Linoleic Acid Oxidation Catalysed by Various Amino Acids and Cupric Ions in Aqueous Media

Model systems were designed to study the linoleic acid oxidation in the presence and absence of various amino acids and with or without cupric ions. The tested amino acids have shown to possess potential pro-oxidant capacity in linoleic acid dispersed in aqueous media. The effectiveness of various amino acids on linoleic acid oxidation decreased in the following order: cysteine > serine > tryptophan > phenylalanine > histidine > alanine. The addition of alanine, serine, phenylalanine, histidine or tryptophan to linoleic acid have shown features of an autocatalytic oxidation chain reaction. With cysteine, there was a linear relation between concentration of hydroperoxides and time during the early stages of oxidation. The pro-oxidative activity of the tested amino acids in general could be attributed to the presence of the α-amino group in the form H₃-N-R. The apparent difference in the pro-oxidative activity is mainly due to the functional groups attached to β-carbon in the amino acid molecules. The addition of cupric ions at concentration of 10^–5 M to linoleic acid catalysed with various α-amino acids have shown that these amino acids had no significant effect. The increasing copper concentration from 10^–5 to 10^–1 M shortened the induction period of linoleic acid catalysed by amino acids having aromatic side chain, had no effect on the induction period but increased the oxidation rate during the propagation step in the model systems catalysed by alanine and serine and in the model system containing cysteine increased the linoleic acid oxidation linearly from the start of the reaction.     

Interaction of Copper,Zinc, and Manganese Cations with Lignite and Humic Acids

By IR Fourier spectroscopy, EPR, and ¹³C NMR analysis in solids, the sorption of copper, zinc, and manganese cations by various materials from aqueous solutions is studied. The materials considered are Tyul’gansk lignite, Tisul’sk lignite in unoxidized and oxidized forms, humic acids, and the coal residues remaining after separation of the humic acids. The zinc cations are sorbed by ion exchange; copper and manganese cations are sorbed by a mixed mechanism: ion exchange and complex formation. All the samples are selective in terms of sorption of the cations: Cu²⁺ > Zn²⁺ > Mn²⁺.     

Enhancement of lignite char reactivity to steam by cation addition

Chars produced from lignites typically have much higher reactivities to gasification than those produced from bituminous coals. This has been attributed previously to the presence of carboxylate salts of inorganic constituents on the lignites. Upon charring of the lignites, the carboxylate salts decompose leaving behind well dispersed inorganic constituents which act as catalysts for gasification. In this study, a raw lignite has been treated with HCl and HF to demineralize it and to increase its carboxyl content prior to exchanging selected cations with the hydrogen on the carboxyl groups. Up to 2.14 mmol of calcium per g of coal could be added using this procedure. Addition of varying amounts of calcium to the lignite resulted in the production of chars containing calcium contents ranging from 1.1 to 12.9 wt %. Such addition resulted in a rectilinear increase in reactivity of the char to steam with increasing amount of calcium added. Maximum reactivity attained was over ten times the reactivity found for the char produced from the raw lignite. At comparable molar loadings of metal cations onto the acid-treated lignite, the chars subsequently produced had reactivities in steam in the order: K >Na ≈ Ca >Fe >Mg. Char reactivity could also be enhanced by the addition of cations to nitric acid-treated char which had been produced, in turn, from demineralized lignite.     

Electrochemical oxidation of lignite in basic media

Electrolysis of lignite slurries in 1N NaOH at Pt electrodes produced humic acids, CO₂, H₂, relatively small amounts of O₂ and traces of CH₄ and C₂H₂. The amount of humic acids that could be precipitated from the electrolyte increased with the applied potential, reached a maximum at E = 2.7 V, SCE and then declined with further increase in electrode potential. The rates of reaction increased with increasing temperature and activation energies computed from limiting currents and overall rates of reaction indicate that the reaction pathway is complex and involves more than one reaction. The current efficiencies for H₂ production were in the range 80–90% and > 50% of the lignite could be reacted at E = 2.0 V (SCE) in 48 h with 4 cm² Pt gauze electrodes. Although a graphite anode is itself electrochemically oxidized when used in this process, it increases reaction rates, ≈ 2–3 times higher with graphite than with Pt. Many aromatic organic compounds can be extracted from the residual reacted coal into suitable solvents. A significant amount of oxygenated organic compounds can also be recovered from the electrolyte as a precipitate after neutralization and by solvent extraction of the filtrate. Various products were characterized by elemental analysis, and gas chromatography-mass spectrometry. Data are also presented to show the influence of electrode potential on the rate of gas production and on the composition of the organic products. Various reaction pathways are hypothesized for the processes which lead to the products observed.     

New polyacetylene-based chemosensory materials for the “turn-on” sensing of α-amino acids

For the first time, a new disubstituted polyacetylene (P1) was utilized to sense α-amino acids based on a “turn-on” model, through an indirect approach. Thus, first, the strong blue fluorescence of P1 was quenched by trace copper ions efficiently, then the addition of α-amino acids to the P1/Cu²⁺ complex could recover the strong fluorescence of P1 to report the presence of α-amino acids. Interestingly, the P1/Cu²⁺ complex demonstrated much higher sensitivity towards histidine, with the detection limit of ∼2 ppm (∼1.3 × 10⁻⁵ mol/L). With the aid of a normal UV lamp, histidine could be differed from other α-amino acids visually by the observation of its strong blue fluorescence, at the concentration as low as 4.0 × 10⁻⁵ mol/L. Due to the convenient synthesis of P1, and the so far reported many other conjugated fluorescent polymers, the work reported here might open up a new avenue to develop new biosensors.     

Cloud Point Extraction of α-Amino Acids

Cloud point extraction with a polyethoxylated alcohol (Oxo-C₁₀E₄) is used to separate five α-amino acids: alanine, valine, leucine, isoleucine, and phenylalanine (0.75 wt.% in water), and their extraction efficiencies are compared. The variables affecting phase separation and extraction (wt.% surfactant and equilibrium temperature) are optimized using experimental design. The four responses are: percentage of solute extracted (E), residual concentrations of solute (amino acid) and surfactant in the dilute phase, and volume fraction of coacervate at equilibrium. E increases with surfactant concentration and amino acid hydrophobicity in the following order: alanin < valin < leucin < isoleucine < phenylalanine, with respective maximum values: 73, 74, 76, 78.5, and 95%, and decreases with a temperature rise. It also makes sense that aspartic and glutamic acids, much more hydrophilic, are poorly extracted (E ? 10%). The trend observed is consistent with water/n-octanol partition coefficient (Log P) of amino acids in pure water. A more detailed study is presented for alanine and phenylalanine. Addition of sodium sulphate or cetylammonium bromide greatly raises extraction rates.     

New poly(N-δ-acryloyl ornithine) gels cross-linked with N,N′-methylenebisacrylamide. Sorption properties

To make a polymer from ornithine the acryloyl group was added to δ-amino group of the amino acid and N-δ-acryloyl ornithine was polymerized. The presence of α-amino acid groups attached to the polymeric network of the gels enables the complexation of some di- and trivalent metal cations. Copper ions, which can form two complexes of different stoichiometry (1:1 and 1:2) with amino acids, were used to investigate the influence of the complexation process on the swelling behavior and sorption properties of the obtained gels. The swelling ratio decreased as copper ion concentration increased. The poly(N-δ-acryloyl ornithine) gel was most sensitive to the copper ions in the concentration range of 1-100 mg/mL. The obtained UV-Vis spectra indicated that the copper ions mainly formed complexes of stoichiomery 1:2 with the α-amino acid group. Copper ion uptake was found to exceed 94% in a wide pH range (4-10). The maximum sorption capacity calculated by applying the Langmuir equation was 18.0 mg/g. Kinetic data showed that the sorption process reached equilibrium within 30 min and indicated the importance of the intraparticle diffusion step.     

Introduction of two polyvinyl alcohol resins for efficient solid support Cu-catalyzed N-arylation of α-aminoacids with aryl halides in aqueous media

In this article, two polyvinyl alcohol (PVA)-based resins were prepared by crosslinking of epoxidized PVA-chains using of 4-(4-aminobenzyl)benzenamine as a crosslinker and polymerization of acrylated PVA chains in the another approach. The prepared PVA resins showed well hydrophilic and swelling properties in various organic solvents, which are used in solid-phase organic synthesis (SPOS). Swelling properties of these resins were examined in dimethylformamide, tetrahydrofuran, water, ethanol, methanol, dichloromethane, and dioxane. Furthermore, the both resins were characterized by FTIR and ¹H-NMR and their properties such as epoxy equivalent weight (EEW) of epoxidized PVA and density of the resins were determined by analytical methods. Then, α-amino acids such as L-aspartic acid, L-leucine, L-alanine, L-serine, L-valine, L-threonine, and L-tyrosine were immobilized on both resins through esterification reaction between these α-amino acids with the present hydroxyl groups on PVA resines, to carry out their solid-phase N-arylation reaction in the presence of CuI as a catalyst in milder and greener conditions than free resin protocols. Hydrolysis of the correponding N-arylated α-amino acids immobilized on the resins gave the N-arylated α-amino acids in high to excellent yields. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47597.     

Mutagenicity of eluent by hot water extraction of various coals: Effect of chlorination

Six kinds of powdery coals (two bituminous coals, two sub-bituminous coals, and two lignites) were extracted by hot water, and the eluents obtained were analyzed for total organic carbon (TOC), absorbance at 260 nm (A₂₆₀), and pH. The TOC in the eluents decreased in the order, lignites > sub-bituminous coals > bituminous coals. The eluents of lignite gave high A₂₆₀/TOC values and fairly low pH compared to other coals. Chemical structure of the organic matter eluted from coals was discussed with the aid of FTIR analysis. The coal eluents were analyzed by the Ames mutagenicity assay using Salmonella typhimurium TA100 and TA98 strains, and no mutagenicity was observed for all of the six coals. However, especially for the lignites, chlorination of the eluents produced an appreciable mutagenicity, and the expression of mutagenicity was dependent upon the type of coal. The mutagenicity was extinguished when metabolic activation (rat liver homogenate, +S9) was applied.     

Cotton Seed Oil Oxidation Catalysed by Amino Acids and Albumin in Aqueous and Non-Aqueous Media

The oxidation of refined cotton seed oil catalysed by various α-amino acids and albumin have been studied in aqueous and non-aqueous media. Cysteine, phenylalanine and albumin possessed pro-oxidant effect in cotton seed oil in aqueous and non-aqueous media. Serine exhibited pro-oxidant activity in aqueous media and minor anti-oxidant effect in non-aqueous media. The effectiveness of the amino acids on cotton seed oil oxidation was in the following descending order in both aqueous and non-aqueous media: cysteine > phenylalanine > serine. The pro-oxidant effect in aqueous media might be due to the predominant presence of the protonated amino nitrogen. Whilst, amino acid-metal complex might be responsible for the pro-oxidant effect in non-aqueous media.     

Linoleic Acid Oxidation Catalysed by Various Amino Acids and Cupric Ions in Non-Aqueous Media

The effect of amino acids under the present investigation on linoleic acid oxidation in non-aqueous media has shown feature of an autocatalytic chain reaction and possessed minor antioxidant behaviour except cysteine. The antioxidant effect might be attributed to the absence of protonated amino nitrogen. Linoleic acid alone had an induction period of 15 hr and on the addition of various α-amino acids, the systems had an induction period ranged from 16–19 hr. This increase did not exhibit any specific function for the studied amino acids. Cysteine exceptionally possessed pro-oxidant effect and that was due to the role of HS-group. The addition of copper at concentrations of 10^?5 M and 10^?3 M to the model systems composed of linoleic acid and various α-amino acids in non-aqueous media have shown to exhibit minor and highly pro-oxidant effects respectively. The pro-oxidant effect of these amino acids in the presence of copper might be due to amino acids-copper complexes.     

DPP-4 Cleaves α/β-Peptide Bonds: Substrate Specificity and Half-Lives

The incorporation of β-amino acids into a peptide sequence has gained particular attention as β- and α/β-peptides have shown remarkable proteolytic stability, even after a single homologation at the scissile bond. Several peptidases have been shown to cleave such bonds with high specificity but at a much slower rate compared to α-peptide bonds. In this study, a series of analogs of dipeptidyl peptidase-4 (DPP-4) substrate inhibitors were synthesized in order to investigate whether β-amino acid homologation at the scissile bond could be a valid approach to improving peptide stability towards DPP-4 degradation. DPP-4 cleaved the α/β-peptide bond after the N-terminal penultimate Pro with a broad specificity and retained full activity regardless of the β³-amino acid side chain and peptide length. Significantly improved half-lives were observed for β³Ile-containing peptides. Replacing the penultimate Pro with a conformationally constrained Pro mimetic led to proteolytic resistance. DPP-4 cleavage of α/β-peptide bonds with a broad promiscuity represents a new insight into the stability of peptide analogs containing β-amino acids as such analogs were thought to be stable towards enzymatic degradation.     

Ambient-pressure thermogravimetric characterization of four different coals and their chars

Ambient-pressure thermogravimetric characterization of four different coals and their chars was performed to obtain fundamental information on pyrolysis and coal and char reactivity for these materials. Using a Perkin-Elmer TGS-1 thermobalance, weight loss as a function of temperature was systematically determined for each coal heated in helium at 40 and 160 °C/min under various experimental conditions, and for its derived char heated in air over a temperature range of 20 to 1000 °C. The results indicate that the temperature of maximum rate of devolatilization increases with increasing heating rate for all four coals. However, heating rate does not have a significant effect on the ultimate yield of total volatiles upon heating in helium to 1000 °C; furthermore, coupled with previous data⁹ for identical coal samples, this conclusion extends over a wide range of heating rate from 0.7 to 1.5 × 10⁴ °C/s. Using the temperature of maximum rate of devolatilization as an indication of relative reactivity, the devolatilization reactivity differences among the four coals tested that were suggested by this criterion are not large. For combustion in air, the overall coal/char reactivity sequence as determined by comparison of sample ignition temperature is: N. Dakota lignite coal ≈ Montana lignite coal > North Dakota lignite char > III. No. 6 bituminous coal ≈ Pittsburgh Seam bituminous coal > Montana lignite char > III. No. 6 bituminous char > Pittsburgh Seam bituminous char. The reactivity differences are significantly larger than those for devolatilization. The reactivity results obtained suggest that coal type appears to be the most important determinant of coal and char reactivity in air. The weight loss data were fitted to a distributed-activation-energy model for coal pyrolysis; the kinetic parameters so computed are consistent with the view that coal pyrolysis involves numerous parallel first-order organic decomposition reactions.     

A new one-pot synthesis of α-amino phosphonates catalyzed by H3PW12O40

A new and highly flexible procedure is described for the synthesis of α-amino Phosphonates by in situ generated imines or iminium salts with using dodecatungestophosphoric acid (0.5 mol%) as catalyst in dichloromethane at room temperature in short reaction times (<15 min).     

Cyclic poly(dimethylsiloxane) from kinetically controlled cyclodepolymerization of linear precursors in dilute solution

Cyclic poly(dimethylsiloxane) (PDMS), [(CH₃)₂SiO]_x or D_x, was prepared in high yield (>70% for x > 12) from commercially available linear α,ω-dihydroxy-PDMS by base-catalyzed unimolecular ring closure in dilute solution. Cyclization, which occurs with formation of charged linear byproducts, was confirmed by GPC, FTIR, MALDI-ToF and NMR spectroscopy. Product mixtures were analyzed with a newly developed dual-detector GPC method in which the linear byproducts were end-labeled with a UV-absorbing group and separately detectable with a UV detector. Alternatively, charged linear byproducts were removed with anion-exchange resin. Yields and molecular weight distributions of the cyclic products are consistent with Monte Carlo simulations of kinetically controlled cyclodepolymerization. Large cycles from this cyclodepolymerization route are obtained in much higher yields (>70% for x > 12) than those reported for the traditional base-catalyzed ring-chain equilibration of D₄ and D₅ (∼13% for x > 6) [1].     

Enantioselective Cascade Biocatalysis for Deracemization of Racemic β-Amino Alcohols to Enantiopure (S)-β-Amino Alcohols by Employing Cyclohexylamine Oxidase and ω-Transaminase

Optically active β-amino alcohols are very useful chiral intermediates frequently used in the preparation of pharmaceutically active substances. Here, a novel cyclohexylamine oxidase (ArCHAO) was identified from the genome sequence of Arthrobacter sp. TYUT010-15 with the R-stereoselective deamination activity of β-amino alcohol. ArCHAO was cloned and successfully expressed in E. coli BL21, purified and characterized. Substrate-specific analysis revealed that ArCHAO has high activity (4.15 to 6.34 U mg⁻¹ protein) and excellent enantioselectivity toward the tested β-amino alcohols. By using purified ArCHAO, a wide range of racemic β-amino alcohols were resolved, (S)-β-amino alcohols were obtained in >99 % ee. Deracemization of racemic β-amino alcohols was conducted by ArCHAO-catalyzed enantioselective deamination and transaminase-catalyzed enantioselective amination to afford (S)-β-amino alcohols in excellent conversion (78–94 %) and enantiomeric excess (>99 %). Preparative-scale deracemization was carried out with 50 mM (6.859 g L⁻¹) racemic 2-amino-2-phenylethanol, (S)-2-amino-2-phenylethanol was obtained in 75 % isolated yield and >99 % ee.     

Dithio and thiono. Esters. 61. Synthesis of α-Amino Dithioesters and Endothiodipeptides

The α-amino ester hydrochlorides ( 1 ) are converted into N-protected α-amino amides ( 3 ), α-amino thioamides ( 4 ) and α-amino dithiomethylesters ( 5 ). Condensation of 5 with the alkali salts of α-amino acids gives rise to the endothiodipeptide alkali salts ( 7 ).     

Response surface optimization of supercritical CO2 extraction of α-tocopherol from gel and skin of Aloe vera and almond leaves

Supercritical fluid extraction (SFE) was studied as an alternative technology in the pharmaceutical industry for the separation of α-tocopherol from gel and skin of Aloe vera and almond leaves. The influence of operating conditions was investigated on the recovery of supercritical carbon dioxide (SC-CO₂) extraction of α-tocopherol from three-year old Aloe vera (Aloe barbadensis Miller) leaf gel. The obtained results were compared with the conventional Soxhlet extraction. Response surface methodology (RSM) was applied to optimize effective variables on the extracted recovery of α-tocopherol. The maximum α-tocopherol recovery of 53.41% from Aloe vera gel was obtained with employing RSM predicted optimal operating conditions of 32 MPa, 45.91 °C, 0.84 ml SC-CO₂/min and 140 min for extraction. The α-tocopherol extraction yield for gel and skin of Aloe vera and almond leaves at these optimal operating conditions were obtained 1.53, 16.29 and 2.61 mg/100 g dry sample, respectively.     

Fatty Acid Composition and Some Physicochemical Properties of Oils from Allanblackia gabonensis and A. stanerana Kernels

The physicochemical properties and chemical composition of oils extracted from two varieties of mature seeds of Allanblackia gabonensis and A. stanerana were assessed. The physicochemical properties of oils from Allanblackia gabonensis and A. stanerana were respectively 5.35 and 22.023 % for the water content; 68.15 and 69.87 % for the extraction yield on a dry basis; 0.35 and 0.30 mg KOH/g oil for the acid index; 35.57 and 29.75 g of I₂/100 g oil for the iodine index; 1.3740 and 1.4150 for the refractive index. The fatty acid profile of those oils showed respectively four saturated fatty acids 60.61 and 70.94 %, two monounsaturated fatty acids 37.46 and 28.22 %, two polyunsaturated fatty acids 0.82 and 0.81 % for Allanblackia gabonensis and A. stanerana oils respectively. In both cases, fatty acids C18:0 and C18:1 were dominant. Most of the physicochemical properties showed significant variation (P < 0.05) from one oil to other, the difference being insignificant (P > 0.05) between the two chemical compositions. The analysis of these characteristics showed interesting application features for these oils.     

Supercritical fluid extracts from brown coal lithotypes and their group components—molecular composition of non-polar compounds

The two Tertiary brown coals, i.e. xylitic brown coal (XBC) and humodetritous brown coal (HBC), from the ‘Turów’ and ‘Konin’ deposits in Poland and their group components were investigated on their behaviour to Soxhlet and supercritical fluid (SFE process) extractions. The raw coals were Soxhlet pre-extracted to remove unbound lipids (bitumens). Humic acids, lignin and cellulose were obtained from the pre-extracted XBC, while humic acids and residual coal were separated from the HBC. Raw coals and their group components were extracted under supercritical conditions with toluene (653 K, 8 MPa, 1 h). The yield of non-polar fractions from the Soxhlet and supercritical extracts were determined and analysed by gas chromatography-mass spectrometry (GC-MS).The diversity in biomarker compositions (n-alkanes, n-alkylbenzenes, iso-alkanes, fatty acids, diterpanes and pentacyclic triterpanes and their aromatised derivatives, methylphenanthrenes) of the supercritical fluid extracts (SFEs) were compared and contrasted with the Soxhlet extracts. The biomarker geochemical indices in Soxhlet extracts are typical of low maturity, while these released by SFE process have characteristic of a higher maturation level. The Soxhlet extracts of both coals show a dominance of 17α(H),21β(H)-homohopane with the precursor configuration of 22R. The pentacyclic triterpanes found in the SFEs are diverse structures, i.e. 17α(H),21β(H)-hopanes, moretanes and small amounts of benzohopanes, as well as geochemically unaltered homohopane with the biological configuration of 17β(H),21β(H)-(22R). Isopimarane is the characteristic of SFEs from humic acids of the coals. Partially aromatised pentacyclic triterpanes related to α- and β-amyrin are characteristic of free lipids and SFEs of humic acid fractions from both coals. The diversity in the phenanthro[4,5-bcd]furan, methylphenanthrenes and 2-methylanthracene compositions is dependent on chemical nature of the brown coal group component.