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Cation-cation contact pairing in water: Guanidinium
- Shih, Orion;
- England, Alice H;
- Dallinger, Gregory C;
- Smith, Jacob W;
- Duffey, Kaitlin C;
- Cohen, Ronald C;
- Prendergast, David;
- Saykally, Richard J
Abstract
The formation of like-charge guanidinium-guanidinium contact ion pairs in water is evidenced and characterized by X-ray absorption spectroscopy and first-principles spectral simulations based on molecular dynamics sampling. Observed concentration-induced nitrogen K-edge resonance shifts result from π* state mixing and the release of water molecules from each first solvation sphere as two solvated guanidinium ions associate into a stacked pair configuration. Possible biological implications of this counterintuitive cation-cation pairing are discussed.
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