Enhanced rectal absorption of insulin in rabbits from hollow-type suppositories containing insulin and glyceryl-1-monooctanoate.

The absorption of two kinds of insulin (from porcine or bovine pancreas) from the rectum of rabbits after the administration of hollow-type suppositories containing insulin and glyceryl-1-monooctanoate (GMO) as an absorption-enhancing agent was investigated. Two types of suppositories were employed: type I containing insulin in an aqueous solution (approx. 25 IU/mg/100 microliters citric buffer solution at pH 3.0) in the cavity of the suppository and GMO mixed with a base material (Witepsol H-15), and type II containing insulin in a crystalline form in the same amount as in type I. Without GMO, the insulin and glucose levels in plasma were unchanged, whereas a marked increase in the plasma levels of insulin and a decrease of glucose concentrations were found following coadministration of insulin and GMO by the type I suppository. Similar enhancement of rectal absorption of insulin was obtained from porcine and bovine sources. In the case of the crystalline insulin, despite the use of the same amount of GMO, porcine insulin was more efficiently absorbed than bovine insulin by the type II suppository. GMO enhances the absorption of insulin in an aqueous solution or a crystalline form, and the dissolution rate of insulin may be an important factor in the rectal absorption of insulin.     

Tris(1‐ethyl‐3‐methyl­imidazolium) hexa­chloro­lanthanate

In the title complex, (C₆H₁₁N₂)₃[LaCl₆], centrosymmetric octahedral hexa­chloro­lanthanate anions are located at the corners and face‐centers of the monoclinic unit cell. The ring H atoms of the cations interact with the Cl atoms of the anions via hydrogen bonding, and bifurcation of the hydrogen bonding is observed. Cation–cation interactions via hydrogen bonding between the ring H atoms and π‐electrons of aromatic rings are also observed as in other imidazolium salts.     

Copper(II)-catalyzed oxidation of d-alpha-tocopherol by oxygen in aqueous solution

alpha-Tocopherol (alpha-Toc) was solubilized in aqueous solutions using 13 solubilizing agents and the products of oxidation by oxygen in the presence and the absence of Cu(II) were analyzed by HPLC. In the presence of Cu(II), the oxidation was accelerated and 5-formyl-7,8-dimethyltocol and alpha-tocoquinone were the major oxidation products. Their yields greatly increased in the presence of Cu(II). The yields and the rates of formation of the products were dependent on the properties of solubilizing agents and other conditions as well as the presence of Cu(II) or other metal ions. It is suggested that slight changes in the structure of the solubilizing agents affect the course of the reaction.     

Borderline of hydrogen bonding of silanols

Two new silanols bearing very bulky silyl groups, (i-Pr₃ Si)₃SiOH and (t − BuMe₂Si)₃SiOH were prepared by peracidoxidation of their respective silanes. The X − ray crystallographic analysis revealed that (t − BuMe₂Si)₃ SiOH forms a dimeric structure with hydrogen bonding, while (i − Pr₃ Si)₃ SiOH exists as a monomer in the crystal. The effects of the size of the substituents as well as the reactivity of these silanols are discussed.     

Reactions of hydropolysilanes with alcohols catalysed by tris(triphenylphosphine)chlororhodium

[RhCl(PPh₃)₃] is a very effective catalyst for the cleavage of Si-Si bonds by alcohols.