Is restricted M–P rotation a common feature of enantioselective monophos catalysts? An example of restricted Rh–P rotation in a secondary phosphine complex

The enantioselective hydrogenation catalyst [Rh(α-CgPH)₂(cod)]BF₄, (CgPH = 6-phospha-2,4,8-trioxa-adamantane) exists in solution as a mixture of two slowly interconverting rotamers, one with C₂- and the other with C₁-symmetry.     

Synthesis and Chemical Transformations of 6‐(Morpholine‐4‐sulfonyl)‐quinoline‐2,3,4‐tricarboxylic Acid

The article describes an effective synthesis and chemical transformations of 6‐(morpholine‐4‐sulfonyl)‐2,3,4‐quinolinetricarboxylic acid. The key step is the Pfitzinger reaction of 3,3‐dichloro‐2‐oxo‐2,3‐dihydro‐1H‐indole with diethyl 2‐oxosuccinate. Selective 2‐decarboxylation of the tricarboxylic acid followed by reaction of the resulting anhydride with a primary amine led to the formation of the 1,3‐dioxo‐2,3‐dihydro‐1H‐pyrrolo[3,4‐c]quinoline scaffold with interesting pharmacological activity.     

Modulation of cross polarization in motionally averaged solids by Variable Angle Spinning NMR

In systems where the dipolar couplings are partially averaged by molecular motion, cross-polarization is modulated by sample spinning. The cross-polariation efficiency in Variable Angle Spinning (VAS) and Switched Angle Spinning (SAS) experiments on mobile samples is therefore strongly dependent on the spinning angle. We describe simulations and experimental measurements of these effects over a range of spinning angles from 0° to 90°.     

Subgroup properties of fully residually free groups

We prove that fully residually free groups have the Howson property, that is the intersection of any two finitely generated subgroups in such a group is again finitely generated. We also establish some commensurability properties for finitely generated fully residually free groups which are similar to those of free groups. Finally we prove that for a finitely generated fully residually free group the membership problem is solvable with respect to any finitely generated subgroup.

     

Electromagnetic unidirectionality and frozen modes in magnetic photonic crystals

Magnetic photonic crystals are periodic arrays of lossless materials, at least one of which being magnetically polarized. Magnetization, either spontaneous or induced, is associated with nonreciprocal effects, such as Faraday rotation. Magnetic photonic crystals of certain configuration can also display strong spectral asymmetry, implying that light propagates in one direction much faster or slower than in the opposite direction. This essentially nonreciprocal phenomenon can result in electromagnetic unidirectionality. A unidirectional medium, being perfectly transmissive for electromagnetic waves of certain frequency, freezes the radiation of the same frequency propagating in the opposite direction. The frozen mode has zero group velocity and drastically enhanced amplitude. The focus of our investigation is the frozen mode regime. Particular attention is given to the case of weak nonreciprocity, related to the infrared and optical frequencies. It appears that even if the nonreciprocal effects become vanishingly small, there is still a viable alternative to the frozen mode regime that can be very attractive for a variety of practical applications.     

Recursive error correction for general Reed-Muller codes

Reed-Muller (RM) codes of growing length n and distance d are considered over a binary symmetric channel. A recursive decoding algorithm is designed that has complexity of order nlogn and corrects most error patterns of weight (dlnd)/2. The presented algorithm outperforms other algorithms with nonexponential decoding complexity, which are known for RM codes. We evaluate code performance using a new probabilistic technique that disintegrates decoding into a sequence of recursive steps. This allows us to define the most error-prone information symbols and find the highest transition error probability p, which yields a vanishing output error probability on long codes.