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.     

Zur Charakterisierung von Eigenschaften der versteiften dreizähnigen Aminophosphanliganden N,N'-Bis(diphenylphosphino)-2,6-diaminopyridin und N,N-Bis(diphenylphosphino)-2-aminopyridin mit Metallen der Chromgruppe

Inhaltsübersicht. Edukte von Typ M(CO)₆ (M = Cr, Mo,W), N,N'-Bis(diphenylphosphino)-2,6-diaminopyridin (PNP) und Trimethylaminoxid setzen sich bei Raumtemperatur nicht zu dem bekannten Verbindungstyp mer-M(CO)₃PNP, sondern zu Verbindungen der beiden Typen M(CO)₄(PNP=O) mit zweizähnig koordinierten Liganden PNP=O und M(CO)₅(NMe₃) um. Die zu Vergleichszwecken untersuchte Oxidation eines koordinierten PNP-Liganden von mer-Mo(CO)₃(PNP) in Tetramethylbenzollösung ergibt mit Luftsauerstoff bei 180°C eine Reaktion unter Spaltung der P–N-Bindung zur cubanartigen Verbindung Mo₄(μ₃-O)₄(μ-Ph₂PO₂)₄O₄ (Ausbeute 48%). In einem Glaseinschlußrohr reagiert der ambidente N,N-Bis(diphenyIphosphino)-2-nminopyridin-Ligand (NPP) mit den Hexacarbonylen M(CO)₆ in Toluollösung bei 140°C zu Verbindungen des Typs M(CO)₄(NPP) mit zweizähniger Verknüpfung des NPP-Liganden. Hierbei bilden die beiden P-Donoratome am Aminstickstoffatom einen MP₂N-Chelatvierring an Stelle des ebenfalls möglichen P, N_py-Chelatfünfrings. Der analoge Chelatvierring entsteht gleichfalls bei einer Ligandensubstitutions-reaktion zwischen Verbindungen des Zweikernkomplextyps MM′(CO)₈(μ-PPh₂)₂ (M = M′ = W; M = Mo, M′ = W) bzw. \V(CO)₄(μ-PPh₂)₂IrH(CO)(PPh₃) und NPP. Er bildet sich außerdem bei der Thermolyse von Mo(CO)₄(NPP) zu Mo₂(CO)₆(μ-PPh₂)₂(NPP). Die Identifizierung erfolgt im Falle der Verbindungen Mo(CO)₄(PNP=O), Mo₄(μ₃-O)₄(μ-Ph₂PO₂)₄O_4′ Mo₂(CO)₆(μ-PPh₂)₂(NPP) und W(CO)₄(μ-PPh₂)₂IrH(CO)(NPP) durch Einkristall-Röntgenstrukturanalysen. Alle isolierten Produkte werden durch spektroskopische Messungen insbesondere ³¹P-NMR-Daten charakterisiert. Characterization of Properties of the Rigid Tridentate Chelate Ligand N,N′-Bis(diphenylphosphino)-2,6-diaminopyridine and N,N-Bis(diphenylphosphino)-2-aminopyridine with Transition Metals of the Chromium Group Hexacarbonyls M(CO)₆ (M = Cr, Mo, W), N,N′-Bis(diphenylphosphino)-2,6-diaminopyridine (PNP) and trimethylamine oxide gave products of two types M(CO)₄(PNP=O) having a bidentate ligand PNP=O and M(CO)₅(NMe₃) instead of the desired mer-M(CO)₃PNP. For the purpose of a comparison, aerial oxidation of mer-Mo(CO)₃PNP in tetramethyl benzene solution at 180°C was examined which resulted a P–N bond rupture under formation of the cubane-like product Mo₄(μ₃-O)₄(μ-Ph₂PO₂C₄O₄){yield 48%). In sealed glass tubes the ambidentate ligand N,N-bis(diphenylphosphino)-2-aminopyridine (NPP) was reacted with the hexacarbonyls M(CO)₆ in toluene solution at 140°C to products of the type M(CO)₄NPP with NPP as bidentate ligand. Under this reaction conditions the four-membered chelate ring of the type MP₂N was formed with the two P donor atoms attached to the amine N atom instead of the possible competitive five-membered chelate ring formation with a P and pyridyl nitrogen. The analogous four-membered chelate ring was formed in ligand substitution reactions between the substance NPP and each of the dinuclear coordination compounds MM′(CO)₈(μ-PPh₂)₂ (M = M′ = W, M = Mo, M′ = W) including W(CO)₄(μ-PPh₂)₂IrH(CO)(PPh₃); Mo₂(CO)6(μ-PPh₂)₂(NPP) was obtained via thermolysis of Mo(CO)₄(PNP=O). The given structural identification of the compounds Mo(CO)₄(PNP=O), Mo₄(μ₃-O)₄(μ-Ph₂PO₂)₄O₄, Mo₂(CO)₆ (μ-PPh₂)₂(NPP) and W(CO)₄(μ-PPh₂)₂IrH(CO) (NPP) was done by single-crystal X-ray analysis. All seperated products have been characterized by means of spectroscopic measurements especially ³¹P n.m.r. data.     

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.     

Dithiol proteins as guardians of the intracellular redox milieu in parasites: old and new drug targets in trypanosomes and malaria-causing plasmodia

Parasitic diseases such as sleeping sickness, Chagas' heart disease, and malaria are major health problems in poverty-stricken areas. Antiparasitic drugs that are not only active but also affordable and readily available are urgently required. One approach to finding new drugs and rediscovering old ones is based on enzyme inhibitors that paralyze antioxidant systems in the pathogens. These antioxidant ensembles are essential to the parasites as they are attacked in the human host by strong oxidants such as peroxynitrite, hypochlorite, and H2O2. The pathogen-protecting system consists of some 20 thiol and dithiol proteins, which buffer the intraparasitic redox milieu at a potential of -250 mV. In trypanosomes and leishmania the network is centered around the unique dithiol trypanothione (N1,N8-bis(glutathionyl)spermidine). In contrast, malaria parasites have a more conservative dual antioxidative system based on glutathione and thioredoxin. Inhibitors of antioxidant enzymes such as trypanothione reductase are, indeed, parasiticidal but they can also delay or prevent resistance against a number of other antiparasitic drugs.