We have employed mass spectrometry, ion mobility, and computational techniques to characterize complexes of n-alkylammonium ions with cucurbit5uril (CB5) and cucurbit6uril (CB6) ligands in the gas ...phase. Nonrotaxane structures are energetically preferred and experimentally observed for all CB5 complexes. Pseudorotaxane structures are computationally favored and experimentally observed for CB6·n-alkylammonium+ complexes, but the addition of a second cation (proton, alkali metal ion, another alkylammonium ion, or guanidinium) on the opposite rim of CB6 causes sufficiently unfavorable steric interactions that n-pentylammonium and longer chains no longer remain threaded through the CB6 cavity; nonrotaxane topologies are then favored. This provides a very simple example of negative allosteric interactions and molecular structure switching in these complexes.
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With the potential decline in supplies of today's most widely used supplementary cementitious materials (SCMs) such as fly ash and slag, there is growing interest in the use of natural pozzolans (for ...example, pumice, volcanic ash), processed pozzolans (for example, calcined clays and shales), and manufactured pozzolans (for example, ground glass). Establishing the pozzolanic reactivity of these materials is an essential part of the evaluation process. Currently, pozzolans are assessed using ASTM C618 and C311, with the strength activity test being the only real performance indicator. Unfortunately, it is not possible to accurately determine the contribution of the pozzolanic reactivity to the strength in this test. This paper presents the development of a new pozzolanic reactivity test method based on the previous strength-activity-with-lime test but modified to increase the rate of the pozzolanic reaction. In this test, the solution-to-binder ratio is kept constant with workability adjusted using chemical admixtures. A range of mixing solutions containing combinations of KOH, NaOH, and K.sub.2SO.sub.4 and various curing regimes were investigated. The outcome of the test is compared with results from the current ASTM C311 and CSA A3004-E1 test methods for a wide range of pozzolanic (and inert) materials. Keywords: ASTM C618; bound water; compressive strength; lime reactivity; natural pozzolans; pozzolanic reactivity; strength activity index; thermogravimetric analysis.
Astrocytes play multifaceted and vital roles in maintaining neurophysiological function of the central nervous system by regulating homeostasis, increasing synaptic plasticity, and sustaining ...neuroprotective effects. Astrocytes become activated as a result of inflammatory responses during the progression of pathological changes associated with neurodegenerative disorders. Reactive astrocytes (neurotoxic A1 and neuroprotective A2) are triggered during disease progression and pathogenesis due to neuroinflammation and ischemia. However, only a limited body of literature describes morphological and functional changes of astrocytes during the progression of neurodegenerative diseases. The present review investigated the detrimental and beneficial roles of astrocytes in neurodegenerative diseases reported in recent studies, as these cells have promising therapeutic potential and offer new approaches for treatment of neurodegenerative diseases.
Study of sulfur (S) centered hydrogen bonding (SCHB) interactions in the literature is mostly limited to the molecular systems where S acts as a hydrogen-bond acceptor. It has been found that this ...unconventional SCHB is similar in strength to any conventional hydrogen bonding interaction involving electronegative atoms. However, SCHB involving S as a hydrogen-bond donor is not explored much in the literature. Herein, we have studied the nature and strength of an unconventional S–H···O hydrogen bond in a 1:1 complex of 2-fluorothiophenol (2-FTP) and H2O using gas-phase electronic and IR spectroscopy in combination with quantum chemistry calculations. Both of the two conformers of 2-FTP···H2O observed in the experiment are found to be stabilized primarily by S–H···O hydrogen bonding interaction. O–H···S hydrogen-bonded conformers of the complex, which are higher in energy, are not observed in the experiment. There is a nice agreement between the theoretical and experimental IR spectra of the two observed conformers. The observed IR red-shift of 25–30 cm–1 in the S–H stretching frequency of both the conformers of the complex with respect to that of the 2-FTP monomer bespeaks that the S–H···O hydrogen bond present in 2-FTP···H2O is weak in nature. The present work demonstrates that the S–H···O hydrogen bond can have preference over the O–H···S hydrogen bond depending on the pK a values or proton affinities of the hydrogen bonding partners in a complex.
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Direct catalytic asymmetric Michael addition reactions of ketones to nitroolefins using newly developed chiral pyrrolidine−pyridine conjugate bases as catalysts are described. The desired 1,4-adducts ...are obtained in excellent yields with high enantio- and diastereoselectivities.
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We report a crossed-beam imaging experiment on the title reactions at two collisional energies (E c) of 5.3 and 10 kcal mol–1. Both the integral cross sections relative to the ground-state reactivity ...and the differential cross sections were measured and compared. We found that one-quantum excitations of the CH3-stretching vibrations of the CH3D reagent exerted profound mode-specificity in forming the umbrella-mode-excited CH2D(41) products with the vibrational efficacy of v 4 > v 1-I > v 1-II at both E c values. The concomitantly formed HCl(v) coproducts were vibrationally cold. Interestingly, the branching ratios of (v = 1)/(v = 0) appeared invariant to the initial stretch-modes of excitation at E c = 5.3 kcal mol–1, yet exhibited a pronounced mode-specific dependency in the order of v 1-II > v 1-I > v 4 at E c = 10.3 kcal mol–1. This large and E c-dependent disparity between the two Fermi-coupled reagents, v 1-I and v 1-II, is particularly significant and could be another facetin addition to that in the recently reported vibrational enhancement factorsof the Fermi-phase-induced interference effect manifested in the product vibrational branching ratio. The pair-correlated angular distributions (v CH2D, v HCl)s = (41, 0)s in the three stretch-excited reactions were globally alike and resembled that of the ground-state reaction pair (00, 0)g, suggestive of a direct abstraction mechanism of the peripheral type. This is in sharp contrast to all other vibrationally excited pairs of (11, 0)s, (31, 0)s, and (61, 0)s previously reported in the CH2D + HCl isotopic channel, for which both the direct abstraction and a time-delayed resonance pathway partake.
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Aromatic molecules are key constituents of many pharmaceuticals, electronic materials, and commodity plastics. The utility of these molecules directly reflects the identity and pattern of ...substituents on the aromatic ring. Here, we report a palladium(II) catalyst system, incorporating an unconventional ortho-dimethylaminopyridine ligand, for the conversion of substituted cyclohexanones to the corresponding phenols. The reaction proceeds via successive dehydrogenation of two saturated carbon-carbon bonds of the six-membered ring and uses molecular oxygen as the hydrogen acceptor. This reactivity demonstrates a versatile and efficient strategy for the synthesis of substituted aromatic molecules with fundamentally different selectivity constraints from the numerous known synthetic methods that rely on substitution of a preexisting aromatic ring.
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Cellular processes are carried out by many genes, and their study and optimization requires multiple levers by which they can be independently controlled. The most common method is via a genetically ...encoded sensor that responds to a small molecule. However, these sensors are often suboptimal, exhibiting high background expression and low dynamic range. Further, using multiple sensors in one cell is limited by cross-talk and the taxing of cellular resources. Here, we have developed a directed evolution strategy to simultaneously select for lower background, high dynamic range, increased sensitivity, and low cross-talk. This is applied to generate a set of 12 high-performance sensors that exhibit >100-fold induction with low background and cross-reactivity. These are combined to build a single "sensor array" in the genomes of E. coli MG1655 (wild-type), DH10B (cloning), and BL21 (protein expression). These "Marionette" strains allow for the independent control of gene expression using 12 small-molecule inducers.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
A full-dimensional global potential energy surface (PES) for the reaction 23Na87Rb + 23Na87Rb → 23Na2 + 87Rb2 was constructed based on high-level ab initio calculations. The short-range part was ...expressed as a permutation invariant polynomial-neural network (PIP-NN) fit of 22 003 ab initio points calculated using a coupled cluster method with the one-electron basis 5s5p5d2f plus effective core potentials and core polarizability potentials, while the long-range part was represented in an asymptotically correct form based on multipole expansion. The formation rate of the 23Na2 87Rb2 complex calculated using a quantum statistical method is in good agreement with experiment, while the estimated 19.20 μs lifetime of the complex from Rice–Ramsperger–Kassel–Marcus (RRKM) theory is significantly shorter than the measured millisecond decay rate, signaling either the inadequacy of RRKM theory or a yet unresolved loss mechanism.
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The linear and nonlinear properties of the stilbazolium derivative, 2-2-(3-hydroxy-4-methoxy-phenyl)-vinyl-1-methyl-pyridinium naphthalene-2-sulfonate dihydrate crystal (VSNS), were investigated ...using an iterative electrostatic embedding scheme and density functional theory (DFT). The dipole moment and second hyperpolarizability of the VSNS molecule are sharply influenced by its crystalline phase. Standard DFT global hybrids such as B3LYP and M06 are strongly benefited by the effects of crystalline polarization. The performance can be further improved by making small changes in the amount of Hartree–Fock exchange included in the hybrid, delivering good hyperpolarizability and spectroscopy.
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