bluuebunny/crossref_metadata_2025_split huggingface dataset:
Olefin Isomerization via Radical‐Ion Pairs in Triplet States Studied by Chemically Induced Dynamic Nuclear Polarization (CIDNP)
Authors: Goez Martin , Eckert Gerd 
Published: October 2006

AbstractGeometric isomerizations of olefins following photoinduced electron transfer (PET) are classified according to the relative energetic positions of the radical‐ion pairs and the reactant triplets. Each class exhibits characteristic CIDNP (chemically induced dynamic nuclear polarization) effects, for which typical examples are presented. Time‐resolved CIDNP experiments on the system triphenylamine/fumarodinitrile (= (2E)‐but‐2‐enedinitrile), where formation of the olefin triplet is impossible, show that there is also no isomerization of the olefin radical anion. With triisopropylamine or fumarodinitrile as the reaction partner for 4,4′‐dimethoxystilbene (= 1,1′‐[(1E)‐ethane‐1,2‐diyl]bis[4‐methoxybenzene]), both oxidative and reductive quenching give almost mirror‐image CIDNP spectra because of the pairing theorem; reverse electron transfer of the triplet radical‐ion pairs populates the stilbene triplet only, which then isomerizes. With anethole (= 1‐methoxy‐4‐(prop‐1‐enyl)benzene; M), the competition between electron return of triplet pairs $\rm{{}^{{3}}\overline {{{M}}^{ \bullet + } {{X}}^{ \bullet - } } }$ to give either M + 3X or 3M + X was studied by using a second isomerizable olefin (diethyl fumarate (= diethyl (2E)‐but‐2‐enedioate) or cinnamonitrile (= (2E)‐3‐phenylprop‐2‐enenitrile)) as the reaction partner X. Classes can be changed by employing PET sensitization. With ACN (anthracene‐9‐carbonitrile) as the sensitizer, anethole does not produce any directly observable polarizations, but a substitution of ACN.− by the radical anion of 1,4‐benzoquinone (= cyclohexa‐2,5‐diene‐1,4‐dione) or fumarodinitrile within the lifetime of the spin‐correlated radical‐ion pairs leads to very strong CIDNP signals that reflect the effects of both pairs.
A New Sterically Highly Hindered 7‐Membered Cyclic Nitroxide for the Controlled Living Radical Polymerization
Authors: Chang Che‐Chien , Siegenthaler Kai Oliver , Studer Armido 
Published: October 2006

AbstractThe synthesis of a new sterically highly hindered 7‐membered alkoxyamine, 2,2,7,7‐tetraethyl‐1‐(1‐phenylethoxy)‐1,4‐diazepan‐5‐one (4), starting from known 2,2,6,6‐tetraethyl‐1‐(1‐phenylethoxy)piperidin‐4‐one (3) via a Beckmann‐type rearrangement is presented. It is shown that ring‐enlargement by insertion of an NH moiety in going from 3 to 4 leads to a more efficient regulator for nitroxide‐mediated controlled living radical styrene (= ethenylbenzene) and butyl acrylate (= butyl prop‐2‐enoate) polymerization. In addition to the polymerization experiments, kinetic data on the reversible CO bond homolysis of alkoxyamines 3 and 4 are presented.
Alkoxyamines of Stable Aromatic Nitroxides: NO vs. CO Bond Homolysis
Authors: Gigmes Didier , Gaudel‐Siri Anouk , Marque Sylvain R. A. , Bertin Denis , Tordo Paul , Astolfi Paola , Greci Lucedio , Rizzoli Corrado 
Published: October 2006

AbstractA series of stable 2,2‐disubstituted 3‐(phenylimino)indol‐1‐oxyls, the alkoxyamines 3, were prepared, characterized, and tested as possible candidates in controlled radical polymerization (CRP). The sturctures of 3d and 10 were additionally solved by X‐ray diffraction. The lability of the NO(C) and (N)OC bonds of compounds 3 were compared, and the possibility of NO vs. OC bond cleavage was evaluated by thermal degradation, ESR spin trapping, MS experiments, and DFT calculations. Alkoxyamines with a primary‐ or secondary‐alkyl group bound to the O‐atom of the nitroxide function (hexyl and i‐Pr) mainly underwent (undesired) NO bond homolysis. When the O‐alkyl radical was a tertiary or a benzyl group (crotonyl or styryl), OC bond cleavage occurred as the main process, thus suggesting a possible use of these compounds in CRP processes.
Absolute Rate Constants for the Addition of the 1‐(tert‐Butoxy)carbonylethyl Radical onto Cyclic Alkenes in Solution
Authors: Fischer Hanns , Knühl Bernhard , Marque Sylvain R. A. 
Published: October 2006

AbstractAbsolute rate constants are reported for the addition of the 1‐[(tert‐butoxy)carbonyl]ethyl (= 2‐(1,1‐dimethylethoxy)‐1‐methyl‐2‐oxoethyl) radical .CHMeCO2(t‐Bu) to several cyclic and monosubstituted alkenes in MeCN as obtained by time‐resolved electron paramagnetic resonance (EPR). The activation energies for the addition of this alkyl radical are mainly governed by the addition enthalpy but are also substantially lowered by the ambiphilic effect and by relief of cyclic strain.
Oxidative and Photochemical Stability of Ionomers for Fuel‐Cell Membranes
Authors: Mitov Svetlin , Delmer Olga , Kerres Jochen , Roduner Emil 
Published: October 2006

AbstractTo predict hydroxyl‐radical‐initiated degradation of new proton‐conducting polymer membranes based on sulfonated polyetherketones (PEK) and polysulfones (PSU), three nonfluorinated aromatics are chosen as model compounds for EPR experiments, aiming at the identification of products of HO.‐radical reactions with these monomers. Photolysis of H2O2 was chosen as the source of HO. radicals. To distinguish HO.‐radical attack from direct photolysis of the monomers, experiments were carried out in the presence and absence of H2O2. A detailed investigation of the pH dependence was performed for 4,4′‐sulfonylbis[phenol] (SBP), bisphenol A (= 4,4′‐isopropylidenebis[phenol]; BPA), and [1,1′‐biphenyl]‐4,4′‐diol (BPD). At pH ≥ pKA of HO. and H2O2, reactions between the model compounds and O2.− or 1O2 are the most probable ways to the phenoxy and ‘semiquinone’ radicals observed in this pH range in our EPR spectra. A large number of new radicals give evidence of multiple hydroxylation of the aromatic rings. Investigations at low pH are particularly relevant for understanding degradation in polymer‐electrolyte fuel cells (PEFCs). However, the chemistry depends strongly on pH, a fact that is highly significant in view of possible pH inhomogeneities in fuel cells at high currents. It is shown that also direct photolysis of the monomers leads to ‘semiquinone’‐type radicals. For SBP and BPA, this involves cleavage of a CC bond.
Antioxidant and Antiradical Activity of Hydroxy‐Substituted 4‐Thiaflavanes
Authors: Amorati Riccardo , Fumo Maria Grazia , Pedulli Gian Franco , Menichetti Stefano , Pagliuca Chiara , Viglianisi Caterina 
Published: October 2006

AbstractThe antioxidant activities of several hydroxy‐substituted 4‐thiaflavanes, compounds 1–3, were determined by measuring their ability of inhibiting the autoxidation of styrene or cumene. On this basis, the role played by the number and position of OH groups and by the oxidation state of the S‐atom was quantified and rationalized. With these data, it should be possible to optimize the structural features of these ‘double‐faced’ antioxidants for structureactivity‐relationship studies. A comparison between the kinetic data (kinh) reported in this paper and the previously reported values of the antiradical activities (SC50), measured by the DPPH. bleaching method, for 1–3 is made (Table).
Pulse EPR Methods for Studying Chemical and Biological Samples Containing Transition Metals
Authors: Calle Carlos , Sreekanth Anandaram , Fedin Matvey V. , Forrer Jörg , Garcia‐Rubio Inés , Gromov Igor A. , Hinderberger Dariush , Kasumaj Besnik , Léger Patrick , Mancosu Bruno , Mitrikas George , Santangelo Maria Grazia , Stoll Stefan , Schweiger Arthur , Tschaggelar René , Harmer Jeffrey 
Published: October 2006

AbstractThis review discusses the application of pulse EPR to the characterization of disordered systems, with an emphasis on samples containing transition metals. Electron nuclear double‐resonance (ENDOR), electron‐spin‐echo envelope‐modulation (ESEEM), and double electron–electron resonance (DEER) methodologies are outlined. The theory of field modulation is outlined, and its application is illustrated with DEER experiments. The simulation of powder spectra in EPR is discussed, and strategies for optimization are given. The implementation of this armory of techniques is demonstrated on a rich variety of chemical systems: several porphyrin derivatives that are found in proteins and used as model systems, otherwise highly reactive aminyl radicals stabilized with electron‐rich transition metals, and nitroxide–copper–nitroxide clusters. These examples show that multi‐frequency continuous‐wave (CW) and pulse EPR provides detailed information about disordered systems.
Photochemical Reactions and Photoinduced Electron‐Transfer Processes in Liquids, Frozen Solutions, and Proteins as Studied by Multifrequency Time‐Resolved EPR Spectroscopy
Authors: Savitsky Anton , Möbius Klaus 
Published: October 2006

AbstractIn this overview, modern multifrequency EPR spectroscopy, in particular at high magnetic fields, is shown to provide detailed information about structure, motional dynamics, and spin chemistry of transient radicals and radical pairs occurring in photochemical reactions. Examples discussed comprise photochemical reactions in liquid solution and light‐initiated electron transfer processes both in biomimetic donor–acceptor model systems in frozen solution or liquid crystals and in natural photosynthetic‐reaction‐center protein complexes. The transient paramagnetic states exhibit characteristic electron polarization (CIDEP) effects. They contain valuable information about structure and dynamics of the transient reaction intermediates. Moreover, they are exploited for signal enhancement. Continuous‐wave (cw) and pulsed versions of time‐resolved high‐field EPR spectroscopy, such as cw‐transient‐EPR (TREPR) and pulsed‐electron‐spin‐echo (ESE) experiments, are compared with respect to their advantages and limitations for the specific system under study. For example, W‐band (95‐GHz) TREPR spectroscopy in conjunction with a continuous‐flow system for light‐generated short‐lived transient spin‐polarized radicals of organic photoinitiators in solution was performed with a time resolution of 10 ns. The increased Boltzmann polarization at high fields even allows detection of transient radicals without CIDEP effects. This enables one to determine initial radical polarization contributions as well as radical‐addition reaction constants. Another example of the power of combined X‐band and W‐band TREPR spectroscopy is given for the complex electron‐transfer and spin dynamics of covalently linked porphyrin–quinone as well as Watson–Crick base‐paired porphyrin–dinitrobenzene donor–acceptor biomimetic model systems. Furthermore, W‐band ESE experiments on the spin‐correlated coupled radical pair $\rm{{{P}}_{865}^{\bullet + } }$$\rm{{{Q}}_{{A}}^{\bullet - } }$ in reaction centers of the purple photosynthetic bacterium Rb. sphaeroides reveal details of distance and orientation of the pair partners in their charge‐separated transient state. The results are compared with those of the ground‐state P865QA. The high orientation selectivity of high‐field EPR provides single‐crystal‐like information even from disordered frozen‐solution samples. The examples given demonstrate that high‐field EPR adds substantially to the capability of ‘classical’ spectroscopic and diffraction techniques for determining structure–dynamics–function relations of biochemical systems, since transient intermediates can be observed in real time in their working states on biologically relevant time scales.
Reactivation of Kaposi's sarcoma‐associated herpesvirus by natural products from Kaposi's sarcoma endemic regions
Authors: Whitby Denise , Marshall Vickie A. , Bagni Rachel K. , Miley Wendell J. , McCloud Thomas G. , Hines‐Boykin Rebecca , Goedert James J. , A.Conde Betty , Nagashima Kunio , Mikovits Judy , Dittmer Dirk P. , Newman David J. 
Published: October 2006

AbstractKaposi's sarcoma (KS) and its causative agent, Kaposi's sarcoma associated herpesvirus (KSHV/HHV‐8), a gamma2 herpesvirus, have distinctive geographical distributions that are largely unexplained. We propose the “oncoweed” hypothesis to explain these differences, namely that environmental cofactors present in KS endemic regions cause frequent reactivation of KSHV in infected subjects, leading to increased viral shedding and transmission leading to increased prevalence of KSHV infection as well as high viral load levels and antibody titers. Reactivation also plays a role in the pathogenesis of KSHV‐associated malignancies. To test this hypothesis, we employed an in vitro KSHV reactivation assay that measured increases in KSHV viral load in KSHV infected primary effusion lymphoma (PEL) cells and screened aqueous natural product extracts from KS endemic regions. Of 4,842 extracts from 38 countries, 184 (5%) caused KSHV reactivation. Extracts that caused reactivation came from a wide variety of plant families, and extracts from Africa, where KSHV is highly prevalent, caused the greatest level of reactivation. Time course experiments were performed using 28 extracts that caused the highest levels of reactivation. The specificity of the effects on viral replication was examined using transcriptional profiling of all viral mRNAs. The array data indicated that the natural extracts caused an ordered cascade of lytic replication similar to that seen after induction with synthetic activators. These in vitro data provide support for the “oncoweed” hypothesis by demonstrating basic biological plausibility. © 2006 Wiley‐Liss, Inc.
Diet supplemented with citrus unshiu segment membrane suppresses chemically induced colonic preneoplastic lesions and fatty liver in male db/db mice
Authors: Suzuki Rikako , Kohno Hiroyuki , Yasui Yumiko , Hata Kazuya , Sugie Shigeyuki , Miyamoto Shingo , Sugawara Kuniaki , Sumida Takashi , Hirose Yoshinobu , Tanaka Takuji 
Published: October 2006

AbstractThe modulatory effects of dietary citrus unshiu segment membrane (CUSM) on the occurrence of aberrant crypt foci (ACF) and β‐catenin accumulated crypts (BCACs) were determined in male C57BL/KsJ‐db/db (db/db) mice initiated with azoxymethane (AOM). Male db/db, db/+ and +/+ mice were given 5 weekly subcutaneous injections of AOM (15 mg/kg body weight), and then they were fed the diet containing 0.02%, 0.1% or 0.5% CUSM for 7 weeks. At Week 12, a significant increase in the numbers of ACF and BCAC was noted in the db/db mice in comparison with the db/+ and +/+ mice. Feeding with CUSM caused reduction in the frequency of ACF in all genotypes of mice and the potency was high in order of the db/db mice, db/+ mice and +/+ mice. The number of BCACs was also reduced by feeding with CUSM, thus resulting in a 28–61% reduction in the db/db mice, possibly due to suppression of cell proliferation activity in the lesions by feeding with CUSM‐containing diet. Clinical chemistry revealed a low serum level of triglyceride in mice fed CUSM. In addition, CUSM feeding inhibited fatty metamorphosis and fibrosis in the liver of db/db mice. Our findings show that CUSM in the diet has a chemopreventive ability against the early phase of AOM‐induced colon carcinogenesis in the db/db as well as db/+ and +/+ mice, indicating potential use of CUSM in cancer chemoprevention in obese people. © 2006 Wiley‐Liss, Inc.
Inhibition of heme oxygenase‐1 by zinc protoporphyrin IX reduces tumor growth of LL/2 lung cancer in C57BL mice
Authors: Hirai Kaeko , Sasahira Tomonori , Ohmori Hitoshi , Fujii Kiyomu , Kuniyasu Hiroki 
Published: October 2006

AbstractHeme oxygenase (HO)‐1 is a key player reducing cytotoxicity and enhancing protumoral effects of nitric oxide (NO). We examined zinc protoporphyrin (ZnPP) IX, an HO‐1 inhibitor, to affect tumor growth of LL/2 mouse lung cancer cells. ZnPPIX reduced HO‐1 expression and HO activity in LL/2 cells, whereas cobalt PPIX (CoPPIX), an HO‐1 activator, increased both. LL/2 cells treated with sodium nitropurusside, an NO donor, showed growth inhibition dose‐dependently, which was enhanced by ZnPPIX cotreatment, but was reduced by CoPPIX. In mice tumors, ZnPPIX decreased HO‐1 expression. LL/2‐tumors were found in 88% (7/8) vehicle‐treated mice, whereas tumors were found in 38% (3/8) and 25% (2/8) mice treated with 5 and 20 μg/mouse ZnPPIX, respectively (p = 0.0302). Tumor growth was inhibited dose‐dependently by ZnPPIX. Vascular endothealial growth factor concentration in tumors was reduced by ZnPPIX (p = 0.0341). Microvessel density (MVD) in ZnPPIX‐treated tumors was lower than that in vehicle‐treated tumors (p = 0.0362). Apoptotic cell count in ZnPPIX‐treated tumors was higher than that in vehicle‐treated tumors (p = 0.0003). In contrast, CoPPIX treatment increased HO‐1 expression, enhanced tumorigenicity and MVD and reduced apoptosis. From these findings, inhibition of HO‐1 by ZnPPIX provides relevant antitumoral effects. © 2006 Wiley‐Liss, Inc.
Expression of activation‐induced cytidine deaminase in human hepatocytes during hepatocarcinogenesis
Authors: Kou Tadayuki , Marusawa Hiroyuki , Kinoshita Kazuo , Endo Yoko , Okazaki Il‐mi , Ueda Yoshihide , Kodama Yuzo , Haga Hironori , Ikai Iwao , Chiba Tsutomu 
Published: October 2006

AbstractActivation‐induced cytidine deaminase (AID) plays a role as a genome mutator in activated B cells, and inappropriate expression of AID has been implicated in the immunopathological phenotype of human B‐cell malignancies. Notably, we found that the transgenic mice overexpressing AID developed lung adenocarcinoma and hepatocellular carcinoma (HCC), suggesting that ectopic expression of AID can lead to tumorigenesis in epithelial tissues as well. To examine the involvement of AID in the development of human HCC, we analyzed the AID expression and its correlation with mutation frequencies of the p53 gene in liver tissues from 51 patients who underwent resection of primary HCCs. The specific expression, inducibility by cytokine stimulation and mutagenic activity of AID were investigated in cultured human hepatocytes. Only trace amounts of AID transcripts were detected in the normal liver; however, endogenous AID was significantly upregulated in both HCC and surrounding noncancerous liver tissues with underlying chronic hepatitis or liver cirrhosis (p < 0.05). Most liver tissues with underlying chronic inflammation with endogenous AID upregulation already contained multiple genetic changes in the p53 gene. In both hepatoma cell lines and cultured human primary hepatocytes, the expression of AID was substantially induced by TGF‐β stimulation. Aberrant activation of AID in hepatocytes resulted in accumulation of multiple genetic alterations in the p53 gene. Our findings suggest that the aberrant expression of AID is observed in human hepatocytes with several pathological settings, including chronic liver disease and HCC, which might enhance the genetic susceptibility to mutagenesis leading to hepatocarcinogenesis. © 2006 Wiley‐Liss, Inc.
The involvement of hypoxia‐inducible factor‐1α in the susceptibility to γ‐rays and chemotherapeutic drugs of oral squamous cell carcinoma cells
Authors: Sasabe Eri , Zhou Xuan , Li Dechao , Oku Naohisa , Yamamoto Tetsuya , Osaki Tokio 
Published: October 2006

AbstractThe transcription factor hypoxia‐inducible factor‐1α (HIF‐1α) is the key regulator that controls the hypoxic response of mammalian cells. The overexpression of HIF‐1α has been demonstrated in many human tumors. However, the role of HIF‐1α in the therapeutic efficacy of chemotherapy and radiotherapy in cancer cells is poorly understood. In this study, we investigated the influence of HIF‐1α expression on the susceptibility of oral squamous cell carcinoma (OSCC) cells to chemotherapeutic drugs (cis‐diamminedichloroplatinum and 5‐fluorouracil) and γ‐rays. Treatment with chemotherapeutic drugs and γ‐rays enhanced the expression and nuclear translocation of HIF‐1α, and the susceptibility of OSCC cells to the drugs and γ‐rays was negatively correlated with the expression level of HIF‐1α protein. The overexpression of HIF‐1α induced OSCC cells to become more resistant to the anticancer agents, and down‐regulation of HIF‐1α expression by small interfering RNA enhanced the susceptibility of OSCC cells to them. In the HIF‐1α‐knockdown OSCC cells, the expression of P‐glycoprotein, heme oxygenase‐1, manganese‐superoxide dismutase and ceruloplasmin were downregulated and the intracellular levels of chemotherapeutic drugs and reactive oxygen species were sustained at higher levels after the treatment with the anticancer agents. These results suggest that enhanced HIF‐1α expression is related to the resistance of tumor cells to chemo‐ and radio‐therapy and that HIF‐1α is an effective therapeutic target for cancer treatment. © 2006 Wiley‐Liss, Inc.
Downregulation of the upstream binding factor1 by glycogen synthase kinase3β in myeloid cells induced to differentiate
Authors: Liu Mingli , Tu Xiao , Ferrari‐Amorotti Giovanna , Calabretta Bruno , Baserga Renato 
Published: October 2006

AbstractThe upstream binding factor 1 (UBF1), one of the
proteins that regulate the activity of RNA polymerase I, is downregulated in 32D myeloid cells induced to differentiate into granulocytes, either by the type 1 insulin‐like growth factor (IGF‐1) or the granulocytic colony stimulating factor (G‐CSF). Downregulation of UBF1 is largely due to protein degradation, while mRNA levels are not affected. Inhibition of UBF1 degradation by lithium chloride (LiCl)and lactacystin suggest a role of glycogen synthase kinase β (GSK3β) in a proteasome‐dependent degradation of UBF. GSK3β phosphorylates in vitro and in vivo the UBF protein, which has five putative motifs for phosphorylation by GSK3β. Elimination and/or mutations of these motifs stabilize the UBF1 protein even in cells induced to differentiate. Conversely, a stably transfected, constitutively active GSK3β accelerates the downregulation of UBF1. We show further that activation of the differentiating protein C/EPBα in 32D cells transformed by the oncogenic BCR/ABL protein causes downregulation of UBF1. Finally, inhibition of differentiation of myeloid cells by a dominant negative mutant of Stat3 stabilizes the UBF1 protein, while rapamycin‐induced differentiation of myeloid cells downregulates UBF1 levels. Taken together, our results indicate that the induction of granulocytic differentiation in 32D murine myeloid cells causes the degradation of UBF1, via GSK3β and the proteasome pathway. J. Cell. Biochem. 100: 1154–1169, 2007. © 2006 Wiley‐Liss, Inc.
Valence and extra‐valence orbitals in main group and transition metal bonding
Authors: Landis C. R. , Weinhold F. 
Published: October 2006

AbstractWe address the issue first raised by Maseras and Morokuma with regard to the questionable treatment of empty p‐orbitals in the algorithm for natural atomic/bond orbitals (NAOs, NBOs) and associated natural population analysis. We quantify this issue in terms of the numerical error (root‐mean‐square density deviation) resulting from the two alternative treatments of empty p‐sets, leading to distinct NAOs, atomic charges, and idealized Lewis structural representations. Computational application of this criterion to a broad spectrum of main group and transition group species (employing both single‐ and multi‐structure resonance models) reveals the interesting general pattern of (i) relatively insignificant differences for normal‐valent species, where a single resonance structure is usually adequate, but (ii) clear superiority of the standard NAO algorithm for hypervalent species, where multi‐resonance character is pronounced. These comparisons show how the divisive issue of “valence shell expansion” in transition metal bonding is deeply linked to competing conceptual models of hypervalency (viz., “p‐orbital participation” in skeletal hybridization vs. 3c/4e resonance character). The results provide a quantitative measure of superiority both for the standard NAO evaluation of atomic charges as well as the general 3c/4e (A: B‐C ↔ A‐B :C resonance) picture of main‐ and transition‐group hypervalency. © 2006 Wiley Periodicals, Inc. J Comput Chem, 2007