Nitrophenol, cyclodextrin complex

The importance of the proximity effect in cyclodextrin catalysis has been discussed on the basis of the structural data. Harata et al. 31,35> have determined the crystal structures of a-cyclodextrin complexes with m- and p-nitrophenols by the X-ray method. Upon the assumption that m- and p-nitrophenyl acetates form inclusion complexes in the same manner as the corresponding nitrophenols, they estimated the distances between the carbonyl carbon atoms of the acetates and the adjacent second-... 

Aqueous a-cyclodextrin solutions seem to be generally applicable for TLC separation of a wide variety of substituted aromatics on polyamide thin-layer stationary sheet (13-14). In most cases, the compounds moved as distinct spots and their R, values were dependent on the concentration of the cyclodextrin in tne mobile phase. In a given family of compounds, (o-, m-, and p-nitrophenols, for example) the isomer with the largest stability constant for a-cyclodextrin complex formation had the larger value. In general, the para-substituted isomers have larger R values than the meta-isomers, which in turn have larger R values than the ortho substituted ones. 

In further studies on the crystal structures of cyclodextrin complexes, the a-cyclodextrin 4-nitrophenol (1 2) complex was found to have an orthorhombic unit cell. The a-cyclodextrin methylsulphoxide methanol (1 1 2) dihydrate complex had a monoclinic unit cell. In this structure, the methylsulphoxide molecule is on the side of the secondary hydroxy-groups in the a-cyclodextrin cavity such that it forms two hydrogen bonds with adjacent a-cyclodextrin molecules. One methanol molecule is found on the side of the primary hydroxy-group in the cavity while the other is located outside the cavity. The two water molecules are distributed in the space between the a-cyclodextrin molecules. 

Figure 2. Solid state CP/MAS 25 MHz CNMR spectra of (A) a-cyclodextrin-p-nitrophenol inclusion complex I and, (B) p-nitrophenol, recrystallized from water.

Harata K (1997) The structure of the cyclodextrin complex. V. Crystal structures of a-cyclodextiin complexes with p-nitrophenol and p-hydroxybenzoic acid. Bull Chem Soc Jpn 50 1416-1424... 

Figure 5.2. Spectral changes on incremental addition of p-nitrophenolate to a-cyclodextrin illustrating complex formation (from Cramer, Saenger Spatz, 1967).

It was pointed ouF that while ionomer-modified electrodes have greater selectivity than naked electrodes, ionomers provide only a general form of selectivity (charge type and mass or hydrophobicity selectivity), and special methods were suggested to improve specific selectivity. For example, it was thought that applying an additional cellulose acetate layer over the Nafion film would make the electrode selective with respect to dopamine specifically (in contrast to other neurotransmitters). To make the electrode system specifically selective to o-nitrophenol (in contrast to /(-isomer), a complexation with cyclodextrin was performed, which increased the selectivity ratio one order of magnitude with respect to the o-isomer. ... 

Section 6.2, the crystal forces are of magnitude comparable to those inducing complex formation. Thus a complex in the solid state can have a different structure from that in solution. The complex of p-nitrophenol 74 with hexakis(2,6-di-OMe)-a-cyclodextrin 75 illustrates this point, exhibiting strikingly different modes of entrance of the guest into the host cavity in these two states (Figure 3.4) [39]. Nevertheless, numerous solid state studies ofthe complexes... 

This review will illustrate examples of computer projected models of inclusion complexes of structural isomers (ortho, meta, para nitrophenol), enantiomers (d- and 1- propranolol) and diastereomers [cis and trans. l(p-B-dimethylaminoethoxy-phenyl-butene), tamoxifen] in either a- or B-cyclodextrin. The use of these computer projections of the crystal structures of these complexes allows for the demonstration and prediction of the chromatographic behavior of these agents on immobilized cyclodextrin. 

Figure 2. Computer imaging of crystal structures of the inclusion complexes of para (A), meta (B) and ortho (C) nitrophenol with a-cyclodextrin. The complex is shown with van der Waal s radii, and the front section of the complex cut away in order to expose the nitrophenol molecule.

Attachment of a cyclodextrin unit to an N-CH3 form of the CR macrocycle (Fig. 39) yielded a zinc complex with only modestly improved effectiveness (k2 = 21.7x 10 2M 1s 1) over the mononuclear system (k2 — (3.80 + 0.05) x 10 2M 1s 1) for the hydrolysis of diphenyl 4-nitrophenyl phosphate under identical conditions.109 This enhancement is proposed to be due to binding of 4-nitrophenolate moiety in the cyclodextrin cavity. 

Fig. 5. The time-averaged conformation of the a-cyclodextrin-m-nitrophenol complex ----------H3— and...

For example, the time-averaged conformation of the inclusion complex between a-cyclodextrin and w-nitrophenol was determined by this method as shown in Fig. 

This paper describes the elution behavior of benzene, ortho-, meta-, and para-nitrophenol, naphthalene, and biphenyl in aqueous and methanolic cyclodextrin mobile phases. The inclusion complex formation constants of these selected compounds in e-CD mobile phases containing 0%, 10%, and 20% methanol are reported. The formation constants obtained using a CN column/CD mobile phase were determined and used to predict the elution behavior of the test compounds on C-18 columns. Also, the elution behavior of solutes on C-18, e-CD, and Y-CD stationary phases are compared. 

ABSTRACT. The geometries of inclusion complexes of a-cyclodextrin(a-CD) with guests, benzoic acid, p-hydroxy benzoic acid, and p-nitrophenol in aqueous solution have been determined by comparing the complexation induced C-13 shifts of guest molecules with quantum chemical predictions. In the calculations, the non-polar environmental effect produced by the a-CD cavity on the C-13 shifts of included guest molecule has been formulated by the so-called solvent effect theory. The geometries of the complexes predicted theoretically were consistent with those... 

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