### Abstract

Simulations and experiments show oligo-glycines, polypeptides lacking any side chains, can collapse in water. We assess the hydration thermodynamics of this collapse by calculating the hydration free energy at each of the end points of the reaction coordinate, here taken as the end-to-end distance (r) in the chain. To examine the role of the various conformations for a given r, we study the conditional distribution, P(R_{g}|r), of the radius of gyration for a given value of r. The free energy change versus R_{g}, -k_{B}T ln P(R_{g}|r), is found to vary more gently compared to the corresponding variation in the excess hydration free energy. Using this observation within a multistate generalization of the potential distribution theorem, we calculate a tight upper bound for the hydration free energy of the peptide for a given r. On this basis, we find that peptide hydration greatly favors the expanded state of the chain, despite primitive hydrophobic effects favoring chain collapse. The net free energy of collapse is seen to be a delicate balance between opposing intrapeptide and hydration effects, with intrapeptide contributions favoring collapse.

Original language | English (US) |
---|---|

Pages (from-to) | 8078-8084 |

Number of pages | 7 |

Journal | Journal of Physical Chemistry B |

Volume | 121 |

Issue number | 34 |

DOIs | |

State | Published - Aug 31 2017 |

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### ASJC Scopus subject areas

- Surfaces, Coatings and Films
- Physical and Theoretical Chemistry
- Materials Chemistry

### Cite this

_{15}

*Journal of Physical Chemistry B*,

*121*(34), 8078-8084. https://doi.org/10.1021/acs.jpcb.7b05469

**Intramolecular Interactions Overcome Hydration to Drive the Collapse Transition of Gly _{15} .** / Asthagiri, D.; Karandur, Deepti; Tomar, Dheeraj S.; Pettitt, Bernard.

Research output: Contribution to journal › Article

_{15}',

*Journal of Physical Chemistry B*, vol. 121, no. 34, pp. 8078-8084. https://doi.org/10.1021/acs.jpcb.7b05469

_{15}Journal of Physical Chemistry B. 2017 Aug 31;121(34):8078-8084. https://doi.org/10.1021/acs.jpcb.7b05469

}

TY - JOUR

T1 - Intramolecular Interactions Overcome Hydration to Drive the Collapse Transition of Gly15

AU - Asthagiri, D.

AU - Karandur, Deepti

AU - Tomar, Dheeraj S.

AU - Pettitt, Bernard

PY - 2017/8/31

Y1 - 2017/8/31

N2 - Simulations and experiments show oligo-glycines, polypeptides lacking any side chains, can collapse in water. We assess the hydration thermodynamics of this collapse by calculating the hydration free energy at each of the end points of the reaction coordinate, here taken as the end-to-end distance (r) in the chain. To examine the role of the various conformations for a given r, we study the conditional distribution, P(Rg|r), of the radius of gyration for a given value of r. The free energy change versus Rg, -kBT ln P(Rg|r), is found to vary more gently compared to the corresponding variation in the excess hydration free energy. Using this observation within a multistate generalization of the potential distribution theorem, we calculate a tight upper bound for the hydration free energy of the peptide for a given r. On this basis, we find that peptide hydration greatly favors the expanded state of the chain, despite primitive hydrophobic effects favoring chain collapse. The net free energy of collapse is seen to be a delicate balance between opposing intrapeptide and hydration effects, with intrapeptide contributions favoring collapse.

AB - Simulations and experiments show oligo-glycines, polypeptides lacking any side chains, can collapse in water. We assess the hydration thermodynamics of this collapse by calculating the hydration free energy at each of the end points of the reaction coordinate, here taken as the end-to-end distance (r) in the chain. To examine the role of the various conformations for a given r, we study the conditional distribution, P(Rg|r), of the radius of gyration for a given value of r. The free energy change versus Rg, -kBT ln P(Rg|r), is found to vary more gently compared to the corresponding variation in the excess hydration free energy. Using this observation within a multistate generalization of the potential distribution theorem, we calculate a tight upper bound for the hydration free energy of the peptide for a given r. On this basis, we find that peptide hydration greatly favors the expanded state of the chain, despite primitive hydrophobic effects favoring chain collapse. The net free energy of collapse is seen to be a delicate balance between opposing intrapeptide and hydration effects, with intrapeptide contributions favoring collapse.

UR - http://www.scopus.com/inward/record.url?scp=85028654123&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85028654123&partnerID=8YFLogxK

U2 - 10.1021/acs.jpcb.7b05469

DO - 10.1021/acs.jpcb.7b05469

M3 - Article

VL - 121

SP - 8078

EP - 8084

JO - Journal of Physical Chemistry B

JF - Journal of Physical Chemistry B

SN - 1520-6106

IS - 34

ER -