Catalytic hydrogenation of glutamic acid

Technology to convert biomass into chemical building blocks provides an opportunity to displace fossil fuels and increase the economic viability of biorefineries. Coupling fermentation capability with aqueous-phase catalysis provides novel routes to monomers and chemicals, including those not accessible from petrochemical routes. Glutamic acid provides a platform to numerous compounds through thermochemical approaches including hydrogenation, cyclization, decarboxylation, and deamination. Hydrogenation of amino acids also provides access to chiral compounds with high enantiopurity. This article detals aqueous-phase hydrogenation reactions that we have developed that lead to valuable chemical intermediates from glutamic acid. In addition, ¹³C nuclear magnetic resonance and matrix-assisted laser desorption ionization mass spectral data are presented that provide a mechanistic picture of the reactions. The results show that hydrogenation of glutamic acid has unique characteristics from other amino acids and that paradigms in the literature do not hold up for this transformation.     

A Cytotoxic Bis(1,2,3-triazol-5-ylidene)carbazolide Gold(III) Complex Targets DNA by Partial Intercalation

The syntheses of bis(triazolium)carbazole precursors and their corresponding coinage metal (Au, Ag) complexes are reported. For alkylated triazolium salts, di- or tetranuclear complexes with bridging ligands were isolated, while the bis(aryl) analogue afforded a bis(carbene) Au^I-CNC pincer complex suitable for oxidation to the redox-stable [Au^III(CNC)Cl]⁺ cation. Although the ligand salt and the [Au^III(CNC)Cl]⁺ complex were both notably cytotoxic toward the breast cancer cell line MDA-MB-231, the Au^III complex was somewhat more selective. Electrophoresis, viscometry, UV-vis, CD and LD spectroscopy suggest the cytotoxic [Au^III(CNC)Cl]⁺ complex behaves as a partial DNA intercalator. In silico screening indicated that the [Au^III(CNC)Cl]⁺ complex can target DNA three-way junctions with good specificity, several other regular B-DNA forms, and Z-DNA. Multiple hydrophobic π-type interactions involving T and A bases appear to be important for B-form DNA binding, while phosphate O⋅⋅⋅Au interactions evidently underpin Z-DNA binding. The CNC ligand effectively stabilizes the Au^III ion, preventing reduction in the presence of glutathione. Both the redox stability and DNA affinity of the hit compound might be key factors underpinning its cytotoxicity in vitro.     

From CO2 to dimethyl carbonate with dialkyldimethoxystannanes: the key role of monomeric species

The formation of dimethyl carbonate (DMC) from CO(2) and methanol with the dimer [n-Bu(2)Sn(OCH(3))(2)](2) was investigated by experimental kinetics in support of DFT calculations. Under the reaction conditions (357-423 K, 10-20 MPa), identical initial rates are observed with three different reacting mixtures, CO(2)/toluene, supercritical CO(2), and CO(2)/methanol, and are consistent with the formation of monomeric di-n-butyltin(iv) species. An intramolecular mechanism is, therefore, proposed with an Arrhenius activation energy amounting to 104 ± 10 kJ mol(-1) for DMC synthesis. DFT calculations on the [(CH(3))(2)Sn(OCH(3))(2)](2)/CO(2) system show that the exothermic insertion of CO(2) into the Sn-OCH(3) bond occurs by a concerted Lewis acid-base interaction involving the tin center and the oxygen atom of the methoxy ligand. The Gibbs energy diagrams highlight that, under the reaction conditions, the dimer-monomer equilibrium is significantly shifted towards monomeric species, in agreement with the experimental kinetics. Importantly, the two Sn-OCH(3) bonds are prompt to insert CO(2). These results provide new insight into the reaction mechanism and catalyst design to enhance the turnover numbers.     

In vitro photodynamic inactivation of Candida spp. growth and adhesion to buccal epithelial cells

In this study, photodynamic inactivation (PDI) was used to inhibit in vitro growth and adhesion of different Candida isolates to buccal epithelial cells (BEC). Experimental conditions were optimized and 25 μM toluidine blue O (TBO) and 15 min of irradiation time by light emitting diode (LED) (energy density of 180 J/cm²) were selected due to higher reductions in cellular viability obtained after treatment. Reduction media of Log₁₀ 3.41 in viable cellular growth and media of 55% in the inhibition of adhesion to buccal epithelial cells were obtained. Two fluconazole resistant isolates were susceptible to PDI (Log₁₀ 3.54 in IB05 and Log₁₀ 1.95 in CG09) and a second session of this treatment for CG09 isolate inhibited cellular viability in 100%, without producing heat. The results permit to conclude that photodynamic inactivation under these experimental conditions would be a possible alternative approach to inhibit Candida spp. cellular growth and adhesion to buccal epithelial cells.     

Connecting ruthenium substituted Keggin-type tungstophosphates by oxotungstic bridges: Evidence for the steric effect of {RuL3}2+ (L3 = η6-arene, (DMSO)3) fragments

The intrinsic reactivity of the organoruthenium-grafted tungstophosphates [α-PW₁₁O₃₉{Ru(η⁶-arene)(H₂O)}]^5? and [α-PW₁₁O₃₉{Ru(DMSO)₃(H₂O)}]^5? has been studied as a prerequisite for later catalytic studies. Upon reflux in aqueous solution, they partially transform into [{PW₁₁O₃₉Ru(η⁶-arene)}₂{WO₂}]^8? (when arene = benzene, toluene…) and [α-PW₁₁O₃₉{Ru(DMSO)}]^5?, respectively. In the former case, the conversion is markedly increased by deliberate addition of tungstate: through a solution NMR study, we show that [{PW₁₁O₃₉Ru(η⁶-p-cymene)}₂{WO₂}]^8? is quantitatively obtained by refluxing a 2:1:2 mixture of [α-PW₁₁O₃₉]^7?, [Ru(η⁶-p-cymene)Cl₂]₂ and [WO₄]^2? at pH 3. In contrast, a different type of complex, [{PW₁₁O₃₉Ru(DMSO)₃}₂{(WO₂(H₂O))₂O}]^8?, is formed by reaction of [α-PW₁₁O₃₉{Ru(DMSO)₃(H₂O)}]^5? with tungstate; it has been characterized by single crystal X-ray diffraction analysis of an acidic potassium salt, and by ¹⁸³W solution NMR. The more sterically demanding {Ru(DMSO)₃}²⁺ fragment probably does not allow the formation of [{PW₁₁O₃₉Ru(DMSO)₃}₂{WO₂}]^8?, while connection of {PW₁₁O₃₉Ru(DMSO)₃}^5? subunits is possible through the larger {(WO₂(H₂O))₂O}²⁺ bridge.     

Structural and physical–chemical evaluation of Bradykinin Potentiating Peptide and its high soluble supramolecular complex

The supramolecular interactions between a Bradykinin Potentiating Peptide (BPP10c) and β-cyclodextrin (βCD) have been investigated by using several techniques. These new properties acquired by the inclusion phenomena are important in developing a strategy for pharmaceutical formulation. The BPP10c structural elucidation and its inclusion complex formed have been investigated using Nuclear Magnetic Resonance techniques. The peptide secondary structure was investigated using infrared spectroscopy in solution, Circular Dichroism and NMR. In addition, the thermodynamic parameters of the inclusion process were also evaluated using Isothermal Titration Calorimetry. The results obtained by these physical–chemical techniques suggested a 1:1 complex formed by interaction between the Tryptophan amino acid residue and the βCD cavity. The peptide secondary structure was not substantially modified for the inclusion process. In addition, the inclusion process proved to be spontaneous (ΔGº = ?2.53 kcal mol^?1), with an enthalpy reduction (ΔHº = ?3.72 kcal mol^?1) and a favored entropic variation (TΔSº = ?1.19 kcal mol^?1).     

Electron‐Poor Thiophene 1,1‐Dioxides: Synthesis,Characterization, and Application as Electron Relays in Photocatalytic Hydrogen Generation

The synthesis and characterization of electron‐poor thiophene 1,1‐dioxides bearing cyanated phenyl groups are reported. The electron‐accepting nature of these compounds was evaluated by cyclic voltammetry, and highly reversible and facile reductions were observed for several derivatives. Moreover, some of the reduced thiophene dioxides form colorful anions, which were investigated spectroelectrochemically. Photoluminescence spectra of the electron‐deficient sulfones were measured in CH₂Cl₂, and they emit in the blue‐green region with significant variation in the quantum yield depending on the aryl substituents. By expanding the degree of substitution on the phenyl rings, quantum yields up to 34 % were obtained. X‐ray diffraction data are reported for two of the thiophene 1,1‐dioxides, and the electronic structure was probed for all synthesized derivatives through DFT calculations. The dioxides were also examined as electron relays in a photocatalytic water reduction reaction, and they showed potential to boost the efficiency.     

Degradation of Lignin Model Compounds in Organic Solvents. Part 1. Preliminary Studies

Preliminary studies were conducted on the degradation of guaiacylglycerol-β-aryl ether (β-O-4′), phenylcoumaran (β-5′) and biphenyl (5–5′) type lignin model compounds in the organic solvent systems such as ethanol-water (1:1, v/v) and 2-butanone-water (1:1, v/v), in the presence of a di- or trivalent inorganic salt to act as a Lewis acid in the temperature range 140–170°C and with a reaction time up to 60 minutes. The inorganic salts investigated include aluminum chloride, aluminum sulfate, ferric chloride, ferric sulfate, and stannic chloride. The results indicate that lignin model compounds of both phenolic and non-phenolicβ-O-4′ types are susceptible to degradation in organic solvent systems in the presence of one of these salts. Stannic chloride was found to be the most suitable catalyst for the degradation of β-O-4′ type lignin model compounds in the organic solvent systems. In contrast, lignin model compounds of β-5′ and 5–5′ types did not undergo degradation under the same reaction conditions. A possible reaction mechanism for the degradation of β-O-4′ type lignin model compounds in organic solvent system in the presence of stannic chloride is discussed.     

Starch Nanocrystal Fillers in an Acrylic Polymer Matrix

Aqueous suspensions of nanocrystals can be obtained by acid hydrolysis of native waxy maize starch granules. The disruption of waxy maize starch granules by 2.2N HCl hydrolysis has been followed by scanning and transmission electron microscopy and laser granulometry. The mechanical properties of composite materials made of poly(styrene-co-butyl acrylate) filled with starch nanocrystals were characterized by dynamic mechanical analysis. These nanocrystals appeared to be an interesting reinforcing phase in a thermoplastic matrix.     

ChemInform Abstract: Theoretical Study of the Relative Stabilities of the α/β3‐[XW11O39]m‐ Lacunary Polyoxometalates (X: P,Si).

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.