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  • Molecular biophysics
  • Springer  (30)
  • American Physical Society  (1)
  • Periodicals Archive Online (PAO)
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  • Springer  (30)
  • American Physical Society  (1)
  • Periodicals Archive Online (PAO)
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  • 1
    Publication Date: 2022-05-25
    Description: Author Posting. © The Authors, 2006. This article is posted here by permission of American Physical Society for personal use, not for redistribution. The definitive version was published in Physical Review Letters 96 (2006): 018305, doi:10.1103/PhysRevLett.96.018305.
    Description: We study the liquid-crystalline phase behavior of a concentrated suspension of helical flagella isolated from Salmonella typhimurium. Flagella are prepared with different polymorphic states, some of which have a pronounced helical character while others assume a rodlike shape. We show that the static phase behavior and dynamics of chiral helices are very different when compared to simpler achiral hard rods. With increasing concentration, helical flagella undergo an entropy-driven first order phase transition to a liquid-crystalline state having a novel chiral symmetry.
    Description: M. S. and R. O. are supported by NIH Grant No. EB002583.
    Keywords: Entropy ; Molecular biophysics ; Liquid crystal phase transformations ; Symmetry ; Chirality
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: 765344 bytes
    Format: application/pdf
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 6 (1985), S. 593-608 
    ISSN: 0392-6737
    Keywords: Chemical thermodynamics ; Molecular biophysics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto In questo lavoro è stata studiata l'interazione fra bromuro di etidio (EB) e DNA in soluzione acqua-metanolo a varie temperature. Si è trovato che l'energia libera di Gibbs associata al legame DNA-EB può essere ben descritta da una relazione lineare nella costante dielettrica della soluzione, come visto anche per altri alcoli. Il ruolo dell'entalpia e dell'entropia di legame è piú semplice se queste quantità sono ricavate isodielettricamente (ε = costance). Con questa procedura, inoltre, è possibile separare le proprietà del solvente dalle caratteristiche del legame DNA-EB mostrando con chiarezza la presenza d'interazioni idrofobiche.
    Abstract: Резюме Исследуется взаимодействие ДНК с бромистым этидием (EB) в присутствии метанола ири различных температурах. Найдено, что свободная энергия Гиббса в случае связи ДНК-ЕВ линейно зависит от диэлектрической постоянной раствора. Указанное свойство обнаружено и для других спиртов. При рассмотрении энтальпии и энтропии в случае связи ДНК-ЕВ установлено, что их роль становится довольно простой, если их изменение осушествляется изодиэлектрически (ε=const). С помощью этой методики можно отличитя свойства, обусловленные растворителем, от свойств, овусловлениых взаимодействием ДНК и ЕВ. Таким образом, можно установить наличие гидрофобного взаимодействия.
    Notes: Summary The interaction of DNA with the dye ethidium bromide (EB) has been investigated under the presence of methanol at varying temperatures. The Gibbs free energy associated with the DNA-EB binding is found to be well described by its linear dependence upon the dielectric constant of the solution, a property also found for other alcohols. When the enthalpy and entropy associated with the binding are considered, it is found that their role becomes rather simple if their evaluation is performed isodielectrically (ε=const). According to this procedure, the varying properties of the solvent can be separated from those of the interacting DNA and EB and the presence of hydrophobic interactions becomes then well established.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 6 (1985), S. 618-630 
    ISSN: 0392-6737
    Keywords: Chemical thermodynamics ; Molecular biophysics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Si è studiata la denaturazione isoterma del DNA da timo di vitello indotta dalla presenza di quattro alcoli semplici in soluzione. Sono state eseguite sia misure a 67.2 °C, temperatura alla quale la frazione denaturata senza alcoli vale circa 20%, che profili di ≪fusione≫ a temperature variabili. I risultati mostrano che, al crescere della concentrazione e del gruppo alchilico degli alcoli la denaturazione dapprima raggiunge un valore massimo e poi torna indietro. Questo comportamento, attribuito alle proprietà ≪insolite≫ dell'acqua come risulta anche da misure di compressibilità indica che gli effetti idrofobici ed elettrostatici intervengono in modo complicato.
    Abstract: Резюме Исследуется изотермическая денатурация DNA тимуса, индуцированная наличием моногидридных спиртов в растворе. Измерения проводятся при температуре 67.2 °C, при которой денатурация в присутствии спиртов составляет около 20%. Также регистрируются профили плавления при различных температурах. Полученные результаты показывают, что при увеличении концентрации мума, а затем убывает. Это поведение, приписываемое свойствам ≪необыкновенной≫ воды, что получено также из измерений сжимаемости, указывает, что гидрофобные и электростатические эффекты связаны сложным образом.
    Notes: Summary The isothermal denaturation of calf thymus DNA, induced by the presence of some monohydric alcohols in the solution, was investigated. Measurements were performed at a temperature (67.2°C) at which the denaturation, in the absence of alcohols, is about 20% and melting profiles at varying temperatures were also recorded. Results show that with increasing alcohol concentration and alkyl group size DNA denaturation first reaches a maximum and then falls back. This behaviour, ascribed to «unusual» water properties as inferred also from compressibility measurements, indicates that hydrophobic and electrostatic effects are connected in a complex way.
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  • 4
    Electronic Resource
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    Springer
    Il nuovo cimento della Società Italiana di Fisica 5 (1985), S. 348-357 
    ISSN: 0392-6737
    Keywords: Molecular biophysics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto La formazione dei complessi di rame (II) con molecole di adenosina-5′-monofosfato (AMP), adenosina-5′-difosfato (ADP), adenosina-5′-trifosfato (ATP) e con polifosfati inorganici è stata studiata in soluzione acquosa, nell’intervallo dipH da 3 a 12, analizzando l’effetto del campo legante sulle transizioni ottiche tra livellid dello ione Cu(II). I risultati mostrano, al variare delpH, l’esistenza di diversi complessi tra loro in equilibrio in relazione allo stato di ionizzazione dell’adenina e dei gruppi fosfato e ribosio. In particolare, per valori dipH maggiori di 8, il rame interagisce con il gruppo ribosio dei ribonucleotidi esaminati, mentre tale interazione non si osserva nel caso dei corrispondenti desossiribonucleotidi.
    Notes: Summary The interaction of copper(II) with the 5′-nucleotides: adenosine monophosphate (AMP), adenosine diphosphate (ADP), adenosine triphosphate (ATP) and with inorganic polyphosphate solutions has been studied as a function ofpH in thepH range 3 to 12. Our approach is the study of the effects that the field of ligands produces on the opticald-d transitions of the cupric ion. The results show that the Cu(II)-adenosine phosphate complexes exist in a variety of forms in equilibrium, the percentage of each species varying according to the state of ionization of the intrinsic adenine, phosphate and ribose groups. AtpH values greater than 8 an interaction becomes manifest between the copper ions and the hydroxyl groups of ribose, while this effect is not observed in the case of the Cu(II)-deoxyadenosine systems.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 13 (1991), S. 261-271 
    ISSN: 0392-6737
    Keywords: Diffusion and ionic conduction in liquids ; Nuclear magnetic resonance and relaxation ; Molecular biophysics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Water proton spin-lattice relaxation and self-diffusion in aqueous solutions of human serum albumin have been studied by1H NMR as a function of the protein concentration. Spin-lattice relaxation data, which display a nonlinear behaviour with the protein concentration, could be fitted with a two-phase model taking into account the experimentally determined hydration («bound») water values. Despite a similar trend is registered for the water self-diffusion coefficient, such a model has been found unable to explain the related experimental data taken as a function of the biomolecule concentration. On the other hand, the solute-induced proton self-diffusion decrease could be satisfactorily interpreted by postulating an enhanced probability of hydrogen-bond formation occurring within the «vicinal» water surrounding the biomolecules for several hydration shells. The consistency within the two models is discussed in connection with the magnetic interactions occurring within the solute-solvent systems.
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  • 6
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    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1585-1594 
    ISSN: 0392-6737
    Keywords: Molecular biophysics ; Defects in liquid crystals ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The effect of adding the defect-forming molecules melittin and C12E5 to DMPC membranes has been studied and the corresponding phase diagrams established. Light, X-ray and neutron small-angle scattering have been used to characterize the mixed membranes. Both systems show a melting of the lamellar Lα into an isotropic phase upon addition of the second membrane constituent. The molar ratio, where the melting occurs is the same in concentrated and dilute samples. For the DMPC/C12E5 system not only membrane composition, but also temperature can be used to induce a transition from an isotropic to a lamellar phase.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1447-1455 
    ISSN: 0392-6737
    Keywords: Disperse systems ; Molecular biophysics ; Physical chemistry of solutions of biological macromolecules ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The aggregation behaviour of zinc-free insulin has been studied by small-angle neutron scattering as a function of protein concentration,pH, and ionic strength of the solution. The distance distribution functions for the 12 samples have been obtained by indirect Fourier transformation. The weight-averaged molecular mass and thez-averaged radius of gyration were determined. Both quantities vary systematically with the experimental conditions. They increase with decreasingpH and with increasing ionic strength. The radius of gyration scales as a power law of the weight-average mass with the exponent 0.44. A similar scaling is found for a set of oligomers structures based on the crystal structure of zinc-free insulin. The mass distribution between the oligomers was determined by a model based on these oligomers. The results from this model and the Fourier transformations have been compared to an equilibrium model recently introduced by Kadimaet al. The model takes into account the variation of the effective charge of the monomer withpH and ionic strength. The neutron scattering results agree well with the predictions of the model.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 1347-1354 
    ISSN: 0392-6737
    Keywords: Molecular biophysics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary All denaturational thermodynamic changes (ΔH, ΔS, ΔG) were calculated for the thermal unfolding of azurin fromPseudomonas Aeruginosa. DSC data could not be directly studied in terms of classical thermodynamics, because the thermal unfolding of azurin is an irreversible process. However, a mathematical extrapolation of heat capacity curves to infinite scan rate allowed us to obtain the denaturational enthalpy change and the melting temperature related to the reversible step. The denaturational heat capacity change (ΔC p ), together with all the relevant contributions of polar and apolar groups to the thermodynamic parameters of azurin were calculated according to an approach taking into account the common features of protein unfolding and dissolution of model compounds. A comparison between the experimental and the expected denaturational thermodynamic values was briefly discussed.
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  • 9
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    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 371-374 
    ISSN: 0392-6737
    Keywords: X-ray ; Mössbauer and other γ-ray spectroscopic analysis methods ; Molecular biophysics ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The Rayleigh scattering of Mössbauer radiation has been measured on highly oriented fibres of Na-hyaluronate at different hydration levels. The elastic-and inelastic-scattering intensities, measured as a function of the scattering vectorQ, have provided information on the dynamic structuring of the water molecules to the polysaccharidic chains.
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  • 10
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    Springer
    Il nuovo cimento della Società Italiana di Fisica 11 (1989), S. 1481-1487 
    ISSN: 0392-6737
    Keywords: Molecular biophysics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Sono stati analizzati spettri in dicroismo circolare (CD) di DNA di calf thymus in soluzioni acquose di LiCl, NaCl, KCl e CsCl a 25°C nell’intervallo spettrale (215÷300) nm. È stata messa in evidenza una correlazione tra le variazioni osservate negli spettri CD, al variare della concentrazione di sale, e la concentrazione d’acqua libera presente in soluzione (vedi lavoro precedente). È stato mostrato che effetti specifici, presenti nel processo studiato, trovano corrispondenza in semplici proprietà di idratazione degli ioni considerati.
    Abstract: Резюме Исследуются спектры кругового дихроизма ДчК тимуса теленка в водных раствоах LiCl, NaCl, KCl и CsCl при 25°C в спектральном интервале (215÷300) нм. Обнаружена корреляция между наблюденными изменениями спектров кругового дихроизма и измененениями концентрации электролита и концентрации свободной воды, присутствующей в растворе (см. предыдщую статью). Показывается, что специфические катионные эффекты, обнауженные в этом продессе, обьясњяются простыми свойствами гидратадии рассматриваемых катионов.
    Notes: Summary The circular dichroism (CD) spectra of calf thymus deoxyribonucleic acid have been examined at 25°C over the wavelength range (215÷300) nm in aqueus solutions of LiCl, NaCl, KCl, and CsCl. The CD changes observed as the electrolyte concentration is varied have been correlated quantitatively with the magnitude of the hydration of the ions in these solutions (see a preceding paper). It is shown that specific cation effects present in this process correspond consistently to simple hydration properties of these same cations.
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