Unusual optical properties of porphyrin fractal J-aggregates

A simple mix and shake procedure in aqueous solution from water-soluble tetrakis(4-sulfonatophenyl)porphyrin and spermine leads to fractal non-covalent supramolecular systems which exhibit unusual large enhancement of resonant light scattering, behaving as metal particles.     

Reduction and adduct formation from electrosprayed solutions of porphyrin salts

The solutions of four meso-tetrakis(N-alkylpyridinium-4-yl)porphyrin salts and of the p-toluenesulfonate salt of meso-tetrakis(4-trimethylammoniumphenyl)porphyrin, in methanol, were studied by electrospray mass spectrometry, in order to investigate the influence of the type of counter ion, the length of the substituent N-alkyl groups of the four (N-alkylpyridinium-4-yl)porphyrins and the presence of an aromatic (alkylpyridinium) or aliphatic (trimethylammonium) nitrogen, in ion formation.In our experimental conditions, adducts with the counter ions were formed only for the meso-tetrakis(4-trimethylammoniumphenyl)porphyrin and were not observed for the other porphyrins, even when the counter ion was the same. In contrast, formation of reduced species, such as the [M(4+) + e(-)]3+, [M(4+) + 2e(-)]2+, [M(4+) + 4e(-) + 2H(+)]2+, and [M(4+) + 5e(-) + 2H(+)]+ ions was observed only for the (N-alkylpyridinium-4-yl)porphyrins and the appearance of these species is apparently solvent related and may occur via counter ion/solvent adducts.     

Sodium dodecyl sulfate self-diffusion in premicellar and low-concentrated micellar solutions in the presence of a background electrolyte

The Fourier transform pulsed field gradient NMR method is employed to investigate the self-diffusion of surface active sodium dodecyl sulfate ions in premicellar and low-concentrated micellar solutions at different NaCl concentrations in a system. The self-diffusion coefficient of the surfactant is found to markedly decrease in the premicellar region. An analysis of the experimental data carried out using a model implying the presence of sodium dodecyl sulfate monomers, dimers, and micelles in the system made it possible to determine the self-diffusion coefficients of the monomers and dimers, as well as the corresponding sizes of kinetic units.     

Unusual rheological effects observed in polyacrylonitrile solutions

Unusual rheological effects have been revealed during the deformation of polyacrylonitrile (PAN) solutions in DMSO. The effects are observed during the study of rheological properties in a wide range of PAN concentrations and are explained by the structuring occurring at low polymer concentrations. At concentrations of at most 0.1%, the solutions exhibit the behavior of soft gels, which are characterized by yield stresses and frequency-independent storage moduli. As concentration is increased, both effects gradually vanish and the solutions are almost transformed into Newtonian liquids. The results have been explained by the formation of a supramolecular spatial structure at low polymer concentrations. As concentration is increased, the role of structuring is suppressed by the formation of a network of intermacromolecular entanglements. The ability of dilute PAN solutions to exist in two states, i.e., with destroyed structuring and in the form of a physical polymer gel, leads to stress self-oscillations and thixotropic effects. The addition of a precipitant (water) to the PAN-DMSO solutions leads to the formation of a gel throughout the concentration range.     

Microscopy of large-scale porphyrin aggregates formed from protonated TPP dimers in water–organic solutions

Properties of porphyrin aggregates were investigated by absorption spectroscopy (UV–Vis and IR) in water–tetrahydrofuran (THF) solutions in the presence of different concentrations of HCl. The morphology of the aggregates was observed by scanning electron microscopy (SEM) and atomic force microscopy in thin films. A new protonated meso-tetraphenylporphine (TPP) form that shows characteristic absorptions in the UV–Vis spectra was found in the aggregated porphyrin in the presence of 2N HCl. Two types of changes with time were observed in these spectra, one of which is due to sticking together of the porphyrin aggregates. The second is associated with the formation of complexes between the protonated TPP dimer with λ_max=465 nm and metal ions that are probably leached out from the support by the acid. IR spectra of porphyrin aggregates prepared in the presence of different concentrations of HCl show huge water contents in the thin films and different characteristics of the water bound in the aggregates. Porphyrin aggregates prepared at different concentrations of HCl exhibited different surface properties. TPP aggregates prepared in the presence of 0.4N HCl and observed by SEM exhibit smooth surfaces over ranges of several micrometers. TPP aggregates prepared in the presence of 2N HCl form a continuous thin layer with 3–5 μm wide domains that consist of submicroscopic grains. These appear to be the result of 200–400 nm wide spherical particles that stick together.     

Transmembrane nanopores from porphyrin supramolecules

A porphyrin-based nanopore was constructed through a bilayer lipid membrane (BLM). The macrocyclic porphyrin (the inner diameter = ca. 2.1 nm) having six carboxylic acid groups directed up and down was synthesized by self-assembly of three trisporphyrins, metathesis linking, and subsequent hydrolysis. The porphyrin was incorporated into soybean lecithin based BLM, and the ion currents through the nanopore were observed under 500 mM KCl, LiCl, CaCl2, and tetraalkylammonium chloride solutions, indicating formation of a large pore through BLM. Blocking of the ion current was achieved by addition of the polycationic fourth-generation PAMAM dendrimer.     

Chirality amplification of porphyrin assemblies exclusively constructed from achiral porphyrin derivatives.

Two achiral porphyrin derivatives, 5,10,15,20-tetrakis(4-methoxyphenyl)-21H,23H-porphine (TPPOMe) and 5,10,15,20-tetrakis(4-hydroxyphenyl)-21H,23H-porphine (TPPOH), were spread onto an air/water interface. The spreading films were transferred onto solid substrates by the Langmuir-Schaefer (LS) method. Although both of the porphyrin derivatives are achiral species, the transferred LS multilayer films shows macroscopic supramolecular chirality, which is suggested to be due to the spontaneous symmetry breaking that occurs at the air/water interface. A strong CD signal is observed from the as-deposited TPPOH LS film, while a relatively weak CD signal is detected from that of TPPOMe. Interestingly, when the TPPOMe LS film was annealed in high vacuum, a significant amplification of the supramolecular chirality is observed. Atomic force microscopy observations confirm that TPPOMe form more ordered aggregates upon annealing. It is suggested that the small amount of chiral assemblies formed in the as-deposited LS film grow into larger ones following the "sergeants and soldiers" principle during the annealing process.     

Unusual wetting dynamics of aqueous surfactant solutions on polymer surfaces

Static and dynamic contact angles of aqueous solutions of three surfactants--anionic sodium dodecyl sulfate (SDS), cationic dodecyltrimethylammonium bromide (DTAB), and nonionic pentaethylene glycol monododecyl ether (C(12)E(5))--were measured in the pre- and micellar concentration ranges on polymer surfaces of different surface free energy. The influence of the degree of substrate hydrophobicity, concentration of the solution, and ionic/nonionic character of surfactant on the drop spreading was investigated. Evaporation losses due to relatively low humidity during measurements were taken into account as well. It was shown that, in contrast to the highly hydrophobic surfaces, contact angles for ionic surfactant solutions on the moderately hydrophobic surfaces strongly depend on time. As far as the nonionic surfactant is considered, it spreads well over all the hydrophobic polymer surfaces used. Moreover, the results obtained indicate that spreading (if it occurs) in the long-time regime is controlled not only by the diffusive transport of surfactant to the expanding liquid-vapor interface. Obviously, another process involving adsorption at the expanding solid-liquid interface (near the three-phase contact line), which goes more slowly than diffusion, has to be active.     

One‐pot direct synthesis of fluorescent polyaniline‐porphyrin macrospheres from porphyrin

Porphyrins are very important chromophores as sensitizer in solar cell. Hole and electron transport layers are being used as an important layer to move the electrons and holes away from the sensitizer molecule to electrodes. In this work, a simple process has been developed for the synthesis of one layer combination of sensitizer and hole transport, that is, polyaniline‐porphyrin (PANI‐TPPS₄) system as a bulk heterojunction. Macrospheres of fluorescent PANI‐TPPS₄ materials were synthesized by one‐pot as well as two step processes directly from porphyrin for the first time. The advantage of this process is no need to isolate sulfonated porphyrin (TPPS₄), which is a difficult process. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Unusual nitrogenous derivatives from Alstonia

Five new nitrogenous compounds were isolated from the Malayan Alstonia angustifolia and their structures determined based on interpretation of spectroscopic data.     

SDS disc electrophoresis of proteins in homogeneous, low-concentrated polyacrylamide gels

In the attempt to separate in a single gel run low- and high-molecular-weight proteins, we present here a multiphasic buffer system designed for this purpose. It avoids the continuous stacking of SDS as it occurs in the 'classical' SDS-PAGE. The system allows complete stacking and destacking of proteins in the 3.5-250 kDa range at acrylamide concentrations as low as 4.5% T (total acrylamide concentration in %) and 2.6% C (degree of cross-linking in %). Taurine is used as the trailing ion in the cathode buffer and in the resolving zone of the gel, and two different counterions (Tris and imidazole) in the stacking zone. The gel system is easy to prepare and, due to the very low acrylamide concentrations, it is ideal for analytical as well as for preparative tasks.     

Near-infrared dual luminescence from an extended zinc porphyrin

The photophysical characterization of an extended zinc porphyrin is reported. Fusion of bis-tetraazaanthracene on the porphyrin ring causes an unusual dual luminescence ascribed to two non-equilibrated singlet excited states.     

Gas-chromatographic determination of volatile sulfur-containing impurities in industrial emissions and aqueous solutions

Procedures are developed for determining volatile sulfur-containing impurities, hydrogen sulfide, simple mercaptans, sulfides, and disulfides in air and aqueous solutions. The procedures are based on the principle’s headspace gas chromatography and equilibrium preconcentration. The procedures differ from the officially approved ones in that the operations of sampling and sample preparation to gas-chromatographic analysis considerably reduce the loss of hydrogen sulfide and mercaptans unstable in humid air. The procedures provide the determination of sulfur-containing substances at the level of their maximum permissible concentrations (MPC) in industrial emissions and natural waters and the analytical range of four orders of magnitude; they can be implemented on gas chromatographs with flame ionization and flame photometric detectors, a quartz capillary column, and a thermostated gas-sampling valve.     

Unusual Guaiane Sesquiterpenoids from Artemisia rupestris

Two new guaiane sesquiterpenoids, (1β,5β)‐1‐hydroxyguaia‐4(15),11(13)‐dieno‐12,5‐lactone ( 1 ) and 1,5‐epoxy‐4‐hydroxyguai‐11(13)‐en‐12‐oic acid ( 2 ), together with five known compounds, rupestonic acid ( 3 ), strobilactone A ( 4 ), antiquorin ( 5 ), isosclerone ( 6 ), and 5‐hydroxy‐2′,3′,4′,7,8‐pentamethoxyflavone ( 7 ), were isolated from a 95% EtOH extract of Artemisia rupestris. Compounds 1 and 2 are rare examples of guaiane sesquiterpenoids, incorporating a 12,5‐lactone group or featuring a 1,5‐epoxy ring, respectively. The structures of 1 and 2 were identified by various spectroscopic methods. Compounds 1, 4 , and 5 exhibited moderate cytotoxic activities against the human lung cancer 95‐D cell line with IC₅₀ values of 11.3, 19.8, and 34.5 μM , respectively.     

Sulfur-assisted interconversion between N-confused porphyrin and N-fused porphyrin

The ring-opening reaction of N-fused tetraphenylporphyrin (NFTPP-H, 2) to C3-substituted N-confused tetraphenylporphyrin (NCTPP-S-Ar, 4) proceeded efficiently in 85-95% yields. Furthermore, removal of the C3-arylthio-substituents in 4 was achieved by the two types of desulfurization reactions. The Ni₂B-mediated desulfurization afforded C3-free N-confused tetraphenylporphyrin (NCTPP-H, 1) whereas the radical-mediated desulfurization with (n-Bu)₃Sn-H and AIBN promoted the ring-fusion to afford 2.     

Unusual Nortriterpenoid Saponins from Stauntonia chinensis

Four new saponins, yemuosides YM₁₇–YM₂₀ ( 1 – 4 , resp.), were isolated from the rattan of Stauntonia chinensis DC. (Lardizabalaceae) along with a known saponin, nipponoside D ( 5 ). Their structures were elucidated by spectroscopic analysis and chemical evidence as 20,30‐dihydroxy‐29‐noroleanolic acid 28‐O‐α‐L ‐rhamnopyranosyl‐(1→4)‐β‐D ‐glucopyranosyl‐(1→6)‐β‐D ‐glucopyranosyl ester ( 1 ), 20,29‐dihydroxy‐30‐noroleanolic acid 28‐O‐α‐L ‐rhamnopyranosyl‐(1→4)‐β‐D ‐glucopyranosyl‐(1→6)‐β‐D ‐glucopyranosyl ester ( 2 ), 29‐hydroxy‐30‐norolean‐20(21)‐enolic acid 28‐O‐α‐L ‐rhamnopyranosyl‐(1→4)‐β‐D ‐glucopyranosyl‐(1→6)‐β‐D ‐glucopyranosyl ester ( 3 ), 29‐hydroxyoleanolic acid 28‐O‐α‐L ‐rhamnopyranosyl‐(1→4)‐β‐D ‐glucopyranosyl‐(1→6)‐β‐D ‐glucopyranosyl ester ( 4 ), and 23,29‐dihydroxyoleanolic acid 28‐O‐α‐L ‐rhamnopyranosyl‐(1→4)‐β‐D ‐glucopyranosyl‐(1→6)‐β‐D ‐glucopyranosyl ester ( 5 ). Yemuoside YM₁₇–YM₁₉ ( 1 – 3 , resp.) contain novel unusual nortriterpene aglycones.