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A closed-form analytical expression for [ H 3 O + ] has been obtained for aqueous solutions of diprotic acids and its soluble salts. This formula allows to calculate the pH of aqueous solutions of diprotic acids, their buffer solutions, and the titrations of these two by a strong base, from the values of p K 1 , p K 2 , and the effective concentrations of the acid and the base, C ¯ a and C ¯ b respectively. It is shown that a strong base titration of an acid, or its buffer solutions, is always a linear path in the C ¯ a – C ¯ b plane, which allows a simple analysis of the pH stability of buffer solutions. The mathematical analysis of the equilibrium equations of the dissolution of a diprotic acid in water and the physical constraints allowed to obtain two approximate equations for the diprotic acids. One of the approximations is useful for acids with p K 2 - p K 1 ≤ log 10 4 , the other for acids with p K 2 - p K 1 ≤ - log 10 4 .

A buffer solution is often used to maintain tissue hydration during mechanical testing. The most commonly used buffer solution is a physiological concentration of phosphate buffered saline (PBS); however, PBS increases the tissue’s water content and decreases its tensile stiffness. In addition, solutes from the buffer can diffuse into the tissue and interact with its structure and mechanics. These bathing solution effects can confound the outcome and interpretation of mechanical tests. Potential bathing solution artifacts, including solute diffusion, and their effect on mechanical properties, are not well understood. The objective of this study was to measure the effects of long-term exposure of rat tail tendon fascicles to several concentrations (0.9–25%) of NaCl, sucrose, polyethylene glycol (PEG), and SPEG (NaCl+PEG) solutions on water content, solute diffusion, and mechanical properties. We found that with an increase in solute concentration the apparent water content decreased for all solution types. Solutes diffused into the tissue for NaCl and sucrose, however, no solute diffusion was observed for PEG or SPEG. The mechanical properties changed for both NaCl solutions, in particular after long-term (8h) incubation the modulus and equilibrium stress decreased compared to short-term (15min) for 25% NaCl, and the cross sectional area increased for 0.9% NaCl. However, the mechanical properties were unchanged for both PEG and SPEG except for minor alterations in stress relaxation parameters. This study shows that NaCl and sucrose buffer solutions are not suitable for long-term mechanical tests. We therefore propose using PEG or SPEG as alternative buffer solutions that after long-term incubation can maintain tissue hydration without solute diffusion and produce a consistent mechanical response.

The extraction of phenolic compounds from natural sources is crucial for their utilization in various applications, including food, pharmaceuticals, and cosmetics. However, current extraction methods often suffer from drawbacks such as low yield, long extraction times, and the use of harsh chemicals. The present study aimed to assess in vitro the antioxidant activities of solvent extracts from different wild plants (green tea, al sidr, and sage), in addition to introducing a novel, environmentally friendly method for extracting phenolic compounds from different wild plants and finding the best solvent system for extraction of different phenolic compounds. In the present work, 15 solvent extracts from 3 plant samples were evaluated against 2, 2-diphenyl-1-picrylhydrazyl (DPPH) and potassium permanganate (KMnO 4 ) as non-radical reagents and compared with ascorbic acid as a natural standard antioxidant, in addition to the analysis of the chemical constituents of promising extracts from wild plants using HPLC. The obtained results revealed that both methods go in parallel, showing that the concentration of extract and incubation time are dependent and proportional to the concentration of phenolic compounds. Buffer-ethanol extract from green tea plant recorded the highest antioxidant activity when compared with other solvent extracts, with more than 95% against the DPPH radical method, but the activities decreased in the case of the KMnO 4 method. Thus, the HPLC analysis of aqueous extracts of promising buffer and buffer-ethanol solvent systems for the 3 plants showed a highly complex profile, containing approximately 14 and 18 different components. From these compounds, gallic acid recorded the highest concentration for green tea in both extracts at 982.06 and 275.06 µg/ml, respectively. While rosmarinic acid recorded the highest concentration for sage in buffer-ethanol extract at 395.93 µg/ml. From the obtained results, it could be concluded that the solvent extracts of plant samples are rich in different active ingredients, especially phenolic compounds and their derivatives. The extracts from green tea, especially with buffer solution, are more acceptable when compared with other extracts. Buffer, ethanol, and ethanol-buffer extracts (from al sidr, sage, and green tea) recorded high concentrations of phenolic compounds and their derivatives and exhibited antioxidant activity, respectively.

Selective laser melting (SLM) is a rapid prototyping additive manufacturing technology that has been widely utilized in the biomedical field. Surface texturing is an effective surface treatment used to improve tribological performance. In this work, both SLM and surface texturing were applied to prepare textured 316L stainless steel (SS) samples with different parameters. The tribological performance of the SLM-prepared textured 316L SS under dry and phosphate buffer solution (PBS)-lubricated friction conditions was investigated. The results show that the circular textured sample has the smallest percentage reduction in texture characteristic size and hence has a larger volume to store more wear debris generated during the friction process. Moreover, reducing the texture area ratio and characteristic size increase the friction coefficient of the 316L SS textured samples under the two friction conditions. The friction coefficient and wear loss of the textured samples are larger than those of the untextured sample under dry friction conditions. Under the PBS-lubricated friction conditions, the friction coefficient and wear loss of the textured samples decrease significantly compared to the untextured sample, except for the wear loss of textured samples prepared with a small characteristic size. Simultaneously, the triangular textured sample has better wear resistance than the circular textured samples. Therefore, 316L SS textured samples prepared by SLM technology can achieve stable friction and less wear loss under simulated body fluid conditions by selecting reasonable texturing parameters.

This work was aimed at creating a new, fast, and accurate UV spectrophotometric method for quantifying prazosin hydrochloride in pure and tablet dosage forms. A phosphate buffer solution of pH 6 was used as a diluent. The highest absorbance of prazosin hydrochloride was measured at 247 nm, and the linearity ranged from 2 to 8 μg/mL. The regression equation for prazosin hydrochloride was y= 0.087x + 0.236, with a correlation value 0.987. The percentage of recovery ranged from 99.6 to 101%. The relative standard deviation for intraday precision and interday precision was determined to be less than 2. The LOD and LOQ of prazosin hydrochloride were determined to be 0.0375 and 0.113 μg/mL, respectively. International Council for Harmonisation criteria validated the spectrometric technique and was suitable for routine quantitative measurement of prazosin hydrochloride in pure and tablet dosage forms.

Purpose The purpose of this study is to investigate the initial corrosion behavior of pure Mg, AZ31 and AZ91 alloys in phosphate buffer solution (PBS) and to characterize the features in corrosion type and resistance of the corrosion product layer. Design/methodology/approach The scanning electron microscopy, equipped with energy-dispersive spectroscopy, X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy have been used to characterize the as-corroded samples. Besides, the Mg2+ concentration in PBSs has been determined by inductively coupled plasma atomic emission spectrum. Findings It has been found that pure Mg suffers pit corrosion, and AZ31 initially undergoes pit corrosion and then uniform corrosion dominates with an extended immersion duration. However, AZ91 exhibits the uniform corrosion with the highest corrosion rate among the three materials. Besides, the corrosion product layer on AZ31 has the best compactness and corrosion resistance. Originality/value The findings add depth in understanding the corrosion of pure Mg and its alloys in PBS and also have guiding significance in exploring the effects by alloyed elements to develop new biomaterials with better performance.

In this study, a wet chemical method was used to produce iron-doped CuO nanostructures. Cyclic voltammetry was employed to record sensor signals in a saline phosphate buffer solution of pH 7.3. Iron added into CuO nanostructures contributed electrons to the conduction band of CuO, showing a well-resolved electro-oxidation peak for uric acid. The developed sensor exhibits a wide linear range of uric acid concentrations from 0.05 mM to 4 mM. The limit of detection for the sensor was found to be 0.01 mM. The sensor is highly selective, sensitive, and stable. The results of the in vitro analysis of uric acid motivated the researchers to measure the uric acid from the marine shellfish Perna viridis and razor clam Solen dactylus. The obtained results reveal that the proposed sensor will help to avoid the gout and could be used as an early safeguard of human health.

ABSTRACT A novel approach was developed to extract the extracellular DNA (eDNA), i.e. the free DNA outside the microbial cell, compared to the intracellular DNA (iDNA). The two DNA fractions were investigated in seven long-ripened cheeses. Among different buffer solutions tested, EDTA 0.5 M at pH 8 enabled a mild homogenization of cheese samples and the highest eDNA recovery. The extraction protocol was tested on single strains of lactic acid bacteria characterizing many Italian long-ripened cheeses, such as Streptococcus thermophilus, Lactobacillus helveticus, and Lactobacillus rhamnosus. The method resulted suitable for eDNA extraction because it minimized cell-lysis, avoiding the leakage of iDNA from the cells. The yields of eDNA, ranging from 0.01 to 0.36 µg g−1 cheese, were generally higher than the iDNA, indicating that autolytic phenomena prevailed over intact cells after 8–12 months of ripening. In four of the seven cheeses, the same LAB species were detected in the eDNA and iDNA fractions by length-heterogeneity PCR, while in the remaining three samples, a higher number of species was highlighted in the eDNA compared to the corresponding iDNA. The sequential extraction of eDNA and iDNA can be applied to obtain additional information on the composition of the bacterial community in long-aged cheeses. Determination of extracellular and intracellular DNA to obtain a more complete bacterial profile of long-ripened cheeses.

In this paper, surface-enhanced Raman spectroscopy (SERS) was used to investigate the adsorption process of cysteine (Cys). Studies were carried out in the presence of phosphate-buffered saline solution (PBS), at pH 7.4, and acidified to pH 5, 3, and 1, on the surface of Ti for implant application. In situ SERS spectra obtained for the Cys/Ti solution system, after 24 h of immersion time, indicated that the buffer solution strongly influences the adsorption behavior of Cys on the Ti surface. This results in a decrease in Cys adsorption on the Ti surface, in the range of pH 7.4 to 3. The strong interaction between a sulfur atom of Cys and a Ti surface was observed only at pH = 1, under strongly acidic conditions. In contrast, ex situ SERS spectra recorded for the same samples but in a dried Cys/Ti system show a completely different behavior of Cys on the Ti surface. Formation of a disulfide (S-S) bond has occurred as a result of the dimerization or aggregation of Cys molecules on the Ti surface. Detailed analysis of the adsorption behavior of Cys on the Ti surface can be very important in the preparation of bioactive materials (i.e., coated by organic layers).

The chemical coupling of NiO nanostructures with thermally treated multiwall carbon nanotubes (MWCNTs) is not reported as it provides an enhanced dispersion of composite material in water. The dispersion of MWCNTs has been considered a big challenge. For this purpose, we first thermally treated MWCNTs at 1000°C in air for 30 min. Then, thermally treated MWCNTs were chemically coupled with NiO nanostructures by a hydrothermal method. The material characterization in terms of structure, morphology, and composition is well studied by different analytical techniques. The NiO composite (sample 2) with highest weight of MWCNTs had a leaf-like morphology and it exhibits a cubic phase of NiO. Cyclic voltammetry (CV) was used to study the electrochemical activity of prepared composite material towards the oxidation of uric acid in the phosphate buffer solution of pH 7.0. Sample 2 showed a well-behaved anodic peak with enhanced peak current and exhibited a linear range from 0.01  mM to 2.5 mM for uric acid with a low limit of detection 0.001mM. Sample 2 was found to be very selective under the environment of competing interferents such as urea, glucose, lactic acid and ethanol. This sample exhibits significant stability, thus it is a potential protocol for the monitoring of uric acid from real samples. This study provides a low-cost platform for the fabrication of efficient materials for various applications such as batteries, fuel cells and water splitting.