How is the phase problem solved for proteins?

The phase problem can in general be solved by using heavy atom derivatized crystals (see e.g., Watenpaugh, 1985). For each set of Bragg indices hkl the structure factor of the native form Fp is compared with that from a heavy atom derivative crystal Fph.

What is phase determination?

Each reflection on the diffraction pattern or structure factor corresponds to a wave consisting of an amplitude and a phase. The amplitude is easily calculated by taking the square root of the intensity, but the phase is lost during the data collection.

Why is phase information lost?

But really what happens is that photons are reflected from the crystal in different directions with a probability proportional to the square of the amplitude of this wave. We count the photons, and we lose any information about the relative phases of different diffraction.

What is a phase in XRD?

A phase is a crystalline solid with a regular 3-dimensional arrangement of the atoms. The measured diffraction peak positions and intensities are like a fingerprint of a particular crystalline phase. This is also known as qualitative phase analysis.

How is the phase problem solved?

The phase problem must be solved in x-ray crystallography, neutron crystallography, and electron crystallography. Not all of the methods of phase retrieval work with every wavelength (x-ray, neutron, and electron) used in crystallography.

What is the phase of a wave?

Wave phase is the offset of a wave from a given point. When two waves cross paths, they either cancel each other out or compliment each other, depending on their phase. These effects are called constructive and destructive. The word phase is used to describe a specific location within a given cycle of a periodic wave.

What is the phase problem and how does one solve it?

In physics, the phase problem is the problem of loss of information concerning the phase that can occur when making a physical measurement. The name comes from the field of X-ray crystallography, where the phase problem has to be solved for the determination of a structure from diffraction data.

What is a crystalline phase?

Liquid crystalline phases, also referred to as mesophases, are surfactant-based systems that comprise properties of both liquids and solids. They show the flow behavior of liquids but likewise exhibit a birefringent, ordered crystalline structure.

What do you mean phase?

1 : a step or part in a series of events or actions : stage I have completed the first phase of my training. 2 : the way that the moon or a planet looks to the eye at any time in its series of changes with respect to how it shines The new moon and the full moon are two phases of the moon. phase. noun.

What is mad in xray crystallography?

Multi-wavelength anomalous diffraction (sometimes Multi-wavelength anomalous dispersion; abbreviated MAD) is a technique used in X-ray crystallography that facilitates the determination of the three-dimensional structure of biological macromolecules (e.g. DNA, drug receptors) via solution of the phase problem.