Infrared photodissociation spectroscopy of electrosprayed ions in a Fourier transform mass spectrometer

Previous gas-phase methods for infrared photodissociation spectroscopy (IRPD) require sample volatility. Our method instead uses electrospray ionization to introduce even large nonvolatile molecules into a Fourier transform mass spectrometer, where extended (>15 s) ion storage makes possible high sensitivity spectral measurements with an OPO laser over a range of 3050-3800 cm(-1). The spectra of 22 gaseous proton-bound amino acid complexes are generally correlated with the H-stretching frequencies established for O-H and N-H functional groups in solution. For theoretical structure predictions of the Gly2H+ and N-acylated Asp2H+ dimers, IRPD spectra clearly differentiate between the predicted lowest energy conformers. In contrast to solution, in the gas phase the glycine zwitterion is approximately 20 kcal/mol less stable than the neutral; however, glycine is clearly zwitterionic in the gaseous GlyLysH+ dimer. The level of theory is inadequate for the larger Lys2H+ dimer, as all low energy predicted structures have free carboxyl O-H groups, in contrast to the IR spectrum. IRPD appears to be a promising new technique for providing unique information on a broad range of biomolecular and other gaseous ions, especially on noncovalent bonding involving O-H and N-H groups.     

Highly stereospecific epimerization of alpha-amino acids: conducted tour mechanism

The highly stereospecific and regiospecific recognition of alpha-amino acids exhibited by a novel Co(III) metal complex embodied in the experimental work (Nature 1999, 401, 254) is rationalized from the energetics and structural characteristics with the use of density functional calculations. The steric repulsion between the chiral center of the receptor [Co(III) complex] and alanine has been a cause for the discrimination of complex stabilities. The energies evaluated for all possible alanine binding modes clearly reveal regiospecificity. Our main emphasis is laid on the base-catalyzed epimerization reaction that drives the stereospecific recognition to near completion. The conducted tour mechanism is found to be the most likely candidate. A similar role by the equivalent Zn(II) complex is found.     

Kinetics and mechanism of the aminolysis of aryl N-ethyl thiocarbamates in acetonitrile

The aminolysis of aryl N-ethyl thiocarbamates (EtNHC(=O)SC(6)H(4)Z) with benzylamines (XC(6)H(4)CN(2)NH(2)) in acetonitrile at 30.0 degrees C is investigated. The rates are faster than the corresponding values for aryl N-phenyl thiocarbamates (PhNHC(=O)SC(6)H(4)Z), reflecting a stronger push to expel the leaving group by EtNH than the PhNH nonleaving group in a concerted process. The negative rho(XZ) (-0.86) and failure of the reactivity-selectivity principle found are consistent with the concerted mechanism. The kinetic isotope effects involving deuterated nucleophiles (k(H)/k(D) = 1.5-1.7) and low Delta H(++) with large negative Delta S(++) values suggest a hydrogen bond cyclic transition state.     

Fabric‐hydrogel composite membranes for culturing microalgae in semipermeable membrane‐based photobioreactors

In this article, we demonstrate that hydrogel‐based composite membranes are used as semipermeable materials for the construction of photobioreactors (PBRs). PBRs are developed to culture microalgae using nutrients dissolved in seawater, and thus they need to be fabricated with membranes possessing sufficient material‐transport properties. While hydrogels are characterized by their highly swelling nature in water and therefore have desirable transport of dissolved matter, they lack the mechanical strength to be cast into thin structures of large surface area. This issue motivated us to design a new concept, i.e., fabric‐hydrogel composite membranes ( FHCM s). A cotton fabric inside the hydrogel matrix endows the composite with tensile strength, which enables casting of FHCM s into thin membranes. Several FHCM s were prepared with 2‐hydroxyethyl methacrylate ( HEMA ), cross‐linking poly(ethylene glycol) dimethacrylate ( PEGDMA ) and a sheet of gauze by controlling the composition of the monomers and water. In the permeability measurement of nitrate ions, a key ingredient for the growth of microalgae, the permeability coefficient reached as high as 1.2 x 10^?8 m² min^?1, which is roughly three times higher than that of a commercially available semipermeable membrane (3.3 x 10^?9 m² min^?1). In the following evaluation of microalgal culture, a PBR constructed with a FHCM was able to maintain sufficient ion concentration and pH of the culture broth, supporting microalgal growth. These results suggest that the composite membranes with hydrogel and fabric have potential in the application of microalgal culture for bio‐diesel production in a marine environment. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 108–114     

Structural determination of sildenafil and its analogues in dietary supplements by fast‐atom bombardment collision‐induced dissociation tandem mass spectrometry

Sildenafil and its analogues, which are used as illegal additives in several dietary supplements, were isolated by liquid‐liquid extraction and column chromatography and analyzed by fast‐atom bombardment mass spectrometry (FAB‐MS). Structures of sildenafil and its derivatives were elucidated by FAB‐tandem mass spectrometry (MS/MS) with exact mass measurement in the positive‐ion mode. To find structurally diagnostic ions for the sildenafil analogues, authentic sildenafil was preferentially analyzed by high‐energy collision‐induced dissociation (CID)‐MS/MS. The CID‐MS/MS spectra of [M+H]⁺ precursor ions resulted in the formation of numerous characteristic ions via a series of dissociative processes. The product ions formed by CID provided important information on the modification of the piperazine ring, the phenylsulfonyl group and the pyrazolopyrimidine moiety of sildenafil. By interpreting their MS/MS spectra, the chemical structures of sildenafil analogues isolated from dietary supplements could be elucidated and fragmentation patterns were proposed. To clearly identify the sidenafil derivatives in dietary supplements, some of the derivatives such as acetildenafil, homosildenafil and hydroxyhomosildenafil which are not commercially available were synthesized and compared with their MS/MS spectra. In addition, high‐resolution mass measurements were conducted to obtain the elemental compositions of sildenafil and its analogues. Copyright © 2009 John Wiley & Sons, Ltd.     

Surface modification of a titanium alloy with a phospholipid polymer prepared by a plasma-induced grafting technique to improve surface thromboresistance

To improve the thromboresistance of a titanium alloy (TiAl₆V₄) surface which is currently utilized in several ventricular assist devices (VADs), a plasma-induced graft polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) was carried out and poly(MPC) (PMPC) chains were covalently attached onto a TiAl₆V₄ surface by a plasma induced technique. Cleaned TiAl₆V₄ surfaces were pretreated with H₂O-vapor-plasma and silanated with 3-methacryloylpropyltrimethoxysilane (MPS). Next, a plasma-induced graft polymerization with MPC was performed after the surfaces were pretreated with Ar plasma. Surface compositions were verified by X-ray photoelectron spectroscopy (XPS). In vitro blood biocompatibility was evaluated by contacting the modified surfaces with ovine blood under continuous mixing. Bulk phase platelet activation was quantified by flow cytometric analysis, and surfaces were observed with scanning electron microscopy after blood contact. XPS data demonstrated successful modification of the TiAl₆V₄ surfaces with PMPC as evidenced by increased N and P on modified surfaces. Platelet deposition was markedly reduced on the PMPC grafted surfaces and platelet activation in blood that contacted the PMPC-grafted samples was significantly reduced relative to the unmodified TiAl₆V₄ and polystyrene control surfaces. Durability studies under continuously mixed water suggested no change in surface modification over a 1-month period. This modification strategy shows promise for further investigation as a means to reduce the thromboembolic risk associated with the metallic blood-contacting surfaces of VADs and other cardiovascular devices under development.     

Impregnation of tungstophosphoric acid on poly(methacrylamide-co-methyl methacrylate) and its acid catalytic activity in TMB alkylation

A poly(methacrylamide-co-methylmethacrylate) (abbreviated PMAA-MMA) polymer support was studied for supporting a heteropolyacid (tungstophosphoric acid, H₃PW₁₂O₄₀) with its surface positively charged in the polymerization step. PMAA-MMA supports could be obtained in a porous form by eliminating template reagent molecules (benzylmalonic acid) combined with properly selected monomer (methacrylamide). The amount of amine groups in PMAA-MMA directly determined the amount of H₃PW₁₂O₄₀ impregnated, because the amine groups induced a positive charge on the PMAA-MMA surface. Finally, H₃PW₁₂O₄₀/PMAA-MMA showed better acid catalytic activities than unsupported H₃PW₁₂O₄₀ in alkylation of 1,3,5-trimethylbenzene with cyclohexene, which confirmed that PMAA-MMA supported H₃PW₁₂O₄₀ effectively.     

c-axis-textured LiNbO3 thin films on Si (111) substrates

We have successfully prepared highly c-axis-textured LiNbO₃ films on hydrogen-terminated Si (111) substrate using sol-gel spin-coating and rapid thermal annealing. These highly c-axis-textured films were obtained with a preheating at 300 °C for 15 min followed by a rapid thermal annealing at 500–700 °C for 120 s. The c-axis orientation of the LiNbO₃ film is due to a weak effect caused by the 3-fold symmetry match between the film and the Si (111) substrate. The c-axis orientation of LiNbO₃ films is very useful in integrated optics devices and metal–ferroelectric–semiconductor nonvolatile memory applications. Received: 15 September / Accepted: 4 December / Published online: 3 April 2001