Phosphorylation of phospholipase D1 and the modulation of its interaction with RhoA by cAMP-dependent protein kinase

Agents that elevate cellular cAMP are known to inhibit the activation of phospholipase D (PLD). We investigated whether PLD can be phosphorylated by cAMP-dependent protein kinase (PKA) and PKA-mediated phosphorylation affects the interaction between PLD and RhoA, a membrane regulator of PLD. PLD1, but not PLD2 was found to be phosphorylated in vivo by the treatment of dibutyryl cAMP (dbcAMP) and in vitro by PKA. PKA inhibitor (KT5720) abolished the dbcAMP-induced phosphorylation of PLD1, but dibutyryl cGMP (dbcGMP) failed to phosphorylate PLD1. The association between PLD1 and Val14RhoA in an immunoprecipitation assay was abolished by both dbcAMP and dbcGMP. Moreover, RhoA but not PLD1 was dissociated from the membrane to the cytosolic fraction in dbcAMP-treated cells. These results suggest that both PLD1 and RhoA are phosphorylated by PKA and the interaction between PLD1 and RhoA is inhibited by the phosphorylation of RhoA rather than by the phosphorylation of PLD1.     

Gold-catalyzed hydrosilyloxylation driving tandem aldol and mannich reactions

The chemoselective formation of an enolate from alkyne in the presence of a carbonyl and imine group was realized, which constructed a variety of structural motifs under exceedingly mild reaction conditions in a tandem process. Reaction driving tandem hydrosilyloxylation/aldol reactions was achieved through the formation of enol silyl ethers catalytically generated in situ from readily available alkynes. These reactions were expanded to obtain β-amino enol silyl ethers in good yields via the tandem hydrosilyloxylation/isomerization/Mannich reaction.     

Self-organization of bent rod molecules into hexagonally ordered vesicular columns

Bent-shaped rigid-core molecules with flexible chiral dendrons grafted to the outer side of the bend were synthesized and characterized by circular dichroism, differential scanning calorimetry, X-ray scatterings, and transmission electron microscopy in solution and the solid state. The bent aromatic rods based on hepta- and nonaphenylene with nitrile groups at both ends self-assemble into well-ordered hollow tubular structures in aqueous solution, while the bent rod based on heptaphenylene without nitrile groups showed no apparent aggregations in aqueous solution. In the solid state, the rigid-flexible molecules based on heptaphenylene rod without the nitrile group self-assemble into a 2D oblique columnar structure with the columnar cross-section containing two interlocked molecules. Remarkably, the rigid flexible molecules based on hepta-, nona-, and undecaphenylene with nitrile groups self-assemble into a hexagonal columnar structure with weak 3D order. A model of vesicular channel structure is proposed based on small- and wide-angle X-ray diffraction on oriented fibers, density measurement, reconstruction and simulation of electron density maps, and molecular dynamics simulation. In contrast to the hollow tubular structure found in solution, in the solid both the outside and the interior of the columns are filled by the pendant aliphatic coils. Filling of the interior of these vesicular channels is made possible by some bent rod molecules turning their obtuse apex inward. One in 7, 2 in 8, and 4 in 10 molecules are thus inverted in a column slice in compounds with hepta-, nona-, and undecaphenylene cores, respectively. These are new examples of vesicular double-segregated columnar structures recently discovered in some dendrons.     

Deprotection of dithioacetals with 30% hydrogen peroxide catalyzed by tantalum(V) chloride–sodium iodide or niobium(V) chloride–sodium iodide

The reaction of dithioacetals with 30% hydrogen peroxide in the presence of catalytic amounts of tantalum(V) and iodide ion effectively produced carbonyl compounds in high yields. Dithioacetals also can be deprotected using the niobium(V) catalyzed oxidation of iodide ion by hydrogen peroxide under mild conditions.     

Metal ion affinity purification of proteins by genetically incorporating metal-chelating amino acids

Affinity tags are efficient tools for protein purification. They allow simple one-step purification of proteins to high purity. However, in some cases the tags cause structural and functional changes in a protein, and need to be removed. Therefore, affinity tags that are readily introduced into proteins with minimal perturbation and have specific affinity for purification are desired. Herein, two metal-chelating amino acids derived from 2,2′-bipyridine and 8-hydroxyquinoline were genetically incorporated into glutathione S-transferase (GST) and the mutant proteins were purified by using the metal ion affinity of the unnatural amino acids. The purification of the GST mutants containing 2-amino-3-(8-hydroxyquinolin-3-yl)propanoic acid (HQA) showed that the proteins could be efficiently enriched in Ni–NTA by the metal ion affinity of the unnatural amino acid and purified to excellent purity. This method should be very useful for general protein affinity purification, especially for proteins whose structure or function is affected by affinity tags fused to N- or C-terminals.     

Calculation of molecular weight distribution in a batch thermal polymerization of styrene

Molecular weight averages have long been used as a measure of polymer molecular weight properties in industrial polymer manufacturing processes. With a kinetic model, it is possible to directly calculate the polymer chain length distribution by integrating an infinite number of the polymer population balance equations. However, when the polymer chain length is very large, such a direct integration of polymer population balance equations can be computationally demanding. In this paper, the method of finite molecular weight moments is applied to the calculation of polymer chain length distribution in a batch free radical thermal polymerization of styrene. The weight fraction of a finite chain length interval is directly calculated in conjunction with a kinetic model. The method of calculation is illustrated through model simulations.     

The importance of temperature and viscosity effects for surfactant adsorption measurements made using the electrochemical quartz crystal microbalance

The measurement of adsorbed surfactant is important to fields such as corrosion inhibition, metal cleaning, and separation technologies. The electrochemical quartz crystal microbalance (EQCM) is an important tool that can be used to measure adsorbed surfactant. However, such measurements are subject to significant temperature and viscosity effects that must be appropriately considered. This paper discusses the effect of temperature and viscosity on EQCM measurements in solution environments and the ability of the EQCM to measure surfactant adsorption.     

Two types of intramolecular homolytic substitution reactions at group XIV atoms: unusual radical 1,4-Sn shifts from Si to C and carbonylative SHi reaction at Si

4-[(Trimethylstannyl)diphenylsilyl]butanoyl radical, arising from the corresponding 3-(stannylsilyl)propyl radical and CO, undergoes an SHi reaction at Si with extrusion of trimethyltin radical to give silacyclopentanone. The parent 3-(stannylsilyl)propyl radical was also found to isomerize to (3-stannylpropyl)silyl radical via a 1,4-Sn shift from Si to C with a rate constant of 9.3 x 10(4) s-1 at 80 degrees C. Ab initio and DFT MO calculations support a front-side attack mechanism.     

Organolathanide-catalyzed regioselective intermolecular hydroamination of alkenes, alkynes, vinylarenes, di- and trivinylarenes, and methylenecyclopropanes. Scope and mechanistic comparison to intramolecular cyclohydroaminations

Organolanthanide complexes of the type Cp'(2)LnCH(SiMe(3))(2) (Cp' = eta(5)-Me(5)C(5); Ln = La, Nd, Sm, Lu) and Me(2)SiCp' '(2)LnCH(SiMe(3))(2) (Cp' ' = eta(5)-Me(4)C(5); Ln = Nd, Sm, Lu) serve as efficient precatalysts for the regioselective intermolecular hydroamination of alkynes R'Ctbd1;CMe (R' = SiMe(3), C(6)H(5), Me), alkenes RCH=CH(2) (R = SiMe(3), CH(3)CH(2)CH(2)), butadiene, vinylarenes ArCH=CH(2) (Ar = phenyl, 4-methylbenzene, naphthyl, 4-fluorobenzene, 4-(trifluoromethyl)benzene, 4-methoxybenzene, 4-(dimethylamino)benzene, 4-(methylthio)benzene), di- and trivinylarenes, and methylenecyclopropanes with primary amines R' 'NH(2) (R' ' = n-propyl, n-butyl, isobutyl, phenyl, 4-methylphenyl, 4-(dimethylamino)phenyl) to yield the corresponding amines and imines. For R = SiMe(3), R = CH(2)=CH lanthanide-mediated intermolecular hydroamination regioselectively generates the anti-Markovnikov addition products (Me(3)SiCH(2)CH(2)NHR' ', (E)-CH(3)CH=CHCH(2)NHR' '). However, for R = CH(3)CH(2)CH(2), the Markovnikov addition product is observed (CH(3)CH(2)CH(2)CHNHR' 'CH(3)). For internal alkynes, it appears that these regioselective transformations occur under significant stereoelectronic control, and for R' = SiMe(3), rearrangement of the product enamines occurs via tautomerization to imines, followed by a 1,3-trimethylsilyl group shift to stable N-SiMe(3)-bonded CH(2)=CMeN(SiMe(3))R' ' structures. For vinylarenes, intermolecular hydroamination with n-propylamine affords the anti-Markovnikov addition product beta-phenylethylamine. In addition, hydroamination of divinylarenes provides a concise synthesis of tetrahydroisoquinoline structures via coupled intermolecular hydroamination/subsequent intramolecular cyclohydroamination sequences. Intermolecular hydroamination of methylenecyclopropane proceeds via highly regioselective exo-methylene C=C insertion into Ln-N bonds, followed by regioselective cyclopropane ring opening to afford the corresponding imine. For the Me(2)SiCp' '(2)Nd-catalyzed reaction of Me(3)SiCtbd1;CMe and H(2)NCH(2)CH(2)CH(2)CH(3), DeltaH() = 17.2 (1.1) kcal mol(-)(1) and DeltaS() = -25.9 (9.7) eu, while the reaction kinetics are zero-order in [amine] and first-order in both [catalyst] and [alkyne]. For the same substrate pair, catalytic turnover frequencies under identical conditions decrease in the order Me(2)SiCp' '(2)NdCH(SiMe(3))(2) > Me(2)SiCp' '(2)SmCH(SiMe(3))(2) > Me(2)SiCp' '(2)LuCH(SiMe(3))(2) > Cp'(2)SmCH(SiMe(3))(2), in accord with documented steric requirements for the insertion of olefinic functionalities into lanthanide-alkyl and -heteroatom sigma-bonds. Kinetic and mechanistic evidence argues that the turnover-limiting step is intermolecular C=C/Ctbd1;C bond insertion into the Ln-N bond followed by rapid protonolysis of the resulting Ln-C bond.     

A new quasi-one-dimensional ternary chalcogenide: synthesis,crystal structure,and electronic structure of Nb1+xV1-xS5 (x = 0.18)

The new low-dimensional ternary chalcogenide, Nb(1+x)V(1-x)S(5) (x = 0.18), has been prepared and characterized. This compound crystallizes in the monoclinic space group, C2(2h)-P2(1)/m with two formula units in a cell with dimensions a = 9.881(4) A, b = 3.329(1) A, c = 8.775(3) A, and beta = 114.82(3) degrees. The layer is composed of two unique chains of face-sharing Nb-centered bicapped trigonal prisms and edge-sharing M-centered octahedra (M = Nb or V). The electronic structures of the monomeric basic building units, NbS(8) and VS(6), and hypothetical and real one-, two-, and three-dimensional structures making up the compound are examined to understand the nature of inter- and intrachain interactions and orbital overlapping among metals and sulfur atoms. The electronic structure of Nb(1+x)V(1-x)S(5) is essentially given by superimposing those of the individual chains. V d orbitals are found to be crucial for the one-dimensional metallic conductivity along the chain axis.