Interactions of poly(amidoamine) dendrimers with the surfactants SDS, DTAB, and C12EO6: an equilibrium and structural study using a SDS selective electrode, isothermal titration calorimetry, and small angle neutron scattering

Interactions in aqueous solutions of different generations of poly(amidoamine) (PAMAM) dendrimers containing amine, hydroxyl, or delta-glucolactone functional groups at the periphery with the anionic surfactant sodium dodecyl sulfate (SDS) were investigated. We used a SDS-specific electrode (EMF) for SDS monomer concentration monitoring, isothermal titration calorimetry (ITC) for binding information, and small angle neutron scattering (SANS) for structural studies. ITC experiments monitoring the interaction of the dendrimers with cationic dodecyltrimethylammonium bromide (DTAB) and nonionic hexaethylene glycol mono-n-dodecyl ether (C12EO6) showed no significant binding effects. In contrast, SDS binds to all of the above dendrimers. EMF and ITC data demonstrated a regular trend for both the onset of binding and binding saturation as the generation in each family of dendrimers increased. In addition, generation G6 exhibited a noncooperative binding process at very low SDS concentrations. Furthermore, the onset of cooperative binding in the EMF experiments started at lower concentrations as the weight % (w/v), the size, and the numbers of the internal or surface groups increased. On the other hand, the binding capacity of the dendrimers showed only a small dependence on the above parameters. At SDS concentrations approaching the binding limit and also at selective concentrations within the binding range, SANS measurements indicated that in all cases the bound surfactant is in the micellar form. From the electromotive force (EMF) measurements, ITC data, and SANS data, the stoichiometry of the supramolecular complexes was determined.     

Photochemical reduction of uranyl ion with aromatic alkanes

Uranyl ion is photochemically reduced to uranium(IV) in the presence of diphenylmethane and triphenylmethane. Quantum yields for uranium(IV) formation are accelerated with time suggesting the free radical formation, which triggers off a secondary reaction. Lower quantum yield and higherK _sv value for photochemical reduction of uranyl ion with triphenylmethane relative to the respective values observed with diphenylmethane reveals the competition between photophysical and photochemical deactivation of excited uranyl ion due to the presence of three and two phenyl groups in respective aromatic hydrocarbons for photophysical deactivation.     

Structural aspects of crown complexes with alkali and alkaline earth cations. Benzo-15-crown-5 as a discriminating macrocycle

X-ray structural results have been reviewed for the related M^z+ L _z ^– -B15C5 complexes where M^z+=Li⁺ to Cs⁺ and Mg²⁺ to Ba²⁺, L^–=2,4,6-trinitrophenolate (Picrate or Pic) and 3,5-dinitrobenzoate (Dnb), and B15C5=benzo-15-crown-5. These results combined with those for come MX_z-B15C5 (X=NCS^–, I^–, NO ₃ ^– , ClO ₄ ^– , BPh ₄ ^– ) complexes have revealed that B15C5 is a useful macrocycle with regard to the within-the-group and between-the-groups discriminations of M^z+ in the solid state.     

Excess molar volumes of methylcyclohexane+benzene, +methylbenzene, +1,4-dioxane,and +tetrahydrofuran at 303.15 K

Excess molar volumes V_m^E as function of mole fraction x for methylcyclohexane + benzene, + methylbenzene, + 1,4-dioxane, and + tetrahydrofuran are reported at 303.15 K. The excess molar volumes are positive and indicate the presence of weak interactions.     

The effect of Lewis number variation on combustion waves in a model with chain-branching reaction

In this paper we investigate the linear stability and properties of the travelling premixed combustion waves in a model with two-step chain-branching reaction mechanism in the adiabatic limit in one spatial dimension. It is shown that the Lewis number for fuel has a significant effect on the properties and stability of premixed flames, whereas the Lewis number for the radicals has only quantitative (but not qualitative) effect on the combustion waves. We demonstrate that when the Lewis number for fuel is less than unity the flame speed is unique and is a monotonically decreasing function of the dimensionless activation energy. The combustion wave is stable and exhibits extinction for finite values of activation energy as the flame speed decreases to zero. For fuel Lewis number greater than unity the flame speed is a double-valued function. The slow solution branch is shown to be unstable whereas the fast solution branch is either stable or exhibits the onset of pulsating instabilities via the Hopf bifurcation. The evolution of these instabilities leads to flame extinction.     

Aspherical‐Atom Modeling of Coordination Compounds by Single‐Crystal X‐ray Diffraction Allows the Correct Metal Atom To Be Identified

Single‐crystal X‐ray diffraction (XRD) is often considered the gold standard in analytical chemistry, as it allows element identification as well as determination of atom connectivity and the solid‐state structure of completely unknown samples. Element assignment is based on the number of electrons of an atom, so that a distinction of neighboring heavier elements in the periodic table by XRD is often difficult. A computationally efficient procedure for aspherical‐atom least‐squares refinement of conventional diffraction data of organometallic compounds is proposed. The iterative procedure is conceptually similar to Hirshfeld‐atom refinement (Acta Crystallogr. Sect. A­ 2008 , 64, 383–393; IUCrJ. 2014 , 1,61–79), but it relies on tabulated invariom scattering factors (Acta Crystallogr. Sect. B­ 2013 , 69, 91–104) and the Hansen/Coppens multipole model; disordered structures can be handled as well. Five linear‐coordinate 3d metal complexes, for which the wrong element is found if standard independent‐atom model scattering factors are relied upon, are studied, and it is shown that only aspherical‐atom scattering factors allow a reliable assignment. The influence of anomalous dispersion in identifying the correct element is investigated and discussed.     

High spin spectroscopy of 139Pr

The high spin states in N=80 ¹³⁹Pr have been investigated by in-beam γ-spectroscopic techniques following the reaction ¹³⁰Te (¹⁴N, 5n) reaction at E=75 MeV, using a gamma detector array, consisting of seven 23% compton-suppressed high purity germanium detectors and a multiplicity ball of fourteen bismuth germanate elements. Based on γ-γ coincidence data, the level scheme of ¹³⁹Pr has been considerably extended up to 7.2 MeV excitation. Tentative spin-parity assignments are done for the newly proposed levels on the basis of the DCO ratios corresponding to strong gates and the available information from the earlier light ion experiments.     

Dynamical analysis of an elementary X + Y → P reaction in a continuously stirred tank reactor

This paper investigates the bifurcation behaviour of a model oxidation reaction in a continuously stirred tank reactor (CSTR). We assume that two gaseous chemical species are pumped separately into the CSTR, at constant total pressure, reacting to produce an inert product. The reaction is assumed to be a single step reaction that is described by Arrhenius kinetics. It is capable of producing oscillatory behaviour as well as steady state multiplicity in certain parameter regions. Bifurcation diagrams in various control parameter spaces are presented. We show that the system always possesses a globally attracting invariant region. The equivalence of a CSTR having n feed streams and the one pipe version, by appropriate rescaling, is also discussed.     

Intrinsically conducting polymer blends

Polyaniline (PANI) doped with different dopants (HCl, dodecyl benzene sulfonic acid, (+)‐Camphor‐10 sulfonic acid, dinonyl naphthalene disulfonic acid) was synthesized by chemical oxidation method. The FTIR studies indicated that the back bone structure of doped PANI was similar. Thermal stability was evaluated in nitrogen atmosphere by dynamic thermogravimetry and PANI‐HCl sample showed minimum weight loss below 400°C. The electrical conductivity of PANI was not affected by the structure of dopants. The microwave absorption studies of several polymers blends containing PANI‐HCl and/or carbon black were also carried out by using wave guide technique.     

Bayesian estimation of generalized gamma shared frailty model

Multivariate survival analysis comprises of event times that are generally grouped together in clusters. Observations in each of these clusters relate to data belonging to the same individual or individuals with a common factor. Frailty models can be used when there is unaccounted association between survival times of a cluster. The frailty variable describes the heterogeneity in the data caused by unknown covariates or randomness in the data. In this article, we use the generalized gamma distribution to describe the frailty variable and discuss the Bayesian method of estimation for the parameters of the model. The baseline hazard function is assumed to follow the two parameter Weibull distribution. Data is simulated from the given model and the Metropolis–Hastings MCMC algorithm is used to obtain parameter estimates. It is shown that increasing the size of the dataset improves estimates. It is also shown that high heterogeneity within clusters does not affect the estimates of treatment effects significantly. The model is also applied to a real life dataset.