Figure 2. (IMAGE)
Caption
(A-C) Spatial arrangements of phosphate groups (PO4)- (phosphorus: golden, oxygen: red), water molecules H2O (oxygen: red, hydrogen: white) and magnesium ions (blue) as derived from theoretical simulations. The remaining backbone is shown as a blue ribbon. In (A) the phosphate group is surrounded by six water molecules, in (B) by an ordered water structure. In (C) a magnesium ion forms a contact pair with an oxygen of the phosphate group. (D) Infrared absorption spectrum of the asymmetric phosphate stretching vibration of the phosphate group of tRNA for different magnesium concentrations. The quantity R is the ratio of magnesium to tRNA concentration in the sample. The molecular geometries shown in (A-C) result in three different infrared absorption bands A, B and C. With increasing magnesium concentration, the relative strength of component C (contact ion pairs) increases. (E) Differential infrared spectra derived from the data in panel (D). The absorption of contact ion pairs appears as a positive band. (F) Two-dimensional infrared spectrum of tRNA for R=15. The components A, B and C of infrared absorption lead to separate signal contributions (yellow-red contours). The shape of the different bands encodes ultrafast vibrational dynamics of tRNA in its ion/water environment.
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MBI
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