Condensation-crystallization structures

Disperse structures with phase contacts can form in a variety of physical-chemical processes, such as in the sintering of ceramic powders and in the course of pressing powders into pellets. Disperse structures with phase contacts that are formed in the process of generating a new phase in metastable solutions or melts are referred to as condensation structures. If the particles forming structures are crystalline, then the structures are referred to as condensation-crystallization structures. These structures can be viewed as opposite to the condensation structures composed of amorphous particles. 

Quite recently, Ciampolini and coworkers have reported the synthesis of two isomeric mked oxygen-phosphorus macrocycles and the crystal structures of their cobalt complexes. Synthesis of macrocycle 27 was accomplished by condensation of 1,2-bis-(phenylphosphino)ethane dianion with 2,2 -dichlorodiethyl ether in THE. The two isomers of 27 were isolated in 1.5% and 2% yield. The synthesis is formulated in Eq. (6.17), below. 

Conversely, when A-alkyl tryptophan methyl esters were condensed with aldehydes, the trans diastereomers were observed as the major products." X-ray-crystal structures of 1,2,3-trisubstituted tetrahydro-P-carbolines revealed that the Cl substituent preferentially adopted a pseudo-axial position, forcing the C3 substituent into a pseudo-equatorial orientation to give the kinetically and thermodynamically preferred trans isomer." As the steric size of the Cl and N2 substituents increased, the selectivity for the trans isomer became greater. A-alkyl-L-tryptophan methyl ester 42 was condensed with various aliphatic aldehydes in the presence of trifluoroacetic acid to give predominantly the trans isomers. ... 

Cowley s group reported in 1987 the condensation of a dichlorophosphine with Collman s reagent to form stable complex 12, for which they obtained an X-ray crystal structure [57]. However, the two nearly equally long P-N bond lengths of 1.777(7) and 1.764(7) indicate that 12 is not an unencumbered species. 

When two metals A and B are melted together and the liquid mixture is then slowly cooled, different equilibrium phases appear as a function of composition and temperature. These equilibrium phases are summarized in a condensed phase diagram. The solid region of a binary phase diagram usually contains one or more intermediate phases, in addition to terminal solid solutions. In solid solutions, the solute atoms may occupy random substitution positions in the host lattice, preserving the crystal structure of the host. Interstitial soHd solutions also exist wherein the significantly smaller atoms occupy interstitial sites... 

A number of other thermodynamic properties of adamantane and diamantane in different phases are reported by Kabo et al. [5]. They include (1) standard molar thermodynamic functions for adamantane in the ideal gas state as calculated by statistical thermodynamics methods and (2) temperature dependence of the heat capacities of adamantane in the condensed state between 340 and 600 K as measured by a scanning calorimeter and reported here in Fig. 8. According to this figure, liquid adamantane converts to a solid plastic with simple cubic crystal structure upon freezing. After further cooling it moves into another solid state, an fee crystalline phase. 

Identification of proteins that bind to Z-DNA added one further step to the establishment of the presence of Z-DNA in vivo and its possible biological role. Herbert and Rich [22] demonstrated an in vitro assay system where one type of double-stranded RNA adenosine deaminase, called DRAD-binding Z-DNA. There are evidences that topoisomerase II from Drosophila, hiunan and calf thymus recognizes a number of DNA shapes, including Z-DNA [34,35]. Bloomfield and coworkers [36] have found that the condensation of plasmids is enhanced by Z-DNA conformation in d(CG)n repeats. The information related to B-Z transition [31], the effect of ligands on it [28,29] and X-ray crystal structure data [37,38] appear to suggest that the possible biological role of this polymorphic form of DNA will be soon established. 

The complex [Co(NH3)5(OS02CF3)]2+ undergoes triflate substitution by cyanate and condensation with acetone to form the unusual bis-bidentate imine complex (213)917 in a reaction reminiscent of the classic Curtis condensation of acetone with ethylenediamine. Apart from the novelty of the synthesis, the reported crystal structure was only the second of a CoN6 complex bearing a cyanate ligand. 

Open M4 units are also quite rare. In the selenobromides M4Se16Br2 (M=Nb, Ta) there are tetranuclear units M4(p-Se2)r,, which result from condensation of three M2( r-Se2)2 clusters. The M-M distances within them are about 3.1 A.52 Single crystal structure determination of V5S8 revealed the presence of rhombic vanadium clusters in the structure with hinge V-V bond of 2.88 A, peripheral bonds of 3.04 A and strong intercluster bonding (V-V 2.92 A).53... 

To resolve the issue of cyclization specificity, the x-ray crystal structure of the stilbene synthase from pine was determined to atomic resolution. This information allowed the mutagenic conversion of alfalfa CHS to a functional STS, and crystal structures of this engineered STS were solved, in the apo form and with resveratrol bound in the active site (Austin and Noel, unpublished). These experiments support a mechanistic proposal, which prompted further mutagenic and modeling experiments. This work has allowed the elucidation of the structural and mechanistic basis for cyclization specificity (aldol versus Claisen condensation) in the CHS family of type III PKSs. 

HUANG W, JIA, J EDWARDS, P., DEHESH, K., SCHNEIDER, G., LINDQVIST, Y., Crystal structure of P-ketoacyl-acyl carrier protein synthase II from E. coli reveals the molecular architecture of condensing enzymes, EMBO J., 1998,17, 1183-1191. 

Fig. 3.1-10. Crystal structures of (a) [Ba3N]Na5, (b) [Ba3N]Na and (c) [Ba3 N] viewed along the chains of condensed [Ba6/2N] octahedra. Ba-Ba contacts outlined, Na light shading.

Fig. 3.1-11. Crystal structure of [Ba2N] viewed along the layers of edge-condensed [Ba6/3N] octahedra which are outlined.

Lehn and coworkers52 reported the synthesis, crystal structure and dinuclear copper(I) complexes of tris-carotenoid macrobicyclic ligands. The macrobicycles 89 and 90 were obtained in good yields in a one-step macrobicyclisation condensation between the tripode N(CH2CH2NH2)3 and the polyolefinic dialdehydes 93 and 94. 

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