Air-water interfacial behavior of linear-dendritic block copolymers containing PEG and azobenzene chromophores

Fabrication of Langmuir films at the air-water interface of four linear-dendritic block copolymers (LDBCs) is described. The LDBCs are composed of a linear hydrophilic chain of poly(ethylene glycol) (PEG) and the first four generations of hydrophobic aliphatic polyester dendrons functionalized at the periphery with cyanoazobenzene chromophores. Langmuir films of the LDBCs, coded as PEG-AZOn (n indicates the number of cyanoazobenzene units at the periphery of the dendritic block), have been characterized by a combination of surface pressure versus area per molecule isotherms, UV-vis reflection spectroscopy and Brewster angle microscopy. The observed PEG-AZOn Langmuir film behavior depends strongly on the hydrophilic/hydrophobic ratio. A typical transition, related to PEG chains desorption from the air-water interface into the water subphase is observed for all the LDBCs, except for PEG-AZO16. In addition, PEG-AZO2 and PEG-AZO4 show a second transition whose nature has been studied in detail. Azobenzene chromophore interactions have been shown to be relevant in the organization of PEG-AZOn (n=4, 8 and 16) Langmuir films. Moreover, for PEG-AZO16 the orientation of the azobenzene units has been determined, revealing the formation of a well organized structure of azobenzene moieties at the air-water interface.     

Analytical procedures for the determination of the selective serotonin reuptake inhibitor antidepressant citalopram and its metabolites

The antidepressant citalopram (CIT) is a potent and highly selective serotonin reuptake inhibitor (SSRI) which has been introduced in therapy as a racemic drug. CIT has been used to treat central nervous system affective disorders such as depression, anxiety, obsessive-compulsive disorders, various phobias, borderline personality disorders, bipolar disorders as well as indications wherein inhibition of serotonin reuptake is desired. CIT is demethylated to demethylcitalopram (DCIT) and didemethylcitalopram (DDCIT), which retain considerable activity as SSRIs. Therefore, in recent years, the monitoring of the levels of these analytes in biological fluids for toxicological and therapeutic purposes has been a target worthy of interest. In addition, the differences in activity between CIT enantiomers established the need to assess its behaviour in the field of pharmacological research. It is also necessary to develop analytical methodologies that make it possible to determine the levels of enantiomer concentrations. This review includes most of the published analytical methods for achiral assay of racemic CIT and its metabolites based on high-performance liquid chromatography coupled with UV, fluorescence and mass spectrometry detectors, capillary electrophoresis and gas chromatography with mass spectrometry detectors among others. With regard to the monitoring of enantiomers of CIT and of its metabolites, stereoselective methods based on chiral chromatographic columns, chiral additives in mobile phases and on the derivatization with a chiral reagent are also collected. In addition, different procedures of extraction are mentioned as well as liquid-liquid extraction, solid-phase extraction, solid-phase microextraction, automated online extraction or liquid-phase microextraction in different biological and environmental samples.     

Thermal and light control of the chiral order of azopolymers

The control of the chiroptical properties of two azopolymers, which contain chiral terminal alkyl chains, by means of thermal and light irradiation processes has been studied. Both UV–vis and CD spectra of films and dichloromethane (DCM)/hexane solutions of the polymers have been registered and analyzed before and after different irradiation conditions: 488 nm circularly polarized light (CPL) and 365 nm unpolarized light. The chiroptical properties of the polymer containing chiral 1-methylheptyloxy terminal chains depended on the thermal history of the sample. As a result, the photocontrol of the chiral response in the bulk material by CPL irradiation has been evaluated on samples cooled from the isotropic state to room temperature at different rates. The chiroptical properties of these azopolymers show an intriguing combination of control from both the supramolecular and molecular chirality level as well as the thermal history of the sample and CPL irradiation.     

Letter to the editor

This letter shows how the main result contained in a paper recently appeared in the Journal of Multivariate Analysis was in fact a particular case of a more general theorem published three years before.     

Pulsed infrared selective dissociation of CF3Br as a function of pressure,temperature, fluence and wavelength

The pulsed InfraRed (IR) photodissociation of pure CF₃Br and a 1:3 mixture with H₂ has been studied as a function of pressure, temperature, fluence and wavelength. The results have been obtained by mass spectrometry. Maximum enrichment for carbon 13 is obtained when irradiating with the 1046.9 cm^–1 (9P20) line, but the selectivity is stronger at longer wavelengths. The enrichment factor tends towards 1 when pressure increases with the pure substance, but it is less affected in the mixture. It seems that hydrogen has a buffer effect. The selectivity shows maxima for all lines with the fluence and increases when the temperature is decreased from 22 to – 85°C. Some enrichment is observed for the bromine 79 isotope when irradiating with 1046.9 cm^–1 (9P20).