bluuebunny/crossref_metadata_2025 huggingface dataset:
Protective effects of antioxidants on age‐related changes in the electrophoretic patterns of cardiac LDH, hepatic ALP and serum proteins in male golden hamster
Authors: El‐Zayat Emad , Amin Amer Sayed
Published: May 2003

Basal and antioxidant‐induced changes in the isoenzyme and isoform patterns of cardiac lactate dehydrogenase (EC 1.1.1.27) and hepatic alkaline phosphatase (EC 3.1.3.1), respectively, as well as the electrophoretic patterns of serum proteins in different age groups of male golden hamster were compared. This is to test whether age‐induced changes could be corrected by long‐term administration of antioxidants. Data indicated that aging causes no remarkable change in the total activity of either cardiac LDH or hepatic ALP, however a significant increase in the fractional activity of some cardiac LDH isoenzymes and a significant reduction in the fractional activity of some hepatic ALP isoforms were induced by aging. On the other hand, long‐term administration of antioxidants appeared to manifest a clear counteracting effect on the age‐related changes in old age. This effect was indicated in the fractional activity of cardiac LDH isoenzymes and of hepatic ALP isoforms. The present study has also shown a wide‐range variation in serum protein patterns due to aging and/or antioxidant administration, which indirectly reflect a parallel variation in the process of gene expression and/or proteolytic activity. Copyright © 2003 John Wiley & Sons, Ltd.
Sodium selenite modulates tumour marker indices in N‐nitrosodiethylamine‐initiated and phenobarbital‐promoted rat liver carcinogenesis
Authors: Thirunavukkarasu C. , Sakthisekaran D.
Published: May 2003

The effect of sodium selenite (Se) was investigated against two‐stage rat liver carcinogenesis initiated by a single intraperitoneal injection of N‐nitrosodiethylamine (DEN, 200 mg kg−1 i.p.) followed by promotion with phenobarbital (PB, 0.05%) in a basal diet. Se (4 p.p.m.) was administered per os daily throughout the entire experiment, before the initiation, or during the promotion stage. The plasma, liver (hepatoma and surrounding tissue) and kidney tissue were investigated biochemically for lactate dehydrogenase, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase and 5′‐nucleotidase. These enzyme activities were increased (p < 0.001) in plasma of hepatoma‐bearing rats compared with normal control rats. The elevation of these enzyme activities in plasma was indicative of the persistent deteriorating effect of DEN in cancer‐bearing animals. Aminotransferase levels were decreased in hepatoma and surrounding liver tissue, whereas lactate dehydrogenase, alkaline phosphatase and 5′‐nucleotidase were increased in the cancer condition. These enzyme activities were reversed to near normal control values in animals treated with Se. It is apparent that the beneficial effect of Se is primarily exerted on the initiation phase and secondarily during the promotion stage of DEN‐initiated rat liver carcinogenesis. The analysis of marker enzyme activities taken together with our previous findings clearly indicates the antitumour efficacy of sodium selenite on DEN‐induced hepatoma animals. Copyright © 2003 John Wiley & Sons, Ltd.
Arachidonic acid cytotoxicity: can arachidonic acid be a physiological mediator of cell death?
Authors: Pompeia Celine , Lima Thais , Curi Rui
Published: May 2003

Arachidonic acid is a polyunsaturated fatty acid that mediates inflammation and the functioning of several organs and systems either directly or upon its conversion into eicosanoids. However, arachidonic acid is found to be cytotoxic in vitro at concentrations that overlap physiological ones. It is tempting therefore to speculate that arachidonic acid may be a physiological inducer of apoptosis and that such cytotoxic action may be another of its roles in vivo. Nevertheless its pro‐inflammatory and oxidative stress‐inducing features are characteristic of necrosis and pathological conditions. We hereby review the cytotoxic action of arachidonic acid, indicate the possible pathways that lead to cell death and contemplate the cytotoxic role of arachidonic acid in vivo. Copyright © 2003 John Wiley & Sons, Ltd.
Experimental researches on the role of phosphoinositide‐specific phospholipase C in 4‐hydroxynonenal induced exocytosis
Authors: Maggiora Marina , Armida Rossi Maria
Published: May 2003

The action of 4‐hydroxynonenal (HNE), a chemotactic aldehyde produced by lipid peroxidation, was analysed on exocytosis in parallel with its effects on phosphoinositide‐specific phospholipase C (PLC) both in undifferentiated HL‐60 cells and in cells induced to differentiate toward the granulocytic cell line by 1.25% DMSO. Exocytosis was evaluated by the secretion of β‐glucuronidase from cells incubated at 37°C for 10 min in the presence of various aldehyde concentrations. HNE action was more pronounced in DMSO‐differentiated cells, where concentrations between 10−8 and 10−6 m were able both to trigger exocytosis and to strongly activate PLC; in both processes maximal stimulation was given by 10−7 m. HNE‐induced exocytosis was completely prevented by pertussis toxin and by the PLC inhibitor U73122. The comparison between HNE and formyl‐methionyl‐leucyl‐phenylalanine (fMLP), used as a positive control, showed that the tripeptide produced an higher stimulation of exocytosis than the aldehyde; by contrast HNE induced a stronger increase of PLC activity. Wortmannin, an inhibitor of phosphatidylinositol‐3‐kinase (PI3K), strongly inhibited the exocytosis induced by fMLP, while it failed to induce a statistically significant inhibition of HNE action. We conclude that both compounds trigger exocytosis through a Ptx‐sensitive G protein; the present data support the hypothesis that the lower ability of the aldehyde to trigger exocytosis as compared to fMLP might depend upon a low ability to activate PI3K, while PLC activation appears to play a key role in HNE‐induced exocytosis. Copyright © 2003 John Wiley & Sons, Ltd.
Trypsin induces tumour necrosis factor‐α secretion from a human leukemic mast cell line
Authors: Kang Ok‐Hwa , Jeong Hyun‐Ja , Kim Dae‐Ki , Choi Suck‐Chei , Kim Tae‐Hyun , Nah Yong‐Ho , Kim Hyung‐Min , Lee Young‐Mi
Published: May 2003

Trypsin activating both proteinase‐activated receptor (PAR) 2 and PAR4 plays an important role in inflammation. We have investigated the potential of trypsin to induce TNF‐α secretion from the human leukemic mast cell line (HMC‐1). HMC‐1 cells co‐express both PAR2 and PAR4, and their agonist trypsin signals to HMC‐1 cells. Trypsin (100 nm), SLIGKV‐NH2 (100 μm, corresponding to the PAR2 tethered ligand), or GYPGQV‐NH2 (100 μm, corresponding to the PAR4 tethered ligand) induced tumour necrosis factor (TNF)‐α secretion from HMC‐1 cells. TNF‐α secretion by trypsin was significantly blocked by pretreatment with 50 μm PD098059, MEK‐1 inhibitor. Furthermore, trypsin stimulated the activation of extracellular signal‐regulated kinase (ERK) in HMC‐1 cells without any detectable activation of c‐Jun N‐terminal kinase (JNK) and p38 MAP kinase homologue. These results show that trypsin may induce TNF‐α secretion following activation of ERK via both PAR2 and PAR4 on HMC‐1 cells. Copyright © 2003 John Wiley & Sons, Ltd.
Effects of vitamin E on microsomal Ca2+‐ATPase activity and calcium levels in streptozotocin‐induced diabetic rat kidney
Authors: Doǧru Pekiner Bilgehan , Daş Evcimen Net , Ulusu Nuray N. , Bali Musa , Karasu Çimen
Published: May 2003

Vitamin E treatment has been found to be beneficial in preventing or reducing diabetic nephropathy. Increased tissue calcium and abnormal microsomal Ca2+‐ATPase activity have been suggested as contributing factors in the development of diabetic nephropathy. This study was undertaken to test the hypothesis that vitamin E reduces lipid peroxidation and can prevent the abnormalities in microsomal Ca2+‐ATPase activity and calcium levels in kidney of streptozotocin (STZ)‐induced diabetic rats. Male rats were rendered diabetic by a single STZ injection (55 mg kg−1 i.p.). After diabetes was verified, diabetic and age‐matched control rats were untreated or treated with vitamin E (400–500 IU kg−1 day−1, orally) for 10 weeks. Ca2+‐ATPase activity and lipid peroxidation (MDA) were determined spectrophotometrically. Blood glucose levels increased approximately five‐fold (> 500 mg dl−1) in untreated‐diabetic rats but decreased to 340±27 mg dl−1 in the vitamin E treated‐diabetic group. Kidney MDA levels did not significantly change in the diabetic state. However, vitamin E treatment markedly inhibited MDA levels in both control and diabetic animals. Ca2+‐ATPase activity was 0.483±0.008 U l−1 in the control group and significantly increased to 0.754±0.010 U l−1 in the STZ‐diabetic group (p < 0.001). Vitamin E treatment completely prevented the diabetes‐induced increase in Ca2+‐ATPase activity (0.307±0.025 U l−1, p < 0.001) and also reduced the enzyme activity in normal control rats. STZ‐diabetes resulted in approximately two‐fold increase in total calcium content of kidney. Vitamin E treatment led to a significant reduction in kidney calcium levels of both control and diabetic animals (p < 0.001). Thus, vitamin E treatment can lower blood glucose and lipid peroxidation, which in turn prevents the abnormalities in kidney calcium metabolism of diabetic rats. This study describes a potential biochemical mechanism by which vitamin E supplementation may delay or inhibit the development of cellular damage and nephropathy in diabetes. Copyright © 2003 John Wiley & Sons, Ltd.
The inhibitory effect of BSP‐A1/‐A2 on protein kinase C and tyrosine protein kinase
Authors: Yu Bingzhi , Zhao Yongmei , Zhao Wei , Chen Fei , Liu Ying , Zhang Jie , Fu Wei , Zong Zhihong , Yu Aiming , Guan Yi
Published: May 2003

Bovine seminal plasma contains a group of similar proteins, namely BSP‐A1, BSP‐A2, BSP‐A3, and BSP‐30‐kDa (collectively called BSP proteins), and they are secreted by the seminal vesicles. In our study, we purified the BSP‐A1/‐A2 through affinity chromatography and found for the first time that BSP‐A1/‐A2 can inhibit the activity of protein kinase C (PKC) and tyrosine protein kinase (TPK). The inhibition was dose dependent. When the PKC and TPK activities are expressed as the logarithm of percentage activity taking the activity in the absence of the BSP‐A1/‐A2 as 100%, there is a linear relationship between the their activities and the dose of BSP‐A1/‐A2. Copyright © 2003 John Wiley & Sons, Ltd.
Prolonged effect of a single serotonin treatment in adult age on the serotonin and histamine content of white blood cells and mast cells of rats
Authors: Csaba G. , Kovács P. , Pállinger Éva
Published: May 2003

Hormonal imprinting was provoked by serotonin treatment in adult age. Three weeks after treatment with 100 μg serotonin, the serotonin and histamine content of peritoneal cells (mast cells, lymphocytes and the monocyte–macrophage–granulocyte group), white blood cells (lymphocytes, granulocytes and monocytes) and thymic lymphocytes was studied by flow cytometry. The content of both amines was significantly higher in the mast cells of males and lower in females. Blood lymphocytes contained a higher serotonin and histamine level in males, and a lower serotonin level in females. The peritoneal monocyte–macrophage–granulocyte group contained less serotonin in both males and females. Thymocytes contained higher levels of both amines in females and higher histamine level in males. The experiments demonstrate that a single treatment at adult age can provoke imprinting, which alters—in the present case—the serotonin and histamine content of immune cells durably. Copyright © 2003 John Wiley & Sons, Ltd.
Effects of indomethacin on the divisional morphogenesis and cytoskeleton‐dependent processes of Tetrahymena
Authors: Kovács Péter , Pállinger Éva
Published: May 2003

Indomethacin (0.1 mM) causes significantly altered phospholipid synthesis in Tetrahymena and is able to influence the inositol phospholipid signalling system.9 In the present study the effects of indomethacin on the course of cell division, cyclin expression, the cortical microtubular system and on cytoskeleton‐dependent processes (motility, phagocytosis) were investigated. As expected from its interference with the synthesis of phospholipids, indomethacin affected Tetrahymena in a number of ways: the structure of the cortical microtubular system became irregular; in many cells the stomatogenesis (development of new oral apparatus) and the development of the fission furrow was not accompanied by elongation of the macronucleus, which is a typical phenomenon of the normal course of mitosis: apparently indomethacin uncouples these phenomena. After indomethacin treatment, the expression of both cyclin A and cyclin B1 were reduced significantly. The cell growth rate, motility and phagocytotic activity were all considerably reduced. There are probably additional mechanisms responsible for the effect of indomethacin on the systems that control divisional morphogenesis, for microtubule‐dependent processes and for the connection between nuclear and cortical alterations during the cell cycle. Effects on protein phosphorylation/dephosphorylation, on cyclin expression and on microtubular functions are probably involved. These possibilities are discussed. Copyright © 2003 John Wiley & Sons, Ltd.
Comparison of the Chemical Properties of Iron and Cobalt Porphyrins and Corrins
Authors: Jensen Kasper P. , Ryde Ulf
Published: May 2003

Density functional calculations have been used to compare various geometric, electronic and functional properties of iron and cobalt porphyrin (Por) and corrin (Cor) species. The investigation is focussed on octahedral MII/III complexes (where M is the metal) with two axial imidazole ligands (as a model of b and c type cytochromes) or with one imidazole and one methyl ligand (as a model of methylcobalamin). However, we have also studied some five‐coordinate MII complexes with an imidazole ligand and four‐coordinate MI/II complexes without any axial ligands as models of other intermediates in the reaction cycle of coenzyme B12. The central cavity of the corrin ring is smaller than that of porphine. We show that the cavity of corrin is close to ideal for low‐spin CoIII, CoII, and CoI with the axial ligands encountered in biology, whereas the cavity in porphine is better suited for intermediate‐spin states. Therefore, the low‐spin state of Co is strongly favoured in complexes with corrins, whereas there is a small energy difference between the various spin states in iron porphyrin species. There are no clear differences for the reduction potentials of the octahedral complexes, but [CoICor] is more easily formed (by at least 40 kJ mole−1) than [FeIPor]. Cobalt and corrin form a strong CoC bond that is more stable against hydrolysis than iron and porphine. Finally, FeII/III gives a much lower reorganisation energy than CoII/III; this is owing to the occupied d orbital in CoII. Altogether, these results give some clues about how nature has chosen the tetrapyrrole rings and their central metal ion.
Signaling Effects of Demethylasterriquinone B1, a Selective Insulin Receptor Modulator
Authors: Webster Nicholas J. G. , Park Kaapjoo , Pirrung Michael C.
Published: May 2003

A possible breakthrough in the treatment of diabetes was made with the discovery that a fungal natural product, demethylasterriquinone B1 (DAQ B1), is an orally active, small‐molecule mimic of insulin. Subsequent work has shown that the glucose‐lowering effects of DAQ B1 are not accompanied by enhanced vascular proliferation, which is a side effect of chronic insulin administration that can lead to arteriosclerosis. Our recent short and modular total synthesis of DAQ B1 could be readily modified to create congeners and afforded ample supplies of the natural product, which permitted intracellular signal transduction of DAQ B1 to be examined. The activities of DAQ B1 and over a dozen related structures were studied for insulin receptor (IR) and insulin receptor substrate‐1 phosphorylation. Examination of the effect of DAQ B1 on kinases downstream of the IR in insulin signal transduction showed selective activation of Akt kinase (a metabolic effect) but not of extracellular‐regulated kinase (a proliferative effect). The influence of DAQ B1 on gene expression (determined by a microarray study) was also divergent from that of insulin, which activates both proliferative and metabolic pathways. The action of DAQ B1 as a selective insulin receptor modulator can be accounted for by its ability to selectively activate one kinase among the many emanating from insulin receptor autophosphorylation and its reduced effects on gene expression.
Indolocarbazole Glycosides in Inactive Conformations
Authors: Facompré Michaël , Carrasco Carolina , Vezin Hervé , Chisholm John D. , Yoburn Joshua C. , Van Vranken David L. , Bailly Christian
Published: May 2003

Indolocarbazole glycosides related to rebeccamycin represent a promising category of antitumor agents targeting DNA and topoisomerase I. These drugs prefer to adopt a closed conformation with an intramolecular hydrogen bond between the indole NH group and the pyranose oxygen atom. Three pairs of indolocarbazole monoglycosides bearing an NH or an N‐methyl indole moiety were synthesized and their biological properties investigated at the molecular and cellular level. Replacing the indole NH proton with a methyl group reduces DNA interaction and abolishes activity against DNA topoisomerase I. Surface plasmon resonance studies performed with a pair of water‐soluble indolocarbazole glycosides and two hairpin oligonucleotides containing an [AT]4 or a [CG]4 sequence indicate that both the NH and the N‐methyl derivative maintain a relatively high affinity for DNA (Keq=2–6×105 M−1) but the incorporation of the methyl group restricts access to the DNA. The number of ligand binding sites (n) on the oligonucleotides is about twice as high for the NH compound compared to its N‐methyl analogue. Modeling and 1H NMR studies demonstrate that addition of the N‐methyl group drives a radical change in conformation in which the orientation of the aglycone relative to the β‐glucoside is reversed. The loss of the closed conformation by the N‐methyl derivatives perturbs thir ability to access DNA binding sites and prevents the drug from inhibiting topoisomerase I. As a consequence, the NH compounds exhibit potent cytotoxicity against CEM leukemia cells with an IC50 value in the 1 μM range, whereas the N‐methyl analogues are 10 to 100 times less cytotoxic. These studies offer circumstantial evidence supporting the importance of the closed conformation in the interaction of indolocarbazole glycosides with their molecular targets, DNA and topoisomerase I.
Monitoring the Cellular Surface Display of Recombinant Proteins by Cysteine Labeling and Flow Cytometry
Authors: Jose Joachim , Handel Steffen
Published: May 2003

A general method is described that allows one to follow the surface display of recombinant proteins in Escherichia coli without having to use specific antibodies or enzymatic reactions. The method is based on cysteine‐specific labeling through Michael addition to the double bond of maleimide and its derivatives, and takes advantage of the fact that naturally occurring surface proteins in E. coli contain no accessible cysteine residues. The method is easy to perform and could be simply applied to different analytic procedures including Western blot, spectral photometry, and flow cytometry. By using this new labeling method, single cells bearing a distinct protein at the surface could be selected by fluorescence‐activated cell sorting. The data were obtained by using autodisplay, an efficient surface display system established for E. coli, but the method presented here represents rather a general solution for analyzing the surface display of recombinant proteins, independent of the cellular system used.
Aspartic Proteases Involved in Alzheimer's Disease
Authors: Schmidt Boris
Published: May 2003

Alzheimer's disease afflicts every tenth human aged over 65. Despite the dramatic progress that has been made in understanding the disease, the exact cause of Alzheimer's disease is still unknown. Most gene mutations associated with Alzheimer's disease point at the same culprits: amyloid precursor protein and ultimately amyloid β. The enigmatic proteases α‐,β‐, and γ‐secretase are the three executioners of amyloid precursor protein processing, and disruption of their delicate balance is suspected to result in Alzheimer's disease. Significant progress has been made in the selective control of these proteases, regardless of the availability of structural information. Not even the absence of a robust cell‐free assay for γ‐secretase could hamper the identification of nonpeptidic inhibitors of this enzyme for long. Within five years, four distinctly different structural moieties were developed and the first drug candidates are in clinical trials. Unfortunately, selective inhibition of amyloid β formation remains a crucial issue because fundamental fragments of the γ‐secretase complex are important for other signaling events. This problem makes β‐secretase inhibition and α‐secretase induction even more appealing.
Large‐Scale In Vivo Synthesis of the Carbohydrate Moieties of Gangliosides GM1 and GM2 by Metabolically Engineered Escherichia coli
Authors: Antoine Tatiana , Priem Bernard , Heyraud Alain , Greffe Lionel , Gilbert Michel , Wakarchuk Warren W. , Lam Joseph S. , Samain Eric
Published: May 2003

Two metabolically engineered Escherichia coli strains have been constructed to produce the carbohydrate moieties of gangliosides GM2 (GalNAcβ‐4(NeuAcα‐3)Galβ‐4Glc; Gal=galactose, Glc=glucose, Ac=acetyl) and GM1 (Galβ‐3GalNAcβ‐4(NeuAcα‐3)Galβ‐4Glc. The GM2 oligosaccharide‐producing strain TA02 was devoid of both β‐galactosidase and sialic acid aldolase activities and overexpressed the genes for CMP‐NeuAc synthase (CMP=cytidine monophosphate), α‐2,3‐sialyltransferase, UDP‐GlcNAc (UDP=uridine diphosphate) C4 epimerase, and β‐1,4‐GalNAc transferase. When this strain was cultivated on glycerol, exogenously added lactose and sialic acid were shown to be actively internalized into the cytoplasm and converted into GM2 oligosaccharide. The in vivo synthesis of GM1 oligosaccharide was achieved by taking a similar approach but using strain TA05, which additionally overexpressed the gene for β‐1,3‐galactosyltransferase. In high‐cell‐density cultures, the production yields for the GM2 and GM1 oligosaccharides were 1.25 g L−1 and 0.89 g L−1, respectively.
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

Enzymatic 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

[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

The 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

Over 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.
Heat Transfer in Catalytic Fixed‐Bed Reactors with a Gas Flow, Characterized through Low Tube/Particle Diameter Ratios
Authors: Bauer M. , Adler R.
Published: May 2003

Heat transfer in charge layers has been a subject of research for many decades. Progress has been made but calculation methods, specifically with regard to forecasting heat transfer processes in catalyst‐filled tubular reactors for low tube/particle diameter ratios and low flow rates, still lack in accuracy. In this study, previously open issues of heat transfer in such reactors could be clarified by using a new examination and evaluation strategy. As a result, very simple, semi‐empirical correlations were formulated for the effective thermal conductivity of the fixed bed, and for the wall heat transfer coefficient.
Determination of the Zeta Potential of a Filter Cake by Means of Permeation Experiments
Authors: Weber K. , Stahl W.
Published: May 2003

So far, the zeta potential has been determined by using the microelectrophoresis method, the ESA (electrokinetic sonic amplitude) method or ultrasonic spectroscopy. A main drawback of these measuring techniques is that the measured potentials can only be understood as approximations. This paper presents a possibility of calculating the zeta potential of a filter cake from permeation experiments by considering the influence of an electric field. Further research work has to be conducted, though, to verify this method.
Prediction of Centrifugal Deliquoring for Changing Particle Composition
Authors: Stiborsky M. , Anlauf H.
Published: May 2003

A better understanding of the influence of particle size distribution on mechanical deliquoring in a centrifugal field is attempted. Based on well‐known models, the influence of the entire particle size distribution on filtering deliquoring in the centrifugal field was studied. A second objective is to develop a procedure in order to minimize the necessary experimental effort to characterize materials with variable particle size distributions.
Integrated Product Modelling of Special Forms in Vessel and Pipeline Construction
Authors: Köhler P. , Strohmeier O.
Published: May 2003

The launch of efficient parametric CAx‐systems and a constant engineering data management system are the current objectives of many enterprises. Investigations of a number of commercial CAD systems and their sheet metal tools showed that two weak points needed to be eliminated, they had to be compensated for in the field of the sheet metal design. In view of the application, three major tasks had to be solved: layout of suitable construction and geometry features, balancing of weaknesses of the CAD systems for the attention of differential‐geometrical boundary conditions with the generation of rule surfaces, and the development of special forms of the sheet metal tools in the CAD systems.
Investigations of Catalytic Activity of Nonnoble Metal Catalysts for the Electrochemical Reduction of Oxygen
Authors: Lindermeir A. , Mecklenburg A. , Rosenthal G. , Kunz U. , Hoffmann U.
Published: May 2003

Nonnoble metal catalysts are discussed as an appropriate alternative to conventional noble metal compounds in fuel cell systems. Two different kinds of catalysts based on iron phthalocyanine and iron sulfate are prepared and characterized for the electrochemical oxygen reduction. Both types show catalytic activity depending on the conditions of preparation.
Selective Hydrogenation of 4‐Substituted Phenols to the Cyclohexanone Analogues – Catalyst Optimization and Kinetics
Authors: Wydra M. , Vogel H.
Published: May 2003

4‐position substituted cyclohexanones are of great importance as key intermediates for the synthesis of liquid‐crystal materials. Unsubstituted cyclohexanone can be manufactured by the selective hydrogenation of phenol. Industrial processes exist, in which phenol is hydrogenated by a heterogeneous catalyst in the vapor or liquid phase melt with high selectivity leading to high amounts of cyclohexanone. However, very little kinetic data exists to date for the selective hydrogenation of phenol and the cresols in an inert solvent. The aim of this work is to optimize the selective liquid‐phase hydrogenation of 4‐(4′‐trans‐n‐propylcyclohexyl)‐phenol.
Production of Emulsions in High‐Pressure Homogenizers – Part I: Disruption and Stabilization of Droplets
Authors: Tesch S. , Freudig B. , Schubert H.
Published: May 2003

In continuous mechanical emulsification, disruption and stabilization of droplets determine the resulting droplet size and, thus, the emulsion’s microstructure. Without the need of adding any stabilizer, w/o emulsions provide the possibility of a high viscosity of the continuous phase and, in consequence, of decreasing the probability of coalescence. The present work presents investigations on the production of w/o emulsions in high‐pressure homogenizers: the different geometries of standard valve, microfluidizer and orifice valve are compared to each other with reference to disruption and stabilization of droplets.
Design of Spring Loaded Safety Valves with Inlet and Discharge Pipe against Chatter in the Case of Gas Flow
Authors: Cremers J. , Friedel L.
Published: May 2003

Pressure loaded installations are often protected against overpressure by spring loaded full lift safety valves. Damage to the relief valve itself or to the piping and equipment can result from the so called ‘chattering’ of the relief valve during discharge. With all sizing rules a maximum allowable inlet pipe length can be calculated for which no chatter should occur. Experiments have been performed with the objective of checking the validity of these rules. The result is that none of the sizing rules is capable of predicting the safe allowable inlet pipe lengths for all given experimental conditions. Based also on experimental results taken from the literature, a modified pressure surge sizing method is recommended.
Coupled Pressure Pulse (CPP) Recleaning System for Ceramic Hot‐Gas Filters with an Integrated Safety Filter
Authors: Mai R. , Leibold H. , Seifert H. , Heidenreich S. , Haag W. , Walch A.
Published: May 2003

In order to ensure that the positive properties of ceramic filter elements are guaranteed in a safe mode of operation, ceramic filter candles have been equipped with a safety filter as an integral component of a newly developed recleaning system. Compared to the conventional jet pulse recleaning method, the so‐called coupled pressure pulse recleaning technique offers significant advantages: higher recleaning intensities at low recleaning pressure, reduced capital costs and operating expenses as well as safe and stable operation in the case of candle failure.
Liquid Flow on Structured Packing: CFD Simulation and Experimental Study
Authors: Szulczewska B. , Zbicinski I. , Górak A.
Published: May 2003

A 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

In 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.
Geometric Calculations for the Spiral Heat Exchanger
Authors: Dongwu W.
Published: May 2003

The present paper deals with the calculation methods for semicircled spirals, from which are derived the geometric calculating formulas for spiral heat exchangers. This series of formulas are characterized by their universality, accuracy, and convenience.
On the Degradation and Stabilization of Poly(Methyl Methacrylate) in a Continuous Process
Authors: Nising P. , Zeilmann T. , Meyer T.
Published: May 2003

Thermally 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

Flexible 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

Cu/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

The 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

A 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

The 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

Novel 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

The 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.