Synthesis and Spectroscopic Characterization of Thienopyrazine-Based Fluorophores for Application in Luminescent Solar Concentrators (LSCs)

Organic fluorophores have found broad application as emitters in luminescent solar concentrators (LSCs) for silicon photovoltaics. In particular, the preparation of organic conjugated systems with intense light-harvesting ability, emissions in the deep-red and NIR regions, and large Stokes shift values represent a very challenging undertaking. Here, we report a simple and easy way to prepare three symmetrical donor–acceptor–donor (DAD) organic-emitting materials based on a thienopyrazine core. The central core in the three dyes was modified with the introduction of aromatic substituents, aiming to affect their optical properties. The fluorophores were characterized by spectroscopic studies. In all cases, visible-NIR emissions with large Stokes shifts were found, highlighting these molecules as promising materials for the application in LSCs.     

New half sandwich Ru(II) coordination compounds for anticancer activity

With the aim of expanding the structure-activity relationship investigation, the series of Ru(II) half sandwich coordination compounds of the type [Ru([9]aneS3)(chel)(L)](n+) previously described by us (where [9]aneS3 is the neutral face-capping ligand 1,4,7-trithiacyclononane, chel is a neutral or anonic chelating ligand, L = Cl(-) or dmso-S, n = 0-2) was extended to 1,4,7-triazacyclononane ([9]aneN3). In addition, new neutral N-N, and anionic N-O and O-O chelating ligands, i.e. dach (trans-1,2-diaminocyclohexane), pic(-) (picolinate), and acac(-) (acetylacetonate), were investigated in combination with both [9]aneS3 and [9]aneN3. Overall, ten new half-sandwich complexes were prepared and fully characterized and their chemical behaviour in aqueous solution was established. The single-crystal X-ray structures of eight of them, including the versatile precursor [Ru([9]aneN3)(dmso-S)(2)Cl]Cl (9), were also determined. The results of in vitro antiproliferative tests performed on selected compounds against MDA-MB-231 human mammary carcinoma cells confirmed that, in this series, only compounds that hydrolyse the monodentate ligand at a reasonable rate show moderate activity, provided that the chelate ligand is a hydrogen bond donor.     

Complexes of tetracyclines with divalent metal cations investigated by stationary and femtosecond-pulsed techniques

Spectroscopic techniques both in steady-state (in absorption and emission) and pulsed (absorption of excited states with femtosecond resolution) conditions were used to study the complexation process between six molecules belonging to the tetracycline family and Mg(2+); in the case of TC the study was extended to the metal ions Ca(2+) and Cu(2+). The study was carried out in aqueous solution at various pH values, where one acid-base form of the substrate prevails over the others. The processing of experimental results, performed by means of Singular Value Decomposition and Global Analysis methods, allowed us to evaluate the extent of interaction through the association constants, to identify the number of equilibria present in solution and the stoichiometry (1:1 or 1:2) of the tetracycline:metal ion complex, and to define the spectral and photophysical properties of the latter (in terms of fluorescence quantum yields, lifetimes and rate constants). In fact, the (allowed) radiative decay process is a minor root for the lowest excited state of the complexes which mainly decay to the ground state by internal conversion. Details of the complexation sites are proposed for the various protonated forms of tetracyclines, and for the various cations in the case of TC. In particular, the molecular structure seems to affect significantly the dynamics of interaction when the upper peripheral region of tetracycline is rich in additional hydroxyl groups. Moreover, the state of protonation of the substrate produces changes in the order of the complexation sites, whose affinity for the cation increases significantly when they are negatively charged owing to the loss of protons. Magnesium and calcium (hard cations) give similar interactions, at least in acid solution, while copper(ii) (borderline cation) binds more efficiently on different sites, thus forming complexes with different properties.     

Ab-initio molecular dynamics and hybrid explicit-implicit solvation model for aqueous and nonaqueous solvents: GFP chromophore in water and methanol solution as case study

Solute–solvent interactions are proxies for understanding how the electronic density of a chromophore interacts with the environment in a more exhaustive way. The subtle balance between polarization, electrostatic, and non-bonded interactions need to be accurately described to obtain good agreement between simulations and experiments. First principles approaches providing accurate configurational sampling through molecular dynamics may be a suitable choice to describe solvent effects on solute chemical–physical properties and spectroscopic features, such as optical absorption of dyes. In this context, accurate energy potentials, obtained by hybrid implicit/explicit solvation methods along with employing nonperiodic boundary conditions, are required to represent bulk solvent around a large solute–solvent cluster. In this work, a novel strategy to simulate methanol solutions is proposed combining ab initio molecular dynamics, a hybrid implicit/explicit flexible solvent model, nonperiodic boundary conditions, and time dependent density functional theory. As case study, the robustness of the proposed protocol has been gauged by investigating the microsolvation and electronic absorption of the anionic green fluorescent protein chromophore in methanol and aqueous solution. Satisfactory results are obtained, reproducing the microsolvation layout of the chromophore and, as a consequence, the experimental trends shown by the optical absorption in different solvents.     

Characterization of the first beta-class carbonic anhydrase from an arthropod (Drosophila melanogaster) and phylogenetic analysis of beta-class carbonic anhydrases in invertebrates

Background

The β-carbonic anhydrase (CA, EC 4.2.1.1) enzymes have been reported in a variety of organisms, but their existence in animals has been unclear. The purpose of the present study was to perform extensive sequence analysis to show that the β-CAs are present in invertebrates and to clone and characterize a member of this enzyme family from a representative model organism of the animal kingdom, e.g., Drosophila melanogaster.

Results

The novel β-CA gene, here named DmBCA, was identified from FlyBase, and its orthologs were searched and reconstructed from sequence databases, confirming the presence of β-CA sequences in 55 metazoan species. The corresponding recombinant enzyme was produced in Sf9 insect cells, purified, kinetically characterized, and its inhibition was investigated with a series of simple, inorganic anions. Holoenzyme molecular mass was defined by dynamic light scattering analysis and gel filtration, and the results suggested that the holoenzyme is a dimer. Double immunostaining confirmed predictions based on sequence analysis and localized DmBCA protein to mitochondria. The enzyme showed high CO₂ hydratase activity, with a k_cat of 9.5 × 10⁵ s^-1 and a k_cat/K_M of 1.1 × 10⁸ M^{- 1}s^{- 1}. DmBCA was appreciably inhibited by the clinically-used sulfonamide acetazolamide, with an inhibition constant of 49 nM. It was moderately inhibited by halides, pseudohalides, hydrogen sulfide, bisulfite and sulfate (K_I values of 0.67 - 1.36 mM) and more potently by sulfamide (K_I of 0.15 mM). Bicarbonate, nitrate, nitrite and phenylarsonic/boronic acids were much weaker inhibitors (K_Is of 26.9 - 43.7 mM).

Conclusions

The Drosophila β-CA represents a highly active mitochondrial enzyme that is a potential model enzyme for anti-parasitic drug development.     

X-Ray Crystal Structure of Phyllostin,a Metabolite Produced by <Emphasis Type="Italic">Phyllosticta cirsii</Emphasis>, a Potential Mycoherbicide of <Emphasis Type="Italic">Cirsium arvense</Emphasis>

Abstract  

The X-ray crystal structure of phyllostin (8-hydroxy-3-methyl-2-oxo-2,3,4a,5,8,8a-hexahydro-benzo[1,4]dioxine-6-carboxylic acid methyl ester) is reported. Phyllostin was recently and for the first time isolated, together with phytotoxin phyllostoxin and the phyllostictines A–D, from the culture filtrates of Phyllosticta cirsii, a fungal pathogen isolated from diseased Cirsium arvense leaves and evaluated as biocontrol agent of this noxious perennial weed. Phyllostin crystallizes in the monoclinic space group P2₁ with unit cell parameters: a = 8.371(2), b = 7.026(1), c = 9.918(1) ?, β = 92.013(8)°, Z = 2. The final refinement converged to R1 = 0.0530 for 1026 observed reflections having I > 2σ(I). In the molecule two trans joined six-membered rings are present. The cyclohexene ring adopts a half-chair conformation. The 2-oxo-1,4-dioxan ring adopts a distorted half-chair conformation. The relative stereochemistry of the four chiral centers turns out to be 3R,4aS,8R,8aS. In the crystal packing molecules form infinite chains through O–H···O intermolecular hydrogen bonds. Chains run along the crystallographic a axis forming layers of molecules stacking in the [0 1 0] direction.     

Freudenthal duality and generalized special geometry

Freudenthal duality, introduced in Borsten et al. (2009) [1] and defined as an anti-involution on the dyonic charge vector in d=4 space-time dimensions for those dualities admitting a quartic invariant, is proved to be a symmetry not only of the classical Bekenstein-Hawking entropy but also of the critical points of the black hole potential.Furthermore, Freudenthal duality is extended to any generalized special geometry, thus encompassing all N>2 supergravities, as well as N=2 generic special geometry, not necessarily having a coset space structure.     

Fractal regularity results on optimal irrigation patterns

In this paper the problem of the regularity, i.e. fractal behaviour, of the minima of the branched transport problem is addressed. We show that, under suitable conditions on the irrigated measure, the minima present a fractal regularity, that is on a given branch of length l the number of branches bifurcating from it whose length is comparable with ε   can be estimated both from above and below by l/ε$l/\epsilon$.     

BMO‐Type Norms Related to the Perimeter of Sets

In this paper we consider an isotropic variant of the BMO‐type norm recently introduced (Bourgain, Brezis, and Mironescu, 2015). We prove that, when considering characteristic functions of sets, this norm is related to the perimeter. A byproduct of our analysis is a new characterization of the perimeter of sets in terms of this norm, independent of the theory of distributions.© 2016 Wiley Periodicals, Inc.     

Perimeter of sets and BMO-type norms

The aim of this note is to announce some recent results showing that an isotropic variant of the BMO-type norm introduced in [3] can be related via a precise formula to the perimeter of sets.