World Health Organization estimates that 60,000 deaths occur in 2000 from melanoma and other skin cancers due to solar ultraviolet (UV) radiation
. Exposure to sunlight is unavoidable as we go about our daily errands. Sunscreen is our last defense against UV radiation. However, protection with sunscreen deemed inadequate due to photodegradation of organic UV absorber in sunscreen products that not only causes decrease in UV protection but also degrades with the occurrence of toxic degradation products. Therefore, development of a new sunscreen formulation is called for, to avoid previously mentioned effects.
Layered metal hydroxides can be categorized into layered double hydroxide (LDH) and layered hydroxide salt (LHS). Several studies have been done on the use of layered metal hydroxide-based sunscreen carrier system, in particular, LDH
[2–4]. LDH can be represented by the general formula of [M3+
z/n.yH2O where An- is the interlayer anion, M2+ and M3+ are di- and trivalent metallic cation, respectively
. Previous work has shown that cinnamate intercalated into Zn/Al LDH showed excellent UV ray shielding properties
. However, to the best of our knowledge application of LHS as host has yet to be explored.
Zinc layered hydroxide (ZLH) is a type of LHS, having the general formula of; M2+(OH)2-x
∙nH2O where M2+ in this case is the metal cation Zn2+ and A
is the counter ion
. They boast a structure consisting of positively charged layers that can expand or contract depending on the nature of interlayer anions. In recent years, there has been extensive research on the use of ZLH as drug carriers
[6, 7], slow release herbicides
, flame retardants
 and anti-corrosion agents
. In this study we further exploit its potential as an efficient host to organic molecules for possible application in sunscreen formulation.
In the present work, we investigated the intercalation of anion, cinnamate, into interlayer galleries of ZLH via direct method, as well as properties of the resulting cinnamate-ZLH (ZCA) intercalation compound. Direct method used involved a direct reaction between anion solution and ZnO precursor. Unlike other LHS synthesis methods like hydrolysis of salts and oxides
, urea hydrolysis
, precipitation with alkaline solution
 and solid state reactions
, this method is simple, environmentally friendly and economical as it involves fewer steps and fewer chemicals.
By intercalating organic UV absorbers into interlayer galleries of ZLH, the expected advantages are; UV absorber stabilization in interlayer region of a lamellar host to increase photo-stability and decrease degradation of UV absorber, absorption of ultraviolet light rays in UVA and UVB region and the absence of close contact between skin that subsequently eliminates allergy problems
In the present investigation, we selected human dermal fibroblast (HDF) cells as a model to evaluate possible toxicity induction on the cells. Dermal fibroblasts are the most abundant cell in the human skin and represent the primary level of exposure to various environmental and other toxicants. Human skin is the primary anatomical barrier for various pathogens and damage, which acts as an important boundary marker between internal and external environment in the bodily defense system. Hence, the resulting intercalation compound of the present study was investigated for toxicity on human dermal fibroblast cells.