Search results for "OXETANE"

Revisiting the Nonadiabatic Process in 1,2-Dioxetane.

2015

Determining the ground and excited-state decomposition mechanisms of 1,2-dioxetane is essential to understand the chemiluminescence and bioluminescence phenomena. Several experimental and theoretical studies has been performed in the past without reaching a converged description. The reason is in part associated with the complex nonadiabatic process taking place along the reaction. The present study is an extension of a previous work (De Vico, L.; Liu, Y.-J.; Krogh, J. W.; Lindh, R. J. Phys. Chem. A 2007, 111, 8013-8019) in which a two-step mechanism was established for the chemiluminescence involving asynchronous O-O' and C-C' bond dissociations. New high-level multistate multi configurati…

Theoretical Study on the Photo-Oxidation and Photoreduction of an Azetidine Derivative as a Model of DNA Repair

2021

Photocycloreversion plays a central role in the study of the repair of DNA lesions, reverting them into the original pyrimidine nucleobases. Particularly, among the proposed mechanisms for the repair of DNA (6-4) photoproducts by photolyases, it has been suggested that it takes place through an intermediate characterized by a four-membered heterocyclic oxetane or azetidine ring, whose opening requires the reduction of the fused nucleobases. The specific role of this electron transfer step and its impact on the ring opening energetics remain to be understood. These processes are studied herein by means of quantum-chemical calculations on the two azetidine stereoisomers obtained from photocyc…

Kristallisations- und schmelzverhalten von copolymeren aus 3,3-bis(chlormethyl)oxetan und ß-propiolacton

1974

Einkristalle von Copolymeren aus 3,3-Bis(chlormethyl)oxetan und s-Propiolacton wurden bezuglich Schmelzverhalten, Schmelzenthalpie, Dichte und Langperiode untersucht. Aus der Messung der Schmelzenthalpie und der Dichte berechnen sich Kristallisationsgrade von 50—60% in guter Ubereinstimmung mit einem Modell, welches den Ausschlus der aus s-Propiolacton (PL) entstandenen Grundbausteine von dem aus Sequenzen der 3,3-Bis(chlormethyl)oxetan (BCMO-)Einheiten aufgebauten Gitter verlangt. Im Vergleich zu reinem Poly-BCMO wird die Dicke der Copolymereinkristalle nur wenig durch Anderung der Kristallisationstemperatur beEinflust. Wegen des blockartigen Aufbaus der Copolymeren bestimmt die mittlere S…

Theoretical study of the dark photochemistry of 1,3-butadiene via the chemiexcitation of Dewar dioxetane.

2015

Excited-state chemistry is usually ascribed to photo-induced processes, such as fluorescence, phosphorescence, and photochemistry, or to bio-and chemiluminescence, in which light emission originates from a chemical reaction. A third class of excited-state chemistry is, however, possible. It corresponds to the photochemical phenomena produced by chemienergizing certain chemical groups without light - chemiexcitation. By studying Dewar dioxetane, which can be viewed as the combination of 1,2-dioxetane and 1,3-butadiene, we show here how the photo-isomerization channel of 1,3-butadiene can be reached at a later stage after the thermal decomposition of the dioxetane moiety. Multi-reference mult…

Regiochemical memory in the adiabatic photolysis of thymine-derived oxetanes. A combined ultrafast spectroscopic and CASSCF/CASPT2 computational stud…

2020

[EN] The photoinduced cycloreversion of oxetanes has been thoroughly investigated in connection with the photorepair of the well-known DNA (6-4) photoproducts. In the present work, the direct photolysis of the two regioisomers arising from the irradiation of benzophenone (BP) and 1,3-dimethylthymine (DMT), namely the head-to-head (HH-1) and head-to-tail (HT-1) oxetane adducts, has been investigated by combining ultrafast spectroscopy and theoretical multiconfigurational quantum chemistry analysis. Both the experimental and computational results agree with the involvement of an excited triplet exciplex(3)[BPMIDLINE HORIZONTAL ELLIPSISDMT]* for the photoinduced oxetane cleavage to generate(3)…

Recent Advances in Enantioselective Desymmetrizations of Prochiral Oxetanes

2021

Abstract Strain relief of oxetanes offers a plethora of opportunities for the synthesis of chiral alcohols and ethers. In this context, enantioselective desymmetrization has been identified as a powerful tool to construct molecular complexity and this has led to the development of elegant strategies on the basis of transition metal, Lewis acid, and Brønsted acid catalysis. This review highlights recent examples that harness the inherent reactivity of prochiral oxetanes and offers an outlook on the immense possibilities for synthetic application.

Neo-clerodane diterpenoids from Teucrium sandrasicum

1997

WOS: A1997XM24100019

Intramolecular Interactions in the Triplet Excited States of Benzophenone–Thymine Dyads

2005

Time-resolved and product studies on the synthesized dyads 1 and 2 have provided evidence that the benzophenone-to-thymine orientation strongly influences intramolecular photophysical and photochemical processes. The prevailing reaction mechanism has been established as a Paterno-Büchi cycloaddition to give oxetanes 3-6; however, the ability of benzophenone to achieve a formal hydrogen abstraction from the methyl group of thymidine has also been evidenced by the formation of photoproducts 7 and 8. These processes have been observed only in the case of the cisoid dyad 1. Adiabatic photochemical cycloreversion of the oxetane ring is achieved upon direct photolysis to give the starting dyad 1 …

Hydroxyfunctional oxetane-inimers with varied polarity for the synthesis of hyperbranched polyether polyols via cationic ROP

2014

Cationic Copolymerization of 3,3-Bis(hydroxymethyl)oxetane and Glycidol: Biocompatible Hyperbranched Polyether Polyols with High Content of Primary H…

2015

The cationic ring-opening copolymerization of 3,3-bis(hydroxymethyl)oxetane (BHMO) with glycidol using different comonomer ratios (BHMO content from 25 to 90%) and BF3OEt2 as an initiator has been studied. Apparent molecular weights of the resulting hyperbranched polyether copolymers ranged from 1400 to 3300 g mol(-1) (PDI: 1.21-1.48; method: SEC, linear PEG standards). Incorporation of both comonomers is evidenced by MALDI-TOF mass spectroscopy. All hyperbranched polyether polyols with high content of primary hydroxyl groups portray good solubility in water, which correlates with an increasing content of glycerol units. Detailed NMR characterization was employed to elucidate the copolymer …