bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phenotype of the neural tube defect mouse model bent tail is not sensitive to maternal folinic acid, myo‐inositol, or zinc supplementation
Authors: Franke Barbara , Klootwijk Riko , Lemmers Bianca , De Kovel Carolien G.F. , Steegers‐Theunissen Regine P.M. , Mariman Edwin C.M. 
Published: December 2003

AbstractBACKGROUNDBent tail is a mouse model for X‐linked neural tube defects (NTDs) that is characterized by the presence of exencephaly, a delayed posterior neuropore closure, and a tail phenotype. In addition, Bent tail shows laterality defects and increased prenatal mortality. The congenital malformations of this mouse are caused by a submicroscopic deletion that completely encompasses the gene coding for the zinc finger transcription factor Zic3. In this study we investigated the sensitivity of the phenotype of Bent tail to the nutrients folinic acid, myo‐inositol, and zinc. These nutrients are thought to be involved in the etiology of NTDs, in combination with a genetic predisposition.METHODSThe most penetrant phenotype of the Bent tail mouse, the tail malformation, was used as a marker for the nutrient sensitivity of the neural phenotype. The size of the litters and the survival of the offspring, subdivided according to genotype, were analyzed as markers for the nutrient sensitivity of other phenotypic features of Bent tail.RESULTSIn confirmation of earlier studies, we observed the prenatal loss of a number of homozygous females and hemizygous males, as well as the effect of genotype on the tail phenotype of Bent tail. However, periconceptional supplementation of the maternal diet with folinic acid, myo‐inositol, or zinc produced no significant effects on either the tail phenotype of the offspring or the size and genotypic composition of the litters.CONCLUSIONSBent tail appears to be a folinic acid‐, myo‐inositol‐, and zinc‐insensitive mouse model for NTDs. Birth Defects Research (Part A), 2003. © 2003 Wiley‐Liss, Inc.
First trimester exposure to corticosteroids and oral clefts
Authors: Pradat Pierre , Robert‐Gnansia Elisabeth , Di Tanna Gian Luca , Rosano Aldo , Lisi Alessandra , Mastroiacovo Pierpaolo ,   all contributors to the MADRE database
Published: December 2003

AbstractBACKGROUNDThe possible association between oral cleft in the newborn and maternal exposure to corticoids during pregnancy is still controversial. The aim of this study was to test this association by a case‐control analysis using the large multicentric MADRE database.METHODSThe MADRE database is a collection of information on malformed infants with a history of maternal first‐trimester drug exposure. Nine malformation registries participate in the data collection. Cases were defined as infants presenting with a cleft palate or cleft lip, and exposure was defined by the use of corticosteroids during the first trimester of pregnancy.RESULTSAfter 12 years of data collection, the database includes data on 11,150 malformed infants. A slight association is observed between exposure to corticoids for systemic use and the occurrence of cleft lip with or without cleft palate (OR, 2.59; 95% CI, 1.18–5.67).CONCLUSIONSIf the observed association is real, an interpretation is suggested, based on a likely interaction between corticosteroids and environmental dioxins. It is indeed possible that human fetuses may become sensitive to the teratogenic effect of corticosteroids when they are exposed in utero to environmental pesticides as well. Birth Defects Research (Part A), 2003. © 2003 Wiley‐Liss, Inc.
Aufstieg und Fall der Kolonialwissenschaften im Nationalsozialismus
Authors: Linne Karsten 
Published: December 2003

AbstractThe German colonial plans concerning Africa in the era of National Socialism ascribed a central role the sciences. Scientists of all possible fields launched into activities. Especially subjects which were directly related to the practice of colonial policies, e.g., African languages, ethnology, law, economic sciences, and medicine, were developed. There were colonial ambitions at nearly every German university, but there was one which was designated to become the centre of colonial sciences: the university of Hamburg. It has to be realized that working in this field of studies protected scientists from being drafted by the army for a long time.
Valence Charge Concentrations, Electron Delocalization and β‐Agostic Bonding in d0Metal Alkyl Complexes
Authors: Scherer Wolfgang , Sirsch Peter , Shorokhov Dmitry , Tafipolsky Maxim , McGrady G. Sean , Gullo Emanuel 
Published: December 2003

AbstractIn this paper we describe a range of model d0metal ethyl compounds and related complexes, studied by DFT calculations and high resolution X‐ray diffraction. The concept of ligand‐opposed charge concentrations (LOCCs) for d0metal complexes is extended to include bothcis‐andtrans‐ligand‐induced charge concentrations (LICCs) at the metal, which arise as a natural consequence of covalent metal–ligand bond formation in transition metal alkyl complexes. The interplay betweenlocallyinduced sites of increased Lewis acidity and an ethyl ligand is crucial to the development of a β‐agostic interaction in d0metal alkyl complexes, which is driven by delocalization of the MC bonding electrons. Topological analysis of theoretical and experimental charge densities reveals LICCs at the metal atom, and indicates delocalization of the MC valence electrons over the alkyl fragment, with depletion of the metal‐directed charge concentration (CC) at the α‐carbon atom, and a characteristic ellipticity profile for the CαCβbond. These ellipticity profiles and the magnitude of the CC values at Cαand Cβprovide experimentally observable criteria for assessing quantitatively the extent of delocalization, with excellent agreement between experiment and theory. Finally, a concept is proposed which promises systematic control of the extent of CH activation in agostic complexes.
A Bifunctional Platinum(II) Complex Capable of Intercalation and Hydrogen‐Bonding Interactions with DNA: Binding Studies and Cytotoxicity
Authors: Ma Dik‐Lung , Che Chi‐Ming 
Published: December 2003

AbstractThe interactions of [Pt(CNN)(4‐dpt)]PF6, (1; 4‐dpt=2,4‐diamino‐6‐(4‐pyridyl)‐1,3,5‐triazine, HCNN=6‐phenyl‐2,2′‐bipyridine) with double‐stranded DNA, poly(dA‐dT)2, and poly(dG‐dC)2 were examined by spectroscopic, electrophoretic, and hydrodynamic methods. The spectroscopic data were analyzed with McGhee, van′t Hoff, and Gibbs–Helmholtz equations. In a comparative study, [Pt(CNN)(py)]PF6 (2; py=pyridine) was prepared and the nature of its binding towards DNA was investigated [preliminary results: ChemBioChem 2003, 4, 62–68]. For reactions with calf thymus DNA at 20 °C, the intrinsic binding constants for 1 and 2 are (4.6±0.2)×105 and (2.3±0.3)×104 mol−1 dm3, respectively. Results of DNA‐binding reactions revealed that 1 and 2 preferentially bind to the AT sequence of duplex DNA. Intercalation is the preferred binding mode for 2, whereas both intercalation and minor‐groove binding are observed for 1. Complex 1 is cytotoxic against a number of carcinoma cell lines, including KB‐3‐1, CNE‐3, and HepG2, and remains potent against multidrug‐ or cisplatin‐resistant KB‐V‐1 and CNE1 cell lines, for which the resistance ratios are 1.6 and 1.5, respectively. Importantly, 1 is almost an order of magnitude less toxic to the normal cell line CCD‐19Lu (IC50=176±1.7 μM) and it selectively induced apoptosis leading to cancer cell death with less than 5 % detectable necrosis.
Electron Transfer and Dynamic Infrared‐Band Coalescence: It Looks Like Dynamic NMR Spectroscopy, but a Billion Times Faster
Authors: Londergan Casey H. , Kubiak Clifford P. 
Published: December 2003

AbstractBroadening and coalescence of infrared bands can occur due to chemical exchange processes occurring on very fast, femtosecond‐to‐picosecond timescales. One such fast process of recent investigation is intramolecular electron transfer in transition‐metal complexes with strong communication between electron‐donor and ‐acceptor sites. The observation of partial coalescence of metal–carbonyl stretching bands in hexanuclear ruthenium mixed‐valence complexes due to electron‐transfer rates on the order of 1011–1012 s−1 is chronicled here. Several important advances have been made with the aid of dynamic infrared‐band coalescence in these complexes, including the observation of dynamic solvent relaxation effects on electron‐transfer rates, the determination of the equilibrium constant between charge‐transfer isomers, and a reconsideration of the theory of electron transfer and delocalization in bridged, near‐delocalized electron‐transfer systems.
Photocurrent Generation in Multilayer Self‐Assembly Films Fabricated from Water‐Soluble Poly(phenylene vinylene)
Authors: Li Hongmei , Li Yuliang , Zhai Jin , Cui Guanglei , Liu Huibiao , Xiao Shengqiang , Liu Yang , Lu Fushen , Jiang Lei , Zhu Daoben 
Published: December 2003

AbstractA novel, water‐soluble, cationic PPV derivative poly{(2,5‐bis(3‐bromotrimethylammoniopropoxy)‐phenylene‐1,4‐divinylene)‐alt‐1,4‐(2,5‐bis(2‐(2‐hydroxyethoxy)ethoxy))phenylene vinylene} (BH‐PPV) has been synthesized by a Heck coupling reaction. Multilayered assemblies of the BH‐PPV and the sodium salt of hexa(sulfobutyl)fullerenes (C60‐HS) were fabricated successfully by an alternate deposition technique. The multilayer structures were studied by UV/Vis spectroscopy, small angle X‐ray diffraction, and atomic force microscopy. The photoinduced charge transfer property of the self‐assembled multilayer film was also measured by a three‐electrode cell technique. A steady and rapid cathodic 5.5 μA cm−2 photocurrent response was measured as the irradiation of the multilayer film was switched on and off. Importantly, the response of on/off cycling is prompt and reproducible. A possible mechanism for the electron‐transfer process is proposed.
Efficient Synthesis of High Molar Mass, First‐ to Fourth‐Generation Distributed Dendronized Polymers by the Macromonomer Approach
Authors: Zhang Afang , Zhang Bin , Wächtersbach Eva , Schmidt Manfred , Schlüter A. Dieter 
Published: December 2003

AbstractA homologous series of first‐ to fourth‐generation (G1–G4) dendronized macromonomers, 5, 7, 10, and 12, was synthesized, and their polymerization behavior under radical conditions investigated. These conditions were thermally induced radical polymerization (TRP) and atom‐transfer radical poymerization (ATRP). TRP was applied to all monomers and gave polymers PG1–PG4, whose molar masses range from several millions for PG1 to estimated several hundreds of thousands for PG2 and PG3, and to the oligomeric regime for PG4. ATRP was applied only to the G1 and G2 monomers 5 and 7. Kinetic studies on monomer 5 provide evidence that its polymerization proceeds in a controlled fashion. The highest monomer‐to‐initiator ratios which still gave monomodal molar mass distributions were 300:1 (for 5) and 100:1 (for 7), which correspond to achievable molar mass regime for PG1 and PG2 of approximately Mn=100 000 (DPcalcd(PG1)=200, DPcalcd(PG2)=90). The polydispersities lie in the usual range (PDI=1.1–1.2). The molar masses were determined by GPC in DMF with calibration against absolute molar masses of PG1 determined by light scattering.
X‐ray Structure and Circular Dichroism of Pure Rotamers of Bis[guanosine‐5′‐monophosphate(−1)](N,N,N′,N′‐tetramethylcyclohexyl‐1,2‐diamine)platinum(II) Complexes That HaveR,RandS,SConfigurations at the Asymmetric Diamine
Authors: Benedetti Michele , Tamasi Gabriella , Cini Renzo , Natile Giovanni 
Published: December 2003

AbstractThe use of a sterically hindered diamine ligand (Me4DACH) has allowed for the first time, the isolation and characterization, both in the solid state (X‐ray crystallography) and in solution (circular dichroism), of pure ΔHT rotamers of [Pt(Me4dach)(5′‐GMP)2] (compounds1and2forR,RandS,Sconfigurations of the Me4DACH ligand, respectively). Comparison of the CD spectra obtained for each rotamer, which differ only in the chirality of the Me4DACH ligand (R,RorS,S) or in the chirality of the HT conformation (Δ or Λ), allowed us to conclude that, in the 200–350 nm range, the contributions to the overall CD spectrum that stem from diamine chirality and diamine‐induced chirality of platinum d‐‐d transitions or from sugar chirality are negligible relative to the exciton chiral coupling that occurs for π–π* transitions of thecisguanines. Accurate molecular structures of1⋅10 D2O and2⋅14 D2O (conventional crystallographic agreement indexesR1convergent to 2.07 % and 2.18 %, respectively) revealed that the crystallized rotamers have a ΔHT conformation that is in agreement with all previously reported X‐ray structures of [Pt(diamine)(nucleos(t)ide)2] complexes. This conformation allows the 5′‐phosphate to be located in proximity to the Me4DACH ligand so that (P)O⋅⋅⋅HC(N) hydrogen‐bond interactions exists in both complexes. For both structures, the canting of the guanine planes on the coordination plane is right‐handed (R; canting angle (Φ) of 80.9° and 73.2°, respectively); this indicates that the canting direction is driven by the HT conformation chirality (Δ for both compounds) and not by the chirality of the carrier ligand (different for the two compounds). Density functional theory analysis of the conformational space as a function ofΦindicated a good agreement between the computed and experimental structures. The increase in energy forΦvalues below 65° and 55° (for1and2, respectively) is mainly due to the short intramolecular contacts between C(8)H and thecisNMe groups on the same side of the platinum coordination plane.
A Definitive Synthesis ofD‐myo‐Inositol 1,4,5,6‐Tetrakisphosphate and Its EnantiomerD‐myo‐Inositol 3,4,5,6‐Tetrakisphosphate from a Novel Butane‐2,3‐diacetal‐Protected Inositol
Authors: Mills Stephen J. , Riley Andrew M. , Liu Changsheng , Mahon Mary F. , Potter Barry V. L. 
Published: December 2003

AbstractNew and rapid syntheses of the enantiomeric intracellular signalling moleculesd‐myo‐inositol 1,4,5,6‐tetrakisphosphate (1 a) andD‐myo‐inositol 3,4,5,6‐tetrakisphosphate (1 b) are described. The synthetic strategy employs the novel butane‐2,3‐diacetal‐protected (BDA‐protected)myo‐inositol (±)‐3 ab, directly accessible frommyo‐inositol on a large scale, and an optical resolution with diastereoisomeric (R)‐(−)‐acetylmandelate esters. The X‐ray crystal structure of (±)‐4, an unusual side product of acid‐catalysed reaction ofmyo‐inositol with butanedione is also presented, and the absolute configurations of1 aand1 bare definitively assigned by conversion of key precursors into (+)‐bornesitol andL‐iditol hexaacetate, respectively. Biological activity of synthetic1 bwas confirmed in comparison with the natural polyphosphate.
Total Synthesis and Biological Evaluation of (−)Apicularen A and Analogues Thereof
Authors: Nicolaou K. C. , Kim David W. , Baati Rachid , O′Brate Aurora , Giannakakou Paraskevi 
Published: December 2003

AbstractApicularen A (1) and related benzolactone acylenamines belong to a growing class of novel natural products possessing highly cytotoxic properties. The challenging structure of 1 includes a 10‐membered macrolactone ring, a tetrahydropyran system, an o,m‐substituted phenol and a doubly unsaturated acyl group attached on the side chain enamine functionality. The total synthesis of apicularen A described herein involves a strategy equivalent to its proposed biosynthesis and entails a reiterative two‐step procedure featuring allylation and ozonolytic cleavage to grow the molecule's chain by one acetate unit at a time. The developed synthetic technology was applied to the construction of a series of apicularen A analogues whose biological evaluation established a set of structure–activity relationships in this new area of potential importance in cancer chemotherapy.
Synthesis of Conjugated Polyrotaxanes
Authors: Michels Jasper J. , O'Connell Michael J. , Taylor Peter N. , Wilson Joanne S. , Cacialli Franco , Anderson Harry L. 
Published: December 2003

AbstractA series of conjugated polyrotaxane insulated molecular wires are synthesised by aqueous Suzuki polymerisation, using hydrophobic binding to promote threading of the cyclodextrin units. These polyrotaxanes have conjugated polymer cores based on poly(para‐phenylene), polyfluorene, and poly(diphenylene‐vinylene), threaded through 0.9–1.6 cyclodextrins per repeat unit. Bulky naphthalene‐3,6‐disulfonate endgroups prevent the macrocycles from slipping off the conjugated polymer chains. Dialysis experiments show that the cyclodextrins become unthreaded only if smaller stoppers are used. MALDI TOF mass spectra detect oligomers with up to ten threaded cyclodextrins, and reveal the presence of some defects that result for oxidative homo‐coupling of boronic acids. Weight‐average molecular weights were determined by analytical ultracentrifugation, demonstrating that step‐growth polymerisation is efficient enough to achieve degrees of polymerisation up to ≈20 repeat units (84 para‐phenylenes). The fluorescence spectra of these polyrotaxanes indicate that the presence of the threaded cyclodextrin macrocycles reduces the flexibility of the conjugated polymer π‐systems. Both the solution and the solid‐state photoluminescence quantum yields are enhanced upon threading of the conjugated polyaromatic cores through α‐ or β‐cyclodextrins, and the emission spectra of the polyrotaxanes are blue‐shifted compared to the corresponding unthreaded polymers. The greater weight of the 0–0 transition in the emission spectra, as well as the smaller Stokes shift, indicate that the polyrotaxanes are more rigid than the unthreaded polymers.
Generation and Coupling of [Mn(dmpe)2(CCR)(CC)]. Radicals Producing Redox‐Active C4‐Bridged Rigid‐Rod Complexes
Authors: Fernández Francisco J. , Venkatesan Koushik , Blacque Olivier , Alfonso Montserrat , Schmalle Helmut W. , Berke Heinz 
Published: December 2003

AbstractThe symmetric d5 trans‐bis‐alkynyl complexes [Mn(dmpe)2(CCSiR3)2] (R = Me, 1 a; Et, 1 b; Ph, 1 c) (dmpe = 1,2‐bis(dimethylphosphino)ethane) have been prepared by the reaction of [Mn(dmpe)2Br2] with two equivalents of the corresponding acetylide LiCCSiR3. The reactions of species 1 with [Cp2Fe][PF6] yield the corresponding d4 complexes [Mn(dmpe)2(CCSiR3)2][PF6] (R = Me, 2 a; Et, 2 b; Ph, 2 c). These complexes react with NBu4F (TBAF) at −10 °C to give the desilylated parent acetylide compound [Mn(dmpe)2(CCH)2][PF6] (6), which is stable only in solution at below 0 °C. The asymmetrically substituted trans‐bis‐alkynyl complexes [Mn(dmpe)2(CCSiR3)(CCH)][PF6] (R = Me, 7 a; Et, 7 b) related to 6 have been prepared by the reaction of the vinylidene compounds [Mn(dmpe)2(CCSiR3)(CCH2)] (R = Me, 5 a; Et, 5 b) with two equivalents of [Cp2Fe][PF6] and one equivalent of quinuclidine. The conversion of [Mn(C5H4Me)(dmpe)I] with Me3SiCCSnMe3 and dmpe afforded the trans‐iodide‐alkynyl d5 complex [Mn(dmpe)2(CCSiMe3)I] (9). Complex 9 proved to be unstable with regard to ligand disproportionation reactions and could therefore not be oxidized to a unique MnIII product, which prevented its further use in acetylide coupling reactions. Compounds 2 react at room temperature with one equivalent of TBAF to form the mixed‐valent species [{Mn(dmpe)2(CCH)}2(μ‐C4)][PF6] (11) by C–C coupling of [Mn(dmpe)2(CCH)(CC.)] radicals generated by deprotonation of 6. In a similar way, the mixed‐valent complex [{Mn(dmpe)2(CCSiMe3)}2(μ‐C4)][PF6] [12]+ is obtained by the reaction of 7 a with one equivalent of DBU (1,8‐diazabicyclo[5.4.0]undec‐7‐ene). The relatively long‐lived radical intermediate [Mn(dmpe)2(CCH)(CC.)] could be trapped as the MnI complex [Mn(dmpe)2(CCH)(CCO2)] (14) by addition of an excess of TEMPO (2,2,6,6‐tetramethyl‐1‐piperidinyloxy) to the reaction mixtures of species 2 and TBAF. The neutral dinuclear MnII/MnII compounds [{Mn(dmpe)2(CCR3)}2(μ‐C4)] (R = H, 11; R = SiMe3, 12) are produced by the reduction of [11]+ and [12]+, respectively, with [FeCp(C6Me6)]. [11]+ and [12]+ can also be oxidized with [Cp2Fe][PF6] to produce the dicationic MnIII/MnIII species [{Mn(dmpe)2(CCR3)}2(μ‐C4)][PF6]2 (R = H, [11]2+; R = SiMe3, [12]2+). Both redox processes are fully reversible. The dinuclear compounds have been characterized by NMR, IR, UV/Vis, and Raman spectroscopies, CV, and magnetic susceptibilities, as well as elemental analyses. X‐ray diffraction studies have been performed on complexes 4 b, 7 b, 9, [12]+, [12]2+, and 14.
Selection and Amplification of Mixed‐Metal Porphyrin Cages from Dynamic Combinatorial Libraries
Authors: Stulz Eugen , Scott Sonya M. , Bond Andrew D. , Teat Simon J. , Sanders Jeremy K. M. 
Published: December 2003

AbstractMixed metallo–porphyrin cages were selected and amplified from dynamic combinatorial libraries (DCLs) by using appropriate templates. The cages are composed of two bisphosphine substituted zinc(II) porphyrins as ligand donors and two rhodium(III) or ruthenium(II) porphyrins as ligand acceptors, and are connected through metal–phosphorus coordination. Ru and Rh porphyrins that display a large structural diversity were employed. The templating was achieved by using 4,4′‐bpy, 3,3′‐dimethyl‐4,4′‐bipyridine and benzo[lmn]‐3,8‐phenanthroline, and acts through zinc–nitrogen coordination. The absolute amount of amplification from the DCLs is strongly dependent on the combination of the Ru/Rh porphyrin and the template; cages with sterically demanding porphyrins can only form with smaller templates. In the case of tert‐butyl‐substituted TPP (TPP=tetraphenylporphyrin), cages are not formed at all. The formation of the cages is usually complete within 24 h at an ambient temperature; in the case of the cage containing RhIIIOEP (OEP=octaethylporphyrin) and bpy, the pseudo‐first‐order rate constant of cage formation was determined to be 2.1±0.1×10−4 s−1 (CDCl3, 25 °C). Alternatively, heating the mixtures to 65 °C and cooling to room temperature yields the cages within minutes. The 1H NMR chemical shifts of several characteristic protons show large differences upon changing the identity of the Ru/Rh porphyrin and the central metal; this is most likely to arise from variations in the geometry of the cages. The X‐ray crystal structure of a cage, which contains RhIIIOEP as a porphyrin acceptor and bpy as template, demonstrates that the cages can adopt severely distorted conformations to accommodate the relatively short templates. An extension to mixed DCLs showed that only limited selectivity is displayed by the various templates. Formation of mixed cages that contain two different rhodium porphyrins prevents effective selection, although the kinetic lability of the systems allows for some amplification. This lability, however, also prevents isolation of the individual cages. Removal of the template leads to re‐equilibration, thus the templates act as scaffolds to keep the structures intact.
Oligosaccharide–Peptide Ligation of Glycosyl Thiolates with Dehydropeptides: Synthesis of S‐Linked Mucin‐Related Glycopeptide Conjugates
Authors: Galonić Danica P. , van der Donk Wilfred A. , Gin David Y. 
Published: December 2003

AbstractA chemoselective strategy for oligosaccharide–peptide ligation is described in which α‐thio analogues of mucin‐related glycoconjugates can be readily accessed through site‐selective conjugate addition of complex oligosaccharide thiolates to dehydroalanine‐containing peptides. The efficiency of the ligation is highlighted by the rapid convergent assembly of thio‐isosteres of the four tumor‐associated carbohydrate antigens, TN, T, STN, and 2,6‐ST, as a pair of diastereoisomers at the newly formed cysteine stereocenter. The process proceeds in high yield and with complete retention of the α‐anomeric configuration.