Swallowtail porphyrins: synthesis, characterization and incorporation into porphyrin dyads

The incorporation of symmetrically branched tridecyl ("swallowtail") substituents at the meso positions of porphyrins results in highly soluble building blocks. Synthetic routes have been investigated to obtain porphyrin building blocks bearing 1-4 swallowtail groups. Porphyrin dyads have been synthesized in which the zinc or free base (Fb) porphyrins are joined by a 4,4'-diphenylethyne linker and bear swallowtail (or n-pentyl) groups at the nonlinking meso positions. The swallowtail-substituted Zn(2)- and ZnFb-dyads are readily soluble in common organic solvents. Static absorption and fluorescence spectra and electrochemical data show that the presence of the swallowtail groups slightly raises the energy level of the filled a(2u)(pi) HOMO. EPR studies of the pi-cation radicals of the swallowtail porphyrins indicate that the torsional angle between the proton on the alkyl carbon and p-orbital on the meso carbon of the porphyrin is different from that of a porphyrin bearing linear pentyl groups. Regardless, the swallowtail substituents do not significantly affect the photophysical properties of the porphyrins or the electronic interactions between the porphyrins in the dyads. In particular, time-resolved spectroscopic studies indicate that facile excited-state energy transfer occurs in the ZnFb dyad, and EPR studies of the monocation radical of the Zn(2)-dyad show that interporphyrin ground-state hole transfer is rapid.     

Self-mode-locking in a Q-switched Nd: doped silica fibre laser

Operating characteristics of a Q-switched Nd³⁺: doped single-mode silica fibre with a mechanical chopper as a Q-switching device are presented. Peak powers as high as 16 W with pulse duration of 146 ns are demonstrated. Self-mode-locking in Nd³⁺:doped fibre is also reported. An output power of 312 W with a centre pulse duration of 4 ns is observed.     

Front-End Electron Transfer Dissociation Coupled to a 21 Tesla FT-ICR Mass Spectrometer for Intact Protein Sequence Analysis

High resolution mass spectrometry is a key technology for in-depth protein characterization. High-field Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) enables high-level interrogation of intact proteins in the most detail to date. However, an appropriate complement of fragmentation technologies must be paired with FTMS to provide comprehensive sequence coverage, as well as characterization of sequence variants, and post-translational modifications. Here we describe the integration of front-end electron transfer dissociation (FETD) with a custom-built 21 tesla FT-ICR mass spectrometer, which yields unprecedented sequence coverage for proteins ranging from 2.8 to 29 kDa, without the need for extensive spectral averaging (e.g., ~60% sequence coverage for apo-myoglobin with four averaged acquisitions). The system is equipped with a multipole storage device separate from the ETD reaction device, which allows accumulation of multiple ETD fragment ion fills. Consequently, an optimally large product ion population is accumulated prior to transfer to the ICR cell for mass analysis, which improves mass spectral signal-to-noise ratio, dynamic range, and scan rate. We find a linear relationship between protein molecular weight and minimum number of ETD reaction fills to achieve optimum sequence coverage, thereby enabling more efficient use of instrument data acquisition time. Finally, real-time scaling of the number of ETD reactions fills during method-based acquisition is shown, and the implications for LC-MS/MS top-down analysis are discussed.

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Synthesis and excited-state photodynamics of a chlorin-bacteriochlorin dyad--through-space versus through-bond energy transfer in tetrapyrrole arrays.

Understanding energy transfer among hydroporphyrins is of fundamental interest and essential for a wide variety of photochemical applications. Toward this goal, a synthetic free base ethynylphenylchlorin has been coupled with a synthetic free base bromobacteriochlorin to give a phenylethyne-linked chlorin-bacteriochlorin dyad (FbC-pe-FbB). The chlorin and bacteriochlorin are each stable toward adventitious oxidation because of the presence of a geminal dimethyl group in each reduced pyrrole ring. A combination of static and transient optical spectroscopic studies indicate that excitation into the Qy band of the chlorin constituent (675 nm) of FbC-pe-FbB in toluene results in rapid energy transfer to the bacteriochlorin constituent with a rate of approximately (5 ps)(-1) and efficiency of >99%. The excited bacteriochlorin resulting from the energy-transfer process in FbC-pe-FbB has essentially the same fluorescence characteristics as an isolated monomeric reference compound, namely a narrow (12 nm fwhm) fluorescence emission band at 760 nm and a long-lived (5.4 ns) Qy excited state that exhibits a significant fluorescence quantum yield (Phif=0.19). F?rster calculations are consistent with energy transfer in FbC-pe-FbB occurring predominantly by a through-space mechanism. The energy-transfer characteristics of FbC-pe-FbB are compared with those previously obtained for analogous phenylethyne-linked dyads consisting of two porphyrins or two oxochlorins. The comparisons among the sets of dyads are facilitated by density functional theory calculations that elucidate the molecular-orbital characteristics of the energy donor and acceptor constituents. The electron-density distributions in the frontier molecular orbitals provide insights into the through-bond electronic interactions that can also contribute to the energy-transfer process in the different types of dyads.     

Photophysical characterization of imidazolium-substituted Pd(II), In(III), and Zn(II) porphyrins as photosensitizers for photodynamic therapy

The photophysical properties of four imidazolium-substituted metalloporphyrins have been assessed to gain insights into the relative efficacy of the compounds for photodynamic therapy (PDT). A set of zinc(II), palladium(II), and chloro-indium(III) porphyrins all bear a net positive charge owing to the diethylimidazolium unit; one zinc chelate bears a negative charge owing to a bis(sulfobutyl)imidazolium unit. The photophysical properties of the cationic and anionic zinc porphyrins are very similar to one another in organic solvents, phosphate-buffered saline, and in the presence of bovine serum albumin. The properties of the zinc and palladium porphyrins bearing charged peripheral groups are generally similar to those of neutral analogs in organic solvents. The palladium porphyrin shows an essentially quantitative yield (≥0.99) of the triplet excited state compared to the zinc porphyrins (0.9), and all are quantitatively quenched (at the diffusion limit) by molecular oxygen in air-saturated fluid solution. If the rate constant and yield of quenching of the triplet excited state by energy or electron transfer to molecular oxygen is the same in the cellular environment as in solution, then these processes combined with the triplet yield contribute only a factor of 1.3 to the higher PDT activity of analogous palladium versus zinc porphyrins, which is much smaller than what is observed. Therefore, other factors such as transient reduction of the excited porphyrin or delivery to the target site must predominantly underlie the difference in PDT efficacy of these sensitizers.     

多肽和蛋白质的反相高效液相色谱研究--色谱行为的多样性

以Ｃ８柱为固定相,研究了微管结合蛋白２中两段重要肽段（肽１,肽２）和猪胰岛素在反相色谱上的保留行为。当以甲醇溶液为流动相时,猪胰岛素保留因子的对数值（ｌｎＫ’）随流动相有机溶剂体积分数（ψ）的变化呈现很好的线性关系。当以乙腈为流动相测定肽１的ｌｎＫ’随ψ变化关系时,所得结果显示ｉｎＫ’与ψ呈现良好的二次曲线关系。以乙腈为流动相测定肽１和肽２和Ｖａｎ’ｔ Ｈｏｆｆ曲线（ｌｎｋ’与１／Ｔ的关系图）时,     

Separation of structurally related synthetic peptides by capillary zone electrophoresis

The separation of two different sets of synthetic peptides has been investigated by high-performance capillary zone electrophoresis utilising naked, fused silica capillaries. The effects of electrolyte pH, buffer concentration, capillary length and electric field strength on the separation efficiency and selectivity were systematically varied, with the highest resolution achieved with buffer electrolytes of low pH and relatively high ionic strength. Under optimised separation conditions utilising the "short end injection" separation approach with negative electric field polarity, a series of eight structurally-related synthetic peptides were baseline resolved within 4 min without addition of any modifier of the background electrolyte with separation efficiencies in the vicinity of 600000 theoretical plates/m. Further significant enhancement of separation efficiencies could be achieved by taking advantage of the "long end injection" approach with positive electric field polarity. The outcome of these experimental variations parallels the "sweeping" effect that has been observed in the capillary electrochromatographic and micellar electrokinetic separations of polar molecules and permits rapid resolution of peptides with focusing effects. In addition, small changes in the electrolyte buffer pH and concentration were found to have a significant impact on the selectivity of synthetic peptides of similar intrinsic charge. These observations indicate that multi-modal separation mechanisms operated under these conditions with the unmodified fused silica capillaries. This study, moreover, documents additional examples of peptide-specific multi-zoning behaviour in the high-performance capillary zone electrophoretic separation of synthetic peptides.     

Phytochemical investigation of Gynura bicolor leaves and cytotoxicity evaluation of the chemical constituents against HCT 116 cells

Gynura bicolor (Compositae) is a popular vegetable in Asia and believed to confer a wide range of benefits including anti-cancer. Our previous findings showed that the ethyl acetate extract of G. bicolor possessed cytotoxicity and induced apoptotic and necrotic cell death in human colon carcinoma cells (HCT 116). A combination of column chromatography had been used to purify chemical constituents from the ethyl acetate and water extract of G. bicolor leaves. Eight chemical constituents 5-p-trans-coumaroylquinic acid (I), 4-hydroxybenzoic acid (II), rutin (III), kampferol-3-O-rutinoside (IV), 3,5-dicaffeoylquinic acid (V), kampferol-3-O-glucoside (VI), guanosine (VII) and chlorogenic acid (VIII) were isolated from G. bicolor grown in Malaysia. To our best knowledge, all chemical constituents were isolated for the first time from G. bicolor leaves except rutin (III). 3,5-dicaffeoylquinic acid (V), guanosine (VII) and chlorogenic acid (VIII) demonstrated selective cytotoxicity (selective index>3) against HCT 116 cancer cells compared to CCD-18Co human normal colon cells.