Search results for "Negative charge"
showing 9 items of 9 documents
Anionic Lipids Modulate the Activity of the Aquaglyceroporin GlpF
2015
AbstractThe structure and composition of a biological membrane can severely influence the activity of membrane-embedded proteins. Here, we show that the E. coli aquaglyceroporin GlpF has only little activity in lipid bilayers formed from native E. coli lipids. Thus, at first glance, GlpF appears to not be optimized for its natural membrane environment. In fact, we found that GlpF activity was severely affected by negatively charged lipids regardless of the exact chemical nature of the lipid headgroup, whereas GlpF was not sensitive to changes in the lateral membrane pressure. These observations illustrate a potential mechanism by which the activity of an α-helical membrane protein is modula…
Hierarchical, Lithium‐Templated Assembly of Helicate‐Type Complexes: How Versatile Is This Reaction?
2007
Catechol ligands that bear carbonyl functions such as esters or aldehydes in the 3-position (1a–c-H2) form triple-stranded, helicate-type complexes [Li3(1a–c)6Ti2]– with titanium(IV) and the corresponding double-stranded compounds [Li2(1a–c)4B2] with boron(III) in hierarchical, lithium-templatedprocesses. The related 8-hydroxyquinoline ligands 2a,b-H can be used for the formation of similar complexes[Li3(2a,b)6M2]+ with cobalt(II), nickel(II), or zinc(II). A prerequisite for the formation of the lithium-bridged dimers is a negative charge of the mononuclear complexes, which are able to electrostatically attract the lithium cations and thus compensate the repulsion between the cations. (© Wi…
Guidelines to design new spin crossover materials
2010
International audience; This review focuses on new families of spin crossover (SCO) complexes based on polynitrile anions as new anionic ligands or on polyazamacrocycles as neutral macrocyclic ligands. We have shown that the structural and electronic characteristics (original coordination modes and high electronic delocalization) of the polynitrile anions can be tuned by slight chemical modifications such as substitution of functional groups or variation of the negative charge to design new discrete or polymeric SCO systems.In our ongoing work on the design of new molecular systems based on new ligands that can be fine-tuned via chemical modifications, another promising way which has been r…
Identification of binding peptides on calcium silicate hydrate: a novel view on cement additives.
2014
Cement is the most used industrial product in the world. Although the chemical composition of the material has stayed more or less the same since its discovery by the Romans around 2000 years ago, [ 1 ] the performance has been increased by chemical additives. Spectacular buildings like the Willis Tower in Chicago, Taipei 101 or lately the over 800 m high Burj Khalifa in Dubai were realizable thanks to the development of high performance building materials. [ 2 ] Not only for such prestige objects but also in daily building processes, the trend goes towards always higher buildings because of the continued urbanization which was identifi ed already in 1982 as one of the so-called “megatrends…
Comparative Structural Studies of 4-Diazopyrazole Derivatives by X-Ray Diffraction and Theoretical Investigation
2005
The X-Ray crystal and molecular structures of the 4-pyrazol derivatives 3-methyl-4-diazo-5-benzamido-1H-pyrazole (4) and 3-benzamido-5-methyl-1H-pyrazole (3) have been determined. A dimeric structure has been found for the first and polymeric for the second. A comparison of 4 with 1,3-dimethyl-4-diazo-5-benzamido-lH-pyrazole (2) shows differences in the geometrical parameters of the pyrazole ring due to electron delocalization in 2 consequent to the nitrogen negative charge in the latter. Theoretical investigation at the density functional theory (DFT) level shows difference in the molecular electronic distribution of 2 and 4, in agreement with the structural parameters and the IR stretchin…
The foaming properties of camel and bovine whey: The impact of pH and heat treatment
2018
International audience; he effect of heat treatment (70 degrees C or 90 degrees C for 30 min) on the foaming and interfacial properties of acid and sweet whey obtained from bovine and camel fresh milk was examined. The maximum foamability and foam stability were observed for acid whey when compared to sweet whey for both milks, with higher values for the camel whey. This behavior for acid whey was explained by the proximity of the pI of whey protein (4.9-5.2), where proteins were found to carry the lowest negative charge as confirmed by the zeta potential measurements. Interfacial properties of acid camel whey and acid bovine whey were preserved at air water interface even after a heat trea…
Modified Halloysite Nanotubes: Nanoarchitectures for Enhancing the Capture of Oils from Vapor and Liquid Phases
2013
We prepared hybrid halloysite nanotubes (HNT/sodium alkanoates) in which the inner cavity of the nanoclay was selectively modified. Physicochemical studies evidenced the interactions between HNT and sodium alkanoates, ruled out clay exfoliation, quantified the amount of the loaded substance, and showed an increase of the total net negative charge, allowing us to obtain rather stable aqueous nanoclay dispersions. These dispersions were exploited as inorganic micelles to capture hydrocarbon and aromatic oils in the vapor and liquid states and were revealed to be nonfoaming but very efficient in encapsulating oils. Here, we have fabricated biocompatibile and low-cost inorganic micelles that ca…
Rearrangements of Nitrile-Stabilized Ammonium Ylides
2014
Rearrangements of nitrile-stabilized ammonium ylides are useful reactions for the construction of alkylamines, nitrogen heterocycles, or carbonyl compounds. In spite of their attractive synthetic potential, they are much less frequently used than rearrangements of ammonium ylides either carrying charge-stabilizing carbonyl groups or being devoid of additional stabilization of the negative charge. This review focuses on different classes of rearrangements of nitrile-stabilized ammonium ylides as well as their application in synthetic organic chemistry. 1 Introduction 2 [1,2]-Stevens Rearrangements 3 [2,3]-Sommelet–Hauser Rearrangement 4 [2,3]-Stevens Rearrangements 5 Competitive [1,2]-, [2,3…
ChemInform Abstract: Rearrangements of Nitrile-Stabilized Ammonium Ylides
2014
Rearrangements of nitrile-stabilized ammonium ylides are useful reactions for the construction of alkylamines, nitrogen heterocycles, or carbonyl compounds. In spite of their attractive synthetic potential, they are much less frequently used than rearrangements of ammonium ylides either carrying charge-stabilizing carbonyl groups or being devoid of additional stabilization of the negative charge. This review focuses on different classes of rearrangements of nitrile-stabilized ammonium ylides as well as their application in synthetic organic chemistry. 1 Introduction 2 [1,2]-Stevens Rearrangements 3 [2,3]-Sommelet–Hauser Rearrangement 4 [2,3]-Stevens Rearrangements 5 Competitive [1,2]-, [2,3…