Molecular Mechanism for the Hofmeister Effect Derived from NMR and DSC Measurements on Barnase

The effects of sodium thiocyanate, sodium chloride, and sodium sulfate on the ribonuclease barnase were studied using differential scanning calorimetry (DSC) and NMR. Both measurements reveal specific and saturable binding at low anion concentrations (up to 250 mM), which produces localized conformational and energetic effects that are unrelated to the Hofmeister series. The binding of sulfate slows intramolecular motions, as revealed by peak broadening in 13 C heteronuclear single quantum coherence spectroscopy. None of the anions shows significant binding to hydrophobic groups. Above 250 mM, the DSC results are consistent with the expected Hofmeister effects in that the chaotropic anion thiocyanate destabilizes barnase. In this higher concentration range, the anions have approximately linear effects on protein NMR chemical shifts, with no evidence for direct interaction of the anions with the protein surface. We conclude that the effects of the anions on barnase are mediated by solvent interactions. The results are not consistent with the predictions of the preferential interaction, preferential hydration, and excluded volume models commonly used to describe Hofmeister effects. Instead, they suggest that the Hofmeister anion effects on both stability and solubility of barnase are due to the way in which the protein interacts with water molecules, and in particular with water dipoles, which are more ordered around sulfate anions and less ordered around thiocyanate anions

Analysis of Mesoscopic Structured 2-Propanol/Water Mixtures Using Pressure Perturbation Calorimetry and Molecular Dynamic Simulation

In this paper we demonstrate the application of pressure perturbation calorimetry (PPC) to the characterization of 2-propanol/water mixtures. PPC of different 2-propanol/water mixtures provides two useful measurements: (i) the change in heat (ΔQ); and (ii) the [δC¯p/δp]T[δC¯p/δp]T value. The results demonstrate that the ΔQ values of the mixtures deviate from that expected for a random mixture, with a maximum at ~20–25 mol% 2-propanol. This coincides with the concentration at which molecular dynamics (MD) simulations show a maximum deviation from random distribution, and also the point at which alcohol–alcohol hydrogen bonds become dominant over alcohol–water hydrogen bonds. Furthermore, the [δC¯p/δp]T[δC¯p/δp]T value showed transitions at 2.5 mol% 2-propanol and at approximately 14 mol% 2-propanol. Below 2.5 mol% 2-propanol the values of [δC¯p/δp]T[δC¯p/δp]T are negative; this is indicative of the presence of isolated 2-propanol molecules surrounded by water molecules. Above 2.5 mol% 2-propanol [δC¯p/δp]T[δC¯p/δp]T rises, reaching a maximum at ~14 mol% corresponding to a point where mixed alcohol–water networks are thought to dominate. The values and trends identified by PPC show excellent agreement not only with those obtained from MD simulations but also with results in the literature derived using viscometry, THz spectroscopy, NMR and neutron diffraction

The Asymptotics of Wilkinson's Iteration: Loss of Cubic Convergence

One of the most widely used methods for eigenvalue computation is the $QR$ iteration with Wilkinson's shift: here the shift $s$ is the eigenvalue of the bottom $2\times 2$ principal minor closest to the corner entry. It has been a long-standing conjecture that the rate of convergence of the algorithm is cubic. In contrast, we show that there exist matrices for which the rate of convergence is strictly quadratic. More precisely, let $T_X$ be the $3 \times 3$ matrix having only two nonzero entries $(T_X)_{12} = (T_X)_{21} = 1$ and let $T_L$ be the set of real, symmetric tridiagonal matrices with the same spectrum as $T_X$. There exists a neighborhood $U \subset T_L$ of $T_X$ which is invariant under Wilkinson's shift strategy with the following properties. For $T_0 \in U$, the sequence of iterates $(T_k)$ exhibits either strictly quadratic or strictly cubic convergence to zero of the entry $(T_k)_{23}$. In fact, quadratic convergence occurs exactly when $\lim T_k = T_X$. Let $X$ be the union of such quadratically convergent sequences $(T_k)$: the set $X$ has Hausdorff dimension 1 and is a union of disjoint arcs $X^\sigma$ meeting at $T_X$, where $\sigma$ ranges over a Cantor set.Comment: 20 pages, 8 figures. Some passages rewritten for clarit

Inheritance of resistance to bacterial spot in tomato

A herança da resistência do tomateiro (Lycopersicon esculentum) à mancha-bacteriana (Xanthomonas campestris pv. vesicatoria, raça T2) foi estudada, em condições de campo, cruzando-se os genótipos resistentes 'Ohio 8245' e 'Hawaii 7998' com os genótipos suscetíveis 'CNPH 401-08' e 'CNPH 416.81.01.02', em um esquema dialélico desconsiderando-se os recíprocos. Foram obtidas cinco famílias, cada uma constituída por seis gerações: Genitor1, Genitor2, F1, F2 e os retrocruzamentos (RC1 e RC2). A família 'Ohio 8245 ' Hawaii 7998' apresentou menor média para severidade da doença, seguida por 'Hawaii 7998 ' CNPH 416.81.01.02' e 'Ohio 8245 ' CNPH 416.81.01.02', as quais, apresentaram maiores estimativas de herdabilidade e de predição de ganho por seleção. Em todas combinações, a herança da resistência genética à mancha-bacteriana foi do tipo quantitativa, com estimativa do número de genes variando de quatro a oito genes, conforme a família analisada. Foi observada segregação transgressiva nas famílias 'Ohio 8245 ' CNPH 401-08', 'Hawaii 7998 ' CNPH 401-08' e 'Hawaii 7998 ' CNPH 416.81.01.02'. Os efeitos gênicos foram do tipo aditivo para todas as famílias e os dados ajustados ao modelo aditivo-dominante, com o componente aditivo apresentando maior magnitude.The inheritance of resistance to bacterial spot (Xanthomonas campestris pv. vesicatoria, race T2) in tomato (Lycopersicon esculentum) was investigated in a field trial. The genotypes 'Ohio 8245' and 'Hawaii 7998' (resistant), 'CNPH 401-08' and 'CNPH 416.81.01.02' (susceptible) were crossed in a diallel scheme without reciprocals. Each cross was labeled as one family, represented by six different generations: Parent1, Parent2, F1, F2 and Backcrosses to parents (BC1 and BC2). The family 'Ohio 8245 ' Hawaii 7998' presented the lowest disease severity, followed by the family 'Hawaii 7998 ' CNPH 416.81.01.02' and by the family 'Ohio 8245 ' CNPH 416.81.01.02'. These last two families showed both higher broad and narrow sense inheritability estimates and the highest prediction of selection gain. The resistance was found to be quantitative, with four to eight genes involved, depending on the family. Transgressive segregation was observed in the 'Ohio 8245 ' CNPH 401-08', the 'Hawaii 7998 ' CNPH 401-08' and the 'Hawaii 7998 ' CNPH 416.81.01.02' families. The relevance of the additive effects was observed and for all the families the data fitted to additive-dominant model, with the additive component showing greater magnitude