Aminocyclodextrins to facilitate the deprotonation of 4-tert-butyl-alpha-nitrotoluene

6A-Amino-6A-deoxy-beta-cyclodextrin enhances the rate of the deprotonation of 4-tert-butyl-alpha-nitrotoluene. The rate constants for reaction of the cyclodextrin-bound species, kinc = 4 x 10(-3), 9 x 10(-3) and 19 x 10(-3) s(-1), at pH 6.0, 6.5 and 7.0, respectively, in 0.1 mol dm(-3) aqueous phosphate buffer containing 1% methanol at 298 K. These rate constants correspond to a rate acceleration (kinc/kun) of ca. 10 times at each pH. Under the same conditions, 6A-dimethylamino-6A-deoxy-beta-cyclodextrin and 6A-(2-aminoethylamino)-6A-deoxy-beta-cyclodextrin are more effective; at pH 6.0, 6.5 and 7.0, for the former, kinc = 3 x 10(-2), 7 x 10(-2) and 12 x 10(-2) s(-1), whilst for the latter, kinc = 4 x 10(-2), 5 x 10(-2) and 9 x 10(-2) s(-1), respectively. Each cyclodextrin also decreases the pKa of the nitrotoluene, from 6.8 in free solution, to 6.2 when bound. The accelerated deprotonation by 6A-amino-6A-deoxy-beta-cyclodextrin is reflected in the enhanced rates of hydrogen-deuterium exchange of the nitrotoluene in deuterium oxide, and in the conjugate addition of the nitrotoluene to methyl vinyl ketone in aqueous solution.     

Conformational interconversion in the monovalent ions of 1,2,3,6,7,8-hexahydropyrene II

The E.P.R. spectra of the monovalent positive and negative ions of 1,2,3,6,7,8-hexahydropyrene reveal an alternating line broadening, caused by the non-synchronized motion of the two aliphatic bridges in the molecule. When this motion is described by the modified Bloch equations, using a four-sites jump model, spectra are obtained which agree quite well with the experimental ones.

The potential barrier for the conformational interconversion can be calculated from the temperature dependence of the lifetime of each configuration and is found to be 10·0±0·4 kcal mole^-1 for the radical anion and 3·5±0·4 kcal mole^-1 for the radical cation. The inversion rate at 0°C equals 2·8 × 10⁶ s^-1 for the anion and 4·2 × 10⁶s^-1 for the cation.     

Mössbauer study of magnetic ordering in K2FeF4

The sublattice magnetization of the quadratic-layer basal-plane antiferromagnet K₂FeF₄ has been studied by use of Mössbauer spectroscopy. A distribution of Néel temperatures with a width ～3 K is found at a mean T_N = 67.2±0.3 K. For 0.3 < T/T_N < 0.99 the sublattice magnetization is described by a power law with critical exponent β = 0.17±0.01.     

An exactly solvable non-linear Boltzmann equation

The initial value problem for a model Boltzmann equation of a two dimensional gas with a continuous or discrete energy distribution function and a transition probability δ(? - ?') is solved exactly; ? and ?' are the total energies before and after collision.     

Stable isotope analysis of white-tailed deer teeth as a paleoenvironmental proxy at the Maya site of La Joyanca,northwestern Petén,Guatemala*

ABSTRACT

Carbon and oxygen isotopes ratios from herbivore teeth have previously been used as paleo-environmental proxies in temperate zones. However, their utility in tropical zones remains uncertain. In this study, sequential sub-samples from white-tailed deer (Odocoileus virginianus) teeth (second and third molars) from the Maya archaeological site of La Joyanca, located in northwestern Petén, Guatemala, show that δ¹⁸O of enamel carbonate corresponds broadly to modern observed precipitation δ¹⁸O over the 10-month period of tooth formation, capturing rainfall seasonality. The analyses also detect significant diachronic differences in the δ¹⁸O between the periods 1100–1000 BP (850–950 A.D.) and 1000–900 BP (950–1050 A.D.) at La Joyanca. The δ¹³C in both periods are indicative of a C₃-plant based diet, which suggests cultivation of maize did not differentially affect deer diet during this period.     

Uptake of silver nanoparticles by monocytic THP-1 cells depends on particle size and presence of serum proteins

Human health risks by silver nanoparticle (AgNP) exposure are likely to increase due to the increasing number of NP-containing products and demonstrated adverse effects in various cell lines. Unfortunately, results from (toxicity) studies are often based on exposure dose and are often measured only at a fixed time point. NP uptake kinetics and the time-dependent internal cellular concentration are often not considered. Macrophages are the first line of defense against invading foreign agents including NPs. How macrophages deal with the particles is essential for potential toxicity of the NPs. However, there is a considerable lack of uptake studies of particles in the nanometer range and macrophage-like cells. Therefore, uptake rates were determined over 24 h for three different AgNPs sizes (20, 50 and 75 nm) in medium with and without fetal calf serum. Non-toxic concentrations of 10 ng Ag/mL for monocytic THP-1 cells, representing realistic exposure concentration for short-term exposures, were chosen. The uptake of Ag was higher in medium without fetal calf serum and showed increasing uptake for decreasing NP sizes, both on NP mass and on number basis. Internal cellular concentrations reached roughly 32/10 %, 25/18 % and 21/15 % of the nominal concentration in the absence of fetal calf serum/with fetal calf serum for 20-, 50- and 75-nm NPs, respectively. Our research shows that uptake kinetics in macrophages differ for various NP sizes. To increase the understanding of the mechanism of NP toxicity in cells, the process of uptake (timing) should be considered.     

Physical properties from association models

Equation of state models with a ‘chemical’ contribution that accounts for association and solvation effects, are computationally intensive as they have to solve an internal chemical equilibrium calculation.

Frequently, only the final results of this internal calculation are used in the subsequent evaluation of physical properties from the model. As a consequence, a substantial amount of unneeded work is performed. We show here how the state function minimization in the chemical equilibrium calculation can be utilized to simplify the calculation of physical properties like pressure and chemical potentials and the derivatives of these properties with respect to temperature, volume and composition.     

Integrated Transmission Electron and Single‐Molecule Fluorescence Microscopy Correlates Reactivity with Ultrastructure in a Single Catalyst Particle

Establishing structure–activity relationships in complex, hierarchically structured nanomaterials, such as fluid catalytic cracking (FCC) catalysts, requires characterization with complementary, correlated analysis techniques. An integrated setup has been developed to perform transmission electron microscopy (TEM) and single‐molecule fluorescence (SMF) microscopy on such nanostructured samples. Correlated structure–reactivity information was obtained for 100 nm thin, microtomed sections of a single FCC catalyst particle using this novel SMF‐TEM high‐resolution combination. High reactivity in a thiophene oligomerization probe reaction correlated well with TEM‐derived zeolite locations, while matrix components, such as clay and amorphous binder material, were found not to display activity. Differences in fluorescence intensity were also observed within and between distinct zeolite aggregate domains, indicating that not all zeolite domains are equally active.