Passivation of the calcite surface with phenylmalonate and benzylmalonate ions

We explored the affinity of calcite to adsorbed organic molecules as an approach to the conservation of cultural heritage built of marble and limestone. The utilization of phenylmalonic and benzylmalonic acids provided a hydrophobic adsorptive interface, adequate to prevent processes of aqueous weathering. Samples of marble powder (polycrystalline calcite) were impregnated with solutions of phenylmalonic and benzylmalonic acid at three concentrations (5 x 10(-2), 5 x 10(-3), and 5 x 10(-4) M) and different pH values (6.00, 7.00, and 8.00). The surface charge of the calcite suspensions was determined by potentiometric measurements under equilibrium conditions at room temperature in aqueous solution of the dicarboxylic acids, in order to understand the influence of the electrokinetic potential in the surface association. The adsorbed amounts were determined by calculation of the thermodynamic equilibria of solutions. The presence of the organic interface on the mineral surface was corroborated by Raman spectroscopy and small-angle X-ray scattering (SAXS). The results indicate effective adsorption of both dicarboxylic acids as a function of the concentration and pH, and several other conditions that favors coulombic interaction, an absence of electrophoretic mobility or surface electroneutrality related to the solid surface potentials. The coverage of pores by dicarboxylic adsorbate modified the geometrical pore shape and the pore size distribution, filling all the pores of larger than 80 A diameter, giving as a result a mesoporous structure. This change in the surface morphology by organic adsorbates constitutes a modification in the diffusional processes of the environment on the mineral surface.     

Molecular ordering of ethanol at the calcite surface

To produce biominerals, such as shells, bones, and teeth, living beings create organic compounds that control the growth of the solid phase. Investigating the atomic scale behavior of individual functional groups at the mineral-fluid interface provides fundamental information that is useful for constructing accurate predictive models for natural systems. Previous investigations of the activity of coccolith-associated polysaccharides (CAP) on calcite, using atomic force microscopy (AFM) [Henriksen, K., Young, J. R., Bown, P. R., and Stipp, S. L. S. Palentology 2004, 43 (Part 3), 725-743] and molecular dynamics (MD) modeling [Yang, M., Stipp, S. L. S., and Harding, J. H. Cryst. Growth Des. 2008, 8 (11), 4066-4074], have suggested that OH functional groups control polysaccharide attachment. The purpose of this work was to characterize, using X-ray reflectivity (XR) combined with molecular dynamics (MD) simulations, the structuring on calcite of a layer of the simplest carbon chain molecule that contains an OH group, ethanol (CH(3)-CH(2)-OH). We found evidence that EtOH forms a highly ordered structure at the calcite surface, where the first layer molecules bond with calcite. The ethanol molecules stand up perpendicularly at the interface or nearly so. As a consequence, the fatty, CH(3) ends form a new surface, about 6 ? from the termination of the bulk calcite, and beyond that, there is a thin gap where ethanol density is low. Following is a more disordered layer that is two to three ethanol molecules thick, about 14 ?, where density more resembles that of bulk liquid ethanol. The good agreement between theory and experiment gives confidence that a theoretical approach can offer information about behavior in more complex systems.     

Ab initio surface phase diagram of the {104} calcite surface

Electronic structure calculations, performed at the density functional theory level, were employed to study the surface termination of the {104} calcite surface in contact with a gaseous phase containing water and carbon dioxide. A surface phase diagram was generated to investigate the change in surface termination as a function of temperature, pressure, and gas-phase composition. This diagram revealed that a nonstoichiometric termination could occur in atmospheric conditions at high relative humidity, hence suggesting that nonstoichiometric surfaces can play a major role in the chemistry of calcite surfaces.     

Modeling steps and kinks on the surface of calcite

This work presents modeling results on the cleavage face of calcite as well as on steps and isolated kinks on this face. We used static lattice energy minimization and interatomic potentials fitted to bulk properties. The energy needed to cleave a bulk calcite crystal along the [1 0 (-)1 4] plane was calculated to be 0.59 J m(-2) in agreement with previous studies using the same potentials. The perfect surface reconstructs in the top few atomic layers, but its symmetry corresponds to the bulk termination. By contrast, the (1 0 (-)1 4) surface with cleavage steps present reconstructs to form a (2 x 1) super cell. This may help explain experimental observations of (2 x 1) symmetry on calcite surfaces. The energy required to form a monatomic obtuse step is calculated to be 1.3 x 10(-10) J m(-1) and for the acute step, 2.4 x 10(-10) J m(-1), suggesting that obtuse steps dominate on cleaved surfaces. Along the two types of steps, a total of 16 kink geometries exist. We calculated kink defect energy with two different approaches: one where kink pairs were added onto infinitely long steps and one where kinks were placed inside pits on a cleavage surface. Calculations on infinitely long steps show that for vacuum conditions, kink pairs possess roughly identical formation energy, about 1.2-2.2 eV, so based on energetics one cannot expect significant differences in kink site frequency     

Structure of surface films of malonate mono- and dinitroxyl methanofullerenes

An effect of aqueous subphases composition on the character of change of the bilayer structure of malonate mono- and dinitroxyl methanofullerenes surface films has been established. Their transformation to monolayers takes place in the presence of hydroxy-containing compounds (quercetin, dihydroquercetin, 4-methylphenol, ascorbic acid, as well as in a buffer mixture with pH 10). A loosening of mixed films on the basis of nitroxyl methanofullerenes in the presence of compounds affecting radical processes (2,4,6-tri(tert-butyl)phenol, 2-methyl-3-nitrosopropane, and TEMPO) has been demonstrated. The character of compression isotherms π = f(A ₀) (π is a surface pressure, A ₀ is an effective molecular area of methanofullerene) of the mixed films on water depends on the nature of component incorporated and the reaction time in solution: in all the cases, A ₀ increased almost 2-fold, to 1.05 nm² molecule⁻¹, whereas a compressibility parameter β decreased 2–3-fold, to (1–2)·10¹⁷ N m⁻³. Visualization of the thin film surfaces (atomic force spectroscopy) showed that a decrease of parameter β in the Langmuir layers corresponds to the particle aggregation and structurization of the films. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1920–1931, September, 2008.     

Water-induced reconstruction that affects mobile ions on the surface of calcite

Time-sequenced contact-force micrographs show that the (104) calcite cleavage surface reconstructs in humid air through pit formation and film growth. After 8 h at 80% relative humidity (RH), 50% to 80% of the surface is covered by islands that are flat-topped and 1-nm high. The lateral growth rates of individual islands are 4.2+/-0.4 nm min-1 in the 41 direction and 1.8+/-0.4 nm min-1 in the 48 direction, resulting in islands having distinct major and minor axes. On some samples, a contiguous, 1.5-nm-high film rapidly grows between the islands and the pits. The areal expansion rate of the film is 500 times faster than that of the islands. Gaps between the contiguous film and the islands expand and contract, which suggests that mass is exchanged between them and that both are loosely bound. Complementing the topographic images, polarization heights are simultaneously measured by polarization-force microscopy. The polarization heights of the islands and the contiguous film are -6 to -10 nm and -4 to -5 nm, respectively, compared to their respective topographic heights of +1.0 and +1.5 nm. Under our experimental conditions, the polarization heights are a surrogate for the local dielectric constant of the sample epsilon and arise from a convolution of the mobility and the density of surface ions. The polarization heights imply that epsilonsubstrate>epsilonfilm>epsilonisland. Changes in topographic and polarization heights at 20% and 50% RH suggest that the structures of the islands are in dynamic equilibrium with the adsorbed water. Our evidence suggests that the islands contain loosely bound water and may therefore be a hydrated calcium carbonate phase stabilized by the calcite surface.     

Covalent attachment of proteins to calcite surface for the single molecule experiments

Two protocols of covalent attachment of proteins onto the calcite surface, viz. one using the metallochelat and second using the aminohexil, are elaborated. Single molecule force spectroscopy method has been used to test their efficiency and practical applicability. Experiments were performed measuring the specific interaction force between bovine serum albumin (BSA) fixed onto the freshly cleaved calcite single crystal surface (procedure under the study here) and its polyclonal antibody (Ab-BSA) immobilized onto an AFM tip using standard and well studied procedure. We found the conditions, when up to 3–3.5% of tip-sample approaches lead to the formation of a single specific bond.     

Humidity-induced restructuring of the calcite surface and the effect of divalent heavy metals

The composition and topography of calcite 10114 cleavage surfaces, with and without exposure to divalent metals, have been investigated as a function of relative humidity. Atomic force microscopy (AFM) was used to understand topographical changes on the calcite surface due to the presence of divalent metal and exposure to different humid environments. Ion scattering spectroscopy (ISS) was used to determine the composition of the near and outermost surface of the calcite after exposure to Cd and Pb and before exposure to the varying humidity conditions. In general, the extent of topographical changes observed on the calcite surface increased with the humidity level, though the initial step density of the cleaved calcite surface affects the extent of surface restructuring. Pretreatment of the calcite surface with aqueous divalent Pb prior to humidity exposure did not appear to alter the humidity-induced structural changes that occurred on the calcite surface. In contrast, calcite pretreated with divalent Cd showed little topographical change following exposure to high humidity. The results suggest that while Pb forms surface precipitates on the calcite surface, Cd exhibits a stronger interaction with the step edges of the calcite surface, which inhibits the ability of the calcite surface to restructure when exposed to a high relative humidity environment.     

Reaction of α-ethoxyarolein with diethyl malonate

The reaction of α-ethoxyacrolein with diethyl malonate in the presence of EtONa, lithium diisopropylamide, or the Na₂CO₃−benzene−Et₃(PhCH₂)NCl catalytic system proceeds as the Michael addition. In the presence of an equimolar amount of triethylamine, selective 1,2-addition followed by dehydration of the 1,2-adduct occurs. Owing to the strong +M effect of the EtO group, α-ethoxyacrolein is a substantially less active Michael acceptor than acrolein. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 12, pp. 2508–2510, December, 1998.     

Modelling excess surface energy in dry and wetted calcite systems

We have combined the calcite force field of Hwang et al. (J. Phys. Chem. B 105:4,122–4,127, 2001) with the F3C water model and a hybrid Lennard-Jones/van der Waals 3-site potential for CO₂ to investigate the (10[`1]4){\left({10\overline14}\right)} and ( 10[`1]0){\left( {10\overline10}\right)} cleaving surfaces of calcite under dry and wetted conditions. The wetting fluid included both pure water and water–carbon dioxide mixture. Excess surface energies and structural features of the calcite–fluid interface were analyzed, with the simulation results for the relaxed surfaces confirming the experimentally observed morphology and supporting our conclusion that the relative stability order of calcite cleaving surfaces under investigation will remain unchanged in the presence of water–carbon dioxide mixture as well.     

A theoretical study of malonate ion and its metal binding by ab initio and semiempirical techniques

STO-3G and CNDO calculations have been performed on malonate ion and its Mg²⁺ complexes. The parallel carboxyl group arrangement is found to be the single minimum energy conformation with both techniques. In the metal binding studies, the binding of a Mg²⁺ to a single carboxyl is preferred over binding symmetrically to both carboxyls in their parallel conformation. These results are consistent with X-ray structure results on calcium malonate.     

Passivation agent with dipole moment for surface modification towards efficient and stable perovskite solar cells

Recently,there has been renewed interest in interface engineering as a means to further push the performance of perovskite solar cells closer to the Schockly-Queisser limit.Herein,for the first time we employ a multi-functional 4-chlorobenzoic acid to produce a self-assembled monolayer on a perovskite surface.With this interlayer we observe passivation of perovskite surface defects and a significant suppression of non-radiative charge recombination.Furthermore,at the surface of the interlayer we observe,charge dipoles which tune the energy level alignment,enabling a larger energetic driving force for hole extraction.The perovskite surface becomes more hydrophilic due to the presence of the interlayer.Consequently,we observe an improvement in open-circuit voltage from 1.08 to 1.16 V,a power conversion efficiency improvement from 18%to 21%and an improved stability under ambient conditions.Our work highlights the potential of SAMs to engineer the photo-electronic properties and stability of perovskite interfaces to achieve high-performance light harvesting devices.     

Reaction of isopropylidene malonate with N-arylidene-2-naphthylamines

It is shown that 4-aryl-2-oxo-1,2,3,4-tetrahydro-5,6-benzoquinolines are formed in the reaction of N-arylidene-2-naphthylamines with isopropylidene malonate. The reaction takes place with cleavage of the isopropylidene malonate ring and the production of carbon dioxide and acetone. The structure of the benzotetrahydroquinolines obtained were confirmed by identification of the compound obtained by sulfur dehydrogenation of the product of the reaction of isopropylidene malonate with arylidenenaphthylamine (aryl=phenyl) with an authentic sample of 1,2-dihydro-2-oxo-4-phenyl-5,6-benzoquinoline and of the reaction product (in which the aryl group was absent) with an authentic sample of 2-oxo-1,2,3,4-tetrahydro-5,6-benzoquinoline. The IR and PMR spectra data are presented.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 973–976, July, 1977.     

Reaction of isopropylidene malonate with N-arylidene-1-naphthylamines

4-Aryl-2-oxo-1,2,3,4-tetrahydro-7,8-benzoquinolines were obtained by reaction of isopropylidene malonate with N-arylidene-1-naphthylamines. It is shown that the products are associated in the solid state by intermolecular hydrogen bonds. The IR and PMR spectral data are presented.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 977–979, July, 1977.     

Composites with a porous bipolar surface for ion chromatography

A method for the preparation of a bipolar ion-exchange surface was proposed; it consists in the dynamic arrangement of the nanoparticles of an ion-exchanger modifier in the macropores of a matrix ion exchanger of opposite polarity and the retention of these nanoparticles by Coulomb forces. The NACATEX analytical cation-exchange column with the separating surface of a new type was prepared, which is suitable for the separation of the mixtures of alkaline element and ammonium ions and also calcium and magnesium ions.     

Reaction of diethyl (phthalimidoacetyl)malonate with hydroxylamine

The reaction of diethyl (phthalimidoacetyl)malonate with hydroxylamine was investigated. Depending upon the reaction conditions, N-phthaloylglycinehydroxamic acid ( 2 ) and the cyclized product, 4-ethoxycarbonyl-5-hydroxy-3-(phthalimidomethyl)isoxazole ( 4 ), were obtained.     

Electrochemical dehydrodimerization of malonate esters with double bond formation

Russian Chemical Bulletin -     

Mixed-ligand complexes of copper with some amino-acids and malonate

The mixed-ligand complexes formed by copper(II) with an amino-acid (valine, threonine, isoleucine, aspartic acid, glutamic acid, lysine) and malonic acid have been investigated polarographically and their stability constants determined. The complexes are less stable than the corresponding complexes with oxalic acid instead of malonic, but also exhibit less disproportionation into the simple complexes, because the simple oxalate complexes are more stable than the malonate complexes.     

Free energy of adsorption of water and metal ions on the [1014] calcite surface

We calculated the free energy profiles of water and three metal ions (magnesium, calcium, and strontium) adsorbing on the [1014] calcite surface in aqueous solution. The approach uses molecular dynamics with parametrized equations to describe the interatomic forces. The potential model is able to reproduce the interactions between water and the metal ions regardless of whether they are at the mineral surface or in bulk water. The simulations predict that the free energy of adsorption of water is relatively small compared to the enthalpy of adsorption calculated in previous papers. This suggests a large change in entropy associated with the water adsorption on the surface. We also demonstrate that the free energy profile of a metal ion adsorbing on the surface correlates with the solvent density and that the rate of formation of an innersphere complex depends on overcoming a large free energy barrier, which is mainly electrostatic in nature. Furthermore, comparison among the rates of desorption of magnesium, calcium, and strontium from the calcite surface suggests that magnesium has a much lower rate of desorption due to its strong interactions with both water and the surface.