Boundary conditions for free A-DNA in solution and the relation of local to global DNA structures at reduced water activity.

Because of repeated claims that A-DNA cannot exist without aggregation or condensation, the state of DNA restriction fragments with 84-859bp has been analyzed in aqueous solutions upon reduction of the water activity. Rotational diffusion times tau (d) measured by electric dichroism at different water activities with a wide variation of viscosities are normalized to values tau (c) at the viscosity of water, which indicate DNA structures at a high sensitivity. For short helices (chain lengths [Formula: see text]≤persistence length p), cooperative formation of A-DNA is reflected by the expected reduction of the hydrodynamic length; the transition to the A-form is without aggregation or condensation upon addition of ethanol at monovalent salt ≤1mM. The aggregation boundary, indicated by a strong increase of tau (c), is shifted to higher monovalent salt (≥4mM) when ethanol is replaced by trifluoroethanol. The BA transition is not indicated anymore by a cooperative change of tau (c) for [Formula: see text]p; tau (c) values for these long chains decrease upon reduction of the water activity continuously over the full range, including the BA transition interval. This suggests a non-cooperative BC transition, which induces DNA curvature. The resulting wide distribution of global structures hides changes of local length during the BA transition. Free A-DNA without aggregation/condensation is found at low-salt concentrations where aggregation is inhibited and/or very slow. In an intermediate range of solvent conditions, where the A-form starts to aggregate, a time window remains that can be used for analysis of free A-DNA in a quasi-equilibrium state

Dipole reversal in bacteriorhodopsin and separation of dipole components

The electrostatics of purple membranes has been analyzed by measurements of the electric dichroism in dc and ac fields in a broad pH range. The dc data are mainly used to characterize the permanent dipole, whereas the ac data serve as control for changes of global structure and of the induced dipole. At pH values from 8 to 3.5, the dc dichroism is negative at low field strengths and turns to positive values at higher field strengths, in qualitative agreement with the orientation function for disks having a permanent dipole moment perpendicular to the plane and an induced dipole moment in the plane. The minimum value of the dichroism, ξmin/dc , indicates the permanent dipole and shows a complex dependence on the pH but does not approach zero at any pH between 3.5 and 8, which would be expected for a simple reversal of the permanent dipole. However, the dependence of ξmin/dc on pH shows a λ point at pH 4.9, which reflects reversal of the dipole. Fitting of the stationary dichroism for E smaller or equal to 12 kV m-1 to the orientation function shows a decrease of the permanent dipole λ in the pH range 5 to about 50% of the value found at pH 7. In the same pH range, the limit dichroism, ξdc/infinity, derived from dc data also decreases to about 50% of the value at pH 7, whereas parallel measurements of the ac dichroism show almost constant ξac/infinity values. The combined observations indicate reversal of the permanent dipole, changes of disk bending, and the existence of a fluctuating dipole moment, probably resulting from bending fluctuations. Reversal of the dipole moment at pH 4.9 is confirmed by combined pH and field jump experiments. The direction of the dipole is reverted in the same pH range as the direction of stationary pH changes upon illumination, indicating an important function of the dipole for vectorial proton transfer. Comparison of experimental data with simple calculations of the protein dipole from the crystal structure indicates the existence of a large dipole component, which is directed opposite to the protein dipole at pH 7 and is probably due to a nonsymmetric distribution of charges on lipid residues. The results indicate a high degree of compensation in the electric asymmetry, which seems to be necessary for stability of purple membranes

Effect of aminoacylation on tRNA conformation.

Translational diffusion coefficients have been simulated for various conformations of tRNAPhe (yeast) by bead models, in order to analyze data obtained by dynamic light scattering on the free and the aminoacylated form. The 18% increase of the translational diffusion coefficient upon deacylation, reported by Potts et al. (1981), could not be represented by any change of the L-hinge angle, but could only be simulated by a conformation change to an extended form with extensive dissociation of base pairs. Since extensive unpairing is not consistent with evidence accumulated in the literature, the change of the diffusion coefficient must be mainly due to processes other than intramolecular conformational changes

Unfolding Collapsed Polyelectrolytes in Alternating-Current Electric Fields

We investigate the unfolding of single polyelectrolyte (PE) chains collapsed by trivalent salt under the action of alternating-current (AC) electric fields through computer simulations and theoretical scaling. The results show that a collapsed chain can be unfolded by an AC field when the field strength exceeds the direct-current (DC) threshold and the frequency is below a critical value, corresponding to the inverse charge relaxation/dissociation time of condensed trivalent counterions at the interface of the collapsed electrolyte. This relaxation time is also shown to be identical to the DC chain fluctuation time, suggesting that the dissociation of condensed polyvalent counterion on the collapsed PE interface controls the polyelectrolyte dipole formation and unfolding dynamics under an AC electric field.Comment: 18 pages, 5 figures, submitte

An unusual electrooptical effect observed for DNA fragments and its apparent relation to a permanent electric moment associated with bent DNA.

Dichroism decay curves of DNA fragments with chain lengths in the range of 179–256 bp show an amplitude inversion suggesting the existence of a positive dichroism component, when these fragments are dissolved at monovalent salt concentrations above approx. 5 mM and are exposed to field pulses with amplitudes and/or lengths above critical values. At the critical values, the unusual dichroism is reflected by an apparent acceleration of the decay curves, which can be fitted by single exponentials with time constants much below the values expected from the DNA contour lengths. The critical pulse amplitudes and lengths decrease with increasing DNA chain length and increasing salt concentration. The experimental data are consistent with results obtained by hydrodynamic and electric model calculations on smoothly bent DNA double helices. The DNA is represented by a string of overlapping beads, which is used to calculate the rotational diffusion tensor and the center of diffusion. The distribution of phosphate charges is asymmetric with respect to this center and thus gives rise to a substantial permanent dipole moment. The magnitude of this dipole moment is calculated as a function of DNA curvature and is used together with experimental values of polarizabilities for simulations of dichroism decay curves. The curves simulated for bent DNA show the same phenomenon as observed experimentally. The ionic strength dependence of the unusual dichroism is explained by an independently observed strong decrease of the polarizability with increasing salt concentration. The field strength dependence is probably due to field-induced bending of double helices driven by the change of the dipole moment. Although our calculations are on rigid models of DNA and thus any flexibility of the double helix has not been considered, we conclude that the essential part of our experimental results can be explained by our model

Psychologische Faktoren der Steuergerechtigkeit

"Die Wirtschaftswissenschaften betrachten Probleme der Steuergerechtigkeit vor allem unter Aspekten des Trade-off zwischen „equity“ und „efficiency“. Dabei werden psychologische Faktoren weitgehend unberücksichtigt gelassen. Psychologische Arbeiten zur Gerechtigkeit jedoch befassen sich in der Regel nur mit der Verteilung positiver, selten aber mit der Verteilung negativer Güter. Aus dieser Perspektive stellt die Perzeption von Steuern grundsätzlich etwas Besonderes dar. Die Literatur zur Motivation der Steuerhinterziehung und zu sozialen Dilemmata legt den Gedanken nahe, dass zur Vorhersage subjektiv erlebter Steuergerechtigkeit die gängigen Gerechtigkeitstheorien nicht ausreichen: Es lässt sich nicht allein durch Equity- und Mehr-Prinzipien-Ansätze erklären, warum und unter welchen Umständen Menschen Steuern als gerecht empfinden. Es bedarf offensichtlich der Berücksichtigung weiterer Aspekte aus den Bereichen des prosozialen Handelns, der Ethik , der sozialen Integration und angrenzenden Problemkreisen. In der vorliegenden Untersuchung ist ein erster Schritt in diese Richtung unternommen worden. Hierzu wurde in einem varianzanalytischen 3x2x2 Design eine Auswahl von Variablen mit Hilfe eines Ensembles von Szenarien systematisch variiert. Es zeigt sich, dass in der Bevölkerung kein konsistentes Konzept zu Steuern verankert ist, dass Steuern eher als Last empfunden werden, dass die steuerpolitische Lage keinen Einfluss auf die soziale Integration einer Person hat und dass es zur Rechtfertigung höherer Steuern vor allem auf eine utilitaristische und deontologische Argumentation ankommt, bei der die Hilfeleistung positiv besetzt wird."[Autorenreferat]"Thinking about taxes and justice, economists focus on the trade-off-relationship between equity and efficiency and tend to neglect psychological aspects. Psychologists on the other hand usually only deal with the distribution of positive goods, neglecting the distribution of negative goods. From this point of view taxes are something special. It can be seen from the literature on tax evasion and social dilemmas that the commonly used theories of justice and injustice (principles like equity, equality and need) are not a sufficient explanation for people´s feelings about taxes and justice.It seems to be necessary also to regard aspects which are dealt with in prosocial behaviour, ethics, social integration etc. We tried to integrate these different aspects by applying an variance-analytical 3x2x2 design. The variables were systematically changed in different scenarios. It can be seen from the results that people have no consistent attitudes toward taxes, that they think negatively of taxes, that their tax and financial status has no influence on their social integration and that higher taxes could only be employed successfully by using utilitarian and deontological arguments and thereby pointing out that this kind of prosocial behaviour is something useful."[author´s abstract

The effects of exercise on sleep in unipolar depression: A systematic review and network meta-analysis

Insomnia predicts the onset, course, and reoccurrence of unipolar depression. However, systematic reviews of treatment options for insomnia in unipolar depression are lacking. After screening 7725 records, 17 trials comprising 1645 patients randomized to 13 treatments were included for quantitative synthesis. Network meta-analysis showed that compared to a passive control condition, all exercise interventions except moderate aerobic exercise alone resulted in significantly better sleep outcomes. Compared with treatment as usual, mind-body exercise plus treatment as usual (SMD: −0.46; 95% CI: −0.80, −0.12) and vigorous strength exercise (SMD: −0.61; 95% CI: −1.12, −0.10) were significantly more effective. Pairwise meta-analyses showed that mind-body exercise (SMD: −0.54; 95% CI: −0.85, −0.23) had beneficial effects compared to passive control. The network meta-analysis is statistically very robust with low heterogeneity, incoherence, and indirectness. However, confidence in the findings was moderate to very low, primarily due to within-study bias. This is the first network meta-analysis to assess exercise's efficacy to improve sleep quality in patients with depression. The findings confirm the benefits of exercise as an add-on treatment for depression. This consolidation of the current state of evidence can help clinicians make evidence-based decisions