Synthetic and Structural Studies of Cyclophosphathiazenes and their Adducts with Lewis Acids

Abstract

The reactions of (Me₃SiNR)PPh₂ (NSiMe₃) (R=H, SiMe₃) with (NSCl)₃ or S_xCl₂ (x=1, 2) provide improved preparative routes to mixed phosphazene-thia-zene ring systems, e.g. (Ph₂PN) (SN)₂, 1,3- and 1,5-(Ph₂PN)₂(SN)₂. The interaction of these heterocycles with protonic and Lewis acids, e.g. HBF₄, BCl₃, MeSO₃CF₃, has been investigated in order to determine the site of attack and the effect of adduct formation on the molecular and electronic structures of these ring systems. These reactions have been monitored by UV-visible and ³¹P NMR spectroscopies and the structures of crystalline adducts have been determined by X-ray crystallography. For example, the interaction of 1,3-(Ph₂PN)₂(SN)₂ with MeSO₃CF₃ gives a product in which the methyl group is attached to a nitrogen atom between phosphorus and sulfur. The resulting structural distortion in this and related adducts will be analyzed in the context of the electronic structures of mixed phosphazene-thiazene systems and their adducts with Lewis acids.     

Structural studies of laterally attached liquid crystalline polymers

Abstract

Structural studies of a series of laterally attached side chain liquid crystalline polysiloxanes have been made by X-ray diffraction. All but one exhibit a nematic phase with S_C-like short range ordering. The diffraction has been interpreted in terms of a model in which the mesogenic units form a ‘jacket’ around the polymer backbone. The backbone conformation has been studied by small angle X-ray scattering from oriented samples of mesomorphic solutions and by infrared dichroism measurements on oriented samples of the polymers. In both cases the results were consistent with the mesogens being oriented parallel to the backbone which is consistent with the ‘mesogen jacket’ model.     

Strong supramolecular-based magnetic exchange in pi-stacked radicals. Structure and magnetism of a hydrogen-bonded verdazyl radical:hydroquinone molecular solid.

The X-ray crystal structure and magnetic properties of a molecular crystal consisting of 1,5-dimethyl-3-(2-pyridyl)-6-oxoverdazyl radical and hydroquinone (pyvd:hq) are presented. The structure contains a two-dimensional network of hydrogen bonds involving the hydroquinones and the pyridine ring of the pyvd radical. The radicals adopt an unusual head-over-tail (antiparallel) pi-stacked array perpendicular to the hydrogen-bonded planes. The variable-temperature magnetic susceptibility data can be modeled using a one-dimensional antiferromagnetic chain model, with J = -58 cm(-1). The strength of the magnetic coupling is very unusual because there are no close intermolecular radical-radical contacts to provide conventional pathways for magnetic interactions. A pathway for coupling is proposed involving the mediation of magnetic exchange interactions between radical centers by the pyridine rings. Density functional calculations on the pyvd radical, as well as aggregates thereof based on the X-ray structure, have been employed in attempts to understand the possible mechanisms by which the strong magnetic interactions are achieved.     

The Role of Early-Career Chemists in European Policy-Making

Global societal challenges emphasize the importance of collaboration between scientists and policy-makers, while the participation of a diverse group of professionals, including early-career scientists, is critical towards a sustainable future. The European Young Chemists’ Network (EYCN) has been actively working with the European Chemical Society (EuChemS) to create a platform for early-career chemists in policy advice. This article comments on the possible roles of scientists in policy-making and provides an overview of relevant initiatives and platforms at the European level that could facilitate involvement. Opportunities for participation in policy advice from the perspective of early-career chemists are discussed and examples of impact are provided, hoping to stimulate further discussions and engagement in policy-making.     

Investigating the spectrum of biological activity of ring-substituted salicylanilides and carbamoylphenylcarbamates

In this study, a series of twelve ring-substituted salicylanilides and carbamoylphenylcarbamates were prepared and characterized. The compounds were analyzed using RP-HPLC to determine lipophilicity. They were tested for their activity related to the inhibition of photosynthetic electron transport (PET) in spinach (Spinacia oleracea L.) chloroplasts. Moreover, their site of action in the photosynthetic apparatus was determined. Primary in vitro screening of the synthesized compounds was also performed against mycobacterial, bacterial and fungal strains. Several compounds showed biological activity comparable with or higher than the standards 3-(3,4-dichlorophenyl)-1,1-dimethylurea, isoniazid, penicillin G, ciprofloxacin or fluconazole. The most active compounds showed minimal anti-proliferative activity against human cells in culture, indicating they would have low cytotoxicity. For all compounds, the relationships between lipophilicity and the chemical structure are discussed.     

Compact, high-pulse-energy, picosecond optical parametric oscillator

We report a high-energy optical parametric oscillator (OPO) synchronously pumped by a 7.19 MHz, Yb:fiber-amplified, picosecond, gain-switched laser diode. The 42-m-long ring cavity maintains a compact design through the use of an intracavity optical fiber. The periodically poled MgO-doped LiNbO(3) OPO provides output pulse energies as high as 0.49 μJ at 1.5 μm (signal) and 0.19 μJ at 3.6 μm (idler). Tunability from 1.5 to 1.7 μm and from 2.9 to 3.6 μm is demonstrated, and typical M(2) values of 1.5 × 1.3 and 2.8 × 1.9 are measured for the signal and idler, respectively, at high power.     

Lattice-valued fuzzy interior operators

A category of lattice-valued fuzzy interior operator spaces is defined and studied. Axioms are given in order for this category to be isomorphic to the category whose objects consist of all the stratified, lattice-valued, pretopological convergence spaces.     

Palladium-catalyzed chemo- and enantioselective oxidation of allylic esters and carbonates

The palladium-catalyzed oxidation of allylic esters and carbonates using a novel potassium nitronate has been developed. This method is highly chemoselective, leaving other esters, alcohols, thioethers, and amines undisturbed. The oxidation can be operated in two modes: an achiral mode, using either PPh3 or rac-2 as ligand, or a chiral and highly enantioselective mode, using 2 as ligand. The oxidative enantioselective desymmetrization of meso bis-esters provides a significantly shorter method to arrive at commonly used synthetic intermediates compared to other strategies. Highly efficient kinetic resolution is also possible using this methodology.     

Formation of hydrogen-bridged cytosine dimers on Cu(110)

Cytosine was adsorbed onto a Cu(110) surface under UHV conditions. Annealing to 370 K resulted in the formation of a (6 x 6)gg low energy electron diffraction (LEED) pattern, even at submonolayer coverages. Examination of this structure with scanning tunneling microscopy (STM) revealed islands of zigzag chains at low coverages and large ordered domains at monolayer saturation. Further annealing to 480 K initiated a phase transition to a (6 x 2)gg structure observed both by LEED and STM. High resolution electron energy loss spectroscopy spectra for both overlayer structures exhibited mainly in-plane modes suggesting upright/tilted species on the surface. Based on the experimental data and supported by density functional theory calculations, a model is proposed for the (6 x 2)gg structure, which involves the formation of deprotonated hydrogen bridge-bonded cytosine dimers, adsorbed through the oxygen atoms.     

Fluorogenic phospholipid substrate to detect lysophospholipase D/autotaxin activity

[reaction: see text] Lysophospholipase D (lysoPLD), also known as autotaxin (ATX), is an important source of the potent mitogen lysophosphatidic acid (LPA). Two fluorogenic substrate analogues for lysoPLD were synthesized in nine steps from (S)-PMB-glycerol. The substrates (FS-2 and FS-3) show significant increases in fluorescence when treated with recombinant ATX and have potential applications in screening for this emerging drug target.