[P 2 V 3 W 15 O 62 ] 9 - cluster based covalent polyoxometalate-organic hybrid: Synthesis, structure, self-assembly and in vitro antioxidant activities Pulikanti Guruprasad Reddy a , V.S.V. Satyanarayana a , Vinay Dubey b , Asit Ranjan Ghosh b , Chullikkattil P. Pradeep a, ⁎ a School of Basic Sciences, Indian Institute of Technology Mandi, Mandi 175001, Himachal Pradesh, India b Centre for Infectious Diseases & Control, School of Biosciences and Technology, VIT University, Vellore, 632014 Tamil Nadu, India abstract article info Article history: Received 6 February 2015 Received in revised form 22 March 2015 Accepted 27 March 2015 Available online 31 March 2015 Keywords: Polyoxometalates Organic–inorganic hybrid Self-assembly Crystal structure Antioxidant activity A new [P 2 V 3 W 15 O 62 ] 9- cluster based covalent polyoxometalate-organic hybrid (P1) containing a naphthol- amide-Tris derivative has been synthesized and characterized using standard analytical and spectroscopic tech- niques including single crystal X-ray diffraction analyses. P1 exhibits interesting self-assembly behaviour leading to the generation of ~200 nm spherical aggregates in solutions as revealed by DLS and TEM analyses. Standard in vitro experiments revealed that P1 is capable of exhibiting moderate antioxidant properties under standard experimental conditions. © 2015 Elsevier B.V. All rights reserved. Polyoxometalates (POMs) are discrete, soluble, anionic metal oxide clusters of early transition metals like Mo, W, V, Nb and Ta capable of exhibiting versatile structural features and properties [1]. The proper- ties as well as the applicability of POM clusters can be fine-tuned by combining them with organic moieties resulting in POM-organic hy- brids. POM-organic hybrids have found extensive applications in a vari- ety of fields including catalysis, materials science, biological fields etc. [2]. In biological fields, organic derivatization is expected to increase the bio-compatibility of POM clusters and thus help to minimize their adverse side-effects [3]. POM-organic hybrids are broadly classified as Class I and Class II type hybrids depending on the mode of connectivity between organic and POM units [2b]. Hybrids in which POM cluster and organic groups are connected through non-covalent interactions are called Class-I hybrids while those in which POM cluster and organic groups are connected through covalent bonds are called Class-II hy- brids. Covalent bonding is expected to result in stable POM-organic hy- brids facilitating synergistic interactions between organic and POM moieties. Tris(hydroxymethyl)aminomethane (Tris) is an important bi-functional linker molecule commonly used for the generation of Class II hybrids from certain POM cluster types such as Mn-Anderson cluster [4] and Wells–Dawson type [P 2 V 3 W 15 O 62 ] 9- cluster [5]. Cova- lent hybrids based on these cluster types are widely explored for a vari- ety of applications in the last few decades [4,5]. But compared to the Mn-Anderson cluster based hybrids, the number of structurally characterized Class II hybrids based on [P 2 V 3 W 15 O 62 ] 9- cluster is rather limited in the literature. Meanwhile, reactive oxygen species (ROS), the inevitable free radi- cal by-products of cellular respiration, are known to cause oxidative stress and subsequent damage to cellular components in aerobic living systems [6]. Oxidative stress, caused by the uncontrolled and excessive production of ROS, is implicated in the pathogenesis of various disorders and diseases including cancer in human beings [7]. At the same time, re- cent studies have shown that the oxidative stress caused by ROS can also be used as an effective method of killing cancer cells [8]. Substances that delay, prevent or remove the oxidative damages to a target mole- cule are known as antioxidants [9]. Antioxidants often cause termina- tion of chain reactions by removing the free radical intermediates and are useful in various industries including the food industry, fuel and lu- bricant industry, polymer industry etc. Because of the relevance of anti- oxidants in medicines as well as in industry, much effort has been devoted to the development of synthetic antioxidants in recent years; some examples of synthetic antioxidants being butylated hydroxyl tol- uene and butylated hydroxyanisole [10]. Generally, antioxidants function as reducing agents, donating protonic hydrogen to the unpaired oxygen electron or by stabilizing or relocating the free radical electron [11]. POMs are known to function as electron banks, i.e., they are capable of accepting and donating a number of elec- trons without cluster disintegration [1]. POM clusters in their reduced state, are known to act as good reducing agents [12], which is a desirable property for antioxidant compounds. Considering all these, in the pres- ent study, we have synthesized a new [P 2 V 3 W 15 O 62 ] 9- cluster based Inorganic Chemistry Communications 56 (2015) 65–68 ⁎ Corresponding author. E-mail address: pradeep@iitmandi.ac.in (C.P. Pradeep). http://dx.doi.org/10.1016/j.inoche.2015.03.052 1387-7003/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche