Conformational Isomers of Calcineurin Follow Distinct Dissociation Pathways

In the gas-phase, ions of protein complexes typically follow an asymmetric dissociation pathway upon collisional activation, whereby an expelled small monomer takes a disproportionately large amount of the charges from the precursor ion. This phenomenon has been rationalized by assuming that upon activation, a single monomer becomes unfolded, thereby attracting charges to its newly exposed basic residues. Here, we report on the atypical gas-phase dissociation of the therapeutically important, heterodimeric calcium/calmodulin-dependent serine/threonine phosphatase calcineurin, using a combination of tandem mass spectrometry, ion mobility mass spectrometry, and computational modeling. Therefore, a hetero-dimeric calcineurin construct (62?kDa), composed of CNa (44?kDa, a truncation mutant missing the calmodulin binding and auto-inhibitory domains), and CNb (18?kDa), was used. Upon collisional activation, this hetero-dimer follows the commonly observed dissociation behavior, whereby the smaller CNb becomes highly charged and is expelled. Surprisingly, in addition, a second atypical dissociation pathway, whereby the charge partitioning over the two entities is more symmetric is observed. The presence of two gas-phase conformational isomers of calcineurin as revealed by ion mobility mass spectrometry (IM-MS) may explain the co-occurrence of these two dissociation pathways. We reveal the direct relationship between the conformation of the calcineurin precursor ion and its concomitant dissociation pathway and provide insights into the mechanisms underlying this co-occurrence of the typical and atypical fragmentation mechanisms.     

Methyl (SR)‐10‐chloro‐1,2,3,4,5,6‐hexahydro‐6‐hydroxy‐8‐methoxy‐1‐methyl‐1,9‐phenanthroline‐6‐carboxylate

In the title compound, C₁₆H₁₉ClN₂O₄, the pyridine ring is nearly planar, the piperidine ring is non‐planar and the cyclo­hexane ring adopts a screw‐boat conformation. The carboxyl­ate group makes a dihedral angle of 80.9 (2)° with the least‐squares plane through the cyclo­hexane ring.     

Electrochemical synthesis and optical analysis of poly[(2,2′-dithienyl)-5,5′-diylvinylene]

The electrochemical synthesis of poly[(2,2′-dithienyl)-5,5′-diylvinylene tetrafluoroborate] (PDTE/BF₄) has been accomplished and provides coppery-black free-standing films with a room-temperature four-probe conductivity as high as 15 (Ω cm)^?1. The conductivity and morphology of the films were found to be strongly dependent on synthetic conditions. The oxidized form of PDTE is not air stable, as evidenced by a rapid, three order of magnitude drop in the conductivity. Optoelectrochemical experiments demonstrate that bipolarons are the main charge-carrying species in conductive PDTE and allow their evolution to be followed as a function of oxidation.     

Separation of variables and explicit theta-function solution of the classical Steklov-Lyapunov systems: A geometric and algebraic geometric background

The paper revises the explicit integration of the classical Steklov-Lyapunov systems via separation of variables, which had been first made by F. Kötter in 1900, but was not well understood until recently. We give a geometric interpretation of the separating variables and then, applying the Weierstrass hyperelliptic root functions, obtain explicit theta-function solution to the problem. We also analyze the structure of poles of the solution on the Jacobian on the corresponding hyperelliptic curve. This enables us to obtain a solution for an alternative set of phase variables of the systems that has a specific compact form. In conclusion we discuss the problem of integration of the Rubanovsky gyroscopic generalizations of the above systems.     

Interplay of matrix element, self-energy and geometric effects in various spectroscopies of the cuprates

We discuss a comprehensive scheme for modeling various highly resolved spectroscopies of the cuprates where effects of matrix element, crystal structure, strong electron correlations, and superconductivity are included realistically in material-specific detail. A number of illustrative examples drawn from our recent work are presented. Specific issues in the cuprate physics considered are: (i) Origin of high-energy kink or the waterfall effect; (ii) Dichroic effects in angle-resolved photoemission spectrum; (iii) Asymmetry of the scanning tunneling spectrum between the processes of electron extraction and injection; (iv) Persistence of ‘Mott’ like high-energy features with doping in optical spectra; (v) Magnetic excitations in electron and hole doped cuprates.     

Dynamics of zero-Prandtl number convection near onset

We present a detailed bifurcation scenario of zero-Prandtl number Rayleigh-Be?nard convection using direct numerical simulations (DNS) and a 27-mode low-dimensional model containing the most energetic modes of DNS. The bifurcation analysis reveals a rich variety of convective flow patterns and chaotic solutions, some of which are common to that of the 13-mode model of Pal et al. [EPL 87, 54003 (2009)]. We also observed a set of periodic and chaotic wavy rolls in DNS and in the model similar to those observed in experiments and numerical simulations. The time period of the wavy rolls is closely related to the eigenvalues of the stability matrix of the Hopf bifurcation points at the onset of convection. This time period is in good agreement with the experimental results for low-Prandtl number fluids. The chaotic attractor of the wavy roll solutions is born through a quasiperiodic and phase-locking route to chaos.