bluuebunny/crossref_metadata_2025_split huggingface dataset:
How Strong Are Hydrogen Bonds in Metalla‐β‐diketones?
Authors: Steinborn Dirk , Schwieger Sebastian 
Published: September 2007

AbstractThe energies of the kinetically inert, electronically saturated Lukehart‐type metalla‐β‐diketone [Re{(COMe)2H}(CO)4] (9 a) and of the kinetically labile, electronically unsaturated platina‐β‐diketones [Pt{(COMe)2H}Cl2]− (10 a), [Pt2{(COMe)2H}2(μ‐Cl)2] (11 a), and [Pt{(COMe)2H}(bpy)]+ (12 a) have been calculated by DFT at the B3LYP/6‐311++G(d,p) level using effective core potentials with consideration of relativistic effects for the transition metals. Analogously, energies of the requisite open (non‐hydrogen‐bonded) equilibrium conformers (9 b, 10 c, 11 b, 12 b) and energies which were obtained from the hydrogen‐bonded conformers by rigid rotation of the OH group around the CO bond by 180° followed by relaxation of all bond lengths and angles (9 c, 10 d, 11 c, 12 d) have been calculated. These energies were found to be higher by 14.7/27.2 (9 b/9 c), 20.7/27.2 (10 c/10 d), 19.2/25.7 (11 b/11 c), and 9.4/19.6 kcal mol−1 (12 b/12 d) than those of the intramolecularly OH⋅⋅⋅O hydrogen‐bonded metalla‐β‐diketones 9 a, 10 a, 11 a, and 12 a, respectively. In acetylacetone (Hacac), the generic organic analogue of metalla‐β‐diketones, the energies of the most stable non‐hydrogen‐bonded enol isomer (6 b) and of the conformer derived from the H‐bonded form by rigid rotation of the OH group by 180° followed by subsequent relaxation of all bond lengths and angles (6 k) were found to be 10.9/16.1 kcal mol−1 (6 b/6 k) higher compared to the intramolecularly OH⋅⋅⋅O bonded isomer 6 a. Thus, the hydrogen bonds in metalla‐β‐ diketones must be regarded as strong and were found to be up to twice as strong as that in acetylacetone. A linear relationship was found between the hydrogen‐bond energies based on the rigidly rotated structures and the O⋅⋅⋅O separation in the hydrogen‐bonded structures. Furthermore, these energies were also found to be correlated with the electron densities at the O⋅⋅⋅H bond critical points (ρbcp) in the OH⋅⋅⋅O bonds of metalla‐β‐diketones 9 a, 10 a, 11 a, and 12 a (calculated using the AIM theory). The comparison of the energies of the doubly intermolecularly hydrogen‐bonded dinuclear platina‐β‐diketone [{Pt{(COMe)2H}(bpy)}2]2+ (14) with that of the mononuclear intramolecularly hydrogen‐bonded cation [Pt{(COMe)2H}(bpy)]+ (12 a) showed that the intermolecular hydrogen bonds in 14 are weaker than the intramolecular hydrogen bond in 12.
Role of myosin II activity and the regulation of myosin light chain phosphorylation in astrocytomas
Authors: Salhia Bodour , Hwang Jeong Hyun , Smith Christian A. , Nakada Mitsutoshi , Rutka Fiona , Symons Marc , Rutka James T. 
Published: September 2007

AbstractThe generation of contractile force mediated by actin‐myosin interactions is essential for cell motility. Myosin activity is promoted by phosphorylation of myosin light chain (MLC). MLC phosphorylation in large part is controlled by kinases that are effectors of Rho family GTPases. Accordingly, in this study we examined the effects of ROCK and Rac1 inhibition on MLC phosphorylation in astrocytoma cells. We found that low concentrations of the ROCK inhibitor Y27632 increased the phosphorylation state of the Triton X‐100 soluble fraction of MLC, whereas higher concentrations of Y27632 decreased soluble phospho‐MLC. These effects of Y27632 were dependent on Rac1. The soluble form of phospho‐MLC comprises about 10% of total phospho‐MLC in control cells. Interestingly, ROCK inhibition led to a decrease in the phosphorylation state of total MLC, whereas Rac1 inhibition had little effect. Thus, the soluble form of MLC is differentially regulated by ROCK and Rac1 compared with MLC examined in a total cell extract. We also observed that astrocytoma migration is stimulated by low concentrations of the myosin II inhibitor blebbistatin. However, higher concentrations of blebbistatin inhibit migration leading us to believe that migration has a biphasic dependence on myosin II activity. Taken together, our data show that modulation of myosin II activity is important in determining optimal astrocytoma migration. In addition, these findings suggest that there are at least two populations of MLC that are differentially regulated. Cell Motil. Cytoskeleton 2008. © 2007 Wiley‐Liss, Inc.
Solid‐State Anion–Guest Encapsulation by Metallosupramolecular Capsules Made from Two Tetranuclear Copper(II) Complexes (Eur. J. Inorg. Chem. 29/2007)
Authors: Pardo Emilio , Bernot Kevin , Lloret Francesc , Julve Miguel , Ruiz‐García Rafael , Pasán Jorge , Ruiz‐Pérez Catalina , Cangussu Danielle , Costa Valeria , Lescouëzec Rodrigue , Journaux Yves 
Published: September 2007

AbstractThe cover picture shows unique examples of homo‐ and heterochiral, dimeric metal capsules resulting from the self‐assembly of two helical, bowl‐shaped tetranuclear copper(II) complexes that encapsulate different anions in the solid state, like pearls in an oyster (shown as the background). This kind of self‐assembled, coordination‐bonded motifs are a major topic in metallosupramolecular chemistry because of their binding capabilities and associated host–guest chemistry. However, their magnetic properties are largely unexplored, and here we provide one of the rare magnetic studies on these host–guest systems. For more details on the combined structural and magnetic investigations of this class of synthetic “oyster” molecules, see the article by F. Lloret, Y. Journaux et al. on page 4569 ff.
Synthesis of Tyrosine‐Derived Tetrahydroisoquinolines by Lewis Acid Catalyzed Cyclization of N‐(Phenylsulfonyl)alkyloxazolidinones
Authors: Tussetschläger Stefan , Baro Angelika , Laschat Sabine , Frey Wolfgang 
Published: September 2007

AbstractN‐Boc‐protected tyrosine esters 5a,b were converted into tetrahydroisoquinolines 13 and 14 in four steps by reduction and ring closure to oxazolidinones 9 and 10, addition of benzenesulfinic acid and aldehydes to sulfones 11 and 12 and subsequent Lewis acid catalyzed cyclization. In the case of m‐tyrosine derivative 5a, selective protection with bromine prevented the formation of undesired regioisomers. Debromination of target compounds 13 was readily achieved under radical reduction conditions by using Bu3SnH/AIBN. Tetrahydroisoquinolines 13 and 14 were isolated as single diastereomers whose trans configuration was confirmed by X‐ray crystal structure analysis. Partial epimerization of trans‐13i and trans‐21 to the corresponding cis diastereomers was achieved under basic conditions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Non‐Phenolic Dicinnamamides from Pholiota Spumosa: Isolation, Synthesis and Antitumour Activity
Authors: Clericuzio Marco , Tabasso Silvia , Garbarino Juan A. , Piovano Marisa , Cardile Venera , Russo Alessandra , Vidari Giovanni 
Published: September 2007

AbstractTwo new amides derived from cinnamic acid, namely,(R)‐2‐hydroxyputrescine dicinnamamide (4) and pholiotic acid {(2R)‐2‐[(S)‐3‐hydroxy‐3‐methylglutaryloxy]putrescine dicinnamamide} (5), in addition to the known compound maytenine (N1,N8‐dicinnamoyl spermidine) (3) were isolated from the fruiting bodies of the Basidiomycete Pholiota spumosa. The absolute configuration of 4 was established as (R) by its total synthesis starting from (S)‐dimethylmalate, whereas that of 5 was determined by conversion into the known compound methyl (S)‐4‐[(S)‐1‐(1‐naphthalen‐1‐yl)ethylcarbamoyl]‐3‐hydroxy‐3‐methylbutanoate (14). Compounds 3 and 5 exhibited an inhibitory effect on cell growth of the androgen‐insensitive DU‐145 prostate cancer cells, which suggests that these fungal polyamine conjugates, like other polyamine analogues, might have chemotherapeutic potential against androgen‐independent prostatic cancer. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Retipolides – Unusual Spiromacrolactones from the Mushrooms Retiboletus retipes and R. ornatipes
Authors: Justus Karl , Herrmann Rupert , Klamann Jörg‐Dieter , Gruber Gertraud , Hellwig Veronika , Ingerl Andrea , Polborn Kurt , Steffan Bert , Steglich Wolfgang 
Published: September 2007

AbstractMushrooms of the genus Retiboletus contain the retipolides A–D (1, 6–8), unusual 14‐membered spiromacrolides with a biphenyl ether linkage. The structures of these metabolites suggested a biogenetic sequence starting from retipolide E (16), which could furnish the unique 2(3H)‐oxepinone unit of retipolide C (7) via an oxidative enlargement of the 4‐hydroxyphenyl ring. A subsequent O/C‐acyl shift would then lead to the cyclopenta[c]pyran system of retipolide A (1). The proposed precursor 16 was synthesized and subsequently detected in the fungal extract in addition to the probable biosynthetic intermediates butyrolactone II (13), tyrosol (14), and secoretipolide E (15). The structural elucidation of retipolide A (1) was accomplished after transformation into a methoxyfulvene derivative 2a, and the absolute (R) configuration of 1 was assigned by a single‐crystal X‐ray analysis of the corresponding (S)‐sec‐butoxyfulvene analogue 2b. Some samples of R. retipes/ornatipes contained isoretipolide A (9), an isomer of 1 with a highly strained 12‐membered lactone ring incorporating two C,C‐coupled 4‐hydroxyphenyl units. A comparison of the CD spectrum of retipolide A (1) with those of the other retipolides and isoretipolide A (9) indicates that all of these macrolides possess R configuration. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Expedient Syntheses of β‐Iodofurans by 5‐endo‐dig Cyclisations
Authors: Bew Sean P. , El‐Taeb Gamila M. M. , Jones Simon , Knight David W. , Tan Wen‐Fei 
Published: September 2007

Abstract5‐endo‐dig cyclisations of 3‐alkyne‐1,2‐diols using iodine as the electrophile proceed smoothly to deliver excellent yields of the corresponding β‐iodofurans. The necessary precursors are available from a number of different approaches, notably regioselective bis‐hydroxylation of conjugated enynes and the addition of acetylides to α‐hydroxy carbonyl groups. The initial iodofurans can be homologated using a number of strategies, ranging from various transition metal‐catalysed couplings to halogen–metal exchange and subsequent coupling with an electrophile. Hence, this method overall represents a flexible, relatively brief and very efficient approach to a variety of highly substituted furans. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Synthesis of Pyrrolidine‐Based Imino Sugars as Glycosidase Inhibitors
Authors: Doddi Venkata Ramana , Vankar Yashwant D. 
Published: September 2007

AbstractTwo pyrrolidine‐based imino sugars have been synthesized in an efficient manner, using regiospecific amination, ring closing metathesis, and diastereospecific dihydroxylations as key steps. These azasugars are found to be moderate inhibitors of glycosidases. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Isocratic Liquid Chromatography with Segmented Columns and Simultaneous UV and Dual Electrochemical Detection: Application to the Selectivity Enhancement for the Determination of Explosives
Authors: Matysik Frank‐Michael , Schumann Ulrike , Engewald Werner 
Published: September 2007

AbstractThe concept of stationary‐phase optimized liquid chromatography (POPLC) was studied in the context of separation and detection aspects for the determination of explosives. A tailor‐made segmented column assembly with three complementary reverse‐phase materials enabled the separation of 14 priority target nitroaromatic explosives. This experimental approach resulted in excellent selectivity without using gradient‐elution protocols which can considerably deteriorate the performance of electrochemical detection. Consequently, the POPLC separations could be operated under isocratic conditions which were very important for the reliable use of electrochemical detection. Simultaneous UV and dual electrochemical detection resulting in three detection traces was exploited as an additional means for the further enhancement of selectivity in more complex samples.
Nonaqueous CE using contactless conductivity detection and ionic liquids as BGEs in ACN
Authors: Borissova Maria , Gorbatšova Jelena , Ebber Arkadi , Kaljurand Mihkel , Koel Mihkel , Vaher Merike 
Published: September 2007

AbstractN,N′‐Alkylmethylimidazolium cations have been separated in NACE when one of the N,N′‐dialkylimidazolium salts (ionic liquids (ILs)) was used as an electrolyte additive to the organic solvent separation medium. The separated species were 1‐methyl‐, 1‐ethyl‐, 1‐butyl‐, 1‐octyl‐, 1‐decyl‐3‐methylimidazolium and N‐butyl‐3‐methylpyridinium cations and BGE composed of 1‐ethyl‐3‐methylimidazolium ethylsulfate or 1‐butyl‐3‐methylimidazolium trifluoroacetate [BMIm][FAcO] (A6; B2) diluted in ACN. It was demonstrated that contactless conductivity detection (CCD) may be applied to monitoring the separation process in nonaqueous separation media, allowing to use the UV light‐absorbing imidazolium‐based electrolyte additives. There could be marked three concentration regions of added ILs; at first ionic strength of BGE below 1–2 mM, and then the actual electrophoretic mobility of analytes rises from 0. At concentrations above 1–2 mM, the added IL facilitated separation. In concentration region of 1–20 mM, the actual electrophoretic mobility of analyzed imidazolium cations was increasing with decrease in separation medium ionic strength. At higher concentrations of BGE (above 30 mM), the conductivity of the separation media became too high for this detector. Some organic dyes were also successfully separated and detected by contactless conductivity detector in a 20 mM A6 separation electrolyte in ACN.
CE of tricyclic antidepressant clomipramine and metabolites: Electromigration and wall adsorption
Authors: Martello Rita , Kolivoska Viliam , Raggi Maria Augusta , Kenndler Ernst 
Published: September 2007

AbstractCE of tricyclic antidepressants clomipramine and its metabolites demethylclomipramine, didemethylclomipramine and 8‐hydroxyclomipramine resulted in partly extremely tailing peaks in bare fused‐silica capillaries. Especially at high pH of the BGE this behavior was not unexpected as adsorption of the cationic analytes onto the negatively charged wall due to electrostatic attraction can be supposed. Less expected was the observation that peak tailing could not be overcome neither by using a capillary with dynamic coating with cationic CTAB added to the BGE, nor by the usage of a capillary permanently coated with polyvinyl alcohol (PVA), both operated at acidic pH. As this tailing was even more pronounced than with bare fused silica, and was suppressed upon addition of MeCN to the BGE, another source of adsorption than pure ion–ion interaction seems plausible. In the bare silica capillary the mobility, μ, of the analytes followed roughly the pH dependence of a monoacidic base, but two deviations from the sigmoid theoretical curve were evident: (i) even at low pH the mobilities were not constant; they decreased in contrary with pH over the entire range; (ii) the apparent pKa values of two analytes, derived at the pH with halve the mobility at low pH, are significantly smaller than the thermodynamic pKa. Upon modifying the expression for μ = f(pH), and considering the pH dependence of the negative charge density at the wall by an additional term which takes chromatographic retention into account, an equation was derived which enables the description of the observed electromigration of the analytes as function of pH, pKa of analytes and surface silanol groups, actual mobility of analytes, distribution coefficient (or retention factor) due to adsorption including its pH dependence. The interplay of electrophoretic movement and residual adsorptive retention allowed to resolve the analytes finally in an uncoated capillary, namely at pH 7.65 (30 mM ionic strength), whereas at the cost of the robustness of the separation system.
Effect of detergent on electromigration of proteins: CE of very low density lipoprotein receptor modules and viral proteins
Authors: Kremser Leopold , Bilek Gerhard , Kenndler Ernst 
Published: September 2007

AbstractThe different electrophoretic behavior of the members of two groups of proteins with respect to the absence or presence of detergent additives in the BGE was explored. Recombinant soluble concatemers of repeat 3 of the very low density lipoprotein (VLDL)‐receptor fused at their N‐terminus to maltose‐binding protein (MBP) exhibited different electrophoretic mobilities in borate buffer (pH 8.3) in the absence and in the presence of dodecyl‐PEG ether (D‐PEG). This enabled the separation of the receptor fragments from MBP after enzymatic cleavage. In the presence of SDS, the mobilities of all proteins approached the same values with increase in detergent concentrations. In contrast, viral capsid proteins of a human rhinovirus (HRV) exhibited different migration in the presence of the additive. For the receptor proteins, extreme apparent high plate numbers were observed when the SDS concentration in the sample and the separation buffer differed. This effect might be erroneously interpreted as a high efficiency. However, it is due to the conductivity boundaries caused by the sample and leads to a total loss of separation.
Sensitive determination of herbicides in food samples by nonaqueous CE using pressurized liquid extraction
Authors: Carabias‐Martínez Rita , Rodríguez‐Gonzalo Encarnacion , Miranda‐Cruz Edith , Domínguez‐Álvarez Javier , Hernández‐Méndez Jesus 
Published: September 2007

AbstractWe have developed a method involving extraction with mixtures of solvents under pressure (pressurized liquid extraction (PLE)) for the determination of triazine herbicides in a series of samples from the food industry. The organic extracts obtained were subjected to a clean‐up step with SPE, using Oasis MCX® sorbents, after which they were analyzed by NACE. Potato was chosen as a representative matrix of horticultural products since it has a high water content. Spiked potato samples were used to optimize extraction conditions. In order to compare the results obtained with NACE, different studies were also conducted using HPLC. The detection limits in NACE were similar to those found with HPLC and were of the order of 10–15 μg/kg, depending on the analyte. Satisfactory results were obtained on applying the method proposed for the potato matrix (PLE with separation by electrophoresis) to other food matrices such as other tubercles, fruits, vegetables and cereals.
Separation of corticosteroids by microemulsion EKC with diethyl L‐tartrate as the oil phase
Authors: Wu Chi‐Hung , Chen Tse‐Hsien , Huang Kuan‐Pin , Wang Guan‐Ren , Liu Chuen‐Ying 
Published: September 2007

AbstractA novel microemulsion based on a mixture of diethyl L‐tartrate (DET) and SDS was developed for the microemulsion EKC (MEEKC) determination of structurally related steroids. The system consisted of 0.5% w/w DET, 1.7% w/w SDS, 1.2% w/w 1‐butanol, 89.6% w/w phosphate buffer (40 mM, pH 7.0), and 7% w/w ACN. With an applied voltage of +10 kV, a baseline separation of aldosterone (A), cortisone acetate (CA), dexamethasone (D), hydrocortisone (H), hydrocortisone acetate (HA), prednisolone (P), prednisolone acetate (PA), prednisone (Ps), triamcinolone (T), and triamcinolone acetonide (TA) could be achieved. Under the optimized conditions, the reproducibility of the retention time (n = 4) for most of the compounds was less than ±0.8% with the exception of  A, Ps, and T. The average number of theoretical plates was 18 800 plates/m. The results were compared with those achieved by the modified micellar EKC (MEKC). MEEKC showed obvious advantages over MEKC for the separation of highly hydrophobic substances. To further evaluate the system, we tested the MEEKC method by analyzing corticosteroids in a spiked urine sample.
Comparison of computational times and accuracy for finite element solution of Navier–Stokes equations and Ladyzhenskaya equations
Authors: Fairag Faisal A. 
Published: September 2007

AbstractIn this paper we consider a pure‐streamfunction equation of the Ladyzhenskaya equations. For certain values of the parameters of the equation, the studied equation becomes identical to the pure‐streamfunction equation of the Navier–Stokes equations. A weak form, a finite element method approximation procedures, and an iterative method for solving the discrete nonlinear problems are provided. Using the Bogner–Fox–Schmidt element, the steady 2‐D incompressible flow in a driven cavity is solved using a grid mesh of 16 × 16. Streamfunction contours are also displayed showing the main features of the flow. Copyright © 2007 John Wiley & Sons, Ltd.
A method to discretize non‐planar fractures for 3D subsurface flow and transport simulations
Authors: Graf Thomas , Therrien René 
Published: September 2007

AbstractA method is presented to discretize inclined non‐planar 2D fractures within a 3D finite element grid for subsurface flow and transport simulations. Each 2D fracture is represented as a triangulated surface. Each triangle is then discretized by 2D fracture elements that can be horizontal, vertical or inclined and that can be triangular or rectangular. The 3D grid representing a porous rock formation consists of hexahedra and can be irregular to allow grid refinement. An inclined fracture was discretized by (a) inclined triangles and (b) orthogonal rectangles and flow/transport simulations were run to compare the results. The comparison showed that (i) inclined fracture elements must be used to simulate 2D transient flow, (ii) results of 2D/3D steady‐state and 3D transient flow simulations are identical for both discretization methods, (iii) inclined fracture elements must be used to simulate 2D/3D transport because orthogonal fracture elements significantly underestimate concentrations, and (iv) orthogonal elements can be used to simulate 2D/3D transport if fracture permeability is corrected and multiplied by the ratio of fracture surface areas (orthogonal to inclined). Groundwater flow at a potential site for long‐term disposal of spent nuclear fuel was simulated where a complex 3D fracture network was discretized with this technique. The large‐scale simulation demonstrates that the proposed discretization procedure offers new possibilities to simulate flow and transport in complex 3D fracture networks. The new procedure has the further advantage that the same grid can be used for different realizations of a fracture network model with no need to regenerate the grid. Copyright © 2007 John Wiley & Sons, Ltd.