Stereochemistry and EPR investigation of a chiral molecular magnet

An electron paramagnetic resonance investigation of an indexed single crystal of the chiral molecular magnet (R)-3MLNN·Mn(hfac)₂ which is comprised of a chiral phenyl α-nitronyl nitroxide and a manganese(II) ion is presented. The crystal of the compound, which consists of ferrimagnetic chains of radical and metal ion and orders ferromagnetically below 4 K, shows temperature and angle-dependent spectra which may give clues as to the nature of the anisotropy in the system and the types of interaction at play.     

Sufficient Conditions for Error Bounds and Applications

Our aim in this paper is to present sufficient conditions for error bounds in terms of Fréchet and limiting Fréchet subdifferentials in general Banach spaces. This allows us to develop sufficient conditions in terms of the approximate subdifferential for systems of the form (x, y) C × D, g(x, y, u) = 0, where g takes values in an infinite-dimensional space and u plays the role of a parameter. This symmetric structure offers us the choice of imposing conditions either on C or D. We use these results to prove the nonemptiness and weak-star compactness of Fritz–John and Karush–Kuhn–Tucker multiplier sets, to establish the Lipschitz continuity of the value function and to compute its subdifferential and finally to obtain results on local controllability in control problems of nonconvex unbounded differential inclusions.     

Affinity distribution functions in multicomponent heterogeneous adsorption. Analytical inversion of isotherms to obtain affinity spectra

An analytical approach for the interpretation of multicomponent heterogeneous adsorption or complexation isotherms in terms of multidimensional affinity spectra is presented. Fourier transform, applied to analyze the corresponding integral equation, leads to an inversion formula which allows the computation of the multicomponent affinity spectrum underlying a given competitive isotherm. Although a different mathematical methodology is used, this procedure can be seen as the extension to multicomponent systems of the classical Sips's work devoted to monocomponent systems. Furthermore, a methodology which yields analytical expressions for the main statistical properties (mean free energies of binding and covariance matrix) of multidimensional affinity spectra is reported. Thus, the level of binding correlation between the different components can be quantified. It has to be highlighted that the reported methodology does not require the knowledge of the affinity spectrum to calculate the means, variances, and covariance of the binding energies of the different components. Nonideal competitive consistent adsorption isotherm, widely used in metal/proton competitive complexation to environmental macromolecules, and Frumkin competitive isotherms are selected to illustrate the application of the reported results. Explicit analytical expressions for the affinity spectrum as well as for the matrix correlation are obtained for the NICCA case.     

Ionic equilibria in neutral amphiprotic solvents of low dielectric constant: Buffer solutions

The ionic equilibria in neutral amphiprotic solvents (isopropyl and tert-butyl alcohols) have been established, and equations to calculate pH values in solutions of acids, bases, salts or their mixtures, developed. The effect, on the dissociation equilibria, of the presence of small quantities of water or other solvents in the bulk solvent used has been taken into account in the proposed equations. On the basis of these equations some buffer solutions have been studied and recommended for electrode standardization. The results, tested by experimental work, show the importance of the incompleteness of dissociation of salts in these solvents, which decreases the pH of acid buffers and increases the buffer capacity.     

Benzomorphan related compounds. III.. Structural determination of Δ3 - and Δ4-tetrahydropyridines by nuclear magnetic resonance

Observation of the nmr spectra of several Δ³ - and Δ⁴-tetrahydropyridines hydrochlorides provides a useful method for the structural determination of this type of compound. The Δ³ - Isomers exist as one predominant epimer only whereas the Δ⁴-isomers exist as a mixture of the two possible epimers. The respective assignments are discussed in view of the criteria previously applied in the study of this type of compound.     

Perturbation of gamma-ray angular correlations following continual random reorientation of the axis of interaction

Attenuation coefficients of perturbed gamma-ray angular correlations are calculated for classical extranuclear fields which fluctuate at random both in direction and in magnitude. Explicit expressions are given for time-integral attenuation coefficients. Time-differential attenuation coefficients have been calculated numerically. The theory applies to any correlation time.     

Fluorescent probes for sensing processes in polymers

Fluorescence spectroscopy is an important analytical technique that has been widely used in a variety of applications, such as biomedicine, biology, and science of materials, because it presents some properties which makes it unique, that is, extraordinary sensitivity and selectivity, short delay time (<10(-9) s), and it is neither invasive nor destructive, so it can be used for in situ measurements. Generally, intrinsic fluorescence of many materials, like polymers, is unspecific so it is not useful to analyse their properties or to be correlated to changes in their microenvironment. The incorporation of additives with fluorescent groups would be necessary. When the fluorescence emission of these molecules is sensitive to changes of properties, such as polarity, fluidity, order, molecular mobility, pH, or electric potential, they can be used for detecting such changes in their microenvironment, and they are called fluorescent probes. As long as these probes can follow processes of practical interest, they can be employed as sensors, if the information given by the measure of fluorescence adequately reflects the changes in the system. In addition, a sensor must fulfil some other requirements in order to make them of practical use, the most important being that the material support in which the sensor molecule is inserted. This support should permit a rapid detection of the process and should allow easy processing in a variety of forms. Polymers are well-known systems in which estimation of local parameters are possible by means of fluorimetric techniques. It allows the study of dynamic processes of interest, such as polymerization kinetics and mechanisms, thermal transitions, photodegradation, swelling morphology changes, and so forth.     

Highly enantioselective dynamic kinetic resolution and desymmetrization processes by cyclocondensation of chiral aminoalcohols with racemic or prochiral delta-oxoacid derivatives

Cyclocondensation reactions of aminoalcohols and with racemic or prochiral delta-oxoacid derivatives provide polysubstituted lactams with high enantioselectivity in a process that involves dynamic kinetic resolution and/or desymmetrization of enantiotopic or diastereotopic ester groups.