Inclusion of DNA into organic gelator fibers made of amphipathic molecules and its controlled release

When methyl 4,6-O-(p-nitrobenzylidene)-alpha-D-glucopyranoside (p-NO(2)Glu) was dissolved in water, p-NO(2)Glu molecules self-assembled to form a fiber (elemental fiber), and as a result, the solution became a partially transparent gel. When an equal (or more) amount of DNA was added to the gel, a white and crystalline gel was obtained. Energy-dispersive X-ray spectroscopy coupled with TEM and confocal microscopy suggested that DNA was included in the gel fibers made of p-NO(2)Glu molecules. The results imply that p-NO(2)Glu molecules are self-assembled to form an elemental fiber and these elemental fibers and DNA are twisted together to form higher hierarchic fibers. When the complexed gel made of plasmid DNA (pDNA) and p-NO(2)Glu was added to E. coli T7 S30 extract solution, the pDNA had less expression ability compared with naked one. When we added methyl-beta-cyclodextrin (MbetaCyD), the expression rate was recovered with increasing added amount of MbetaCyD. The present paper shows inclusion and controlled release of DNA from a novel supporting material of DNA and that technology could play an important role in the development of localized approaches to gene therapy.     

Coenzyme models. 19. Oxidation of furoin by a flavin immobilized in cationic polyelectrolytes: A flavoenzyme model

The rate constants for the oxidation of furoin by a flavin (vitamin B₂ analog) immobilized in cationic polymers were evaluated under anaerobic conditions, and the influence of reaction environments was discussed in connection with the enzymatic reactivity. It was found that (1) proton abstraction from furoin which forms the carbanionic intermediate is rate determining in the initial stage of the reaction and is facilitated by the environment of cationic polymers, (2) proton abstraction is efficiently accelerated by added cationic surfactant (CTAB), and (3) N-dodecylbenzohydroxamic acid in aqueous CTAB acts as an excellent proton-abstracting reagent. The polymers with high dodecyl group content served, in all cases, as better oxidizing reagents. As a summary of these conclusions, the importance of hydrophobic environments in flavin-mediated oxidation was emphasized.     

Coupling a natural receptor protein with an artificial receptor to afford a semisynthetic fluorescent biosensor

An artificial receptor and a signal transducer have been engineered on a lectin (saccharide-binding protein) surface by a post-photoaffinity labeling modification method. Saccharide binding can be directly and selectively read out by the fluorescence changes of the fluorophore via photoinduced electron transfer (PET) mode. Fluorescence titration with various saccharides reveals that molecular recognition by the artificial receptor is successfully coupled to the native binding site of the lectin, producing a novel fluorescent saccharide biosensor showing modulated specificity and enhanced affinity. Designed cooperativity between artificial and native molecular recognition modules was quantitatively demonstrated by the comparison of the binding affinities, and it represents a new strategy in molecular recognition. By using appropriate artificial receptors and various native lectins, this approach may provide many new semisynthetic biosensors for saccharide derivatives such as glycolipids and glycopeptides/proteins. An extended library of lectin-based biosensors is envisioned to be useful for glycome research, a newly emerging field of the post-genomic era.     

Automated two-dimensional liquid chromatographic system for mapping proteins in highly complex mixtures.

An automated two-dimensional liquid chromatographic system was developed for systematic protein separations which could serve for analytical mapping and preparative separations of proteins. The system applies the principles of the column-switching technique, and consists of two different columns connected in tandem through an electrical column switching valve, two pumping systems to operate each column independently and a system controller to perform sequential chromatography on the two columns. A protein mixture is applied to the first-dimensional anion-exchange column and is separated by stepwise elution with an increasing sodium chloride concentration. The eluent is introduced directly to the second-dimensional reversed-phase column, and is further separated by gradient elution with an increasing acetonitrile concentration. The two elution stages are synchronized by a computer program. By this system, very complex protein mixtures such as crude cerebellar extracts were resolved reproducibly into ca. 200 peaks within 12 h. The method can be used for the total analysis of proteins in various tissues and cells without complicated premanupulation of samples, and allows the simultaneous analysis of a protein isolated by chromatography. The isolated protein is most suitable for use in the strategy of protein and gene sequence analysis.     

60]fullerene-motivated organogel formation in a porphyrin derivative bearing programmed hydrogen-bonding sites

A tetraphenylporphyrin (1b) bearing amide groups at the 3,5-positions of the meso-phenyl groups is assembled into a two-dimensional sheetlike structure and acts as an organogelator. When [60]fullerene was added, the sheetlike structure was dramatically changed into a one-dimensional fibrous structure, and both the gelation ability and the gel stability were improved. The stoichiometry between [60]fullerene and 1b was determined to be 1:2. Examination utilizing SEM and TEM observations, UV-vis and ATR IR spectral analyses, and XRD analysis revealed that an amide-amide hydrogen-bonding interaction creates a cavity, the size of which is complementary to that of [60]fullerene, and these cavities are connected by another amide-amide hydrogen-bonding interaction to provide a one-dimensional multicapsular structure. This is a novel example that the superstructure constructed in an organogel system is drastically changed by added [60]fullerene.     

Electrochemical fabrication of single-walled carbon nanotubes-DNA complexes by poly(ethylenedioxythiophene) and photocurrent generation by excitation of an intercalated chromophore

It was found that single-walled carbon nanotubes (SWNTs) solubilized into water by complexation with DNA (salmon testes) can be readily deposited on the ITO electrode by electrochemical oxidative polymerization of ethylenedioxythiophene (EDOT). The driving force for this novel deposition is an electrostatic interaction between the anionic charges of wrapping DNA and the cationic charges of poly(EDOT) formed in the oxidative polymerization process. The presence of poly(EDOT), SWNTs and DNA in the composite was confirmed by measurements of UV-Vis, IR, resonance Raman spectra, cyclic voltammetry (CV) and confocal laser scanning microscopy (CLSM). The composite adsorbed a DNA intercalator (ethidium bromide: EB) very efficiently, which is regarded to be further evidence for inclusion of DNA. The surface morphology, characterized by CLSM, SEM and AFM, featured the network structure consisting of 0.5-ca. 10 microm nanorods. Very interestingly, we found that photoexcitation of EB bound to the DNA generates the photocurrent, indicating that the excited energy of EB is injected into SWNTs, which is collected by the electroconductive poly(EDOT) film on the ITO electrode. We believe, therefore, that the present system is a very convenient method to explore new materials related to redox and photochemical functions.     

Helical structures of conjugate polymers created by oxidative polymerization using synthetic lipid assemblies as templates

The morphology of conjugate polymers (such as poly(ethylenedioxythiophene), poly(pyrrole), and poly(aniline)) can be controlled in their polymerization processes, by applying the concept of the templating method to oxidative polymerization. As oxidative polymerization of these monomers produces cationic intermediates, the anionic assemblies can act as potential templates due to the mutual electrostatic attractive force. Oxidative polymerization of ethylenedioxythiophene (EDOT), pyrrole, and aniline was carried out using helical superstructures of synthetic lipid assemblies as templates. Interestingly, we have found that oxidative polymerization of these monomers results in novel polymeric aggregates, such as a helical-tape structure and an intertwined helical structure, and that both the right-handed and left-handed helical structures can be created by a change in the hydrophilic head groups. This is the first example of helical superstructures composed of conjugate polymers that have been designed utilizing a convenient templating method.     

A self-assembled porphyrin-based dimeric capsule constructed by a Pd(II)-pyridine interaction which shows efficient guest inclusion

Novel self-assembled molecular capsules were constructed from two moles of pyridine-containing porphyrin derivatives and four moles of Pd(II) complexes utilizing a pyridine-Pd(II) interaction. The (1)H NMR spectral studies established that these self-assembled molecular capsules 5 and 6 have a highly symmetrical D(4)(h)() structure as well as a large inside cavity. It was shown that molecular capsule 6 can include a large bipyridine guest by a two-point simultaneous pyridine-Zn(II) interaction.     

Thermal equilibrium between “isoxazolidine” and “enamine”

Nitrones formed from the reaction of $\text{N}$-phenylhydroxylamine and aldehydes dimerized to isoxazolidines. A new thermal equilibrium between isoxazolidine and $\text{N}$-hydroxyenamine in DMSO was studied by ¹H and ¹³C NMR.