One-pot synthesis of 1,4-disubstituted 1,2,3-triazoles from terminal acetylenes and in situ generated azides

1,4-Disubstituted 1,2,3-triazoles were obtained by a high-yielding copper(I) catalyzed 1,3-dipolar cycloaddition reaction between in situ generated azides and terminal acetylenes. This one-pot, two-step procedure tolerates most functional groups and circumvents the problems associated with the isolation of potentially toxic and explosive organic azides.     

Probing the surface polarity of native celluloses using genuine solvatochromic dyes

The surface polarity of native celluloses has been investigated by the following solvatochromic dyes: dicyano-bis (1,10)-phenanthroline iron (II) Fe(phen)2 (CN)2 (1), bis(4-N,N-dimethylamino)-benzophenone (2), and cou-marine 153 (3). Linear Solvation Energy (LSE) relationships and the UV/Vis data have been used to characterize the surface polarity of different native cellulose batches in terms of the empirical Kamlet–Taft polarity parameters (hydrogen bond acidity), (hydrogen bond basicity), and * (dipolarity/polarizability). , , *and calculated Reichardt's E T (30) values are reported for various native and regenerated cellulose samples with different degrees of crystallinity. The degree of crystallinity of the cellulose samples has been determined by X-ray. The microcrystalline environment of cellulose can be exactly parameterized in terms of the , and *values. It shows a fairly strong acidity and a low dipolarity/polarizability. For the amorphous sections smaller and larger * values are observed. The correspondence of the empirical polarity parameters determined has been discussed in relation to results from pyrene fluorescence and zetapotential measurements.     

A chemically consistent graph architecture for massive reaction networks applied to solid-electrolyte interphase formation

Modeling reactivity with chemical reaction networks could yield fundamental mechanistic understanding that would expedite the development of processes and technologies for energy storage, medicine, catalysis, and more. Thus far, reaction networks have been limited in size by chemically inconsistent graph representations of multi-reactant reactions (e.g. A + B → C) that cannot enforce stoichiometric constraints, precluding the use of optimized shortest-path algorithms. Here, we report a chemically consistent graph architecture that overcomes these limitations using a novel multi-reactant representation and iterative cost-solving procedure. Our approach enables the identification of all low-cost pathways to desired products in massive reaction networks containing reactions of any stoichiometry, allowing for the investigation of vastly more complex systems than previously possible. Leveraging our architecture, we construct the first ever electrochemical reaction network from first-principles thermodynamic calculations to describe the formation of the Li-ion solid electrolyte interphase (SEI), which is critical for passivation of the negative electrode. Using this network comprised of nearly 6000 species and 4.5 million reactions, we interrogate the formation of a key SEI component, lithium ethylene dicarbonate. We automatically identify previously proposed mechanisms as well as multiple novel pathways containing counter-intuitive reactions that have not, to our knowledge, been reported in the literature. We envision that our framework and data-driven methodology will facilitate efforts to engineer the composition-related properties of the SEI – or of any complex chemical process – through selective control of reactivity.

A chemically consistent graph architecture enables autonomous identification of novel solid-electrolyte interphase formation pathways from a massive reaction network.     

An addition to the oxoacid family: H2B12(OH)12

The acid H(2)B(12)(OH)(12) can be isolated as a crystalline solid by protonation of the hydroxylated borane anion, B(12)(OH)(12)(2)(-). This acidic compound has low solubility in water, conducts protons in the solid state, and has thermal stability to a temperature of 400 degrees C. The conductivity mechanism is a Grotthuss mechanism with a low activation enthalpy (9-13 kcal/mol). This new acid represents an addition to the class of oxoacids, of which sulfuric and phosphoric acid are the most prominent examples.     

Application of time-resolved infrared spectroscopy to electronic structure in metal-to-ligand charge-transfer excited states

Infrared data in the nu(CO) region (1800-2150 cm(-1), in acetonitrile at 298 K) are reported for the ground (nu(gs)) and polypyridyl-based, metal-to-ligand charge-transfer (MLCT) excited (nu(es)) states of cis-[Os(pp)2(CO)(L)](n)(+) (pp = 1,10-phenanthroline (phen) or 2,2'-bipyridine (bpy); L = PPh3, CH(3)CN, pyridine, Cl, or H) and fac-[Re(pp)(CO)3(4-Etpy)](+) (pp = phen, bpy, 4,4'-(CH3)2bpy, 4,4'-(CH3O)2bpy, or 4,4'-(CO2Et)2bpy; 4-Etpy = 4-ethylpyridine). Systematic variations in nu(gs), nu(es), and Delta(nu) (Delta(nu) = nu(es) - nu(gs)) are observed with the excited-to-ground-state energy gap (E(0)) derived by a Franck-Condon analysis of emission spectra. These variations can be explained qualitatively by invoking a series of electronic interactions. Variations in dpi(M)-pi(CO) back-bonding are important in the ground state. In the excited state, the important interactions are (1) loss of back-bonding and sigma(M-CO) bond polarization, (2) pi(pp*-)-pi(CO) mixing, which provides the orbital basis for mixing pi(CO)- and pi(4,4'-X(2)bpy)-based MLCT excited states, and (3) dpi(M)-pi(pp) mixing, which provides the orbital basis for mixing pipi- and pi(4,4'-X(2)bpy*-)-based MLCT states. The results of density functional theory (DFT) calculations on the ground and excited states of fac-[Re(I)(bpy)(CO)3(4-Etpy)](+) provide assignments for the nu(CO) modes in the MLCT excited state. They also support the importance of pi(4,4'-X2bpy*-)-pi(CO) mixing, provide an explanation for the relative intensities of the A'(2) and A' ' excited-state bands, and provide an explanation for the large excited-to-ground-state nu(CO) shift for the A'(2) mode and its relative insensitivity to variations in X.     

Influence of the polydispersity of polymeric surfactants on the enantioselectivity of chiral compounds in micellar electrokinetic chromatography

Poly(sodium undecenoyl-L-leucinate) (poly-L-SUL) was fractionated by the use of different molecular weight cutoff (MWCO) filters to narrow the polydispersity of the macromolecular sizes of the polymeric surfactant. The resulting polymeric surfactant fractions were characterized by the use of three techniques: (1) pulsed field gradient nuclear magnetic resonance (PFG-NMR) was used to determine the hydrodynamic radii, (2) analytical ultracentrifugation (AUC) was used to determine the molecular weights, and (3) steady-state fluorescence was used to determine the polarity of the nonfractionated and fractionated polymeric surfactants. From the data acquired from PFG-NMR, AUC, and fluorescence, it was noted that the hydrodynamic radii and molecular weight of the fractionated poly-L-SUL increased, while the polarity decreased with the increase in the size of the MWCO filter. However, a similarity in physical properties was observed between the nonfractionated and 10-30K fractionated poly-L-SUL except for the hydrodynamic radius and diffusion coefficients. The influence of different macromolecular sizes of poly-L-SUL on the chiral separation of phenylthiohydantion (PTH)-amino acids and coumarinic derivatives, as test analytes, was elucidated by the use of micellar electrokinetic chromatography (MEKC). The size of polymeric surfactants as a prerequisite for chiral separation was demonstrated by comparing the separation properties of fractionated versus nonfractionated polymeric surfactants. Fractionated poly-L-SUL resulted in enhanced resolution and separation efficiency of the test analytes as compared to the case of the nonfractionated poly-L-SUL. This observation indicates that minimizing polydispersity of polymeric surfactants may be important for some chiral separation applications.     

High-speed peak matching algorithm for retention time alignment of gas chromatographic data for chemometric analysis

A rapid retention time alignment algorithm was developed as a preprocessing utility to be used prior to chemometric analysis of large datasets of diesel fuel profiles obtained using gas chromatography (GC). Retention time variation from chromatogram-to-chromatogram has been a significant impediment against the use of chemometric techniques in the analysis of chromatographic data due to the inability of current chemometric techniques to correctly model information that shifts from variable to variable within a dataset. The alignment algorithm developed is shown to increase the efficacy of pattern recognition methods applied to diesel fuel chromatograms by retaining chemical selectivity while reducing chromatogram-to-chromatogram retention time variations and to do so on a time scale that makes analysis of large sets of chromatographic data practical. Two sets of diesel fuel gas chromatograms were studied using the novel alignment algorithm followed by principal component analysis (PCA). In the first study, retention times for corresponding chromatographic peaks in 60 chromatograms varied by as much as 300 ms between chromatograms before alignment. In the second study of 42 chromatograms, the retention time shifting exhibited was on the order of 10 s between corresponding chromatographic peaks, and required a coarse retention time correction prior to alignment with the algorithm. In both cases, an increase in retention time precision afforded by the algorithm was clearly visible in plots of overlaid chromatograms before and then after applying the retention time alignment algorithm. Using the alignment algorithm, the standard deviation for corresponding peak retention times following alignment was 17 ms throughout a given chromatogram, corresponding to a relative standard deviation of 0.003% at an average retention time of 8 min. This level of retention time precision is a 5-fold improvement over the retention time precision initially provided by a state-of-the-art GC instrument equipped with electronic pressure control and was critical to the performance of the chemometric analysis. This increase in retention time precision does not come at the expense of chemical selectivity, since the PCA results suggest that essentially all of the chemical selectivity is preserved. Cluster resolution between dissimilar groups of diesel fuel chromatograms in a two-dimensional scores space generated with PCA is shown to substantially increase after alignment. The alignment method is robust against missing or extra peaks relative to a target chromatogram used in the alignment, and operates at high speed, requiring roughly 1 s of computation time per GC chromatogram.     

Critical re-investigation of the alditol acetate method for analysis of substituent distribution in methyl cellulose

The alditol acetate method is a common procedure for sugar analysis, also applied to determine the substituent distribution in monomer units of polysaccharide ethers like methyl cellulose by gas liquid chromatography. Consisting of several preparation and work-up steps this procedure is both time consuming and prone to side reactions that promote discrimination of single constituents, especially when no peralkylation step is performed prior to hydrolysis. As a consequence results scatter in dependence on individual treatment and conditions. In the context of this work these critical points were overcome by strict but simplified work-up procedures and using acid instead of alkaline catalyzed acetylation. Under the acidic conditions the tedious removal of borate is no longer necessary and a reduced time requirement was achieved as well as good reproducibility. Comparison with independent reference methods excluded a systematic error of the method and confirmed the results obtained. Without peralkylation, i.e. in the presence of free hydroxyl groups, another fast modification of the method using DMSO as solvent, no removal of borate, and 1-methylimidazole as catalyst for acetylation was found to produce a systematic error.     

A Water Molecule Triggers Guest Exchange at a Mono-Zinc Centre Confined in a Biomimetic Calixarene Pocket: a Model for Understanding Ligand Stability in Zn Proteins

In this study, the ligand exchange mechanism at a biomimetic Zn^II centre, embedded in a pocket mimicking the possible constrains induced by a proteic structure, is explored. The residence time of different guest ligands (dimethylformamide, acetonitrile and ethanol) inside the cavity of a calix[6]arene-based tris(imidazole) tetrahedral zinc complex was probed using 1D EXchange SpectroscopY NMR experiments. A strong dependence of residence time on water content was observed with no exchange occurring under anhydrous conditions, even in the presence of a large excess of guest ligand. These results advocate for an associative exchange mechanism involving the transient exo-coordination of a water molecule, giving rise to 5-coordinate Zn^II intermediates, and inversion of the pyramid at the Zn^II centre. Theoretical modelling by DFT confirmed that the associative mechanism is at stake. These results are particularly relevant in the context of the understanding of kinetic stability/lability in Zn proteins and highlight the key role that a single water molecule can play in catalysing ligand exchange and controlling the lability of Zn^II in proteins.