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  • 1
    Electronic Resource
    Electronic Resource
    Determination of equilibrium properties of biomolecular systems using multidimensional adaptive umbrella sampling (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 8048-8067 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two-dimensional adaptive umbrella sampling with the first umbrella coordinate equal to the potential energy of the system and the second umbrella coordinate equal to a function that discriminates important folded conformations from unfolded conformations is used to determine the equilibrium properties of complex biological systems. Compared to one-dimensional adaptive umbrella sampling with the potential energy as umbrella coordinate (multicanonical sampling), more reliable results can be obtained in certain cases. The method is applied to a helical peptide (RN24) with an analytical continuum solvent potential in combination with the PARAM19 force field of CHARMM. This effective potential energy function has been shown to describe the structural preferences of solvated peptides. With the two-dimensional approach and the deviation from the helical structure as the second umbrella coordinate, a converged description of the structural properties and the thermodynamics of the peptide RN24 is obtained. In particular, we find that the formation of the helix of RN24 occurs as a transition accompanied by a characteristic peak in the heat capacity. A formalism is described that uses the weighting factors obtained from a self-consistent solution of the weighted histogram analysis method equations to combine the results from a series of simulations with different biases and calculate the ensemble average of any dynamical variable as a function of the temperature without the need for extracting the density of states from the simulations. It is shown how the formalism can be used to calculate thermodynamic properties of the system. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480139
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  • 2
    Electronic Resource
    Electronic Resource
    Molecular dynamics simulation of a bilayer of 200 lipids in the gel and in the liquid crystal phase (1993)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 97 (1993), S. 8343-8360 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100133a034
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  • 3
    Electronic Resource
    Electronic Resource
    Evaluation of Auditors' Going-Concern Risk in Family Businesses (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Family business review 5 (1992), S. 0 
    Details
    ISSN: 1741-6248
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Sociology , Economics
    Notes: This article discusses recently altered mandates for auditors considering an entity's ability to continue as a going concern. The authors evaluate the appropriateness of these standards in engagements involving family firms and conclude that existing procedures are inadequate to assess the risks unique to family businesses. A detailed checklist of questions is proposed as warning signals in family businesses about problems affecting the going-concern status.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1741-6248.1992.00063.x
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  • 4
    Electronic Resource
    Electronic Resource
    Attacking pain at its source: new perspectives on opioids (2003)
    [s.l.] : Nature Publishing Group
    Nature medicine 9 (2003), S. 1003-1008 
    Details
    ISSN: 1546-170X
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] The treatment of severe pain with opioids has thus far been limited by their unwanted central side effects. Recent research promises new approaches, including opioid analgesics acting outside the central nervous system, targeting of opioid peptide–containing immune cells to peripheral damaged ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nm908
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  • 5
    Electronic Resource
    Electronic Resource
    Direct activation of human TRPC6 and TRPC3 channels by diacylglycerol (1999)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 397 (1999), S. 259-263 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Eukaryotic cells respond to many hormones and neurotransmitters with increased activity of the enzyme phospholipase C and a subsequent rise in the concentration of intracellular free calcium ([Ca2+]i). The increase in [Ca2+]i occurs ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/16711
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  • 6
    Electronic Resource
    Electronic Resource
    Solution conformations of structured peptides: continuum electrostatics versus distance-dependent dielectric functions (1999)
    Springer
    Theoretical chemistry accounts 101 (1999), S. 194-204 
    Details
    ISSN: 1432-2234
    Keywords: Key words: Helical peptide ; β-Hairpin ; Random coil ; Umbrella sampling ; Multicanonical sampling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. To compare different implicit solvent potentials, the folding thermodynamics of the helical peptide RN24 and the β-hairpin peptide BH8 are studied by molecular dynamics simulation with adaptive umbrella sampling. As the potential energy functions, the analytical continuum solvent (ACS) potential and three simplified variants, termed EPSR1, EPSR4, and EPSR10, are used. The ACS potential is a combination of the standard CHARMM force field for the internal energy (bonds, angles, dihedrals) and the van der Waals energy with the analytical continuum electrostatic (ACE) potential and a non-polar solvation potential. The EPSR potentials differ from the ACS potential by the use of Coulomb's law with a distance-dependent dielectric function to calculate the electrostatic energy. With the ACS potential, quantitative agreement with experiment is obtained for the helix propensity (RN24: 62% calculated vs 50–60% experiment) and the β-hairpin propensity (BH8: 33% calculated vs 19–37% experiment) of the peptides. During the simulations with the EPSR potentials, no significant formation of secondary structure is observed. It is shown that the preference for coil conformations over conformations with secondary structure by the EPSR potentials is due to an overestimation of the energy of salt bridge formation, independent of the magnitude of the Coulomb energy relative to the other energy terms. Possible improvements of the distance-dependent dielectric functions which may permit their application to the simulation of peptide folding, are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002140050429
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  • 7
    Electronic Resource
    Electronic Resource
    Adaptive umbrella sampling of the potential energy: modified updating procedure of the umbrella potential and application to peptide folding (1999)
    Springer
    Theoretical chemistry accounts 101 (1999), S. 62-66 
    Details
    ISSN: 1432-2234
    Keywords: Key words: Adaptive umbrella sampling ; Multicanonical sampling ; Helical peptide ; β-hairpin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. Adaptive umbrella sampling of the potential energy is used as a search method to determine the structures and thermodynamics of peptides in solution. It leads to uniform sampling of the potential energy, so as to combine sampling of low-energy conformations that dominate the properties of the system at room temperature with sampling of high-energy conformations that are important for transitions between different minima. A modification of the procedure for updating the umbrella potential is introduced to increase the number of transitions between folded and unfolded conformations. The method does not depend on assumptions about the geometry of the native state. Two peptides with 12 and 13 residues, respectively, are studied using the CHARMM polar-hydrogen energy function and the analytical continuum solvent potential for treatment of solvation. In the original adaptive umbrella sampling simulations of the two peptides, two and six transitions occur between folded and unfolded conformations, respectively, over a simulation time of 10 ns. The modification increases the number of transitions to 6 and 12, respectively, in the same simulation time. The precision of estimates of the average effective energy of the system as a function of temperature and of the contributions to the average effective energy of folded conformations obtained with the adaptive methods is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002140050407
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  • 8
    Electronic Resource
    Electronic Resource
    General effect of photosynthetic electron transport inhibitors on translation precludes their use for investigating regulation of D1 biosynthesis in Synechococcus sp. strain PCC 7942 (1999)
    Springer
    Photosynthesis research 62 (1999), S. 261-271 
    Details
    ISSN: 1573-5079
    Keywords: cyanobacteria ; light-regulated genes ; photosynthetic electron transport ; psbA ; translation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Both light itself and excitation pressure have been implicated as the environmental signal that stimulates interchange of the two forms of the D1 protein of photosystem II (PS II) in Synechococcus sp. strain PCC 7942. We sought an explanation for conflicting reports regarding the role of photosynthetic electron transport in regulation of psbA expression and D1 interchange. Inhibitors that block at different points in the photosynthetic electron transport chain were administered and the effect on expression of psbAII, which encodes the high-light-induced form II of D1, was examined by measuring changes in transcript levels and in the activities of reporter enzymes. Both 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of PSII, and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB), an inhibitor of the cytochrome b6/f complex, prevented high-light-induced increase in β-galactosidase activity from a psbAII::lacZ gene fusion when added at a concentration that completely inhibits photosynthetic electron transport (1 μM). The same effect was observed for luciferase activity from transcriptional and translational fusions of psbAII to the luxAB genes from Vibrio harveyi. DCMU (1 μM) arrested luciferase expression at low-light levels – thus eliminating the high light response – whereas a sublethal concentration (50 nM), which reduces electron transport by 50%, had intermediate effects on psbAII-driven luciferase activity. However, psbAII transcript levels, monitored by northern blot analysis, were not altered by electron transport inhibitors, either at low-light intensity or following a high-light exposure. The suppressive effect of DCMU on expression of reporter enzymes was not restricted to the high-light response of psbAII-driven reporter systems, but was also observed using an isopropyl-(-d)-thiogalactopyranoside (IPTG)-inducible trc promoter fused to luxAB. This construct only marginally responded to IPTG addition when DCMU was present. Thus, blocking electron transport in Synechococcus affects the translation machinery in a general way, and the use of electron transport inhibitors is of limited value when focusing on specific redox regulation of D1 protein synthesis or degradation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006340423948
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  • 9
    Electronic Resource
    Electronic Resource
    Report Joint Meeting of GVC Committees on “Particle Characterization” and “Crystallization”, Winterthur 1988 (1989)
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 6 (1989), S. 81-85 
    Details
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This Committee stood under the banner of joint meetings with the Crystallization Committee. Further it was characterized by two aspects, namely technological innovation in connection with measurement methods and their (on-line) application in engineering processes, whether for the sake of model formation or for process control or quality assurance in industry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ppsc.19890060113
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  • 10
    Electronic Resource
    Electronic Resource
    Preparation Technology for Fine Particle MeasurementDedicated to Professor Kurt Leschonski on the occasion of his 60th birthday (1991)
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 8 (1991), S. 1-7 
    Details
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Describing the disperse state is important for quality assurance, operational safety and the design and modelling of processes, especially in solids technology. Starting materials, intermediates and end products have to be characterized. Apart from representative sampling, preparation greatly influences the results of particle characterization. Very fine particles are normally agglomerated unless a highly dispersed state is stabilized by an additive. For a meaningful measurement, they must be preserved in this state or be definitely dispersed, depending on the type of problem.If the point of interest is the present disperse state with regard to the processing characteristics, e.g. for a filtration, the system should not be changed by the preparation method. If it is necessary to determine the property functions, i. e. the functional relationship between technological and physical properties, it is necessary in general to use a high dispersion energy or a long dispersing time in order to obtain the best achievable dispersion. The finer and more unstable a disperse phase is, the more the correct processing is important for the result. The problems of dispersion in gases and liquids are discussed with some examples.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ppsc.19910080102
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