Investigation of the Antioxidant and UV Absorption Properties of 2-(2’-hydroxy-5’-methylphenyl)-benzotriazole and Its Ortho-Substituted Derivatives via DFT/TD-DFT

The demand and pursuit of chemical entities with UV filtration and antioxidant properties for enhanced photoprotection have been driven in recent times by acute exposure of humans to solar ultraviolet radiations. The structural, electronic, antioxidant and UV absorption properties of drometrizole (PBT) and designed ortho-substituted derivatives are reported via DFT and TD-DFT in the gas and aqueous phases. DFT and TD-DFT computations were performed at the M062x-D3Zero/6-311++G(d,p)//B97-3c and PBE0-D3(BJ)/def2-TZVP levels of theory respectively. Reaction enthalpies related to hydrogen atom transfer (HAT), single-electron transfer followed by proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET) mechanisms were computed and compared with those of phenol. Results show that the presence of -NH2 substituent reduces the O-H bond dissociation enthalpy and ionization potential, while that of -CN increases the proton affinity. The HAT and SPLET mechanisms are the most plausible in the gas and aqueous phases respectively. The molecule with the -NH2 substituent (PBT1) was identified to be the compound with the highest antioxidant activity. The UV spectra of the studied compounds are characterized by two bands in the 280 - 400 nm regions. Results from this study provide a better comprehension antioxidant mechanism of drometrizole and present a new perspective for the design of electron-donor antioxidant molecules with enhanced antioxidant-photoprotective efficiencies for applications in commercial sunscreens.

Facile Synthesis of Broadleaf-Shaped Titanate Nanosheets with Excellent UV Absorption Behavior

Broadleaf-shaped titanate nanosheets(B-TNSs)were synthesized via one-pot solvothermal method,and characterized by scanning electron microscopy,transmission electron microscopy,and X-ray diffraction etc.It is found that the synthesized B-TNSs consist of broadleaf-shaped nanosheet with a lateral size of ca.100 nm and a thickness of ca.1.2 nm.Owing to the ultrathin thickness,obvious blue shift of the absorption band edge can be observed in the absorption spectrum of B-TNSs resulting from quantum size effect.Besides,the specific surface area of B-TNSs is determined to be 348 m2/g,which is ca.6-fold larger than that of commercial P25 TiO2 nanoparticles.In the optical absorption experiment,B-TNSs exhibit much stronger absorption for ultraviolet light than P25 TiO2.These advantages of B-TNSs in morphological structure and optical absorption may make it a potential application in ultraviolet absorption and photocatalytic field.

Simultaneous Raman and reflection UV/Vis absorption spectroelectrochemistry

In the present work,a new combination of Raman and ultraviolet and visible(UV/Vis)absorption spectroelectrochemistry in reflection mode is proposed.The new experimental setup allows obtaining the two kinds of spectroscopic data without interferences concomitantly with the electrochemical information.To the best of our knowledge,it is the first time to report the simultaneous obtention of electrochemical,electronic,and vibrational information in the same experiment.This new combination provides time-resolved information about the processes that are taking place on the electrode/solution interface which has significant implications in different fields of chemistry,such as modification of electrodes,studies of electrocatalytic reaction mechanisms,development of sensors,among others.Two different systems were used to demonstrate the advantages and capabilities of the brand-new technique,namely,the oxidation of potassium ferrocyanide,an out-sphere system that is usually employed in the validation of SEC techniques,and the electrochemical-surface enhanced Raman spectroscopy(EC-SERS)detection of crystal violet by in-situ formation of the silver SERS substrate,where the UV/Vis spectra were used to follow the formation of the SERS substrate,whereas the Raman response of a probe molecule was used to confirm either the formation of a nanostructured surface and to obtain the fingerprint of the molecule with a high time resolution.The brand-new experimental setup has shown to be useful,versatile,robust,compact,and easy to use for future applications.

Influence of high-temperature oxidation of SiC powders on curing properties of SiC slurry for digital light processing

Fabrication of silicon carbide(SiC)ceramics by digital light processing(DLP)technology is difficult owing to high refractive index and high ultraviolet(UV)absorptivity of SiC powders.The surface of the SiC powders can be coated with silicon oxide(SiO_(2))with low refractive index and low UV absorptivity via high-temperature oxidation,reducing the loss of UV energy in the DLP process and realizing the DLP preparation of the SiC ceramics.However,it is necessary to explore a high-temperature modification process to obtain a better modification effect of the SiC powders.Therefore,the high-temperature modification behavior of the SiC powders is thoroughly investigated in this paper.The results show that nano-scale oxide film is formed on the surface of the SiC powders by short-time high-temperature oxidation,effectively reducing the UV absorptivity and the surface refractive index(nʹ)of the SiC powders.When the oxidation temperature is 1300℃,compared with that of unoxidized SiC powders,the UV absorptivity of oxidized SiC powders decreases from 0.5065 to 0.4654,and a curing depth of SiC slurry increases from 22±4 to 59±4μm.Finally,SiC green bodies are successfully prepared by the DLP with the the oxidized powders,and flexural strength of SiC sintered parts reaches 47.9±2.3 MPa after 3 h of atmospheric sintering at 2000℃without any sintering aid.