Cross-correlation analysis of X-ray photon correlation spectroscopy to extract rotational diffusion coefficients

Coefficients for translational and rotational diffusion characterize the Brownian motion of particles. Emerging X-ray photon correlation spectroscopy (XPCS) experiments probe a broad range of length scales and time scales and are well-suited for investigation of Brownian motion. While methods for estimating the translational diffusion coefficients from XPCS are well-developed, there are no algorithms for measuring the rotational diffusion coefficients based on XPCS, even though the required raw data are accessible from such experiments. In this paper, we propose angular-temporal cross-correlation analysis of XPCS data and show that this information can be used to design a numerical algorithm (Multi-Tiered Estimation for Correlation Spectroscopy [MTECS]) for predicting the rotational diffusion coefficient utilizing the cross-correlation: This approach is applicable to other wavelengths beyond this regime. We verify the accuracy of this algorithmic approach across a range of simulated data.

Translational and rotational diffusion coefficients of gold nanorods functionalized with a high molecular weight, thermoresponsive ligand: A depolarized dynamic light scattering study

Probing the rotational and translational diffusion and colloidal stability of nanorods is of significant fundamental interest with implications for many different applications. Recently R. Nixon-Luke and G. Bryant presented a...

C60 in a peptidic cage: a case of symmetry mismatch studied by crystallography and solid-state NMR

A supramolecular complex, formed by encapsulation of C60 fullerene in a molecular container built from two resorcin[4]arene rims zipped together by peptidic arms hydrogen bonded into a cylindrical β-sheet, was studied by X-ray crystallography, solid-state and solution NMR, EPR spectroscopy and differential scanning calorimetry (DSC). The crystal structure, determined at 100 K, reveals that the complex occupies 422 site symmetry, which is compatible with the molecular symmetry of the container but not of the fullerene molecule, which has only 222 symmetry. The additional crystallographic symmetry leads to a complicated but discrete disorder, which could be resolved and modelled using advanced features of the existing refinement software. Solid-state NMR measurements at 184–333 K indicate that the thermal motion of C60 in this temperature range is fast but has different activation energies at different temperatures, which was attributed to a phase transition, which was confirmed by DSC. Intriguingly, the activation energy for reorientations of C60 in the solid state is very similar for the free and encaged molecules. Also, the rotational diffusion coefficients seem to be very similar or even slightly higher for the encaged fullerene compared to the free molecule. We also found that chemical shift anisotropy (CSA) is not the main relaxation mechanism for the 13C spins of C60 in the studied complex.

Detection of domain motion in NADPH-cytochrome P450 oxidoreductase through polarization anisotropy measurements

ABSTRACTConformational transitions between closed and open states in the NADPH-cytochrome P450 oxidoreductase (POR) play a critical role in its electron-transport function. In this study, we determined rotational diffusion coefficients of the EDANS fluorophore attached to the cytosolic POR construct lacking the N-terminal transmembrane region. We identified two dynamic modes, slow and fast, which are interpreted as the rotational diffusion of POR as a whole and the local domain motion, respectively. Timescale of the local rotational diffusion component suggests that it may correspond to the transient opening of the fully oxidized POR structure.

Study on Nanoparticle Sizing Using Fluorescent Polarization Method with DNA Fluorescent Probe

Fluorescent polarization methods are used to detect complementary base pairing of DNA in biological fields. These methods work by measuring the rotational diffusion coefficient of Brownian motion of the fluorescent particles in solution. The rotational diffusion coefficient corresponds to the inverse third power of diameter according to the Debye-Stokes-Einstein equation for nanoparticles as hard spheres. We develop a novel method to measure the rotational diffusion coefficient using a fluorescent probe with a DNA spacer connected to a gold nanoparticle. We studied the physical characteristics of this probe to verify the feasibility of the proposed method. The rotational diffusion coefficients of gold nanoparticles with diameters ranging between 5–20 nm were measured using this developed system. In this manuscript we describe a novel fluorescent polarization method for nanoparticle sizing using a fluorescent DNA probe.