Rb2REGaSi4O12 (RE = Y, Eu, Gd, Tb): luminescent mixed-anion double layer silicates containing chains of edge-sharing REO7 pentagonal bipyramids

Four new rare earth gallosilicates, Rb 2REGaSi4O12 (RE = Y, Eu, Gd, and Tb, denoted as REGS-1), have been synthesized under high-temperature, high-pressure hydrothermal conditions and characterized by single-crystal X-ray diffraction. They are the first examples of rare earth gallosilicates that contain individually occupied tetrahedral Ga(3+) and Si(4+) centers. The unique structure is formed of two 1D and one 2D substructural units: unbranched achter single chains which are seldom observed in silicates, the PaCl 5-type infinite chains formed of edge-sharing REO7 petagonal bipyramids and the unprecedented mixed-anion double layers with the composition [GaSi4O12]. The photoluminescence properties of EuGS-1 and TbGS-1 have been studied. The Y(3+) ion in YGS-1 can be partially replaced by Eu(3+) and Tb(3+) to yield luminescent materials.     

Energy transfer of highly vibrationally excited naphthalene. II. Vibrational energy dependence and isotope and mass effects

The vibrational energy dependence, H and D atom isotope effects, and the mass effects in the energy transfer between rare gas atoms and highly vibrationally excited naphthalene in the triplet state were investigated using crossed-beam/time-sliced velocity-map ion imaging at various translational collision energies. Increase of vibrational energy from 16 194 to 18 922 cm(-1) does not make a significant difference in energy transfer. The energy transfer properties also remain the same when H atoms in naphthalene are replaced by D atoms, indicating that the high vibrational frequency modes do not play important roles in energy transfer. They are not important in supercollisions either. However, as the Kr atoms are replaced by Xe atoms, the shapes of energy transfer probability density functions change. The probabilities for large translation to vibration/rotation energy transfer (T-->VR) and large vibration to translation energy transfer (V-->T) decrease. High energy tails in the backward scatterings disappear, and the probability for very large vibration to translation energy transfer such as supercollisions also decreases.     

Star-shaped mesogens of triazine-based dendrons and dendrimers as unconventional columnar liquid crystals

Dendrons Gn-Cl and Gn-NH (n = 2-4) and novel dendrimers Gn-N approximately N-Gn (n = 2-4) based on triazine and piperazine units were efficiently prepared in good yields without employing the protection and deprotection processes and are fully characterized by 1H NMR and 13C NMR spectroscopies, elemental analysis, and mass spectroscopy. These compounds are transparent and possess good thermal stability. G4-Cl shows a monotropic columnar phase in a narrow range with a coexisting crystalline phase. Dendron G4-NH shows a rectangular column-phase, and dendrimer G4-N approximately N-G4 exhibits a monotropic hexagonal columnar phase. These identifications were supported by the polarizing optical scope and powder XRD studies.     

13C‐Isotope Labeled Surrogate for Estimating Organophosphorus Pesticides in Agricultural Products by Gas Chromatography‐Mass Spectrometry

¹³C‐isotope labeled paraoxon‐ethyl (¹³C₂‐EP) and deuterium‐labeled paraoxon‐methyl (D₆‐MP) were synthesized and employed as the surrogate (SS) and the internal standard (IS) in organophosphorus pesticides (OPs) spiking agricultural QC samples. The residual amounts of OPs were determined with gas chromatography‐mass spectrometry (GC‐MS) method. The isotope‐labeled compounds used in this study could assist the analysts to estimate the appropriateness and the uncertainties produced by pre‐treatment process. It was found that these isotope labeled compounds could improve the accuracy (10% to 40% of quantitative analysis), and provide efficacious calibration for the spiking recoveries of OPs in some agricultural samples.     

The Excitation Spectra of Naphthalene Dimers: Frenkel and Charge‐transfer Excitons

Vertical electronic excitation energies have been calculated at the second‐order approximate coupled‐cluster (CC2) level for a series of dimeric naphthalene systems. The calculated excitation energies are compared with values obtained for a single naphthalene molecule and provide information about the coupling between the naphthalene moieties in the dimers. The calculations show that the coupling between the naphthalenes depends on the distance and the energy of the exciton. At long distances and high energies the excitons on the two naphthalenes are strongly coupled, whereas the excitation energies of the few lowest states are almost unaffected by the presence of the neighboring molecules. We have also analyzed the composition of the dimeric states that consist of the individual monomer states, to investigate the charge‐transfer (CT) and the Frenkel character of the excitons. Our results indicate that the CT exciton exists at short distances, and that its population drops as the distance between the two naphthalene increases.     

Mass spectral studies of 1-(2-chloroethoxy)-2-[(2-chloroethyl)thio]ethane and related compounds using gas chromatography–mass spectrometry (GC-MS) and gas chromatography–triple quad mass spectrometry (GC-QQQ)

The electron impact and collision-ion-dissociation mass spectra of 1-(2-chloroethoxy)-2-[(2-chloroethyl) thio]ethane (1) and 10 related molecules were obtained using gas chromatography–mass spectrometry and gas chromatography–triple quad mass spectrometry. These mass spectral studies were performed to facilitate the development of a spectral database of mustard-related compounds for verification purposes of the Chemical Weapons Convention. The proposed fragmentation pathways of each individual molecule (1–11) are reported along with rationalizations for the most characteristic ions.     

Two-dimensional densely packed DNA nanostructure derived from DNA complexation with a low-generation poly(amidoamine) dendrimer

One of the keys for using deoxyribonucleic acid (DNA) as a nanomaterial relies on how the individual DNA chain can be aligned and how a multitude of DNA chains can be packed into ordered nanostructures. Here we present a simple method for constructing a 2-D densely packed DNA nanostructure using the electrostatic complex of DNA with a poly(amidoamine) (PAMAM) dendrimer of generation two. Ordered DNA arrays are formed by drop-casting an aqueous solution containing positively overcharged complexes onto mica followed by a prolonged incubation. During the incubation, the complexes tend to adsorb onto the negatively charged mica surface through electrostatic attraction. The rodlike complexes organize to form ordered arrays to increase the surface density of the adsorbed complexes and hence the attractive free energy of adsorption. The densely packed nanostructure obtained here is distinguished from the previously reported spheroid or toroid structure derived from DNA complexations with the higher-generation dendrimers.     

Application of microcontact printing to electroless plating for the fabrication of microscale silver patterns on glass

Microcontact printing (microCP) and electroless plating are combined to produce microscale patterns of silver on glass substrates. Silver patterns with feature sizes of 0.6-10 microm stripes are fabricated using two methods. (1) The printing seeding layer (PSL) method is to apply microCP to directly print the catalyst Sn pattern for further electroless plating. (2) The printing masking layer (PML) method is to use microCP to print the octadecyltrichlorosilane (OTS) self-assembled monolayer as a masking layer on glass substrates, which then become Sn-activated in the unstamped regions by immersing the substrates in stannous chloride solution. After the electroless silver plating, the PML method has a better selectivity of silver deposition than the PSL method. In addition, variation of the deposited silver thickness as a function of the plating time and temperature is discussed.     

Rapid screening assay of trimethylaminuria in urine with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Trimethyamine (TMA) and trimethylamine N-oxide (TMAO) are the most important urine parameters for diagnosing and monitoring trimethylaminuria. A rapid, simple, and specific method based on matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) was developed to determine the presence of TMA and TMAO in urine samples from patients with trimethylaminuria. Formation of the quaternary tetramethylamino iodide by derivatization of TMA with methyl iodide allows measurement of TMA by MALDI-TOFMS. The method is repeatable and reproducible, with coefficients of variance (CVs)<3%. This new method was used for direct determination of TMA and TMAO in urine specimens obtained from normal children and patients. The proposed method allows for rapid and reliable measurements of TMA and TMAO in urine specimens from patients affected by trimethylaminuria.     

Deliberate design of a 3D homochiral Cu(II)/l-met/Ag(I) coordination network based on the distinct soft-hard recognition principle

A homochiral amino acid coordination network [{Ag3Cu3(l-methioninato)6(NO3)3(H2O)3}.7H2O]n, self-assembled from CuII, AgI, and l-methionine via a distinct soft-hard recognition process, shows interesting characteristics, in that it is constructed from 1D helical building blocks and contains homochiral channels in which 1D water chains are hosted. This result provides an effective and controllable strategy for the preparation of enantiopure heterometallic supramolecular structures that are relevant to biopolymers.