Structures and bonding on a colloidal silver surface of the various length carboxyl terminal fragments of bombesin

Raman (RS) and surface-enhanced Raman scattering spectra (SERS) were measured for various length carboxyl terminal fragments (X-14 of amino acid sequence) of bombesin ( BN): BN13-14, BN12-14, BN11-14, BN10-14, BN9-14, and BN8-14 in silver colloidal solutions. Density functional theory (DFT) calculations of Raman wavenumbers and intensities with extended basis sets (B3LYP/6-31++G**) were performed with the aim of providing the definitive band allocations to the normal coordinates. The proposed band assignment is consistent with the assignment for similar compounds reported in the literature. The nonadsorbed and adsorbed molecular structures were deducted by detailed spectral analysis of the RS and SERS spectra, respectively. This analysis also allowed us to propose the particular surface geometry and orientation of these peptides on silver surface, and their specific interaction with the surface. For example, a SERS spectrum of BN8-14 indicates that the interaction of a thioether atom and Trp8 with the silver surface is favorable and may dictate the orientation and conformation of adsorbed peptide. One of the most prominent and common features in all of the fragments' SERS spectra is a approximately 692 cm (-1) band due to nu(C-S) accompanied by two or three bands of different C-S conformers for all, except BN8-14, which suggests that all of the above-mentioned compounds adsorb on the silver surface through the thioether atom and that the attachment of Trp8 produces limitation in a number of possible C-S conformers adopted on this surface. Our results also show clearly that His12 and CO do not interact with the colloid surface, which supports our earlier results.     

Surface-imprinted nanostructured layer-by-layer film for molecular recognition of theophylline derivatives

In this article we report the introduction of the cooperativity of various specific interactions combined with photo-cross-linking of the interlayers to yield binding sites that can realize better selectivity and imprinting efficiency of a surface molecularly imprinted LbL film (SMILbL), thus providing a new approach toward fabrication of nanostructured molecularly imprinted thin films. It involves preassembly of poly(acrylic acid) (PAA) conjugated of the theophylline residue template via a disulfide bridge, denoted as PAAtheo 15, in solution, and layer-by-layer (LbL) assembly of PAAtheo 15 and a positively charged photoreactive diazo resin (DAR) to form multilayer thin film with designed architecture. After photo-cross-linking of the film and template removal, binding sites specific to 7-(beta-hydroxyethyl)theophylline (Theo-ol) molecules are introduced within the film. Binding assay demonstrates that the SMILbL has a high selectivity of SMILbL to Theo-ol over caffeine. A control experiment demonstrates that the selectivity of SMILbL derives from nanostructured recognition sites among the layers. The imprinting amount per unit mass of the film can be 1 order of magnitude larger than that of the conventional bulk molecular imprinting systems. As this concept of construction SMILbL can be easily extended to the other molecules by the following similar protocol: its applications in building many other different molecular recognition systems are greatly anticipated.     

Self-modeling curve resolution (SMCR) analysis of near-infrared (NIR) imaging data of pharmaceutical tablets

The idea of quality by design (QbD) has been proposed in pharmaceutical field. QbD is a systematic approach to control the product performance based on the scientific understanding of the product quality and its manufacturing process. In the present study, near-infrared (NIR) imaging is utilized as a tool to achieve this concept. A practical use of a chemometrics technique called self-modeling curve resolution (SMCR) is demonstrated with NIR imaging analysis of pharmaceutical tablets containing two ingredients, a soluble active ingredient, pentoxifylline (PTX), and an insoluble excipient, palmitic acid. Concentration profiles obtained by SMCR reveal that the homogenous distribution of chemical ingredients strongly depends on the grinding time and that its process plays a central role in quantitative control, say sustained-release of PTX. In addition, pure component spectra by SMCR indicate a sequential change of specific NIR peak intensities following the increase of the grinding time. The spectra change shows a molecular structure change related to its crystallinity during grinding process. Accordingly, this study clearly demonstrates that NIR imaging combined with SMCR can be a powerful tool to reveal chemical or physical mechanism induced by the manufacturing process of pharmaceutical products and that it may be a solid solution for QbD of pharmaceutical products.     

Asymmetric Induction by a Nitrogen 14N/15N Isotopomer in Conjunction with Asymmetric Autocatalysis

Chirality arising from isotope substitution, especially with atoms heavier than the hydrogen isotopes, is usually not considered a source of chirality in a chemical reaction. An N²,N²,N³,N³‐tetramethyl‐2,3‐butanediamine containing nitrogen (¹⁴N/¹⁵N) isotope chirality was synthesized and it was revealed that this isotopically chiral diamine compound acts as a chiral initiator for asymmetric autocatalysis.     

Solvent free mechanochemical oxygenation of fullerene under oxygen atmosphere

Oxygenation of fullerene took place under mechanical stressing by a simple vibration mill in an oxygen atmosphere at 1 atm. Milled products were mixtures of poly-oxidized fullerene, C₆₀O_n, containing C-O-C and CO bonds. We observed a concurrent reaction as well, that is, polymerization of C₆₀ and C₆₀O. The average number of oxygen, n, of the overall products obtained by milling for 5 h was 8.6 per molecule of C₆₀. We confirmed generation of singlet oxygen during the present mechanochemical reaction by an ESR spin trapping method. Trapping of ¹O₂ was completely inhibited the oxygenation of fullerene. Formation of ¹O₂ is attributed to the energy transfer from mechanically excited state of fullerene and plays a decisive role on the present oxygenation of fullerene under mechanical stressing in O₂. In contrast, no ¹O₂ was observed by mechanically stressing the conventional photo-sensitizer, rosebengal. The difference in the behavior of C₆₀ and rosebengal is interpreted in terms of molecular deformation, being much easier for a 3D molecule, C₆₀, than a planar molecule, in line with the concept of inverse Jahn-Teller effects.     

Ultraviolet resonance Raman evidence for utilization of the heme 6-propionate hydrogen-bond network in signal transmission from heme to protein in Ec DOS protein

The direct oxygen sensor protein from Escherichia coli (Ec DOS) is a heme-based signal transducer protein responsible for phosphodiesterase (PDE) activity. Binding of either O2 or CO molecule to a reduced heme enhances the PDE activity toward 3',5'-cyclic diguanylic acid. We report ultraviolet resonance Raman (UVRR) spectroscopic investigations of the reduced, O2- and CO-bound forms of heme-bound PAS domain of Ec DOS. The UVRR results show that heme discriminates different ligands, resulting in altered conformations in the protein moiety. Specifically, the environment around Trp53 that contacts the 2-vinyl group of heme, is changed to a more hydrophobic environment by O2 binding, whereas it is changed to a more hydrophilic environment by CO-binding. In addition, the PDE activity of the O2- and CO-bound forms for the Trp53Phe mutant is significantly decreased compared with that of the wild type (WT), demonstrating the importance of Trp53 for the catalytic reaction. On the other hand, the binding of O2 or CO to the heme produces drastic changes in the Tyr126 of Ibeta-strand at the surface of the sensor domain. Furthermore, we found that Asn84 forms a hydrogen bond with Tyr126 either in the O2- or CO-bound forms but not in the reduced form. Finally, the PDE activities of the ligand-bound forms for Asn84Val and Tyr126Phe mutants are significantly reduced as compared with that of WT, suggesting the importance of the hydrogen-bonding network from heme 6-propionate to Tyr126 through Asn84 in signal transmission.     

Reuse of chiral cationic Pd-phosphinooxazolidine catalysts in ionic liquids: highly efficient catalytic asymmetric Diels-Alder reactions

Chiral cationic palladium-phosphinooxazolidine catalysts in ionic liquid afforded excellent enantioselectivity in Diels-Alder reactions and the catalyst was easily recycled eight times without any significant decrease in chemical yields or enantioselectivity (89-99%, 88-99% ee).     

Insertion of arynes into carbon-halogen sigma-bonds: regioselective acylation of aromatic rings

Arynes were found to insert into carbon-halogen sigma-bonds of various acid halides, enabling acyl and halogen moieties to be introduced simultaneously into adjacent positions of aromatic rings.     

Time-resolved in situ ATR-IR observations of the process of sorption of water into a poly(2-methoxyethyl acrylate) film

A process of water sorption into a biocompatible polymer, poly(2-methoxyethyl acrylate) (PMEA), was investigated by time-resolved, in situ, attenuated total reflection infrared spectroscopy. Evidence for three different types of hydrated water in PMEA, that is, nonfreezing water, freezing bound water, and freezing water, were found. Each hydration structure was elucidated at the functional group level. Nonfreezing water, which never crystallizes, even at -100 degrees C, has a C=O...H-O type of hydrogen bonding interaction with the carbonyl group of PMEA. Freezing bound water, which crystallizes in a heating process below 0 degrees C, interacts with the methoxy moiety in the PMEA side chain terminal. Freezing water, which crystallizes approximately 0 degrees C, has bulk-water-like structure with an O-H...O-H hydrogen bonds network. It has been concluded from the present study that the methoxy moiety in the PMEA side chain terminal plays an important role for the excellent biocompatibility of PMEA.