bluuebunny/crossref_metadata_2025_split huggingface dataset:
Semisynthesis and Characterization of the First Analogues of Pro‐Neuropeptide Y
Authors: von Eggelkraut‐Gottanka Regula , Machova Zuzana , Grouzmann Eric , Beck‐Sickinger Annette G. 
Published: May 2003

AbstractEnzymatic cleavage of prohormone neuropeptide Y (proNPY) leads to mature neuropeptide Y (NPY), a widely distributed neuropeptide with multiple functions both peripherally and centrally. A single dibasic pair of amino acids, Lys38‐Arg39, represents the recognition motif for a class of hormone‐processing enzymes known as prohormone convertases (PCs). Two members of this PC family, PC1/3 and PC2, are involved in proNPY cleavage. The aim of this work was to establish an effective method for the generation of full‐length 69‐amino acid proNPY analogues for further studies of prohormone convertase interaction. We have chosen two ligation sites in order to perform the semisynthesis of proNPY analogues by expressed protein ligation (EPL). By using the intein‐mediated purification system (IMPACT) with improved conditions for intein splicing, we were able to isolate proNPY 1–40 and proNPY 1–54 fragments as Cterminal thioesters. Peptides bearing Nterminal cysteine instead of the naturally occurring Ser41 and Thr55 residues, respectively, were generated by solid‐phase peptide synthesis. Moreover, labels (carboxyfluorescein and biotin) were inserted into the peptide sequences. The synthesis of the [C41]proNPY 41–69 fragment, which proved to be a difficult peptide sequence, could be achieved by the incorporation of two pseudo‐proline derivatives. Western blot analysis revealed that all five proNPY analogues are recognized by monoclonal antibodies directed against NPY as well as against the Cflanking peptide of NPY (CPON).
[7‐(Dialkylamino)coumarin‐4‐yl]methyl‐Caged Compounds as Ultrafast and Effective Long‐Wavelength Phototriggers of 8Bromo‐Substituted Cyclic Nucleotides
Authors: Hagen Volker , Frings Stephan , Wiesner Burkhard , Helm Siegrun , Kaupp U. Benjamin , Bendig Jürgen 
Published: May 2003

Abstract[7‐(Dimethylamino)coumarin‐4‐yl]methyl (DMACM) and [7‐(diethylamino)coumarin‐4‐yl]methyl (DEACM) esters of 8bromoadenosine 3′,5′‐cyclic monophosphate (8‐Br‐cAMP) and 8bromoguanosine 3′,5′‐cyclic monophosphate (8‐Br‐cGMP) are described as novel caged compounds for 8bromo‐substituted cyclic nucleotides. Synthesis is accomplished by treatment of the free acids of the cyclic nucleotides with the corresponding 7(dialkylamino)‐substituted 4(diazomethyl)coumarins. Irradiation of the DMACM‐ and DEACM‐caged cyclic nucleotides with UV light stimulates the release of the cyclic nucleotides within roughly a nanosecond. The new caged compounds are resistant to hydrolysis in aqueous buffers and exhibit long‐wavelength absorption properties with maxima at 400 nm, high extinction coefficients, and high quantum yields (0.15–0.31). Their favorable properties render these compounds the most efficient and rapid phototriggers of 8bromo‐substituted cyclic nucleotides known. The usefulness of the compounds for physiological studies under nondamaging light conditions was examined in HEK293 cells expressing the α subunit of the cyclic‐nucleotide‐gated (CNG) channel of cone photoreceptors (CNGA3) and of olfactory neurons (CNGA2) by using confocal laser scanning microscopy and the patch clamp technique.
Cover Picture: Semisynthesis and Characterization of the First Analogues of Pro‐Neuropeptide Y (ChemBioChem 5/2003)
Authors: von Eggelkraut‐Gottanka Regula , Machova Zuzana , Grouzmann Eric , Beck‐Sickinger Annette G. 
Published: May 2003

AbstractThe cover picture shows how a combination of recombinant synthesis and chemical synthesis has been used to obtain chemically modified proteins. N‐terminal protein segments of pro‐neuropeptide Y (proNPY) were produced as intein‐fusion proteins in Escherischia coli in order to obtain thioesters. C‐terminal segments were synthesized by parallel automated peptide synthesis and derivatized to obtain carboxyfluorescein‐ (CF) and biotin‐labeled peptides. Native chemical ligation yielded chemically modified full‐length analogues of proNPY that can be used to monitor the biosynthesis of neuropeptide Y. Futher information can be found in the article by Beck‐Sickinger and co‐workers on p. 425 ff.
Microchemical Engineering: Components, Plant Concepts, User Acceptance – Part III
Authors: Hessel V. , Löwe H. 
Published: May 2003

AbstractOver the last five years, many activities have focused on the unexploited field of carrying out reactions on small scales. Due to the rapid development of new components, this paper deals with recent developments only in a compressed form. An important point is the analysis of possible plant concepts for microreactors and whether these are a sensible option. Due to the enormous difference in size between the microchannels and the fluid periphery of possible components this is not just a technical question. It touches on the microtechnology concept as a whole. The direction in which the field should be developed and which measures can be taken to influence its development are questions that are addressed here with respect to the big industrial interest in microreactors.
Liquid Flow on Structured Packing: CFD Simulation and Experimental Study
Authors: Szulczewska B. , Zbicinski I. , Górak A. 
Published: May 2003

AbstractA CFD model of the two‐phase countercurrent flow in the geometry of the plate‐type structured packing Mellapak 250.Y was built, tested and verified. The model was applied to determine the effect of liquid and gas flow rates and physicochemical properties of the flowing liquids on the interfacial area formed on structured packing. The CFD model allowed us to determine the minimum liquid flow rate at which an unbroken liquid film was observed on the packing surface. The simulations confirmed that with an increase of the wetting rate the surface of the packing covered with a liquid film increased until the surface was totally covered up, while further slight changes of an interfacial area were the result of wave formation. The effect of gas load (F factor) on the film surface was in the range of a calculation error. Results of the CFD simulation allow us to predict the stages of film formation during liquid flow, to follow local velocity oscillations, film thickness and velocity profiles of phases.
Simulation of Droplet Generation by Mixing Nozzles
Authors: Schönfeld F. , Rensink D. 
Published: May 2003

AbstractIn various chemical processes thorough homogeneous mixing is of great importance. Due to their small characteristic dimensions, micromixers have a great potential to achieve fast and uniform mixing. However, in the field of powder synthesis from precipitation processes the use of standard micromixers is severely limited because of rapid clogging of the microchannels. As an alternative, mixing nozzles which are less susceptible to fouling can provide a sufficient mixing quality. The flow field and fluid distribution inside multi‐fluid droplets during droplet formation is simulated. Depending on the geometry and flow rates, complex velocity fields and flow distributions are found and the impact on the mixing efficiency is qualitatively deduced. Furthermore, we point out how the tendency of fouling can be further reduced with the help of improved nozzle geometries.
On the Degradation and Stabilization of Poly(Methyl Methacrylate) in a Continuous Process
Authors: Nising P. , Zeilmann T. , Meyer T. 
Published: May 2003

AbstractThermally unstable polymers such as poly(methyl methacrylate) are degraded considerably during industrial processing. This degradation and its reduction to a minimum have been investigated in both lab and continuous pilot‐scale experiments. A three‐step degradation mechanism, starting at 180 °C, was proved by Thermogravimetrical Analysis (TGA) and a kinetic approach to describe it was derived. The knowledge of this degradation behavior was then applied to a pilot‐scale process with a production rate of 10 kg/h and the process yield loss during the devolatilization step was investigated. Using heat stabilizers, the overall process yield could be improved by 10 %, whereas the residual organic volatiles concentration (VOC) was drastically reduced to values below 1000 ppm. In order to preserve the molecular weight of the final product these stabilizers were added into the process, separately, at the end of the polymerization reaction but before the devolatilization step.
Inorganic Layers on Polymeric Films – Influence of Defects and Morphology on Barrier Properties
Authors: Hanika M. , Langowski H.‐C. , Moosheimer U. , Peukert W. 
Published: May 2003

AbstractFlexible polymeric films are not only widely used in conventional packaging as substitute for glass and aluminum foil packaging but are also proposed as encapsulation for novel products, like flexible solar cells or organic light‐emitting devices. The two essential properties of the polymeric packaging are flexibility and good permeation barrier properties against gases and vapors. This article deals with vacuum web coating as a common way of increasing barrier properties of polymeric films and the problems related to this procedure. Defects caused by particles and surface imperfections are found to dominate the permeation rate for such coated polymeric films. Atomic force microscopy, electron and also optical microscopy was used for analysis of the coating layer. Three‐dimensional numerical simulations were performed for modeling of the influence of defect size, spacing and film thickness. Results of numerical modeling and of many practical experiments show that the permeability is almost independent of the substrate film thickness when a critical thickness is exceeded. In most cases the defects can be treated as independent of each other. The gas permeability of vacuum web‐coated polymeric films can be quantitatively predicted by a simple formula. For gases, like oxygen, it is shown that a statistic analysis of the defect sizes by optical microscopy is sufficient. For water vapor transmission, however, the structure of the coating layer itself has also to be taken into account.
Relations between Synthesis and Microstructural Properties of Copper/Zinc Hydroxycarbonates
Authors: Bems Bettina , Schur Michael , Dassenoy Alina , Junkes Heinz , Herein Daniel , Schlögl Robert 
Published: May 2003

AbstractCu/Zn Hydroxycarbonates obtained by co‐precipitation of Cu2+ and Zn2+ with Na2CO3 have been investigated regarding phase formation and thermal decomposition in two series with varying Cu/Zn ratios prepared according to the decreasing pH and constant pH method. Hydrozincite, aurichalcite and (zincian)‐malachite were found to form at differing Cu/Zn ratios for both series. For the constant pH preparation the Cu/Zn ratio in zincian‐malachite was close to the nominal values whereas excess values were found for the decreasing pH samples. The degree of crystallinity as well as the thermal decomposition temperatures were lower for the constant pH series. All samples containing aurichalcite revealed an unexpected decomposition step at high temperatures evolving exclusively CO2. The differences in composition and microstucture were traced back to the different pathways of solid formation for the two preparation methods. Substantial changes were observed during the post‐precipitation processes of ageing and washing. The effects were studied in detail on samples with a cation ratio of Cu/Zn 70:30 mol %. Ageing of the precipitates in their own solutions is accompanied by a spontaneous crystallization of the initially amorphous solids. The decreasing pH sample develops from a hydroxy‐rich material comprising basic copper nitrate (gerhardtite) as an intermediate. Only small changes in the chemistry of the samples were detected for the constant pH precipitation. The findings are summarised into a scheme of solid formation processes that explains the phenomenon of a “chemical memory” of the precipitates when they are converted into Cu/ZnO model catalysts.
Solution‐ and Bound‐State Conformational Study of N,N′,N″‐Triacetyl Chitotriose and Other Analogous Potential Inhibitors of Hevamine: Application of trNOESY and STD NMR Spectroscopy
Authors: Germer Antje , Mügge Clemens , Peter Martin G. , Rottmann Antje , Kleinpeter Erich 
Published: May 2003

AbstractThe solution‐state conformations of N,N′,N″‐triacetyl chitotriose (1) and other potential chitinase inhibitors 2–4 were studied using a combination of NMR spectroscopy (NOESY) and molecular mechanics calculations. Determination solely of the global energy minimum conformation was found to be insufficient for an agreement with the NMR results. An appropriate consistency between the NMR experimental data and theoretical calculations was only reached by assessing the structures as population‐weighted average conformers based on Boltzmann distributions derived from the calculated relative energies. Analogies, but also particular differences, between the synthetic compounds 2–4 and the naturally‐occurring N,N′,N″‐triacetyl chitotriose were found. Furthermore, the conformation of compounds 1 and 2 when bound to hevamine was also studied using transferred NOESY experiments and the binding process was found to impart a level of conformational restriction on the ligands. The preferred conformation as determined for 1 in the bound state to hevamine belonged to one of the conformational families found for the compound when free in solution, although full characterisation of the bound‐state conformations was impeded due to severe signal overlap. Saturation transfer difference NMR experiments were also employed to analyse the binding epitopes of the bound compounds. We thus determined that it is mainly the acetyl amido groups of the trisaccharide and the heterocyclic moiety which are in close contact with hevamine.
Constant‐Distance Mode Scanning Electrochemical Microscopy (SECM)—Part I: Adaptation of a Non‐Optical Shear‐Force‐Based Positioning Mode for SECM Tips
Authors: Ballesteros Katemann Bernardo , Schulte Albert , Schuhmann Wolfgang 
Published: May 2003

AbstractA non‐optical shear‐force‐based detection scheme for accurately controlling the tip‐to‐sample distance in scanning electrochemical microscopy (SECM) is presented. With this approach, the detection of the shear force is accomplished by mechanically attaching a set of two piezoelectric plates to the scanning probe. One of the plates is used to excite the SECM tip causing it to resonate, and the other acts as a piezoelectric detector of the amplitude of the tip oscillation. Increasing shear forces in close proximity to the sample surface lead to a damping of the vibration amplitude and a phase shift, effects that are registered by connecting the detecting piezoelectric plate to a dual‐phase analogue lock‐in amplifier. The shear force and hence distance‐dependent signal of the lock‐in amplifier is used to establish an efficient, computer‐controlled closed feedback loop enabling SECM imaging in a constant‐distance mode of operation. The details of the SECM setup with an integrated piezoelectric shear‐force distance control are described, and approach curves are shown. The performance of the constant‐distance mode SECM with a non‐optical detection of shear forces is illustrated by imaging simultaneously the topography and conductivity of an array of Pt‐band microelectrodes.
Isomeric Alkyl Cation/Arene Complexes in the Gas Phase
Authors: Filippi Antonello , Roselli Graziella , Renzi Gabriele , Grandinetti Felice , Speranza Maurizio 
Published: May 2003

AbstractThe kinetics and the stereochemistry of the protonation‐induced unimolecular isomerization of (S)‐(+)‐1‐D1‐3‐(p‐tolyl)butane have been investigated in the gas phase in the 100–160 °C range. The process leads to the almost exclusive formation of the relevant meta isomer with complete racemization and partial 1,2‐H shift in the migrating sec‐butyl group. These results, together with the relevant activation parameters, point to the occurrence of low‐energy, tightly bound isomeric sec‐butyl cation/toluene complexes of defined structure and stability along the isomerization coordinate. The existence and the η1‐type structure of these low‐energy intermediate species are confirmed by ab initio calculations on closely related systems at the MP2(full)/6‐311++G**//HF/6‐31+G** level of theory. Their role in the relevant energy surface clearly emerges from the comparison of the present results with those concerning sec‐butylation of toluene carried out under comparable experimental conditions.
Syntheses and Structures of Magnesium Pyridine Thiolates—Model Compounds for Magnesium Binding in Photosystem I
Authors: Sousa Pedrares Antonio , Teng Weijie , Ruhlandt‐Senge Karin 
Published: May 2003

AbstractNovel magnesium pyridine‐2‐thiolates were prepared by using alkane elimination chemistry. The resulting complexes display a metal coordination environment composed of sulfur/nitrogen bonding from the intramolecularly stabilized mercaptopyridine ligand, in addition to coordination by the oxygen centers from two THF donors. The compounds are well‐suited model compounds for the magnesium centers in Photosystem I, in which magnesium, situated in the central chlorophyll ligand, is bound to sulfur from a nearby methionine residue. All compounds were characterized by 1H, 13C NMR, and IR spectroscopy, in addition to Xray crystallography.
Palladium(II) Complexes of the Reducing Sugars D‐Arabinose, D‐Ribose, rac‐Mannose, and D‐Galactose
Authors: Klüfers Peter , Kunte Thomas 
Published: May 2003

AbstractThe cellulose solvent Pd‐en, an aqueous solution of [(en)PdII(OH)2] (en=ethylenediamine), reacts with the monosaccharides D‐arabinose (D‐Ara), D‐ribose (D‐Rib), rac‐mannose (rac‐Man), and D‐galactose (D‐Gal) under formation of dimetalated aldose complexes, if the molar ratio of Pd and sugar is 2:1 or larger. In the Pd2 complexes, the aldoses are tetra‐deprotonated and act as bisdiolato ligands. Two crystalline pentose complexes were isolated: [(en)2Pd2(β‐D‐Arap1,2,3,4 H−4)]⋅5 H2O (1) and [(en)2Pd2(β‐D‐Ribp1,2,3,4 H−4)]⋅6.5 H2O (2), along with two hexose complexes. With rac‐Man, the major solution species is crystallized as the 9.4‐hydrate [(en)2Pd2(β‐rac‐Manp1,2,3,4 H−4)]⋅9.4 H2O (3). From the respective D‐Gal solutions, [(en)2Pd2(β‐D‐Galf1,3,5,6 H−4)]⋅5 H2O⋅C2H5OH (4), with the sugar tetraanion in its furanose form, is crystallized though it is not the major species, rather the second most abundant in purely aqueous solutions. The Galf species is enriched in the mother liquors to the extent of 25 % of total sugar content. Substitution of the en ligand by two molecules of ammonia, methylamine, or isopropylamine, respectively, results in the formation of different solution species. With the bulkiest ligand, isopropylamine, monometalation of the aldoses in the 1,2‐position is exclusively observed.
A Distinctive Example of the Cooperative Interplay of Structure and Environment in Tuning of Intramolecular Charge Transfer in Second‐Order Nonlinear Optical Chromophores
Authors: Abbotto Alessandro , Beverina Luca , Bradamante Silvia , Facchetti Antonio , Klein Christopher , Pagani Giorgio A. , Redi‐Abshiro Mesfin , Wortmann Rüdiger 
Published: May 2003

AbstractThe strongly enhanced cooperative influence of medium polarity and organic structural design on the first hyperpolarizability β of a novel family of highly polarizable azinium‐(CHCH‐thienyl)‐dicyanomethanido chromophores 1–3 is described. The dyes can be efficiently synthesized by regioselective protonation/alkylation of the corresponding bidentate anion precursors. Consecutive annelation of the pyridyl ring of 1 (pyridine→quinoline→acridine) and medium polarity effects are responsible for an extraordinarily variable range of intramolecular charge transfer (ICT), leading to a large set of π‐electron distribution patterns. Accordingly, systems with remarkably different zwitterionic/quinoid character in the ground and excited states present β values in a broad range, eventually switching from negative to positive. Our investigation is based on a combination of experimental (UV/Vis spectroscopy, multinuclear NMR spectroscopy, and electrooptical absorption measurements) and computational (ab initio) approaches. It is shown that: 1) β and μβ are dramatically influenced, even by orders of magnitude, by a complex, non‐monotonic interplay of structure and medium action, which in turn affects molecular ICT and bond length alternation (BLA), 2) the computations, validated by different experimental data, are to be recommended as an extremely useful tool in the search for a greatly improved set of molecular nonlinear optical (NLO) responses (in the case of 1–3 they show that such conditions may be attained only in a narrow and limited range of dielectric constants in which the annelation effect operates most efficiently), and 3) the search for the most favorable molecular NLO response of a highly polarizable chromophore both in solution and in solid matrices should simultaneously take into account not only the molecular design supplemented by annelation effects but also the polarity of the medium.
Mechanisms of Electrochemically‐Induced Retro‐Cyclopropanation Reactions of Fullerene Derivatives Using Digital Simulations
Authors: Carano Maurizio , Echegoyen Luis 
Published: May 2003

AbstractThree C60 derivatives, 1, 2 and 3, have been studied by cyclic voltammetry (CV) under high vacuum in anhydrous tetrahydrofuran (THF). The CV behavior was essentially similar to that already observed for other cyclopropanated fullerene derivatives. After the second reduction processes all compounds undergo a chemical reaction that generates another electroactive species. This “new” chemical species is likely to be the compound with the cyclopropane ring open. Differences in CV behavior were observed for the different addends. Electrochemical data obtained at different scan rates for a given potential window, were fit with the BAS digital simulation program, DigiSim. The purpose of this study was to probe the proposed mechanisms and to obtain reliable estimations of the kinetic constants for the homogeneous chemical reactions taking place during the CV experiments. Calculations at the PM3 level lend additional support to the conclusions derived from digital simulations. The proposed mechanism is similar for all the compounds and involves two main chemical reactions in a reversible square scheme.