arXiv subjects

Alexandria Guinness

Publications and source records attributed to Alexandria Guinness.

4 recordsLinked to original sources

arXiv2024

Exchange and Microviscosity of Dynamic Nanocompartments

RMs (reverse micelles) provide a controlled system for studying the unique structural and dynamic behaviors of confined water, thus gaining a general insight into the behavior or water under confinement and at interfaces. This study employs ESR (Electron Spin Resonance) to study the dynamics inside RMs and capitalizes on the fact that different preparations of RMs can precisely manipulate both the size of water pools as well as whether or not different pools can come into contact. A small spin label moiety, less than a half nanometer in size tumbles in solution, offering insight into the rotational diffusion from room temperature down to deeply super-cooled temperatures. Two different spin probes can separately probe the dynamics of the interfacial layer vs. those at the core of the reverse micelle. The results provide critical insights into how thermodynamic transitions affect the stability and behavior of water in confined spaces, enhancing the understanding of nucleation and ice crystal growth, as well as the broader understanding of confined water's role in various chemical and biological systems. The ability to more precisely understand and control reaction dynamics and thermodynamics inside confined aqueous systems across a broad range of temperatures will prove useful to fields ranging from biophysics to the development of new nano-materials.

cond-mat.soft↗

arXiv2023

Contiguous Patches of Translational Hydration Dynamics on the Surface of K-Ras

Proteins involved in signaling pathways represent an interesting target for experimental analysis by ODNP (Overhauser Dynamic Nuclear Polarization), which determines the translational mobility at the surface of proteins. They also represent a challenge, since the hydration dynamics at all sites remains relatively rapid, requiring sensitive measurements capable of drawing finer distinctions. Targeting the protein K-Ras, we find ODNP cross-relaxivity values that appear consistent within similar regions of 3D space, regardless of the specific residue where the spin probe used to select the location has been attached. The similar dynamics observed from nearby residues indicate a persistence/uniformity of the translational dynamics of water on the nanometer scale. This results makes sense, since it essentially means that the dynamics of water remains consistent over a lengthscale (a nanometer) over which liquid water exhibits structural persistence (i.e. its correlation length). This opens up the possibility of strategically and comprehensively mapping out the hydration layer in aqueous solution and identifying regions that contribute significantly to the free energy of binding interactions -- for example, slow water that might contribute significant entropy, or regions with strongly temperature-dependent water mobility that might contribute significant enthalpy.

cond-mat.soft↗

arXiv2023

Rapidly Screening the Correlation Between the Rotational Mobility and the Hydrogen Bonding Strength of Confined Water

Past research has conclusively shown that confined pockets of water exhibit properties that differ from those of unconfined ("bulk") water. The differences between confined water and bulk, as well as between different types of confined water environments impact a far-reaching range of target applications. However, the measurements that discriminate between different variants of confined water tend to rely on sophisticated techniques that frequently involve specialized instrumentation or facilities. Here, we demonstrate a straightforward and automated technique compatible with most NMR spectrometers that can analyze a wide range of nanoporous or mesoporous systems. It generates a 2D plot that correlates the approximate rotational correlation time (from deuterium relaxation measurements) against the approximate average hydrogen bond strength (from the diamagnetic shielding, i.e., chemical shift). The water pools inside reverse micelles (RMs), chosen here as a demonstration system, exhibit a range of properties as the water loading ($w_0$, or water to surfactant molar ratio) changes. Small $w_0$ correspond to severe confinement (isolation of tens to hundreds of water molecules), and as the $w_0$ increases, the RMs grow in size. As a result, measurements of RMs with differently sized water pools ($w_0$) sweep out a characteristic shape in the 2D correlation spectrum. This simple, automated measurement demonstrates striking differences in how the properties of differently confined waters change as the lengthscale of the confinement (controlled in RMs by $w_0$) changes. The results here report on a total of 45 different RM samples prepared with a range of $w_0$, surfactants, dispersants, and guest molecules. This technique should be widely applicable both in terms of facilities where it can be implemented as well as chemical systems to which it applies.

cond-mat.mtrl-sci↗

arXiv2022

A Modernized View of Coherence Pathways Applied to Magnetic Resonance Experiments in Unstable, Inhomogeneous Fields

Over recent decades, the value of conducting experiments at lower frequencies and in inhomogeneous and/or time-variable fields has grown. For example, an interest in the nanoscale heterogeneities of hydration dynamics demands increasingly sophisticated and automated measurements deploying Overhauser Dynamic Nuclear Polarization (ODNP) at low field. The development of these methods poses various challenges that drove us to develop a standardized alternative to the traditional schema for acquiring and analyzing coherence pathway information employed by the overwhelming majority of contemporary Nuclear Magnetic Resonance (NMR) research. Specifically, on well-tested, stable NMR systems running well-tested pulse sequences in highly optimized, homogeneous magnetic fields, traditional hardware and software quickly isolate a meaningful subset of data by averaging and discarding between 3/4 and 127/128 of the digitized data. In contrast, spurred by recent advances in the capabilities of open-source libraries, the domain colored coherence transfer (DCCT) schema implemented here builds on the long-extant concept of Fourier transformation along the pulse phase cycle domain to enable data visualization that more fully reflects the rich physics underlying these NMR experiments. In addition to discussing the outline and implementation of the general DCCT schema and associated plotting methods, this manuscript presents a collection of algorithms that provide robust phasing, avoidance of baseline distortion, and the ability to realize relatively weak signals amidst background noise through signal-averaged correlation alignment. The methods for visualizing the raw data, together with the processing routines whose development they guide should apply directly to or extend easily to other techniques facing similar challenges.

physics.chem-ph↗