Photochemical behaviour of propranolol in environmental waters: the hydroxylated photoproducts

The UV irradiation of propranolol, one of the beta-blockers currently used in cardiac medicine, was studied. During irradiation, the samples were analysed by LC/MS/MS, using a Waters Symmetry C₁₈ (3.5?µm 150?×?2.1?mm) column. The main photoproducts were identified from mono-, di- and tri-hydroxylation of the propranolol naphthalenic skeleton. Hydroxyl group positions were predicted by means of theoretical calculations. Partial charge calculations of the propranolol atoms predicted the formation of four mono-hydroxylated compounds, two of them being the most probable. From these two compounds, three di-hydroxylated compounds were predicted. Then the calculations from the two most probable di-hydroxylated compounds were used to propose three tri-hydroxylated propranolol compounds. It was found that the same hydroxylated photoproducts are formed in pure water and in treatment plant waste water.     

Photocontrol of Polar Aromatic Interactions by a Bis‐Hemithioindigo Based Helical Receptor

The first example of a bis‐hemithioindigo (bis‐HTI)‐based molecular receptor was realized. Its folding and selective binding affinity for aromatic guest molecules can be precisely controlled by visible light and heat. The thermodynamically stable state of the bis‐HTI is the s‐shaped planar Z,Z‐configuration. After irradiation with 420 nm light only the E,Z‐configuration is formed in a highly selective photoisomerization. The E,Z‐isomer adopts a helical conformation because of the implementation of repulsive steric interactions. The E,Z‐configured helix is able to recognize electron‐poor aromatic guests exclusively through polar aromatic interactions and also distinguishes between regioisomers. After heating, the Z,Z‐configuration is completely restored and the aromatic guest molecule is efficiently released.     

Structure of Supramers Formed by the Amphiphile Biotin-CMG-DOPE

The synthetic function-spacer-lipid (FSL) amphiphile biotin-CMG-DOPE is widely used for delicate ligation of living cells with biotin residues under physiological conditions. Since this molecule has an “apolar-polar-hydrophobic” gemini structure, the supramolecular organization is expected to differ significantly from the classical micelle. Its organization is investigated with experimental methods and molecular dynamics simulations (MDS). Although the linear length of a single biotin-CMG-DOPE molecule is 9.5 nm, the size of the dominant supramer globule is only 14.6 nm. Investigations found that while the DOPE tails form a hydrophobic core, the polar CMG spacer folds back upon itself and predominantly places the biotin reside inside the globule or planar layer. MDS demonstrates that <10 % of biotin residues on the highly water dispersible globules and only 1 % of biotin residues in layer coatings are in an linear conformation and exposing biotin into the aqueous medium. This explains why in biotin-CMG-DOPE apolar biotin residues both in water dispersible globules and coatings on solid surfaces are still capable of interacting with streptavidin.     

Dual wavelength asymmetric photochemical synthesis with circularly polarized light

Asymmetric photochemical synthesis using circularly polarized (CP) light is theoretically attractive as a means of absolute asymmetric synthesis and postulated as an explanation for homochirality on Earth. Using an asymmetric photochemical synthesis of a dihydrohelicene as an example, we demonstrate the principle that two wavelengths of CP light can be used to control separate reactions. In doing so, a photostationary state (PSS) is set up in such a way that the enantiomeric induction intrinsic to each step can combine additively, significantly increasing the asymmetric induction possible in these reactions. Moreover, we show that the effects of this dual wavelength approach can be accurately determined by kinetic modelling of the PSS. Finally, by coupling a PSS to a thermal reaction to trap the photoproduct, we demonstrate that higher enantioselectivity can be achieved than that obtainable with single wavelength irradiation, without compromising the yield of the final product.     

Elasticity solutions for constant and linearly varying loads applied to a rectangular surface patch on the elastic half-space

The solution of the point load problem in the half-space is well known in the theory of elasticity. Using direct integration, the point solution can theoretically be used to develop the solution for loading various contact areas with a variety of loading profiles. Unfortunately, anything more complicated than constant pressure loading has previously required numerical integration, and hence, no closed form solution was obtainable. Partial solutions, i.e. solutions valid only on the surface of the half-space have also been available. This paper presents the methodology to generate complete solutions to the integrals for constant and linearly varying loads applied in both the normal and tangential directions everywhere in the half-space.