Highly active zinc alkyl cations for the controlled and immortal ring-opening polymerization of ε-caprolactone

Zinc alkyl cations supported by N,N-BIAN-type bidentate ligands were found to be highly active in the immortal ROP of ε-caprolactone to yield narrowly disperse and chain length-controlled poly(ε-caprolactone), whether in solution or bulk polymerization conditions.     

Triangular nickel complexes derived from 2-pyridylcyanoxime: an approach to the magnetic properties of the [Ni3(μ3-OH){pyC(R)NO}3]2+ core

A series of nickel complexes with nuclearity ranging from Ni(3) to Ni(6) have been obtained by treatment of a variety of nickel salts with the 2-pyridylcyanoxime ligand. The reported compounds have as a common structural feature the triangular arrangement of nickel cations bridged by a central μ(3)-oxo/alkoxo ligand. These compounds are simultaneously the first nickel derivatives of the 2-pyridylcyanoxime ligand and the first examples of isolated, μ(3)-O triangular pyridyloximate nickel complexes. Magnetic measurements reveal antiferromagnetic interactions promoted by the μ(3)-O and oximato superexchange pathways and comparison of the experimental structural and magnetic data with DFT calculations give an in-depth explanation of the factors that determine the magnetic interaction in this kind of system.     

Spectroscopy study of 5-amino-1,10-phenanthroline

Acidity constants for the 5-amino-1,10-phenanthroline (5-Aphen) were determined in aqueous media, using SQUAD and SUPERQUAD programs. Spectrophotometry and potentiometry data were fitted to the best model to enable correlation of the following acidity equilibria: 5-AphenH = 5-Aphen + H+ (-log K = 5.78 +/= 0.03) and 5-AphenH2 = 5-AphenH2 = 5-Aphen + 2H+ (-log K = 6.89 +/= 0.07). UV absorptivity coefficients obtained suggest that the first protonation takes place on the nitrogens of the heterocycle ring and the second protonation could take place on the amino group. As expected, the electrochemical evidence of the 5-Aphen species depends on the degree of protonation.     

Raman spectroscopic study of layered quaternary ferrite Ba12Fe28Ti15O84

Ba–Fe–Ti oxides are nowadays attracting considerable interest for the production of permanent magnets and microwave devices, due to their high dielectric constant. Among these materials, recently the quaternary ferrite Ba₁₂Fe₂₈Ti₁₅O₈₄ (BFT) was discovered to possess ferrimagnetic properties at room temperature with a main magnetic transition at about 420?K and complete disappearance of magnetisation above 700?K. In this study, we report for the first time on the Raman spectrum of BFT samples prepared with different methods. Raman spectra were recorded in dependence of temperature and a preliminary assignment of modes was attempted. Coupling the Raman results with previous magnetic studies allowed gaining more insight on the structural mechanism at play in correspondence of the main magnetic transition.     

Fluorescent Properties of Vitamin a Derivative,Retinyl Palmitate,in Binary Solvents with Aqueous Phase

Fluorescence emission and fluorescence excitation spactra of retinyl palmitate molecules in binary water/p-dioxane and water/isopropyl alcohol solvents under different solvents polarities were studied. The binary solvents polarities were changed by changing the molar ratios of water to p-dioxane (or isopropyl alcohol). It was suggested that the observed changes of spectral properties were caused by the formation of different retinyl palmitate self- organised structures that were induced by environments of different polarity. The role of non (low) polar components of binary solvents in the process of resultant structures creation is also discussed.     

Relationships Between Student,Teacher, and School Characteristics and Mathematics Achievement

A variety of factors contributes to student achievement in mathematics, including but not limited to student behaviors and student, teacher, and school characteristics. The purpose of this study was to explore which of these factors have an impact on student mathematics achievement. The target population for this study was North Carolina Algebra II students. Analyses of variance models were examined for group differences and a Three‐level Hierarchical Linear Modeling method was employed to examine individual predictors of student achievement in mathematics. Statistically, significant differences were found between students of different ethnicities, socioeconomic statuses (SES), and parental education levels. No gender effects were statistically significant. All teacher‐level variables investigated were found to be statistically significant, impacting student achievement in mathematics. School size and SES were not found to significantly contribute to student achievement. More research on the relationships between these factors shown to make statistically significant differences on mathematics achievement is needed to further explain several phenomena that this research reveals.     

Characterization of Closed Densely Defined Semi-Browder Linear Operators

In the present paper we characterize the closed densely defined semi-Browder operators through the Kato decomposition. Furthermore, we apply the obtained results to give a new characterization of Browder’s essential defect spectrum and Browder’s essential approximate point spectrum under finite rank operator perturbations.     

Direct Arylation in the Presence of Palladium Pincer Complexes

Direct arylation is an atom-economical alternative to more established procedures such as Stille, Suzuki or Negishi arylation reactions. In comparison with other palladium sources and ligands, the use of palladium pincer complexes as catalysts or pre-catalysts for direct arylation has resulted in improved efficiency, higher reaction yields, and advantageous reaction conditions. In addition to a revision of the literature concerning intra- and intermolecular direct arylation reactions performed in the presence of palladium pincer complexes, the role of these remarkably active catalysts will also be discussed.     

Modulation of DNA binding by reversible metal-controlled molecular reorganizations of scorpiand-like ligands

DNA interaction with scorpiand azamacrocycles has been achieved through modulation of their binding affinities. Studies performed with different experimental techniques provided evidence that pH or metal-driven molecular reorganizations of these ligands regulate their ability to interact with calf thymus DNA (ctDNA) through an intercalative mode. Interestingly enough, metal-driven molecular reorganizations serve to increase or decrease the biological activities of these compounds significantly.