|
Static Light Scattering
Static light scattering is a technique in physical chemistry that measures the intensity of the scattered light to obtain the average molecular weight ''Mw'' of a macromolecule like a polymer or a protein in solution. Measurement of the scattering intensity at many angles allows calculation of the root mean square radius, also called the radius of gyration ''Rg''. By measuring the scattering intensity for many samples of various concentrations, the second virial coefficient, ''A2'', can be calculated. Static light scattering is also commonly utilized to determine the size of particle suspensions in the sub-μm and supra-μm ranges, via the Lorenz-Mie (see Mie scattering) and Fraunhofer diffraction formalisms, respectively. For static light scattering experiments, a high-intensity monochromatic light, usually a laser, is launched into a solution containing the macromolecules. One or many detectors are used to measure the scattering intensity at one or many angles. The angular depen ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
André Guinier
André Guinier (1 August 1911 – 3 July 2000) was a French physicist who did important work in the field of X-ray diffraction and solid-state physics. He worked at the Conservatoire National des Arts et Métiers, then taught at the University of Paris and later at the University of Paris-Sud in Orsay, where he co-founded the Laboratory of Solid State Physics. He was elected to the French Academy of Sciences in 1971 and won the Gregori Aminoff Prize in 1985. In the field of small-angle scattering he discovered the relationship of particle size to intensity which is called Guinier's Law. He developed the Guinier camera for use in X-ray diffraction and contributed to the development of the electron microprobe by Raimond Castaing. Together with Prof George Dawson Preston he also gives his name to the Guinier-Preston zone Publications *Guinier, André (1955) ''Small-angle scattering of X-rays''. OCLC number: 01646250. *Guinier, André (1963). "X-ray Diffraction. In Crystals, Imper ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Physical Chemistry
Physical chemistry is the study of macroscopic and microscopic phenomena in chemical systems in terms of the principles, practices, and concepts of physics such as motion, energy, force, time, thermodynamics, quantum chemistry, statistical mechanics, analytical dynamics and chemical equilibria. Physical chemistry, in contrast to chemical physics, is predominantly (but not always) a supra-molecular science, as the majority of the principles on which it was founded relate to the bulk rather than the molecular or atomic structure alone (for example, chemical equilibrium and colloids). Some of the relationships that physical chemistry strives to resolve include the effects of: # Intermolecular forces that act upon the physical properties of materials ( plasticity, tensile strength, surface tension in liquids). # Reaction kinetics on the rate of a reaction. # The identity of ions and the electrical conductivity of materials. # Surface science and electrochemistry of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Virial Coefficient
Virial coefficients B_i appear as coefficients in the virial expansion of the pressure of a many-particle system in powers of the density, providing systematic corrections to the ideal gas law. They are characteristic of the interaction potential between the particles and in general depend on the temperature. The second virial coefficient B_2 depends only on the pair interaction between the particles, the third (B_3) depends on 2- and non-additive 3-body interactions, and so on. Derivation The first step in obtaining a closed expression for virial coefficients is a cluster expansion of the grand canonical partition function : \Xi = \sum_ = e^ Here p is the pressure, V is the volume of the vessel containing the particles, k_B is Boltzmann's constant, T is the absolute temperature, \lambda =\exp mu/(k_BT) is the fugacity, with \mu the chemical potential. The quantity Q_n is the canonical partition function of a subsystem of n particles: : Q_n = \operatorname e^ Here H(1,2, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scattering
Scattering is a term used in physics to describe a wide range of physical processes where moving particles or radiation of some form, such as light or sound, are forced to deviate from a straight trajectory by localized non-uniformities (including particles and radiation) in the medium through which they pass. In conventional use, this also includes deviation of reflected radiation from the angle predicted by the law of reflection. Reflections of radiation that undergo scattering are often called ''diffuse reflections'' and unscattered reflections are called '' specular'' (mirror-like) reflections. Originally, the term was confined to light scattering (going back at least as far as Isaac Newton in the 17th century). As more "ray"-like phenomena were discovered, the idea of scattering was extended to them, so that William Herschel could refer to the scattering of "heat rays" (not then recognized as electromagnetic in nature) in 1800. John Tyndall, a pioneer in light scattering rese ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Differential Static Light Scatter (DSLS)
Differential static light scatter (DSLS) is a term coined to represent the change in total light scatter of a system over time or temperature in a static environment. Static light scattering or SLS and its many types are well outlined in literature and is the base principal for DSLS but varies specifically in that the difference (before and after) is the focus of this measurement. Typically the system will commence measurement at T0 and over the course of time measure the change in light scatter. One of the more practical applications of DSLS is in the area of proteomic research and protein based chemistry. Solution conditions can be varied across samples of a specific protein in a screening scenario and the system can be kept at either a static temperature or be ramped up, or in some cases down. The change will be observed over time and the focus of the calculation is on the amount of change in signal from T0 to Tfinal . This method of analysis provides researchers with data t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Light Scattering
Scattering is a term used in physics to describe a wide range of physical processes where moving particles or radiation of some form, such as light or sound, are forced to deviate from a straight trajectory by localized non-uniformities (including particles and radiation) in the medium through which they pass. In conventional use, this also includes deviation of reflected radiation from the angle predicted by the law of reflection. Reflections of radiation that undergo scattering are often called ''diffuse reflections'' and unscattered reflections are called '' specular'' (mirror-like) reflections. Originally, the term was confined to light scattering (going back at least as far as Isaac Newton in the 17th century). As more "ray"-like phenomena were discovered, the idea of scattering was extended to them, so that William Herschel could refer to the scattering of "heat rays" (not then recognized as electromagnetic in nature) in 1800. John Tyndall, a pioneer in light scattering rese ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dynamic Light Scattering
Dynamic light scattering (DLS) is a technique in physics that can be used to determine the size distribution profile of small particles in suspension or polymers in solution. In the scope of DLS, temporal fluctuations are usually analyzed using the intensity or photon auto-correlation function (also known as photon correlation spectroscopy or quasi-elastic light scattering). In the time domain analysis, the autocorrelation function (ACF) usually decays starting from zero delay time, and faster dynamics due to smaller particles lead to faster decorrelation of scattered intensity trace. It has been shown that the intensity ACF is the Fourier transform of the power spectrum, and therefore the DLS measurements can be equally well performed in the spectral domain. DLS can also be used to probe the behavior of complex fluids such as concentrated polymer solutions. Setup A monochromatic light source, usually a laser, is shot through a polarizer and into a sample. The scattered light the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrophoretic Light Scattering
Electrophoretic light scattering (also known as laser Doppler electrophoresis and phase analysis light scattering ) is based on dynamic light scattering. The frequency shift or phase (waves), phase shift of an incident laser beam depends on the dispersed particles mobility. With ''dynamic light scattering'', Brownian motion causes particle motion. With ''electrophoretic'' light scattering, oscillating electric field performs this function. The method is used for measuring electrophoretic mobility, from which zeta potential can then be calculated. Instruments for applying the method are commercially available from several manufacturers. The last set of calculations requires information on viscosity and dielectric permittivity of the dispersion medium; appropriate electrophoresis theory is also required. Sample dilution is often necessary to eliminate multiple scattering of the incident laser beam and/or particle interactions. Instrumentation A laser beam passes through the electro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Size-exclusion Chromatography
Size-exclusion chromatography (SEC), also known as molecular sieve chromatography, is a chromatographic method in which molecules in solution are separated by their size, and in some cases molecular weight. It is usually applied to large molecules or macromolecular complexes such as proteins and industrial polymers. Typically, when an aqueous solution is used to transport the sample through the column, the technique is known as gel-filtration chromatography, versus the name gel permeation chromatography, which is used when an organic solvent is used as a mobile phase. The chromatography column is packed with fine, porous beads which are commonly composed of dextran, agarose, or polyacrylamide polymers. The pore sizes of these beads are used to estimate the dimensions of macromolecules. SEC is a widely used polymer characterization method because of its ability to provide good molar mass distribution (Mw) results for polymers. Applications The main application of gel-filtration chr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Methods To Investigate Protein–protein Interactions
There are many methods to investigate protein–protein interactions which are the physical contacts of high specificity established between two or more protein molecules involving electrostatic forces and hydrophobic effects. Each of the approaches has its own strengths and weaknesses, especially with regard to the sensitivity and specificity of the method. A high sensitivity means that many of the interactions that occur are detected by the screen. A high specificity indicates that most of the interactions detected by the screen are occurring in reality. Biochemical methods Co-immunoprecipitation is considered to be the gold standard assay for protein–protein interactions, especially when it is performed with endogenous (not overexpressed and not tagged) proteins. The protein of interest is isolated with a specific antibody. Interaction partners which stick to this protein are subsequently identified by Western blotting. Interactions detected by this approach are considered to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
