pinecone/core-2020-05-10-deduplication huggingface dataset:
Efficient intramolecular charge transfer in oligoyne-linked donor–π–acceptor molecules.

Studies are reported on a series of triphenylamine–(C[TRIPLE BOND]C)n–2,5-diphenyl-1,3,4-oxadiazole dyad molecules (n=1–4, 1, 2, 3 and 4, respectively) and the related triphenylamine-C6H4–(C[TRIPLE BOND]C)3–oxadiazole dyad 5. The oligoyne-linked D–π–A (D=electron donor, A=electron acceptor) dyad systems have been synthesised by palladium-catalysed cross-coupling of terminal alkynyl and butadiynyl synthons with the corresponding bromoalkynyl moieties. Cyclic voltammetric studies reveal a reduction in the HOMO–LUMO gap in the series of compounds 1–4 as the oligoyne chain length increases, which is consistent with extended conjugation through the elongated bridges. Photophysical studies provide new insights into conjugative effects in oligoyne molecular wires. In non-polar solvents the emission from these dyad systems has two different origins: a locally excited (LE) state, which is responsible for a π*[RIGHTWARDS ARROW]π fluorescence, and an intramolecular charge transfer (ICT) state, which produces charge-transfer emission. In polar solvents the LE state emission vanishes and only ICT emission is observed. This emission displays strong solvatochromism and analysis according to the Lippert–Mataga–Oshika formalism shows significant ICT for all the luminescent compounds with high efficiency even for the longer more conjugated systems. The excited-state properties of the dyads in non-polar solvents vary with the extent of conjugation. For more conjugated systems a fast non-radiative route dominates the excited-state decay and follows the Engelman–Jortner energy gap law. The data suggest that the non-radiative decay is driven by the weak coupling limit
On the Synthesis and Chemical Behaviour of the Elusive Bis(hydrosulfido)-Bridged Dinuclear Rhodium(I) Complexes [{Rh(μ-SH)(CO)(PR3)}2]

11 páginas, 6 figuras, 5 tablas, 4 esquemas.Several bis(hydrosulfido)-bridged dinuclear rhodium(I) compounds, [{Rh(μ-SH)(L)2}2], have been prepared from rhodium(I) acetylacetonato complexes, [Rh(acac)(L)2], and H2S(g). Reaction of [Rh(acac){P(OPh)3}2] with H2S(g) affords the dinuclear bis(hydrosulfido)-bridged compound [{Rh(μ-SH){P(OPh)3}2}2] (1). However, reaction of complexes [Rh(acac)(CO)(PR3)] with H2S(g) gives the dinuclear compound [{Rh(μ-SH)(CO)(PR3)}2] (R=Cy, 2; R=Ph, 4) and the trinuclear cluster [Rh3(μ-H)(μ3-S)2(CO)3(PR3)3] (R=Cy, 3; R=Ph, 5). The selective synthesis of both type of compounds has been carried out by control of the H2S(g) concentration in the reaction media. The trinuclear hydrido–sulfido cluster [Rh3(μ-H)(μ3-S)2(CO)3(PPh3)3] (5) has been also obtained by reaction of [{Rh(μ-SH)(CO)(PPh3)}2] (4) with [Rh(acac)(CO)(PPh3)], proceeding through the trinuclear hydrosulfido–sulfido intermediate [Rh3(μ3-SH)(μ3-S)(CO)3(PPh3)3]. The molecular structures of complexes 1 and 3 have been determined by X-ray diffraction methods. Compound 1 is stable in solution, but complexes 2 and 4 slowly transform in solution into the trinuclear hydrido–sulfido clusters 3 and 5, respectively, with the release of H2S(g) in a reversible way. 1H NMR kinetic experiments for the transformation of 4 into 5 have revealed that this transformation follows second-order-type kinetic. The following activation parameters, ΔH≠=24±3 kJ mol−1 and of ΔS≠=−223±8 J K−1 mol−1, have been calculated from the determination of the second-order rate constants in the temperature range 30–45 °C. The large negative value of the activation entropy is consistent with an associative character of the rate-determining step. A plausible multistep mechanism based on the chemical behaviour of hydrosulfido–metal complexes and compatible with the kinetic behaviour has been proposed.The financial support from Ministerio de Educación y Ciencia (MEC/\ud
FEDER) is gratefully acknowledged (Project CTQ2006-03973/BQU).Peer reviewe
Preparation and characterization of a bifunctional aldolase/kinase enzyme. A more efficient biocatalyst for C-C bond formation

“This is the pre-peer reviewed version of the following article: Iturrate, L., Sánchez-Moreno, I., Oroz-Guinea, I., Pérez-Gil, J., García-Junceda, E. (2010) “Preparation and characterization of a bifunctional aldolase/kinase enzyme. A more efficient biocatalyst for C-C bond formation“ Chem. Eur. J., 16, 4018-4030, which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/chem.200903096/abstract”A bifunctional\ud
aldolase/kinase enzyme named DLF\ud
has been constructed by gene fusion\ud
through overlap extension. This fusion\ud
enzyme consists of monomeric\ud
fructose-1,6-bisphosphate aldolase\ud
(FBPA) from Staphylococcus carnosus\ud
and the homodimeric dihydroxyacetone\ud
kinase (DHAK) from Citrobacter\ud
freundii CECT 4626 with an\ud
intervening five amino acid linker. The\ud
fusion protein was expressed soluble\ud
and retained both kinase and aldolase\ud
activities. The secondary structure of\ud
the bifuctional enzyme has been\ud
analysed by CD spectroscopy, as well\ud
as that of the parental enzymes, in order\ud
to study the effect of the covalent\ud
coupling of the two parent proteins on\ud
the structure of the fused enzyme. Since\ud
S. carnosus FBPA is a thermostable\ud
protein, the effect of the fusion on the\ud
thermal stability of the bifunctional\ud
enzyme has also been studied. The\ud
proximity of the active centres in the\ud
fused enzyme promotes a kinetic\ud
advantage as the 20-fold increment in\ud
the initial velocity of the overall aldol\ud
reaction indicates. Experimental\ud
evidence supports that this increase in\ud
the reaction rate can be explained in\ud
terms of substrate channellingWe thank the Spanish Ministerio de Ciencia e Innovación for financial support (Grant\ud
CTQ2007-67403/BQU). J. P.-G. has been supported by grants BIO2009-09694 and\ud
CSD2007-00010. L. Iturrate and I. Sánchez-Moreno acknowledges the Predoctoral\ud
Fellowship from Comunidad de Madrid. I. Oroz-Guinea is a JAEPredoc fellow from\ud
CSIC. We thank E. G. Doyagüez for her assistance on NMR characterization
Synthesis of symmetrical multichromophoric bodipy dyes and their facile transformation into energy transfer cassettes

Multichromophoric boron-dipyrromethene (Bodipy) dyes synthesized on phenylene-ethynylene platforms have been be converted to energy transfer cassettes in a one-step chemical transformation. Excitation energy transfer processes in these highly symmetrical derivatives were studied in detail, including time-re-solved fluorescence spectroscopy techniques. Excitation spectra and the emission lifetimes suggest efficient energy transfer between the donor and acceptor chromophore. These novel energy transfer cassettes, while highlighting a short-cut approach to similar energy transfer systems, could be useful as large pseudo-Stokes shift multichromophoric dyes with potential applications in diverse applications. © 2010 Wiley-VCH Verlag GmbH & Cu. KGaA. Weinheim
Two-Step Thermal Spin Transition and LIESST Relaxation of the Polymeric Spin-Crossover Compounds Fe(X-py)2[Ag(CN)2]2 (X=H, 3-methyl, 4-methyl, 3,4-dimethyl, 3-Cl)

12 páginas, 7 figuras, 4 tablas.In the series of polymeric spin-crossover compounds Fe(X-py)2[Ag(CN)2)]2 (py=pyridine, X=H, 3-Cl, 3-methyl, 4-methyl, 3,4-dimethyl), magnetic and calorimetric measurements have revealed that the conversion from the high-spin (HS) to the low-spin (LS) state occurs by two-step transitions for three out of five members of the family (X=H, 4-methyl, and X=3,4-dimethyl). The two other compounds (X=3-Cl and 3-methyl) show respectively an incomplete spin transition and no transition at all, the latter remaining in the HS state in the whole temperature range. The spin-crossover behaviour of the compound undergoing two-step transitions is well described by a thermodynamic model that considers both steps. Calculations with this model show low cooperativity in this type of systems. Reflectivity and photomagnetic experiments reveal that all of the compounds except that with X=3-methyl undergo light-induced excited spin state trapping (LIESST) at low temperatures. Isothermal HS-to-LS relaxation curves at different temperatures support the low-cooperativity character by following an exponential decay law, although in the thermally activated regime and for aX=H and X=3,4-dimethyl the behaviour is well described by a double exponential function in accordance with the two-step thermal spin transition. The thermodynamic parameters determined from this isothermal analysis were used for simulation of thermal relaxation curves, which nicely reproduce the experimental data.This work was supported by the Spanish MICINN and FEDER, projects MAT2007-61621 and CSD2007-00010.Peer reviewe
Synthetic and structural studies of 1-halo-8-(alkylchalcogeno)naphthalene derivatives

This work is funded by the EPSRCA series of eight 1-halo-8-(alkylchalcogeno)naphthalene derivatives ( 1 – 8 ; halogen=Br, I; alkylchalcogen=SEt, SPh, SePh, TePh) containing a halogen and a chalcogen atom occupying the peri positions have been prepared and fully characterised by using X-ray crystallography, multinuclear NMR spectroscopy, IR spectroscopy and MS. Naphthalene distortion due to non-covalent substituent interactions was studied as a function of the bulk of the interacting chalcogen atoms and the size and nature of the alkyl group attached to them. X-ray data for 1 , 2 , 4 and 5 – 8 were compared. Molecular structures were analysed in terms of naphthalene ring torsions, peri-atom displacement, splay angle magnitude, X⋅⋅⋅E interactions, aromatic ring orientations and quasi-linear X⋅⋅⋅EC arrangements. A general increase in the X⋅⋅⋅E distance was observed for molecules that contain bulkier atoms at the peri positions. The I⋅⋅⋅S distance of 4 is comparable with the I⋅⋅⋅Te distance of 8 , and is ascribed to a stronger lone pair–lone pair repulsion due to the presence of an axial S(naphthyl) ring conformation. Density functional theory (B3LYP) calculations performed on 5 – 8 revealed Wiberg bond index values of 0.05–0.08, which indicate minor interactions taking place between the non-bonded atoms in these compounds.PostprintPeer reviewe
Sterically crowded peri-substituted naphthalene phosphines and their PV derivatives

This work is funded by the EPSRC UKThree sterically crowded peri-substituted naphthalene phosphines, Nap[PPh2][ER] (Nap=naphthalene-1,8-diyl; ER=SEt, SPh, SePh) 1–3 , which contain phosphorus and chalcogen functional groups at the peri positions have been prepared. Each phosphine reacts to form a complete series of PV chalcogenides Nap[P(E′)(Ph2)(ER)] (E′=O, S, Se). The novel compounds were fully characterised by using X-ray crystallography and multinuclear NMR spectroscopy, IR spectroscopy and MS. X-ray data for 1 , 2 , n   O , n   S , n   Se (n=1–3) are compared. Eleven molecular structures have been analysed by naphthalene ring torsions, peri-atom displacement, splay angle magnitude, X⋅⋅⋅E interactions, aromatic ring orientations and quasi-linear arrangements. An increase in the congestion of the peri region following the introduction of heavy chalcogen atoms is accompanied by a general increase in naphthalene distortion. P⋅⋅⋅E distances increase for molecules that contain bulkier atoms at the peri positions and also when larger chalcogen atoms are bound to phosphorus. The chalcogenides adopt similar conformations that contain a quasi-linear E⋅⋅⋅PC fragment, except for 3 O , which displays a twist-axial-twist conformation resulting in the formation of a linear O⋅⋅⋅SeC alignment. Ab initio MO calculations performed on 2 O , 3 O , 3 S and 3 Se reveal Wiberg bond index values of 0.02 to 0.04, which indicates only minor non-bonded interactions; however, calculations on radical cations of 3 O , 3 S and 3 Se reveal increased values (0.14–0.19).PostprintPeer reviewe
The impact of amino acid side chain mutations in conformational design of peptides and proteins

Local energetic effects of amino acid replacements are often considered to have only a moderate influence on the backbone conformation of proteins or peptides. As these effects are difficult to determine experimentally, no comparison has yet been performed. However, knowledge of the influence of side chain mutations is essential in protein homology modeling and in optimizing biologically active peptide ligands in medicinal chemistry. Furthermore, the tool of N-methylation of peptides is of increasing importance for the design of peptidic drugs to gain oral availability or receptor selectivity. However, N-methylation is often accompanied by considerable population of cis-peptide bond structures, resulting in completely different conformations compared with the parent peptide. To retain a favored structure, it might be important to understand the effect of different side chains on the backbone conformation and to enable the introduction of an N-methylation at the right position without disturbing a biologically active conformation. In order to detect even small energetic effects due to side chain mutations, we employed a trick to investigate the structural equilibrium of a selected cyclic pentapeptide in which two conformations are equally populated. Very small energetic differences between both conformations could easily be determined experimentally by identifying shifts in the population of both isomers.Peer ReviewedPostprint (published version
Mechanistic Insights into the One-Pot Synthesis of Propargylamines from Terminal Alkynes and Amines in Chlorinated Solvents Catalyzed by Gold Compounds and Nanoparticles

Propargylamines can be obtained from secondary amines and terminal alkynes in chlorinated solvents by a three- and two-component synthesis catalyzed by gold compounds and nanoparticles (Au-NP) under mild conditions. The use of dichloromethane allows for the activation of two CCl bonds and a clean transfer of the methylene fragment to the final product. The scope of the reaction as well as the influence of different gold(III) cycloaurated complexes and salts has been investigated. The involvement of gold nanoparticles generated in situ in the process is discussed and a plausible reaction mechanism is proposed on the basis of the data obtained.Funding from MICINN (CTQ2008-01784, Spain) and Brooklyn College (US) is gratefully acknowledged. D.A. thanks DGA (Spain) for a Ph.D. grant.Peer Reviewe
Sodium-mediated magnesiation of thiophene and tetrahydrothiophene: structural contrasts with furan and tetrahydrofuran

Sulfur-containing heterocycles are currently attracting a great deal of interest in several diverse fields. For instance, substituted tetrahydrothiophenes[1] have received considerable attention due to their extremely wide-ranging chemical and biological applications.[2] These include their use as potent a-glucosidase inhibitors,[3] as an inhibitor of copper amine oxidases[4] and as selective A3 agonists and antagonists.[5] In addition, they have been utilised in chemical transformations, such as catalytic asymmetric epoxidation, catalytic intramolecular cyclopropanation, and asymmetric metal catalysis hydrogenation.[6] From a nanochemical perspective, the adsorption chemistries and physical properties of various thiophenes and tetrahydrothiophenes on gold surfaces have recently come to the fore.[7] Polythiophenes are also key compounds in modern materials research, currently utilised in, for example, the fabrication of semi-conducting, fluorescent, and electronic and optoelectronic materials.[8]In this work, metallation (exchange of a hydrogen atom with a metal atom) of the parent heterocycles, tetrahydrothiophene (THT) and thiophene is considered. Metallation is one of the most fundamental reactions in modern day synthesis and is a key tool in the preparation of functionalised aromatic and heterocyclic compounds. It is usually achieved by the utilisation of commercially accessible organolithiums (or lithium amides); however, these reactions do have their drawbacks, including the intolerance of certain functional groups, the need for cryoscopic temperatures and the inadvertent reactivity with polar reaction solvents
Synthesis of diverse indole-containing scaffolds by gold(I)-catalyzed tandem reactions of 3-propargylindoles initiated by 1,2-indole migrations: scope and computational studies

Similar to propargylic\ud
carboxylates and sulphides, 3-\ud
propargylindoles undergo 1,2-indole\ud
migrations under cationic gold(I)-\ud
catalysis. The intermediate Aucarbenoid\ud
complex may evolve through\ud
different pathways depending on the\ud
substituents at the propargylic and\ud
terminal positions of the alkyne moiety.\ud
Thus, 3-indenylindole derivatives were\ud
easily obtained through formal iso-\ud
Nazarov or Nazarov cyclizations. DFT\ud
computations support the formation of\ud
an alkylidenecyclopropane intermediate\ud
that undergoes aura-iso-Nazarov or\ud
aura-Nazarov cyclizations upon\ud
torquoselective ring opening. In\ud
addition, 3-dienylindoles could be\ud
accessed when none of the referred\ud
pathways were accessible and so the\ud
intermediate Au-carbenoid complex\ud
evolved via a 1,2-CH insertion\ud
reaction. We have also demonstrated\ud
that the final products can be obtained\ud
in a one-pot protocol from easily\ud
available propargylic alcohols and\ud
indolesMEC/FEDER (CTQ2007-61436/BQU) and Junta de Castilla y León (BU021A09) for financial support. We are also grateful to MEC (FPU predoctoral fellowship to D.M., “Young Foreign Researchers” contract (SB2006-0215) to M.G., “Ramón y Cajal” contract to M.A.F.-R., and “Juan de la Cierva” contract to P.G.-G.) and Fundación Ramón Areces (predoctoral fellowship to A.G.P.).This is the peer reviewed version of the following article: Sanz, R., Miguel, D., Gohain, M., García-García, P., Fernández-Rodríguez, Manuel A., González-Pérez, A., Nieto-Faza, O., de Lera, Ángel R. and Rodríguez, F. (2010), Synthesis of Diverse Indole-Containing Scaffolds by Gold(I)-Catalyzed Tandem Reactions of 3-Propargylindoles Initiated by 1,2-Indole Migrations: Scope and Computational Studies. Chem. Eur. J., 16: 9818–9828. doi:10.1002/chem.201001162, which has been published in final form at doi:10.1002/chem.201001162. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archivin
Rhodium Mediated C-H Bond Functionalisation Leading to Carboxylate Derivatives

Selective functionalisation of 1,5-cyclooctadiene, either to a carboxylic acid or to a γ-lactone, is achieved by a novel sequence of reactions involving quantitative oxygenation with --- oxygen and CC coupling with carbon monoxide (see graphic). The rhodium hydroxy–alkyl–allyl complex shown is the active intermediate that promotes the elimination of the organic compounds.Generous financial support from MICINN/FEDER (Project CTQ2008- 03860) and GA (Gobierno de Aragón, PM 36/2007) is gratefully acknowledged.Peer Reviewe
Efficient Utilization of Higher-Lying Excited States to Trigger Charge-Transfer Events

International audienceSeveral new fullerene- heptamethine conjugates absorbing as far as 800 nm have been synthesized and fully characterized by physic-chemical means.  In terms of optical and electrochemical characteristics appreciable electronic coupling between both electroactive species is deduced.  The latter also reflects the excited state features.  To this end, time resolved transient absorption measurements revealed that photoexcitation is followed by a sequence of charge transfer evolving from higher singlet excited states (i.e., S2 – fast charge transfer) and the lowest singlet excited state (i.e., S1 – slow charge transfer) of the heptamethine cyanine as electron donor to an either covalently linked C60 or C70 as electron acceptor.  Finally, charge transfer from photoexcited C60 / C70 completes the charge transfer sequence. The slow internal conversion within the light harvesting heptamethine cyanine and the strong electronic coupling between the individual constituents are particularly beneficial
Hydrogen Bonding Versus van der Waals Interactions: Competitive Influence of Noncovalent Interactions on 2D Self-Assembly at the Liquid-Solid Interface

The structures of the self-assembled monolayers of various 4-alkoxybenzoic acids physisorbed at the liquid-solid interface were established by employing scanning tunnelling microscopy (STM). This study has been essentially undertaken to explore the competitive influence of van der Waals and hydrogen-bonding interactions on the process of two-dimensional self-assembly. These acid derivatives form hydrogen-bonded dimers as expected; however, the dimers organise themselves in the form of relatively complex lamellae. The characteristic feature of these lamellae is the presence of regular discommensurations or kinks along the lamella propagation direction. The formation of kinked lamellae is discussed in light of the registry mechanism of the alkyl chains with the underlying graphite substrate. The location of the kinks along a lamella depends on the number (odd or even) of carbon atoms in the alkyl chain. This result indicates that concerted van der Waals interactions of the alkyl chain units introduce the odd/even chain-length effect on the surface-assembled supramolecular patterns. The odd/even effects are retained even upon complexation with a hydrogen-bond acceptor. However, as the solvent is changed from 1-phenyloctane to 1-octanoic acid, the kinked lamellae as well as the odd/even effects disappear. This solvent-induced convergence of supramolecular patterns is attained by means of co-crystallisation of octanoic acid molecules in the 2D crystal lattice, which is evident from high-resolution STM images. The solvent co-adsorption phenomenon is discussed in terms of competing van der Waals and hydrogen-bonding interactions.status: publishe
T-Shaped Ionic Liquid Crystals Based on the Imidazolium Motif: Exploring Substitution of the C2 Imidazolium Carbon Atom

In this contribution the first examples of so-called rigid-core, T-shaped imidazolium ionic liquid crystals, in which the C-2 atom of the imidazolium ring is substituted with an aryl moiety decorated with one or two alkoxy chains, are described. The length of the alkoxy chain(s) was varied from six to eighteen carbon atoms (n=6, 10, 14–18). Whereas the compounds with one long alkoxy chain display only smectic A phases, the salts containing two alkoxy chains exhibit smectic A, multicontinuous cubic, as well as hexagonal columnar phases, as evidenced by polarising optical microscopy, differential scanning calorimetry, and powder X-ray diffraction. Structural models are proposed for the self-assembly of the molecules within the mesophases. The imidazolium head groups and the iodide counterions were found to adopt a peculiar orientation in the central part of the columns of the hexagonal columnar phases. The enantiotropic cubic phase shown by the 1,3-dimethyl-2-[3,4-bis(pentadecyloxy)phenyl]imidazolium iodide salt has a multicontinuous Pmequation imagem structure. To the best of our knowledge, this is the first example of a thermotropic cubic mesophase of this symmetry.status: publishe
Enhanced functionality for donor-acceptor oligothiophenes via Inclusion of BODIPY : synthesis, electrochemistry, photophysics and model chemistry

We have synthesized several new push-pull oligothiophenes based on the BODIPY moiety as the electron acceptor and the well known oligothiophenes substituted with N,N-dialkylamino groups to enhance the electron donor ability. A complete characterization of the electronic properties has been done consisting of their photophysical, electrochemical and vibrational properties. The compounds have been studied after chemical treatment with acids and after oxidation. In this regard, they can be termed as NIR dyes and amphoteric redox electroactive molecules. We have described the presence of dual fluorescence in these molecules and fluorescence quenching either by energy transfer or, in the push-pull molecules, by the electron exchange.  The combination of electrochemical and proton reversibility combined with the interesting optical properties of the new species offer an interesting platform for sensor and material applications.DGES, MEC (Spain) and Fundação para a Ciência e a Tecnologia (FCT