bluuebunny/crossref_metadata_2025 huggingface dataset:
Quasi‐splitting subspaces in a pre‐Hilbert space
Authors: Buhagiar David , Chetcuti Emmanuel
Published: March 2007

Let S be a pre‐Hilbert space. Two classes of closed subspaces of S that can naturally replace the lattice of projections in a Hilbert space are E (S) and F (S), the classes of splitting subspaces and orthogonally closed subspaces of S respectively. It is well‐known that in general the algebraic structure of E (S) differs considerably from that of F (S) and the two coalesce if and only if S is a Hilbert space. In the present note we introduce the class Eq (S) of quasi‐splitting subspaces of S. First it is shown that Eq (S) falls between E (S) and F (S). It is also shown that, in contrast to the other two classes, Eq (S) can sometimes be a complete lattice (without S being complete) and yet, in other examples Eq (S) is not a lattice. At the end, the algebraic structure of Eq (S) is used to characterize Hilbert spaces. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On finite elements in sublattices of Banach lattices
Authors: Chen Z. L. , Weber M. R.
Published: March 2007

Let E be a Banach lattice. Let H stand for a sublattice, an ideal or a band in E, and denote by Φ1(E) and Φ1(H) the ideals of finite elements in the vector lattices E and H, respectively. In this paper we first present some sufficient conditions and some counterexamples for the inclusions Φ1(H) ⊂ Φ1(E) and Φ1(E) ∩ H ⊂ Φ1(H) to hold or not. For closed ideals (and therefore bands) H there always holds Φ1(H) ⊂ Φ1(E). If H is a projection band then even PH Φ1(E) = Φ1(E) ∩ H = Φ1(H). It is proved that every finite element of E is also finite both in its Dedekind completion Ê and in its bidual space E ″. Some results concerning the finite elements in direct sums of Banach lattices are also included. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On a linear differential equation with a proportional delay
Authors: Čermák Jan
Published: March 2007

This paper deals with the delay differential equation

We impose some growth conditions on c, under which we are able to give a precise description of the asymptotic properties of all solutions of this equation. Although we naturally have to distinguish the cases c eventually positive and c eventually negative, we show a certain resemblance between the asymptotic formulae corresponding to both cases. Moreover, using the transformation approach we generalize these results to the equation with a general form of a delay. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Weight of closed subsets topologically generating a compact group
Authors: Dikranjan Dikran , Shakhmatov Dmitri
Published: March 2007

LetGbe a compact Hausdorff group. A subspaceXofG topologically generates GifGis the smallest closed subgroup ofGcontainingX. Define

tgw(G) =ω· min{w(X):Xis closed inGand topologically generatesG},

wherew(X) is the weight ofX, i.e., the smallest size of a base for the topology ofX. We prove that:

(i)tgw(G) =w(G) ifGis totally disconnected,

(ii)tgw(G) =$ \root \omega \of {w(G)} $= min{τ≥ω:w(G) ≤τω} in caseGis connected, and

(iii)tgw(G) =w(G/c(G)) ·$ \root \omega \of {w(c(G))} $, wherec(G) is the connected component ofG.

IfGis connected, then eithertgw(G) =w(G), or cf(tgw(G)) =ω(and, moreover,w(G) =tgw(G)+under the Singular Cardinal Hypothesis).

We also prove that

tgw(G) =ω· min{|X|:X⊆Gis a compact Hausdorff space with at most one non‐isolated point topologically generatingG}. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Anisotropic wavelet bases and thresholding
Authors: Hochmuth Reinhard
Published: March 2007

We consider thresholding with respect to anisotropic wavelet bases measuring the approximation error in anisotropic Hardy spaces $ H^a_p $ for p > 0, which are known to be equal to Lp for p > 1. In particular, we characterize those functions that provide a specific convergence rate by intrinsic smoothness properties. To this end we apply restricted nonlinear approximation, see [3], which is a generalization of n ‐term approximation in which a weight function is used to control the terms of the approximations. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Dirichlet problems for the Stokes resolvent equations in bounded and exterior domains in ℝn
Authors: Kohr Mirela
Published: March 2007

The Dirichlet problems for the Stokes resolvent equations are studied from the point of view of the theory of hydrodynamic potentials. Existence and uniqueness results as well as boundary integral representations of classical solutions are given for domains having compact but not connected boundaries of class C1,α (0 < α ≤ 1) in both the bounded and exterior cases. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Metric approximation properties and trace mappings
Authors: Lima Åsvald , Oja Eve
Published: March 2007

We establish necessary and sufficient conditions involving trace mappings and Hahn–Banach extension operators for a Banach space to have metric or metric compact approximation properties. We also study metric approximation properties for dual spaces. As an application, alternative (hopefully enlightening) proofs are given for the well‐known result that the dual space has the metric approximation property whenever it has the approximation property and the Radon–Nikodým property. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Some Lp analogues of Weyl's theorem of invariability
Authors: Osipov Andrey
Published: March 2007

A well‐known result on Sturm–Liouville operators due to H. Weyl states that the property of all solutions of the equation

‐(p (x)y ′)′ + q (x)y = λy, x ≥ 0, λ ∈ ℂ,

to be in L2[0, ∞) is invariable with respect to the value of λ. Here we obtain some extensions of this theorem with the second order differential equation replaced by a quasi‐differential equation of an arbitrary order and the space L2 replaced by Lp , 1 ≤ p ≤ ∞. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Discrete canonical system and non‐Abelian Toda lattice: Bäcklund–Darboux transformation, Weyl functions, and explicit solutions
Authors: Sakhnovich A. L.
Published: March 2007

A version of the iterated Bäcklund–Darboux transformation, where Darboux matrix takes a form of the transfer matrix function from the system theory, is constructed for the discrete canonical system and non‐Abelian Toda lattice. Results on the transformations of the Weyl functions, insertion of the eigenvalues, and construction of the bound states are obtained. A wide class of the explicit solutions is given. An application to the semi‐infinite block Jacobi matrices is treated. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Entropy of Sobolev embeddings of radial functions and radial eigenvalues of Schrödinger operators on isotropic manifolds
Authors: Skrzypczak Leszek , Tomasz Bernadeta
Published: March 2007

We consider Sobolev embeddings between Sobolev and Besov spaces of radial functions on noncompact symmetric spaces of rank one. An asymptotic behaviour of entropy numbers of the compact embeddings is described. The estimates are used for investigation of the negative spectrum of Schrödinger type operators. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The finite groups with thirteen and fourteen conjugacy classes
Authors: Vera–López A. , Sangroniz Josu
Published: March 2007

Up to isomorphism, there are only finitely many finite groups with a given number of conjugacy classes. Those with up to twelve classes have already been classified. In this work we extend the classification to thirteen and fourteen classes. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Boundary value problems in edge representation
Authors: Liu Xiaochun , Schulze Bert‐Wolfgang
Published: March 2007

Edge representations of operators on closed manifolds are known to induce large classes of operators that are elliptic on specific manifolds with edges, cf. [11]. We apply this idea to the case of boundary value problems. We establish a correspondence between standard ellipticity and ellipticity with respect to the principal symbolic hierarchy of the edge algebra of boundary value problems, where an embedded submanifold on the boundary plays the role of an edge. We first consider the case that the weight is equal to the smoothness and calculate the dimensions of kernels and cokernels of the associated principal edge symbols. Then we pass to elliptic edge operators for arbitrary weights and construct the additional edge conditions by applying relative index results for conormal symbols. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Developing heuristic‐based quality judgments: Blocking in consumer choice
Authors: Oxoby Robert J. , Finnigan Hugh
Published: March 2007

This article provides an experimental demonstration of how the sequential order in which consumers receive information can influence the way information is processed and affect consumers' decisions. Specifically, when participants initially receive information regarding brand/quality or price/quality associations, these associations can block consumers' attention to more relevant quality‐determining physical attributes. Moreover, this process of blocking can carry over to affect quality judgments pertaining to similarly branded or priced products beyond the product in which blocking was initiated. This implies that consumers' judgments of quality may be heavily dependent on first impressions that develop into brand and price heuristics. © 2007 Wiley Periodicals, Inc.
Isobutene Polymerization Using [CuII(NCMe)6]2+ with Non‐Coordinating Anions as Catalysts
Authors: Hijazi Ahmed K. , Yeong Hui Y. , Zhang Yanmei , Herdtweck Eberhardt , Nuyken Oskar , Kühn Fritz E.
Published: March 2007

CuII compounds coordinated octahedrally with nitriles and associated with bulky, non‐coordinating counter ions can be applied in the polymerization of isobutene at 30 °C. High yields and a high content of terminal double bonds are reached in the resulting highly reactive polyisobutylenes, while the molecular masses are moderate. Two of the coordinating nitriles are more weakly coordinated than the other four, as can be concluded from an exemplary X‐ray structure and from vibrational spectra, thus providing easily accessible sites for substrate coordination.

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Dissolution and Doping of Polyaniline Emeraldine Base in Imidazolium Ionic Liquids Investigated by Spectroscopic Techniques
Authors: Rodrigues Fabio , do Nascimento Gustavo M. , Santos Paulo S.
Published: March 2007

Polyaniline is a model molecular system in the study of conductive polymers. Ionic liquids, on the other hand, are becoming more and more a very convenient alternative for conventional organic solvents. The dissolution of polyaniline‐emeraldine base (PANI‐EB) in imidazolium ILs leads to its doping, as indicated by optical and resonance Raman spectroscopies. In this study, it is proposed that the interaction of PANI‐EB and imidazolium ILs involves the specific interaction of the quinoid moiety of the former with the imidazolium ring of the latter, an interpretation that is also based on N K‐edge XANES measurements of neat PANI‐EB, neat ILs, and of their solutions.

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Influence of Cyclodextrin and Temperature on the Kinetics of Free Radical Polymerization of N‐Adamantylacrylamide in Water
Authors: Steffens Christopher , Kretschmann Oliver , Ritter Helmut
Published: March 2007

N‐Adamantylacrylamide (3) was complexed with randomly methylated β‐cyclodextrin (RAMEB) forming the water‐soluble host–guest monomer‐complex 3a. A 1:1 complex stoichiometry was proven by NMR titration (Job's method). We investigated the free radical polymerization of the complex 3a using the water‐soluble azoinitiator 2,2′‐azobis[2‐(2‐imidazolin‐2‐yl)‐propane]dihydrochloride (VA044) at different temperatures. We observed that, below Tcrit a solution polymerization of 3a takes place. Above Tcrit, a precipitation mechanism leads to an increase in the relative polymerization rate.

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Water‐Soluble Methyl Orange Fibrils as Versatile Templates for the Fabrication of Conducting Polymer Microtubules
Authors: Dai Tingyang , Lu Yun
Published: March 2007

One‐dimensional methyl orange fibrils can be easily prepared. They are stable in acidic aqueous solutions and soluble in neutral water. When used to synthesize conducting polymer microtubules, the fibrils act as “hard templates” formally but as “soft templates” effectively. Microtubular structures of polypyrrole, polyaniline, and poly(3,4‐ethylenedioxythiophene) have been achieved successfully via such water‐soluble versatile templates.

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Synthesis and Properties of Novel Polyimides Bearing Sulfonated Benzimidazole Pendant Groups
Authors: Álvarez‐Gallego Yolanda , Nunes Suzana Pereira , Lozano Angel E. , de la Campa José G. , de Abajo Javier
Published: March 2007

A new diamine monomer containing benzimidazole‐5‐sulfonic acid has been synthesised. It has been reacted, alone or mixed with diaminodiphenyl ether, with naphthalenic dianhydride to attain polynaphthalimides in which the sulfonic acid functionality is borne by pendant benzimidazole groups. The presence of sulfonic and benzimidazole groups greatly affected the physical properties of the polyimides as the novel polymers were found to be soluble in polar organic solvents and exhibited a lower thermal resistance than their non‐sulfonated counterparts. The polymer films exhibited good mechanical properties with tensile strength in the range 100–120 MPa and with moduli in the range 2.2–3.1 GPa. Sulfonic and benzimidazole groups significantly enhanced the hydrophilicity of the copolyimides, which showed water uptake up to 39%.

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Synthesis and Ionic Interactions of a Proton Donor Terminated Polyalkylene Ether
Authors: Savitsky Andrew , Tenkovtsev Andrey V. , Oertel Ulrich , Komber Hartmut , Böhme Frank
Published: March 2007

A chromophore terminated aliphatic polyether was obtained by polymer analogous conversion of the amino groups of Jeffamine® ED‐600 with 4‐[5‐(4‐acetoxy‐phenyl)‐3‐oxo‐penta‐1,4‐dienyl]benzoic acid and subsequent saponification of the acetoxy group. UV/Vis spectroscopic investigations showed that deprotonation of the chromophoric groups by organic or inorganic bases as for example poly(1,8‐octamethyleneacetamidine) and NaOH, respectively, results in a distinct bathochromic shift of the chromophores longest wavelength absorption band by about 100 nm. This effect is discussed in terms of polymer blends where the covalently bound chromophore can act as optical probe for acid–base interactions between the components.

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Tuning Mechanical Properties of Block Copolymer/Aluminosilicate Hybrid Materials
Authors: Verploegen Eric , Dworken Benjamin T. , Faught Marybeth , Kamperman Marleen , Zhang Yuanming , Wiesner Ulrich
Published: March 2007

In this work the primary mechanical property profiles of a specific class of nano‐structured polymer/inorganic hybrid materials are characterized. By utilizing sol‐gel aluminosilicate synthesis with amphiphilic polyisoprene‐block‐poly(ethylene oxide) block copolymers as structure‐directing agents, block copolymer/aluminosilicate hybrid materials are prepared with nanometer scale hexagonally packed cylinders and lamellae of the inorganic hybrid components, as evidenced by small‐angle X‐ray scattering. Systematic thermal and dynamic mechanical analyses are performed on these hybrids as well as on the constituting components. Results reveal two transitions from the low temperature, glassy state of the hybrids into high temperature elastic plateau regions, with moduli that vary over orders of magnitude as a function of compositionandmorphology. The first transition can be assigned to the glass transition of the PI domains while the second is ascribed to a temperature induced softening of the organic components within the PEO/hybrid domains. The results suggest that in the present nanostructured block copolymer/aluminosilicate hybrid materials compositionandmorphology provide a powerful tool to tailor mechanical property profiles.

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Effect of Cocatalysts on the Catalytic Activities of Tantalum‐ and Niobium‐Based Catalysts for Ring‐Opening Metathesis Polymerization of Norbornene
Authors: Nakayama Yuushou , Tanimoto Masaya , Shiono Takeshi
Published: March 2007

A series of pentavalent tantalum and niobium complexes with aryloxy ligands was prepared, and their catalytic behavior for the ROMP of norbornene was studied in the presence of an alkylaluminum cocatalyst. Tantalum complexes 1–4 showed very high activity for the ROMP of NBE in combination with iBu3Al to give high‐molecular‐weight polymers. In contrast, the niobium complexes 5 and 6, as well as NbCl5, exhibited very high activity upon activation with Me3Al to give high‐molecular‐weight polymers.

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Stability and Drug Loading of Spontaneous Vesicles of Comb‐Like PEG Derivates
Authors: Li Xiaolin , Ji Jian , Wang Xiaoli , Wang Youxiang , Shen Jiacong
Published: March 2007

A novel comb‐like derivative CPEG‐g‐cholesterol was prepared by the reaction of cholesteryl chloroformate with hydroxyl groups of CPEG. The TEM and SEM results showed that CPEG‐cholesterol spontaneously aggregated vesicles with the membrane thickness of 4.27 ± 0.48 nm. Compared with the vesicles formed by comb‐like PEG (CPEG), the derivation of cholesteryl chloroformate increased the thickness of vesicle membrane and developed corrugations. The hydrophobic doxorubicin (Dox) was added into the solution of CPEG and CPEG‐g‐cholesterol to test their vesicle stability. The drug‐loaded vesicles of CPEG‐g‐cholesterol still existed but those of CPEG disappeared, which indicated that stability of vesicles was enhanced by the derived cholesteryl chloroformate. The vesicles were further cross‐linked by the reaction between divinyl sulfone (DVS) and the hydroxy groups in the side chains of the CPEG and CPEG‐g‐cholesterol. Both cross‐linked vesicles of CPEG and CPEG‐g‐cholesterol entrapped considerable hydrophobic Dox in the vesicles membrane. The spontaneous vesicles of CPEG‐g‐cholesterol and the crosslinked vesicles of CPEG and CPEG‐g‐cholesterol might have great potential as a cargo of the hydrophobic drug.

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Chemical One Step Method to Prepare Polyaniline Nanofibers with Electromagnetic Function
Authors: Zhang Zhiming , Deng Junying , Shen Jiaoyan , Wan Meixiang , Chen Zhaojia
Published: March 2007

A “Chemical one step method” (COSM) is proposed to prepare electromagnetic functional composite nanofibers of polyaniline (PANI/γ‐Fe2O3) having a diameter of ≈20 nm. In this approach FeCl3 is acts as the oxidant either for polymerization of aniline or for preparation of γ‐Fe2O3 magnets. Besides, it also provides protons produced by the hydrolysis process for doping PANI. It is found that the composite nanofibers have a high conductivity (10−1 ∼ 100 S · cm−1) and super‐paramagnetic properties (Ms = 0.46 ∼ 6.03 emu · g−1 and Hc = 0) at room temperature, where the conductivity is mainly affected by the molar ratio of FeCl3 to aniline monomer whereas the magnetic properties are dominated by the amount of FeCl2.

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Rings of Hydrogel Fabricated by a Micro‐Transfer Technique
Authors: Wang Bo , Hong Yi , Feng Jie , Gong Yihong , Gao Changyou
Published: March 2007

Microgel rings have been fabricated on a glass surface by a micro‐transfer technique. The polymer melt is transferred to the substrate surface in a confined space with a picoliter volume along the boundary of the polymeric stamp. The surface of the polymer features is smoothened by surface tension in an annealing cycle, which results in isotropic rings. After cross‐linking, the microgels respond swiftly when immersed in water. Asymmetric rings are also obtained by tilting the substrate. The microgels can detach from the substrate to form a suspension of the rings. Conjugated rings have also been fabricated by supplementing functional molecules into the poly(ethylene glycol) network.

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Polymer‐Bound Thiol Groups on Poly(2‐oxazoline)s
Authors: Cesana Sonia , Kurek Alexander , Baur Markus A. , Auernheimer Jörg , Nuyken Oskar
Published: March 2007

A new 2‐oxazoline monomer with a protected thiol group, 2‐[2‐(4‐methoxybenzylsulfanyl)ethyl]‐2‐oxazoline, MOB‐SOx, was synthesized from commercially available compounds. MOB‐SOx and 2‐ethyl‐2‐oxazoline (EtOx) were simultaneously polymerized yielding well defined copolymers with narrow molar mass distributions and target polymer chain length. The copolymerization was initiated by N‐methyl‐2‐methyl‐2‐oxazolinium triflate (MeOxOTf). After quantitative deprotection, poly(2‐oxazoline) with pendant thiol groups was obtained. The thiol groups were quantitatively added to the double bond of N‐phenyl‐acrylamide (PhA) and benzylmaleimide (BzM). Graft copolymers were obtained by reaction of those SH containing polymers with poly(2‐methyl‐2‐oxazoline)s bearing acrylamide (PMeOx10A) and maleimide (PMeOx10M) as terminal reactive groups.

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Multi‐Compartment Unimolecular Micelles from (ABC)n Multi‐Arm Star Triblock Terpolymers
Authors: Stavrouli Nikoletta , Triftaridou Aggeliki I. , Patrickios Costas S. , Tsitsilianis Constantinos
Published: March 2007

Four linear and four star equimolar terpolymers based on non‐ionic hydrophilic methoxy hexa(ethylene glycol) methacrylate, ionizable hydrophilic 2‐(dimethylamino)ethyl methacrylate and neutral hydrophobic methyl methacrylate were synthesized using group transfer polymerization and investigated in aqueous dilute solutions. It was found that the (ABC)n multi‐arm star terpolymers formed unimolecular micelles comprising three centrosymmetric compartments. The position of each compartment could be determined by the block sequence (ABC, ACB or BAC) at will. On the other hand, the ABC linear counterparts formed loose associates with very low aggregation numbers. It was shown that the polymer architecture (linear versus star) greatly affected the micellization phenomena of the terpolymers in selective media.

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Microwave‐Assisted Aqueous Polyimidization Using High‐Throughput Techniques
Authors: Dao Buu N. , Groth Andrew M. , Hodgkin Jonathan H.
Published: March 2007

High‐throughput methodology, as used in pharmaceutical drug discovery, was successfully applied to high performance polyimide development. Using a Biotage® microwave reactor fitted with a flask handling robot and a high‐throughput approach, we have optimized a copolyimide material with high Tg, yet maintaining solution processability. Additionally, the development time for this material has been reduced from months to just weeks. The polyimide was produced using combinations of the monomers 4,4′‐ODA, 6‐FDA and PMDA. The optimal combination was found to be 2:1:1 of 4,4′‐ODA/6‐FDA/PMDA with a molecular weight (MW) of 31 500 and Tg of 347 °C. The resulting polymer can be solution‐cast into strong, flexible membranes for solution and gas phase separations.

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Self‐Assembly of Large Multimolecular Micelles from Hyperbranched Star Copolymers
Authors: Hong Haiyan , Mai Yiyong , Zhou Yongfeng , Yan Deyue , Cui Jun
Published: March 2007

This work focused on the synthesis and aqueous self‐assembly of a series of novel hyperbranched star copolymers with a hyperbranched poly[3‐ethyl‐3‐(hydroxymethyl)oxetane] (HBPO) core and many linear poly[2‐(dimethylamino)ethyl methacrylate] (PDMAEMA) arms. The copolymers can synchronously form unimolecular micelles (around 10 nm) and large multimolecular micelles (around 100 nm) in water at room temperature. TEM measurements have provided direct evidence that the large micelles are a kind of multimicelle aggregates (MMAs) with the basic building units of unimolecular micelles. It is the first demonstration of the self‐assembly mechanism for the large multimolecular micelles generated from the solution self‐assembly of hyperbranched copolymers.

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Direct Metallization of Gold Nanoparticles on a Polystyrene Bead Surface using Cationic Gold Ligands
Authors: Lee Jun‐Ho , Kim Dong Ouk , Song Gyu‐Seok , Lee Youngkwan , Jung Seung‐Boo , Nam Jae‐Do
Published: March 2007

Gold nanoparticles are formed to cover the surface of sulfonated‐polystyrene (PS) beads by the in‐situ ion‐exchange and chemical reduction of a stable cationic gold ligand, which makes it different from the physical adsorption or multiple electroless metallization methods. PS beads are synthesized by dispersion polymerization with a diameter of 2.7 µm, and their surface is modified by introducing sulfonic acid groups (SO) to give an ion exchange capacity of up to 2.25 mequiv. · g−1, which provides 1.289 × 1010SOper bead. Subsequently, the anionic surface of the PS beads is incorporated with a cationic gold ligand, dichlorophenanthrolinegold(III) chloride ([AuCl2(phen)]Cl), through an electrostatic interaction in the liquid phase to give gold nanoparticles (ca. 1–4 nm in diameter) formed on the PS surface. Assuming that approximately three SOgroups interact with one [AuCl2(phen)]+ion in the ion‐exchange process, the gold coverage on a PS bead is estimated as 12.0 wt.‐%, which compares well with the 16.8 wt.‐% of gold loading measured by inductively coupled plasma–mass spectrometry. Because of the adjustable IEC values of the polymer surface and the in‐situ metallization of Au in the presence of S atoms, both of which are of a soft nature, the developed methodology could provide a simple and controllable route to synthesize a robust metal coating on the polymer bead surface.

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Effect of the Molecular Weight of AB Diblock Copolymers on the Lamellar Orientation in Thin Films: Theory and Experiment
Authors: Potemkin Igor I. , Busch Peter , Smilgies Detlef‐M. , Posselt Dorthe , Papadakis Christine M.
Published: March 2007

We propose a theoretical explanation of the parallel and perpendicular lamellar orientations in free surface films of symmetric polystyrene‐block‐polybutadiene diblock copolymers on silicon substrates (with a native SiOx layer). Two approaches are developed: A correction to the strong segregation theory and a qualitative analysis of the intermediate segregation regime. We show that the perpendicular orientation of the lamellae formed by the molecules of high molecular weight is stabilized by A–B interfacial interactions. They are weaker in the case of the perpendicular orientation of the lamellae, whereas the surface tension coefficient of the A–B interface decreases with the increase of the molecular weight.

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Color Change of Electrospun Polystyrene/MEH‐PPV Fibers from Orange to Yellow through Partial Decomposition of MEH Side Groups
Authors: Chuangchote Surawut , Srikhirin Toemsak , Supaphol Pitt
Published: March 2007

The present contribution reports the electrospinning of PS/MEH‐PPV fibers with average diameters ranging from 0.165 to 1.190 µm from solutions of PS/MEH‐PPV (PS/MEH‐PPV = 7.5:1, w/w) in 1,2‐dichloroethane. With the addition of pyridinium formate (PF), a volatile organic salt, to the PS/MEH‐PPV solution, the electrospinnability of the resulting solution is enhanced significantly. Both the fiber diameters and the number of fibers are found to increase, while the number of beads is found to decrease with increasing applied electrical potential, the addition of PF, and increasing aging period of the spinning solution after PF addition. FT‐IR analysis shows that ≈15% of the MEH side groups are removed from the MEH‐PPV component in the fibers obtained from the solution that is left to age for 1 month after PF addition, which corresponds well to the loss of mass of ≈7% as observed by thermogravimetric analysis. As a result, partial decomposition of the MEH side groups should be responsible for the observed yellow emission color of the PS/MEH‐PPV fibers obtained from the same solution.

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Exploring Microfluidic Routes to Microgels of Biological Polymers
Authors: Zhang Hong , Tumarkin Ethan , Sullan Ruby May A. , Walker Gilbert C. , Kumacheva Eugenia
Published: March 2007

Polymer microgels in the size range from several micrometers to hundreds of micrometers are used in the pharmaceutical, cosmetics, nutrition, pesticide, and food industries, as well as in the encapsulation of cells. To date, a broad range of strategies for the generation of polymer microgels exist, however, these methods involve multistage processes, do not utilize biocompatible components or do not allow precise control of the dimensions and internal structure of the microgels. Recently, microfluidic strategies for the production of polymer particles have offered precise control over the shapes, morphologies, and size distributions of polymer colloids. This paper discusses the most recent results obtained by the authors in the area of the microfluidic production of biopolymer microgels. It provides a brief review of the microfluidic methods for the continuous synthesis and fabrication of microgels, sets the criteria for the successful microfluidic generation of biomicrogels, and describes two methods for the preparation of microgels by microfluidic means. The article concludes with a summary and an outlook.

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Novel Acid‐Labile, Thermoresponsive Poly(methacrylamide)s with Pendent Ortho Ester Moieties
Authors: Huang Xiaonan , Du Fusheng , Ju Rong , Li Zichen
Published: March 2007

Novel acid‐labile, thermoresponsive methacrylamide‐based (co)polymers with pendent ortho ester groups were prepared by free radical polymerization of N‐(2‐methoxy‐1,3‐dioxan‐5‐yl) methacrylamide (NMM) and N‐(2‐ethoxy‐1,3‐dioxan‐5‐yl)methacrylamide (NEM). These polymers are both thermoresponsive and acid‐sensitive in aqueous solution, which was proved by transmittance measurements, fluorescence, and 1H NMR spectroscopy. The LCSTs of the (co)polymers were shifted to higher temperature by increasing the content of the more hydrophilic NMM units. All of these polymers can be hydrolyzed under acidic condition and the hydrolysis rate increased with the decrease in the pH value.

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Complex Macromolecular Architectures by Reversible Addition Fragmentation Chain Transfer Chemistry: Theory and Practice
Authors: Barner Leonie , Davis Thomas P. , Stenzel Martina H. , Barner‐Kowollik Christopher
Published: March 2007

Reversible addition–fragmentation chain transfer (RAFT) chemistry can be effectively employed to construct macromolecular architectures of varying topologies. The present article explores the principle design routes to star, block, and comb polymers in the context of theoretical design criteria for the so‐called Z‐ and R‐group approaches. The specific advantages and disadvantages of each approach are underpinned by selected examples generated in the CAMD laboratories. In particular, we demonstrate how the modeling of full molecular weight distributions can be employed to guide the synthetic effort. We further explore the theory and practice of generating amphiphilic block copolymer structures and their self‐assembly. In addition, the article foreshadows how modern synthetic techniques that combine RAFT chemistry with highly orthogonal click chemistry can be employed as a powerful tool that furthers the enhancement of macromolecular design possibilities to generate block (star) copolymers of monomers with extremely disparate reactivities. Finally, the ability of RAFT chemistry to modify the surface of well‐defined nano‐ and microspheres as devices in biomedical application is detailed.

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Macromol. Rapid Commun. 5/2007
Authors: Potemkin Igor I. , Busch Peter , Smilgies Detlef‐M. , Posselt Dorthe , Papadakis Christine M.
Published: March 2007

Cover: The article by Potemkin and coworkers provides free‐energy considerations to explain the molar mass dependent morphology of lamellar diblock copolymer thin films of poly(styrene‐b‐butadiene). Atomic force microscopy (AFM) and grazing‐incidence small‐angle scattering (GISAXS) data were instrumental to establish the lamellar orientation as a function of the interaction parameter χN and the ratio of film thickness over lamellar thickness Dred. The relevant free‐energy contributions are discussed that determine the boundary between the observed orientational phases. Further details can be found in the article by I. I. Potemkin,* P. Busch, D.‐M. Smilgies, D. Posselt, and C. M. Papadakis on page 579.
Kinetic Aspects of RAFT Polymerization
Authors: Vana Philipp
Published: March 2007

In this short review, selected experimental approaches for probing the mechanism and kinetics of RAFT polymerization are highlighted. Methods for studying RAFT polymerization via varying reaction conditions, such as pressure, temperature, and solution properties, are reviewed. A technique for the measurement of the RAFT specific addition and fragmentation reaction rates via combination of pulsed‐laser‐initiated RAFT polymerization and µs‐time‐resolved electron spin resonance (ESR) spectroscopy is detailed. Mechanistic investigations using mass spectrometry are exemplified on dithiobenzoic‐acid‐mediated methyl methacrylate polymerization.
Synthesis of Poly(methyl acrylate) Grafted onto Silica Particles by Z‐supported RAFT Polymerization
Authors: Zhao Youliang , Perrier Sébastien
Published: March 2007

RAFT polymerization of methyl acrylate (MA) mediated by silica‐supported 3‐(methoxycarbonyl‐phenyl‐methylsulfanylthiocarbonylsulfanyl) propionic acid (Si‐ MPPA) and 3‐(benzylsulfanylthiocarbonylsulfanyl) propionic acid (Si‐BSPA) was investigated. The molecular weight and polydispersity of grafted polymeric chains and the grafted chain transfer agent (CTA) efficiency (Ge) were strongly dependent on the types and loading of Si‐CTAs and free CTA used in solution. Under similar reaction conditions, the graft polymerization mediated by Si‐MPPA was better controlled than that using Si‐BSPA. The introduction of a free CTA in solution during Si‐MPPA mediated polymerization could significantly decrease the polydispersity of free and grafted polymeric chains and enhance the grafted CTA efficiency, and longer polymeric chains could be grafted onto silica support when Si‐MPPA with a higher CTA loading was used to mediate the polymerization. In all cases, the RAFT polymerization using 2‐(2‐cyanopropyl) dithiobenzoate (CPDB) as a free CTA could afford well‐defined grafted PMA and significantly increased Ge value, while the polymerization rate was also decreased.
Verdazyl‐Mediated Polymerization of Styrene
Authors: Teertstra Steven J. , Chen Eric , Chan‐Seng Delphine , Otieno Peter O. , Hicks Robin G. , Georges Michael K.
Published: March 2007

Attempted controlled polymerizations of styrene, conducted in the presence of either 1,3,5‐triphenyl‐6‐oxoverdazyl or 1,5‐dimethyl‐3‐phenyl‐6‐oxoverdazyl radicals initiated with benzoyl peroxide or 1,1′‐azobis(cyclohexanecarbonitrile) were universally unsuccessful regardless of the reaction temperature and the initiator/verdazyl molar ratio. No improvement was observed using a verdazyl‐terminated styrene initiator adduct prepared by an exchange reaction between a styrene‐TEMPO alkoxyamine and a 1,3,5‐triphenyl‐6‐oxoverdazyl radical. However, controlled polymerizations of styrene were achieved at 125 °C using a styrene‐verdazyl adduct containing the 1,5‐dimethyl‐3‐phenyl‐6‐oxoverdazyl radical. Polydispersity indexes remained low throughout the polymerizations and plots of number average molecular weight ($\overline M _{\rm n}$) versus time were linear. However, the actual $\overline M _{\rm n}$ values were considerably lower than theoretical, an unexpected result that is under investigation.
Germanium‐ and Tin‐Catalyzed Living Radical Polymerizations of Styrene and Methacrylates
Authors: Goto Atsushi , Zushi Hirokazu , Hirai Norihiro , Wakada Tsutomu , Kwak Yungwan , Fukuda Takeshi
Published: March 2007

Summary: Ge and Sn (non‐transition‐metal) catalyzed living radical polymerizations were developed. Low‐polydispersity (Mw/Mn ∼ 1.1–1.3) polystyrenes, poly(methyl methacrylate)s, poly(glycidyl methacrylate)s, and poly(2‐hydroxyethyl methacrylate) with predicted molecular weights were obtained with a fairly high conversion in a fairly short time. The pseudo‐first‐order activation rate constant kact for the styrene/GeI4 (catalyst) system was large enough, even with a small amount of GeI4, to explain why the system provides low‐polydispersity polymers from an early stage of polymerization. The retardation in the polymerization rate observed for the styrene/GeI4 system was kinetically proved to be mainly due to the cross‐termination between the propagating radical with GeI. Attractive features of the Ge and Sn catalysts include their high reactivity hence small amounts (1–5 mM) being required under a mild condition (at 60–80 °C), high solubility in organic media without ligands, insensitivity to air hence sample preparation being allowed in the air, and minor color and smell. The Ge catalysts may also be attractive for their low toxicity.
Designing Organic/Inorganic Colloids by Heterophase Polymerization
Authors: Bourgeat‐Lami Elodie , Herrera Norma Negrete , Putaux Jean‐Luc , Perro Adeline , Reculusa Stéphane , Ravaine Serge , Duguet Etienne
Published: March 2007

Polymer/silica and polymer/Laponite nanocomposite colloids with various morphologies have been elaborated through emulsion polymerization using a polymerizable organosilane (route I) and a methyl methacrylate‐terminated macromonomer (route II) as coupling agents. Depending on the synthetic strategy and on the nature of the mineral particles, either core‐shell, raspberry‐like, multipod‐like, currant bun or inverted core‐shell morphologies (the mineral forming the shell) were achieved. Beyond the control of particle shape, we have demonstrated that some of the polymerizations exhibited particular kinetics behaviors which could be correlated to the mechanism of formation of the composite particles. Interestingly, conversion versus time curves of a series of soap free polymerizations performed in the presence of the macromonomer showed a significant increase in the polymerization rate with increasing the inorganic particles concentration. Characterization of the composite latexes by transmission electron microscopy showed that the mineral was located at the surface of the latex spheres and participated therefore to their stabilization. The higher the amount of inorganic particles, the lower the particles size and the higher the polymerization rate.
Spectral resolution analysis of resonant grating waveguides
Authors: Delmdahl R. F. , Spiecker G. , Bader M. A. , Selle A.
Published: March 2007

A high spectral resolution analysis of narrowband reflection filters based on resonant grating waveguide structures is presented. A tunable high‐performance dye laser with ∼0.15 cm‐1 line width and a beam analyzing system consisting of three simultaneously controlled CCD cameras were used to investigate grating waveguide resonances at wavelengths ∼694 nm and ∼633 nm. A reflectivity of 91 % and a line width of ∼0.3 nm were measured and theoretically modeled for a resonant reflection filter specifically designed for the ruby laser wavelength 694.2 nm. A resonance shift of several nanometers was observed for a second grating waveguide structure in the region of the helium‐neon laser emission wavelength 632.8 nm by changing the sample temperature. We discuss the potential of grating waveguide devices combining the narrow line width and the tunability of the resonant response as promising candidates for implementation in innovative concepts for reflection filter and sensor applications.
Broadband proton‐decoupled proton spectra
Authors: Pell Andrew J. , Edden Richard A. E. , Keeler James
Published: March 2007

We present a new method for recording broadband proton‐decoupled proton spectra with absorption mode lineshapes and substantially correct integrals; in both these respects, the new method has significant advantages over conventional J‐spectroscopy. In our approach, the decoupled spectrum is simply obtained from the 45° projection of the diagonal‐peak multiplets of an anti z‐COSY spectrum. This method is straightforward to apply, and does not require any unusual data processing. However, there is a significant reduction in sensitivity when compared to a conventional proton spectrum. The method is demonstrated for typical medium‐sized molecules, and it is also shown how such a decoupled spectrum can be used to advantage in measurements of diffusion constants (DOSY), the measurement of relaxation parameters, and the analysis of complex mixtures. Copyright © 2007 John Wiley & Sons, Ltd.
A quantitative application of the J‐based configuration analysis method to a flexible small molecule
Authors: Sharman Gary J.
Published: March 2007

An example of the use of the J‐based configuration analysis method to determine relative stereochemistry of a small molecule related to reboxetine is described. This study was complicated by the fact that the molecule did not exhibit J‐couplings and NOEs consistent with a single conformation, but rather an ensemble average. A quantitative fitting procedure using predicted couplings and NOEs from all possible conformers was used. This gave a clear indication of the stereochemistry, and the populations of the conformers involved. Copyright © 2007 John Wiley & Sons, Ltd.
Unambiguous NMR spectral assignments of salvinorin A
Authors: Giner José‐Luis , Kiemle David J. , Kutrzeba Lukasz , Zjawiony Jordan
Published: March 2007

The complete assignments of the 1H and 13C NMR spectra of the hallucinogenic neoclerodane diterpenoid salvinorin A were determined in three different NMR solvents using HSQC, HMBC and COSY. Solvent systems are described that allow the resolution of all 1H signals. Virtual coupling was observed for the protons at C‐2, C‐3 and C‐4 in the 600 MHz 1H spectrum in CDCl3. The complete assignments of the 1H and 13C NMR spectra of salvinorin B are also reported. Copyright © 2007 John Wiley & Sons, Ltd.
Optimizing sensitivity and resolution in time‐shared NMR experiments
Authors: Pérez‐Trujillo Miriam , Nolis Pau , Bermel Wolfgang , Parella Teodor
Published: March 2007

An improved approach to optimize the overall sensitivity and the resolution requirements in the indirect dimension of 13C/15N time‐shared (TS) NMR experiments is presented. A different data sampling acquisition procedure is applied for 13C and 15N in the indirect dimension, and a proper data recombination before conventional data processing allows a customized adjustment of spectral widths, number of scans and number of increments individually for 13C and 15N. The major benefit is an important improvement on the detection limits of the TS experiment that overcomes the lower sensitivity of 15N over 13C at natural abundance. We evaluate such enhancements from 2D TS‐HMBC experiments recorded on a nitrogen‐containing synthetic azole derivative of pharmaceutical interest. Copyright © 2007 John Wiley & Sons, Ltd.
Synthesis and structure of some azo coupled cyclic β‐enaminones
Authors: Šimůnek Petr , Lusková Lucie , Svobodová Markéta , Bertolasi Valerio , Lyčka Antonín , Macháček Vladimír
Published: March 2007

The reaction of 3‐phenylaminocyclopent‐2‐en‐1‐one with 4‐methyl, 4‐methoxy and 4‐chlorobenzenediazonium tetrafluoroborates was used to prepare the azo coupling products 3a‐c. It was found that these compounds are present in both CDCl3 solution and solid phase practically exclusively as (E)‐3‐phenylamino‐2‐(4‐subst.phenyldiazenyl)cyclopent‐2‐en‐1‐ones with NH···N intramolecular hydrogen bond. The substitution of the phenyl residue of the diazonium salt has no effect on the position of the tautomeric equilibrium. On the other hand, the compounds 4a, b formed by the reaction of 3‐phenylamino‐1H‐inden‐1‐one with 4‐methylbenzene‐ or benzenediazonium tetrafluoroborates exist in CDCl3 solution and in solid phase as hydrazone compounds. In the solution they occur as a mixture of three forms, out of which two were identified as E/Z isomers with different types of hydrogen bonds. Compound 5 formed by the reaction of 3‐amino‐5,5‐dimethylcyclohex‐2‐en‐1‐one with 4‐methoxybenzenediazonium tetrafluoroborate is converted into a stable hydrochloride 5·HCl on standing in CHCl3 solution; this product exhibits a high degree of delocalization of the positive charge. Its structure was studied by means of X‐ray. Copyright © 2007 John Wiley & Sons, Ltd.
NMR studies of the conformational effect of single and double 3′‐S‐phosphorothiolate substitutions within deoxythymidine trinucleotides
Authors: Jayakumar Hannah K. , Buckingham Joanne L. , Brazier John A. , Berry Neil G. , Cosstick Richard , Fisher Julie
Published: March 2007

NMR spectroscopy has been used to investigate the conformational effects of single and two consecutive 3′‐S‐phosphorothiolate modifications within a deoxythymidine trinucleotide. The presence of a single 3′‐phosphorothioate modification shifts the conformation of the sugar ring it is attached to, from a mainly south to north pucker; this effect is also transmitted to the 3′‐neighbour deoxyribose. This transmission is thought to be caused by favourable stacking of the heterocyclic bases. Similar observations have been made previously by this group. When two adjacent modifications are present, the conformations of the attached deoxyribose rings are again shifted almost completely to the north, however, there is no transmission to the 3′ deoxyribose ring. Base proton chemical shift analysis and molecular modelling have been used to aid elucidation of the origin of this feature. The observation for the dimodified sequence is consistent with our previously reported results for a related system in which spaced modifications are more thermodynamically stable than consecutive ones. Copyright © 2007 John Wiley & Sons, Ltd.
Wagner‐Meerwein rearrangement of a [3.3.3]‐ to a [4.3.3]propellane: deuterium tracer and conformational analysis
Authors: Reyes‐Trejo Benito , Morales‐Ríos Martha S. , Joseph‐Nathan Pedro
Published: March 2007

Formation of (−)‐[4.3.3]propellane 4 from (−)‐14‐hydroxymodhephene (2) proceeds through a Wagner‐Meerwein rearrangement via C3C4 bond‐shift to give a stable intermediate, dimethylcyclohexadienyl cation A, which undergoes deprotonation. Herein, this mechanism was investigated by using a deuterium labeled substrate at the C‐14 methylene group of (−)‐2, which was incorporated into the C‐4 position of (−)‐[4.3.3]propellane 4. The stereostructure of (−)‐4 was investigated by applying a combination of NMR experimental and theoretical approaches. Copyright © 2007 John Wiley & Sons, Ltd.
Kallisteine A and B, two new coumarins from the roots of Peucedanum paniculatum L, a species endemic to Corsica
Authors: Vellutini Muriel , Tomi Félix , Richomme Pascal , Casanova Joseph
Published: March 2007

From the dichloromethane extract of the roots of Peucedanum paniculatum L., two new coumarins, a species endemic to Corsica, have been isolated. Their structures were elucidated, on the basis of spectroscopic studies, particularly 1D and 2D NMR spectroscopy, as 6‐(7′‐β‐cyclolavandulyl)‐7‐hydroxycoumarin 1 and a spirodihydrofurano‐coumarin 2 (Kallisteine A and B). Copyright © 2007 John Wiley & Sons, Ltd.
Comparison of the BOLD‐ and EPISTAR‐technique for functional brain imaging by using signal detection theory
Authors: Siewert Bettina , Bly Benjamin Martin , Schlaug Gottfried , Darby David G. , Thangaraj Venkatesan , Warach Steven , Edelman Robert R.
Published: March 2007

Two magnetic resonance imaging techniques, BOLD (blood oxygenation level dependent) and EPISTAR (echo‐planar imaging and signal targeting with alternating radio‐frequency), were compared for functional brain imaging. Ten volunteers were imaged performing a sequential finger to thumb opposition task alternating with no movement conditions. Techniques were compared using variance maps and signal detection theory (ROC analysis). True positive activation in regions of interest with expected task‐dependent signal changes were computed versus false activation rates in regions in which no activation was expected. D‐prime coefficients were calculated for each comparison and statistically compared using a paired t test. Activation in the perirolandic region was seen in all volunteers with both techniques. There was no significant difference for the d‐prime between BOLD and EPISTAR. These results indicate that based on a different physiologic principle, EPISTAR is an alternative to BOLD to perform fMRI with similar results.