Synthesis and Relaxometric Properties of Gadolinium(III) Complexes of New Triazine‐Based Polydentate Ligands

Two new derivatives based on an s‐triazine structural motif were synthesized by attaching two 2,2′‐hydrazinylidenebis[acetic acid] moieties to the triazine ring to reach an overall heptadenticity for the complexation of lanthanide(III) cations. The remaining reactive site was exploited for the substitution with a functionizable amino group (see H₄ L1 ) and a lipophilic moiety (see H₄ L2 ). Luminescence‐lifetime determinations revealed the presence of a single H₂O molecule coordinated for [Eu( L1 )]. A complete ¹H‐NMR relaxometric study was carried out for the octacoordinated [Gd( L1 )] and [Gd( L2 )] complexes. A remarkably long H₂O residence lifetime (²⁹⁸τ_M =5.2 μs) was found by ¹⁷O‐NMR in the case of [Gd( L1 )]. Micelle formation of the lipophilic complex [Gd( L2 )] was evidenced, the critical micellization concentration (cmc) determined, and relaxometric properties of the system investigated.     

Enhancement of Lewis Acidity of Cr-Doped Nanocrystalline SnO2: Effect on Surface NH3 Oxidation and Sensory Detection Pattern

Understanding ammonia oxidation over metal oxide surfaces is crucial for improving its detection with resistive type gas sensors. Formation of NO_x during this process makes sensor response and calibration unstable. Cr-doping of nanocrystalline metal oxides has been reported to suppress NO₂ sensitivity and improve response towards NH₃, however the exact mechanism of such chromium action remained unknown. Herein, by using EPR spectroscopy we demonstrate formation of Cr(VI) lattice defects on the surface of nanocrystalline Cr-doped SnO₂. Enhancement of Cr-doped SnO₂ surface acidity and ammonia adsorption as a result has been revealed by using in situ IR spectroscopy. Moreover, a decrease in concentration of free electrons in the conduction band has been shown as a result of substitutional Cr(III) defects formation. Weaker NO_x chemisorption during ammonia oxidation over SnO₂ surface after Cr doping has been found with the use of mass-spectrometry assisted NH₃ thermo-programmed desorption. The given example of surface acidity adjustment and electronic configuration by means of doping may find use in the design of new gas-sensing metal oxide materials.     

Analysis of flavonoid glycosides with potential medicinal properties on Bauhinia uruguayensis and Bauhinia forficata subspecies pruinosa.

Several Bauhinia species are widely used in Southern South America in the treatment of infections, pain and several diseases including diabetes. Flavonoid compounds based on quercetin and kaempferol glycoside derivatives are believed to be responsible for their therapeutic properties. To investigate this, we have studied two native species from Argentina: B. uruguayensis (BU) and B. forficata subsp. pruinosa (BF). We have analyzed the major polyphenol components in hydro-methanolic extracts of leaves, by high performance liquid chromatography tandem mass spectrometry. Chromatographic analysis yielded five main compounds in BF, corresponding to rutinosides and rhamnosides derivatives of kaempferol and quercetin, which are considered chemotaxonomic markers and responsible for antioxidant activity. The presence of kaempferitrin, an antidiabetic agent, has been confirmed. In extracts of BU, four major compounds were identified as rhamnosides and galloyl derivates from quercetin and kaempferol. One of these compounds, quercitrin-3-rhamnoside may confer anti-inflammatory and analgesic properties to BU extracts.     

Naphthalene derivatives of a conformationally locked GFP chromophore with large stokes shifts

The active development of fluorescence microscopy requires an increase in the variety of the dyes and their characteristics. Compounds with a large Stokes shift, i.e., a large difference between the positions of the absorption and emission maxima, have attracted the interest of researchers as a tool that can be used for multicolor labeling. One of the known approaches to increase the Stokes shift is the introduction of additional polycyclic fragments. Herein, we report novel derivatives of a conformationally locked GFP chromophore containing the naphthalene ring. The proposed modification leads not only to the enhancement of the Stokes shift up to 100 nm but also leads to the noticeable red-shift of the emission and absorption spectra in contrast with the corresponding derivatives with one benzene ring.     

Synthesis of novel 1,2,3-triazolyl nucleoside analogues bearing uracil, 6-methyluracil, 3,6-dimethyluracil,thymine, and quinazoline-2,4-dione moieties

A series of novel 1,2,3-triazolyl nucleoside analogues was synthesized via the CuAAC reaction of N1-alkynyl uracil, 6-methyluracil, 3,6-dimethyl uracil, thymine and quinazolin-2,4-dione with protected azido β-d-ribofuranose. The obtained compounds differ in both the nature of the pyrimidine-2,4-dione fragment and the length of the polymethylene linker connecting it with the β-d-ribofuranosyl-1,2,3-triazol-4-yl moiety. The 1,2,3-triazolyl nucleoside analogues were evaluated for their cytotoxicity in vitro.     

Cyclic Tribismuthide as a Piano Stool Complex Ligand – Synthesis and Crystal Structure of (η3‐Bi3)M(CO)33– (M = Cr,Mo)

The reactions between K₅Bi₄, [(C₆H₆)Cr(CO)₃] or [(C₇H₈)Mo(CO)₃], and [2.2.2]crypt in liquid ammonia yielded the compounds [K([2.2.2]crypt)]₃(η³‐Bi₃)M(CO)₃ · 10NH₃ (M = Cr, Mo), which crystallize isostructurally in P2₁/n. Both contain an 18 valence electron piano‐stool complex with a η³‐coordinated Bi₃‐ring ligand. The Bi–Bi distances range from 2.9560(5) to 2.9867(3) Å and are slightly shorter than known Bi–Bi single bonds but longer than Bi–Bi double bonds. The newly found compounds complete the family of similar complexes with E₃‐ring ligands (E = P‐Bi).     

Dynamic Nuclear Polarization of 13C Nuclei in the Liquid State over a 10 Tesla Field Range

Nuclear magnetic resonance (NMR) techniques play an essential role in natural science and medicine. In spite of the tremendous utility associated with the small energies detected, the most severe limitation is the low signal‐to‐noise ratio. Dynamic nuclear polarization (DNP), a technique based on transfer of polarization from electron to nuclear spins, has emerged as a tool to enhance sensitivity of NMR. However, the approach in liquids still faces several challenges. Herein we report the observation of room‐temperature, liquid DNP ¹³C signal enhancements in organic small molecules as high as 600 at 9.4 Tesla and 800 at 1.2 Tesla. A mechanistic investigation of the ¹³C‐DNP field dependence shows that DNP efficiency is raised by proper choice of the polarizing agent (paramagnetic center) and by halogen atoms as mediators of scalar hyperfine interaction. Observation of sizable DNP of ¹³CH₂ and ¹³CH₃ groups in organic molecules at 9.4 T opens perspective for a broader application of this method.     

Linear‐Dendritic Alternating Copolymers

Herein, the design, synthesis, and characterization of an unprecedented copolymer consisting of alternating linear and dendritic segments is described. First, a 4th‐generation Hawker‐type dendron with two azide groups was synthesized, followed by a step‐growth azide‐alkyne “click” reaction between the 4th‐generation diazido dendron and poly(ethylene glycol) diacetylene to create the target polymers. Unequal reactivity of the functional groups was observed in the step‐growth polymerization. The resulting copolymers, with alternating hydrophilic linear and hydrophobic dendritic segments, can spontaneously associate into a unique type of microphase‐segregated nanorods in water.     

Fluorescent probes on the basis of coumarin derivatives for determining biogenic thiols and thiophenols

Chemistry of Heterocyclic Compounds - In this minireview, we consider the reactivity of fluorescent probes on the basis of coumarin derivatives for the purpose of detecting biogenic thiols...     

Viability of Using Glycerin as a Co-substrate in Anaerobic Digestion of Sugarcane Stillage (Vinasse): Effect of Diversified Operational Strategies

Vinasse, from sugar and ethanol production, stands out as one of the most problematic agroindustry wastes due to its high chemical oxygen demand, large production volume, and recalcitrant compounds. Therefore, the viability of using glycerin as a co-substrate in vinasse anaerobic digestion was tested, to increase process efficiency and biogas productivity. The effect of feeding strategy, influent concentration, cycle length, and temperature were assessed to optimize methane production. Glycerin (1.53% v/v) proved to be a good co-substrate since it increased the overall methane production in co-digestion assays. CH₄ productivity enhanced exponentially as influent concentration increased, but when temperature was increased to 35 °C, biogas production was impaired. The highest methane productivity and yield were achieved using fed-batch mode, at 30 °C and at an organic loading rate of 10.1 kg COD m⁻³ day⁻¹: 139.32 mol CH₄ m⁻³ day⁻¹, 13.86 mol CH₄ kg COD_applied, and 15.30 mol CH₄ kg COD_removed. Methane was predominantly produced through the hydrogenotrophic route. In order to treat all the vinasse produced by a mid-size sugar and ethanol plant, nine reactors with 7263.4 m³ each would be needed. The energy generated by burning the biogas in boilers would reach approximately 92,000 MW h per season and could save up to US$ 240,000.00 per month in diesel oil demand.