Crystallization solvent effects

The magnetic moments rise only slightly at elevated temperatures (see Table 5), which led the authors to conclude that some population of the higher sT2(Oh) state is possible. No clear distinction can be made as to which of the influencing factors, viz. electronic effects, steric hindrance, and crystal solvent effects, plays the dominant role here, because all of these are operative to some extent. Data from the UV-vis spectra of the nickel(II) complexes indicate that the ligands have field strengths in the iron(II) crossover region. 

The above crystal solvent effect on the ethanolate and the methanolate of [Fe(2-pic)3] CI2 Sol has later been confirmed by magnetic susceptibility measurements181 . Sinn et al. 181) have also investigated the unsolvated bromide [Fe(2-pic)3] Br2 as well as its solvates with Sol = C2HsOH and CH3OH, respectively these systems all show temperature dependent spin transition with pronounced differences in the transition behaviour. Differences in the spin transition behaviour of corresponding solvates [Fe(2-pic)3] X2 Sol (X = Cl, Br) with different anions are also noticeable 181). 

When crystallisation is complete, the mixture of crystals and crude mother-liquor is filtered at the pump, again using a Buchner funnel and flask as described on p. 10, and the crystals remaining in the funnel are then pressed well down with a spatula whilst continual suction of the pump is applied, in order to drain the mother-liquor from the crystals as effectively as possible. If it has been found in the preliminary tests that the crystalline material is almost insoluble in the cold solvent, the crystals in the... 

The following is taken from U.S. Patent 3,061,517. Sixteen grams of racemic 3-(2-pYridyl)-3-p-bromophenyl-N,N,-dimethylpropylamine and 9,7 grams of d-phenylsuccinic acid are dissolved in 150 ml of absolute alcohol and kept at room temperature until crystallization is effected. The crystals are filtered, washed with absolute ethyl alcohol, and recrystallized from the same solvent using 5 ml thereof per gram of solid. Three subsequent crystallizations from 80% alcohol give d-3-(2-pYridYl)-3-p-bromophenYl-N,N-dimethylpropYlamine-d-phenylsuccinate MP 152°-154°C 91 (concentration, 1% in dimethylformamide). 

Twenty grams of d-phenylsuccinic acid and 28 grams of 3-(2-pyridyl)-3-p-chlorophenyl-N,N-dimethylpropylamine are dissolved in 400 ml of absolute ethyl alcohol and allowed to stand at room temperature until crystallization is effected. The crystals are filtered, washed with absolute ethyl alcohol and recrystallized from 300 ml of this solvent in the same manner. The crystals are recrystallized twice from 80% ethyl alcohol using 3.5 ml per gram of compound in the manner described above and pure d-3-(2-pyridyl)-3-p-chlorophenyl-N,N-dimethylpropylamine-d-phenylsuccinate is obtained, melting point 145°-147°C. 

The dissolving of electrolytes in water is one of the most extreme and most important solvent effects that can be attributed to electric dipoles. Crystalline sodium chloride is quite stable, as shown by its high melting point, yet it dissolves readily in water. To break up the stable crystal arrangement, there must be a strong interaction between water molecules and the ions that are formed in the solution. This interaction can be explained in terms of the dipolar properties of water. 

Giitlich et al. [4, 6] have studied SCO in solid [Fe(2-pic)3]Cl2-EtOH (2-pic = 2-picolylamine), particularly the influence of dilution with Zn and Co, the nature of noncoordinated anions and crystal solvent, the HID and isotope effect,... 

More recent work has focused on understanding the mechanism or mechanisms of selectivity. Some of these studies have been performed on well-characterized catalysts about which particle size information is available. Still others have been performed on single crystals. So conclusions may be reached about the effects on chemoselectivity of planes, edges, and corners that are related to particle size (structure sensitivity). A number of these studies, mostly on Pt, are summarized in Table 2.6. Since these studies have usually been performed in the vapor phase, information about solvent effects and their possible influence on chemoselectivity is unavailable. 

The effect of polymorphism becomes especially critical on solubility since the rate of compound dissolution must also be dictated by the balance of attractive and disruptive forces existing at the crystal-solvent interface. A solid having a higher lattice free energy (i.e., a less stable polymorph) will tend to dissolve faster, since the release of a higher amount of stored lattice free energy will... 

As discussed in section 2.4.4 the coordinating ability of a solvent will often affect the rate of nucleation and crystal growth differently between two polymorphs. This can be used as an effective means of process control and information on solvent effects can often be obtained from polymorph screening experiments. There are no theoretical methods available at the present time which accurately predict the effect of solvents on nucleation rates in the industrial environment. 

We reported in the previous papers [8, 9] that the effect of the operational factors such as temperature and solvents on the polymorphic crystallization of a thiazole derivative - 2-(3 -Cyano-4-(2-methylpropoxy)-phenyl)-4-methyl-thiazole-5-car-boxylic acid (BPT) - which is an enzyme inhibitor. In this paper, we synthesized the esters of BPT and studied the effect of the molecular structure on polymorphic nucleation systemically, and at the same time we also examined the solvent effect on the polymorphic nucleation of the ester. 

As described previously in the crystallization from ethanol (EtOH) solutions A and B polymorphs appeared. However, with kinds of the solvent the polymorphic nucleation behavior may change. In this section the solvent effect in the nucleation behavior of Pr-est is shown. 

These results suggest that the crystallographic determination of the structure of a productive enzyme-substrate complex is feasible for lysozyme and oligosaccharide substrates. They also provide the information of pH, temperature, and solvent effects on activity which are necessary to choose the best conditions for crystal structure work. The system of choice for human lysozyme is mixed aqueous-organic solvents at -25°C, pH 4.7. Data gathered on the dielectric constant, viscosity, and pH behavior of mixed solvents (Douzou, 1974) enable these conditions to be achieved with precision. 

The work discussed in the previous paragraphs provides the framework for the prediction of crystal habit from internal structure. The challenge is to add realistic methods for the calculation of solvent and impurities effects on the attachment energies (hence the crystal habits) to allow this method to provide prediction of crystal habit. Initial attempts of including solvent effects have been recently described (71. 721. The combination of prediction of crystal habit from attachment energies (including solvent and impurity effects) and the development of tailor made additives (based on structural properties) hold promise that practical routine control and prediction of crystal habit in realistic industrial situations could eventually become a reality. 

Incorporation of Solvent Effects in Crystal Habit Calculations... 

Figure 4. A nine-molecule space-filling model of the (100) sucrose crystal. Atoms of one of the molecules are labeled. The sub-layer of the screw-axis related molecules is completely shielded from possible solvent effects.

Even though still in a prelinainaiy stage, it is hoped that this approach will result in a better solvent - effect corrector to the attachment energy calculations (IS) than the broken hydrogen bond model and a better fit of the predicted sucrose crystal habits with the observed ones. It is already clear that the present model can, at least qualitatively, distinguish between the fast growing ri t pole of the crystal and its slow left pole. 

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