Complexes of DOTA-bisphosphonate conjugates: probes for determination of adsorption capacity and affinity constants of hydroxyapatite

The adsorption on hydroxyapatite of three conjugates of a bisphosphonate and a macrocycle having C1, C2, and C3 spacers and their terbium complexes was studied by the radiotracer method using 160Tb as the label. The radiotracer-containing complex of the conjugate with the C3 spacer was used as a probe for the determination of the adsorption parameters of other bisphosphonates that lack a DOTA unit. A physicochemical model describing the competitive adsorption was successfully applied in the fitting of the obtained data. The maximum adsorption capacity of bisphosphonates containing bulky substituents is determined mainly by their size. For bisphosphonates having no DOTA moiety, the maximum adsorption capacity is determined by the electrostatic repulsion between negatively charged bisphosphonate groups. Compounds with a hydroxy or amino group attached to the alpha-carbon atom show higher affinities. Macrocyclic compounds containing a short spacer between the different bisphosphonic acid groups and the macrocyclic unit exhibit high affinities, indicating a synergic effect of the bisphosphonic and the macrocyclic groups during adsorption. The competition method described uses a well-characterized complex and allows a simple evaluation of the adsorption behavior of bisphosphonates. The application of the macrocycle-bisphosphonate conjugates allows easy radiolabeling via complexation of a suitable metal isotope.     

Extremal acidity of Rees polycyanated hydrocarbons in the gas phase and DMSO--a density functional study

It is shown by using the density functional theory (DFT) calculations that Rees tricyclic[10]annulene 1 and its benzo-annelated derivative 2, substituted by CN groups at all peripheral sp2 carbon positions, represent hyperstrong neutral superacids in the gas-phase and DMSO.     

On maximal cyclic subgroups in finite p-groups

In this note we consider finite noncyclic p-groups G all of whose maximal cyclic subgroups X satisfy one of the following two properties. (a) If each subgroup H of G containing X properly is nonabelian, then p = 2 and G is generalized quaternion. (b) If X is contained in exactly one maximal subgroup of G, then G is metacyclic. This solves the problems Nr.1541 and Nr. 1594 from [1].     

Chemical profile of the organic residue from ancient amphora found in the Adriatic Sea determined by direct GC and GC-MS analysis

An ancient organic residue was collected from the bottom of a Greco-Italian amphora found in the Adriatic Sea and investigated by direct GC and GC-MS analysis. The headspace composition was determined by HS-SPME using: (1) DVB/CAR/PDMS and (2) PDMS/DVB fibres. Higher percentages of benzene derivatives, monoterpenes and other low-molecular aliphatic compounds were obtained by method (1) in contrast to higher percentage of naphthalene and phenanthrene derivatives found by method (2). In comparison with the composition of pine resin, it is more likely that the found low-molecular aliphatic alcohols, acids, esters and carbonyls with 2-phenylethanol were trapped and preserved within the organic residue from stored wine - the amphora's originally content. Semi-volatile diterpenes methyl dehydroabietate (33.6%) and retene (24.1%) were dominant in the residue CH(2)Cl(2) solution. Other abundant compounds were 1,4-dimethoxyphenanthrene (6.8%) as well as other naphthalene and/or phenanthrene derivatives [7-(1-methylethyl)-1,4a-dimethyl-1,2,3,4,4a,9,10,10a-octahydronaphthalene, 7-(1-methylethyl)-1,4a-dimethyl-2,3,4,4a,9,10-hexahydrophenanthrene, 7-(1-methylethyl)-1,4a-dimethyl-1,2,3,4,4a,9,10,10a-octahydro-phenanthrene, 3,6-dimethylphenanthrene and 2,3,5-trimethylphenanthrene]. Possible sources and formation pathways of the major compounds in the residue were discussed.     

Finite nonabelian <Emphasis Type="Italic">p</Emphasis>-groups having exactly one maximal subgroup with a noncyclic center

We prove here that a nonabelian finite p-group G has exactly one maximal subgroup with a noncyclic center if and only if Z(G) is cyclic and G has exactly one normal abelian subgroup of type (p, p).     

Study of flammability and thermal properties of high-impact polystyrene nanocomposites

To increase thermal stability and flammability of high-impact polystyrene (HIPS) nanocomposites with silica nanoparticles and two types of polyphosphate flame retardants were prepared by extrusion. Nanocomposites were characterized by thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, limiting oxygen index (LOI) analysis and the evaluation of mechanical properties. It was found that organic polyphosphate in combination with silica increased thermal stability and fire retardancy by 50% in LOI test. Morphology characterization revealed existence of crystalline order which affected mechanical properties; tensile strength was approximately the same as virgin HIPS while elasticity was sharply decreased. Ammonium polyphosphate did not affect mechanical properties as much as the organic material but was not equally efficient in flame retardancy which was just marginally increased.     

Synthesis and characterization of poly(styrene-co-methyl methacrylate)/layered double hydroxide nanocomposites via in situ polymerization

Intercalated poly(styrene-co-methyl methacrylate)/layered double hydroxide nanocomposites (PS-PMMA/LDH-B) have been synthesized by the in situ bulk multistep polymerization of styrene and methyl methacrylate in the presence of the Ca-Al layered double hydroxide, previously modified by the incorporation of benzoate anions [Ca₄Al₂(OH)₁₂(C₆H₅COO)₂·xH₂O, LDH-B]. Nanocomposites were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM). XRD and TGA results pointed to the successful incorporation of the LDH-B within the copolymer matrix. XRD results indicated that the characteristic layered structure of the LDH-B had disappeared due to disordering. TEM analysis confirmed that LDH-B was partially dispersed within the matrix forming a structure with alternating matrix-particle regions, where particles appear in a form of intercalated nanocomposite structure. TGA results showed improved thermal properties in comparison to the neat PS-PMMA copolymer.