Thermal decomposition of magnesian kutnahorite

This work investigates the thermal decomposition of magnesian kutnahorite, which belongs to the dolomite group.The DTA curve measured in static air using a small amount of sample (5.0 mg) is quite different from those published previously. This difference might be due to the effect of a self-generated CO₂ atmosphere.In a CO₂ flow of 100 ml min^?1, magnesian kutnahorite decomposes in four steps. Mg-kutnahorite → CaCO₃ + Mg₂MnO₄ + Mn₃O₄ + MgO → CaCO₃ + CaMnO₃ + MgO → CaCO₃ + CaMnO₃ + Ca₂MnO₄ + MgO → CaMnO₃ + Ca₂MnO₄ + MgO + CaO.However, in a mixed gas flow of CO₂ at 95 ml min^?1 and CO at 5 ml min^?1, it decomposes, like dolomite, in two steps. Mg-kutnahorite → CaCO₃ + (Mg,Mn)$\text{O}\text{-}$ → (Ca, Mn)O + (Mg,Mn)$\text{O}\text{-}$.It has been found that the equilibrium redistribution of Mn between (Ca, Mn)$\text{O}\text{-}$ and (Mg, Mn)$\text{O}\text{-}$ is achieved at the second decomposition step. This is supported by theoretical considerations.Consequently, when the O₂ partial pressure in the atmosphere is low enough to keep Mn in a bivalent state, the Mn bearing dolomite group mineral decomposes in a similar manner to dolomite itself.     

Calcium overload is essential for the acceleration of staurosporine-induced cell death following neuronal differentiation in PC12 cells

Differentiation of neuronal cells has been shown to accelerate stress-induced cell death, but the underlying mechanisms are not completely understood. Here, we find that early and sustained increase in cytosolic ([Ca²⁺]_c) and mitochondrial Ca²⁺ levels ([Ca²⁺]_m) is essential for the increased sensitivity to staurosporine-induced cell death following neuronal differentiation in PC12 cells. Consistently, pretreatment of differentiated PC12 cells with the intracellular Ca²⁺-chelator EGTA-AM diminished staurosporine-induced PARP cleavage and cell death. Furthermore, Ca²⁺ overload and enhanced vulnerability to staurosporine in differentiated cells were prevented by Bcl-X_L overexpression. Our data reveal a new regulatory role for differentiation-dependent alteration of Ca²⁺ signaling in cell death in response to staurosporine.     

Programmed Release of Dihydroartemisinin for Synergistic Cancer Therapy Using a CaCO3 Mineralized Metal–Organic Framework

Dihydroartemisinin (DHA) has attracted increasing attention as an anticancer agent. However, using DHA to treat cancer usually depends on the synergistic effects of exogenous components, and the loss of DHA during delivery reduces its effectiveness in cancer therapy. Reported herein is a programmed release nanoplatform of DHA to synergistically treat cancer with a Fe‐TCPP [(4,4,4,4‐(porphine‐5,10,15,20‐tetrayl) tetrakis(benzoic acid)] NMOF (nanoscale MOF) having a CaCO₃ mineralized coating, which prevents DHA leakage during transport in the bloodstream. When the nanoplatform arrives at the tumor site, the weakly acidic microenvironment and high concentration of glutathione (GSH) trigger DHA release and TCPP activation, enabling the synergistic Fe²⁺‐DHA‐mediated chemodynamic therapy, Ca²⁺‐DHA‐mediated oncosis therapy, and TCPP‐mediated photodynamic therapy. In vivo experiments demonstrated that the nanoplatform showed enhanced anticancer efficiency and negligible toxicity.     

Light Irradiation of Mouse Spermatozoa: Stimulation of In Vitro Fertilization and Calcium Signals

Irradiation of mouse spermatozoa by 630 nm He-Ne laser was found to enhance the intracellular calcium levels and fertilizing potential of these cells. The effect of light on calcium transport and on fertilization rate was abrogated in the absence of Ca²⁺during the irradiation time, indicating that the effect of light is Ca²⁺dependent. The stimulatory effect of light on Ca²⁺uptake was abolished in the presence of a voltage-dependent Ca²⁺-channel inhibitor nifedipine, indicating the involvement of a plasma membrane voltage-dependent Ca²⁺channel. Furthermore, the stimulatory effect of light was completely inhibited by the mitochondrial uncoupler FCCP, indicating that laser irradiation might affect the mitochondrial Ca²⁺transport mechanisms. A causal association between laser irradiation, reactive oxygen species (ROS) generation and sperm function was indicated by studies with ROS scavengers, superoxide dismutase (SOD) and catalase, and exogenous hydrogen peroxide. The SOD treatment, which enhanced H₂O₂ production, resulted in increased Ca²⁺uptake and enhanced fertilization rate. On the other hand, catalase, which decomposes H₂O₂, impaired the light-induced stimulation in Ca²⁺uptake and the fertilization rate. Taken together, the data suggest that H₂O₂ might be involved in the irradiation effects, and indeed laser irradiation enhances the production of H₂O₂, by spermatozoa. These results indicate that the effect of 630 nm He-Ne laser irradiation is mediated through the generation of H₂O₂ by the spermatozoa and that this effect plays a significant role in the augmentation of the sperm cells' capability to fertilize metaphase H-arrested eggs in vitro.     

Proton‐Transfer Reaction Dynamics and Energetics in Calcification and Decalcification

CaCO₃‐saturated saline waters at pH values below 8.5 are characterized by two stationary equilibrium states: reversible chemical calcification/decalcification associated with acid dissociation, Ca²⁺+HCO₃^??CaCO₃+H⁺; and reversible static physical precipitation/dissolution, Ca²⁺+CO₃^2??CaCO₃. The former reversible reaction was determined using a strong base and acid titration. The saturation state described by the pH/P_CO2‐independent solubility product, [Ca²⁺][CO₃^2?], may not be observed at pH below 8.5 because [Ca²⁺][CO₃^2?]/([Ca²⁺][HCO₃^?]) ?1. Since proton transfer dynamics controls all reversible acid dissociation reactions in saline waters, the concentrations of calcium ion and dissolved inorganic carbon (DIC) were expressed as a function of dual variables, pH and P_CO2. The negative impact of ocean acidification on marine calcifying organisms was confirmed by applying the experimental culture data of each P_CO2/pH‐dependent coral polyp skeleton weight (Wskel) to the proton transfer idea. The skeleton formation of each coral polyp was performed in microspaces beneath its aboral ectoderm. This resulted in a decalcification of 14 weight %, a normalized CaCO₃ saturation state Λ of 1.3 at P_CO2 ≈400 ppm and pH ≈8.0, and serious decalcification of 45 % and Λ 2.5 at P_CO2 ≈1000 ppm and pH ≈7.8.     

Design and synthesis of optically transparent calcium‐incorporated polymer complexes

Transparent thin films of calcium‐ion‐incorporated polymer composites were synthesized with calcium carbonate (CaCO₃) and polymers such as poly(acrylic acid) (PAA), poly(ethylene glycol) (PEG), and methylcellulose. The homogeneous distribution of Ca²⁺ in the composite films was observed because of the high concentration of COO^? groups along the PAA backbone for the complexation of Ca²⁺ ions. The optical transparency of the composites depends on the weight percentages of the three polymers and the molar concentration of CaCO₃ in the composites. Maximum transparency was obtained for a composite film with a PAA/CaCO₃ ratio of 9:1. The results indicated that methylcellulose improved the film‐forming capabilities and that PEG improved the transparency of the composites. All polymer complexes were characterized with X‐ray diffraction, fourier transfer infrared spectroscopy, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, dynamic mechanical analysis, and optical transparency measurements. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4459–4465, 2004     

Purification of Biliary Protein and Its Effect on Calcium Carbonate Mineralization

The biliary protein (BP) was isolated from pig bile by gel filtration. The interaction between Ca²⁺ and protein was measured by fluorescence spectra. The result showed that there was a strong coordination between biliary protein and Ca²⁺. The CaCO₃ crystals obtained in systems with and without BP were characterized by scanning electron microscopy, Fourier transform infrared spectrography and powder X‐ray diffractometry. The possible formation mechanism of CaCO₃ in biliary protein solution was discussed.     

Conditional Singlet Oxygen Generation through a Bioorthogonal DNA‐targeted Tetrazine Reaction

We report the use of bioorthogonal reactions as an original strategy in photodynamic therapy to achieve conditional phototoxicity and specific subcellular localization simultaneously. Our novel halogenated BODIPY‐tetrazine probes only become efficient photosensitizers (Φ_Δ≈0.50) through an intracellular inverse‐electron‐demand Diels–Alder reaction with a suitable dienophile. Ab initio computations reveal an activation‐dependent change in decay channels that controls ¹O₂ generation. Our bioorthogonal approach also enables spatial control. As a proof‐of‐concept, we demonstrate the feasibility of the selective activation of our dormant photosensitizer in cellular nuclei, causing cancer cell death upon irradiation. Thus, our dual biorthogonal, activatable photosensitizers open new venues to combat current limitations of photodynamic therapy.     

A Smart DNAzyme–MnO2 Nanosystem for Efficient Gene Silencing

DNAzymes hold promise for gene‐silencing therapy, but the lack of sufficient cofactors in the cell cytoplasm, poor membrane permeability, and poor biostability have limited the use of DNAzymes in therapeutics. We report a DNAzyme–MnO₂ nanosystem for gene‐silencing therapy. MnO₂ nanosheets adsorb chlorin e6‐labelled DNAzymes (Ce6), protect them from enzymatic digestion, and efficiently deliver them into cells. The nanosystem can also inhibit ¹O₂ generation by Ce6 in the circulatory system. In the presence of intracellular glutathione (GSH), MnO₂ is reduced to Mn²⁺ ions, which serve as cofactors of 10–23 DNAzyme for gene silencing. The release of Ce6 generates ¹O₂ for more efficient photodynamic therapy. The Mn²⁺ ions also enhance magnetic resonance contrast, providing GSH‐activated magnetic resonance imaging (MRI) of tumor cells. The integration of fluorescence recovery and MRI activation provides fluorescence/MRI bimodality for monitoring the delivery of DNAzymes.     

Photoluminescence Properties of a Promising Red-emitting Phosphor CaNb2O6:EU3+for Trichromatic White Light Emitting Diodes Application

Motivated by the need for new phosphors of white light emitting diode (WLED) application, Ca_0.95Nb₂ O₆:Eu³⁺_0.05 phosphors were synthesized by high temperature solid‐state reaction. Increasing the content of doped‐Eu³⁺ and adding the co‐activator Bi³⁺ to improve the photoluminescence (PL) intensity of Ca_1?xNb₂ O₆Eu³⁺_x phosphors were investigated in detail. The effects of Eu³⁺ were better than that of Bi³⁺ on the PL intensity of Ca_1?xNb₂ O₆Eu³⁺_x phosphors. Compared with Y₂O₂ S:0.05Eu³⁺ the Ca_0.70Nb₂ O₆:Eu³⁺_0.03 phosphor could be excited efficiently by UV (395 nm) light and emit the red light at 614 nm with line spectra, which were coupled well with the characteristic emission from UV‐Near UV LED. The CIE (International Commission on Illumination) chromaticity coordinates (x?0.654, y?0.348) of Ca_0.70Nb₂O₆:Eu³⁺_0.03 were close to the NTSC (National Television Standard Committee) standard values. Therefore Ca_0.70Nb₂ O₆:Eu³⁺_0.03 might find application to UV‐Near UV InGaN chip‐based white light emitting diodes, which is further proved by the LED fabrication with the Ca_0.70Nb₂ O₆:Eu³⁺_0.03 phosphor.     

Kinetics of Heterogeneous Isotopic Exchange Reaction in Finite Bath

A general method to find the rate constant and particle self-diffusion coefficient is suggested for a heterogeneous isotopic exchange reaction which is controlled by surface mass reaction or controlled by a combination of surface mass reaction and intraparticle diffusion. The values of the kinetic parameter, ξ₁ (ratio of the forward surface mass reaction rate to the intraparticle diffusion rate), particle self-diffusion coefficient D and rate constant k are obtained by the proposed method for the isotopic exchange reaction systems CaCO₃(s)/Ca²⁺(aq) and CaC₂O₄(s)/Ca²⁺(aq).     

Reversible Ca2+ Switch of An Engineered Allosteric Antioxidant Selenoenzyme

A Ca²⁺‐responsive artificial selenoenzyme was constructed by computational design and engineering of recoverin with the active center of glutathione peroxidase (GPx). By combining the recognition capacity for the glutathione (GSH) substrate and the steric orientation of the catalytic selenium moiety, the engineered selenium‐containing recoverin exhibits high GPx activity for the catalyzed reduction of H₂O₂ by glutathione (GSH). Moreover, the engineered selenoenzyme can be switched on/off by Ca²⁺‐induced allosterism of the protein recoverin. This artificial selenoenzyme also displays excellent antioxidant ability when it was evaluated using a mitochondrial oxidative damage model, showing great potential for controlled catalysis in biomedical applications.     

Specific Generation of Singlet Oxygen through the Russell Mechanism in Hypoxic Tumors and GSH Depletion by Cu‐TCPP Nanosheets for Cancer Therapy

The generation of singlet oxygen (¹O₂) during photodynamic therapy is limited by the precise cooperation of light, photosensitizer, and oxygen, and the therapeutic efficiency is restricted by the elevated glutathione (GSH) levels in cancer cells. Herein, we report that an ultrathin two‐dimensional metal–organic framework of Cu‐TCPP nanosheets (TCPP=tetrakis(4‐carboxyphenyl)porphyrin) can selectively generate ¹O₂ in a tumor microenvironment. This process is based on the peroxidation of the TCPP ligand by acidic H₂O₂ followed by reduction to peroxyl radicals under the action of the peroxidase‐like nanosheets and Cu²⁺, and their spontaneous recombination reaction by the Russell mechanism. In addition, the nanosheets can also deplete GSH. Consequently, the Cu‐TCPP nanosheets can selectively destroy tumor cells with high efficiency, constituting an attractive way to overcome current limitations of photodynamic therapy.     

Cu2+-Anchored Carbon Nano-Photocatalysts for Visible Water Splitting to Boost Hydrogen Cuproptosis

Both hydrogen (H₂) and copper ions (Cu⁺) can be used as anti-cancer treatments. However, the continuous generation of H₂ molecules and Cu⁺ in specific sites of tumors is challenging. Here we anchored Cu²⁺ on carbon photocatalyst (Cu@CDCN) to allow the continuous generation of H₂ and hydrogen peroxide (H₂O₂) in tumors using the two-electron process of visible water splitting. The photocatalytic process also generated redox-active Cu-carbon centers. Meanwhile, the Cu²⁺ residues reacted with H₂O₂ (the obstacle to the photocatalytic process) to accelerate the two-electron process of water splitting and cuprous ion (Cu⁺) generation, in which the Cu²⁺ residue promoted a pro-oxidant effect with glutathione through metal-reducing actions. Both H₂ and Cu⁺ induced mitochondrial dysfunction and intracellular redox homeostasis destruction, which enabled hydrogen therapy and cuproptosis to inhibit cancer cell growth and suppress tumor growth. Our research is the first attempt to integrate hydrogen therapy and cuproptosis using metal-enhanced visible solar water splitting in nanomedicine, which may provide a safe and effective cancer treatment.     

A Highly Copper‐Selective Ratiometric Fluorescent Sensor Based on BODIPY

A new ratiometric fluorescent sensor ( 1 ) for Cu²⁺ based on 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) with di(2‐picolyl)amine (DPA) as ion recognition subunit has been synthesized and investigated in this work. The binding abilities of 1 towards different metal ions such as alkali and alkaline earth metal ions (Na⁺, K⁺, Mg²⁺, Ca²⁺) and other metal ions ( Ba²⁺, Zn²⁺, Cd²⁺, Fe²⁺, Fe³⁺, Pb²⁺, Ni²⁺, Co²⁺, Hg²⁺, Ag⁺) have been examined by UV‐vis and fluorescence spectroscopies. 1 displays high selectivity for Cu²⁺ among all test metal ions and a ～10‐fold fluorescence enhancement in I₅₈₂/I₅₅₈ upon excitation at visible excitation wavelength. The binding mode of 1 and Cu²⁺ is a 1:1 stoichiometry determined via studies of Job plot, the nonlinear fitting of the fluorometric titration and ESI mass.     

Ca2+‐Induced Oxygen Generation by FeO42− at pH 9–10

Although FeO₄^2? (ferrate(IV)) is a very strong oxidant that readily oxidizes water in acidic medium, at pH 9–10 it is relatively stable (<2 % decomposition after 1 h at 298 K). However, FeO₄^2? is readily activated by Ca²⁺ at pH 9–10 to generate O₂. The reaction has the following rate law: d[O₂]/dt=k_Ca[Ca²⁺][FeO₄^2?]². ¹⁸O‐labeling experiments show that both O atoms in O₂ come from FeO₄^2?. These results together with DFT calculations suggest that the function of Ca²⁺ is to facilitate O–O coupling between two FeO₄^2‐ions by bridging them together. Similar activating effects are also observed with Mg²⁺ and Sr²⁺.     

Structural Variations in the Solid‐Solution Series LnxCa2−xAl[Al1+xSi1−xO7] with 0 ≤ x ≤ 1 and Ln = La,Eu, Er

Gehlenite, Ca₂Al[AlSiO₇], has melilite‐type structure with space group . It contains two topologically distinct positions coordinated tetrahedrally by oxygen. One is completely occupied by Al³⁺, whereas the other one contains Al³⁺ and Si⁴⁺. Normally, the Al³⁺ molar fraction in the second tetrahedrally coordinated position does not exceed x_Al = 0.5, i.e. the so‐called Loewenstein‐rule is obeyed. In this contribution the structural variations in the melilite‐type compounds of the compositions La_xCa_2?xAl[Al_1+xSi_1?xO₇], Eu_xCa_2?xAl[Al_1+xSi_1?xO₇] and Er_xCa_2?xAl[Al_1+xSi_1?xO₇] are discussed. All members of the solid solution except the end‐members violate Loewenstein's rule. Rietveld refinements against X‐ray powder diffraction patterns confirm that the compounds have space group , without changes in the Wyckoff‐positions of the ions compared to gehlenite.     

{[Ca5(C8H4O4)5(H2O)9]·8H2O}n: the first crystallographically characterized non‐transition metal salt of isophthalic acid

The reaction of CaCO₃ with isophthalic acid in water yields nona­aqua­penta‐μ‐isophthalato‐pentacalcium octahydrate, {[Ca₅(C₈H₄O₄)₅(H₂O)₉]·8H₂O}_n, a complex polymeric one‐dimensional column structure bearing metal–carboxyl­ate bonds and Ca‐bound terminal and bridging water mol­ecules, in addition to hydrogen‐bonded water mol­ecules of crystallization. The asymmetric unit comprises half of the formula unit, with one Ca²⁺ ion located on a twofold axis, and contains 16 unique strong O—H⋯O hydrogen bonds, some of which link the columns together.     

Peanut-shaped aggregation of CaCO<Subscript>3</Subscript> crystallites in the presence of an amphiphilic derivative of carboxymethylchitosan

An amphiphilic derivative of carboxymethylchitosan (CMCS), (2-hydroxyl-3-butoxyl)propyl-CMCS (HBP-CMCS), was used as an organic additive in the precipitation process of calcium carbonate (CaCO₃). HBP-CMCS molecules can interact with calcium ions, the functional groups of which act as active sites for the nucleation and crystallization of CaCO₃. Simultaneously, HBP-CMCS molecule also functionalizes as a colloidal stabilizer to prohibit the sedimentation of the grown CaCO₃ crystals, depending upon the molar ratio of the initial Ca²⁺ ions to the repeat units of HBP-CMCS molecules. The combination investigations of scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy on the precipitated CaCO₃ crystals proved that concentrations of HBP-CMCS and Ca²⁺ exert great influence on the crystallization habit of CaCO₃, such as the nucleation, growth, morphology, crystal form, etc. The formation of the peanut-shaped CaCO₃ particles suggests the template effect of HBP-CMCS molecules on the aggregation behavior of CaCO₃ nanocrystals.     

Photosynthetic Tumor Oxygenation by Photosensitizer‐Containing Cyanobacteria for Enhanced Photodynamic Therapy

Sustained tumor oxygenation is of critical importance during type‐II photodynamic therapy (PDT), which depends on the intratumoral oxygen level for the generation of reactive oxygen species. Herein, the modification of photosynthetic cyanobacteria with the photosensitizer chlorin e6 (ce6) to form ce6‐integrated photosensitive cells, termed ceCyan, is reported. Upon 660 nm laser irradiation, sustained photosynthetic O₂ evolution by the cyanobacteria and the immediate generation of reactive singlet oxygen species (¹O₂) by the integrated photosensitizer could be almost simultaneously achieved for tumor therapy using type‐II PDT both in vitro and in vivo. This work contributes a conceptual while practical paradigm for biocompatible and effective PDT using hybrid microorganisms, displaying a bright future in clinical PDT by microbiotic nanomedicine.