Synthesis and Biological Activity of 2′-Fluoro-D-arabinofuranosylpyrazolo[3,4-d]pyrimidine Nucleosides

Coupling of 2-fluoro-3,5-di-O-benzoyl-α-D -arabinofuranosyl bromide with 4-methoxypyrazolo[3,4-d]pyrimidine gave an α-D /β-D mixture of N¹- and N²-coupled products. All the anomers were separated and deblocked to yield the corresponding nucleosides. The β-D -anomer 7 was converted to the 4-amino derivative 11 , which was deaminated by adenosine deaminase to give the 4-oxo compound 12 . Compound 7 showed significant activity against human cytomegalovirus and hepatitis B virus, and compound 11 showed activity against human herpes virus 8. All the compounds were noncytotoxic in several human tumor-cell lines in culture.     

X‐ray photoelectron spectroscopy process optimization for characterization of trace contamination elements for extreme ultraviolet resist outgassing study

X‐ray photoelectron spectroscopy (XPS) is used for elemental identification and quantification in a number of fields, and the optimization of XPS performance can help in making better use of the limited XPS tool availability. In the field of extreme ultraviolet (EUV) lithography, one of the requirements is having a clean vacuum environment to minimize contamination of the EUV optics. EUV resist outgassing is viewed as one of the main issues that could affect the vacuum environment. There is a program underway to measure the relative contamination rates from different resists following the ASML (provider of lithography systems) approved protocols for witness plate testing. One of the key steps is the XPS measurement of residue on the optics after cleaning. The role of XPS in quantification of species that adhere to the ruthenium‐coated silicon witness plate sample is discussed. The various XPS tool parameters like the pass energy and source setting were optimized for our application of witness plate analysis. The statistics of our XPS tool were studied, and combined with the fundamental XPS equations, a simple mathematical model was developed to optimize the number of scans for the various elements of interest in our witness plate study. Using the optimized number of scans, the acquisition time to measure the contaminant elements to a precision better than 0.1 at.% was minimized. The model devised in the paper can be adapted to other XPS measurements requiring different levels of precision. Copyright © 2013 John Wiley & Sons, Ltd.     

Emissive and Cell‐Permeable 3‐Pyridyl‐ and 3‐Pyrazolyl‐4‐azaxanthone Lanthanide Complexes and Their Behaviour in cellulo

A series of seven emissive europium(III) and terbium(III) complexes was prepared, incorporating a 3‐pyridyl‐4‐azaxanthone or 3‐pyrazolyl‐4‐azaxanthone sensitising moiety within a polydentate macrocyclic ligand. High overall emission quantum yields in aqueous media are attenuated in the presence of protein or certain oxy anions due to displacement of the N,N′‐chelated sensitiser. Nevertheless, these complexes are taken into cells and tend to localise over the first few hours in mitochondria before being trafficked to endosomal compartments. Cell uptake studies, in the presence of competitive inhibitors or promoters of well‐defined uptake pathways, reveal a common uptake mechanism involving macropinocytosis.     

Representations of Some Hopf Algebras Associated to the Symmetric Group S n

We prove that all irreducible representations of the bismash product have Frobenius–Schur indicator +1, where k is an algebraically closed field of characteristic 0. If n = p, a prime, we find all indicators for . We also study more general bismash products. Both authors were supported by NSF grants DMS-07-01291 and DMS-04-01399.     

A restricted-open-shell complete-basis-set model chemistry

A restricted-open-shell model chemistry based on the complete basis set-quadratic Becke3 (CBS-QB3) model is formulated and denoted ROCBS-QB3. As the name implies, this method uses spin-restricted wave functions, both for the direct calculations of the various components of the electronic energy and for extrapolating the correlation energy to the complete-basis-set limit. These modifications eliminate the need for empirical corrections that are incorporated in standard CBS-QB3 to compensate for spin contamination when spin-unrestricted wave functions are used. We employ an initial test set of 19 severely spin-contaminated species including doublet radicals and both singlet and triplet biradicals. The mean absolute deviation (MAD) from experiment for the new ROCBS-QB3 model (3.6+/-1.5 kJ mol(-1)) is slightly smaller than that of the standard unrestricted CBS-QB3 version (4.8+/-1.5 kJ mol(-1)) and substantially smaller than the MAD for the unrestricted CBS-QB3 before inclusion of the spin correction (16.1+/-1.5 kJ mol(-1)). However, when applied to calculate the heats of formation at 298 K for the moderately spin-contaminated radicals in the G2/97 test set, ROCBS-QB3 does not perform quite as well as the standard unrestricted CBS-QB3, with a MAD from experiment of 3.8+/-1.6 kJ mol(-1) (compared with 2.9+/-1.6 kJ mol(-1) for standard CBS-QB3). ROCBS-QB3 performs marginally better than standard CBS-QB3 for the G2/97 set of ionization energies with a MAD of 4.1+/-0.1 kJ mol(-1) (compared with 4.4+/-0.1 kJ mol(-1)) and electron affinities with a MAD of 3.9+/-0.2 kJ mol(-1) (compared with 4.3+/-0.2 kJ mol(-1)), but the differences in MAD values are comparable to the experimental uncertainties. Our overall conclusion is that ROCBS-QB3 eliminates the spin correction in standard CBS-QB3 with no loss in accuracy.     

Dynamics of fluorescence depolarisation in star-shaped oligofluorene-truxene molecules

Star-shaped molecules are of growing interest as organic optoelectronic materials. Here a detailed study of their photophysics using fluorescence depolarisation is reported. Fluorescence depolarisation dynamics are studied in branched oligofluorene-truxene molecules with a truxene core and well-defined three-fold symmetry, and are compared with linear fluorene oligomers. An initial anisotropy value of 0.4 is observed which shows a two-exponential decay with time constants of 500 fs and 3-8 ps in addition to a long-lived component. The femtosecond component is attributed to exciton localisation on one branch of the molecule and its amplitude reduces when the excitation is tuned to the low energy tail of the absorption spectrum. The picosecond component shows a weak dependence on the excitation wavelength and is similar to the calculated rate of the resonant energy transfer of the localised exciton between the branches. These assignments are supported by density-functional theory calculations which show a disorder-induced splitting of the two degenerate excited states. Exciton localisation is much slower than previously reported in other branched molecules which suggests that efficient light-harvesting systems can be designed using oligofluorenes and truxenes as building blocks.     

Enantioselective conversion of primary alcohols to α-exo-methylene γ-butyrolactones via iridium-catalyzed C-C bond-forming transfer hydrogenation: 2-(alkoxycarbonyl)allylation

Upon exposure of acrylic ester 1 to alcohols 2a-i in the presence of a cyclometalated iridium catalyst modified by (-)-TMBTP, catalytic C-C coupling occurs, providing enantiomerically enriched 5-substituted α-exo-methylene γ-butyrolactones 3a-i. Bromination of the methylene butyrolactone products followed by zinc-mediated reductive aldehyde addition provides the disubstituted α-exo-methylene γ-butyrolactones 6a and 6b with good to excellent levels of diastereoselectivity.     

Jump Conditions for Hyperbolic Systems of Forced Conservation Laws with an Application to Gravity Currents

Weak solutions to systems of nonlinear hyperbolic conservation laws admit discontinuities that result from either an initial value or as part of the temporally developing solution itself. The propagation of such shocks or jumps is affected by forcing terms for the nonlinear system in a way that has not been investigated fully in standard references. Jump conditions for systems of conservation laws with discontinuous forcing terms are derived herein, following the method used to derive the Rankine–Hugoniot jump conditions, and the generalized results are illustrated for the one-dimensional inviscid Burger's equation with discontinuous forcing. The main application of this type of jump condition, and the primary motivation for its study, is its application to a shallow-water model of gravity currents previously described by the authors. Specifically, a new result relation between the front and height at a gravity current front is obtained by using the existing model. Front speeds for gravity currents resulting from instantaneous release are calculated numerically and used to determine the suitability of the jump conditions, which are then compared with existing theoretical expressions and experimental observations. New numerical results are portrayed for the gravity current model, suggesting that the standard method of modeling shallow-water gravity currents with a simple Froude number front condition may tend to suppress some of the finer details of the flow resolved by the numerical scheme used by the authors.     

Derivatives of 2,4-diamino-6-methylpteridine

Eighteen derivatives of 2,4-diamino-6-methylpteridine related to methotrexate and aminopterin have been prepared from 6-(bromomethyl)-2,4-pteridinediamine by nucleophilic displacement reactions. None of these compounds showed any antileukemic acitivity.     

Fractional clique decompositions of dense graphs

For each , we show that any graph G with minimum degree at least has a fractional K_r‐decomposition. This improves the best previous bounds on the minimum degree required to guarantee a fractional K_r‐decomposition given by Dukes (for small r) and Barber, Kühn, Lo, Montgomery, and Osthus (for large r), giving the first bound that is tight up to the constant multiple of r (seen, for example, by considering Turán graphs). In combination with work by Glock, Kühn, Lo, Montgomery, and Osthus, this shows that, for any graph F with chromatic number , and any , any sufficiently large graph G with minimum degree at least has, subject to some further simple necessary divisibility conditions, an (exact) F‐decomposition.