Energy and Photoinduced Electron Transfer in a Wheel-Shaped Artificial Photosynthetic Antenna-Reaction Center Complex

Functional mimics of a photosynthetic antenna-reaction center complex comprising five bis(phenylethynyl)anthracene antenna moieties and a porphyrin-fullerene dyad organized by a central hexaphenylbenzene core have been prepared and studied spectroscopically. The molecules successfully integrate singlet-singlet energy transfer and photoinduced electron transfer. Energy transfer from the five antennas to the porphyrin occurs on the picosecond time scale with a quantum yield of 1.0. Comparisons with model compounds and theory suggest that the Förster mechanism plays a major role in the extremely rapid energy transfer, which occurs at rates comparable to those seen in some photosynthetic antenna systems. A through-bond, electron exchange mechanism also contributes. The porphyrin first excited singlet state donates an electron to the attached fullerene to yield a P(*+)-C(60)(*-) charge-separated state, which has a lifetime of several nanoseconds. The quantum yield of charge separation based on light absorbed by the antenna chromophores is 80% for the free base molecule and 96% for the zinc analogue.

A Versatile Bis-Porphyrin Tweezer Host for the Assembly of Noncovalent Photoactive Architectures: A Photophysical Characterization of the Tweezers and Their Association with Porphyrins and Other Guests

A bis(Zn(II)-porphyrin) tweezer host with anthracene components as apex and side-arms has been synthesized. Mono- (pyridine) and bidentate (4,4'-bipyridine) guests were used as models for single and double axial coordination inside the cavity, respectively. A series of dipyridylporphyrin guests with different substitution patterns and excited-state energy levels have association constants with the tweezers that are of the order of 10(6) M(-1), which is indicative of complexation with the inside of the cavity. This complexation can only occur upon an important distortion of the cavity that opens the bite by about 30 %. This characteristic, in conjunction with their ability to reduce the bite distance by rotation around single bonds, makes these porphyrin tweezers amongst the most versatile so far reported, with tuning of the bite distance in the range of approximately 5-20 Angstroms. Energy transfer to the free-base guest within the triporphyrin complex is nearly quantitative (95-98 %) and the rates of transfer are consistent with a Förster mechanism that is characterized by a reduced orientation factor.

Novel Monodisperse PEG−Dendrons as New Tools for Targeted Drug Delivery: Synthesis, Characterization and Cellular Uptake

Dendrimers, dendrons, and hyperbranched polymers are gaining popularity as novel drugs, imaging agents, and drug delivery systems. They present advantages of well-defined molecular weight, multivalent surfaces, and high drug carrying capacity. Moreover, it is emerging that such architectures can display unique endocytic properties. As poly(ethylene glycol) (PEG) is widely used for protein and drug conjugation, the aim of this study was for the first time to synthesize novel, branched PEG-based architectures, to define their cytotoxicity and, via preparation of Oregon green (OG) conjugates define the effect of structure on their cellular uptake. Five PEG-based dendrons were synthesized using monodisperse Fmoc-amino PEG propionic acid (M(w) = 840) as a monomer, and cadaverine, tris(2-aminoethyl)amine or lysine as the branching moieties. These were diamino,bisPEG (M(w) = 1300); triamino,trisPEG (Mw = 1946); tetraamino,tetraPEG (M(w) = 3956); monocarboxy,diamino,bisPEG (M(w) = 1346); and monocarboxy,tetraamino,tetraPEG (M(w) = 3999). These products had NH(2) or both NH(2) and COOH terminal groups and the identity was verified by amino group analysis and ESI-TOF mass spectroscopy. Purity was determined by HPLC. Representative structures were not toxic towards an endothelial-like cell line (ECV304) at concentrations up to 4 mg/mL (over 72 h). At 37 degrees C, all of the OG-labeled PEG dendrons showed progressive uptake by ECV304 cells, but tetraamino,tetraPEG showed the greatest rate of internalization over the first 20 min. Cellular uptake was inhibited at 4 degrees C, and PEG dendron localization to perinuclear vesicles was confirmed by fluorescence microscopy. These well-defined novel architectures have potential for further development as targetable drug delivery systems or tools for construction of structurally defined modified surfaces.

Synthesis and calculated properties of some 1,4-bis(amino)anthracene-9,10-diones

The synthesis of a number of 1,4-bis(amino)anthracene-9,10-diones containing chlorine or sulfur which are related to the anti-cancer drugs Ametantrone and Mitoxantrone are reported. 1,4-Dichloro-2,3-dihydro-5,8-dihydroxyanthracene-9,10-dione reacts readily with a series of alkylamines to yield the corresponding 1,4-bis(alkylamino)-5,8-dichloroanthracene-9,10-dione after oxidation. The subsequent reaction of the products with ethanethiol or thiophenol gives the corresponding 1,4-bis(alkylamino)-5,8-bis(sulfanyl)anthracene-9,10-dione in good yield. Theoretical calculations at the RHF 6-31G** level indicate that the introduction of either chlorine or the phenylsulfanyl group into the 5- and 8-positions of 1,4-bis(alkylamino)anthracene-9,10-diones results in a lowering of the LUMO energies suggesting that related functionalised derivatives might have lower cardiotoxicities than Mitoxantrone.

Highly diastereoselective Diels–Alder cycloadditions of 9R-(1-methoxyethyl)anthracene with p-benzoquinone

Diels-Alder cycloadditions of p-benzoquinone with 9R-(1-methoxyethyl)anthracene provides a 60:40 ratio of cycloadducts when heated at reflux in xylene. Mechanistic studies to explore the origins of this selectivity have shown that at lower temperatures the kinetic product predominates, giving a 96:4 ratio of cycloadducts.

N-Alkyl oxazolidines as stereocontrol elements in asymmetric Diels–Alder cycloadditions of 9-substituted anthracene derivatives

Chiral 9-oxazolidinyl anthracene derivatives have been prepared as single diastereoisomers by condensation of 9-anthraldehyde with the appropriate N-alkyl amino alcohol. Asymmetric Diels-Alder cycloadditions of these with N-methyl maleimide proceeds in good yield and in good diastereoselectivity, the sense of which may be controlled by judicious choice of the N-alkyl group.

Synthesis and Biological Activity of Isoxazolidinyl Polycyclic Aromatic Hydrocarbons: Potential DNA Intercalators

Isoxazolidinyl polycyclic aromatic hydrocarbons (isoxazolidinyl-PAHs) have been synthesized in good yields by 1,3-dipolar cycloaddition methodology promoted by microwave irradiation. The structures of the obtained cycloadducts have been determined by NOE experiments and supported by computational studies at the AM1 level. The cytotoxicity and antiviral activity of the synthesized compounds have been investigated. In particular, compounds 7c and 7e show high levels of cytotoxicity on MOLT-3 leukemia cells; 7e exerts a remarkable enhancing activity on apoptosis caused by anti-fas antibody addition. Furthermore, compounds 7b and 8b exhibit specific antiviral effects against the Punta Toro virus.

Enhancing the Rate of the Diels−Alder Reaction Using CO2 + Ethanol and CO2 + n-Hexane Mixed Solvents of Different Phase Regions

The reaction rate of the Diels-Alder reaction between N-ethylmaleimide and 9-hydroxymethylanthrance in CO2 + ethanol and CO2 + hexane mixed solvents of different compositions were determined by in situ UV/vis spectroscopy at 318.15 K and different pressures. The density of the mixed solvents at different pressures was also determined and the isothermal compressibility was calculated using the density data. The activation volume of the reaction was calculated based on the dependence of rate constant (kc) on pressure. It was demonstrated that the kc was very sensitive to the pressure in the mixed solvents near the critical region and the kc increased dramatically as pressure approached dew points, critical point, and bubble points of the mixed solvents. However, the kc in the mixed solvents outside the critical region or in pure CO2 was not sensitive to pressure. At suitable conditions, kc could be 40 times larger than that in acetonitrile. The activation volume of the reaction was nearly independent of pressure as the pressure was much higher than the phase separation pressure of the mixed solvents, while it increased considerably as pressure approached the bubble points, critical point, and dew points from high pressure. The clustering of the solvent molecules with the reactants and the activated complex in the reaction systems near the phase boundary in the critical region may be the main reason for the interesting phenomena observed. This work also shows that, using pure CO2 as the solvent, the reaction cannot be carried out in the critical region of the solvent due to the limitations of the reactants, while it can be conducted in the critical region of mixed solvents of suitable compositions, where the solvents are highly compressible and the reaction rate can be tuned effectively by pressure.

Unique Nanoscale Morphologies Underpinning Organic Gel-Phase Materials

This study investigates the self-assembly of simple aliphatic diamines with a dendritic peptide. By controlling the molar ratio of this two-component system, new nanoscale morphologies were generated. In the presence of relatively long aliphatic chains (C10, C12) a transition from nanoscale fibres to platelets was observed on changing the molar ratio, whereas, for shorter spacer chains (e.g., C9 and C8), interesting and unique morphological changes were observed by low voltage field emission gun scanning electron microscopy (SEM), with "nanosquares" or nanoscale "rosette" structures being formed. Remarkably, these discrete nanoscale structures were able to form sample-spanning networks capable of supporting a gel-phase material; whereas, most gels are usually based on fibrillar assemblies. In addition to SEM, the gels were characterised by using thermal measurements and circular dichroism spectroscopy. The length of the diamine spacer and the molar ratio of components controlled the self-assembly process by modifying the spatial organisation of the dendritic head groups at the molecular level, which is transcribed into the aspect ratio of the self-assembled state at the microscopic level. Ultimately, this led to diamine-induced control of the macroscopic material's behaviour. When present in excess, the diamine controlled the observed nanoscale morphology as a consequence of undergoing a dendritically controlled nanocrystallisation process to form a network, an unusual and significant result.

Bicyclo[2.2.2]octene-Based “Crab-like” Molecules: Synthesis, Complexation, Luminescence Properties, and Solid-State Structures

[structure, reaction: see text] The U-shaped, multifunctionalized tetraetheno-bridged dicyclopenta[b,i]anthracenediol 10 was synthesized to serve as a platform molecule. The molecule was prepared from the Diels-Alder adduct 5a of tricycloundecatriene 3 and bicyclo[2.2.2]octene-fused p-benzoquinone 4. Functionalization of 10 to construct crab-like molecules was achieved via the base-promoted bis-O-alkylation of two endo-oriented hydroxyl groups at termini in 10 with the following alkyl halides: allyl, propagyl, and benzyl bromides; 1-bromo- and 1-iodo-4-(bromomethyl)benzene; 9-(bromomethyl)anthracene; 1-(bromomethyl)pyrene; and isomeric bromomethylpyridines. Single-crystal X-ray structures were obtained for bis-phenyl (21) and bis-pyrenyl (25) crabs, and for the silver(I) complex (32 and 33) crabs. The silver(I) complex 32 from bis-o-pyridyl crab 30 is a [2+2] dimeric dimetallocyclophane, and 33 from bis-m-pyridyl crab 29 is a [1+1] metallo-bridged cyclophane. The self-assembled intramolecular pi-stacking of pyrenyl rings in 25 with an interplanar distance of 3.40 A and the consequent pi-pi interactions were revealed by the X-ray crystal structure and its luminescence property.

Exploratory Chemistry toward the Identification of a New Class of Multidrug Resistance Reverters Inspired by Pervilleine and Verapamil Models

On the basis of the present knowledge of the substrate recognition site of ABC transporter proteins and inspired by the structures of verapamil and pervilleine A, a new class of Pgp-mediated multidrug resistance (MDR) reverters has been designed and synthesized. The new compounds are flexible molecules carrying one or two basic nitrogen atoms flanked, at properly modulated distance, by two aromatic moieties. Most of the molecules studied possess MDR inhibitory activity on anthracycline-resistant erythroleukemia K 562 cells, showing a potency that is higher than that of the reference compound verapamil and, in a few cases (7, 12, 13,17, 20, 22, 28), is in the high nanomolar range. These compounds may be useful leads to develop new MDR reverting agents. In fact, the chemical structure of the class is fairly simple and can be implemented in a variety of ways that will allow the synthesis of new compounds that might be useful leads for the development of drugs to control Pgp-dependent MDR.

Oxoazabenzo[de]anthracenes Conjugated to Amino Acids: Synthesis and Evaluation as DNA-Binding Antitumor Agents

We report the synthesis of an original series of oxoazabenzo[de]anthracenes conjugated to an amino acid: Ala, Phe, Pro, Lys, or Gly (4a-e, respectively). The compounds, derived from 1,8-dihydroxyanthracene-9,10-dione, were studied for DNA binding and cytotoxicity. Melting temperature, fluorescence quenching, and surface plasmon resonance methods all indicated that the lysine derivative 4d binds to DNA much more strongly that the Pro, Ala, and Gly conjugates whereas the Phe analogue showed the lowest DNA binding capacity. These compounds form intercalation complexes with DNA, as judged from electric linear dichroism and topoisomerase I-based DNA unwinding experiments. Preferential binding of 4d to defined sequences such as 5'-CTAAAGG and 5'-ATGC was evidenced by DNase I footprinting. This Lys conjugate was found to be over 20 times more cytotoxic to CEM human leukemia cells than the other conjugates, with an IC50 in the submicromolar range. A high antiproliferative activity, likely attributable to the enhanced DNA binding capacity, is maintained despite the incapacity of the compound to stabilize topoisomerase-DNA covalent complexes. The cell cycle effects of 4d consisted in an S phase accumulation of cells coupled with a pro-apoptotic action (appearance of hypodiploid sub-G1 cells) which were confirmed by measuring the inhibition of BrdU incorporation into DNA and labeling of phosphatidylserine residues with annexin V-FITC by means of flow cytometry. Altogether, the work provides interesting structure-activity relationships in the oxoazabenzo[de]anthracene-amino acid conjugate series and identifies the lysine derivative 4d as a promising candidate for further in vivo evaluation and drug design.

Synthesis and Biological Evaluation of Dihydromotuporamine Derivatives in Cells Containing Active Polyamine Transporters

Dihydromotuporamine C (4) and its 4,4-triamine analogue (5) were synthesized in good yield using ring-closing metathesis (RCM) methods. Comparison of their biological activities (Ki determinations in L1210 cells and IC50 determinations in L1210, CHO, and CHO-MG cells) revealed that the motuporamine derivatives do not use the polyamine transporter (PAT) for cellular entry. Bioevaluation of a N1-(anthracen-9-ylmethyl)-N1-(ethyl)homospermidine control (7) revealed that the presence of a N1 tertiary amine center imparted a significant reduction in the PAT affinity of the polyamine conjugate and abolished its PAT-targeting selectivity.

Novel methyl helianthrones as photosensitizers: synthesis and biological evaluation

A combination of light, oxygen and a photosensitizer is used to induce death of cancer cells by photodynamic therapy. In this study, we have synthesized several new methyl helianthrone derivatives and compared their phototoxicity with that of hypericin. In contrast to hypericin, methyl helianthrones are soluble in aqueous solutions and have a broad range of light absorbance, which allows the use of polychromatic light. Structural modifications of methyl helianthrone demonstrated that substitution of hydrogen atoms of methyl helianthrone at Positions 2 and 5 with Br atoms or methylation of its phenolic hydroxyls, significantly increases the corresponding singlet oxygen quantum yield and their phototoxicity toward alphaT3-1, M2R and LNCaP cells. The phototoxicity of some of these compounds was similar to that of hypericin. Methyl helianthrones, like hypericin, accumulated mainly in the perinuclear region as evident by confocal microscopy. Irradiation of cells pretreated with methyl helianthrone derivatives generates intracellular reactive oxygen species and lipid free radicals, as shown by a fluorescentic probe and electron paramagnetic resonance methods, respectively. The phototoxicity of these methyl helianthrones as well as their ability to oxidize membrane lipids were significantly decreased on addition of specific Type-II inhibitors, suggesting the involvement of singlet oxygen as the main oxidant.

N1-substituent effects in the selective delivery of polyamine conjugates into cells containing active polyamine transporters

Several N(1)-arylalkylpolyamines containing various aromatic ring systems were synthesized as their respective HCl salts. The N(1)-substituents evaluated ranged in size from N(1)-benzyl, N(1)-naphthalen-1-ylmethyl, N(1)-2-(naphthalen-1-yl)ethyl, N(1)-3-(naphthalen-1-yl)propyl, N(1)-anthracen-9-ylmethyl, N(1)-2-(anthracen-9-yl)ethyl, N(1)-3-(anthracen-9-yl)propyl, and pyren-1-ylmethyl. The polyamine architecture was also altered and ranged from diamine to triamine and tetraamine systems. Biological activities in L1210 (murine leukemia), Chinese hamster ovary (CHO), and CHO's polyamine transport-deficient mutant (CHO-MG) cell lines were investigated via IC(50) cytotoxicity determinations. K(i) values for spermidine uptake were also determined in L1210 cells. The size of the N(1)-arylalkyl substituent as well as the polyamine sequence used had direct bearing on the observed cytotoxicity profiles. N(1)-Tethers longer than ethylene showed dramatic loss of selectivity for the polyamine transporter (PAT) as shown in a CHO/CHO-MG cytotoxicity screen. In summary, there are clear limits to the size of N(1)-substituents, which can be accommodated by the polyamine transporter. A direct correlation was observed between polyamine-conjugate uptake and cytotoxicity. In this regard, a cytotoxicity model was proposed, which describes a hydrophobic pocket of set dimensions adjacent to the putative PAT polyamine-binding site.

A spectroscopic and photophysical study on molecular recognition via hydrogen-bonding and π–π stacking interactions

Spectroscopic and photophysical properties of a Kemp's tricarboxylic acid derivative having an anthracene chromophore (I) upon recognition of 9-butyladenine (BA) in chloroform were studied in detail. Molecular recognition of BA by I via hydrogen-bonding and pi-pi stacking interactions were sensed successfully on the basis of absorption and fluorescence spectroscopies, by which the binding constant of the I:BA complex was determined to be 240 M(-1). The fluorescence quantum yield and lifetime of I in the absence of BA were 0.24 and 5.6 ns, respectively, while those in the presence of an enough amount of BA increased to 0.35 and 13 ns, respectively. These values demonstrated that the nonradiative decay rate constant of I decreased from 13.6 x 10(7) to 5.0 x 10(7) s(-1) upon binding with BA. Such changes in the photophysical properties of I before and after complexation with BA were discussed in terms of hydrogen-bonding and pi-pi stacking interactions between I and BA. In particular, intramolecular hydrogen-bonding between the amide and imide groups in was shown to play important roles in determining the photophysical characteristics of I before complexation, while intermolecular hydrogen-bonding between I and BA governed the excited-state properties of the I:BA complex. The change in the hydrodynamic diameter of I before and after complexation with BA was also discussed on the basis of the results by fluorescence dynamic anisotropy measurements.

Photophysical behavior and intramolecular energy transfer in Os(ii) diimine complexes covalently linked to anthracene

The photophysical behavior of two Os(II) complexes having a bipyridine ligand with anthracene attached directly to the bipyridine (4-(9-anthryl)-2,2'-bipyridine, bpy-AN) is reported. The two complexes [(bpy)2Os(bpy-AN)]2+ and [(bpy-AN)2Os(CO)Br]+ have (3)MLCT excited states that differ in energy by less than 800 cm(-1). Despite this fact, the observed photophysical behavior of the two complexes is entirely different. The complex with the higher energy 3MCLT state, [(bpy-AN)2Os(CO)Br]+, is nonemissive at room temperature, but has a long lived excited state that is localized on the 3(pi-pi*) state of the anthracene substituent. The other complex, [(bpy)2Os(bpy-AN)]2+, exhibits emission at room temperature and has a transient absorption spectrum that is consistent with a localized 3MLCT state. The excited state decay behavior of the two complexes can be fit well assuming a model in which noninteracting 3MLCT and 3(pi-pi*) states are in equilibrium.

Complementarity in bimolecular photochromism

Irradiating 2,3,6,7-tetraphenylanthracene in the presence of 9,10-dimethylanthracene leads to exclusive formation of the cross-dimer. No photochemical reaction is observed when either of these chromophores is irradiated in the absence of the other.

2,6-Bis[4-(p-dihexylaminostyryl)styryl]anthracene Derivatives with Large Two-Photon Cross Sections

[Structure: see text] Anthracene derivatives with a variety of donor-acceptor substituents have been synthesized and shown to exhibit large two-photon cross sections over a wide range of wavelengths.

[Fluorescent properties of 9-anthracenecarboxamides]

A number of new 9-anthracenecarboxamides are synthesized in order to create new fluorescent probes for studying biological systems. The parameters of their fluorescence in organic solvents of various polarities are investigated, and possible mechanisms of internal quenching of fluorescence of these compounds are discussed. One of the compounds, 4-ethoxycarbonylphenylamide of 9-anthracenecarboxylic acid, is shown to be a promising basis for the development of a new fluorescent probe. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2004, vol. 30, no. 6; see also http://www.maik.ru.

Fluorescent GTP-sensing in aqueous solution of physiological pH

A new water-soluble imidazolium anthracene derivative not only differentiates two structurally similar compounds GTP and ATP but also acts as potential fluorescent chemosensors (as a quencher and an enhancer, respectively) for GTP and ATP in 100% aqueous solution (pH = 7.4, 10 mM HEPES).

Synthesis and antitumor activity of 10-substituted benzylidene anthrone

Fifteen compounds of 10-substituted benzylidene anthrone were prepared with moderate yield by reaction of anthrone and substituted benzaldehydes under the presence of pyridine and piperidine as catalyst. Their antitumor activities in vitro were evaluated. The results show that the electron-withdrawing substitutes decrease the activities, the electron-donor substitutes increase the activities; the compound with substitute at ortho or para position has stronger activities than that of compound with the same substitute but located at the meta position. There are six compounds which appear as strong effective inhibition for A-549 cancer cell growth. This is a kind of good leading compound which is worth researching further.

Synthesis of a Polymer-Supported Anthracene and Its Application as a Dienophile Scavenger

A polymer-supported anthracene has been prepared and employed as a dienophile scavenger in Diels-Alder cycloadditions. [structure: see text]