Catalytic flow-injection determination of copper at nanogram levels by using color formation of N-phenyl-p-phenylenediamine with m-phenylenediamine in the presence of pyridine and ammonia as activators

A spectrophotometric flow-injection method for determining copper(II) has been developed. It is based on the catalytic effect of copper(II) on the oxidative coupling of N-phenyl-p-phenylenediamine with m-phenylenediamine in the presence of hydrogen peroxide. Pyridine and ammonia as activators increased the absorbance for the copper(II)-catalyzed coloration, and the dye formed was stabilized by adding a non-ionic surfactant. The working range of the method was 0.1-2.0 ng ml(-1) of cooper(II) with a relative standard deviation 2.4% at a sampling rate of 30 h(-1). Interference from iron(III) was effectively suppressed by citric acid. Copper in natural water samples can be determined easily.     

Interaction of cubosomes with plasma components resulting in the destabilization of cubosomes in plasma

Cubosomes are novel dispersed nanoparticles with bicontinuous cubic phases of monoolein in their interior. We investigated their disintegration process in plasma by in vitro and in vivo studies. Cubosomes were incubated with whole plasma or plasma components such as HDL, LDL, and albumin. The lypolysis study indicated lipolytic activity of whole plasma towards cubosomes. Gel filtration chromatography revealed that HDL, LDL and albumin interacted with cubosomes. HDL affected cubosomes’ integrity and gave rise to smaller particles which contained the components of both cubosomes and HDL. Upon incubation with LDL, cubosomes fused with LDL. Albumin was shown to take up monoolein out of the particles. Cubosomes were disintegrated by whole plasma as a result of the interaction with plasma components. It was concluded that in vivo observation of a long circulation time of a hydrophobic substance in cubosomes was due to the sustained behavior of cubosome remnant particles.     

Backbone rearrangements of methyl (-)-kaur-9(11)-en-19-oate and its epoxide: structures of two diterpenes of a new skeletal type

cleavage of the epoxide ($\text{2}$) of methyl (-)-kaur-9(11)-en-19-oate ($\text{1b}$) with boron trifluoride-ether in benzene and in acetic anhydride yielded ($\text{3a}$) and ($\text{3b}$), respectively. On epoxidation with $\text{m}$-chloroperbenzoic acid in the presence of $\text{N}$-nitrosomethyl urea, ($\text{1b}$) suffered a backbone rearrangement to form ($\text{6}$).     

Site-selective RNA cleavage by DNA bearing a base pair-mimic nucleoside

We have synthesized the deoxyadenosine derivative tethering a phenyl group (X), which mimics the Watson-Crick A/T base pair. The RNA/DNA hybrid duplexes containing X in the middle of the DNA sequence showed a similar thermal stability regardless of the ribonucleotide species (A, G, C, or U) opposite to X, probably because of the phenyl group stacking inside of the duplex accompanied by the opposite ribonucleotide base flipped in an extrahelical position. The RNA strand hybridized with the DNA strand bearing X was cleaved on the 3'-side of the ribonucleotide opposite to X in the presence of MgCl2, and the RNA sequence to be cleaved was not restricted. The site-specific RNA hydrolysis suggests that the DNA strand bearing X has the advantage of the site-selective base flipping in the target sequence and the development of a "universal deoxyribozyme" to exclusively cleave a target RNA sequence.