Binding Of Calcium Ions Research Articles

Templating effect of alginate and related biopolymers as hydration accelerators for calcium alumina cement - A mechanistic study

In earlier publications it has been demonstrated that alginate and similarly structured biopolymers unexpectedly accelerate the hydration of calcium alumina cement. Here, this effect is investigated by applying 27Al MAS NMR spectroscopy and XRD technique to track the hydration reaction and identify the hydration products. In the presence of these biopolymers an earlier consumption of clinker phases was observed indicating a shortened induction period. The subsequent formation of hydration products occurs earlier, resulting in the formation of C-A-H phases (CAH10 and C2AH8). No further reaction products like intercalation compounds were detected. An in-depth mechanistic study revealed that alginate does not adsorb on cement, but captures Ca2+ ions from the pore solution, thus resulting in a positively charged biopolymer chain which then attracts [Al(OH)4]− ions to its surface. Through this binding of calcium and aluminate ions and alignment to the alginate molecule, a precursor for calcium aluminate hydrates is formed which acts as a nucleation seed and triggers continued growth into large C-A-H crystals, similar as in related biotemplating processes which are known for calcite or brushite formation.

Structural and functional analyses of organic molecules regulating biomineralization.

Biomineralization by living organisms are common phenomena observed everywhere. Molluskan shells are representative biominerals that have fine microstructures with controlled morphology, polymorph, and orientation of CaCO3 crystals. A few organic molecules involved in the biominerals play important roles in the formation of such microstructures. Analyses of structure-function relationships for matrix proteins in biominerals revealed that almost all matrix proteins have an acidic region for the binding of calcium ion in CaCO3 crystals and interaction domains for other organic molecules. On the other hand, biomineralization of metal nanoparticles by microorganisms were also investigated. Gold nanoparticles and quantum dots containing cadmium were successfully synthesized by bacteria or a fungus. The analyses of components revealed that glycolipids, oligosaccharides, and lactic acids have key roles to synthesize the gold nanoparticle in Lactobacillus casei as reductants and dispersants. These researches about biomineralization will give new insights for material and environmental sciences in the human society.

Functional wheat bread with calcium chelate complexes

Bakery products are promising objects for enrichment with functional food ingredients, as they are mass consumption products. The problem of hypo-elementosis in people makes it advisable to develop functional food ingredients based on easily digestible and safe forms of essential biometals, including calcium. In this study, it has been shown that wheat bread can be enriched with calcium chelate complexes. This functional food ingredient was obtained by complexation of Ca2+ with bioligands of probiotic origin, followed by immobilizing the complexes on dietary fiber of wheat bran. Mixed-ligand systems were obtained by combining a metabolite (lactic acid) and degradation products of peptidoglycans of Lactobacillus delbrueckii subsp. Bulgaricus B-3964. The peptidoglycans of the biomass autolysate were degraded by enzymatic hydrolysis with papain. This resulted in obtaining a mixture that contained amino acids, low molecular weight peptides, and muropeptides, in the concentrations 12.44 mg/cm3, 6.85 mg/cm3, and 2.76 mg/cm3, respectively. The nephelometric method has shown that this mixed-ligand system binds calcium ions in an amount of 18 mg/cm3. The soluble complexes obtained were immobilized on the dietary fiber to solve the problem of concentrating, drying, and dosing these ingredients. It has been proved that immobilization only occurs due to physical sorption that completely releases the active component from the dietary fiber matrix under conditions that simulate the gastrointestinal environment. The functional ingredient developed was added to the classic wheat bread recipe, where it replaced 1 %, 3 %, and 5 % of the flour. Bread was made without pre-fermentation to reduce the total production time and to prevent the ingredient’s biologically active components from being assimilated by yeast during long fermentation. The study of the experimental and control samples of wheat bread has shown that the introduction of chelate complexes of calcium immobilized on dietary fiber causes no deterioration of the physico-chemical parameters of the finished bread: they are all within the limits approved by the regulatory documentation. The sensory properties of the samples with 1 % and 3 % of flour replaced are close to those of the control sample. So 3 % of the ingredient is the recommended amount to be added, as it provides 98 % of the daily requirement of calcium as a functional ingredient and covers about 25 % of the daily allowance of dietary fiber.

Coupling of Conformational Switches in Calcium Sensor Unraveled with Local Markov Models and Transfer Entropy.

Proteins often have multiple switching domains that are coupled to each other and to the binding of ligands in order to realize signaling functions. Here we investigate the C2A domain of Synaptotagmin-1 (Syt-1), a calcium sensor in the neurotransmitter release machinery and a model system for the large family of C2 membrane binding domains. We combine extensive molecular dynamics (MD) simulations with Markov modeling in order to model conformational switching domains, their states, and their dependence on bound calcium ions. Then, we use transfer entropy to characterize how the switching domains are coupled via directed or allosteric mechanisms and give rise to the calcium sensing function of the protein. Our proposed switching mechanism contributes to the understanding of the neurotransmitter release machinery. Furthermore, the methodological approach we develop serves as a template to analyze conformational switching domains and the broad study of their coupling in macromolecular machines.

The Leptospira interrogans LIC10774 is a multifunctional surface protein that binds calcium and interacts with host components

Leptospirosis is a global re-emerging zoonosis, caused by pathogenic bacteria of the genus Leptospira. Humans are infected mainly through contact with contaminated water or soil. The understanding of the molecular mechanisms of leptospirosis through the characterization of unknown outer membrane proteins may contribute to the development of new treatments, diagnostic methods and vaccines. We have identified using bioinformatics analysis a protein that is encoded by the gene LIC10774, predicted to be localized at the leptospiral outer membrane and exhibit beta-roll folding. Surface exposure was confirmed by flow cytometry, ELISA and immunofluorescence-based confocal microscopy. Through circular dichroism spectroscopy and hydrophobic dye binding we have shown that rLIC10774 binds calcium ions, which imposes changes to secondary and tertiary structures. The recombinant protein was capable of binding to several host extracellular matrix and serum components. Therefore, we describe LIC10774 as a calcium-binding protein exposed in the outer surface of pathogenic leptospires with possible multifunctional roles in adhesion to host tissues, evasion of the immune system and participation in dissemination processes during leptospirosis. In addition, we hypothesize that the calcium binding is important for temperature-dependent functional roles during leptospirosis.

Mouse S100G protein exhibits properties characteristic of a calcium sensor

Bovine S100 G (calbindin D9k, small Ca2+-binding protein of the EF-hand superfamily) is considered as a calcium buffer protein; i.e., the binding of Ca2+ practically does not change its general conformation. A set of experimental approaches has been used to study structural properties of apo- and Ca2+-loaded forms of mouse S100 G (81.4% identity in amino acid sequence with bovine S100 G). This analysis revealed that, in contrast to bovine S100 G, the removal of calcium ions increases α-helices content of mouse S100 G protein and enhances its accessibility to digestion by α-chymotrypsin. Furthermore, mouse apo-S100 G is characterized by a decreased surface hydrophobicity and reduced tendency for oligomerization. Such behavior is typical of calcium sensor proteins. Apo-state of mouse S100 G still has rather compact structure, which can be cooperatively unfolded by temperature and GdnHCl. Computational analysis of amino acid sequences of S100 G proteins shows that these proteins could be in a disordered state upon a removal of the bound calcium ions. The experimental data show that, although mouse apo-S100 G is flexible compared to the Ca2+-loaded state, the apo-form is not completely disordered and preserves some cooperatively meting structure. The origin of the unexpectedly high stability of mouse S100 G can be rationalized by an exceptionally strong association of its N- and C-terminal parts containing the EF-hands I and II, respectively.

Ruolo del citrato nel metabolismo osseo

Citrate is an organic compound involved in tricarboxylic acid cycle, regulation of acid-base balance, lipid metabolism and bone formation. The 90% of body citrate is deposited in bone tissue and is released with calcium ions during bone resorption; therefore, bone resorption contributes to maintain normal plasma levels of citrate together with kidney excretion. The parallel release of citrate and calcium from bones decreases the possibility of calcium-phosphate precipitation in soft tissues, as citrate can bind calcium ions in organic fluids. Citrate may also take part to the bone formation as it sustains the correct mineralization of bone organic matrix: its molecule binds calcium ions at the surface of hydroxyapatite nanocrystals and maintains the correct spatial disposition of nanocrystals, thus, stabilizing the structure of bone lamellae and sustaining biomechanical characteristics of bone tissue. Multiple studies observed that citrate administration significantly increased areal and volumetric bone mineral density at different locations of 1-2% per year and improved bone resorption markers as well. Therefore, it has been hypothesised a therapeutic role of citrate in osteoporosis; however, this role has to be better clarified to understand its real anti-fracture effect.

Structural Changes of Sarco/Endoplasmic Reticulum Ca2+-ATPase Induced by Rutin Arachidonate: A Molecular Dynamics Study.

Sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) maintains the level of calcium concentration in cells by pumping calcium ions from the cytoplasm to the lumen while undergoing substantial conformational changes, which can be stabilized or prevented by various compounds. Here we attempted to clarify the molecular mechanism of action of new inhibitor rutin arachidonate, one of the series of the acylated rutin derivatives. We performed molecular dynamics simulations of SERCA1a protein bound to rutin arachidonate positioned in a pure dipalmitoylphosphatidylcholine bilayer membrane. Our study predicted the molecular basis for the binding of rutin arachidonate towards SERCA1a in the vicinity of the binding site of calcium ions and near the location of the well-known inhibitor thapsigargin. The stable hydrogen bond between Glu771 and rutin arachidonate plays a key role in the binding. SERCA1a is kept in the E2 conformation preventing the formation of important salt bridges between the side chains of several residues, primarily Glu90 and Lys297. All in all, the structural changes induced by the binding of rutin arachidonate to SERCA1a may shift proton balance near the titrable residues Glu771 and Glu309 into neutral species, hence preventing the binding of calcium ions to the transmembrane binding sites and thus affecting calcium homeostasis. Our results could lead towards the design of new types of inhibitors, potential drug candidates for cancer treatment, which could be anchored to the transmembrane region of SERCA1a by a lipophilic fatty acid group.

Calcium Buffering by Fluorescent Indicators - Implications and Easy Solutions

Fluorescent indicators are powerful tools to determine intracellular free Ca2+ concentrations ([Ca2+]). Although their properties vary widely, indicators share common design and operation principles. Being composed of a Ca2+ binding moiety, usually BAPTA-derived, and a fluorophore such as fluorescein, an indicator must bind calcium ions to change its fluorescence. Therefore, within cells, indicators compete with the endogenous buffers for calcium and act as additional buffers, which, in turn, can thwart comparisons of indicator responses and complicate estimating free [Ca2+] within the cell ([Ca2+]in). As lower indicator concentrations tend to report higher [Ca2+], we hypothesized that the true (i.e. indicator-free) [Ca2+]in could be determined by extrapolating the reported [Ca2+]in to the indicator free environment. Although conceptually similar to predecessors, we present a steady state method that avoids the complexities of earlier approaches, and requires only data collected in AM ester-loaded cells. As such, it can be applied to determine the indicator-independent peak [Ca2+]in that is induced by any stimulus in any cell type. To test this approach, we used fura-2 in well-defined in vitro systems and found that it estimated not only [Ca2+]in, but also, albeit less accurately, the concentration and affinity of endogenous buffers. When applied to data collected in fura-2 loaded neurons depolarized with 50 mM K+, the method estimated an indicator independent [Ca2+]in in resting (22 nM) and stimulated (1.18 µM) neurons and characterized the endogenous buffer (∼600 µM) as having relatively low affinity (0.78≤Kb≤1.63 µM), results close to those reported previously. While the method does not account for indicator-distorted Ca2+ decay rates (a consequence of omitting the time component), it does create a simple and general way to fix peak [Ca2+] amplitudes, the values that are most often measured and compared in routine Ca2+ imaging experiments.

Exploring the Structural Elements Responsible for Cis-Homodimerization of Inner Ear Cadherin-23

Cadherin-23 (CDH23) is an enormous protein essential for hearing, balance, and proper eyesight. There are over 100 mutations in CDH23 that affect these processes with varying severity, some leading to deafness, balance disorders, and progressive blindness (Usher Syndrome). In the inner ear, CDH23 makes up the upper half of a proteinaceous filament known as the tip link, which is essential for hearing. Upon stimulation by sound or head movements, the tip link is stretched and conveys force to open the ion channels in the inner ear, thereby leading to the conversion of vibrational stimulus into electrical signals interpreted by the brain as sound. CDH23 is a non-classical cadherin with 27 extracellular cadherin (EC) repeats and a membrane adjacent domain (MAD28). The EC repeats are connected by a linker region containing highly conserved residues that bind calcium ions essential for tip-link function. Electron microscopy images suggest that CDH23 exists as a cis-homodimer within the tip link, however, the structural elements mediating this dimerization are not well determined. To better understand inner-ear mechanotransduction at the molecular level, we have solved high- resolution X-ray crystal structures of 18 CDH23 EC repeats along with 13 of the 26 EC linker regions (Jaiganesh et al., 2018). Here, we present several biochemical experiments that suggest potential sites of parallel dimerization on the extracellular domain of CDH23. Additionally, we present structures of various fragments of CDH23 allowing for closer analysis of deafness causing mutations. These results provide information on the cis-homodimerization of CDH23 and provide deeper insights about how mutations can result in inherited deafness.

Beneficial factors for biomineralization by ureolytic bacterium Sporosarcina pasteurii

BackgroundThe ureolytic bacterium Sporosarcina pasteurii is well-known for its capability of microbially induced calcite precipitation (MICP), representing a great potential in constructional engineering and material applications. However, the molecular mechanism for its biomineralization remains unresolved, as few studies were carried out.ResultsThe addition of urea into the culture medium provided an alkaline environment that is suitable for S. pasteurii. As compared to S. pasteurii cultivated without urea, S. pasteurii grown with urea showed faster growth and urease production, better shape, more negative surface charge and higher biomineralization ability. To survive the unfavorable growth environment due to the absence of urea, S. pasteurii up-regulated the expression of genes involved in urease production, ATPase synthesis and flagella, possibly occupying resources that can be deployed for MICP. As compared to non-mineralizing bacteria, S. pasteurii exhibited more negative cell surface charge for binding calcium ions and more robust cell structure as nucleation sites. During MICP process, the genes for ATPase synthesis in S. pasteurii was up-regulated while genes for urease production were unchanged. Interestingly, genes involved in flagella were down-regulated during MICP, which might lead to poor mobility of S. pasteurii. Meanwhile, genes in fatty acid degradation pathway were inhibited to maintain the intact cell structure found in calcite precipitation. Both weak mobility and intact cell structure are advantageous for S. pasteurii to serve as nucleation sites during MICP.ConclusionsFour factors are demonstrated to benefit the super performance of S. pasteurii in MICP. First, the good correlation of biomass growth and urease production of S. pasteurii provides sufficient biomass and urease simultaneously for improved biomineralization. Second, the highly negative cell surface charge of S. pasteurii is good for binding calcium ions. Third, the robust cell structure and fourth, the weak mobility, are key for S. pasteurii to be nucleation sites during MICP.

Understanding Calcium-Dependent Conformational Changes in S100A1 Protein: A Combination of Molecular Dynamics and Gene Expression Study in Skeletal Muscle.

The S100A1 protein, involved in various physiological activities through the binding of calcium ions (Ca2+), participates in several protein-protein interaction (PPI) events after Ca2+-dependent activation. The present work investigates Ca2+-dependent conformational changes in the helix-EF hand-helix using the molecular dynamics (MD) simulation approach that facilitates the understanding of Ca2+-dependent structural and dynamic distinctions between the apo and holo forms of the protein. Furthermore, the process of ion binding by inserting Ca2+ into the bulk of the apo structure was simulated by molecular dynamics. Expectations of the simulation were demonstrated using cluster analysis and a variety of structural metrics, such as interhelical angle estimation, solvent accessible surface area, hydrogen bond analysis, and contact analysis. Ca2+ triggered a rise in the interhelical angles of S100A1 on the binding site and solvent accessible surface area. Significant configurational regulations were observed in the holo protein. The findings would contribute to understanding the molecular basis of the association of Ca2+ with the S100A1 protein, which may be an appropriate study to understand the Ca2+-mediated conformational changes in the protein target. In addition, we investigated the expression profile of S100A1 in myoblast differentiation and muscle regeneration. These data showed that S100A1 is expressed in skeletal muscles. However, the expression decreases with time during the process of myoblast differentiation.

Divalent Cations and the Divergence of βγ-Crystallin Function.

The βγ-crystallin superfamily contains both β- and γ-crystallins of the vertebrate eye lens and the microbial calcium-binding proteins, all of which are characterized by a common double-Greek key domain structure. The vertebrate βγ-crystallins are long-lived structural proteins that refract light onto the retina. In contrast, the microbial βγ-crystallins bind calcium ions. The βγ-crystallin from the tunicate Ciona intestinalis (Ci-βγ) provides a potential link between these two functions. It binds calcium with high affinity and is found in a light-sensitive sensory organ that is highly enriched in metal ions. Thus, Ci-βγ is valuable for investigating the evolution of the βγ-crystallin fold away from calcium binding and toward stability in the apo form as part of the vertebrate lens. Here, we investigate the effect of Ca2+ and other divalent cations on the stability and aggregation propensity of Ci-βγ and human γS-crystallin (HγS). Beyond Ca2+, Ci-βγ is capable of coordinating Mg2+, Sr2+, Co2+, Mn2+, Ni2+, and Zn2+, although only Sr2+ is bound with comparable affinity to its preferred metal ion. The extent to which the tested divalent cations stabilize Ci-βγ structure correlates strongly with ionic radius. In contrast, none of the tested divalent cations improved the stability of HγS, and some of them induced aggregation. Zn2+, Ni2+, and Co2+ induce aggregation by interacting with cysteine residues, whereas Cu2+-mediated aggregation proceeds via a different binding site.

GmANN, a glutathione S-transferase-interacting annexin, is involved in high temperature and humidity tolerance and seed vigor formation in transgenic Arabidopsis

Plant annexins are proteins with various functions, such as binding calcium ions and negatively charging lipids. Although their importance in plant stress responses has been widely reported, their function in seeds is rarely studied. A putative annexin was found in developing seed of soybean [Glycine max (L.) Merr] in our previous comparative proteomics study. In this study, it was identified as a soybean annexin, GmANN, through sequence analysis. Quantitative real time PCR (qRT-PCR) analysis indicated that the transcription levels of GmANN were increased significantly under high temperature and humidity (HTH) stress. Moreover, GmANN-transgenic Arabidopsis seeds showed greater resistance and higher seed vitality under HTH stress in contrast to the wild type (WT) seeds. GmANN overexpression plants showed increased peroxidase activities, decreased lipid peroxidation levels and decreased reactive oxygen species release levels compared to the WT plants. Yeast two-hybrid and bimolecular fluorescence complementation assays demonstrated that GmANN interacted with soybean glutathione S-transferase (GmGST). Taken together, our results implied that GmANN might take part in response to HTH stress and be involved in seed vigor formation in plant. GmANN, a soybean annexin, plays an important role in response to plant HTH tolerance and in seed vigor.

Radiation-damage investigation of a DNA 16-mer.

In macromolecular crystallography, a great deal of effort has been invested in understanding radiation-damage progression. While the sensitivity of protein crystals has been well characterized, crystals of DNA and of DNA-protein complexes have not thus far been studied as thoroughly. Here, a systematic investigation of radiation damage to a crystal of a DNA 16-mer diffracting to 1.8 Å resolution and held at 100 K, up to an absorbed dose of 45 MGy, is reported. The RIDL (Radiation-Induced Density Loss) automated computational tool was used for electron-density analysis. Both the global and specific damage to the DNA crystal as a function of dose were monitored, following careful calibration of the X-ray flux and beam profile. The DNA crystal was found to be fairly radiation insensitive to both global and specific damage, with half of the initial diffraction intensity being lost at an absorbed average diffraction-weighted dose, D1/2, of 19 MGy, compared with 9 MGy for chicken egg-white lysozyme crystals under the same beam conditions but at the higher resolution of 1.4 Å. The coefficient of sensitivity of the DNA crystal was 0.014 Å2 MGy-1, which is similar to that observed for proteins. These results imply that the significantly greater radiation hardness of DNA and RNA compared with protein observed in a DNA-protein complex and an RNA-protein complex could be due to scavenging action by the protein, thereby protecting the DNA and RNA in these studies. In terms of specific damage, the regions of DNA that were found to be sensitive were those associated with some of the bound calcium ions sequestered from the crystallization buffer. In contrast, moieties farther from these sites showed only small changes even at higher doses.

Rapid Purification of Endotoxin-Free RTX Toxins.

Cytolytic leukotoxins of the repeat in toxin (RTX) family are large proteins excreted by gram-negative bacterial pathogens through the type 1 secretion system (T1SS). Due to low yields and poor stability in cultures of the original pathogens, it is useful to purify recombinant fatty-acylated RTX cytolysins from inclusion bodies produced in E. coli. Such preparations are, however, typically contaminated by high amounts of E. coli lipopolysaccharide (LPS or endotoxin). We report a simple procedure for purification of large amounts of biologically active and endotoxin-free RTX toxins. It is based on the common feature of RTX cytolysins that are T1SS-excreted as unfolded polypeptides and fold into a biologically active toxin only upon binding of calcium ions outside of the bacterial cell. Mimicking this process, the RTX proteins are solubilized from inclusion bodies with buffered 8 M urea, bound onto a suitable chromatographic medium under denaturing conditions and the contaminating LPS is removed through extensive on-column washes with buffers containing 6 to 8 M urea and 1% Triton X-100 or Triton X-114. Extensive on-column rinsing with 8 M urea buffer removes residual detergent and the eluted highly active RTX protein preparations then contain only trace amounts of LPS. The procedure is exemplified using four prototypic RTX cytolysins, the Bordetella pertussis CyaA and the hemolysins of Escherichia coli (HlyA), Kingella kingae (RtxA), and Actinobacillus pleuropneumoniae (ApxIA).

Single-molecule nanomechanical spectroscopy shows calcium ions contribute to chain association and structural flexibility of blood clotting factor VIII

Blood coagulation factor VIII (FVIII) can bind calcium ions and ion-protein interactions appear central importance for both their structure and function in coagulation cascade. However, the mechanism and details of how calcium dependent structure change of proteins to fulfill their function remain to be fully defined. In this work, PeakForce Quantitative Nanomechanics (PF-QNM) mode atomic force microscopy (AFM) was used to map the topography and mechanical properties of FVIII with single protein resolution under different calcium concentrations. The obtained nanomechanical spectroscopy showed that calcium ions play dual roles in the chain association and structural flexibility of FVIII. Low concentration of calcium ions prefer to bind isolated chains and increase their mechanical properties, whereas they link the heavy and light chains to keep the protein re-association under higher ions concentration. Our results provide a novel insight into the mechanistic details of the metal ions on the stability and function of blood clotting proteins.

Virus-Like Particle Facilitated Deposition of Hydroxyapatite Bone Mineral on Nanocellulose after Exposure to Phosphate and Calcium Precursors.

We produced and isolated tobacco mosaic virus-like particles (TMV VLPs) from bacteria, which are devoid of infectious genomes, and found that they have a net negative charge and can bind calcium ions. Moreover, we showed that the TMV VLPs could associate strongly with nanocellulose slurry after a simple mixing step. We sequentially exposed nanocellulose alone or slurries mixed with the TMV VLPs to calcium and phosphate salts and utilized physicochemical approaches to demonstrate that bone mineral (hydroxyapatite) was deposited only in nanocellulose mixed with the TMV VLPs. The TMV VLPs confer mineralization properties to the nanocellulose for the generation of new composite materials.

On the early events of the calcium-induced activation of coagulation factor XIII-A2 and tissue transglutaminase: an in silico study

Both coagulation factor XIII-A2 (FXIII-A2) and tissue transglutaminase (TG2) play distinctive and important roles in homeostasis by crosslinking proteins or peptides via isopeptide bonds. In this present study, a series of microsecond-long all-atom molecular dynamics (MD) simulations were carried out in order to reveal the dynamic, atomic-level events which may contribute to the activation of these proteins via the binding of calcium ions. In addition to previously conducted in vitro and crystallographic studies, further suggestions have been made concerning the calcium binding features of these enzymes. The different systems used for running the simulations were based on the zymogen, computationally cleaved and even the activation peptide (AP-FXIII) free FXIII-A2’ homodimer form. The effects of various ionic environments have also been explored in the simulations of FXIII-A2. Our results suggest that the presence of calcium ions can cause increased AP fluctuations, which ultimately could lead to their relocation on the homodimer surface. The release of these APs seems to be crucial for rotation of the A subunits based on equilibrium MD simulations. The primary evidence for this assumption comes from the predicted principal component eigenvector which is considered as the first, large-scale event of the overall activation process. To get a more accurate atomic-level description, the calcium binding sites of TG2 have also been investigated in our extensive in silico experiments, which suggests the presence of previously unidentified binding sites as well.Communicated by Ramaswamy H. Sarma

Structure formation of gypsum binder with zinc hydrosilicates

Due to high danger of mold fungi spores for humans, it is necessary to develop new fungicidal building materials, especially – materials that help to maintain biosafety in interior rooms. One of such materials is the fungicidal gypsum binder. The aim of the present work was to study the process of structure formation of gypsum in case of the presence of a previously developed fungicidal modifier which is based on hydrosilicate systems with zinc in different quantities. The studies were carried out in accordance with current regulations. The rheological and mechanical properties, including normal density, setting time and compressive strength were determined. The titrimetric method of analysis was used for determination of the content of calcium ions in the solution. It was revealed that the zinc content in the modifier does not affect the mobility of the mixture; however, it changes the rate of formation of the gypsum stone and also affects its strength. In particular, when the ratio ν(Zn)/ν(Si) is equal to 0.9, there was an increase of setting time. The mechanism of the formation of gypsum stone also changes: influence of both constructive and destructive factors simultaneously decreases. The latter was confirmed by the peculiarities of the binding of calcium ions in the presence of a fungicidal modifier.