bluuebunny/crossref_metadata_2025_split huggingface dataset:
Post‐translational Modification in Microviridin Biosynthesis
Authors: Philmus Benjamin , Christiansen Guntram , Yoshida Wesley Y. , Hemscheidt Thomas K. 
Published: November 2008

AbstractCyanobacteria are prolific producers of bioactive natural products that mostly belong to the nonribosomal peptide and polyketide classes. We show here how a linear precursor peptide of microviridin K, a new member of the microviridin class of peptidase inhibitors, is processed to become the mature tricyclic peptidase inhibitor. The microviridin (mvd) biosynthetic gene cluster of P. agardhii comprises six genes encoding microviridin K, an apparently unexpressed second microviridin, two RimK homologues, an acetyltransferase, and an ABC transporter. We have over‐expressed three enzymes of this pathway and have demonstrated their biochemical function in vitro through chemical degradation and mass spectrometry. We show that a prepeptide undergoes post‐translational modification through cross‐linking by ester and amide bond formation by the RimK homologues MvdD and MvdC, respectively. In silico analysis of the mvd gene cluster suggests the potential for widespread occurrence of microviridin‐like compounds in a broad range of bacteria.
Orientational Properties of Poly‐γ‐benzyl‐L‐glutamate: Influence of Molecular Weight and Solvent on Order Parameters of the Solute
Authors: Marx Andreas , Thiele Christina 
Published: November 2008

AbstractResidual dipolar couplings (RDCs) have recently become increasingly important in organic structure determination due to their unique information content. One main limitation for the use of RDCs in organic compounds, however, is that the compound in question needs to be oriented with respect to the magnetic field in order to measure RDCs. So far, there are very few possibilities for modulating the induced degree of orientation. The situation is even worse when chiral orienting media are considered, which could allow absolute configuration determination in the future. We have conducted a systematic investigation into modulating the orientation induced by one chiral orienting medium, namely organic solutions of PBLG (poly‐γ‐benzyl‐L‐glutamate), as a function of its molecular weight and the organic co‐solvent used, and have obtained significant insights into factors that influence the order induced. With increasing molecular weight of the polypeptide the orientation of the solutes decreases, leading to well‐resolved spectra with improved line shapes. This can be attributed exclusively to the fact that the critical concentration of the liquid‐crystalline phase decreases with increasing molecular weight (pure dilution effect). Any influence of increasing flexibility on the orientation can be ruled out.
Robust and Electron‐Rich cis‐Palladium(II) Complexes with Phosphine and Carbene Ligands as Catalytic Precursors in Suzuki Coupling Reactions
Authors: Liao Chuang‐Yi , Chan Kai‐Ting , Tu Cheng‐Yi , Chang Yu‐Wei , Hu Ching‐Han , Lee Hon Man 
Published: November 2008

AbstractA new imidazolinium ligand precursor [L2H]Cl (2) was prepared in 86 % yield. Compared with its imidazolium counterpart, [L1H]Cl (1), 2 is very sensitive to moisture and can undergo ring‐opening reactions very readily. Palladium complexes with the ring‐opened products from imidazolinium salts were isolated and characterized by X‐ray crystallography. Theoretical studies confirmed that the imidazolinium salt has a higher propensity for the ring‐opening reaction than the imidazolium counterpart. New mixed phosphine/carbene palladium complexes, cis‐[PdCl2(L)(PR3)] (L=L1 and L2; R=Ph, Cy), were successfully prepared. These complexes are highly robust as revealed by variable‐temperature NMR spectroscopic studies and thermal gravimetric analysis. The structural and electronic properties of the new complexes on varying the carbene group (imidazol‐2‐ylidene group (unsaturated carbene) vs. imidazolin‐2‐ylidene (saturated carbene)) and the phosphine group (PPh3 vs. PCy3) were studied in detail by X‐ray crystallography, X‐ray photoelectron spectroscopy, and theoretical calculations. The catalytic study reveals that cis‐[PdCl2(L2)(PCy3)] is a competent PdII precatalyst for Suzuki coupling reactions, in which unreactive aryl chlorides can be applied as substrates.
Asymmetric Claisen Rearrangements on Chiral Vinyl Sulfoxides
Authors: Fernández de la Pradilla Roberto , Montero Carlos , Tortosa Mariola , Viso Alma 
Published: November 2008

AbstractHighly diastereoselective Claisen rearrangements of acyclic allyl vinyl ethers bearing a chiral sulfoxide at C‐5 provide γ‐δ‐unsaturated aldehydes or ketones with up to two consecutive asymmetric centers in the molecule whilst preserving a useful vinyl sulfoxide. The reactivity of related vinyl sulfides and sulfones has also been examined in this work.
Syntheses of High‐Valent fac‐[99mTcO3]+ Complexes and [3+2] Cycloadditions with Alkenes in Water as a Direct Labelling Strategy
Authors: Braband Henrik , Tooyama Yuji , Fox Thomas , Alberto Roger 
Published: November 2008

AbstractReported herein is a new concept for the labelling of biomolecules with small [99 mTcO3]+ complexes through a [3+2] cycloaddition with alkenes for radiopharmaceutical applications. We developed convenient reactions for the synthesis of small, water stable fac‐[TcO3(tacn‐R)]+ complexes (99Tc and 99mTc, tacn=1,4,7‐triazacyclononane, R=H, ‐CH2‐C6H5, ‐CH2‐C6H4COOH). With alkenes, these high valent [99mTcO3]+ complexes undergo [3+2] cycloaddition with formation of the corresponding TcV–glycolato complexes. The 99mTcV and 99mTcVII complexes are stable at 37 °C in water and in the presence of serum proteins. Therefore, new opportunities in technetium chemistry are enabled with a high potential for medicinal and biological applications. In contrast to classical labelling, the presented strategy is ligand and not metal‐centred.
Curvature‐ and displacement‐based finite element analyses of flexible slider crank mechanisms
Authors: Kuo Y. L. , Cleghorn W. L. 
Published: November 2008

AbstractThe paper presents the applications of the curvature‐ and displacement‐based finite element methods to flexible slider crank mechanisms. The displacement‐based method usually needs more elements or high‐degree polynomials to obtain highly accurate solutions. The curvature‐based method assumes a polynomial to approximate a curvature distribution, and the expressions are investigated to obtain the displacement and rotation distributions. During the process, the boundary conditions associated with displacement, rotation, and curvature are imposed, which leads the great reduction of the number of degrees of freedom that are required. The numerical results demonstrate that the errors obtained by applying the curvature‐based method are much smaller than those by applying the displacement‐based method, based on the comparison of the same number of degrees of freedom. Copyright © 2008 John Wiley & Sons, Ltd.
Potential Proton‐Release Channels in Bacteriorhodopsin
Authors: Chaumont Alain , Baer Marcel , Mathias Gerald , Marx Dominik 
Published: November 2008

AbstractThe protein bacteriorhodopsin pumps protons across a bacterial membrane; its pumping cycle is triggered by the photoisomerization of a retinal cofactor and involves multiple proton‐transfer reactions between intermittent protonation sites. These transfers are either direct or mediated by hydrogen‐bonded networks, which may include internal water molecules. The terminal step of the proton‐transfer sequence is the proton release from a pocket near Glu194 and Glu204 to the extracellular bulk during the transition from the L to the M photointermediate states. The polar and charged side chains connecting these two regions in the crystal structures show no structural changes between the initial bR state and the L/M states, and no intermittent protonation changes have been detected so far in this region. Based on biomolecular simulations, we propose two potential proton‐release channels, which connect the release pocket to the extracellular medium. In simulations of the L photointermediate we observe bulk water entering these channels and forming transient hydrogen‐bonded networks, which could serve as fast deprotonation pathways from the release pocket to the bulk via a Grotthuss mechanism. For the first channel, we find that the triple Arg7, Glu9, and Tyr79 acts as a valve, thereby gating water uptake and release. The second channel has two release paths, which split at the position Asn76/Pro77 underneath the release group. Here, water molecules either exchange directly with the bulk or diffuse within the protein towards Arg 134/Lys129, where the exchange with the bulk occurs.
Effects of Isomerization on the Measured Thermochemical Properties of Deprotonated Glycine/Protic‐Solvent Clusters
Authors: Nieckarz Robert J. , Atkins Chad G. , McMahon Terry B. 
Published: November 2008

AbstractThe thermochemical properties associated with the formation of an isomeric distribution of ROH⋅⋅⋅NH2CH2COO− clusters (R=H, CH3, C2H5) are measured by using high‐pressure mass spectrometry. A comparison of the measured properties with calculated values provides new insights into the thermochemical effects arising from the isomeric nature of this clustering system. When the distribution of isomers is correctly accounted for, the measured values of ΔH°, ΔS°, and ΔG°298 consistently agree, to a very high degree of accuracy, with those predicted by MP2(full)/6‐311++G(d,p)//B3LYP/6‐311++G(d,p) calculations.
Dendrimers with a Pentaphenylene Core: A Photophysical Study
Authors: Bergamini Giacomo , Ceroni Paola , Balzani Vincenzo , Kandre Ramchandra , Lukin Oleg 
Published: November 2008

AbstractNovel dendrimers G2PC and G4PC consisting of a p‐pentaphenylene core (PC) appended in the para position with two second‐generation (G2) or two fourth‐generation (G4) sulfonimide branches and two n‐octyl chains, as well as a model compound of the pentaphenylene core (G0PC), are prepared. The photophysical properties (absorption, emission, and excitation spectra; fluorescence decay lifetime; and fluorescence anisotropy spectra) of the three compounds are investigated under different experimental conditions (dichloromethane solution and solid state at 293 K, dichloromethane/methanol rigid matrix at 77 K). In the absorption spectra contributions from both the branches and the core can be clearly identified. The fluorescence spectra show only the characteristic fluorescence of the pentaphenylene unit with λmax around 410 nm in fluid solution and 420 nm in the solid state. In solution the fluorescence quantum yields are 0.78, 0.76, and 0.72 for G0PC, G2PC, and G4PC, respectively, and the fluorescence lifetime is about 0.7 ns in all cases. Energy transfer from the chromophoric groups of the dendrimer branches to the core does not occur. The three compounds show the same, high steady‐state anisotropy value (0.35) in dilute rigid‐matrix solution at 77 K. In dichloromethane at 293 K, the increasing anisotropy values along the series G0PC (0.17), G2PC (0.27), and G4PC (0.32), with increasing molecular volume of the three compounds, show that depolarization takes place by molecular rotation. In the solid state the anisotropy is very low (0.015, 0.017, and 0.035 for G0PC, G2PC, and G4PC, respectively), probably because of fast depolarization via energy migration.
L‐type Ca2+ channel opener BayK 8644‐induced Ca2+ influx and Ca2+ release in human oral cancer cells (OC2)
Authors: Chi Chao‐Chuan , Huang Chorng‐Chih , Chien Jau‐Min , Chu Sau‐Tung , Chen Wei‐Chuan , Chang Hong‐Tai , Lin Ko‐Long , Tsai Jeng‐Yu , Liao Wei‐Chuan , Chou Chiang‐Ting , Jan Chung‐Ren 
Published: November 2008

AbstractThe effect of BayK 8644, a chemical widely used to activate L‐type Ca2+ channels, on cytosolic free Ca2+ concentrations ([Ca2+]i) in human oral cancer cells (OC2) has not been explored to date. The present study examined whether BayK 8644 altered basal [Ca2+]i levels in suspended OC2 cells by using fura‐2. BayK 8644 (10 pM–10 µM) increased [Ca2+]i in a concentration‐dependent manner. The Ca2+ signal was reduced partly by removing extracellular Ca2+. BayK 8644‐induced Ca2+ influx was blocked by nifedipine, but was not altered by the store‐operated Ca2+ entry inhibitors, econazole and SKF96365; protein kinase C modulators phorbol 12‐myristate 13‐acetate (PMA) and GF109203X; the protein kinase A inhibitor H89; and the phospholipase A2 inhibitor, aristolochic acid. In Ca2+‐free medium, after pretreatment with 1 µM BayK 8644, 1 µM thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor)‐induced [Ca2+]i rises were abolished; and conversely, thapsigargin pretreatment abolished BayK 8644‐induced [Ca2+]i rises. Inhibition of phospholipase C with U73122 did not change BayK 8644‐induced [Ca2+]i rises. Collectively, in OC2 cells, BayK 8644 induced [Ca2+]i rises by causing phospholipase C‐independent Ca2+ release from the endoplasmic reticulum; and Ca2+ influx via L‐type Ca2+ channels. Drug Dev Res 69: 2008. © 2008 Wiley‐Liss, Inc.
The woody weed encroachment puzzle: gathering pieces
Authors: Patrick Graz F. 
Published: November 2008

AbstractIncreases in woody plant densities in savanna grazing lands worldwide have resulted in a decline in the grazing capacity of these rangelands. At present, the actual cause of the problem is unknown although a vast body of literature deals with various aspects relevant to the issue.It is generally assumed, however, that the changes in the tree:grass ratio are a response to changes in soil‐water development brought about by rangeland utilization. These utilization patterns differ from those under which the savanna system evolved. While changes in physiognomy are very prominent, these are generally preceded by changes in grass species assemblage.The development of species composition has been used as an indicator of rangeland condition for many years; the increase or decrease of individual species is considered in this context. Thus far, however, the shift from perennial to annual grasses has not been evaluated for its effect on soil moisture development, and subsequent implications for woody plant establishment and growth.The review presented here consolidates the existing information in order to provide a basis for understanding the woody weed encroachment problem. Copyright © 2008 John Wiley & Sons, Ltd.
CEC with tris(2,2′‐bipyridyl) ruthenium(II) electrochemiluminescent detection
Authors: Li Haijuan , Liu Xiaoqing , Niu Wenxin , Zhu Shuyun , Fan Lishuang , Shi Lihong , Xu Guobao 
Published: November 2008

AbstractFor the first time, CEC was coupled with tris(2,2‐bipyridyl) ruthenium(II) (
Ru(bpy) electrochemiluminescence detection. Efficient CEC separations of proline, putrescine, spermidine and spermine were achieved when the pH of the mobile phase is in the range of 3.5–7.0. The optimum mobile phase for CEC separation is much less acidic than that for CZE separation, which matches better with the optimum pH for Ru(bpy) electrochemiluminescence detection and dramatically shortens the analysis time because of larger EOF at higher pH. The time for CEC separation of the polyamines is less than 12.5 min, which is about half as much as the time needed for CZE. The detection limits were 1.7, 0.2, and 0.2 μM for putrescine, spermidine, and spermine, respectively. The RSD of retention time and peak height of these polyamines were less than 0.85 and 6.1%, respectively. The column showed good long‐term stability, and the RSD of retention time is below 5% for 150 runs over one‐month use. The method was successfully used for the determination of polyamines in urine samples.
Focusing and stabilization of bis‐intercalating dye–DNA complexes for high‐sensitive CE‐LIF DNA analysis
Authors: Wang Zhixin , Wang Chao , Yin Junfa , Li Tao , Song Maoyong , Lu Meiling , Wang Hailin 
Published: November 2008

AbstractMultiple labeling of nucleic acids by intercalative dyes is a promising method for ultrasensitive nucleic acid assays. The properties of the fast dissociation and instability of dye–DNA complexes may prevent from their wide applications in CE‐LIF nucleic acid analysis. Here, we describe an optimum CE focusing method by using appropriately paired sample and separation buffers, Tris‐glycine buffer and Tris‐glycine‐acetic acid buffer. The developed method was applied in both uncoated and polyacrylamide coated fused‐silica capillary‐based CE‐LIF analysis while the sample and separation buffers were conversely used. The complexes of intercalative dye benzoxazolium‐4‐pyridinium dimer and dsDNA were greatly focused (separation efficiency: 1.8 million theoretical plates per meter) by transient isotachophoresis mechanism in uncoated capillary, and moderately focused by transient isotachophoresis in combination of field amplified sample stacking and further stabilized by the paired buffer in polyacrylamide coated capillary. Based on the developed focusing strategy, an ultrasensitive DNA assay was developed for quantitation of calf thymus dsDNA (from 0.02 to 2.14 pM). By the use of an excitation laser power as low as 1 mW, the detection limits of calf thymus dsDNA (3.5 kb) are 7.9 fM in concentration and 2.4×10−22 mol (150 molecules) in mass. We further demonstrate that the non‐gel sieving CE‐LIF analysis of DNA fragments can be enhanced by the same strategy. Since the presented strategy can be applied to uncoated and coated capillaries and does not require special device, it is also reasonable to extend to the applications in chip‐based CE DNA analysis.
A new approximation for spectral velocity ordinates at short periods
Authors: Gupta Vinay K. 
Published: November 2008

AbstractResponse spectrum methods in earthquake‐resistant design sometimes require information on the spectral velocity (SV) for a given single‐degree‐of‐freedom oscillator and specified seismic hazard. SV has been conventionally approximated as pseudo spectral velocity (PSV) in the case of lightly damped structures that are not too flexible. This study shows that the PSV approximation may lead to large overestimation errors when the structure is stiffer to the ground motion and the ground motion is a long‐period motion. It is also shown that a new approximation requiring the use of peak ground acceleration of the motion may significantly reduce these errors. Copyright © 2008 John Wiley & Sons, Ltd.
Deformation during exhumation of medium‐ and high‐grade metamorphic rocks in the Variscan chain in northern Sardinia (Italy)
Authors: Carosi Rodolfo , Frassi Chiara , Montomoli Chiara 
Published: November 2008

AbstractThe Anglona and SW Gallura regions represent key places to investigate the tectonic evolution of medium‐ and high‐grade metamorphic rocks cropping out in northern Sardinia (Italy). From south to north we distinguish two different metamorphic complexes recording similar deformation histories but different metamorphic evolution: the Medium Grade Metamorphic Complex (MGMC) and the High Grade Metamorphic Complex (HGMC).After the initial collisional stage (D1 deformation phase), both complexes were affected by three contractional deformational phases (D2, D3 and D4) followed by later extensional tectonics. The D2 deformation phase was the most significant event producing an important deformation partitioning that produced localized shearing and folding domains at the boundary between the two metamorphic complexes.We highlight the presence of two previously undocumented systems of shear belts with different kinematics but analogous orientation in the axial zone of Sardinia. They became active at the boundary between the MGMC and HGMC from the beginning of D2. They formed a transpressive regime responsible for the exhumation of the medium‐ and high‐grade metamorphic rocks, and overall represent a change from orthogonal to orogen‐parallel tectonic transport. Copyright © 2008 John Wiley & Sons, Ltd.
Synthetic Studies on Camptothecins. Part 1
Authors: Zhang Li‐Peng , Bao Yong , Kuang Yun‐Yan , Chen Fen‐Er 
Published: November 2008

AbstractA six‐step asymmetric total synthesis of (20S)‐camptothecin (1) has been accomplished in 25% overall yield starting from the known pyridone 3. The key steps in this synthesis are the chemoselective Ni‐catalyzed hydrogenation of 3‐cyanopyridone 6 to 3‐formylpyridone 7 in AcOH/pyridine/H2O and the Davis asymmetric hydroxylation of tricyclic lactone 4 utilizing a chiral N‐sulfonyloxaziridine into (4′S)‐tricyclic hydroxylactone 2.
Two Novel Triterpenoids from Portulaca oleracea L.
Authors: Xin Hai‐Liang , Xu Yan‐Feng , Hou Yin‐Huan , Zhang Ya‐Ni , Yue Xiao‐Qiang , Lu Jin‐Cai , Ling Chang‐Quan 
Published: November 2008

AbstractTwo novel triterpenoids, (2α,3α)‐3‐{[4‐O‐(β‐D‐glucopyranosyl)‐β‐D‐xylopyranosyl]oxy}‐2,23‐dihydroxy‐30‐methoxy‐30‐oxoolean‐12‐en‐28‐oic acid (1) and (2α,3α)‐2,23,30‐trihydroxy‐3‐[(β‐D‐xylopyranosyl)oxy]olean‐12‐en‐28‐oic acid (2) were isolated from Portulaca oleracea L., and they both showed weak cytotoxic activity assayed with the MTT method.
Eight New Diterpenoids from the Roots of Euphorbia nematocypha
Authors: He Fei , Pu Jian‐Xin , Huang Sheng‐Xiong , Xiao Wei‐Lie , Yang Li‐Bin , Li Xiao‐Nian , Zhao Yong , Ding Jian , Xu Cheng‐Hui , Sun Han‐Dong 
Published: November 2008

AbstractFrom the dried roots of Euphorbia nematocypha, eight new diterpenoids, with ent‐atisane (i.e., 1–5) and isopimarane (i.e., 6–8) type skeletons, together with five known compounds, were isolated. The structures of these new compounds were elucidated by spectroscopic data. Compounds 1–8 were evaluated for their cytotoxicity against a small panel of human cancer cell lines.
Three New Alkaloids, Paxiphyllines C – E, from Daphniphyllum paxianum
Authors: Zhang Yu , Di Ying‐Tong , Liu Hai‐Yang , Li Chun‐Shun , Tan Cheng‐Jian , Zhang Qiang , Fang Xin , Li Shun‐Lin , Hao Xiao‐Jiang 
Published: November 2008

AbstractNine Daphniphyllum alkaloids, including three new ones, paxiphyllines C–E (1–3, resp.), were isolated from the twigs and the leaves of Daphniphyllum paxianum. Paxiphylline C (1) represents the first example of Daphniphyllum alkaloids with a carbonyldioxy group. Their structures were elucidated on the basis of spectroscopic data.
Adipokine genes and prostate cancer risk
Authors: Moore Steven C. , Leitzmann Michael F. , Albanes Demetrius , Weinstein Stephanie J. , Snyder Kirk , Virtamo Jarmo , Ahn Jiyoung , Mayne Susan T. , Yu Herbert , Peters Ulrike , Gunter Marc J. 
Published: November 2008

AbstractAdiposity and adipocyte‐derived cytokines have been implicated in prostate carcinogenesis. However, the relationship of adipokine gene variants with prostate cancer risk has not been thoroughly investigated. We therefore examined common variants of the IL6, LEP, LEPR, TNF and ADIPOQ genes in relation to prostate cancer in a case‐control study nested within a large cohort of Finnish men. The study sample consisted of 1,053 cases of prostate cancer, diagnosed over an average 11 years of follow up, and 1,053 controls matched to the cases on age, intervention group and date of baseline blood draw. Logistic regression was used to model the relative odds of prostate cancer. We also examined genotypes in relation to serum insulin, IGF‐1 and IGF‐1:IGFBP‐3 among 196 controls. Variant alleles at three loci (−14858A>G, −13973A>C, −13736C>A) in a potential regulatory region of the LEP gene conferred a statistically significant 20% reduced risk of prostate cancer. For example, at the −14858A>G locus, heterozygotes and homozygotes for the A allele had an odds ratio (OR) of prostate cancer of 0.76 [95% confidence interval (CI) 0.62, 0.93] and 0.79 (95% CI 0.60, 1.04), respectively. At 13288G>A, relative to the GG genotype, the AA genotype was associated with a suggestive increased risk of prostate cancer (OR = 1.29; 95% CI 0.99,1.67; ptrend = 0.05). Polymorphisms in the IL6, LEPR, TNF and ADIPOQ genes were not associated with prostate cancer. Allelic variants in the LEP gene are related to prostate cancer risk, supporting a role for leptin in prostate carcinogenesis. © 2008 Wiley‐Liss, Inc.