The interaction of an azo compound with a surfactant and ion pair adsorption to solid phases

The adsorption of SPADNS (trisodium salt of 2-(p-sulfophenylazo)-1,8-dihydroxynaphthalene-3,6-disulfonic acid) onto resins XAD 2, XAD 7 and silica gel was studied in the presence and in the absence of the cationic surfactant CTAB (cetyl trimethylammonium bromide). At a ratio of 2.5 CTAB to 1 SPADNS, the surfactant caused a marked increase in SPADNS adsorption. The experimental results for adsorption versus time were applied on the basis of three kinetic models (pseudo-first-order Lagergren, pseudo-second-order, and intraparticle diffusion). The interaction between CTAB and SPADNS was investigated using spectrophotometric, conductometric, and computational techniques. Theoretical results point to the formation of an ion pair between CTAB and SPADNS that influences the solution spectra, in agreement with conductometric and spectrophotometric data.     

Measurement uncertainty of food carotenoid determination

For consistent interpretation of an analytical method result it is necessary to evaluate the confidence that can be placed in it, in the form of a measurement uncertainty estimate. The Guide to the expression of Uncertainty in Measurement issued by ISO establishes rules for evaluating and expressing uncertainty. Carotenoid determination in food is a complex analytical process involving several mass transfer steps (extraction, evaporation, saponification, etc.), making difficult the application of these guidelines. The ISO guide was interpreted for analytical chemistry by EURACHEM, which includes the possibility of using intra- and interlaboratory information. Measurement uncertainty was estimated based on laboratory validation data, including precision and method performance studies, and also, based on laboratory participation in proficiency tests. These methods of uncertainty estimation were applied to analytical results of different food matrices of fruits and vegetables. Measurement uncertainty of food carotenoid determination was 10–30% of the composition value in the great majority of cases. Higher values were found for measurements near instrumental quantification limits (e.g. 75% for β-cryptoxanthin, and 99% for lutein, in pear) or when sample chromatograms presented interferences with the analyte peak (e.g. 44% for α-carotene in orange). Lower relative expanded measurement uncertainty values (3–13%) were obtained for food matrices/analytes not requiring the saponification step. Based on these results, the saponification step should be avoided if food carotenoids are not present in the ester form. Food carotenoid content should be expressed taking into account the measurement uncertainty; therefore the maximum number of significant figures of a result should be 2.     

Silver(I) and copper(I) complexes supported by fully fluorinated 1,3,5-triazapentadienyl ligands

Synthesis of the perfluorinated 1,3,5-triazapentadiene [N{(CF(3))C(C(6)F(5))N}(2)]H and the use of its conjugate base as a supporting ligand for the isolation of silver(i) and copper(i) complexes are reported. Some of the related chemistry involving [N{(C(3)F(7))C(C(6)F(5))N}(2)](-) (that has bulkier -C(3)F(7) groups on the 1,3,5-triazapentadienyl ligand backbone) is also presented. X-ray crystallographic data show a wide variety of structures ranging from intermolecular, hydrogen-bonded chain structure for [N{(CF(3))C(C(6)F(5))N}(2)]H with a twisted W-shaped N(3)C(2) core, monomeric [N{(CF(3))C(C(6)F(5))N}(2)]Ag(CN(t)Bu)(2) and [N{(C(3)F(7))C(C(6)F(5))N}(2)]Ag(CN(t)Bu)(2) where the κ(1)-bonded triazapentadienyl ligand bonding to the metal fragment via the central nitrogen atom, monomeric [N{(CF(3))C(C(6)F(5))N}(2)]Ag(PPh(3))(2) and [N{(C(3)F(7))C(C(6)F(5))N}(2)]Ag(PPh(3))(2) that feature κ(1)-bonded triazapentadienyl ligand bonding to the metal fragment via one of the terminal nitrogen atoms, to that of the monomeric [N{(CF(3))C(C(6)F(5))N}(2)]Cu(CN(t)Bu)(2) containing a κ(2)-bonded triazapentadienyl ligand and a U-shaped NCNCN ligand backbone. The isocyanide adducts show relatively high ν(CN) values in the IR spectra.     

p53‐Dependent and p53‐Independent Responses of Cells Challenged by Photosensitization

The p53 protein exerts fundamental roles in cell responses to a variety of stress stimuli. It has clear roles in controlling cell cycle, triggering apoptosis, activating autophagy and modulating DNA damage response. Little is known about the role of p53 in autophagy‐associated cell death, which can be induced by photoactivation of photosensitizers within cells. The photosensitizer 1,9‐dimethyl methylene blue (DMMB) within nanomolar concentration regimes has specific intracellular targets (mitochondria and lysosomes), photoinducing a typical scenario of cell death with autophagy. Importantly, in consequence of its subcellular localization, photoactive DMMB induces selective damage to mitochondrial DNA, saving nuclear DNA. By challenging cells having different p53 protein levels, we investigated whether p53 modulates DMMB/light‐induced phototoxicity and cell cycle dynamics. Cells lacking p53 activity were slightly more resistant to photoactivated DMMB, which was correlated with a smaller sub‐G1 population, indicative of a lower level of apoptosis. DMMB photosensitization seems to induce mostly autophagy‐associated cell death and S‐phase cell cycle arrest with replication stress. Remarkably, these responses were independent on the p53 status, indicating that p53 is not involved in either process. Despite describing some p53‐related responses in cells challenged by photosensitization, our results also provide novel information on the consequences of DMMB phototoxicity.     

Formation of cinnoline derivatives by a gold(I)-catalyzed hydroarylation of N-propargyl-N′-arylhydrazines

A study concerning the gold(I)-catalyzed hydroarylation of N-propargyl-N′-arylhydrazinecarboxylic acid methyl esters is described. The use of the gold complex [XPhosAu(NCCH₃)SbF₆] as the catalyst in refluxing nitromethane allows the generally rapid and efficient synthesis of a range of functionalized 4-exo-methylene-1,2-dihydrocinnolines.     

Selective Sulfenylative Desulfonylation or Decarbalkoxylation of α-Sulfonyl Malonates with DABCO or Bu3N: Reactivity and Conformational Analysis

The study on reactivity of several α-substituted α-sulfonyl malonates toward 1,4-diazabicyclo[2.2.2]octane (DABCO) and Bu₃N is described. The reactivity with DABCO revealed the possible competition between decarbalkoxylation and unexpected desulfonylation, depending on the α-substituent, because of sterical hindrance around the electrophilic centers (SO₂ and CO₂R). The derivatives with crowded α-substituents suffer selective desulfonylation, and a novel and efficient desulfonylation method can be proposed. The dependence of the reactivity of α-sulfonyl malonates on the sterical hindrance around the electrophilic centers is confirmed by conformational analysis (Macromodel/MM2? and Mopac/MP3). The carbanionic mechanism is proved because the corresponding protonated, deuterated, and sulfenylated products were obtained by addition of the corresponding electrophilic agents. Bu₃N showed itself to be a novel selective decarbalkoxylation agent for any α-substituted α-sulfonyl malonate.     

Universal behavior of transverse momentum distributions of baryons and mesons in the framework of percolation of strings

In the framework of percolation of strings, the transverse momentum distributions in AA and hh collisions at all centralities and energies show a universal behavior. The width of these distributions is related to the width of the distribution of the size of the clusters formed by the overlapping of the strings produced. The difference between the distributions for baryons and mesons originates in the fragmentation of clusters of several strings, which enhances the particles with a higher number of constituents. The results agree with SPS and RHIC data. The predictions for LHC show differences for baryons compared with RHIC. At LHC energies we obtain also a high p_T suppression for pp high multiplicity events compared with the pp minimum bias. PACS 25.75.Nq; 12.38.Mh; 24.85.+p