Reconstructing seesaws

We explore some aspects of “reconstructing” the heavy singlet sector of supersymmetric type I seesaw models, for two, three or four singlets. We work in the limit where one light neutrino is massless. In an ideal world, where selected coefficients of the TeV-scale effective Lagrangian could be measured with arbitrary accuracy, the two-singlet case can be reconstructed, two three or more singlets can be differentiated, and an inverse seesaw with four singlets can be reconstructed. In a more realistic world, we estimate ℓ _α →ℓ _β γ expectations with a “Minimal-Flavour-Violation-like” ansatz, which gives a relation between ratios of the three branching ratios. The two-singlet model predicts a discrete set of ratios.     

Formal total synthesis of (+/-)-vindoline by tandem radical cyclization

A formal total synthesis of (+/-)-vindoline 1 has been achieved featuring the tandem cyclization of radicals produced from the iodoaryl azide 19a.     

Field-induced formation of nanometer-sized water bridges

A method to form and manipulate the properties of nanometer-size liquid bridges by an external electric field is discussed. The properties of bridges are shown to be the result of an interplay among the field-induced polarization of the water layer adsorbed on the surface, the surface energy, and the water condensation from the humid air. For a given tip-sample separation, a simple model predicts the existence of a threshold voltage V(th) to form the bridge in full agreement with experiments.     

Time-resolved quantum dynamics of double ionization in strong laser fields

Quantum calculations of a (1+1)-dimensional model for double ionization in strong laser fields are used to trace the time evolution from the ground state through ionization and rescattering to the two-electron escape. The subspace of symmetric escape, a prime characteristic of nonsequential double ionization, remains accessible by a judicious choice of 1D coordinates for the electrons. The time-resolved ionization fluxes show the onset of single and double ionization, the sequence of events during the pulse, and the influences of pulse duration and reveal the relative importance of sequential and nonsequential double ionization, even when ionization takes place during the same field cycle.     

Synthesis and Diversification of Macrocyclic Alkynediyl Sulfide Peptides

The synthesis of rare macrocyclic alkynediyl sulfides by a Cu-catalyzed C_sp−S cross-coupling is presented. The catalytic protocol (Cu(MeCN)₄PF₆/dtbbpy) promotes macrocyclization of peptides, dipeptides and tripeptides at ambient temperature (14 examples, 23→73 % yields) via thiols and bromoalkynes, and is chemoselective with regards to terminal alkynes. Importantly, the underexplored alkynediyl sulfide functionality incorporates a rigidifying structural element and opens new opportunities for diversification of macrocyclic frameworks through S oxidation, halide addition and azide–alkyne cycloaddition chemistries to integrate sulfones, halides or valuable fluorophores (7 examples, 37→92 % yields).