Simplified method for determination of polycarbamate fungicide in water samples by liquid chromatography with tandem mass spectrometry following derivatization with dimethyl sulfate

A simple and sensitive analytical method for the determination of polycarbamate in water samples was developed. In this method, polycarbamate was cleaved under alkaline conditions and derivatized with dimethyl sulfate to methyl dimethyldithiocarbamate (DMDC-methyl) and dimethyl ethylenebisdithiocarbamate (EBDC-dimethyl). After the solid-phase extraction of the resulting methyl derivatives, they were measured by liquid chromatography with tandem mass spectrometry (LC-MS/MS), based on reversed-phase separation and MS/MS detection with positive atmospheric pressure chemical ionization. The absolute recoveries (mean+/-SD) all through the procedure from polycarbamate to DMDC-methyl and EBDC-dimethyl were 62.6+/-4.3 and 73.5+/-5.9%, respectively. The limits of detection and quantification of polycarbamate in the water samples were 0.061 and 0.20 microg/L in the form of DMDC-methyl, and 0.032 and 0.11 microg/L in the form of EBDC-dimethyl, respectively. The method was validated at levels of 0.25, 1.0, and 5.0 microg/L in the tap water and river water samples, and accuracy was achieved in the range of 94-109%. The proposed method can be applied to the determination of trace amounts of polycarbamate in environmental water samples.     

Surface-assisted photoalignment of discotic liquid crystals by nonpolarized light irradiation of photo-cross-linkable polymer thin films

In this article, we describe the surface-assisted photoalignment of discotic liquid crystals (DLCs) on thin films of photo-cross-linkable polymers with cinnamoyl moieties as the side chains. Oblique irradiation of the polymer thin films with nonpolarized UV light at 313 nm brought about inclined orientation of the cinnamoyl residues as a result of their direction-selective photoisomerization and photodimerization. The DLC molecules on the photoirradiated polymer films were aligned in a tilted hybrid manner. This means that the DLC directors are continuously altered from the substrate to the DLC film surface so as to minimize the elastic free energy. Interestingly, we found that the tilted direction of aligned DLC molecules is clearly influenced by the chemical structures of the cinnamate-containing polymers. When a poly(vinyl cinnamate) thin film was obliquely exposed to nonpolarized UV light, the DLCs were inclined to the direction opposite to the UV light propagation. In a keen contrast, the thin film of poly(methacrylate)s tethering cinnamoyl groups, which was obliquely exposed to nonpolarized UV light in advance, provided the tilting DLC direction in parallel with the light propagation. The results were supported by tilted orientation of calamitic (rod-shaped) liquid crystal on the obliquely irradiated polymer films. Such photoalignment behavior of the DLCs can be rationalized by anchoring balance between intermolecular interaction of the DLC molecules with the photodimers of polymer films and those with the remaining E-isomers of cinnamoyl side chains at the film interface. The present technique of DLC photoalignment opens promising ways not only to understand anisotropic physical properties of DLCs, but also to design and fabricate novel nanodevices for photonics and electronics applications.     

Global minimum structure search in Li(x)CoO(2) composition using a hybrid evolutionary algorithm

The global minimum structures for Li(x)CoO(2) compositions where 0 ≤ x ≤ 1 were probed by using a hybrid evolutionary algorithm with an underlying ab initio structural relaxation scheme. The method successfully predicted experimentally observed variants of layered configurations at various degrees of lithiation and the spinel (Fd3[combining macron]m) phase at x = 1/2. New low-energy non-layered host structures at x < 1/2 were also revealed. These structures can be formed from the usual layered configuration through coherent stacking faults along the c-axis and the migration of Co ions into the Li-poor intercalation layer.     

Synthesis and thermal properties of poly(methyl methacrylate)-graft-(cellobiosylamine-C15)

Model experiments for synthesis of a comb-shaped copolymer with cellulose side-chains were performed with cellobiose derivatives. A novel cellobiose monomer, N-(15-methacryloyloxypentadecanoyl)-2,3,6-tri-O-acetyl-4-O-(2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl)-β-d-glucopyranosylamine (2) was prepared from heptaacetylcellobiosyl- amine. Homopolymerization of cellobiose monomer 2 and copolymerization of monomer 2 with methyl methacrylate (MMA) were performed using 2,2′-azobis(isobutyronitrile) (AIBN) as an initiator to obtain homopolymers 3-i (i = 1–4) and copolymers 3-i (i = 5–7), poly(methyl methacrylate)-graft-(heptaacetylcellobiosylamine-C15). The size exclusion chromatography—multi-angle laser light scattering (SEC-MALS) measurements revealed that comb-shaped homopolymers 3-i (i = 1–4) had more compact structures compared to copolymers 3-i (i = 5–7) at the same elution volume. Selective deacetylation of polymers 3-i (i = 1–7) gave novel cellobiose polymers 4-i (i = 1–7), poly(methyl methacrylate)-graft-(cellobiosylamine-C15). The amide linkages between cellobiose moiety and long-chain alkyl group, and the ester linkages between PMMA main-chain and long-chain alkyl group remained after deprotection. The differential scanning calorimetry (DSC) measurements revealed that the T _gs of the polymers 4-i (i = 1, 5, 6, 7) increased with increasing cellobiose composition in the polymers. It was indicated that cellobiose moieties of polymers 4-i (i = 1, 5, 6, 7) reduced the mobility of PMMA main-chain.     

DMSO-Quenched H/D-Exchange 2D NMR Spectroscopy and Its Applications in Protein Science

Hydrogen/deuterium (H/D) exchange combined with two-dimensional (2D) NMR spectroscopy has been widely used for studying the structure, stability, and dynamics of proteins. When we apply the H/D-exchange method to investigate non-native states of proteins such as equilibrium and kinetic folding intermediates, H/D-exchange quenching techniques are indispensable, because the exchange reaction is usually too fast to follow by 2D NMR. In this article, we will describe the dimethylsulfoxide (DMSO)-quenched H/D-exchange method and its applications in protein science. In this method, the H/D-exchange buffer is replaced by an aprotic DMSO solution, which quenches the exchange reaction. We have improved the DMSO-quenched method by using spin desalting columns, which are used for medium exchange from the H/D-exchange buffer to the DMSO solution. This improvement has allowed us to monitor the H/D exchange of proteins at a high concentration of salts or denaturants. We describe methodological details of the improved DMSO-quenched method and present a case study using the improved method on the H/D-exchange behavior of unfolded human ubiquitin in 6 M guanidinium chloride.     

Relaxation spectra of concentrated polystyrene solutions

The relaxation modulus G(t) and the stress decay after cessation of steady shear flow were measured on concentrated solutions of polystyrenes in diethyl phthalate. Ranges of concentration c and molecular weight M of the polymer were from 0.112 to 0.329 g/ml and from 1.23 × 10⁶ to 7.62 × 10⁶, respectively. The relaxation spectrum H(τ) as calculated from G(t) for the solution of very high M was found to be composed of two parts. One, at relatively short times, was a broad distribution (plateau zone) with height proportional to c². The second, at the long-time end, was very sensitive to concentration and gave rise to a maximum in H(τ) for very high concentrations. The behavior of H(τ) at long times was examined quantitatively by evaluating the longest relaxation time τ₁⁰ and the corresponding relaxation strength G₁⁰ from G(t) and from the stress decay function, on the assumption of a discrete distribution of relaxation times at long times. The longest relaxation time was approximately proportional to M^3.5, even at relatively low concentrations where the zero-shear viscosity was not proportional to M^3.5. The strengths of relaxation modes with the longest few relaxation times are proportional to the third power of concentration.     

Application of a high-performance,special-purpose computer,GRAPE-2A,to molecular dynamics

The special-purpose computer GRAPE-2A accelerates the calculation of pairwise interactions in many-body systems. This computer is a back-end processor connected to a host computer through a Versa Module Europe (VME) bus. GRAPE-2A receives coordinates and other physical data for particles from the host and then calculates the pairwise interactions. The host then integrates an equation of motion by using these interactions. We did molecular dynamics simulations for two systems of liquid water: System 1 (1000 molecules), and System 2 (1728 molecules). The time spent for one step of molecular dynamics was 3.9 s (System l), and 10.2 s (System 2). The larger the molecular system, the higher the performance. The speed of GRAPE-2A did not depend on the formula describing the pairwise interaction. The cost performance was about 20 times better than that of the fastest workstations available today, and GRAPE-2A cost only $22,000. © 1994 by John Wiley & Sons, Inc.     

Highly strained tricyclic molecules: tricyclo[p.q.0.0]alkanes and phosphatricyclo[m.1.0.0]alkanes

We theoretically investigate ring strains of tricyclic molecules or tricyclo[p.q.0.0^1,f]alkanes by calculating the strain energies as heat of the homodesmotic reactions. The strain energies are well correlated with the deformation from the tetrahedral configuration of the C₁ atom. We theoretically design less strained tricyclic molecules by replacing some carbon atoms with phosphorus atoms.     

Determination of thyroid hormones in pharmaceutical preparations,after derivatization with 9-anthroylnitrile,by high-performance liquid chromatography with fluorescence detection

Fast ion-exchange chromatography has been developed and applied to the separation of common inorganic anions. Using a didodecyldimethylammonium bromide (DDAB) coated short (30 mm x 4.6 mm) ODS analytical column (3-microm particle size) and a 5 mM phthalate eluent (pH 7.5) the isocratic separation of nine common anions in 160 s was possible, with the first seven anions, including phosphate, chloride and sulphate, separated within 65 s. Detection was achieved using indirect UV at 279 nm. The high capacity, highly hydrophobic ion-exchange coating demonstrated excellent stability over time, even at elevated temperatures (45 degrees C) and exhibited unusual selectivity for common anions (retention order=fluoride, carbonate, phosphate, chloride, bromate, nitrite, sulphate, bromide and nitrate). The developed chromatography was successfully applied to the rapid analysis of river water and seawater samples.