- Pyridinium trifluoroacetate: Spoked columns of hydrogen-bonded cyclic dimers
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The crystal structure of C5H6N+.C2F3O2- consists of three unique ion pairs. Each unique ion pair packs along a threefold screw axis to generate a distinct spoked column. The three distinct spoked columns are pseudosymmetrically related through a threefold screw axis. Each column comprises an ionic core and non-polar spokes. Columns pack in a manner that maximizes the non-polar interactions between them.
- Tayhas,Palmore,McBride-Wieser
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Read Online
- Macrolide compound and synthesis method, pharmaceutical composition and application of compound
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The invention discloses a macrolide compound and a synthesis method, a pharmaceutical composition and application of the compound. When the macrolide compound or the pharmaceutically acceptable salt thereof provided by the invention is used together with beta-lactam antibiotics, the effect of the beta-lactam antibiotics on inhibiting methicillin-resistant staphylococcus aureus can be obviously improved. A test result shows that the in-vitro synergistic effect is good, and the compound is a novel synergist, can relieve the drug resistance of methicillin-resistant staphylococcus aureus (MRSA) to oxacillin, and has a good market development prospect.
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Paragraph 0174; 0177-0178
(2021/07/17)
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- Carbonyl Hypoiodites as Extremely Strong Halogen Bond Donors
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Neutral halogen-bonded O?I?N complexes were prepared from in situ formed carbonyl hypoiodites and aromatic organic bases. The carbonyl hypoiodites have a strongly polarized iodine atom with larger σ-holes than any known uncharged halogen bond donor. Modulating the Lewis basicity of the selected pyridine derivatives and carboxylates leads to halogen-bonded complexes where the classical O?I???N halogen bond transforms more into a halogen-bonded COO????I?N+ ion-pair (salt) with an asymmetric O?I?N moiety. X-ray analyses, NMR studies, and calculations reveal the halogen bonding geometries of the carbonyl hypoiodite-based O?I?N complexes, confirming that in the solid-state the iodine atom is much closer to the N-atom of the pyridine derivatives than its original position at the carboxylate O-atom.
- Rissanen, Kari,Truong, Khai-Nghi,Ward, Jas S.,Yu, Shilin
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supporting information
p. 20739 - 20743
(2021/08/25)
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- Bringing a Molecular plus One: Synergistic Binding Creates Guest-Mediated Three-Component Complexes
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Cethyl-2-methylresorcinarene (A), pyridine (B), and a set of 10 carboxylic acids (Cn) associate to form A·B·Cn ternary assemblies with 1:1:1 stoichiometry, representing a useful class of ternary systems where the guest mediates complex formation between the host and a third component. Although individually weak in solution, the combined strength of the multiple noncovalent interactions organizes the complexes even in a highly hydrogen-bond competing methanol solution, as explored by both experimental and computational methods. The interactions between A·B and Cn are dependent on the pKa values of carboxylic acids. The weak interactions between A and C further reinforce the interactions between A and B, demonstrating positive cooperativity. Our results reveal that the two-component system such as that formed by A and B can form the basis for the development of specific sensors for the molecular recognition of carboxylic acids.
- Beyeh, Ngong Kodiah,Dashti, Mohadeseh,Lahtinen, Manu,Pan, Fangfang,Puttreddy, Rakesh,Rissanen, Kari,Taimoory, S. Maryamdokht,Trant, John F.,Twum, Kwaku
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p. 5884 - 5894
(2020/05/20)
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- Ionic Liquids as “Masking” Solvents of the Relative Strength of Bases in Proton Transfer Reactions
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Equilibrium constants for the proton transfer reaction between pyridines and trifluoroacetic acid were measured in room-temperature ionic liquids (ILs) of different cation–anion compositions. The experimental equilibrium constants for ion-pair formation were corrected according to the Fuoss equation. The calculated equilibrium constants for the formation of free ions were taken as a quantitative measure of the base strength in IL solutions and compared with the relative constants in water. The effect of IL composition is discussed for a series of fixed IL anions and fixed IL cations. Finally, the sensitivity of the proton transfer reaction to the electronic effects of the substituent groups on the pyridine ring was quantified by applying the Hammett equation. A more marked levelling effect on the base strength was observed in ILs than in water. The Hammett reaction constants ρ were then correlated with solvent parameters according to a multi-parametric analysis, which showed that both specific hydrogen-bond donor/acceptor and non-specific interactions play an important role, with α and permittivity being the main parameters affecting the ability of the IL to differentiate the strength of the base.
- Zappacosta, Romina,Di Crescenzo, Antonello,Ettorre, Valeria,Fontana, Antonella,Pierini, Marco,Siani, Gabriella
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- Nucleoside phosphitylation using ionic liquid stabilised phosphorodiamidites and mechanochemistry
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A range of nucleoside phosphoramidites incorporating small amino substituents have been readily synthesised using ionic liquid stabilised phosphorodiamidites coupled with mechanochemistry. The Royal Society of Chemistry.
- Crossey, Kerri,Hardacre, Christopher,Migaud, Marie E.
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supporting information
p. 11969 - 11971
(2013/01/16)
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- Tunable protic ionic liquids as solvent-catalysts for improved synthesis of multiply substituted 1,2,4-triazoles from oxadiazoles and organoamines
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More than green alternatives to traditional volatile molecular organic solvents, protic ionic liquids as dual solvent-catalysts have been successfully used to promote reactions of organoamines with oxadiazoles to afford sterically hindered 1,2,4-triazoles. Among the tested protic ionic liquids, pyridinium trifluoroacetate and acetate showed the highest efficiency for the reactions of arylamines and alkylamines, respectively, indicating that tunable catalysis could be readily effected with protic ionic liquid solvent-catalysts by simply tuning their cation and anion counterparts. A general and efficient approach has been developed for synthesis of multiply substituted 1,2,4-triazoles based on the tunable protic ionic liquid solvent-catalyst systems.
- Chen, Xiaofeng,Liu, Rui,Xu, Yuan,Zou, Gang
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body text
p. 4813 - 4819
(2012/07/31)
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- Measurement of the barrier to inversion of configuration in acyclic phosphite triesters
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Synthesis of three acyclic chiral phosphites is reported, in the form of dithymidine phosphite triesters. These diastereomerically pure P-stereogenic phosphites undergo epimerization at a measurable rate at 150 °C. When the alcohols on the deoxyribose moieties are protected as acyls, decomposition is minimized and by computer fitting, rate constants for epimerization can be extracted. These allow for the first time calculation of the barrier to inversion of configuration in phosphite triesters, giving ΔG ?(150 °C) = 33.0 ± 0.2 kcal mol-1, comparable to the inversion barrier seen for phosphines.
- Mukhlall, Joshua A.,Hersh, William H.
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experimental part
p. 62 - 70
(2011/06/24)
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- Basicity of pyridine and some substituted pyridines in ionic liquids
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Figure presented The equilibrium constants for ion pair formation of some pyridines have been evaluated by spectrophotometric titration with trifluoroacetic acid in different ionic liquids. The basicity order is the same in ionic liquids and in water. The substituent effect on the equilibrium constant has been discussed in terms of the Hammett equation. Pyridine basicity appears to be less sensitive to the substituent effect in ionic liquids than in water.
- Angelini, Guido,De Maria, Paolo,Chiappe, Cinzia,Fontana, Antonella,Pierini, Marco,Siani, Gabriella
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experimental part
p. 3912 - 3915
(2010/08/06)
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- Hydrogen-Bonded Species of Pyridinium Halogenoacetetes. 2. Thermometric Behavior in Aprotic Solvents
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The enthalpies of reaction of a series of substituted pyridines and of triethylamine, quinoline, and isoquinoline (for the sake of comparison) with trifluoroacetic acid (TFA) in chloroform were measured at 25 deg C at final solution concentrations ranging from 1E-2 to 5E-2 M.The enthalpies of reaction of 2,4,6-trimethylpyridine, pyridine, and 4-cyanopyridine with trichloroacetic acid (TCA), dichloroacetic acid (DCA), monochloroacetic acid (MCA), and acetic acid (AcOH) in chloroform were also measured at 25 deg C.The concentration dependence of enthalpies of reaction was examined by measuring them for 2,4,6-trimethylpyridine-TFA, pyridine-TFA, and 4-cyanopyridine-TFA in chloroform over the entire possible solution concentration range at 25 deg C.In order to study the energetic behavior of H-bonded species of the ptridine-TFA system in media of different dielectric constants, the enthalpy measurements were made in p-dioxane, o-xylene, and carbon tetrachloride.The thermometric results have been discussed in terms of interactions present in the H-bonded species of these systems in nonaqueous solutions.
- Chawla, B.,Mehta, S. K.
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p. 2650 - 2655
(2007/10/02)
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- Study of Reactions Between Alkyl(pyridine)cobaloximes and Trifluoroacetic Acid; Formation and Crystal Structure of cis-Bis(butane-2,3-dione dioxime)bis(trifluoroacetoxy)cobalt(II)
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The reactions between several alkyl(pyridine)cobaloximes i, Bun, CH2CH2CH=CH2, or CH2CHMeCH=CH2, (1a)-(1h) respectively; py = pyridine; Hdmg = monoanion of dimethylglyoxime> and trifluoroacetic acid in deuteriochloroform have been monitored by 1H n.m.r. spectroscopy.This techique indicates that addition of trifluoroacetic acid to an alkyl(pyridine)cobaloxime initially causesreversible protonation without loss of pyridine, then a second protonation occurs leading to the loss of pyridine as pyridinium trifluoroacetate.With excess of trifluoroacetic acid, the alkylcobaloximes lose their alkyl group as RH and slowly deposit a red crystalline solid, identified as the title complex (4) by analysis of its crystal structure.Crystals of (4) are triclinic, space group P, with a = 10.068(3), b = 10.716(5), c = 13.030(3) Angstroem, α = 100.15(3), β = 116.76(3), γ = 88.97(3) deg, and Z= 2. 1 873 Reflections collected at -80 deg C by a fourcircle diffractometer were refined to R = 0.053.The Co-O distances are 2.069(2) and 2.057(2) Angstroem and Co-N are 2.126(3), 2.138(2), 2.139(3), and 2.149(3) Angstroem.
- Alcock, Nathaniel W.,Atkins, Martin P.,Golding, Bernard T.,Sellars, Philip J.
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p. 337 - 344
(2007/10/02)
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