Should the Gibbs analysis be revised?

Recently, some arguments were published that cast doubt on the validity of the Gibbs adsorption isotherm. The doubt was on whether the often visible linearly declining part in the surface tension versus logarithm of concentration plot of a surfactant solution, just before the critical micelle concentration, really represents a situation of constant adsorption. Those published arguments are partly of a conceptual nature and partly based on experimental evidence. The conceptual arguments appear to be based on a misunderstanding of the theory, while the arguments based on experimental evidence stem from an inaccurate treatment of these data. Our conclusion is that none of the relevant arguments put forward are valid. The experimental evidence, if properly treated, is in line with the Gibbs theory.     

Hahnen und Maassstäbe aus Bergkrystall

Analytical and Bioanalytical Chemistry -     

How can enzymes be so efficient?

Dudley Williams and his colleagues discuss how ligands can gain binding energy to their receptors, and substrate transition states to their enzymes, by tightening the protein structures, with a decrease in their dynamic behaviour.     

Can Nonpolar Polyisobutylenes be Measured by Electrospray Ionization Mass Spectrometry? Anion-Attachment Proved to be an Appropriate Method

Polyisobutylenes (PIBs) with different end-groups including chlorine, exo-olefin, hydroxyl, and methyl prepared from aliphatic and aromatic initiators were studied by electrospray ionization mass spectrometry (ESI-MS). Independently of the end-groups, presence or absence of aromatic initiator moiety, these PIB derivatives were capable of forming adduct ions with NO₃ ^– and Cl^– ions, thus allowing the direct characterization of these compounds in the negative ion mode of ESI-MS. To obtain [PIB + NO₃]^– and [PIB + Cl]^– adduct ions with appreciable intensities, addition of polar solvents such as acetone, 2-propanol, or ethanol to the dichloromethane solution of PIBs was necessary. Furthermore, increasing both the polarity (by increasing the acetone content) and the ion-source temperature give rise to enhanced intensities for both [PIB + NO₃]^– and [PIB + Cl]^– ions. Energy-dependent collision induced dissociation studies (CID) revealed that increasing the collision voltages resulted in the shift of the apparent molecular masses to higher ones. CID studies also showed that dissociation of the [PIB + Cl]^– ions requires higher collision energy than that of [PIB + NO₃]^–. In addition, Density Functional Theory calculations were performed to gain insights into the nature of the interactions between the highly non-polar PIB chains and anions NO₃ ^– and Cl^– as well as to determine the zero-point corrected electronic energies for the formation of [PIB + NO₃]^– and [PIB + Cl]^– adduct ions.

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Graphical Abstract ?

     

Can ortho-para transitions for water be observed?

The spectrum of water can be considered as the juxtaposition of the spectra of two molecules, with different total nuclear spin: ortho-H2O, and para-H2O. No transitions have ever been observed between the two different nuclear-spin isotopomers. The interconversion time is unknown and it is widely assumed that interconversion is forbidden without some other intervention. However, weak nuclear spin-rotation interaction occurs and can drive ortho to para transitions. Ab initio calculations show that the hyperfine nuclear spin-rotational coupling constants are about 30 kHz. These constants are used to explore the whole vibration-rotation spectrum with special emphasis on the coupling between nearby levels. Predictions are made for different spectral regions where the strongest transitions between ortho and para levels of water could be experimentally observed.     

To be or not to be – nematic liquid crystals from shape-persistent V-shaped nematogens with the ‘magic angle’

The tetrahedral bending angle in V-shaped nematogens was claimed to be the optimum for finding a biaxial nematic liquid crystal phase. The benzo[1,2-b:4,3-b’]dithiophene core, recently successfully applied as a tetrahedral bending unit in mesogens with lateral flexible chains, is here embedded in a scaffold with only terminal chains, which conventionally promotes the formation of nematic phases at low temperature. A series of new mesogens has been successfully prepared, realising hockey-stick, hockey-stick dimer and V-shaped molecular topologies. Only the hockey-stick mesogens assemble in uniaxial nematic phases over a broad temperature range. Single crystal structure analysis of a hockey-stick and V-shaped compound reveal remarkable similarities with the benzodithiophene core wrapped by aliphatic chains. A model explaining the absence of nematic mesophases in the family of V-shaped, shape-persistent mesogens with terminal aliphatic chains is presented and results in the proposal of a new design for biaxial nematogens.     

Can enantiomers be separated in achiral chromatographic systems?

Consideration of chromatography of a nonracemic mixture on an achiral sorbent from a stereochemical point of view allows the claim that partial separation of the excess enantiomer zone from the racemate zone is possible only with analytes capable of self-associating under the conditions of the chromatographic column. It is from these positions that features of this process can be explained and conditions for its maximal proceeding formulated.     

Could be radiolabeled flavonoid used to evaluate infection?

The aim of this study was to determine whether [¹³¹I]apigenin is a powerful and discrimination infection from inflammation for scintigraphic imaging. The study was carried out in inflamed rats with Staphylococcus aureus (S. aureus) and sterile inflamed rats with turpentine oil. Biodistribution study of [¹³¹I]apigenin was performed in the rats. Apigenin was labeled with ¹³¹I by iodogen method. Obtained [¹³¹I]apigenin with high yield (98%) was injected i.v. to both group rats. The results were expressed as the percent uptake of injected dose per gram of organ (%ID/g), the bacterial infected and sterile inflamed muscles. Binding of [¹³¹I]apigenin to the infected thigh muscle (target muscle = T) and normal thigh muscle (non-target muscle = NT) ratio (T/NT = 4.51 at 15 min) was higher than binding to bacterial inflamed muscle (T/NT = 2.25 at 15 min) of rats. [¹³¹I]apigenin showed good localization in both inflamed tissues. This uptake in the sterile inflamed tissue is higher than bacterial infected tissue. [¹³¹I]apigenin might be useful for imaging of inflamed tissues. However, it is not discriminate sterile inflamed tissue from bacterial infected tissue.     

Can ring strain be realized in momentum space?

An increased electron momentum density (EMD) at low momentum is proposed to be an indicator of ring strain, with the nature of the function tending toward a maximum. A p-space Hirshfeld atomic partitioning scheme is applied for analyzing the effect of strain on molecular EMDs. The Hirshfeld momentum densities for a strained system show an increase in the population for the carbons with the hydrogens becoming more positive in comparison with an unstrained reference molecule. The manifestation of strain in cage-like hydrocarbons such as tetrahedrane, cubane, prismane, etc. as well as their nitrogen-substituted analogues is clearly seen in terms of EMDs.     

Can nanofiltration be fully predicted by a model?

There is an increasing need for model-based tools to design membrane processes for new industrial applications or to optimise existing membrane installations. The advantage of such tools is that costs can be saved by reducing the number of expermiments. In this study, the requirements for a membrane filtration model, suitable for practical use, are summarised. It is investigated to what extent it is possible to set-up such a model with the current available literature and knowledge. A membrane filtration model has been set-up based on the Maxwell–Stefan transport equations. A Freundlich equation is used to describe the membrane charge by means of adsorption of ions. With the model the permeate flux and rejections of multi-component liquid feeds can be calculated as a function of membrane properties (mean pore size, porosity, thickness, surface charge characteristic) and feed pressure. With two NF-membranes (Desal 5DK and a prototype capillary type 2 membrane) rejection experiments have been carried out with glucose, single salt solutions (NaCl, CaCl₂, Na₂SO₄) and ternary ion mixtures of these salts. With the model the experimental flux-rejection curves can be fitted reasonably well. However, each salt mixture needs its own set of fitted parameters for the membrane charge isotherms. Furthermore, the fitted membrane charges are in contradiction with values from the literature obtained by electrokinetic measurements. Obviously, the membrane charge parameters have lost their physical meaning and are used to compensate for physical phenomena not included in the model. Extending the model with an electrostatic free energy term will be a step forward in development. Further research is needed to fulfil all requirements for the wide scope of industrial applications.     

What can be Learned from Silage Breeding Programs?

Improving the quality of cellulosic ethanol feedstocks through breeding and genetic manipulation could significantly impact the economics of this industry. Attaining this will require comprehensive and rapid characterization of large numbers of samples. There are many similarities between improving corn silage quality for dairy production and improving feedstock quality for cellulosic ethanol. It was our objective to provide insight into what is needed for genetic improvement of cellulosic feedstocks by reviewing the development and operation of a corn silage breeding program. We discuss the evolving definition of silage quality and relate what we have learned about silage quality to what is needed for measuring and improving feedstock quality. In addition, repeatability estimates of corn stover traits are reported for a set of hybrids. Repeatability of theoretical ethanol potential measured by near-infrared spectroscopy is high, suggesting that this trait may be easily improved through breeding. Just as cell wall digestibility has been factored into the latest measurements of silage quality, conversion efficiency should be standardized and included in indices of feedstock quality to maximize overall, economical energy availability.     

How could the program of aging be arranged?

Aging could be a consequence of the programmed partial dedifferentiation of brain neurons that is performed through nonrandom losses of chronomeres-short perichromosomal DNA molecules that also participate in maintenance of cellular differentiation state. Process of their sequential losses, implementing as the “relay-race partial dedifferentiations,” serves as a basis for the activity of the lifelong brain clock that regulates a physiological age of multicellular animals. These relay-race dedifferentiations are performed in a consecutive mode by different groups of neurons during the peaks of a so called T-rhythm, whose length of period is different in various animal species.     

To what extent can aromaticity be defined uniquely?

Statistical analyses of quantitative definitions of aromaticity, ASE (aromatic stabilization energies), RE (resonance energies), Lambda (magnetic susceptibility exaltation), NICS, HOMA, I5, and A(J), evaluated for a set of 75 five-membered pi-electron systems: aza and phospha derivatives of furan, thiophene, pyrrole, and phosphole (aromatic systems), and a set of 30 ring-monosubstituted compounds (aromatic, nonaromatic, and antiaromatic systems) revealed statistically significant correlations among the various aromaticity criteria, provided the whole set of compounds is involved. Hence, broadly considered, the various manifestations of aromaticity are related and aromaticity can be regarded statistically as a one-dimensional phenomenon. In contrast, when comparisons are restricted to some regions or groups of compounds, e.g., aromatic compounds with ASE > 5 kcal/mol or polyhetero-five-membered rings, the quality of the correlations can deteriorate or even vanish. In practical applications, energetic, geometric, and magnetic desriptors of aromaticity do not speak with the same voice. Thus, in this sense, the phenomenon of aromaticity is regarded as being statistically multidimensional.     

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