Unusual face-to-face pi-pi stacking interactions within an indigo-pillared M3(tpt)-based triangular metalloprism

A triangular metalloprism, [((CO)3Re(mu-2)Re(CO)3)3(mu3-1)2], self-assembled from Re2(CO)10, 2,4,6-tri-4-pyridyl-1,3,5-triazine (tpt, 1), and indigo (H2(2)), represents a fairly novel example of strong face-to-face pi-pi interactions between the central triazine rings of the tpt ligands that bow significantly inward distorting the prismatic structure.     

Sodium hydroxide as pretreatment and fluorosurfactant-capped gold nanoparticles as sensor for the highly selective detection of cysteine

A sensor for detecting cysteine (Cys) in a solution of fluorosurfactant (FSN)-capped gold nanoparticles (AuNPs) has been developed. Under acidic conditions, FSN-capped AuNPs are aggregated in the presence of homocysteine (HCys) and Cys but not in the presence of cysteinylglycine, glutathione, and gamma-glutamycysteine. When adding NaOH to a solution of HCys, the five-membered ring transition state is formed through intramolecular hydrogen abstraction. By contrast, it is difficult for Cys to form a four-membered ring transition state after Cys has been pretreated with NaOH. As a result, the HCys-induced aggregation of the FSN-capped AuNPs is suppressed because the five-membered ring transition state exhibits relatively larger steric hindrance and has stronger interaction with the FSN molecules. Thus, we can discriminate between Cys and HCys on the basis of different aggregation kinetics. Under the optimum condition, the selectivity of the probe for Cys in aqueous solutions is remarkably high over the other aminthiols. Note that HCys and Cys have very similar structure and pK(a) value. We have validated the applicability of our method through the analyses of Cys in urine samples. It is believed that this approach has great potential for the detection of Cys in biological samples.     

On-line concentration of proteins by SDS-CGE with LIF detection

We present a simple approach for on-line concentration of SDS-protein complexes by using poly(vinyl alcohol) (PVA) solution in CGE. In comparison to the coated capillary, the presence of EOF in CGE omitted the need to fill the capillaries with polymer solutions prior to the analysis. More importantly, we found that highly reproducible separation of eight proteins by 3.5% PVA was achieved between runs and without the regeneration of high bulk EOF; the RSD of migration times was less than 0.7%. To further improve the concentration sensitivity, neutral PVA was introduced into the capillary with the help of EOF to act as sieving matrix. The occurrence of stacking at the boundary between the PVA and the sample zone is mainly due to the retardation of proteins by PVA. As a result, the LODs at an S/N of 3 for SDS-protein complexes are of the order of sub-nM to several nM. For example, the LOD for BSA is 0.78 nM, which is a 91-fold sensitivity enhancement over the normal injection. In addition, our stacking method has been applied to the analyses of proteins in Escherichia coli cells. The peak for beta-galactosidase (E. coli) was observed after 0.1 microM beta-galactosidase was spiked into the E. coli samples.     

Syntheses and pyrolyses of benzofuran analogues of alpha-oxo-o-quinodimethane. A study on vinylcarbene-cyclopropene rearrangement

Flash vacuum pyrolyses (FVP) of benzoic 3-methyl-2-benzofurancarboxylic anhydride (12) and benzoic 2-methyl-3-benzofurancarboxylic anhydride (13) at 550 degrees C and ca. 10(-2) torr both give methylenebenzocyclobutenone (21) as the major product and indenone (22) as the minor one. A mechanism involving generation of alpha-oxo-o-quinodimethane 11 as the primary pyrolysis product from FVP of 13, followed by elimination of a CO molecule to give carbene 24, which undergoes a vinylcarbene-cyclopropene rearrangement and a ring contraction of the resulting carbene 23, is proposed to account for the observed results. The proposed mechanism is further supported by a deuterium-labeling study on FVP of (2-benzofuryl)methyl-alpha,alpha-d2 benzoate (28-d2).     

Ru(II) complexes of tetradentate ligands related to 2,9-di(pyrid-2'-yl)-1,10-phenanthroline

A series of 1,10-phenanthrolines were prepared having additional ligating substituents at the 2,9-positions. These substituents were either a 4-substituted pyrid-2-yl, quinolin-2-yl, 1,8-naphthyrid-2-yl, N-methyl imidazo-2-yl, or N-methyl benzimidazo-2-yl group. Additionally, 3,6-di-(pyrid-2'-yl)-dipyrido[3,2-a:2',3'-c]phenazine was prepared. All but two of these ligands coordinated Ru(II) in a tetradentate equatorial fashion with two 4-methylpyridines bound in the axial sites. An X-ray structure analysis of the diimidazoyl system indicates considerable distortion from square planar geometry in the equatorial plane. Previously reported variations in the axial ligand for such complexes appear to have a stronger effect on the electronic absorption and redox properties of the system than similar changes in the equatorial ligand. In the presence of excess Ce(IV) as a sacrificial oxidant at pH 1, all the systems examined catalyze the decomposition of water to generate oxygen. Turnover numbers are modest, ranging from 146 to 416.     

Broadband Light-Emitting Diodes with One-Dimensional Photonic Crystal Layer

In this article, a broadband gallium-nitride-based light-emitting diode with a one-dimensional photonic crystal layer is investigated. The broadband light-emitting diode using the proposed backside reflector has high reflectance (>95%) over a 270-nm bandwidth in visible light at an arbitrary incidence angle. A broadband light-emitting diode of high output power due to the high reflectivity is achieved. Also reported are the results for light-emitting diodes by the transistor outline can (TO-can) package. The proposed light-emitting diodes possess broadband high reflected spectra, high output power for light extraction, and a good view angle.     

Synthesis of Blue‐, Green‐, Yellow‐, and Red‐Emitting Graphene‐Quantum‐Dot‐Based Nanomaterials with Excitation‐Independent Emission

A one‐pot method is described for the preparation of graphene quantum dots/graphene oxide (GQDs/GO) hybrid composites with emission in the visible region, through heteroatom doping and hydroxyl‐radical‐induced decomposition of GO. The NH₄OH‐ and thiourea‐mediated dissociation of H₂O₂ produces hydroxyl radicals. Treatment of GO with hydroxyl radicals results in the production of small‐sized GO sheets and GQDs, which self‐assemble to form GQDs/GO through strong π–π interactions. For example, the reaction of GO with a mixture of NH₄OH and H₂O₂ for 40, 120, and 270 min generates yellow‐emitting GQDs/GO (Y‐GQDs/GO), green‐emitting GQDs/GO, and blue‐emitting GQDs, while red‐emitting GQDs/GO (R‐GQDs/GO) are prepared by incubating GO with a mixture of thiourea and H₂O₂. From the analysis of these four GQD‐based nanomaterials by transmission electron microscopy, atomic force microscopy, and fluorescence lifetime spectroscopy, it is found that this tunable fluorescence wavelength results from the differences in particle size. All four GQD‐based nanomaterials exhibit moderate quantum yields (1–10%), nanosecond fluorescence lifetimes, and excitation‐independent emissions. Except for R‐GQDs/GO, the other three GQD‐based nanomaterials are stable in a high‐concentration salt solution (e.g., 1.6 m NaCl) and under high‐power irradiation, enabling the sensitive (high‐temperature resolution and large activation energy) and reversible detection of temperature change. It is further demonstrated that Y‐GQD/GO can be used to image HeLa cells.     

Photodissociation dynamics of small aromatic molecules studied by multimass ion imaging

The photodissociation dynamics of various aromatic molecules, studied using multimass ion imaging techniques, is reviewed. The experimental data reveals new isomerization and dissociation mechanisms. Our investigation of benzene, pyridine, and pyrimidine finds that H-atom elimination thresholds remain the same for the three molecules. We also notice that ring-opening dissociation thresholds decrease rapidly with the increase of the number of nitrogen atoms in the aromatic ring. Hydrogen atom elimination is the sole dissociation channel for benzene at 193 nm. Along with H-atom elimination, we observe five distinct ring-opening dissociation channels for pyridine at 193 nm. No dissociation channels were observed for benzene and pyridine at 248 nm. Ring-opening dissociation channels are the major channels for pyrimidine, which dissociates at 193 nm and also at 248 nm. A six-membered to seven-membered ring isomerization was observed for photodissociation processes involving toluene, m-xylene, aniline, 4-methylpyridine, alpha-fluorotoluene, and 4-fluorotoluene, indicating a general isomerization mechanism for all such aromatic molecules. What is significant, is that during the isomerization, atoms (i.e., carbon, nitrogen, fluorine, and hydrogen) belonging to respective alkyl or amino groups are involved in an exchange with atoms within the aromatic ring. This type of isomerization is not observed in other aromatic isomerization mechanisms. For small tyrosine chromophores, such as phenol, 4-methylphenol, and 4-ethylphenol, H-atom elimination from a repulsive excited state plays a key role. However, dissociation is quenched in large chromophores like 4-(2-aminoethyl)-phenol. Our work demonstrates the capability and high sensitivity of multimass ion imaging techniques in the study of aromatic compounds.     

Profiling of amine metabolites in human biofluids by micellar electrokinetic chromatography with laser-induced fluorescence detection

A rapid and sensitive capillary electrophoresis (CE) method has been developed for profiling organic metabolites containing amine functional groups in mammalian biofluids. Metabolites containing an amine group were derivatized with 4-fluoro-7-nitrobenzo-2,1,3-oxadiazol (NBD-F), separated by micellar electrokinetic chromatography (MEKC), and detected by argon-ion (488 nm) laser-induced fluorescence detection. The optimized MEKC background electrolyte conditions were: 50 mmol L⁻¹ sodium cholate, 5 mmol L⁻¹ β-cyclodextrin, and 20 mmol L⁻¹ Brij 35 in 20 mmol L⁻¹ aqueous borate buffer, pH 9.3, containing 7% methanol. Under these conditions all the amine compounds in mammalian biofluids, for example plasma, saliva, and urine, were derivatized directly, without extraction, in a minimum volume of 100 nL and the derivatives could be separated within 16 min. Up to 90% of the amine-containing metabolites in plasma and saliva could be identified by reference to standard compounds. For twenty amine standards linearity of calibration was better than R ² = 0.99. Migration-time and peak-area reproducibility were better than RSD 1.5% and 15% respectively. In replicate analysis of human plasma bioanalytical precision ranged between 0.7 and 3.8 RSD% for a 5.0-μL volume and between 1.7 and 5.5 RSD% for 100-nL volume. The concentrations measured were found to be in agreement with literature values.