Dynamics of Dental Enamel Surface Remineralization under the Action of Toothpastes with Substituted Hydroxyapatite and Birch Extract.

To address tooth enamel demineralization resulting from factors such as acid erosion, abrasion, and chronic illness treatments, it is important to develop effective daily dental care products promoting enamel preservation and surface remineralization. This study focused on formulating four toothpastes, each containing calcined synthetic hydroxyapatite (HAP) in distinct compositions, each at 4%, along with 1.3% birch extract. Substitution elements were introduced within the HAP structure to enhance enamel remineralization. The efficacy of each toothpaste formulation was evaluated for repairing enamel and for establishing the dynamic of the remineralization. This was performed by using an in vitro assessment of artificially demineralized enamel slices. The structural HAP features explored by XRD and enamel surface quality by AFM revealed notable restorative properties of these toothpastes. Topographic images and the self-assembly of HAP nanoparticles into thin films on enamel surfaces showcased the formulations' effectiveness. Surface roughness was evaluated through statistical analysis using one-way ANOVA followed by post-test Bonferroni's multiple comparison test with a p value < 0.05 significance setting. Remarkably, enamel nanostructure normalization was observed within a short 10-day period of toothpaste treatment. Optimal remineralization for all toothpastes was reached after about 30 days of treatment. These toothpastes containing birch extract also have a dual function of mineralizing enamel while simultaneously promoting enamel health and restoration.

Spherical Closo Deltahedra with Surface Metal-Metal Multiple Bonding versus Oblate Deltahedra with Internal Metal-Metal Bonding in Dichromadicarbaborane Structures: The Nature of Stone's Icosahedral Dichromadicarbaborane.

The dichromadicarbaboranes Cp2Cr2C2B n-4H n-2 ( n = 8-12) related to the icosahedral structure reported in 1983 by Stone and co-workers and formulated by them as Cp2Cr2C2B8H10 have been investigated using density functional theory. In most cases, the lowest-energy structures are flattened oblatocloso structures with degree 6 and 7 chromium vertices similar to the lowest-energy and experimental structures of the isoelectronic dirhenaboranes Cp2Re2B n-2H n-2. However, most isomeric spherical closo deltahedral structures with surface Cr≣Cr quadruple bonds as well as isocloso structures with surface metal-metal Cr≡Cr triple bonds lie at accessible energies, typically lower than those in the corresponding dirhenaborane systems. However, for the 11-vertex Cp2Cr2C2B7H9 system, the most spherical closo/ isocloso deltahedral structure with a degree 6 metal vertex and degree 4 carbon vertices as well as a surface M≡M triple bond lies energetically below the lowest-energy oblatocloso structure. Calculations of the Cr-Cr distances in an icosahedral Cp2Cr2C2B8H10 structure and in a dihydrogenated icosahedral Cp2Cr2(µ-H)2C2B8H10 structure suggest the latter structure for "Cp2Cr2C2B8H10" reported by Stone and co-workers.

Paramagnetism in Metallacarboranes: The Polyhedral Chromadicarbaborane Systems.

The chromadicarbaboranes CpCrC2Bn-3Hn-1 (8 ≤ n ≤ 12) are of interest in providing stable paramagnetic deltahedral metallaboranes among which the 12-vertex CpCrC2B9H11 has been synthesized by Hawthorne and co-workers. Density functional theory shows that the lowest-energy such structures are quartet spin-state Cr(III) structures in which the central CrC2Bn-3 units exhibit most spherical closo deltahedral geometries similar to those found in the borane dianions BnHn2-. Higher-energy doublet CpCrC2Bn-3Hn-1 (8 ≤ n ≤ 11) structures are found exhibiting central CrC2Bn-3 isocloso deltahedral geometries, thereby providing a degree 6 vertex for the chromium atom. The lowest-energy CpCrC2Bn-3Hn-1 (8 ≤ n ≤ 11) structures all have both carbon atoms at degree 4 vertices. However, the lowest-energy CpCrC2B9H11 structures all have central CrC2B9 icosahedra and thus lack degree 4 vertices for the carbon atoms. For all of the CpCrC2Bn-3Hn-1 (8 ≤ n ≤ 12) systems the lowest-energy isomers are those with the maximum number of Cr-C edges in contrast to the related CpCoC2Bn-3Hn-1 systems.

Hypoelectronicity and Chirality in Dimetallaboranes of Group 9 Metals.

The structures and energetics of the dimetallaboranes Cp2M2Bn-2Hn-2 (n = 8, 9, 10, 11, 12; M = Co, Rh, Ir; Cp = η5-C5H5) were studied using density functional theory. The lowest energy Cp2M2B6H6 and Cp2M2B7H7 structures are chiral C2 structures based on the corresponding closo deltahedra, namely the bisdisphenoid and the tricapped trigonal prism. The permethylated iridaboranes Cp*2Ir2B6H6 and Cp*2Ir2B7H7 (Cp* = η5-Me5C5) were synthesized by Ghosh and co-workers. However, they were found by X-ray crystallography to have nondeltahedral structures containing a quadrilateral face, namely a bicapped trigonal prism and a capped square antiprism for the 8- and 9-vertex systems, respectively. These structures correspond to a mean of the two opposite enantiomers and can also represent the "square" intermediate in the interconversion of the two enantiomers. The lowest energy structures for the 10-vertex Cp2M2B8H8 systems are two isocloso deltahedra with one metal atom at a degree 6 vertex and the other metal atom at a degree 5 vertex. Both isomers have been realized experimentally for Cp2Ir2B8H8. The lowest energy structures for the 11-vertex Cp2M2B9H9 systems have central closo/isocloso deltahedra with one metal atom at a degree 6 vertex and the other metal atom at a nonadjacent degree 5 vertex. This structure type has been found experimentally in both the rhodaboranes and iridaboranes Cp*2M2B9H9 (M = Rh, Ir). The lowest energy structures for the 12-vertex systems Cp2M2B10H10 (M = Co, Rh, Ir) are deltahedra with two adjacent degree 6 vertices for the metal atoms. This type of structure is found experimentally in the rhodium complexes Cp*2Rh2B10H10-n(OH)n (n = 1, 2).

On the roles of the alanine and serine in the ß-sheet structure of fibroin.

In its silk II form, fibroin is almost exclusively formed from layers of ß-sheets, rich in glycine, alanine and serine. Reported here are computational results on fibroin models at semi-empirical, DFT levels of theory and molecular dynamics (MD) for (Gly)10, (Gly-Ala)5 and (Gly-Ser)5 decapeptides. While alanine and serine introduce steric repulsions, the alanine side-chain adds to the rigidity of the sheet, allowing it to maintain a properly pleated structure even in a single ß-sheet, and thus avoiding two alternative conformations which would interfere with the formation of the multi-layer pleated-sheet structure. The role of the serine is proposed to involve modulation of the hydrophobicity in order to construct the supramolecular assembly as opposed to random precipitation due to hydrophobicity.

Performance comparison of computational methods for modeling alpha-helical structures.

Geometry optimization results are reported for secondary structural elements of small proteins and polypeptides. Emphasis is placed on how well molecular mechanics as well as semiempirical, ab initio, and density functional methods describe α-helical and related structures in purely theoretical models (Gly10, Ile10) as well as in realistic models (an α-helical region of calmodulin, and the complete structure of a small protein). Many of the methods examined here were found to provide unsatisfactory descriptions of the hydrogen-bonding interactions within polypeptide-type structures, as the α-helical canonical secondary structure motif was not reproduced accurately. Ab initio and DFT methods provided reasonable results only when solvation models were included, although Hartree-Fock failed even with solvation in one of the test cases; among the semiempirical methods, one of the PM6 implementations performed very well.

(Diethyl-enetriamine)bis-(theophyllinato)zinc(II) dihydrate.

In the title compound, [Zn(C(7)H(7)N(4)O(2))(2)(C(4)H(13)N(3))]·2H(2)O, the Zn(II) ion is penta-coordinated by three N atoms of the diethyl-enetriamine ligand and one N atom of each of the two theophyllinate anions in a distorted trigonal-bipyramidal geometry. The Zn-N distances range from 2.076 (3) to 2.221 (3) Å. The crystal packing is stabilized by O-H⋯O, O-H⋯N and N-H⋯O hydrogen bonds involving the theophylline and diethyl-enetriamine ligands and uncoordinated water mol-ecules.