Synthesis and In Silico Study of 4-Substituted 1-Aminoanthraquinones

Russian Journal of Organic Chemistry - Eight new 4-substituted 1-amino-9,10-anthraquinones containing a primary amino group were syn­the­sized by nucleophilic substitution of bromine in...     

Cytochrome c(2) Exit Strategy: Dissociation Studies and Evolutionary Implications

Small, water-soluble, type c cytochromes form a transient network connecting major bioenergetic membrane protein complexes in both photosynthesis and respiration. In the photosynthesis cycle of Rhodobacter sphaeroides, cytochrome c2 (cyt c2) docks to the reaction center (RC), undergoes electron transfer, and exits for the cytochrome bc1 complex. Translations of cyt c2 about the RC-cyt c2 docking interface and surrounding membrane reveal possible exit pathways. A pathway at a minimal elevation allowed by the architecture of the RC is analyzed using both an all-atom steered molecular dynamics simulation of the RC-cyt c2 complex and a bioinformatic analysis of the structures and sequences of cyt c. The structure-based phylogenetic analysis allows for the identification of structural elements that have evolved to satisfy the requirements of having multiple functional partners. The patterns of evolutionary variation obtained from the phylogenetic analysis of both docking partners of cyt c2 reveal conservation of key residues involved in the interaction interfaces that would be candidates for further experimental studies. Additionally, using the molecular mechanics Poisson-Boltzmann surface area method we calculate that the binding free energy of reduced cyt c2 to the RC is nearly 6 kcal/mol more favorable than with oxidized cyt c2. The redox-dependent variations lead to changes in structural flexibility, behavior of the interfacial water molecules, and eventually changes in the binding free energy of the complex.     

Centerpole sets for colorings of abelian groups

A subset C?G of a group G is called k-centerpole if for each k-coloring of G there is an infinite monochromatic subset G, which is symmetric with respect to a point c??C in the sense that S=cS ^?1 c. By c _k (G) we denote the smallest cardinality c _k (G) of a k-centerpole subset in G. We prove that c _k (G)=c _k (? ^m ) if G is an abelian group of free rank m??k. Also we prove that c ₁(? ⁿ⁺¹)=1, c ₂(? ⁿ⁺²)=3, c ₃(? ⁿ⁺³)=6, 8??c ₄(? ⁿ⁺⁴)??c ₄(?⁴)=12 for all n????, and ${\frac{1}{2}(k^{2}+3k-4)\le c_{k}(\mathbb{Z}^{n})\le2^{k}-1-\max_{s\le k-2}\binom {k-1}{s-1}}$ for all n??k??4.     

Electron detachment dissociation for top-down mass spectrometry of acidic proteins

Electron detachment dissociation (EDD) is an emerging mass spectrometry (MS) technique for the primary structure analysis of peptides, carbohydrates, and oligonucleotides. Herein, we explore the potential of EDD for sequencing of proteins of up to 147 amino acid residues by using top-down MS. Sequence coverage ranged from 72% for Melittin, which lacks carboxylic acid functionalities, to 19% for an acidic 147-residue protein, to 12% for Ferredoxin, which showed unusual backbone fragmentation next to cysteine residues. A limiting factor for protein sequencing by EDD is the facile loss of small molecules from amino acid side chains, in particular CO(2). Based on the types of fragments observed and fragmentation patterns found, we propose detailed mechanisms for protein backbone cleavage and side chain dissociation in EDD. The insights from this study should further the development of EDD for top-down MS of acidic proteins.     

Field theory of mesoscopic fluctuations in superconductor-normal-metal systems

Thermodynamic and transport properties of mesoscopic conductors are strongly influenced by the proximity of a superconductor: an interplay between the large scale quantum coherent wave functions in the normal mesoscopic and the superconducting region, respectively, leads to unusual mechanisms of quantum interference. These manifest themselves in both the mean and the mesoscopic fluctuation behaviour of superconductor-normal-metal (SN) hybrid systems being strikingly different from those of conventional mesoscopic systems. After reviewing some established theories of SN quantum interference phenomena, we introduce a new approach to the analysis of SN mesoscopic physics. Essentially, our formalism represents a unification of the quasi-classical formalism for describing mean properties of SN systems on the one hand, with more recent field theories of mesoscopic fluctuations on the other hand. Thus, by its very construction, the new approach is capable of exploring both averaged and fluctuation properties of SN systems on the same microscopic footing. As an example, the method is applied to the study of various characteristics of the single particle spectrum of SNS structures.     

On the equivalence of quadratic optimization problems commonly used in portfolio theory

In the paper, we consider three quadratic optimization problems which are frequently applied in portfolio theory, i.e., the Markowitz mean–variance problem as well as the problems based on the mean–variance utility function and the quadratic utility. Conditions are derived under which the solutions of these three optimization procedures coincide and are lying on the efficient frontier, the set of mean–variance optimal portfolios. It is shown that the solutions of the Markowitz optimization problem and the quadratic utility problem are not always mean–variance efficient.     

Malliavin regularity of solutions to mixed stochastic differential equations

For a mixed stochastic differential equation driven by independent fractional Brownian motions and Wiener processes, the existence and integrability of the Malliavin derivative of the solution are established. It is also proved that the solution possesses exponential moments.     

Topologizations of G-spaces

For a G-space X, we put and explore a question whether X admits a non-discrete Hausdorff G-invariant topology.     

Decoupling the electrical conductivity and Seebeck coefficient in the RE2SbO2 compounds through local structural perturbations

Compromise between the electrical conductivity and Seebeck coefficient limits the efficiency of chemical doping in the thermoelectric research. An alternative strategy, involving the control of a local crystal structure, is demonstrated to improve the thermoelectric performance in the RE(2)SbO(2) system. The RE(2)SbO(2) phases, adopting a disordered anti-ThCr(2)Si(2)-type structure (I4/mmm), were prepared for RE = La, Nd, Sm, Gd, Ho, and Er. By traversing the rare earth series, the lattice parameters of the RE(2)SbO(2) phases are gradually reduced, thus increasing chemical pressure on the Sb environment. As the Sb displacements are perturbed, different charge carrier activation mechanisms dominate the transport properties of these compounds. As a result, the electrical conductivity and Seebeck coefficient are improved simultaneously, while the number of charge carriers in the series remains constant.     

Raman spectroscopy of natural cordierite at high water pressure up to 5 GPa

The high‐pressure behaviour of cordierite, a widespread ring aluminosilicate with channels incorporating fluid compounds (H₂O, CO₂), is characterized by the absence of phase transitions up to 2.5 GPa. However, the distortion of the ring tetrahedra observed previously at 2.3 GPa is supposed to introduce a phase transition at higher pressure, which has not been checked so far. This work presents a high‐pressure Raman spectroscopic study of natural cordierite compressed in water medium up to 4.7 GPa in a diamond anvil cell. At P > 4 GPa, a disordering of both the framework and intrachannel H₂O subsystem is apparent from significant broadening of Raman peaks and the evolution of short‐range order parameters. This is followed by abrupt shifts of the framework and O–H stretching modes at about 4.5 GPa, indicating a first‐order phase transition. Its reversibility is seen from the recovery of the initial spectrum at P < 3 GPa. The shift amplitudes of different framework modes indicate the predominance of distortion over contraction of the framework polyhedra upon this transition. The disordering of the H₂O subsystem in the high‐pressure phase is likely a consequence of distortion of the channel‐forming framework elements, which is supposed to be a driving force of this transition. Copyright © 2011 John Wiley & Sons, Ltd.