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Direct Ultraviolet Effects on Biological Systems
Published in Thomas M. Nordlund, Peter M. Hoffmann, Quantitative Understanding of Biosystems, 2019
Thomas M. Nordlund, Peter M. Hoffmann
The sunscreen PABA has largely disappeared from the commercial sunscreen market. As the author understands it, the reason was related to allergic responses in certain users. It was later shown that UV excitation of PABA resulted in production of singlet oxygen, 1O2, which is a likely culprit for producing biologically unfavorable responses in living tissue.30 Singlet oxygen has also been observed to result from UV irradiation of other sunscreen agents.31,32 We see that designing sunscreens is not such a simple matter. In fact, the latter study suggests even the use of sunscreens is a tricky business. We have seen that sun-screening agents move down into the skin, as they are designed to. As time goes on, more and more of the sunscreen will be in the deeper layers, where a more aqueous environment dominates and more active cells are located, and less sunscreen in the upper layers. Increasingly, deeper-lying molecules will absorb; if they produce radicals or other unpleasant products, more living cells will be affected. A possible bottom line of this matter: either reapply sunscreen frequently, replenishing the concentration in the upper layers of skin, or consider not using sunscreen at all and not staying in the sun very long. Protecting the skin from solar UV damage is not a trivial matter: designing agents that absorb efficiently and also dispose of the energy in a safe way is difficult.
Pharmaceuticals
Published in James G. Speight, Handbook of Petrochemical Processes, 2019
Benzocaine is the ethyl ester of p-aminobenzoic acid (PABA) and can be prepared by the reaction of p-aminobenzoic acid with ethanol or via the reduction of ethyl p-nitrobenzoate. Benzocaine is sparingly soluble in water; it is more soluble in dilute acids and very soluble in ethanol, chloroform, and ethyl ether. It can be synthesized from toluene by a three-step process.
Preparation and evaluation of polymer-encapsulated UV filter nanocapsules with miniemulsion polymerization
Published in Journal of Dispersion Science and Technology, 2021
Qing An, Xinjiong Ni, Dong Liu, Yun Zhang, Yuhua Cao
To confirm the structure of the sunscreen further, the FTIR spectra of the PMMA nanoparticles, OD-PABA and the UV filter nanocapsules were shown in Figure 2. In FTIR spectrum of OD-PABA, there were characteristic peaks at 1700 cm−1, 1605 cm−1, 1526 cm−1, and 1277 cm−1 attributed to stretching vibration of C = O in ester group, benzene skeleton vibration, and C–N stretching vibration. The FTIR spectrum of PMMA nanoparticles showed 1730 cm−1, 1700 cm−1 and 1155 cm−1 absorbance peaks which represented for stretching vibration of C = O in ester group and stretching vibration of C–O–C. Besides, 3025 cm−1, 1602 cm−1 and 1525 cm−1, 756 cm−1 and 700 cm−1 peaks revealed there were characteristic peaks of = C–H, benzene ring, and mono-substituted benzene. It testified that P(St-co-MAA) existed in the surface of PMMA nanoparticles. In comparison, all above-mentioned peaks were existed in IR spectrum of UV filter nanocapsules. Therefore, the UV filter nanocapsules encapsuled OD-PABA successfully, and the amphiphilic copolymer emulsifier was anchored on the surface of the nanocapsules.