Electrophoretic analysis of phosphorylation of the yeast 20S proteasome

The 26S proteasome complex, consisting of two multisubunit complexes, a 20S proteasome and a pair of 19S regulatory particles, plays a major role in the nonlysosomal degradation of intracellular proteins. The 20S proteasome was purified from yeast and separated by two-dimensional gel electrophoresis (2-DE). A total of 18 spots separated by 2-DE were identified as the 20S proteasome subunits by peptide mass fingerprinting with matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS). The alpha2-, alpha4- and alpha7-subunits gave multiple spots, which converged into one spot for each subunit when treated with alkaline phosphatase. The difference of pI between phosphorylated and dephosphorylated spots and their reaction against anti-phosphotyrosine antibody suggested that the alpha2- and alpha4-subunits are phosphorylated either at Ser or at Thr residue, and the alpha7-subunit is phosphorylated at Tyr residue(s). These phosphorylated subunits were analyzed by electrospray ionization-quadrupole time of flight-tandem MS (ESI-QTOF-MS/MS) to deduce the phosphorylation sites. The 20S proteasome has three different protease activities: chymotrypsin-like, trypsin-like and peptidylglutamyl peptide-hydrolyzing activities. The phosphatase treatment increased K(m) value for chymotrypsin-like activity of the 20S proteasome, indicating that phosphorylation may play an important role in regulating the proteasome activity.     

Designed self-assembly of molecular necklaces

This paper reports an efficient strategy to synthesize molecular necklaces, in which a number of small rings are threaded onto a large ring, utilizing the principles of self-assembly and coordination chemistry. Our strategy involves (1) threading a molecular "bead" with a short "string" to make a pseudorotaxane and then (2) linking the pseudorotaxanes with a metal complex with two cis labile ligands acting as an "angle connector" to form a cyclic product (molecular necklace). A 4- or 3-pyridylmethyl group is attached to each end of 1,4-diaminobutane or 1,5-diaminopentane to produce the short "strings" (C4N4(2+), C4N3(2+), C5N4(2+), and C5N3(2+)), which then react with a cucurbituril (CB) "bead" to form stable pseudorotaxanes (PR44(2+), PR43(2+), PR54(2+), and PR53(2+), respectively). The reaction of the pseudorotaxanes with Pt(en)(NO(3))(2) (en = ethylenediamine) produces a molecular necklace [4]MN, in which three molecular "beads" are threaded on a triangular framework, and/or a molecular necklace [5]MN, in which four molecular "beads" are threaded on a square framework. Under refluxing conditions, the reaction with PR44(2+) or PR54(2+) yields exclusively [4]MN (MN44T or MN54T, respectively), whereas that with PR43(2+) or PR53(2+) produces exclusively [5]MN (MN43S or MN53S, respectively). The products have been characterized by various methods including X-ray crystallography. At lower temperatures, on the other hand, the reaction with PR44(2+) or PR54(2+) affords both [4]MN and [5]MN. The supermolecules reported here are the first series of molecular necklaces obtained as thermodynamic products. The overall structures of the molecular necklaces are strongly influenced by the structures of pseudorotaxane building blocks, which is discussed in detail on the basis of the X-ray crystal structures. The temperature dependence of the product distribution observed in this self-assembly process is also discussed.     

The participation of the anion and alkyl substituent of diaryliodonium salts in photo‐initiated cationic polymerization reactions

The photo‐initiated cationic polymerization (PCP) of epoxides using diaryliodonium salt photoacid generators (PAGs) bearing alkyl groups and anions was investigated. The properties and reactivities of a series of iodonium salts containing various cations and anions were compared in the context of a PCP reaction. The products from the decomposition of the cations of these salts were analyzed using gas chromatography‐mass spectrometry (GC‐MS) spectra. The relationship between the molecular structure of the salts and their reaction mechanism in the PCP reaction was investigated. Based on the results of the investigation, it was concluded that the structures of the cations and anions of theiodonium salts affect the PCP reaction rate, which was controlled by the products from the diaryliodonium salts. As part of an additional investigation, the diaryliodonium salts‐epoxide materials were applied to 254 nm‐photo‐patterning. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis and structure of 5,6,7,12-tetrahydrodibenz[c,f][1,5]azabismocines

Hypervalent organobismuth compounds, 6-tert-butyl-5,6,7,12-tetrahydrodibenz[c,f][1,5]azabismocines, with 13 different substituents on the bismuth atom including halogens, alkyl, alkenyl, alkynyl, aryl, or phenylthio groups have been synthesized. A key compound, 12-chloro-6-tert-butyl-5,6,7,12-tetrahydrodibenz[c,f][1,5]azabismocine, which is a precursor for other azabismocines, has been synthesized by two different procedures; one is based on Akiba’s method using 2-bromobenzylbromide as one of the starting materials and the other is a newly developed one using a cheaper starting material, 2-chlorobenzyl chloride. The structures of 12 new bismuth compounds were determined by X-ray diffraction. The eight-membered tetrahydroazabismocine ring has proved to be highly flexible and the hypervalent Bi-N bond distances vary ranging from 2.568(3) to 2.896(5) Å, depending on the electronic nature of the substituents on the bismuth atom. The Bi-N bond distances have good linear relationship against Hammett’s σ_m constants.     

Photoinduced chemical reactions on natural single crystals and synthesized crystallites of mercury(II) sulfide in aqueous solution containing naturally occurring amino acids

Photoirradiation at >300 nm of aqueous suspensions of several natural crystal specimens and synthesized crystallites of mercury(II) sulfide (HgS) induced deaminocyclization of optically active or racemic lysine into pipecolinic acid (PCA) under deaerated conditions. This is the first example, to the best of our knowledge, of photoinduced chemical reactions of natural biological compounds over natural minerals. It was found that the natural HgS crystals had activity higher than those of synthesized ones but lower than those of other sulfides of transition metals, e.g., CdS and ZnS, belonging to the same II-IV chalcogenides. In almost all of the photoreactions, decompostion of HgS occurred to liberate hydrogen sulfide (H(2)S) and Hg(2+), and the latter seemed to have undergone in-situ reductive deposition on HgS as Hg(0) after a certain induction period (24-70 h) during the photoirradiation, as indicated by the darkened color of the suspensions. The formation of PCA, presumably through combination of oxidation of lysine and reduction of an intermediate, cyclic Schiff base, could also be seen after a certain induction time of the Hg(0) formation. This was supported by the fact that the addition of small amount of Hg(2+) (0.5 wt % of HgS) increased the PCA yield by almost 2-fold. We also tried to elucidate certain aspects of the plausible stereochemical reactions in relation to the chiral crystal structure of HgS. Although, in some experiments, slight enantiomeric excess of the product PCA was observed, the excess was below or equal to the experimental error and no other supporting analytical data could not be obtained; we cannot conclude the enantiomeric photoproduction of PCA by the natural chiral HgS specimen.     

Supramolecular steric effects as the means of making reactive carbon radicals persistent. Quantitative characterization of the external surface of MFI zeolites through a persistent radical probe and a langmuir adsorption isotherm

The photochemistry of tetraphenylacetone (1) adsorbed on the external surface of a MFI zeolite (the sodium form of LZ-105) has been investigated in combination with computational chemistry, surface area measurements, EPR analysis, and classical adsorption isotherms. All of the methods are consistent with a supramolecular structural model in which 1 is first adsorbed strongly through intercalation of a single benzene ring into a hole on the LZ-105 external surface (site I) followed by a weaker binding to the external framework between the holes (site II) until a monolayer of 1 is formed. From both computational and surface area measurements, it is estimated that the site I holes on the external surface will be filled at ca. 0.3-0.5 wt %/wt loading of 1/LZ-105, which corresponds to 6.5 x 10(18) (ca. 10(-)(5) mol) of holes or molecules of 1 adsorbed in holes per gram of zeolite. The supramolecular composition of ca. 0.3-0.5% of 1 on LZ-105 characterizes a "break point" for the photochemistry and the EPR measurements, since it represents the value for saturation of the site I holes with 1. These conclusions are supported quantitatively by experimental isotherms of the adsorption of 1 on LZ-105. Photolysis of 1 intercalated in the site I holes causes fragmentation into two isomeric supramolecular diphenylmethyl (DPM) radicals, one (DMP)(in) which is adsorbed into the internal surface and becomes strongly persistent (half-life of many weeks) and the other (DMP)(ex) which diffuses on the external surface and rapidly dimerizes (less than a few minutes) to produce the radical-radical combination product tetraphenylethane (2). Photolysis of 1 adsorbed on the solid external surface produces two supramolecularly equivalent DPM radicals (DMP)(ex) that diffuse on the external surface and rapidly dimerize to produce 2, and do not produce persistent DPM radicals.     

Determination of the double-bond position in hexadecenols by mass spectrometry without prior chemical modification

Fourteen isomers of chemically unmodified hexadecenol were analysed by two types of quadrupole mass spectrometer, coupled with a gas chromatograph, for the location of the double-bond position. A series of spectra were interpreted in terms of mass spectral patterns on a fuzzy classification, in which the intensity ratios of six diagnostic pairs of the predominant ions were preferred in devising similarity indices. The accuracy of the method in the location of double-bond position was confirmed by testing with other series of spectra.     

Theoretical study of endohedral metallofullerenes: Sc3−nLanN@C80 (n=0–3)

To provide theoretical insight into the structures and properties of Sc₃N@C₈₀, which has been isolated in high yield and purity as a new stable endohedral metallofullerene, density functional calculations are carried out for the Sc_3?nLa_nN@C₈₀ (n=0–3) series. Because of electron transfer from Sc₃N to C₈₀, the electronic structure of Sc₃N@C₈₀ is formally described as (Sc₃N)⁶⁺C$_{80}^{6-}$. The encapsulated Sc₃N cluster takes a planar structure with long Sc–Sc distances and is highly stabilized inside the I_h cage of C₈₀, which rotates rapidly. As the number of La atoms increases, the Sc_3?nLa_nN cluster is forced to maintain a pyramidal structure in Sc_3?nLa_nN@C₈₀. In addition, the C₈₀ cage takes an open‐shell electronic structure due to an increase in the number of electrons transferring from Sc_3?nLa_nN. These make the endohedral structure less stable and more reactive. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1353–1358, 2001     

Water‐Soluble N‐(n‐Fatty acyl)chitosans

Chitosan was partially N‐acylated by treatment with n‐fatty acid anhydrides in a homogeneous solution in 2 vol.‐% aqueous acetic acid‐methanol (1:2 v/v). The degree of substitution (d.s.) for N‐acyl groups in the water‐soluble N‐acylchitosan derivatives was in the range of 0.42–0.82 for N‐acetyl, 0.37–0.76 for N‐propionyl, 0.52–0.71 for N‐butyryl and 0.54–0.64 for N‐pentanoyl and ca. 0.58 for N‐hexanoyl, respectively.

Water soluble N‐(n‐fatty acyl)chitosans.