Projective MV-algebras and rational polyhedra

Let M be an n-generator projective MV-algebra. Then there is a rational polyhedron P in the n-cube [0, 1] ⁿ such that M is isomorphic to the MV-algebra M(P){{\rm{\mathcal {M}}}(P)} of restrictions to P of the McNaughton functions of the free n-generator MV-algebra. P necessarily contains a vertex vP of the n-cube. We characterize those polyhedra contained in the n-cube such that M(P){{\mathcal {M}}(P)} is projective. In particular, if the rational polyhedron P is a union of segments originating at some fixed vertex vP of the n-cube, then M(P){{\mathcal {M}}(P)} is projective. Using this result, we prove that if A = M(P){A = {\mathcal {M}}(P)} and B = M(Q){B = {\mathcal {M}}(Q)} are projective, then so is the subalgebra of A × B given by {(f, g) | f(v _P ) = g(v _Q ), and so is the free product A \coprod B{A \coprod B} .     

Canonicity in subvarieties of BL-algebras

We prove that every subvariety of BL-algebras which is not finitely generated is not σ-canonical. We also prove π-canonicity for an infinite family of subvarieties of BL-algebras that are not finitely generated. To do so we study the behavior of canonical extensions of ordered sums of posets.     

Restructuring the crystalline cellulose hydrogen bond network enhances its depolymerization rate

Conversion of lignocellulose to biofuels is partly inefficient due to the deleterious impact of cellulose crystallinity on enzymatic saccharification. We demonstrate how the synergistic activity of cellulases was enhanced by altering the hydrogen bond network within crystalline cellulose fibrils. We provide a molecular-scale explanation of these phenomena through molecular dynamics (MD) simulations and enzymatic assays. Ammonia transformed the naturally occurring crystalline allomorph I(β) to III(I), which led to a decrease in the number of cellulose intrasheet hydrogen bonds and an increase in the number of intersheet hydrogen bonds. This rearrangement of the hydrogen bond network within cellulose III(I), which increased the number of solvent-exposed glucan chain hydrogen bonds with water by ~50%, was accompanied by enhanced saccharification rates by up to 5-fold (closest to amorphous cellulose) and 60-70% lower maximum surface-bound cellulase capacity. The enhancement in apparent cellulase activity was attributed to the "amorphous-like" nature of the cellulose III(I) fibril surface that facilitated easier glucan chain extraction. Unrestricted substrate accessibility to active-site clefts of certain endocellulase families further accelerated deconstruction of cellulose III(I). Structural and dynamical features of cellulose III(I), revealed by MD simulations, gave additional insights into the role of cellulose crystal structure on fibril surface hydration that influences interfacial enzyme binding. Subtle alterations within the cellulose hydrogen bond network provide an attractive way to enhance its deconstruction and offer unique insight into the nature of cellulose recalcitrance. This approach can lead to unconventional pathways for development of novel pretreatments and engineered cellulases for cost-effective biofuels production.     

Fluoride as a probe for H-bonding interactions in the active site of heme proteins: the case of Thermobifida fusca hemoglobin

The structural and functional properties of the active site of the bacterial hemoglobin from Thermobifida fusca are largely determined by three polar amino acids: TrpG8, TyrCD1, and TyrB10. We have exploited the availability of a combinatorial set of mutants, in each of which these three amino acids have been singly, doubly, or triply replaced by a Phe residue, to perform a detailed study on H-bonding interactions between the protein and heme-bound fluoride. By appropriate choice of the excitation conditions, ν(Fe-F) stretching bands have been detected in the resonance Raman spectra. In the wild-type protein and one of the mutants, two ν(Fe-F) bands have been observed and assigned to the presence of two protein conformers where fluoride is singly or doubly H-bonded. Furthermore, by plotting the CT1 charge-transfer transition energy vs the ν(Fe-F) wavenumbers, an empirical correlation has been found. The data are well fitted by a straight line with a positive slope. The position along the correlation line can be considered as a novel, general spectroscopic indicator of the extent of H-bonding in the active site of heme proteins. In agreement with the spectroscopic results, we have observed that the rate of ligand dissociation in stopped-flow kinetic measurements progressively increases upon substitution of the H-bonding amino acids. Molecular dynamics simulations have been performed on the fluoride complexes of native and mutated forms, indicating the prevalent interactions at the active site. All the techniques yield evidence that TrpG8 and TyrCD1 can form strong H bonds with fluoride, whereas TyrB10 plays only a minor role in the stabilization of the ligand.     

Communication: Turnover behavior of effective mobility in a tube with periodic entropy potential

Using Brownian dynamics simulations, we study the effective mobility and diffusion coefficient of a point particle in a tube formed from identical compartments of varying diameter, as functions of the driving force applied along the tube axis. Our primary focus is on how the driving force dependences of these transport coefficients are modified by the changes in the compartment shape. In addition to monotonically increasing or decreasing behavior of the effective mobility in periodic entropy potentials reported earlier, we now show that the effective mobility can even be nonmonotonic in the driving force.     

Anisotropic optical functions of α-1,4,4-tetraphenyl-1,3-butadiene

One of the known monoclinic polymorphs of 1,1,4,4-tetraphenyl-1,3-butadiene was grown by the floating-drop technique. This material is of interest for blue emitting devices and for fundamental studies on intermolecular interactions, excited states and vibronic coupling in the fields of chemical physics and materials science. Polarized UV-visible spectra are reported. The origin of the optical bands is resolved. The results give information on the intermolecular interactions and are compared with theoretical predictions and modeling. The full material dielectric tensor is provided, as deduced from generalized spectroscopic ellipsometry. Details on the use of this technique on strongly anisotropic and absorbing molecular materials are given. Some typical features of the optical spectra are also demonstrated to be very sensitive to the presence of misaligned domains, which, in our samples, are found to be rotated around the normal to the surface and whose amount is determined. The method allows discriminating among monocrystals, in-plane polycrystalline samples, layered samples formed by misaligned successive layers, or samples with both types of disorder. Two independent parameters giving the fraction of misaligned domains or layers are suggested for the characterization and optimization of the growth and deposition of molecular organic materials.     

Efficient Photoinduced Energy Transfer in a Newly Developed Hybrid SBA‐15 Photonic Antenna

A new hybrid photostable donor–acceptor mesoporous SBA‐15 silica system was designed and prepared. It consists of an encapsulated donor, the Super Yellow (SY) polymer, which transfers the photoexcitation energy directly to an acceptor dye that is linked outside the framework. The obtained composite material was characterized by X‐ray diffraction, nitrogen‐physisorption porosimetry, diffuse‐reflectance (DR)‐UV/Vis spectroscopy and photoluminescence, space‐ and time‐resolved confocal microscopy. The physico‐chemical analyses showed that the system behaves as an efficient Förster resonance energy transfer (FRET) pair, and high photoluminescence was observed from the acceptor. The presented photonic antenna is the first example of dye sensitization by polymer‐loaded mesoporous silica and represents a step forward in the search for new efficient and stable materials with opto‐electronic applications.     

Chemical genetics approach to identify new small molecule modulators of cell growth by phenotypic screening of Saccharomyces cerevisiae strains with a library of morpholine-derived compounds

A chemical genetics approach has been applied in the screening of yeast deletants strains with a pool of morpholine-derived compounds in order to identify candidate small molecules able to produce phenotypic effects on yeast cells. The analysis of the effects of structurally diverse molecules towards cell growth rate in both exponential and stationary phases provides a tool to select candidate compounds for subsequent assays to identify new chemical entities as chemical probes for drug discovery.     

Host–guest complexation of a nitroheterocyclic compound with cyclodextrins: a spectrofluorimetric and molecular modeling study

Nitroheterocyclic compounds (NC) were candidate drugs proposed for Chagas disease chemotherapy. In this study, we investigated the complexation of hydroxymethylnitrofurazone (NFOH), a potential antichagasic compound, with α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), Hydroxypropyl-β-cyclodextrin (HP-β-CD), Dimethyl-β-cyclodextrin (DM-β-CD) and γ-cyclodextrin (γ-CD) by fluorescence spectroscopy and molecular modeling studies. Hildebrand–Benesi equation was used to calculate the formation constants of NFOH with cyclodextrins based on the fluorescence differences in the CDs solution. The complexing capacity of NFOH with different CDs was compared through the results of association constant according to the following order: DM-β-CD > β-CD > α-CD > HP-β-CD > γ-CD. Molecular modeling studies give support for the experimental assignments, in favor of the formation of an inclusion complex between cyclodextrins with NFOH. This is an important study to investigate the effects of different kinds of cyclodextrins on the inclusion complex formation with NFOH and to better characterize a potential formulations to be used as therapeutic options for the oral treatment of Chagas disease.