Quantum chemical modeling for 157 nm photolithography

In its continuing quest for smaller length scales, the electronics industry plans to introduce 157 nm as the next lithographic wavelength. Accordingly, there is a pressing need to develop photoresists that are more transparent, and pellicles that are both more transparent and more durable. With the advent and popularization of time-dependent density functional theory (TD-DFT), we now have a practical quantum chemical method for calculating excitation energies and transition moments in the vacuum ultraviolet (VUV) which can greatly assist in the scouting of highly transparent materials. We have performed TD-DFT calculations for a broad variety of fluorinated molecules and we will report calculated VUV photoabsorption spectra for a large family of model fluorohexanes. These calculations, which span a range from 1-fluorohexane to CH₃CF₂CF₂CF₂CF₂CH₃, illustrate some of the principles one may use to design low absorption polymeric materials.     

Aerobic alcohol oxidation catalyzed by a new, oxygen-bridged heterometallic compound [PPh4][Ru(N)Me2(μ2-O)2Pd((−)-sparteine)]

The reaction between the new hydroxy compound [PPh₄][Ru(N)(OH)₂Me₂] and Pd(OSiMe₃)₂((−)-sparteine) produces (Me₃Si)₂O, H₂O and a new heterobimetallic compound [PPh₄][Ru(N)Me₂(μ₂-O)₂Pd((−)-sparteine)] in good yield. The Ru/Pd bimetallic compound catalyzes the oxidation of aryl and allyl alcohols to the corresponding carbonyl compound in air and the rearrangement of allylic alcohols unsaturated aldehydes. It also oxidizes PPh₃ to O-PPh₃ under O₂.     

The equilibrium properties and folding kinetics of an all-atom Go model of the Trp-cage

The ultrafast-folding 20-residue Trp-cage protein is quickly becoming a new benchmark for molecular dynamics studies. Already several all-atom simulations have probed its equilibrium and kinetic properties. In this work an all-atom Go model is used to accurately represent the side-chain packing and native atomic contacts of the Trp-cage. The model reproduces the hallmark thermodynamics cooperativity of small proteins. Folding simulations observe that in the fast-folding dominant pathway, partial alpha-helical structure forms before hydrophobic core collapse. In the slow-folding secondary pathway, partial core collapse occurs before helical structure. The slow-folding rate of the secondary pathway is attributed to the loss of side-chain rotational freedom, due to the early core collapse, which impedes the helix formation. A major finding is the observation of a low-temperature kinetic intermediate stabilized by a salt bridge between residues Asp-9 and Arg-16. Similar observations [R. Zhou, Proc. Natl. Acad. Sci. U.S.A. 100, 13280 (2003)] were reported in a recent study using an all-atom model of the Trp-cage in explicit water, in which the salt-bridge stabilized intermediate was hypothesized to be the origin of the ultrafast-folding mechanism. A theoretical mutation that eliminates the Asp-9-Arg-16 salt bridge, but leaves the residues intact, is performed. Folding simulations of the mutant Trp-cage observe a two-state free-energy landscape with no kinetic intermediate and a significant decrease in the folding rate, in support of the hypothesis.     

Synthesis of some dibenzodiazepinone derivatives as potent and m2-selective antimuscarinic compounds

Two series of 5-[[4-[4-(dialkylamino)butyl]-l-cyclohexyl]acetyl], and 5-[(dialkylamino)acyl]-10,11-dihydro-5H- dibenzo[b,e][1,4]diazepin-11-ones were synthesized as potential m2-selective ligands 1,2. Their affinity and selectivity for the muscarinic cholinergic receptor m-AChR subtypes were determined. Replacing a nitrogen with CH in the piperidine ring of 5-[[4-[4-(dialkylamino)butyl]-l-piperidinyl]acetyl]-10,11-dihydro-5H-dibenzo-[b,e][1,4]diazepin-11-ones 3 significantly altered the affinity and selectivity to the muscarinic receptor subtypes.     

Propagating transverse electric and transverse magnetic modes in liquid crystal-clad planar waveguides

ABSTRACT

In a planar dielectric waveguide, weak confinement of a propagating mode in a high index core leads to a measurable evanescent interaction with the cladding. In this work, we study the effect of a reorientable anisotropic cladding on the behaviour of Transverse Electric (TE) and Transverse Magnetic (TM) mode polarisations using a liquid crystal (LC)-clad waveguide architecture. The polarised evanescent field of a guided mode interacts with a voltage-tunable birefringent LC cladding to deflect an out-coupled beam. Experimental measurements are coupled with a theoretical framework and show good consistency with simulation results. We isolate the effect of mode confinement by changing the thickness of the high index core. Interactions between the LC index ellipsoid and the mode polarisation are probed by changing the initial alignment of the LC. Finally, we examine the difference in deflection between TE and TM modes, which incorporates both a change in mode confinement and a difference in LC index components.     

Cyano-bridged hexanuclear Fe4M2 (M = Ni, Co, Mn) clusters: spin-canted antiferromagnetic ordering of Fe4Ni2 cluster

Heterobimetallic hexanuclear cyano-bridged complexes, [{Fe(Tp)(CN)3}4{M(MeCN)(H2O)2}(2)].10H2O.2MeCN [M = Ni (1), Co (2), Mn (3); Tp = hydrotris(1-pyrazolyl)borate], have been synthesized in H2O-MeCN solution. Complexes 1-3 are isostructural and hexanuclear with [{Fe(Tp)(CN)3}4{M(MeCN)(H2O)2}2] units linked by hydrogen bonds to form a 2D-structure in the solid state. Complex 1 is a canted antiferromagnet that undergoes a field-induced spin-flop-like transition at approximately 1 T and 2 K. At 4.45 K 1 has a transition to paramagnetic state of noninteracting S = 4 magnetic clusters. However, 2 and 3 show antiferromagnetic intracluster coupling. Facile loss of solvent from 2 alters the local symmetry resulting in changing the intracluster interaction from antiferro- to ferromagnetic.     

Highly diastereoselective conjugate additions of monoorganocopper reagents to chiral imides

Stereoselective conjugate additions to chiral N-enoyl amides employing various monoorganocuprate reagents, Li[RCuI], are described. The presence of TMSI in the addition of Li[RCuI] in THF provided the highest stereoselectivities. Reversed major diastereomeric ratios were obtained employing Li[RCuI] in ether or conventional copper-promoted Grignard reagents. The results presented support the favored anti-s-cis conformation of the substrates using Li[RCuI]/TMSI in THF, while the copper-promoted Grignard reagents or the Li[RCuI] reagents in ether favor the opposite syn-s-cis conformation. Influence of lithium ions on the stereoselective conjugate addition of the monoorganocuprate reagent, Li[BuCuI], has been investigated and two different mechanistic pathways are presented. The results show that iodotrimethylsilane (TMSI) is crucial for the asymmetric conjugate addition of the copper reagent, but only in THF or when 12-crown-4 is used. The reaction is thought not to involve any halosilane in any critical steps in the organocopper mechanisms conducted in ether. The (CuI)₄(SMe₂)₃ complex precursor plays an instrumental role for the conjugate addition using monoorganocopper reagents.     

Fast atom bombardment mass spectrometry; a promising tool for structural studies

Fast atom bombardment mass spectrometry (FABMS) is a powerful new structural tool. Ionization is effected by bombarding a glycerol matrix with neon or argon atoms of 5–10 KeV energy. Positive and negative secondary ions are sputtered from the surface and can be detected for inorganic ion clusters to mass 25 800 and biologically important compounds to mass 5 700. FABMS is especially valuable in determining the sequence of amino acids in polypeptides.     

Thyonosides A and B, two new saponins isolated from the holothurian Thyone aurea

The structures of two saponins, thyonosides A and B, isolated from the holothurian Thyone aurea collected in Namibia, were elucidated by 1D and 2D NMR (¹H, ¹³C, ¹H-¹H COSY, ¹H-¹H J-resolved, TOCSY, HMQC, HMBC and NOESY). The two compounds have the same aglycon but different oligosaccharidic chains. Thyonoside A has a 3-O-methyl-β-d-xylopyranosyl-(1→3)-6-O-sodium sulphate-β-d-glucopyranosyl-(1→4)-β-d-quinovopyranosyl-(1→2)-4-O-sodium sulphate-β-d-xylopyranosyl chain, and thyonoside B a 3-O-methyl-β-d-xylopyranosyl-(1→4)-β-d-xylopyranosyl-(1→4)-β-d-quinovopyranosyl-(1→2)-4-O-sodium sulphate-β-d-xylopyranosyl chain. The holostane-type aglycon features an endocyclic double bond at position 7-8, a double bond at position 25-26 and a β-acetoxy group at C16.