Quasipatterns versus superlattices resulting from the superposition of two hexagonal patterns

We present a short review of the experimental observations and mechanisms related to the generation of quasipatterns and superlattices by the Faraday instability with two-frequency forcing. We show how two-frequency forcing makes possible triad interactions that generate hexagonal patterns, twelvefold quasipatterns or superlattices that consist of two hexagonal patterns rotated by an angle α relative to each other. We then consider which patterns could be observed when α does not belong to the set of prescribed values that give rise to periodic superlattices. Using the Swift–Hohenberg equation as a model, we find that quasipattern solutions exist for nearly all values of α. However, these quasipatterns have not been observed in experiments with the Faraday instability for $\alpha \ne \mathrm{\pi }/6$. We discuss possible reasons and mention a simpler framework that could give some hint about this problem.     

A Cucurbit[8]uril 2:2 Complex with a Negative pKa Shift

A viologen derivative carrying a benzimidazole group ( V-P-I ²⁺; viologen–phenylene–imidazole V-P-I ) can be dimerized in water using cucurbit[8]uril (CB[8]) in the form of a 2:2 complex resulting in a negative shift of the guest pK_a, by more than 1 pH unit, contrasting with the positive pK_a shift usually observed for CB-based complexes. Whereas 2:2 complex protonation is unclear by NMR, silver cations have been used for probing the accessibility of the imidazole groups of the 2:2 complexes. The protonation capacity of the buried imidazole groups is reduced, suggesting that CB[8] could trigger proton release upon 2:2 complex formation. The addition of CB[8] to a solution containing V-P- I ³⁺ indeed released protons as monitored by pH-metry and visualized by a coloured indicator. This property was used to induce a host/guest swapping, accompanied by a proton transfer, between V-P-I ³⁺ ⋅ CB[7] and a CB[8] complex of 1-methyl-4-(4-pyridyl)pyridinium. The origin of this negative pK_a shift is proposed to stand in an ideal charge state, and in the position of the two pH-responsive fragments inside the two CB[8] which, alike residues engulfed in proteins, favour the deprotonated form of the guest molecules. Such proton release triggered by a recognition event is reminiscent of several biological processes and may open new avenues toward bioinspired enzyme mimics catalyzing proton transfer or chemical reactions.     

Fast and solvent-free microwave-assisted synthesis of thermoresponsive oligo(glycidyl ether)s

Low-molecular weight linear poly(glycidyl ether)s are typically synthesized via the “classical,” oxy-anionic ring-opening polymerization (ROP) of glycidyl ether monomers at elevated temperatures. To reduce reaction times, a fast process was developed to synthesize oligo(glycidyl ether)s (OGEs) in bulk at a gram-scale utilizing microwave heating. Well-defined thermoresponsive copolymers comprising glycidyl methyl ether and ethyl glycidyl ether with molecular weights of up to 3 kDa were synthesized via microwave-assisted ROP with reaction times of approximately 10 min. The fast reaction kinetics were attributed to the rapid and uniform heating and high temperatures reached during the reaction. Consequently, no significant microwave-specific acceleration of the oxy-anionic ROP was observed. The temperature-triggered phase transition of the OGEs in aqueous solution revealed cloud point temperatures that are highly dependent on the OGE molecular weight, concentration, and comonomer composition, which extends previously reported data. Furthermore, oligo(glycidyl ether) acrylates (OGEAs) with reactive, functional end groups were directly accessible via in situ quenching of the anionic, microwave-assisted ROP with acrylic acid chloride. The obtained thermoresponsive OGEA macromonomers represent a promising material for the functionalization of surfaces via radical grafting methods to obtain functional, thermoresponsive coatings with potential application in cell culture. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2496–2504     

Synthesis and Characterization of the Titanium Containing Mesoporous Molecular Sieve MCM-48

Ti-MCM-48 mesoporous materials have been synthesized by sequential addition of alkoxides. The atomic ratio of Si and Ti in the synthesis gel was 40 and 5, respectively. The materials were characterized by means of powder XRD, N₂ adsorption-desorption measurements. HREM, ²⁹Si MAS NMR, diffuse reflectance FT-IR spectroscopy, electrophoretic mobility measurements and electron probe microanalysis.     

Conformational Study of Glycal-Type Neuraminidase Inhibitors

The conformational flexibility of two glycal-type neuraminidase inhibitors has been studied, using several molecular modeling techniques. In agreement with the experimental data available, an intramolecular hydrogen bond, representing a key structural feature that controls the conformer distribution in solution, has been identified. The contribution of each substituent to the overall equilibrium was evaluated using simplified derivatives. Additionally, four methods for estimating NMR coupling constants from dihedral angles were evaluated and the Haasnoot method was found to be appropriate for this class of sugars. These results should allow a better understanding of the structural parameters governing physico-chemical properties of glycal-like compounds. Supplemental materials are available for this article. Go to the publisher's online edition of Journal of Carbohydrate Chemistry to view the free supplemental file.     

Forever Young: Structural Stability of Telomeric Guanine Quadruplexes in the Presence of Oxidative DNA Lesions**

Human telomeric DNA, in G-quadruplex (G4) conformation, is characterized by a remarkable structural stability that confers it the capacity to resist to oxidative stress producing one or even clustered 8-oxoguanine (8oxoG) lesions. We present a combined experimental/computational investigation, by using circular dichroism in aqueous solutions, cellular immunofluorescence assays and molecular dynamics simulations, that identifies the crucial role of the stability of G4s to oxidative lesions, related also to their biological role as inhibitors of telomerase, an enzyme overexpressed in most cancers associated to oxidative stress.     

QSAR with experimental and predictive distributions: an information theoretic approach for assessing model quality

We propose that quantitative structure–activity relationship (QSAR) predictions should be explicitly represented as predictive (probability) distributions. If both predictions and experimental measurements are treated as probability distributions, the quality of a set of predictive distributions output by a model can be assessed with Kullback–Leibler (KL) divergence: a widely used information theoretic measure of the distance between two probability distributions. We have assessed a range of different machine learning algorithms and error estimation methods for producing predictive distributions with an analysis against three of AstraZeneca’s global DMPK datasets. Using the KL-divergence framework, we have identified a few combinations of algorithms that produce accurate and valid compound-specific predictive distributions. These methods use reliability indices to assign predictive distributions to the predictions output by QSAR models so that reliable predictions have tight distributions and vice versa. Finally we show how valid predictive distributions can be used to estimate the probability that a test compound has properties that hit single- or multi- objective target profiles.     

Synchrotron radiation analysis in the study of pollution in the ring‐billed gull (larus delawarensis): a novel application of the technique

Synchrotron radiation analysis is a powerful tool for identifying pollutants. Here, we explore the distribution of elements in the flight feathers of ring‐billed gulls, Larus delawarensis, to identify potential pollutants and their distribution throughout the feather. Our analysis using Synchrotron Radiation Analysis and Environmental Scanning Electron Microscopy has identified a variety of metals that are integral parts of the feather structure including: calcium (Ca), strontium (Sr), zinc (Zn) and iron (Fe). The darker portions of the flight feather were enriched with Zn and Fe, which supports the suggestion that feather melanins are efficient ligands of some metals found in the environment, sequestering potentially harmful particles away from the body. However, trace lead (Pb) acquired from the regional pollution was detected only in females, and it was distributed across both the melanized and non‐melanized portions of the feather suggesting that only some metals are efficiently sequestered by melanins. Overall this study highlights a potential method for identifying pollutants using bird feathers, which has broader implications on environmental sensing as well as avian and human health. Copyright © 2013 John Wiley & Sons, Ltd.