Study of the effect of organic acids on the crystal stability of wines

The loss of solubility of tartaric acid salts of potassium and calcium is the reason for precipitation of crystal sediment in wine. The aim of this work was to study the morphological characteristics of crystal sediment of wines obtained by varying the acidic complex of the must using different technological methods. The approach of must de-oxidation, as well as the introduction of citric acid, provided a decrease in the temperature of saturation with calcium tartrate by 5.8-11.3 °C. At the same time, when introducing the tartaric acid, an inverse relation was noted - the indicator value increased by 34%. According to the results of the study, the relationship between quantitative content of potassium and calcium ions and temperature of saturation with potassium bitartrate (Tsat (KHTar) and calcium tartrate Tsat (CaTar)) was not established (r = -0.48 and 0.50, respectively). It was shown that acidifying of the must with 1 g/l of tartaric acid provided the formation of very large crystals of calcium tartrate, and 2 g/l of tartaric acid - a stabilizing effect for young wine by the end of the experiment. Regardless the method of varying acid composition of the must, the value of Tsat (KHTar) was in the range of 14.8-19.5 oC. The obtained results are intended to prove the necessity of preventive measures in wine production to ensure their crystal stability.

Magnesium–halobenzene bonding: mapping the halogen sigma-hole with a Lewis-acidic complex

Complexes of a highly Lewis acidic Mg cation and the full series of Ph–X (X = F, Cl, Br, I) have been structurally characterized. The Mg⋯X–Ph angle decreases with halogen size on account of the growing halogen σ-hole.

Lewis acid enhancement by hydrogen-bond donors for asymmetric catalysis

Small-molecule dual hydrogen-bond (H-bond) donors such as ureas, thioureas, squaramides, and guanidinium ions enjoy widespread use as effective catalysts for promoting a variety of enantioselective reactions. However, these catalysts are only weakly acidic and therefore require highly reactive electrophilic substrates to be effective. We introduce here a mode of catalytic activity with chiral H-bond donors that enables enantioselective reactions of relatively unreactive electrophiles. Squaramides are shown to interact with silyl triflates by binding the triflate counterion to form a stable, yet highly Lewis acidic, complex. The silyl triflate-chiral squaramide combination promotes the generation of oxocarbenium intermediates from acetal substrates at low temperatures. Enantioselectivity in nucleophile additions to the cationic intermediates is then controlled through a network of noncovalent interactions between the squaramide catalyst and the oxocarbenium triflate.

Synthesis and processing of molecules bearing thymus leukemia antigen.

Thymus-leukemia (TL) antigens are expressed in murine lymphocytes under strict developmental regulation. To elucidate the molecular basis of TL expression, we have identified the molecular species that react with TL antiserum. At least three species can be resolved by metabolic radiolabeling of thymocytes and ASL1 leukemia cells, lysis, immune precipitation, and sodium dodecyl sulfate-polyacrylamide. After a brief incubation with [35S]methionine, the only radioactive molecule recognized by TL antiserum is a homogeneous species with an apparent Mr of 45,000 daltons. This molecule, 45K TL, includes high-mannose-type carbohydrate attached to a 45,000 dalton glycosidase-resistant backbone. In this form, 45K, it is never exposed on the cell surface. If pulse-labeled cells are further incubated with nonradioactive methionine before lysis, however, radioactivity disappears from the 45K TL species and appears in the slower migrating species 46K and 48K TL. Thus, 46K and 48K appear to represent products generated from the 45K TL precursor by posttranslational modification. These TL forms are displayed on the cell surface; they lack high-mannose carbohydrate but evidently include acidic complex-type carbohydrate. Normal thymocytes from Qa:Tla-negative mice lack not only the surface forms of TL but also the intracellular 45K TL form. Peripheral lymphoid cells of Qa:Tla-positive mice synthesize none of these TL species. But the TL antiserum, which contains Qa antibody, recognizes a distinct gene product in spleen and thymus of Qa-Tla-positive mice. In its pulse-labeled form, this molecule, which may represent Qa-1, has an apparent Mr of 44,000 daltons, and consists of a glycosidase-resistant polypeptide core of only 35,000 daltons linked to more high mannose carbohydrate than 45K TL.

Cytochemical properties of mitochondria in the gastric parietal cell.

The matrix of some mitochondria in gastric parietal cells of rat and guinea pig evidenced affinity for the high iron diamine method which localizes sulfated complex carbohydrates selectively by light and electron microscopy. Such staining has not been observed elsewhere in the stomach. The high iron diamine reactive mitochondria about equaled in number those which were unreactive, and the two groups were indistinguishable morphologically. The distinction was not apparent either when mitochondria were stained by other cytochemical procedures including dialyzed iron for acidic complex carbohydrates, 3-3' diaminobenzidine-H2O2 at pH 6.0 for cytochrome oxidase, and Kominick's pyroantimonate osmium tetroxide for antimonate precipitable cations. The dialyzed iron method stained acid glycoconjugates in the outer intermembrane space in parietal cell mitochondria. These mitochondria stained more strongly with dialyzed iron than have any others examined heretofore with this method and comprised the only reactive mitochondria in the stomach. Parietal cell mitochondria also stained strongly for cytochrome oxidase but those of other gastric cells failed to evidence this reactivity.