Contact Restraints Research Articles

Addition of symmetry-related contact restraints to PROTIN and PROLSQ

Symmetry-related van der Waals contacts and hydrogen bonds are stereochemical restraints which are often ignored in macromolecular structure refinement programs. PROTIN and PROLSQ have been modified to account for symmetry-related contacts. The derivatives calculated for an atom in its symmetry-transformed position need only be multiplied by the appropriate rotation matrix to be applied to the atom in its untransformed position. Therefore the code already present in PROLSQ for van der Waals contacts is readily adapted to account for symmetry-related contacts. The `cubing' algorithm, shown to be much faster than residue-by-residue center and radius methods for generating potential contacts, has been incorporated in PROTIN.

The Synthesis of Point Contact Restraint of a Rigid Body

This paper outlines the background of work in the area of kinematic restraint and the associated aspects of screw and vector theory, and presents methods for the synthesis of any required state of kinematic restraint of a rigid body, using point contacts. The applications of the theory are discussed, and an example is given.

Direct Gravimetric Calibration of a Quartz Crystal Microbalance

A commercial quartz crystal microbalance has been calibrated via simultaneous comparison with a reference vacuum electrobalance. Aluminum, copper, and gold thermally deposited on 10 MHz AT-cut oscillators gave a composite linear calibration to a precision of ±0.2%. For a uniformly distributed deposition, the ratio K of the fractional change of mass Δm/m to the fractional change of frequency Δf/f is shown to be 0.991 with a probable error of 0.6% for a configuration having peripheral contact restraints of the oscillators. The response function δf/δm (sensitivity variation over the face of the crystal) was determined to exhibit asymmetries about the central axes.