Co-C bond dissociation energy and reaction volume change of 2',5'-dideoxyadenosylcobalamin studied by laser-induced time-resolved photoacoustic calorimetry

Time resolved photoacoustic calorimetry (PAC) was applied to a study of the photolysis of a coenzyme B(12) analog 2',5'-dideoxyadenosylcobalamin, which lacks an -OH group at the 2' position of ribofuranose ring. In aqueous solution, we report for the first time the quantum yield Phi(d) (0.25+/-0.02), Co-C bond dissociation energy (BDE; 31.8+/-2.5 kcal mol(-1)) and reaction volume change deltaV(R) (6.5+/-0.5 ml mol(-1)) due to conformation changes of the corrin ring and its side chains accompanying the cleavage of the Co-C bond. These values for the analog are very similar to those for the natural cofactor. Based our results and previous studies, a possible explanation for the similarity in their structure and properties versus the large difference in their enzymatic activity is discussed.     

Fundamental equilibrium analysis on the ion-pair extraction of dibenzo-18-crown-6 complex of alkali metal ions with picrate ion into 1,2-dichloroethane

The ion-pair extraction equilibria of dibenzo-18-crown-6 (DB18C6) complexes of Na⁺, K⁺, Rb⁺ and Cs⁺ (M⁺) with picrate ion (Pic⁻) into 1,2-dichloroethane (1,2-DCE) have been studied at 25.0°C. In the case of the Rb⁺ and Cs⁺ systems, the extraction results were interpreted by taking into consideration the formation of a (DB18C6)₂ -M⁺ complex in 1,2-DCE. The thermodynamic constants of extraction, , and ion-pair formation in 1,2-DCE, , of ion pairs of the DB18C6-M⁺ complexes with Pic⁻ were determined. By using the distribution coefficient of M⁺·Pic⁻ the thermodynamic formation constants of the DB18C6-M⁺ complexes in 1,2-DCE, , were evaluated. Consequently the component equilibrium constants of the ion-pair extraction were completely determined and a contribution of these constants to the difference of value was discussed. The value in 1,2-DCE is quite high compared with that in solvating solvents and log decreases linearly with increasing Gutmann donor number of solvents.     

Single molecule force spectroscopy reveals the context dependent folding pathway of the C-terminal fragment of Top7

Top7 is a de novo designed protein with atomic level accuracy and shows a folded structure not found in nature. Previous studies showed that the folding of Top7 is not cooperative and involves various folding intermediate states. In addition, various fragments of Top7 were found to fold on their own in isolation. These features displayed by Top7 are distinct from those of naturally occurring proteins of a similar size and suggest a rough folding energy landscape. However, it remains unknown if and how the intra-polypeptide chain interactions among the neighboring sequences of Top7 affect the folding of these Top7 fragments. Here we used single-molecule optical tweezers to investigate the folding–unfolding pathways of full length Top7 as well as its C-terminal fragment (CFr) in different sequence environments. Our results showed that the mechanical folding of Top7 involves an intermediate state that likely involves non-native interactions/structure. More importantly, we found that the folding of CFr is entirely dependent upon its sequence context in which it is located. When in isolation, CFr indeed folds into a cooperative structure showing near-equilibrium unfolding–folding transitions at ∼6.5 pN in OT experiments. However, CFr loses its autonomous cooperative folding ability and displays a folding pathway that is dependent on its interactions with its neighboring sequence/structure. This context-dependent folding dynamics and pathway of CFr are distinct from those of naturally occurring proteins and highlight the critical importance of intra-chain interactions in shaping the overall energy landscape and the folding pathway of Top7. These new insights may have important implications on the de novo design of proteins.

Optical tweezers experiments reveal that the folding of the C-terminal fragment of Top7 (cFr) is context-dependent. Depending on its neighboring sequence, cFr shows very different folding pathways and folding kinetics.      

Oscillatory reactions of sakhalin oil oxidation

After light irradiation of oil films on water surface the autoxidation process has been found to be of nonsteady auto-oscillatory character, which can be observed in rate oscillations of O₂ absorption. Also recorded have been intensity oscillations of the EPR signal from the radical counter added into an oil sample. Complex dynamics of autoxidation can be due to an autocatalytic process involving the participation of peroxides accumulated in oil during photooxidation., , , , O₂. , , . , , .     

Testing the photocatalytic activity of cyanogen-and thiocyanogen-based inorganic polymers

The photocatalytic properties of some cyanogen-and thiocyanogen-based inorganic polymers, such as paracyanogens containing different metals (Hg, Ag, Cu), polythiocyanogens of different iodine contents, polycyanogen and poly (cyanogenthiocyanate), have been tested in two systems. Cu-containing paracyanogen and the iodine-poor polythiocyanogens catalyze the photoreduction of methylviologen under visible light, furthermore the Cu-containing paracyanogen catalyzes the photoreduction of water to hydrogen under UV irradiation.

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, , , , (Hg, Ag, Cu), , (), . , , , , , , -.

     

Properties of χ-alumina as related to catalysis

-Alumina was synthesized by thermal decomposition of aluminium(III) isopropoxide, and its properties were investigated. The change in its surface area with increasing calcination temperature resembled that of -alumina. Both aluminas had the same acid strength, and their activities in isomerization of 1-butene were the same. -Alumina as a support for molybdenum catalyst in the epoxidation of allyl alcohol also behavedin the same manner as -alumina. Thus -alumina has almost the same catalytic properties as -alumina.     

Trihydroxy-2-thiaquinolizidine derivatives as a new class of bicyclic glycosidase inhibitors

Trihydroxy-2-thiaquinolizidines, a new class of bicyclic dideoxy-iminohexitol glycosidase inhibitor derivatives with nominally the d-gluco, l-ido, d-manno and l-gulo configurations were synthesized. X-ray analyses indicated that the preferred conformation for d-gluco and d-manno derivatives was a flat trans-fused system. Unlike deoxynojirimycin, the compound with d-gluco configuration was selective for α-glucosidases (yeast and rice) and showed no inhibitory activity towards β-glucosidase (almond), α-galactosidase (green coffee beans), α-galactosidase (E. coli) and α-mannosidase (jack bean), while the l-ido derivative was specific for β-glucosidase (almond).     

EDXRF as an analytical tool in art: Case studies from pigment identification and treatment assessment

Energy dispersive X-ray fluorescence (EDXRF) was employed for the identification of pigments decorating Hellenistic figurines, and the assessment of the efficiency of a treatment with barium hydroxide applied to stone. Elements present in the colored areas of the figurines, as well as the treated stone was identified by EDXRF. These data together with complementary information obtained by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction analysis (XRD) led to the identification of several precious pigments. As far as the treatment efficiency is concerned, EDXRF analysis revealed that barium is unevenly distributed on the treated surface and reaches a maximum depth of 2.5 mm.