bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiple Bonds between Main‐Group Elements and Transition Metals, CLXV. Rhenium(V) Oxo Complexes with Bidentate Schiff Bases: Structures and Catalytic Applications
Authors: Kühn Fritz E. , Rauch Monika U. , Lobmaier Gerhard M. , Artus Georg R. J. , Herrmann Wolfgang A.
Published: July 2007

Reaction of [NBu4][ReOCl4] (1) with bidentate salicylidene amine ligands (salen = HL) (2a‐c) leads to the formation of monomeric octahedral rhenium (V) compounds of formula [ReOCl (L)2] (3a‐c). Spectroscopic date indicate asymmetric arrangement of the ligands in the complexes. This is confirmed by the X‐ray crystal structures of 3b and 3c. Complexes 3a, b have been tested as catalysts for the epoxidation of cyclooctene. No evidence for decomposition for decomposition of the catalysts is observed during the reaction (as in the case for tri‐and tetra‐dentate salen complexes). No undesired byproducts are formed in the catalytic reactions.
Hydrocarbon‐Bridged Complexes, XL. Polyene‐Bridged Iridium(III), Palladium(II), and Platinum(II) Complexes of Schiff Bases from α,ω‐Polyene Dialdehydes and α‐Amino Acids or o‐Aminophenol
Authors: Fehn Armin , Briel Oliver , Beck Wolfgang
Published: July 2007

Schiff bases 111 were synthesized from α‐amino acids or o‐aminophenol and crocetindialdehyde, 2,7‐dimethyloctatrienedial, terephthalaldehyde, or β,β′ ‐p‐phenylendiacroleine. The reactions of these Schiff bases with chloro‐bridged complexes [(R3P)(Cl)M(η‐Cl)]2 (M = Pd, Pt) and [(C5Me5)(Cl)Ir(°Cl)]2 gave the dinuclear complexes 12–31.
New Phosphorus Heterocycles by Rearrangement of a [1,4‐Bis(trimethylsilyl) η8‐cyclooctatetraene‐1,3,5‐triphospha‐7‐hafnanorbornadiene Complex
Authors: Binger Paul , Leininger Stefan , Günther Klaus , Bergsträßer Uwe
Published: July 2007

[1,4‐Bis(trimethylsilyl)‐n8‐cyclooctatetraene]‐2, 4, 6‐tri‐tert‐butyl‐1, 3, 5‐triphospha‐7‐hafnanorbornadiene (3) rearranges nearly quantitatively to the corresponding 3,5,6‐tri‐tert‐butyl‐1,2,4‐triphospha‐7‐hafnanorbornadiene complex 5 upon heating at 70°C. Treatment of complex 5 with trimethylphosphane at 50°C induces the displacement of di‐tert‐butylacetylene to give the new (n4‐triphosphacyclobutadiene)hafnium complex 7, the crystalstructure of which has been determined by X‐ray analysis. From complex 5 3,5,6,‐tri‐tert‐butyl‐1,2,4‐triphospha Dewar benzene (6) can be synthesized by a redox reaction with hexachloroethane.
Synthesis and Characterization of Substituted Benzyl Zinc Derivatives ‐ Molecular Structures of (tmeda) Li‐CH (GeMe3)Ph, (tmeda)Zn(CH2Ph)2, (tmeda)Zn[CH(SiMe3)Ph]2, and (tmeda)Zn[CH(SiMe3)Ph]N(H)Si(SiMe3)3
Authors: Westerhausen Matthias , Wieneke Michael , Rademacher Bernd B. , Schwarz Wolfgang
Published: July 2007

The reaction of lithium phenyl(trimethylsilyl)methanide with phenyl(trimethylsilyl)methylzinc chloride‐tmeda in the presence of tmeda yields the addition product, a bis(tmeda)‐lithium dialkylchlorozincate. The elimination of lithium chloride leads to the formation of a tmeda adduct of bis[phenyl‐(trimethylsilyl)methyl]zinc. The metathesis reaction of phenyl(trimethylsilyl)methylzinc chloride‐tmeda with lithium tris(trimethylsilyl)silylamide allows the isolation of the corresponding heteroleptic tmeda complex of an alkylzinc amide. The metalation of phenyl(trimethylstannyl)methane with butyllithium yields the transmetalation product benzyllithium. From the metathesis reaction of this lithium base with anhydrous zinc(II) chloride in the presence of tmeda, the tmeda adduct of dibenzylzinc crystallizes. The molecular structures of (tmeda)LiCH(GeMe3)Ph, (tmeda)Zn(CH2Ph)2, (tmeda)Zn[CH(SiMe3)Ph]2, and (tmeda)Zn[CH(SiMe3)‐Ph[N(H)Si(SiMe3)3 are reported. Whereas lithium bonds in an η3‐fashion, the zinc atom forms a σ(ZnC) bond. The extremely wide ZnNSi angle in (tmeda)Zn[CH(SiMe3)‐Ph[N(H)Si(SiMe3)3 of 157° is remarkable.
Dirhenium Complexes with S2CPR3 Bridges Donating Four and Eight Electrons — X‐ray Structures of [Re2(CO)8{μ‐η1;η1‐S2CPCy3}] and {Re2(CO)6{μ‐η3;‐S2CPCy3}] and [Re2(CO)6{μ‐η2; η3‐S2CPCy3}]
Authors: Alvarez Bernardo , Li Jing , Miguel Daniel , Morales M. Dolores , Riera Victor , García‐Granda Santiago
Published: July 2007

The reaction of fac‐[Re(CO)3(S2CPR3)Br] with [Rc(CO)5]− affords the dinuclear octacarbonyl compounds [Re2(CO)8(μ‐S2CPR3)] (3ab), which have been isolated and characterized by spectroscopic methods. An X‐ray crystal‐structure determination of the derivative 3a (RCy) shows that the S2CPCY3 ligand acts as an η1(S);η1(S′) bridge donating two electrons to each metal atom of a symmetrical (CO)4ReRe(CO)4 unit. This unit is presumably formed through a concerted process involving carbonyl/sulfur exchange in the nonsymmetrical octacarbonyl (CO)3(S2CPR3)ReRe(CO)5 generated after the coupling of the bromo derivative with the carbonyl anion. Complexes 3ab can be obtained more directly by adding S2CPR3 to [Re2(CO)8(μ‐H)(μ‐CHCHnBu)], which is formed by irradiation of Re2(CO)10 with 1‐hexene. Hydride addition to the central carbon atom of the S2CPR3 ligand of 3a–b occurs with loss of PR3, to give the anion [Re2(CO)8(μ‐S2CH)]− which may be isolated as a salt with the PPN+ cation. The octacarbonyl compounds 3a–b can be converted into hexacarbonyl complexes [Re2(CO)6(μ‐S2CPR3)] (5a–b) by heating in toluene or octane at reflux temperature. According to an X‐ray crystal‐structure determination of the derivative 5a (RCy), the loss of one carbonyl ligand from each rhenium atom is accompanied by the rearrangement of the S2CPR3 ligand which changes its bonding mode from η1(S);η1(S′) donating four electrons to η3(S,C,S′);η2(S,S′) donating eight electrons.
Synthesis of Novel Optically Active Tin Hydrides Containing Chiral Ligands
Authors: Schwarzkopf Kay , Metzger Jürgen O. , Saak Wolfgang , Pohl Siegfried
Published: July 2007

The synthesis of the chiral tin bromides 1‐4 and hydrides 5‐8, containing the potentially bidentate, optically active 2‐[ (1 S/R)‐ 1 ‐dimethylaminoethyl]phenyl and 2 ‐[( 1 S) ‐ 1 ‐dimethylamino‐2,2‐dimethylpropyl]phenyl ligands, is reported. The tin hydrides 5‐8, with the tin atom as the stereogenic centre, were isolated as diastereomeric mixtures with diastereomeric ratios of dr = 50:50 up to dr = 80:20. The absolute configuration of (—) ‐ (1 S)‐ 1 ‐ (2‐bromophenyl) ‐2,2‐dimethylpropylamine [(S)‐10] was determined by single‐crystal X‐ray structure analysis.
Cobalt Phthalocyanine Derivatives Supported on TiO2 by Sol‐Gel Processing. Part 1: Preparation and Microstructure
Authors: Schubert Ulrich , Lornez Anne , Kundo Nicolay , Stuchinskaya Tatiana , Gogina Ludmila , Salanov Alexel , Zalkovskii Vladimir , Maizlish Vladmir , Shaposhmikov Gennadii P.
Published: July 2007

Cobalt(II) 2,9,16,23‐tetrasulphophthalocyanine and cobalt(II) 2,9,16,23‐tetra(chlorosulphonyl)phthalocyanine were supported on TiO2 by reaction of the phthalocyanines with Ti(OR)4 followed by sol‐gel synthesis. The thus obtained solid materials are stable in sulfide‐containing media and are therefore suitable as catalysts for HS oxidation. The structure of the samples was characterized by electron microscopy diffraction. The morphology of the matrix strongly depends on the cobalt phthalocyanine derivative. The pathalocyanines in the titania matrices are monomeric or dimeric depending both on the type of substituents of the CoPc derivative and on the titanium alkoxide used as precursors.
Dichlorogermylene‐Alkyldichlorophosphane Reactions Revisited: Characterisation of Bis(trichlorogermyl)phosphanes, Trichlorogermyldiphosphanes, and Ge‐P Heterocycles
Authors: Karnop Michael , Mont Wolf‐Walther Du , Jones Peter G. , Jeske Jörg
Published: July 2007

The reactions of alkyldichlorophosphanes 1 (RPCl2; R = tert‐butyl: 1a, R = isopropyl; 1b, R = 1‐adamantyl: 1c) with the germanium dichloride dioxane complex were followed by 31P NMR. Depending on the organic substituents and the reaction conditions, mixtures of trichlorogermylphosphanes RP(GeCl3)2 4a‐c, RPHGeCl3 5a‐c, diphosphanes R(H)PP(H)GeCl3 6a‐c, R(Cl)PP(H)GeCl3 7a, b cyclophosphanes, and Ge‐P heterocycles such as triphosphadigermolanes (RP)3(GeCl2)2 8a, b and tetraphosphagermolane (RP)4)GeCl2 10b are formed. As a further unexpected byproduct of the reaction of 1a with GeCl2–dioxane, a small amount of tri‐tert‐butyl(trichlorogermyl)cyclotetraphosphane 9a was isolated. From the reaction of 1c with two equivalents of GeCl2–dioxane, separation from byproducts 5c and 6c by crystallisation furnished colourless crystals of 4c (R = 1‐adamantyl) as the first pure organylbis(trichlorogermyl)phosphane. Surprisingly, the reaction of isoprophylphosphane with germanium tetrachloride, intended to prepare 5a, led to crystalline isopropylphosphonium trichlorogermanate(II) 11. The structures of molecular 4c and 9a and ionic 11 were determined by X‐ray crystallography.
Coordination Chemistry of Functional Phosphanes, VI. Rhodium and Iridium Complexes with 2‐(Diphenylphosphophanyl)phenylamido Ligands
Authors: Dahlenburg Lutz , Herbst Kourad
Published: July 2007

Treatment of trans‐[MCl(CO)(PPH3)2] (M = Rh, Ir) with the lithium salts fof the bidentate hybride ligands 2‐Ph2PC6H4N(R)H [‘PN(R)H’ R = H, Me] produced the chelate complexes [M(CO)(PPH3)(‘PNR’)] [M/NR = Rh/NH (1a), Ir/ NH (2a), Rh/NMe (1b), Ir/NMe (2b)] containing the CO ligand and the NR substituent in mutual trans‐arrangement. 2b was shown by single‐crystal X‐ray diffraction to possess an amido‐nitrogen atom in a trigonal‐planar environment. Oxidative addition of H2 to 2b reversibly formed cis‐[IrH2(CO)(PPh3)(‘PNMe’)] (3), in which H2 has added perpendicular to the N–Ir–CO axis. While both 1a,b and 2a, b proved to the completely unreactive toward CO2 at ambient temperature and pressure, reactions of 1a and 2a/b with sulfur dioxide reversibly formed pentacoordinate SO2 adducts, [M(SO2)(CO(PPh3)(‘PNR’)][M/NR = Rh/Nh (4a), Ir/NH (5a), Ir/NMe (5b) with M–S‐bonded pyramidal MSO2 units as established by an X‐ray structure analysis of 5a. Complex 5b reacted with dioxygen to form the sulfato compound [Ir(O2SO2)(CO)(‘PNMe’)] (6). Combination of 2a with HCl in CHCl3 at −60°C resulted in protonation of both the iridium and the nitrogen atom to give an ionic chelate complex, [IrHCl(CO)(PPh3)(‘PNH2’)]Cl (7), containing one of its NH groups hydrogen‐bonded to Ir–Cl. Ring opening of the chelate structure with formation of [IrHCl2(CO)(PPh3)(PPh2C6H4N(Me)H‐o)] (8) was observed in the analogous reaction of 2b with hydrogen chloride. NMR spectroscopy showed 8 to exist in CDCl3 solution as a mixture of three Ir–PPh2C6H4N(Me)H‐o rotamers, stabilized by intramolecular –N(Me)H —ClIr hydrogen bonding.
Tetra(amino)methanes: Implications of Their Structure and Reactivity Pattern for Hypothetical Carbon Nitride Frameworks
Authors: Jockisch Alexander , Schier Annette , Schmidbaur Hubert
Published: July 2007

Because of their possible role as model compounds for the structural units of carbon nitride C3N4, the preparation, structural chemistry, and some representative reactions of tetra(amino)methanes have been (re)investigated. In the crystal, C(NMe2)4 (1) has a molecular geometry close to D2a symmetry as proposed by theoretical calculations using state‐of‐the‐art density functional methods. The coordination of the central carbon atom is distorted tetrahedral and the configuration of the nitrogen atoms is strongly pyramidal, as opposed to almost planar in the tetra(amino)silanes. Tetra(pyrrolidinyl)methane has a similar core structure, with all heterocyclic substituents in an envelop conformation flexible in solution. Tetra(piperidinyl)methane is more rigid in solution, owing to a more congested structure, with much higher inversion barriers for the six‐membered rings. Hydrolysis of 1 leads to MezNH and hexamethylguanidinium hydroxide, and treatment of 1 with HAuCl4(aq) affords crystalline [C(NMe2)3]4 AuCl4− the structure of which has also been determined. Compound 1 is a strong nucleophile and can be used as an aminating agent, converting e.g. halosilanes into dimethylaminosilanes, with the guanidinium cation as the leaving group. The experimental results are discussed in the light of recent predictions regarding bulk carbon nitrides.
Density Functional Studies on Amino‐Substituted Methane and Silane
Authors: Albert Katrin , Rösch Notker
Published: July 2007

In all‐electron density functional calculations on mono‐ and tetraaminosubstituted methane and silane the coordination around the nitrogen center is found, in complete agreement with experiment, to be less pyramidal in the silicon compounds. The calculated barrier to inversion at nitrogen is only 0.6 kcal/mol in silylamine, while in methylamine it is 5.5 kcal/mol. The larger flexibility is attributed to the greater ionic character of the Si‐N bond compared to that of the C‐N bond. In tetra(amino)methane, inversion of one amino group leads to a local minimum (calculated inversion barrier: 6.4 kcal/mol), while a corresponding structure (or barrier) does not exist for the silicon compound. Due to the steric influence of the amino groups, the barrier to rotation around the C‐N bond is larger in the tetrasubstituted compound (6.4 kcal/mol compared to 2.3 kcal/mol in methylamine). While the average binding energy of the amino groups is similar in both tetra(amino)compounds, the binding energy of the fourth ligand is about 25% larger in the silicon compound for both homolytic and heterolytic bond cleavage. This difference arises from the relative stabilization of the tri(amino)‐methyl species, due to some n contribution to the C‐N bond.
Synthesis of the Diazadisilatitanacyclopentane RSi(NH2)NHTiMe(cp*)NHSi(NH2)R (R =PhNSiMe3, cp *=η5‐C5Me5
Authors: Böttcher Peter , Wraage Karsten , Roesky Herbert W. , Lanfranchi Maurizio , Tiripicchio Antonio
Published: July 2007

Reaction of two equivalents of N‐trimethylsilylaniline (1) with two equivalents of n‐butyllithium, followed by subsequent treatment with Si2Cl6 (2) leads to the formation of the tetrachlorodisilane RSiCl2SiCl2R (3) (R = PhNSiMe3). 3 is converted to RSi(NH2)2Si(NH2)2R (4) by reaction with liquid ammonia. 4 reacts with cp*TiMe3 (5) (cp* = η5‐CsMe5) to yield the diazadisilatitanacyclopentane RSi(NH2)NHTiMe(cp*)NHSi(NH2)R (6). The crystal structure of 6 is reported.
N′,N′,N″,N″‐Tetramethylguanidine‐Substituted Phosphoryl Compounds as Ligands in Transition Metal Chemistry – Unusual Modes of Coordination
Authors: Münchenberg Jochen , Thönnessen Holger , Jones Peter G. , Schmutzler Reinhard
Published: July 2007

Methyl‐ and tert‐butylphosphonic bis(N′,N′,N″,N″‐tetramethylguanidinide) 1 and 2 were allowed to react with various transition metal compounds. The resulting complexes were studied by IR spectroscopy, mass spectrometry and, in the case of 10, by NMR spectroscopy. In the case of the compounds 7–10 the metal was coordinated only via the imino nitrogen atoms of 2, (IR evidence). X‐ray structure analyses were performed for [L1CoBr2]2 6, L2CuCl2 9, and L2PdCl2 10 (L1 = 1, L2 = 2). In 5 L1 acts as an N,O bridging ligand, leading to tetrahedral coordination at Co and eightmembered (‐Co‐O‐P‐N‐)2 rings. In 6 coordination by L2 chelates the metal atom through two N atoms, leading to PN2M rings; the coordination geometry is distorted planar.
Synthesis and Characterization of Novel Octakis(2′‐aminophenoxy and 2′‐Aminophenylsulfanyl)‐Substituted Metallophthalocyanines
Authors: Kandaz Mehmet , Bekaro.Lu özer
Published: July 2007

Novel phthalocyanines (M = Ni, Zn, Co) bearing eight 2′‐aminophenoxy and 2′‐amino phenylsulfanyl substitutents on peripheral positions have been prepared starting from 4,5‐bis(2′‐aminophnoxy)−1,2‐dicyanobenzene and the corresponding anhydrous metal salts [NiCl2, Zn(O2CMe)2, CoCl2]‐ Complexation of octakis(2′‐amino phenylsulfanyl)‐substituted metallo phthalocyanines (2b, 3b and 4b) with Pd11 to form the pentanuclear product was accomplished from their mixtures.
Mass Transfer Coefficients in Mechanically Agitated Gas‐Liquid Contactors
Authors: Markopoulos J. , Christofi C. , Katsinaris I.
Published: July 2007

There are a large number of correlations given in literature for the prediction of volume‐related liquid‐side mass transfer coefficients in mechanically agitated gas‐liquid contactors. Significant disagreement can be observed concerning the proposed correlations, so that no single correlation exists representing all of the mass transfer data given in the literature. The observed differences can mainly be ascribed to the differences in the geometry of the system, the range of operational conditions and the measurement method used. On the basis of a comparative study of mass transfer phenomena in agitated Newtonian and non‐Newtonian aerated liquids, a critical discussion of the literature results is presented in this review article, so that final conclusions can be drawn for the kLα values in the different single‐ and multiple‐impeller agitated systems studied in the literature.
Enzymatic Hydrolysis of Corn Stover after Pretreatment with Dilute Sulfuric Acid
Authors: Lu X. B. , Zhang Y. M. , Yang J. , Liang Y.
Published: July 2007

Although many previous studies have been carried on the enzymatic hydrolysis of corn stover after pretreatment with dilute sulfuric acid, this paper emphasizes the use of different conditions to attain the highest yields of two sugars, xylose and glucose, from both stages. The pretreatment was performed at a range of sulfuric acid concentrations of 2, 4 and 6 % at 80, 100 and 120 °C. Up to 77 % xylose yield was obtained while the glucose yield was only 8.4 %. The corresponding solid phase was hydrolyzed by cellulase and the influences of five factors and their interactions on enzyme hydrolysis were evaluated by response surface methodology based on one‐factor‐at‐a‐time experiments. The optimal levels for each variable to obtain the highest reducing sugar yield were as follows: enzyme concentration of 22 FPU/g substrate, substrate concentration of 77 g/L, temperature of 49 °C, pH 4.8 and reaction time of 38 h. A reducing sugar yield of 42.11 g/100 g substrate was achieved, which was consistent with the predicted value of 42.13 g/100 g substrate. Compared with the one‐factor‐at‐a‐time experiments, there was a 9.4 % increase in reducing sugar yield when the enzyme concentration was decreased to 3 FPU/g substrate, the substrate concentration increased to 17 g/L and the reaction time dropped to 22 h. The total sugar released from the two stages was 62.81 g/100 g substrate.
Effect of CaSO4 Pelletization Conditions on a Novel Process for Converting SO2 to Elemental Sulfur by Reaction Cycles Involving CaSO4/CaS – Part II: Reduction of SO2 with CaS
Authors: Choi M. E. , Sohn H. Y. , Ahmed Y. M. Z. , Mohamed F. M. , Han G. , Shalabi M. E. H.
Published: July 2007

A new process for converting sulfur dioxide to elemental sulfur by a cyclic process involving calcium sulfide and calcium sulfate without generating secondary pollutants, developed at the University of Utah, was described in Part I of this series. In this process, sulfur dioxide is reacted with calcium sulfide to produce elemental sulfur and calcium sulfate; the latter is reduced by hydrogen to regenerate calcium sulfide. Here, in Part II, the effects of different pelletization conditions for the initial reactant calcium sulfate on the reactivity of CaS pellets produced from calcium sulfate pellets toward sulfur dioxide were studied. Experiments were performed to investigate the effects of temperature in the range 1023–1173 K, pellet size, cycle repetition, and water vapor or carbon dioxide content in the sulfur dioxide stream. The binder amount and the presence of nickel catalyst did not significantly affect the reaction rate.
Process and Laboratory Scale UV Inactivation of Viruses and Bacteria Using an Innovative Coiled Tube Reactor
Authors: Schmidt S. , Kauling J.
Published: July 2007

Avoidance and elimination of viral contamination in biotechnological and pharmaceutical processes is a crucial issue. The novel UVivatec coiled tube reactor was designed for UV irradiation of cloudy liquid media. It very effectively inactivates especially critical viruses and avoids high product losses. The method proposed is an ideal complement to existing and established processes.
Conversion of Biomass Based Slurry in an Entrained Flow Gasifier
Authors: Santo U. , Seifert H. , Kolb T. , Krebs L. , Kuhn D. , Wiemer H.‐J. , Pantouflas E. , Zarzalis N.
Published: July 2007

A two‐step process, BIOLIQ, with pyrolysis and subsequent entrained flow gasification has been developed at the Forschungszentrum Karlsruhe to produce synfuel from biomass. Experiments in a 60 kW pilot‐scale atmospheric entrained flow gasifier allow quantitative evaluation of the combustion behavior of biomass‐based slurry, leading to a better understanding of the gasification process.
Extended Dötz‐Like Cyclization Reactions Towards the Synthesis of Eight‐Membered Ring‐Containing Polycycles: Scope and Theoretical Studies
Authors: Barluenga José , Fañanás‐Mastral Martín , Palomero M. Angel , Aznar Fernando , Valdés Carlos
Published: July 2007

The reaction between cyclobutene‐containing dienyl Fischer carbene complexes (FCCs) and alkynes has been studied from both an experimental and a theoretical point of view. We have found that the reaction follows different pathways depending on the nature of the terminal double bond of the carbene complex. Thus, eight‐membered carbocycles have been obtained from an extended Dötz‐like reaction of dienyl FCCs and indolyl‐ or benzofuryl‐substituted alkenyl FCCs. On the other hand, phenyl‐ and naphthyl‐substituted alkenyl FCCs follow a typical benzannulation pathway giving rise to cyclohexadienones. DFT calculations have allowed us to formulate detailed mechanistic proposals and to provide an explanation for the formation of either the benzannulation products or the eight‐membered carbocycles.
Antimalarial Cation‐dimers Synthesized in Two Steps from an Inexpensive Starting Material, Isonicotinic Acid
Authors: Motoshima Kazunori , Hiwasa Yoshiko , Yoshikawa Mai , Fujimoto Kanji , Tai Akihiro , Kakuta Hiroki , Sasaki Kenji
Published: July 2007

Malaria is one of the three major serious infectious diseases in the world. As the area affected by malaria includes a large proportion of developing countries, there is a need for new antimalarials that can be synthesized and supplied inexpensively. To generate low‐cost antimalarials, the MAP series 6–10, bis‐cation dimers, synthesized by amidating the carboxyl group of isonicotinic acid (11) with various amines and by cationizing the nitrogen atoms of the pyridine ring with the corresponding alkyl bromides, were designed. This design enabled expansion of the structural variations of bis‐cation‐type antimalarial compounds. The compounds bearing alkyl or phenyl groups in the amide moieties showed remarkable antimalarial activities in vitro. Moreover, 1,1′‐(1,12‐dodecanediyl)bis[4‐[(buthylamino)carbonyl]pyridinium bromide], MAP‐412 (6 d), exhibited a potent antimalarial activity (ED50=8.2 mg kg−1). Being prepared at low cost, our bis‐cation‐type antimalarial compounds may be useful as lead compounds for inexpensive antimalarials.
Tyings in linear systems of equations modelled with positive and negative penalty functions
Authors: Askes Harm , Piercy Stewart , Ilanko Sinniah
Published: July 2007

In this short note, we focus on tyings (constraints that relate multiple degrees of freedom) modelled by means of penalty functions. In contrast to what is commonly thought, it is possible to obtain convergent results when negative penalty parameters are taken. A mathematical proof and an illustrating example are provided. In particular, we have proven that the results obtained with positive and negative penalty parameters enclose the exact solution from opposite sides. To this end, we have investigated a pseudo‐force that is defined as the derivative of the constraint with respect to the inverse penalty parameter. Copyright © 2007 John Wiley & Sons, Ltd.
Symplectic rigidity, symplectic fixed points, and global perturbations of Hamiltonian systems
Authors: Dragnev Dragomir L.
Published: July 2007

In this paper we study a generalized symplectic fixed‐point problem, first considered by J. Moser in [20], from the point of view of some relatively recently discovered symplectic rigidity phenomena. This problem has interesting applications concerning global perturbations of Hamiltonian systems. © 2007 Wiley Periodicals, Inc.
Partial regularity for harmonic maps and related problems
Authors: Rivière Tristan , Struwe Michael
Published: July 2007

Via gauge theory, we give a new proof of partial regularity for harmonic maps in dimensionsm≥ 3 into arbitrary targets. This proof avoids the use of adapted frames and permits us to consider targets of “minimal”C2‐regularity. The proof we present extends to a large class of elliptic systems. © 2007 Wiley Periodicals, Inc.
Theory of weakly non‐linear noisy systems
Authors: Larsen Torben
Published: July 2007

This paper gives a treatment of the theory of noise in general non‐linear multiport systems by use of the Volterra series representation. Expressions for the response of a non‐linear noisy (N + l)‐port system with N signal input ports and one output port under excitation of noise and a deterministic signal at each input port are determined. Noise generated in the system itself is accounted for by equivalent random variable noise voltage or current generators. These internal noise generators are extracted from the system and applied at separate external ports. A noise‐free equivalent of the noisy system is obtained with N signal input ports and Q – I input ports accounting for the systemgenerated noise. the Volterra series representation is used to describe the input‐output response relation of the system. Once the Volterra transfer functions of the system are determined and cross‐and autocorrelations of the noise generators are specified, it is possible to determine the noise performance of the system under arbitrary noise and deterministic signal excitation. the investigation leads to the determination of expressions for the equivalent average exchangeable output noise power density and the average output noise power flow from the system. Expressions for the noise power densitypand the noise power flow at the load of the non‐linear system are determined. As an example of the theory an expression is derived for the effective input noise temperature of a non‐linear system.
Foreground memory management in data path synthesis
Authors: Stok L. , Jess J. A. G.
Published: July 2007

The management of foreground memory is a main issue in data path synthesis. the storage of values in registers and register files not only determines the number of each of them but also has a major impact on the interconnect structure. Both the amount of multiplexing and interconnect are crucial factors to both the delay and area of a circuit. In this paper it is shown that when values are grouped into register files before being assigned to actual registers, significant savings (20 per cent) can be obtained in the number of local interconnections and the amount of global interconnect at the expense of only slightly more register area. These results can be enhanced by splitting the read and write phases of registers and even more by introducing serial (re)write operations for the same value. the value grouping is based on edge‐colouring algorithms that provide a sharp upper bound on the number of register groups needed.

After value grouping, the registers are allocated for each register file separately. Algorithms for register allocation published up till now have only considered loop‐free data flow graphs. When these algorithms are applied to data flow graphs with loops, unnecessary register transfer operations can be introduced. In this paper a new algorithm is presented that performs a minimal register allocation eliminating all superfluous register transfer operations. Experiments on a benchmark set have shown that in all cases all register transfers could be eliminated at no increase in register cost.

This paper provides a deeper insight to the computational complexity of some problems in the area of data path synthesis. It shows that the various subtasks can be solved exactly using polynomial time algorithms.
Trade‐off prediction and circuit performance optimization using a second‐order model
Authors: Xiangming Xiao , Spence Robert
Published: July 2007

A new approach to constrained optimization which is suited to integrated circuit (IC) design is presented and is shown to be additionally capable of the efficient generation of useful trade‐off information. In contrast to existing optimization methods in which the constraint functions are only linearized, the new algorithm employs a newly developed method of using optimization history data to obtain, without extra simulation, a second‐order approximation to both objective and constraint functions. In the new algorithm the search direction created at each optimization iteration is based on this second‐order approximation. As a result the computational efficiency has been greatly improved compared with other constrained optimization methods in terms of the number of function evaluations required, a measure which is crucial in the context of IC design. the effectiveness and efficiency of the new algorithm have been demonstrated by means of some numerical examples which are commonly employed as benchmarks for existing optimization methods and by several electronic circuit examples. In all cases encouraging results have been obtained. It is also demonstrated that the information generated during the last stage of the optimization allows the generation of accurate trade‐off information valid over a wide range of circuit performance.
Analysis of switched networks
Authors: Bedrosian David , Vlach Jiri
Published: July 2007

Ideal switches are rarely modelled in network analysis because inconsistent conditions can occur at the instant of switching. This causes standard integration routines to fail. If the initial conditions can be determined, the use of ideal switches can considerably speed up analysis and can make the results easier to understand. This paper, partly a review, presents a method which can handle ideal switching, inconsistent initial conditions, Dirac impulses and signals with discontinuities. It is applicable to networks containing linear or non‐linear elements.
Theory of Transmission Switches and Its Application to Design of CMOS Digital Circuits
Authors: Wu X.
Published: July 2007

This paper distinguishes two kinds of algebra, namely switching algebra and binary signal algebra, in which switching and binary signal variables describe switching states of MOS transistors and signals in digital circuits respectively. Threshold comparison operations, transmission operation and union operation are introduced to connect these two algebras. These new operations conform to the action principle of MOS transistors. Based on the theory of transmission switches proposed in this paper, new design procedures for both constant and variable transmission sources are presented. the logic design of CMOS circuits at switch level is realized and CMOS circuits with simpler construction may be obtained by using variable transmission sources.
Transmission line analysis via taylor series
Authors: Semagina Evelina P. , Beznosova Olga I.
Published: July 2007

A simulation technique for transients in transmission lines is presented in which mathematical models of the line and load in the form of integral Volterra equations of the second kind are used. A procedure of numerical analytical solution of these equations is developed on the basis of differential Taylor transforms. A calculation example for the transients in an inductance‐loaded line is presented.
On the universe of stable cellular neural networks
Authors: Chua Leon O. , Wu Chai Wah
Published: July 2007

A cellular neural network (CNN) is a novel analogue circuit architecture with many desirable features. This paper extends previous stability results of CNNs to include classes of strictly sign‐symmetric and acyclic templates. We show that most of the 3×3 strictly sign‐symmetric templates are stable almost everywhere, with the unknown templates reduced to three classes. We also introduce template graphs and CNN graphs and utilize them to obtain results concerning stability and irreducibility of CNN templates.
Testability in analogue cellular neural networks
Authors: Rueda A. , Huertas J. L.
Published: July 2007

This paper addresses the problem of testing an ACNN by postulating the need for including some extra hardware to render feasible a postfabrication test. the work presented here deals with a test methodology based on adding some extra circuitry to every cell of a regular ACNN. This methodology is just an initial proposal for taking advantage of the network regularity to perform a global test which can be externally interpreted and hence has potential application for reconfiguring the network.
A digital multiprocessor hardware accelerator board for cellular neural networks: CNN‐HAC
Authors: Roska T. , Bártfai G. , Szolgay P. , Szirányi T. , Radványi A. , Kozek T. , Ugray Z. S. , Zarándy A.
Published: July 2007

Analogue realizations of neural networks are superior in speed. the hardware accelerator boards using catalogue programmable VLSI ICs represent a trade‐off having higher reconfigurability and lower cost. This paper presents such a solution for a cellular neural network (CNN).

The architecture of the present design (CNN‐HAC) using four standard DSPs to calculate the transient response of a one‐layer CNN containing (0.25–0.75) × 106 analogue neural cells (depending on the type of template) is presented. the architecture and also the design principles are independent of the number of processors. the actual design was made in the form of a PC add‐on board.

The global control unit, which connects the board to the host firmware and communicates control signals to/from the local control units of the DSPs, was realized mainly with EPLDs.

A special correspondence between the virtual processing elements—calculating the time‐discrete models of the analogue neural cells—and the physical ones is discussed in detail. It is realized in an architecture with a simple, two‐directional interprocessor communication. This architecture can be ‘scaled down’ using faster processors, EPLDs and memories. the present version runs with 2 μs/cell/iteration speed.
A CNN handwritten character recognizer
Authors: Suzuki H. , Matsumoto T. , Chua Leon O.
Published: July 2007

CNNs are used for feature detection in handwritten character recognition. Detected features are fed to a simple classifier network. Performance was tested by using two well‐known ETL data base series: (i) ETL3 consisting of numerals, alphabets and several symbols and (ii) ETL8B2 consisting of Japanese Hirakana characters. the average recognition rate for ETL3 is 94.8%, while that for ETL8B2 is 85.7%. Both series include ‘hard’ characters so distorted that even humans cannot recognize them.
On the evaluation of higher harmonics in nearly sinusoidal oscillators
Authors: Buonomo A. , di Bello C. , Greco O.
Published: July 2007

An approximation method for calculating the periodic oscillations of nearly sinusoidal oscillators is presented which is based upon the classical pertubation method. Both the frequency and the amplitude of the harmonics of the oscillation are calculated to a first approximation by very simple relations which are useful for deriving a design criterion.

To demonstrate the possibilities of the proposed method, some illustrative examples are provided.
Synchronization of a forced relaxation oscillator
Authors: Roppel Carsten
Published: July 2007

The paper presents a method of synchronizing a relaxation oscillator to an external signal. the synchronization mechanism is linear and a detailed analysis is given. Very fast acquisition is shown to be possible. the oscillator synchronizes to the frequency of the forcing input or to a sub‐ or superharmonic. Possible applications include highspeed timing recovery systems where high acquisition speed is required.
Linear networks and systems depending polynomially on parameters: Stability for large values subject to tolerance errors
Authors: Ciampa Maurizio , Poletti Mario , Terreni Pierangelo
Published: July 2007

This paper studies the problem of the stability of linear networks or systems depending polynomially on parameters when considering large values of the parameters. It has been taken into account that only the specification of nominal values and tolerances—and not of actual values—is physically meaningful.

Algorithms to test the existence of arbitrarily large nominal values of the parameters which ensure stability either with zero tolerance, with non‐zero tolerances depending on the particular nominal values or with a non‐zero tolerance independent of the particular nominal values are proved to exist.

Depending on the type of response of the above‐mentioned algorithms, analytic, polynomial and monomial functions—in a single suitable variable—that describe arbitrarily large nominal values which ensure stability in the case of zero tolerance, polynomially decreasing non‐zero tolerance and constant non‐zero tolerance respectively are proved to exist.

When a monomial description with constant non‐zero tolerance is assured, algorithms which give the degrees and—in terms of rational numbers—the coefficients of the monomials and the constant non‐zero tolerance are proved to exist.

Similar algorithms when only an analytic description with zero tolerance or a polynomial description with polynomially decreasing non‐zero tolerance is ensured cannot exist.
Design of high‐power multiplexers with interacting, synchronously tunable channels
Authors: Rhodes J. D.
Published: July 2007

A novel circuit configuration is presented for tunable combining multiplexers. Using reciprocal devices, the new circuit enables any channel to be tuned without the adverse effect of frequency pulling on the other channels. Experimental results in the 900 MHz band using dual‐mode dielectric resonators are in close agreement with theory.
Linear transformation of transfer function variables of an m‐D system
Authors: Gałkowski K.
Published: July 2007

A linear transformation of transfer function variables is applied in order to transform a non‐monic multivariable polynomial to a monic form and a singular state space Roesser model to a non‐singular model.
An approach to modelling DC‐DC converter circuits using graph theoretic concepts
Authors: Tse C. K. , Lee Y. S. , So W. C.
Published: July 2007

An approach to modelling DC‐DC converter circuits based on graph theoretic concepts is discussed in this paper. the DC‐DC converter circuits are treated as networks containing switches, with the magnitudes of their associated eigenvalues much smaller than the switching frequency. the procedure for modelling this class of networks essentially involves separating the original network into two N‐port networks, one containing those branches responsible for all phenomena peculiar to the switching action and the other containing the remaining branches of the network. the two N‐port networks thus formed lead to a systematic and convenient way of developing low‐frequency circuit models for DC‐DC converter circuits.
The averaging perturbation method for the dominant behaviour analysis of adiabatic single‐controlled oscillators
Authors: Sommariva Antonino M.
Published: July 2007

Electrical oscillators are called single‐controlled when their non‐linear elements depend on a unique variable, while they are termed adiabatic when their transient operation signal can be represented as a narrowband‐modulated Fourier series with only a finite number of dominant components, including the DC one. the novel method presented here allows one to analyse the dominant dynamics, steady state and dynamical stability of such oscillators. the approach devised is perturbative and is termed averaging, since it moves from the differential equation in the oscillator signal to provide a set of simultaneous differential equations in the complex envelopes of the dominant components of that variable. Owing to the treatment generality, investigable circuit topologies comprise a linear lumped time‐invariant network of any order with bias sources, and any number of non‐linear elements, with or without memory, with a common control variable. to illustrate the use of the method, formulae concerning a seventh‐order oscillator are derived.
A spice‐based approach to steady state circuit analysis
Authors: D'Amore Dario , Fornaciari William
Published: July 2007

A new SPICE‐based approach for steady state circuit analysis is presented which uses SPICE computational capabilities and a master programme to carry out the periodic response. the master programme implements a suitable method for steady state analysis and is linked with SPICE only via I/O SPICE files. This allows the use of all SPICE analyses together with the new one simply by adding a new statement in the input SPICE file. In this paper the bases of this technique, including the chosen steady state method and the whole system structure, are discussed. Simulation results produced by this technique have been compared, by means of two meaningful examples, with those obtained both by SPICE and by a dedicated simulator for steady state analysis working in the frequency domain.
Tangential nevanlinna‐pick interpolation problem for bounded real matrices—A network approach
Authors: Piekarski Marian S. , Uruski Marceli
Published: July 2007

This paper deals with the so‐called tangential Nevanlinna—Pick interpolation problem for bounded real matrices. This problem can be formulated as follows: given a set of n pairs {(pi,Ki)}, where pi are distinct complex numbers with Re pi > 0 and Ki stands for 2m × li constant matrices, assuming that for every pair (pi, Ki) with pi complex there exists a complex conjugate pair (pi, Ki) and that for every pair (pi, Ki) in which pi is real Ki is also real, find an m × m bounded real matrix S(p) such that [S(pi) 1m]Ki = 0 for i= 1,…,n.

The solution of this problem is obtained in an inductive way through the construction at each step of a real lossless multiport section that realizes two complex conjugate pairs or one real pair. After each step the number of pairs (pi, Ki) is reduced by two (if pi is complex) or by one (if pi is real). the procedure is continued until all pairs have been considered. After the last step the final section may be terminated with any bounded real load. the scattering matrix S(p) of the resulting cascade multiport network is bounded real and satisfies the desired interpolation conditions. In this way the tangential interpolation problem is reduced to classical network cascade synthesis by the use of real lossless multiport sections.
Analysis of the effect of periodic fluctuation of switching instants on the transfer characteristics of switched capacitor networks
Authors: Nacaroglu A. , Koksal M.
Published: July 2007

A complete description of switched capacitor networks which include an arbitrary number of non‐uniform input and output phases is presented on the basis of the generalized phase transfer matrix by extending a previously introduced state space approach. the input frequency harmonic (main harmonic) of the periodically time‐varying system transfer function is obtained and the effect of periodic fluctuation of the switching instants on the transfer characteristics of the switched capacitor filters is analysed. This procedure also facilitates the evaluation of the effects of non‐uniform multiphase switching. Application of the results to a switched capacitor filter shows that the frequency response is very sensitive to the fluctuation of switching instants.
Design of efficient fir digital differentiators of second and higher degrees by using universal weights
Authors: Kumar Balbir , Roy S. C. Dutta
Published: July 2007

We propose in this paper an efficient design of FIR digital differentiators of degree k, k= 1, 2, 3,…, and their implementation in a novel structure which allows the order to be varied without having to alter the weights used in it. More precisely, we show that by using these ‘universal weights’ in a structure of order Nmax, the order can be varied from N= 3 to Nmax while keeping the weights fixed and retaining the optimality of performance. Mathematical formulae have been derived for these ‘universal weights’ for differentiators performing in the low‐ or midband‐frequency ranges.
Periodic steady state analysis using shooting and wave‐form‐newton
Authors: Kevenaar Tom A. M.
Published: July 2007

This paper describes a method of determining the forced periodic steady state response of non‐linear circuits. the method is closely related to the work of Aprille and Trick Proc. IEEE, 60, 108‐114 (1972) and also to the finite difference method for solving a boundary value problem.

The new approach is a shooting method in the sense that in every iteration an initial value problem is solved. It is, however, also a relaxation method, because in every iteration a periodic wave‐form is obtained. This is achieved by solving in each step a linear time‐dependent differential equation whose solution can be easily transformed into a periodic solution satisfying this linear equation. Because the iteration takes place on wave‐forms rather than initial values and every solution satisfies the boundary conditions, the method is robust. It will be shown that for a causal approximation of the time derivatives the iterated wave‐forms are equal to those found using the finite difference methods.
Switched bandstop filters
Authors: Rhodes J. D.
Published: July 2007

A new prototype network is derived for a class of allpass networks from which, by a simple switch operation, a cascaded element bandstop filter results. an explicit solution for element values is obtained for the even‐ and odddegree solutions of arbitrary degree. the performance of various degrees is investigated and experimental results are presented for a fifth‐degree suspended substrate stripline bandstop filter operating over a narrow band at 10 GHz.
Design of a notch filter with improved performance
Authors: Agarwal Rajeev , Plotkin E. I. , Swamy M. N. S.
Published: July 2007

The frequency response of a constrained notch filter (CNF) of Rao and Kung or Nehorai becomes ideal as the polecontraction factor α approaches unity while the transient duration approaches infinity. However, for practically useful values of α the phase and magnitude distortions so caused can reduce the allpass nature of the CNFs (i.e. the transparency property) and cause large errors. In this paper we define a measure for the transparency misadjustment and propose two suboptimal methods of minimizing these distortions. One of these methods is based on increasing the filter order by a strategic pole/zero placement. We present a closed‐form solution for this method. In the second method we increase the order by manipulating the error filter associated with the standard CNF; the coefficients of the resulting filter are determined directly. an important feature of these methods is the significant improvement in the transient performance.
Piecewise‐linear analysis of the Wien Bridge Oscillator
Authors: Perfetti R.
Published: July 2007

This paper presents a quantitative analysis of the Wien bridge oscillator based on a piecewise‐linear approximation of the op‐amp characteristic. Usually the circuit parameters are chosen in such a way that the linearized circuit has a pair of complex conjugate natural frequencies which lie slightly to the right of the jw‐axis. the frequency of oscillation is assumed to coincide with the value jω0 at which the poles cross the jω‐axis. However, this simplified approach is unable to predict the true frequency of oscillation and the amount of distortion. the aim of the present analysis is to determine the exact waveform, frequency and spectral content corresponding to the steady state behaviour. the phase plane is partitioned into three regions, in each of which the vector field is linear. the limit cycle corresponding to the steady state oscillation is reconstructed by using the Poincaré map method. Expressions for the frequency of oscillation and the Fourier coefficients are given which depend on a critical parameter representing the voltage gain of the amplifier.