Biomedical subjects

Ya Chen

Publications and source records attributed to Ya Chen.

4 recordsLinked to original sources

PubMed2006

Anthrax lethal factor protease inhibitors: synthesis, SAR, and structure-based 3D QSAR studies.

We have recently identified a series of compounds that efficiently inhibit anthrax lethal factor (LF) metallo-protease. Here we present further structure-activity relationship and CoMFA (comparative molecular field analysis) studies on newly derived inhibitors. The obtained 3D QSAR model was subsequently compared with the X-ray structure of the complex between LF and a representative compound. Our studies form the basis for the rational design of additional compounds with improved activity and selectivity.

Antigens, Bacterial↗

PubMed2002

Loss of activities for mRNA synthesis accompanies loss of lambda2 spikes from reovirus cores: an effect of lambda2 on lambda1 shell structure.

The 144-kDa lambda2 protein, a component of the transcriptionally active reovirus core particle, catalyzes the last three enzymatic activities for formation of the 5' cap 1 structure on the viral plus-strand transcripts. Limited evidence suggests it may also play a role in transcription per se. Particle-associated lambda2 forms pentameric turrets ("spikes") around the fivefold axes of the icosahedral core. To address the requirements for lambda2 in core functions other than the known functions in RNA capping, particles depleted of lambda2 were generated from cores in vitro by a series of treatments involving heat, protease, and ionic detergent. The resulting particles contained less than 5% of pretreatment levels of lambda2 but showed negligible loss of the other four core proteins or the 10 double-stranded RNA genome segments. Transmission cryo-electron microscopy (cryo-TEM) and scanning cryo-electron microscopy demonstrated loss of the lambda2 spikes from these otherwise intact particles. In functional analyses, the "spikeless cores" showed greatly reduced activities not only for RNA capping but also for transcription and nucleoside triphosphate hydrolysis, suggesting enzymatic or structural roles for lambda2 in all these activities. Comparison of the core and spikeless core structures obtained by cryo-TEM and three-dimensional image reconstruction revealed changes in the lambda1 core shell that accompany lambda2 loss, most notably the elimination of small pores that span the shell near the icosahedral fivefold axes. Changes in the shell may explain the reductions in transcriptase-related activities by spikeless cores.

Cryoelectron Microscopy↗

PubMed1999

15N NMR and Electrochemical Studies of [Ru(II)(hedta)](-) Complexes of NO, NO(+), NO(2)(-), and NO(-).

[Ru(II)(hedta)L](n)()(-) complexes (hedta(3)(-) = N-(hydroxyethyl)ethylenediaminetriacetate; L = NO(+), n = 0; L = NO, n = 1; L = NO(-), n = 2) have been prepared by the displacement of H(2)O/D(2)O via NO(g) or NO(2)(-). This is the first reported entire set of NO(+), NO, and NO(-) as ligands for the same metal center in a constant oxidation state and with a constant ligand environment (here Ru(II) and the amino carboxylate hedta(3)(-)). From the NO stretching frequencies of isolated salts, the net influence of back-donation by Ru(II) and its sigma-withdrawal was observed to be that the bond order for the NO(+) complex is virtually the same (ca. 2.46) as that for the NO complex (ca. 2.48). The back-donation to NO(-) is also small, as is that to NO, but orbital mixing of NO(-) and Ru(II) is sufficiently important to induce a singlet NO(-) complex. Values for the nu(NO) in cm(-)(1) for the (14)N- and (15)N-labeled complexes, respectively, are as follows: NO(+), 1846, 1827; NO, 1858, 1842; NO(-), 1383, 1370. Combined results of (15)N, (13)C, and (1)H NMR spectra of the complexes in D(2)O show that [Ru(II)(hedta)((15)NO(+))] is a single cis-equatorial isomer with its (15)NO(+) resonance at 249.6 ppm vs [(15)N]formamide. The two-electron-reduced [Ru(II)(hedta)((15)NO(-))](2)(-) complex exists as trans- and cis-equatorial isomers having (15)NO(-) resonances at 609.4 and 607.4 ppm. The (15)N resonances appear at 260.0 ppm for the (15)NO(+) ligand and at 348.8 ppm for the bound (15)NO(2)(-) ligand in the [Ru(II)(hedta)((15)NO(2)(-))((15)NO(+))(D(2)O)] complex. Differential pulse voltammetric waves for the [Ru(II)(hedta)L](n)()(-) series occur at -0.37 V for the Ru(II)(NO(-))/Ru(II)(NO) couple, at -0.10 V for the Ru(II)(NO)/Ru(II)(NO(+)) couple, and at +0.98 V for the Ru(II)(NO(+))/Ru(III)(NO(+)) couple. The coordinated nitrosyl ion/nitro equilibrium (L')Ru(II)(NO(+)) + 2OH(-) right harpoon over left harpoon (L')Ru(II)(NO(2)(-)) + H(2)O (K(NO)()2()-) was observed for L' = hedta(3)(-), as for previous examples with L' = violurate, polypyridyl ligands, and (CN(-))(5) and (NH(3))(5) ligand sets. K(NO)()2()- = 1.44 x 10(13) for L' = hedta(3)(-). log(K(NO)()2()-) is linearly related through the ion-pairing equilibrium constant expression to -z(1)z(2), the charge product of the reacting ions (here the (L')Ru(NO(+)) complex and OH(-)) from -4 through +3, excluding the (NH(3))(m)() ammine series with m = 4 and 5. The opposite behavior of the ammines is attributed to strong solvent H-bonding that changes for reactant and product in the nitrosyl/nitro equilibrium. The pK(a) of coordinated nitrous acid in [Ru(II)(hedta)(HONO)](-) is calculated to be -0.80, a 3.85 log unit enhancement over free HONO due to the Ru(II) charge. An MO explanation is presented to interrelate the {Fe(III)-(NO(-) triplet)} complexes, the {Ru(II)-(NO(-) singlet)} type observed for [Ru(II)(hedta)((15)NO(-))](2)(-), and the NO(+) complexes of other strong-field metals. When both d(z)()()2 and d(x)()()2(-)(y)()()2 metal orbitals reside below the NO pi pair, the electronic repulsions favor a bent NO(-) triplet ligand. If both metal orbitals reside above the NO pi pair, the orbital mixing and back-donation induce a coordinated NO(-) singlet ligand, and if the NO pi pair reside between the two sigma-based d orbitals, an NO(+) ligand and reduced metal center obtain.

Journal Article↗

PubMed1998

A Proton-Induced N-1 to eta(2) Migration of the Fluxional Pyrazine in the [Ru(II)(hedta)(pz)](-) Complex.

[Ru(II)(hedta)(D(2)O)](-), hedta(3)(-) = N-(hydroxyethyl)ethylenediaminetriacetate, reacts with pyrazine in D(2)O at 25 degrees C to yield several isomers and </=20% of the pyrazine-bridged binuclear complex. Two isomers of 56.2% combined abundance have differentiated alpha (near) and beta (remote) (1)H NMR pyrazine resonances at 9.09 ppm (alpha or H2, H6 pair) and 8.33 ppm (beta or H3, H5 pair). The other isomer of ca. 24% abundance exhibits only a singlet at 8.76 ppm, indicative of fluxional pyrazine movement from N-1 to N-4. This is believed to be the cis-polar isomer. Within 24 h the differentiated isomers convert to the fluxional isomer, which remains fluxional in 50% D(2)O/50% CD(3)OD down to 237 K. The fluxional isomer has all equivalent (13)C NMR resonances at 152.44 ppm, 5.18 ppm downfield of free pyrazine. Comparison with the bridged binuclear ion {[Ru(hedta)](2)(pz)}(2)(-) revealed fortuitously similar shifts; the (1)H NMR spectrum shows a singlet at 8.76 ppm, and the (13)C NMR spectrum, a singlet at 152.40 ppm. These species have different electrochemical signatures, however, with the 1:1 fluxional complex having a Ru(II/III) wave at 0.20 V that shifts to 0.35 V upon protonation of the N-4 position, whereas the binuclear complex has two waves at 0.18 and 0.33 V which are independent of pH. (1)H NMR indicates stereochemically rigid coordination of 2-methylpyrazine (2-CH(3)pz) at N-4 with the 2-CH(3) position remote in the major species (65.5%) and at N-2 with the 2-CH(3) site adjacent (34.4%) in the lesser isomer. The proton resonances are as follows. Remote isomer (N-4): H2, 8.22 ppm; H3, 8.97 ppm; H5, 8.88 ppm; CH(3), 2.53 ppm. Adjacent (N-1) isomer: H2, 8.73 ppm; H3, 8.42 ppm, H5, 8.50 ppm; CH(3), 2.45 ppm. A slow conversion of the strained adjacent isomer to the remote isomer is observed. Remote and adjacent isomers were also prepared for [(NH(3))(5)Ru(2-CH(3)pz)](2+) in 87.7% and 12.3% yield. Protonation of [Ru(hedta)(pz)](-) yields nonfluxional complexes: a major species (63%) bound eta(2)(1,2) with four complicated resonance patterns at 8.72, 8.57, 8.00, and 7.91 ppm, each signal having across-the-ring couplings which require couplings to at least two different ring protons and a minor N-1-coordinated N-4 protonated species (16%) with alpha and beta proton pairs resonating at 8.81 and 8.25 ppm. An eta(2)(2,3) isomer is also detectable (20%) which has four types of (1)H resonances at 9.51, 9.01, 8.85, and 8.15 ppm. The weakened sigma bonding from pzH(+) and enhanced pi-acceptor capacity power of pzH(+) combine to induce a switch in coordination to either eta(2)(1,2) or eta(2)(2,3).

Journal Article↗