Melanopsin and the Non‐visual Photochemistry in the Inner Retina of Vertebrates

Melanopsin (Opn4), a member of the G‐protein‐coupled receptor family, is a vitamin A‐based opsin in the vertebrate retina that has been shown to be involved in the synchronization of circadian rhythms, pupillary light reflexes, melatonin suppression and other light‐regulated tasks. In nonmammalian vertebrates there are two Opn4 genes, Opn4m and Opn4x, the mammalian and Xenopus orthologs respectively. Opn4x is only expressed in nonmammalian vertebrates including reptiles, fish and birds, while Opn4m is found in a subset of retinal ganglion cells (RGCs), the intrinsically photosensitive (ip) RGCs of the inner retina of both mammals and nonmammalian vertebrates. All opsins described utilize retinaldehyde as chromophore, photoisomerized from 11‐cis‐ to all‐trans‐retinal upon light exposure. Visual retinal photoreceptor cones and rods, responsible for day and night vision respectively, recycle retinoids through a process called the visual cycle that involves the retinal pigment epithelium or glial Müller cells. Although Opn4 has been characterized as a bistable photopigment, little is known about the mechanism/s involved in its chromophore regeneration. In this review, we will attempt to shed light on the visual cycle taking place in the inner retina and discuss the state of the art in the nonvisual photochemistry of vertebrates.     

Poly‐l‐Lactic Acid Nanofiber–Polyamidoamine Hydrogel Composites: Preparation,Properties, and Preliminary Evaluation as Scaffolds for Human Pluripotent Stem Cell Culturing

Electrospun poly‐l ‐lactic acid (PLLA) nanofiber mats carrying surface amine groups, previously introduced by nitrogen atmospheric pressure nonequilibrium plasma, are embedded into aqueous solutions of oligomeric acrylamide‐end capped AGMA1, a biocompatible polyamidoamine with arg‐gly‐asp (RGD)‐reminiscent repeating units. The resultant mixture is finally cured giving PLLA‐AGMA1 hydrogel composites that absorb large amounts of water and, in the swollen state, are translucent, soft, and pliable, yet as strong as the parent PLLA mat. They do not split apart from each other when swollen in water and remain highly flexible and resistant, since the hydrogel portion is covalently grafted onto the PLLA nanofibers via the addition reaction of the surface amine groups to a part of the terminal acrylic double bonds of AGMA1 oligomers. Preliminary tested as scaffolds, the composites prove capable of maintaining short‐term undifferentiated cultures of human pluripotent stem cells in feeder‐free conditions.

     

Nucleophilicity of indole derivatives: activating and deactivating effects based on proton affinities and electron density properties

Activating and deactivating abilities of several substituents (-CH3, -F, -NH2, -NO2) in indole have been theoretically studied using a series of electron density based reactivity indices. Calculations have been performed at the B3LYP/6-311++G(2d,2p) level. An energetic criterion based on the proton affinities (PAs) has been employed to check the validity of these reactivity indices. Relative PAs reflect the ortho and para orientation ability of -CH3, -F, and -NH2 groups, whereas the large deactivating effect of -NO2 is mainly observed at these positions. Also, substitutions in carbons 2 and 6 (IUPAC nomenclature) activate/deactivate carbons 6 and 2, respectively. Inductive effects are also reflected on the values of the relative PAs. The -CH3 group is shown to have inductive electron-withdrawing character instead of electron-releasing with its activating ability being due to a small mesomeric electron-releasing character. pi atomic electron populations and the zz component of the atomic quadrupole electric tensor qualitatively explain the order of PAs. Fukui indices approximately predict the results obtained by the previous properties, whereas no correlation is found between the values of the (triangle down)2rho(r) at the secondary charge concentrations and the PA scale.     

A finite element model of loading and unloading of an asperity contact with adhesion and plasticity

An elastic-plastic microcontact with adhesion was studied using a finite element model. This model differs from the existing models, in that it includes the effect of adhesion on the deformation and stresses field, making it applicable to a wide range of material properties. It shows two distinct separation modes, brittle separation and ductile separation. To the best of our knowledge this is the first time that a finite element model has predicted ductile separation in an adhesive contact. Three key parameters affecting the contact and separation modes are also discussed. Further work is expected to fully reveal the effect of these parameters on the separation modes.     

Ab initio and DFT Study on 2H-Isoxazol-5-one: Consequences of Strong Intermolecular Hydrogen-Bond Formation in Supramolecular Structures

Ab initio and density-functional-theory (DFT) calculations on 2H-isoxazol-5-one (A), its linear dimer (LD), cyclic dimer (CD), and cyclic trimer (CT), have been performed with several basis sets in the gas phase, including electron correlation by second-order Møller-Plesset perturbation theory. The calculated complexation energy for the intermolecular H-bonded trimer as well as the corresponding geometric changes are in good agreement with the notion of resonance-assisted intermolecular H-bond formation. Bond distances and angles of the optimized geometry of CT are in accordance with the X-ray-diffraction data found on a trimeric supramolecular complex of parent compound 4-(2-methoxybenzyl)-3-phenyl-4H-isoxazol-5-one. Ab initio and DFT geometry optimizations are also reproducing exactly the large asymmetry in bond angles around the CO group that is systematically present in all literature available X-ray data for analogous heterocyclic penta-atomic compounds.     

On pointed Hopf algebras associated with the symmetric groups

Let G be the symmetric group . It is an important open problem whether the dimension of the Nichols algebra is finite when is the class of the transpositions and ρ is the sign representation, with m ≥ 6. In the present paper, we discard most of the other conjugacy classes showing that very few pairs might give rise to finite-dimensional Nichols algebras. This work was partially supported by CONICET, ANPCyT and Secyt (UNC).     

Balance in Stable Categories

We study when the stable category ${\mathcal A}/\langle{\mathcal T}\rangleWe study when the stable category A/áT?{\mathcal A}/\langle{\mathcal T}\rangle of an abelian category A{\mathcal A} modulo a full additive subcategory T{\mathcal T} is balanced and, in case T{\mathcal T} is functorially finite in A{\mathcal A}, we study a weak version of balance for A/áT?{\mathcal A}/\langle{\mathcal T}\rangle. Precise necessary and sufficient conditions are given in case T{\mathcal T} is either a Serre class or a class consisting of projective objects. The results in this second case apply very neatly to (generalizations of) hereditary abelian categories.     

Protonated Bis(quinuclidine) Included in Channel Thiourea-Bromide and Ribbons Thiourea-Iodide Lattice: New Thiourea Inclusion Compounds

Host-guest supramolecular complexes are of special interest for understanding the chemistry in low dimensional spaces. The molecular recognition involved in the formation of such structures sometimes may be a relevant model for the kind of organized system usually found in living organisms. Matrix effects and anisotropic features which are habitual of the chemistry in restricted spaces also appear as useful for the development of new material of scientific and technological importance (Takemoto and Sonoda, 1984). Urea and thiourea clathrates constitute interesting systems in which the matrix being structured by hydrogen bond interactions has a relatively high liability to structural changes caused by the interaction with the host (Lehn, 1996). The syntheses and crystal structure of two novel ternary inclusion compounds having protonated bis (quinuclidine) as a guest into anionic thiourea-bromide and thiourea-iodide hosts are reported: (thiourea₂[quinuclidine₂H]⁺Br^?), 1 and (thiourea₂[(quinuclidine₂H)⁺]₂(I^?)₂), 2. In the two structures thiourea molecules interact with each other via N–H....S hydrogen bonds to produce ribbon-like arrangements. In structure 1 these ribbons do not contain the halogen and define two non intersecting sets running along the a and b axis, linked through N–H....Br hydrogen bonds having the external halide ions as acceptors. This ribbon-crossover defines a channel structure along c with a cavity cross section of ca. 5.85 × 15.50 Å. In structure 2, ribbons contain iodide anions as well, bridging thiourea dimers into parallel 1D structures which align their flat side parallel to the (110) set of planes leaving a free spacing of ca. 8.25 Å.     

Five-to-six membered ring-rearrangements in the reaction of 5-perfluoroalkyl-1,2,4-oxadiazoles with hydrazine and methylhydrazine

The hydrazinolysis reaction of 5-perfluoroalkyl-1,2,4-oxadiazoles with hydrazine or methylhydrazine as bidentate nucleophiles has been investigated. The reaction occurred through the addition of the bidentate nucleophile to the C(5)-N(4) double bond of the 1,2,4-oxadiazole followed by ring-opening and ring-closure (ANRORC) involving the second nucleophilic site of the reagent. This ring-closure step could involve either the original C(3) of the 1,2,4-oxadiazole (giving a five-to-five membered ring rearrangement) or an additional electrophilic center linked to it (exploiting a five-to-six membered ring rearrangement). An alternative initial nucleophilic attack may involve the additional electrophilic center linked at C(3), that is the carbonyl group, leading to the formation of the hydrazones which undergo the Boulton-Katritzky rearrangement (BKR). The chosen reaction path is a function of the used nucleophile and of the nature of the substituent at C(3). At variance with previous hypotheses, when methylhydrazine was used, the observed regiochemistry always showed the preferred initial attack by the less hindered NH(2) end of the nucleophile on C(5). Moreover, new spectroscopic evidence allowed the assignment of correct structures to the products formed by reaction of 5-perfluoroalkyl-3-phenyl-1,2,4-oxadiazoles with methylhydrazine.     

Extreme gravity tests with gravitational waves from compact binary coalescences: (I) inspiral–merger

The observation of the inspiral and merger of compact binaries by the LIGO/Virgo collaboration ushered in a new era in the study of strong-field gravity. We review current and future tests of strong gravity and of the Kerr paradigm with gravitational-wave interferometers, both within a theory-agnostic framework (the parametrized post-Einsteinian formalism) and in the context of specific modified theories of gravity (scalar–tensor, Einstein–dilaton–Gauss–Bonnet, dynamical Chern–Simons, Lorentz-violating, and extra dimensional theories). In this contribution we focus on (i) the information carried by the inspiral radiation, and (ii) recent progress in numerical simulations of compact binary mergers in modified gravity.