Correlation of counterions with rodlike macroions as assessed by anomalous small-angle X-ray scattering

Guilleaume, Birgit; Ballauff, Matthias; Goerigk, G.; Wittemann, Matthias; Rehahn, Matthias

doi:10.1007/s003960100521

Cited by 27 publications

(36 citation statements)

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“…(16), and get the cross-term from Eq. (18). Examples of how this analysis is used are given in Section III.…”

Section: Solvent Is Pure Watermentioning

confidence: 99%

“…Changing the energy of the incident beam in an anomalous SAXS (ASAXS) experiment is one approach, varying the atomic scattering factor of a given ion. [14][15][16]18,34,35 Another approach uses heavy ion replacement, assuming the ion and water distributions are similar for the same type of ions (alkalies, for example). 14,20 By doing this, onlyF ion is allowed to vary while the co-ion and hydration terms are fixed.…”

Section: Solvent Contains Ions and Watermentioning

confidence: 99%

“…13 Anomalous small angle X-ray scattering (ASAXS) data in principle yield additional information about the extent of perturbations of the ion/water environment, [14][15][16][17] but the ASAXS signal is known to be intertwined with all components in the system, complicating the analysis. 13,18 Efforts to extract the contribution from ions to ASAXS profiles date back to 2003 with the work of Ballauff and coworkers. 15,19 Using multiple energy ASAXS, they were able to decompose the total scattering intensity into solute-ion and ion-ion contributions, though limited to spherical solutes.…”

Section: Introductionmentioning

confidence: 99%

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Extracting water and ion distributions from solution x-ray scattering experiments

Nguyên

Pabit

Pollack

et al. 2016

The Journal of Chemical Physics

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Small-angle X-ray scattering measurements can provide valuable information about the solvent environment around biomolecules, but it can be difficult to extract solvent-specific information from observed intensity profiles. Intensities are proportional to the square of scattering amplitudes, which are complex quantities. Amplitudes in the forward direction are real, and the contribution from a solute of known structure (and from the waters it excludes) can be estimated from theory; hence, the amplitude arising from the solvent environment can be computed by difference. We have found that this "square root subtraction scheme" can be extended to non-zero q values, out to 0.1 Å −1 for the systems considered here, since the phases arising from the solute and from the water environment are nearly identical in this angle range. This allows us to extract aspects of the water and ion distributions (beyond their total numbers), by combining experimental data for the complete system with calculations for the solutes. We use this approach to test molecular dynamics and integral-equation (3D-RISM (three-dimensional reference interaction site model)) models for solvent structure around myoglobin, lysozyme, and a 25 base-pair duplex DNA. Comparisons can be made both in Fourier space and in terms of the distribution of interatomic distances in real space. Generally, computed solvent distributions arising from the MD simulations fit experimental data better than those from 3D-RISM, even though the total small-angle X-ray scattering patterns are very similar; this illustrates the potential power of this sort of analysis to guide the development of computational models. Published by AIP Publishing. [http://dx

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“…(16), and get the cross-term from Eq. (18). Examples of how this analysis is used are given in Section III.…”

Section: Solvent Is Pure Watermentioning

confidence: 99%

Section: Solvent Contains Ions and Watermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Extracting water and ion distributions from solution x-ray scattering experiments

Nguyên

Pabit

Pollack

et al. 2016

The Journal of Chemical Physics

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“…Thus the chains act as a template and may provide access to their shape. Above this, anomalous small angle x-ray scattering (ASAXS) offers additional information if the wavelength of the scattered X-rays is varied [32][33][34][35][36][37][38]. This enabled Goerigk et al [23] and Ballauff et al [37,38] for the first time to isolate the scattering factor of the counterions condensing on polyelectrolytes.…”

mentioning

confidence: 99%

Shrinking of anionic polyacrylate coils induced by Ca2+, Sr2+ and Ba2+: A combined light scattering and ASAXS study

2006

Self Cite

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Abstract. Anionic polyacrylate chains (NaPA) form precipitates if alkaline earth cations are added in stoichiometric amounts. Accordingly, precipitation thresholds were established for three different alkaline earth cations Ca 2+, Sr 2+ and Ba 2+. Close to the precipitation threshold, the NaPA chains significantly decrease in size. This shrinking process was followed by means of combined static and dynamic light scattering. Intermediates were generated by varying the ratio MCl 2 /[NaPA] with M denoting the respective alkaline earth cation. All experiments were performed at an inert salt level of 0.01 M NaCl. Similar coil -to -sphere transitions could be observed with all three alkaline earth cations Ca 2+ , Sr 2+ and Ba 2+. Based on these findings, supplementary conventional and anomalous small angle x-ray scattering experiments using selected intermediates close to the precipitation threshold of SrPA were performed. The distribution of Sr-counterions around the polyacrylate chains in aqueous solution provided the desired scattering contrast. Energy dependent scattering experiments enabled successful separation of the pure-resonant terms, which solely stem from the counterions. The Sr 2+ scattering roughly reflects the monomer distribution of the polyacrylate chains. Different ratios of the concentrations of [SrCl 2 ]/[NaPA] revealed dramatic changes in the scattering curves. The scattering curve at the lowest ratio indicated an almost coil-like behaviour, while at the higher ratios the scattering curves supported the model of highly contracted polymer chains. Most of X-ray scattering experiments on intermediate states revealed compact structural elements which were significantly smaller than the respective overall size of the NaPA particles.

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“…We assume that only the counterions have an anomalous contribution according to Equation (1.1). For ions immersed in a medium with electron density ρ s the number of excess electrons per ion is f ion = f ion − ρ s V ion , [5,12,13] where V ion is the volume of a single ion. The quantity f 0 hence denotes the scattering contribution of a single counterion that is independent of the energy of the incident radiation.…”

Section: Scattering Cross-sections In Asaxsmentioning

confidence: 99%

Correlations and Fluctuations of Charged Colloids as Determined by Anomalous Small‐Angle X‐Ray Scattering

Jusufi

Ballauff

2006

Macro Theory & Simulations

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Summary:We performed molecular dynamics simulation of a charged colloidal particle with explicit counterions. Our work provides a direct comparison between simulations and ASAXS-experiments, offering insight into the counterion distribution of charged colloidal suspensions. We give a detailed constitution of the appearing scattering terms with their physical meaning. It is shown that the crosscorrelation between a macroion and its counterions gives the meanfield approximation of the counterion density even if the counterion system is highly fluctuating. Furthermore, it is shown that cross-correlations can be negative due to oscillations of the density amplitudes of the macroion and counterions and, therefore, must be distinguished from other scattering contributions. These oscillations become more pronounced if the counterions exhibit a fixed shape and if the size of the macroion and that of the counterion system are different.Simulation sanpshot of a charged colloid (big central sphere) with counterions (small spheres).

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Correlation of counterions with rodlike macroions as assessed by anomalous small-angle X-ray scattering

Cited by 27 publications

References 0 publications

Extracting water and ion distributions from solution x-ray scattering experiments

Extracting water and ion distributions from solution x-ray scattering experiments

Shrinking of anionic polyacrylate coils induced by Ca2+, Sr2+ and Ba2+: A combined light scattering and ASAXS study

Correlations and Fluctuations of Charged Colloids as Determined by Anomalous Small‐Angle X‐Ray Scattering

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