Specific interaction between water-soluble phospholipid polymer and liposome

A water-soluble polymer having both a phospholipid polar group and an azobenzene group, poly(2-methacryloyloxyethyl phosphorylcholine-co-p-phenylazoacrylanilide) (poly(MPC-co-PAAn)) was synthesized and the interaction between the liposome of the phospholipid was investigated in comparison with other water-soluble azoaromatic polymers. When the poly(MPC-co-PAAn) was incubated with dipalmitoylphosphatidylcholine (DPPC) lipo-somes above these gel-liquid crystalline temperatures, an electronic spectrum of azobenzene moiety, which is a hydrophobic probe, showed that the a copolymer chain exists under nonpolar circumstances. Thus, poly(MPC-co-PAAn) interacts with DPPC liposomes. On the other hand, other copolymers do not interact with the liposomes. Moreover, heat of the gel-liquid crystalline transition of DPPC liposomes was increased by the presence of poly(MPC-co-PAAn). These findings clearly indicate that the poly(MPC-co-PAAn) has an affinity to the DPPC liposomes and hybridizes with liposomes based on the phospholipid polar group of the copolymer.     

Strong two-photon absorption in new asymmetrically substituted porphyrins: interference between charge-transfer and intermediate-resonance pathways

We study two-photon absorption (2PA) in two series of new free-base porphyrins with 4-(diphenylamino)stilbene or 4,4'-bis-(diphenylamino)stilbene (BDPAS) attached via pi-conjugating linkers at the porphyrin meso-position. We show that this new substitution modality increases the 2PA cross section in the Soret band region (excitation wavelength 750-900 nm) of the core porphyrin by nearly 2 orders of magnitude, from sigma(2) approximately 10 GM for the meso-phenyl-substituted analogue to sigma(2) approximately 10(3) GM for the ethynyl-linked BDPAS-porphyrin dyad. The 2PA properties are quantitatively described by considering two different and interfering 2PA quantum transition pathways. The first path involves virtual transition via intermediate one-photon resonance. The second path bypasses the intermediate resonance and occurs due to a large permanent dipole moment difference between the ground and the final electronic states. To our best knowledge, this is the first experimental observation of the combined effect of these two pathways on one particular two-photon transition, resulting in quantum-interference-modulated 2PA strength.     

水溶性不对称卟啉及其金属配合物合成及与DNA的 作用

合成并表征了三(4-N-甲基吡啶基)卟啉为母体,带有乙氧羰基甲氧基或羧基甲氧基侧链的水溶正电性卟啉及其金属配合物(M=Cu,Ni),并研究了它们与DNA的相互作用。卟啉对EB－DNA荧光猝灭研究表明：卟啉与DNA作用存在单一结合模式。EB荧光竞争法测得它们与DNA作用的结合常数介于3×10^5～3×10^6L·mol^-1。电子吸收研究谱表明：DNA引起卟啉Soret带的不同程度的红移(≤9nm)和减色(≤35%)。卟啉及其金属配合物都引起DNA的熔点升高(≤2.5℃)和DNA粘度的略微下降。所有这些研究表明：这些带较长侧链的水溶性卟啉及其金属配合物与DNA作用不存在插入作用模式,只是在DNA的外部结合。     

cis-Pyridyl core-modified porphyrins for the synthesis of cationic water-soluble porphyrins and unsymmetrical non-covalent porphyrin arrays

Synthesis of a series of 21-thia and 21-oxoporphyrin building blocks containing two pyridyl functional groups at the meso positions in a cis fashion is reported. The building blocks were used to synthesize a series of cationic water-soluble 21-thia and 21-oxoporphyrins. An unsymmetrical non-covalent trimer containing two dissimilar porphyrin cores such as one N₃S and two N₄ porphyrins cores was also constructed using the pyridyl porphyrin building blocks reported here.     

Kinetic evidence for a charge-transfer mechanism in the interaction of ammonia with 2,4-dinitrophenylhydrazine in dimethylsulphoxide

Kinetic evidence is adduced to show that charge-transfer is involved in the interaction of ammonia with 2,4-dinitrophenylhydrazine in dimethylsulphoxide. The charge-transfer mechanism is further confirmed by the linear relation between the ionization potential and molar absorptivity of the complex for three aliphatic amines.     

A density functional theory study of interaction between formamide and guanine

Hydrogen bonding in complexes formed between formamide and guanine molecules was completely investigated using density functional theory (DFT) at the 6-311++G(d, p) level. For comparison, the HF and MP2 methods were also used. Nine stable cyclic structures stabilized by two hydrogen bonds were found. One of these was a six-membered ring, five were seven-membered rings, and the others were eight-membered rings. The eight-membered ring is preferable to the seven-and six-membered ones as follows from H-bond lengths and interaction energies. The FG4 structure was calculated to be the most stable, and another cyclic structure, FG5, was least stable because of the six-membered ring and the weakest interaction. The infrared spectrum frequencies, intensities, and vibrational frequency shifts are also reported. The text was submitted by the authors in English.     

Synthesis and DNA binding of novel water-soluble cationic methylcobalt porphyrins

Organocobalt derivatives of tetracationic water-soluble porphyrins are difficult to prepare via the typical reductive alkylation of the Co(II)(por) (porH(2) = porphyrin ligand). None have been reported. The problem may arise because the porphyrin core is made relatively electron poor by the positively charged peripheral groups. We have circumvented this problem by using the [Co(III)(NH(3))(5)CH(3)](2+) reagent, which inserts the Co(III)-CH(3) moiety directly into porH(2) in water under basic conditions. The method afforded two new [CH(3)Co(por)](4+) derivatives, [CH(3)CoTMpyP(4)](4+) and [CH(3)CoTMAP](4+), where [TMpyP(4)](4+) and [TMAP](4+) are the coordinated, NH-deprotonated forms of meso-tetrakis(N-methyl-4-pyridiniumyl)porphyrin and meso-tetrakis(N,N,N-trimethylaniliniumyl)porphyrin, respectively. The binding of the two new [CH(3)Co(por)](4+) cations to DNA and to the synthetic DNA polymers [poly(dA-dT)](2) and [poly(dG-dC)](2) was studied. Using published criteria by which changes in DNA viscosity and in the visible and CD spectra in the Soret region can be used to assess DNA binding, we conclude that both are outside binders. A large hypochromicity of the Soret bands of the [CH(3)Co(por)](4+) cations observed upon outside binding to DNA may indicate a high degree of self-stacking. The visible absorption and CD spectra of the [CH(3)Co(por)](4+) cations in the presence of 1:1 mixtures of [poly(dA-dT)](2) and [poly(dG-dC)](2) are nearly identical to those with [poly(dA-dT)](2) alone and are very different from those of [poly(dG-dC)](2) alone. Thus, both cations show a high preference for outside binding at AT-rich over GC-rich DNA sites. Upon binding of each of the [CH(3)Co(por)](4+) cations to all of the DNA polymers, the Soret bands exhibit blue shifts, whereas the Soret bands of the corresponding [(H(2)O)(2)Co(por)](5+) cations exhibit red shifts. The blue shifts strongly suggest that the [CH(3)Co(por)](4+) cations, particularly [CH(3)CoTMAP](4+), become five-coordinate forms to some extent on DNA binding; this result is the first good evidence for the presence at equilibrium of five-coordinate CH(3)Co(III)(N(4)) forms in water.     

Direct chemical evidence for charge transfer between photoexcited 2-aminopurine and guanine in duplex DNA

Photoexcited 2-aminopurine (Ap*) is extensively exploited as a fluorescent base analogue in the study of DNA structure and dynamics. Quenching of Ap* in DNA is often attributed to stacking interactions between Ap* and DNA bases, despite compelling evidence indicating that charge transfer (CT) between Ap* and DNA bases contributes to quenching. Here we present direct chemical evidence that Ap* undergoes CT with guanine residues in duplex DNA, generating oxidative damage at a distance. Irradiation of Ap in DNA containing the modified guanine, cyclopropylguanosine (CPG), initiates hole transfer from Ap* followed by rapid ring opening of the CPG radical cation. Ring opening accelerates hole trapping to a much shorter time regime than for guanine radicals in DNA; consequently, trapping effectively competes with back electron transfer (BET) leading to permanent CT chemistry. Significantly, BET remains competitive, even with this much faster trapping reaction, consistent with measured kinetics of DNA-mediated CT. The distance dependence of BET is sharper than that of forward CT, leading to an inverted dependence of product yield on distance; at short distances product yield is inhibited by BET, while at longer distances trapping dominates, leading to permanent products. The distance dependence of product yield is distinct from forward CT, or charge injection. As with photoinduced charge transfer in other chemical and biological systems, rapid kinetics for charge injection into DNA need not be associated with a high yield of DNA damage products.     

NMR evidence for planar chirality in natural porphyrins

The ¹H NMR spectra of several six-coordinate cobalt(III) porphyrins of general formula L₂Co(DPDME)CI, where DPDME=deuteroporphyrin dimethyl ester and L is an optically active ligand, have been measured at 250 or 400 MHz. In a few cases, two signals of equal intensity are observed for the L ligand protons. This magnetic non-equivalence, which never exceeds 0.04 ppm, is thought to arise from the planar chirality of the porphyrin ring, which makes a proton in the ligand L above the porphyrin ring and the corresponding proton below this ring diastereotopic.     

Methoxy-isoporphyrins of water-soluble porphyrins: synthesis,characterization and electrochemical properties

Abstract

Methoxy-isoporphyrins of zinc [5,10,15,20-tetrakis(4-sulfonatophenyl)]porphyrin, ZnTSPP (1a) and zinc [5,10,15,20-tetrakis(4-carboxyphenyl)]porphyrin, ZnTCPP (1b) have been synthesized and characterized using standard spectroscopic techniques (Uv-visible, ¹H NMR) , ESI-mass spectrometry and powder X-ray diffraction studies. The isoporphyrins [5-(methoxy)-5,10,15,20-tetrakis(4-sulfonatophenyl)-5H,15H-porphinato]zinc(II) (2a) and [5-(methoxy)-5,10,15,20-tetrakis(4-carboxyphenyl)-5H,21H-porphinato]zinc(II) (2b) are formed due to nucleophilic attack of the methanol to the zinc porphyrin dication. Ceric ammonium nitrate (CAN) was used to oxidize zinc porphyrin and to form zinc porphyrin dication. The electronic spectra of the isoporphyrin complexes 2a and 2b exhibit an intense peak at near IR region . Electrochemical measurements of the synthesized isoporphyrins showed a typical irreversible reduction peak at lower potential. S-containing nucleophiles, which work as reducing agents, convert the zinc isoporphyrins to their parent porphyrins, which supports the electrochemical observations. Their structural properties have been studied using powder X-ray diffraction. The luminescence properties of isoporphyrins were compared with the parent zinc porphyrins.     

Interfacial self-assembly of water-soluble cationic porphyrins for the reduction of oxygen to water

Meet at the border: Assembly of the water-soluble cobalt tetrakis(N-methylpyridinium-4-yl)porphyrin [CoTMPyP](4+) at soft interfaces is enhanced and stabilized by its interfacial interaction with the lipophilic anion (C(6)F(5))(4)B(-). The supramolecular structure thus formed provides excellent catalytic activity in the four-electron reduction of oxygen.     

Electrostatic interaction between cationic calix[4]pyrroles and anionic porphyrins in water

The formation and characterization of molecular assemblies resulting from mixing of solutions of tetracationic calix[4]pyrroles and tetraanionic porphyrins in water are reported. The self-assembly of the complementary building blocks was quantitatively studied by UV–vis, ¹H NMR, Fluorescence and ESI–MS. Binding constants calculated by absorption spectroscopic titrations were in the range of 10³–10⁵ M^?1. The results indicate that the cationic thiacalix[4]pyrroles show greater binding affinity towards metal free porphyrins than metalloporphyrins under neutral conditions.     

Further evidence for the intramolecular charge-transfer interaction between tropylium ion and remote benzene rings in 9,10-dihydro-9,10-(1,2-tropylio)anthracene tetrafluoroborate and its methyl derivatives

A series of 9,10-dihydro-9,10-(1,2-tropylio)anthracene tetrafluoroborates

has been prepared. The intramolecular charge-transfer interactions in

were confirmed by their UV spectra and pK_R+ values. As a model compound 1,2,3,4-tetrahydro-1,4-(1,2-tropylio)naphthalene tetrafluoroborate ($\text{5}$)_was also examined.     

Stacking interaction between tryptophan and uracil in a synthetic model compound

Stacking interaction between tryptophan and uracil in model compound 1 has been confirmed in solution by means of hypochromism and fluorescence emission, whereas 1 holds an unfolded conformation in a crystalline state as determined by X-ray analysis.     

Discrimination of nitroxyl and nitric oxide by water-soluble Mn(III) porphyrins

The water-soluble manganese(III) meso-tetrakis (N-ethylpyridinium-2-yl) porphyrin (Mn(III)TEPyP) and manganese(III) meso-(tetrakis(4-sulfonato-phenyl)) porphyrinate (Mn(III)TPPS) are able to chemically distinguish between HNO and NO donors, reacting with the former in a fast, efficient, and selective manner with concomitant formation of the {MnNO}(7) complex (k(on(HNO)) approximately equal to 10(5) M(-1) s(-1)), while they are inert or react very slowly with NO donors. DFT calculations and kinetic data suggest that HNO trapping is operative at least in the case of Mn(III)TPPS, while catalytic decomposition of the HNO donors (sodium trioxodinitrate and toluene sulfohydroxamic acid) seems to be the main pathway for Mn(III)TEPyP. In the presence of oxygen, the product Mn(II)TEPyP(NO) oxidizes back to Mn(III)TEPyP, making it possible to process large ratios of nitroxyl donor with small amounts of porphyrin.     

Synthesis and intramolecular charge-transfer interaction of o-tropyliobiphenyl tetrafluoroborates

A series of o-tropyliobiphenyl tetradfluoroborates

has been synthesized. Evidences are presented to show that

exhibit strong intramolecular charge-transfer interaction between tropylium ion and remote aryl ring. The structure of

was determined by single crystal X-ray diffraction study.     

Chemical reactions between muonium and porphyrins

The rate constants for reaction of muonium atoms with hemin and the protoporphyrin are found to be 2.7 × 10⁹ and 6 × 10⁸ M^?1 s^?1, respectively. The reaction mechanisms are mainly through the addition to the conjugated double bond for the protoporphyrin and by reductions or partial spin conversion processes for the hemin solutions. The point of reaction is suggested to be the peripheral site of the porphyrin molecules.