What is Guinier analysis?
Guinier analysis allows model-free determination of the radius of gyration (Rg) of a biomolecule from X-ray or neutron scattering data, in the limit of very small scattering angles. The method is straightforward to implement and extends the range of validity to a maximum qRg of ∼ 2, versus ∼ 1.1 for Guinier analysis.
What is Guinier region?
The Guinier region in small-angle X-ray scattering (SAXS) defines the radius of gyration, R g, and the forward scattering intensity, I(0). In Guinier peak analysis (GPA), the plot of qI(q) versus q 2 transforms the Guinier region into a characteristic peak for visual and automated inspection of data.
What is q in Guinier plot?
A straight-line in such a plot is indicative of Guinier scaling. Such an analysis is typically only done with the low-q portion of the data. Linear (Guinier) scaling suggests that the system is essentially monodisperse; it can thus be used as a means of quality control before further data analysis (e.g. Form factor).
What is porod volume?
The ratio of I(0) to Q determines the volume of the scattering particle sometimes known as the Porod volume, VP. Application of the Porod-Debye law determines the surface area, S, of the scattering particle that is scaled by concentration and Δρ that can be normalized using Q.
What is SAXS technique?
Small-angle X-ray scattering (SAXS) is an analytical technique that measures the intensities of X-rays scattered by a sample as a function of the scattering angle. A SAXS signal is observed whenever a material contains structural features on the length scale of nanometers, typically in the range of 1-100 nm.
What is mass fractal?
A mass fractal is a structure containing branching and crosslinking to form a 3D network. Figure 1: Schematic representation of a mass fractal structure containing branching points and crosslinks. This structure is made out of monomeric units or small particles that are clustered.
What is pair distance distribution function?
The pair-distance distribution function P(r) is a measure of the frequency of interatomic vector lengths within a protein molecule and can provide information about the shape of the scattering particle.
Is there a way to load the Analysis Toolpak?
If you are prompted that the Analysis ToolPak is not currently installed on your computer, click Yes to install it. Note: To include Visual Basic for Application (VBA) functions for the Analysis ToolPak, you can load the Analysis ToolPak – VBA Add-in the same way that you load the Analysis ToolPak.
How does the Guinier analysis of SAXS work?
Importantly, the Guinier analysis allows the direct estimation of the radius of gyration, Rg, and the extrapolated intensity at zero scattering angle, I (0), critical information about the mass and the structure of molecule (s) under investigation. Fig. 4. Guinier analysis of the SAXS data shown in Fig. 3.
How did the Guinier approximation get its name?
The Guinier approximation, named after André Guinier, refers to the analysis of the SAXS scattering profile at very small scattering angles, in which the data in the q region closest to the zero can be treated as linearly varying vs q ( Guinier & Fournet, 1955 ).
What can a Guinier plot be used for?
Guinier plots are also a sensitive method of detecting aggregation of proteins. Fig. 8.8B is a Guinier plot taken from SAXS of a 20 mg/mL solution of hemoglobin.