Ab initio MO calculations were carried out, at the MP2/6-311G(d,p) level of approximation, to investigate the conformation of levopimaric acid. It has been found that the folded conformation is more stable than the extended conformation. The result is consistent with the documented experimental data. The reason for the relative stability of the folded conformation has been sought in the context of the CH/π hydrogen bond. Short non-bond distances have been disclosed between CHs in the 10β angular methyl group and sp2 carbons of the conjugated diene ring in the more stable folded conformers of model compounds. We suggest that the folded conformation of levopimaric acid is a consequence of an attractive molecular force, the CH/π hydrogen bond. 相似文献
Minimum requirements : Crystals and thin films of 1,4‐bis(alkenyl)‐2,5‐dipiperidinobenzenes, which contain only one benzene ring as the aromatic component, emit visible light with excellent solid‐state quantum yields upon irradiation with UV light. Polystyrene thin films doped with the benzenes also exhibit brilliant fluorescence. By modifying the alkenyl groups, the emission color can be tuned in the range from blue to red.
Double Horner–Wadsworth–Emmons reaction of (E)‐2,3‐diaryl‐1,4‐bis(diethylphosphonyl)but‐2‐ene with (p‐substituted) benzaldehydes gave (1E,3E,5E)‐1,3,4,6‐tetraarylhexa‐1,3,5‐trienes in moderate to good yields. Substitution of electron‐withdrawing or ‐donating groups at the para position of the 1,6‐diphenyl groups induced a slight bathochromic shift of UV spectra measured in CHCl3 compared with that of the parent 1,3,4,6‐tetraphenylhexa‐1,3,5‐triene. Although fluorescence was not observed with all the trienes in CHCl3, they markedly emitted visible light in powder forms with quantum yields of 0.15–0.44. Introduction of amino groups at the para position of the 3,4‐diphenyl groups induced a bathochromic shift of emission maxima with good solid‐state quantum yields. Thus, the tetraarylated triene framework is found to serve as a new class of fluorophores that exhibit aggregation‐induced emission. 相似文献
The electrocatalytic reduction of nitrite to NO by [CuMe2bpa(H2O)(ClO4)]+ ( 1 ), which is a model for the active site of copper‐containing nitrite reductase, incorporated in Nafion film was investigated. The Cu complex in the Nafion matrix exhibits an intense band at 267 nm and a broad band around 680 nm, assigned to d–d and ligand field transitions, respectively. The 77‐K EPR spectrum of 1 in the Nafion matrix reveals the typical axial signals (g//=2.28, g =2.08, A//=13.3 mT) of a tetragonal Cu2+ chromophore. The redox potential, which is related to the Cu+/Cu2+ couple, was ?146 mV (ΔE=72 mV) at pH 5.5. The redox reaction of 1 in Nafion was not dependent on pH and was a diffusion‐controlled process. The electronic structure and redox properties of 1 in the negatively charged polymer matrix were almost the same as those in aqueous solution. In the presence of nitrite, an increase in the cathodic current was observed in the cyclic voltammogram of 1 in the Nafion matrix. The current increase was dependent on the nitrite concentration and pH in solution. Upon reaching ?400 mV, a linear generation of NO was observed for the 1 /Nafion film coated electrode. The relationship between the rate of NO generation and the nitrite concentration in solution was analyzed with the Michaelis–Menten equation, where Vmax=45.1 nM s?1 and Km=15.8 mM at pH 5.5. The Cu complex serves the function of both the catalyst and electron transport in the Nafion matrix. The sensitivity of the electrode was estimated to be 3.23 μA mM?1 in the range of 0.1–0.4 mM nitrite. 相似文献
An improved method is proposed to determine the content of 210Pb in lead using 210Po measured by alpha-ray spectrometry. This improved method, which is based on radiochemical separation by DDTC–toluene extraction,
employs EDTA and citrate as masking reagents for the lead ions. To selectively extract polonium from an alkaline solution,
the pH dependency was examined using a liquid scintillation counting method. And pH 9 was chosen as an extraction condition.
Then 210Po was electrodeposited on a stainless steel disk, and the chemical recovery was followed by 209Po tracer. The effectiveness of the new method was validated by the agreement with the analytical results from five samples
as determined by gamma-ray spectrometry. 相似文献
An improved two-step synthetic route to functionalized cyclic carbonate monomers that features a novel cyclic carbonate intermediate with an active pentafluorophenyl ester group (MTC-OPhF(5)) has been developed. The versatile pentafluorophenyl ester intermediate can be synthesized on the gram to kilogram scale in one high-yielding step and is easy to store and handle on the benchtop. The active pentafluorophenyl ester of MTC-OPhF(5) is amenable to further substitution with suitable nucleophiles such as alcohols and amines to generate functionalized cyclic carbonates in high yields. The substitution reaction is tolerant of a wide variety of functionalities, including various hydrophobic and hydrophilic groups, reactive functionalities (via thiol-ene click chemistry or alkyl halides), and protected acids, alcohols, thiols, and amines. In view of the ever-increasing need for biodegradable and biocompatible polymers, this new methodology provides a simple and versatile platform for the synthesis of new and innovative materials. 相似文献
The synthesis and molecular structure of a dimeric aluminium complex composed of tri-lacunary α-Keggin polyoxometalate is described. The polyoxometalate, K(6)Na[(A-PW(9)O(34))(2){W(OH)(OH(2))}{Al(OH)(OH(2))}{Al(μ-OH)(OH(2))(2)}(2)]·19H(2)O (KNa-1), afforded by the reaction in water of a tri-lacunary Keggin polyoxotungstate with excess aluminium nitrate, followed by crystallization from water, was obtained as analytically pure, homogeneous, colorless crystals. The compound KNa-1 was characterized by elemental analysis, TG/DTA, FT-IR, solution NMR ((31)P, (27)Al, and (183)W), and X-ray crystallography. The single-crystal X-ray structure analysis revealed that two 6-coordinate aluminium ions linked with two bridging hydroxyl groups and four water molecules, i.e., [Al(III)(2)(μ-OH)(2)(OH(2))(4)](4+); a unit of a 6-coordinate tungsten ion linked with a hydroxyl group and a water molecule, i.e., [W(OH)(OH(2))](5+); a unit of a 6-coordinate aluminium ion linked with a hydroxyl group and a water molecule, i.e., [Al(OH)(OH(2))](2+), were sandwiched between two tri-lacunary α-Keggin polyoxotungstates, resulting in an overall C(s) symmetry. 相似文献
The stereochemical diversity-oriented conformational restriction strategy can be an efficient method for developing specific ligands for drug target proteins. To develop potent histamine H(3) and/or H(4) receptor ligands, a series of conformationally restricted analogs of histamine with a chiral trans- or cis-4-amino-2,3-methano-1-(1H-imidazol-4-yl)butane structure was designed based on this strategy. These stereochemically diverse compounds were synthesized from previously developed versatile chiral cyclopropane units. Among these analogs, a trans-cyclopropane-type compound, (2S,3R)-4-(4-chlorobenzylamino)-2,3-methano-1-(1H-imidazol-4-yl)butane (5b), has remarkable antagonistic activity to both the H(3) (K(i) = 4.4 nM) and H(4) (K(i) = 5.5 nM) receptors, and a cis-cyclopropane-type compound, (2R,3R)-4-amino-2,3-methano-1-(1H-imidazol-4-yl)butane (6a), is a potent and selective H(3) receptor partial agonist (K(i) = 5.4 nM). Although (2S,3R)-4-amino-2,3-methano-1-(1H-imidazol-4-yl)butane (5a) does not have a hydrophobic group which the usual H(3) receptor antagonists have, it was found to be a potent H(3) receptor antagonist (K(i) = 20.1 nM). Thus, a variety of compounds with different pharmacological properties depending on the cyclopropane backbones and also on the side-chain functional groups were identified. In addition to the previously used 1,2-methanobutane backbone, the 2,3-methanobutane backbone also worked effectively as a cyclopropane-based conformational restriction structure. Therefore, the combination of these two cyclopropane backbones increases the stereochemical and three-dimensional diversity of compounds in this strategy, which can provide a variety of useful compounds with different pharmacological properties. 相似文献
A diagram of energies between the HOMO of donor (D) and LUMO of acceptor (A) vs.ΔE(1/2)(DA) (= E(1/2)(D) - E(1/2)(A): E(1/2) = first-redox potential) clearly demonstrates the ionicity in the series of D/A assemblies, [{Ru(2)(CF(3)CO(2))(4)}(2)(TCNQR(x))]·n(solv) (TCNQR(x) = 2,5- or 2,3,5,6-R-substituted 7,7,8,8-tetracyano-p-quinodimethane; R(x) = H(4), F(2), Cl(2), Br(2), F(4), Me(2), (OMe)(2)). 相似文献