Tag: M.W:300-400

The reaction rate of a catalyzed reaction is faster than the reaction rate of the uncatalyzed reaction at the same temperature.14187-32-7, Name is Dibenzo-18-crown-6, molecular formula is C20H24O6. In a Article£¬once mentioned of 14187-32-7, Recommanded Product: Dibenzo-18-crown-6

THE INTERACTION OF GROUP III METAL ALKYLS WITH CROWN ETHERS. THE SYNTHESIS AND STRUCTURE OF 2 AND 2

2 and 2 were prepared by the reaction of Ga(CH3)3 or Al(CH3)3 with the appropriate crown ether in toluene.After filtering and cooling, both products were obtained as colorless, air-sensitive, rectangular crystals.The structures of both compounds were determined from single crystal X-ray diffraction data collected on a CAD-4 diffractometer. 2 belongs to the monoclinic space group P21/c with unit cell parameters a 11.460(5), b 18.000(7), c 7.495(4) Angstroem, beta 105.65(4) degree, and rho(calc) 1.32 g cm-3 for Z = 2.Least-squares refinement gave a final R value of 0.061 for 1179 independent observed reflections.The molecule resides on a crystallographic center of inversion.The Ga-O distance of 2.198(8) Angstroem is among the longest yet observed.In order to accomodate the two trialkylgallium units, the crown ether is forced to adopt a chair configuration. 2 crystallizes in the space group P21/a with cell parameters a 16.423(7), b 9.812(5), c 20.935(8) Angstroem, beta 107.41(5) degree, and rho(calc) 1.07 g cm-3 for Z = 4.Least-squares refinement gave a final R value of 0.079.The greater flexibility of the crown ether in this case allows the bonded oxygen atoms to be positioned on the outside of the crown, with all six oxygen atoms in a near-planar arrangement.

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Application of 14187-32-7, Catalysts are substances that increase the reaction rate of a chemical reaction without being consumed in the process. 14187-32-7, Name is Dibenzo-18-crown-6, molecular formula is C20H24O6. In a Article£¬once mentioned of 14187-32-7

“Separated” versus “contact” ion-pair structures in solution from their crystalline states: Dynamic effects on dinitrobenzenide as a mixed-valence anion

Qualitative structural concepts about dynamic ion pairs, historically deduced in solution as labile solvent-separated and contact species, are now quantified by the low-temperature isolation of crystalline (reactive) salts suitable for direct X-ray analysis. Thus, dinitrobenzenide anion (DNB -) can be prepared in the two basic ion-paired forms by potassium-mirror reduction of p-dinitrobenzene in the presence of macrocyclic polyether ligands: LC (cryptand) and LE (crown-ethers). The crystalline “separated” ion-pair salt isolated as K(L C)+//DNB- is crystallographically differentiated from the “contact” ion-pair salt isolated as K(L E)+DNB- by their distinctive interionic separations. Spectral analysis reveals pronounced near-IR absorptions arising from intervalence transitions that characterize dinitrobenzenide to be a prototypical mixed-valence anion. Most importantly, the unique patterns of vibronic (fine-structure) progressions that also distinguish the “separated” from the “contact” ion pair in the crystalline solid state are the same as those dissolved into THF solvent and ensure that the same X-ray structures persist in solution. Moreover, these distinctive NIR patterns are assigned with the aid of Marcus-Hush (two-state) theory to the “separated” ion pair in which the unpaired electron is equally delocalized between both NO2-centers in the symmetric ground state of dinitrobenzenide, and by contrast, the asymmetric electron distribution inherent to “contact” ion pairs favors only that single NO 2-center intimately paired to the counterion. The labilities of these dynamic ion pairs in solution are thoroughly elucidated by temperature- dependent ESR spectral changes that provide intimate details of facile isomerizations, ionic separations, and counterion-mediated exchanges.

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Br¡ãnsted acid-promoted [3 + 3] cycloaddition of azomethine ylides with quinone monoimine: A practical method towards dihydrobenzoxazine derivatives

The binaphthol-derived phosphoric acid-promoted [3 + 3] cycloaddition of azomethine ylides with quinone monoimine has been achieved in the presence of 3 A MS at room temperature, providing dihydrobenzoxazine derivatives in moderate to excellent yields.

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Could LogP be a principal determinant of biological activity in 18-crown-6 ethers? Synthesis of biologically active adamantane-substituted diaza-crowns

18-crown-6 ethers are known to exert their biological activity by transporting K+ ions across cell membranes. Using non-linear Support Vector Machines regression, we searched for structural features that influence antiproliferative activity in a diverse set of 19 known oxa-, monoaza- and diaza-18-crown-6 ethers. Here, we show that the logP of the molecule is the most important molecular descriptor, among ?1300 tested descriptors, in determining biological potency (R2cv = 0.704). The optimal logP was at 5.5 (Ghose-Crippen ALOGP estimate) while both higher and lower values were detrimental to biological potency. After controlling for logP, we found that the antiproliferative activity of the molecule was generally not affected by side chain length, molecular symmetry, or presence of side chain amide links. To validate this QSAR model, we synthesized six novel, highly lipophilic diaza-18-crown-6 derivatives with adamantane moieties attached to the side arms. These compounds have near-optimal logP values and consequently exhibit strong growth inhibition in various human cancer cell lines and a bacterial system. The bioactivities of different diaza-18-crown-6 analogs in Bacillus subtilis and cancer cells were correlated, suggesting conserved molecular features may be mediating the cytotoxic response. We conclude that relying primarily on the logP is a sensible strategy in preparing future 18-crown-6 analogs with optimized biological activity.

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Bis(allyl)gallium Cation, tris(allyl)gallium, and tetrakis(allyl)gallate: Synthesis, characterization, and reactivity

A series of cationic, neutral, and anionic allylgallium complexes has been isolated and fully characterized. It includes neutral [Ga(nu1- C3H5)3(L)] (1, L = THF; 2, L = OPPh 3), cationic [Ga(nu1-C3H5) 2(THF)2]+[A]-(3, [A]-= [B(C6F5)4]-; 4, [A]-= [B(C6H3Cl2)4]-), as well as anionic [Cat]+[Ga(nu1-C3H 5)4]-(5, [Cat]+= K+; 6, [Cat]+= [K(dibenzo-18-c-6]+; 7, [Cat]+= [PPh4]+). Binding modes of the allyl ligand in solution and in the solid state have been studied comparatively. Single crystal X-ray analyses revealed a fourcoordinate neutral gallium center in 2, a five-coordinate cationic gallium center in 4 and [4¡¤THF], and a four-coordinate anionic gallium center with a bridging mu2- nu1:nu2coordination mode of the allyl ligand in 6. The reactivity of this series of allylgallium complexes toward benzophenone and N-heteroaromatics has been investigated. Counterion effects have also been studied. Reactions of 1 and 5 with isoquinoline revealed the first examples of organogallium complexes reacting under 1,2-insertion with pyridine derivatives.

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Enantioselective Syntheses of alpha-exo-Methylene-Lactones via Organocatalytic Halolactonization

alpha-exo-Methylene-gamma-butyrolactones and alpha-exo-methylene-delta-valerolactones constitute an important group of natural and bioactive products. An enantioselective halolactonization of dienoic acids using (DHQD)2PHAL catalyst is described. Various halogenated alpha-exo-methylene-gamma-butyrolactones and alpha-exo-methylene-delta-valerolactones were obtained in high yields and enantioselectivities. The resulting enantioenriched halogenated alpha-exo-methylene-lactones were found to exhibit significant tumor-inhibiting activities. (Figure presented.).

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Macroheterocycles. 27. Amidomethylation of Benzo-crown Ethers

The synthesis of some novel benzo-crown ethers by alpha-amidomethylation is described.

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The Complexation of the Diquat Dication by Dibenzo-3n-crown-n Ethers

Spectrophotometric investigations of equimolar mixtures of diquat bis(hexafluorophosphate) (2) and a range of dibenzo-3n-crown-n ethers < n = 6-12; (10)-(16)> in acetonitrile reveal the existence of charge-transfer absorption bands at ca. lambdamax 400 nm.These absorptions are attributable to intermolecular ?-? charge transfer between the electron-rich catechol units of the dibenzo-crown ethers and the electron-deficient bipyridinium ring system of the diquat dication.The qualitative conclusion from these experiments, that the most stable 1:1 complex is formed between dibenzo-30-crown-10 (14) and diquat bis(hexafluorophosphate) (2), led to the isolation from dichloromethane methanol-n-heptane of red crystals of 2 suitable for X-ray crystallography.Although the crystal structure analysis revealed that there are two independent sets of 1:1 complexes (I and II) in the unit cell, the gross structural features of the two complexes are very similar.In addition to the paralell alignment of their three aromatic rings to accommodate the stabilising intermolecular ?-? charge-transfer interaction, there is probably some further host-guest stabilisation to be gained on account of favourable electrostatic interactions between the phenolic oxygen atoms in the host and the nitrogen atoms in the pyridinium rings of the guest.Moreover, there is some evidence for weak C-H…O hydrogen bonding involving principally H-6 and H-6′ on the bipyridinium ring system of the guest and certain -CH2OCH2- oxygen atoms in the host.As evidenced by 1H n.m.r. spectroscopy in CD3COCD3, these non-covalent bonding interactions are probably responsible for the formation of stable and ordered 1:1 complexes with similar gross structural features in solution, at least in the cases where dibenzo-30-crown-10 (14), dibenzo-33-crown-11 (15), and dibenzo-36-crown-12 (16) are the hosts.Further evidence for the 1:1 stoicheiometry of these solution complexes, as well as for the complex involving dibenzo-27-crown-9 (13), has come from equilibrium constant measurements for the association between the dibenzo-3n-crown-n (n = 9-12) hosts (13)-(16) and diquat bis(hexafluorophosphate) (2) in acetone.A quantitative treatment of the charge-transfer absorption bands at 400 nm, which affords Ka values of 410, 17500, 10800, and 2000 M-1 for n = 9, 10, 11, and 12, respectively, provides convincing quantitative evidence for (a) 1:1 stoicheiometry and (b) the relative stabilities of the 1:1 complexes in solution.In the case of dibenzo-24-crown-8 (11), a complex of 2:1 (guest-host) stoicheiometry is believed to be formed in acetone with a Ka value of 385000 M-2, as shown by a successfull quantitative treatment of the charge-transfer absorption data by an independent method.

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The reaction rate of a catalyzed reaction is faster than the reaction rate of the uncatalyzed reaction at the same temperature.14187-32-7, Name is Dibenzo-18-crown-6, molecular formula is C20H24O6. In a Article£¬once mentioned of 14187-32-7, SDS of cas: 14187-32-7

Complexation of macrocyclic compounds with metal ions: 2. Mg(II), Ca(II), Sr(II), Ba(II), Cu(II), and Ag(I) in 20 mass % propylene carbonate + ethylene carbonate

The conductance behavior of magnesium, calcium, strontium, barium, copper, and silver perchlorates and their complexes with seven crown ethers have been studied in 20 mass % propylene carbonate + ethylene carbonate. The conductance studies indicate 1:1 complex formation between the metal ion and crown ether. For the alkaline earth metal ions, the order of stability constants with all crown ethers is found to be Mg(II) > Ca(II) > Sr(II) > Ba(II). The limiting ionic conductivities of metal ions and the complexed metal ions are also reported. In addition, complexation studies of Cu(II) and Ag(I) were carried out by potentiometry and voltammetry to compare the results with those obtained by conductivity measurements, which were found to be in good agreement with each other.

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Related Products of 14187-32-7, Catalysts are substances that increase the reaction rate of a chemical reaction without being consumed in the process. 14187-32-7, Name is Dibenzo-18-crown-6, molecular formula is C20H24O6. In a Article£¬once mentioned of 14187-32-7

Further development of the structure-property concept on the basis of thermodynamic parameters of solvation

A thermodynamic study is made of the model systems consisting of a metal ion (Na, K), a crown ether (18-crown-6, dibenzo-18-crown-6), and an aqueous-organic solvent (water-methanol, water-2-propanol, water-acetonitrile). The contributions of reagent solvation to the strength and stability of mono complexes of crown ethers with alkali metal ions are found out. Attraction of the excess thermodynamic functions along with the complexation and solvation characteristics allows expansion of the capabilities of search and selection of biologically active compounds with desired properties on the basis of correlations between the bioligand structure and the process thermodynamics.

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