Ultrafast Water H-Bond Rearrangement in a Metal-Organic Framework Probed by Femtosecond Time-Resolved Infrared Spectroscopy.

We investigated the water H-bond network and its dynamics in NiClBTDD, a prototypical MOF for atmospheric water harvesting, using linear and ultrafast IR spectroscopy. Utilizing isotopic labeling and infrared spectroscopy, we found that water forms an extensive H-bonding network in NiClBTDD. Further investigation with ultrafast spectroscopy revealed that water can reorient in a confined cone up to ∼50° within 1.

An Evaluation of Maximum Determination Methods for Center Line Slope Analysis.

Ultrafast molecular dynamics are frequently extracted from two-dimensional (2D) spectra via the center line slope (CLS) method. The CLS method depends on the accurate determination of frequencies where the 2D signal is at a maximum, and multiple approaches exist for the determination of that maximum. Various versions of peak fitting for CLS analyses have been utilized; however, the impact of peak fitting on the accuracy and precision of the CLS method has not been reported in detail.

Structure and thermodynamics of water adsorption in NU-1500-Cr.

Metal-organic frameworks (MOFs) are a class of materials with diverse chemical and structural properties, and have been shown to effectively adsorb various types of guest molecules. The mechanism of water adsorption in NU-1500-Cr, a high-performance atmospheric water harvesting MOF, is investigated using a combination of molecular dynamics simulations and infrared spectroscopy. Calculations of thermodynamic and dynamical properties of water as a function of relative humidity allow for following the adsorption process from the initial hydration stage to complete filling of the MOF pores.

Pump Slice Amplitudes: A Simple and Robust Method for Connecting Two-Dimensional Infrared and Fourier Transform Infrared Spectra.

Ultrafast two-dimensional infrared (2D IR) spectroscopy and Fourier transform infrared (FTIR) spectroscopy are often performed in tandem, with FTIR typically used to interpret and provide hypotheses for 2D IR experiments. Comparisons between 2D IR and FTIR spectra can also be used to examine the structure and orientation in systems of coupled vibrational chromophores. The most common method for comparing 2D IR and FTIR lineshapes, the diagonal slice method, contains significant artifacts when applied to oscillators with low anharmonicities.

Interfacial Dynamics in Lipid Membranes: The Effects of Headgroup Structures.

Phospholipid membranes support essential biochemical processes, yet remain difficult to characterize due to their compositional and structural heterogeneity. The two most common phospholipid headgroup structures in biological membranes are phosphatidylcholine (PC) and phosphatidylethanolamine (PE), but interactions between PC and PE lipids remain underexplored. In this study, we apply ultrafast two-dimensional infrared (2D IR) spectroscopy to quantify the headgroup effects on interfacial dynamics in PC/PE lipid mixtures.

Ultrafast Dynamics at Lipid-Water Interfaces.

Lipid membranes are more than just barriers between cell compartments; they provide molecular environments with a finely tuned balance between hydrophilic and hydrophobic interactions that enable proteins to dynamically fold and self-assemble to regulate biological function. Characterizing dynamics at the lipid-water interface is essential to understanding molecular complexities from the thermodynamics of liquid-liquid phase separation down to picosecond-scale reorganization of interfacial hydrogen-bond networks.Ultrafast vibrational spectroscopy, including two-dimensional infrared (2D IR) and vibrational sum-frequency generation (VSFG) spectroscopies, is a powerful tool to examine picosecond interfacial dynamics.

Phase Transition in a Heterogeneous Membrane: Atomically Detailed Picture.

Membranes serve diverse functions in biological systems. Variations in their molecular compositions impact their physical properties and lead to rich phase behavior such as switching from the gel to fluid phase and/or separation to micro- and macrodomains with different molecular compositions. We present a combined computational and experimental study of the phase behavior of a mixed membrane of 1,2-dipalmitoyl--glycero-3-phosphocholine (DPPC) and 1,2-dilauroyl--glycero-3-phosphocholine (DLPC) molecules.

Calcium-Lipid Interactions Observed with Isotope-Edited Infrared Spectroscopy.

Calcium ions bind to lipid membranes containing anionic lipids; however, characterizing the specific ion-lipid interactions in multicomponent membranes has remained challenging because it requires nonperturbative lipid-specific probes. Here, using a combination of isotope-edited infrared spectroscopy and molecular dynamics simulations, we characterize the effects of a physiologically relevant (2 mM) Ca concentration on zwitterionic phosphatidylcholine and anionic phosphatidylserine lipids in mixed lipid membranes. We show that Ca alters hydrogen bonding between water and lipid headgroups by forming a coordination complex involving the lipid headgroups and water.

Physiological Calcium Concentrations Slow Dynamics at the Lipid-Water Interface.

Phospholipids can interact strongly with ions at physiological concentrations, and these interactions can alter membrane properties. Here, we describe the effects of calcium ions on the dynamics in phospholipid membranes. We used a combination of time-resolved ultrafast two-dimensional infrared spectroscopy and molecular dynamics simulations.