No abstract

Since their discovery, over the years, molecular gels have been constantly drawing the attention of chemists from various scientific fields. Their structural softness together with the orderliness at the molecular level provides such molecules immense potential for the amplification of their properties. Using this chemistry, one can easily realize a macroscopic outcome from a molecular level modulation. This phenomenon is governed by the principle of supramolecular interactions that introduce a unique "reversibility" to the system. The new generation of gel chemistry is now tending more towards the development of new attractive functions to create smart materials for achieving outstanding response or unprecedented selectivity over a process. However, for the successful implementation of this mission, it is really essential to correlate gel functions with their structures. This focus review is an attempt to find such a correlation, which can motivate and stimulate this existing field towards precisely designing molecular gels for the desired functions.

Single-walled carbon nanotubes (SWNTs) show unique photoluminescence (PL) in the near-infrared (NIR) region. Here we propose a concept based on the proximal modification in local covalent functionalization of SWNTs. Quantum mechanical simulations reveal that the SWNT band gap changes specifically based on the proximal doped-site design. Thus, we synthesize newly-designed bisdiazonium molecules and conduct local fucntionalisation of SWNTs. Consequently, new red-shifted PL (E112*) from the bisdiazonium-modified SWNTs with (6, 5) chirality is recognized around 1250 nm with over ~270 nm Stokes shift from the PL of the pristine SWNTs and the PL wavelengths are shifted depending on the methylene spacer lengths of the modifiers. The present study revealed that SWNT PL modulation is enable by close-proximity-local covalent modification, which is highly important for fundamental understanding of intrinsic SWNT PL properties as well as exciton engineering–based applications including photonic devices and (bio)imaging/sensing.

Dynemicin is a hybrid containing anthraquinone and enediyne cores, which contribute to binding and cleavage of DNA, respectively. DNA strand scission by the antitumor antibiotic is significantly enhanced by the addition of NADPH or thiol compounds. The preferential cutting site of dynemicin is on the 3' side of purine bases (i.e., 5'-GC, -GT, and -AG) and is clearly different from the cutting sites of esperamicin and calicheamicin. The double-stranded and the stem regions of single-stranded DNAs are preferentially cleaved by dynemicin. Therefore, dynemicin may be a useful reagent for probing secondary structures of DNA. Pretreatment of DNA with Adriamycin and actinomycin D alters the cutting mode of dynemicin. Dynemicin-mediated DNA breakage is strongly inhibited by pretreatment of the DNA with distamycin A and anthramycin, suggestng that dynemicin interacts with the minor groove of the DNA helix. Intercalation of the anthraquinone core into the DNA followed by the attack of the phenyl diradical formed from the enediyne core is considered as a possible mechanism of action of dynemicin.Dynemicin, isolated from the fermentation broth of Micromonospora chersina, possesses potent cytotoxicity and in vivo antitumor activity (1). This antibiotic is a hybrid molecule of two typical chemotypes of antitumor agent, enediyne and anthraquinone (Fig. 1). Esperamicin, calicheamicin, and neocarzinostatin, which produce DNA strand breaks, belong to the family of enediyne antitumor antibiotics (2)(3)(4)(5). DNA cleavage by esperamicin and calicheamicin appears to involve rearrangement of the enediyne unit, a phenylene diradical that can abstract hydrogen atoms from the sugar phosphate backbone of DNA. On the other hand, daunomycin, Adriamycin, and aclacinomycin belong to the class of anthracycline antitumor antibiotics and can intercalate into DNA through the planar aromatic rings (6, 7). Indeed, an x-ray diffraction study (8) demonstrated that two daunomycin molecules intercalate between the GC base pairs in the self-complementary hexanucleotide CGTACG. Evidently, dynemicin possesses these two structural features in one molecule and hence we were interested in clarifying the mechanism through which dynemicin cleaves DNA. MATERIALS AND METHODSDrugs and Chemicals. Dynemicin was isolated from the fermentation broth of Micromonospora chersin and purified as described (1) tTo whom reprint requests should be addressed. 3831The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement"in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Agarwood oil and spikenard extract were examined for their sedative activity using a spontaneous vapor administration system. It was shown that inhalation of agarwood oil vapor sedated mice. The main volatile constituents of the oil were found to be benzylacetone [agarwood oil from a Hong Kong market (1)], or alpha-gurjunene and (+)-calarene [agarwood oil made in Vietnam (2)]. A hexane extract of spikenard contained a lot of calarene, and its vapor inhalation had a sedative effect on mice. Individual principles benzylacetone, calarene, and alpha-gurjunene were administered to mice, which reproduced the result of the corresponding oil or extract. However, the most effective dose of the compounds was lower than their original content in the oil and extract (benzylacetone 0.1%, calarene 0.17%, alpha-gurjunene 1.5%).

Two different classes of water-soluble fullerene derivatives, detergent-type and sphere-type, were synthesized. The derivatives were evaluated for their biological activities including cytotoxicity, DNA cleavage, and inhibition of HIV-protease and other enzymes. Both classes of compounds display generally similar behavior except for their cytotoxicity spectra against several cell lines. The fullerene derivatives bearing N-methylpyrrole were found to be photo-inactive with respect to DNA cleaving activity and cytotoxicity. A study on the kinetics for the inhibition of HIV-protease with detergent type derivative revealed that the compound is a potent fullerene-based HIV protease inhibitor, inhibiting the enzyme activity in a reversible and competitive manner with a Ki value of 0.32 μM.

Silica nanoparticles grafted with poly(methyl acrylate) (PMA) chains anchored by a maleimide-anthracene cycloadduct were synthesized to demonstrate mechanochemically selective activation of mechanophores at heterogeneous interfaces. By quantifying the anthracene-containing cleaved PMA polymers, which are generated via retro-[4 + 2] cycloaddition reactions, the first-order kinetic coefficient was determined. Activation characteristics of mechanophores anchored to a nanoparticle exhibit behavior similar to mechanophore-linked polymers, e.g., threshold molecular weight and linear increase in rate coefficient with molecular weight above the threshold. This model system is thus valuable as a probe to test stress activation of interfacially bonded mechanophores relevant to the design of fiber-reinforced polymer composites.

We present a concept to modulate near infrared photoluminescence (NIR-PL) from locally-functionalized single-walled carbon nanotubes (local-f-SWNTs) based on a molecular recognition approach using newly synthesized phenylboronic acid (PB)-functionalized local-f-SWNTs (PB-SWNTs) and saccharides, in which a selective PL spectral shift is observed by addition of the saccharides.