Phase behaviour of transkarbam 12.

Transkarbam 12 (T12), the carbamic acid salt of omega-aminocaproic acid dodecyl ester, is a recently synthesized substance, whose high permeation enhancing activity through the human skin was found for certain drugs. In this work, the thermotropic phase behaviour of T12 has been studied by means of various techniques, namely, DSC, FTIR and FT-Raman spectroscopy, X-ray powder diffraction, and DRS. The temperature development of the X-ray reflections as well as of the conformationally sensitive Raman bands and the IR bands have been observed. At room temperature, the hydrocarbon chains of T12 exhibit a highly ordered structure, arranged in an orthorhombic perpendicular subcell. On heating, two transitions occur at 54 and at 66 degrees C. The first transition is related to the disruption of the carbamate structure and changes in the polar head group. The other transition represents the melting of hydrocarbon chains and the subsequent release of carbon dioxide. The time required for the rebinding of carbon dioxide and the reformation of the carbamate structure is dependent upon numerous factors and it was not possible to precisely determine the length of this process.

Polymorphism of ceramide 3. Part 1: an investigation focused on the head group of N-octadecanoylphytosphingosine.

The thermotropic phase behaviour of the ceramide N-octadecanoylphytosphingosine (CER3) was investigated using differential scanning calorimetry, X-ray powder diffraction and FT-IR spectroscopy. CER3 was shown to be a polymorphic substance depending on the crystallisation conditions. Three different solid states were found. The FT-IR results elucidate changes in the hydrogen bonding interactions of the ceramide head group. It was shown that the amide I and the amide II vibration bands are quite sensitive to the phase transitions of CER. There are clear shifts in the band positions of those bands passing the phase transitions. Furthermore, changes were observed in the NH- and OH- stretching region. The study shows that there are strong inter- and intramolecular hydrogen bonds between hydroxy groups in the ceramide head group. There are also strong hydrogen bonds to the amide oxygen as shown by the band positions of the amide vibrations. The H-bonding network and conformation of the head group of CER3 alters due to the phase transitions.

Thermodynamic and spectroscopic characterization of the berenil and pentamidine complexes with the dodecanucleotide d(CGCGATATCGCG)2.

The dodecanucleotide d(CGCGATATCGCG)2 was characterized by thermodynamic and UV-spectrophotometric measurements. A van't Hoff enthalpy of delta H(uv)v.H. approximately -190 kJ/mol was determined for the thermal transition using UV spectroscopy. This value was confirmed by differential scanning calorimetry (DSC). In addition we obtained the thermodynamic data delta HDSC = -405.1 kJ/mol, delta SDSC = -1290 J/mol.K and delta GDSC = -53.2 kJ/mol for the helix to coil transition of the dodecanucleotide. The association of berenil and the oligonucleotide was accompanied with a stabilization of the host duplex (increase in Tm) and an increase in the van't Hoff enthalpy. The berenil binding parameters (delta delta HDSC = -32.6 kJ/mol, delta delta SDSC = -72 J/mol.K and delta delta GDSC = -11.1 kJ/mol) revealed significant differences compared to those of the pentamidine aggregation (delta delta HDSC = -23.7 kJ/mol, delta delta SDSC = -53 J/mol.K and delta delta GDSC = -7.8 kJ/mol). The transition of the pure oligonucleotide was characterized by a substantial amount of intermediate states (sigma DSC = 0.43) which decreased significantly upon binding of the drugs (sigma DSC approximately 0.80). The structural features of the complexes were analyzed by FT-IR spectroscopy. From these experiments we conclude that the configurations in the berenil and pentamidine complexes are different.