Participation Of Carboxyl Groups Research Articles

Study of the Cyanide Leaching of Gold from Low-Grade Raw Materials in the Presence of Amino Acids

The article discusses the interaction in amino acid–gold cyanide systems using amino acids of different structures. The formation of complex compounds of gold cyanide with amino acids with the participation of carboxyl and amino groups is shown. A relationship has been established between the formation of gold complexes with amino acids and the degree of its extraction in the process of leaching from low-grade ore with sodium cyanide together with amino acids: the higher the degree of participation of the amino group in the formation of the complex, i.e., covalent bond, the more pronounced the effect of the amino acid on the degree of gold leaching. The contribution to the formation of the complex of the carboxyl group (ionic bond) and the amino group (covalent donor–acceptor) can be assessed by the intensity of the band at a wave number of 1419 cm−1 of the IR spectra of the systems: gold cyanide–amino acid. This approach makes it possible to predict the effect of amino acid structure on gold recovery during cyanide leaching based on IR spectra.

ФУНКЦИОНАЛЬНЫЙ ПОКРОВ ПОВЕРХНОСТИ УГЛЕРОДНОГО МАТЕРИАЛА СИБУНИТ И НАНЕСЁННЫХ МЕТАЛЛИЧЕСКИХ КАТАЛИЗАТОРОВ НА ЕГО ОСНОВЕ

Surface O-functionalization of the carbon mesoporous support Sibunit with nitric acid was carried out and Pd/C and Zn/C catalyst samples were prepared by incipient wetness impregnation with aqueous solution of palladium and zinc nitrates varying the temperature of the reduction treatment in hydrogen. A quantitative analysis of oxygen-containing functional groups was carried out using the Boehm potentiometric titration method. It was found that the titration results are in good agreement with the IR spectroscopy data of similar samples and show that the coupling of palladium to the Sibunit surface occurs predominantly with the participation of carboxyl groups, and the coupling of zinc occurs with the participation of phenolic groups.

Insights into the crystal structure and optical property for complexes of iminodiacetic‐terpyridine

AbstractIATPY, a multidentate ligand with strong coordination ability was prepared by connecting iminodiacetic acid with phenylterpyridine, and its Ir(III), Zn(II) and Tb(III) complexes were synthesized in solution or by solvothermal method. The iminodiacetic group on IATPY will be substituted by solvent molecules under weakly basic condition. Coordination reactions will take place between Zn(II) and Tb(III) with IATPY under weakly acidic condition solvothermally. With the contribution from water molecules, a variety of intermolecular hydrogen bonds are formed that make IATPY parallelly arranged in crystals, resulted in intense π‐π stacking and induced its absorption and emission spectra obtained in solution dramatically different from that in solid state. With the participation of terpyridine moiety and carboxyl groups simultaneously, coordination polymers [Zn(IATPY)]n and [Tb2(IATPY)3]n were obtained when Zn(NO3)2 and Tb(CH3COO)3 reacted with IATPY. Intense π‐π stacking effects can be observed in the crystal structures of [Zn(IATPY)]n and [Tb2(IATPY)3]n, which influence their optical properties in solid state.

Features of the Pentaphenylantimony Reaction with 3-Hydroxybenzoic and Benzene-1,2,4,5-Tetracarboxylic Acids

Pentaphenylantimony reacts on heating with 3-hydroxybenzoic acid in dioxane with the participation of carboxyl and hydroxyl groups to form tetraphenylantimony 3-tetraphenylstiboxybenzoate. Benzene-1,2,4,5-tetracarboxylic acid in the reaction with pentaphenylantimony acts as a polyfunctional compound and forms a tetranuclear complex – tetrakis(tetraphenylantimony) benzene-1,2,4,5-tetracarboxylate. Structural features of the synthesized compounds were determined by the X-ray diffraction analysis.

The transformation and degradation of Nafion® solutions under ultrasonic treatment. The effect on transport and mechanical properties of the resultant membranes

This work addresses the study of the effect of ultrasonic (US) treatment on the properties of alcohol solutions of perfluorinated sulfonic acid polymer Nafion® and cast membranes. The effect of the duration of US treatment on the physico-chemical properties (water uptake, transport and mechanical properties) of the resulted membranes is described for the first time. Upon the US treatment, viscosity of the polymer solutions irreversibly decreases due to deagglomeration and rupture of macromolecular chains. As a result of the US treatment, mechanical properties of the Nafion® membranes are deteriorated. The dependences of water uptake and conductivity of the Nafion® membranes in the proton form on sonication time pass the maximum (at 30–45 min). Due to the sonication of polymer solutions, proton conductivity of the membranes increases by 40–45%. Upon extended sonication, the content of sulfonic acid groups decreases, and carboxyl groups are formed at the ends of macromolecules. Thus, water uptake of the membranes prepared from the polymer solutions after the US treatment for 60 min decreases, and conductivity of the obtained membranes in the H+-form is reduced. However, for the Nafion® membranes in the Na+-form, as the duration of the US treatment is extended, their conductivity and diffusion permeability tend to increase due to the enhanced connectivity of pores and channels as well as due to the participation of carboxyl groups in the ionic transport. Upon extended sonication, selectivity of the cation transfer through the membranes is reduced. The results of this work highlight the importance of the proper selection of favorable conditions of the US treatment of the solutions of perfluorinated sulfonic acid polymers for the preparation of hybrid membranes and for the development of catalytic layers of membrane-electrode assemblies for fuel cells.

Synthesis and Structure of Tetraphenylphosphonium Carboxylates

Hydrates of tetraphenylphosphonium carboxylates were synthesized by the reaction of equimolar amounts of pentaphenylphosphorus with 2-methoxybenzoic, 2-nitrobenzoic, and maleic acids in benzene. The product of the pentaphenylphosphorus reaction with tetrafluorophthalic acid (mole ratio 2: 1) is bis- (tetraphenylphosphonium) tetrafluorophthalate hydrate. According to the X-ray analysis data, crystals of tetraphenylphosphonim carboxylates are formed by tetraphenylphosphonim tetrahedral cations and single- or double-charged carboxylate anions. Structural organization of the crystals is determined by C–H···O weak hydrogen bonds formed with the participation of carboxylate groups and water molecules or manifold C–H···F interactions between cations and anions.

Qualitative assessments of the biomass from oil palm calyxes and its application in heavy metals removal from polluted water

The efficiency of oil palm calyxes (OPC) in removing heavy metals from aqueous solution is presented in this report. Qualitative analyses showed the participation of hydroxyl, carboxylate and methoxyl groups in the binding process. OPC surface was observed to be amorphous, highly ordered and multilayered. Quantitative analyses indicated that the removal of Cd2+, Pb2+ and Ni2+ occurred at fast kinetics, with uptake of 38.24, 47.66 and 32.61 mg/g respectively, after 5 min. Optimum Cr3+ adsorption was however not reached after 3 h, indicating slow kinetics. Pseudo-second-order model best described the kinetics of the adsorption, suggesting chemisorption as the rate-limiting step. Metal uptake increased with rise in adsorbate concentration. However, no further rise in uptake was observed with increase in Pb2+ concentration beyond 200 mg/L. Data from the sorption of Cd2+, Ni2+ and Cr3+ were best described by Freundlich isotherm, while those of Pb2+ obeyed Langmuir isotherm, with maximum adsorption capacity (qmax) of 120.48 mg/g. Thermodynamic studies indicated that the removal of Cd2+, Ni2+ and Cr3+ was exothermic and occurred with decreased disorderliness, while Pb2+ removal was endothermic with increased entropy. The negative values of ΔG° indicated the spontaneity of the biosorption of Cd2+, Pb2+, Ni2+ and Cr3+ onto OPC.

Structure and Properties of Nanosized Composites Based on Fe3O4 and Humic Acids

Nanocrystalline composite materials based on magnetite Fe3O4 and humic acids (HA) were synthesized and characterized. Investigation of these materials by EPR, fluorescence spectroscopy, electron microscopy, and XRD analysis showed that the surface of magnetite nanoparticles was densely covered with HA molecules, the size of the Fe3O4 nucleus decreasing when the HA : Fe3O4 ratio increased. An EPR study showed that the structure of the ferromagnetic magnetite nanoparticles changed at increased HA contents. The IR and fluorescence spectroscopy data suggest active participation of carboxyl and hydroxyl groups of HA in the adsorption of HAs on the Fe3O4 surface. The main types of interaction of Fe3O4 with HA were considered, and a scheme of possible chemical reactions was proposed.

Biosorption and equilibrium isotherms study of cadmium removal by Nostoc muscorum Meg 1: morphological, physiological and biochemical alterations

Rice fields of Meghalaya especially in the coal mining belt receive water contaminated by effluents from mines that are known to carry harmful heavy metal ions such as Cu, Fe, Zn, Ni, Cd, As, Pb, Cr, etc. Cd exposure was analyzed in the cyanobacterium Nostoc muscorum Meg 1 isolated from a contaminated rice field in Sohra, Meghalaya, India. Toxicity study established 0.5 ppm on day 3 to be the LD50. At LD50 chlorophyll a and total protein concentration was reduced by 50.9 and 52.5%, while nitrogenase and glutamine synthetase activities were inhibited by 40.8 and 38.4%. EDX and FTIR analyses confirmed Cd binding and participation of hydroxyl, carbonyl, carboxyl and phosphate groups in biosorption of Cd onto the cell surfaces. SEM study established morphological changes. At pH 8.0 and temperature 25 ± 2 °C, the cyanobacterium removed 92% Cd within 24 h. Of this, 91% Cd was adsorbed on the cell surface while 4% was internally accumulated. The energy required for internal accumulation of Cd was partly provided in the form of ATP synthesized during active photosynthesis. The Langmuir isotherm was found best fitted with a R2 value 0.98 when compared to Freundlich and Temkin adsorption isotherms. The maximum sorption capacity, Qmax, of the organism was 71.4 mg of Cd per g of biomass. RL value of 0.29 indicated favorable interaction between cyanobacterial biomass and Cd. The adsorption intensity, n value 7.69 g/L obtained from Freundlich isotherm showed that the organism possessed high Cd sorption capacity.

Biosorption of nickel (II) and zinc (II) from aqueous solutions by the biomass of yeast Yarrowia lipolytica

Abstract This study examined the biosorption process of Ni(II) and Zn(II) from an aqueous solution by dead biomass of Yarrowia lipolytica. Optimum biosorption conditions were determined as a function of pH, biomass dosage, contact time, and temperature. The biosorbent was characterized by FTIR, which indicated the participation of hydroxyl, carboxyl, amide and amine groups in the process of binding the metal ions. The results showed that the biosorption processes of both metal ions closely followed pseudo-second order kinetics. The equilibrium data of Ni(II) and Zn(II) ions at 20, 30 and 40°C fitted the Langmuir and Freundlich isotherm models. Langmuir isotherm provided a better fit to the equilibrium data, with a maximum biosorption capacity of the Y. lipolytica biomass for Ni(II) and Zn(II) of 30.12 and 44.44 mg/g respectively. The calculated thermodynamic parameters demonstrated that the biosorption of Ni(II) and Zn(II) ions onto the Y. lipolytica was feasible, spontaneous and endothermic.

Biosorption of B-aflatoxins Using Biomasses Obtained from Formosa Firethorn [Pyracantha koidzumii (Hayata) Rehder

Mycotoxin adsorption onto biomaterials is considered as a promising alternative for decontamination without harmful chemicals. In this research, the adsorption of B-aflatoxins (AFB1 and AFB2) using Pyracantha koidzumii biomasses (leaves, berries and the mixture of leaves/berries) from aqueous solutions was explored. The biosorbent was used at 0.5% (w/v) in samples spiked with 100 ng/mL of B-aflatoxin standards and incubated at 40 °C for up to 24 h. A standard biosorption methodology was employed and aflatoxins were quantified by an immunoaffinity column and UPLC methodologies. The biosorbent-aflatoxin interaction mechanism was investigated from a combination of zeta potential (ζ), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The highest aflatoxin uptakes were 86% and 82% at 6 h using leaves and the mixture of leaves/berries biomasses, respectively. A moderate biosorption of 46% was attained when using berries biomass. From kinetic studies, the biosorption process is described using the first order adsorption model. Evidence from FTIR spectra suggests the participation of hydroxyl, amine, carboxyl, amide, phosphate and ketone groups in the biosorption and the mechanism was proposed to be dominated by the electrostatic interaction between the negatively charged functional groups and the positively charged aflatoxin molecules. Biosorption by P. koidzumii biomasses has been demonstrated to be an alternative to conventional systems for B-aflatoxins removal.

Remediation of Some Selected Heavy Metals from Water Using Modified and Unmodified Mushrooms

The dispersal of toxic heavy metals by water from natural and anthropogenic is a worldwide environmental concern due to pollution. Despite some metals playing an important role in body, they are toxic when the level exceeds the tolerance limits while others such as lead have no known physiological value to human beings. Since heavy metals cannot be degraded, then their removal from drinking water is necessary. Mushrooms are readily available in Bomet County and their metal removal ability was investigated. The study aimed at removing heavy metals from water by adsorption using mushroom, as a cost-effective and sustainable method. The raw mushroom was modified with sodium hydroxide and characterization of both the parent material and its modified form was done using Fourier Transform Infrared spectrometry (FTIR). Sorption experiments were carried out using the batch adsorption method and sorption parameters including pH, contact time, adsorbent dose and initial metal ion concentration investigated. The results found out that the sorption capacity for cadmium ions ranged from 1.826- 25.285 mg/g by the unmodified edible mushroom (UEM), the modified edible mushroom (EM), unmodified toxic mushroom (UTM) and modified toxic mushroom (TM). For copper ions, sorption capacity ranged from 0.002-4.097 mg/g, while that of the lead ions ranged from 1.345-2.593 mg/g by the UEM, EM, UTM and TM respectively. The sorption capacity showed improvement on modification as sorption of cadmium increased from 1.826-25.285 mg/g by the UEM, EM, UTM and TM. At a pH range of 4-6, the sorbent material was found to remove up to 90% of the metals. The sorbent material had a removal efficiency of 95% of the metals in less than 20 minutes. The UEM and UTM fitted well in Langmuir adsorption isotherm model for cadmium and lead ions. For copper ions, UEM, EM, UTM and TM fitted in the Freundlich model. TM for lead ions best fitted in the Freundlich model. The bio-sorption kinetics was determined by fitting first-order-Lagergreg and Pseudo-second-order kinetics models to the experimental data. It was found that the data for lead was better described by the pseudo-second-order model. For copper ion, the data was best described by Ho’s pseudo second order for UEM and UTM, cadmium ions for all sorbents was best described by Lagergreg’s first-order kinetics. The FTIR analysis suggested the possibility of the participation of carboxyl groups in metal uptake. The levels of dissolved organic carbon (DOC) were found to be 19.0 mg/L in the raw material and 2.19 mg/L after modification. It was confirmed that modification minimized secondary pollution. This indicated that mushrooms have a potential application for the remediation of metal polluted waters.

Kinetic and Thermodynamic Properties of Partially Purified Dextranase from Paecilomyces lilacinus and Its Application in Dextran Removal from Cane Juice

Dextran is a high molecular weight polysaccharide formed in sugarcane during post harvest staling resulting in loss of sucrose as well as quality of sugar. Information regarding the removal of polysaccharides from the sugarcane milled juice is limited. In the present study, enzyme dextranase was produced from Paecilomyces lilacinus by submerged fermentation using Mandel medium and substrate dextran. The crude enzyme was partially purified by 80 % ammonium sulphate saturation followed by DEAE-cellulose column chromatography. Two isoforms of dextranase D-I and D-II each with optimum pH 5.0 and temperature 50 °C were identified. Both the isoforms were most efficient kinetically at pH 5.0 and temperature 50 °C and were found to be thermostable in the temperature range 0–50 °C. The pKa values of ionizing groups in free enzyme and enzyme-substrate complex were found to be between 4.1 and 5.8 indicating the possible participation of carboxylate groups of aspartate/ glutamate and imidazolium group of histidine in dextranase catalysed hydrolysis of dextran by both the isoforms. Activation energy (Ea) values for D-I and D-II were 22.07 and 31.68 kJ/mol and corresponding enthalpy change (ΔH) values were 17.01 and 8.70 kJ/mol, respectively. Cu2+ activated whereas Mg2+, Ca2+, Mn2+, Fe2+ and Pb2+ inhibited the activity of dextranase. With the application of 5, 10 and 15 units of partially purified dextranase per 100 mL of juice, dextran content decreased by 56.39, 73.88 and 80.27 %, respectively as compared to the control (with no dextranase added) after 24 h of storage of cane juice.

Bifunctionalized Allenes, Part XI: Competitive Electrophilic Cyclization and Addition Reactions of 4‐Phosphorylated Allenecarboxylates

ABSTRACTThe reaction of the 4‐phosphorylated allenecarboxylates with different electrophilic reagents such as sulfuryl chloride, bromine, benzenesulfanyl, and benzeneselanyl chlorides takes place with a 5‐endo‐trig cyclization or 2,3‐addition reaction depending on the kind of the substituents in the phosphoryl group. Treatment of the 4‐(dimethoxyphosphopyl)‐allenoates with electrophiles gives a mixture of 2,5‐dihydro‐1,2‐oxaphospholes and furan‐2(5H)‐ones in the ratio of about 1.7:1 as a result of the neighboring group participation of phosphonate and carboxylate groups in the cyclization. On the other hand, (3E)‐4‐(diphenylphosphoryl)‐alk‐3‐enoates were prepared, in moderate yields, by chemo‐, regio, and stereoselective electrophilic addition to the C2C3‐double bond in the allenoate moiety. A possible mechanism involving cyclization and addition reactions of the 4‐phosphorylated allenecarboxylates was proposed.

A Crystallographic, Spectroscopic, Thermal, and DFT Investigation of Mixed Ligand Cu(II) Complexes of 2-benzoylbenzoate

Two mixed ligand complexes of copper(II)-2-benzoylbenzoate (bba) with pyridazine and 4-picoline, namely bis(2-benzoylben- zoate)di(pyridazine)copper(II) 1 and bis(2-benzoylbenzoate)bis(4-picoline)copper(II) 2, have been synthesized and characterized by X-ray crystallography. Complexes 1 and 2 crystallize in the monoclinic P21/c space groups. The calculated frequency shifts have shown that the participation of carboxylate groups in coordination to the metal centers in monodentate fashion (Δ(OCO) > 200 cm−1). The structural features of the complexes have been further studied by DFT/X3LYP extended hybrid functional. The thermal behavior of the complexes was studied by means of simultaneous thermogravimetry, differental thermogravimetry, and differential thermal analysis methods in a static air atmosphere.

Lead sorption by living biomass of Chroococcus multicoloratus and Oscillatoria trichoides: kinetics and equilibrium studies

We report here the ability of two freshwater living cyanobacteria, Chroococcus multicoloratus Wood and Oscillatoria trichoides Szafer, to remove lead (Pb2+) from aqueous solutions in batch system, wherein the effect of Pb2+ on the growth rate of both the cyanobacteria was evaluated. The influence of sorption time, initial pH, initial Pb2+ ion concentration, culture density and the biosorption equilibrium kinetics was examined. Biosorption capacity was found to be maximum between a pH of 5 and 5.14, on the second day of exposure and at an initial concentration of 80 and 60 mg L−1 for C. multicoloratus and O. trichoides, respectively. An initial concentration in the range of 10–120 mg L−1 significantly decreased the growth and efficiency of Pb2+ removal. The maximum sorptive capacity (q max) obtained from the Langmuir isotherm for C. multicoloratus and O. trichoides was 178.57 and 106.38 mg g−1, respectively. The pseudo-second-order model was found to correlate well with the experimental data. Metal recovery of 70–77 % was obtained with HCl as a desorbing agent. The results of Fourier transform infrared spectroscopy indicated the participation of hydroxyl, carboxyl and amino groups in the biosorption process. Based on our observations, we suggest that both species appear to be potential viable biosorbents for mildly acidic water contaminated with Pb2+.

Starch/polyaniline nanocomposite for enhanced removal of reactive dyes from synthetic effluent

Starch/polyaniline nanocomposite was synthesized by chemical oxidative polymerization of aniline and was subsequently analyzed for dye removal from aqueous solution. Batch experiment results showed that nanocomposite removed 99% of Reactive Black 5, 98% of Reactive Violet 4, and decolorized 87% of dye bath effluent. The Toth isotherm model better described single component equilibrium adsorption, whereas the modified Freundlich model showed satisfactory fit for dye bath. In kinetic modeling, single system followed pseudo-second-order and dye bath followed the modified pseudo-first-order model. Fourier transform infrared spectroscopy pattern of the nanocomposite showed the participation of aromatic, amino, hydroxyl, and carboxyl groups. The results indicate that starch/polyaniline nanocomposite can be used as an effective adsorbent for removal of dyes from textile effluents.

Determination of calcium-binding constants of caseins, phosphoserine, citrate and pyrophosphate: A modelling approach using free calcium measurement

Dairy products contain large amount of calcium which is bound to caseins and different chelating agents like citrate and polyphosphates. The present study aimed to determine the calcium-binding capacities of phosphoserine (SerP), caseinophosphopeptide (CPP), β-casein, caseinate, citrate and pyrophosphate in the same conditions of temperature, pH and ionic strength. The free calcium (Ca2+) was measured using a calcium ion-selective electrode and plotted as a function of total calcium concentration. The association constants and the number of calcium-binding sites were determined by fitting the experimental data to a theoretical model. The phosphate groups of caseins were the main binding sites with evidence for participation of carboxylate groups. The intrinsic association constants determined by the best fit of the data were in the order: pyrophosphate (557×103M−1)>citrate (20×103M−1)>β-casein (5×103M−1)>caseinate, CPP and SerP (∼103M−1). These findings may be of interest for the development of calcium-enriched products to overcome calcium deficiency in specific populations.

The electrochemical behaviour of [Co(sep)]3+ bound with p-sulfonatothiacalix[4]arene and tetracarboxy-p-sulfonatocalix[4]arene in correlation with inclusive and non-inclusive binding modes

The comparative study of the ion-pairing of Co(III) sepulchrate ([Co(sep)]3+) with p-sulfonatothiacalix[4]arene and p-sulfonatocalix[4]arene tetracarbonic acid by 1H NMR and pH-metric data in solution and X-ray data in solid state elucidates pH dependent effect of carboxylate groups on the stoichiometry and the mode of the ion pairing. The electrochemical data of [Co(sep)]3+ bound with both calix[4]arenes have been analyzed in the correlation with stoichiometry and the mode of their binding. The pH-dependent effect of tetracarboxy-p-sulfonatocalix[4]arene on the electrochemical behavior of [Co(sep)]3+ has been found to correlate with the participation of carboxylate groups in the host–guest binding.

Study of pepsin phosphorylation using immobilized metal affinity chromatography

The interactions of pepsin with immobilized trivalent metal ions and the participation of the enzyme phosphate group in this process were investigated using high performance immobilized metal affinity chromatography. Two different sorbents were used: the newly prepared one, consisting of Ga(3+ )chelate of (6-amino-1-hydroxyhexane-1,1-diyl) bis(phosphonic acid) covalently bound to a methacrylate support (BP-Ga(3+)), and the commercial one, containing immobilized Fe(3+ )ions (POROS MC20-Fe(3+)). The comparison of the behavior of porcine pepsin A and its partially dephosphorylated form on both sorbents showed that both forms of pepsin were adsorbed under the same conditions. To eliminate the participation of free carboxyl groups in pepsin adsorption, both enzyme forms were modified by amidation or esterification. Native enzyme and its partially dephosphorylated form both with modified carboxyl groups differed in their interaction with immobilized Ga(3+ )and Fe(3+). Phosphorylated pepsin molecules with esterified carboxyl groups were adsorbed on both sorbents while nonphosphorylated ones with esterified carboxyl groups were not adsorbed.