Investigation of calcium silicate as a natural clay-based sunblock: Formulation and characterization

BACKGROUND

Sunlight exposure causes several types of health issues to humans, and in particular, it affects especially the skin. Among the most common harmful issues developed by UV exposure are erythema, pigmentation, and lesions in DNA, which may lead to cancer. These long-term effects can be minimized with the use of sunscreen.

OBJECTIVE

The use of commercial UV filters causes severe side effects such as skin allergy and whitening of the skin. Therefore, in this study the effectiveness of Ca₂ SiO₄ , a compound abundantly present in the soils of certain South Asian regions, has been the first time explored as UV filter. This compound leaves a low amount of white residue on the skin and is highly stable.

METHOD

The comparative study of a cosmetic formulation having 5% Ca₂ SiO₄ , and other formulations containing 5% TiO₂ and 5% ZnO as inorganic UV filters, was performed to evaluate the physical and chemical stability.

RESULT

The zeta potential and chemical stability of formulations containing these different UV filters were investigated by using UV-Vis spectroscopy, FTIR-ATR, and X-ray diffraction. Results indicated Ca₂ SiO₄ as a promising innovative UV filter with an SPF value of 37.94. One of the reasons is its low interaction with organic filter, that is, PABA, as compared to commercial ZnO and TiO₂ inorganic UV filters. Biological absorption in organs was studied by ICP-MS on model mice.

CONCLUSION

It also has a low photocatalytic activity; thus, formation of radicals is minimum. Moreover, Ca₂ SiO₄ showed a recognized ability to leave a low amount of white residue on the skin combined with great stability.

Synthesis and Toxicity Evaluation of Some N4-Aryl Substituted 5-Trifluoromethoxyisatin-3-thiosemicarbazones

A series of twenty one N4-aryl substituted 5-trifluoromethoxyisatin-3-thiosemicarbazones 3a-3u was synthesized by the reaction of trifluoromethoxyisatin 1 with different arylthiosemicarbazides 2 in aqueous ethanol (50%), containing a few drops of acetic acid. Their structures were established on the basis of analytical (CHN) and spectral (IR, 1H-NMR, EIMS) data. All the synthesized compounds were evaluated for their toxicity potential by a brine shrimp lethality bioassay. Ten compounds i.e., 3a, 3e, 3i-3l and 3n-3q proved to be active in this assay, displaying promising toxicity (LD50 = 1.11 × 10-5 M - 1.80 × 10-4 M). Amongst these, 3k, 3n and 3o were found to be the most active ones (LD50 = 1.11 × 10-5 M - 1.43 × 10-5 M). Compound 3k showed the highest activity with a LD50 value of 1.11 × 10-5 M and can, therefore, be used as a lead for further studies. Structure-activity relationship (SAR) studies revealed that the presence of strong inductively electron-attracting trifluoromethoxy substituent at position-5 of the isatin moiety played an important role in inducing or enhancing toxic potentiality of some of the synthesized compounds.

N-{2-[N-(4-Methyl-phen-yl)oxamo-yl]phen-yl}propanamide

The title compound, C(18)H(18)N(2)O(3), is the product of the heterocyclic ring cleavage at position 2 of 1-propionylisatin. Two centrosymmetric cyclic motifs, viz. R(2) (2)(14) and R(2) (2)(18), are formed by N-H⋯O hydrogen bonds with the propanamide and amino-phenyl units, respectively, as the N-H donors. These motifs combine into two C(2) (2)(8) chain motifs parallel to the b axis. The chain structure is stabilized by C-H⋯π inter-actions between the benzene rings, where C-H is from the phenyl ring of the cleaved part of 1-pro-pionylisatin.

1-[2-Oxo-5-(trifluoro-meth-oxy)indolin-3-yl-idene]-4-[4-(trifluoro-methyl)-phen-yl]thio-semicarbazide

In the title compound, C₁₇H₁₀F₆N₄O₂S, an intra­molecular N—H⋯N hydrogen bonds forms an S(5) ring whereas N—H⋯O and C—H⋯S inter­actions complete S(6) ring motifs. The dihedral angle between the fused ring system and the phenyl ring is 6.68 (8)°. In the crystal, the mol­ecules are dimerized due to N—H⋯O inter­actions. π–π inter­actions are present between the benzene rings [centroid–centroid distance = 3.6913 (15) Å] and between the five membered ring and the trifluoro­meth­yl)phenyl ring [centroids–centroid distance = 3.7827 (16) Å]. One of the trifluoro­meth­oxy F atoms is disordered over two sites with occupancy ratio of 0.76 (3):0.24 (3). The F atoms of the p-trifluoro­methyl substituent are disordered over three sets of sites with an occupancy ratio of 0.70 (2):0.152 (11):0.147 (13).

4-(3-Nitrophenyl)-1-(2-oxoindolin-3-ylidene)thiosemicarbazide

In the title compound, C₁₅H₁₁N₅O₃S, intra­molecular N—H⋯N hydrogen bonding forms an S(5) ring motif, whereas N—H⋯O and C—H⋯S inter­actions type complete S(6) ring motifs. The 2-oxoindoline and 3-methoxy­phenyl rings are almost planar, with r.m.s. deviations of 0.0178 and 0.0149 Å, respectively, and form a dihedral angle of 33.59 (3)°. In the crystal, mol­ecules are inter­linked through the nitro groups in an end-to-end fashion via N—H⋯O and C—H⋯O inter­actions.

4-(3-Methoxyphenyl)-1-(2-oxoindolin-3-ylidene)thiosemicarbazide

In the title compound, C₁₆H₁₄N₄O₂S, intra­molecular N—H⋯N hydrogen bonding forms an S(5) ring, whereas N—H⋯O and C—H⋯S inter­actions complete S(6) ring motifs. In the crystal, mol­ecules form inversion dimers due to N—H⋯O inter­actions. The dimers are inter­linked through N—H⋯S hydrogen bonds and π–π inter­actions occur with a centroid–centroid distance of 3.8422 (11) Å between the meth­oxy-containing benzene ring and the five-membered heterocyclic ring.

4-(5-Chloro-2-methyl-phen-yl)-1-[2-oxo-5-(trifluoro-meth-oxy)indolin-3-yl-idene]thio-semicarbazide

The asymmetric unit of the title compound, C₁₇H₁₂ClF₃N₄O₂S, contains two mol­ecules, which differ in their planarity and hydrogen bonding. In one mol­ecule, the 2-oxoindolin (C₈/N/O A), thio­semicarbazide (N₃/C/S B) and 5-chloro-2-methyl­phenyl (C₇/Cl C) units are planar with r.m.s. deviations of 0.0110, 0.0173 and 0.0259 Å, respectively. The dihedral angles A/B, B/C and A/C are 1.74 (15), 40.70 (13) and 41.00 (11)°, respectively. In the other mol­ecule the deviations are 0.0455, 0.0007 and 0.0143 Å, respectively, and the dihedral angles are 5.01 (14), 4.53 (16) and 3.38 (13)°, respectively. In both mol­ecules, intra­molecular N—H⋯N and N—H⋯O hydrogen bonds form S(5) and S(6) ring motifs, respectively and C—H⋯S interactions occur. In one of the molecules, an intramolecular C—H⋯F interaction is also present. In the crystal, the mol­ecules are linked by N—H⋯O, C—H⋯F, C—H⋯O and N—H⋯S hydrogen bonding, forming a polymeric network.