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61.
Nino Bašić Gunnar Brinkmann Patrick W. Fowler Tomaž Pisanski Nico Van Cleemput 《Journal of mathematical chemistry》2017,55(8):1669-1682
Stability and chemistry, both exohedral and endohedral, of fullerenes are critically dependent on the distribution of their obligatory 12 pentagonal faces. It is well known that there are infinitely many IPR-fullerenes and that the pentagons in these fullerenes can be at an arbitrarily large distance from each other. IPR-fullerenes can be described as fullerenes in which each connected cluster of pentagons has size 1. In this paper we study the combinations of cluster sizes that can occur in fullerenes and whether the clusters can be at an arbitrarily large distance from each other. For each possible partition of the number 12, we are able to decide whether the partition describes the sizes of pentagon clusters in a possible fullerene, and state whether the different clusters can be at an arbitrarily large distance from each other. We will prove that all partitions with largest cluster of size 5 or less can occur in an infinite number of fullerenes with the clusters at an arbitrarily large distance of each other, that 9 partitions occur in only a finite number of fullerene isomers and that 15 partitions do not occur at all in fullerenes. 相似文献
62.
Vladimir P. Rybalkin Gennadii S. Borodkin Valerii V. Tkachev Sofiya Yu. Zmeeva Lidiya L. Popova Alexander D. Dubonosov Vladimir A. Bren Sergey M. Aldoshin Vladimir I. Minkin 《Tetrahedron letters》2017,58(27):2648-2650
The first derivative of a novel heterocyclic system, (7E,10aE)-2,7-dimethylfuro[3′,4′:6,7]-cycloocta[1,2,3-cd]indole-8,10(2H,6H)-dione, was synthesized based on the Stobbe condensation of 3-chloro-1-methylindole-2-carbaldehyde with diethyl isopropylidenesuccinate. Cyclization of the 2-indolyl-containing diacid, formed by subsequent hydrolysis of the condensation product, did not lead to the expected fulgide, but rather to an unprecedented tetracyclic compound, the structure of which was established by 1H, 13C NMR, IR spectroscopy, mass-spectrometry and single crystal X-ray diffraction. 相似文献
63.
For every smooth (irreducible) cubic surface S we give an explicit construction of a representative for each of the 72 equivalence classes of determinantal representations. Equivalence classes (under GL3 × GL3 action by left and right multiplication) of determinantal representations are in one to one correspondence with the sets of six mutually skew lines on S and with the 72 (two-dimensional) linear systems of twisted cubic curves on S. Moreover, if a determinantal representation M corresponds to lines (a 1,...,a 6) then its transpose M t corresponds to lines (b 1,...,b 6) which together form a Schläfli’s double-six \(a_1\ldots a_6 \choose b_1\ldots b_6\) . We also discuss the existence of self-adjoint and definite determinantal representation for smooth real cubic surfaces. The number of these representations depends on the Segre type F i . We show that a surface of type F i , i = 1,2,3,4 has exactly 2(i?1) nonequivalent self-adjoint determinantal representations none of which is definite, while a surface of type F 5 has 24 nonequivalent self-adjoint determinantal representations, 16 of which are definite. 相似文献
64.
Dr. Robert F. Higgins Dr. Thibault Cheisson Dr. Bren E. Cole Dr. Brian C. Manor Dr. Patrick J. Carroll Prof. Eric J. Schelter 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(5):1867-1872
The separation of rare-earth ions from one another is challenging due to their chemical and physical similarities. Nearly all rare-earth separations rely upon small changes in ionic radii to direct speciation or reactivity. Herein, we show that the intrinsic magnetic properties of the rare-earth ions impact the separations of light/heavy and selected heavy/heavy binary mixtures. Using TriNOx3− ([{(2-tBuNO)C6H4CH2}3N]3−) rare-earth complexes, we efficiently and selectively crystallized heavy rare earths (Tb–Yb) from a mixture with light rare earths (La and Nd) in the presence of an external Fe14Nd2B magnet, concomitant with the introduction of a concentration gradient (decrease in temperature). The optimal separation was observed for an equimolar mixture of La:Dy, which gave an enrichment factor of EFLa:Dy=297±31 for the solid fraction, compared to EFLa:Dy=159±22 in the absence of the field, and achieving a 99.7 % pure Dy sample in one step. These results indicate that the application of a magnetic field can improve performance in a molecular separation system for paramagnetic rare-earth cations. 相似文献
65.
Volatile organic compounds (VOCs) play an important role in the chemistry of the atmosphere and in biogeochemistry. They contribute to the oxidative capacity of the atmosphere, particle and air pollutants, as well as to the production of greenhouse gases (for instance ozone). Among analytical techniques for their determination in the atmosphere gas chromatography coupled with mass spectrometry (GC-MS) offers several advantages. However, for an accurate quantification calibration with standard substances is necessary. A quantitative structure-property relationship (QSPR) model for the prediction of MS response factors was developed on basis of our experimental measurements for the quantification of ozone precursors present in the atmosphere. A linear correlation between chemical structures and response factors was established by using a 7-parameter MLR model. The average error in the prediction of response factors was calculated by cross-validation procedure and was below 20%, which is sufficient for the determination of VOCs in the air. The proposed procedure is time consuming so it is more suited for the quantification of tentatively identified organic compounds during the reprocessing of MS chromatograms in cases when the original sample is no longer available. 相似文献
66.
Using molecular dynamics simulations in conjunction with home-developed Split Integration Symplectic Method we effectively decouple individual degrees of freedom of water molecules and connect them to corresponding thermostats. In this way, we facilitate elucidation of structural, dynamical, spectral, and hydration properties of bulk water at any given combination of rotational, translational, and vibrational temperatures. Elevated rotational temperature of the water medium is found to severely hinder hydration of polar molecules, to affect hydration of ionic species in a nonmonotonous way and to somewhat improve hydration of nonpolar species. As proteins consist of charged, polar, and nonpolar amino-acid residues, the developed methodology is also applied to critically evaluate the hypothesis that the overall decrease in protein hydration and the change in the subtle balance between hydration of various types of amino-acid residues provide a plausible physical mechanism through which microwaves enhance aberrant protein folding and aggregation. 相似文献
67.
I. E. Tolpygin Yu. V. Revinskii A. G. Starikov A. D. Dubonosov V. A. Bren V. I. Minkin 《Chemistry of Heterocyclic Compounds》2012,47(10):1230-1236
1-(Anthracen-9-ylmethyl)-1H-benzimidazol-2-amine was synthesized by alkylation of benzimidazol-2-amine with 9-chloromethylanthracene, and a series of
azomethines based on it was obtained. Spectral investigations of the 9-anthrylmethylbenzimidazole derivatives revealed their
high chemosensor activity with respect to hydrogen cations. Quantum-chemical investigation of the structures obtained showed
that they possess high proton affinity and can be regarded as analogs of “proton sponges”. 相似文献
68.
Ion transfer at aqueous-organogel interfaces enables the non-redox detection of ions and ionisable species by voltammetry. In this study, a non-thermal method for preparation of an organogel was employed and used for the detection of hen-egg-white-lysozyme (HEWL) via adsorptive stripping voltammetry at an array of aqueous-organogel microinterfaces. Tetrahydrofuran solvent casting was employed to prepare the organogel mixture, hence removing the need for heating of the solution to be gelled, as used in previous studies. Cyclic voltammetry of HEWL at the microinterface array revealed a broad adsorption process on the forward scan, at positive applied potentials, followed by a desorption peak at ca. 0.68 V, indicating the detection of HEWL in this region. Application of an adsorption step, where a constant optimized potential of 0.95 V was applied, followed by voltammetric detection provided for a linear response range of 0.02–0.84 μM and a detection limit of 0.030 μM for 300 s adsorption. The detection limit was further improved by utilizing differential pulse stripping voltammetry, resulting in detection limits of 0.017 μM, 0.014 μM, and 0.010 μM for adsorptive pre-concentration times of 60, 120 and 300 s, respectively, in unstirred solutions. These results are an improvement over other methods for the detection of HEWL at aqueous–organic interfaces and offers a basis for the label-free detection of protein. 相似文献
69.
Alexandru T. Balaban Donald C. Young Janez Plavec Klemen Pečnik Matevž Pompe Jeremy E. Dahl Robert M. K. Carlson 《Magnetic resonance in chemistry : MRC》2015,53(12):1003-1018
Tetramantanes, and all diamondoid hydrocarbons, possess carbon frameworks that are superimposable upon the cubic diamond lattice. This characteristic is invaluable in assigning their 1H and 13C NMR spectra because it translates into repeating structural features, such as diamond‐cage isobutyl moieties with distinctively complex methine to methylene signatures in COSY and HMBC data, connected to variable, but systematic linkages of methine and quaternary carbons. In all tetramantane C22H28 isomers, diamond‐lattice structures result in long‐range 4JHH, W‐coupling in COSY data, except where negated by symmetry; there are two highly symmetrical and one chiral tetramantane (showing seven 4JHH). Isobutyl‐cage methines of lower diamondoids and tetramantanes are the most shielded resonances in their 13C spectra (<29.5 ppm). The isobutyl methylenes are bonded to additional methines and at least one quaternary carbon in the tetramantanes. W‐couplings between these methines and methylenes clarify spin‐network interconnections and detailed surface hydrogen stereochemistry. Vicinal couplings of the isobutyl methylenes reveal positions of the quaternary carbons: HMBC data then tie the more remote spin systems together. Diamondoid 13C NMR chemical shifts are largely determined by α and β effects, however γ‐shielding effects are important in [123]tetramantane. 1H NMR chemical shifts generally correlate with numbers of 1,3‐diaxial H–H interactions. Tight van der Waals contacts within [123]tetramantane's molecular groove, however, form improper hydrogen bonds, deshielding hydrogen nuclei inside the groove, while shielding those outside, indicated by Δδ of 1.47 ppm for geminal hydrogens bonded to C‐3,21 . These findings should be valuable in future NMR studies of diamondoids/nanodiamonds of increasing size. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
70.
We have used protein film voltammetry (PFV) to determine the midpoint potentials of the Pseudomonas aeruginosa, Hydrogenobacter thermophilus, and Nitrosomonas europaea wild-type monoheme cytochromes c (cyts c; PA, HT, and NE, respectively), as well as PA N64Q, HT Q64N, and NE V65delta mutants, as a function of pH, and buffer conditions. Recent studies have suggested that the identity of the 64 position of the heme-binding loop (either Asn or Gln) strongly influences the conformation of the Met ligand that binds the heme iron. The PFV studies reveal that HT and NE possess significantly lower potentials (wild-type cyts c having E(m) values of +227 and +250 mV vs SHE) than PA (+290 mV) in 50 mM phosphate buffer, pH 7 at 3 degrees C. The HT Q64N mutant rises in potential compared to wild-type, and the PA N64Q mutant has a lower potential, indicating relationships between Met ligand fluxion, hydrogen bonding to the Met ligand, and redox chemistry. Surprisingly, NE V65delta, possessing a heme binding loop nearly identical to that of the PA protein, displayed an E(m) of +232 mV, even lower than wild-type NE. These data are discussed in terms of models of Met ligand properties and proton dependence. 相似文献