Spectral stability results for higher-order operators under perturbations of the domain

We analyze the spectral behavior of higher-order elliptic operators when the domain is perturbed. We provide general spectral stability results for Dirichlet and Neumann boundary conditions. Moreover, we study the bi-harmonic operator with the so-called intermediate boundary conditions. We give special attention to this last case and analyze its behavior when the boundary of the domain has some oscillatory behavior. We will show that there is a critical oscillatory behavior and that the limit problem depends on whether we are above, below or just sitting on this critical value.     

A convenient synthetic approach to alpha-amino-beta-lactam synthesis promoted by phenyl dichlorophosphate reagent

The ready and economical phenyl dichlorophosphate, in contrast to many reagents developed for activating carboxyl groups for the beta-lactam synthesis, is shown to be very efficient for the synthesis of alpha-vinylamino-beta-lactams from Dane salts and Schiff bases. Some observations toward the scope of the method are also briefly described. The interaction of acetic acids with ethanolimines afforded beta-lactams and/or oxazolidines according to the synthetic methodology used.     

Synthesis,characterization and thermal behaviour of 2,6- and 3,4-dimethylpyridinium and 2,4,6-trimethylpyridinium octamolybdates

2,6- and 3,4-dimethylpyridinium and 2,4,6-trimethylpyridinium octamolybdates were synthesized and characterized and their thermal decompositions were studied by means of thermogravimetry. The thermal stabilities follow the sequence: 2,4,6-TMPO <2,6-DMPO <3,4-DMPO, which seems to be related to the positions of the methyl groups on the pyridine ring. Kinetic parameters were calculated for the first decomposition step of the two dimethylpyridinium octamolybdates. A nucleation mechanism is proposed. The best fit corresponds to a random nucleation (one nucleus per particle) controlled equation. The calculated activation energies were 120.9 and 133.7 kJ/mol^?1 for the 2,6- and the 3,4 derivative, respectively.     

Theoretical study in gas phase of linear and nonlinear optical properties of the ortho-, meta- and para-nitrophenol isomers

The linear (α), and nonlinear (β, γ) optical NLO properties of ortho-, meta- and para-nitrophenol (ONP, MNP and PNP) isomers have been calculated in gas phase by using ab initio (HF, MP2 and MP4) and density functional theory (DFT) (B3LYP, CAM-B3LYP) methods, with the 6-31+G(d,p) and 6-311+G(3d,3p) standard and the Sadlej specialized basis sets. These properties were evaluated both at static and at dynamic regime within the finite field FF numerical techniques and the time-dependent-Hartree–Fock approach at 1,910 nm, respectively. Additional calculations were performed for the β static hyperpolarizability of these isomers in presence of p-dioxane solvent with the Onsager Model and the SCRF-PCM approach, using B3LYP/6-31+G(d,p) and MP2/6-31+G(d,p) levels of theory. Additionally, CCSD/6-31+G(d,p) calculations were performed for the α, β and γ properties of PNP isomer. The B3LYP and MP2 α _ave results of the nitrophenol isomers are comparable to the experimental α _ave reports; while the tendency for the β _v calculated values (β _v PNP > β _v MNP > β _v ONP), that can be explained in terms of the O _x atomic charge of the –NO₂ group, does not follow exactly the experimental ones. The B3LYP γ _ave results are in correspondence to the experimental measurements, the correlation of which is r ² = 0.99. The use of FF methodology in conjunction with the B3LYP and MP2 methods and the 6-31+G(d,p) basis set show to be appropriate approaches to predict qualitative optical properties of Push–Pull like organic molecules, provided are considered the solvent effects or frequency dependence. However, to have a clear picture of the NLO properties of an isolated molecule, higher order correlation effects combined with specialized basis sets, frequency and solvent effects should be employed. We have demonstrated that MP4/Sadlej level of theory is able to reproduce NLO properties that can be considered equivalent to those from more sophisticated approaches, such as CCSD together with extended basis sets.     

Thermodynamic study of the influence of polyols and glucose on the thermal stability of holo-bovine α-lactalbumin

Thermal stability of bovine α-lactalbumin in buffer and dilute aqueous solutions of erythritol, xylitol, sorbitol, inositol and glucose was evaluated by fluorescence spectroscopy and circular dichroism. Results show that at the selected conditions, the transition is reversible and is well described by a two-state model. At low concentration the cosolutes do not show a structure stabilizing effect, and some of them even destabilize the protein. At higher concentration, all of them stabilize the native protein conformation; however, the extent of stabilization is lower than the effect shown with other proteins, presumably due to the lactalbumin incomplete unfolding.