Chemical algebra. II: Discriminating pairing products

The algebra of stereogenic pairing equlibria is presented in a very general context. Starting from the notions of fuzzy subgroup and conjugacy link, chemical pairing constants between molecular speciesu andv having a skeletal symmetry groupG are formulated as pairing products on aG-Hilbert space. Discriminating pairing productsK are defined by the conditions: K 1 and K = 1 the representative vectors of the paired species areG-equivalent. WhenG has only two elements, the pairing product is always discriminating. For several skeletal symmetries, if the vectors are enantiomorphic (v = u, ² =e, G), thenK is greater than 1 and reaches 1 only ifu is achiral: chirality indexes and general permutational indexes are then defined fromK(u u). The general model is illustrated by some examples.     

Chemical algebra. IV: “Length” of transformation pathways between skeletal analogs

Even if the eq. of completely G-invariant distance extensions derived from a pairing product is not resolved, a distance is defined by means of a metric obtained by differential resolution. Under specified conditions, the linear element solution do² is homogeneous to square coordinate differentials. Integration of da along a curve of E affords a length relative to doe. Boundaries of the curve represent skeletal analogs u and v, whereas inner points represent intermediates in the transformation u v, where the ligand parameters are supposed to vary continuously: a stereogenic pairing equilibrium between infinitesimally close skeletal analogs is assumed. If the curve runs orthogonal to a unit representation space of G, the length is infinite and the curve might be regarded as a fractal transformation pathway. The thermodynamic gap D_p is always shorter than the kinetic distance of the metric do².     

Biocompatible hydrogels based on chitosan,cellulose/starch,PVA and PEDOT:PSS with high flexibility and high mechanical strength

Fabricating mechanically strong hydrogels that can withstand the conditions in internal tissues is a challenging task. We have designed hydrogels based on multicomponent systems by combining chitosan, starch/cellulose, PVA, and PEDOT:PSS via one-pot synthesis. The starch-based hydrogels were homogeneous, while the cellulose-based hydrogels showed the presence of cellulose micro- and nanofibers. The cellulose-based hydrogels demonstrated a swelling ratio between 121 and 156%, while the starch-based hydrogels showed higher values, from 234 to 280%. Tensile tests indicated that the presence of starch in the hydrogels provided high flexibility (strain at break?>?300%), while combination with cellulose led to the formation of stiffer hydrogels (elastic moduli 3.9–6.6 MPa). The ultimate tensile strength for both types of hydrogels was similar (2.8–3.9 MPa). The adhesion and growth of human osteoblast-like SAOS-2 cells was higher on hydrogels with cellulose than on hydrogels with starch, and was higher on hydrogels with PEDOT:PSS than on hydrogels without this polymer. The metabolic activity of cells cultivated for 3 days in the hydrogel infusions indicated that no acutely toxic compounds were released. This is promising for further possible applications of these hydrogels in tissue engineering or in wound dressings.

Graphical abstract

     

Hydrous ferric oxide: evaluation of Cd-HFO surface complexation models combining Cd(K) EXAFS data,potentiometric titration results,and surface site structures identified from mineralogical knowledge

The surface properties of ferrihydrite were studied by combining wet chemical data, Cd(K) EXAFS data, and a surface structure and protonation model of the ferrihydrite surface. Acid-base titration experiments and Cd(II)-ferrihydrite sorption experiments were performed within 3<-log[H(+)]<10.5 and 0.5<[Cd(t)]<12 mM in 0.3 M NaClO(4) at 25 degrees C, where [Cd(t)] refers to total Cd concentration. Measurements at -5.5triple bond Fe-OH(-1/2),logk((int))=-8.29, assuming the existence of a unique intrinsic microscopic constant, logk((int)), and consequently the existence of a single significant type of acid-base reactive functional groups. The surface structure model indicates that these groups are terminal water groups. The Cd(II) data were modeled assuming the existence of a single reactive site. The model fits the data set at low Cd(II) concentration and up to 50% surface coverage. At high coverage more Cd(II) ions than predicted are adsorbed, which is indicative of the existence of a second type of site of lower affinity. This agrees with the surface structure and protonation model developed, which indicates comparable concentrations of high- and low-affinity sites. The model further shows that for each class of low- and high-affinity sites there exists a variety of corresponding Cd surface complex structure, depending on the model crystal faces on which the complexes develop. Generally, high-affinity surface structures have surface coordinations of 3 and 4, as compared to 1 and 2 for low-affinity surface structures.     

Facile access to γ-aminothiols from 1,3-thiazines via a microwave-assisted three-component reaction

A new efficient and general synthetic methodology to access γ-aminothiols was investigated and developed. 1,3-Thiazines were used as convenient precursors and were prepared by a fast microwave-assisted three-component reaction (3CR) of thioamides, aldehydes, and alkenes. The transformation of thiazines into aminothiols was achieved via a thiazinium salt hydrolysis, in three very facile steps.     

Ion chromatograph with three-dimensional printed absorbance detector for indirect ultraviolet absorbance detection of phosphate in effluent and natural waters

An ion chromatography system employing a low-cost three-dimensional printed absorbance detector for indirect ultraviolet detection towards portable phosphate analysis of environmental and industrial waters has been developed. The optical detection cell was fabricated using stereolithography three-dimensional printing of nanocomposite material. Chromatographic analysis and detection of phosphate were carried out using a CS5A 4 × 250 mm analytical column with indirect ultraviolet detection using a 255 nm light-emitting diode. Isocratic elution using a 0.6 mM potassium phthalate eluent combined with 1.44 mM sodium bicarbonate was employed at a flow rate of 0.75 mL/min. A linear calibration range of 0.5 to 30 mg/L PO₄³⁻ applicable to environmental and wastewater analysis was achieved. For retention time and peak area repeatability, relative standard deviation values were 0.68 and 4.09%, respectively. Environmental and wastewater samples were analyzed with the optimized ion chromatography platform and the results were compared to values obtained by an accredited ion chromatograph. For the analysis of environmental samples, relative errors of <14 % were achieved. Recovery analysis was also carried out on both freshwater and wastewater samples and recovery results were within the acceptable range for water analysis using standard ion chromatography methods.     

Thermo-cleavable polymers: Materials with enhanced photochemical stability

Photochemical stability of three thermo-cleavable polymers was investigated as thin films under atmospheric conditions. A significant increase in lifetime was observed once the side-chain was cleaved emphasizing the detrimental effect of solubilizing groups on the photochemical stability of conjugated polymers. In addition to their ease of processing, thermo-cleavable polymers thus also offer a greater intrinsic stability under illumination.     

Michael addition to a chiral non-racemic 2-phosphono-2,3-didehydrothiolane S-oxide

The Michael addition of selected sulfur and nitrogen nucleophiles to a chiral non-racemic 2-phosphono-2,3-didehydrothiolane S-oxide is fully diastereoselective. The enantiomeric excesses of the adducts obtained could be determined by ³¹P NMR spectroscopy using (R)-(+)-tert-butyl(phenyl)phosphinothioic acid as a chiral solvating agent. The addition of thiophenol was monitored by ³¹P NMR spectroscopy which made it possible to observe the formation and evolution of the kinetic and thermodynamic adducts in the reaction mixture. The structures of both enantiomeric thiophenol adducts have been determined by X-ray analysis.