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131.
Joseph S. Alper Robert I. Gelb Marietta H. Schwartz 《Journal of inclusion phenomena and macrocyclic chemistry》1991,11(4):333-348
Complexation stoichiometries and formation constants of tri- and tetra-protonated forms of 1,4,8,12-tetraazacyclopentadecane with NO
3
–
, Cl–, IO
3
–
and SO
4
2–
ions are determined by pH potentiometric and13C NMR spectrometric measurements. Estimates of H and S are obtained from the values of the temperature dependent formation constants and acid dissociation constants. All four anions form only 1 : 1 complexes with the triprotonated amine species. NO
3
–
and Cl– form 1 : 1 complexes only with the tetraprotonated amine, while IO
3
–
and SO
4
2–
form both 1 : 1 and 2 : 1 complexes. The complexation behavior is interpreted in terms of solvation and internal hydrogen bonding interactions. 相似文献
132.
The most stable structure of CB2H3
–, as established computationally, is the aromatic diboracyclopropenyl (diboriranyl) anion (5), while open-chainC
2v, isomer H2BCBH (7) is only 3 kcal/mol higher in energy at the QCISD(T)/6-311 +G**//MP2/6-31+G*+ZPE (HF/6-31 +G*). The 47-kcal/mol barrier between cyclic,5, and open-chain,7, structures suggests that both of them may be observed. The aromatic stabilization energy of the diboriranyl anion (18 kcal/mol) is half the value in the isoelectronic cyclopropenium ion, C3H3
+. The computed, by IGLO method (5a), and experimental (6a) chemical shifts,(13C) and(11B), agree within 4 ppm range. The theoretical vibrational frequencies of the most stable isomers,5 and7, are presented for experimental verification of these species. 相似文献
133.
134.
A ChaiyanurakkulR Jitchati M KaewpetS Rajviroongit Y Thebtaranonth P ThongyooW Watcharin 《Tetrahedron》2003,59(49):9825-9837
Deprotonation of an oxiranyl β-proton takes place in a stereoselective manner providing the corresponding oxiranyl ‘remote’ anion. The anion is stabilized by chelation between the lithium and the carbonyl moiety of an ester, lactone, imide, or keto-group in the form of a five-membered cyclic intermediate. Certain ester-stabilized oxiranyl anions are stable and can be left in THF solution at −78°C for several hours. The generated anions undergo a stereoselective alkylation reaction to provide products, which could be useful intermediates in the synthesis of bioactive naturally occurring α-methylene bis-γ-butyrolactones. 相似文献
135.
HU Rong TIAN Jinping & YIN Yingwu . College of Chemistry & Environment Protection Engineering Southwest University for Nationalities Chengdu China . TH-UNIS Insight Co. Ltd. Beijing China . Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology Ministry of Education Department of Chemistry Tsinghua University Beijing China 《中国科学B辑(英文版)》2006,49(4):351-356
The formation of peptides and then protein by small abiological molecules clusters such as amino acid is a key stage in the origin of life[1]. More and more ex- perimental results showed that phosphate plays an important role in the formation of biomolecules in prebiotic chemical evolution. The principal reservoirs of biochemical energy are phosphates (such as ATP). The peculiar role of phosphates in contemporary life might suggest its essential role in prebiotic energy conversion, syntheses … 相似文献
136.
137.
Alexei A. Belik Shinya Uji Eiji Takayama-Muromachi 《Journal of solid state chemistry》2005,178(11):3461-3463
Magnetic properties of quasi-one-dimensional S=1/2 Heisenberg antiferromagnet Sr2Cu(PO4)2 were investigated by temperature and field dependence of AC susceptibility down to 0.03 K. A sharp peak was observed at on the temperature dependence of AC susceptibility indicating long-range magnetic ordering. Taking into account the exchange constant, (Hamiltonian =J∑SiSi+1), the ratio kBTN/J is 0.06%. Sr2Cu(PO4)2 is, therefore, one of the best one-dimensional Heisenberg antiferromagnet known so far. 相似文献
138.
《Arabian Journal of Chemistry》2022,15(4):103712
Although recent decades have witnessed the synthesis of 1,3,4-thiadiazoles via phosphorus POCl3-promoted cyclization reaction, simultaneous access to 2-amino-1,3,4-thiadiazole and 2-amino-1,3,4-oxadiazole analogs remains unexpected and elusive. Herein, a detailed regiocontrolled synthesis of 2-amino-1,3,4-thiadiazoles in good to high yields with good regioselectivities from readily available thiosemicarbazides using POCl3 was disclosed. Meantime, to establish a comprehensive structure–activity relationship, 2-amino-1,3,4-oxadiazole derivatives as single regioisomers were prepared via EDCI·HCl-triggered cyclization of the thiosemicarbazide intermediates. The in vitro anti-influenza assays proved that the selected compounds with the pyrazine/pyridine ring exhibited certain inhibitory activities against influenza A virus strains A/HK/68 (H3N2) and A/PR/8/34 (H1N1) in MDCK cells. Among them, N-(adamantan-1-yl)-5-(5-(azepan-1-yl)pyrazin-2-yl)-1,3,4-thiadiazol-2-amine (4j) was the most active compound, and exhibited favorable activity with EC50 values of 3.5 μM and 7.5 μM, respectively. In addition, the molecular docking results explained the reason why compound 4j had dual inhibitory activity and revealed the reasonable binding mode of this compound with the M2-S31N and M2-WT ion channels. This compound had the potential to be further developed as an anti-influenza drug. 相似文献
139.
TiO2 has been tested to be toxic to DNA under the photo-irradiation of ultraviolet A (UVA). However, in the dark conditions, after several days of treatment with TiO2 in aqueous solution, the interaction between TiO2 and two types of DNA was detected and the mechanisms were studied by the methods of gel-electrophoresis, IR spectroscopy and TEM. The results showed that the DNA would be bound to TiO2; the ratio of binding was related to the concentration and the treating time; the mechanism of binding is related to phosphate groups of DNA. Besides, DNA with different structure showed different degree of binding. These findings showed a new possible way through which the TiO2 nanoparticles interact with DNA. 相似文献
140.
Sulfonylation of alkenes through photoredox‐catalyzed functionalization of alkenes with thiourea dioxide under visible‐light irradiation is achieved. The reaction of alkenes, thiourea dioxide and electrophiles provides a green and efficient access to alkyl sulfones and sulfonamides. A broad reaction scope is presented with good functional group compatibility and excellent regioselectivity. A plausible mechanism involving a radical addition process with sulfur dioxide radical anion (SO2‐) derived from the oxidation of sulfur dioxide anion (SO22–) is proposed, which is supported by fluorescence quenching experiments. 相似文献