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Al-Sayah, Mohammad

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Al-Sayah

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Mohammad

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Al-Sayah, Mohammad

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2013 - 20153

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Author's Publications: search.filters.isAuthorOfPublication.aae3c2b5-f2e2-4447-b9df-0f3dade7564d

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    Water Networks Contribute to Enthalpy/Entropy Compensation in Protein–Ligand Binding
    (American Chemical Society, 2013) Breiten, Benjamin; Lockett, Matthew R.; Sherman, Woody; Fujita, Shuji; Al-Sayah, Mohammad; Lange, Heiko; Bowers, Carleen; Heroux, Annie; Krilov, Goran; Whitesides, George
    The mechanism (or mechanisms) of enthalpy–entropy (H/S) compensation in protein–ligand binding remains controversial, and there are still no predictive models (theoretical or experimental) in which hypotheses of ligand binding can be readily tested. Here we describe a particularly well-defined system of protein and ligands—human carbonic anhydrase (HCA) and a series of benzothiazole sulfonamide ligands with different patterns of fluorination—that we use to define enthalpy/entropy (H/S) compensation in this system thermodynamically and structurally. The binding affinities of these ligands (with the exception of one ligand, in which the deviation is understood) to HCA are, despite differences in fluorination pattern, indistinguishable; they nonetheless reflect significant and compensating changes in enthalpy and entropy of binding. Analysis reveals that differences in the structure and thermodynamic properties of the waters surrounding the bound ligands are an important contributor to the observed H/S compensation. These results support the hypothesis that the molecules of water filling the active site of a protein, and surrounding the ligand, are as important as the contact interactions between the protein and the ligand for biomolecular recognition, and in determining the thermodynamics of binding.
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    Polymerization-based Signal Amplification for Paper-Based Immunoassays
    (Royal Society of Chemistry (RSC), 2015) Badu-Tawiah, Abraham K.; Lathwal, Shefali; Kaastrup, Kaja; Al-Sayah, Mohammad; Christodouleas, Dionysios; Smith, Barbara; Whitesides, George; Sikes, Hadley D.
    Diagnostic tests in resource-limited settings require technologies that are affordable and easy to use with minimal infrastructure. Colorimetric detection methods that produce results that are readable by eye, without reliance on specialized and expensive equipment, have great utility in these settings. We report a colorimetric method that integrates a paper-based immunoassay with a rapid, visible-light-induced polymerization to provide high visual contrast between a positive and a negative result. Using Plasmodium falciparum histidine-rich protein 2 as an example, we demonstrate that this method allows visual detection of proteins in complex matrices such as human serum and provides quantitative information regarding analyte levels when combined with cellphone-based imaging. It also allows the user to decouple the capture of analyte from signal amplification and visualization steps.
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    Charge Tunneling along Short Oligoglycine Chains
    (Wiley-Blackwell, 2015) Baghbanzadeh, Mostafa; Bowers, Carleen; Rappoport, Dmitrij; Zaba, Tomasz; Gonidec, Mathieu; Al-Sayah, Mohammad; Cyganik, Piotr; Aspuru-Guzik, Alan; Whitesides, George
    This work examines charge transport (CT) through self-assembled monolayers (SAMs) of oligoglycines having an N-terminal cysteine group that anchors the molecule to a gold substrate, and demonstrate that CT is rapid (relative to SAMs of n-alkanethiolates). Comparisons of rates of charge transport-using junctions with the structure AuTS /SAM//Ga2 O3 /EGaIn (across these SAMs of oligoglycines, and across SAMs of a number of structurally and electronically related molecules) established that rates of charge tunneling along SAMs of oligoglycines are comparable to that along SAMs of oligophenyl groups (of comparable length). The mechanism of tunneling in oligoglycines is compatible with superexchange, and involves interactions among high-energy occupied orbitals in multiple, consecutive amide bonds, which may by separated by one to three methylene groups. This mechanistic conclusion is supported by density functional theory (DFT).