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131.
Jean-Manuel Raimundo Philippe Blanchard Nuria Gallego-Planas Nicolas Mercier Isabelle Ledoux-Rak Rolland Hierle Jean Roncali 《The Journal of organic chemistry》2002,67(1):205-218
Two series of push-pull chromophores built around thiophene-based pi-conjugating spacers rigidified either by covalent bonds or by noncovalent intramolecular interactions have been synthesized and characterized by UV-vis spectroscopy, electric field induced second harmonic generation (EFISH) and differential scanning calorimetry. Comparison of the linear and second-order nonlinear optical properties of chromophores based on a covalently bridged dithienylethylene (DTE) spacer with those of their analogues based on open chain DTE shows that the rigidification of the spacer produces a considerable bathochromic shift of the absorption maximum together with a dramatic enhancement of the molecular quadratic hyperpolarizability (mu beta) which reaches values among the highest reported so far. A second series of NLO-phores has been derived from a 2,2'-bi(3,4-ethylenedioxythiophene) (BEDOT) pi-conjugating spacer. As indicated by X-ray and UV-vis data, rigidification of the spacer originates in that case, from noncovalent intramolecular interactions between sulfur and oxygen atoms. Again, comparison with the parent compounds based on an unsubstituted bithiophene spacer reveals a marked red shift of the absorption maximum and a large enhancement of mu beta. In an attempt to distinguish the contribution of the electronic and geometrical effects of the ethylenedioxy group, a third series of NLO-phores based on 3,4-ethylenedioxythiophene (EDOT) and 3,4-dihexyloxythiophene spacers has been synthesized. Comparison with compounds based on unsubstituted thiophene shows that, despite a red shift of lambda(max), introduction of alkoxy groups leads to a decrease of mu beta. Theoretical calculations indicate that this effect results from a decrease of the dipole moment (mu) caused by the auxiliary electron-donor alkoxy groups on the thiophene ring. In contrast, replacement of BT by BEDOT produces an increase of mu, which associated with the noncovalent rigidification of the BT system accounts for the observed enhancement of mu beta. 相似文献
132.
Vasse JL Levacher V Bourguignon J Dupas G 《Chemical communications (Cambridge, England)》2002,(19):2256-2257
Asymmetric reduction of methyl benzoylformate by a new NADH mimic is reported; depending on the hydride source used to reduce the NAD+ precursor, NADH mimics so obtained lead to an inversion of enantioselectivity, affording either (R)-methyl mandelate in 88% ee or (S)-methyl mandelate in 78% ee. 相似文献
133.
The esterfication of ethylene glycol (EG) with benzoic acid (BA) is an acid-catalyzed reaction which leads, as a first intermediate, to ethylene glycol monobenzoate (EGMB). This compound has an ? OH group which is more active towards carboxylic groups than the first ? OH group of EG. Moreover, it is a key intermediate in the formation of sideproducts containing diethylene glycol (DEG) moieties. The condensation reaction of EGMB was particularly studied in the presence of carboxylic acids or metal derivatives as catalysts. Titanium is the most active. Sb, which is widely used in the industrial synthesis of PET, needs to be present at a high level of concentration to show an activity. The presence of carboxylic groups in the reaction medium does not affect its activity, but it is necessary to remove the ethylene glycol as soon as it is formed in order to keep it active during the condensation reaction. 相似文献
134.
Two polyesters containing rigid biphenyl and hydroquinone bisbenzoate groups and presenting flexible thioether moieties with different lengths (14 elements in the flexible group) have been carried out using a reaction of the Michaël type. The properties of these polyesters have been compared to those of polyesters of the same type presenting shorter flexible groups (11 elements). All these polymers present thermotropic properties: the biphenyl ones are smectic and the bisbenzoate ones are nematic. The biphenyl polyesters present two types of dielectric relaxations: α and β. The bisbenzoate ones show three relaxations, α and two β (β and β′). The lengthening of the flexible group increases significantly the flexibility of the molecular chains. 相似文献
135.
Mathieu D Frapart YM Bartoli JF Boucher JL Battioni P Mansuy D 《Chemical communications (Cambridge, England)》2004,(1):54-55
Electron transfer from tetrahydropterins to iron porphyrins, with formation of intermediate tetrahydropterin cation radicals, is a very general reaction that was shown to occur not only with tetrahydrobiopterin, as originally found in NO-synthases, but also with another important biological cofactor, tetrahydrofolate, and various iron porphyrins, either in their ferric state, or in the Fe(II)O(2) state, as in the first model of the corresponding NO-synthase reaction described in this paper. 相似文献
136.
A sensor for measuring adsorption on a substrate has been designed including a contactless detection scheme, called supercapacitive admittance tomoscopy (SCAT). The sensor comprises a thin dielectric layer with two parallel band electrodes on the one side and a chemically modified surface on the other onto which the adsorption of molecules occurs. Upon application of a high frequency ac voltage between the two electrodes, a capacitive coupling is established across the dielectric layer, and the admittance measured depends on the surface state of the chemically modified interface. On the basis of this principle, a flow sensor has been developed to measure sensorgrams to follow the dynamics of the adsorption and has been tested for the adsorption of IgG on the modified surface. 相似文献
137.
Queiroz MJ Abreu AS Ferreira PM Oliveira MM Dubest R Aubard J Samat A 《Organic letters》2005,7(22):4811-4814
[structure: see text] A new photochromic thieno-2H-chromene alpha-amino acid derivative was prepared by C-N palladium-catalyzed cross-coupling of a bromothieno-2H-chromene with the aminated aromatic side chain of the methyl ester of a N,N-diprotected amino acid. Its good photochromic properties demonstrated by flash photolysis and continuous irradiation indicate a possible application in ophthalmic lenses. It may also be inserted into peptides to give photoinduced reversible structural changes. 相似文献
138.
Jean F. M. Oth 《Colloid and polymer science》1960,168(1):49-56
Résumé Nous avons mesuré, en fonction de la température, le degré de gonflement dans l'eau de fibres de collagène amorphes qui ont
été tannées différemment, ceci dans le but de pouvoir déterminer, pour chaque degré de tannage (pontage chimique) la chaleur
de mélange du collagène amorphe sec avec l'eau de gonflement.
En utilisant la théorie relative au gonflement des réseaux polymériques amorphes dans un excès de diluant, on a pu montrer
que le paramètre thermodynamiqueχ
1 caractéristique du système collagène-eau (paramètre deFlory-Huggins) varie avec la composition du réseau gonflé. Par contre, le paramètre ?enthalpique? correspondantϰ
1=−
=−0,34 est indépendant de cette composition.
La chaleur de mélangeΔH
mél/V
0 d'un cm3 de collagène amorphe sec avec l'eau de gonflement peut être calculée pour les différents degrées de tannage. Elle a le signe
deϰ
1, i. e. elle est négative et est donnée par:ΔH
mél/V
0=RT gK1(1−v2
éq).
Sa valeur absolue est donc d'autant moins importante que le degré de tannage des fibres est poussé; v2
éq augmente en effet avec la concentration en liens intermoléculaires introduits dans les échantillons.
La variation d'enthalpie accompagnant la transformation d'une fibre de collagène cristalline sèche en fibre amorphe gonflée
(enthalpie de rétraction dans l'eau) diminuée de la chaleur de mélange correspondant au gonflement de la fibre amorphe sèche
dans l'eau donne la chaleur de fusion du collagène sec. Cette quantité est égale à:ΔH/V
0=28±1,5 cal./cm3 et est indépendante du degré de tannage comme on doit s'y attendre.
Travail effectué au Laboratoire de Chimie-Physique de l'Université de Liège, Liège (Belgique). 相似文献
Summary We have measured the temperature dependence of the swelling of amorphous collagen fibres of different degrees of tanning in an excess of water. This was done for the purpose of determining the heat of mixing of amorphous dry collagen with the equilibrium swelling water for each degree of tanning (chemical crosslinking). Using the theory of swelling of polymeric networks in an excess of diluent we were able to show that the parameterχ 1 of the system collagen-water (Flory-Huggins parameter) is a function of the composition of the swollen network. On the other hand, the energy parameterϰ 1=− =−0,34 is found to be concentration independent. The heat of mixingΔH mél/V 0 of 1 cm3 of dry amorphous collagen with the equilibrium swelling water can be calculated for the different degrees of tanning. It has the same sign asϰ 1, i. e. is negative, and is given byΔH mél/V 0=RTϰ 1 (1−v2 éq). Its absolute value decreases therefore with increasing degrees of tanning, sincev 2 éq increases with the density of the cross-links in the sample. The change in heat content on transforming 1 cm3 of dry crystalline collagen fibre into amorphous swollen fibre (heat of shrinking in water), decreased by the heat of swelling of the dry amorphous fibre in water, gives the heat of fusion of dry collagen. This latter equalsΔH/V 0=28±1.5 cal/cm3 and is, as expected, independent of the degree of tanning.
Zusammenfassung Um die Mischungsw?rme des amorphen trockenen Kollagens mit dem Quellungswasser zu bestimmen, wurde die Temperaturabh?ngigkeit des Quellungsgrades von verschieden stark gegerbten amorphen Kollagenfasern gemessen. Auf Grund der Theorie der Quellung von amorphen polymeren Netzwerken in einem überschu? von Quellungsmittel konnte gezeigt werden, da? der thermodynamische (Flory- Huggins) Parameterχ 1 für das System Kollagen-Wasser vom Quellungsgrad des Netzwerkes abh?ngt. Hingegen ist der Enthalpieparameterϰ 1=− =−0,34 davon unabh?ngig. Die Mischungsw?rmeΔH mél/V0 eines cm3 trockenen amorphen Kollagens mit dem Quellungswasser kann für verschiedene Gerbungsgrade (Vernetzungsgrade) berechnet werden. Sie hat das gleiche Vorzeichen wieϰ 1 d. h. ist negativ, und gehorcht der Gleichung:ΔH mél/V 0=RTϰ 1 (1−v2 éq). Der Betrag der Mischungsw?rme ist um so kleiner, je h?her der Gerbungsgrad der Faser ist; in der Tat w?chstv 2 éq mit der Konzentration der Vernetzungspunkte an. Wenn von der Enthalpie?nderung, welche mit dem übergang von einer trockenen kristallinen Faser zu einer gequollenen amorphen verbunden ist, (Schrumfungsenthalpie im Wasser), die oben definierte QuellungsenthalpieΔH mél/V 0 abgezogen wird, so bleibt die Schmelzw?rme des trockenen Kollagens übrig. Diese Schmelzw?rme betr?gt:ΔH/V 0=28±1,5 cal./cm3 und ist, wie zu erwarten, vom Vernetzungsgrad (Gerbungsgrad) des Fadens unabh?ngig.
Travail effectué au Laboratoire de Chimie-Physique de l'Université de Liège, Liège (Belgique). 相似文献
139.
Furuta P Brooks J Thompson ME Fréchet JM 《Journal of the American Chemical Society》2003,125(43):13165-13172
The site isolation of two dyes capable of electronic interaction via Forster energy transfer has been studied with the two dyes coumarin 343 and pentathiophene encapsulated by dendrons containing both solubilizing and electroactive moieties. Photoluminescence studies of mixtures of the dendritic dyes show that at high dendron generation, significant site isolation is achieved with relative emission characteristics influenced by both the degree of site isolation and the emission quantum yield of the dyes. Electroluminescence studies carried out in organic light emitting diode devices confirm that color tuning may be achieved by mixing the two encapsulated dyes in a single layer. However, selective carrier trapping by one of the core component dyes can dramatically influence the effectiveness of other components in the device. 相似文献
140.
Chemical investigation of the dichloromethane extract of the Red Sea marine sponge Lamellodysidea herbacea led to the isolation of seven new polychlorinated derivatives 3-6 and 8-10 in addition to the known dysidamide 1, dysidamide B 2 and dysidamide C 7. Their structures were established by extensive NMR spectroscopic data. The absolute configuration of compound 9 was determined by X-ray crystallographic diffraction analysis. Dysidamide 1 exhibited neurotoxic effects towards both mesencephalic and cortical murine neurones at 0.8 μg/ml. 相似文献