Synthesis and temperature dependence of physical properties of four pyridinium-based ionic liquids: Influence of the size of the cation

In this paper, the ionic liquids 1,2-diethylpyridinium ethylsulfate, EEpyESO₄; 1-methylpyridinium methylsulfate, MpyMSO₄; 1,3-dimethylpyridinium methylsulfate, MMpyMSO₄; and 2-ethyl-1-methylpyridinium methylsulfate, EMpyMSO₄; were synthesized in our laboratory, and their experimental densities, speeds of sound, dynamic viscosities, and refractive indices were studied as a function of temperature at atmospheric pressure. Thermal expansion coefficient, molar volume, and molar refraction of these ionic liquids were calculated from the experimental density and refractive index values.     

A crystalline sponge based on dispersive forces suitable for X-ray structure determination of included molecular guests

A crystalline porous material showing one-dimensional (1-D) rectangular micropores (12 × 9 Ų) has been assembled from a semirigid macrocyclic tetraimine and EtOAc as the templating agent. The 1-D nature of the material is intrinsic to the conformationally rigid structure of a macrocyclic sub-unit bearing four cyclohexylidene residues. The multiple dispersive forces established among the aliphatic residues glutted the 1-D channels and provided thermal stability to the material at temperatures below 160 °C. Upon removal of the template, the structure of the empty solid exhibited permanent microporosity (S _BET = 342 m² g^–1). Being a true molecular sponge, the channel framework of this material allowed the inclusion of a variety of molecular sample guests without compromising its crystalline nature. Remarkably, this crystalline material enabled the structure determination by X-ray diffraction of the included molecules. Theoretical studies demonstrated the vital role played by the dispersive forces in the overall stabilization of the crystal packing.     

The preparation,crystal structure and electrochemistry of (5Z,5′Z)-2,2′-(alkane-α,ω-diylsulfanyldiyl)bis(5-(3-pyridylmethylene)-3,5-dihydro-4H-imidazol-4-ones) and their complexes with cobalt(II) chloride

A series of S-alkylated derivatives of 2-thiohydantoins, containing two 5-(3-pyridylmethylene)-3,5-dihydro-4H-imiazole-4-one fragments joined by polymethylene bridges with different numbers of carbon atoms, was synthesized. The title (5Z,5′Z)-2,2′-(alkane-α,ω-diylsulfanyldiyl)bis(5-(3-pyridylmethylene)-3,5-dihydro-4H-imidazol-4-ones) (L) were obtained by alkylation of 5-(3-pyridylmethylene)-3-phenyl-2-thiohydantoine by 1,2-dibromoethane, 1,6-dibromohexane or 1,10-dibromodecane in DMF in the presence of potassium carbonate. The complexes of ligands L with CoCl₂ · 6H₂O have been synthesized. It is shown that, regardless of the L:CoCl₂ ratio, complexes with LCoCl₂ composition are obtained in all cases. The structure of the cobalt(II) chloride complex with (5Z,5′Z)-2,2′-(ethane-1,2-diyldisulfanyldiyl)bis(5-(3-pyridylmethylene)-3-phenyl-3,5-dihydro-4H-imidazol-4-one) was determined by means of the RSA method. The cobalt atom in this complex has a tetrahedral ligand environment and it is coordinated by two chloride anions and two nitrogen atoms of pyridine fragments, forming a 19-membered metallocycle. Electrochemical investigations of the synthesized ligands and complexes have been made by CVA and RDE methods. It is established that the first stage of reduction for the complexes takes place on the metal, whereas the first stage of oxidation takes place on the coordinated chloride-anions.     

Direct Bioelectrocatalysis by NADP‐Reducing Hydrogenase from Pyrococcus furiosus

The direct bioelectrocatalysis by an NAD(P)‐reducing hydrogenase is reported for the first time. In contrast to previous attempts to involve similar enzymes in bioelectrocatalysis [1–4], which were in fact unsuccessful, in our report an effective electrocatalysis by Pyrococcus furiosus hydrogenase is convincingly shown by (i) achievement of the hydrogen equilibrium potential and (ii) a high current of hydrogen oxidation (0.3 mA cm^?2 at 100 mV overpotential and at 75 °C). The latter is just a few times lower compared to enzyme electrodes based on NAD(P)‐independent hydrogenases.     

Dimerization mechanism of bis(triphenylphosphine)copper(I) tetrahydroborate: proton transfer via a dihydrogen bond

The mechanism of transition-metal tetrahydroborate dimerization was established for the first time on the example of (Ph(3)P)(2)Cu(η(2)-BH(4)) interaction with different proton donors [MeOH, CH(2)FCH(2)OH, CF(3)CH(2)OH, (CF(3))(2)CHOH, (CF(3))(3)CHOH, p-NO(2)C(6)H(4)OH, p-NO(2)C(6)H(4)N═NC(6)H(4)OH, p-NO(2)C(6)H(4)NH(2)] using the combination of experimental (IR, 190-300 K) and quantum-chemical (DFT/M06) methods. The formation of dihydrogen-bonded complexes as the first reaction step was established experimentally. Their structural, electronic, energetic, and spectroscopic features were thoroughly analyzed by means of quantum-chemical calculations. Bifurcate complexes involving both bridging and terminal hydride hydrogen atoms become thermodynamically preferred for strong proton donors. Their formation was found to be a prerequisite for the subsequent proton transfer and dimerization to occur. Reaction kinetics was studied at variable temperature, showing that proton transfer is the rate-determining step. This result is in agreement with the computed potential energy profile of (Ph(3)P)(2)Cu(η(2)-BH(4)) dimerization, yielding [{(Ph(3)P)(2)Cu}(2)(μ,η(4)-BH(4))](+).     

Mercury determination in urine samples by gold nanostructured screen-printed carbon electrodes after vortex-assisted ionic liquid dispersive liquid–liquid microextraction

A novel approach is presented to determine mercury in urine samples, employing vortex-assisted ionic liquid dispersive liquid–liquid microextraction and microvolume back-extraction to prepare samples, and screen-printed electrodes modified with gold nanoparticles for voltammetric analysis. Mercury was extracted directly from non-digested urine samples in a water-immiscible ionic liquid, being back-extracted into an acidic aqueous solution. Subsequently, it was determined using gold nanoparticle-modified screen-printed electrodes. Under optimized microextraction conditions, standard addition calibration was applied to urine samples containing 5, 10 and 15 μg L⁻¹ of mercury. Standard addition calibration curves using standards between 0 and 20 μg L⁻¹ gave a high level of linearity with correlation coefficients ranging from 0.990 to 0.999 (N = 5). The limit of detection was empirical and statistically evaluated, obtaining values that ranged from 0.5 to 1.5 μg L⁻¹, and from 1.1 to 1.3 μg L⁻¹, respectively, which are significantly lower than the threshold level established by the World Health Organization for normal mercury content in urine (i.e., 10–20 μg L⁻¹). A certified reference material (REC-8848/Level II) was analyzed to assess method accuracy finding 87% and 3 μg L⁻¹ as the recovery (trueness) and standard deviation values, respectively. Finally, the method was used to analyze spiked urine samples, obtaining good agreement between spiked and found concentrations (recovery ranged from 97 to 100%).     

Atomistic Insight Into the Host–Guest Interaction of a Photoresponsive Metal–Organic Framework

Photoresponsive functional materials have gained increasing attention due to their externally tunable properties. Molecular switches embedded in these materials enable the control of phenomena at the atomic level by light. Metal–organic frameworks (MOFs) provide a versatile platform to immobilize these photoresponsive units within defined molecular environments to optimize the intended functionality. For the application of these photoresponsive MOFs (pho-MOFs), it is crucial to understand the influence of the switching state on the host–guest interaction. Therefore, we present a detailed insight into the impact of molecular switching on the intermolecular interactions. By performing atomistic simulations, we revealed that due to different interactions of the guest molecules with the two isomeric states of an azobenzene-functionalized MOF, both the adsorption sites and the orientation of the molecules within the pores are modulated. By shedding light on the host–guest interaction, our study highlights the unique potential of pho-MOFs to tailor molecular interaction by light.     

A small molecule discrimination map of the antibiotic resistance kinome

Kinase-mediated resistance to antibiotics is a significant clinical challenge. These enzymes share a common protein fold characteristic of Ser/Thr/Tyr protein kinases. We screened 14 antibiotic resistance kinases against 80 chemically diverse protein kinase inhibitors to map resistance kinase chemical space. The screens identified molecules with both broad and narrow inhibition profiles, proving that protein kinase inhibitors offer privileged chemical matter with the potential to block antibiotic resistance. One example is the flavonol quercetin, which inhibited a number of resistance kinases in vitro and in vivo. This activity was rationalized by determination of the crystal structure of the aminoglycoside kinase APH(2″)-IVa in complex with quercetin and its antibiotic substrate kanamycin. Our data demonstrate that protein kinase inhibitors offer chemical scaffolds that can block antibiotic resistance, providing leads for co-drug design.     

Divalent cations reduce the pH sensitivity of OmpF channel inducing the pK(a) shift of key acidic residues

In contrast to the highly-selective channels of neurophysiology employing mostly the exclusion mechanism, different factors account for the selectivity of large channels. Elucidation of these factors is essential for understanding the permeation mechanisms in ion channels and their regulation in vivo. The interaction between divalent cations and a protein channel, the bacterial porin OmpF, has been investigated paying attention to the channel selectivity and its dependence on the solution pH. Unlike the experiments performed in salts of monovalent cations, the channel is now practically insensitive to pH, being anion selective all over the pH range considered. Electrostatic calculations based on the available structural data suggest that the binding of divalent cations has two main effects: (i) the pK(a) values of key ionizable groups differ significantly from those of the isolated groups in solution and (ii) the cation binding has a decisive impact on the effective electric charge regulating the channel selectivity. A simple molecular model based on statistical thermodynamics provides additional qualitative explanations to the experimental findings that could also be useful for other related systems like synthetic nanopores, ion exchange membranes, and polyelectrolyte multilayers.