Evaluation of surfactant monomer concentrations in equilibrium with micelles and their temperature dependence for oxyethylene/oxypropylene/oxyethylene triblock copolymers using DSC

A method is presented that may be used to calculate the concentration of surfactant (C-mon) in thermodynamic equilibrium with micellar aggregates using high sensitivity differential scanning calorimetry (HSDSC) output. The temperature dependence of this equilibrium process has been evaluated for a number of oxyethylene/oxypropylene/oxyethylene triblock copolymers and the results are compared with previously published CMC data that were obtained using a dye solubilization technique. The polydispersity of the block copolymers preclude identifying C-mon with the CMC. However, the C-mon values obtained using the HSDSC technique are of the same order of magnitude and show the same functional relationship with temperature as the reported CMC data. It is therefore proposed that HSDSC provides a suitable method for the rapid evaluation of C-mon for the surfactants examined over a fairly wide range of temperatures. Analysis of the derived C-mon data points to the importance of the oxypropylene block in determining C-mon values. At any particular temperature the greater the size of the oxypropylene block the lower the C-mon value. On the other hand, increasing the oxyethylene block size increases the value of C-mon

Experimental and theoretical studies of cyclic di-amino acid peptides in the solid state

Cyclic di-amino acid peptides (CDAPs) i.e. diketopiperazine (DKP) derivatives have been of long-standing interdisciplinary scientific interest, particularly as potential anti-cancer and anti-microbial agents [1, 2]. Single crystal x-ray studies of different derivatives have indicated that the six membered DKP ring adopts either a planar (cyclo(Gly-Gly), cyclo(L-Ser-L-Ser)) or boat conformation (cyclo(L-Ala-L-Ala) cyclo(L-Asp-L-Asp), cyclo(L-Glu-L-Glu)), in the solid state [3]. In addition, due to steric constraints, both amide bonds always adopt a cis conformation. Unfortunately, the inability to grow crystals of suitable diffraction quality makes it necessary to use other methods for determining solid state structures. In this study a selection of different CDAPs, have been investigated by experimental techniques such as Raman, infra-red spectroscopy and solid state NMR spectroscopy in order to relate structural and conformational relationships with theoretically calculated data. Theoretical gas phase structures have been calculated using DFT calculations (Gaussian03 molecular modeling package), utilizing the B3-LYP/cc-pVDZ basis set. Solid state DFT calculations have also been undertaken, using the pseudopotential-plane-wave CASTEP program. The minimum energy conformation (gas phase) for cyclo(Gly-Gly), cyclo(L-Ala-Gly), cyclo(L-Ala-L-Ala), cyclo(L-Ser-L-Ser), cyclo(L-Asp-L-Asp) and cyclo(L-Glu-L-Glu) indicates that the DKP ring preferentially adopts a boat conformation. When the DKP ring is constrained to adopt a planar conformation a higher energy structure is produced. In the case of cyclo(GlyGly) the planar conformation is higher in energy by only 0.945 kJ mol-1. Simulated theoretical Raman spectra for both planar and boat conformations of cyclo(Gly-Gly) have indicated significant conformational shifts for both the CH2 stretching vibrations and the cis amide II mode. The cis amide II mode is, predominantly, an out of phase C-C-N stretch with a lower degree of contribution from the N-H in plane bend than in the trans amide II mode. The cis amide II mode appears as quite a strong signal in the Raman spectra, but is not observed in the FT-IR spectra [3]. The theoretical calculations are in good agreement with the experimental Raman results, which indicate a potential link with respect to the conformation of the DKP ring, in that a boat conformation has a cis amide II mode at a lower wavenumber than that with a planar/near planar DKP ring conformation. For example, the amide II vibrations for the planar/near planar conformations in cyclo(Gly-Gly), cyclo(D-Ala-L-Ala) and cyclo(L-Ala-Gly) are observed at wavenumbers of 1517, 1523, and 1522 cm-1, respectively, whereas the amide II modes for the boat conformations of cyclo(L-Glu-L-Glu), cyclo(L-Asp-L-Asp) and cyclo(L-Met-L-Met) are located at 1493, 1489, and 1493 cm-1, respectively [3]. The results indicate the significant potential for structural and conformational analysis using a combination of molecular modeling and experimental spectroscopic results

The impact of early infant feeding on the development of atopic disease

Abstract not availabl

Design and formulation of a novel polymer-based buccal film

The aim of this work was to develop a novel film for delivering amorphous drugs into the systemic circulation via the buccal mucosa. The advantage of the buccal mucosa over the sublingual, such as better systemic effects, has led to its exploration as a functional administration route [1]. Buccal formulations can be developed as films, freeze- dried wafers [2] which are suitable alternatives to deliver drugs promptly and safely