Manganese(I)‐Catalyzed C−H Activation: The Key Role of a 7‐Membered Manganacycle in H‐Transfer and Reductive Elimination

Manganese‐catalyzed C?H bond activation chemistry is emerging as a powerful and complementary method for molecular functionalization. A highly reactive seven‐membered Mn^I intermediate is detected and characterized that is effective for H‐transfer or reductive elimination to deliver alkenylated or pyridinium products, respectively. The two pathways are determined at Mn^I by judicious choice of an electron‐deficient 2‐pyrone substrate containing a 2‐pyridyl directing group, which undergoes regioselective C?H bond activation, serving as a valuable system for probing the mechanistic features of Mn C?H bond activation chemistry.     

Fast characterization of intact proteins using a high-throughput eight-channel parallel liquid chromatography/mass spectrometry system

The preparation of protein substrates requires that a large number of chromatographic fractions be analyzed for the presence of reactants, products and by-products. Analyses using linear matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) or single column liquid chromatography/mass spectrometry (LC/MS) have been inadequate because of mass resolution or throughput. Therefore, a high-throughput method employing an eight-channel parallel reverse-phase LC/MS system was developed. This system is capable of screening fractions from preparative ion-exchange chromatography with the required mass accuracy and throughput so that the protein purification process can be monitored in a relatively short period of time. As an example, the purification and analysis of an acylated protein with a molecular weight of 8.9 kDa is described and the detection of a contaminating by-product that differs in size by less than 20 Da is demonstrated. Using the current instrumentation and approach, it is practical to analyze 50 protein-containing fractions from column chromatography in less than 1 hour using parallel LC/MS.     

Oxidative Addition to Gold(I) by Photoredox Catalysis: Straightforward Access to Diverse (C,N)‐Cyclometalated Gold(III) Complexes

Herein, we report the oxidative addition of aryldiazonium salts to ligand‐supported gold(I) complexes under visible light photoredox conditions. This method provides experimental evidence for the involvement of such a process in dual gold/photoredox‐catalyzed reactions and delivers well‐defined (C,N)‐cyclometalated gold(III) species. The remarkably mild reaction conditions and the ability to widely vary the ancillary ligand make this method a potentially powerful synthetic tool to access diverse gold(III) complexes for systematic studies into their properties and reactivity. Initial studies show that these species can undergo chloride abstraction to afford Lewis acidic dicationic gold(III) species.     

Changes in the magnetic structure of (La0.25Pr0.75)0.7Ca0.3MnO3 upon the isotopic substitution of 18O for 16O

A giant isotope effect, wherein the low-temperature metallic state is replaced by an insulator state, was recently observed when ¹⁸O was substituted for ¹⁶O in (La_0.25Pr_0.75)_0.7Ca_0.3MnO₃ [N. A. Babushkina, L. M. Belova, O. Yu. Gorbenko et al., Nature (London) 391, 159 (1998)]. In the present work, the temperature evolution of the magnetic structure of two samples of this compound is studied by neutron diffraction. One sample contained a natural mixture of oxygen isotopes, 99.7% ¹⁶O, while the other was enriched to 75% with the isotope ¹⁸O. It is established that the samples are crystallographically identical at room temperature. As the temperature decreases, the sample with ¹⁶O undergoes successive antiferromagnetic (T _AFM=5150 K) and ferromagnetic (T _FM=110 K) transitions, which lead to the establishment of a noncollinear ferromagnetic structure, while a purely antiferromagnetic (T _AFM=150 K) order arises in the sample with ¹⁸O. The temperature dependences of the intensities of the diffraction peaks associated with the charge ordering differ substantially in samples with ¹⁶O and ¹⁸O, and they correlate with the behavior of their electric resistance and magnetic structure. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 1, 46–51 (10 January 1999)     

Financing biotechnology projects

An increasing number of biotechnology projects are being brought to commercialization using conventional structured finance sources, which have traditionally only been available to proven technologies and primary industries. Attracting and securing competitive cost financing from main-stream lenders, however, will require the sponsor of a new technology or process to undergo a greater level of due diligence. The specific areas and intensity of investigation, which are typically required by lenders in order to secure long-term financing for biotechnology-based manufacturing systems, is reviewed. The processes for evaluating the adequacy of prior laboratory testing and pilot plant demonstrations is discussed. Particular emphasis is given to scale-up considerations and the ability of the proposed facility design to accommodate significant modifications, in the event that scale-up problems are encountered.     

High-power diode-pumped passively mode-locked Yb:YAG lasers

We obtained 74-kW peak power and 3.5-W average output power in 1-ps pulses from a diode-pumped Yb:YAG laser at 1030 nm that was passively mode locked with a semiconductor saturable-absorber mirror. Another laser produced 57-kW peak power and as much as 8.1-W average output power in 2.2-ps pulses, split into two nearly diffraction-limited beams (M(2)<1.2) . To our knowledge, these are by far the highest reported peak and average output powers from a diode-pumped mode-locked laser in this pulse-duration regime.     

Zeolite micromembranes

Free-standing silicalite-1 (Sil-1) zeolite micromembranes have been successfully fabricated onto silicon substrate. Gas permeation test using permanent gases (i.e., helium, hydrogen, argon and nitrogen) and hydrocarbons (i.e., methane and n-butane) indicates that the micromembranes have excellent permeance flux and high permselectivity.     

Geodesic flow on the diffeomorphism group of the circle

We show that certain right-invariant metrics endow the infinite-dimensional Lie group of all smooth orientation-preserving diffeomorphisms of the circle with a Riemannian structure. The study of the Riemannian exponential map allows us to prove infinite-dimensional counterparts of results from classical Riemannian geometry: the Riemannian exponential map is a smooth local diffeomorphism and the length-minimizing property of the geodesics holds.