bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mapping the Stereochemistry and Symmetry of Tetracoordinate Transition‐Metal Complexes
Authors: Cirera Jordi , Alemany Pere , Alvarez Santiago 
Published: December 2003

AbstractA continuous shape and symmetry study of tetracoordinate transition‐metal complexes is presented, in an attempt to provide a systematic description of the stereochemistry of the metal coordination sphere in this important family of compounds. A tetrahedron/square‐planar symmetry map has been developed, the main distortion paths of the ideal geometries are presented, and the applicability of a sawhorse shape measure is discussed. More than 13,000 structural data sets have been analyzed and the corresponding stereochemistries assigned from the values of their tetrahedral and square‐planar symmetry measures. A good number of structures that are quite distant from the two ideal geometries can be adequately described as snapshots along the spread pathway for their interconversion, making use of the corresponding path deviation function. Further analysis of the structural data by metal electron configuration or by the denticity and conformation of the ligands provide general rules to describe the stereochemical preferences of tetracoordinate transition metal centers.
Synthesis of Novel Chiral and Acentric Coordination Polymers by the Reaction of Zinc or Cadmium Salts with Racemic 3‐Pyridyl‐3‐aminopropionic Acid
Authors: Qu Zhi‐Rong , Zhao Hong , Wang Yi‐Ping , Wang Xi‐Sen , Ye Qiong , Li Yong‐Hua , Xiong Ren‐Gen , Abrahams Brendan F. , Liu Zhi‐Guo , Xue Zi‐Ling , You Xiao‐Zeng 
Published: December 2003

AbstractUnder hydrothermal (solvothermal) reaction conditions chiral compounds 1, 2, and 3 and one acentric compound 4 were obtained by the reaction of Zn2+ or Cd2+ with racemic 3‐(3‐pyridyl)‐3‐aminopropionic acid (rac‐HPAPA). Compounds 1 and 2 crystallized in chiral space group P212121. At 105 °C, racemic 3‐pyridyl‐3‐aminopropionic acid (rac‐HPAPA) reacted with Zn(ClO4)2⋅6 H2O and dehydrogenated in situ to form the first chiral coordination polymer [Zn{(E)‐3‐C5H4NC(NH2)CHCOO}]ClO4 (1) with a β‐dehydroamino acid. Beyond 120 °C, the reaction of rac‐HPAPA with Zn(ClO4)2⋅6 H2O deaminates in situ to form chiral coordination polymer [Zn{(E)‐3‐C5H4NCHCHCOO}(OH)] (2). At relatively low temperatures (70 °C), the solvothermal reaction of Zn(NO3)2⋅6 H2O with rac‐HPAPA in methanol does not lead to any change in the ligand and results in the formation of a chiral (P212121) coordination polymer [Zn(papa)(NO3)] (3). The same reaction of Cd(ClO4)2⋅6 H2O with HPAPA also does not lead to any change in ligand and results in the formation of noncentric (Cc) coordination polymer [Cd(papa)(Hpapa)]ClO4⋅H2O (4). The network topology of both 1 and 3 is 10,3a, while 2 has a diamondoid‐like (KDP‐like, KDP=potassium dideuterophosphate) network. Particularly interesting from a topological perspective is that 4 has an unprecedented three‐dimensional network. Compounds 1, 2, 3, and 4 are all second harmonic generation (SHG) active with 1 exhibiting the strongest response, while only 4 also displays good ferroelectric properties.
Crystal, Molecular and Electronic Structure of N,N′‐Diphenyl‐N,N′‐bis(2,4‐dimethylphenyl)‐(1,1′‐biphenyl)‐4,4′‐diamine and the Corresponding Radical Cation
Authors: Low Paul J. , Paterson Michael A. J. , Puschmann Horst , Goeta Andrés E. , Howard Judith A. K. , Lambert Christoph , Cherryman Julian C. , Tackley Daniel R. , Leeming Stephen , Brown Bev 
Published: December 2003

AbstractOxidation of N,N′‐diphenyl‐N,N′‐bis(3‐methylphenyl)‐(1,1′‐biphenyl)‐4,4′‐diamine (TPD, 1 a) and N,N′‐diphenyl‐N,N′‐bis(2,4‐dimethylphenyl)‐(1,1′‐biphenyl)‐4,4′‐diamine (1 b) with SbCl5 affords the corresponding radical cations quantitatively. The crystal and molecular structure of 1 b and [1 b]SbCl6, the first tetraphenyl benzidene derivatives to be characterised crystallographically in both the neutral and radical cation states, reveal molecular parameters in agreement with the predictions made on the basis of DFT studies. Analysis of the NIR transition in the radical cations [1]+. allows an estimate of the electronic coupling parameter V (1 a+. 3200 cm−1; 1 b+. 3300 cm−1), the reorganisation energy λ(1 a+. 7500 cm−1; 1 b+. 7800 cm−1), and the linear coupling constant l (1 a+. 3100 cm−1; 1 b+. 2700 cm−1) of the symmetric mode.
Quantitative Evaluation of d–π Interaction in Copper(i) Complexes and Control of Copper(i)–Dioxygen Reactivity
Authors: Osako Takao , Tachi Yoshimitsu , Doe Matsumi , Shiro Motoo , Ohkubo Kei , Fukuzumi Shunichi , Itoh Shinobu 
Published: December 2003

AbstractCrystal structures of the copper(i) complexes 1X, 2, and 3 of a series of tridentate ligands L1X, L2, and L3, respectively (L1X: p‐substituted derivatives of N,N‐bis[2‐(2‐pyridyl)ethyl]‐2‐phenylethylamine; X=H, Me, OMe, Cl, NO2; L2: N,N‐bis[2‐(2‐pyridyl)ethyl]‐2‐methyl‐2‐phenylethylamine; L3: N,N‐bis[2‐(2‐pyridyl)ethyl]‐2,2‐diphenylethylamine) were solved to demonstrate that all the copper(i) complexes involve an η2 copper–arene interaction with the phenyl ring of the ligand sidearm. The CuI ion in each complex has a distorted tetrahedral geometry consisting of the three nitrogen atoms (one tertiary amine nitrogen atom and two pyridine nitrogen atoms) and C1C2 of the phenyl ring of ligand sidearm, whereby the CuC distances of the copper–arene interaction significantly depend on the para substituents. The existence of the copper–arene interaction in a nonpolar organic solvent (CH2Cl2) was demonstrated by the observation of an intense MLCT band around 290 nm, and the magnitude of the interaction was evaluated by detailed analysis of the 1H and 13C NMR spectra and the redox potentials E1/2 of the copper ion, as well as by means of the ligand‐exchange reaction between the phenyl ring and CH3CN as an external ligand. The thermodynamic parameters ΔHo and ΔSo for the ligand‐exchange reaction with CH3CN afforded a quantitative measure for the energy difference of the copper–arene interaction in the series of copper(i) complexes. Density functional studies indicated that the copper(i)–arene interaction mainly consists of the interaction between the d orbital of CuI and a π orbital of the phenyl ring. The copper(i) complexes 1X reacted with O2 at −80 °C in CH2Cl2 to give the corresponding (μ‐η2:η2‐peroxo)dicopper(II) complexes 4, the formation rates kobs of which were significantly retarded by stronger d–π interaction, while complexes 2 and 3, which exhibit the strongest d–π interaction showed significantly lower reactivity toward O2 under the same experimental conditions. Thus, the d–π interaction has been demonstrated for the first time to affect the copper(i)–dioxygen reactivity, and represents a new aspect of ligand effects in copper(i)–dioxygen chemistry.
A Chiroptical Molecular Switch with Distinct Chiral and Photochromic Entities and Its Application in Optical Switching of a Cholesteric Liquid Crystal
Authors: Delden Richard A. van , Mecca Tommaso , Rosini Carlo , Feringa Ben L. 
Published: December 2003

AbstractTwo new structurally related photoswitches are described, in which azobenzene photochromism is combined with the chirality of a 2,2′‐dihydroxy‐1,1′‐binaphthyl unit. In system 1 the chiral binaphthyl moiety is bridged by a methylene tether, locking the biaryl chirality while in system 2 the biaryl core is unbridged and has considerable conformational flexibility. Both compound are capable of inducing cholesteric liquid crystalline phases and proved to be good photoswitches both in solution and in a liquid crystalline matrix. Compound 2 is capable of completely reversing the liquid crystalline chirality which is unique for a chiroptical molecular switch where the switching unit and the chiral moiety are separate entities.
Detection and Amplification of Chirality by Helical Polymers
Authors: Yashima Eiji , Maeda Katsuhiro , Nishimura Tatsuya 
Published: December 2003

AbstractA unique feature of synthetic helical polymers for the detection and amplification of chirality is briefly described in this article. In sharp contrast to host–guest and supramolecular systems that use small synthetic receptor molecules, chirality can be significantly amplified in a helical polymer, such as poly(phenylacetylene)s with functional pendants, which enable the detection of a tiny imbalance in biologically important chiral molecules through a noncovalent bonding interaction with high cooperativity. The rational design of polymeric receptors can be possible by using chromophoric helical polymers combined with functional groups as the pendants, which target particular chiral guest molecules for developing a highly efficient chirality‐sensing system. The chirality sensing of other small molecular and supramolecular systems is also briefly described for comparison.
Zirconium‐Mediated Cross‐Coupling of Terminal Alkynes and Vinyl Bromides: Selective Synthesis of Cyclobutene and 1,3‐Diene Derivatives
Authors: Barluenga José , Rodríguez Félix , Álvarez‐Rodrigo Lucía , Fañanás Francisco J. 
Published: December 2003

AbstractA diastereoselective synthesis of 1,3‐butadiene or cyclobutene derivatives by a zirconium‐mediated reaction of alkenyllithium compounds and vinyl bromides is reported. The key steps involve the generation of zirconocene–alkyne complexes from haloalkenes and subsequent coupling with alkenyl bromides. Thus, formally the process supposes the cross‐coupling reaction between a terminal alkyne and an alkenyl bromide. Moreover, the use of butyl vinyl ether instead of vinyl bromide as the unsaturated system allows an alternative access to different 1,3‐butadiene regioisomers.
A Concave Fluorescent Sensor for Anions Based on 6‐Methoxy‐1‐methylquinolinium
Authors: Amendola Valeria , Fabbrizzi Luigi , Monzani Enrico 
Published: December 2003

AbstractThe ligand 2, in which three fluorogenic 6‐methoxy‐1‐methylquinolinium fragments are appended to a mesityl platform, in MeCN forms 1:1 adducts with halides and other inorganic anions. 1H NMR studies and molecular modelling indicate that 2 provides a cavity for anion inclusion and establishes electrostatic interactions with the guest. Anion inclusion induces quenching of the fluorogenic fragments with an efficiency decreasing along the series Br−≫I−>NCS−≫Cl−>NO3−>HSO4−. The fluorimetric response of 2 to anions is orders of magnitude more sensitive than that of just 6‐methoxy‐1‐methylquinolinium, ligand 1.
Theoretical Insights into the Mechanism for Thiol/Disulfide Exchange
Authors: Fernandes Pedro Alexandrino , Ramos Maria João 
Published: December 2003

AbstractThe mechanism for thiol/disulfide exchange has been studied with high‐level theoretical calculations. Free energies, transition structures, charge densities, and solvent effects along the reaction pathway have been determined for the first time. Mechanistic results agree with experimental data, and support the idea that the thiolate is the reacting species and that the reaction indeed proceeds through an uncomplicated SN2 transition state. The transition structures have the charge density evenly concentrated in the attacking and leaving sulfur atoms. The charge densities allow us to rationalize the solvent effects. As transition structures have the charge density more widely distributed than reactants, hydrophobic environments catalyze the reaction. The effect can be so dramatic that disulfide exchange inside the active site of ribonucleotide reductase is estimated to be catalyzed 103 times faster than the reaction in water. It was also found that attack by thiol is much faster than previously assumed, if mediated through water chains. Although the present results, as well as experimental data, still suggest that thiolate is the main reaction species, water‐mediated thiol attack is almost kinetically competitive, and can eventually become competitive under specific experimental conditions.
Synthesis and Spectroscopic and Electrochemical Studies of Novel Benzo‐ or 2,3‐Naphtho‐Fused Tetraazachlorins, Bacteriochlorins, and Isobacteriochlorins
Authors: Fukuda Takamitsu , Makarova Elena A. , Luk′yanets Evgeny A. , Kobayashi Nagao 
Published: December 2003

AbstractBenzene‐ or 2,3‐naphthalene‐ring‐expanded tetraazachlorins (TACs), tetraazabacteriochlorins (TABCs), and tetraazaisobacteriochlorins (TAiBCs) have been synthesized by using tetramethylsuccinonitrile as a source of hydrogenated sites. The derived compounds were characterized by using NMR spectroscopy, X‐ray crystallography, electronic and magnetic circular dichroism (MCD) spectroscopy, and electrochemical and spectroelectrochemical methods. X‐ray analysis revealed that the benzene‐fused TAiBC deviates slightly from planarity at the hydrogenated sites as a result of the presence of sp3 carbons, which prefer a nonplanar tetrahedral conformation. The spectral data were analyzed by using a band deconvolution technique. In the electronic absorption spectra of TAC and TABC species, the Q band splits into two intense components and smaller splittings were observed for the 2,3‐naphthalene‐fused derivatives relative to the benzo‐fused species. In contrast, in the case of TAiBCs, the Q band splitting was apparently not observed in absorption spectra, as expected from the C2v molecular symmetry. However, MCD signals of the Q band in TAiBCs showed Faraday B terms, implying that the accidental degeneracy of the LUMO and LUMO+1 was broken even for adjacently ring‐fused species. Relative molecular orbital energies were estimated by using cyclic and differential pulse voltammetry. The first reduction potentials were close for TACs and TABCs, although those of TAiBCs shifted to more negative potentials. In contrast, although TABCs and TAiBCs exhibited similar first oxidation potentials, those of TACs appeared at more positive potentials. These properties were reproduced and rationalized by molecular orbital and configuration interaction calculations within the framework of the ZINDO/S Hamiltonian. DFT‐level frequency calculations have succeeded in reproducing the IR spectra for low‐symmetry tetraazaporphyrin (TAP) derivatives for the first time. The relationship between structures and spectral features is discussed.
Zirconium‐Mediated Coupling Reactions of Amines and Enol or Allyl Ethers: Synthesis of Allyl‐ and Homoallylamines
Authors: Barluenga José , Rodríguez Félix , Álvarez‐Rodrigo Lucía , Zapico José M. , Fañanás Francisco J. 
Published: December 2003

AbstractAn easy and efficient zirconium‐mediated synthesis of allylamines from simple amines and enol ethers is described. This strategy also allows the synthesis of amino alcohol derivatives containing a Z double bond in their structure when 2,3‐dihydrofuran is used. Simple conventional modification of these amino alcohols leads to 2‐substituted piperidine derivatives. By applying this approach, a formal total synthesis of the alkaloid coniine is easily achieved from a protected butylamine. Finally, the zirconium‐mediated reaction of amines and allyl phenyl ether furnishes homoallylamines or amino ethers depending on the structure of the starting amine.
Framework Fluxionality of Organometallic Oxides: Synthesis, Crystal Structure, EXAFS, and DFT Studies on [{Ru(η6‐arene)}4Mo4O16] Complexes
Authors: Laurencin Danielle , Garcia Fidalgo Eva , Villanneau Richard , Villain Françoise , Herson Patrick , Pacifico Jessica , Stoeckli‐Evans Helen , Bénard Marc , Rohmer Marie‐Madeleine , Süss‐Fink Georg , Proust Anna 
Published: December 2003

AbstractReactions of the molybdates Na2MoO4⋅2 H2O and (nBu4N)2[Mo2O7] with [{Ru(arene)Cl2}2] (arene=C6H5CH3, 1,3,5‐C6H3(CH3)3, 1,2,4,5‐C6H2(CH3)4) in water or organic solvents led to formation of the triple‐cubane organometallic oxides [{Ru(η6‐arene)}4Mo4O16], whose crystal and molecular structures were determined. Refluxing triple cubane [{Ru(η6‐C6H5CH3)}4Mo4O16] in methanol caused partial isomerization to the windmill form. The two isomers of [{Ru(η6‐C6H5CH3)}4Mo4O16] were characterized by Raman and Mo K‐edge X‐ray absorption spectroscopy (XAS), both in the solid‐state and in solution. This triple‐cubane isomer was also used as a spectroscopic model to account for isomerization of the p‐cymene windmill [{Ru(η6‐1,4‐CH3C6H4CH(CH3)2)}4Mo4O16] in solution. Using both Raman and XAS techniques, we were then able to determine the ratio between the windmill and triple‐cubane isomers in dichloromethane and in chloroform. Density functional calculations on [{Ru(η6‐arene)}4Mo4O16] (arene=C6H6, C6H5CH3, 1,3,5‐C6H3(CH3)3, 1,4‐CH3C6H4CH(CH3)2, C6(CH3)6) suggest that the windmill form is intrinsically more stable, provided the complexes are assumed to be isolated. Intramolecular electrostatic interactions and steric bulk induced by substituted arenes were found to modulate but not to reverse the energy difference between the isomers. The stability of the triple‐cubane isomers should therefore be accounted for by effects of the surroundings that induce a shift in the energy balance between both forms.
Solid‐Phase Synthesis and Screening of Macrocyclic Nucleotide‐Hybrid Compounds Targeted to Hepatitis C NS5B
Authors: Smietana Michael , Johnson Robert B. , Wang Q. May , Kool Eric T. 
Published: December 2003

AbstractA convergent strategy for the synthesis of cyclic nucleotide‐hybrid molecules on controlled pore glass is reported. A major advantage of the approach is the lack of restrictions on the sequence and structural variation, allowing the incorporation of modified ribonucleosides (such as 2′‐OMe‐ribonucleotides), as well as threoninol derivatives. This methodology allows a fully automated assembly by means of standard phosphoramidite chemistry and is based on a recently published procedure for the preparation of cyclic oligodinucleotides in the DNA series (M. Smietana, E. T. Kool, Angew. Chem. 2002, 114, 3856–3859; Angew. Chem. Int. Ed. Engl. 2002, 41, 3704–3707). A library of potential cyclic hybrid inhibitor compounds targeting hepatitis C virus NS5B enzyme (the replicating polymerase of HCV) was generated by means of the parallel‐pool strategy. Screening of the library revealed that cyclic hybrid c(COMEEthenodA) was a significant inhibitor of NS5B, with an IC50 of 40 μM. Preliminary structure–activity studies of this lead compound are described.
Selective Adsorption of Polychlorinated Dibenzo‐p‐dioxins and Dibenzofurans by the Zeosils UTD‐1, SSZ‐24, and ITQ‐4
Authors: Jäger Ralph , Schneider Andreas M. , Behrens Peter , Henkelmann Bernhard , Schramm Karl‐Werner , Lenoir Dieter 
Published: December 2003

AbstractZeosils are microporous solids with a pure silica framework. Due to their hydrophobic properties, zeosils are ideal host materials for the adsorption of hydrophobic guest molecules. We tested zeosils with different pore diameters (UTD‐1, SSZ‐24 and ITQ‐4 as well as CIT‐5) for the selective adsorption of the polychlorinated dibenzo‐p‐dioxins and dibenzofurans. This group of highly toxic substances contains 210 congeners that possess similar chemical properties, but differ in their size and shape. In the experiment, polychlorinated dibenzo‐p‐dioxins and dibenzofurans were extracted from fly ash of a waste incinerator, adsorbed on amorphous silica, then thermally desorbed and flushed over a sequential arrangement of the zeosils at elevated temperature by a stream of nitrogen. ITQ‐4 with the smallest pore diameter was placed first, followed by SSZ‐24 and, finally, by UTD‐1 with the largest pore diameter. After the experiment, the zeosils were analysed for their contents of the different congeners. The results show that the sorption of the congeners occurs selectively and that it is governed by the size and the shape of the dioxin molecules, which in turn depend on the number of chlorine atoms and the pattern of chlorine substitution (regioisomers). Geometrical reasoning as well as molecular dynamics calculations on the zeosil structures and on the dioxin molecules were helpful in rationalising the results. This work represents an especially complex case of the molecular sieving effect and may lead to a selective on‐line monitoring of the concentrations of dioxin molecules in waste gases of industrial combustion processes. The size‐ and shape‐selective sorption of dioxin molecules may also bear some resemblance to the molecular recognition process that occurs in nature at the aryl hydrocarbon receptor.
Highly Enantioselective Ruthenium‐Catalyzed Reduction of Ketones Employing Readily Available Peptide Ligands
Authors: Bøgevig Anders , Pastor Isidro M. , Adolfsson Hans 
Published: December 2003

AbstractHighly efficient and selective catalysts for the asymmetric reduction of aryl alkyl ketones under hydrogen‐transfer conditions (2‐propanol) were obtained by combining a novel class of pseudo‐dipeptide ligands with [{RuCl2(p‐cymene)}2]. A library of 36 dipeptide‐like ligands was prepared from N‐Boc‐protected α‐amino acids and the enantiomers of 2‐amino‐1‐phenylethanol and 1‐amino‐2‐propanol. The catalyst library was evaluated with the reduction of acetophenone and excellent enantioselectivity of 1‐phenylethanol was obtained with several of the novel catalysts. A ligand based on the combination of N‐Boc‐L‐alanine and (S)‐1‐amino‐2‐propanol (ligand A‐(S)‐4) was found to be particular effective. When the situ formed ruthenium complex of this ligand was employed as the catalyst in the hydrogen‐transfer reaction of various aryl alkyl ketones, the corresponding alcohol products were achieved in excellent enantioselectivity (up to 98 % ee).
Focused motor stereotypies do not require enhanced activation of neurons in striosomes
Authors: Glickstein Sara B. , Schmauss Claudia 
Published: December 2003

AbstractStereotypic motor behavior is a widespread phenomenon of many neurologic and psychiatric disorders. Studies on the mechanisms controlling motor stereotypies have focused on the role of dopamine in modulating the activity of basal ganglia neuronal circuits, and recent results demonstrated that stereotypic motor responses characteristic of psychomotor stimulant sensitization correlate with an enhanced activation of neurons located in striatal striosomes that substantially exceeds that of the surrounding matrix. The present study tested whether predominant striosomal activation is a general predictor for stereotypy. Wild‐type and dopamine D2 and D3 receptor knockout mice were treated either three times with methamphetamine (METH; 3 × 5 mg/kg every 2 hours) or once with a full D1 agonist. Depending on the genotype, both treatments elicit the same focused stereotypy (taffy pulling). Repeated METH‐treatment elicits intense stereotypy in wild‐type and D3 mutants but not in D2 single and D2/D3 double mutants. The stereotypic response of wild‐type and D3 mutants correlates with a predominant activation of neurons located in striosomes. No striosomal predominance is detected in METH‐treated D2 single and D2/D3 double mutants. In contrast, D2 single and D2/D3 double mutants exhibited the most severe stereotypic response to D1‐agonist treatment. However, this treatment did not result in enhanced striosomal activation. Thus, whereas the expression of stereotypy in response to repeated METH treatment requires D2 receptor expression, D2 receptor expression diminishes stereotypic responses to an acute dose of a D1 agonist. Enhanced striosomal activation, however, is a reliable indicator of D1‐ and D2‐receptor coactivation but not a predictor for repetitive motor behavior in general. J. Comp. Neurol. 469:227–238, 2004. © 2003 Wiley‐Liss, Inc.