On rational connectedness of globally F-regular threefolds

In this paper, we show that projective globally F  -regular threefolds, defined over an algebraically closed field of characteristic p≥11$p\ge 11$, are rationally chain connected.     

Induced Decompositions of Highly Dense Graphs

Given two graphs F and G, an induced F‐decomposition of G is a partition of into induced subgraphs isomorphic to F. Bondy and Szwarcfiter [J. Graph Theory, DOI: 10.1002/jgt.21654] defined the value as the maximum number of edges in a graph of order n admitting an induced F‐decomposition and determined the value of for some graphs (and families of graphs). In this article, we prove that is valid for all graphs F. We also present tighter asymptotic bounds for some of the small graphs for which the exact value of remains unknown. The proofs are based on the heavy use of various classes of Kneser graphs and hypergraphs.     

Fluorescence quenching studies on the interaction of a novel deepened cavitand towards some transition metal ions

A novel ‘three-level’ deepened cavitand featuring a significantly sizable portal has been synthesized and its interaction with some transition metal ions has been investigated in THF/H₂O binary solvent using fluorescence quenching technique. The results suggest that among the used transition metal ions including Ag⁺, Cd²⁺, Cu²⁺, Fe³⁺, Cr³⁺, Hg²⁺, La³⁺, Mn²⁺, Ni²⁺, Zn²⁺ and Co²⁺, only Fe³⁺ and Cu²⁺ show good quenching ability. In order to interpret the quenching mechanism, the Stern–Volmer kinetics, and the presence of both the dynamic and static quenching have been discussed. It was found that the simultaneous presence of the sphere-of-action static quenching and dynamic quenching model agrees very well with the experimental results. The limits of detection for Fe³⁺ and Cu²⁺ were found to be 2.1 × 10⁻⁶ mol L⁻¹ (3σ) and 3.6 × 10⁻⁶ mol L⁻¹ (3σ), respectively. Cations with potential interference, such as K⁺, Na⁺, Mg²⁺, Ca²⁺, Co²⁺, La³⁺ and Mn²⁺ do not have significant effects on the determinations of Fe³⁺ and Cu²⁺. This cavitand can be potentially applied as optical sensor for the detection of Fe³⁺ and Cu²⁺.     

Synthesis of elongated cavitands via click reactions and their use as chemosensors

A very efficient modular reaction protocol was developed to attach various functionalities to a rigid cavitand scaffold. In this way, aryl, iodoaryl, benzyl, pyrrolidylmethyl groups, as well as a polyethylene-glycol chain were attached to the ‘triazol-level’ of the cavitand. The palladium-catalyzed ethynylation of the iodoarene moieties, followed by the copper(I)-catalyzed azide–alkyne cycloaddition produced novel cavitands with significantly elongated binding pockets. The dimensions of these molecules are calculated to be at least 9 Å×18 Å, which place them amongst the largest unimolecular hosts obtained by pure covalent synthesis. A cavitand-based click conjugate is used for selective complexation of Cu²⁺ and Fe³⁺, providing significant fluorescent quenching.     

Comparison of Crystal Structures of New Racemic Chiral Compounds Showing and Not Showing the Phenomenon of Preferential Enrichment

Abstract

The crystal structures of (±)-[2-[4-(3-ethoxy-2-hydroxypropoxy)phenylcarbamoyl]ethyl] trimethylammonium p-chlorobenzenesulfonate [(±)-NCMe₃] and its terminal methoxy derivative, (±)-NCMe₃-OMe, are compared. The former racemate exhibited the phenomenon of Preferential Enrichment, whereas the latter failed to do so. Crystal data, (±)-NCMe₃: CuKα radiation, space group P 1, Z = 2, a = 9.848(5), b = 14.823(3), c = 9.147(1) Å, α = 97.81(1), β = 92.68(3), γ = 105.92(2)°, D _calc = 1.355 g/cm³, R = 0.056 for 3213 observed reflections; (±)-NCMe₃-OMe: CuKα radiation, space group P 1, Z = 2, a = 11.350(1), b = 14.568(2), c = 8.2981(4) Å, α = 94.346(7), β = 112.376(5), γ = 78.622(9)°, D _calc = 1.343 g/cm³, R = 0.069 for 1519 observed reflections.     

Living Carbocationic Polymerization of Styrene in the Presence of Proton Trap

Abstract

The living polymerization of styrene was achieved with the 2,4,4-trimethyl-2-pentyl chloride/TiCl₄/MeCl:methylcyclohexane 40:60 v:v/?80°C polymerization system in the presence of di-tert-butylpyridine in concentrations comparable to the concentration of protic impurities. It was determined that the living nature of the polymerization is not due to carbocation stabilization. The polymerization is second order in TiCl₄. Side reactions, namely polymerization by direct initiation and intermolecular alkylation, are operational, and a careful selection of experimental conditions is necessary to minimize their effect and obtain apparently living behavior. Polymerization by direct initiation can be minimized by increasing the initiator concentration, and intermolecular alkylation can be reduced by quenching the polymerization system when the conversion reaches close to 100%.     

Improving molecular docking through eHiTS’ tunable scoring function

We present three complementary approaches for score-tuning that improve docking performance in pose prediction, virtual screening and binding affinity assessment. The methodology utilizes experimental data to customize the scoring function for the system of interest considering the specific docking scenario. The tuning approach, which has been implemented as an automated utility in eHiTS, is introduced as a solution to one of the conundrums of the molecular docking paradigm, namely, the lack of a universally well performing scoring function. The accuracy of scoring functions has been shown to be generally system-dependent, and particularly lacking for binding energy and bio-activity predictions. In the proposed approach, pose and energy predictions are enhanced by adjusting the relative weights of the eHiTS energy terms to improve score-RMSD or score-affinity correlations. In a virtual screening context ligand-based similarity is used to rescale the docking score such that better enrichment factors are achieved. We discuss the algorithmic details of the methods, and demonstrate the effects of score tuning on a variety of targets, including CDK2, BACE1 and neuraminidase, as well as on the popular benchmarks—the Directory of Useful Decoys and the PDBBind database.     

The role of defects in chemical sensing properties of carbon nanotube films

The electrical resistance of 24 different carbon nanotube (CNT) thin film samples in blowing ambient air and 10 different analyte vapor environments was measured. The effects of the CNT growth method, different chemical treatments, ball milling, sample preparation conditions and Ar⁺-ion irradiation are compared. Significant differences in the response signal curves as a function of time in the case of the studied sensor/vapor combinations show the important role of the defect structure and attached functional groups in the chemical sensing properties of CNTs.     

Modeling high density microholographic data storage: Using linear, quadratic, thresholding and hard clipping material characteristics

Crosstalk related raw signal-to-noise ratio (SNR) and bit error rate (BER) of high density bitwise microholographic data storage is investigated by numerical modeling. Scattering and diffraction of light is calculated in non-paraxial scalar approximation. A multiple thin slice implementation of the perturbative volume integral equation is used, which can be easily parallelized. The effect of bit and track spacing, and the different local characteristics of the holographic recording material on the SNR, BER and diffraction efficiency are investigated. The results show that these lateral spacing parameters have much more effect on crosstalk noise than the number of layers. Using two-photon, thresholding or hard clipping materials generates less crosstalk noise at the same data density than a linear material, and the dynamic range of these materials can be used more effectively resulting in higher single microhologram diffraction efficiencies.