Aqueous Solutions Of Calcium Research Articles

Comparative Analysis of Crosslinking Methods and Their Impact on the Physicochemical Properties of SA/PVA Hydrogels.

Hydrogels, versatile materials used in various applications such as medicine, possess properties crucial for their specific applications, significantly influenced by their preparation methods. This study synthesized 18 different types of hydrogels using sodium alginate (SA) and two molecular weights of polyvinyl alcohol (PVA). Crosslinking agents such as aqueous solutions of calcium (Ca2+) and copper (Cu2+) ions and solutions of these ions in boric acid were utilized. The hydrogels were subjected to compression strength tests and drying kinetics analysis. Additionally, six hydrogel variants containing larger PVA particles underwent Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) post-drying. Some samples were lyophilized, and their surface morphology was examined using scanning electron microscopy (SEM). The results indicate that the choice of crosslinking method significantly impacts the physicochemical properties of the hydrogels. Crosslinking in solutions with higher concentrations of crosslinking ions enhanced mechanical properties and thermal stability. Conversely, using copper ions instead of calcium resulted in slower drying kinetics and reduced thermal stability. Notably, employing boric acid as a crosslinking agent for hydrogels containing heavier PVA molecules led to considerable improvements in mechanical properties and thermal stability.

MOLECULAR MECHANISM OF RELAXATION ABSORPTION OF ULTRASONIC WAVES IN AN AQUEOUS SOLUTION OF CALCIUM ACETATE

The absorption of ultrasonic waves in the frequency range from 6 to 146 MHz in aqueous solutions of sodium acetate, sodium chloride and calcium has been studied. It was found that only in solutions of calcium cations and acetate anion present simultaneously, relaxation absorption of ultrasonic waves is observed. The experimental data obtained indicate that the observed relaxation absorption of ultrasound in the studied frequency range by an aqueous solution of calcium acetate is associated with the interaction of the acetate anion with the calcium cation in the solution.

A PHBA-functionalized organic-inorganic hybrid polyoxometalate as a luminescent probe for selectively sensing chromium and calcium in aqueous solution

Detection of trace metal ions in drinking as well as irrigation water is crucial in understanding their roles among living humans and animals. Herein, an organic PHBA-functionalized polyoxometalate (POM) derivative [N(CH3)4]3K2Eu(PHBA)(H2O)2(α-PW11O39)]·7H2O (1) (PHBA = p-hydroxybenzoic acid) was successfully synthesized which acts as a luminescent probe for selective sensing of chromium and calcium in aqueous solution. The aqueous solution photoluminescence properties of 1 were carefully investigated, indicating PHBA ligand can sensitize the luminescence of Eu3+ ion in 1. The time-resolved emission spectroscopy was also performed to authenticate the energy transfer from π-π* transition of PHBA group to Eu3+ ion. The sensing properties of 1 were performed on Cd2+, Cr3+, Ba2+, K+, Li+, Pb2+, Zn2+, Al3+, Ag+, Hg2+, Co2+, Sr2+, Ca2+, Na+, Mg2+ ions in aqueous solution, and the photoluminescence intensity for Cr3+ ion display a quenching phenomenon, whereas, Ca2+ ion displays an enhancement signal in their photophysical behavior. The detection limits for detecting Cr3+ and Ca2+ ion were 1.423 μM and 0.676 mM, respectively. In the detection process of Cr3+ ion, the values of quenching rate constant (Kq) were varied from 4.34 × 106 L (mol s)−1 to 4.29 × 109 L (mol s)−1, which were lower than the value of the maximum scatter collision quenching constant (2.0 × 1010 L (mol s)−1). The results reveal that the quenching mechanism between 1 and Cr3+ ion can be attributed to dynamic collision quenching mechanism. Furthermore, the active sites for sensing Cr3+ and Ca2+ ions also have been investigated, determining the different interaction mechanisms exist in detection of Cr3+ and Ca2+ ions in solution.

Synthesis and Properties of Calcium, Strontium, and Barium Uranates

Pure crystalline compounds MIIU3O10 · n H2O (MII = Ca, Sr) and BaU2O7 · 3 H2O were obtained by reactions of synthetic schoepite (UO3 · 2.25 H2O) with aqueous solutions of calcium, strontium, and barium nitrates under hydrothermal conditions at 200°C and pH 7‒8. Their structure, dehydration, and thermal decomposition were studied by chemical analysis, X-ray fluorescence spectrometry, X-ray powder diffraction, IR spectroscopy, and thermogravimetric analysis.

Interactions between octenyl-succinic-anhydride-modified starches and calcium in oil-in-water emulsions

This study examined the effects of the interactions between octenyl succinic anhydride (OSA)-modified starches and calcium on the structure and stability of emulsions at neutral pH and pH 3.0. OSA-modified starches were characterized by Fourier transform infrared spectroscopy, and the interactions between starch and calcium in aqueous solutions and in emulsions were determined using turbidity, light scattering and confocal scanning laser microscopy. At pH 7.0, the OSA-modified starch solutions containing CaCl2 had greater turbidity and lower negative charge. The OSA-modified starch solutions at pH 3.0 had greater turbidity and lower zeta-potential than those at pH 7.0, but were not affected by the addition of CaCl2. At pH 7.0, the particle size of OSA-modified starch emulsions increased and the size distribution changed from monomodal to bimodal when the concentration of added CaCl2 increased because of both flocculation and coalescence between emulsion droplets. Increasing the degree of substitution (DS) of the OSA-modified starch led to greater stability to coalescence but lower creaming stability of emulsions. At pH 3.0, the emulsions had larger particle size, remained stable and were not affected by the addition of CaCl2. The observation of the coalescence occurred in the Ca2+-induced flocculated emulsions stabilized by low DS OSA-modified starches provided interesting information for emulsification and stability of starch-stabilized emulsions and application of modified starches.

Short communication: Electrospinning of casein/pullulan blends for food-grade applications

Electrospinning is a complex process that produces fibers with diameters on the micrometer or nano-scale from an electrified jet of a polymer solution. The objective of this study was to create electrospun fibers for food use from aqueous solutions of calcium (CaCAS) or sodium caseinate (NaCAS). Fibers were not formed from electrospinning of solutions of either caseinate (CAS) at 50°C, but were formed from blends of either CAS solution with aqueous solutions of the food-grade polysaccharide, pullulan (PUL), when using mass ratios from 2:1 to 1:4 of PUL/CAS. The CAS in the spinning solutions ranged from 3 to 15% (wt/wt) and the PUL ranged from 5 to 15% (wt/wt). The PUL/CaCAS 1:2 fibers showed the lowest fiber diameter sizes (FDS) of 172±43nm, as determined by scanning electron microscopy, and were smaller in size than fibers electrospun from 15% (wt/wt) PUL solution. The PUL/NaCAS solutions were more viscous and formed fibers with occasional branching and less uniform FDS at higher NaCAS contents. Reductions in NaCAS in these solutions reduced viscosity and improved jet stabilities with consequent improvement in fiber morphology leading to more uniform FDS. Fibers with less defects and more homogeneous FDS were formed from PUL/CaCAS blends with more CaCAS, showing that each CAS interacted differently with PUL and formed the best fibers at different solution conditions. Calcium bridging may also underlie the anomalous behavior of the PUL/CaCAS blends by forming crosslinks with the phosphoserine residues, further enabling chain entanglements for fiber formation. The PUL/NaCAS fibers tended to be larger than the PUL/CaCAS fibers, which may also be due to other factors such as solution surface tension and conductivity, which also affect fiber quality and size. The shear viscosities at 100 s−1 of the solutions producing fibers were within the range of 0.07 to 0.16 Pa/s, with the smallest standard deviations in FDS noted for solutions with viscosities within about 25% that of PUL. This is the first example of caseinate fibers prepared using a food-grade carrier rendering a product with potential use in food and packaging applications.

Development of composite scaffolds in the system of gelatin−calcium phosphate whiskers/fibrous spherulites for bone tissue engineering

Calcium phosphate whiskers have been suggested to be effective as the reinforcement in improving mechanical properties of composite biomaterials. Therefore, composite scaffolds of varying compositions were prepared by freeze drying of gelatin foams containing increasing amounts of calcium phosphate whiskers/fibrous spherulites, up to 50wt%. The whiskers were attempted to synthesize in acidic solutions under thermal conditions using two different methods: aging of a highly crystalline beta-tricalcium phosphate powder in H2O2 solution, and the precipitation−hydrolysis method using aqueous solutions of calcium and phosphate ions in HNO3 solution and urea as an additive. The morphology and phase analysis of the whiskers were studied by scanning electron microscopy (SEM) and X-ray diffractometry (XRD), respectively. The results proved that the whiskers could not be obtained by first method at an appropriate period, but using the second method, a mixed plate-like and long whiskers, and fibrous spherulites could be formed. The XRD patterns revealed the biphasic mixture of octacalcium phosphate (OCP) and dicalcium phosphate anhydrate (DCPA). The composite scaffolds containing whiskers obtained by freeze drying were characterized by SEM, Fourier transform infrared spectroscopy and compressive mechanical test. Scaffolds with interconnective pores in a range of 150–350μm and porosity of 65–74%, as well as homogenous dispersion of the whiskers could be produced which indicates their potential to use in bone tissue engineering applications. The prepared scaffolds showed the compressive yield strength of 4.3−6.2MPa and Young modulus of 28−38MPa. In the view of mechanical and microstructural features, the composite of 25wt% calcium phosphate phase was introduced as the optimal composite for bone tissue engineering.

Energy-resolved CT imaging with a photon-counting silicon-strip detector

Photon-counting detectors are promising candidates for use in the next generation of x-ray computed tomography (CT) scanners. Among the foreseen benefits are higher spatial resolution, better trade-off between noise and dose and energy discriminating capabilities.Silicon is an attractive detector material because of its low cost, mature manufacturing process and high hole mobility. However, it is sometimes overlooked for CT applications because of its low absorption efficiency and high fraction of Compton scatter. The purpose of this work is to demonstrate that silicon is a feasible material for CT detectors by showing energy-resolved CT images acquired with an 80 kVp x-ray tube spectrum using a photon-counting silicon-strip detector with eight energy thresholds developed in our group.We use a single detector module, consisting of a linear array of 50 0.5 × 0.4 mm detector elements, to image a phantom in a table-top lab setup. The phantom consists of a plastic cylinder with circular inserts containing water, fat and aqueous solutions of calcium, iodine and gadolinium, in different concentrations.By using basis material decomposition we obtain water, calcium, iodine and gadolinium basis images and demonstrate that these basis images can be used to separate the different materials in the inserts. We also show results showing that the detector has potential for quantitative measurements of substance concentrations.

Chemical precipitation of sulfur nanoparticles from aqueous solutions

Process of formation and coarsening of sulfur nanoparticles deposited from aqueous solutions of calcium and sodium polysulfides and sodium thiosulfate and from solutions of elementary sulfur in a mixture of hydrazine hydrate and monoethanolamine was considered. The sulfur nanoparticles were characterized with a laser analyzer of particle sizes, X-ray diffraction analysis, and electron probe microscopy. It was shown that the sizes of primary particles strongly depend on the concentration of an acid and on the molar ratio between the sulfur-containing solutions and the acid. The antifungal effects of sulfur with nano- and micrometer dimensions were compared. The experimental results demonstrated a strong antifungal effect of sulfur nanoparticles on various kinds of fungi.

Characterization and Degradation of Masonry Mortar in Historic Brick Structures

This study characterized mortars from a masonry fortification in Charleston, South Carolina (USA), harbor where construction was during the period 1839–1860. This location for analysis was interesting because of the sea water impingement on the structure. The study was included as part of an overall structural assessment with restoration as an objective. The mortars were found to be cement, lime, and sand mixtures in proportions similar to ones expected from the historic literature, that is, one part binder to two parts of sand. The binder was found to be American natural cement, a substance analogous to the European Roman cement. The results suggest that the thermal history of the cement during manufacturing affected setting rate explaining why the cements were considered as variable during the mid-to-late 1800s. Fine pores were found in mortars exposed to sea water resulting from corrosion. Contemporary natural cement was shown to release calcium in aqueous solution. While this release of calcium is necessary for setting in natural and Portland cements, excessive calcium solution, as exacerbated by sea water contact and repointing with Portland cement mortars, was shown to result in brick scaling or decay through cryptoflorescence.

Continuous-flow precipitation of hydroxyapatite in ultrasonic microsystems

This paper describes the continuous-flow precipitation of hydroxyapatite Ca5(PO4)3OH (HAp) in two ultrasonic microreactors using diluted aqueous solutions of calcium and phosphate at 37°C. Precipitation of HAp was first carried out in a tubular microreactor immersed in an ultrasonic bath, where single-phase (laminar) flow and segmented gas–liquid flow were both evaluated. The single-phase flow study was then conducted in a novel microfluidic device developed at MIT. It consists of a Teflon stack microreactor with an integrated piezoelectric element (Teflon microreactor), thereby allowing the direct transmission of ultrasound to the reactor. Both microsystems produce single-phased calcium-deficient carbonated HAp under near-physiological conditions of temperature and pH. In addition, particle aggregation and primary particle size were significantly reduced in the segmented-flow tubular microreactor and in the Teflon microreactor. The as-prepared particles mostly consisted of rod-like shape nanoparticles with dimensions below 100nm in length and around 20nm in width. Further, the microreactors used yielded HAp particles with improved characteristics, namely higher crystallinity and less carbonate contamination, when compared to the HAp particles produced in a stirred tank batch reactor.

Controlling the Formation of Hydroxyapatite Nanorods with Dendrimers

A facile procedure to direct the formation of hydroxyapatite (HAP) in preference to all other calcium phosphate phases and control over nanoparticle size distribution and morphology, with potential application in biomedical implants, is reported. The synthesis is performed in the presence of amine terminated diaminobutane poly(propylene imine) dendrimer (DAB). Aqueous solutions of calcium, phosphate, and DAB were used at different calcium:DAB molar ratios, viz. 2:1, 1:1, and 1:2 and the resulting suspensions were either kept at room temperature or hydrothermally treated at 80°C for 16 h, or at 130°C for 6 h. The resulting nanomaterials were fully characterized in terms of their physicochemical properties by means of XRD, TEM, SEM, and FTIR. It was found that DAB affects nucleation and crystal growth, as, in all cases, nanorods of hexagonal HAP with homogeneous and narrow size distributions (with mean sizes ranging from 10 nm × 5 nm up to 81 nm × 22 nm depending on synthesis conditions) were obtained.

Preparation of nanosized sulfur particles from aqueous solutions of calcium and sodium polysulfides

Preparation of nanosized sulfur from solutions of calcium and sodium polysulfides was considered. Via measuring the optical density of dilute aqueous solutions of the polysulfides the sulfur hydrosol particle size was studied in relation to the storage time and viscosity of the solutions. It was found that the sulfur nanoparticle size can be controlled by varying the viscosity of solution and introducing polymer additions. The temporal stability of nanosized sulfur hydrosol particles was examined.

Langmuir-Blodgett composite films for the selective determination of calcium in aqueous solutions

A sensitive membrane of a new type was suggested for the determination of calcium ions in aqueous solutions. Polylayer membranes were formed by the Langmuir-Blodgett method from octadecylamine and 1,2-bis-(2-aminophenoxy)ethane-N,N,N,N-tetraacetic acid. When brought in contact with an aqueous solution of a calcium salt, the ultrathin film sorbs metal ions. The chelator then transports metal ions over the whole membrane volume, and the ions are accumulated in the form of calcium hydroxide crystallites in regions enriched in the diphilic base. The main analytic parameters were determined by piezoquartz weighing, electrochemical impedance spectroscopy, and surface plasmon resonance spectroscopy. The response of sensor elements of this type was shown to be a linear function of the logarithm of the concentration of calcium ions over the concentration range 10−8–10−1 mol/l at the contact time between the film and the solution under study no more than 10 s. The conclusion was drawn that the membranes obtained remained highly sensitive with respect to calcium ions in 0.1 M solutions of NaCl and were selective with respect to other biologically relevant cations.

Solubility of α-and β-gypsum in aqueous solutions of calcium, magnesium, and sodium chlorides

The interaction of multicomponent water-salt systems including calcium, magnesium, and sodium chlorides, gypsum, air, and water were studied by the methods of thermodynamic modeling. The solubility of α-CaSO4 · 2H2O and β-CaSO4 · 2H2O were determined in aqueous solutions of calcium, magnesium, and sodium chlorides and their mixtures at 25°C and carbon dioxide partial pressure of 10−1.53 kPa, metal chloride concentrations of 10−4 to 1.0 mol/kg H2O, and their molar ratio of 1: 1.

A novel ultra-sensing composed Langmuir–Blodgett membrane for selective calcium determination in aqueous solutions

A novel sensing membrane to determine concentration of calcium in aqueous solutions is demonstrated. The multilayer organized membranes were formed from octadecylamine and calcium chelator 1,2-bis-(2-aminophenoxy)ethane- N, N, N, N-tetraacetic acid via Langmuir–Blodgett (LB) technique. The structure and composition of membrane enable the conversion of calcium bound by the chelator to the metal hydroxide and its accumulation in the film, thus maintaining the availability of ligands for continuous binding. The formation of Ca(OH) 2 crystals in the film was verified by optical microscopy. Major analytical parameters were determined by means of quartz crystal microbalance. The logarithm of the sensor's response was a linear function of calcium concentrations ranging from 10 −8 to 10 −1 mol L −1, the response time was 10 s. The repeatability of the response determined as relative standard deviation and measured by five membranes for each of eight calcium standards was 4.2 ± 0.3%. The membrane can be applied to the calcium determination in solution of 0.1 M NaCl at neutral pH and is selective with respect to other biologically relevant cations. The electrochemical impedance and surface plasmon resonance spectroscopies were used to demonstrate the applicability of the membrane to different registration methods.

Erosion resistance of 40Kh steel after mechanical-pulse treatment

The mechanical-pulse treatment of 40Kh steel by means of frictional contact of the working surface with a special tool in different technological media enhances the resistance of steel to cavitation- erosion fracture. Mechanical-pulse treatment in a technological medium based on aqueous solutions of calcium and magnesium mineral salts enhances the resistance of 40Kh steel to cavitation- erosion fracture over the entire range of cavitation intensities under study.

New Ca2+ fluoroionophores based on the BODIPY fluorophore.

Calcium (Ca(2+)) fluoroionophores are useful in cell-based functional assays of G-protein coupled receptor (GPCR) activation or ion channel modulation. In this paper we describe new calcium probes that improve or overcome certain deficiencies in existing probes. These new fluoroionophores are based on acylation of amino-BAPTA [BAPTA = glycine, N,N'-(1,2-ethanediyl-bis(oxy-2,1-phenylene)) bis(N-(carboxymethyl))] with fluorescent BODIPY(R) propionates [BODIPY = 4,4-difluoro-5,7-dimethyl- 4-bora-3a,4a-diaza-s-indacene]. The resulting probes show high affinity to aqueous calcium solutions, and respond to calcium binding with significant fluorescence increases. The BODIPY fluorophores are uncharged and their fluorescence is pH-insensitive. The wide range of excitation/emission wavelength choices available within the BODIPY fluorophore series allows several different colors of new calcium indicators to be prepared. Cell permeable versions respond well with increasing fluorescence intensities in live cells after calcium influx.

Paper Conservation Using Aqueous Solutions of Calcium Hydroxide/Methyl Cellulose 2. The influence of accelerated ageing temperature on properties of treated paper

Sur la base des resultats obtenus par le vieillissement accelere de papiers fabriques a partir de cellulose de bois tendre blanchie et de chiffons, l'energie d'activation apparente de la degradation de la cellulose a ete estimee a 103-106 kl/mol. Les temperatures de vieillissement de 40° et 60°C ne semblent pas appropriees pour etudier la degradation de la cellulose dans les echantillons traites a l'hydroxyde de calcium Ca(OH)2 ou Ca(OH)2 + solutions de conservation de MC parce que dans ces conditions aucun changement du degre de polymerisation ne peut etre observe. Les resultats obtenus ont demontre qu'une reduction de la resistance des feuilles de papier traitees par ces solutions au cours du vieillissement accelere etait causee par la degradation de la cellulose de methyle. L'augmentation de la reserve alcaline obtenue par le traitement fournit au papier une meilleure protection contre la degradation hydrolytique de la cellulose. Le renforcement de la resistance du papier de pâte de sulphite de bois tendre blanchi, traite a 40° et 60°C, est le resultat d'une formation de corne qui est due plutot a la formation de ponts d'hydrogene qu'a un reseau de liaisons covalentes.

Paper Conservation Using Aqueous Solutions of Calcium Hydroxide/Methyl Cellulose: 1. Preparation of the solution

Les resultats du traitement de conservation des papiers traites et non traites au moyen de solutions aqueuses de Ca(OH) 2 /methylcellulose preparees de facons differentes ont ete soumis a differents tests de mesures des proprietes chimiques, mecaniques et optiques. Afin de determiner la permanence du papier a long terme les echantillons de papier ont ete soumis a un traitement de vieillissement accelere. Les resultats revelent que la solution preparee a partir des deux substances sous leur forme solide Ca(OH) 2 et la cellulose de methyle (solid phase method, SFM) aboutit a une reserve alcaline superieure a celle de la solution preparee a partir du melange des deux substances liquides isolees (liquid phase method LFM). La reserve alcaline superieure deposee par SFM assure une meilleure protection lors du traitement de vieillissement accelere.