Use of the pseudophase model in the interpretation of reactivity under restricted geometry conditions. An application to the study of the [Ru(NH(3))(5)pz](2+) + S(2)O(8)(2-) electron-transfer reaction in different microheterogeneous systems

The title reaction has been studied under restricted geometry conditions, comprising aqueous solutions of a polymer (DNA), cyclodextrins, and dendrimers as well as (CTA)Cl micellar solutions and sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/water/oil microemulsions. The results are interpreted by taking as a general basis the pseudophase model, modified in some cases in order to take into account the specificity of the reaction medium. These modifications describe the anti-cooperative character of the binding of the substrates to the surfaces and the changes of the electric potential at the surfaces. The conclusion is that the pseudophase model is a powerful tool for the interpretation of kinetic data in the reaction media considered in this work, provided that the specificity of these media were incorporated into the model.     

Ion chemistry of OV(OCH3)3 in the gas phase: molecular cations and anions and their primary fragmentations

Trimethyl vanadate(V), OV(OCH(3))(3) (1), is examined by various mass spectrometric means. Photoionization experiments yield an ionization energy of IE(OV(OCH(3))(3)) = 9.54 +/- 0.05 eV for the neutral molecule. The primary fragmentation of the molecular cation 1(+), i.e., loss of neutral formaldehyde, can occur via two independent routes of hydrogen migrations to afford the formal V(IV) compounds HOV(OCH(3))(2)(+) and OV(OCH(3))(CH(3)OH)(+), respectively. These two pathways are associated with low-lying activation barriers of almost identical height. At elevated energies, direct V-O bond cleavage of 1(+) allows for expulsion of a methoxy radical concomitant with the generation of the cationic fragment OV(OCH(3))(2)(+), a formal V(V) compound. Trimethyl vanadate can also form a molecular anion, 1(-), whose most abundant dissociation channel involves loss of a methyl radical, thereby leading to the formal V(V) compound OV(OCH(3))(2)O(-). Various mass spectrometric experiments and extensive theoretical studies provide detailed insight into the ion structures and the relative energetics of the primary dissociation reactions of the molecular cations and anions of 1.     

The parallel synthesis of a disaccharide library using a solid phase, peptide-templated strategy

A novel strategy for the synthesis of oligosaccharides, involving the use of a solid phase peptide template, has been successfully applied to the construction of a twelve member disaccharide library.     

Vibration frequencies for a uniform beam with one end spring-hinged and subjected to a translational restraint at the other end

The purpose of the present study is to deal with the free vibration of a beam hinged at one end by a rotational spring and subjected to the restraining action of a translational spring at the other end. The eigenfrequencies for the fundamental mode are presented for different values of the parameters K_RL/EI and K_TL³/EI, where KR and K_T are the stiffness constants of the springs.     

Clifford Cauchy type integrals on Ahlfors-David regular surfaces in $$\mathbb{R}^{m + 1} $$

The main goal of this paper is centred around the study of the behavior of the Cauchy type integral and its corresponding singular version, both over nonsmooth domains in Euclidean space. This approach is based on a recently developed quaternionic Cauchy integrals theory [1, 5, 7] within the three-dimensional setting. The present work involves the extension of fundamental results of the already cited references showing that the Clifford singular integral operator has a proper invariant subspace of generalized H?lder continuous functions defined in a surface of the (m+1)-dimensional Euclidean space.     

Raman scattering in Ag-intercalated TiS2

Ag-intercalated TiS₂ has been investigated using electron diffraction and Raman scattering. The energies of the E_g-1 and A_1g modes in 1T-TiS₂ at 300 K were found to be 232 and 336 cm^-1, respectively. In Ag_0.3TiS₂, at an ambient temperature of 4.2 K, modes were observed at 207, 239, 277, 311, and 347 cm^-1. Three of these modes have been associated with the formation of a superlattice at low temperatures. The superlattice formation was observed by electron diffraction and is attributed to an ordering of the silver atoms at interlayer interstices.     

Analyticity and ergodicity in the maximum-entropy approach to statistical nuclear reactions

In the maximum-entropy approach to statistical nuclear reactions one imposes naturally the constraints of unitarity and symmetry of theS-matrix, and of a fixed expectation value ofS. We show that the analytical structure of theS-matrix and the requirement that the problem be ergodic (so that energy averages can be replaced by ensemble averages) impose certain restrictions on the distribution of statisticalS-matrices. Some of these additional constraints are then imposed numerically in a two-channel calculation, and are shown to improve the results for the fluctuation cross sections, the elastic enhancement factor, etc.     

Homogenization of magnetodielectric photonic crystals

We calculate the low-frequency index of refraction of a medium which is homogeneous along axis z and possesses a periodic dependence of the permittivity epsilon(r) and permeability micro(r) in the x-y plane (2D magnetodielectric photonic crystal). Exact analytical formulas for the effective index of refraction for two eigenmodes with vector E or H polarized along axis z are obtained. We show that, unlike nonmagnetic photonic crystals where the E mode is ordinary and the H mode is extraordinary, now both modes exhibit extraordinary behavior. Because of this distinction, the magnetodielectric photonic crystals exhibit optical properties that do not exist for natural crystals. We also discuss the limiting case of perfectly conducting cylinders and clarify the so-called problem of noncommuting limits, omega-->0 and epsilon--> infinity.     

Archaeometry of pre‐Hispanic pottery from San Luis Potosi, México

Neutron activation analysis, Mössbauer spectroscopy and X‐ray diffraction techniques were used to characterize pre‐Hispanic potsherds and modern ceramic pottery, samples of which were collected in Tenexco, San Luis Potosi, Mexico. Elementary and spectroscopic analysis showed differences between ancient and modern ceramics. While the modern ceramics studied were practically new and not used at all, the ancient ones were probably used in domestic or ceremonial activities. Besides, the latter were kept buried for a long time, and it is quite probable that their manufacture was also slightly different from that of the former. These assumptions could provide the clues to understand some of the observed differences between the composition of ancient and modern ceramics whose raw materials may have the same origin.     

Fast and eco-friendly method using atmospheric solids analysis probe mass spectrometry to characterize orange varieties

Orange fruit is one of the most popular types of fruit in the world, and its juice is the main product of its processing. This study aimed to evaluate a simple, fast, and eco-friendly methodology, atmospheric solids analysis probe mass spectrometry (ASAP-MS), to assess the chemical profile of four oranges varieties (Valencia, Folha Murcha, Pera, and Iapar). The oranges' varieties were evaluated for the physicochemical composition (extraction yield, pH, total titratable acidity, total soluble solids [TSS], °Brix), ratio (TSS/TA), and bioactive compounds (ASAP-MS analysis). The characterization of oranges resulted in great values of oranges yield according to the varieties (44.00–48.10% [w/w], adequate and characteristic acidity [0.73–1.35%], soluble solids content (10.24–13.80°Brix), pH (3.30–3.96), and ratio (7.59–19.90) level for this fruit. This powerful method showed that all analysis procedures were simple, fast, and easy because there is no need to prepare the sample and the analysis time lasted 2 min. Besides, results obtained exhibited a vast array of chemical groups. Principal component analysis (PCA) defined and distinguished the varieties of the orange. Therefore, ASAP-MS and PCA showed that they are very attractive candidates for routine analysis to monitor the varieties of the orange with its pronounced advantages, besides being contributing to the environment because it does not use any quantities of organic solvents. This methodology was applied for the first time to this type of sample.