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Concentration Dependence (concentration + dependence)
Selected AbstractsExtent and mechanism of solvation and partitioning of isomers of substituted benzoic acids: A thermodynamic study in the solid state and in solutionJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2008German L. Perlovich Abstract Temperature dependency of saturated vapour pressure and thermochemical characteristics of fusion processes for 2-, 3- and 4-methoxybenzoic acids (anisic acids) were measured and thermodynamic functions of sublimation, fusion, and evaporation calculated. A new approach to split specific and nonspecific energetic terms in the crystal lattice was developed. For methoxybenzoic acid isomers as well as for a number of analogous molecules, a parameter describing molecular packing density by the ratio of free volume of the molecules in the crystal lattice and van der Waals molecular volume is defined. Its relationship to Gibbs energy of sublimation and to the respective melting points was analysed. Temperature dependencies of solubility in buffers with pH 2.0 and 7.4, n -octanol and n -hexane were measured. The thermodynamic functions of solubility, solvation and transfer processes were deduced. Concentration dependence of partition coefficients for the outlined isomers was measured. Specific and nonspecific solvation terms were distinguished using the transfer from the ,inert' n -hexane to the other solvents. Comparison analysis of specific and nonspecific interactions in the solid state and in solution was carried out. A diagram enabling analysis of the mechanism of the partitioning process was applied. It was found that position of substituents essentially affects the mechanism of partitioning in buffer pH 2.0, however, at pH 7.4, the mechanism is independent of the position of the substituent. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:3883,3896, 2008 [source] Concentration dependence of the hopping mobility in disordered organic solidsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2004O. Rubel Abstract Traditionally the dependance of the drift mobility, ,, on the concentration of localized states, N, in disordered organic solids is plotted in the form , , exp[,C(N,3),p] with p = 1/3 and constant C. This representation cannot be correct, because transport in disordered organic solids is essentially a variablerange-hopping process with a weaker dependence ,(N). We study this dependence theoretically and show that both parameters p and C strongly depend on temperature and hence they are not universal. Only at very high temperatures the formula with p = 1/3 is valid. The result is significant in particular for a correct diagnostics of the localization length , from the measured dependence ,(N). (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Placebo-controlled evaluation of the irritant potential of tacalcitol (1,, 24-dihydroxyvitamin D3) in healthy volunteersCONTACT DERMATITIS, Issue 5 2000K. Schlotmann In the treatment of psoriasis with topical vitamin D3 analogues, lesional and perilesional irritation is the main side-effect. The aim of this study was to investigate whether local side-effects generated by tacalcitol, a vitamin D3 analogue, show concentration dependence. 3 different concentrations of tacalcitol (0.4; 4; 40 ,g/g ointment) and the vehicle were applied on normal skin of the back of 25 healthy volunteers under occlusive conditions for 5 days. Assessment of erythema, infiltration and scaling as well as measurement of transepidermal water loss (TEWL) was performed on days 1 to 5. On day 5, additional skin barrier tests (DMSO test, alkali resistance test) were performed. Erythema and slight infiltration, but no scaling, were observed in a number of subjects without significant differences. TEWL also did not show significant differences for the test formulations, though there was a tendency towards lower values in the untreated areas. In the skin barrier tests, a tendency towards higher alkali resistance in the test areas treated with 40 ,g tacalcitol/g ointment was detected. Thus, under occlusive conditions, the irritant potential of tacalcitol is very low. There is no convincing evidence of concentration dependence in irritation generated by tacalcitol when applied under occlusive conditions. [source] Crystal growth and scintillating properties of (Pr,Si)-doped YAlO3CRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2007M. Zhuravleva Abstract This paper deals with Pr-doped and Pr, Si-codoped YAlO3 single crystal growth by the micro-pulling-down method and investigation of their spectroscopic and scintillating properties. The Pr3+ 5d -4f radioluminescence intensity is more than 10 times higher than that of Bi4Ge3O12 standard sample, but the Si-codoping decreases it. Absorption spectra of as-grown and air-annealed Si,Pr-codoped YAlO3 samples show along with an onset of 4f -5d transition round 230 nm the induced absorption band at 400 nm which possibly related to a hole center absorption (Pr4+ or O - ). Thermoluminescence measurements above the room temperature were performed in order to monitor deep electron traps. Strong concentration dependence of thermoluminescence was observed for Pr:YAlO3 glow curves. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Substrate-dependent hysteretic behavior in StEH1-catalyzed hydrolysis of styrene oxide derivativesFEBS JOURNAL, Issue 24 2008Diana Lindberg The substrate selectivity and enantioselectivity of Solanum tuberosum epoxide hydrolase 1 (StEH1) have been explored by steady-state and pre-steady-state measurements on a series of styrene oxide derivatives. A preference for the (S)- or (S,S)-enantiomers of styrene oxide, 2-methylstyrene oxide and trans -stilbene oxide was established, with E -values of 43, 160 and 2.9, respectively. Monitoring of the pre-steady-state phase of the reaction with (S,S)-2-methylstyrene oxide revealed two observed rates for alkylenzyme formation. The slower of these rates showed a negative substrate concentration dependence, as did the rate of alkylenzyme formation in the reaction with the (R,R)-enantiomer. Such kinetic behavior is indicative of an additional, off-pathway step in the mechanism, referred to as hysteresis. On the basis of these data, a kinetic mechanism that explains the kinetic behavior with all tested substrates transformed by this enzyme is proposed. Regioselectivity of StEH1 in the catalyzed hydrolysis of 2-methylstyrene oxide was determined by 13C-NMR spectroscopy of 18O-labeled diol products. The (S,S)-enantiomer is attacked exclusively at the C-1 epoxide carbon, whereas the (R,R)-enantiomer is attacked at either position at a ratio of 65 : 35 in favor of the C-1 carbon. On the basis of the results, we conclude that differences in efficiency in stabilization of the alkylenzyme intermediates by StEH1 are important for enantioselectivity with styrene oxide or trans -stilbene oxide as substrate. With 2-methylstyrene oxide, slow conformational changes in the enzyme also influence the catalytic efficiency. [source] Co-operative effect of the isoforms of type III antifreeze protein expressed in Notched-fin eelpout, Zoarces elongatus KnerFEBS JOURNAL, Issue 2 2005Yoshiyuki Nishimiya We found that Notched-fin eelpout, which lives off the north east coast of Japan, expresses an antifreeze protein (AFP). The liver of this fish contains DNAs that encode at least 13 type III AFP isoforms (denoted nfeAFPs). The primary sequences of the nfeAFP isoforms were categorized into SP- and QAE-sephadex binding groups, and the latter were further divided into two subgroups, QAE1 and QAE2 groups. Ice crystals observed in HPLC-pure nfeAFP fractions are bipyramidal in shape with different ratios of c and a axes, suggesting that all the isoforms are able to bind ice. We expressed five recombinant isoforms of nfeAFP and analyzed the thermal hysteresis (TH) activity of each as a function of protein concentration. We also examined the change in activity on mixing the isoforms. TH was estimated to be 0.60 °C for the QAE1 isoform, 0.11 °C for QAE2, and almost zero for the SP isoforms when the concentrations of these isoforms was standardized to 1.0 mm. Significantly, the TH activity of the SP isoforms showed concentration dependence in the presence of 0.2 mm QAE1, indicating that the less active SP isoform becomes ,active' when a small amount of QAE1 is added. In contrast, it does not become active on the addition of another SP isoform. These results suggest that the SP and QAE isoforms of type III AFP have different levels of TH activity, and they accomplish the antifreeze function in a co-operative manner. [source] Influence of factor IX on overall plasma coagulability and fibrinolytic potential as measured by global assay: monitoring in haemophilia BHAEMOPHILIA, Issue 1 2008N. A. GOLDENBERG Summary., We sought to determine the influence of factor IX (FIX) deficiency upon overall coagulative and fibrinolytic capacities in plasma using the clot formation and lysis (CloFAL) assay, and to investigate the role of this global assay as an adjunctive monitoring tool in haemophilia B. CloFAL assay parameters were measured in vitro in platelet-poor plasma in relation to FIX activity and antigen (FIX:Ag), and were determined ex vivo among FIX-deficient patients (n = 41) in comparison to healthy individuals (n = 48). Supplementation of FIX-deficient plasma with FIX in vitro demonstrated a non-linear concentration dependence of FIX upon overall plasma coagulability. Ex vivo, coagulability was significantly decreased in FIX-deficient vs. healthy subjects among adults [median coagulation index (CI): 4% vs. 104% respectively; P < 0.001] and children (median CI: 9% vs. 63%; P < 0.001). Fibrinolytic capacity was increased in adult FIX-deficient vs. healthy subjects (median fibrinolytic index: 216% vs. 125%, respectively, P < 0.001), and was supported by a trend in shortened euglobulin lysis time (ELT). Severe haemophilia B patients showed heterogeneity in aberrant CloFAL assay waveforms, influenced partly by FIX:Ag levels. Patients with relatively preserved FIX:Ag (i.e. dysfunctional FIX) exhibited a shorter time to maximal amplitude in clot formation than those with type I deficiency. During patient treatment monitoring, markedly hypocoagulable CloFAL assay waveforms normalized following 100% correction with infused FIX. The CloFAL global assay detects FIX deficiency, demonstrates differences in coagulability between dysfunctional FIX and type I deficiency, and appears useful as an adjunctive test to routine FIX measurement in monitoring haemophilia B treatment. [source] Biochemical characterization of human glutamate carboxypeptidase IIIJOURNAL OF NEUROCHEMISTRY, Issue 3 2007Klįra Hlouchovį Abstract Human glutamate carboxypeptidase II (GCPII) is a transmembrane metallopeptidase found mainly in the brain, small intestine, and prostate. In the brain, it cleaves N -acetyl- l -aspartyl-glutamate, liberating free glutamate. Inhibition of GCPII has been shown to be neuroprotective in models of stroke and other neurodegenerations. In prostate, it is known as prostate-specific membrane antigen, a cancer marker. Recently, human glutamate carboxypeptidase III (GCPIII), a GCPII homolog with 67% amino acid identity, was cloned. While GCPII is recognized as an important pharmaceutical target, no biochemical study of human GCPIII is available at present. Here, we report the cloning, expression, and characterization of recombinant human GCPIII. We show that GCPIII lacks dipeptidylpeptidase IV-like activity, its activity is dependent on N -glycosylation, and it is effectively inhibited by several known inhibitors of GCPII. In comparison to GCPII, GCPIII has lower N -acetyl- l -aspartyl-glutamate-hydrolyzing activity, different pH and salt concentration dependence, and distinct substrate specificity, indicating that these homologs might play different biological roles. Based on a molecular model, we provide interpretation of the distinct substrate specificity of both enzymes, and examine the amino acid residues responsible for the differences by site-directed mutagenesis. These results may help to design potent and selective inhibitors of both enzymes. [source] On the possibility of self-induction of drug protein bindingJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 10 2010Leonid M. Berezhkovskiy Abstract The equilibrium unbound drug fraction (fu) is an important pharmacokinetic parameter, which influences drug elimination and distribution in the body. Commonly the drug plasma concentration is substantially less then that of drug binding proteins, so that fu can be assumed constant independent of drug concentration. A general consideration of protein binding based on the mass-action law provides that the unbound drug fraction increases with the increase of drug concentration, which is also a usual experimental observation. For several drugs, though, a seemingly unusual sharp decrease of the unbound drug fraction with the increase of total drug concentration (Ro) in the interval 0,<,Ro,,,5,µM was experimentally observed. A possible explanation of this apparently strange phenomenon is presented. The explanation is based on the consideration of a two-step mechanism of drug protein binding. The first step occurs as a drug binding to the site with relatively low affinity. Consequently this binding leads to the activation of a high affinity site, which otherwise is not available for binding. The suggested binding scheme yields the curves for fu dependence on the total drug concentration that are in good agreement with experimental measurements. The interpretation of pharmacokinetic data for the drugs with such unusual concentration dependence of fu appears to be a formidable problem. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:4400,4405, 2010 [source] The effective hard particle model provides a simple, robust, and broadly applicable description of nonideal behavior in concentrated solutions of bovine serum albumin and other nonassociating proteinsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 12 2007Allen P. Minton Abstract Published data on the concentration dependence of osmotic pressure of solutions of bovine serum albumin in 0.15 M NaCl at concentrations up to greater than 400 g/L are shown to be described to within experimental uncertainty by a simple one-parameter model in which protein molecules are represented by effective hard spherical particles. The volume of the effective hard particle reflects both steric and electrostatic repulsion and thus varies with pH and ionic strength. The pH dependence of the effective volume is shown to agree well with that previously obtained from analysis of the concentration dependence of sedimentation equilibrium and static light scattering. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96: 3466,3469, 2007 [source] On the calculation of the concentration dependence of drug binding to plasma proteins with multiple binding sites of different affinities: Determination of the possible variation of the unbound drug fraction and calculation of the number of binding sites of the proteinJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2007Leonid M. Berezhkovskiy Abstract The measurement of the unbound drug fraction in plasma is routinely performed at drug concentrations much less than that of plasma proteins. Commonly, the protein has several binding sites of different affinities. The obtained value of the unbound drug fraction does not yield the affinity of each binding site separately. For drug binding to a single type of protein, it is shown that the assumption that all binding sites of the protein have the same affinity yields the slowest possible concentration increase of the unbound drug fraction, while the assumption that a drug binds to a single binding site yields the highest possible value of the unbound fraction for a given drug concentration. The conditions to be imposed on the affinities of binding sites, to provide the fastest and the slowest possible concentration increase of the unbound drug fraction are also obtained for the case of drug binding to several types of plasma proteins. The suggested approach is applied to the determination of the number of binding sites of the protein from the measured values of the unbound drug fraction at different drug concentrations. ©2006 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96:249,257, 2007 [source] Excess thermodynamic properties in liquid binary mixturesJOURNAL OF RAMAN SPECTROSCOPY, Issue 2 2008F. Aliotta Abstract Excess volumes and adiabatic compressibility have been measured in several binary liquid mixtures to answer the question whether structural information can be gained through the analysis of the concentration dependence of the excess quantities. The obtained results are compared with independent indications from Raman spectroscopy, which is able to probe directly the occurrence and the nature of effective intermolecular interactions. Some doubts have arisen against the usual approach adopted for estimating the excess quantities and about the adequacy of the usual assumptions for the reference ideal behaviours. In particular, it is shown how excess compressibility can result just from statistical effects also in absence of any excess volume contribution. The leading idea is supported by the comparison of the experimental data with the results from a naive model for binary mixtures of hard spheres. The model turns out to be able to produce a very wide spectrum of structural and thermodynamic behaviours depending on the values of its parameters and on the nature (additive or non-additive) of the hard-sphere potential. A discussion is proposed on the re-evaluation of excess thermodynamic data and on their ability in providing direct information on intermolecular interactions. Copyright © 2008 John Wiley & Sons, Ltd. [source] Anomalous concentration dependence of the coordination behavior of Cl, ion to Ln3+ ion (Ln3+ = rare-earth ion) in anhydrous LnCl3 alcohol solutionsJOURNAL OF RAMAN SPECTROSCOPY, Issue 7 2007Y. Yoshimura Abstract Raman spectroscopic measurements were carried out for the anhydrous LnCl3·20ROH·XLiCl solutions (Ln3+ = La3+, Lu3+, X = 0,3; ROH = MeOH, EtOH, n -PrOH) in the liquid state. The salt concentration (X) dependence of the wavenumber for the Ln,Cl stretching Raman band (,Ln,Cl) is examined in conjunction with the formation of chloro-rare-earth complexes. We have obtained very intriguing results including the fact that the chloro complexations of the middle rare-earth ions (e.g. gadolinium, holmium ions, etc.) in the MeOH and EtOH solutions show peculiar behavior with regard to the salt concentration dependence: the ,Ln,Cl wavenumber increases with the increasing chloride concentration. However, the ,Ln,Cl wavenumbers of the light and heavy rare-earth (e.g. lanthanum, lutetium, etc.) salt solutions show normal behavior; i.e. ,Ln,Cl decreases with the increasing chloride concentration. On the other hand, in the n -PrOH solutions, the ,Ln,Cl frequency in the solutions of all the rare-earth elements exhibits a normal behavior. We now present a possible mechanism for this anomalous concentration dependence of coordination of Cl, ions to Ln3+ ions in anhydrous LnCl3 alcohol solutions. Copyright © 2007 John Wiley & Sons, Ltd. [source] EFFECTS OF SAMPLING CONDITIONS ON TEMPORAL PERCEPTION OF BITTERNESS IN YERBA MATE (ILEX PARAGUARIENSIS) INFUSIONSJOURNAL OF SENSORY STUDIES, Issue 3 2004AMALIA CALVIŃO ABSTRACT Time-intensity (TI) methodology and a trained panel were used to characterize the perceived bitterness of Yerba mate (YM) Ilex paraguariensis infusions. Two sampling procedures (sip and spit; sip and swallow) and two conditions for residence time in mouth (free or fixed duration of 5 s until spit or swallow) were evaluated. At a fixed duration the maximum bitterness as well as the time to reach it showed a significant YM concentration dependence. No change on bitterness was observed by swallowing or spitting YM infusions except a larger rate of decay of the response (vr) at spit condition. Dynamic bitterness at free sampling time showed that the decision period to spit or swallow the YM infusion approximately duplicated the fixed one of 5 s. [source] Ethylene Polymerization Kinetics with a Heterogeneous Metallocene Catalyst , Comparison of Gas and Slurry PhasesMACROMOLECULAR MATERIALS & ENGINEERING, Issue 6 2005Michiel F. Bergstra Abstract Summary: Ethylene homopolymerizations were executed with a supported Ind2ZrCl2/MAO catalyst using the so-called Reactive Bed Preparation method. This RBP method combined a slurry polymerization with a gas phase polymerization with the same polymerizing particles, i.e., a reactive bed. Polymerization kinetics were measured with high accuracy and reproducibility. Slurry and gas phase polymerization rates showed the same dependency on monomer bulk concentration. A complexation model has been proposed to describe the non-first order polymerization rate-monomer concentration dependence observed. This model also explains the non-Arrhenius temperature dependence and the observed pressure dependence of the activation energy of the commonly used polymerization rate model: Rp,=,kp,·,C*,·,M. [source] Calculation of Singlet Oxygen Dose from Photosensitizer Fluorescence and Photobleaching During mTHPC Photodynamic Therapy of MLL Cells,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2005Jonathan S. Dysart ABSTRACT Predicting the therapeutic outcome of photodynamic therapy (PDT) requires knowledge of the amount of cytoxic species generated. An implicit approach to assessing PDT efficacy has been proposed where changes in photosensitizer (PS) fluorescence during treatment are used to predict treatment outcome. To investigate this, in vitro experiments were performed in which Mat-LyLu cells were incubated in meta -tetra(hydroxyphenyl)chlorin (mTHPC) and then irradiated with 652 nm light. PS concentration, fluence rate and oxygenation were independently controlled and monitored during the treatment. Fluorescence of mTHPC was monitored during treatment and, at selected fluence levels, cell viability was determined using a colony-formation assay. Singlet oxygen dose was calculated using four different models and was compared with cell survival. For the dose metric based on singlet oxygen,mediated PS photobleaching, a universal relationship between cell survival and singlet oxygen dose was found for all treatment parameters. Analysis of the concentration dependence of bleaching suggests that the lifetime of singlet oxygen within the cell is 0.05,0.25 ,s. Generation of about 9 × 108 molecules of singlet oxygen per cell reduces the surviving fraction by 1/e. [source] Photo-induced improvement of radiative efficiency and structural changes in GaAsN alloysPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006H. Yaguchi Abstract We have investigated the excitation power density and nitrogen concentration dependence of the changes in the radiative efficiency of GaAsN alloys to examine the mechanism of the photo-induced improvement of radiative efficiency. With increasing excitation power density, the radiative efficiency increased more rapidly. The measure of the improvement Iafter/Ibefore superlinearly increased with increasing nitrogen concentration x up to ,1%. This suggests that the nonradiative recombination centers eliminated by photoexcitation are not defects formed by a single nitrogen atom but complexes formed by gathering of several nitrogen atoms. Micro Raman study revealed that the GaAs-like LO mode phonon peak intensity increased with photoexcitation time in a similar way to the increase in the radiative efficiency. Considering that this phenomenon is in a time scale of several seconds, the photo-induced structural changes correspond not to long range inter-diffusion but to local changes in atomic configuration which lead to the decrease in the density of nonradiative recombination centers. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Luminescent chiral organoboron 8-aminoquinolate-coordination polymersAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 8 2010Yuichiro Tokoro Abstract We have successfully synthesized optically active organoboron aminoquinolate-based coordination polymers bearing the chiral side chain derived from L -alanine, and studied their optical behavior by UV,vis and photoluminescence spectroscopies. Higher absolute quantum yields (,F) of the obtained polymers, measured by integrating sphere method, were observed with electron-withdrawing substituent (,F = 0.80) than with electron-donating substituent (,F = 0.52). The circular dichroism (CD) study in the mixed solvents of CHCl3 and DMF showed that the secondary structures of the obtained polymers were stabilized by hydrogen-bonding interaction in the side chain. From concentration dependence on the CD spectra, the chirality of the obtained polymers originated from the nature of one molecule. Copyright © 2009 John Wiley & Sons, Ltd. [source] Superparamagnetic iron oxide particles: contrast media for magnetic resonance imaging,APPLIED ORGANOMETALLIC CHEMISTRY, Issue 10 2004Rüdiger Lawaczeck Abstract The mainstream magnetic iron oxide particles used as contrast media for magnetic resonance (MR) imaging are composed of a magnetic iron oxide core surrounded by a dextran or carboxydextran coat. The core size ranges from 2 nm to less than 10 nm, and the hydrodynamic diameter ranges from 20 nm to about 120 nm. The coat prevents aggregation and sedimentation of the particles in aqueous solutions, achieves high biological tolerance, and prevents toxic side effects. Two kinds of particles are considered: (i) large particles (>30 nm), called superparamagnetic iron oxide particles (SPIOs) for liver imaging; (ii) smaller particles (<30 nm hydrodynamic diameter), called ultrasmall SPIOs (USPIOs), e.g. for MR angiography. To characterize the particles, Mössbauer spectra are presented for the two particle ensembles. These spectra allow insight into the magnetic coupling, the valency of the iron ions and a rough estimate of the core size to be deduced. On the basis of the concentration dependence of the MR signal intensities, two applications are discussed together with two representative clinical examples. Future indications for MR diagnostics, e.g. the labeling and tracking of stem cells during stem-cell therapy control, are outlined. Copyright © 2004 John Wiley & Sons, Ltd. [source] Surface-enhanced Raman and steady fluorescence study of interaction between antitumoral drug 9-aminoacridine and trypsin-like protease related to metastasis processes, guanidinobenzoataseBIOPOLYMERS, Issue 2 2001Adrian Murza Abstract Fluorescence spectroscopy and surface-enhanced Raman spectroscopy (SERS) were applied to study the interaction of the antitumoral drug 9-aminoacridine (9AA) with a trypsin-like protease guanidinobenzoatase (GB) extracted from a mouse Erlich tumor. As a consequence of this interaction, a strong 9AA exciplex emission was detected in the emission fluorescence spectra at certain drug and enzyme concentrations. A SERS study was accomplished on silver colloids at several excitation wavelengths in order to obtain more information about the interaction mechanism. The results derived from Raman spectroscopy indicated that 9AA in the amino monomeric form may interact with the enzyme by means of two different bonds: an ionic bond with a negatively charged amino acid and a ring stacking interaction with an aromatic residue placed in the catalytic site of GB. This interaction mechanism was responsible for a strong exciplex emission detected at a longer wavelength than the expected value of the normal fluorescence emission. Moreover, the GB concentration dependence of the interaction suggested that the drug was sensitive to the quaternary structure of the enzyme. © 2001 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 62: 85,94, 2001 [source] Modeling the competition between aggregation and self-assembly during virus-like particle processing,BIOTECHNOLOGY & BIOENGINEERING, Issue 3 2010Yong Ding Abstract Understanding and controlling aggregation is an essential aspect in the development of pharmaceutical proteins to improve product yield, potency and quality consistency. Even a minute quantity of aggregates may be reactogenic and can render the final product unusable. Self-assembly processing of virus-like particles (VLPs) is an efficient method to quicken the delivery of safe and efficacious vaccines to the market at low cost. VLP production, as with the manufacture of many biotherapeutics, is susceptible to aggregation, which may be minimized through the use of accurate and practical mathematical models. However, existing models for virus assembly are idealized, and do not predict the non-native aggregation behavior of self-assembling viral subunits in a tractable nor useful way. Here we present a mechanistic mathematical model describing VLP self-assembly that accounts for partitioning of reactive subunits between the correct and aggregation pathways. Our results show that unproductive aggregation causes up to 38% product loss by competing favorably with the productive nucleation of self-assembling subunits, therefore limiting the availability of nuclei for subsequent capsid growth. The protein subunit aggregation reaction exhibits an apparent second-order concentration dependence, suggesting a dimerization-controlled agglomeration pathway. Despite the plethora of possible assembly intermediates and aggregation pathways, protein aggregation behavior may be predicted by a relatively simple yet realistic model. More importantly, we have shown that our bioengineering model is amenable to different reactor formats, thus opening the way to rational scale-up strategies for products that comprise biomolecular assemblies. Biotechnol. Bioeng. 2010;107: 550,560. © 2010 Wiley Periodicals, Inc. [source] Characteristics of protein partitioning in an aqueous micellar-gel systemBIOTECHNOLOGY & BIOENGINEERING, Issue 2 2006L.J.P. van den Broeke Abstract Partitioning of proteins has been studied experimentally in a system combining a gel-bead phase and a nonionic micellar phase. The micellar phase consists of cylindrically shaped micelles, which are completely excluded from the gel-bead phase. Partitioning of single-component protein solutions (myoglobin, ovalbumin, and BSA) is determined by excluded-volume interactions in the micellar phase, and as a result the proteins prefer the gel-bead phase to the micellar phase. The protein concentration inside the gel beads increases with an increase in volume fraction of the micelles and increases with an increase in the size of the proteins. The protein partition coefficients obtained for a binary mixture of myoglobin and bovine serum albumin (BSA) show the same protein concentration dependence as the single-component protein partition coefficients. © 2005 Wiley Periodicals, Inc. [source] Rapid Matrix-Assisted Refolding of Histidine-Tagged ProteinsCHEMBIOCHEM, Issue 5 2009Tetyana Dashivets Abstract Matrix refolded: The formation of inclusion bodies, which are amorphous aggregates of misfolded insoluble protein, during recombinant protein expression, is one of the biggest bottlenecks in protein science. We report a stepwise, rational optimization procedure for refolding of insoluble proteins (see scheme). In comparison to refolding in-solution, this parallelized, matrix-assisted approach allows the refolding of various proteins in a fast and efficient manner. The formation of inclusion bodies (IBs),amorphous aggregates of misfolded insoluble protein,during recombinant protein expression, is still one of the biggest bottlenecks in protein science. We have developed and analyzed a rapid parallel approach for matrix-assisted refolding of recombinant His6 -tagged proteins. Efficiencies of matrix-assisted refolding were screened in a 96-well format. The developed methodology allowed the efficient refolding of five different test proteins, including monomeric and oligomeric proteins. Compared to refolding in-solution, the matrix-assisted refolding strategy proved equal or better for all five proteins tested. Interestingly, specifically oligomeric proteins displayed significantly higher levels of refolding compared to refolding in-solution. Mechanistically, matrix-assisted folding seems to differ from folding in-solution, as the reaction proceeds more rapidly and shows a remarkably different concentration dependence,it allows refolding at up to 1000-fold higher protein concentration than folding in-solution. [source] Surfactant Effects on Aeration Performance of Stirred Tank ReactorsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 10 2008M. Martinov Abstract The effect of surfactants on aeration performance in stirred tank reactors (STR) at high rates of foaming is studied. The volumetric oxygen transfer coefficient (kLa) and foaming activity estimated as foaming height (Hf) were determined. Biotechnology of lipopeptide biosurfactants from aerobic organisms, e.g., Bacillus subtilis were addressed. Using model solutions of known foam-generating properties, high-molecular weight surfactin and low-molecular weight sodium dodecyl sulphate (SDS), as well as impellers of different types, with flat and fluid-foil blades, clues on the concentration dependence of STR oxygen transfer and foaming as well as options for foam reduction in the presence of biosurfactant were sought. In response to a two-fold decrease of surface tension by surfactin, kLa values decreased up to 30,% but remained within the range expected for the mixing system in water; the experiments with SDS showing stronger dependence on surfactant concentration and surface tension. Mixing of surfactant media by a standard six-blade disc turbine (RT) imposed rate limitations on gassing. A low-shear impeller Narcissus (NS) could be used to avoid bulk foam outflow, while preserving kLa values that remained unchanged. The ,power per unit volume' correlation of kLa in stirred tanks is tested in the presence of surfactin. [source] Oxygen Uptake and Involvement of Superoxide Radicals upon Photolysis of Ketones in Air-saturated Aqueous Alcohol, Formate, Amine or Ascorbic Acid SolutionsPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2006Helmut Görner ABSTRACT The photolysis of acetophenone, benzophenone, 4-carboxy-benzophenone and benzil was studied in air-saturated aqueous solution in the presence of alcohols. The overall reaction is an oxidation of 2-propanol to acetone. The quantum yield of oxygen uptake (, -O2) increases with increasing 2-propanol concentration up to 0.9. The photoreaction can also be initiated by quenching of the ketone triplet state by ascorbic acid, formate or an amine e.g. triethylamine. Subsequent reactions of the involved radicals with oxygen yield the super-oxide radical and eventually hydrogen peroxide. For the ketones in the presence of 3,30 mM ascorbic acid or triethylamine , -O2= 0.3,0.9. The specific properties of ketones, including 4-methoxyacetophenone and 2-acetonaphthone, the radicals involved and the pH and concentration dependences of , -O2 are discussed. [source] | |||||||||||||||||||