Experimental and Theoretical Investigations in Solid Phase<br /> Reaction Kinetics and Noncovalent Interactions in Water

Factors affecting reaction rates in polystyrene beads used in solid phase organic synthesis have been studied. The role of diffusion and reagent partitioning has been examined theoretically and experimentally. Both of these factors have been found to influence the reaction kinetics of common solid phase organic synthesis reactions. A mathematical model to analyze a simple bimolecular reaction inside a bead has been developed and successfully applied to the experimental data to obtain quantitative information on the influence of diffusion and reagent partitioning on the reaction rates. The effects of diffusion generally increase with the size and decreased swelling of the beads. Under many common reaction conditions, however, these effects may not be very significant. General guidelines to identify these conditions have been developed. A water-soluble torsion balance to study noncovalent interactions in aqueous media has been synthesized. The folding energies of new balances were found to be higher in water than in organic solvents. This increase can be partially attributed to hydrophobic forces. Aggregation and micelle formation were found to increase folding in water, indicating differences between microscopic and mesoscopic hydrophobic effects. The experimental data have been analyzed in the context of the Lum, Chandler and Weeks theory of hydrophobicity and evidences in its favor have been found. The hydrophobic response of a fluoromethyl group was found to be similar to a methyl group in two complementary torsion balances.<br /

Cortisol-induced immune suppression by a blockade of lymphocyte egress in traumatic brain injury

Background: Acute traumatic brain injury (TBI) represents one of major causes of mortality and disability in the USA. Neuroinflammation has been regarded both beneficial and detrimental, probably in a time-dependent fashion. Methods: To address a role for neuroinflammation in brain injury, C57BL/6 mice were subjected to a closed head mild TBI (mTBI) by a standard controlled cortical impact, along with or without treatment of sphingosine 1-phosphate (S1P) or rolipram, after which the brain tissue of the impact site was evaluated for cell morphology via histology, inflammation by qRT-PCR and T cell staining, and cell death with Caspase-3 and TUNEL staining. Circulating lymphocytes were quantified by flow cytometry, and plasma hydrocortisone was analyzed by LC-MS/MS. To investigate the mechanism whereby cortisol lowered the number of peripheral T cells, T cell egress was tracked in lymph nodes by intravital confocal microscopy after hydrocortisone administration. Results: We detected a decreased number of circulating lymphocytes, in particular, T cells soon after mTBI, which was inversely correlated with a transient and robust increase of plasma cortisol. The transient lymphocytopenia might be caused by cortisol in part via a blockade of lymphocyte egress as demonstrated by the ability of cortisol to inhibit T cell egress from the secondary lymphoid tissues. Moreover, exogenous hydrocortisone severely suppressed periphery lymphocytes in uninjured mice, whereas administering an egress-promoting agent S1P normalized circulating T cells in mTBI mice and increased T cells in the injured brain. Likewise, rolipram, a cAMP phosphodiesterase inhibitor, was also able to elevate cAMP levels in T cells in the presence of hydrocortisone in vitro and abrogate the action of cortisol in mTBI mice. The investigation demonstrated that the number of circulating T cells in the early phase of TBI was positively correlated with T cell infiltration and inflammatory responses as well as cell death at the cerebral cortex and hippocampus beneath the impact site. Conclusions: Decreases in intracellular cAMP might be part of the mechanism behind cortisol-mediated blockade of T cell egress. The study argues strongly for a protective role of cortisol-induced immune suppression in the early stage of TBI

Two-photon excited photoconversion of cyanine-based dyes

The advent of phototransformable fluorescent proteins has led to significant advances in optical imaging, including the unambiguous tracking of cells over large spatiotemporal scales. However, these proteins typically require activating light in the UV-blue spectrum, which limits their in vivo applicability due to poor light penetration and associated phototoxicity on cells and tissue. We report that cyanine-based, organic dyes can be efficiently photoconverted by nonlinear excitation at the near infrared (NIR) window. Photoconversion likely involves singlet-oxygen mediated photochemical cleavage, yielding blue-shifted fluorescent products. Using SYTO62, a biocompatible and cell-permeable dye, we demonstrate photoconversion in a variety of cell lines, including depth-resolved labeling of cells in 3D culture. Two-photon photoconversion of cyanine-based dyes offer several advantages over existing photoconvertible proteins, including use of minimally toxic NIR light, labeling without need for genetic intervention, rapid kinetics, remote subsurface targeting, and long persistence of photoconverted signal. These findings are expected to be useful for applications involving rapid labeling of cells deep in tissue

Wilcox Molecular Torsion Balance with Rigid Side Arm and Separable Atropisomers for Investigating CH−π Interactions

A new variant of the Wilcox molecular torsion balance featuring a naphthyl-alkyl side arm was synthesized. The energy barrier for axial isomerization in the new balance was sufficiently high to allow for separation of the two rotamers and to observe their isomerization kinetics. The CH−π interaction energies in derivatives of the new and the original ester balance were in close agreement, suggesting that the motion in ester linkage is not an important factor in folding in the ester balance

Mechanistic Studies on the Copper-Catalyzed N-Arylation of Amides

The copper-catalyzed N-arylation of amides, i.e., the Goldberg reaction, is an efficient method for the construction of products relevant to both industry and academic settings. Herein, we present mechanistic details concerning the catalytic and stoichiometric N-arylation of amides. In the context of the catalytic reaction, our findings reveal the importance of chelating diamine ligands in controlling the concentration of the active catalytic species. The consistency between the catalytic and stoichiometric results suggests that the activation of aryl halides occurs through a 1,2-diamine-ligated copper(I) amidate complex. Kinetic studies on the stoichiometric N-arylation of aryl iodides using 1,2-diamine ligated Cu(I) amidates also provide insights into the mechanism of aryl halide activation.National Institutes of Health (U.S.) (GM 58160)American Chemical SocietyMerck & Co., Inc.Novartis (Firm

Enantioselective Synthesis of Axially Chiral Biaryls by the Pd- Catalyzed Suzuki-Miyaura Reaction: Substrate Scope and Quantum Mechanical Investigations

We report efficient syntheses of axially chiral biaryl amides in yields ranging from 80−92%, and with enantioselectivity in the range 88−94% ee employing an asymmetric Suzuki−Miyaura process with Pd(OAc)[subscript 2] and KenPhos as ligand. These studies demonstrate that electron-rich and electron-deficient o-halobenzamides can be efficiently coupled with 2-methyl-1-naphthylboronic acid and 2-ethoxy-1-naphthylboronic acid. The yields and selectivities of the reactions are independent of the nature of halogen substituent on the benzamide coupling partner. Our investigations demonstrate that axially chiral heterocyclic and biphenyl compounds can also be synthesized with this methodology. We also report computational studies used to determine the origin of stereoselectivity during the selectivity-determining reductive elimination step of the related coupling of tolyl boronic acid with naphthylphosphonate bromide that was reported in a previous publication (J. Am. Chem. Soc. 2000, 122, 12051−12052). These studies indicate that the stereoselectivity arises from a combination of weak -(C)H··O interactions as well as steric interactions between the tolyl and naphthylphosphonate addends in the transition state for C−C coupling.National Institutes of Health (U.S.) (Grant Number GM-46059)National Natural Science Foundation (National Center for Supercomputing Applications

Two-photon excited photoconversion of cyanine-based dyes

The advent of phototransformable fluorescent proteins has led to significant advances in optical imaging, including the unambiguous tracking of cells over large spatiotemporal scales. However, these proteins typically require activating light in the UV-blue spectrum, which limits their in vivo applicability due to poor light penetration and associated phototoxicity on cells and tissue. We report that cyanine-based, organic dyes can be efficiently photoconverted by nonlinear excitation at the near infrared (NIR) window. Photoconversion likely involves singlet-oxygen mediated photochemical cleavage, yielding blue-shifted fluorescent products. Using SYTO62, a biocompatible and cell-permeable dye, we demonstrate photoconversion in a variety of cell lines, including depth-resolved labeling of cells in 3D culture. Two-photon photoconversion of cyanine-based dyes offer several advantages over existing photoconvertible proteins, including use of minimally toxic NIR light, labeling without need for genetic intervention, rapid kinetics, remote subsurface targeting, and long persistence of photoconverted signal. These findings are expected to be useful for applications involving rapid labeling of cells deep in tissue.1421sciescopu