Some properties of the solvent in monoclinic lysozyme crystals

Study by the luminescent-probe (Eu³⁺) method has demonstrated that water in monoclinic lysozyme crystals is readily exchanged with water from the environment. Molecules of certain organic molecules about 2 nm in size equally readily penetrate into crystals. The state of water directly surrounding protein molecules both in the protein solution and crystals differs from the state of other water molecules. The percentage of water molecules of the former type is higher in crystals than in solution. Water was found to be removed in two steps during crystal drying. The weight loss of samples upon storage at a constant temperature of ～30°C under nitrogen for 3 h is about 24%. Heating of crystals, which were dried under the above-mentioned conditions, led to the additional loss of 2.1 wt % of water. Therefore, the total water content in crystals is ～26 wt %.     

Shape of steps on the (010) face of orthorhombic lysozyme crystals

An attempt is made to explain the shape of the curved steps at the (010) face of orthorhombic lysozyme crystals and to determine the density, the rate of formation, and the velocity of kinks. The interpretation is performed in terms of the concepts developed in studies on the crystallization of long-chain polymers within the Frank model. It is demonstrated that this model is incorrectly generalized to the case of high kink densities. A algorithm for determining the coordinates of the growth front in images obtained with atomicforce microscopes is proposed and implemented.     

Formation of a dislocation spiral on the (010) face of a potassium hydrogen phthalate crystal

The atomic-force microscopy method is used to study the structure of the surface and the formation of a dislocation spiral on the (010) face of a potassium hydrogen phthalate crystal grown from a water-alcohol solution. It is shown that the face grows according to the dislocation mechanism. Channels surrounding dislocation sources with a large Burgers vector are discovered. The density of kinks at the steps was so high that no smooth regions were observed between kinks. The velocity of a step fluctuates, with the fluctuations growing in proportion to the fourth root of time. During the formation of a spiral, a segment of a step acquires a constant velocity independent of its length after attainment of the critical length.     

Non-Kossel crystals: Calcium and magnesium oxalates

The rate of movement of elementary growth layers at faces of CaC₂O₄ · H₂O and MgC₂O₄ · 2H₂O crystals is measured in situ by atomic force microscopy under kinetic growth conditions at a constant supersaturation with a varying excess of cations or anions in the solution. It is shown that, as the deviation of the Ca²⁺/C₂O ₄ ^2? (or Mg²⁺/C₂O ₄ ^2? ) ratio from unity increases, the rate of movement of the growth layers decreases abruptly and nonlinearly. A model describing this effect is discussed.     

Changes in the Raman spectrum of OH stretching vibrations of water in an ultrasonic cavitation field

A modification of the local structure of molecular aggregates in liquid water subjected to the action of an ultrasonic cavitation field is found. This modification is detected by the shift of the center of the Raman band contour of the OH stretching vibrations. It was also found that both the structure and the growth rate of lysozyme crystals grown in redistilled Milli-Q water and in water subjected to cavitation treatment differ considerably from each other.     

Fluctuations of steps at the faces of potassium dihydrophosphate crystals in a solution

The time dependence of the step-displacement fluctuations at the faces of a prism and a bipyramid of potassium dihydrophosphate (KDP) crystals is determined by in situ atomic-force microscopy in the line-by-line scanning mode. It is shown that the build-up of fluctuations follows a t ^1/4 law and not a t ^1/2 dependence as for a single diffusing particle. Measurements are made during growth and dissolution in the vicinity of the equilibrium position. It is found that the fluctuations at the prism face during dissolution are stronger than those during growth. Voronkov’s theory is used to compute the basic parameters of crystallization and to interpret the obtained results.     

Dependence of the step velocity on its length on the (010) face of the orthorhombic lysozyme crystal

The length of a two-dimensional critical nucleus has been measured, and the Gibbs-Thomson formula has been experimentally verified on orthorhombic lysozyme crystals. The step velocity was found to be independent of its length. The critical length initiating the step motion can be determined by a low density of kinks on a step, and not the critical-nucleus size. The invalidity of the Gibbs-Thomson formula in this case is discussed.     

Fluctuations in the step velocity and the generation of a dislocation spiral on the (101) face of monoclinic lysozyme crystals

The generation of a dislocation spiral and fluctuations in the step velocity on the (101) face of monoclinic lysozyme crystals have been studied by in situ atomic force microscopy (AFM). It is shown that the (101) face grows by the dislocation mechanism and that the steps move via the formation of one-dimensional nuclei. The velocity of a part of the step fluctuates, with the fluctuations increasing proportionally to the fourth-order root of time. In the process of spiral generation, a segment of the step attains a certain critical length and then moves with a constant velocity. Even under constant supersaturation, the fluctuations can give rise to changes in the segment length. The interstep distance in the step echelon also varies.     

Observation of crystal growth of lysozyme protein crystals by atomic force microscopy

Surface structure and the propagation of elementary growth layers over the (010) face of orthorhombic lysozyme crystal is examined at a molecular‐scale resolution by the method of atomic force microscopy (AFM). The steps have a small number of kinks spaced by about 150 growth units. The step motion occurs via successive deposition of rows of growth units. The data obtained are discussed in terms of the model of one‐dimensional nucleation.