Synthesis of trifluoromethylated heterocycles using partially fluorinated epoxides

Reaction of 2-trifluoromethyl- (1) and 2,2-bis(trifluoromethyl)- (2) oxiranes with a variety of sulfur nucleophiles proceeds rapidly and under mild conditions. For example, epoxide 2 reacts with aqueous solution of Na₂S, producing S[CH₂C(CF₃)₂OH]₂. Reaction of 2 with Na₂S₂O₃ leads to the formation of the corresponding Bunte salt. Interaction of 2 with NaSCN in water proceeds exothermically and results in high-yield formation of cyclic imine 5. Although this material can be isolated, it has limited stability and undergoes cyclotrimerization at ambient temperature, giving the corresponding 1,3,5-triazine. A number of heterocyclic compounds containing pendant -CH₂C(CF₃)₂OH group were prepared by the reaction of the corresponding thio-derivatives, such as pyridine-2-thiole with epoxide 2. It was found that fluoride anion catalyzes the reaction of epoxides 1 and 2 with isothiocyanates carrying electron withdrawing groups at nitrogen. The reaction results in nucleophilic cyclization and formation of the corresponding exocyclic imines containing a 1,3-oxothiolane moiety. Carbon disulfide was also found to be active in this process, reacting with epoxides 1 and 2 at ambient to give the corresponding trifluoromethylated 1,3-oxathiolane-2-thiones in 58-65% yield.     

Sbottom signature of supersymmetric golden region

The experimental search limit on the Higgs boson mass points to a “golden region” in the Minimal Supersymmetric Standard Model parameter space in which the fine-tuning in the electroweak sector is minimized. One of the sbottoms is relatively light since its mass parameter is related to that of the stop. The decay products of the light sbottom typically include a W boson and a b jet. We studied the pair production of the light sbottoms at the Large Hadron Collider and examined its discovery potential via collider signature of 4 jets + 1 lepton + missing E _T . Such channel differs from conventional sbottom searches of either \(\tilde{b}_{1} \rightarrow b \chi_{2}^{0} \rightarrow b \ell^{+}\ell^{-} \chi_{1}^{0}\) or \(\tilde{b}_{1} \rightarrow t \chi_{1}^{-}\) with reconstructed top quark. We analyzed the Standard Model backgrounds for this channel and developed a set of cuts to identify the signal and suppress the backgrounds. We showed that with 100 fb^?1 integrated luminosity, a significance level of 5–6 σ could be reached for the light sbottom discovery at the LHC.     

Vacancy growth and migration dynamics in atomically thin hexagonal boron nitride under electron beam irradiation

Atomically thin hexagonal boron nitride (h‐BN) is investigated using aberration‐corrected ultra‐high resolution electron microscopy under 80 kV electron beam. This study focuses on the in situ formation, growth and migration of vacancies in h‐BN. This study also reveals interaction dynamics of edges and vacancies with adatoms and molecules under the electron beam. According to this investigation, boron monovacancies migrate through their second neighbor to reduce the surface energy of the membrane. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

From Intercalation to Groove Binding: Switching the DNA‐Binding Mode of Isostructural Transition‐Metal Complexes

The interaction with duplex DNA of a small library of structurally related complexes that all contain a d⁶‐metal ion coordinated to either the 2,2 ′ :4,4 ′′ :4 ′ ,4 ′′′ ‐quaterpyridyl ligand or its methylated derivative are reported. This library is made up of a mixture of newly synthesised and previously reported systems. Despite their structural similarities the complexes display an almost 20‐fold variation in binding affinities. Although effects due to the overall charge of the complexes are apparent, the differences in binding characteristics are deeper than this; indeed, in a number of cases, changes in overall charge have little effect on binding affinity. Intriguingly, despite interacting with DNA through unfused ring systems, although two of the complexes studied are groove binders, the majority are non‐classical intercalators. A rationale for these effects has been obtained through a combination of experimental and computational studies.     

Discrete diffraction in two-dimensional arrays of coupled waveguides in silica

The propagation of light in 5 x 5 and 7 x 7 cubic lattices of evanescently coupled waveguides is investigated for the first time, to the authors' knowledge. The results reveal ideal discrete diffraction and demonstrate the excellent quality of the waveguide arrays, which were manufactured in fused silica by femtosecond-laser-induced refractive-index modifications.     

Synthesis and Evaluation of Novel Ring-Strained Noncanonical Amino Acids for Residue-Specific Bioorthogonal Reactions in Living Cells

Bioorthogonal reactions are ideally suited to selectively modify proteins in complex environments, even in vivo. Kinetics and product stability of these reactions are crucial parameters to evaluate their usefulness for specific applications. Strain promoted inverse electron demand Diels–Alder cycloadditions (SPIEDAC) between tetrazines and strained alkenes or alkynes are particularly popular, as they allow ultrafast labeling inside cells. In combination with genetic code expansion (GCE)-a method that allows to incorporate noncanonical amino acids (ncAAs) site-specifically into proteins in vivo. These reactions enable residue-specific fluorophore attachment to proteins in living mammalian cells. Several SPIEDAC capable ncAAs have been presented and studied under diverse conditions, revealing different instabilities ranging from educt decomposition to product loss due to β-elimination. To identify which compounds yield the best labeling inside living mammalian cells has frequently been difficult. In this study we present a) the synthesis of four new SPIEDAC reactive ncAAs that cannot undergo β-elimination and b) a fluorescence flow cytometry based FRET-assay to measure reaction kinetics inside living cells. Our results, which at first sight can be seen conflicting with some other studies, capture GCE-specific experimental conditions, such as long-term exposure of the ring-strained ncAA to living cells, that are not taken into account in other assays.     

Spaces of distributions, interpolation by translates of a basis function and error estimates

Summary. Interpolation with translates of a basis function is a common process in approximation theory. The most elementary form of the interpolant consists of a linear combination of all translates by interpolation points of a single basis function. Frequently, low degree polynomials are added to the interpolant. One of the significant features of this type of interpolant is that it is often the solution of a variational problem. In this paper we concentrate on developing a wide variety of spaces for which a variational theory is available. For each of these spaces, we show that there is a natural choice of basis function. We also show how the theory leads to efficient ways of calculating the interpolant and to new error estimates. Received December 10, 1996 / Revised version received August 29, 1997     

Direct form seminorms arising in the theory of interpolation by translates of a basis function

In the error analysis of the process of interpolation by translates of a single basis function, certain spaces of functions arise naturally. These spaces are defined with respect to a seminorm which is given in terms of the Fourier transform of the function. We call this an indirect seminorm. In certain well‐understood cases, the seminorm can be rewritten trivially in terms of the function, rather than its Fourier transform. We call this a direct seminorm. The direct form allows better error estimates to be obtained. In this paper, we shown how to rewrite most of the commonly arising indirect form seminorms in direct form, and begin a little of the analysis required to obtain the improved error estimates. This revised version was published online in June 2006 with corrections to the Cover Date.