Structural aspects of the complexation of N-nitroso-N'-(2-chloroethyl)-N'-sulfamide piperidine (CENS) with b-cyclodextrin (b-CD) were investigated using standard B3LYP and MPW1PW91 Density Functional Theory (DFT) calculations. Two orientations of the incoming CENS inside b-CD were considered to determine the lowest energy complex, namely the head (ring first) and tail (chain first) orientations. The calculations confirm that the tail orientation is more favorable than the head one by 5.9 kcal/mol (B3LYP) and 5.9-6.1 kcal/mol (MPW1PW91) the driving factor being the deformation energy undergone by b-CD. This preference is also due to the fact that the complexation with tail orientation of CENS occurs with a favourable anti-parallel disposition of the dipole moments of b-CD and CENS. The computed structure for the CENS -b-CD complex is in good agreement with mass and 15 N NMR spectroscopy observations. Moreover, this complexation mode leads to the formation of four intermolecular H-bonds between CENS and CD, i.e. two conventional H-bonds, one between N atom (N136) of the NO bond of CENS and H-6-O atom (H129) of b-CD and the other one between O atom (O137) of CENS SO 2 group and H-6-O (H120) and two weak (C-H. . .O) bonds. These interactions were investigated using the Natural Bond Orbital (NBO) approach. To cite this article: F.
Fluorescent behaviour of lomustine, a DNA cross-linking agent, was investigated in different solvents, pH and in the presence of b-cyclodextrin (b-CD). The solvents in which fluorescence spectra were observed play a major role in determining the spectral intensity of fluorophore, since it was found to exhibit new fluorescent properties essentially influenced by intermolecular interactions, particularly by intermolecular H-bonding formed with solvents. The pH-dependence profile was typically U-shape with a maximum at pH between 3.51 and 6.58. It was corroborated that the fluorescence emission band of lomustine is significantly intensified in the presence of b-CD. From the changes in the fluorescence spectra, it was concluded that b-CD forms a 1:1 inclusion complex with lomustine and its association constant was calculated.
A series of nine inclusion complexes have been prepared in the solid state between three different 2-chloroethylnitrososulfamides (CENS) and three different cyclodextrins ( -cyclodextrin , methyl--cyclodextrin and (2-hydroxylpropyl)--cyclodextrin). The formation of inclusion complexes with a 1/1 stoichiometry has been confirmed. NMR studies showed that the CENS moiety is encapsulated in CDs cavities in a tilted equatorial orientation. Since biological evaluation showed that the cyclodextrins have only a slight effect on the activity of the drugs toward two cancer cell lines, the possibility exists that the complexes may find pharmaceutical use by improving the drugs' in vivo bioavailability and stability. 2-chloroethylnitrososulfamides, inclusion complexes, cyclodextrins, NMR, ESI-MS, thermogravimetry.2-chloroethylnitrososulfamides (CENSs) are oncostatic drugs which differ from the 2-chloroethylnitrosoureas (CENUs), a major class of alkylating agents [1, 2], by the presence of a sulfonyl group in place of the carbonyl moiety (Fig. 1), and are devoid, therefore, of any carbamoylating activity. The route for the preparation of CENS has been described in previous articles, and the first pharmacological evaluations have shown promising therapeutic applications [3][4][5][6]. However, aqueous decomposition studies of those
The structure of N-nitroso, N-(2-chloroethyl), N',N'-dibenzylsulfamid (CENS) was established by X-ray crystallography. The atomic coordinates, factors of isotropic thermal agitation, bond lengths and valence angles were determined. The solvent effects on the electronic absorption and fluorescence spectra of CENS were investigated at room temperature. The effects of solvent polarity and of hydrogen bonding were interpreted by means of linear solvation energy relationships (LSERs). Multiple linear regression analysis indicated that the hydrogen donation properties of the solvent play an important role in determining the position of the absorption maximum, while the classical polarity of the medium is the only dominating parameter in determining the emission maximum and the Stokes' shift. Complexation of the investigated compound by two different transition metal ions was studied. Fluorescence measurements show that fluorescence quenching by cobalt(II) is more important than that by copper(II). This phenomenon can be attributed to good stereo-structural matching between the electronic configuration of the Co(2+) ion and the active site distribution of CENS in aqueous solution.
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