ABSTRACT
Aerosols of submicron polystyrene particles were oxidized by either vacuum-ultraviolet (VUV) irradiation in the presence of molecular oxygen (O(2)) and/or by ozone (O(3)). Different degrees of oxidation and oxidative degradation were reached by VUV-photolysis depending on radiant energy, O(2) and H(2)O concentrations in the bulk gas mixture as well as on particle diameter. The same functionalization was obtained by exposing the aerosol to O(3), however, oxidation, in particular oxidative degradation, was less efficient. The evolution of hydroxyl and carbonyl functions introduced was quantified by ATR-FTIR spectroscopy of filtered particles, and oxidative degradation of the polymer particles was confirmed by determining size and number of aerosol particles before and after oxidation. Efficiency analyses are based on the results of an O(3) actinometry and on an evaluation of the rate of absorbed photons by the aerosol particles in function of their size.
Subject(s)
Aerosols/chemistry , Ozone/chemistry , Polystyrenes/chemistry , Ultraviolet Rays , Oxidation-Reduction , Oxygen/chemistry , Particle Size , Spectroscopy, Fourier Transform Infrared , VacuumABSTRACT
We have revisited the photochromic spiro-dihydroindolizine/betaine (DHI/B) system applying state-of-the-art density functional theory (DFT) calculations in combination with stationary and time-resolved absorption measurements. DHI/B-systems are becoming increasingly important as potential molecular machines, molecular switches, and photoswitchable electron-acceptors. The knowledge of the exact mechanisms of ring opening and closure, as well as of the geometries of DHI and betaine can provide critical information that will enable the design of better molecular machines and optical switches. The first surprising result concerns the electronic structure of the betaines, which is quite different than commonly assumed. The photochemical ring opening of DHI's to betaines is a conrotatory 1,5 electrocyclic reaction, whereas the thermal ring-closing occurs in the disrotatory mode. According to our results, the electrocyclic back reaction of the betaines to the DHI is NOT rate determining, as previously thought, but instead the kinetics are dictated by the cis-trans-isomerization of the betaine.
ABSTRACT
Nanostructures with long-term stability at the surface of gold electrodes are generated by reconstituting the porin MspA from Mycobacterium smegmatis into a specially designed monolayer of long-chain lipid surfactant on gold. Tailored surface coverage of gold electrodes with long-chain surfactants is achieved by electrochemically assisted deposition of organic thiosulfates (Bunte salts). The subsequent reconstitution of the octameric-pore MspA is guided by its extraordinary self-assembling properties. Importantly, electrochemical reduction of copper(II) yields copper nanoparticles within the MspA nanopores. Electrochemical impedance spectroscopy, reflection electron microscopy, and atomic force microscopy (AFM) show that: 1) the MspA pores within the self-assembled monolayer (SAM) are monodisperse and electrochemically active, 2) MspA reconstitutes in SAMs and with a 10-nm thickness, 3) AFM is a suitable method to detect pores within SAMs, and 4) the electrochemical reduction of Cu2+ to Cu0 under overpotential conditions starts within the MspA pores.
Subject(s)
Mycobacterium smegmatis/chemistry , Nanostructures/chemistry , Porins/chemistry , Cell Membrane , Copper/chemistry , Electrochemistry , Electrodes , Electrons , Gold/chemistry , Image Processing, Computer-Assisted , Microscopy, Atomic Force , Models, Molecular , Molecular Mimicry , Mutant Proteins , Porins/ultrastructure , Porosity , Surface-Active Agents , Thiosulfates/chemistryABSTRACT
New molecules incorporating a uracil nucleic base and a dihydroindolizine (DHI) unit linked via spacer arms, i.e., uracil-spyrodihydroindolizine (4), were synthesised as models for light sensitive systems for nucleic acid labelling. The uracil-DHI (4) undergoes easy photocoloration to the uracil-betaine (5) generating the UV-detectable species. Preliminary results show rather weak binding of uracil-DHI (4) to calf thymus-DNA.
