A micro procedure for the estimation of the protein content of mucus glycoproteins

A sensitive automated procedure for the estimation of the protein content of glycoproteins has been developed using 0.5-mg samples (10–250 μg of protein). The method employs a modification of the conventional amino acid analysis using the unresolved neutral and acidic amino acid peak to estimate the total protein content. Hexosamines, sialic acid, and amide amino acids do not interfere.     

Two similar dibenzo cyclic ethers with dissimilar conformations

Two dibenzo cyclic ether compounds, 6,12‐dibromodibenzo[d,i]‐1,2,3,6,7,8‐hexahydro‐1,3‐dioxecin (systematic name: 8,16‐dibromo‐2,4‐dioxatricyclo[12.4.0.0^5,10]octadeca‐5,7,9,14,16,18‐hexaene), C₁₆H₁₄Br₂O₂, (II), and 8,14‐dibromodibenzo[f,k]‐1,5‐dioxa‐1,2,3,4,5,8,9,10‐octahydrocyclododecene (systematic name: 7,19‐dibromo‐11,15‐dioxatricyclo[14.4.0.0^5,10]icosa‐5,7,9,16,18,20‐hexaene), C₁₈H₁₈Br₂O₂, (III), were prepared as scaffolding for phosphate‐anion receptors. In both compounds, the two aromatic rings are linked by three methylene units ortho to the oxygen substituent of each ring. The only difference between the two compounds is the number of methylene units linking the two ether O atoms. The dibenzo cyclic ether with an ether linkage of one methylene unit adopts a chair‐like conformation, where the two aromatic rings are parallel to each other. On the other hand, the dibenzo cyclic ether with an oxygen linkage of three methylene units adopts a bowl‐like conformation. The latter scaffold configuration is the only structure of the two that would allow for the placement of convergent functional groups necessary for the establishment of an anion‐selective binding pocket.     

Phase separation of polymer‐functionalized SWNTs within a PMMA/polystyrene blend

Phase separation of polystyrene (PS) and poly(methyl methacrylate) (PMMA) blends was used as a means to segregate PS‐ or PMMA‐functionalized single‐walled carbon nanotubes (SWNTs) in thin films. Dilute solutions (5 wt % in THF) of 1:1 PS/PMMA blends containing the functionalized nanotubes were spin cast and annealed at 180 °C for 12 h. Two different polymer molecular weights were used (M_n = 8000 or M_n = 22,000), and were of approximately equivalent molecular weight to those attached to the surface of the nanotubes. Nanotube functionalization was accomplished using the Cu(I)‐catalyzed [3 + 2] Huisgen cycloaddition, in which alkyne‐decorated nanotubes were coupled with azide‐terminated polymers, resulting in polymer‐SWNT conjugates that were soluble in THF. Characterization of the annealed films by scanning Raman spectroscopy, which utilized the unique Raman fingerprint of carbon nanotubes, enabled accurate mapping of the functionalized SWNTs within the films relative to the two phase‐separated polymers. It was found that nanotube localization within the phase‐separated polymer films was influenced by the type of polymer attached to the nanotube surface, as well as its molecular weight. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 450–458, 2009     

Fragmentation of doubly-protonated Pro-His-Xaa tripeptides: Formation of b 2 2+ ions

When ionized by electrospray from acidic solutions, the tripeptides Pro-His-Xaa (Xaa=Gly, Ala, Leu) form abundant doubly-protonated ions, [M+2H]²⁺. Collision-induced dissociation (CID) of these doubly-protonated species results, in part, in formation of b ₂ ²⁺ ions, which fragment further by loss of CO to form a ₂ ²⁺ ions; the latter fragment by loss of CO to form the Pro and His iminium [immonium is commonly used in peptide MS work] ions. Although larger doubly-charged b ions are known, this represents the first detailed study of b ₂ ²⁺ ions in CID of small doubly protonated peptides. The most abundant CID products of the studied doubly-protonated peptides arise mainly in charge separation involving two primary fragmentation channels, formation of the b ₂ /y ₁ pair and formation of the a ₁ /y ₂ pair. Combined molecular dynamics and density functional theory calculations are used to gain insight into the structures and fragmentation pathways of doubly-protonated Pro-His-Gly including the energetics of potential protonation sites, backbone cleavages, post-cleavage charge-separation reactions and the isomeric structures of b ₂ ²⁺ ions. Three possible structures are considered for the b ₂ ²⁺ ions: the oxazolone, diketopiperazine, and fused ring isomers. The last is formed by cleavage of the His-Gly amide bond on a pathway that is initiated by nucleophilic attack of one of the His side-chain imidazole nitrogens. Our calculations indicate the b ₂ ²⁺ ion population is dominated by the oxazolone and/or fused ring isomers.     

Projective semimodules over semirings with valuations in nonnegative integers

We introduce semirings with valuations in nonnegative integers and prove that all projective semimodules over them are free.     

NMR assignments and histone specificity of the ING2 PHD finger

The ING2 plant homeodomain (PHD) finger is recruited to the nucleosome through specific binding to histone H3 trimethylated at lysine 4 (H3K4me3). Here, we describe backbone and side chain assignments of the ING2 PHD finger, analyze its binding to the unmodified and modified histone and p53 peptides, and map the histone H3 and H3K4me3 binding sites based on chemical shift perturbation analysis. Copyright © 2009 John Wiley & Sons, Ltd.