Search results for "AROMA"
showing 10 items of 1006 documents
Highly Sensitive Detection of Naphthalene in Solvent Vapor Using a Functionalized PBG Refractive Index Sensor
2012
We report an optical refractive index sensor system based on a planar Bragg grating which is functionalized by substituted γ-cyclodextrin to determine low concentrations of naphthalene in solvent vapor. The sensor system exhibits a quasi-instantaneous shift of the Bragg wavelength and is therefore capable for online detection. The overall shift of the Bragg wavelength reveals a linear relationship to the analyte concentration with a gradient of 12.5 ± 1.5 pm/ppm. Due to the spectral resolution and repeatability of the interrogation system, this corresponds to acquisition steps of 80 ppb. Taking into account the experimentally detected signal noise a minimum detection limit of 0.48 ± 0.05 pp…
Comparison of the solid-phase extraction efficiency of a bounded and an included cyclodextrin-silica microporous composite for polycyclic aromatic hy…
2016
Solid-phase extraction is one of the most important techniques for sample purification and concentration. A wide variety of solid phases have been used for sample preparation over time. In this work, the efficiency of a new kind of solid-phase extraction adsorbent, which is a microporous material made from modified cyclodextrin bounded to a silica network, is evaluated through an analytical method which combines solid-phase extraction with high-performance liquid chromatography to determine polycyclic aromatic hydrocarbons in water samples. Several parameters that affected the analytes recovery, such as the amount of solid phase, the nature and volume of the eluent or the sample volume and …
Brown Carbon Aerosol in Urban Xi'an, Northwest China: The Composition and Light Absorption Properties.
2018
Light-absorbing organic carbon (i.e., brown carbon or BrC) in the atmospheric aerosol has significant contribution to light absorption and radiative forcing. However, the link between BrC optical properties and chemical composition remains poorly constrained. In this study, we combine spectrophotometric measurements and chemical analyses of BrC samples collected from July 2008 to June 2009 in urban Xi'an, Northwest China. Elevated BrC was observed in winter (5 times higher than in summer), largely due to increased emissions from wintertime domestic biomass burning. The light absorption coefficient of methanol-soluble BrC at 365 nm (on average approximately twice that of water-soluble BrC) w…
Scope and Limitations of Baird's Theory on Triplet State Aromaticity: Application to the Tuning of Singlet–Triplet Energy Gaps in Fulvenes
2007
Utilizing Baird's theory on triplet state aromaticity, we show that the singlet-triplet energy gaps (DeltaE(ST)) of pentafulvenes are easily varied through substitution by as much as 36 kcal mol(-1). This exploits the fact that fulvenes act as aromatic chameleons in which the dipoles reverse on going from the singlet ground state (S(0)) to the lowest pipi* triplet state (T1); thus, their electron distributions are adapted so as to achieve some aromaticity in both states. The results are based on quantum chemical calculations with the OLYP density functional theory method and the CASPT2 ab initio method, as well as spectroscopic determination of DeltaE(ST) by triplet sensitization. The findi…
Simultaneous endo and exo Complex Formation of Pyridine[4]arene Dimers with Neutral and Anionic Guests
2017
The formation of complexes between hexafluorophosphate (PF6- ) and tetraisobutyloctahydroxypyridine[4]arene has been thoroughly studied in the gas phase (ESI-QTOF-MS, IM-MS, DFT calculations), in the solid state (X-ray crystallography), and in chloroform solution (1 H, 19 F, and DOSY NMR spectroscopy). In all states of matter, simultaneous endo complexation of solvent molecules and exo complexation of a PF6- anion within a pyridine[4]arene dimer was observed. While similar ternary complexes are often observed in the solid state, this is a unique example of such behavior in the gas phase.
Island Homoaromaticity in the W-Shaped 2,4-Diphospha-3-arsapentadienide Anion and Related Compounds - Theoretical and Experimental Investigations
2012
A series of anions with general formula (R2C=P)2Pn– (Pn = N, P, As, Sb; R = H, Me, CF3, SiH3, SiMe3, SiF3) was investigated theoretically at the DFT (RI-BP86/TZVP) and RI-MP2/TZVP levels of approximation. Significantly sharpened central PPnP bond angles were predicted for the species with π-acceptor R substituents. The corresponding bond angle values decrease in the order Pn = N >> P > As > Sb. This finding is in agreement with the previously published structural data for [(Me3Si)2C=P]2P–. An island homoaromaticity was proposed as a suitable explanation for the observed effect. In more detail, it consists of shifting negative charge to the electron-withdrawing terminal groups with formation…
Polyfunctional recognition of pyridinedicarboxylate anions with macrocyclic polyamine receptors containing heteroaromatic groups.
2008
The interaction of the biologically relevant anions deriving from the six pyridinedicarboxylic acids (H2PDC) with two macrocyclic receptors containing a pentamine chain and a bipyridine (1) or a phenanthroline (2) moiety, as well as with the aliphatic analogue [21]aneN7 (3), was studied by means of spectroscopic methods (UV-vis, NMR) and potentiometric titrations affording the stability constants of the adducts formed. All three receptors form stable complexes with the substrates thanks to the formation of several salt bridges and hydrogen bond contacts, as observed in the crystal structure of the H8[3(2,6-PDC)4] x H2O x 0.5 EtOH solid compound. Additional pi-stacking interactions between t…
Effect of π-Electron Delocalization on Tautomeric Equilibria – Benzoannulated 2-Phenacylpyridines
2006
Most benzoannulated 2-methylpyridines react with phenyllithium and substituted alkyl benzoates to give the corresponding 2-phenacylpyridines. 3-Methylisoquinoline is transformed into 2-benzoyl-3-methyl-1-phenyl-1,2-dihydroisoquinoline under these conditions, but replacement of phenyllithium with lithium isopropylcyclohexylamide is effective for production of 3-phenacylisoquinolines. Except in the cases of some substituted 6-phenacylphenanthridines, tautomeric mixtures of benzoannulated 2-phenacylpyridines in chloroform solution always contain the ketimine forms.(Z)-2-(2-Hydroxy-2-phenylvinyl)pyridine (enolimine) forms also contribute if the pyridine ring is not benzoannulated or if such ann…
Investigation on the influence of spray-drying technology on the quality of Sicilian Nero d’Avola wines
2018
The purpose of the present work was to find a correlation between microencapsulation technology applied to wines and the resulting quality of the wine itself in terms of volatile composition and phenolic profile. To this aim, samples of Nero d'Avola wines produced in Sicily (Italy) were investigated in order to: i) elucidate the aromatic composition by means of HSâSPME coupled with GCâMS; ii) assess the polyphenolic content by UHPLC mass spectrometry; iii) compare the results obtained from both the screenings with those relative to the same wines that had previously been subjected to spray-drying. The results showed a marked reductionThe results here obtained evidenced a marked reductio…
Palladium-Catalysed Amination of 1,8- and 1,5-Dichloroanthracenes and 1,8- and 1,5-Dichloroanthraquinones
2005
Diamino derivatives of anthracene and anthraquinone have been synthesised by palladium-catalysed coupling of 1,8-dichloroanthracene and 1,8-dichloroanthraquinone with a wide range of aliphatic and aromatic primary and secondary amines. The use of polyamines gave rise to a large number of new nitrogen- and oxygen-containing macrocycles incorporating anthracene or anthraquinone moieties. The method has also been employed for the preparation of bismacrocycles in which two cyclam or azacrown units are linked together by an anthracene bridge through C(sp2)−N bonds. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)