Complejación de metales por sustancias húmicas acuáticas como proceso natural, tomando como caso de estudio el Lago de Xochimilco

22 This work discusses the importance of organic matter, specifically Aquatic Humic Substances (SHA) 23 within the speciation and distribution of metals within an aquatic system, in this case Xochimilco 24 Lake, a site with great ecological importance. This lake is the natural habitat of the endemic species 25 “axolotl” (ajolote). In this research, complexation reactions between SHA and metals (Cu, Mn, Pb 26 and Zn) were carried out under different reaction conditions, the source of AHS was water samples 27 taken in Xochimilco Lake in presence and absence of pH buffer dissolution and varying the 28 concentration of metals. The results show that there is a direct competition between the major 29 elements and trace elements to react with the AHS. Under the pH conditions of Xochimilco Lake 30 complexes formation is possible. 31

Comparative Study of Salivary pH, Buffer Capacity, and Flow in Patients with and without Gastroesophageal Reflux Disease

The oral cavity has specific and individualized characteristics, with pH, saliva flow, buffer capacity, temperature, and microorganisms content influencing oral health. Currently, the prevalence of gastroesophageal reflux disease (GERD) is constantly increasing. The objective of this study was to evaluate and compare the saliva quantity at 5 min, salivary pH, and salivary buffer capacity in patients with and without GERD, necessary for establishing the correct dental treatment plan. A Saliva-Check Buffer (GC) kit was used for the determination of salivary variables. The total number of 80 patients included in the study were divided into a study group and a control group, each containing 40 patients. Saliva quantity at 5 min was lower in patients suffering from GERD. The salivary pH of these patients turned to acid values compared to the salivary pH of controls, where the values were within the normal range. In patients with GERD, the determined salivary buffer capacity was low or very low. The use of the Saliva-Check Buffer (GC) kit is a simple, easy, non-invasive and patient-accepted method, which can also be used in the dentist’s office to assess the saliva buffer capacity and pH, variables that are important for establishing a correct dental treatment plan.

Accelerated Weathering and Carbonation (Mild to Intensified) of Natural Canadian Silicates (Kimberlite and Wollastonite) for CO2 Sequestration

Canada’s mineral reserves can play a very important role in curbing climate change if natural alkaline minerals are used for the process of mineral carbonation. In this work, the potential of using two Canadian natural silicates for accelerated carbonation is experimentally assessed: kimberlite mine tailing (Mg0.846Al0.165Fe0.147Ca0.067SiO3.381) from the Northwest Territories, and mined wollastonite ore (Ca0.609Mg0.132Al0.091Fe0.024SiO2.914) from Ontario. The aim of this work was to evaluate the weathering reactivity and CO2 uptake capacity via carbonation of these two comminuted rocks, both of which are made up of a mixture of alkaline minerals, under process conditions that spanned from milder to intensified. Research questions addressed include: does kimberlite contain a sufficient amount of reactive minerals to act as an effective carbon sink; is dehydroxylation necessary to activate kimberlite, and to what extent does it do this; do secondary phases of wollastonite hinder its reactivity; and can either of these minerals be carbonated without pH buffering, or only weathered? Incubator, slurry, and pressurized slurry methods of accelerated weathering and carbonation were used, and the effect of the process parameters (temperature, solid-to-liquid ration, reaction time, CO2 level, pH buffer) on the CO2 uptake and crystalline carbonates formation is tested. The reacted samples were analyzed by pH test, loss-on-ignition test, calcimeter test, and X-ray diffraction analysis. Results showed that wollastonite ore (rich in fast-weathering CaSiO3) is more suitable for accelerated carbonation than kimberlite tailing (containing slow-weathering hydrated magnesium silicates and aluminosilicates) when only its capability to rapidly form solid carbonates is considered. Incubator and pressurized buffered slurry methods proved to be most effective as under these conditions the precipitation of carbonates was more favorable, while the unbuffered slurry reaction conditions were more akin to accelerated weathering rather than accelerated carbonation.

Ocular Application of Oleuropein in Dry Eye Treatment: Formulation Studies and Biological Evaluation

Background. Oleuropein is already known for its numerous pharmacological properties, but its activity in the ocular field has not yet been investigated. The study aims to verify a possible use of oleuropein (OLE)-based eye drops both in terms of efficacy in dry eye syndrome and stability in aqueous solution. Methods. OLE was co-precipitated with HP-β-cyclodextrin, and the obtained complex was encapsulated into liposomes prepared by hydration of a lipid film composed of Lipoid S100 and cholesterol with different pH buffer solutions. The hydrated vesicles were shrunk by ultrasonication or extrusion. The preparations were characterized from the physicochemical point of view by subjecting them to differential scanning calorimetry, ATR-FTIR, dynamic light scattering analysis, and microscopy. Subsequently, OLE protective activity against hyperosmotic and oxidative stress on rabbit corneal epithelial cells (RCE) was evaluated. Results. The liposomal vesicles obtained after extrusion showed a tendency towards greater encapsulation efficiency (up to 80.77%) compared to that obtained by sonication, and the liposomes hydrated in pH 5.5 solution tended to incapsulate more than the neutral ones. Ultrasonication produced two-dimensional populations of liposomes, the largest of which reached 2149 nm. On the contrary, the extruded liposomes showed homogeneous diameters of about 250 nm. Complexation with cyclodextrin and subsequent encapsulation in liposomes greatly increased the OLE stability in aqueous solution, especially at 4 °C and for the extruded formulations. OLE aqueous solution (OLE7.4-sol, reference) and neutral extruded liposomes (F7.4-e) were well tolerated on RCE cells. Moreover, OLE was able to control the effects of hyperosmolarity on ocular surface cells and to prevent oxidative stress-induced loss of cell viability.

Biological macromolecule chitosan grafted co-polymeric composite: bio-adsorption probe on cationic dyes

Chitosan biological macromolecule is a versatile polymer; chemical modification has been carried out that lead to the formation of chitosan grafted polymers composites (Chito-g-PC). We proposed synthesis of six various Chito-g-PC as sorbents for toxic dyes. A novel graft copolymerization method based on radical polymerization with vinyl monomer like acrylic acid, acrylamide, N-isopropylacrylamide, methacrylic acid and polyacrylonitrile were utilized in order to address the large amount of swelling at four different pH buffers solution. The effect of initiator and monomer concentration, time and temperature on % grafting and % grafting efficiency were performed. Comparative characterization of Chito and Chito-g-PC were evaluated by SEM, XRD and FTIR, as well as solubility characteristics of the composites were determined by various pH buffer solution. Cationic toxic dyes Malachite green (MG) and Methylene blue (MB) were selected as the sorbet, and Chito-g-PC were used as biosorbents. Thermodynamic analysis showed that the sorption process was spontaneous and endothermic with an increased randomness. The sorption experiments were realized with six different Chito-g-PC for MG and MB at various pH.

Synthesis of Sitagliptin Intermediate by a Multi-Enzymatic Cascade System Using Lipase and Transaminase With Benzylamine as an Amino Donor

Herein, we report the development of a multi-enzyme cascade using transaminase (TA), esterase, aldehyde reductase (AHR), and formate dehydrogenase (FDH), using benzylamine as an amino donor to synthesize the industrially important compound sitagliptin intermediate. A panel of 16 TAs was screened using ethyl 3-oxo-4-(2,4,5-trifluorophenyl) butanoate as a substrate (1). Amongst these enzymes, TA from Roseomonas deserti (TARO) was found to be the most suitable, showing the highest activity towards benzylamine (∼70%). The inhibitory effect of benzaldehyde was resolved by using AHR from Synechocystis sp. and FDH from Pseudomonas sp., which catalyzed the conversion of benzaldehyde to benzyl alcohol at the expense of NAD(P)H. Reaction parameters, such as pH, buffer system, and concentration of amino donor, were optimized. A single whole-cell system was developed for co-expressing TARO and esterase, and the promoter engineering strategy was adopted to control the expression level of each biocatalyst. The whole-cell reactions were performed with varying substrate concentrations (10–100 mM), resulting in excellent conversions (ranging from 72 to 91%) into the desired product. Finally, the applicability of this cascade was highlighted on Gram scale, indicating production of 70% of the sitagliptin intermediate with 61% isolated yield. The protocol reported herein may be considered an alternative to existing methods with respect to the use of cheaper amine donors as well as improved synthesis of (R) and (S) enantiomers with the use of non-chiral amino donors.

Feasibility of multifunction calibration of H+-responsive glass electrodes in seawater (IUPAC Technical Report)

Seawater pH values are of the highest relevance in marine chemistry studies, not only through being acidity indicators but also due to the control provided by H+(aq) over the various simultaneous equilibria occurring in seawater. Although the concept of p H = − l g a H + = − lg ( m H + γ H + / m 0 ) $\mathrm{p}\mathrm{H}=-\mathrm{l}\mathrm{g}{\mathit{a}}_{{\mathrm{H}}^{+}}=-\mathrm{lg}({\mathit{m}}_{{\mathrm{H}}^{+}}{\mathit{\gamma }}_{{\mathrm{H}}^{+}}/{\mathit{m}}^{0})$ , where m H + ${m}_{{\text{H}}^{+}}$ is the relative (molality basis) activity, γ H + ${\gamma }_{{\text{H}}^{+}}$ is the molal activity coefficient of the hydrogen ion H+ at molality m H + ${m}_{{\text{H}}^{+}}$ , and m 0 is the standard molality, was introduced in 1910 and reaffirmed on successive occasions by relevant bodies, different conceptual definitions and alternative measurement procedures have been adopted and are in use by some, namely among oceanographers, often leading to confusion. This leads to major difficulties with the use of data, e.g., on what concerns comparison of results in space and time. Primary pH values, the highest quality level in terms of the metrological chain, have been assigned to primary reference pH buffer solutions of low ionic strength, by a primary method based on measurements of the Harned cell potential in association with the Nernst equation, as well as on the adoption of extra-thermodynamic model assumptions for electrolyte solutions. Although equivalent types of recommendations dealing with standards and procedures based on metrological traceability are still lacking for higher ionic strength media, as it is in the case of seawater, reference Tris–Tris·HCl buffer solutions in artificial seawater have been suggested for use in the calibration of pH meter systems. In this work, Tris–Tris·HCl buffer saline solutions of three different molality ratios mTris:mTris.HCl, m/mol kg−1 H2O, have been assigned reference values for free p H = − lg a H + $\mathrm{p}\mathrm{H}=-\mathrm{lg}\,{a}_{{\text{H}}^{+}}$ and total pH T = − lg ( m H + * / m 0 ) ${\mathrm{pH}}^{\mathrm{T}}=-\text{lg}({m}_{{\text{H}}^{+}}^{\text{{\ast}}}/{m}^{0})$ , where m 0 = 1 mol kg−1 and m H + * = lim m → m SW [ m ( H + ) + m ( HSO 4 − ) ] ${m}_{{\text{H}}^{+}}^{\text{{\ast}}}=\underset{m\to {m}_{\text{SW}}}{\mathrm{lim}}[m({\mathrm{H}}^{\mathrm{+}})+m({\mathrm{HSO}}_{4}^{\mathbf{-}})]$ . Multi-point calibration of pH meters in terms of either pH or pHT is thus possible and supports measurement of their respective values under routine conditions at a high metrological level.

Solubility and Partition Coefficient of Salicylamide in Various pH Buffer Solutions

The solubility and partition coefficient are essential physicochemical parameters in developing a pharmaceutical dosage form of medicine. In addition, these parameters help to predict the absorption of an active compound in oral or topical dosage forms. Salicylamide, an active ingredient available in oral and topical dosage forms, is a weak acid (pKa 8.2) and is sparingly soluble in water. Meanwhile, its solubility and partition coefficients are influenced by the pH of the environment. The Henderson-Hasselbalch equation is used to predict solubility-pH and partition-pH profiles at various pH solutions. This study aims to determine salicylamide's solubility and partition coefficient in various pH (2–11). Both tests were carried out in various pH buffer solutions (at a concentration of 0.02 M and 0.2 ionic strength) in a water bath shaker at a temperature of 37 ± 0.5 °C. In addition, the salicylamide content was determined using the UV spectrophotometer method at the maximum wavelength at each pH. The results showed that the solubility increased at pH 2–10, while the partition coefficient value decreased. On the other hand, at pH 11, there was an increase in the number of ionized species, but the solubility decreased.