Crystallization experiments, seeded

D Arcy, A., MacSweeny, A., Stihle, M. and Haber, A. (2003). Using natural seeding material to generate nucleation in protein crystallization experiments. Acta Crystallogr. D 59,1343-1346. 

Scheme 3 The solid yielded by mechanical mixing of the reactants can be used to seed crystal growth from solution to obtain crystals for single-crystal X-ray diffraction experiments. This procedure allows one to compare the X-ray powder diffraction pattern measured on the mechanochemical sample with that calculated on the basis of the single-crystal experiment for the solids obtained by crystallization via seeding of a solution of the ground powder of the adduct...

Since the growth conditions are uncontrolled in the growth of natural quartz crystals, it is probable that the growing crystals experience major conditional changes, such as cessation of growth and regrowth from new solution. Under such circumstances, crystals formed early on may act as seed crystals. 

Crystallization experiments using rALBP were immediately successful. With seeding, octahedral crystals of the apo-protein grew to a length of 0.4 mm and a height of 0.3 mm. These crystals give diffraction data to 2.4 A. An entire data set was collected to 2.7-A resolution using the area detector system. Statistical details of the combined X-ray data set are presented in Table 8.1. 

Seeded Crystallization Experiments. A detailed description of the seeded growth technique has been published recently (2J ). 

Figure 4. Plots of solution total calcium concentration and pH as a function of time for a typical calcite-seeded crystallization experiment in simulated natural...

To illustrate the impact of seed surface area and sonication. Table 7-1 summarizes the results of four consecutive crystallization experiments at the 3 wt% seed level. In each experiment, the seed used is the final crystals from the previous experiment. As can be seen from the table for the first two experiments, seed surface area has a strong impact on the final product surface area. This is anticipated when crystal growth on the seed bed is the predominant mechanism. 

Run crystallization experiments to determine the seed quantity and addition time or cooling rate to achieve growth. 

Scheme 2.2.7 Seed crystal experiments in the inclusion complexation between solid host and gaseous Et20 guest.

Crystallization. The crystallization procedure is taken from that described by Fujii et For crystallization experiments, the Sulfolobus sp. ferredoxin solution obtained from a preparative Sephadex G-50 gel filtration column (Amersham Pharmacia Biotech) is concentrated by pressure filtration through an Amicon YM3 or YMIO membrane at 4° and made to 5 mg/ml in 0.5 M Tris-maleate-NaOH buffer, pH 5.0, containing 1% 2-methyl-2,4-pentanediol. Crystals suitable for X-ray diffraction analysis are obtained by a batch method performed under aerobic conditions. Fine-powdered ammonium sulfate is slowly added to 300 p.1 of 5 mg/ml protein solution until the turbidity is observed to persist (1.9-2.1 M). The crystallization solution is stored at 37° in an incubator. Dark brown crystals with appropriate dimensions of 0.3 x 0.3 x 0.5 mm are obtained in 3-5 weeks. Fujii etaO reported that reproducibility of the crystallization is enhanced by seeding a drop of the mother liquor containing microcrystals into the crystallization solution just before the crystallization begins. 

These ribbons are also formed if thin spin cast films of dialkyl-PPEs are annealed. The seeding through solution-formed aggregates does not seem to be necessary. Crystallization experiments were conducted by aimealing of a dialkyl PPE of the structure 108 containing both racemic and chiral side chains. The same type of 30-nm wide ribbons was found, but these ribbons showed an internal helical order according to dark field electron microscopy. They displayed very large chiroptical anisotropies, g-values, on the order of-0.38. Thin film preparations of chirally substituted PPEs that are spin cast and... 

The study started with a batch crystallization experiment using seeded method. The purpose of this batch experiment was to deteimine the parameters needed for the subsequent experiment, i.e. the seeded continuous crystallization experiment using an MSMPR (mixed-suspension-mixed-product-removal) crystallizer. These parameters were levels of supersaturation, residence time, stirring rate, and concentration of additives, respectively. 

It may also be difficult to reproduce the crystallizatioii of a metastable form and there are accounts of the so-called disappearing polymorphs, that is, forms that could be obtained at some stage but not reproduced later. Since nudeation is a stochastic process, it is possible that two crystallization experiments that are performed in exactly the same way may lead to a different outcome. But if conditions are chosen properly and any potential seeds of other forms are carefully removed, it should always be possible to reproduce any form if a large enough number of experiments are performed. 

Steinbock reminds us that polymeric materials need not be organic. In Chapter 11, he examines self-organization in the silica garden system. This fun system is a common demonstration and actually dates back to the seventeenth century. In the conventional chemical garden experiment, small salt particles or crystals are seeded into aqueous solutions containing anions such as silicate, carbonate, borate, or phosphate. Such experiments are uncontrolled and caimot be made continuous. Steinbock explains how they replaced the salt crystals by a continuous flow of salt solution. He details the variety of instabiHties that can occur and how bubbles can be used as templates for tube growth. 

Doki, N., Kubota, N., Sato, A., Yokota, M., Hamada, O. and Masumi, F., 1999. Scaleup experiments on seeded batch cooling crystallization of potassium alum. American Institution of Chemical Engineers Journal, 45(12), 2527-2533. 

A comparative study [10] is made for crystal-growth kinetics of Na2HP04 in SCISR and a fluidized bed crystallizer (FBC). The details of the latter cem be found in [11]. Experiments are carried out at rigorously controlled super-saturations without nucleation. The overall growth rate coefficient, K, are determined from the measured values for the initial mean diameter, t/po, masses of seed crystals before and after growth. The results show that the values for K measured in ISC are systematically greater than those in FBC by 15 to 20%, as can be seen in Table 2. On the other hand, the values for the overall active energy measured in ISC and FBC are essentially the same. 

Wayne Genck (7 8) has recently published several useful articles about batch crystallization. Often lab filtration after crystallization is done with a thin cake and no problem is observed. But when taken to the plant, this operation takes days to build and wash a cake. To avoid this problem it is best to operate a crystallizer that is properly seeded and cooled according to a profile that follows the equation in reference (7), slow at first and fastest at the end. The other reference (8) discusses the challenges without seeding. Experience by the author confirms that a large amount of seed crystal is required, about 1-2 % wt of the final crystal yield. 

These results for spread film and equilibrium spreading suggest that films of racemic N-(a-methylbenzy 1) stearamide may be resolved by seeding the racemic film with crystals of either pure enantiomer. Indeed, when a monolayer of racemic jV- (a-methylbenzyl) stearamide is compressed to 45 A2/molecule (27 dyn cm-1), deposition of a crystal of either R( +)- or S( — )-enantiomer results in a decay of surface pressure from the initial 28 dyn cm-1 film pressure to 3.0 dyn cm-1, the ESP of the enantiomeric systems on a pure 10n sulfuric acid subphase (Table 1). When the experiment is repeated with racemic crystals, the system reaches an equilibrium surface pressure of 11 dyn cm-1, nearly the ESP of the racemic crystal on the clean acidic interface. In either case, equilibrium pressure is reached within a two hour time period. 

Chen et al. [92] also performed self-nucleation experiments by DSC in PB-fr-PEO diblock copolymers and PB/PB-b-PEO blends. The cooling scans presented in their work showed that a classical self-nucleation behavior was obtained for PEO homopolymer and for the PB/PB-b-PEO blend where the weight fraction of PEO was 0.64 and the morphology was lamellar in the melt. For PB/PB-fr-PEO blends with cylinder or sphere morphology, the crystallization temperature remained nearly constant for several self-seeding temperatures evaluated. This observation indicates that domain II or the self-nucleation domain was not observable for these systems, as expected in view of the general trend outlined earlier. 

All experiments up to this time employed only minute quantities of seed crystals. In investigating the variables affecting the growth of the dextrose crystals, Newkirk found that the operation could be controlled by using much greater proportions of seed crystals than had hitherto been employed.8 The excessive formation of crystal nuclei too small and numerous to be able to grow to satisfactory size could be avoided by this means. The operation was most economically carried out by leaving in the crystallizer 25 to 30% of a finished batch to act as seed for the... 

A racemic film was compressed nearly to its collapse point. It was then seeded by sprinkling crystals of pure enantiomeric amide on the surface. A rapid decrease in surface pressure was observed approaching the equilibrium spreading pressure of the enantiomer. A control experiment in which racemic crystals were sprinkled on the compressed racemic film produced a pressure drop that slowly approached, but did not reach, the ESP of the racemic film. The observed behavior was consistent with what would be expected if the enantiomer seed crystals had removed molecules of the same enantiomer from the racemic film, leaving a monolayer composed mainly of molecules of the opposite configuration. 

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