Visible-Light-Driven Synthesis of Phenanthridin-6(5H)-one and N-Substituted Carbazole Derivatives through Intramolecular C-H Arylation

A visible-light-driven approach towards phenanthridin-6(5H)-one and carbazole rings synthesis under transition-metal-free conditions is here reported. Phenanthridinones and carbazoles are synthesized through an intramolecular arylation of the corresponding N-(2-halobenzyl)-N-methylanilines or N-substituted-N-phenyl anilines using KO^tBu as base in dimethyl sulfoxide (DMSO) at room temperature (rt), employing blue light emitting diodes (LEDs) as the light source. The reaction proceeds through photo- and base-promoted homolytic aromatic substitution via photoinduced electron transfer mechanism and it exhibits good tolerance to different functional groups, resulting in good to very good yields (up to 86 %).     

Fully automated open access platform for rapid, combined serial evaporation and sample reformatting

This paper reports a novel evaporator and its integration with an automated sample handling system to create a high throughput evaporation platform. The Vaportec V-10 evaporator uses a high speed rotation motor ( approximately 6000 rpm) to spin the vial containing a sample, creating a thin film of solvent which can be readily evaporated by the application of heat to the vial, while the consequent centrifugal force prevents "bumping". An intelligent algorithm controls pressure and temperature for optimum solvent removal conditions and end of run detection, critical for automation. The system allows the option of evaporation directly from a sample source vial, or alternatively, integrated liquid handling facilities provide the capability of transferring samples portionwise from a (large) source vial or bottle to a (small) daughter container, enabling efficient sample reformatting, with minimum user intervention. The open access system makes significant advances over current vacuum centrifugal evaporators in terms of evaporation rate and ease of automation. The evaporator's main features, the integration of robotics to provide automation, and examples of evaporation rates of a wide range of solvents from a variety of containers are described.     

Palladium-catalyzed conjugate allylation reactions of alpha,beta-unsaturated N-acylpyrroles

Conjugate allylation reactions of alpha,beta-unsaturated N-acylpyrroles using allylboronic ester are catalyzed by a palladium complex that is ligated by a bidentate N-heterocyclic carbene. A variety of functional groups are tolerated, and substrates functionalized with electron-withdrawing groups react to afford the highest yields of products. Regioselectivity for 1,4-allylation over 1,2-allylation is demonstrated, and mechanistic experiments are consistent with formation of nucleophilic allylpalladium intermediates.     

The effect of different representations on Years 3 to 5 students’ ability to generalise

Over the past 3 years, in our Early Algebra Thinking project, we have been studying Years 3 to 5 students’ ability to generalise in a variety of situations, namely, compensation principles in computation, the balance principle in equivalence and equations, change and inverse change rules with function machines, and pattern rules with growing patterns. In these studies, we have attempted to involve a variety of representations and to build students’ abilities to switch between them (in line with the theories of Dreyfus in Advanced mathematical thinking. Kluwer, Dordtrecht, pp. 25–41, 1991, and Duval in Proceedings of the 21st conference of the North American chapter of the international group for the psychology of mathematics education, vol. 1, pp. 3–26, 1999). The studies have shown the negative effect of closure on generalisation in symbolic representations, the predominance of single variance generalisation over covariant generalisation in tabular representations, and the reduced ability to readily identify commonalities and relationships in enactive and iconic representations. This presentation will use a variety of studies to explore the interrelation between verbal and visual comprehension of context and generalisation. The studies showed in a variety of contexts the importance of understanding and communicating aspects of representational forms which allowed commonalities to be seen across or between representations.     

Air–water interfacial behavior of amphiphilic peptide analogs of synthetic chloride ion transporters

A family of heptapeptide-based chloride transporters (called synthetic anion transporters, SATs) were designed to insert into phospholipid membrane bilayers and form pores. Many of these compounds have proved to be chloride selective transporters. The transporters were designed to incorporate hydrophilic heptapeptides that could serves as headgroups and hydrocarbon tails that could serve as hydrophobic membrane anchors. Insertion of the SAT molecules into a bilayer requires approach to and insertion at the aqueous-membrane surface. The studies reported here were conducted to model and understand this process by studying SAT behavior at the air–water interface. A Langmuir trough was used to obtain surface pressure–area isotherm data. These data for amphiphilic SATs were augmented by Brewster angle microscopy (BAM), molecular modeling, and calculations of the hydrophobicity parameter log P. The analyses showed that the heptapeptide (hydrophilic) module of the SAT molecule rested on the water surface while the dialkyl (hydrophobic) tails oriented themselves in the air, perpendicular to the water surface. Brewster angle microscopy visually confirmed a high order of molecular organization. Results from these studies are consistent with the previously proposed mechanism of SAT membrane insertion and pore formation.     

Molecular dynamics investigation of the effects of a water surface on the aggregation of bent-core molecules

Molecular dynamics simulations are used to determine how the presence of a water surface affects the way that bent-core surfactant molecules interact with one another. The simulations are carried out for isolated pairs of bent-core molecules, and for pairs of bent-core molecules on a water surface. The results show that the water surface fundamentally alters the nature of the interaction between the bent-core molecules: a stable complex is formed when the two molecules are on the water surface, but not for an isolated pair of molecules. This difference occurs because the water surface constrains the internal structure and orientation of the molecules, which makes the packing of the molecules into a stable complex more thermodynamically favorable.     

Aminoethylglycine-functionalized Ru(bpy)3(2+) with pendant bipyridines self-assemble multimetallic complexes by copper and zinc coordination

Directed self-assembly using inorganic coordination chemistry is an attractive approach for making functional supramolecular structures. In this article, the synthesis and characterization of Ru(bpy) 3 (2+) compounds derivatized with aminoethylglycine (aeg) substituents containing pendant bipyridine (bpy) ligands is presented. The free bpy ligands in these complexes are available for metal chelation to form coordinative cross-links; addition of Cu (2+) or Zn (2+) assembles heterometallic structures containing two or three transition-metal complexes. Control over relative placement of metal complexes is accomplished using two strategies: two bipyridine-containing aeg strands tethered to Ru(bpy) 3 (2+) allow intramolecular coordination and result in a dimetallic hairpin motif. Ru(bpy) 3 (2+) modified with a single strand forms intermolecular cross-links forming the trimetallic complex. Each of these is characterized by a range of methods, and their photophysical properties are compared. These data, and comparison to an acetyl aeg- modified Ru(bpy) 3 (2+) complex, confirm that the metal ions cross-link bpy-containing aeg strands. Heterometallic complexes containing bound Cu (2+) cause a dramatic reduction in the Ru(bpy) 3 (2+) quantum yields and lifetimes. In contrast, the Ru(bpy) 3 (2+) hairpin with coordinated Zn (2+) has only a slight decrease in quantum yield but no change in lifetime, which could be a result of steric impacts on structure in the dimetallic species. Analogous effects are not observed in the trimetallic Ru-Zn-Ru structures in which this constraint is absent. Each of these heterometallic structures represents a facile and reconfigurable means to construct multimetallic structures by metal-coordination-based self-assembly of modular artificial peptide units.     

Hetero-bimetallic complexes involving vanadium(V) and rhenium(VII) centers, connected by unsupported mu-oxido bridge: synthesis, characterization, and redox study

Heterobimetallic complexes of a vanadium(V) and rhenium(VII) combination connected by a mu-oxido bridge [LVO(mu-O)ReO 3].H 2O [H 2L = N, N'-ethylene bis(salicylideneimine) (H 2salen) and its methoxy derivative] ( 1, 2) are reported. The compounds have been prepared by a single-pot synthesis in which the precursor [V (IV)OL] complexes are allowed to be oxidized aerially in the presence of added perrhenate. The oxidized [V (V)OL] (+) species accommodate the ReO 4 (-) anion in their vacant coordination site, trans to the terminal oxido group, providing the complexes 1 and 2. The later generates a binuclear oxovanadium(V) compound [H 2en][(TBC)VO(mu-TBC) 2OV(TBC)].5H 2O ( 3) when treated with tetrabromocatechol. Single crystal X-ray diffraction analysis and (1)H NMR spectroscopy have been used to establish their identities. In compound 2, the Re(1)-O(11)-V(1) bridge angle is barely linear [170.2(3) degrees ] with a Re...V separation of 3.9647(9) A. The redox behavior of 1 and 2 are quite interesting, each undergoing two reductions both in the positive potential range at E 1/2 = 0.59 (process I) and E 1/2 = 0.16 V (process II) versus Ag/AgCl reference (corresponding potentials are 0.59 and 0.18 V for 2). Process I has a single-electron stoichiometry involving the [VO(salen)] part of the complexes as established by combined coulometry-Electron Paramagnetic Resonance (EPR) experiments which provide an eight-line isotropic EPR pattern at room temperature ( = 1.967; = 87 x 10 (-4) cm (-1)), characteristic of an unpaired electron being coupled to a vanadium nuclear spin ( (51)V, I = 7/2). The almost linear V-O-Re bridge in 1 and 2 allows this unpaired electron to interact effectively with the neighboring Re nuclear spin, leading to familiar " two-line pattern" superhyperfine coupling ( A ( (185,187)Re) = 20.7 x 10 (-4) cm (-1)). Process II, on the other hand, is based on a Re(VII/VI) electron transfer as confirmed by differential pulse and normal pulse voltammetric experiments.     

An ab initio study of substituent effects on the excited states of purine derivatives

Several excited singlet electronic states of purine nucleobases and related derivatives have been calculated using high-level multireference perturbation theory methods. Purine derivatives with one or two amino or carbonyl groups substituted at positions C(2) and/or C(6) of the purine ring have been included in the study. The effect of the substituents on excited-state energies and wave functions is examined. Some trends have been observed, such as the fact that substitution at the C(2) position decreases the energy of the first pi --> pi* state considerably. Although basic qualitative features of the effects can be explained with the simple frontier molecular orbital theory, ab initio calculations are required to describe the effects quantitatively.     

Multiphoton control of the 1,3-cyclohexadiene ring-opening reaction in the presence of competing solvent reactions

Although physical chemistry has often concentrated on the observation and understanding of chemical systems, the defining characteristic of chemistry remains the direction and control of chemical reactivity. Optical control of molecular dynamics, and thus of chemical reactivity provides a path to use photon energy as a smart reagent in a chemical system. In this paper, we discuss recent research in this field in the context of our studies of the multiphoton optical control of the photo-initiated ring-opening reaction of 1,3-cyclohexadiene (CHD) to form 1,3,5- cis-hexatriene (Z-HT). Closed-loop feedback and learning algorithms are able to identify pulses that increase the desired target state by as much as a factor of two. Mechanisms for control are discussed through the influence of the intensity dependence, the nonlinear power spectrum, and the projection of the pulses onto low orders of polynomial phase. Control measurements in neat solvents demonstrate that competing solvent fragmentation reactions must also be considered. In particular, multiphoton excitation of cyclohexane alone is capable of producing hexatriene. Statistical analyses of data sets obtained in learning algorithm searches in neat cyclohexane and for CHD in hexane and cyclohexane highlight the importance of linear and quadratic chirp, while demonstrating that the control features are not so easily defined. Higher order phase components are also important. On the basis of these results the involvement of low-frequency ground-state vibrational modes is proposed. When the population is transferred to the excited state, momentum along the torsional coordinate may keep the wave packet localized as it moves toward the conical intersections controlling the yield of Z-HT.