Hypervalent iodine-mediated vicinal syn diazidation: application to the total synthesis of (+/-)-dibromophakellstatin

[reaction: see text] The total synthesis of (+/-)-dibromophakellstatin is described. The molecule is constructed from a key syn-diazide, formed by a hypervalent iodine-mediated diazidation of a dihydrodipyrrolopyrazinone ring structure.     

Role of molecular size in ratchet fractionation

We show the importance of finite particle size in microfluidic asymmetric continuous-flow diffusion arrays, specifically the critical nature of the particle size with respect to the barrier gaps. We show that particles much smaller than the barrier gap follow individual field lines through narrow gaps and are poorly fractionated. In contrast, particles comparable to the gap size lose memory of their incoming field line and can be fractionated with high resolution. We demonstrate this effect using a new technological approach to create very straight and narrow injection bands in such arrays, and completely resolve bands of DNA of lengths 48,500 and 16,7000 base pairs.     

Dynamical Bonding Driving Mixed Valency in a Metal Boride

Samarium hexaboride is an anomaly, having many exotic and seemingly mutually incompatible properties. It was proposed to be a mixed‐valent semiconductor, and later a topological Kondo insulator, and yet has a Fermi surface despite being an insulator. We propose a new and unified understanding of SmB₆ centered on the hitherto unrecognized dynamical bonding effect: the coexistence of two Sm?B bonding modes within SmB₆, corresponding to different oxidation states of the Sm. The mixed valency arises in SmB₆ from thermal population of these distinct minima enabled by motion of B. Our model simultaneously explains the thermal valence fluctuations, appearance of magnetic Fermi surface, excess entropy at low temperatures, pressure‐induced phase transitions, and related features in Raman spectra and their unexpected dependence on temperature and boron isotope.     

The Michigan State University Cyclotron Laboratory: Its Early Years

The Michigan State University Cyclotron Laboratory was founded in 1958 and over the years grew in stature, becoming the highest-ranked university-based program in nuclear science. Its K50 cyclotron had unmatched capability as a light-ion accelerator and helped to define what a modern cyclotron could do to advance our understanding of nuclei. This paper describes the first twenty years of the Cyclotron Laboratory’s evolution and gives some insight into the cultural characteristics of the laboratory, and of its early members, that led it to thrive.     

The Status of the Australian Synchrotron

The earliest Australian use of a synchrotron can be dated to 1976 using the accelerator at Daresbury to perform energy dispersive diffraction crystallography of complex mineral structures. This was while it was operating in a parasitic mode in the days before it became a synchrotron storage ring. During the 1970s and 1980s, Australian researchers undertook experiments to study gas-phase atomic structures using Auger spectroscopy at the LURE facility in Paris; protein crystallography at Daresbury, DESY, Photon Factory, and SPEAR; NEXAFS experiments on thin polymer films at SSRL; development of a novel toroidal analyzer for angle-resolved photoelectron spectroscopy at BESSY 1 and later on BESSY 2; and carry out X-ray diffraction and XAFS at the Photon Factory.