Mixed Valence Tin Oxides as Novel van der Waals Materials: Theoretical Predictions and Potential Applications

Van der Waals (vdW) heterostructures, which can be assembled by combining 2D atomic crystals in a precisely chosen sequence, enable a wide range of potential applications in optoelectronics, photovoltaics, and photocatalysis. However, the difficulty of peeling isolated atomic planes and the lattice mismatch between different materials is the main obstacle to hinder vdW materials from more practical applications. In this work, the mixed valence tin oxides, Sn_xO_y (0.5 < x/y < 1), are proposed as a new member of vdW materials and these mixed valence tin oxides show promise to overcome the above‐mentioned obstacle. Density‐functional theory calculations are combined with an evolutionary algorithm to predict the crystal structures of a series of previously reported tin oxides (Sn₂O₃, Sn₃O₄, Sn₄O₅, and Sn₅O₆), unreported compositions (Sn₇O₈, Sn₉O₁₀, and Sn₁₁O₁₂), and a new β ‐ SnO phase. These structures consist of β‐SnO, Sn₂O₃, and Sn₃O₄ monolayers. Their band gaps can be engineered in the 1.56–3.25 eV range by stacking the monolayers appropriately. The band gap depends linearly on the interlayer distance, as understood from interlayer Sn²⁺–Sn²⁺ and intralayer Sn²⁺–O interactions. Sn_xO_y structures exhibit high photoabsorption coefficients and suitable band‐edge positions for photoexcited H₂ evolution; this indicates potential for environmentally benign solar energy conversion in photovoltaic and photocatalytic applications.     

Purification and Characterization of Streptomyces Sialidases

Some strains of Streptomyces produce sialidases. Two sialidases were purified over 1,000-fold from a culture filtrate of two Streptomyces species. They had the same properties in molecular weight, behavior to ions and other reagents, and substrate specificity. They showed very small differences in kinetic properties, pH optima, and heat stability. These Streptomyces sialidases differed markedly from Clostridium perfringens sialidase in molecular weight, p-chloromercuribenzoate sensitivity, and substrate specificity. Approximate molecular weights of the sialidases from Streptomyces and C. perfringens were 32,000 and 57,000, respectively. p-Chloromercuribenzoate (10(-3) M) caused complete inhibition of C. perfringens sialidase but not of Streptomyces sialidases.     

Change of enzyme activities during the early stage of influenza virus infection

Intracellular activities of various hydrolytic enzymes were investigated in monkey kidney cells infected with the $\text{A}\text{NWS}$ strain of influenza virus. At the early stage of infection, there was a significant decrease in the activity of β-D-galactosidase, α-D-mannosidase, $\text{N}$-acetyl-β-D-glucosaminidase, acid and alkaline phosphatase. The decrease was roughly proportional to the multiplicity of infection, and restored at 2 hr after the infection. Corresponding to this intracellular decrease, there was an increase in the activities of these enzyme outside the cells. The results suggested that these hydrolytic enzymes would be released from the cell membrane or the lysosomes near the membrane in the process of adsorption and penetration of the virus particles.     

Assay of plasma leupeptin using the reversible binding of leupeptin to bovine pancreatic trypsin

A competitive binding radioassay for leupeptin has been developed utilizing the reversible binding of leupeptin to bovine pancreatic trypsin. An ethanol precipitation step was introduced to separate trypsin-bound leupeptin from its free form. Advantages of this method are simplicity of the procedure and avoidance of the preparation of antiserum. The possible metabolites of leupeptin exhibit no significant inhibitory effect on leupeptin-trypsin binding in this system. This method was applied to the determination of plasma leupeptin levels in dogs after oral administration of the peptide.     

Immobilized phenylalanine hydroxylase through the SH groups

Purified rat liver phenylalanine hydroxylase [L-phenylalanine:tetrahydropteridine:oxygen oxidoreductase (4-hydroxylating), EC 1.14.16.1] was immobilized with activated thiol-Sepharose 4B via disulfide bond formation, which is expected to immobilize the enzyme in its activated form through the SH modification. This immobilized enzyme was more stable against thermal denaturation than the free enzyme. When tetrahydrobiopterin was used as the natural cofactor, the K(m) value for phenylalanine was decreased and that for the cofactor was increased. Constant conversion from phenylalanine to tyrosine was demonstrated continuously for over 8 h at 25 degrees C.     

The dissociation between the plasma levels of aminopeptidases A and B in spontaneously hypertensive rats

We performed a longitudinal study for 20 weeks on spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKR) to determine the relationship between peptide metabolism and the age-dependent increase in blood pressure. In both SHR and WKR, the plasma level of aminopeptidase A (AP-A) clearly showed an age-dependent decrease. The plasma level of aminopeptidase B paralleled that of AP-A in WKR, but such an age-dependency was not observed in SHR, thus showing a dissociation between the two aminopeptidases. With age in both strains, the level of angiotensin-converting enzyme tended to decrease, while that of kallikrein activity tended to increase. In addition to these findings, a multivariate study testing the relationship of blood pressure to these enzyme activities, as well as to plasma levels of angiotensin I and renin activity, suggested abnormalities in the networks of proteolytic enzymes and in the peptide metabolism surrounding the renin-angiotensin system in SHR. These abnormalities may play some important roles in pathophysiological mechanisms of hypertension in SHR.     

Synthesis of 5-deoxy-5-fluorosporaricin A

The structures of the O-specific side-chains in the lipopolysaccharides of Salmonella greenside, group Z, and Salmonella adelaide, group O, have been investigated. The former proved to be identical with that of Escherichia coli O 55. The latter, which was more extensively studied, was composed of repeating units having the structure

in which Col is colitose (3,6-dideoxy-l-xylo-hexose). This was also shown to be the biological repeating-unit. The same structure has been proposed for the O-antigen of E. coli O 111. The biological repeating-unit for the S. greenside O-antigen was also defined. The structural studies also confirmed that both lipopolysaccharides contain the hexose region typical for the Salmonella core.     

Hematological and serum biochemical changes with age in term fetuses, offspring and dams in normal Sprague-Dawley rats]

Hematological and serum biochemical values of dams and offspring of Sprague-Dawley rats were measured during late gestation, lactation and postweaning. In dams, slightly low erythrocytic parameters, high platelets and high frequency of neutrophils were seen after parturition although WBC showed no marked changes. On Day 20 of gestation, glucose and triglycerides were extremely high and TP and albumin were low. These changes may be attributed to pregnancy or parturition. In fetuses on Day 20 of gestation and offspring immediately after birth, erythrocytes showed anisocytosis, polychromasia, basophilic stipplings and Howell-Jolly bodies and erythroblasts were found. RBC was low. MCV and MCH were extremely high, compared to adult erythrocyte levels. Hemoglobin and hematocrit slightly decreased before weaning. RBC, hemoglobin and hematocrit increased with age and reached adult levels by Day 56. MCV and MCH values decreased, towards adult levels, until weaning. Platelets rapidly increased and reached adult levels before weaning. WBC increased after birth having higher counts in males than in females on Day 35 and thereafter. Glucose, TP and albumin increased with age and reached adult levels by Day 28. ALP was high in fetuses and changed with age having two peaks similar to those reported in man. Cholesterols gradually increased after birth and had a peak on Day 14. Urea nitrogen, inorganic phosphorus and calcium were slightly high in fetuses and preweaned offspring. Potassium was high in fetuses but no age-related trends were seen in offspring.     

Synthesis of 4'-deoxy-4'-fluorokanamycin A and B.

4'-Deoxy-4'-fluorokanamycins A (17) and B (25) have been prepared through fluorinative ring-opening of the D-galacto-3',4'-oxiranes (8 and 21) derived from kanamycin A and B with potassium hydrogenfluoride in ethane-1,2-diol. The mechanism of preponderant formation of the 4'-deoxy-4'-fluoro-D-gluco (9 and 22) over the 3'-deoxy-3'-fluoro-D-gulo derivatives was discussed. In the synthesis of 25, the unusual 3',6'-epimine (23) was the main product along with the 4'-deoxy-4'-fluoro derivative. The mechanism of this reaction is also discussed. Both 17 and 25 were active against resistant bacteria producing aminoglycoside-adenylylating enzymes for HO-4'.