bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of a nipi delta‐doping superlattice on In1−xGaxAs/In1−yAlyAs amplitude modulator parameters
Authors: Tribuzy C. V.‐B. , Pires M. P. , Souza P. L. 
Published: August 2004

AbstractA theoretical study of the performance of amplitude modulators using a nipi delta‐doping superlattice in InGaAs/InAlAs multiple quantum‐well (QW) structures is presented. The structure is such that an n‐type delta‐doping layer is placed at the center of the InGaAs QWs and a p‐type is placed at the center of the InAlAs barriers. From the calculated absorption curves, modulator parameters such as CR, IL, and chirp are estimated and a comparison of the performance of an InGaAs/InAlAs modulator with and without the nipi delta‐doping superlattice is carried out. The study shows that an amplitude modulator containing a nipi delta‐doping superlattice in the InGaAs/InAlAs multiple QW structure presents an improved performance, compared to that without the doping superlattice, as long as the QW composition is adequately chosen. It is shown that for such structures, contrary to the undoped counterpart, it is, in principle, possible to achieve polarization insensitivity and appropriate chirp parameters simultaneously. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 168–173, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20410
Analysis of waveguide discontinuities using a hybrid method combining the Helmholtz weak form and mode expansion
Authors: Wu H. C. , Dou W. B. 
Published: August 2004

AbstractA new approach for the analysis of waveguide multiports discontinuities is presented in this paper. This approach is a combined method of the mode‐expansion method and finite‐element method, which is based on the weak form of the Helmholtz equation. We use a mode expansion technique other than PML to truncate the computing space of finite element. Multiport structures such as H‐Plane forked T‐junction, waveguide loaded with two dielectric posts, and E‐plane filter are studied as examples. The calculated results of these structures are shown and compared, respectively, to those in references. Good agreement between them is observed. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 173–177, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20411
57Fe NMR spectroscopy of ferrocenes bearing π‐acceptor substituents
Authors: Wrackmeyer Bernd , Tok Oleg L. , Ayazi Anahid , Maisel Heidi E. , Herberhold Max 
Published: August 2004

AbstractFerrocene derivatives bearing π‐acceptor substituents in 1‐ or 1,1′‐positions such as carbonyl group(s) (1, 2), a sulfinyl group (4) or boryl group(s) (5, 6, 9) and related [3]ferrocenophanes (3, 7, 10, 12, 13) and a [4]ferrocenophane (8) were studied by 57Fe NMR spectroscopy. The deshielding effect of the respective π‐acceptor substituent can be partially or fully compensated by distortion of the ferrocene geometry. Both aspects become apparent by comparing δ57Fe data of the [n]ferrocenophanes with those of related non‐cyclic derivatives. Copyright © 2004 John Wiley & Sons, Ltd.
Triphenylphosphane complex formation with hexyn‐1‐yl silver
Authors: Létinois‐Halbes Ulla , Pale Patrick , Berger Stefan 
Published: August 2004

AbstractHexyn‐1‐yl silver shows broad signals in 1H, 13C and 109Ag NMR. In the presence of 1 equiv. of triphenylphosphane, the signals are much sharper and at low temperature 109Ag,31P and 107Ag,31P coupling can be observed. On 109Ag decoupling, the 31P spectrum still shows the 107Ag,31P coupling indicating the formation of a coordination complex. Copyright © 2004 John Wiley & Sons, Ltd.
Density functional computation of 49Ti NMR chemical shifts
Authors: Bühl Michael , Mauschick Frank T. 
Published: August 2004

Abstract49Ti chemical shifts of TiX4 (X = Cl, Br, F), TiClnMe(4−n) (n = 0–3), Ti(C5H5)2X2 (X = F, Cl, Br) and Ti(CO)62− were computed, using geometries optimized with the gradient‐corrected BP86 density functional, at the GIAO (gauge‐including atomic orbitals)–Hartree–Fock, BPW91, and B3LYP levels. For this set of compounds, substituent effects on δ(49Ti) are reasonably well described with all methods considered; judged from mean absolute deviations from experiment, B3LYP performs best. Zero‐point corrections to the δ(49Ti) values, evaluated from a perturbational approach based on vibrationally averaged effective geometries, turn out to be fairly small. Electric field gradients computed with the B3LYP functional do not correlate with trends in 49Ti NMR linewidths. Attempts are reported to correlate the δ(49Ti) values of Ti[YC(O)CHC(O)Y]2Cl2 (Y = H, Me, CF3, CN, F, Cl and Br) with the rate‐limiting propagation barrier for ethylene polymerization using catalysts derived from these precursors. Copyright © 2004 John Wiley & Sons, Ltd.
PGSE diffusion, 1H–19F HOESY and NMR studies on several [Rh(1,5‐COD)(Biphemp)]X complexes: detecting positional anion effects
Authors: Anil Kumar P. G. , Pregosin Paul S. , Schmid Thomas M. , Consiglio Giambattista 
Published: August 2004

AbstractThree new salts of Rh(I), [Rh(1,5‐COD)(Biphemp)]X, Biphemp = (6,6′‐dimethylbiphenyl‐2,2′‐diyl)bis(diphenylphosphine), X = BF4−, 2a, PF6−, 2b, and CF3SO3−, 2c, were prepared and studied using PGSE diffusion, 1H–19F HOESY and inverse 103Rh (amongst other) NMR methods. Although the immediate coordination sphere of the cation does not sense the change in the anion, the PGSE diffusion and 1H–19F HOESY data suggest that, in addition to some ion pairing, each of the anions in 2 demonstrates selectivity in its approach towards the cation. Copyright © 2004 John Wiley & Sons, Ltd.
Multinuclear NMR study of some organoplatinum complexes containing multifunctional azines as chelating ligands
Authors: Gudat Dietrich , Dogan Akbey , Kaim Wolfgang , Klein Axel 
Published: August 2004

Abstract1H‐detected indirect NMR techniques were used to determine 15N and 195Pt NMR parameters for a series of organoplatinum(IV) complexes and one platinum(II) complex containing nitrogen‐based azobispyridine, bispyridyltetrazine, and bipyrimidine ligands. The inverse technique permitted the detection of small 4J(Pt,H) and 5J(Pt,H) long‐range couplings and the acquisition of 15N NMR data in natural isotopic abundance via nJ(N,H) intra‐ and inter‐ligand couplings, but failed in cases where coherence transfer is quenched by rapid relaxation of the metal atom. In one case, analysis of satellite patterns in a set of 1H,15N, 1H,195Pt and 1H,13C correlation spectra allowed a positive sign to be determined for 1J(Pt,15N). Qualitative arguments are presented to explain the observed 15N coordination shifts in complexes with different azine ligands in terms of azine–M dative bond formation and LnM–azine back‐donation. Copyright © 2004 John Wiley & Sons, Ltd.
A vanadium‐51 NMR study of the binding of vanadate and peroxovanadate to proteins
Authors: Rehder Dieter , Časný Marian , Grosse Reiner 
Published: August 2004

Abstract51V quadrupolar central transition NMR spectra of buffered (pH 7.6–8.0) solutions of bovine apo‐transferrin (Tf) and bovine prostatic acid phosphatase (Pp) treated with vanadate show normal features (chemical shifts between −515 and −542 ppm) corresponding to the complexation of VO2+ to the Tf binding site and the Pp active centre, respectively. Addition of H2O2 leads to the temporary formation of complexed VO(O2)+(δ ≈ −595). Vanadate‐dependent bromoperoxidase from the alga Ascophyllum nodosum exhibits an unusually high shielding both for the native (δ = −931) and the peroxo form (δ = −1135) of the enzyme. A resonance at −471 ppm is traced back to an inactive form with oxovanadium(V) in a trigonal‐bipyramidal array. Copyright © 2004 John Wiley & Sons, Ltd.
Solid‐state 109Ag CP/MAS NMR spectroscopy of some diammine silver(I) complexes
Authors: Bowmaker Graham A. , Harris Robin K. , Assadollahzadeh Behnam , Apperley David C. , Hodgkinson Paul , Amornsakchai Pornsawan 
Published: August 2004

AbstractSolid‐state cross‐polarization magic‐angle spinning (CP/MAS) NMR spectra were recorded for the compounds [Ag(NH3)2]2SO4, [Ag(NH3)2]2SeO4 and [Ag(NH3)2]NO3, all of which contain the linear or nearly linear two‐coordinate [Ag(NH3)2]+ ion. The 109Ag CP/MAS NMR spectra show centrebands and associated spinning sideband manifolds typical for systems with moderately large shielding anisotropy, and splittings due to indirect 1J(109Ag,14N) spin–spin coupling. Spinning sideband analysis was used to determine the 109Ag shielding anisotropy and asymmetry parameters Δσ and η from these spectra, yielding anisotropies in the range 1500–1600 ppm and asymmetry parameters in the range 0–0.3. Spectra were also recorded for 15N and (for the selenate) 77Se. In all cases the number of resonances observed is as expected for the crystallographic asymmetric units. The crystal structure of the selenate is reported for the first time. One‐bond (107, 109Ag,15N) coupling constants are found to have magnitudes in the range 60–65 Hz. Density functional calculations of the Ag shielding tensor for model systems yield results that are in good agreement with the experimentally determined shielding parameters, and suggest that in the solid compounds Δσ and η are reduced and increased, respectively, from the values calculated for the free [Ag(NH3)2]+ ion (1920 ppm and 0, respectively), primarily as a result of cation–cation interactions, for which there is evidence from the presence of metal‐over‐metal stacks of [Ag(NH3)2]+ ions in the solid‐state structures of these compounds. Copyright © 2004 John Wiley & Sons, Ltd.
Application of HMQC spectroscopy to the observation of the metal resonance in polymetallic compounds: the effect of multiple‐metal spin transitions
Authors: Heaton B. T. , Iggo J. A. , Podkorytov I. S. , Tunik S. P. 
Published: August 2004

AbstractMultiple‐metal spin transitions which distort the HMQC spectra of rhodium carbonyl clusters are discussed. These effects are seen whenever the detector nucleus, e.g. 13C or 31P, couples to more than one metal spin and are not restricted to detector ligands occupying edge‐ or face‐bridging sites. These effects are illustrated in, but not limited to, the 13C‐{103Rh} and 31P‐{103Rh} HMQC spectra of [Rh6(CO)15L], (where L = P(4‐F‐C6H4)3), [Rh4(CO)11{P(OPh)3}], [Rh6C(CO)15]2 − and [Rh2(carboxylate)2PPh3]. The effect is to modulate the intensity and position of the correlations in the metal dimension; cross peaks are displaced from the true chemical shift, additional cross peaks are seen and the intensity of the coherences varies as a function of the preparation delay, d2, and coupling constant, and may go to zero at the conventional value of 1/(2J). Analyses of the relevant spin systems are given together with experimental strategies to overcome these effects. Copyright © 2004 John Wiley & Sons, Ltd.
Indirect nuclear 57Fe13C and 57Fe1H spin–spin coupling in ferrocenes and cyclopentadienyliron complexes: measurements and DFT calculations
Authors: Wrackmeyer Bernd , Tok Oleg L. , Koridze Avthandil A. 
Published: August 2004

AbstractSeveral 57Fe‐labeled ferrocene derivatives and other cyclopentadienyliron complexes were studied by 57Fe and 13C NMR with respect to isotope‐induced chemical shifts 1Δ12/13C(57Fe) and the magnitude and sign of coupling constants 1J(57Fe,13C) and 2J(57Fe,1H). The geometries of the complexes were optimized by DFT methods [B3LYP/6–311+G(d,p)] and chemical shifts (GIAO) and coupling constants were calculated at the same level of theory. The trends in calculated 57Fe nuclear shielding agree well with the experimental data and, in the case of coupling constants 1J(57Fe,13C) and 2J(57Fe,1H), both sign and magnitude are correctly reproduced. Copyright © 2004 John Wiley & Sons, Ltd.
Indirect coupling to quadrupolar nuclei: observation of 1J(105Pd,31P) in one‐ and two‐dimensional 31P CP/MAS spectra
Authors: Rüegger Heinz 
Published: August 2004

AbstractHigh‐resolution solid‐state 31P cross‐polarization magic angle spinning (CP/MAS) spectra of a series of Pd(II) complexes were obtained. All of these spectra exhibit low‐intensity satellite peaks flanking the main resonances which are assigned to originate from a combination of direct (D) and indirect (J) spin–spin coupling between the 31P and the 105Pd spins. The parameter 1J(105Pd,31P) is found to be sensitive to the nature of the ligand in a trans position and thus of great value in assigning the configuration, i.e. cis or trans, in square‐planar complexes of Pd(II). A linear relationship between 1J(105Pd,31P) and 1J(195Pt,31P) in analogous Pd(II) and Pt(II) complexes is suggested, the latter parameter being a factor of ca 14 larger. Two‐dimensional exchange spectroscopy proved valuable in resolving overlapping resonances and relating pairs of inequivalent 31P spins within the same complex and spreading their satellite manifolds into two dimensions. These two spectral features are unrelated, being due to dipolar coupling among the phosphorus spins in the former and finite lifetimes of the spin states of the 105Pd isotope in the latter case. Copyright © 2004 John Wiley & Sons, Ltd.
Rhodium‐103 NMR of [Rh(X)(PPh3)3] [X = Cl, N3, NCO, NCS, N(CN)2, NCBPh3, CNBPh3, CN] and derivatives containing CO, isocyanide, pyridine, H2 and O2. Ligand, solvent and temperature effects
Authors: Carlton Laurence 
Published: August 2004

AbstractRhodium‐103 chemical shifts are reported for 62 compounds, namely [Rh(X)(PPh3)3] [X = Cl, N3, NCO, NCS, N(CN)2, NCBPh3, CNBPh3, CN] and derivatives formed by replacement of a phosphine by CO, xylyl isocyanide (XNC) and pyridine and/or by oxidative addition of H2 or O2 to give trans‐[Rh(X)(PPh3)2(CO)] (δ in the range −816 to −368 ppm) trans‐[Rh(X)(PPh3)2(XNC)] (δ −817 to −250 ppm), cis‐[Rh(X)(PPh3)2(py)] (the trans isomer is formed with X = CN, CNBPh3) (δ −233 to 170 ppm), [Rh(X)(H)2(PPh3)3] (δ −611 to 119), trans‐[Rh(X)(H)2(PPh3)2(py)] (δ −30 to 566 ppm), [Rh(X)(O2)(PPh3)3] (δ 1393 to 3273 ppm) and cis‐[Rh(X)(O2)(PPh3)2(py)] (δ 1949 to 3374 ppm). For the majority of these compounds data were obtained from solutions in chloroform and in toluene at temperatures of 247 and 300 K; for [Rh(X)(PPh3)3] (δ −562 to −4 ppm) data are reported at a number of temperatures in the range 195–300 K for solutions in chloroform, toluene and dichloromethane and at 300 K for solutions in DMSO. The expected trend to lower δ(103Rh) with decreasing temperature (vibrational shielding) is observed for the dichloromethane data, but data from solutions {of [Rh(X)(PPh3)3]} in chloroform and toluene show a number of features which diverge from this pattern, i.e. shifts to higher δ are found to accompany a decrease in temperature, most noticeably where X = CN and Cl [on changing the solvent from dichloromethane to chloroform changes in δ(103Rh) of up to 172 ppm are observed]. These results are interpreted in terms of a hydrogen‐bonded interaction with the solvent that is enhanced by the presence of a polarizable ligand (CN, Cl). With a ligand (O2CCF3) that is only weakly polarizable the solvent dependence of δ(103Rh) is minimal. Copyright © 2004 John Wiley & Sons, Ltd.
Richness of isomerism in labile octahedral Werner‐type cobalt(II) complexes demonstrated by 19F NMR spectroscopy: structure and stability
Authors: Novitchi Ghenadie , Riblet Fabrice , Helm Lothar , Scopelliti Rosario , Gulea Aurélian , Merbach André E. 
Published: August 2004

AbstractThe cobalt(II) complexes [CoL2(R2‐Py)2] (1–4) where HLA = 1,1,1‐trifluoro‐5,5‐dimethyl‐2,4‐hexanedione, R2‐Py = 4‐methylpyridine (1), HLB = 4,4,4‐trifluoro‐1‐(2‐thienyl)‐1,3‐butanedione, R2‐Py = 4‐methylpyridine (2), 4‐phenylpyridine (3) and S‐(−)‐1‐(4‐pyridyl)ethanol (4) were prepared by two‐step reactions. X‐ray structure analysis of [CoLA2(CH3‐Py)2] revealed the {trans(N)‐trans(CF3)‐trans} configuration for the complex obtained by crystallization from ethanol. A dynamic equilibrium between the five possible stereoisomers was observed for each complex 1–4 in solution by 19F NMR spectroscopy. The criteria used for full NMR assignment (180–265 K) include comparison of integral ratios, cis(N) and trans(N) differentiation in presence of the chiral amine [S‐(−)‐1‐(4‐pyridyl)ethanol], effect of solvent polarity on the relative stabilities of the five isomers and observation of trans influences in a mixture of complexes. Thermodynamic parameters for the equilibria between the isomers of 2 in CD2Cl2 (ΔHi,j, ΔSi,j and Ki,j) were obtained from signal integrals. The two trans(N) isomers are slightly more stable than the three cis(N) isomers at low temperature [ΔG°i,j (max) = 2.8 kJ mol−1 at 179.8 K], but this stability difference almost vanishes with increasing temperature [ΔG°i,j (max) = 1.0 kJ mol−1 at 265.0 K]. The values found for ΔH°i,j are relatively small and largely entropy compensated. Copyright © 2004 John Wiley & Sons, Ltd.
103Rh NMR spectroscopy and its application to rhodium chemistry
Authors: Ernsting Jan Meine , Gaemers Sander , Elsevier Cornelis J. 
Published: August 2004

AbstractRhodium is used for a number of large processes that rely on homogeneous rhodium‐catalyzed reactions, for instance rhodium‐catalyzed hydroformylation of alkenes, carbonylation of methanol to acetic acid and hydrodesulfurization of thiophene derivatives (in crude oil). Many laboratory applications in organometallic chemistry and catalysis involve organorhodium chemistry and a wealth of rhodium coordination compounds is known. For these and other areas, 103Rh NMR spectroscopy appears to be a very useful analytical tool. In this review, most of the literature concerning 103Rh NMR spectroscopy published from 1989 up to and including 2003 has been covered. After an introduction to several experimental methods for the detection of the insensitive 103Rh nucleus, a discussion of factors affecting the transition metal chemical shift is given. Computational aspects and calculations of chemical shifts are also briefly addressed. Next, the application of 103Rh NMR in coordination and organometallic chemistry is elaborated in more detail by highlighting recent developments in measurement and interpretation of 103Rh NMR data, in relation to rhodium‐assisted reactions and homogeneous catalysis. The dependence of the 103Rh chemical shift on the ligands at rhodium in the first coordination sphere, on the complex geometry, oxidation state, temperature, solvent and concentration is treated. Several classes of compounds and special cases such as chiral rhodium compounds are reviewed. Finally, a section on scalar coupling to rhodium is provided. Copyright © 2004 John Wiley & Sons, Ltd.
NMR spectroscopy of organolithium compounds. XXVI—The aggregation behaviour of methyllithium in the presence of LiBr and LiI in diethyl ether and tetrahydrofuran
Authors: Fox Thomas , Hausmann Heike , Günther Harald 
Published: August 2004

Abstract1H, 6Li and 13C NMR spectroscopy were used to determine the structure of aggregates formed in mixtures of methyllithium, H3CLi, and lithium bromide and iodide in diethyl ether and tetrahydrofuran. From the chemical shifts, the signal intensity distribution and the isotope shifts observed for partially deuterated systems, it was shown that generally tetrameric structures with different halogen contents dominate. For methyllithium–lithium bromide (1:1) in THF a considerable concentration of an H3CLiLiBr dimer was found. For the first time, deuterium‐induced 6Li isotope shifts over four bonds were observed. Copyright © 2004 John Wiley & Sons, Ltd.
Compaction process in sedimentary basins: the role of stiffness increase and hardening induced by large plastic strains
Authors: Deudé V. , Dormieux L. , Maghous S. , Barthélémy J. F. , Bernaud D. 
Published: August 2004

AbstractThis paper is devoted to the simulation of large strain compaction process in sedimentary basins. Special attention is paid to the effects of large porosity changes on the elastic and plastic mechanical properties of the sediment material. The latter are introduced in the constitutive behaviour in the framework of a micromechanical reasoning. In particular, the proposed approach avoids the problem of negative porosities that are predicted by classical models under high confining pressures.Some closed‐form solutions are presented in the simplified case of one‐dimensional compaction. While the influence of stiffness increase is shown to be negligible as regards the compaction law, it proves to affect significantly the stress and porosity profiles. Copyright © 2004 John Wiley & Sons, Ltd.
Three dimensional simulation of fluid flow in X‐ray CT images of porous media
Authors: Al‐Omari A. , Masad E. 
Published: August 2004

AbstractA numerical scheme is developed in order to simulate fluid flow in three dimensional (3‐D) microstructures. The governing equations for steady incompressible flow are solved using the semi‐implicit method for pressure‐linked equations (SIMPLE) finite difference scheme within a non‐staggered grid system that represents the 3‐D microstructure. This system allows solving the governing equations using only one computational cell. The numerical scheme is verified through simulating fluid flow in idealized 3‐D microstructures with known closed form solutions for permeability. The numerical factors affecting the solution in terms of convergence and accuracy are also discussed. These factors include the resolution of the analysed microstructure and the truncation criterion. Fluid flow in 2‐D X‐ray computed tomography (CT) images of real porous media microstructure is also simulated using this numerical model. These real microstructures include field cores of asphalt mixes, laboratory linear kneading compactor (LKC) specimens, and laboratory Superpave gyratory compactor (SGC) specimens. The numerical results for the permeability of the real microstructures are compared with the results from closed form solutions. Copyright © 2004 John Wiley & Sons, Ltd.
Specific functions of Drosophila amyloid precursor‐like protein in the development of nervous system and nonneural tissues
Authors: Li Yan , Liu Tong , Peng Yueqing , Yuan Chunyan , Guo Aike 
Published: August 2004

AbstractDrosophila amyloid precursor‐like protein (APPL) is expressed extensively in the nervous system soon after neuronal differentiation. By utilizing different transgenic flies, we studied the physiological function of two APPL protein forms, membrane‐bound form (mAPPL) and secreted form (sAPPL), in neural development. We found that neither deletion nor overexpression of APPL protein altered the gross structure of mushroom bodies in the adult brain. No changes were detected in cell types and their relative ration in embryo‐derived cultures from all APPL mutants. However, the neurite length was significantly increased in mutants overexpressing mAPPL. In addition, mutants lacking sAPPL had numerous neurite branches with abnormal lamellate membrane structures (LMSs) and blebs, while no apoptosis was detected in these neurons. The abnormal neurite morphology was most likely due to the disorganization of the cytoskeleton, as shown by double staining of actin filaments and microtubules. Electrophysiologically, A‐type K+ current was significantly enhanced, and spontaneous excitatory postsynaptic potentials (sEPSPs) were greatly increased in APPL mutants lacking sAPPL. Moreover, panneural overexpression of different forms of APPL protein generated different defects of wings and cuticle in adult flies. Taken together, our results suggest that both mAPPL and sAPPL play essential roles in the development of the central nervous system and nonneural tissues. © 2004 Wiley Periodicals, Inc. J Neurobiol, 2004