bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of stresses around beads in stressed epoxy resin by photoelasticity
Authors: Pawlak Andrzej , Galeski Andrzej
Published: September 2002

Microphotoelasticity gives the possibility of determining stresses in systems with small inclusions. We studied four systems with the same matrix (epoxy resin) and different inclusions of spherical shapes. The distributions of stresses and pressure, after the application of external tensile forces, were determined. In a matrix with a hard inclusion, tensile stresses concentrated at the pole. For a soft inclusion, that is, a poly(vinyl acetate) bead or an air bubble, the tensile stresses concentrated at the equator with some compression at the pole. The soft inclusion promoted the stress relaxation by the change in its shape. In the matrix with a stiff inclusion, such as a steel or glass bead, debonding was observed at the interface near the pole area. In such a case, the stress concentration region moved toward the tip of the debonding. For a hard inclusion, the pressure at all points of the interface was negative, and the maximum was found at the pole near the inclusion surface from −6 to −10 MPa. This region was sensitive to the initiation of destruction processes such as cavitation and debonding. For a soft inclusion, the pressures at the pole and equator were comparable, but the signs were opposite, being positive at the pole (compression) and negative at the equator (expansion). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1436–1444, 2002
Ion exchange in (BO)2.4I3 microcrystals: A method for obtaining colorless, transparent, metallically conductive polymer films
Authors: Tracz Adam
Published: September 2002

I obtained colorless, transparent, metallically conductive polymer films by anion exchange in the microcrystals of (BO)2.4I3 [BO = bis(ethylenedioxytetrathiafulvalene)], forming the conductive network in surface‐conducting reticulate‐doped polycarbonate (PC) films. Strongly absorbing I3− anions were replaced by I− or Br− anions, showing weaker absorption in visible light. Interestingly, this transformation proceeded without deterioration of the continuity of the network, and even the shape of the microcrystals was preserved. Particularly, the salt (BO)2.4I3 could be transformed to (BO)2Br(H2O)3 or to (BO)2I(H2O)x. I achieved this by immersing strongly colored PC/(BO)2.4I3 films in the KBr solution or by contact with a Cu plate in KI solution. Depending on the conditions of the ion‐exchange reaction, colorless films showing metallic conductivity down to helium temperatures or showing semiconducting behavior below 100 K were obtained. Electrical properties of some systems are very sensitive to the partial pressure of water. The (BO)2Br(H2O)3 and (BO)2I(H2O)x microcrystals could reversibly change their water content, as shown by comparative X‐ray diffraction and electrical studies performed under reduced pressure or dry atmosphere and under ambient conditions. The controlled anion exchange presented in this article can be considered as a new effective way of modifying the polycrystalline networks of (BO)2.4I3 and other similar salts. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1465–1472, 2002
Recycling of postconsumer poly(ethylene terephthalate) and high‐density polyethylene by compatibilized blending
Authors: Pawlak A. , Morawiec J. , Pazzagli F. , Pracella M. , Galeski A.
Published: September 2002

Two ways of recovering the properties of the scrap plastics poly(ethylene terephthalate) (PET) and high‐density polyethylene (HDPE) were analyzed: (1) blending incompletely segregated polymers with a compatibilizer and (2) blending nonsegregated polymers with a small amount (2 pph) of another compatibilizer. The advancement of the compatibilization reaction in a twin‐screw extruder depended on the residence time and intensity of mixing according to melt viscosity measurements and scanning electron microscopy observations. The acceptable mechanical properties for systems with different PET contents were obtained in blends compatibilized with ethylene–glycidyl methacrylate (EGMA) and styrene–ethylene–butylene–styrene grafted with maleic anhydride. For a blend with 75% PET and 25% HDPE, the optimum content of EGMA was determined to be about 4 pph, and a film was produced with this composition. Admixtures present in recycled HDPE migrated to PET during blending and accelerated the hydrolysis of PET. As a result of migration, differences in the mechanical properties of the blends were observed, depending on the brand of recycled HDPE used. EGMA was also successfully used for the improvement of mechanical properties of a nonsegregated mixture based on PET. Tensile properties of two compatibilized PET‐rich and HDPE‐rich commingled scraps indicated the possibility of using these blends for film extrusion, with potential applications in the packaging of technical products. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1473–1485, 2002
Polylactide/montmorillonite nanocomposites and microcomposites prepared by melt blending: Structure and some physical properties
Authors: Pluta M. , Galeski A. , Alexandre M. , Paul M.‐A. , Dubois P.
Published: September 2002

Polylactide (PLA)/clay nanocomposites loaded with 3 wt % organomodified montmorillonite and PLA/clay microcomposites containing 3 wt % sodium montmorillonite were prepared by melt blending. We investigated the morphology and thermal properties of the nanocomposites and microcomposites and compared them with unfilled PLA, keeping the same thermomechanical history. The influence of the processing temperature on the structural characteristics of the investigated systems was determined. The investigations were performed with differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X‐ray diffraction (XRD), size exclusion chromatography (SEC), and polarized light microscopy (LM). XRD showed that the good affinity between the organomodified clay and the PLA was sufficient to form intercalated structure in the nanocomposite. The microcomposite featured a phase‐separated constitution. DSC and LM studies showed that the nature of the filler affected the ordering of the PLA matrix at the molecular and supermolecular levels. According to TGA, the PLA‐based nanocomposites exhibited improvement in their thermal stability in air. Reduced flammability, together with char formation, was also observed for nanocomposites, compared to the microcomposites and pure PLA. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1497–1506, 2002
Development of the coronary blood supply: Changing concepts and current ideas
Authors: Bernanke David H. , Velkey J. Matthew
Published: September 2002

Earlier views of the development of the coronary vasculature included angiogenic budding and growth of arteries from the aortic sinuses and veins from the coronary sinus. The current concept begins with the establishment of the epicardium from the proepicardial organ, an outgrowth of the dorsal wall of the pericardial cavity. Capillaries form in a subepicardial mesenchymal population, extending as a plexus toward the truncus arteriosus and the atria. Multiple vessels grow from a peritruncal ring of capillaries, preferentially invading the newly formed aorta. In a process involving apoptotic changes of both the aortic wall and the invading capillaries, orifices open at the level of the aortic sinuses. Smooth muscle cells and pericytes, recruited from the surrounding mesenchyme, contribute to the vessel walls, and the definitive coronary artery pattern is established. Similar events are occurring on the venous side of the coronary circulation, following a slightly earlier time course. Multiple factors govern this process, including VEGF and FGF‐1 stimulating vasculogenesis and angiogenesis, and the angiopoietins and their tyrosine kinase receptors modulating interactions between endothelial cells and the mural components. As remodeling of the capillary plexus and the coronary orifices progresses, TGFβ released by apoptotic cells or from other sources likely modulates VEGF and FGF‐1, and also contributes to further apoptotic changes. A better appreciation of the controls of the mechanisms of coronary vessel development may direct further research in the prevention of arteriosclerosis and ischemic tissue injuries. Anat Rec (New Anat) 269:198–208, 2002. © 2002 Wiley‐Liss, Inc.
Magnetic anisotropy of the radula of chiton Acanthochiton rubrolinestus LISCHKE
Authors: Qian Xia , Zhao Jian‐gao , Liu Chuan‐lin , Guo Cheng‐hua
Published: September 2002

The magnetic anisotropy of the whole radula, the major lateral radula teeth, and magnetic material in the major lateral radula teeth of the chiton Acanthochiton rubrolinestus LISCHKE have been studied by a magnetic torque meter and superconducting quantum interference device (SQUID) magnetometer. The length and width axes of the teeth are the easily magnetized axes, while the thickness axis is difficult to magnetize. The width and thickness axes of the radula are the easily magnetized axes, and the length axis is difficult to magnetize. The measurement results of the whole radula and the major lateral radula teeth agree well with each other. The magnetic anisotropy of the magnetic material is given as well as a possible distribution of the magnetic material in the major lateral radula teeth. Bioelectromagnetics 23:480–484, 2002. © 2002 Wiley‐Liss, Inc.
Bioelectrical parameters of the whole human body obtained through bioelectrical impedance analysis
Authors: Lafargue Alcibiades Lara , Cabrales Luis Bergues , Larramendi Ricardo Morales
Published: September 2002

Knowledge of electrical properties of body tissues across the frequency spectrum is useful for tissue characterization. The bioelectric impedance analysis method, operating from 1 to 250 kHz (multi‐frequency), was used in 23 normal male human subjects between the ages of 21 and 52 years, for estimation of their bioelectrical parameters. Amplitude of the output current was set to 800 μARMS. The experimental data showed that bioelectric parameters were highly dependent on frequency and the presence of a threshold frequency around 4 kHz. In order to explain the unusual features observed in our experimental data, the human body was simulated through the Cole–Fricke–Cole model (RC circuit) and the Extended Cole–Fricke–Cole model (RLC circuit). The simulated data showed that the Extended Cole–Fricke–Cole model had a higher accuracy than the traditional Cole–Fricke–Cole model. These results suggest that the unusual features could be due to the possible existence of inductive effects in biological cells and body tissues and that the inductive parameter and the threshold frequency could be used for characterizing the healthy tissues as well as the traditional bioelectric parameters. © 2002 Wiley‐Liss, Inc. Bioelectromagnetics 23:450–454, 2002. © 2002 Wiley‐Liss, Inc.
Effects of non‐uniform static magnetic fields on the rate of myosin phosphorylation
Authors: Engström Stefan , Markov Marko S. , McLean Michael J. , Holcomb Robert R. , Markov Julia M.
Published: September 2002

The effect on myosin phosphorylation from exposure to a magnetic field generated by an array of four permanent magnets was investigated. Two lateral positions in the non‐uniform field over the array were explored, each at four vertical distances over the surface of the device. The rate of myosin phosphorylation was found to depend on the position laterally over the array as well as the distance from the device surface. The square magnet array was comprised of axially magnetized, cylindrical NdFeB permanent magnets arranged with poles of alternating polarity in a plane (MagnaBloc™ therapeutic device). Detailed dosimetry of the magnet array was compiled: the magnetic flux density averaged over the exposure volume spanned the range 0.7–86 mT for the eight different exposure positions. The corresponding range for the absolute field gradient was 0.4–20 T/m. Comparing the dosimetry to the experimental outcome, our results imply that magnetic field amplitude alone is not sufficient to describe the influence of the field in this preparation. Bioelectromagnetics 23:475–479, 2002. © 2002 Wiley‐Liss, Inc.
Determination of safety distance limits for a human near a cellular base station antenna, adopting the IEEE standard or ICNIRP guidelines
Authors: Cooper Justin , Marx Bernd , Buhl Johannes , Hombach Volker
Published: September 2002

This paper investigates the minimum distance for a human body in the near field of a cellular telephone base station antenna for which there is compliance with the IEEE or ICNIRP threshold values for radio frequency electromagnetic energy absorption in the human body. First, local maximum specific absorption rates (SARs), measured and averaged over volumes equivalent to 1 and to 10 g tissue within the trunk region of a physical, liquid filled shell phantom facing and irradiated by a typical GSM 900 base station antenna, were compared to corresponding calculated SAR values. The calculation used a homogeneous Visible Human body model in front of a simulated base station antenna of the same type. Both real and simulated base station antennas operated at 935 MHz. Antenna‐body distances were between 1 and 65 cm. The agreement between measurements and calculations was excellent. This gave confidence in the subsequent calculated SAR values for the heterogeneous Visible Human model, for which each tissue was assigned the currently accepted values for permittivity and conductivity at 935 MHz. Calculated SAR values within the trunk of the body were found to be about double those for the homogeneous case. When the IEEE standard and the ICNIRP guidelines are both to be complied with, the local SAR averaged over 1 g tissue was found to be the determining parameter. Emitted power values from the antenna that produced the maximum SAR value over 1 g specified in the IEEE standard at the base station are less than those needed to reach the ICNIRP threshold specified for the local SAR averaged over 10 g. For the GSM base station antenna investigated here operating at 935 MHz with 40 W emitted power, the model indicates that the human body should not be closer to the antenna than 18 cm for controlled environment exposure, or about 95 cm for uncontrolled environment exposure. These safe distance limits are for SARs averaged over 1 g tissue. The corresponding safety distance limits under the ICNIRP guidelines for SAR taken over 10 g tissue are 5 cm for occupational exposure and about 75 cm for general‐public exposure. Bioelectromagnetics 23:429–443, 2002. © 2002 Wiley‐Liss, Inc.
Contact voltage measured in residences: Implications to the association between magnetic fields and childhood leukemia
Authors: Kavet Robert , Zaffanella Luciano E.
Published: September 2002

We measured magnetic fields and two sources of contact current in 36 homes in Pittsfield, MA. The first source, VP–W, is the voltage due to current in the grounding wire, which extends from the service panel neutral to the water service line. This voltage can cause contact current to flow upon simultaneous contact with a metallic part of the water system, such as the faucet, and the frame of an appliance, which is connected to the panel neutral through the equipment‐grounding conductor. The second is VW–E, the voltage between the water pipe and earth, attributable to ground currents in the water system and magnetic induction from nearby power lines. In homes with conductive water systems and drains, VW–E can produce a voltage between the faucet and drain, which may produce contact current into an individual contacting the faucet while immersed in a bathtub. VP–W was not strongly correlated to the magnetic field (both log transformed) (r = 0.28; P < 0.1). On the other hand, VW–E was correlated to the residential magnetic field (both log transformed) (r = 0.54; P < 0.001), with the highest voltages occurring in homes near high voltage transmission lines, most likely due to magnetic induction on the grounding system. This correlation, combined with both frequent exposure opportunity for bathing children and substantial dose to bone marrow resulting from contact, lead us to suggest that contact current due to VW–E could explain the association between high residential magnetic fields and childhood leukemia. Bioelectromagnetics 23:464–474, 2002. © 2002 Wiley‐Liss, Inc.
Melanophore aggregation in strong static magnetic fields
Authors: Testorf Martin F. , Åke Öberg P. , Iwasaka Masakazu , Ueno Shoogo
Published: September 2002

Contradicting results can be found in the literature on effects from magnetic exposure to pigment cells. We have studied the influence of strong, static, homogenous magnetic fields of 8 and 14 T on melanophore aggregation during exposure to the field. Melanophores, black pigment cells, in fish are large flat cells having intracellular black pigment granules. Due to large size, high optical contrast, and quick response to drugs, melanophores are attractive as biosensors as well as for model studies of intracellular processes. This is especially true for modeling nerve cells, since melanophores share stem cells with axons. Twenty experiments on black tetra fish fins were carried out in the two magnetic flux densities. The same number of control experiments were carried out in the magnet with the magnetic field turned off. Several factors, such as the degree of maximal aggregation, speed of aggregation, and irregularity of the speed, were examined. The statistical analysis showed no significant field effects on the aggregation, with one exception: the irregularity in aggregation speed in the 8 T field, compared to control. The believed reorientation of the cytoskeleton (microtubules) in the field or the induced Lorentz force on moving pigment granules, did not affect the aggregation. Bioelectromagnetics 23:444–449, 2002. © 2002 Wiley‐Liss, Inc.
Secreted Frizzled‐related proteins: searching for relationships and patterns
Authors: Jones Steve E. , Jomary Catherine
Published: September 2002

Secreted Frizzled‐related proteins (SFRPs) are modulators of the intermeshing pathways in which signals are transduced by Wnt ligands through Frizzled (Fz) membrane receptors. The Wnt networks influence biological processes ranging from developmental cell fate, cell polarity and adhesion to tumorigenesis and apoptosis. In the five or six years since their discovery, the SFRPs have emerged as dynamically expressed proteins able to bind both Wnts and Fz, with distinctive structural properties in which cysteine‐rich domains from Fz‐ and from netrin‐like proteins are juxtaposed. The abundant expression of SFRP genes in the early embryo, altered expression patterns in disease states, and potential significance in the evolution of the vertebrate body plan, make these intriguing molecules relevant to investigations in diverse fields of biology and biomedical sciences. BioEssays 24:811–820, 2002. © 2002 Wiley Periodicals, Inc.
Protosilencers as building blocks for heterochromatin
Authors: Fourel Geneviève , Lebrun Eléonore , Gilson Eric
Published: September 2002

DNA repetitions may provoke heterochromatinization. We explore here a model in which multiple cis‐acting sequences that display no silencing activity on their own (protosilencers) may cooperate to establish and maintain a heterochromatin domain efficiently. Protosilencers, first defined in budding yeast, have now been found in a wide range of genomes where they appear to stabilize and to extend the propagation of heterochromatin domains. Strikingly, isolated or moderately repeated protosilencers can also be found in promoters where they participate in transcriptional activation and have insulation functions. This suggests that the proper juxtaposition of a threshold number of protosilencers converts them from neutral or transactivating elements into ones that nucleate heterochromatin. Interactions might be transient or permanent, and are likely to occur over distances by looping. This model provides a conceptual framework for as varied phenomena as telomere‐driven silencing in Drosophila, X inactivation in mammals, and rDNA silencing in S. cerevisiae. It may also account for the silencing that occurs when multiple copies of a transgene are inserted in tandem. BioEssays 24:828–835, 2002. © 2002 Wiley Periodicals, Inc.
Beyond structure: do intermediate filaments modulate cell signalling?
Authors: Paramio Jesus M. , Jorcano José L.
Published: September 2002

Intermediate filament (IF) proteins form the largest family of cytoskeletal proteins in mammalian cells. The function of these proteins has long been thought to be only structural. However, this single function does not explain their diverse tissue‐ and differentiation‐specific expression patterns. Evidence is now emerging that IF also act as an important framework for the modulation and control of essential cell processes, in particular, signal transduction events. Here, we review the most recent developments in this growing and exciting new field. BioEssays 24:836–844, 2002. © 2002 Wiley Periodicals, Inc.
Nucleotide sequence‐based typing of bacteria and the impact of automation
Authors: Clarke Stuart C.
Published: September 2002

DNA‐based typing methods are increasingly important for the characterisation of bacteria. They are used to monitor the epidemiology of pathogens with public health significance and also to help understand the evolution and population biology of bacteria. However, these methods require accuracy and reproducibility and are often of a high‐throughput nature. Laboratory automation is therefore the key to the successful implementation of such methods. This review describes the impact of automation on DNA‐based typing methods, particularly multi‐locus sequence typing (MLST), and the method components that can be automated. BioEssays 24:858–862, 2002. © 2002 Wiley Periodicals, Inc.
Canonical and non‐canonical Wnt signaling pathways in Caenorhabditis elegans: variations on a common signaling theme
Authors: Korswagen Hendrik C.
Published: September 2002

Wnt glycoproteins are signaling molecules that control a wide range of developmental processes in organisms ranging from the simple metazoan Hydra to vertebrates. Wnt signaling also plays a key role in the development of the nematode C. elegans, and is involved in cell fate specification and determination of cell polarity and cell migration. Surprisingly, the first genetic studies of Wnt signaling in C. elegans revealed major differences with the established (canonical) Wnt signaling pathways of Drosophila and vertebrates. Thus, the Wnt‐dependent induction of endoderm in the early embryo and the specification of several asymmetric cell divisions during larval development are mediated by as yet novel Wnt signaling pathways that repress, rather than activate the TCF/LEF‐1 transcription factor POP‐1. Recently, however, it has been shown that, in addition to these divergent Wnt pathways, C. elegans also has a canonical Wnt pathway that converts POP‐1 into an activator and controls the expression of several homeobox genes. Interestingly, these different Wnt pathways use distinct β‐catenins to control POP‐1 function: the endoderm induction pathway requires the β‐catenin WRM‐1 and parallel input from a mitogen‐activated kinase (MAPK) pathway to downregulate POP‐1, whereas the canonical Wnt pathway employs the β‐catenin BAR‐1 to activate Wnt target gene expression. BioEssays 24:801–810, 2002. © 2002 Wiley Periodicals, Inc.
What can humans learn from flies about adenomatous polyposis coli?
Authors: Barth Angela I.M. , Nelson W. James
Published: September 2002

Somatic or inherited mutations in the adenomatous polyposis coli (APC) gene are a frequent cause of colorectal cancer in humans. APC protein has an important tumor suppression function to reduce cellular levels of the signaling protein β‐catenin and, thereby, inhibit β‐catenin and T‐cell‐factor‐mediated gene expression. In addition, APC protein binds to microtubules in vertebrate cells and localizes to actin‐rich adherens junctions in epithelial cells of the fruit fly Drosophila (Fig. 1). Very little is known, however, about the function of these cytoskeletal associations. Recently, Hamada and Bienz have described a potential role for Drosophila E‐APC in cellular adhesion,1 which offers new clues to APC function in embryonic development, and potentially colorectal adenoma formation and tumor progression in humans. BioEssays 24:771–774, 2002. © 2002 Wiley Periodicals, Inc.
Non‐stop decay—a new mRNA surveillance pathway
Authors: Vasudevan Shobha , Peltz Stuart W. , Wilusz Carol J.
Published: September 2002

Gene expression is an inherently complex process and errors often occur during the transcription and processing of mRNAs. Several surveillance mechanisms have evolved to check the fidelity at each step of mRNA manufacture. Two recent reports describe the identification of a novel pathway in eukaryotes that recognizes and degrades mRNAs that lack a stop codon.1,2 The non‐stop decay mechanism releases ribosomes stalled at the 3′ end of a mRNA and stimulates the exosome to rapidly degrade the transcript. BioEssays 24:785–788, 2002. © 2002 Wiley Periodicals, Inc.
Fourier transform IR study of aggregational behavior of N‐acetyl‐L‐ and N‐butyloxycarbonyl‐L‐glutamic acid oligomeric benzyl esters in dioxane and benzene: β‐Turn → antiparallel β‐sheet transition
Authors: Okabayashi Hirofumi , Ishida Makoto , Tamaoki Harushiko , Masuda Hideki , O'Connor Charmian J.
Published: September 2002

Oligomeric N‐acetyl‐L‐glutamic acid benzyl esters (ANpZ) with exact residue numbers (Np = 2, 3, 4, and 5) and N‐butyloxycarbonyl‐L‐glutamic acid benzyl esters (BOCNpZ) with exact residue numbers (Np = 4, 5, 6, and 8) are synthesized by a stepwise procedure in a liquid phase. The aggregational behavior of these oligomeric molecules in dioxane and benzene is examined by Fourier transform IR spectra. In particular, the concentration dependence of the IR spectra for the ANpZ solutions with Np values of 4 (A4Z) and 5 (A5Z) shows that the predominant antiparallel β‐sheet structure is stabilized above the critical aggregation concentration (cac), while other conformations including β‐turns may coexist below the cac. This fact provides evidence that aggregation induces the conformational transition from other conformers (probably β‐turns) to an antiparallel β‐sheet form. The IR results for the A3Z and A2Z solutions indicate that specific conformers (β‐turns), which are different from the β‐sheet structure, may be preferentially stabilized upon aggregation. Thus, the critical residue number of the ANpZ oligopeptides, which is essential for formation of a rodlike aggregate in dioxane and benzene, is 4 or 5. © 2002 Wiley Periodicals, Inc. Biopolymers (Biospectroscopy) 65: 129–141, 2002
Effects of aminooxy analogues of biogenic polyamines on aggregation and stability of calf thymus DNA
Authors: Ramírez F. J. , Thomas T. J. , Antony T. , Ruiz‐Chica J. , Thomas T.
Published: September 2002

The effect of a series of aminooxy analogues of the biogenic polyamines spermidine and spermine on the conformation of calf thymus DNA is studied. These new molecules are isosteric and charge insufficient analogues that are suitable to study the roles of both charge distribution and structural requirements in the molecular physiology of the biogenic polyamines. They are also evidenced as useful tools to inhibit polyamine biosynthesis and cell growth. Circular dichroism (CD) spectra of solutions containing DNA and the aminooxy analogues at different concentrations (100–1000 μM) and different pH values, (5–7.5) are recorded. We use both sonicated and highly polymerized calf thymus DNA. The CD spectra of sonicated DNA showed the formation of Ψ‐DNA, a highly ordered aggregated structure similar to liquid crystals, in the presence of the aminooxy analogues. Aggregation induced by an aminooxy derivative of spermine is followed by DNA collapse when increasing the polyamine concentration. The features of Ψ‐DNA are not detected for highly polymerized DNA. Temperature melting measurements support a high degree of structural order of the aggregates. The CD experiments indicate that dications are unable to induce major changes on the macromolecular structure of DNA. In addition, aggregation is only observed when the trimethylene moiety is present between two adjacent positive charges. The observed differences among the CD spectra of DNA solutions with different aminooxy derivatives of spermidine indicate different roles for different amino groups of this biogenic polyamine when interacting with DNA. Our results support the idea that aminooxy analogues can be used as good models in studying the physiological functions of biogenic polyamines. © 2002 Wiley Periodicals, Inc. Biopolymers (Biospectroscopy) 65: 148–157, 2002
Multinuclear NMR and FTIR studies of new polyoxaalkyl esters of lasalocid and their complexes with lithium and sodium cations
Authors: Pankiewicz Radosław , Schroeder Grzegorz , Gierczyk Błażej , Brzezinski Bogumił , Bartl Franz
Published: September 2002

Three new polyoxaalkyl esters of lasalocid are synthesized. Their ability to form complexes with Li+ and Na+ cations is studied using multinuclear NMR methods, FTIR spectroscopy in the middle and far IR regions, and mass spectrometry. It is found that lasalocid esters form only 1:1 complexes with the metal cations. The results of the NMR study in pyridine show that the polyoxaalkyl chain of the ester does not influence the complex formation of the lasalocid part of the esters. The reason for this is the competition of the pyridine molecules in the complexation process of metal cations. In chloroform the properties of the complex formation have changed and the oxaalkyl chain plays an important role within the complexation process, as demonstrated by the dependence of the respective continuous absorptions in the far IR region on the length of the oxaalkyl chain (i.e., on the number of the oxygen atoms in the chain). The modifications of the lasalocid molecule influences the complexation of the metal cation and probably the interactions with the membrane. An increase in antibiotic activity is found as a consequence of these changed interactions. © 2002 Wiley Periodicals, Inc. Biopolymers (Biospectroscopy) 65: 95–110, 2002
Conformational studies of wheat flour high relative molecular mass glutenin subunits by circular dichroism spectroscopy
Authors: Fisichella S. , Alberghina G. , Amato M. E. , Fichera M. , Mantarro D. , Palermo A. , Savarino A. , Scarlata G.
Published: September 2002

Conformational studies of 1Dx2, 1Bx7, and 1Dy12 high relative molecular mass glutenin subunits, extracted from Alisei 1 flour, are reported. Circular dichroism (CD) spectroscopy is employed to study their conformational polymorphism induced by urea and by urea in the presence of 1% sodium dodecyl sulfate (SDS). The CD spectra indicate that SDS promotes ordered structures. The addition of urea to the SDS‐acetate solution of 1Dx2, 1Bx7, and 1Dy12 subunits eliminates the effect of SDS. Its addition to the acetate solution of proteins induces conformational transitions to form a poly‐L‐proline II‐like structure. All the changes induced by urea follow a multistep transition process that is typical of proteins consisting of different domains. © 2002 Wiley Periodicals, Inc. Biopolymers (Biospectroscopy) 65: 142–147, 2002
Spin trapping study of reactive oxygen species formation during bopindolol peroxidation
Authors: Kruk Irena , Michalska Teresa , Kladna Aleksandra , Aboul‐Enein Hassan Y.
Published: September 2002

The generation of singlet molecular oxygen (1O2) and hydroxyl radicals (HO ·) during peroxidation of bopindolol in the presence of Co(II) ions was studied using electron spin resonance (ESR) and spectrophotometry methods. 2,2,6,6‐Tetramethyl‐4‐piperidone and 5,5‐dimethyl‐1‐pyrroline‐1‐oxide were used as traps. The spectrophotometry determination of 1O2 was based on bleaching of p‐nitrosodimethylaniline (RNO), which was caused by the product of the reaction of 1O2 with imidazole and was followed by monitoring the decrease in optical density at 440 nm. The effect of 1O2 quenchers and oxygen free radical scavengers on the ESR signal and the bleaching of RNO was studied. The data presented here give new evidence for generation of the reactive oxygen species during peroxidation of bopindolol. © 2002 Wiley Periodicals, Inc. Biopolymers (Biospectroscopy) 65: 89–94, 2002
Production of L(+)‐lactic acid from glucose and starch by immobilized cells of Rhizopus oryzae in a rotating fibrous bed bioreactor
Authors: Tay Abdullatif , Yang Shang‐Tian
Published: September 2002

A rotating fibrous‐bed bioreactor (RFB) was developed for fermentation to produce L(+)‐lactic acid from glucose and cornstarch by Rhizopus oryzae. Fungal mycelia were immobilized on cotton cloth in the RFB for a prolonged period to study the fermentation kinetics and process stability. The pH and dissolved oxygen concentration (DO) were found to have significant effects on lactic acid productivity and yield, with pH 6 and 90% DO being the optimal conditions. A high lactic acid yield of 90% (w/w) and productivity of 2.5 g/L·h (467 g/h·m2) was obtained from glucose in fed‐batch fermentation. When cornstarch was used as the substrate, the lactic acid yield was close to 100% (w/w) and the productivity was 1.65 g/L·h (300 g/h·m2). The highest concentration of lactic acid achieved in these fed‐batch fermentations was 127 g/L. The immobilized‐cells fermentation in the RFB gave a virtually cell‐free fermentation broth and provided many advantages over conventional fermentation processes, especially those with freely suspended fungal cells. Without immobilization with the cotton cloth, mycelia grew everywhere in the fermentor and caused serious problems in reactor control and operation and consequently the fermentation was poor in lactic acid production. Oxygen transfer in the RFB was also studied and the volumetric oxygen transfer coefficients under various aeration and agitation conditions were determined and then used to estimate the oxygen transfer rate and uptake rate during the fermentation. The results showed that the oxygen uptake rate increased with increasing DO, indicating that oxygen transfer was limited by the diffusion inside the mycelial layer. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 80: 1–12, 2002.
Controlled enzymatic removal of damaging casein layers on medieval wall paintings
Authors: Beutel Sascha , Klein Kerstin , Knobbe Gabi , Königfeld Peter , Petersen Karin , Ulber Roland , Scheper Thomas
Published: September 2002

A new, gentle enzymatic method was developed for a controlled removal of casein layers from medieval wall paintings. These casein layers were applied over the last 60 years on wall paintings in order to decrease substantial damage due to a peeling off of the frescoes from the roughcast surface due to environmental effects. However, due to the aging of the casein layers (at 40–50 years), a more drastic peeling occurred and the danger of total destruction of the wall paintings is severe. Thus, screening was performed to find the most suitable enzyme for casein digestion. Alcalase 2.5 DX L was the most appropriate enzyme for an effective proteolysis reaction. The enzyme was immobilized on functionalized cellulose membrane. A membrane pad system with immobilized enzymes was developed which could be pressed on the casein layers on the wall painting. A controlled removal of the casein layers by proteolytic digestion was observed and it was possible to continuously wash off the hydrolyzed casein fragments from the wall painting surface by an aqueous carbonate buffer flowing through the membrane pad. The removal and the digestion was monitored by reverse HPLC. Additionally, an on‐line monitoring system was set up in order to continuously follow the casein layer removal and the digestion procedure directly on the wall painting. This technique is based on noninvasive 2D‐fluorescence monitoring. Optical fiber systems were used to continuously monitor the fluorescence intensity of casein‐bound tryptophan. The off‐line data were verified with the on‐line 2D‐fluorescence data. Based on the scientific result an appropriate technique for the controlled enzymatic removal of damaging casein layers on the surface of medieval wall paintings using immobilized enzyme is now available. It is now applied to remove such casein layers from medieval wall paintings in the Allerheiligen‐Kapelle Cloister, Wienhausen, Germany, and the St. Alexander Kirche, Wildeshausen, Germany. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 80: 13–21, 2002.
Recovery and separation of cell lysate proteins using hydrogels guided by aqueous two‐phase extraction principles
Authors: Putka Christopher S. , Gehrke Stevin H. , Willis Mike , Stafford David , Bryant John
Published: September 2002

The addition of poly(ethylene glycol) and salts to clarified cell lysates of Thiosphaera pantotropha increases sorption of microbial proteins into dextran hydrogels, consistent with the thermodynamics of aqueous two‐phase extraction. Addition of 12 wt% PEG‐10,000 to the lysate increased total sorption of protein by the dextran gel from 5.2 mg/g dextran to 37 mg/g; addition of either 0.1 M potassium iodide or tetrabutylammonium fluoride along with PEG to the lysate increased protein sorption to more than 63 mg/g, a 12‐fold increase. SDS‐PAGE demonstrated that the type of salt added controls which proteins are absorbed by the gel. Previously demonstrated only with model solutions, these results suggest another approach to recovery and separation strategies for proteins produced by fermentation. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 80: 139–143, 2002.
Development of a large‐scale biocalorimeter to monitor and control bioprocesses
Authors: Voisard D. , Pugeaud P. , Kumar A. R. , Jenny K. , Jayaraman K. , Marison I. W. , von Stockar U.
Published: September 2002

Calorimetry has shown real potential at bench‐scale for chemical and biochemical processes. The aim of this work was therefore to scale‐up the system by adaptation of a standard commercially available 300‐L pilot‐scale bioreactor. To achieve this, all heat flows entering or leaving the bioreactor were identified and the necessary instrumentation implemented to enable on‐line monitoring and dynamic heat balance estimation. Providing that the signals are sufficiently precise, such a heat balance would enable calculation of the heat released or taken up during an operational (bio)process. Two electrical Wattmeters were developed, the first for determination of the power consumption by the stirrer motor and the second for determination of the power released by an internal calibration heater. Experiments were designed to optimize the temperature controller of the bioreactor such that it was sufficiently rapid so as to enable the heat accumulation terms to be neglected. Further calibration experiments were designed to correlate the measured stirring power to frictional heat losses of the stirrer into the reaction mass. This allows the quantitative measurement of all background heat flows and the on‐line quantitative calculation of the (bio)process power. Three test fermentations were then performed with B. sphaericus 1593M, a spore‐forming bacterium pathogenic to mosquitoes. A first batch culture was performed on a complex medium, to enable optimization of the calorimeter system. A second batch culture, on defined medium containing three carbon sources, was used to show the fast, accurate response of the heat signal and the ability to perfectly monitor the different growth phases associated with growth on mixed substrates, in particular when carbon sources became depleted. A maximum heat output of 1100 W was measured at the end of the log‐phase. A fed‐batch culture on the same defined medium was then carried out with the feed rate controlled as a function of the calorimeter signal. A maximum heat output of 2250 W was measured at the end of the first log‐phase. This work demonstrates that real‐time quantitative calorimetry is not only possible at pilot‐scale, but could be readily applied at even larger scales. The technique requires simple, readily available devices for determination of the few necessary heat flows, making it a robust, cost‐effective technique for process development and routine monitoring and control of production processes. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 80: 125–138, 2002
Optimization of recombinant protein expression level in Escherichia coli by flow cytometry and cell sorting
Authors: Soriano Elena , Borth Nicole , Katinger Hermann , Mattanovich Diethard
Published: September 2002

Overexpression of recombinant proteins in Escherichia coli often leads to a severe growth retardation of the host cells. The phage T7 promoter ϕ10 in a pET vector was utilized to express human superoxide dismutase. Induction with IPTG lead to an increase in protein content and cell size and a termination of cell division, due to the deviation of the general metabolic fluxes from all cellular processes to plasmid maintenance and foreign protein synthesis. To generate promoter mutants which are better tolerated by the host cells we constructed a random mutation library by PCR with degenerated primers in a part of the promoter involved in the binding to the RNA polymerase and the initiation of transcription. This library was sorted by flow cytometry for cells with a lower total protein content as an indicator for continued cell replication and hence a less severe stress situation. The clones obtained had a similar SOD production compared to the original strain, but were able to reach higher densities in a batch culture, which resulted in a higher total yield. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 80: 93–99, 2002.
Interplay of SOS induction, recombinant gene expression, and multimerization of plasmid vectors in Escherichia coli
Authors: Lee Jeewon , Kim Hyung‐Cheol , Kim Sung‐Woo , Kim Seung Wook , Hong Suk In , Park Young‐Hoon
Published: September 2002

Using pBR322‐ and pUC‐derived plasmid vectors, a homologous (Escherichia coli native esterase) and three heterologous proteins (human interleukin‐2, human interleukin‐6, and Zymomonas levansucrase) were synthesized in E. coli IC2015(recA::lacZ) and GY4786 (sfiA::lacZ) strains. Via time‐course measurement of β‐galactosidase activity in each recombinant culture, the SOS induction was estimated in detail and the results were systematically compared. In recombinant E. coli, the SOS response did not happen either with the recombinant insert‐negative plasmid backbone alone or the expression vectors containing the homologous gene. Irrespective of gene expression level and toxic activity of synthesized foreign proteins, the SOS response was induced only when the heterologous genes were expressed using a particular plasmid vector, indicating strong dependence on the recombinant gene clone and the selection of a plasmid vector system. It is suggested that in recombinant E. coli the SOS response (i.e., activation of recA expression and initial sfiA expression) may be related neither to metabolic burden nor toxic cellular event(s) by synthesized heterologous protein, but may be provoked by foreign gene‐specific interaction between a foreign gene and a plasmid vector. Unlike in E. coli XL1‐blue(recA−) strains used, all expression vectors encoding each of the three heterologous proteins were multimerized in E. coli IC2015 strains in the course of cultivation, whereas the expression vectors containing the homologous gene never formed the plasmid multimers. The extent of multimerization was also dependent on a foreign gene insert in the expression vector. As a dominant effect of the SOS induction, recombinant plasmid vectors used for heterologous protein expression appear to significantly form various multimers in the recA+ E. coli host. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 80: 84–92, 2002.
Biodegradation of gasoline by gellan gum‐encapsulated bacterial cells
Authors: Moslemy Peyman , Neufeld Ronald J. , Guiot Serge R.
Published: September 2002

Encapsulated cell bioaugmentation is a novel alternative solution to in situ bioremediation of contaminated aquifers. This study was conducted to evaluate the feasibility of such a remediation strategy based on the performance of encapsulated cells in the biodegradation of gasoline, a major groundwater contaminant. An enriched bacterial consortium, isolated from a gasoline‐polluted site, was encapsulated in gellan gum microbeads (16–53 μm diameter). The capacity of the encapsulated cells to degrade gasoline under aerobic conditions was evaluated in comparison with free (non‐encapsulated) cells. Encapsulated cells (2.6 mgcells g−1 bead) degraded over 90% gasoline hydrocarbons (initial concentration 50–600 mg L−1) within 5–10 days at 10°C. Equivalent levels of free cells removed comparable amounts of gasoline (initial concentration 50–400 mg L−1) within the same period but required up to 30 days to degrade the highest level of gasoline tested (600 mg L−1). Free cells exhibited a lag phase in biodegradation, which increased from 1 to 5 days with an increase in gasoline concentration (200–600 mg L−1). Encapsulation provided cells with a protective barrier against toxic hydrocarbons, eliminating the adaptation period required by free cells. The reduction of encapsulated cell mass loading from 2.6 to 1.0 mgcells g−1 bead caused a substantial decrease in the extent of biodegradation within a 30‐day incubation period. Encapsulated cells dispersed within the porous soil matrix of saturated soil microcosms demonstrated a reduced performance in the removal of gasoline (initial concentrations of 400 and 600 mg L−1), removing 30–50% gasoline hydrocarbons compared to 40–60% by free cells within 21 days of incubation. The results of this study suggest that gellan gum‐encapsulated bacterial cells have the potential to be used for biodegradation of gasoline hydrocarbons in aqueous systems. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 80: 175–184, 2002.