Minor Products Research Articles

Hydrothermal deglycosylation and deconstruction effect of steam explosion: Application to high-valued glycyrrhizic acid derivatives from liquorice

In this work, steam explosion (SE) was exploited as a green and facile process to deconstruct liquorice’s structure and deglycosylate glycyrrhizic acid (GL) to improve conversion and diffusion efficacy of GL and its hydrolyzed products. Results showed SE induced auto-hydrolysis of GL into glycyrrhetic acid 3-O-mono-β-D-glucuronide (GAMG) and glycyrrhetinic acid (GA), by which 30.71% of GL conversion, 5.24% and 21.47% of GAMG and GA formation were obtained. GL hydrolytic pathways were revealed by reaction kinetics and thermodynamics, which possessed complex consecutive and parallel reactions with endothermic, non-spontaneous and entropy-decreasing features. SE referred to cause cleavage of the β-1,3 glycosidic bond in GL which was hydrolyzed to GA as a main product and GAMG and glucuronic acids as minor products. Diffusion of hydrolyzed products was accelerated by raising the diffusion coefficient and shortening the equilibrium time by over 90%. This work provides a sustainable and efficient route for product conversion and function enhancement of bioactive components.

Atmospheric Oxidation of Piperazine Initiated by OH: A Theoretical Kinetics Investigation

Piperazine (Pz) mixed with other amines is a proposed carbon capture solvent, but there is concern about the impact of Pz on air quality, including the potential to produce toxic products. Here, the •OH initiated oxidation of Pz has been studied by ab initio modeling and RRKM/master equation kinetic simulations. The Pz + •OH reaction is found to proceed at around the capture rate, consistent with experiment, with abstraction predominantly from C–H sites, forming an alkyl radical (PzC). The subsequent reaction kinetics of carbon-centered Pz radicals with O2 are also studied, so as to determine the first-generation oxidation products. We find that the PzC radical predominantly reacts with O2 to produce a cyclic imine product + HO2• under tropospheric conditions, with the stabilized peroxyl radical formed as a minor product. Subsequent reaction of the peroxyl radical with NO produces an alkoxyl radical that can react with O2 to yield a cyclic amide or undergo unimolecular ring opening followed by a second O2...

Atmospheric oxidation mechansim of polychlorinated biphenyls (PCBs) initiated by OH radicals

Long-range atmospheric transport (LRAT) is the main route for circulating polychlorinated biphenyls (PCBs) from sources to sinks. In the atmosphere, PCBs containing six and less chlorine substitutions exist mainly as vapour, which can be oxidized by OH radical. Here, using quantum chemistry and transition state theory, we calculated the rate coefficients for reactions of OH radical with selected PCBs. The predicted rate coefficients agree with the available experimental values within a factor of 3. Calculations show that all PCBs considered here are persistent with their half-lives longer than 24 h. Reactions of PCBs with OH radical start with OH addition to the phenyl rings, forming PCB-n-OH adducts. Fate of biphenyl-n-OH (BP-n-OH, n = 2, 3, 4) adducts in the atmosphere is investigated. Calculations show that these radical adducts react similarly to benzene-OH adducts, forming hydroxybiphenyl (HO-BP) as main product and bicyclic radicals as minor products in their reaction with O2. Effective rates of reaction with O2 in the atmosphere are relatively slow, ∼1400, ∼45000, and ∼800 s−1 for BP-2-OH, BP-3-OH, and BP-4-OH, respectively. This suggests considerable reactions between BP-n-OH adducts and NO2, forming nitrobiphenyls. The bicyclic radicals from BP-n-OH + O2 would further transform to highly oxidized products as observed in a previous study. PCB-OH adducts react similarly as BP-n-OH radicals. For the three PCB-OH radicals considered here, their reactions with O2 also form HO-PCBs and bicyclic radicals.

One-Pot Anodic Conversion of Symmetrical Bisamides of Ethylene Diamine to Unsymmetrical gem-Bisamides of Methylene Diamine.

Symmetrical bisamides of ethylene diamine of type ArCONHCH2CH2NHCOAr undergo anodic C-C bond cleavage in acetonitrile-LiClO4 under controlled-potential electrolysis. The electrogenerated carbocation intermediates react with the solvent acetonitrile to afford unsymmetrical gem-bisamides of type ArCONHCH2NHCOMe in aone-potreaction. The yields of the latter products are moderate (up to 60%). Other minor products involve two symmetrical gem-bisamides of type ArCONHCH2NHCOAr and MeCONHCH2NHCOMe and fragmentation products (e.g., ArCONHCHO, ArCONH2, and ArCN).

Synthesis, structural characterization and thermal decomposition studies of (N2H5)2B12H12 and its solvates

A series of salts of the B12H122− anion has been prepared: a solvent-free (N2H5)2B12H12, its solvates – (N2H5)2B12H12·H2O, (N2H5)2B12H12·2(CH3CN), (N2H5)2B12H12·(CH3OH), and the salt of a protonated azine – [(CH3)2CNNHC(CH3)2]2B12H12. These compounds have been synthesized from the commercially available precursors via one- or two-step procedures and fully identified on the basis of single-crystal and powder X-ray diffraction. At room temperature (N2H5)2B12H12 crystallizes in C2/c space group, with a = 18.480(5) Å, b = 6.5344(19) Å, c = 13.106(4) Å and β = 131.911(16)o, V = 1177.8(7) Å3, Z = 4. While this compound nominally contains ca. 10.7 wt% of hydrogen, it thermally decomposes above 200 °C releasing mainly N2 and NH3, with H2 being only the minor gaseous product. Contrary to the recently reported case of hydrazinates of borohydrides, doping with 5 mol% of FeCl3 does not increase the relative amount of hydrogen significantly, however, it alters the ratio of N2 and NH3.

Hydrothermal Decomposition of a Lignin Dimer under Neutral and Basic Conditions: A Mechanism Study

Efficient cleavage of the β-O-4 linkages in lignin is the key to obtaining phenolic chemicals from lignin. The hydrothermal treatment of lignin in neutral and alkaline water is highly utilized but remains poorly understood, preventing the development of strategic depolymerization methods. Herein, the hydrothermal decomposition of a guaiacol-based β-O-4 lignin dimer is systematically explored at varying hydroxide and carbonate base concentrations at 175 °C and supplemented by density functional theory calculations to elucidate the mechanisms of monomeric phenolic product formation. Weakly basic conditions were found to efficiently cleave the β-O-4 linkage yielding guaiacol as the primary product and vanillin and acetovanillone as minor products. Intramolecular substitution, bimolecular elimination, and intermolecular substitution mechanisms are proposed for β-O-4 bond cleavage, and their theoretical rates are compared by transition state theory calculations. The downstream product pathways of this reaction...

Effect of Catalyst Layer Thickness and Porosity on Ethanol Oxidation

The ethanol oxidation reaction (EOR) occurs at the anode in both direct ethanol fuel cells (DEFCs) and in electrochemical alcohol breathalyzers. Acetaldehyde (AAL) and acetic acid (AA) are the main products of EOR at low temperatures, with the minor production of CO2. At low temperatures, both CO and AAL can cause catalyst surface poisoning and thus enhancing the oxidation or removal of AAL from within the catalyst layer should increase the catalyst efficiency and decrease its degree of poisoning. It is known that modifying the catalyst material (e.g., Pt) with a second metal or a metal oxide, can accelerate aldehyde oxidation. However, the investigation of the effect of the catalyst layer porosity and thickness on AAL removal and the EOR efficiency has not been studied in detail as yet. In this study, surfactant-free Pt nanoparticles (NPs) were synthesized in-situ at Vulcan carbon (VC) and colloid imprinted carbon (CICs) supports in one step, aiming for 40% Pt loading, using ethanol as both the solvent and reducing agent. In order to study the effect of catalyst layer porosity, the CICs were synthesized in our lab using silica particles that were 12, 50, and 85 nm in diameter, to obtain carbon supports with an ordered porous structure and controlled pore size. Using the 40% Pt catalyst, a range of film thicknesses were studied, represented as 0.2 mgPt/cm2, 0.4 mgPt/cm2, and 0.6 mgPt/cm2, respectively. All of the electrochemical results were normalized to the real Pt surface area to enable the comparison of the porosity and film thickness with no interference that may arise from the differences in Pt NPs size or utilization. According to the X-ray diffraction (XRD) analysis, the Pt NPs were of a similar size, namely 3.3-3.8 nm, indicating that the Pt NPs size is solely controlled by the synthesis method with almost no substrate effect. The transmission electron microscopy (TEM) images of Pt/VC, Pt/CIC12, Pt/CIC50, and Pt/CIC85 showed that the Pt NPs are homogeneously distributed at the surface of the VC and are located both within the pores of the CICs and on the outer surfaces of the CIC particles with a size that compares well with XRD analysis. Independent of the catalyst film thickness, a Pt electrochemical surface area of 40-50 m2/g and a Pt utilization of 45-60% were obtained, with a better Pt utilization as the specific area of the carbon substrate increase. The oxidation of 1 M ethanol at Pt/VC catalyst showed a positive shift in the onset potential with increasing the catalyst film thickness, while no shift is observed in the case of Pt/CIC85. The superior performance of the CICs compared to VC is due to the better ethanol transport through and product transport out of the catalyst layer pores for the CICs, resulting in less Pt surface poisoning by EOR reaction products. In addition, when a rotating disc electrode was used, a negative shift in the onset potential was observed, also reflecting a less poisoned Pt surface due to the removal of the AAL product. More details about the behavior of ethanol oxidation, at both high and low concentration, and its dependence on Pt/C layer thickness and porosity will be discussed in the presentation.

Distinct metabolic pathways drive monoterpenoid biosynthesis in a natural population of Pelargonium graveolens

Pelargonium graveolens is a wild predecessor to rose-scented geranium hybrids prized for their essential oils used as fragrances and flavorings. However, little is known about their biosynthesis. Here we present metabolic evidence that at least two distinct monoterpene biosynthetic pathways contribute to their volatile profiles, namely, cyclic p-menthanes such as (−)-isomenthone and acyclic monoterpene alcohols such as geraniol and (−)-citronellol and their derivatives (referred to here as citronelloid monoterpenes). We established their common origin via the 2C-methyl-d-erythritol-4-phosphate pathway but found no indication these pathways share common intermediates beyond geranyl diphosphate. Untargeted volatile profiling of 22 seed-grown P. graveolens lines demonstrated distinct chemotypes that preferentially accumulate (−)-isomenthone, geraniol, or (−)-citronellol along with approximately 85 minor volatile products. Whole plant 13CO2 isotopic labeling performed under physiological conditions permitted us to measure the in vivo rates of monoterpenoid accumulation in these lines and quantify differences in metabolic modes between chemotypes. We further determined that p-menthane monoterpenoids in Pelargonium are likely synthesized from (+)-limonene via (+)-piperitone rather than (+)-pulegone. Exploitation of this natural population enabled a detailed dissection of the relative rates of competing p-menthane and citronelloid pathways in this species, providing real time rates of monoterpene accumulation in glandular trichomes.

Correlation functions for determinantal processes defined by infinite block Toeplitz minors

We study the correlation functions for determinantal point processes defined by products of infinite minors of block Toeplitz matrices. The motivation for studying such processes comes from doubly periodically weighted tilings of planar domains, such as the two-periodic Aztec diamond. Our main results are double integral formulas for the correlation kernels. In general, the integrand is a matrix-valued function built out of a factorization of the matrix-valued weight. In concrete examples the factorization can be worked out in detail and we obtain explicit integrands. In particular, we find an alternative proof for a formula for the two-periodic Aztec diamond recently derived in [20]. We strongly believe that also in other concrete cases the double integral formulas are good starting points for asymptotic studies.

New class of non-symmetrical homo-dibenzimidazolium salts and their dinuclear Silver(I) di-NHC complexes

This work describes the synthesis of an uncommon non-symmetrical dibenzimidazolium salts as a precursor for the dinuclear Ag(I) di-NHC complexes with a formula of [Ag2L2]‧2PF6 (L = NHC = bis-N-heterocyclic carbene). Through the reaction of 3-(2-bromoethyl)-1-butylbenzimidazole bromide (i) with n-alkylbenzimidazole (alkyl = methyl, ethyl, propyl, pentyl, hexyl, heptyl, benzyl), seven non-symmetrical dibenzimidazolium bromide salts, 1–3 and 5–8 were obtained. The symmetrical dibenzimidazolium bromide salt 4 was obtained either as a minor product from the reaction resulting i or through the reaction between n-butylbenzimidazole with 1,2-dibromoethane in 2:1 M ratio. Salts 1–8 were then reacted with Ag2O via in-situ deprotonation method to facilitate the formation of dinuclear Ag(I) di-NHC complexes, 9–16. The formation of these complexes is confirmed by the disappearance of both H2’ peaks in 1H NMR and the presence of carbene peaks in the range of 187–191 ppm in the 13C NMR of the complexes. From single crystal X-ray diffraction study, complex 16 is determined to be a dinuclear complex bearing dicarbene ligands which is further stabilized by significant argentophilic interaction with the separation of Ag⋯Ag being 3.358(5) Å. All the bis-benzimidazolium salts 1–8 show no activities while all dinuclear Ag(I) di-NHC complexes, 9–16 show medium to higher activities against E. coli (ATCC 25922) and S. aureus (ATCC 12600) compared to the standard antibiotic drug, Ampicillin.

Ruthenocenyl phosphinated chalcones and their Pt(II) and Pd(II) complexes: Usual bidentate [PO] and unusual tridentate [PCO] coordination

New ruthenocenyl phosphinated chalcones β-(2′-diphenylphosphinophenyl)-acrylruthenocene CpRu(C5H4)C(O)–CHCHC6H4PPh2 (2) and β-(2′-ditolylphosphinophenyl)-acrylruthenocene CpRu(C5H4)C(O)–CHCHC6H4P(tolyl)2 (3) and their Pt(II) and Pd(II) complexes [MCl(κ3-PCO)] (4)–(6) were synthesized as the predominant product, where chalcones coordinate in a tridentate fashion to the metal center and present an unusual η1 coordination at the double bond by activation of C–H bond. During the isolation of Pt(II) (6) complex, a new unstable platinum phosphino-alkene complex (7) [PtCl2(κ2-PO)]was also isolated as a minor product. The X-ray crystal structure of (7) confirms that ligand (2) acts as bidentate ligand and coordinates through phosphorus and η2 double bond ligation to Pt(II) metal. Solution NMR and X-ray crystal structure of chalcone confirm the presence of (E)-stereochemistry at the double bond and s-cis conformation of the enone portion and complexes show square planar geometry around the metal center. Complex (7) decomposes to complex (6) and the oxidized product of ruthenocenyl phosphinated chalcone. Quasi-reversible electrochemistry was found for the ruthenocenyl center in these compounds in acetonitrile solvent. Compared to the ligands, the corresponding metal complexes are easier to oxidize at ruthenocenyl center. From quantum chemical calculations of model systems of (6) and (7) where a platinum atom is replaced by a palladium atom, it was observed that the bonding strength in a η1 coordinated complex is stronger than in a η2 coordinated double bond complex, because of the better chelating effect of the ligand in former complex.

Ruthenium Chloride-Induced Oxidative Cyclization of Trans-Resveratrol to (±)-ε-Viniferin and Antimicrobial and Antibiofilm Activity Against Streptococcus pneumoniae.

Polyphenol ε-viniferin (2) is a protective phytochemical found in several plant families. Here, we report a simple and effective method for the synthesis of (±)-ε-viniferin (2) as major product and (±)-(E)-ω-viniferin (3) as a minor product. Synthesized viniferin compounds and standard viniferin were analyzed for antibacterial and antibiofilm activity against Gram-positive bacteria Streptococcus pneumoniae. The minimum inhibitory concentrations (MICs) of (±)-ε-viniferin (2) and standard viniferin were 20 µm. However, the MICs of (±)-(E)-ω-viniferin (3) and compound 8 were 40 µm. Although viniferin significantly (p < 0.05) reduced pre-established in vitro biofilms and killed bacteria within the biofilm, it was unable to prevent biofilm formation at sub-MIC concentrations. The time kill experiment revealed that viniferin killed bacteria and reduced 2.8 log10 bacteria at 2 × MIC concentration after 24 h. Scanning electron microscope (SEM) analysis and live/dead biofilm staining of pre-established biofilms revealed that viniferin treatment disrupts membrane integrity of biofilm bacteria. Crystal violet absorption, total protein, and DNA and RNA release revealed that viniferin alters bacterial cell permeability, eventually killing bacteria.

Highly efficient and selective extraction of minor bioactive natural products using pure ionic liquids: Application to prenylated flavonoids in licorice

Lots of minor constituents in herbal medicines have shown great potential to devolve into lead compounds, and their extraction is attracting more and more attention in pharmaceutical industry. This study provided an example that showed efficient and selective extraction of minor bioactive natural products (prenylated flavonoids with anti-cancer activities) from an herbal medicine (licorice) using pure ionic liquids as green solvents. After investigation of a variety of hydrophobic ionic liquids with ultrasonic-assisted extraction, we found that [C8MIM]BF4 (1-octyl-3-methylimidazolium tetrafluoroborate) was the most effective one for extraction of five representative compounds (isoangustone A, glycycoumarin, licoisoflavanone, licoricidin and glabridin), and solvent to solid ratio, extraction time, extraction temperature and soaking time were then optimized through single-factor experiments and response surface methodology. As a result, the established method had significantly higher extraction selectivity than conventional organic solvents, which could be attributed to significant physical change of licorice microstructures after extraction, as well as strong interactions (especially hydrogen bond interactions) between [C8MIM]BF4 and prenylated flavonoids by mechanism study. In addition, 78.92% of the extracted prenylated flavonoids could be readily recovered from [C8MIM]BF4 by using reversed-phase solid phase extraction, and the recyclability of [C8MIM]BF4 was also confirmed.

1,2-Bis(diphenylphosphino)ethane-containing commo-ferracarboranes of unusual structure

commo-Ferracarboranes and [8-{(nido-7″,8″-C2B9H11-9″(11″)-)Ph2PCH2CH2PPh2}-commo-3,3′-Fe-{1,2-C2H9B10}{1′2′-C2B9H11}] were prepared as minor products in the metallation reaction of [K]+[nido-7,8-C2B9H12]− with the 14-electron iron complex [Ph2P(CH2)2PPh2]FeCl2. The structures of the complexes were determined by single-crystal X-ray diffraction.

Isothiocyanates as H2S Donors Triggered by Cysteine: Reaction Mechanism and Structure and Activity Relationship.

Isothiocyanates are reported as H2S donors, yet the mechanisms are not clear. Herein, we reported that isothiocyanates (ITCs, R-NCS) rapidly formed adducts with cysteine. These adducts underwent intramolecular cyclization followed by releasing organic amine R-NH2 and raphanusamic acid (RA) as major products with formation of H2S and 2-carbylamino-4,5-dihydrothiazole-4-carboxylic acids as minor products. The ratios of the two groups of products are dependent on the R groups which have strong impact on H2S releasing rates.

Study of Dolutegravir Degradation and Spectroscopic Identification of Products by LCMS, 1H and 13C NMR Techniques

Stability study for dolutegravir bulk drug was performed and the degradation products formed were identified by chromatography (HPLC, LCMS) and spectroscopy (ESI-MS, FTIR, 1H and 13C NMR) techniques. Degradation of the drug in acidic and peroxide environment yielded one common major degradant f ((2,4-difluorophenyl) methanamine) with a mass peak at m/z = 182.44. In addition to this, five more minor degradation products (a, b, c, d and e) were formed. The structure interpretation showed that the drug degraded to its synthetic precursor and no extra structures were formed. Hence, it was suggested that drug dolutegravir should be kept away from acidic and oxygen rich conditions.

The role of homogeneous steam reforming of acetylene in the partial oxidation of methane to syngas in matrix type converters

The conversion of natural gas to syngas is a key and most expensive stage of modern gas chemical technologies. As a promising alternative to existing technologies, a non-catalytic matrix conversion of natural gas to syngas was proposed. However, the reaction products, in addition to CO and H2, also contain unreacted methane, CO2 and acetylene. The latter is the most problem impurity, as it is a precursor of soot and other heavy products. In this work, the kinetic analysis of changes in the composition of the products during the matrix conversion of rich methane-air mixtures up to the establishment of the thermodynamic equilibrium was carried out. Three characteristic stages of the process were identified. The first stage of fast reactions involving oxygen is completed in a very short time (∼10−2 s at 1500 K) with almost complete oxygen consumption and the formation of CO, H2, CO2, H2O and some minor products of methane pyrolysis, mainly acetylene, but at their ratio, far from equilibrium. At the second stage, slow reactions of steam reforming of the formed products significantly increase the amount of hydrogen. The ratio [CO2][H2][CO][H2O] reaches an equilibrium value, but not the concentration of individual products due to incomplete conversion of acetylene and methane. At the third and longest stage, the system reaches equilibrium, and acetylene is not among the equilibrium products. The results of kinetic modeling and experimental study of partial oxidation of methane in matrix-type reformers have shown the important role of acetylene steam conversion in the post-flame zone. This reaction leads to a substantial decrease of methane and acetylene with a simultaneous increase in the yields of hydrogen and CO.

Assessment of Photocatalytic Hydrogen Production from Biomass or Wastewaters Depending on the Metal Co-Catalyst and Its Deposition Method on TiO2

A systematic study on the solar photocatalytic hydrogen production (photoreforming) performance of M/TiO2 (M = Au, Ag, Cu or Pt) using glucose as a model substrate, and further extended to lignocellulose hydrolysates and wastewaters, is herein presented. Three metal (M) co-catalyst loading methods were tested. Variation of the type of metal results in significantly dissimilar H2 production rates, albeit the loading method exerts an even greater effect in most cases. Deposition-precipitation (followed by hydrogenation) or photodeposition provided better results than classical impregnation (followed by calcination). Interestingly, copper as a co-catalyst performed satisfactorily as compared to Au, and slightly below Pt, thus representing a realistic inexpensive alternative to noble metals. Hydrolysates of either α-cellulose or rice husks, obtained under mild conditions (short thermal cycles at 160 °C), were rich in saccharides and thus suitable as feedstocks. Nonetheless, the presence of inhibiting byproducts hindered H2 production. A novel photocatalytic UV pre-treatment method was successful to initially remove the most recalcitrant portion of these minor products along with H2 production (17 µmol gcat−1 h−1 on Cu/TiO2). After a short UV step, simulated sunlight photoreforming was orders of magnitude more efficient than without the pre-treatment. Hydrogen production was also directly tested on two different wastewater streams, that is, a municipal influent and samples from operations in a fruit juice producing plant, with remarkable results obtained for the latter (up to 115 µmol gcat−1 h−1 using Au/TiO2).

Production and Surfactant Properties of Tert-Butyl α-d-Glucopyranosides Catalyzed by Cyclodextrin Glucanotransferase

While testing the ability of cyclodextrin glucanotransferases (CGTases) to glucosylate a series of flavonoids in the presence of organic cosolvents, we found out that this enzyme was able to glycosylate a tertiary alcohol (tert-butyl alcohol). In particular, CGTases from Thermoanaerobacter sp. and Thermoanaerobacterium thermosulfurigenes EM1 gave rise to the appearance of at least two glycosylation products, which were characterized by mass spectrometry (MS) and nuclear magnetic resonance (NMR) as tert-butyl-α-D-glucoside (major product) and tert-butyl-α-D-maltoside (minor product). Using partially hydrolyzed starch as glucose donor, the yield of transglucosylation was approximately 44% (13 g/L of tert-butyl-α-D-glucoside and 4 g/L of tert-butyl-α-D-maltoside). The synthesized tert-butyl-α-D-glucoside exhibited the typical surfactant behavior (critical micellar concentration, 4.0–4.5 mM) and its properties compared well with those of the related octyl-α-D-glucoside. To the best of our knowledge, this is the first description of an enzymatic α-glucosylation of a tertiary alcohol.

Multicomponent reaction of conjugated enynones with malononitrile and sodium alkoxides: Complex reaction mechanism of the formation of pyridine derivatives

Reaction of conjugated enynones,1,5-diarylpent-2-en-4-yn-1-ones, with malononitrile and sodium alkoxides in the corresponding alcohols at room temperature for 3–23 h results in the formation of two types of compounds (E)-/(Z)-6-aryl-4-(2-arylethenyl)-2-alkoxypyridine-3-carbonitriles (substituted nicotinonitriles), as the major reaction products in yields up to ca. 40–80%, and 6-aryl-4-arylethynyl-2-alkoxypyridines, as the minor reaction products in yields of 5–17%. Plausible mechanism of this complex and multistep reaction is discussed. The obtained pyridines possess fluorescent properties.