bluuebunny/crossref_metadata_2025 huggingface dataset:
Pituitary-Thyroid Setpoint and Thyrotropin Receptor Expression in Consomic Rats
Authors: Moeller Lars C. , Alonso Manuela , Liao XiaoHui , Broach Vance , Dumitrescu Alexandra , Van Sande Jacqueline , Montanelli Lucia , Skjei Stephen , Goodwin Charles , Grasberger Helmut , Refetoff Samuel , Weiss Roy E.
Published: July 2007

The genetic basis for differences in TSH sensitivity between two rat strains was examined using consomic rats generated from original strains salt-sensitive Dahl (SS) (TSH 1.8 ± 0.1 ng/ml; free T4 index 4.9 ± 0.4) and Brown Norwegian (BN) (TSH 5.5 ± 0.6 ng/ml, P < 0.05; free T4 index 4.3 ± 0.1, P not significant). Consomic rats SSBN6 [BN chromosome (CH) 6 placed in SS rat] and SSBN2 (BN CH 2 placed in SS rat) have TSH concentrations intermediate between pure SS and BN strains (2.9 ± 0.3 and 3.1 ± 0.3 ng/ml, respectively; P < 0.05). Candidate genes on rat CH 2 included TSH β-subunit and on CH 6 the TSH receptor (TSHR). TSH from sera of BN, SS, SSBN6, and SSBN2 strains had similar in vitro bioactivity suggesting that the cause for the variable TSH concentrations was not due to an altered TSH. Physiological response to TSH was measured by changes in serum T4 concentrations upon administration of bovine TSH (bTSH). Rat strain SS had a greater T4 response to bTSH than BN (change in T4, 1.3 ± 0.1 vs. 0.4 ± 0.1 μg/dl, P < 0.005), suggesting reduced thyrocyte sensitivity to TSH in BN. Sequencing of the TSHR coding region revealed an amino acid difference in BN (Q46R). This substitution is unlikely to contribute to the strain difference in serum TSH because both TSHR variants were equally expressed at the cell surface of transfected cells and responsive to bTSH. Given similar TSH activity and similar TSHR structure, TSHR mRNA expression in thyroid tissue was quantitated by real-time PCR. BN had 54 ± 5% the total TSHR expression compared to SS (100 ± 7%, P < 0.0001), when corrected for GAPDH expression, a difference confirmed at the protein level. Therefore, the higher TSH level in the BN strain appears to reflect an adjustment of the feedback loop to reduced thyrocyte sensitivity to TSH secondary to reduced TSHR expression. These strains of rat provide a model to study the cis- and trans-acting factors underlying the difference in TSHR expression.
Ontogeny and Nutritional Programming of the Hepatic Growth Hormone-Insulin-Like Growth Factor-Prolactin Axis in the Sheep
Authors: Hyatt Melanie A. , Budge Helen , Walker David , Stephenson Terence , Symonds Michael E.
Published: July 2007

The liver is an important metabolic and endocrine organ in the fetus, but the extent to which its hormone receptor sensitivity is developmentally regulated in early life is not fully established. Therefore, we examined developmental changes in mRNA abundance for the GH receptor (GHR) and prolactin receptor (PRLR) plus IGF-I and -II and their receptors. Fetal and postnatal sheep were sampled at either 80 or 140 d gestation, 1 or 30 d, or 6 months of age. The effect of maternal nutrient restriction between early gestation to midgestation (i.e. 28–80 d gestation, the time of early liver growth) on gene expression was also examined in the fetus and juvenile offspring. Gene expression for the GHR, PRLR, and IGF-I receptor increased through gestation peaking at birth, whereas IGF-I was maximal near to term. In contrast, IGF-II mRNA decreased between midgestation and late gestation to increase after birth, whereas IGF-II receptor remained unchanged. A substantial decline in mRNA abundance for GHR, PRLR, and IGF-I receptor then occurred up to 6 months. Maternal nutrient restriction reduced GHR and IGF-II receptor mRNA abundance in the fetus, but caused a precocious increase in the PRLR. Gene expression for IGF-I and -II were increased in juvenile offspring born to nutrient-restricted mothers. In conclusion, there are marked differences in the ontogeny and nutritional programming of specific hormones and their receptors involved in hepatic growth and development in the fetus. These could contribute to changes in liver function during adult life.
Aerodynamic force generation, performance and control of body orientation during gliding in sugar gliders (Petaurus breviceps)
Authors: Bishop Kristin L.
Published: July 2007

Gliding has often been discussed in the literature as a possible precursor to powered flight in vertebrates, but few studies exist on the mechanics of gliding in living animals. In this study I analyzed the 3D kinematics of sugar gliders (Petaurus breviceps) during short glides in an enclosed space. Short segments of the glide were captured on video, and the positions of marked anatomical landmarks were used to compute linear distances and angles, as well as whole body velocities and accelerations. From the whole body accelerations I estimated the aerodynamic forces generated by the animals. I computed the correlations between movements of the limbs and body rotations to examine the control of orientation during flight. Finally, I compared these results to those of my earlier study on the similarly sized and distantly related southern flying squirrel (Glaucomys volans). The sugar gliders in this study accelerated downward slightly (1.0±0.5 m s–2), and also accelerated forward (2.1±0.6 m s–2) in all but one trial, indicating that the body weight was not fully supported by aerodynamic forces and that some of the lift produced forward acceleration rather than just balancing body weight. The gliders used high angles of attack (44.15±3.12°), far higher than the angles at which airplane wings would stall, yet generated higher lift coefficients (1.48±0.18) than would be expected for a stalled wing. Movements of the limbs were strongly correlated with body rotations,suggesting that sugar gliders make extensive use of limb movements to control their orientation during gliding flight. In addition, among individuals,different limb movements were associated with a given body rotation,suggesting that individual variation exists in the control of body rotations. Under similar conditions, flying squirrels generated higher lift coefficients and lower drag coefficients than sugar gliders, yet had only marginally shallower glides. Flying squirrels have a number of morphological specializations not shared by sugar gliders that may help to explain their greater lift generating performance.
Females do it better. Individual recognition experiments reveal sexual dimorphism in Lemur catta (Linnaeus 1758) olfactory motivation and territorial defence
Authors: Palagi Elisabetta , Dapporto Leonardo
Published: July 2007

In this paper, we aim at demonstrating individual recognition of female genital marking in Lemur catta. By gas chromatography and behavioural trials we verified the occurrence of the three components of recognition systems. We showed that each female has a unique chemical signature(expression component), and males and females perceive female individuality(perception component). To verify the presence of the action component (the last component of recognition systems), we designed a bioassay based on territorial competition to verify the functional response to female odours. Only females identified other females on the basis of their scents. The lack of a territorial functional response by males to female secretions may not indicate a male inability to identify females by their scents. In fact, sexual dimorphism in motivation and territorial defence may explain the response by males in the functional experiment. Actually, game theory predicts that males defend their own territories more vigorously against males compared with females. Therefore, the result of individual recognition bioassays of female odours may open interesting scenarios in the evaluation of the territorial defence investment across the different sex combinations.
Plasticity in arthropod cryotypes
Authors: Hawes T. C. , Bale J. S.
Published: July 2007

Low-temperature acclimation and acclimatization produce phenotypic changes in arthropods at multiple levels of biological organization from the molecular to the behavioural. The role and function of plasticity – where a constitutive, reversible change occurs in the phenotype in response to low temperature – may be partitioned hierarchically at evolutionary scales according to cryoprotective strategy, at macrophysiological scales according to climatic variability, and at meso- and micro-scales according to ecological niche and exposure. In correspondence with these scales (which are interdependent rather than mutually exclusive), a hierarchical typology of interaction between thermal history and organism is proposed, descending,respectively, from what we define as `cryotype' (class of cryoprotective strategy) to genotype and, ultimately, phenotype. Alternative (and sometimes complementary) strategies to plasticity include specialization,generalization, bet-hedging, cross-resistance and convergence. The transition of cryotypes from basal to derived states is a continuum of trait optimization, involving the fixation of plasticity and/or its alternatives.
Blood oxygen depletion during rest-associated apneas of northern elephant seals (Mirounga angustirostris)
Authors: Stockard T. K. , Levenson D. H. , Berg L. , Fransioli J. R. , Baranov E. A. , Ponganis P. J.
Published: July 2007

Blood gases (PO2, PCO2, pH), oxygen content, hematocrit and hemoglobin concentration were measured during rest-associated apneas of nine juvenile northern elephant seals. In conjunction with blood volume determinations, these data were used to determine total blood oxygen stores, the rate and magnitude of blood O2 depletion, the contribution of the blood O2 store to apneic metabolic rate, and the degree of hypoxemia that occurs during these breath-holds. Mean body mass was 66±9.7 kg (± s.d.); blood volume was 196±20 ml kg–1; and hemoglobin concentration was 23.5±1.5 g dl–1. Rest apneas ranged in duration from 3.1 to 10.9 min. Arterial PO2 declined exponentially during apnea, ranging between a maximum of 108 mmHg and a minimum of 18 mmHg after a 9.1 min breath-hold. Venous PO2 values were indistinguishable from arterial values after the first minute of apnea; the lowest venous PO2 recorded was 15 mmHg after a 7.8 min apnea. O2 contents were also similar between the arterial and venous systems, declining linearly at rates of 2.3 and 2.0 ml O2 dl–1 min–1, respectively, from mean initial values of 27.2 and 26.0 ml O2 dl–1. These blood O2 depletion rates are approximately twice the reported values during forced submersion and are consistent with maintenance of previously measured high cardiac outputs during rest-associated breath-holds. During a typical 7-min apnea, seals consumed, on average, 56% of the initial blood O2 store of 52 ml O2 kg–1; this contributed 4.2 ml O2 kg–1 min–1to total body metabolic rate during the breath-hold. Extreme hypoxemic tolerance in these seals was demonstrated by arterial PO2 values during late apnea that were less than human thresholds for shallow-water blackout. Despite such low PO2s, there was no evidence of significant anaerobic metabolism, as changes in blood pH were minimal and attributable to increased PCO2. These findings and the previously reported lack of lactate accumulation during these breath-holds are consistent with the maintenance of aerobic metabolism even at low oxygen tensions during rest-associated apneas. Such hypoxemic tolerance is necessary in order to allow dissociation of O2 from hemoglobin and provide effective utilization of the blood O2 store.
Methodology for Rapid Determination of Pozzolanic Activity of Materials
Authors: Dalinaidu A. , Das B. B. , Singh D. N.
Published: July 2007

Determination of pozzolanic activity, and in particular lime reactivity, of various materials such as fly ash, cenospheres, blast furnace slag, etc., is quite essential for their efficient application in cement and concrete. It also plays an important role in the selection of the material as a stabilizer in various environmental cleanup projects, such as heavy metal retention and waste immobilization strategies. Though ASTM C 311, ASTM C 593, and IS 1727 are being followed to determine pozzolanic activity of different materials, they are quite time consuming. This necessitates development of a methodology that can be employed for determining the pozzolanic activity of different materials, quite rapidly and easily. With this in view, a methodology that indirectly estimates pozzolanic activity of different materials, by measuring electrical conductivity of their mixture in partially saturated lime solution, has been developed and its details are presented in this paper.
Masonry Repairs at Cheshire Mill No. 1, Harrisville, New Hampshire
Authors: Willett Linda , O’Connor Frederick
Published: July 2007

The first modern-day application of Rosendale natural cement mortars in a significant historic restoration is described. The background of Cheshire Mill No. 1 in Historic Harrisville, New Hampshire, the analyses of its original mortar composition, and the successful use of natural cement for in-kind repointing are detailed.
Modeling the Interaction of Helium with Dislocations and Grain Boundaries in Alpha-Iron
Authors: Heinisch H. L. , Gao F. , Kurtz R. J.
Published: July 2007

Helium is a ubiquitous impurity in nuclear materials that can have significant deleterious effects on mechanical properties, including deformation and fracture. To determine ways to mitigate the effects of helium it is necessary to understand the behavior of helium with respect to its interaction with various microstructural features. Toward that end, we have employed molecular statics, molecular dynamics, and the dimer method of potential surface mapping to study the fate of helium in the vicinity of dislocations and grain boundaries in alpha-iron. Even at very low temperatures interstitial helium atoms can migrate to dislocations and grain boundaries, where they are strongly bound. The binding energies of helium to these microstructural features relative to the perfect crystal and the migration energies of helium diffusing within them have a strong correlation to the excess atomic volume that exists in these extended defects. Helium atom migration energies within the dislocations and grain boundaries studied are in the range of 0.4–0.5 eV. Helium “kick out” mechanisms have been identified within dislocations and grain boundaries by which interstitial helium atoms replace an Fe lattice atom, creating a stable He-vacancy complex that may be a nucleation site for an He bubble.
Management of teenage pregnancy
Authors: Horgan Richard P , Kenny Louise Clare
Published: July 2007

Key content

The United Kingdom has the highest teenage pregnancy rate in Western Europe.

Risk factors include socioeconomic deprivation, low educational achievement and having teenage parents.

Adverse outcomes associated with teenage pregnancy include premature delivery, infants being small for gestational age, low birthweight and increased neonatal mortality.

Associated risks include high rates of sexually transmitted infections, alcohol and substance misuse, smoking and poor diet.

Attendance at antenatal care is generally poor and teenagers may present late, therefore, it is important to tailor care to their individual needs.

Learning objectives

To learn about current guidance and policies.

To know about the risk factors for teenage pregnancy, adverse outcomes and associated risks.

To learn about the management of teenage pregnancy with particular reference to prevention.

Ethical issues

When is it necessary to obtain parental consent for termination of pregnancy or to prescribe contraception in girls aged less than 16 years of age?

Why do some teenagers see pregnancy as a positive life event?

Please cite this article as: Horgan RP, Kenny LC. Management of teenage pregnancy. The Obstetrician & Gynaecologist 2007;9:153–158.
Transcriptional Profiling of Bipotential Embryonic Liver Cells to Identify Liver Progenitor Cell Surface Markers
Authors: Ochsner Scott A. , Strick-Marchand Hélène , Qiu Qiong , Venable Susan , Dean Adam , Wilde Margaret , Weiss Mary C. , Darlington Gretchen J.
Published: July 2007

The ability to purify to homogeneity a population of hepatic progenitor cells from adult liver is critical for their characterization prior to any therapeutic application. As a step in this direction, we have used a bipotential liver cell line from 14 days postcoitum mouse embryonic liver to compile a list of cell surface markers expressed specifically by liver progenitor cells. These cells, known as bipotential mouse embryonic liver (BMEL) cells, proliferate in an undifferentiated state and are capable of differentiating into hepatocyte-like and cholangiocyte-like cells in vitro. Upon transplantation, BMEL cells are capable of differentiating into hepatocytes and cholangiocytes in vivo. Microarray and Gene Ontology (GO) analysis of gene expression in the 9A1 and 14B3 BMEL cell lines grown under proliferating and differentiating conditions was used to identify cell surface markers preferentially expressed in the bipotential undifferentiated state. This analysis revealed that proliferating BMEL cells express many genes involved in cell cycle regulation, whereas differentiation of BMEL cells by cell aggregation causes a switch in gene expression to functions characteristic of mature hepatocytes. In addition, microarray data and protein analysis indicated that the Notch signaling pathway could be involved in maintaining BMEL cells in an undifferentiated stem cell state. Using GO annotation, a list of cell surface markers preferentially expressed on undifferentiated BMEL cells was generated. One marker, Cd24a, is specifically expressed on progenitor oval cells in livers of diethyl 1,4-dihydro-2,4,6-trimethyl-3,5-pyridinedicarboxylate-treated animals. We therefore consider Cd24a expression a candidate molecule for purification of hepatic progenitor cells.

Disclosure of potential conflicts of interest is found at the end of this article.
Selective Targeting of Adenoviral Vectors to Neural Precursor Cells in the Hippocampus of Adult Mice: New Prospects for In Situ Gene Therapy
Authors: Schmidt Anke , Haas Stefan J.-P. , Hildebrandt Steve , Scheibe Johanna , Eckhoff Birthe , Racek Tomáš , Kempermann Gerd , Wree Andreas , Pützer Brigitte M.
Published: July 2007

The adult brain contains neural precursor cells (NPC) that are attracted to brain lesions, such as areas of neurodegeneration, ischemia, and cancer. This suggests that NPC engineered to promote lineage-specific differentiation or to express therapeutic genes might become a valuable tool for restorative cell therapy and for targeting therapeutic genes to diseased brain regions. Here we report the identification of NPC-specific ligands from phage display peptide libraries and show their potential to selectively direct adenovirus-mediated gene transfer to NPC in adult mice. Identified peptides mediated specific virus binding and internalization to cultured neurospheres. Importantly, peptide-mediated adenoviral vector infection was restricted to precursor cells in the hippocampal dentate gyrus of pNestin-green fluorescent protein transgenic or C57BL/6 mice. Our approach represents a novel method for specific manipulation of NPC in the adult brain and may have major implications for the use of precursor cells as therapeutic delivery vehicles in the central nervous system.

Disclosure of potential conflicts of interest is found at the end of this article.
Synthesis and association properties in water solution of random copolymers of 2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid and isodecyl methacrylate—potential application as surfactants in micellar‐enhanced ultrafiltration processes
Authors: Peinado Carmen , Catalina Fernando , San Miguel Verónica
Published: July 2007

Hydrophobically modified water‐soluble polymers have been prepared by copolymerization of 2‐acrylamido‐2‐methylpropane sulfonic acid (AMPS) and isodecyl methacrylate (iDMA) in N,N‐dimethylformamide under nitrogen atmosphere, varying the composition feed. Fluorescence spectroscopy was used to further confirm the copolymers self‐aggregate in water. Critical concentration of the self‐aggregate formation (CAC) decreased by increasing the molar fraction of iDMA in the AMPSco copolymers and varied between 1.20 and 0.04 g/L depending on the degree of hydrophobic modification. Hence, copolymer composition and charge density allowed tuning the pseudomicellar characteristics of these new amphiphilic copolymers. The addition of a salt or a low‐molecular‐weight surfactant was studied. Binding of CTAB to the AMPSco copolymers leads to a high decrease of CAC, i.e., 0.006 g/L. Effect of the composition in the viscosimetric behavior of the hydrophobically modified copolymers AMPSco was investigated. The removal of single metal ions, Cu2+, and m‐cresol from aqueous solutions by ultrafiltration with the help of the copolymers was investigated. Equilibrium dialysis experiments demonstrate that the formation of hydrophobic microdomains can be used to control the sequestration of foulants, and thus these novel copolymers have potential application as polymeric surfactants in micellar‐enhanced ultrafiltration processes for water purification. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007
Studies of Allylic Substitution Catalysed by a Palladium Complex of a C2‐Symmetric Bis(aziridine): Preparation and NMR Spectroscopic Investigation of a Chiral π‐Allyl Species
Authors: Andersson Pher G. , Harden Adrian , Tanner David , Norrby Per‐Ola
Published: July 2007

The chiral palladium π‐allyl intermediate for the catalytic asymmetric synthesis shown in Scheme 1 has been isolated as the PF salt. MM 2 calculations have been performed and the structure of the palladium complex in solution has also been investigated by means of NMR spectroscopy. Both the computational and spectroscopic results suggest that in the complex the bidentate bis(aziridine) ligand adopts a conformation that forces the π‐allyl moiety out of the normally preferred square‐planar geometry. This nicely explains the very high enantioselectivity observed in the title reaction.
The Design of Selective Chelating Agents: 1,3,5‐Trideoxy‐1,3,5‐tris‐(dimethylamino)‐cis‐inositol, a Powerful Ligand for Hard and Highly Charged Metal Ions
Authors: Hegetschweiler Kaspar , Kradolfer Thomas , Gramlich Volker , Hancock Robert D.
Published: July 2007

A series of compounds containing the mononuclear complexes [M(tdci)2]3+ (tdci = 1,3,5‐trideoxy‐1,3,5‐tris(dimethylamino)‐cis‐inositol, M = Al, Fe, Ga, In) and [M(tdci)2]4+ (M = Ti, Ge, Sn) was prepared and characterized by elemental analysis, NMR spectroscopy, and FAB mass spectrometry. Characteristic fragmentation reactions in the mass spectra were elucidated. X‐ray analysis of the AlIII, FeIII, GaIII, and InIII complexes revealed that two neutral, zwitterionic tdci ligands coordinate to the metal cation exclusively through deprotonated alkoxo groups. The six coordinated oxygen donors and the six NH protons form a hydrophilic pocket, whereas the two cyclohexane rings and the twelve methyl groups form two hydrophobic shells. The hydrophilic pocket is filled with twelve water molecules, which are arranged as a second and a third coordination sphere around the metal cation. The reactivity in aqueous solution was investigated by potentiometric measurements. The bis complexes proved to be stable at pH 7. The evaluated formation constants show an increase of stability in the order AlIII<InIII<GaIII<FeIII. The measurements established that tdci is one of the most effective tridentate ligands for small (r ⩽ 0.8Å) and highly charged cations. The different chelating properties of tdci and of the unmethylated 1,3,5‐triamino‐ 1,3,5‐trideoxy‐cis‐inositol are discussed in terms of different steric requirements and different types of solvation of the corresponding complexes in aqueous solution.
Synthesis of a Methyl Heptaglucoside with Phytoalexin Elicitor Activity Based on Oxidative Coupling of Glucals
Authors: Timmers Cornelis M. , van der Marel Gijsbert A. , van Boom Jacques H.
Published: July 2007

Several suitable building blocks for the construction of the phytoalexin elicitor α‐methyl‐32, 34‐di‐β‐D‐glucopyranosylgentiopentaoside (2) were readily accessible by oxidative coupling of glucals. Block coupling of trimeric phenylseleno‐ and ethylthioglucosyl donors 17 and 18 with tetrasaccharide 16 in the presence of the thiophilic promoter N‐iodosuccinimide and catalytic trifluoromethanesulfonic acid furnished the desired heptaglucan 2 in high overall yield.
Supramolecular Structure, Physical Properties, and Langmuir‐Blodgett Film Formation of an Optically Active Liquid‐Crystalline Phthalocyanine
Authors: van Nostrum Cornelus F. , Bosman Anton W. , Gelinck Gerwin H. , Schouten Pieter G. , Warman John M. , Kentgens Arno P. M. , Devillers Marinus A. C. , Meijerink Andries , Picken Stephen J. , Sohling Ulrich , Schouten Arend‐Jan , Nolte Roeland J. M.
Published: July 2007

The structure and physical properties of optically active, metal‐free 2,3,9,10,16,17,23,24‐octa (S‐3,7‐dimethyloctoxy)phthalocyanine ((S)‐Pc(8,2)) are reported and compared with those of the phthalocyanine with (R,S) side chains (mixture of 43 stereoisomers). Unlike the latter compound, (S)‐Pc(8,2) lacks a crystalline phase. A freshly prepared sample is in a distorted mesophase and reorganizes irreversibly to a more ordered phase above 65 °C. X‐ray diffraction and circular dichroism studies indicate that the molecules are stacked in columns which have a hexagonal arrangement and a left‐handed helical superstructure, that is, a novel chiral Dh* mesophase. Solid state NMR measurements reveal that the phthalocyanine units in the columns begin to vibrate laterally when the temperature is increased. At 111 °C (Dh* → Dr transition) they start to rotate around their columnar axes and at the same time the side chains become liquidlike. Energy migration is very efficient in the chiral Dh* phase and also in the frozen mesophase below 3 °C, as follows from luminescence spectroscopy. Intracolumnar charge transport, studied by the time‐resolved microwave conductivity technique, turns out to be slower in the helically distorted columns than in linear columns. (S)‐Pc(8,2) forms a very stable bilayer at the air‐water interface, which can be transferred to give a high quality Langmuir‐Blodgett film. The fact that this phthalocyanine is mesogenic at room temperature is thought to be responsible for this behavior.
Neutral Cobalt Carbonyl Catalysts for the Equilibration Between CO and P(OPh)3 Ligands in Carbonylcobaltates
Authors: Ciuffarin Ennio , Fachinetti Giuseppe , Funaioli Tiziana , Isola Mauro
Published: July 2007

The substitution reaction of [Co(CO)4]− by P(OPh)3 was investigated in THF. Under a CO atmosphere, the reaction consists of an equilibrium, which, in order to be established, needs [Co2(CO)6(P(OPh)3)2]. The catalysis by this neutral carbonyl is formally related to a previously reported case, where either [Co2(CO)8] or [Co4(CO)12] was found to be necessary for the 13CO scrambling in [Co(CO)4]−. The kinetic analysis reported in this paper indicates, however, that the two CO labilizations differ in their mechanism‐the substitution by P(OPh)3 is ascribed to a disproportionation‐synproportionation of [Co2(CO)6(P(OPh)3)2].
Light‐Triggered Molecular Devices: Photochemical Switching Of optical and Electrochemical Properties in Molecular Wire Type Diarylethene Species
Authors: Gilat Sylvain L. , Kawai Stephen H. , Lehn Jean‐Marie
Published: July 2007

Organic photochromic systems represent a starting point for the elaboration of light‐triggered molecular switching devices. The novel bispyridinium and bispyridine compounds 12+ and 6 were synthesized as their uncyclized isomers from 3,5‐dibromo‐2‐methylthiophene in overall yields of 43 and 44%, respectively. The diarylethene photochromes 2 and 10–13, substituted with electron donors and acceptors, were prepared from 5‐methylthiophene‐2‐carboxaldehyde in 21–32% overall yield. All of the compounds were found to exhibit pronounced photochromic properties. Irradiation with UV light resulted in essentially complete photocyclization of the open forms to the intensely coloured closed isomers which could, in turn, be reconverted back to the open state with visible light of γ>600 nm. The absorption maxima of the described compounds in their closed forms are shifted far towards, and even into, the near‐IR region. Whereas no thermochromic properties were observed for the open isomers, the rates of thermal decolouration of the cyclized forms was found to be highly dependent on the nature of the substituents on the thiophene rings. It was demonstrated that reversible photochemical interconversion between the two photochromic states could be used to effectively switch a number of physical properties. Thus, the molecules 12+ and 12 represent two kinds of redox switches, the former in reduction and the latter in oxidation, in which electron conduction is switched on in the closed state and off in the open state. Compound 12 may also be considered to be a photoswitchable analogue of tetrathiafulvalene type substances. On the other hand, compound 2 displays a marked increase in nonlinear optical activity on conversion from the open to the closed form. Such systems are prototypes of photoswitchable molecular wires where electron conduction and push‐pull interaction can be reversibly modulated by an external stimulus, namely, irradiation by light.
Synthesis, Structure, and Reactivity of Chiral Rhenium N‐Pyrrolyl Complexes Regiochemistry of Electrophilic Addition and Unprecedented Rearrangements to Carbon‐Ligated Species
Authors: Johnson Todd J. , Alvey Luke J. , Brady Monika , Mayne Charles L. , Arif Atta M. , Gladysz J. A.
Published: July 2007

Reaction of [{Re}(OTf)] (1; {Re} — (η5‐C5H5)Re(NO)(PPh3) and potassium pyrrolide gives the N‐pyrrolyl complex magnified image2, 88%). Reactions of 2 with (CF3CO)2O/N(C2H5)3 and CH3O2CC=CCO2CH3 give 3‐ and 2‐substituted pyrrolyl complexes magnified image respectively (3, R/R′ = H/COCF3, 77%; 5, R/R′ = C(CO2CH3)=CHCO2CH3/H, 69–87%). Free pyrrole is much less reactive towards these reagents. Reactions of 2 and TfOH or HBF4·OEt2 give the 2H‐pyrrole adducts magnified image+X− (7+X−; 89–83%). At 0–25°C in CH2Cl2, these rearrange to the carbon‐ligated tautomers magnified image+X−(8+X−) and then magnified image+X−; (9+X−; 72–96 h, 90–96%). Reaction of 1 and pyrrole in refluxing toluene gives 8+TfO− and then 9−TfO− (92%). However, 1 and pyrrole react too slowly in CH2Cl2 to be intermediates in the conversion of 7+TfO− to 9+TfO−. Reaction of 9+ TfO− and KH gives the C‐pyrrolyl complex magnified image (68%), which adds TfOH to give 9+TfO−. Mechanistic aspects of the preceding reactions are discussed. The crystal structures of 2 and 9+TfO− are determined, and the NC4Hx ligand conformations analyzed with extended Hückel MO calculations.
Stereoselective Homologation–Amination of Aldehydes by Addition of Their Nitrones to C‐2 Metalated Thiazoles—A General Entry to α‐Amino Aldehydes and Amino Sugars
Authors: Dondoni Alessandro , Franco Santiago , Junquera Federico , Merchán Francisco L. , Merino Pedro , Tejero Tomás , Bertolasi Valerio
Published: July 2007

A general method for the homologation of aldehydes to α‐amino aldehydes (aminohomologation) has been developed, which employs nitrones as iminium derivatives of the aldehydes. Key operations include a) the addition of a thiazole metalated at C‐2 to the N‐benzylnitrone derived from the aldehyde, b) the reductive dehydroxylation of the resultant thiazolyl N‐benzylhydroxylamine, and c) the unmasking of the formyl group from the thiazole ring. The homologation sequence was studied by employing nitrones derived from various chiral polyalkoxy aldehydes and dialdoses. The addition of 2‐lithiothiazole to these nitrones was syn‐selective, whereas the reaction with the same nitrones precomplexed with Lewis acids was anti‐selective. Hence, from each nitrone a pair of diastereoisomeric hydroxylamines was obtained. These compounds were then converted by the above sequence into α‐epimeric α‐amino aldehydes. Model elaborations of some of these products afforded the amino sugars D‐glucosamine, D‐mannosamine, D‐nojirimycin, and advanced intermediates for the synthesis of destomic acid and lincosamine.
Ligand Design for Securing Ferromagnetic Exchange Coupling in Multimetallic Complexes
Authors: Gordon‐Wylie Scott W. , Bominaar Emile L. , Collins Terrence J. , Workman José M. , Claus Brian L. , Patterson Robert E. , Williams Stacy A. , Conklin Brenda J. , Yee Gordon T. , Weintraub Susan T.
Published: July 2007

An approach is suggested for using ligands to control exchange coupling in multinuclear ions. The idea arose from structural, EPR, and magnetic studies of [PPh4]3 (Scheme 1). Ferromagnetic coupling has been found between the CoII and each CoIII in 3 with J = −22 ± 5 cm−1 (JS1 · S2). It is suggested that dominant antiferromagnetic superexchange is absent because of the strong σ‐donor capacity of the tetradentate ligand [k4‐PAC*]4− (Fig. 1). The ligand interacts at CoIII primarily with a single d orbital; it is thus best able to participate in superexchange. The interaction makes the unique d orbital strongly σ‐antibonding and empty for each d6, S = 1, CoIII ion in 3, that is, unavailable for antiferromagnetic coupling, but available for ferromagnetic pathways by a Goodenough‐Kanamori mechanism. By corollary, when any [k4‐PAC*]4−‐type ligand with any magnetic ion Ma in the tetradentate site binds any magnetic ion Mb in the bidentate site, ferromagnetic coupling should be favored provided Ma is not a d9 ion.
Synthesis, Conformational Analysis and Comparative Protein Binding of a Galabioside and Its Thioglycoside Analogues
Authors: Nilsson Ulf , Johansson Roger , Magnusson Göran
Published: July 2007

The two thio analogues (2 and 3) of TMSEt galabioside [2‐(trimethylsilyl)ethyl 4‐O‐(α‐D‐galactopyranosyl)‐β‐D‐galactopyranoside, 1], having anomeric sulfur instead of anomeric oxygen atoms, were synthesized and their conformations investigated by NMR and computational (MM 3) methods. A spacer galabioside was covalently coupled to aminated microtiter plates, and binding of a bacterial pilus adhesin (PapG) to the plates was inhibited by the soluble ligands 1, 2 and 3. The ligand 2, which has an intersaccharidic sulfur linkage, was a much less efficient inhibitor than 1, which has the natural oxygen linkage. The inhibitory power of ligand 3 was only slightly less than that of 1. An NMR experiment with 1 and 2, in which hydroxyl‐group hydrogens had been partially (50%) substituted by deuterium, demonstrated the presence (in 1) and absence (in 2) of an intramolecular (HO 2′ – HO 6) hydrogen bond. This result indicates that the conformations of 1 and 2 are different and that the difference is sufficient to cause the observed (≈ 30 times) reduction of the saccharide‐protein binding strength.
An Ab Initio Study of Structures and Energetics of Copper Sulfide Clusters
Authors: Dehnen Stefanie , Schäfer Ansgar , Ahlrichs Reinhart , Fenske Dieter
Published: July 2007

The results of ab initio calculations for the sulfur‐bridged copper clusters [Cu2nSn(PR3)m] (n = 1–4, 6; m = 0, 2, 4, 6, 8; RH, CH3) were compared with those of theoretical investigations of the selenium‐containing analogues that have been recently reported. The theoretical work was carried out in order to find a possible explanation for the experimentally observed–different–properties of both cluster types. The structural principles turned out to be independent of the chalcogen, except the necessary shortening of the copper–chalcogen atomic distance that results from the formal substitution of sulfur for selenium. Comparison of the energetics of the sulfur‐ and selenium‐containing compounds showed that it is necessary to discuss the influence of the tertiary phosphine ligands that protect the existing clusters from reaction to give the solids Cu2S and Cu2Se. However the results of the calculations suggest that the different thermodynamic data of the cluster core and the CuP bonds–at least if PH3 or PMe3 are taken into account–cannot be the only cause for the differences in the experimental behaviour. The responsibility rests rather with kinetic effects, such as the steric demand of the actual ligands or the activation energy of decomposition of the ligand shell during the cluster‐forming reaction.
Solution Phase and Single Crystal Diffraction X‐ray Analyses of Diprotonated Porphyrin Isomers—Etioporphyrin, Etioporphycene, and Etiocorrphycene Bishydroperchlorate Salts
Authors: Sessler Jonathan L. , Brucker Eric A. , Lynch Vincent , Choe Michael , Sorey Steven , Vogel Emanuel
Published: July 2007

The diprotonated, bishydroperchlorate forms of three isomeric β‐octaalkyl‐substituted tetrapyrrolic macro‐cycles, namely, etioporphyrin II (1), etio porphycene (2), and etiocorrphycene (3), have been characterized both in chloroform solution, by UV/visible spectroscopy and 1H and proton‐correlated 2D 15N NMR methods, and in the solid state, by single‐crystal X‐ray diffraction analyses. In the solid state, in marked contradistinction to what is observed for the corresponding free‐base forms, the macrocyclic portion of these salts were found to be distorted significantly from planarity with the two perchlorate counteranions being held above and below the average N4 plane by N–H … O hydrogen bonds in all three cases. In solution, 1H and proton‐correlated 2D 15N NMR experiments reveal molecular ions of relatively high symmetry (D2h, D2h, and C2v in the case of 1·(HClO4)2, 2·(HClO4)2, and 3·(HClO4)2, respectively) as would be anticipated on the basis of the solid‐state results. These same NMR analyses, while revealing slight differences between the three salts in the NH and meso 1H NMR spectral regions, also serve to confirm the generalized congeneric nature of 1·(HClO4)2, 2·(HClO4)2, and 3·(HClO4)2 and support the assignment of the latter two species as being porphyrin‐like salts. UV/vis analyses further support this conclusion; in all three instances, strong Soret‐ and Q‐like transitions are observed in dichloromethane that are both distinct from each other (λmax=404, 549, 570, 593; 388, 409, 599, 666; and 419, 559, 604 for 1·(HClO4)2, 2·(HClO4)2, and 3·(HClO4)2, respectively) and from those of the corresponding free‐base forms (λmax=396, 496, 530, 565, 619; 382, 570, 617, 657; and 410, 509, 539, 574, 628 for 1, 2, and 3 respectively). Protonation experiments were carried out by exposing dichloromethane solutions of the isomers to aqueous perchlorate/perchloric acid solutions of differing pH. These studies reveal that while porphycene 2 adds two protons readily and concurrently, becoming 50% diprotonated when exposed to perchlorate/perchloric solutions with a pH of around 3.6, porphyrin 1 and corrphycene 3 are protonated in a stepwise manner; they become 50% monoprotonated when exposed to perchlorate/perchloric solutions of pH≈︁3.7 and 3.9, respectively, and diprotonated at pH≤0.8 and 1.3, respectively.
Covalent Bonding of Crown Ethers to γ‐Zirconium Phosphate—New Layered Ion Exchangers Showing Selective Recognition
Authors: Brunet Ernesto , Huelva Manuel , Vázquez Raquel , Juanes Olga , Rodríguez‐Ubis Juan C.
Published: July 2007

The topotactic exchange reactions of γ‐zirconium phosphate and γ‐zirconium phosphate/methylphosphonate with phosphonic acids derived from azacrown ethers of different sizes was examined. Prior intercalation of hexylamine was necessary in most cases to attain the maximum exchange level predicted by molecular modeling. Materials with imbricated or nonimbricated layers were obtained depending on crown size and exchange level. Exchange of methylphosphonates in γ‐zirconium phosphate/methylphosphonate was only observed when hexylamine had previously been intercalated. The exchange with the bisphosphonic acid derived from 1,10‐diaza[18]‐crown‐6 gave a material with an interlayer distance compatible with pillaring of the γ‐phase. The materials obtained from the exchange reactions of γ‐zirconium phosphate with phosphonic acids derived from [12]crown‐4 and [18]crown‐6 showed thermodynamic selectivities towards Na+ and K+, respectively, that were much higher than those observed for the simple crowns in solution. This observation suggests that the inorganic molecular framework enhances molecular recognition by minimization of solvation effects.
Epoxidation and Oxygen Insertion Into Alkane Ch Bonds by Dioxirane Do Not Involve Detectable Radical Pathways
Authors: Adam Waldemar , Curci Ruggero , D'Accolti Lucia , Dinoi Anna , Fusco Caterina , Gasparrini Francesco , Kluge Ralph , Paredes Rodrigo , Schulz Manfred , Smerz Alexander K. , Angela Veloza L. , Weinkötz Stephan , Winde Roland
Published: July 2007

The dimethyldioxirane oxidation of α‐methylstyrene, trans‐cyclo‐octene, and 1‐vinyl‐2,2‐diphenylcyclopropane gave, under all reaction conditions employed, the corresponding epoxides in high yields. No radical products from allylic oxidation, from trans/cis isomerization, or from cyclopropylcarbinyl rearrangement (radical clock) were observed. Even for these alkenes, which are prone to radical reactions, the previously established electrophilic concerted mechanism applies, rather than the recently proposed radical mechanism. The selective hydroxylation of (–)‐2–phenylbutane by dimethyldioxirane gave only (– )‐2–phenylbutan‐2‐ol with complete retention of configuration and no loss of optical purity. Thus, a radical‐chain oxidation is also discounted in the oxygen insertion into hydrocarbon C‐H bonds for dioxiranes.
1′, 5′ ‐Anhydrohexitol Oligonucleotides: Synthesis, Base Pairing and Recognition by Regular Oligodeoxyribonucleotides and Oligoribonucleotides
Authors: Hendrix Chris , Rosemeyer Helmut , Verheggen Ilse , Van Aerschot Arthur , Seela Frank , Herdewijn Piet
Published: July 2007

Oligonucleotides constructed of 1′, 5′‐anhydrohexitol nucleoside building blocks (hexitol nucleic acids, HNA) are completely stable towards 3′‐exonuclease and form very stable self‐complementary duplexes as well as sequence‐selective stable duplexes with the natural DNA and RNA. Triple‐helix formation has also been observed. These hybridisation characteristics are highly dependent on the base sequence and the experimental conditions. When using a phosphate buffer containing 0.1M NaCl, a homopurine HNA dodecamer gives a δTm of +3.0 °C/ base pair with RNA as complement. These oligomers may therefore be of considerable interest as antisense constructs.
On the Mechanism of Stereospecific Polymerization—Development of a Universal Model to Demonstrate the Relationship Between Metallocene Structure and Polymer Microstructure
Authors: van der Leek Y. , Angermund K. , Reffke M. , Kleinschmidt R. , Goretzki R. , Fink G.
Published: July 2007

With the discovery of stereorigid bridged metallocenes, soluble catalysts became available for the stereospecific polymerization of α‐olefins. A relatively simple mechanism was used to explain the stereospecificity, primarily in terms of the catalyst symmetry. In this paper we demonstrate that the simple rule of thumb that C2‐symmetric catalysts produce isotactic and Cs‐symmetric catalysts syndiotactic polypropylene is too narrow. The introduction of one methyl group at the Cp ring in the [{iPr(CpFlu)}ZrCl2]/ MAO system (Flu = fluorenyl, MAO = methylalumoxan) reduces the Cs symmetry to C1, and the resulting catalyst produces hemiisotactic polypropylene. The analogous catalyst with a bulkier tert‐butyl group at the Cp ring gives isotactic polypropylene. When the C2 symmetry of [{Me2Si(Ind)2}ZrCl2] (Ind = indenyl) is reduced to C1, a metallocene can be obtained that produces atactic polypropylene. We have broken away from the symmetry‐based model and developed a universal model, which accurately describes the experimental microstructures of the polymers by considering the four lowestenergy conformers of the metallocene species coordinating to prochiral propene (Rre, Sre, Ssi, and Rsi) and the positional changes that the polymer chain undergoes during insertion. The relative energy levels of the four diastereomers can be determined by molecular modeling calculations; these energy gradations, in particular the size of the energy gaps, are decisive in determining the stereospecificity. Also, the model permits the stereoerrors to be classified and explained. Through this model the stereosequence of a polymer chain can be calculated and predicted.
Homoleptic Cuprates(II) with Multiply Deprotonated α‐Cyclodextrin Ligands
Authors: Klüfers Peter , Piotrowski Holger , Uhlendorf Jürgen
Published: July 2007

In the presence of cupric ions, α‐cyclodextrin (α‐CD) is multiply deprotonated in alkaline aqueous solution. With lithium or sodium as the counterions, trinuclear sandwich‐type cuprate ions of the formula [Cu3(α‐CDH_6)2]6‐ are formed (1 and 2), whereas dinuclear [Cu2(α‐CDH_4)2]4‐ ions are isolated in the form of the potassium (3a) and the rubidium salts (3b). The structures of the cyclodextrinatocuprate ions resemble cylinders, since the usual conical shape of a cyclodextrin is altered due to the formation of shorter hydrogen bonds on the O2/O3 rim of the α‐cyclodextrin torus. Despite anion formation, the cavity of the cyclodextrin is still hydrophobic, giving rise to the intercalation of acetone guests in 2 and 3.
Biosynthesis of Nitric Oxide—Quantum Chemical Modelling of Nω‐Hydroxy‐l‐arginine Formation
Authors: Wasielewska Ewa , Witko Malgorzata , Stochel Grażyna , Stasicka Zofia
Published: July 2007

The electronic structure (charge distribution, bond indices, character of the frontier orbitals) and geometry (bond distances and angles) of L‐arginine and N‐methyl‐L‐arginine were determined by means of the INDO procedure. The method was also adopted to model the conversion of L‐arginine into N‐hydroxy‐L‐arginine in biological systems. This revealed that the approach of diatomic O species does not result in reaction, whereas the approach of either an O atom or an O2‐ ion leads to insertion of oxygen and formation of hydroxy‐L‐arginine. The insertion of oxygen between the nitrogen and hydrogen atoms leads to more stable products than insertion into the C–H bond. The same results were obtained for N‐methyl‐L‐arginine, and are consistent with the hypothesis that the inhibitive effect of N‐substitution in L‐arginine is of no importance for the first step in the biosynthesis of NO (hydroxylation process). The mechanistic considerations based on the charge distribution and frontier orbital characteristics led to the conclusion that the most probable mechanism of L‐arginine hydroxylation consists in electrophilic attack of [FeO]3+ at the Nω‐H bond, initiated by the reduction of L‐arginine+, followed by insertion of oxygen and product oxidation.
Dimethyl Peroxide Radical Cation: A New Theoretical and Experimental Approach to the C2H6O•+2 Potential Energy Surface
Authors: Schalley Christoph A. , Fiedler Andreas , Hornung Georg , Wesendrup Ralf , Schröder Detlef , Schwarz Helmut
Published: July 2007

The structure and the unimolecular fragmentations of the metastable dimethyl peroxide radical cation have been investigated by mass spectrometric and isotopic labeling methods as well as high‐level ab initio calculations. In line with the theoretical results, neutralization‐reionization and charge reversal experiments suggest that ionized dimethyl peroxide bears a CH3OOCH•3 connectivity. In the cation the O‐O bond dissociation energy is larger than that of the neutral counterpart; in contrast, the C‐O bond strength is slightly and that of the C‐H bond significantly reduced upon ionization. These energetic changes upon one‐electron oxidation of CH3OOCH3 are also reflected in the NR and CR mass spectra of CH3OOCH•+3. Further, for metastable CH3OOCH•3 two major fragmentation pathways are observed: 1) Loss of a hydrogen atom by cleavage of a C‐H bond is associated with a skeletal reorganization, which gives rise to a proton‐bound formaldehyde dimer. 2) The expulsion of a CH3O• radical leads to protonated formaldehyde in a surprisingly specific double hydrogen transfer involving a [CH3OH/CH2O]• ion/dipole complex as central intermediate; this complex also accounts for other minor fragmentation channels. The structures of intermediates and transition states are calculated with the BECKE 3LYP density‐functional method employing a 6‐311++G** basis.