Search

Photophysical measurements of 6-methylcoumarin (1) encapsulated within cucurbit[8]uril (CB[8]) indicate a pronounced red shift in the fluorescence maximum with an increase in the emission quantum yield and fluorescence lifetime. In addition, at 77 K, there is observable phosphorescence upon encapsulation within CB[8]. The photophysical measurements add credibility to our previously proposed dynamic nature of the CB-coumarin complex in solution. The dynamic nature of the CB[8]-coumarin host-guest complex in water is critical to a CB acting as a supramolecular catalytic nanoreaction vessel to facilitate the photodimerization of coumarins leading to syn dimers. Key words: cucurbiturils, supramolecular catalysis, host-guest photochemistry, coumarin photophysics, coumarin-CB[8] host-guest complex, lifetime of coumarin-CB[8]. Des mesures photophysiques sur la 6-methylcoumarine (1) encapsulee dans du cucurbit[8]urile (CB[8]) mettent en evidence un deplacement prononce vers le rouge dans le maximum de fluorescence avec une augmentation dans le rendement quantique d'emission et le temps de vie de fluorescence. De plus, a 77 K, l'encapsulation dans du CB[8] provoque une phosphorescence qui peut etre detectee. Les mesures photophysiques ajoutent de la credibilite a la proposition que nous avons faite anteerieurement relative a la nature dynamique du complexe CB-coumarine en solution. La nature dynamique du complexe hote-invite CB[8]-coumarine dans l'eau est critique pour le CB qui agit comme recipient pour la nanoreacton catalytique supramoleeculaire afin de faciliter la photodimeerisation des coumarines conduisant aux dimeres syn. Mots-cles: cucurbituriles, catalyseur sapramoleeculaire, photochimie hote-invite, coumarine, photophysique, complexe hote-invite coumarine-CB[8], temps de vie du complexe coumarine-CB[8]. [Traduit par la Redaction], Introduction Coumarin has historically been the subject of intense photochemical and spectroscopic interest mainly as a consequence of its importance in biological systems and its use in various materials of [...]

The zeolite interior is clearly able to enhance the power of a chiral auxiliary during reaction from excited singlet and triplet states are reported. The cations and confined space force the molecule to adopt a conformation, which results in a stronger interaction between the chiral center and the site of reaction present within a single molecule.

Research has been conducted on 1,2-diphenylcyclopropanes. Results demonstrate that in this compound cation binds to a phenyl ring in a sandwich-type arrangement which prevents cis-to-trans isomerization.

Disposable sensors are inexpensive, user-friendly sensing tools designed for rapid single-point measurements of a target. Disposable sensors have become more and more essential as diagnostic tools due to the growing demand for quick, easy-to-access, and reliable information related to the target. Dopamine (DA), a prevalent catecholamine neurotransmitter in the human brain, is associated with central nervous system activities and directly promotes neuronal communication. For the sensitive and selective estimation of DA, an enzyme-free amperometric sensor based on polyaniline-doped multi-walled carbon nanotubes (PANI-MWCNTs) drop-coated disposable screen-printed carbon electrodes (SPCEs) was fabricated. This PANI-MWCNTs-2/SPCE sensor boasts exceptional accuracy and sensitivity when working directly with ex vivo mouse brain homogenates. The sensor exhibited a detection limit of 0.05 μM (S/N = 3), and a wide linear range from 1.0 to 200 μM. The sensor’s high selectivity to DA amidst other endogenous interferents was recognized. Since the constructed sensor is enzyme-free yet biocompatible, it exhibited high stability in DA detection using ex vivo mouse brain homogenates extracted from both Parkinson’s disease and control mice models. This research thus presents new insights into understanding DA release dynamics at the tissue level in both of these models.

The various mechanisms involved in the enantiospecific photochemical Norrish/Yang type II reaction of nonbiaryl atropchiral [alpha]-oxoamides are discussed. The results prove that the reaction temperature highly control and affect the extent of enantioselectivity of the reaction.

Molecularly chiral o-tert-butylacrylanilides have undergone enantiospecific 6[pi]-photocyclization to produce 3,4-dihydroquinolin-2-ones with very high enantioselectivity in solution. [beta]-Substitution in the alkene is critical for the transfer of molecular chirality in the reactant to point chirality in the photoproducts.

A study is conducted to examine whether in photoreactions the stereoselectivity can be determined by controlling the lifetimes of excited states along different diastereomeric pathways. It was seen that enecarbanrnates show a relatively high contribution from the entropy term and some contribution from the enthalpy term.

Four strategies for asymmetric induction in organic photochemistry that derive their success from the use of a confined reaction cavity is explored. Examination of the zeolite interior suggests that the most likely factor responsible for the change in diastereomeric excess(de) or enantiomeric excess(ee) is the difference in conformational preference for the reactant molecules.

Melatonin (MT), a pineal gland hormone, regulates the sleep/wake cycle and is a potential biomarker for neurodegenerative disorders, depression, hypertension, and several cancers, including prostate cancer and hepatocarcinoma. The amperometric detection of MT was achieved using a sensor customized with ruthenium-incorporated carbon spheres (Ru–CS), possessing C- and O-rich catalytically active Ru surfaces. The non-covalent interactions and ion–molecule adducts between Ru and CS favor the formation of heterojunctions at the sensor–analyte interface, thus accelerating the reactions towards MT. The Ru–CS/Screen-printed carbon electrode (SPCE) sensor demonstrated the outstanding electrocatalytic oxidation of MT owing to its high surface area and heterogeneous rate constants and afforded a lower detection limit (0.27 μM), high sensitivity (0.85 μA μM −1 cm−2), and excellent selectivity for MT with the co-existence of crucial neurotransmitters, including norepinephrine, epinephrine, dopamine, and serotonin. High concentrations of active biomolecules, such as ascorbic acid and tyrosine, did not interfere with MT detection. The practical feasibility of the sensor for MT detection in pharmaceutical samples was demonstrated, comparable to the data provided on the product labels. The developed amperometric sensor is highly suitable for the quality control of medicines because of its low cost, simplicity, small sample size, speed of analysis, and potential for automation.

A novel electrochemical sensor based on Cu-loaded carbon nanospheres (Cu–CNSs) was designed and fabricated. Initially, the CNSs were synthesized using a natural or inexpensive carbon source (dark brown sugar), and Cu was loaded to enhance the electrocatalytic properties of the material. Subsequently, the synthesized Cu–CNSs were modified onto a screen-printed carbon electrode (SPCE), termed Cu–CNS/SPCE, to simultaneously detect the biomarkers dopamine (DA) and melatonin (MT) through differential pulse voltammetry. The surface characterization of the Cu–CNSs confirmed the formation of carbon spheres and Cu nanoparticles covering the spheres. Electrochemical studies showed that the Cu–CNS/SPCE had a high selectivity and sensitivity toward DA and MT, with a significant peak separation of 0.502 V. The two linear ranges of DA were 0.125–20 μM and 20–100 μM and the linear range of MT was 1.0–100 μM, with corresponding detection limits of 0.34 μM and 0.33 μM (S/N = 3), respectively. The quantification limits for DA and MT were 2.19 and 1.09 μM (S/N = 10), respectively. The sensor performance is attributed to the high conductivity and large, electrochemically active surface area of the Cu–CNS. In human serum samples, the Cu–CNS/SPCE exhibited good selectivity and satisfactory reproducibility for the simultaneous determination of DA and MT.

Chirally modified zeolites are shown to be effective in achieving high stereoselectivity in photoreactions. Herein the high chiral induction within confined spaces viz. zeolite Y supercages, during the photoxidation of the enecarbamates is reported.

The chiral-auxiliary functionalized enecarbamates react in high diastereoselectivity to give the enantiomeric R-methyldesoxybenzoin (MDB) and S-MDB in enantiomeric excess (ee) values of upto 97% (isolated products). The stereochemical control depends on the E/Z substrate geometry, temperature and solvent as internal and external variables.