Structural characterization of poly(amino)ester dendrimers and related impurities by electrospray tandem mass spectrometry

An acid‐terminated poly(amino)ester dendrimer was studied by electrospray ionization tandem mass spectrometry to establish its fragmentation pathways, with the aim of using them to investigate the structure of any defective molecules generated during the dendrimer synthesis. This poly(amino)ester dendrimer could be ionized in both polarities but the most structurally relevant dissociation pathways were found from the deprotonated molecule in negative ion mode. The dissociation pattern of this dendrimer is fully described and supported by accurate mass measurements. The main dissociation reactions of the negatively charged polyacidic dendrimer were shown to consist of (i) the release of carbon dioxide and ethene within a branch, which proceeds as many times as intact neutral branches are available; and (ii) the elimination of an entire dendrimer arm. Monitoring the occurrence of these reactions together with any deviation from these two main routes allowed six major dendritic impurities to be structurally characterized. Copyright © 2010 John Wiley & Sons, Ltd.     

Efficient synthesis of esters containing tertiary amine functionalities via active cyanomethyl ester intermediates

Esters containing tertiary amine functionalities were successfully synthesized under mild conditions and in good yields, using a three-step process involving the activation of acids into their corresponding cyanomethyl esters, followed by transesterification with the alcohol counterparts, and subsequent scavenging of the excess of alcohol to facilitate purification.     

The limiting distributions of large heavy Wigner and arbitrary random matrices

A heavy Wigner matrix $X_N$ is defined similarly to a classical Wigner one. It is Hermitian, with independent sub-diagonal entries. The diagonal entries and the non-diagonal entries are identically distributed. Nevertheless, the moments of the entries of $\sqrt{N}{X}_N$ tend to infinity with N, as for matrices with truncated heavy tailed entries or adjacency matrices of sparse Erdös–Rényi graphs. Consider a family ${\mathbf{X}}_N$ of independent heavy Wigner matrices and an independent family ${\mathbf{Y}}_N$ of arbitrary random matrices with a bound condition and converging in ^?-distribution in the sense of free probability. We characterize the possible limiting joint ^?-distributions of $({\mathbf{X}}_N,{\mathbf{Y}}_N)$, giving explicit formulas for joint ^?-moments. We find that they depend on more than the ^?-distribution of ${\mathbf{Y}}_N$ and that in general ${\mathbf{X}}_N$ and ${\mathbf{Y}}_N$ are not asymptotically ^?-free. We use the traffic distributions and the associated notion of independence [21] to encode the information on ${\mathbf{Y}}_N$ and describe the limiting ^?-distribution of $({\mathbf{X}}_N,{\mathbf{Y}}_N)$. We develop this approach for related models and give recurrence relations for the limiting ^?-distribution of heavy Wigner and independent diagonal matrices.     

Distributed computation of virtual coordinates for greedy routing in sensor networks

Sensor networks are emerging as a paradigm for future computing, but pose a number of challenges in the fields of networking and distributed computation. One challenge is to devise a greedy routing protocol—one that routes messages through the network using only information available at a node or its neighbors. Modeling the connectivity graph of a sensor network as a 3-connected planar graph, we describe how to compute on the network in a distributed and local manner a special geometric embedding of the graph. This embedding supports a geometric routing protocol called “greedy routing” based on the “virtual” coordinates of the nodes derived from the embedding.     

An easily accessible Re-based catalyst for the selective conversion of methanol: evidence for an unprecedented active site structure through combined operando techniques

Heterogeneous Re/SiO(2) catalysts prepared using a one pot sol-gel synthesis were found to display high activity in the direct, selective methanol conversion to methylal, which is correlated to an unprecedented rhenium oxide structure.     

Isoconversional kinetic analysis of stoichiometric and off-stoichiometric epoxy-amine cures

The curing reaction of stoichiometric and off-stoichiometric diglycidyl ether of bisphenol A (DGEBA) and 1,3-phenylene diamine (m-PDA) mixtures was studied by differential scanning calorimetry, thermogravimetric analysis and rheological measurements. In order to highlight the side reactions such as etherification and homopolymerization, the neat DGEBA and DGEBA/DMBA (N,N-dimethylbenzylamine) mixture were examined. The classical model-fitting and the advanced isoconversional methods were used to determine the activation energy of the different reactions. The advanced isoconversional method leads to a good agreement between isothermal, nonisothermal and rheological results. The effective activation energies of primary amine epoxy reaction, etherification and homopolymerization were estimated to about 55-60, 104 and 170 kJ mol⁻¹, respectively.     

Preliminary report on detection of papillomaviruses types 6, 11, 16, and 18 in laryngeal benign and malignant lesions

Recently, clinicians have observed an increase in the incidence of laryngeal papilloma coincident with the rising incidence of venereal warts. The lesions occur in young adults of professional singing age. Different types of human papillomavirus (HPV) are presented. Gynecologic exam revealed cervical tumors, involving 18 HPV in benign and malignant lesions. Thirty patients with the following pathologic conditions were studied: 10 papillomas, 10 severe dysplasias, and 10 invasive cancers. All the lesions were located on the free edge of the vocal folds or the anterior commissure involving the epithelium. The results are as follows: 11 patients (33%) had virus infection, of which four had HPV 6 or HPV 11 on laryngeal papilloma, three had HPV 16 or HPV 18 on severe dysplasia, four had HPV 16 or HPV 18 on carcinoma; and 19 (66%) had no virus infection. Gynecologic research in this field is more advanced. However, this preliminary report raises interesting research questions in laryngology.