Peptide-Controlled Assembly of Macroscopic Calcium Oxalate Nanosheets.

The fabrication of two-dimensional (2D) biomineral nanosheets is of high interest owing to their promise for applications in electronics, filtration, catalysis, and chemical sensing. Using a facile approach inspired by biomineralization in nature, we fabricate laterally macroscopic calcium oxalate nanosheets using ß-folded peptides. The template peptides are composed of repetitive glutamic acid and leucine amino acids, self-organized at the air-water interface. Surface-specific sum frequency generation spectroscopy and molecular dynamics simulations reveal that the formation of oxalate nanosheets relies on the peptide-Ca2+ ion interaction at the interface, which not only restructures the peptides but also templates Ca2+ ions into a calcium oxalate dihydrate lattice. Combined, this enables the formation of a critical structural intermediate in the assembly pathway toward the oxalate sheet formation. These insights into peptide-ion interfacial interaction are important for designing novel inorganic 2D materials.

A hydrated crystalline calcium carbonate phase: Calcium carbonate hemihydrate.

As one of the most abundant materials in the world, calcium carbonate, CaCO3, is the main constituent of the skeletons and shells of various marine organisms. It is used in the cement industry and plays a crucial role in the global carbon cycle and formation of sedimentary rocks. For more than a century, only three polymorphs of pure CaCO3-calcite, aragonite, and vaterite-were known to exist at ambient conditions, as well as two hydrated crystal phases, monohydrocalcite (CaCO3·1H2O) and ikaite (CaCO3·6H2O). While investigating the role of magnesium ions in crystallization pathways of amorphous calcium carbonate, we unexpectedly discovered an unknown crystalline phase, hemihydrate CaCO3·½H2O, with monoclinic structure. This discovery may have important implications in biomineralization, geology, and industrial processes based on hydration of CaCO3.

Calcium-Induced Molecular Rearrangement of Peptide Folds Enables Biomineralization of Vaterite Calcium Carbonate.

Proteins can control mineralization of CaCO3 by selectively triggering the growth of calcite, aragonite or vaterite phases. The templating of CaCO3 by proteins must occur predominantly at the protein/CaCO3 interface, yet molecular-level insights into the interface during active mineralization have been lacking. Here, we investigate the role of peptide folding and structural flexibility on the mineralization of CaCO3. We study two amphiphilic peptides based on glutamic acid and leucine with ß-sheet and α-helical structures. Though both sequences lead to vaterite structures, the ß-sheets yield free-standing vaterite nanosheet with superior stability and purity. Surface-spectroscopy and molecular dynamics simulations reveal that reciprocal structuring of calcium ions and peptides lead to the effective synthesis of vaterite by mimicry of the (001) crystal plane.

Diet affects gut microbiota and modulates hospitalization risk differentially in an international cirrhosis cohort.

The relative ranking of cirrhosis-related deaths differs between high-/middle-income countries. Gut microbiome is affected in cirrhosis and is related to diet. Our aim was to determine the effect of differing dietary habits on gut microbiota and clinical outcomes. Outpatient compensated/decompensated patients with cirrhosis and controls from Turkey and the United States underwent dietary and stool microbiota analysis. Patients with cirrhosis were followed till 90-day hospitalizations. Shannon diversity and multivariable determinants (Cox and binary logistic) of microbial diversity and hospitalizations were studied within/between groups. Two hundred ninety-six subjects (157 U.S.: 48 controls, 59 compensated, 50 decompensated; 139 Turkey: 46 controls, 50 compensated, 43 decompensated) were included. Patients with cirrhosis between cohorts had similar Model for End-Stage Liver Disease (MELD) scores. American patients with cirrhosis had more men, greater rifaximin/lactulose use, and higher hepatitis C/alcohol etiologies. Coffee intake was higher in Americans whereas tea, fermented milk, and chocolate intake were higher in Turkey. The entire Turkish cohort had a significantly higher microbial diversity than Americans, which did not change between their controls and patients with cirrhosis. In contrast, microbial diversity changed in the U.S.-based cohort and was the lowest in decompensated patients. Coffee, tea, vegetable, chocolate, and fermented milk intake predicted a higher diversity whereas MELD score, lactulose use, and carbonated beverage use predicted a lower microbial diversity. The Turkish cohort had a lower risk of 90-day hospitalizations. On Cox and binary logistic regression, microbial diversity was protective against 90-day hospitalizations, along with coffee/tea, vegetable, and cereal intake. CONCLUSION: In this study of patients with cirrhosis and healthy controls from the United States and Turkey, a diet rich in fermented milk, vegetables, cereals, coffee, and tea is associated with a higher microbial diversity. Microbial diversity was associated with an independently lower risk of 90-day hospitalizations. (Hepatology 2018;68:234-247).

Lattice distortions in coccolith calcite crystals originate from occlusion of biomacromolecules.

During biomineralization, organisms control the formation and morphology of a mineral using biomacromolecules. The biomacromolecules that most strongly interact with the growing crystals frequently get occluded within. Such an observation has been recently obtained for the calcium carbonate producing coccolithophore species Pleurochrysis carterae. Coccolithophores are unicellular algae that produce calcified scales built from complex-shaped calcite crystals, termed coccoliths. It is unclear how widespread the phenomenon of biomacromolecular occlusion within calcite crystals is in calcifying haptophytes such as coccolithophores. Here, the coccoliths of biological replicates of the bloom forming Emiliania huxleyi are compared with that of Pleurochrysis carterae, two species with different coccolith morphologies and crystal growth mechanisms. From high-resolution synchrotron X-ray diffraction, changes in the lattice parameters of coccolith calcite, after heating to 450°C, are observed and associated with macrostrain originating from occluded biomacromolecules. We propose a mechanism governing the biomacromolecules' interaction with the growing coccolith crystals and their likely origin.

A vacuole-like compartment concentrates a disordered calcium phase in a key coccolithophorid alga.

Coccoliths are calcitic particles produced inside the cells of unicellular marine algae known as coccolithophores. They are abundant components of sea-floor carbonates, and the stoichiometry of calcium to other elements in fossil coccoliths is widely used to infer past environmental conditions. Here we study cryo-preserved cells of the dominant coccolithophore Emiliania huxleyi using state-of-the-art nanoscale imaging and spectroscopy. We identify a compartment, distinct from the coccolith-producing compartment, filled with high concentrations of a disordered form of calcium. Co-localized with calcium are high concentrations of phosphorus and minor concentrations of other cations. The amounts of calcium stored in this reservoir seem to be dynamic and at a certain stage the compartment is in direct contact with the coccolith-producing vesicle, suggesting an active role in coccolith formation. Our findings provide insights into calcium accumulation in this important calcifying organism.

Biomimetic vaterite formation at surfaces structurally templated by oligo(glutamic acid) peptides.

Previous studies have reported that the metastable vaterite phase of calcium carbonate can be stabilized in solution by acidic additives. Here we demonstrate that vaterite can also be stabilized directly at surfaces by engineered peptides. Our data show that the mineralisation occurs in a 'self-templating' process where calcium ions restructure the peptide backbone, which in turn allows for effective vaterite precipitation.

Synthetic Strategies in the Preparation of Polymer/Inorganic Hybrid Nanoparticles.

This article reviews the recent advances and challenges in the preparation of polymer/inorganic hybrid nanoparticles. We mainly focus on synthetic strategies, basing our classification on whether the inorganic and the polymer components have been formed in situ or ex situ, of the hybrid material. Accordingly, four types of strategies are identified and described, referring to recent examples: (i) ex situ formation of the components and subsequent attachment or integration, either by covalent or noncovalent bonding; (ii) in situ polymerization in the presence of ex situ formed inorganic nanoparticles; (iii) in situ precipitation of the inorganic components on or in polymer structures; and (iv) strategies in which both polymer and inorganic component are simultaneously formed in situ.

On the causes of potential inversion in 1,2,4,5-tetrakis(amino)benzenes.

Three 3,6-difluoro-1,2,4,5-tetrakis(amino)benzene compounds, bearing dimethylamino (1), piperidin-1-yl (3), or morpholin-1-yl (5) substituents, have been synthesized and subsequently defluorinated to give the corresponding 1,2,4,5-tetrakis(amino)benzene compounds 2, 4, and 6; the crystal structures of compounds 1, 4, and 6 have been obtained. Cyclic voltammetry shows that all six compounds will lose two electrons to form dications, and the use of suitable oxidizing agents has allowed isolation and crystallographic characterization of the dications 2(2+) and 6(2+) (as [PF(6)](2) salts) and 4(2+) (as a [I(5)][I(3)] salt). The separation DeltaE between the loss of the first electron and the second varies between compounds, from 0.23 V in 1 to 0.01 V in 6. Electrochemical studies involving the use of the noncoordinating electrolyte [Bu(4)N][B{C(6)H(3)(CF(3))(2)}(4)] show that it is possible to increase this separation, stabilizing the intermediate monocationic phase, and this has allowed the isolation and crystallographic characterization of the radical salts 2[B{C(6)H(3)(CF(3))(2)}(4)] and 4[B{C(6)H(3)(CF(3))(2)}(4)], the first radical cations of this family to be isolated. DFT studies of the ion pairing between oxidized forms of 1 and 2 and anions imply that the location of the ion pairing is different in the two species.