Unseeded, spontaneous nucleation of spherulitic magnesium calcite.

Most of the sedimentary carbonates deposited in the marine environments are composed of calcium carbonate minerals with varying amounts of incorporated Mg2+. However, understanding how interactions of impurities with carbonate and their incorporation affect sediments behavior remains a challenge. Here, a new insight is obtained by monitoring solution composition, morphology, and electrokinetic potential of carbonate particles formed in a spontaneous unseeded batch precipitation experiment using electrochemical and scanning electron microscopy methods. The solid composition and growth rate are extracted from changes in the bulk composition and fitted to chemical affinity rate law, revealing that the precipitation pathway consists of second-order dissolution and first-order precipitation. The molecular dynamics simulations show that the lattice strain induced by randomly substituting Ca2+ by Mg2+ stabilizes spherical nanoparticles and reduces their surface area and volume. Combining kinetics and thermodynamics insight, we conclude that variation in the carbonate bulk and interfacial energies, along with the solution supersaturation, lead to the dissolution-precipitation transformation pathway from Mg-rich to Mg-poor carbonate phase that preserves spherulitic morphology. Our findings are relevant for long-standing questions of how impurities influence diagenesis of carbonate sediments and spherulitic carbonate particles' origin.

Electrophoretic and potentiometric signatures of multistage CaCO3 nucleation.

HYPOTHESIS: Calcium carbonate nucleation is often a complex and multistep process that is difficult to follow in situ. The time-resolved electrochemical and electrophoretic methods can provide a new insight into the nucleation pathway. EXPERIMENTS: Here, we used a combination of speciation calculations with time-resolved electrophoretic and potentiometric methods to monitor calcium carbonate precipitation from a slightly supersaturated solution. FINDINGS: After an initial mixing period of three minutes in which metastable CaCO3 phases may have nucleated and subsequently dissolved due to locally-high supersaturations, bulk solution pH and Ca2+ concentrations stabilize before decreasing in tandem with the precipitation of a CaCO3 phase. After an hour, the precipitate is dominated by calcite that grows at the expense of dissolving vaterite. The time-dependent electrokinetic potential shows analogous signatures of multistage nucleation process: initial rapid changes in ζ-potential are followed by much slower equilibration starting about one hour after reagents are mixed. The changes in ζ-potential, solution pH, saturation indexes, and particle morphology are consistent with vaterite to calcite transformation via dissolution of the former and recrystallization of the latter. These findings highlight the potential use of ζ-potential measurements for monitoring polymorphic transformations of carbonate phases in-situ.

Comparative study of molecular recognition of folic acid subunits with cyclodextrins.

The complexation of pteroic acid and pterine, subunits of folic acid, with native cyclodextrins (α‒, ß‒, and γ‒CDs) was studied in solution (UV-vis), and in the solid state (thermal analysis, IR and Raman). UV-vis titrations at pH = 7.4 provided data regarding stoichiometry of the formed complexes as well as their associations constants. Stability of the complexes increases in the series: γ‒CD < ß‒CD << α‒CD for pterine, and γ‒CD < α‒CD << ß‒CD for pteroic acid. The mode of complexation was further exploited by molecular modeling studies (docking studies, PM6) showing additionally changes in conformation of pteroic acid upon complexation. Comparison of the association constants of the complexes of pterine and pteroic acid with native cyclodextrins with data obtained for analogous complexes with folic acid shows that all folic acid complexes are less stable than those formed from its subunits.

Blood Serum Calorimetry Indicates the Chemotherapeutic Efficacy in Lung Cancer Treatment.

Chemotherapy is a primary treatment for the metastatic lung cancer patients. To select the most effective combination of drugs, we need an efficient way of assessing tumor response. Here, we showed that differential scanning calorimetry (DSC) analysis of blood serum proteins could reveal the patient response to the treatment. If chemotherapy is effective, serum proteins DSC curve of non-small cellular lung cancer (NSCLC) case is similar to the those of the healthy individuals. If treatment fails, notable changes occur in the DSC profile of NSCLC patient's blood serum. Our preliminary work illustrates how thermal analysis of changes in the heat capacity of blood serum proteins can provide an insight into patient response to chemotherapy - the essential information for any successive lung cancer treatment.

Rubber elastomeric nanocomposites with antimicrobial properties.

In this paper we show an elastomeric nanocomposite that exhibits antibacterial and antifungal activity. It comprises a rubber blend matrix and a nanofiller, which is a modified bentonite clay (Nanobent® ZR2). We have developed innovative technology for the nanofiller incorporation into the rubber matrix. This new approach was successfully implemented in pilot production at the Polish chemical manufacturer Spoiwo (Spoldzielnia Pracy Chemiczno-Wytworczej 'Spoiwo', Radom, Poland). Here we reveal that addition of the functionalised bentonite affects the mechanical and thermal behaviour of elastomers. For example, by adding 1-3% of bentonite nanoparticles we strongly enhanced elongation and tensile stress at break, whereas stiffness remained unchanged. We observed improvement of the thermal properties of the nanocomposites yielded and extension of the temperature usage range (from -29 to 311°C). As a proof of concept we present the antimicrobial effect of elastomeric nanocomposites verified on a wide range of both pathogenic and opportunistic reference bacteria strains, as well as reference strains of yeasts. The proposed method of hydrophilic nanofiller introduction into the rubber elastomer is economically viable and enables fabrication of elastomeric elements with high added value. Their significant antibacterial and antifungal activity makes them desirable in medicine, biomedical engineering, and the food industry.

Probing size-dependent electrokinetics of hematite aggregates.

Aqueous particle suspensions of many kinds are stabilized by the electrostatic potential developed at their surfaces from reaction with water and ions. An important and less well understood aspect of this stabilization is the dependence of the electrostatic surface potential on particle size. Surface electrostatics are typically probed by measuring particle electrophoretic mobilities and quantified in the electrokinetic potential (ζ), using commercially available Zeta Potential Analyzers (ZPA). Even though ZPAs provide frequency-spectra (histograms) of electrophoretic mobility and hydrodynamic diameter, typically only the maximal-intensity values are reported, despite the information in the remainder of the spectra. Here we propose a mapping procedure that inter-correlates these histograms to extract additional insight, in this case to probe particle size-dependent electrokinetics. Our method is illustrated for a suspension of prototypical iron (III) oxide (hematite, α-Fe2O3). We found that the electrophoretic mobility and ζ-potential are a linear function of the aggregate size. By analyzing the distribution of surface site types as a function of aggregate size we show that site coordination increases with increasing aggregate diameter. This observation explains why the acidity of the iron oxide particles decreases with increasing particle size.

Potentiometric and electrokinetic signatures of iron(II) interactions with (α,γ)-Fe2O3.

The electrochemical signatures of Fe(II) interactions with iron(III) oxides are poorly understood, despite their importance in controlling the amount of mobilized iron. Here, we report the potentiometric titration of α,γ-Fe2O3 oxides exposed to Fe(II) ions. We monitored in situ surface and ζ potentials, the ratio of mobilized ferric to ferrous, and the periodically analyzed nanoparticle crystal structure using X-ray diffraction. Electrokinetic potential reveals weak but still noticeable specific sorption of Fe(II) to the oxide surface under acidic conditions, and pronounced adsorption under alkaline conditions that results in a surface potential reversal. By monitoring the aqueous iron(II/III) fraction, we found that the addition of Fe(II) ions produces platinum electrode response consistent with the iron solubility-activity curve. Although, XRD analysis showed no evidence of γ-Fe2O3 transformations along the titration pathway despite iron cycling between aqueous and solid reservoirs, the magnetite formation cannot be ruled out.