Experimental determination of the absorption strength in absorbing chaotic cavities

Due to the experimental necessity we present a formula to determine the absorption strength by power losses inside a chaotic system (cavities, graphs, acoustic resonators, etc) when the antenna coupling, always present in experimental measurements, is taken into account. This is done by calculating the average of the absorption coefficient as a function of the absorption strength and the coupling of the antenna to the system, in the one channel case.Comment: 6 pages, 3 figures, Submitted to Phys. Rev.

Interactions and star formation activity in Wolf-Rayet galaxies

We present the main results of the PhD Thesis carried out by L\'opez-S\'anchez (2006), in which a detailed morphological, photometrical and spectroscopical analysis of a sample of 20 Wolf-Rayet (WR) galaxies was realized. The main aims are the study of the star formation and O and WR stellar populations in these galaxies and the role that interactions between low surface companion objects have in the triggering of the bursts. We analyze the morphology, stellar populations, physical conditions, chemical abundances and kinematics of the ionized gas, as well as the star-formation activity of each system.Comment: 16 pages, 15 figure

Norcoclaurine Synthase-Mediated Stereoselective Synthesis of 1,1'-Disubstituted, Spiro- and Bis-Tetrahydroisoquinoline Alkaloids

The Pictet–Spenglerase norcoclaurine synthase (NCS) catalyzes the formation of (S)-norcoclaurine, an important intermediate in the biosynthetic pathway of benzylisoquinoline alkaloids. NCS has been used as a biocatalyst with meta-hydroxy phenethylamines and aldehydes for the preparation of single-isomer tetrahydroisoquinoline alkaloids (THIAs). Recently, it was also reported that some ketones can be accepted as substrates, including 4-substituted cyclohexanones and phenyl acetones. Here, we report the use of wild-type NCS and selected variants with aliphatic, cyclic, α-substituted cyclic, heterocyclic, and bicyclic ketones to access challenging non-natural THIAs. Remarkably, fused bicyclic ketones as well as diketones could also be accepted by some of the NCS variants, and in silico modeling was used to provide insights into the rationale for this

Mean Sombor index

A Special Volume on Chemical Graph Theory in Memory of Nenad TrinajsticWe introduce a degree–based variable topological index inspired on the power (or generalized) mean. We name this new index as the mean Sombor index: SOα(G) = P uv∈E(G) [(d α u + d α v ) /2]1/α. Here, uv denotes the edge of the graph G connecting the vertices u and v, du is the degree of the vertex u, and α ∈ R\{0}. We also consider the limit cases mSOα→0(G) and SOα→±∞(G). Indeed, for given values of α, the mean Sombor index is related to well-known opological indices such as the inverse sum indeg index, the reciprocal Randic index, the first Zagreb index, the Stolarsky–Puebla index and several ´Sombor indices. Moreover, through a quantitative structure property relationship (QSPR) analysis we show that mSOα(G) correlates well with several physicochemical properties of octane isomers. Some mathematical properties of the mean Sombor index as well as bounds and new relationships with known topological indices are also discussed.J.A.M.-B. acknowledges financial support from CONACyT (Grant No. A1-S-22706) and BUAP (Grant No. 100405811VIEP2021) .E.D.M. and J.M.R. were supported by a grant from Agencia Estatal de Investigación (PID 2019-106433GBI00 / AEI / 10.13039 / 501100011033), Spain. J.M.R. was supported by the Madrid Government (Comunidad de Madrid-Spain) under the Multiannual Agreement with UC3M in the line of Excellence of University Professors (EPUC3M23), and in the context of the VPRICIT (Regional Programme of Research and Technological Innovation)

Nuclear Receptors in Nonalcoholic Fatty Liver Disease

Nuclear receptors comprise a superfamily of ligand-activated transcription factors that are involved in important aspects of hepatic physiology and pathophysiology. There are about 48 nuclear receptors in the human. These nuclear receptors are regulators of many hepatic processes including hepatic lipid and glucose metabolism, bile acid homeostasis, drug detoxification, inflammation, regeneration, fibrosis, and tumor formation. Some of these receptors are sensitive to the levels of molecules that control lipid metabolism including fatty acids, oxysterols, and lipophilic molecules. These receptors direct such molecules to the transcriptional networks and may play roles in the pathogenesis and treatment of nonalcoholic fatty liver disease. Understanding the mechanisms underlying the involvement of nuclear receptors in the pathogenesis of nonalcoholic fatty liver disease may offer targets for the development of new treatments for this liver disease

Biomimetic Phosphate-Catalyzed Pictet–Spengler Reaction for the Synthesis of 1,1′-Disubstituted and Spiro-Tetrahydroisoquinoline Alkaloids

Tetrahydroisoquinoline (THIQ) alkaloids are an important group of compounds that exhibit a range of bioactivities. Here, a phosphate buffer-catalyzed Pictet-Spengler reaction (PSR) using unreactive ketone substrates is described. A variety of 1,1'-disubstituted and spiro-tetrahydroisoquinoline alkaloids were readily prepared in one-step and high yields, highlighting the general applicability of this approach. This study features the role of phosphate in the aqueous-based PSR and provides an atom-efficient, sustainable route to new THIQs

Metagenomic ene-reductases for the bioreduction of sterically challenging enones

Ene-reductases (ERs) of the Old Yellow Enzyme family catalyse asymmetric reduction of activated alkenes providing chiral products. They have become an important method in the synthetic chemists' toolbox offering a sustainable alternative to metal-catalysed asymmetric reduction. Development of new biocatalytic alkene reduction routes, however needs easy access to novel biocatalysts. A sequence-based functional metagenomic approach was used to identify novel ERs from a drain metagenome. From the ten putative ER enzymes initially identified, eight exhibited activities towards widely accepted mono-cyclic substrates with several of the ERs giving high reaction yields and stereoselectivities. Two highly performing enzymes that displayed excellent co-solvent tolerance were used for the stereoselective reduction of sterically challenging bicyclic enones where the reactions proceeded in high yields, which is unprecedented to date with wild-type ERs. On a preparative enzymatic scale, reductions of Hajos–Parish, Wieland–Miescher derivatives and a tricyclic ketone proceeded with good to excellent yields

Novel chemoenzymatic oxidation of amines into oximes based on hydrolase-catalysed peracid formation

The efficient transformation of benzylamines into the corresponding oximes has been described by means of a chemoenzymatic process. This strategy is based on a two-step sequence developed in one-pot at 30 °C and atmospheric pressure. First, the formation of a reactive peracid intermediate occurs by means of a lipase-catalysed perhydrolysis reaction, and then this peracid acts as a chemical oxidising agent of the amines. A total of nine ketoximes were isolated in high purity after a simple extraction protocol (90–98% isolated yield), while for the eleven synthesised aldoximes a further column chromatography purification was required (71–82% isolated yield). In all cases excellent selectivities were attained, offering a practical method for amine oxidation in short reaction times (1 hour). The environmental impact of the process was analysed and compared with a recently published alternative chemical synthesis, finding for this metric a good E-factor value

Engineering transketolase to accept both unnatural donor and acceptor substrates and produce α‐hydroxyketones

A narrow substrate range is a major limitation in exploiting enzymes more widely as catalysts in synthetic organic chemistry. For enzymes using two substrates, the simultaneous optimisation of both substrate specificities is also required for the rapid expansion of accepted substrates. Transketolase (TK) catalyses the reversible transfer of a C2‐ketol unit from a donor substrate to an aldehyde acceptor and suffers the limitation of narrow substrate scope for industrial applications. Herein, TK from Escherichia coli was engineered to accept both pyruvate, as a novel donor substrate, and unnatural acceptor aldehydes, including propanal, pentanal, hexanal and 3‐formylbenzoic acid (FBA). Twenty single‐mutant variants were first designed and characterised experimentally. Beneficial mutations were then recombined to construct a small library. Screening of this library identified the best variant with a 9.2‐fold improvement in the yield towards pyruvate and propionaldehyde, relative to wild‐type (WT). Pentanal and hexanal were used as acceptors to determine stereoselectivities of the reactions, which were found to be higher than 98% enantiomeric excess (ee) for the S configuration. Three variants were identified to be active for the reaction between pyruvate and 3‐FBA. The best variant was able to convert 47% of substrate into product within 24 h, whereas no conversion was observed for WT. Docking experiments suggested a cooperation between the mutations responsible for donor and acceptor recognition, which would promote the activity towards both the acceptor and donor. The variants obtained have the potential to be used for developing catalytic pathways to a diverse range of high‐value products

Observational hints of radial migration in disc galaxies from CALIFA

Context. According to numerical simulations, stars are not always kept at their birth galactocentric distances but they have a tendency to migrate. The importance of this radial migration in shaping galactic light distributions is still unclear. However, if radial migration is indeed important, galaxies with different surface brightness (SB) profiles must display differences in their stellar population properties. Aims: We investigate the role of radial migration in the light distribution and radial stellar content by comparing the inner colour, age, and metallicity gradients for galaxies with different SB profiles. We define these inner parts, avoiding the bulge and bar regions and up to around three disc scale lengths (type I, pure exponential) or the break radius (type II, downbending; type III, upbending). Methods: We analysed 214 spiral galaxies from the CALIFA survey covering different SB profiles. We made use of GASP2D and SDSS data to characterise the light distribution and obtain colour profiles of these spiral galaxies. The stellar age and metallicity profiles were computed using a methodology based on full-spectrum fitting techniques (pPXF, GANDALF, and STECKMAP) to the Integral Field Spectroscopic CALIFA data. Results: The distributions of the colour, stellar age, and stellar metallicity gradients in the inner parts for galaxies displaying different SB profiles are unalike as suggested by Kolmogorov-Smirnov and Anderson-Darling tests. We find a trend in which type II galaxies show the steepest profiles of all, type III show the shallowest, and type I display an intermediate behaviour. Conclusions: These results are consistent with a scenario in which radial migration is more efficient for type III galaxies than for type I systems, where type II galaxies present the lowest radial migration efficiency. In such a scenario, radial migration mixes the stellar content, thereby flattening the radial stellar properties and shaping different SB profiles. However, in light of these results we cannot further quantify the importance of radial migration in shaping spiral galaxies, and other processes, such as recent star formation or satellite accretion, might play a role