Cellulose‐based graft copolymers with controlled architecture prepared in a homogeneous phase

Cellulose‐based macroinitiators with predetermined number of initiation sites were synthesized by acylation of microcrystalline cellulose AVICEL PH‐101 with 2‐bromoisobutyryl bromide under homogeneous reaction conditions in the N,N‐dimethylacetamide/LiCl solvent system. The influence of different methods of cellulose activation on acylation efficiency and reproducibility was investigated. Best results were obtained using thermal activation under reduced pressure or the newly introduced protocol based on solvent exchange to 1,4‐dioxane. Prepared macroinitiators were used for grafting with styrene and methyl methacrylate (MMA) using optimized atom transfer radical polymerization reaction conditions to achieve well‐controlled polymerizations with high initiation efficiency. For MMA grafting, the initiation efficiency was shown to be dependent on certain reaction conditions, such as type of solvent, monomer concentration, or the presence of a sacrificial initiator. In addition, single‐electron transfer living radical polymerization with Cu(0) as the catalyst was used for the first time to prepare cellulose‐graft‐polystyrene and cellulose‐graft‐poly(MMA) copolymers in a homogeneous phase. In summary, homogeneous reaction conditions, stoichiometric control in the preparation of macroinitiators, and controlled grafting jointly allowed for an extensive control of copolymers architecture, that is, density of grafting, composition, and molecular parameters of grafts. Moreover, some of the prepared copolymers were characterized by static and dynamic light scattering and microscopic techniques (transmission electron microscopy and atomic force microscopy). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Accurate determination of Be magnetic moment

The determination of the magnetic moment of ⁹Be from the measured ratio of the nuclear to the electron g-factors g_I/g_J in ⁹Be⁺ is presented. The obtained result μ(⁹Be)=-1.17743159(3)μ_N is two orders of magnitude more accurate than the presently accepted value.     

Statefinders and observational measurement of superenergy

The superenergy of the universe is a tensorial quantity and it is a general relativistic analogue of the Appell's energy of acceleration in classical mechanics. We propose the way to measure this quantity by the application of the observational parameters such as the Hubble parameter, the deceleration parameter, the jerk and the snap (kerk), known as statefinders. We show that the superenergy of gravity requires only the Hubble and deceleration parameters to be measured, while the superenergy of matter requires also the measurement of the higher-order characteristics of expansion: the jerk and the snap. In such a way, the superenergy becomes another parameter characterizing the evolution of the universe. One of the interesting points is that the cosmological constant has a purely gravitational interpretation in terms of superenergy.     

Photoreactivity of an Exemplary Anthracene Mixture Revealed by NMR Studies,including a Kinetic Approach

Anthracenes are an important class of acenes. They are being utilized more and more often in chemistry and materials sciences, due to their unique rigid molecular structure and photoreactivity. In particular, photodimerization can be harnessed for the fabrication of novel photoresponsive materials. Photodimerization between the same anthracenes have been investigated and utilized in various fields, while reactions between varying anthracenes have barely been investigated. Here, Nuclear Magnetic Resonance (NMR) spectroscopy is employed for the investigation of the photodimerization of two exemplary anthracenes: anthracene (A) and 9-bromoanthracene (B), in the solutions with only A or B, and in the mixture of A and B. Estimated k values, derived from the presented kinetic model, showed that the dimerization of A was 10 times faster in comparison with B when compounds were investigated in separate samples, and 2 times faster when compounds were prepared in the mixture. Notably, the photoreaction in the mixture, apart from AA and BB, additionally yielded a large amount of the AB mixdimer. Another important advantage of investigating a mixture with different anthracenes is the ability to estimate the relative reactivity for all the reactions under the same experimental conditions. This results in a better understanding of the photodimerization processes. Thus, the rational photofabrication of mix-anthracene-based materials can be facilitated, which is of crucial importance in the field of polymer and material sciences.     

Ancient Wheat and Quinoa Flours as Ingredients for Pasta Dough—Evaluation of Thermal and Rheological Properties

The aim of this study was to investigate thermal and rheological properties of selected ancient grain flours and to evaluate rheological properties of mixtures thereof represented by pasta dough and dry pasta. Flours from spelt, einkorn, and emmer ancient wheat varieties were combined with quinoa flour. All these flour sources are considered healthy grains of high bioactive component content. Research results were compared to durum wheat flour or spelt wheat flour systems. Differential scanning calorimeter (DSC) and a rapid visco analyzer (RVA) were used to investigate the phase transition behavior of the flours and pasting characteristics of the flours and dried pasta. Angular frequency sweep experiments and creep and recovery tests of the pasta dough were performed. The main components modifying the pasta dough structure were starch and water. Moreover, the proportion of the individual flours influenced the rheological properties of the dough. The durum wheat dough was characterized by the lowest values of the K′ and K″ parameters of the power law models (24,861 Pa·sⁿ′ and 10,687 Pa·sⁿ″, respectively) and the highest values of the instantaneous (J₀) and retardation (J₁) compliances (0.453 × 10⁻⁴ Pa and 0.644 × 10⁻⁴ Pa, respectively). Replacing the spelt wheat flour with the other ancient wheat flours and quinoa flour increased the proportion of elastic properties and decreased values of the J₀ and J₁ of the pasta dough. Presence of the quinoa flour increased pasting temperature (from 81.4 up to 83.3 °C) and significantly influenced pasting viscosities of the spelt wheat pasta samples. This study indicates a potential for using mixtures of spelt, einkorn, and emmer wheat flours with quinoa flour in the production of innovative pasta dough and pasta products.     

Halving transversal designs

A factor H of a transversal design TD(k,n) = (V,𝒢, ℬ︁), where V is the set of points, 𝒢 the set of groups of size n and ℬ︁ the set of blocks of size k, is a triple (V,𝒢, 𝒟) such that 𝒟 is a subset of ℬ︁. A halving of a TD (k, n) is a pair of factors H_i = (V, 𝒢, 𝒟_i), i = 1,2 such that 𝒟₁ ∪ 𝒟₂ = ℬ︁, 𝒟₁ ∩ 𝒟₂ = ∅︁ and H₁ is isomorphic to H₂. A path of length q is a sequence x₀, x₁,…,x_q of points such that for each i = 1, 2,…, q the points x_i‐1 and x_i belong to a block B_i and no point appears more than once. The distance between points x and y in a factor H is the length of the shortest path from x to y. The diameter of a connected factor H is the maximum of the set of distances among all pairs of points of H. We prove that a TD (3, n) is halvable into isomorphic factors of diameter d only if d = 2,3,4, or ∞ and we completely determine for which values of n there exists such a halvable TD (3, n). We also show that if any group divisible design with block size at least 3 is decomposed into two factors with the same finite diameter d, then d≤ 4. © 2000 John Wiley & Sons, Inc. J Combin Designs 8: 83–99, 2000     

Going beyond the borders: pyrrolo[3,2-b]pyrroles with deep red emission

A two-step route to strongly absorbing and efficiently orange to deep red fluorescent, doubly B/N-doped, ladder-type pyrrolo[3,2-b]pyrroles has been developed. We synthesize and study a series of derivatives of these four-coordinate boron-containing, nominally quadrupolar materials, which mostly exhibit one-photon absorption in the 500–600 nm range with the peak molar extinction coefficients reaching 150 000, and emission in the 520–670 nm range with the fluorescence quantum yields reaching 0.90. Within the family of these ultrastable dyes even small structural changes lead to significant variations of the photophysical properties, in some cases attributed to reversal of energy ordering of alternate-parity excited electronic states. Effective preservation of ground-state inversion symmetry was evidenced by very weak two-photon absorption (2PA) at excitation wavelengths corresponding to the lowest-energy, strongly one-photon allowed purely electronic transition. π-Expanded derivatives and those possessing electron-donating groups showed the most red-shifted absorption- and emission spectra, while displaying remarkably high peak 2PA cross-section (σ_2PA) values reaching ∼2400 GM at around 760 nm, corresponding to a two-photon allowed higher-energy excited state. At the same time, derivatives lacking π-expansion were found to have a relatively weak 2PA peak centered at ca. 800–900 nm with the maximum σ_2PA ∼50–250 GM. Our findings are augmented by theoretical calculations performed using TD-DFT method, which reproduce the main experimental trends, including the 2PA, in a nearly quantitative manner. Electrochemical studies revealed that the HOMO of the new dyes is located at ca. −5.35 eV making them relatively electron rich in spite of the presence of two B⁻–N⁺ dative bonds. These dyes undergo a fully reversible first oxidation, located on the diphenylpyrrolo[3,2-b]pyrrole core, directly to the di(radical cation) stage.

Ladder-type heterocycles encompassing two B⁻–N⁺ dative bonds possess intense green to red emission, large 2PA cross-sections and superb photostability.     

Exact and Numerical Solution of the Fractional Sturm–Liouville Problem with Neumann Boundary Conditions

In this paper, we study the fractional Sturm–Liouville problem with homogeneous Neumann boundary conditions. We transform the differential problem to an equivalent integral one on a suitable function space. Next, we discretize the integral fractional Sturm–Liouville problem and discuss the orthogonality of eigenvectors. Finally, we present the numerical results for the considered problem obtained by utilizing the midpoint rectangular rule.     

Microspheres by dispersion polymerization of lactides and ϵ-caprolactone

Polyester microspheres were synthesized by the ring-opening polymerization of lactides (racemate or optically active L,L-isomer) and ϵ-caprolactone. Polymerizations were carried out in the 1,4-dioxane-heptane mixed solvents in the presence of poly(dodecyl acrylate)-g-poly(ϵ-caprolactone) (poly(DA-CL)) used as surface-active agent. Polymerizations were initiated with tin(II) 2-ethylhexanoate (lactides), diethylaluminum ethoxide or sodium trimethylsilanolate (ϵ-caprolactone). In the studies of the polymerization of lactides, relations were determined between diameters, the distribution of diameters of synthesized microspheres, and the structure of poly(DA-CL). It was found that it is possible, depending on thermal treatment of microspheres after synthesis, to obtain polylactide microspheres differing in the degree of crystallinity. Kinetics of the dispersion pseudoanionic and anionic polymerizations of ϵ-caprolactone were also investigated and the results of these studies were compared with the data for the corresponding polymerizations of ϵ-caprolactone in solution.     

Electron-ion recombination rate constant in dense gaseous Kr/CH4 mixtures

The rate constant of bulk electron-ion recombination is calculated for dense gaseous krypton doped with methane. In the calculations, the electron scattering is modeled by experimental, energy-dependent collision cross-sections. The recombination rate constant is found to increase with increasing methane concentration, due to efficient dissipation of electron energy in vibrationally inelastic e-CH₄ collisions.