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131.
Piazza ZA Li WL Romanescu C Sergeeva AP Wang LS Boldyrev AI 《The Journal of chemical physics》2012,136(10):104310
The structures and chemical bonding of the B(21)(-) cluster have been investigated by a combined photoelectron spectroscopy and ab initio study. The photoelectron spectrum at 193 nm revealed a very high adiabatic electron binding energy of 4.38 eV for B(21)(-) and a congested spectral pattern. Extensive global minimum searches were conducted using two different methods, followed by high-level calculations of the low-lying isomers. The global minimum of B(21)(-) was found to be a quasiplanar structure with the next low-lying planar isomer only 1.9 kcal/mol higher in energy at the CCSD(T)/6-311-G* level of theory. The calculated vertical detachment energies for the two isomers were found to be in good agreement with the experimental spectrum, suggesting that they were both present experimentally and contributed to the observed spectrum. Chemical bonding analyses showed that both isomers consist of a 14-atom periphery, which is bonded by classical two-center two-electron bonds, and seven interior atoms in the planar structures. A localized two-center two-electron bond is found in the interior of the two planar isomers, in addition to delocalized multi-center σ and π bonds. The structures and the delocalized bonding of the two lowest lying isomers of B(21)(-) were found to be similar to those in the two lowest energy isomers in B(19)(-). 相似文献
132.
Cristina Stere Mihaela‐Corina Iovu Horia Iovu Adrian Boborodea Dan Sorin Vasilescu Simon James Read 《先进技术聚合物》2001,12(5):300-305
The polymerization of ?‐caprolactone initiated by two catalyst systems was studied: (1) carbazole‐potassium in the presence of 18‐crown‐6 ether and (2) NdCl3/TBP/TIBA (neodymiumtrichloride/tri‐n‐butyl‐phosphate/triisobutylaluminium) at the molar ratio 1/3/1. For both initiator systems conversion/time plots were determined and the polymers were characterized by IR, GPC and by 1H‐ and 13C?NMR spectroscopy. Polyesters with the highest molecular weight (M n?44 000 g/mol) were obtained for the polymerizations initiated by the carbazole‐potassium/18‐crown‐6 ether system. The features of the polymerization initiated by the carbazole‐potassium/18‐crown‐6 ether system are discussed on the basis of a simple scheme. The nature of this polymerization is non‐living. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
133.
Polymerisation of vinyl acetate in microemulsions with methanol 总被引:1,自引:0,他引:1
D. Donescu L. Fusulan C. Petcu A.-G. Boborodea D.-S. Vasilescu 《Colloid and polymer science》2000,278(10):927-935
The homogeneity domains for the system vinyl acetate – methanol – monomaleate of nonylphenol ethoxylated with 25 mol ethylene
oxide as an aqueous solution (MEMNPEO25) (33%) have been studied; it has been shown that, due to the shorter chain of methanol,
these domains are more reduced than in the case of ethanol. The changes in refractive indexes and electrical conductivities
have shown the formation of microemulsions with different structures (water-in-oil, bicontinuous or oil-in-water). Ammonium
persulphate is soluble only in oil-in-water or in bicontinuous microemulsions. The initial polymerisation rates as well as
the decomposition rates for the initiator are apparently affected when the microemulsion structure is modified. The polymerisation
rate of vinyl acetate is higher in the presence of methanol than in the presence of ethanol for similar compositions; this
fact may be attributed to a higher degree of ionisation of the initiator in the presence of methanol. Also, in polymerisations
initiated by benzoyl peroxide, the conversions are influenced by the microstructure; thus, the maximum corresponds to water-in-oil
microemulsions. By measuring the amount of unreacted MEMNPEO25 (gel permeation chromatography) we were able to show that the
copolymer formed consisted of vinyl acetate and reactive surfactant.
Received: 9 March 1999/Accepted: 13 March 2000 相似文献
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135.
Yaron Haviv Olga Georgiev Tal Gaver-Bracha Sharleen Hamad Alina Nemirovski Rivka Hadar Yair Sharav Doron J. Aframian Yariv Brotman Joseph Tam 《Molecules (Basel, Switzerland)》2022,27(14)
Background: the endocannabinoid system (ECS) participates in many physiological and pathological processes including pain generation, modulation, and sensation. Its involvement in chronic orofacial pain (OFP) in general, and the reflection of its involvement in OFP in salivary endocannabinoid (eCBs) levels in particular, has not been examined. Objectives: to evaluate the association between salivary (eCBs) levels and chronic OFP. Methods: salivary levels of 2 eCBs, anandamide (AEA), 2-arachidonoylglycerol (2-AG), 2 endocannabinoid-like compoundsN-palmitoylethanolamine (PEA), N-oleoylethanolamine (OEA), and their endogenous precursor and breakdown product, arachidonic acid (AA), were analyzed using liquid chromatography/tandem mass spectrometry in 83 chronic OFP patients and 43 pain-free controls. The chronic OFP patients were divided according to diagnosis into musculoskeletal, neurovascular/migraine, and neuropathic pain types. Results: chronic OFP patients had lower levels of OEA (p = 0.02) and 2-AG (p = 0.01). Analyzing specific pain types revealed lower levels of AEA and OEA in the neurovascular group (p = 0.04, 0.02, respectively), and 2-AG in the neuropathic group compared to controls (p = 0.05). No significant differences were found between the musculoskeletal pain group and controls. Higher pain intensity was accompanied by lower levels of AA (p = 0.028), in neuropathic group. Conclusions: lower levels of eCBs were found in the saliva of chronic OFP patients compared to controls, specifically those with neurovascular/migraine, and neuropathic pain. The detection of changes in salivary endocannabinoids levels related to OFP adds a new dimension to our understanding of OFP mechanisms, and may have diagnostic as well as therapeutic implications for pain. 相似文献
136.
Gisle Atsang Kiki Raluca Maria Pop Octavia Sabin Ioana Corina Bocsan Veronica Sanda Chedea Sonia Ancua Socaci Alina Elena Prvu Egre Finsia Takvou Francis Zramah Mathieu Anca Dana Buzoianu 《Molecules (Basel, Switzerland)》2022,27(17)
Dichrostachys cinerea (L.) Wigth & Arn. (DC) is widely used in traditional medicine against several inflammatory diseases, especially rheumatoid arthritis, because of its antioxidant and anti-inflammatory effects. This study aimed to characterize the polyphenol-rich DC fruit extracts and investigate the analgesic, anti-inflammatory, and antioxidant effects in a rat inflammation model induced by complete Freund’s adjuvant (CFA). Water and ethanolic extracts were characterized using liquid chromatography coupled with mass spectrometry (LC-MS), Fourier-transform infrared (FTIR) spectroscopy, and gas chromatography coupled with mass spectrometry (GC-MS). The polyphenol-rich extracts were administered in three different concentrations for 30 days. Pain threshold, thermal hyperalgesia, edema, and serum biomarkers specific to inflammatory processes or oxidative stress were evaluated. Both extracts were rich in polyphenolic compounds, mainly flavan-3-ols, proanthocyanidins, and flavone glycosides, which had important in vitro antioxidant capacity. DC fruit extracts administration had the maximum antinociceptive and anti-inflammatory effects after one day since the CFA injection and showed promising results for long-term use as well. The measurement of pro-inflammatory cytokines, cortisol, and oxidative stress parameters showed that DC extracts significantly reduced these parameters, being dose and extract-type dependent. These results showed potential anti-inflammatory, analgesic, and antioxidative properties and revealed the necessity of using a standardized polyphenolic DC extract to avoid result variability. 相似文献
137.
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139.
In this paper we show a lower bound for the on-line version of Heilbronn's triangle problem in d dimensions. Specifically,
we provide an incremental construction for positioning n points in the d-dimensional unit cube, for which every simplex defined
by d + 1 of these points has volume Ω(1/n(d+1)ln(d-2)-0.265 d+2.269) (for d ≥ 5). 相似文献
140.