Self-Assembled Fibrillar Networks through Highly Oriented Aggregates of Porphyrin and Pyrene Substituted by Dialkyl l-Glutamine in Organic Media^†

Microfibrous self-aggregation of chromophoric groups of porphyrin and/or pyrene substituted by didodecyl l-glutamic acid in organic media is confirmed by transmission electron microscopic (TEM) observation. Chromophoric probes of porphyrin and pyrene moieties enable evaluation of their assembling behavior photophysically through UV−vis, circular dichroism (CD), and fluorescence spectroscopic characterization. This spectroscopic characterization was able to compensate the lack of TEM observation for the aggregation even at a low concentration below the critical gel concentration. The temperature affects the salient features of the photophysics of porphyrin or pyrene in the microfibrous assemblies. Highly oriented network structures were formed at low temperature since the CD intensities of the porphyrin and pyrene systems increased with lowering the temperature. Fluorescence spectroscopic characterization confirmed the monomer excitation of porphyrin itself, and efficient excimer formation for the pyrene−pyrene charge transfer was detected at low temperature. In particular, we also obtained the preliminary results of fluorescence spectroscopic measurement on singlet−singlet energy migration from pyrene to porphyrin in the mixed assemblies for mimicry of the efficient energy transfer process of the photosynthetic antenna complex

Novel Surface-Attachable Multifunctional Initiators: Synthesis, Grafting, and Polymerization in Aprotic and Protic Solvents

Novel surface attachable AIBN type initiators involving mono-/di-/trichlorosilane anchoring groups have been successfully synthesized and grafted onto silica microspheres (average diameter, pore size and surface area are 5 μm, 12 nm, and 300 m2 g−1 respectively). Graft density of surface-tethered initiators was estimated on the basis of elemental analysis and thermogravimetric measurements giving 0.446, 0.705, and 0.819 group nm−2 respectively. Owing to the presence of two anchoring groups newly described initiators can attach to the surface through both ends avoiding the fragment-initiated polymerization in the solution that was considered as a main drawback of asymmetric AIBN-type initiators. Surface-initiated radical polymerization of styrene and N-vinyl pyrrolidone has been carried out in toluene and water solutions respectively, giving polymer-silica hybrids. Immobilized polystyrene chains were detached from the surface then the molecular weight and molecular weight distribution was determined by gel permeation chromatography giving 141 200 Da (5.58), 145 700 (5.72) and 149 100 Da (5.94), respectively. The connection between the initiator structure and average molecular weight of degrafted polymers furthermore the effect of possible radical−radical termination reaction on the molecular weight is also discussed

Novel Approach for the Separation of Shape-Constrained Isomers with Alternating Copolymer-Grafted Silica in Reversed-Phase Liquid Chromatography

This paper describes a novel packing material for high selective reversed-phase high-performance liquid chromatography (RP-HPLC). The organic phase on silica is chemically designed in a way that the weak interaction sites are integrated with high orientation along the polymer main chain and high selectivity can be realized by multiple interactions with solutes. For the above purpose, we synthesized poly(octadecyl acrylate-alt-N-octadecylmaleimide)-grafted silica (Sil-poly(ODA-alt-OMI)) stationary phase. The alternating copolymerization was carried out from 3-marcaptopropyltrimethoxysilane (MPS)-modified silica via surface-initiated radical-chain transfer reaction. Elemental analysis, diffuse reflectance infrared Fourier transform (DRIFT),1H NMR, solid-state 13C cross polarization magic angle spinning (CP/MAS) NMR, and suspended-state 1H NMR were used to characterize the new organic phase. Aspects of shape selectivity was evaluated with Standard Reference Material (SRM 869b), Column Selectivity Test Mixture for Liquid Chromatography. Enhanced molecular shape selectivity was observed, that lead to the separation of SRM 1647e (16 polycyclic aromatic hydrocarbons, PAHs) in an isocratic elution. The effectiveness of this phase was also demonstrated by the separation of several β-carotene and tocopherol isomers. The complete baseline separation of the tocopherol isomers was achieved using the Sil-poly(ODA-alt-OMI) phase. Chromatographic study revealed that Sil-poly(ODA-alt-OMI) has extremely high separation ability compared to monomeric and polymeric C18 columns. Higher shape selectivity of the new RP material can be explained by a π−π and dipole−dipole interaction mechanism

Dispersible chitosan particles showing bacteriostatic effect against <i>Streptococcus mutans</i> and their dental polishing effect

Nontoxic and biodegradable chitosan is potentially useful in various applications. We prepared submicron chitosan particles with high dispersibility in aqueous solution utilizing the electrostatic interaction phase separation method described in a previous report, but using citric acid as the polyvalent anionic compound instead of sodium sulfate. The submicron chitosan particles showed significant antibacterial activity and anti-adhesive action against Streptococcus mutans, even at around neutral pH. However, chitosan granules showed no antibacterial activity under the same conditions. The addition of the chitosan particles to dental polishing paste provided stainless steel discs (the same hardness as dental enamel) with a smoother surface than polishing paste without additives. In view of their submicron size and antibacterial activity, chitosan particles could potentially be multifunctional components of oral and dental cleaning materials. Dispersible chitosan particles (DCPs) −1.0; 1.0 equivalents of citric acid carboxy groups relative to chitosan amino groups.</p

Polycondensation and Stabilization of Chirally Ordered Molecular Organogels Derived from Alkoxysilyl Group- Containing l-Glutamide Lipid

A lipophilic l-glutamide-derived lipid with a triethoxysilyl headgroup (Si-lipid) was newly synthesized as a self-assembling organogelator to stabilize the chirally ordered state of the aggregates. The Si-lipid formed nanofibrous network structures in various organic solvents such as benzene, cyclohexane, and dimethylformamide and entrapped them to form gels. The gels were transformed to sols by heat, and this gel-to-sol transition was thermally reversible. Polycondensation of the triethoxysilyl groups was carried out by acid-catalyzed hydrolysis and condensation in a benzene gel and confirmed by 29Si CP/MAS NMR and FT-IR measurements. After polycondensation, a gel state was maintained, and the thermal and mechanical stabilities of the aggregates increased markedly. Interestingly, polycondensation in chloroform and acetonitrile induced gelation, whereas no gelation was observed before polycondensation. Xerogel, which was prepared by freeze drying organogels, had fibrous network structures similar to those of the original gels. A strong CD signal was observed around the amide bonds in a cyclohexane gel at 20 °C, indicating that the gel contained chirally oriented structures based on intermolecular hydrogen bonds. An enhanced CD signal was observed even after polycondensation of the ethoxysilyl group of Si-lipid (poly(Si-lipid)) and was maintained at 70 °C, which is above the temperature of the gel-to-sol phase transition of the original gel. These results indicate that the formation of siloxane network structure among the fibrous aggregates stabilizes the chiral orientation of lipid aggregates

Molecular Shape Recognition through Self-Assembled Molecular Ordering: Evaluation with Determining Architecture and Dynamics

The relationship between molecular gel-forming compound-based double-alkylated l-glutamide-derived functional group-integrated organic phase (Sil-FIP) structure and chromatographic performance is investigated and compared with widely used alkyl phases (C₃₀, polymeric and monomeric C₁₈) as references. The functional group-integrated molecular gel on silica is chemically designed newly in a way that the weak interaction sites are integrated with high orientation and high selectivity can be realized by multiple interactions with the solutes. Its functions can be emphasized by being immobilizable with a terminal carboxyl group and the fact that five amide bonds including β-alanine subunit are integrated per molecule. Furthermore, its self-assembling function can be detected by monitoring of the chiroptical property. Temperature-dependent circular dichroism (CD) intensity was determined as an indicator of chirality for the gel forming compounds. ¹³C cross-polarization magic angle spinning (CP/MAS) NMR spectra of the Sil-FIP phase indicate that predominance of gauche conformations exists at higher temperature (above 30 °C). ²⁹Si CP/MAS NMR were carried out to investigate the degree of cross-linking of the silane and silane functionality of the modified silica. Temperature-dependent ¹³C CP/MAS NMR and suspended-state ¹H NMR measurements of the Sil-FIP phase exhibit the dynamic behavior of the alkyl chains. To correlate the NMR and CD results with temperature-dependent chromatographic studies, standard reference materials (SRM 869b and SRM 1647e), column selectivity test mixture for liquid chromatography was employed. Additional shape selectivity text mixtures were also used to clarify the mechanism of shape selectivity performance of Sil-FIP compared with commercially available columns. The evaluation with the spectroscopic and chromatographic analyses presents very important information on the surface morphology of the new organic phase and the molecular recognition process. Integrated and ordered functional groups were investigated to be the main driving force for very high molecular shape selectivity of the Sil-FIP phase

Design of C₁₈ Organic Phases with Multiple Embedded Polar Groups for Ultraversatile Applications with Ultrahigh Selectivity

For the first time, we synthesized multiple embedded polar groups (EPGs) containing linear C₁₈ organic phases. The new materials were characterized by elemental analysis, IR spectroscopy, ¹H NMR, diffuse reflectance infrared Fourier transform (DRIFT), solid-state ¹³C cross-polarization magic angle spinning (CP/MAS) NMR, suspended-state ¹H NMR, and differential scanning calorimetry (DSC). ²⁹Si CP/MAS NMR was carried out to investigate the degree of cross-linking of the silane and silane functionality of the modified silica. Solid-state ¹³C CP/MAS NMR and suspended-state ¹H NMR spectroscopy indicated a higher alkyl chain order for the phase containing four EPGs than for the phase with three EPGs. To correlate the NMR results with temperature-dependent chromatographic studies, standard reference materials (SRM 869b and SRM 1647e), a column selectivity test mixture for liquid chromatography was employed. A single EPG containing the C₁₈ phase was also prepared in a similar manner to be used as a reference column especially for the separation of basic and polar compounds in reversed-phase liquid chromatography (RPLC) and hydrophilic interaction liquid chromatography (HILIC), respectively. Detailed chromatographic characterization of the new phases was performed in terms of their surface coverage, hydrophobic selectivity, shape selectivity, hydrogen bonding capacity, and ion-exchange capacity at pH 2.7 and 7.6 for RPLC as well as their hydrophilicity, the selectivity for hydrophilic–hydrophobic substituents, the selectivity for the region and configurational differences in hydrophilic substituents, the evaluation of electrostatic interactions, and the evaluation of the acidic–basic nature for HILIC-mode separation. Furthermore, peak shapes for the basic analytes propranolol and amitriptyline were studied as a function of the number of EPGs on the C₁₈ phases in the RPLC. The chromatographic performance of multiple EPGs containing C₁₈ HILIC phases is illustrated by the separation of sulfa drugs, β-blockers, xanthines, nucleic acid bases, nucleosides, and water-soluble vitamins. Both of the phases showed the best performance for the separation of shape-constrained isomers, nonpolar, polar, and basic compounds in RPLC- and HILIC-mode separation of sulfa drugs, and other polar and basic analytes compared to the conventional alkyl phases with and without embedded polar groups and HILIC phases. Surprisingly, one phase would be able to serve the performance of three different types of phases with very high selectivity, and we named this phase the “smart phase”. Versatile applications with a single column will reduce the column purchasing cost for the analyst as well as achieve high separation, which is challenging with the commercially available columns

Self-Assembly of Nucleoamphiphiles: Investigating Nucleosides Effect and the Mechanism of Micrometric Helix Formation

A new family of self-assembling systems based on nucleoamphiphiles is described. Nano to micrometric left-handed helix formation in aqueous solution was induced simply by complexing a GMP or an AMP with a nonchiral monocationic amphiphile. The assembling behavior such as micellar formation, monolayer at air−water interface, as well as the aggregates in solution of these nucleoamphiphiles are strongly influenced by the presence of nucleosides in solution. The observed effects depend on the properties of complexed nucleotides and nucleosides with a complex mixture of π stacking, hydrophobicity of the bases, and hydrogen bonding

Nanosized Hybrid Oligoamide Foldamers: Aromatic Templates for the Folding of Multiple Aliphatic Units

Oligoamide sequences comprised of both 8-amino-2-quinolinecarboxylic acid “Q” and 6-aminomethyl-2-pyridinecarboxylic acid “P” have been synthesized. It was found that the aliphatic amine of P greatly facilitates amide couplings, as opposed to the aromatic amine of Q, which enabled us to prepare sequences having up to 40 units. The conformation and conformational stability of these oligomers were characterized in the solid state using X-ray crystallography and in solution using NMR and various chromatographic techniques. Qn oligomers adopt very stable helically folded conformations whereas Pn oligomers do not fold and impart conformational preferences distinct from those of Q units. When a Pn segments is attached at the end of a Q4 segment, a couple P units appear to follow the folding pattern imposed by the Qn segment, but P units remote from the Qn segment do not fold. When a Pn segment is inserted between two Q4 segments, the Pn segment adopts the canonical helical conformation imposed by the Q units at least up to two full helical turns (n = 5). However, the overall stability of the helix tends to decrease as the number of P units increases. When noncontiguous P units separated by Q4 segments are incorporated in a sequence, they all adopt the helical conformation imposed by Q monomers and the overall helix stability increases when helix length increases. For example, a 40mer with a sequence (PQ4)8 folds into a rod-like helix spanning over 16 turns with a length of 5.6 nm. This investigation thus demonstrates that remarkably long (nanometers) yet well-defined foldamers can be efficiently synthesized stepwise and that their helical stability may be continuously tuned upon controlling the ratio and sequence of P and Q monomers

Nanosized Hybrid Oligoamide Foldamers: Aromatic Templates for the Folding of Multiple Aliphatic Units

Oligoamide sequences comprised of both 8-amino-2-quinolinecarboxylic acid “Q” and 6-aminomethyl-2-pyridinecarboxylic acid “P” have been synthesized. It was found that the aliphatic amine of P greatly facilitates amide couplings, as opposed to the aromatic amine of Q, which enabled us to prepare sequences having up to 40 units. The conformation and conformational stability of these oligomers were characterized in the solid state using X-ray crystallography and in solution using NMR and various chromatographic techniques. Qn oligomers adopt very stable helically folded conformations whereas Pn oligomers do not fold and impart conformational preferences distinct from those of Q units. When a Pn segments is attached at the end of a Q4 segment, a couple P units appear to follow the folding pattern imposed by the Qn segment, but P units remote from the Qn segment do not fold. When a Pn segment is inserted between two Q4 segments, the Pn segment adopts the canonical helical conformation imposed by the Q units at least up to two full helical turns (n = 5). However, the overall stability of the helix tends to decrease as the number of P units increases. When noncontiguous P units separated by Q4 segments are incorporated in a sequence, they all adopt the helical conformation imposed by Q monomers and the overall helix stability increases when helix length increases. For example, a 40mer with a sequence (PQ4)8 folds into a rod-like helix spanning over 16 turns with a length of 5.6 nm. This investigation thus demonstrates that remarkably long (nanometers) yet well-defined foldamers can be efficiently synthesized stepwise and that their helical stability may be continuously tuned upon controlling the ratio and sequence of P and Q monomers