Visualization of propagation of boundary diffraction wave

Experimental evidence of the existence of the boundary diffraction wave is presented. The secondary wave occurring at the boundary of a sharp knife edge, interacts with each other while crosses the primary wave. This interaction and its path have been experimentally observed and recorded using a CCD sensor array. The observed diffraction profile of the composite wave has been discussed and briefly compared with the existing model of diffraction.     

A new group of isoquinoline alkaloids : The secoberbines

The new isoquinoline alkaloid (?)-peshawarine (1) has been isolated from Hypecoum parviflorum Kar. & Kir. (Papaveraceae). Its synthesis in the racemic form from coptisine (6b) involves a novel approach to cyclic hemiacetals in which the key step is the transformation of the aldehyde (±)-aobamine (10b) into the hemiacetal 12b using ethyl chloroformate. (±)-Corydalisol (11b) and (±)-canadaline (10a) have also been synthesized for the first time. The absolute configuration of (?)-1 was determined by chemical correlation with (+)-rhoeagenine methiodide (20). The chirality of the alkaloid (+)-canadaline (10a) has also been established by analogy to (+)-corydalisol (11b). (?)-Peshawarine (1), (+)-canadaline (10a), (+)-corydalisol (11b), and aobamine (10b), as well as hypecorine (22) and hypecorinine (23), are members of a new group of isoquinoline alkaloids, the secoberbines.     

Crystal chemistry and synthesis of Ternary Silicates and Germanates containing alkali (Na+, K+) and alkaline earth (Ca2+, Sr2+, Ba2+) cations

The synthesis of new ternary silicate and germanate phases containing large alkali and alkaline-earth cations is described. They are made by solid-state reaction of mixtures of carbonates or oxalates with SiO₂ or GeO₂, or by fusion and subsequent recrystallization of the glass. Representatives of the cubic MM²⁺X₃O₉ family include Na₄CaSi₃O₉ and the isostructural compounds K₄CaGe₃O₉, K₄SrGe₃O₉ and K₄SrSi₃O₉. K₄BaSi₃O₉ is pseudocubic: the symmetry of Na₄SrSi₃O₉ is unknown. The rhombohedral MM²⁺X₁₀O₂₅ family includes K₈CaSi₁₀O₂₅, K₈SrSi₁₀O₂₅ and K₈BaSi₁₀O₂₅. Na₂CaGe₂O₆ and Na₂SrGe₂O₆ are isostructural but both are structurally unrelated to Na₂BaSi₂O₆. Na₂Ba₂Ge₂O₇ and Na₂Ba₂Si₂O₇ are structurally similar.     

Novel cellulose derivatives. III. Thermal analysis of mixed esters with butyric and hexanoic acid

Cellulose derivatives with low degrees of substitution (i.e., DS < 1.5) often fail to reveal glass transition temperatures (T_g) by virtue of their tenacious adherence to moisture, thus preventing systematic analysis of substituent effects (size and DS) on T_g and T_m transitions. On the other hand, cellulose triesters have T_ms that decline with acyl substituent size except when the substituent size becomes very large (i.e., > C₆), and they have T_gs within 5–20°C of their T_ms. This proximity is unusual for a semicrystalline material, and it interferes with the crystallization process that occurs between T_m and T_g. Triesters of cellulose with mixed acyl substituents (one smaller and one larger) allow not only unambiguous observation of T_gs and T_ms but also an adjustable Δ(T_m ? T_g) window that depends upon the size and the DS of the larger substituent. The materials studied including cellulose acetate butyrate triesters (DS_bu 0.8–2.6), cellulose acetate hexanoate triesters (DS_hex 0–3.0), and cellulose acetate (DS_ac 2.44), revealed that only the mixed esters, in which the bulkier acyl group is in the range of DS 0.3–1.0, had a Δ(T_m ? T_g) value in excess of 40°C. Although the T_m of cellulose acetate hexanoate declined by ca. 150°C per unit of DS_hex as DS_hex rose from 0 to 1, this was only ca. 25°C between DS_hex of 1 and 3. Frequently observed dual-melt endotherms were attributed to two separate crystal morphologies. ©1995 John Wiley & Sons, Inc.     

Separation of O- and C-allyl glycoside anomeric mixtures by capillary electrophoresis and high-performance liquid chromatography

Rapid and reliable methods for the analysis of O- and C-allyl galactopyranosides and glucopyranosides are presented, based on capillary zone electrophoresis (CZE) and micellar electrokinetic capillary chromatography (MEKC). In MEKC, the formation of chromophoric and charged complexes between the saccharides and borate as well as the hydrophobic interactions with micelles jointly contributed to the selective separation and sensitive detection of all the investigated anomeric couples. Some non-purified synthesis mixtures of C-allyl glycosides were successfully characterised without pre-treatment. MEKC buffer conditions for which glycosides separation was successfully achieved were then exported and applied to reverse-phase liquid chromatography (RP-HPLC), for the quantitative isolation of each allyl glycoside anomer. Identification of the obtained anomeric products was performed by electrospray mass spectrometry and (13)C NMR spectroscopy. Glycoside-solvent interactions driving the selective anomeric separation were shortly addressed and discussed on the basis of sugar derivatives structural differences.