Determination of glycosylation sites in O-linked glycopeptides: A sensitive mass spectrometric protocol

A sensitive mass spectrometric method for the specific identification of O-glycosylation sites in glycopeptides is presented. Reductive β-elimination liberates a peptide containing a specifically modified amino acid at the former site of carbohydrate attachment. Mass spectrometry is used to determine the sequence of the modified peptide, in which the position of the modified amino acid marks the site of O-glycosylation. The method also provides information on the carbohydrate chain and is applicable at the low nanomolar level.     

Best affine unbiased response decomposition

Given two linear regression models y₁=X₁β₁+u₁ and y₂=X₂β₂+u₂ where the response vectors y₁ and y₂ are unobservable but the sum y=y₁+y₂ is observable, we study the problem of decomposing y into components and , intended to be close to y₁ and y₂, respectively. We develop a theory of best affine unbiased decomposition in this setting. A necessary and sufficient condition for the existence of an affine unbiased decomposition is given. Under this condition, we establish the existence and uniqueness of the best affine unbiased decomposition and provide an expression for it.     

Mass spectrometric characterization of beta-caryophyllene ozonolysis products in the aerosol studied using an electrospray triple quadrupole and time-of-flight analyzer hybrid system and density functional theory

The components of the organic aerosol formed due to gas-phase beta-caryophyllene ozonolysis were characterized by the use of a triple quadrupole and time-of-flight analyzer hybrid system coupled to an electrospray ionization source operated in the negative ion mode. A reversed-phase high-performance liquid chromatography (HPLC) column was used to achieve chromatographic separations at neutral pH which has been proved to induce ionization of organic compounds bearing aldehyde moieties. In addition to the detected oxo- and dicarboxylic acids, isomeric oxidation products, which bear multi-functional groups such as aldehyde, carbonyl and hydroxyl groups, could be differentiated by examining their corresponding collision-induced dissociation (CID) fragmentation pathways. Proposed fragmentation mechanisms were drawn for the experimentally observed fragmentation pathways in all the CID experiments. Cyclic oxidation products could also be discerned and their fragmentation behaviour under low energy collisional conditions was studied in detail. Gas-phase deprotonation potentials were calculated by the use of DFT B3LYP/6-311+G(2d,p)//B3LYP/6-31+G(d) + ZPVE to estimate the most thermodynamically favourable deprotonation site for efficient negative ion formation in the ion source. The optimized gas-phase geometries for the most prominent oxidation products reveal a strong intramolecular interaction between the upper and lower C4 carbon chains, which are formed after the decomposition of the primary ozonide generated by ozone attack of the reactive endocyclic C==C bond.     

Ion‐Mobility Spectrometry Can Assign Exact Fucosyl Positions in Glycans and Prevent Misinterpretation of Mass‐Spectrometry Data After Gas‐Phase Rearrangement

The fucosylation of glycans leads to diverse structures and is associated with many biological and disease processes. The exact determination of fucoside positions by tandem mass spectrometry (MS/MS) is complicated because rearrangements in the gas phase lead to erroneous structural assignments. Here, we demonstrate that the combined use of ion‐mobility MS and well‐defined synthetic glycan standards can prevent misinterpretation of MS/MS spectra and incorrect structural assignments of fucosylated glycans. We show that fucosyl residues do not migrate to hydroxyl groups but to acetamido moieties of N‐acetylneuraminic acid as well as N‐acetylglucosamine residues and nucleophilic sites of an anomeric tag, yielding specific isomeric fragment ions. This mechanistic insight enables the characterization of unique IMS arrival‐time distributions of the isomers which can be used to accurately determine fucosyl positions in glycans.     

Crystallization of polyamide confined in sub‐micrometer droplets dispersed in a molten polyethylene matrix

The crystallization of submicrometer PA6 droplets dispersed in an ethylene‐1‐octene copolymer matrix, using PE‐g‐MA as a compatibilizer agent, is investigated. This system shows a nonconventional mechanical behavior at high temperatures. Up to ～100 °C above the final melting temperature of the ethylene‐1‐octene copolymer matrix, the system shows good thermal and mechanical properties including dimensional stability. Because of the dispersed phase morphology of the system, so‐called fractionated/homogeneous crystallization takes place leading to an extra supercooling of PA6: ～50 °C compared to the bulk PA6 crystallization temperature. Thus—though this is most probably just of interest for small‐scale research—the system can be processed at lowered temperatures while still providing exceptional high‐temperature properties. While the matrix is in the melt state when crystallization of the dispersed PA6 phase occurs, the possibility of matrix induced crystallization is absent, contrary to almost all of the ‘dispersed droplets in a matrix’ systems reported so far. The kinetics of this phenomenon is investigated in detail by DSC: the existence of fractionated/homogeneous crystallization is shown to be related to the lack of active nuclei in the dispersed droplets by means of self‐seeding experiments. The occurrence of extensive cold crystallization of PA6 in the confined environment is studied as is the crystallization kinetics, including the characterization of its time dependences showing its sporadic nature. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 815–825, 2006     

Voice Characteristics in Adults With Neurofibromatosis Type 1

Neurofibromatosis type 1 (NF1) is an autosomal dominant neurocutaneous disorder caused by mutations in the NF1 gene, which is located at the long arm of chromosome 17. Major characteristics include multiple café-au-lait spots and neurofibromas. Voice abnormalities have been reported to occur in this patient group. However, most studies relied on subjective measurements only. The present study reports the results of an objective voice assessment based on a multiparameter approach in 22 adults with NF1. Aerodynamic measurements, voice range profiles, acoustic voice quality and intonation measurements, and dysphonia severity indices were obtained and compared with data from a control group, consisting of 22 healthy adults. It was found that NF1 patients show a poorer overall voice quality compared with controls. Particularly, a reduction of vital capacity and limitations in laryngeal possibilities with respect to frequency and intensity were observed in the NF1 group.     

Increasing the Size of an Aromatic Helical Foldamer Cavity by Strand Intercalation

The postsynthetic modulation of capsules based on helical aromatic oligoamide foldamers would be a powerful approach for controlling their receptor properties without altering the initial monomer sequences. With the goal of developing a method to increase the size of a cavity within a helix, a single‐helical foldamer capsule was synthesized with a wide‐diameter central segment that was designed to intercalate with a second shorter helical strand. Despite the formation of stable double‐helical homodimers (K_dim>10⁷ M ^?1) by the shorter strand, when it was mixed with the single‐helical capsule sequence, a cross‐hybridized double helix was formed with K_a>10⁵ M ^?1. This strategy makes it possible to direct the formation of double‐helical heterodimers. On the basis of solution‐ and solid‐state structural data, this intercalation resulted in an increase in the central‐cavity size to give a new interior volume of approximately 150 ų.     

Cross sections for energetic heavy-ion impact on protonated water clusters

Energetic impact of multiple ionized oxygen on protonated water clusters in the range of eight to twenty-one water molecules is investigated on the ZERNIKE--LEIF facility. The target water clusters are stored in a Paul trap and thermalized by cold buffer gas. This well-controlled approach allows for a direct measurement of the total inelastic cross section leading to trap-loss processes of the target ions.     

A Monte Carlo evaluation of three methods to detect local dependence in binary data latent class models

Binary data latent class analysis is a form of model-based clustering applied in a wide range of fields. A central assumption of this model is that of conditional independence of responses given latent class membership, often referred to as the “local independence” assumption. The results of latent class analysis may be severely biased when this crucial assumption is violated; investigating the degree to which bivariate relationships between observed variables fit this hypothesis therefore provides vital information. This article evaluates three methods of doing so. The first is the commonly applied method of referring the so-called “bivariate residuals” to a Chi-square distribution. We also introduce two alternative methods that are novel to the investigation of local dependence in latent class analysis: bootstrapping the bivariate residuals, and the asymptotic score test or “modification index”. Our Monte Carlo simulation indicates that the latter two methods perform adequately, while the first method does not perform as intended.