Building bridges between the physical and biological sciences

Research School of Physical Sciences and Engineering, Australian National University, 0200 Canberra, Australia.
Cellular and molecular biology (Noisy-le-Grand, France) (Impact Factor: 1.23). 01/2006; 51(8):803-13. DOI: 10.1170/T689
Source: PubMed


This paper attempts to identify major conceptual issues that have inhibited the application of physical chemistry to problems in the biological sciences. We will trace out where theories went wrong, how to repair the present foundations, and discuss current progress toward building a better dialogue.

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Available from: Barry W Ninham,
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    • "While we have presented only two phenomena (protein precipitation and enzyme activity) directly affected by ions, the concerns raised in this paper are applicable to all ion-specific questions previously examined using saltbased experimentation. Ninham and Boström [5] state " . . . physical chemistry and colloid and surface science today sit in splendid disjunction from modern cell and molecular biology " and express frustration regarding the " ancillary and irrelevant " role played by the physical sciences in the life sciences. "
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    ABSTRACT: Ion-specific effects underlie a vast array of physicochemical and biological phenomena ranging from human physiology to biotechnology to ecology. These effects have traditionally been quantified by measuring the response of interest in a series of salt solutions at multiple concentrations; pH has consistently been shown to be of primary concern. However, salt-based approaches violate critical tenets of proper experimental design and introduce confounding errors that make it impossible to quantify ion-specific effects. For example, pH is a variable dependent on the type and concentration of ions in a solution, but is typically treated as an independent factor, thus confounding experiments designed to determine ion-specific effects. We examined the relevancy of ion-specific effects research in relation to these concepts and demonstrated how these ideas impact protein precipitation and enzyme activity. Based on these results, we present a conceptual and experimental framework of general applicability for proper quantification of ion-specific effects.
    Scholarly Research Exchange 01/2008; 2008(4). DOI:10.3814/2008/818461
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    ABSTRACT: Chemical processes at the interfaces often differ kinetically and mechanistically from the bulk counterparts, partly due to the concentration inhomogeneity of different chemicals at the interfaces. The fractionation of chemicals at the interfaces not only determines their interfacial concentrations, but also affects the physicochemical properties of the interfaces. In this thesis, three sets of chemicals/interfaces with important environmental implications are studied: (1) anion fractionation at the gas–liquid microdroplet interfaces, (2) fractionation of perfluoroalkyl surfactants and matrix components at the bubble–water interface in ultrasonically irradiated solutions, and (3) ion fractionation across the ice–water interface during the freeze–thaw cycle of electrolyte solutions. The relative anion affinity for the air–water interface, as measured by Electrospray Mass Spectrometry (ES–MS), is exponentially correlated with ionic radius. The affinities respond differently to different additives, suggesting that specific anion effects are due to different energy levels of physical interactions. Relative anion affinities at the air–methanol interfaces are almost identical to those at the air–water interface, suggesting that surface structure is not the primary driving force for interfacial anion fractionation. Perfluoroalkyl carboxylates and sulfonates can be transferred from the ocean to marine aerosols due to their high affinity for the air–water interface, but transfer to gas phase is unlikely as they remain deprotonated in aqueous phase because of their low pKa. Organic matrix components may reduce the sonochemical kinetics of Perfluorooctanesulfonate (PFOS) and Perfluorooctanoate (PFOA) by competitive adsorption onto the bubble–water interface or by lowering the interfacial temperatures. Inorganic anions, but not cations, may significantly enhance or reduce the sonochemical kinetics of PFOS and PFOA. The specific anion effects following the Hofmeister series are likely related to anions’ partitioning to and interaction with the bubble–water interface. Time–resolved confocal fluorescence microscopy of freezing electrolyte solutions reveals that the thickness of interstitial liquid films depends non–monotonically on electrolyte concentration. It also confirms that selective incorporation of cations (anions) into the ice lattice decreases (increases) the pH of the interstitial liquid films. Since the magnitude of pH change during freezing is smaller than during the subsequent thawing process, it is likely to be limited by the seepage of proton or hydroxide slowly produced via water dissociation.
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    ABSTRACT: The DLVO theory of colloidal particle interactions has been at the core of colloid science for a long time. Quantitatively, agreement between experiment and theory was illusory except at salt concentrations less than about 10-2 molar. The same problem with theory exists for pH measurements, buffers, electrochemistry, zeta potentials, electrolyte activities, interfacial tension of salt solutions and a host of phenomena that depend on so called specific ion effects, This is so, most dramatically in biology, but also in colloid, polymer and surface science generally. The problems date back to Hofmeister whose work stands in the scheme of things as Mendel’s did to genetics. Where problems occurred we have tended to argue them away, capturing specificity in unquantifiable terms embodied in words like cosmotropes, chaotropes, hydrophilicity, hydrophobicity, soft and hard ions, pi-cation interactions, hydration and hydrophobic forces, water structure. To complicate the puzzle further the role of dissolved atmospheric gas or other sparingly soluble (hydrophobic) solutes is sometimes major, and has been completely ignored in theories or simulations. Some progress in unravelling these difficulties has been made. It turns out that theories have been seriously flawed. They depend on an ansatz that separates electrostatic forces from the totality of non electrostatic (NES) quantum mechanical electrodynamic fluctuation (Lifshitz or dispersion) forces. These NES forces are ignored, as for the Born self energy of an ion, or its decorations. Or else the electrostatic forces are treated in a non linear theory (e.g. Poisson Boltzman), and the quantum forces via Lifshitz theory as for DLVO. Even for the continuum solvent approximation this violates both the Gibbs adsorption equation, and the gauge condition on the electromagnetic field. These problems are highly non trivial and occur equally in quantum field theories and biophysical problems that couple electron and photon transfer. When the faults are repaired, the revised theory does seem to account for ion specificity and a veritable zoo of postulated new forces begin to fall into place quantitatively. An account will be given of the emerging situation, the role of dissolved gas and “hydrophobic” forces. This leads to new insights into the necessary cooperativity that occurs with water in biological and other systems.
    08/2006: pages 65-73;
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