bluuebunny/crossref_metadata_2025 huggingface dataset:
Human Chromosome 2 Carries a Gene Required for Production of Infectious Human Immunodeficiency Virus Type 1
Authors: Coskun Ayse K. , van Maanen Marc , Nguyen Van , Sutton Richard E.
Published: March 2006

Human immunodeficiency virus type 1 (HIV) replicates only in certain primate cells. In murine cells expressing cyclin T1, a posttranscriptional block exists such that small amounts of capsid and little infectious virus are released. This block is relieved in part by fusion with human cells. Here we have tested a panel of mouse-human somatic cell hybrids for production of infectious virus. Only those containing human chromosome 2 were permissive, which correlated with capsid production. The effect was specific to HIV in that release of murine leukemia virus was minimally affected by the presence of chromosome 2. Although expression of Vpu markedly increased capsid production in the absence of chromosome 2, it did not result in a corresponding increase in infectious HIV. The presence of chromosome 2 did not have consistent effects on the amount of unspliced viral RNA, whereas the amount of cell-associated Gag p55 was increased a fewfold. These results suggest that processing of HIV Gag can be corrected by one or more genes present on human chromosome 2 to allow production of infectious HIV from murine cells.
Mutagenesis Analysis of the nsp4 Main Proteinase Reveals Determinants of Arterivirus Replicase Polyprotein Autoprocessing
Authors: van Aken Danny , Snijder Eric J. , Gorbalenya Alexander E.
Published: March 2006

Nonstructural protein 4 (nsp4; 204 amino acids) is the chymotrypsin-like serine main proteinase of the arterivirus
Equine arteritis virus
(order
Nidovirales
), which controls the maturation of the replicase complex. nsp4 includes a unique C-terminal domain (CTD) connected to the catalytic two-β-barrel structure by the poorly conserved residues 155 and 156. This dipeptide might be part of a hinge region (HR) that facilitates interdomain movements and thereby regulates (in time and space) autoprocessing of replicase polyproteins pp1a and pp1ab at eight sites that are conserved in arteriviruses. To test this hypothesis, we characterized nsp4 proteinase mutants carrying either point mutations in the putative HR domain or a large deletion in the CTD. When tested in a reverse genetics system, three groups of mutants were recognized (wild-type-like, debilitated, and dead), which was in line with the expected impact of mutations on HR flexibility. When tested in a transient expression system, the effects of the mutations on the production and turnover of replicase proteins varied widely. They were cleavage product specific and revealed a pronounced modulating effect of moieties derived from the nsp1-3 region of pp1a. Mutations that were lethal affected the efficiency of polyprotein autoprocessing most strongly. These mutants may be impaired in the accumulation of nsp5-7 and/or suffer from delayed or otherwise perturbed processing at the nsp5/6 and nsp6/7 junctions. On average, the production of nsp7-8 seems to be the most resistant to debilitating nsp4 mutations. Our results further prove that the CTD is essential for a vital nsp4 property other than catalysis.
Kaposi's Sarcoma-Associated Herpesvirus-Encoded Latency-Associated Nuclear Antigen Modulates K1 Expression through Its
cis
-Acting Elements within the Terminal Repeats
Authors: Verma Subhash C. , Lan Ke , Choudhuri Tathagata , Robertson Erle S.
Published: March 2006

K1 is the first open reading frame encoded by Kaposi's sarcoma-associated herpesvirus (KSHV) and lies positionally to the immediate right of the terminal repeats. K1 is a transmembrane glycoprotein having a functional immunoreceptor tyrosine-based activation motif (ITAM) capable of activating B-cell receptor signaling. K1 is expressed mostly during the lytic cycle of the virus and its promoter lies within the terminal repeat which contains the binding sites for latency-associated nuclear antigen (LANA). The K1 promoter (K1p) having LANA binding sites assayed by reporter assay demonstrated that LANA is capable of down-regulating K1 promoter transcriptional activity. However, the KSHV replication transcription activator RTA up-regulates K1p transcriptional activity. The promoter deleted of LANA binding sites showed loss in LANA-mediated down-regulation but was unaffected for RTA-mediated up-regulation. Increasing amounts of RTA rescued LANA-mediated repression of K1p transcriptional activity in cotransfection experiments. Reporter assay data suggest that LANA binding to its cognate sequence is critical for LANA-mediated repression of K1p as a LANA construct lacking the DNA binding domain was unable to repress K1p transcription. Additionally, KSHV primary infection experiments suggest that K1 is expressed during early infection but is repressed on the establishment of latency and so follows an expression profile similar to that of RTA during infection. Analysis of the promoter sequence revealed the presence of Oct-1 transcription factor binding sites within the −116 to +76 region. Mutational analysis of the Oct-1 sites abolished RTA-mediated transcriptional activation, suggesting that RTA up-regulates K1p transcription through binding to this transcription factor.
Interplay of Cellular and Humoral Immune Responses against BK Virus in Kidney Transplant Recipients with Polyomavirus Nephropathy
Authors: Chen Yiping , Trofe Jennifer , Gordon Jennifer , Du Pasquier Renaud A. , Roy-Chaudhury Prabir , Kuroda Marcelo J. , Woodle E. Steve , Khalili Kamel , Koralnik Igor J.
Published: March 2006

Reactivation of the polyomavirus BK (BKV) causes polyomavirus nephropathy (PVN) in kidney transplant (KTx) recipients and may lead to loss of the renal allograft. We have identified two HLA-A*0201-restricted nine-amino-acid cytotoxic T lymphocyte (CTL) epitopes of the BKV major capsid protein VP1, VP1p44, and VP1p108.Using tetramer staining assays, we showed that these epitopes were recognized by CTLs in 8 of 10 (VP1p44) and 5 of 10 (VP1p108) HLA-A*0201+healthy individuals, while both epitopes elicited a CTL response in 10 of 10 KTx recipients with biopsy-proven PVN, although at variable levels. After in vitro stimulation with the respective peptides, CTLs directed against VP1p44were more abundant than against VP1p108in most healthy individuals, while the converse was true in KTx recipients with PVN, suggesting a shift in epitope immunodominance in the setting of active BKV infection. A strong CTL response in KTx recipients with PVN appeared to be associated with decreased BK viral load in blood and urine and low anti-BKV antibody titers, while a low or undetectable CTL response correlated with viral persistence and high anti-BKV antibody titers. These results suggest that this cellular immune response is present in most BKV-seropositive healthy individuals and plays an important role in the containment of BKV in KTx recipients with PVN. Interestingly, the BKV CTL epitopes bear striking homology with the recently described CTL epitopes of the other human polyomavirus JC (JCV), JCV VP1p36and VP1p100. A high degree of epitope cross-recognition was present between BKV and corresponding JCV-specific CTLs, which indicates that the same population of cells is functionally effective against these two closely related viruses.
Partial Delipidation Improves the T-Cell Antigenicity of Hepatitis B Virus Surface Antigen
Authors: Desombere Isabelle , Willems Annick , Gijbels Yvonne , Leroux-Roels Geert
Published: March 2006

Hepatitis B virus surface antigen (HBsAg) is a complex macromolecular particle composed of glycoproteins and lipids. The latter, representing 25% of the particle mass, are of host origin and determine the solubility, stability, and, indirectly, B-cell immunogenicity of HBsAg. HBsAg is a T-cell-dependent immunogen that does not elicit a detectable humoral immune response in 5% of HBsAg vaccine recipients and in most subjects suffering from chronic hepatitis B. We investigated the influence of the lipid content on the antigenicity of the particle. Lipids were partially removed from HBsAg by treatment with β-d-octyl glucoside and density centrifugation. Sham treatment consisted of density centrifugation of HBsAg only. We compared the in vitro proliferative responses of established T-cell lines and nonfractionated peripheral blood mononuclear cells (PBMC) from HBsAg vaccinees and chronic HBV patients when stimulated with partially delipidated HBsAg, untreated HBsAg, or sham-treated HBsAg. In all experiments, delipidated HBsAg turned out to be 10 to 100 times more antigenic than its untreated or sham-treated counterpart. Remarkably, PBMC from vaccine nonresponders or chronic HBV patients displayed a proliferative response towards delipidated HBsAg, whereas native HBsAg never induced a response. A series of control experiments demonstrated that this enhancement of T-cell antigenicity was HBsAg specific and directly linked to lipid extraction. Nonspecific adjuvant effects of any kind could be ruled out. In vivo evaluation in mice demonstrated that delipidated particles lose most of their B-cell antigenicity. However, when native and delipidated particles were mixed, these mixtures induced equal or slightly superior anti-HBs responses to those induced by the same quantity of native HBsAg alone. In conclusion, our data show that partial delipidation of HBsAg strikingly increases the T-cell antigenicity of this unique viral antigen.
Replication Properties of Human Adenovirus In Vivo and in Cultures of Primary Cells from Different Animal Species
Authors: Jogler Christian , Hoffmann Dennis , Theegarten Dirk , Grunwald Thomas , Überla Klaus , Wildner Oliver
Published: March 2006

Oncolytic adenoviruses have emerged as a promising approach for the treatment of tumors resistant to other treatment modalities. However, preclinical safety studies are hampered by the lack of a permissive nonhuman host. Screening of a panel of primary cell cultures from seven different animal species revealed that porcine cells support productive replication of human adenovirus type 5 (Ad5) nearly as efficiently as human A549 cells, while release of infectious virus by cells from other animal species tested was diminished by several orders of magnitude. Restriction of productive Ad5 replication in rodent and rabbit cells seems to act primarily at a postentry step. Replication efficiency of adenoviral vectors harboring different E1 deletions or mutations in porcine cells was similar to that in A549 cells. Side-by-side comparison of the viral load kinetics in blood of swine and mice injected with Ad5 or a replication-deficient adenoviral vector failed to provide clear evidence for virus replication in mice. In contrast, evidence suggests that adenovirus replication occurs in swine, since adenoviral late gene expression produced a 13.5-fold increase in viral load in an individual swine from day 3 to day 7 and 100-fold increase in viral DNA levels in the Ad5-infected swine compared to the animal receiving a replication-deficient adenovirus. Lung histology of Ad5-infected swine revealed a severe interstitial pneumonia. Although the results in swine are based on a small number of animals and need to be confirmed, our data strongly suggest that infection of swine with human adenovirus or oncolytic adenoviral vectors is a more appropriate animal model to study adenoviral pathogenicity or pharmacodynamic and toxicity profiles of adenoviral vectors than infection of mice.
Adenovirus-Mediated RNA Interference against Foot-and-Mouth Disease Virus Infection both In Vitro and In Vivo
Authors: Chen Weizao , Liu Mingqiu , Jiao Ye , Yan Weiyao , Wei Xuefeng , Chen Jiulian , Fei Liang , Liu Yang , Zuo Xiaoping , Yang Fugui , Lu Yonggan , Zheng Zhaoxin
Published: March 2006

Foot-and-mouth disease virus (FMDV) infection is responsible for the heavy economic losses in stockbreeding each year. Because of the limited effectiveness of existing vaccines and antiviral drugs, the development of new strategies is needed. RNA interference (RNAi) is an effective means of suppressing virus replication in vitro. Here we demonstrate that treatment with recombinant, replication-defective human adenovirus type 5 (Ad5) expressing short-hairpin RNAs (shRNAs) directed against either structural protein 1D (Ad5-NT21) or polymerase 3D (Ad5-POL) of FMDV totally protects swine IBRS-2 cells from homologous FMDV infection, whereas only Ad5-POL inhibits heterologous FMDV replication. Moreover, delivery of these shRNAs significantly reduces the susceptibility of guinea pigs and swine to FMDV infection. Three of five guinea pigs inoculated with 10
6
PFU of Ad5-POL and challenged 24 h later with 50 50% infectious doses (ID
50
) of homologous virus were protected from the major clinical manifestation of disease: the appearance of vesicles on the feet. Two of three swine inoculated with an Ad5-NT21-Ad5-POL mixture containing 2 × 10
9
PFU each and challenged 24 h later with 100 ID
50
of homologous virus were protected from the major clinical disease, but treatment with a higher dose of adenovirus mixture cannot promote protection of animals. The inhibition was rapid and specific because treatment with a control adenovirus construct (Ad5-LacZ) expressing
Escherichia coli
galactosidase-specific shRNA showed no marked antiviral activity. Our data highlight the in vivo potential of RNAi technology in the case of FMD.
Herpes Simplex Virus Type 1 Accumulation, Envelopment, and Exit in Growth Cones and Varicosities in Mid-Distal Regions of Axons
Authors: Saksena Monica Miranda , Wakisaka Hiroyuki , Tijono Bibing , Boadle Ross A. , Rixon Frazer , Takahashi Hirotaka , Cunningham Anthony L.
Published: March 2006

The mechanism of anterograde transport of alphaherpesviruses in axons remains controversial. This study examined the transport, assembly, and egress of herpes simplex virus type 1 (HSV-1) in mid- and distal axons of infected explanted human fetal dorsal root ganglia using confocal microscopy and transmission electron microscopy (TEM) at 19, 24, and 48 h postinfection (p.i.). Confocal-microscopy studies showed that although capsid (VP5) and tegument (UL37) proteins were not uniformly present in axons until 24 h p.i., they colocalized with envelope (gG) proteins in axonal varicosities and in growth cones at 24 and 48 h p.i. TEM of longitudinal sections of axons in situ showed enveloped and unenveloped capsids in the axonal varicosities and growth cones, whereas in the midregion of the axons, predominantly unenveloped capsids were observed. Partially enveloped capsids, apparently budding into vesicles, were observed in axonal varicosities and growth cones, but not during viral attachment and entry into axons. Tegument proteins (VP22) were found associated with vesicles in growth cones, either alone or together with envelope (gD) proteins, by transmission immunoelectron microscopy. Extracellular virions were observed adjacent to axonal varicosities and growth cones, with some virions observed in crescent-shaped invaginations of the axonal plasma membrane, suggesting exit at these sites. These findings suggest that varicosities and growth cones are probable sites of HSV-1 envelopment of at least a proportion of virions in the mid- to distal axon. Envelopment probably occurs by budding of capsids into vesicles with associated tegument and envelope proteins. Virions appear to exit from these sites by exocytosis.
Mechanism of Substrate Recognition by Drug-Resistant Human Immunodeficiency Virus Type 1 Protease Variants Revealed by a Novel Structural Intermediate
Authors: Prabu-Jeyabalan Moses , Nalivaika Ellen A. , Romano Keith , Schiffer Celia A.
Published: March 2006

Human immunodeficiency virus type 1 (HIV-1) protease processes and cleaves the Gag and Gag-Pol polyproteins, allowing viral maturation, and therefore is an important target for antiviral therapy. Ligand binding occurs when the flaps open, allowing access to the active site. This flexibility in flap geometry makes trapping and crystallizing structural intermediates in substrate binding challenging. In this study, we report two crystal structures of two HIV-1 protease variants bound with their corresponding nucleocapsid-p1 variant. One of the flaps in each of these structures exhibits an unusual “intermediate” conformation. Analysis of the flap-intermediate and flap-closed crystal structures reveals that the intermonomer flap movements may be asynchronous and that the flap which wraps over the P3 to P1 (P3-P1) residues of the substrate might close first. This is consistent with our hypothesis that the P3-P1 region is crucial for substrate recognition. The intermediate conformation is conserved in both the wild-type and drug-resistant variants. The structural differences between the variants are evident only when the flaps are closed. Thus, a plausible structural model for the adaptability of HIV-1 protease to recognize substrates in the presence of drug-resistant mutations has been proposed.
Bioluminescence Imaging of Live Infected Salmonids Reveals that the Fin Bases Are the Major Portal of Entry for
Novirhabdovirus
Authors: Harmache Abdallah , LeBerre Monique , Droineau Stéphanie , Giovannini Marco , Brémont Michel
Published: March 2006

Although
Novirhabdovirus
viruses, like the
Infectious hematopietic necrosis virus
(IHNV), have been extensively studied, limited knowledge exists on the route of IHNV entry during natural infection. A recombinant IHNV (rIHNV) expressing the
Renilla
luciferase gene was generated and used to infect trout. A noninvasive bioluminescence assay was developed so that virus replication in live fish could be followed hours after infection. We provide here evidence that the fin bases are the portal of entry into the fish. Confirmation was brought by the use of a nonpathogenic rIHNV, which was shown to persist in fins for 3 weeks postinfection.
Functional Central Polypurine Tract Provides Downstream Protection of the Human Immunodeficiency Virus Type 1 Genome from Editing by APOBEC3G and APOBEC3B
Authors: Wurtzer Sebastien , Goubard Armelle , Mammano Fabrizio , Saragosti Sentob , Lecossier Denise , Hance Allan J. , Clavel François
Published: March 2006

Lentiviruses utilize two polypurine tracts for initiation of plus-strand viral DNA synthesis. We have examined to what extent human immunodeficiency virus type 1 plus-strand initiation at the central polypurine tract (cPPT) could protect the viral genome from DNA editing by APOBEC3G and APOBEC3B. The presence of a functional cPPT, but not of a mutated cPPT, extensively reduced editing by both APOBEC3G and APOBEC3B of sequences downstream, but not upstream, of the cPPT, with significant protection observed as far as 400 bp downstream. Thus, in addition to other potential functions, the cPPT could help protect lentiviruses from editing by cytidine deaminases of the APOBEC family.
Theoretical, thermal, and coordination chemistry of the amphoteric thiazate (NSO)1 ion
Authors: Bohle D Scott , Hung Chen-Hsiung , Smith Bryan D
Published: March 2006

The isomers of thiazate (NSO) have a rich chemistry that is examined theoretically and experimentally for their thermal and coordination characteristics. The intramolecular isomerization of NSO to monothionitrite (ONS) is predicted (B3LYP/6-311+G*) to have a substantial barrier, greater than 418 kJ mol1. Thus, thiazates are expected to be relatively thermally stable towards isomerization, and DSC indicates that KNSO undergoes a two stage irreversible thermolytic decomposition only beginning at 132 °C with ΔH = 116.3 kJ mol1. As a ligand, the thiazate can adopt a range of geometries in response to the metal's oxidation state and ligand sphere. For example, in Ru(TTP)(NO)(NSO) the ligand has a markedly bent Ru-N-S geometry, and when contrasted with other structurally characterized thiazate coordination compounds, it is concluded that in addition to σ donation the thiazate binds to metals in an amphoteric manner because of either a forward or reverse OSN → M π donation similar to transition metal nitrosyl, amido, and imido complexes.Key words: thiazate, isomerization, thermolysis, amphoteric ligand, coordination chemistry.
An overview of organic molecule soft ionization using vacuum ultraviolet laser radiation
Authors: Shi Y J , Lipson R H
Published: March 2006

The utility of coherent vacuum ultraviolet (VUV) single-photon ionization (SPI) combined with time-of-flight mass spectrometry (TOF-MS) for organic molecule detection by parent mass is explored in this short review. Nonresonant tripling in phase-matched XeAr gas mixtures was used to generate photons at a fixed energy of 10.5 eV. Representative organic molecules with different functional groups were examined, including aliphatic and aromatic alkanes, alkenes, alkynes, alkanols, ethers, amines, aldehydes, ketones, carboxylic acids, and esters. In almost every case, the intensity of the resultant parent molecular ion peak detected by TOF-MS was found to be superior to that obtained using 70 eV electron impact (EI), and comparable to that obtained with 12 eV EI. In those instances when fragmentation reactions did occur, the resultant ions were similar to those found using EI but with significantly reduced mass spectral intensities. It was still possible to establish one dominant fragmentation pathway that could be used for molecular identification even if the parent molecular ion was not the strongest feature in the spectrum, for example, in the case of alcohols, alcohol clusters, and alcoholether adducts. Several of the fragment ions were metastably broadened. Not surprisingly, their known appearance energies or estimated reaction enthalpies were very similar to the fixed photon energy used. The success of using VUV for organic molecule soft ionization is attributed to the low photon energy that removes predominantly a π- or non-bonding electron from the functionalized species. As most organic compounds have ionization potentials in the 10.5 eV region, this approach is expected to be near universal.Key words: vacuum ultraviolet laser, single photon ionization, organic molecule detection, soft-ionization, mass spectrometry.
Do electrospray mass spectra reflect the ligand binding state of proteins in solution?
Authors: Hossain Belal M , Simmons Douglas A , Konermann Lars
Published: March 2006

Electrospray ionization (ESI) mass spectrometry (MS) has become a popular tool for monitoring ligandprotein and proteinprotein interactions. Due to the "gentle" nature of the ionization process, it is often possible to transfer weakly bound complexes into the gas phase, thus making them amenable to MS detection. One problem with this technique is the potential occurrence of fragmentation events during ESI. Also, some analytes tend to cluster together during ionization, thus forming nonspecific gas-phase assemblies that do not represent solution-phase complexes. In this work, we implemented a hydrogendeuterium exchange (HDX) approach that can reveal whether or not the free and (or) bound constituents of a complex observed in ESI-MS reflect the binding situation in solution. Proteins are subjected to ESI immediately following an isotopic labeling pulse; only ligand-free and ligand-bound protein ions that were formed directly from the corresponding solution-phase species showed different HDX levels. Using myoglobin as a model system, it is demonstrated that this approach can readily distinguish scenarios where the hemeprotein interactions were disrupted in solution from those where dissociation of the complex occurred in the gas phase. Experiments on cytochrome c strongly suggest that dimeric protein ions observed in ESI-MS reflect aggregates that were formed in solution.Key words: electrospray mass spectrometry, ligandprotein interaction, noncovalent complex, hydrogendeuterium exchange, protein folding.
Electrospray ionization Fourier transform mass spectrometry of polycyclic aromatic hydrocarbons using silver(I)-mediated ionization
Authors: Maziarz III E Peter , Baker Gary A , Wood Troy D
Published: March 2006

Here, a methodology employing doped Ag(I) salt as an in situ cationization reagent for efficient ionization of nonpolar molecules within a conventional electrospray ionization source is described. The effectiveness of Ag(I)-mediated ionization is demonstrated using ESI Fourier transform mass spectrometry for the rapid detection and identification of priority pollutant polyaromatic hydrocarbon (PAH) species. In contrast to earlier coordination ESI-MS reports employing silver salts, argentated species are not typically observed for PAH species. Instead, oxidation of the PAH occurs to produce only the [PAH]+·odd-electron molecular parent ion, simplifying spectral analysis. In addition, the method demonstrates linear quantitative performance. The Ag(I) reagent provides quantifiable PAHs (not ordinarily amenable to ESI-MS) from 64 ppb, and suggests the immediate potential for sampling and on-line monitoring of complex, real world, and otherwise intractable environmental samples. Finally, the high mass accuracy of ESI Fourier transform mass spectrometry further allows unequivocal identification of molecular formulas within PAH mixtures.Key words: electrospray ionization, nonpolar, hydrocarbons, polyaromatic, Fourier transform mass spectrometry.
Predicting ion rearrangement reactions  The energetics of the internal SN2 reaction in gas-phase proton-bound molecular pairs
Authors: Grabowy Julie AD , Mayer Paul M
Published: March 2006

A common rearrangement reaction for gas-phase proton-bound molecular pairs corresponds to an internal SN2 reaction that results in the loss of a small neutral molecule. For pairs (RCN)(ROH)H+, the energies of the two transition states (TSaand TSb) and the intermediate complex (IC) in the isomerization reaction (relative to the proton-bound pair, in kJ mol1) can be estimated using the following relationships: E(TSa) = 87  9(n)  0.33(ΔPA), E(IC) = 83  9(n)  0.33(ΔPA), and E(TSb) = 107  9(n)  0.10(ΔPA), where 87, 83, and 107 kJ mol1are the values for (CH3CN)(CH3OH)H+. Here, n is the number of stablizing alkyl groups on the central SN2 carbon and ΔPA is the difference between the proton affinity of the migrating moiety and that for the base system (in this case, CH3CN). For the analogous pairs (ROH)(R′OH)H+, only the first value in each expression is different (98, 94, and 121 kJ mol1, respectively, calculated for (CH3OH)2H+).Key words: proton-bound molecular pairs, isomerization, internal SN2 reaction, energetics, metastable ions.
Gas-phase reactions of atomic lanthanide cations with methyl chloride  Periodicities in reactivity
Authors: Zhao Xiang , Koyanagi Gregory K , Bohme Diethard K
Published: March 2006

Room temperature reactions of lanthanide atomic cations (excluding Pm+) with CH3Cl are surveyed systematically in the gas phase using an inductively coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. Reaction rate coefficients are reported along with product distributions in He at 0.35 Torr (1 Torr = 133.3224 Pa) and 295 K. Cl atom transfer is the predominant reaction channel observed with all 14 lanthanide cations, but minor CH3Cl addition also occurs with the late lanthanide cations Dy+, Ho+, Er+, Tm+, and Yb+. The reaction efficiency for Cl atom transfer is shown to be governed by the energy required to promote an electron to achieve a d1s1excited electronic configuration in which two non-f electrons are available for bonding: it decreases as the promotion energy increases and the periodic trend in reaction efficiency along the lanthanide series matches the periodic trend in the corresponding electron-promotion energy. This behaviour is consistent with a CCl bond insertion mechanism of the type proposed previously for insertion reactions of Ln+cations with hydrocarbons and methyl fluoride. Direct Cl atom abstraction by a harpoonlike mechanism was excluded because of an observed noncorrelation of reaction efficiency with IE(Ln+). A remarkable Arrhenius-like correlation is observed for the dependence of reactivity on promotion energy: the early and late lanthanide cations exhibit characteristic temperatures of (1.4 ± 0.2) × 104and (4.5 ± 0.3) × 103 K, respectively. A rapid second Cl atom transfer occurs with LaCl+, CeCl+, GdCl+, TbCl+, and LuCl+, but there was no evidence for a third chlorine atom abstraction with any of the LnCl2+cations. Both LnCl+and LnCl2+add up to five methyl chloride molecules under the experimental operating conditions of the ICP/SIFT tandem mass spectrometer.Key words: lanthanide cations, Cl atom transfer, electron promotion, methyl chloride.
The water elimination from the ethyl acetate radical cation  Answers from theory to a longstanding mechanistic problem
Authors: Lee Richard , Ruttink Paul JA , Burgers Peter C , Terlouw Johan K
Published: March 2006

Previous experimental studies of the water elimination from ionized ethyl acetate (EA-1) and its enol, CH2=C(OH)OC2H5·+ (EA-2), provide no mechanistic proposals, but note that the reaction is complex because all hydrogen atoms and both oxygen atoms participate. Loss of H2O is the predominant process observed for the metastable ions, yielding ionized methyl vinyl ketone, CH3C(=O)CH=CH2·+ (MVK), as the product ion. Metastable keto-alcohol ions CH3C(=O)CH2CH2OH·+ (HB-1) also abundantly lose H2O, yielding MVK at the thermochemical threshold. Using the CBS-QB3 model chemistry and complementary RRKM calculations, we have examined plausible mechanisms for the water elimination from metastable ions EA-1/2 and HB-1. Our calculations support the proposal that (i) ions HB-1 dissociate into MVK at the thermochemical threshold via a 1,4-H shift and a consecutive [1,2]-hydroxycarbene shift, and (ii) ions EA-1/2 undergo a three-step isomerization reaction into HB-1, which serves as the precursor for the ensuing water elimination. It is further shown that synergy between theory and experiment leads to a complex, yet transparent, mechanistic picture of the isomerization and dissociation behaviour of ionized ethyl acetate, which accounts for the labelling results.Key words: tandem mass spectrometry, CBS-QB3 model chemistry, reaction mechanism, hydroxycarbene shift.
A collisionally activated dissociation (CAD) and computational investigation of doubly and singly charged DMSO complexes of Cu2+
Authors: Stone John A , Su Timothy , Vukomanovic Dragic
Published: March 2006

The singly and doubly charged Cu(II)DMSO complexes formed by electrospray have been examined by CAD and computation. The CAD spectra were obtained as a function of collision energy. The doubly charged ions, [Cu(DMSO)n]2+, were observed only for n ≥ 2. For n = 3, dissociation leads mainly to [Cu(DMSO)2]+ + DMSO+, with only a trace of [Cu(DMSO)2]2+. Although [Cu(DMSO)]2+ was never detected, computation shows that the n = 1 complex exists in a potential well. Loss of DMSO+ is computed to be exothermic for n = 13, the exothermicity decreasing as n increases. The singly charged complexes in the ESI spectra were [CuX(DMSO)n]+ (X = Cl, Br, NO3, HSO4, n = 1 or 2). The CAD spectra showed competition between electron transfer from anion to metal followed by loss of X and loss of DMSO+. Experiment and computation show that for [CuX(DMSO)]+, loss of X is the preferred decomposition at low collision energy. NBO analysis shows that electron transfer to Cu from DMSO decreases in [Cu(DMSO)n]2+ as n increases, the bonding becoming more electrostatic and less covalent. In [CuX(DMSO)n]+, the negative charge on X is much less than unity with most of the difference appearing on the DMSO ligand(s).Key words: copperDMSO complexes, electrospray, CAD, structures.
Gas-phase ion chemistry of Ti(O-i-Pr)4
Authors: Xavier Luciano A , Riveros José M
Published: March 2006

The positive and negative gas-phase ion chemistry of Ti(O-i-Pr)4 was investigated at low pressures by FT-ICR. The fragment ion, (i-PrO)3Ti-O+=C(H)Me, reacts with the parent neutral by proton transfer and by a nucleophilic additionelimination reaction. The nature of the fragment ion and the ensuing ionmolecule reactions clearly indicate that Ti(O-i-Pr)4 exists as a monomer in the gas phase. In the negative ion mode, F was found to react easily with Ti(O-i-Pr)4 to yield the pentacoordinated complex FTi(O-i-Pr)4 ion. This hypervalent Ti species undergoes a series of sequential fragmentations induced by IR multiphoton excitation. The first step is unusual because two channels are observed by IRMPD: one involves loss of HF, and the other loss of i-PrOH. The subsequent dissociation processes are characterized by progressive elimination of propene giving rise to a number of different titanaoxirane-containing anions with the general formula [(η2-CMe2O)Ti(OH)3n(i-PrO)n]. FTi(O-i-Pr)4 was also observed to undergo multiple alkoxidefluoride exchanges with BF3 leading to the eventual formation of TiF5.Key words: titanium tetraisoproxide, gas-phase ion chemistry, hypervalent Ti, ionmolecule reactions, IRMPD.
Structural and sequence effects in the fragmentation of protonated tripeptides containing tyrosine
Authors: Harrison Alex G
Published: March 2006

The fragmentation reactions of a variety of protonated tripeptides containing tyrosine in the three possible positions have been studied by energy-resolved collision-induced dissociation mass spectrometry. The primary fragmentation reactions involve cleavage of the N-terminal and (or) C-terminal amide bond with the relative importance of the two cleavages depending strongly on the identity and position of the amino acid residues in the tripeptide. The results are interpreted in terms of the a1y mechanism for cleavage of the N-terminal amide bond and the bxyz mechanism for cleavage of the C-terminal amide bond and, indeed, provide support for these mechanisms. However, it appears likely that, for protonated H-Val-Tyr-Pro-OH, the neutral accompanying formation of the y1 (protonated proline) ion is a cyclic dipeptide (cyclo-Val-Tyr) rather than the oxazolone predicted by the bxyz mechanism.Key words: tyrosine-containing peptides, fragmentation mechanisms, tandem mass spectrometry.
The bond dissociation energies of SO3X (X = F, Cl, Br, and I)
Authors: Hao Changtong , Gilbert Thomas M , Sunderlin Lee S
Published: March 2006

The gas-phase strengths of the SO3X- bonds (X = Cl, Br, and I) have been determined to be 222 ± 13, 179 ± 11, and 161 ± 9 kJ/mol, respectively, by measuring thresholds for collision-induced dissociation in a flowing afterglow-tandem mass spectrometer. An upper limit of D(SO3F) ≤ 488 ± 19 kJ/mol was also determined. The periodic trends in the halide affinities of SO3 closely parallel those for SO2 and other Lewis acids. Bond strengths computed using the B3LYP, MP2, QCISD(T), and other models with several basis sets are generally lower than experiment.Key words: bond dissociation energies, computational chemistry, Lewis acids, superacids, halide affinities.
Synthesis and characterization of alkyl- and acyl-substituted oximephosphazenes
Authors: Çil Erol , Arslan Mustafa , Görgülü Ahmet Orhan
Published: March 2006

Two oximecyclophosphazenes were prepared from the hexakis(4-formylphenoxy)cyclotriphosphazene (2) and hexakis(4-acetylphenoxy)cyclotriphosphazene (8). The reactions of these oximes with ethyl bromide, allyl bromide, propanoyl chloride, and acriloyl chloride were studied. Hexasubstituted compounds were obtained from the reactions of hexakis{4-[(hydroxyimino)methyl]phenoxy}cyclotriphosphazene (3) with ethyl bromide (4), allyl bromide (5), and propanoyl chloride (6), however, the oxime groups on 3 rearranged to nitrile (7) in the reaction of 3 with acriloyl chloride. Hexasubstituted compounds were also obtained from the reactions of hexakis{4-[(1)-N-hydroxyethaneimidoyl]phenoxy}cyclotriphosphazene (9) with allyl bromide (11) and propanoyl chloride (12). Tetra- and penta-substituted products were obtained from the reactions of 9 with ethyl bromide (10) and acriloyl chloride (13), respectively. All products were generally obtained in high yields. The structures of the compounds were defined by elemental analysis, IR, 1H, 13C, and 31P NMR spectroscopy. Key words: hexachlorocyclotriphosphazene, phosphazene, oxime, oxime derivatives, oximephosphazenes.
α- and β-Cyclodextrin [2]rotaxanes with (diethylenetriamine)platinum(II) stoppers
Authors: Jin Victor X , Macartney Donal H , Buncel Erwin
Published: March 2006

A series of dinuclear platinum(II) complexes, [(dien)Pt(NH2(CH2)nNH2)Pt(dien)]Cl4 (dien = diethylenetriamine, n = 8, 9, 10, and 12) and their corresponding [2]rotaxanes with α-cyclodextrin (α-CD), [(dien)Pt{NH2(CH2)nNH2·α-CD}Pt(dien)]Cl4, have been synthesized and characterized by 1H, 13C, and 195Pt NMR spectroscopy and electrospray mass spectrometry. The rotaxanes were prepared by reacting the {NH2(CH2)nNH2·α-CD} pseudorotaxanes with [Pt(dien)]Cl, to stopper the included linear α,ω-diaminoalkane chains with the inert Pt(II) end groups. The kinetics of the self-assembly and dissociation of the β-CD rotaxane, [(dien)Pt{NH2(CH2)10NH2·β-CD}Pt(dien)]4+, were investigated by using 1H NMR and are indicative of a slippage mechanism, owing to the comparable sizes of the β-CD cavity and the [Pt(dien)]+ end group. A relatively weak inclusion of the end group in the β-CD cavity precedes a thermally promoted passage of the β-CD over the [Pt(dien)]+ end group onto the hydrophobic polymethylene chain of the bridging ligand of the thread. Key words: rotaxanes, pseudorotaxanes, cyclodextrin, platinum complexes, slippage mechanism.
Theoretical, dynamic, and structural studies of the phenyl rotation in bispentafluorophenyl palladium complexes with scorpion-type ligands
Authors: Carrión M Carmen , Jalón Félix A , López-Solera Isabel , Manzano Blanca R , Sepúlveda Francisco , Santos Lucía , Rodríguez Ana María , Moreno Miquel , Martínez-Ripoll Martín
Published: March 2006

A theoretical study at a DFT level has been carried out on the pentafluorophenyl rotation in the compounds [Pd(C6F5)2(bpzmPh)] (1) and [Pd(C6F5)2(bpz*mPh)] (2) (bpzm = bis(pyrazol-1-yl)phenylmethane and bpz*mPh = bis(3,5-dimethylpyrazol-1-yl)phenylmethane). The orientation of one C6F5with respect to the coordination plane was forced to adopt specific values to simulate ring rotation and several parameters, such as the disposition of the other C6F5group, the energy of the system, and the skeletal conformation of the bpz'm ligand, were analysed. The maximum energy value was found when the C6F5ring was nearly coplanar with the coordination plane. In both complexes the minimum energy corresponds to a situation where the two rings are nearly parallel. A number of distortions that mainly affect the NPdN bite angle were predicted for the complex containing the bpz*mPh ligand (methylated pyrazoles). Four structures of complexes from this family were determined by X-ray diffraction and the same types of distortion were found. The differences in the free energies of activation for the pentafluorophenyl rotation in complexes containing methylated and non-methylated ligands were theoretically calculated. The calculated values were consistent with the data experimentally determined by NMR spectroscopy. The origin of the difference was attributed to the aforementioned distortions of the complexes containing the bpz*mPh ligand, which were more remarkable in the configuration of maximum energy.Key words: N ligands, palladium, theoretical studies, DFT calculations, dynamics.
Reactions of β-alkoxyvinyl trifluoromethyl ketones with terminal alkynes  Reagent-controlled regioselectivity addition reactions
Authors: Zhu Shizheng , Jin Guifang , Jiang Huiling
Published: March 2006

Reactions of β-alkoxyvinyl trifluoromethyl ketones ROCH=CHCOCF3 (1, R = Et, Me2CHCH2), and their cyclic analogues 4-trifluoroacetyl-2,3-dihydrofuran (2a) and 5-trifluoroacetyl-3,4-dihydro-2H-pyran (2b), with terminal alkynes R-C≡CH (3, R = Ph, PhCH2, HOCH2, C5H11) mainly gave the 1,2-addition products (carbonyl alkynylation) in the presence of n-BuLi. However, promoted by ZnCl2Et3N, the reaction of 1 or 2 with equivalent alkyne predominately provided 1,4-addition products.Key words: β-alkoxyvinyl trifluoromethyl ketones, alkynes, 1,2-addition, 1,4-addition, catalysts.
Biomimetic aromatization of Hantzsch 1,4-dihydropyridines with sodium periodate catalyzed by a new polystyrene-bound manganese porphyrin
Authors: Moghadam Majid , Nasr-Esfahani Masoud , Tangestaninejad Shahram , Mirkhani Valiollah , Zolfigol Mohammad Ali
Published: March 2006

Efficient oxidation of Hantzsch 1,4-dihydropyridines with sodium periodate catalyzed by a polystyrene-bound manganese(III) porphyrin is reported. This catalyst shows high activity in the oxidation of various 1,4-dihydropyridines at room temperature. This heterogeneous catalyst can be reused five times without significant loss of its activity.Key words: biomimetic oxidation, supported metalloporphyrin, periodate, 1,4-dihydropyridine.
Total synthesis of 14β-fluorosteroids via a transannular DielsAlder reaction
Authors: Beaubien Sylvie , Deslongchamps Pierre
Published: March 2006

14β-Fluorosteroids 3 and 4 were synthesized to give a new class of unnatural cardenolides. The total synthesis of racemic 14β-fluorosteroids was accomplished using a highly diastereoselective transannular DielsAlder reaction on a trans-cis-cis macrocyclic triene. The α-fluoro analog 4 provided a comparable inhibitory activity to natural digitoxigenin 1.Key words: fluorosteroid, bioisostere, cardiovascular diseases, transannular DielsAlder reaction (TADA), macrocyclization.
Regioselective synthesis of vic-halo alcohols and symmetrical or unsymmetrical vic-dihalides from epoxides using triphenylphosphine  N-halo imides
Authors: Iranpoor Nasser , Firouzabadi Habib , Azadi Roya , Ebrahimzadeh Farzaneh
Published: March 2006

A simple, novel, and highly regioselective cleavage of epoxides into vicinal halo alcohols and symmetrical or unsymmetrical dihalides is described using different stoichiometries of triphenylphosphine (PPh3) and N-halo succinimide (NXS) or N-halo saccharine (NXSac).Key words: N-halo succinimide (NXS), N-halo saccharine (NXSac), triphenylphosphine (PPh3), epoxide, vic-halo alcohol, symmetrical dihalide, unsymmetrical dihalide.
Oxyhalogen-sulfur chemistry  Kinetics and mechanism of the oxidation of cysteamine by acidic iodate and iodine
Authors: Chanakira Alice , Chikwana Edward , Peyton David H , Simoyi Reuben H
Published: March 2006

The oxidation of cysteamine by iodate and aqueous iodine has been studied in neutral to mildly acidic conditions. The reaction is relatively slow and is heavily dependent on acid concentration. The reaction dynamics are complex and display clock behavior, transient iodine production, and even oligooscillatory production of iodine, depending upon initial conditions. The oxidation product was the cysteamine dimer (cystamine), with no further oxidation observed past this product. The stoichiometry of the reaction was deduced to be IO3+ 6H2NCH2CH2SH → I+ 3H2NCH2CH2S-SCH2CH2NH2+ 3H2O in excess cysteamine conditions, whereas in excess iodate the stoichiometry of the reaction is 2IO3+ 10H2NCH2CH2SH → I2+ 5H2NCH2CH2S-SCH2CH2NH2+ 6H2O. The stoichiometry of the oxidation of cysteamine by aqueous iodine was deduced to be I2+ 2H2NCH2CH2SH → 2I+ H2NCH2CH2S-SCH2CH2NH2+ 2H+. The bimolecular rate constant for the oxidation of cysteamine by iodine was experimentally evaluated as 2.7 (mol L1)1s1. The whole reaction scheme was satisfactorily modeled by a network of 14 elementary reactions.Key words: cysteamine, cystamine, Dushman reaction, oligooscillations.
DELAY GUARANTEE BACKUP ROUTE PLANNING FOR MULTICAST NETWORKS
Authors: YANG CHYI-BAO , WEN UE-PYNG , SHYUR CHING-CHIR
Published: March 2006

This paper considers quality of service in terms of end-to-end delay in planning backup routes for multicast communications. The problem of preplanning backup routes considering both cost minimization and end-to-end delay guarantee for multicast communications in the case a single link failure is investigated. Two delay labels, the limited label and the tolerable label, are defined to evaluate the end-to-end delay requirement. Four heuristic algorithms, including two tree-based algorithms, one subtree-based algorithm, and one link-based algorithm, are proposed to determine the delay-constrained backup routes having the minimum costs. Two procedures to determine a node selection sequence, Random and Minimum-Cost, are used in the tree-based algorithm. Experimental results show that the tree-based algorithm by the Minimum-Cost sequence yields the best performance in cost minimization with guarantee of end-to-end delay.
APPLICATION OF ANALYTIC HIERARCHY PROCESS IN MULTI-OBJECTIVE MIXED INTEGER PROGRAMMING FOR AIRLIFT CAPACITY PLANNING
Authors: STANNARD BARRY , ZAHIR SAJJAD , ROSENBLOOM EARL S.
Published: March 2006

The analytic hierarchy process is combined with multi-objective mixed integer programming to determine the optimal allocation of a limited number of aircraft among a group of airlift users with varying levels of priority and length of usage. Canadian Forces airlift planners typically encounter such a capacity planning problem. The solution to this problem requires the constrained assignment of n variable length missions (tasks) integrating hundreds of airlift requests from several users with many priorities to m airframes (parallel machines).
QUANTITY RESTRICTIONS AND THE RESELLER'S RESPONSE TO A TEMPORARY PRICE REDUCTION OR AN ANNOUNCED PRICE INCREASE
Authors: ABAD PRAKASH L.
Published: March 2006

Manufacturers and suppliers offer temporary reductions (or permanent increases) in the price charged to the resellers for a variety of reasons. The trade promotion may be offered to the reseller at a single point in time or over a finite time-span. In addition, in reselling situations, the end demand tends to be sensitive to selling price. It is commonly found that under such trade promotion (or in stockpiling to an announced price increase), not all the quantity purchased by the reseller at discount may be passed on to the final consumer at a reduced selling price. In fact, previous studies have shown that it is optimal for the reseller to carry forward some of the quantity purchased at discount and sell it later at the regular price. It has been suggested in the literature that by placing a restriction on the reseller's purchase quantity, the supplier can restrict the reseller's forward buy quantity. In this paper, we evaluate this approach. In the rest of the paper, we present alternate schemes which are easy to administer and which insure that the supplier avoids the spike in demand that occurs in the unconstrained problem.