Enhancement of biocompatibility and photoacoustic contrast activity of metal clusters Arijit Bag a , Pradip Kr. Ghorai a,* a Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur, WB, India 741246 Abstract Organometallic carbonyl clusters (OMCC) of group VIII elements are wa- ter soluble, bio-compatible and stable high-contrast photoacoustic agents for live cell imaging. But, they have limited application due to weak absorption within 700 nm to 1000 nm wavelength which is known as the biological win- dow of absorption. In this article, we report that hexa-nuclear iron (Fe 6 ) carbonyl cluster derivatized with sodium thio-propanoate has very good ab- sorption within 700 nm to 1600 nm wave length. This modeled compound is water soluble and bio-compatible. The bio-compatibility of this compound is tested through cytotoxicity, Log P and metabolic probability at CYP450-2D6 enzyme. Keywords: Photoacoustic contrast agent, Relative toxicity, Organometallic carbonyl clusters, LogP, bio-compatibility, Density Functional Theory, CC 50 1. Introduction Photoacoustic tomography (PAT) [1, 2] is one of the most important technique for live cell imaging [3, 4, 5, 6, 7, 8] due to its spatial resolu- tion, deeper tissue penetration and less cell damaging activity. As exoge- nous contrast agents [9] enhances visibility of cell images, they are used in most of the cell imaging techniques [7, 8, 10, 11, 12]. There are sev- eral examples of contrast agents like organic dyes [13, 14], nanoparticles * Corresponding author Email address: pradip@iiserkol.ac.in ( Pradip Kr. Ghorai ) Preprint submitted to Journal of Molecular Graphics and Modelling May 12, 2017