Hofmeister sequence

Heterogeneous rate constants, 12, 113 Hofmeister sequence, 153 Hybridization, 183, 185 Hydrodynamic boundary layer, 10 Hydrodynamic modulation, 113 Hydrodynamic voltammetry, 90 Hydrodynamic voltammogram, 88 Hydrogen evolution, 117 Hydrogen overvoltage, 110, 117 Hydrogen peroxide, 123, 176... 

While ionophore-free membranes based on classical ion exchangers are still in use for the determination of lipophilic ions, such sensors often suffer from insufficient selectivity, as it is governed solely by the lipophilicity pattern of ions, also known for anions as the Hofmeister sequence. This pattern for cations is Cs+ > Ag+ >K+ > NH > Na+ > Li+ > Ca2+ > Mg2+ and for anions CIOT > SCN- > I > Sal- > N03- > Br > N02- > Cl- > OAc- HC03- > SO - > HPO4. While the ion exchanger fixes the concentration of hydrophilic analyte ions in the membrane on the basis of the electroneutrality condition within the membrane, the second key membrane component is the ionophore that selectively binds to the analyte ions. The selectivity of... 

In principle, two different mechanisms have been proposed on how the ions influence protein stability. Firstly, it has been suggested that a modification of water s structure is the origin of the Hofmeister sequence (130). It has been hypothesized that some ions kosmotropes enhance the structure that surrounds the ions, which leads to a strengthening of the hydrophobic effect and thereby stabilizes the proteins (131). However, the ions that break the stmcture that surrounds the ions ( chaotropes )... 

While ionophore-free membranes based on classical ion exchangers are still in nse for the determination of lipophilic ions, such sensors often suffer from insufficient selectivity, as it is governed solely by the lipophilicity pattern of ions, also known for anions as the Hofmeister sequence. This pattern for cations is Cs" > Ag+ >K+ >... 

Note Some of Grahame s values for and included in this table. For a common cation, the sequence of anions in order of increasing adsorption is similar to that of the Hofmeister series in coagulation studies, and it is evident that specific adsorption properties are involved. 

Although not strictly relevant to amperometric sensor technology, various metalloporphyrins [Co(III), Mn(III), Fe(III) Fig. 45] have been shown to sense anions potentiometrically with selectivity sequences dependent on the centrally bound metal (Amman et al., 1986 De et al., 1994). For example the anti-Hofmeister selectivity sequence SCN" > I" > CIO4 > N02 > Br > Cl- > NOJ was exhibited by PVC membrane electrodes containing [87]. 

Stability of an enzyme is usually understood to mean temperature stability, although inhibitors, oxygen, an unsuitable pH value, or other factors such as mechanical stress or shear can decisively influence stability (Chapter 17). The thermal stability of a protein, often employed in protein biochemistry, is characterized by the melting temperature Tm, the temperature at which a protein in equilibrium between native (N) and unfolded (U) species, N U, is half unfolded (Chapter 17, Section 17.2). The melting temperature of a protein is influenced on one hand by its amino acid sequence and the number of disulfide bridges and salt pairs, and on the other hand by solvent, added salt type, and added salt concentration. Protein structural stability was found to correlate also with the Hofmeister series (Chapter 3, Section 3.4 Hofmeister, 1888 von Hippel, 1964 Kaushik, 1999) [Eq. (2.18)]. 

The scale is currently known as the Hofmeister (or lyotropic) series to honor Franz Hofmeister, who described the effects of salts on a variety of physiological samples and ranked salts in a sequence that later proved universal. The series of papers he wrote more than a century ago were recently translated into English [22]. Hofmeister simply introduced the concept of ranking salts based on common cations and anions. In this context, it is pertinent to underline that Hofmeister categorically stated that the effect of a salt depends on both its anion and cation. Hofmeister s results were subsequently extrapolated to produce the ion-specific series not connected to... 

The sequence of Mg" " > Ca" " is the reverse of the normal affinity sequence (Hofmeister series) which is observed on most clays and on MnO. The observed sequence on aFeOOH is that expected when interactions between the adsorbed ions and the surface sites are greater than hydration effects (31). 

Salts are known to influence several properties of aqueous solutions in a systematic way (122,123). The effect of different aiuons and cations seems to be ordered in a sequence this theory was already proposed by Hofmeister in 1888 (124) from a series of experiments on the salts ability to precipitate hen-egg white protein. Numerous other properties of aqueous salt solutions are also found to be systematically salt dependent, such as the surface tension or the surface potential (122). However, the exact reason for the observed specific cation and anion sequences is still not fully understood (125). Model calculations (126), as well as nuclear magnetic relaxation experiments (127), propose a delicate balance between ion adsorption and exclusion at the solute interface. This balance is tuned by the solvent (water) stmcture modification according to the ion hydration (128, 129) and hence is possibly subject to molecular details. 

On the other hand, despite the information about long chain sulfates, sulfonates, phosphates, and carboxylates that indicates stronger interaction with Ca2+ than with Mg2+ (i.e., in apparent harmony with the sequence of the Hofmeister (44) series), several difficulties remain. For example, while Miyamoto s data for DS (10) indicate the interaction sequence Mg < Ca < Sr < Ba from solubility measurements (as well as from temperature/CMC measurements if one accepts the Mg—Ca sequence of the present paper), this sequence, with the exception of the position of Mg and Ca, is the opposite of that found by Deamer et al. (33) from condensation effects on the force/area curves of ionized fatty acids. At the same time, the ion sequence obtained by these authors from phase transition temperatures of spread fatty acids (33) differs from that deduced from the above-mentioned condensation effects, and the latter depended strongly on pH. Lastly, definite differences in ion sequence effects exist for the alkaline earth metals in their interaction with long... 

In order to improve the practical application of potentiometric sensors, much effort must be devoted to developing membrane materials whose selectivity deviates fi-om the Hofmeister series. Chloride- and nitrite-selective electrodes based on lipophylic vitamin B12 derivatives have been reported by Simon.xhese electrodes were the first anion-selective electrodes of which selectivity sequence did not obey the Hofmeister series. Since then, a number of anion-selective liquid-membrane electrodes have been developed using a variety of hosts metallocenes, diphosphonium dication salts, diquartemary ammonium dication salts, bisthiourea derivatives, metalloporphyrins, lipophylic macrocyclic polyamines, cytosine-dependent triamine and metallophtalocyamines. " " Among this large variety of compounds studied, the metalloporphyrins seem to be the most promising for the preparation of effective ion-selective potentiometric sensors. " - ... 

Generally, the protonation of expanded porphyrins at the surface of the electrode membrane is a prerequisite for accommodating the guest anions and yielding their potential response. The electrodes strongly respond to benzoates, but rather less to inorganic anions and saturated aliphatic organic carboxylates. The selectivity sequences for the sapphyrin-based electrodes were found in some cases to deviate from the Hofmeister series. Fluoride preference over chloride and bromide is particularly noted. 

Perkins SJ (2001) X-ray and neutron scattering analyses of hydration shells a molecular interpretation based on sequence predictions and modeUing fits. Biophys Chem 93 129-138 Peula-Garcia JM, Ortega-Vinuesa JL, Bastos-Gonzalez D (2010) Inversion of Hofmeister series by changing the surface of coUoidal particles from hydrophobic to hydrophilic. J Phys Chem C 114 11133-11139... 

Amino acids were isolated from natural sources, asparagine from plants, cystine from urinary stones in the first decade of the last century and became known later to be constituents of proteins. The peptide bond, however, as the fundamental feature of protein structure was recognized only in this century (Hofmeister 1902 E. Fischer 1906). Several more decades elapsed until sequence elucidation reached the point of practicality. The turning point was signaled by the determination of the structure of insulin (Sanger et al. 1953). The subsequent development of automated amino acid analysis (Spackman, Stein and Moore 1958) and automatic sequencing (Edman and Begg 1967)... 

Preferential adsorption of one type of ions onto the particle surface coupled with the formation of a diffuse layer of the counterions (ions of opposite charge) leads to electrostatic stabilization due to repulsion between the double layers (Chapter 4). The valence and radius of the counterions can modify the repulsion between the particles and so can influence the stability of the suspension. Counterions with higher valence are more effective for causing flocculation Schulze-Hardy rule), while for ions of the same valence, the smaller ions are more effective. For monovalent cations, the effectiveness of flocculation is in the order Li > Na > K+ > NH4, while for divalent cations, Mg " > Ca " > Sr " > Ba. This sequence is known as the Hofmeister series. For common anions, the effectiveness of flocculation is in the order 804 > Cl > NOJ. 

Hofmeister first established that different ions have different efficiency at salting-out egg-white protein (Hofmeister, 1888). The sequence of ions, based on their effectiveness towards enhancing or diminishing the solubility of proteins, is termed as Hofmeister series. This series is generally written as (Marcus, 2009). 

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