Highly fluorescent rhodamine B nanoparticles entrapped in hybrid glasses

Rhodamine B (RB) nanoparticles entrapped in hybrid glasses show enhanced fluorescent emission (approximately 220-fold larger than that of single RB molecules) thanks to the configuration control of the self-assembled aggregates that form the supramolecular architecture of the nanoparticles. The fluorescence performance reported in this work is around 1 order of magnitude larger than that recently reported for fluorescent Nile Red nanoparticles. The fluorescence enhancement results from the use of a highly efficient fluorescent dye such RB and the formation of larger nanoparticles. Note that the later implies the presence of a large number of emitting centers involved in the fluorescence emission.     

Calorimetric and computational study of indanones

Condensed phase standard (p degrees = 0.1 MPa) molar enthalpies of formation for 1-indanone, 2-indanone, and 1,3-indandione were derived from the standard molar enthalpies of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The standard molar enthalpies of sublimation for 1-indanone and 2-indanone, at T = 298.15 K, were measured both by correlation-gas chromatography and by Calvet microcalorimetry leading to a mean value for each compound. For 1,3-indandione, the standard molar enthalpy of sublimation was derived from the vapor pressure dependence on temperature. The following enthalpies of formation in gas phase, at T = 298.15 K, were then derived: 1-indanone, -64.0 +/- 3.8 kJ mol(-1); 2-indanone, -56.6 +/- 4.8 kJ mol(-1); 1,3-indandione, -165.0 +/- 2.6 kJ mol(-1). The vaporization and fusion enthalpies of the indanones studied are also reported. In addition, theoretical calculations using the density functional theory with the B3LYP and MPW1B95 energy functionals and the 6-311G** and cc-pVTZ basis sets have been performed for these molecules and the corresponding one-ring species to obtain the most stable geometries and to access their energetic stabilities.     

Energetic study applied to the knowledge of the structural and electronic properties of monofluorobenzonitriles

The present work reports an energetic and structural study of 2-fluoro-, 3-fluoro-, and 4-fluorobenzonitrile. The standard molar enthalpies of formation, in the condensed phase, of the three isomers were derived from the standard molar energies of combustion, in oxygen, at T = 298.15 K. The standard molar enthalpies of vaporization or sublimation (for 4-fluorobenzonitrile), at T = 298.15 K, were measured using high-temperature Calvet microcalorimetry. The combination of these two parameters yields the standard molar enthalpies of formation in the gaseous phase. The vapor-pressure study of the referred compounds was performed by a static method, and the enthalpies of phase transition derived from the application of the Clarke and Glew equation. Theoretically estimated gas-phase enthalpies of formation, basicities, proton and electron affinities, and adiabatic ionization enthalpies were calculated from the G3MP2B3 level of theory. In order to evaluate the electronic properties, the geometries were reoptimized at MP2/cc-pVTZ level, and the QTAIM and NICS were computed. On the basis of the donor-acceptor system, another approach for evaluating the electronic effect for these compounds, using the NBO is suggested. The UV-vis spectroscopy study for the three isomers was performed. The intensities and the band positions were correlated with the thermodynamic properties calculated computationally.     

Scanning electron microscopy and roughness study of dental composite degradation

Our aim was to test the hypothesis that the use of mouthwashes, consumption of soft drinks, as well as the type of light curing unit (LCU), would change the surface roughness (Ra) and morphology of a nanofilled composite resin (Z350? 3M ESPE). Samples (80) were divided into eight groups: Halogen LCU, group 1, saliva (control); group 2, Pepsi Twist?; group 3, Listerine?; group 4, Colgate Plax?; LED LCU, group 5, saliva; group 6, Pepsi Twist?; group 7, Listerine?; group 8, Colgate Plax?. Ra values were measured at baseline, and after 7 and 14 days. One specimen of each group was prepared for scanning electron microscopy analysis after 14 days. The data were subjected to multifactor analysis of variance at a 95% confidence followed by Tukey's honestly significant difference post-hoc test. All the treatments resulted in morphological changes in composite resin surface, and the most significant change was in Pepsi Twist? groups. The samples of G6 had the greatest increase in Ra. The immersion of nanofilled resin in mouthwashes with alcohol and soft drink increases the surface roughness. Polymerization by halogen LCU (reduced light intensity) associated with alcohol contained mouthwash resulted in significant roughness on the composite.     

Biaryl-bridged macrocyclic peptides: conformational constraint via carbogenic fusion of natural amino acid side chains

A general method for constraining peptide conformations via linkage of aromatic sidechains has been developed. Macrocyclization of suitably functionalized tri-, tetra- and pentapeptides via Suzuki-Miyaura cross-coupling has been used to generate side chain to side chain, biaryl-bridged 14- to 21-membered macrocyclic peptides. Biaryl bridges possessing three different configurations, meta-meta, meta-ortho, and ortho-meta, were systematically explored through regiochemical variation of the aryl halide and aryl boronate coupling partners, allowing fine-tuning of the resultant macrocycle conformation. Suzuki-Miyaura macrocyclizations were successfully achieved both in solution and on solid phase for all three sizes of peptide. This approach constitutes a means of constraining peptide conformation via direct carbogenic fusion of side chains of naturally occurring amino acids such as phenylalanine and tyrosine, and so is complementary to strategies involving non-natural, for example, hydrocarbon, bridges.     

Low-energy unphysical saddle in polynomial molecular potentials

Vibrational spectra of polyatomic molecules are often obtained from a polynomial expansion of the adiabatic potential around a minimum. For several molecules, we show that such an approximation displays an unphysical saddle point of comparatively small energy, leading to a region where the potential is negative and unbounded. This poses an upper limit for a reliable evaluation of vibrational levels. We argue that the presence of such saddle points is general.     

The level of cross-linking and the structure of anisotropic magnetorheological elastomers

The influence of the concentration of the magnetic powder on the level of cross-linking of magnetorheological elastomers (MREs) has been studied. Afterwards the structural characterisation of manufactured MREs has been performed by using non-destructive method, specifically the computed tomography. The correlation between internal structures of MREs and the developing of its cross-linking level during the curing was found. It was shown that changes in the concentration of the powder significantly affect morphologies of the sample.     

The Embedding of Schwarzschild in Braneworld

The braneworlds models were inspired partly by Kaluza-Klein’s theory, where both the gravitational and the gauge fields are obtained from the geometry of a higher dimensional space. The positive aspects of these models consist in perspectives of modifications it could bring in to particle physics, such as: unification in a TeV scale, quantum gravity in this scale and deviation of Newton’s law for small distances. One of the principles of these models is to suppose that all space-times can be embedded in a bulk of higher dimension. The main result in these notes is a theorem showing a mathematical inconsistency of the Randall-Sundrum braneworld model, namely that the Schwarzschild space-time cannot be embedded locally and isometrically in a five dimensional bulk with constant curvature (for example AdS-5). From the point of view of semi-Riemannian geometry this last result represents a serious restriction to the Randall-Sundrum’s braneworld model.     

CASSCF and multireference CI with singles and doubles study of low-lying valence and Rydberg states of 2H-tetrazole

Complete active space self-consistent field (CASSCF) and multireference CI with singles and doubles (MR-CISD) calculations [including extensivity corrections, at MR-CISD+Q and multireference averaged quadratic coupled cluster (MR-AQCC) levels] have been performed to characterize the low-lying valence and the Rydberg states of 2H-tetrazole. The highest level results (MR-AQCC/d'-aug'-cc-pVDZ) indicate the following ordering of the valence singlet excited states: S(1) (n-pi*), 6.06 eV; S(2) (n-pi*), 6.55 eV; S(3) (pi-pi*), 6.55 eV. The MR-CISD+Q/d'-aug'-cc-pVDZ results indicate the same ordering, but at slight higher energies: 6.16, 6.68, and 6.69 eV, respectively. According to our MR-CISD+Q/d'-aug'-cc-pVDZ results, the next two states are Rydberg states, at 7.69 eV (pi-3s) and 7.89 eV (n-3s). The calculated energies of these two states, as well as their proximity, are consistent with the conclusion reached by Palmer and Beveridge (Chem Phys 1987, 111, 249) that the first band of the photoelectron spectrum of 2H-tetrazole is likely to be associated to the first two ionizations processes (of pi and N lone pair electrons), at energies close to 11.3 eV.