Potentiometric Study of Acid-Base Interactions in Acetonitrile

The potentiometric titration curves of acids of different types were studied using piperidine and tetra-n-butylammonium hydroxide, (Bu4NOH), as titrants in acetonitrile (AN) as solvent. The effect of methanol addition on the shape of the potentiometric curves was discussed. The dissociation constants, KHA, and homoconjugation constants, KHA2- , of some acids were potentiometrically determined in AN. No exact correlation was found between KHA of the studied acids in AN and the corresponding values-in water. It was concluded that the acid characteristics, its anion properties, and the solvent . type are the most important factors determining KHA2-. The heteroconjugation constants, KAHA,- of some anions with different acids were also determined. K AHAc values for some substituted benzoic acids with reference to acetate ion were found to follow a linear free energy relationship with Hammett substituent constants

Exploring Takfir, Its Origins and Contemporary Use: The Case of Takfiri Approach in Daesh’s Media

Muslims have been the primary targets of Daesh’s attacks since 2014 in different countries such as Afghanistan, Iraq, and Syria. These attacks were based on its takfiri ideology. As Daesh official media and documents indicate, kufr (unbelief, infidelity) in Daesh’s approach is not limited to non-Muslims (original disbelievers), but Muslims are the most significant parts of kuffar (unbelievers) in its view and defined as incidental disbelievers. Through studying Daesh’s official documents and various Arabic, English, and Persian media productions, in an explanatory research, this article attempts to display Daesh’s takfiri approach toward Muslims and explains its historical and ideological roots, difference with Al-Qaeda’s takfiri approach, different approaches to takfir inside Daesh, main targets of Daesh’s takfir, and the reasons behinds its takfiri view. This article displays that for Daesh, the Muslims are limited only to Sunni Muslims who are accepting and following its approach. Other Sunni and non-Sunni Muslims are thus kuffar. This study also shows that the assertion of takfir has become a method for Daesh to discredit its opponents, such as Shi’a Muslims and other Muslim groups

Characterization of a unique Caulobacter crescentus aldose-aldose oxidoreductase having dual activities

We describe here the characterization of a novel enzyme called aldose-aldose oxidoreductase (Cc AAOR; EC 1.1.99) from Caulobacter crescentus. The Cc AAOR exists in solution as a dimer, belongs to the Gfo/Idh/MocA family and shows homology with the glucose-fructose oxidoreductase from Zymomonas mobilis. However, unlike other known members of this protein family, Cc AAOR is specific for aldose sugars and can be in the same catalytic cycle both oxidise and reduce a panel of monosaccharides at the C1 position, producing in each case the corresponding aldonolactone and alditol, respectively. Cc AAOR contains a tightly-bound nicotinamide cofactor, which is regenerated in this oxidation-reduction cycle. The highest oxidation activity was detected on d-glucose but significant activity was also observed on d-xylose, l-arabinose and d-galactose, revealing that both hexose and pentose sugars are accepted as substrates by Cc AAOR. The configuration at the C2 and C3 positions of the saccharides was shown to be especially important for the substrate binding. Interestingly, besides monosaccharides, Cc AAOR can also oxidise a range of 1,4-linked oligosaccharides having aldose unit at the reducing end, such as lactose, malto- and cello-oligosaccharides as well as xylotetraose. 1H NMR used to monitor the oxidation and reduction reaction simultaneously, demonstrated that although d-glucose has the highest affinity and is also oxidised most efficiently by Cc AAOR, the reduction of d-glucose is clearly not as efficient. For the overall reaction catalysed by Cc AAOR, the l-arabinose, d-xylose and d-galactose were the most potent substrates

Increasing the open-circuit voltage of photoprotein-based photoelectrochemical cells by manipulation of the vacuum potential of the electrolytes

The innately highly efficient light-powered separation of charge that underpins natural photosynthesis can be exploited for applications in photoelectrochemistry by coupling nanoscale protein photoreaction centers to man-made electrodes. Planar photoelectrochemical cells employing purple bacterial reaction centers have been constructed that produce a direct current under continuous illumination and an alternating current in response to discontinuous illumination. The present work explored the basis of the open-circuit voltage (VOC) produced by such cells with reaction center/antenna (RC-LH1) proteins as the photovoltaic component. It was established that an up to 30-fold increase in VOC could be achieved by simple manipulation of the electrolyte connecting the protein to the counter electrode, with an approximately linear relationship being observed between the vacuum potential of the electrolyte and the resulting VOC. We conclude that the VOC of such a cell is dependent on the potential difference between the electrolyte and the photo-oxidized bacteriochlorophylls in the reaction center. The steady-state short-circuit current (JSC) obtained under continuous illumination also varied with different electrolytes by a factor of 6-fold. The findings demonstrate a simple way to boost the voltage output of such protein-based cells into the hundreds of millivolts range typical of dye-sensitized and polymer-blend solar cells, while maintaining or improving the JSC. Possible strategies for further increasing the VOC of such protein-based photoelectrochemical cells through protein engineering are discusse