Abstract
Microstructuralism in the philosophy of chemistry is the thesis that chemical kinds can be individuated in terms of their microstructural properties (Hendry in Philos Sci 73:864–875, 2006). Elements provide paradigmatic examples, since the atomic number should suffice to individuate the kind. In theory, Microstructuralism should also characterise higher-level chemical kinds such as molecules, compounds, and macromolecules based on their constituent atomic properties. In this paper, several microstructural theses are distinguished. An analysis of macromolecules such as moonlighting proteins suggests that all the forms of microstructuralism cannot accommodate them.
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Notes
I am grateful to an anonymous referee for pointing out the problem of environmental conditions in determining molecular shape.
In contrast, M1 concerns the instances of natural kinds. However, we should not conclude that this problem leads to the rejection of M1, because as we have seen above isomerism is not a problem for this form of microstructuralism anyway.
Heteropolymers can be branched or crosslinked. Branched polymers have branches of considerable length and are bonded to the main chain at several points. Network polymers have three-dimensional structures with each chain being connected to all others at various points. Network heteropolymers at higher levels of complexity can have many heterogeneous monomers in cross-linking chains.
The glass transition temperature is the temperature at which the monomers become free to rotate and so the polymer loses its glassy state. The way in which the monomers are crosslinked also radically affects the glass transition temperature. For example, the presence of side chains off the main chain increases the class transition temperature of the polymer by restricting bond rotation (Young and Lovell 1991: 295–300).
See Consortium (2004).
These natural kind categories often crosscut each other. In author (forthcoming), I argue that crosscutting categories need not entail conventionalism about natural kinds.
Tompa et al. (2005): 488 have argued that structurally disordered proteins have followed a different evolutionary path. Traditional moonlighting proteins were thought to have only one function and then to have developed further functions because of large portions of their unconstrained surfaces. In contrast, it is more likely that the functions associated with structurally disordered proteins have co-evolved since the same binding region is responsible for distinct functions.
See Consortium (2004).
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Acknowledgments
I am grateful to Alexander Bird, Richard Boyd, John Dupré and Jessica Wilson for advise and comments on earlier versions of this paper. I also wish to acknowledge the AHRC for financially supporting a period of postdoctoral research, as a core researcher on the metaphysics of science project, during which this paper was written.
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Tobin, E. Microstructuralism and macromolecules: the case of moonlighting proteins. Found Chem 12, 41–54 (2010). https://doi.org/10.1007/s10698-009-9078-5
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DOI: https://doi.org/10.1007/s10698-009-9078-5