Intracellular Zn(II) induced turn-on fluorescence of an L-phenylalanine-derived pseudopeptide

A C2 symmetric L-phenylalanine-derived pseudopeptide has been synthesized for selective and sensitive recognition of Zn(II) ions in aqueous-organic media. The pseudopeptidic probes exhibit intracellular Zn(II) ion-sensing capabilities as demonstrated via live-cell fluorescence studies on RAW264.7 cells. Hence, we present a bioinspired pseudopeptide for potential biological applications involving intracellular Zn(II) ion detection.

The key role of pretreatment for the one-step and multi-step conversions of European lignocellulosic materials into furan compounds

Nowadays, an increased interest from the chemical industry towards the furanic compounds production, renewable molecules alternatives to fossil molecules, which can be transformed into a wide range of chemicals and biopolymers. These molecules are produced following hexose and pentose dehydration. In this context, lignocellulosic biomass, owing to its richness in carbohydrates, notably cellulose and hemicellulose, can be the starting material for monosaccharide supply to be converted into bio-based products. Nevertheless, processing biomass is essential to overcome the recalcitrance of biomass, cellulose crystallinity, and lignin crosslinked structure. The previous reports describe only the furanic compound production from monosaccharides, without considering the starting raw material from which they would be extracted, and without paying attention to raw material pretreatment for the furan production pathway, nor the mass balance of the whole process. Taking account of these shortcomings, this review focuses, firstly, on the conversion potential of different European abundant lignocellulosic matrices into 5-hydroxymethyl furfural and 2-furfural based on their chemical composition. The second line of discussion is focused on the many technological approaches reported so far for the conversion of feedstocks into furan intermediates for polymer technology but highlighting those adopting the minimum possible steps and with the lowest possible environmental impact. The focus of this review is to providing an updated discussion of the important issues relevant to bringing chemically furan derivatives into a market context within a green European context.

The Debye length and anionic transport properties of composite membranes based on supported ionic liquid-like phases (SILLPS)

An analysis of the ionic transport properties of BMIM [NTf₂] in supported ionic-liquid-like phase (SILLP)-based membranes has been carried out based on experimental impedance spectroscopy measurements. The direct current (dc)-conductivity was analyzed to determine the temperature and frequency dependence. The fit of the loss tangent curve data with the Cole-Cole approximation of the electrode polarization model provides the conductivity, diffusivity, and density of charge carriers. Among these quantities, a significant increase in conductivity is observed when an ionic liquid is added to the polymeric matrix containing imidazolium fragments. The use of a recent generalization of Eyring's absolute rate theory allowed the elucidation of how the local entropy restrictions, due to the porosity of the polymeric matrix, control the conductive process. The fit of the conductivity data as a function of temperature manifests the behavior of the excess entropy with respect to the temperature. The activation entropy and enthalpy were also determined. Our results correlate the Debye length (L_D) with the experimental values of conductivity, electrode polarization relaxation time, and sample relaxation time involved. Our work provides novel insights into the description of ionic transport in membranes as the diffusivity, mobility, and free charge density depend on the L_D. Moreover, we discuss the behavior of the polarization relaxation time, the sample relaxation time, and the static permittivity as a function of the temperature.

Basically, nucleophilicity matters little: towards unravelling the supramolecular driving forces in enzyme-like CO2 conversion

The reaction mechanism for the cycloaddition of CO₂ to styrene oxide in the presence of macrocyclic pseudopeptides has been studied using DFT methods. Computational calculations indicate that the unprecedented catalytic behaviour previously observed experimentally, in which the most reactive species was not the most nucleophilic but the most basic one, can be associated to the tight cooperativity between several supramolecular interactions promoted by simple peptidomimetics able to display a synzymatic behaviour. This bizarre catalytic performance afforded remarkable conversions of a sluggish substrate like styrene oxide into the desired cyclic carbonate, even under relatively mild reaction conditions, opening the way for the practical use of CO₂ as a raw material in the preparation of valuable chemicals. Furthermore, the remote modification of essential structural features of the macrocycle (synzyme engineering) permitted the driving forces of the synzymatic system to be analyzed, stressing the crucial synergic effect between an elegantly preorganized oxyanion hole and additional aromatic interactions.

Unravelling the Supramolecular Driving Forces in the Formation of CO2-Responsive Pseudopeptidic Low-Molecular-Weight Hydrogelators

A new family of C₂-symmetric pseudopeptides with a high functional density for supramolecular interactions has been synthetized through the attachment of four amino acid subunits to a diamino aliphatic spacer. The resulting open-chain compounds present remarkable properties as low-molecular-weight hydrogelators. The self-assembled 3D networks were characterized by SEM analyses, observing regular nanofibres with 80–100 nm diameters. Spectroscopic and molecular modelling experiments revealed the presence of strong synergic effects between the H-bonding and π–π interactions, with the best results obtained for the homoleptic tetra-pseudopeptide derived from l-Phe. In addition, these bioinspired hydrogels possessed pH- and CO₂-responsive sol–gel transitions. The formation of ammonium carbamate derivatives in the presence of carbon dioxide led to a detrimental change in its adequate self-assembly. CO₂ desorption temperatures of ca. 70 °C were assigned to the thermodynamically favoured recovery of the supramolecular gel.

Continuous Flow Processes as an Enabling Tool for the Synthesis of Constrained Pseudopeptidic Macrocycles

Herein we report our efforts to develop a continuous flow methodology for the efficient preparation of pseudopeptidic macrocyclic compounds containing the hexahydropyrrolo-[3,4-f]-isoindolocyclophane scaffold and involving four coupled substitution reactions in the macrocyclization process. Appropriate design of a supported base permitted the continuous production of the macrocycles even at large scales, taking advantage of the positive template effect promoted by the bromide anions. In addition, the use of flow protocols allowed a ca. 20-fold increase in productivity as well as reducing the environmental impact almost 2 orders of magnitude, in comparison with the related batch macrocyclization process.

Pseudopeptidic Host Adaptation in Peptide Recognition Unveiled by Ion Mobility Mass Spectrometry

The complexation of the glutamic-tyrosine-glutamic tripeptide (EYE) with a series of pseudopeptidic cages has been thoroughly investigated using different analytical techniques. Stoichiometry and affinities of the supramolecular host : guest...

Continuous flow system for simple preparation of functionalized polymeric beads from poly(acrylamide-thiolactone)

Going with the flow: continuous flow devices to fabricate functional spherical polymers based on poly(acrylamide-thiolactone).

Rational Design of Simple Organocatalysts for the HSiCl3 Enantioselective Reduction of (E)-N-(1-Phenylethylidene)aniline

Prolinamides are well-known organocatalysts for the HSiCl3 reduction of imines; however, custom design of catalysts is based on trial-and-error experiments. In this work, we have used a combination of computational calculations and experimental work, including kinetic analyses, to properly understand this process and to design optimized catalysts for the benchmark (E)-N-(1-phenylethylidene)aniline. The best results have been obtained with the amide derived from 4-methoxyaniline and the N-pivaloyl protected proline, for which the catalyzed process is almost 600 times faster than the uncatalyzed one. Mechanistic studies reveal that the formation of the component supramolecular complex catalyst-HSiCl3-substrate, involving hydrogen bonding breaking and costly conformational changes in the prolinamide, is an important step in the overall process.

The Suitability of Lipases for the Synthesis of Bioactive Compounds with Cosmeceutical Applications

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Cosmeceuticals are cosmetic products containing biologically active ingredients with attractive properties (e.g. anti-oxidant, anti-inflammatory, anti-aging, photoprotective activity, etc.). The aim of these compounds is to offer pharmaceutically therapeutic benefits. The active ingredients can be extracted and purified from natural sources, including plants and animals, or be obtained by biotechnological methodologies (e.g. fermentation, enzymatic synthesis, etc.). Recent years have been increased interest in the design and development of bioactive compounds with cosmeceutical applications and low toxicity. The enzymatic synthesis of bioactive esters, based on esterification or transesterification, has attracted much interest because of the interesting properties of the resulting products and because, by replacing traditional chemical catalysts, this approach leads towards the development of more sustainable processes that follow the principles of Green Chemistry. This review gives an overview of the excellent suitability of lipases as biocatalysts for producing bioactive compounds with attractive properties for the cosmetics industry.

Correction: Free ion diffusivity and charge concentration on cross-linked polymeric ionic liquid iongel films based on sulfonated zwitterionic salts and lithium ions

Correction for 'Free ion diffusivity and charge concentration on cross-linked polymeric ionic liquid iongel films based on sulfonated zwitterionic salts and lithium ions' by David Valverde et al., Phys. Chem. Chem. Phys., 2019, 21, 17923-17932, DOI: 10.1039/C9CP01903K.

Polymeric Ionic Liquids Derived from L-Valine for the Preparation of Highly Selective Silica-Supported Stationary Phases in Gas Chromatography

A series of silica-supported polymeric ionic liquid (PIL)-based stationary phases derived from a vinylic L-valine ionic liquid monomer and divinylbenzene (DVB) as the crosslinking agent have been prepared and studied as gas chromatographic stationary phases. These coated gas chromatographic columns exhibited good thermal stabilities (230-300 °C) and high efficiencies (1700-2700 plates/m), and were characterized using a linear solvation parameter model in order to understand the effects of the amount of DVB on the features of the resulting composite systems. Their retention behavior and separation efficiencies were demonstrated using the Grob test. By tuning the crosslinking degree for the IL-derived stationary phase, the separation selectivity and resolution of different compounds were improved. The different retention behaviors observed for many analytes indicate that these stationary phases may be applicable as new types of GC stationary phases.

Synergy between supported ionic liquid-like phases and immobilized palladium N-heterocyclic carbene-phosphine complexes for the Negishi reaction under flow conditions

The combination of supported ionic liquids and immobilized NHC-Pd-RuPhos led to active and more stable systems for the Negishi reaction under continuous flow conditions than those solely based on NHC-Pd-RuPhos. The fine tuning of the NHC-Pd catalyst and the SILLPs is a key factor for the optimization of the release and catch mechanism leading to a catalytic system easily recoverable and reusable for a large number of catalytic cycles enhancing the long-term catalytic performance.

Urea-Based Low-Molecular-Weight Pseudopeptidic Organogelators for the Encapsulation and Slow Release of (R)-Limonene

Low-molecular-weight compounds containing alkylurea fragments attached to the amino end of different miminalistic pseudopeptidic structures have been shown to be excellent organogelators in a variety of organic solvents and liquid organic compounds of different nature. The formation of gels in this work is defined through rheological measurements for those cases where G' > G''. Both the topology and the symmetry of the corresponding urea compounds play a role in defining their organogelator behavior. This can also be tuned by the presence of additional supramolecular guests, as is the case for suberic acid. These compounds also achieve the gelation of relevant active substances such as terpene natural oils and complex mixtures of flavors and fragrances. This provides a simple and mass-efficient supramolecular system for the quantitative encapsulation of active substances, without the need for any additional solvent or complex processes, and their consequent controlled release.

Highly Selective Anion Template Effect in the Synthesis of Constrained Pseudopeptidic Macrocyclic Cyclophanes

Herein, we report the synthesis of a novel family of constrained pseudopeptidic macrocyclic compounds containing the hexahydropyrrolo[3,4-f]isoindolocyclophane scaffold and involving four coupled substitution reactions in the macrocyclization process. Although the increase in the number of steps involved in the macrocyclization could lead to a larger number of possible side products, the optimization of the methodology and the study of the driving forces have made it possible to obtain the desired macrocycles in excellent yields. A thorough computational study has been carried out to understand the macrocyclization process, and the results obtained nicely agree with experimental data. Moreover, the bromide anion had a clear catalytic template effect in the macrocyclization reaction, and surprisingly, the chloride anion had a negative template effect in opposition to the results obtained for analogous macrocycles. The parameters responsible for the specific kinetic template effect observed have been studied in detail.

Synthesis of new fluorescent pyrylium dyes and study of their interaction with N-protected amino acids

Six new fluorescent styrylpyrylium dyes have been synthesized and the collisional quenching taking place upon their interaction with Z-protected amino acids has been studied.

Rose Bengal Immobilized on Supported Ionic-Liquid-like Phases: An Efficient Photocatalyst for Batch and Flow Processes

The catalytic activity of Rose Bengal (RB) immobilized on supported ionic liquid (IL)-like phases was evaluated as a polymer-supported photocatalyst. In these systems, the polymer was designed to play a pivotal role. The polymeric backbone adequately modified with IL-like moieties (supported IL-like phases, SILLPs) was not just an inert support for the dye but controlled the accessibility of reagents/substrates to the active sites and provided specific microenvironments for the reaction. The structure of SILLPs could be finetuned to adjust the catalytic efficiency of the RB-SILLP composites, achieving systems that were more active and stable than the related systems in the absence of IL-like units.

Divergent Multistep Continuous Synthetic Transformations of Allylic Alcohol Enabled by Catalysts Immobilized in Ionic Liquid Phases

Two individual catalytic platforms (metal- and organo-catalyzed) based on the use of an ionic liquid phase were successfully integrated for the synthesis of α-cyano-amine and cyanohydrin trimethylsilyl ethers from allylic alcohol. The right combination of continuous flow processes enabled access to the divergent preparation of two alternative and interesting intermediate compounds from the same starting material.

The role of the side chain in the conformational and self-assembly patterns of C2-symmetric Val and Phe pseudopeptidic derivatives

Side chain as the main conformational and self-assembly structural factor for C₂-pseudopeptides.

Free ion diffusivity and charge concentration on cross-linked polymeric ionic liquid iongel films based on sulfonated zwitterionic salts and lithium ions

The properties of various mixtures of a zwitterionic ionic liquid (ZIs-1) and LiNTf2, including their conductivity, have been studied showing how they can be adjusted through their molar composition. Conductivity tends to increase with the LiNTf2 content although it presents a minimum at the region close to the eutectic point. These mixtures also provide excellent features as liquid phases for the preparation of composite materials based on crosslinked PILs. The prepared films display excellent and tuneable properties as conducting materials, with conductivities that can be higher than 10-2 S cm-1 above 100 °C. The selected polymeric compositions show very good mechanical properties and thermal stability, even for low crosslinking degrees, along with a suitable flexibility and good transparency. The final properties of the films correlate with the composition of the monomeric mixture used and with that of the ZIs-1:LiNTf2 mixture.

Supramolecularly assisted synthesis of chiral tripodal imidazolium compounds

Supramolecular interactions based on amide groups direct the preferential formation of tritopic instead of monotopic or ditopic imidazolium compounds.

Sensing, Transport and Other Potential Biomedical Applications of Pseudopeptides

Pseudopeptides are privileged synthetic molecules built from the designed combination of peptide-like and abiotic artificial moieties. Consequently, they are benefited from the advantages of both families of chemical structures: modular synthesis, chemical and functional diversity, tailored three-dimensional structure, usually high stability in biological media and low non-specific toxicity. Accordingly, in the last years, these compounds have been used for different biomedical applications, ranging from bio-sensing, ion transport, the molecular recognition of biologically relevant species, drug delivery or gene transfection. This review highlights a selection of the most remarkable and recent advances in this field.

Chiral catalysts immobilized on achiral polymers: effect of the polymer support on the performance of the catalyst

Achiral polymeric supports can have important positive effects on the activity, stability and selectivity of supported chiral catalysts.

New porous monolithic membranes based on supported ionic liquid-like phases for oil/water separation and homogenous catalyst immobilisation

Membranes based on supported ionic liquid-like phase (SIILP) systems with tunable properties allowed oil/water separation and reaction/separation integration in biphasic systems.

Dimethyl carbonate as a non-innocent benign solvent for the multistep continuous flow synthesis of amino alcohols

An efficient methodology for the production and resolution of amino alcohols with a low environmental impact has been developed.

Cu2+ recognition by N,N'-benzylated bis(amino amides)

Two new C₂-symmetric N,N'-benzylated bis(amino amides) have been synthesised and their interaction with different transition metals studied using a variety of techniques including UV-Vis and CD spectroscopy or ESI-MS. The determination of the corresponding stability constants with Cu²⁺ has been possible, in H₂O/CH₃CN 7/3 v/v, for one of these ligands (4) using potentiometric titrations. The results obtained reveal that N-benzylation affords significant changes to their properties and is accompanied by an appreciable decrease in the corresponding complexation stability constants. However, this, along with the low kinetics associated to Ni²⁺, facilitates the recognition of Cu²⁺ by 4 that can be followed by the naked-eye up to the submillimolar range. Very interestingly, the chiral nature of this ligand provides an intense and well defined CD curve for the corresponding Cu²⁺ complex, very sensitive to the coordination geometry, facilitating the analysis of this interaction even at the μM range. The formation by both ligands (3 and 4) of square planar complexes with Cu²⁺ and Ni²⁺ displaying a 1 : 1 stoichiometry was confirmed by their X-ray crystal structures.

Influence of polymer composition on the sensitivity towards nitrite and nitric oxide of colorimetric disposable test strips

The influence of polymer composition on the sensitivity towards nitrite (NO₂^-) and nitric oxide (NO) of a series of 19 polymeric hydrogel films has been studied. The polymers, based on the hydrophilic monomer 2-hydroxyethylmethacrylate (HEMA), are able to encapsulate the colorimetric indicator 1,2-diaminoanthraquinone (DAQ) and to respond to NO₂^- and NO by visual changes. In the case of nitrite, the calculated limits of detection (LOD) for two of the polymeric sensors (10 μM) are very close to the sensitivity estimated for free DAQ in solution (LOD 5 μM), but with the advantage of a solid supported sensor with the format of a disposable test-strip made with affordable starting chemicals. The results are interpreted taking into account the nature and proportions of monomers and cross-linkers used for the synthesis of polymers. Key factors for obtaining sensitive materials are the hydrophilic character of the film along with the utilization of low levels of cross-linker and the use of an acidic monomer, like acrylic acid, as a building block.

Improving photocatalytic oxygenation mediated by polymer supported photosensitizers using semiconductor quantum dots as ‘light antennas’

Semiconductor nanoparticles (quantum dots) sensitize the photochemical generation of singlet oxygen at the surface of a photoactive polymer.

Poly(acrylamide-homocysteine thiolactone) as a synthetic platform for the preparation of polymeric ionic liquids by post ring-opening-orthogonal modifications

Post-modification of Poly(Acrylamide-Homocysteine Thiolactone) provides a variety of advanced polymeric materials with different morphologies and structural diversity.

The interaction of amino acids with macrocyclic pH probes of pseudopeptidic nature

The fluorescence quenching, by a series of amino acids, of pseudopeptidic compounds acting as probes for cellular acidity has been investigated.

Novel fluorescent anthracene–bodipy dyads displaying sensitivity to pH and turn-on behaviour towards Cu(ii) ions

The effect of the nature of the spacer in three new bichromophoric compounds showing intramolecular PET and EET processes has been studied.

Cu(2+), Zn(2+), and Ni(2+) Complexes of C2-Symmetric Pseudopeptides with an Aromatic Central Spacer

Two new tetradentate C2-symmetric pseudopeptidic ligands derived from Val and Phe containing two amino and two amido groups and a central o-substituted aromatic spacer have been prepared. Their complexes with Cu(2+), Zn(2+), and Ni(2+) have been studied by potentiometry, UV-vis spectrophotometry, FT-IR, and ESI-MS. The presence of the aromatic spacer provides Cu(2+) complexes with stability constants several orders of magnitude higher than those observed for related ligands containing aliphatic central spacers. Besides, the formation of [MH-2L] complex species is favored. Crystal structures for the corresponding Cu(2+) and Ni(2+) have been obtained, revealing the metal atom in an essentially square-planar geometry, although, in several instances, the oxygen atom of an amide carbonyl of a second complex species can act as a fifth coordination site. In the case of Zn(2+), the only crystal structure obtained displays a square-pyramidal arrangement of the metal center. Finally, preliminary experiments show the catalytic activity of some of these complexes, in particular, Zn(2+) complexes, for epoxide ring-opening with using aniline as the nucleophile in a ligand accelerated process.

Characterization of amine stabilized CdSe/ZnS core–shell quantum dots by using triarylpyrylium dyes

A new method to study the stabilizing primary amine ligands coordinated to the surface of CdSe/ZnS core–shell quantum dots has been developed.

Mechanistic implications of the enantioselective addition of alkylzinc reagents to aldehydes catalyzed by nickel complexes with α-amino amide ligands

The enantioselective alkylation of aldehydes catalysed by nickel(ii)-complexes derived from α-amino amides was studied by means of density functional theory (DFT) and ONIOM (B3LYP:UFF) calculations.

Supramolecular protection from the enzymatic tyrosine phosphorylation in a polypeptide

Two pseudopeptidic cages bind the EYE peptide motif of poly(EY) in buffered water, as shown by NMR and fluorescence spectroscopy. This supramolecular interaction protects the Tyr residues from the enzymatic phosphorylation by PTK.

Bisferrocenyl-functionalized pseudopeptides: access to separated ionic and electronic contributions for electrochemical anion sensing

Pseudopeptidic receptors containing ferrocene fragments have been prepared and their response to a series of anions was measured by a voltammetry of microparticles methodology.

Stereoselective recognition of the Ac-Glu-Tyr-OH dipeptide by pseudopeptidic cages

Pseudopeptidic molecular cages are appealing receptors since they can display different polar and non-polar interaction sites in a modular framework and a controlled disposition. Inspired by previous host-guest knowledge, two pseudopeptidic molecular cages based on serine and threonine (CySer and CyThr, respectively) were designed and synthesized as hosts for the binding of the four possible stereoisomers of the Ac-Glu-Tyr-OH dipeptide, a target sequence of tyrosine kinases. The careful NMR titration experiments in aqueous acetonitrile allowed the determination of the binding constants and reflected a difference in the stability of the corresponding diastereomeric host-guest complexes. The CySer cage proved to be slightly more efficient than the CyThr counterpart, although both showed similar stereoselectivity trends: LL > DD ≥ LD > DL. This stereoselective binding was retained in the gas phase, as shown by ESI-MS competition experiments using the enantiomer-labelled method (EL), as well as CID experiments. Thus, the MS-determined discriminations follow the same trends observed by NMR, suggesting that the stereoselectivity observed for these systems must be mainly dictated by the polar host-guest interactions. Despite the stereoselective binding of short peptide sequences in competitive media being a challenging issue in supramolecular chemistry, our results demonstrate the power of pseudopeptidic cages in molecular recognition with foreseen implications in chemical biology.