 1.5–2 nm of the hydrophilic channel breadth. This particular structural trait imparts to the membranes excellent proton conductivities of up to 10⁻¹ S cm⁻¹ as well as low methanol permeability. The DMFC single cell loaded with the demo PEM manifests ca. 20 mW cm⁻² of power output. The attributes of this PEM are elucidated from the bicontinuous structure of microemulsion.     

Tailoring the charge carrier dynamics in ZnO nanowires: the role of surface hole/electron traps

Post-fabrication thermal-annealed ZnO nanowires (NWs) in an oxidizing (or a reducing) ambient were investigated using transient photoluminescence and X-ray photoelectron spectroscopy. Our findings reveal an ultrafast hole-transfer process to the surface adsorbed oxygen species (e.g., O(2)(-)) occurring within a few hundred picoseconds (ps) in the air-annealed samples; and an ultrafast electron-transfer process to charged oxygen vacancies (i.e., V(O)(2+)) occurring within tens of ps in the H(2)-annealed samples. Contrary to the common perception that the band edge emission (BE) dynamics are strongly influenced by the carrier trapping to the green emission related defect states (i.e., V(Zn)), these above processes compete effectively with the ZnO BE. Hole trapping by ionized V(Zn), which occurs in an ultrashort sub-ps-to-ps timescale (and hence limits its effective hole capture radius), however, has less influence on the BE dynamics. Importantly, our findings shed new light on the photoinduced charge transfer processes that underpins the novel properties of enhanced photocatalytic activity, photovoltaic performance, and photoconductivity response of ZnO NWs, thereby suggesting a strategy for tailoring the ultrafast carrier dynamics in ZnO NW-based devices.     

Time-resolved resonance Raman study of the triplet states of p-hydroxyacetophenone and the p-hydroxyphenacyl diethyl phosphate phototrigger compound

Pico- and nanosecond time-resolved resonance Raman (TR3) spectroscopy have been utilized to study the dynamics and structure of p-hydroxyacetophenone (HA) and the p-hydroxyphenacyl-caged phototrigger compound p-hydroxyphenacyl diethyl phosphate (HPDP) in acetonitrile solution. Transient intermediates were detected and attributed to the triplet states of HA and HPDP. Nanosecond-TR3 measurements were done for two isotopically substituted HA molecules to help better assign the triplet state carbonyl C=O stretching and the ring related vibrational modes. The dynamics of formation and the spectral characteristics for the triplet states were found to be similar for the HA and HPDP. The temporal evolution at very early picosecond time scale indicates there is rapid intersystem crossing (ISC) conversion and subsequent relaxation of the excess energy of the initially produced energetic triplet state. B3LYP/6-311G** density functional theory (DFT) calculations were done to determine the structures and vibrational frequencies for both the triplet and ground states of HA and HPDP. The calculated spectra reproduce the experimental spectra and the observed isotopic shifts reasonably well and were used to make tentative assignments to all the experimentally observed features. The triplet states were found to have extensive conjugated pipi* nature with a single-bond-like carbonyl CO bond. We briefly compare the triplet structure and formation dynamics of HA and HPDP as well as the conformational changes upon going from the ground state to the triplet state. We discuss our present results in relation to the initial pathway for the p-hydroxyphenacyl photodeprotection process. We also compare and discuss the properties of the HA pipi* triplet state relative to the published results of other aromatic carbonyl compounds.     

Wald's equation and asymptotic bias of randomly stopped -statistics

In this paper we make use of decoupling arguments and martingale inequalities to extend Wald's equation for sample sums to randomly stopped de-normalized -statistics. We also apply this result in conjunction with nonlinear renewal theory to obtain asymptotic expansions for the means of normalized -statistics from sequential samples.

     

Reusable and Efficient Cul/TBAB‐Catalyzed Iodination of Terminal Alkynes in Water under Air

An environmentally‐friendly and operationally‐simple process for the synthesis of 1‐iodoalk‐1‐ynes under mild conditions catalyzed by CuI/TBAB in water under air was developed in this study. Catalyst loadings of CuI as low as 1–2 mol% gave 1‐iodoalk‐1‐ynes in good to high yields, and the residual aqueous solution after extraction with hexane could be reused for the next reaction without any treatment.     

The influence of different fabrication processes on characteristics of excess Bi2O3-doped 0.95 (Na0.5Bi0.5)TiO3–0.05 BaTiO3 ceramics

In this study, we will develop the influences of the excess x wt% (x=0, 1, 2, and 3) Bi₂O₃-doped and the different fabricating process on the sintering and dielectric characteristics of 0.95 (Na_0.5Bi_0.5)TiO₃–0.05 BaTiO₃ ferroelectric ceramics with the aid of SEM and X-ray diffraction patterns, and dielectric–temperature curves. The 0.95 (Na_0.5Bi_0.5)TiO₃–0.05 BaTiO₃+x wt% Bi₂O₃ ceramics are fabricated by two different processes. The first process is that (Na_0.5Bi_0.5)TiO₃ composition is calcined at 850 °C and BaTiO₃ composition is calcined at 1100 °C, then the calcined (Na_0.5Bi_0.5)TiO₃ and BaTiO₃ powders are mixed in according to 0.95 (Na_0.5Bi_0.5)TiO₃–0.05 BaTiO₃+x wt% Bi₂O₃ compositions. The second process is that the raw materials are mixed in accordance to the 0.95 (Na_0.5Bi_0.5)TiO₃–0.05 BaTiO₃+x wt% Bi₂O₃ compositions and then calcining at 900 °C. The sintering process is carried out in air for 2 h from 1120 to 1240 °C. After sintering, the effects of process parameters on the dielectric characteristics will be developed by the dielectric–temperature curves. Dielectric–temperature properties are also investigated at the temperatures of 30–350 °C and at the frequencies of 10 kHz–1 MHz.     

Infinite number of local conservation laws for the self-dual SU(2) Yang-Mills system within 't Hooft's ansatz

We derive infinite sets of local continuity equations for the four-dimensional classical self-dual SU(2) Yang-Mills fields subjected to 't Hooft's ansatz. In striking analogy to the two-dimensional CP(n) non-linear sigma model where local conservation laws obtain either from complex Cauchy-Riemann analyticity or from a matrix Riccati equation, our local sets derive from quaternionic Fueter analyticity or a Riccati equation associated with the geometric prolongation structure implied by the Belavin-Zakharov linear spectral problem for the self-dual Yang-Mills system. Our analysis underlines the close connection between local and non-local conservation laws and suggests that infinite sets of local continuity equations should be present in the general self-(antiself-)dual gauge field case.     

Lacunary systems and generalized linear processes

Herein we obtain several almost sure and L_p convergence properties of generalized linear processes. When the generalized linear process is generated by an orthonormal S_p system (which includes the classical i.i.d. white noise, L_p bounded martingale difference sequences and weakly multiplicative sequences as special cases), it is shown that these convergence properties are related to certain second order properties of the process.     

Chiral solitons and current algebra

We investigate the possibility of a realistic hadrodynamics based solely on observable currents. The basic idea is to exploit the soliton generation in bosonic chiral theories as a mechanism for finding the fermionic representations of current algebra. A prototype realization is Skyrme's O(4) invariant theory of pions and nucleons. A comprehensive reexamination of this model in the context of chiral dynamics suffices to reveal a strikingly self-consistent dynamical picture. First a differential geometric formulation gives the proper framework for a chiral invariant quantum theory of solitons and allows a compact derivation of Skyrme's main results. While no exact analytic solution is found, the solitons are sufficiently localized so that their singularities can be properly isolated out for analysis. Using Witten's ansatz, a determination of the form of the 1-soliton singularity is obtained from the field equations. It is given by Cayley's steoreographic projection from S³ to $\text{R}{}^3\text{? {∞} ≈ S}{}^3$; a most suitable form for the proof of spinor structure. Williams' proof that the quantized 1-soliton sector gives rise to fermionic spin states is recalled. It is argued that the topological dynamics of this sector induce an invariance group K = SU(2)_I ? SU(2)_J and its associated strong coupling isobaric spectrum for the nucleons. The associated current algebra is derived and resolves the main difficulties of the Sugawara-Sommerfield program. The signature of a field theoretical bootstrap is clear: massive nucleons as soliton bound states of Nambu-Goldstone bosons illustrate a dynamical mechanism dual to that of Nambu and Jona-Lasinio.