Dynamic contact angle and spreading rate measurements for the characterization of the effect of dentin surface treatments

A new methodology capable of providing reliable and reproducible contact angle (theta) data has been employed to study the effect of clinical treatments grinding, acid etching, and deproteinization on medial dentin tissue. It is based on the application of the ADSA-CD algorithm to the determination of low-rate dynamic contact angles, obtained from slowly growing drops, and on contact angle measurement, as well as spreading behavior analysis, during the relaxation of the system (water on treated dentin) after initial drop growth. The theta data obtained were substantially more reproducible than those obtained with classical methods. A net effect of the treatment on theta was found, increasing dentin wettability: theta (polished) >theta (etched) >theta (deproteinized). The spreading rates correlate with the angles and are adequate for the dentin surface characterization. ANOVA and SNK tests show that for advancing contact angles the means corresponding to all treatments are significantly different. In the relaxing phase, mean angle and spreading rates on polished dentin differ significantly from those on etched and deproteinized dentin, but the latter do not differ significantly from each other.     

Ring-opening Sn2'' reactions of 7-oxanorbornenes by organolithium reagents. Regio- and stereospecific synthesis of substituted cyclohexenediols

The nucleophilic Sn2' bridge opening of 7-oxabicyclo[2.2.1] hept-5-en-2-ols with organolithium reagents occurs in a regio- and stereospecific fashion to produce 6-substituted-cyclohex-4-en-1,3-diols, regardless of the stereochemistry at C-2. A free alcohol functionality is necessary to attain complete regiocontrol of the process. The methodology is utilized to prepare an optically pure cyclohexene derivative, (+)-(1S,3S,6R)-6-n-butyl-3-methyl-cyclohex-4-en-1,3-diol (5b), as a model system.     

(+)- and (-)-2-aminocyclobutane-1-carboxylic acids and their incorporation into highly rigid beta-peptides: stereoselective synthesis and a structural study

[Chemical reaction: See text] Several derivatives of (+)- and (-)-2-aminocyclobutane-1-carboxylic acid, 1, have been prepared through enantiodivergent synthetic sequences. The stereoselective synthesis of free amino acid (+)-1 has been achieved, and this product has been fully characterized for the first time. Stereocontrolled alternative synthetic methodologies have been developed for the preparation of bis(cyclobutane) beta-dipeptides in high yields. Among them, enantio and diastereomers have been synthesized. beta,beta- and beta,delta-Dimers resulting from the coupling of a cyclobutane residue and a linear amino acid have also been prepared. The ability of the cyclobutane ring as a structure-promoting unit both in the monomers and in the dimers has been manifested. The NMR structural study and DFT theoretical calculations evidence the formation of strong intramolecular hydrogen bonds giving rise to cis-fused [4.2.0]octane structural units that confer high rigidity on these molecules both in solution and in the gas phase. The contribution of a cis-trans conformational equilibrium derived from the rotation around the carbamate N-C(O) bond has also been observed, the trans form being the major conformer. In the solid state, this equilibrium does not exist, and moreover, intermolecular hydrogen bonds are present.     

The reaction of β-aminoenones with substituted acetonitriles. Regiospecific synthesis of 2(1H)-pyridones

Unsymmetrically substituted β-aminoenones react with malononitrile, cyanomethylphenylsulfone, benzoyl-acetonitrile and ethyl cyanoacetate, in very mild conditions, to yield regiospecifically 3-functionalized 2(1H)-pyridones in high yields.     

Multilayer sol-gel membranes for optical sensing applications: single layer pH and dual layer CO(2) and NH(3) sensors

Organo-silica sol-gel membranes have been prepared and demonstrated in a single layer format for pH measurement and multiple-layer format for both carbon dioxide and ammonia. The sensors are simple and versatile since the same chemistry and membranes are used for each sensor. The sensors use hydroxypyrenetrisulfonic acid (HPTS) as the indicator immobilized in a base-catalyzed sol-gel containing poly(dimethyl)siloxane, aminopropyltriethoxysilane (APTES) and tetraethylorthosilicate (TEOS). This indicator gel is over coated with a hydrophobic sol-gel to reduce cross reactivity to pH when either CO(2) or NH(3) are examined. The gels are very stable and the sensors retain response up to a 12-month period. Sensors can be stored in buffer or dry without loss of function and have response times to that are comparable to literature values.     

Regioselective homogeneous hydrogenation of heteroaromatic nitrogen compounds by use of [RuH(CO)(NCMe)2(PPh3)2]BF4 as the precatalyst

Summary The complex [RuH(CO)(NCMe)₂(PPh₃)₂]BF₄ (1) is an efficient and regioselective catalyst precursor for the hydrogenation of polyaromatic nitrogen compounds such as quinoline (Q), isoquinoline (iQ), indole (ln), 5,6- and 7,8-benzoquinoline (BQ) and acridine (A) under relatively mild reaction conditions (125 °C, 4 atm H₂). The order of individual initial rates was: A > Q > 5,6-BQ > 7,8-BQ > ln > iQ, reflecting both steric and electronic effects. For the regioselective homogeneous hydrogenation of A to 9,10-dihydroacridine (DHA) catalysed by complex (1), a kinetic study was carried out; the experimentally determined rate law was r = k ₁ [Ru] [H₂]. These findings are consistent with a mechanism involving the hydrogenation of [RuH(CO)(A)(NCMe)(PPh₃)₂]BF₄ to yield DHA and the unsaturated species [RuH(CO)(NCMe)(PPh₃)₂]BF₄ in the rate-determining step.     

New zinc phosphates decorated by imidazole-containing ligands

Four new zinc phosphates [Zn(HPO4)(C6H9N3O2)] (1), [Zn(HPO4)(C4H6N2)].H2O (2), [Zn2(HPO4)2(C14H14N4)].2H2O (3), and [Zn(HPO4)(C14H14N4)] (4) were synthesized in the presence of d-histidine, 1-methylimidazole, 1,4-bis(imidazol-1-ylmethyl)benzene (L1), and 1,2-bis(imidazol-1-ylmethyl)benzene (L2), respectively, and their structures were determined by X-ray crystallography. The inorganic framework of compounds 1, 2, and 3 is composed of vertex-shared ZnO3N and HPO4 tetrahedra that form four rings, which, in turn, are linked to generate a one-dimensional ladder structure. In 1 and 2 the organic groups (monoimidazole ligand) are located at each side of the ladders, while in 3 the bisimidazole ligand, 1,4-bis(imidazol-1-ylmethyl)benzene, links the ladders together to form a novel 2D structure. Compound 1 is the first zinc phosphate framework to be templated by an N-bonded chiral amino acid. In 4 the zero-dimensional four rings are joined together by the linear bridging ligand, 1,2-bis(imidazol-1-ylmethyl)benzene, to generate a one-dimensional framework with a new face-to-face structural motif. The 3D structure of compound 4 is stabilized by hydrogen-bonding, pi-pi interactions, and C-H...pi interactions. The approach of incorporating multifunctional ligands into zinc phosphate frameworks and linking the inorganic zinc phosphates subunits by an organic ligand provides opportunities for the design of new inorganic-organic open frameworks.     

Ab initio analytical potential energy surface and quasiclassical trajectory study of the O(+)((4)S)+H(2)(X (1)Sigma(g) (+))-->OH(+)(X (3)Sigma(-))+H((2)S) reaction and isotopic variants

An analytical potential energy surface (PES) representation of the O(+)((4)S)+H(2)(X (1)Sigma(g) (+)) system was developed by fitting around 600 CCSD(T)/cc-pVQZ ab initio points. Rate constant calculations for this reaction and its isotopic variants (D(2) and HD) were performed using the quasiclassical trajectory (QCT) method, obtaining a good agreement with experimental data. Calculations conducted to determine the cross section of the title reaction, considering collision energies (E(T)) below 0.3 eV, also led to good accord with experiments. This PES appears to be suitable for kinetics and dynamics studies. Moreover, the QCT results show that, although the hypotheses of a widely used capture model are not satisfied, the resulting expression for the cross section can be applied within a suitable E(T) interval, due to errors cancellation. This could be a general situation regarding the application of this simple model to ion-molecule processes.     

Mineral content and botanical origin of Spanish honeys

Eleven elements (Zn, P, B, Mn, Mg, Cu, Ca, Ba, Sr, Na and K) were determined by inductively plasma coupled spectrometry in 40 honey samples from different places of Spain and four different botanical origins: Eucalyptus (Eucalyptus sp.), Heather (Erica sp.), Orange-blossom (Citrus sinensis) and Rosemary (Rosmarinus officinalis). K, Ca and P show the higher levels with average concentrations ranged between 434.1-1935 mg kg⁻¹ for K; 42.59-341.0 mg kg⁻¹ for Ca and 51.17-154.3 mg kg⁻¹ for P. Levels of Cu (0.531-2.117 mg kg⁻¹), Ba (0.106-1.264 mg kg⁻¹) and Sr (0.257-1.462 mg kg⁻¹) are the lowest in all honey samples. Zn (1.332-7.825 mg kg⁻¹), Mn (0.133-9.471 mg kg⁻¹), Mg (13.26-74.38 mg kg⁻¹) and Na (11.69-218.5 mg kg⁻¹) concentrations were found strongly dependent on the kind of botanical origin.Results were submitted to pattern recognition procedures, unsupervised methods such as cluster and principal components analysis and supervised learning methods like linear discriminant analysis in order to evaluate the existence of data patterns and the possibility of differentiation of Spanish honeys from different botanical origins according to their mineral content. Cluster analysis shows four clusters corresponding to the four botanical origins of honey and PCA explained 71% of the variance with the first two PC variables. The best-grouped honeys were those from heather; eucalyptus honeys formed a more dispersed group and finally orange-blossom and rosemary honeys formed a less distinguishable group.