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61.
62.
Gonzalo Angulo Dr. Jakob Grilj Eric Vauthey Prof. Luis Serrano‐Andrés Prof. Òscar Rubio‐Pons Dr. Patrice Jacques Prof. 《Chemphyschem》2010,11(2):480-488
The experimental ultrafast photophysics of thioxanthone in several aprotic organic solvents at room temperature is presented, measured using femtosecond transient absorption together with high‐level ab initio CASPT2 calculations of the singlet‐ and triplet‐state manifolds in the gas phase, including computed state minima and conical intersections, transition energies, oscillator strengths, and spin–orbit coupling terms. The initially populated singlet ππ* state is shown to decay through internal conversion and intersystem crossing processes via intermediate nπ* singlet and triplet states, respectively. Two easily accessible conical intersections explain the favorable internal conversion rates and low fluorescence quantum yields in nonpolar media. The presence of a singlet–triplet crossing near the singlet ππ* minimum and the large spin–orbit coupling terms also rationalize the high intersystem crossing rates. A phenomenological kinetic scheme is proposed that accounts for the decrease in internal conversion and intersystem crossing (i.e. the very large experimental crescendo of the fluorescence quantum yield) with the increase of solvent polarity. 相似文献
63.
A broadly useful acid-labile traceless azido linker for the solid-phase synthesis of NH-1,2,3-triazoles is presented. A variety of alkynes were efficiently immobilized on a range of polymeric supports by Cu(I)-mediated azide-alkyne cycloadditions. Supported triazoles showed excellent compatibility with subsequent peptide chemistry. Release of pure material (typically >95%) from the solid support was readily achieved by treatment with aqueous TFA. 相似文献
64.
Divalent dipeptides have been introduced as counter ions in aqueous CZE. The dipeptides form ion pairs with amino alcohols in the BGE and facilitate the separation of amino alcohols. High concentrations of dipeptide caused reversed effective mobility for the analytes. The net charge of the dipeptide can be controlled using a buffer or a strong base, and regulates the interaction between the dipeptide and the amino alcohol. A stronger interaction and higher selectivity of amino alcohols was observed when the dipeptides were used as divalent counter ions, than in monovalent or uncharged form. Association constants for ion pairs between divalent dipeptides and amino alcohols can be used to enhance selectivity for amino alcohols in CZE. No chiral separation of amino alcohols was observed when using the dipeptides as ion‐pairing chiral selectors in aqueous BGE, but addition of methanol to the BGE promoted enantioselectivity. 相似文献
65.
Philipp Wachter Christian Schreiner Hans-Georg Schweiger Heiner Jakob Gores 《The Journal of chemical thermodynamics》2010,42(7):900-903
The determination of phase transition points of nine different ionic liquids (ILs) was performed by thermal analysis with simultaneous recording of conductivity. Conductivity of electrolyte solutions and ILs drastically changes during phase transitions and thus is an additional and very sensitive indicator for measuring phase transition points. Evaluation of temperature–time functions and conductivity–time functions with our computer-coupled automated equipment enabled the determination of melting temperatures with high accuracy and reliability. This claim is based on large samples, low temperature change rates and by regularly repeated measurements, i.e. at least seven measurements per IL. The melting temperatures of 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate, 1-butyl-1-methylpyrrolidinium tris(penta-fluoroethyl)trifluorophosphate, and 1-methyl-3-propylimidazolium iodide were, to our knowledge, determined for the first time. The melting temperatures of the other 1-butyl-1-methylpyrrolidinium-, 1-ethyl-3-methylimidazolium-, 1-hexyl-3-methylimidazolium-, and trimethylsulfonium-based ILs showed either a very good accordance with values published in literature or were distinctly higher. 相似文献
66.
We provide two sharp sufficient conditions for immersed Willmore surfaces in $\mathbb{R }^3$ to be already minimal surfaces, i.e. to have vanishing mean curvature on their entire domains. These results turn out to be particularly suitable for applications to Willmore graphs. We can therefore show that Willmore graphs on bounded $C^4$ -domains $\overline{\varOmega }$ with vanishing mean curvature on the boundary $\partial \varOmega $ must already be minimal graphs, which in particular yields some Bernstein-type result for Willmore graphs on $\mathbb{R }^2$ . Our methods also prove the non-existence of Willmore graphs on bounded $C^4$ -domains $\overline{\varOmega }$ with mean curvature $H$ satisfying $H \ge c_0>0 \,{\text{ on }}\, \partial \varOmega $ if $\varOmega $ contains some closed disc of radius $\frac{1}{c_0} \in (0,\infty )$ , and they yield that any closed Willmore surface in $\mathbb{R }^3$ which can be represented as a smooth graph over $\mathbb{S }^2$ has to be a round sphere. Finally, we demonstrate that our results are sharp by means of an examination of some certain part of the Clifford torus in $\mathbb{R }^3$ . 相似文献
67.
Emilio Celotti Georgios Lazaridis Jakob Figelj Yuri Scutaru Andrea Natolino 《Molecules (Basel, Switzerland)》2022,27(1)
The oxidation processes of white wines can occur during storage and commercialization due to several factors, and these can negatively affect the color, aroma, and quality of the wine. Wineries should have faster and simpler methods that provide valuable information on oxidation stability of wines and allow fast decision-making procedures, able to trigger suitable technological interventions. Using a portable prototype instrument for light irradiations at different wavelengths and times was considered and evaluated on sensorial, spectrophotometric, and colorimetric parameters of white wines. The sensorial analysis revealed that white and light blue were the most significant, after only 1 h of irradiation. The experimental results showed that hydrogen peroxide could enhance the effect of light treatment, allowing a contemporary evaluation of the oxidation stability of wine against light and chemical stresses. As expected, a good correlation (R2 > 0.89) between optical density at 420 nm and b* parameter was highlighted. The synergic effect of light and H2O2 was also studied on the hydrolyzable and condensed tannins’ additions to white wine. The proposed methodology could be used to evaluate the oxidative stability of white wines, but also to evaluate the effect of some oenological adjuvants on wine stability. 相似文献
68.
Jakob Oren Michaela Vardi Rossana Viskin Sarah Abramson Benzion Fuchs 《Helvetica chimica acta》1993,76(3):1182-1193
The title molecules were shown to photorearrange with remarkable selectivity. Wavelength variation steers the rearrangement modes, of which the [1,2]-acyl shift was found to be largely regioselective, diastereoselective, and enantiospecific. Chemical intercorrelation of products and mechanistic studies were carried out all along. The potential significance of these photochemical processes in selective synthetic schemes is discussed. 相似文献
69.
A coherent anti-Stokes Raman scattering microscope based on a Ti:sapphire femtosecond oscillator and a photonic crystal fiber is demonstrated. The nonlinear response of the fiber is used to generate the additional wavelength needed in the Raman process. The applicability of the setup is demonstrated by imaging of micrometer-sized polystyrene beads. 相似文献
70.
Prof. Dr. Tunga Salthammer Friederike Monegel Nicole Schulz Dr. Erik Uhde Prof. Dr. Stefan Grimme Jakob Seibert Prof. Dr. Uwe Hohm Dr. Wolf-Ulrich Palm 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(3):1046-1056
The chemical background of olfactory perception has been subject of intensive research, but no available model can fully explain the sense of smell. There are also inconsistent results on the role of the isotopology of molecules. In experiments with human subjects it was found that the isotope effect is weak with acetone and D6-acetone. In contrast, clear differences were observed in the perception of octanoic acid and D15-octanoic acid. Furthermore, a trained sniffer dog was initially able to distinguish between these isotopologues of octanoic acid. In chromatographic measurements, the respective deuterated molecule showed weaker interaction with a non-polar liquid phase. Quantum chemical calculations give evidence that deuterated octanoic acid binds more strongly to a model receptor than non-deuterated. In contrast, the binding of the non-deuterated molecule is stronger with acetone. The isotope effect is calculated in the framework of statistical mechanics. It results from a complicated interplay between various thermostatistical contributions to the non-covalent free binding energies and it turns out to be very molecule-specific. The vibrational terms including non-classical zero-point energies play about the same role as rotational/translational contributions and are larger than bond length effects for the differential isotope perception of odor for which general rules cannot be derived. 相似文献