Formation Of Supramolecular Aggregates Research Articles

Synthesis and Supramolecular Properties of a Novel Octaphosphonate Porphyrin

AbstractTwo complementary routes were developed for preparing novel octaphosphonate porphyrins. The use of protected/deprotected phosphonate‐substituted precursors in the rational synthesis gave an overall yield 16 %. A more streamlined synthetic path gave 21 % overall yield of the target molecule. Octaphosphonate porphyrin possesses promising properties in supramolecular aggregate formation with cyclam. Cofacial reversible self‐assembly of a meso‐substituted octaphosphonate porphyrin with cyclam yields micrometer‐long nanowires with a height of about 1–1.5 nm. The resulting wires were characterized by UV/Vis absorption, emission and atomic force microscopy and transmission electron microscopy.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

PH-Responsive and Thermoreversible Hydrogels of N-(2-hydroxyalkyl)-l-valine Amphiphiles

Gelation behavior of a series of low-molecular-weight-hydrogelators, N-(2-hydroxydodecyl)-L-amino acid, was studied in aqueous phosphate buffer (pH 12). The effect of head-group structure and chirality and hydrocarbon chain length on the gelation efficiency was investigated. Only N-(2-hydroxyalkyl)-L-valine (L-C(n)HVal, n = 10, 12, 14, and 16) derivatives were found to form gel in aqueous buffer at pH 12. The increase of the chain length of the hydrocarbon tail enhances the ability to gelate buffered water up to C14 chain length. The L-C16HVal amphiphile was found to have gelation ability lower than L-C14HVal. The gelation number, mechanical strength, thermal stability, and morphology of the supramolecular aggregates were studied. The effect of salt concentrations on the gelation was investigated. Addition of NaCl increased gelation number but decreased melting temperature of the hydrogels slightly. The morphology of the hydrogels was characterized by electron microscopy and small-angle X-ray diffraction techniques. Rheology measurements were performed to examine the mechanical strength of the hydrogels. Both hydrogen-bonding and hydrophobic interactions were shown to be the driving forces for supramolecular aggregate formation.

Spectroscopic study of the interaction of NiII-5-triethyl ammonium methyl salicylidene ortho-phenylendiiminate with native DNA

The interaction of native calf thymus DNA with the cationic Ni(II) complex of 5-triethyl ammonium methyl salicylidene ortho-phenylendiimine (NiL(2+)), in 1mM Tris-HCl aqueous solutions at neutral pH, has been monitored as a function of the metal complex-DNA molar ratio by UV absorption spectrophotometry, circular dichroism (CD) and fluorescence spectroscopy. The dramatic modification of the DNA CD spectrum, the appearance of a broad induced CD band in the range 350-400nm, the strong increase of the DNA melting temperature (T(m)) and the fluorescence quenching of ethidium bromide-DNA solutions, in the presence of increasing amounts of the NiL(2+) metal complex, support the existence of a tight intercalative interaction of NiL(2+) with DNA, analogous to that recently reported for both ZnL(2+) and CuL(2+). The intrinsic binding constant (K(b)) and the interaction stoichiometry (s), determined by UV spectrophotometric titration, are equal to 4.3x10(6)M(-1) and 1.0 base pair per metal complex, respectively. Interestingly, the value of K(b) is slightly higher and 10 times higher than that relative to the CuL(2+)-DNA and the ZnL(2+)-DNA systems, respectively. Speculations can be performed to rationalize the observed trend, on the basis of the electronic and geometrical structures of the three complexes of the same ligand. Analogously to what previously observed for CuL(2+), the shape of the CD of the NiL(2+)-DNA system at NiL(2+)-DNA molar ratios higher than 0.5 is indicative of the formation of supramolecular aggregates in solutions, as a possible consequence of the electrostatic interaction between the cationic complex and the negatively charged phosphate groups of DNA.

Effects of Anthraquinone Dye Aggregation on Selective Reflection Spectra of Cholesteric Liquid Crystal

The formation of supramolecular aggregates of anthraquinone dye N,N′-(4-methylphenyl)-1,4-diaminoanthraquinone (AQ) is shown to be clearly manifested in temperature-dependent selective reflection spectra of cholesteric solvents containing AQ as a non-mesogenic dopant. Using cholesteric matrices of different chemical nature (based on cholesterol esters or nematics with chiral dopants), one can distinguish between interactions of a solvent with individual AQ molecules and AQ aggregates, as well as between the aggregation and precipitation of AQ. The calculated relative birefringence data demonstrate the effects of AQ aggregates on the optical anisotropy and the orientational order in the systems under study.

Structural and Relaxometric Characterization of Peptide Aggregates Containing Gadolinium Complexes as Potential Selective Contrast Agents in MRI

The structural and relaxometric characterization of a novel class of supramolecular aggregates, as potential tumor-specific contrast agents in magnetic resonance imaging (MRI), is reported. The aggregates are based on a new monomer with an upsilon shape (MonY) that contains, in the same molecule, all three fundamental tasks that are required: 1) a hydrophobic moiety that allows the formation of supramolecular aggregates; 2) the bioactive CCK8 peptide for target recognition; and 3) a chelating agent able to give stable gadolinium complexes. As indicated by dynamic light scattering and small-angle neutron scattering (SANS) measurements, MonY and its gadolinium complex MonY(Gd) aggregate in aqueous solution to give ellipsoidal micelles with a ratio between the micellar axes of approximately 1.7 and an aggregation number N(agg) of approximately 30. There are no differences in the aggregation behavior of MonY and MonY(Gd), which indicates that the presence of metal ions, and therefore the reduction of the net charge, does not influence the aggregation behavior. When MonY or MonY(Gd) are blended with dioleoyl phosphatidylcholine (DOPC), the aggregation behavior is dictated by the tendency of DOPC to give liposomes. Only when the amount of MonY or MonY(Gd) is higher than 20 % is the coexistence of liposomes and micelles observed. The thickness d of the bilayer is estimated by SANS to be approximately 35-40 A, whereas cryogenic transmission electron microscopy images show that the diameter of the liposomes ranges from approximately 50 to 150 nm. Self-assembling micelles of MonY(Gd) present high relaxivity values (r(1p)=15.03 mM(-1) s(-1)) for each gadolinium complex in the aggregate. Liposomes containing MonY(Gd) inserted in the DOPC bilayer at a molar ratio of 20:80 present slightly lower relaxivity values (r(1p)=12.7 mM(-1) s(-1)), independently of their internal or external position in the liposome.

Ruthenium Complex Fragments as Constituents of Trinuclear Photoactive Supramolecular Assemblies Based on Hydrogen Bond Association

AbstractThe reaction of the octahedral complexes cis‐ or trans‐[Ru(C≡N‐tBu)4(CN)2], (Ru(CN)2), with the photochemically active [bis(bipyridyl)bibenzimidazole‐ruthenium(II)], (RubiH2), component via hydrogen bond association results in the formation of supramolecular aggregates with modified photophysical properties. The first structural characterization of a supramolecular adduct is reported, in which the N–H functions of the ruthenium bound bibenzimidazole ligand via hydrogen bonds serve as an interface directly toward a cyanide ligand acting as a bridge to another transition metal. In addition, the maximum stoichiometry of the supramolecular associates is estimated by NMR titration experiments and association constants of the hydrogen bonded adducts are determined by the decay of the emission intensity during the titration experiments.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

The interaction of native DNA with Zn(II) and Cu(II) complexes of 5-triethyl ammonium methyl salicylidene orto-phenylendiimine

The interaction of native calf thymus DNA with the Zn(II) and Cu(II) complexes of 5-triethyl ammonium methyl salicylidene orto-phenylendiimine (ZnL 2+ and CuL 2+), in 1 mM Tris–HCl aqueous solutions at neutral pH, has been monitored as a function of the metal complex-DNA molar ratio by UV absorption spectrophotometry, circular dichroism (CD) and fluorescence spectroscopy. The results support for an intercalative interaction of both ZnL 2+ and CuL 2+ with DNA, showing CuL 2+ an affinity of approximately 10 times higher than ZnL 2+. In particular, the values of the binding constant, determined by UV spectrophotometric titration, equal to 7.3 × 10 4 and 1.3 × 10 6 M −1, for ZnL 2+ and CuL 2+, respectively, indicate the occurrence of a marked interaction with a binding size of about 0.7 in base pairs. The temperature dependence of the absorbance at 258 nm suggests that both complexes strongly increase the DNA melting temperature (Tm) already at metal complex-DNA molar ratios equal to 0.1. As evidenced by the quenching of the fluorescence of ethidium bromide-DNA solutions in the presence of increasing amounts of metal complex, ZnL 2+ and CuL 2+ are able to displace the ethidium cation intercalated into DNA. A tight ZnL 2+–DNA and CuL 2+–DNA binding has been also proven by the appearance, in both metal complex-DNA solutions, of a broad induced CD band in the range 350–450 nm. In the case of the CuL 2+–DNA system, the shape of the CD spectrum, at high CuL 2+ content, is similar to that observed for ψ-DNA solutions. Such result allowed us to hypothesize that CuL 2+ induces the formation of supramolecular aggregates of DNA in aqueous solutions.

Mn(II) coordination architectures with mixed ligands of 3-(2-pyridyl)pyrazole and carboxylic acids bearing different secondary coordination donors and pendant skeletons

In our efforts to investigate the factors that affect the formation of coordination architectures, such as secondary coordination donors and pendant skeletons of the carboxylic acid ligands, as well as H-bonding and other weak interactions, two kinds of ligands: (a) 3-(2-pyridyl)pyrazole ( L 1 ) with a non-coordinated N atom as a H-bonding donor, a 2,2′-bipyridyl-like chelating ligand, and (b) four carboxylic ligands with different secondary coordination donors and/or pendant skeletons, 1,4-benzenedicarboxylic acid (H 2 L 2 ), 4-sulfobenzoic acid (H 2 L 3 ), quinoline-4-carboxylic acid (H L 4 ) and fumaric acid (H 2 L 5 ), have been selected to react with Mn(II) salts, and five new complexes, [Mn( L 1 ) 2(SO 4)] 2 ( 1), [Mn( L 1 ) 2( L 2 )] ∞ ( 2), [Mn( L 1 )(H L 3 ) 2] ∞ ( 3), Mn( L 1 ) 2( L 4 ) 2 ( 4), and [Mn( L 1 ) 2( L 5 )] ∞ ( 5), have been obtained and structurally characterized. The structural differences of 1– 5 can be attributed to the introduction of the different carboxylic acid ligands (H 2 L 2 , H 2 L 3 , H L 4 , and H 2 L 5 ) with different secondary coordination donors and pendant skeletons, respectively. This result also reveals that the typical H-bonding (i.e. N–H⋯O and O–H⋯O) and some other intra- or inter-molecular weak interactions, such as C–H⋯O weak H-bonding and π⋯π interactions, often play important roles in the formation of supramolecular aggregates, especially in the aspect of linking the multi-nuclear discrete subunits or low-dimensional entities into high-dimensional supramolecular networks.

Intermolecular hydroamination and hydroarylation reactions of alkenes in ionic liquids

Intermolecular hydroamination or hydroarylation reactions of norbornene and cyclohexadiene performed with catalytic amounts of Brönsted or Lewis acid in ionic liquids were found to provide higher selectivity and yields than those performed in classical organic solvents. The ionic liquid increases the acidity of the media and stabilizes ionic intermediates through the formation of supramolecular aggregates.

Twin Probes as a Novel Tool for the Detection of Single‐Nucleotide Polymorphisms

Single-nucleotide polymorphisms (SNPs) are the most common form of DNA sequence variation. There is a strong interest from both academy and industry to develop rapid, sensitive and cost effective methods for SNP detection. Here we report a novel structural concept for DNA detection based on fluorescence dequenching upon hybridization. The so-called "twin probe" consists of a central fluorene derivative as fluorophore to which two identical oligonucleotides are covalently attached. This probe architecture is applied in homogeneous hybridization assays with subsequent fluorescence spectroscopic analysis. The bioorganic hybrid structure is well suited for sequence specific DNA detection and even SNPs are identified with high efficiency. Additionally, the photophysical properties of the twin probe were investigated. The covalent attachment of two single stranded oligonucleotides leads to strong quenching of the central fluorescence dye induced by the nucleobases. The twin probe is characterized by supramolecular aggregate formation accompanied by red-shifted emission and broad fluorescence spectra.

Supramolecular complexes of spin-labelled cyclodextrins

EPR spectra of cyclodextrins labelled with TEMPO derivatives (SL-CDs) are sensitive to complexation with large guest molecules. We used SL-CDs to explore the behaviour of concentrated PEG/PPG solutions. The relationship between rotational correlation times and solvent viscosity showed significant deviations from the Debye-Stokes-Einstein equation, probably due to self-aggregation of alkylene glycols in concentrated solutions. The data fit the fractional Debye-Stokes-Einstein equation well. We have also studied complexation of SL-CDs with adamantane-functionalised DAB dendrimers. The strength of binding increases with dendrimer generation; formation of supramolecular aggregates at high concentrations was observed with the generation 3 dendrimer.

System Approach to Analysis of the Role of the Synthesis Components and Stability of the MCM-41 Mesostructured Silicate Material

The formation of a mesostructured silicate material of the MCM-41 type is studied. The influence of the replacement of components in a reaction medium is investigated experimentally. Analysis of the results obtained and the data available in the literature suggests that the process under investigation is based on the approximate stoichiometric supramolecular interaction between [Si4O4 + x (OH)9 − x ]−(1 + x) silicate polyanions and C16H33(CH3)3N+ cetyltrimethylammonium cations with the formation of supramolecular aggregates, which condense to a mesostructured organosilicate composite. A further evolution of the product involves hydrolysis of the inner surface and the polymerization of the inorganic component. It is demonstrated that the properties of the product are determined, to a large extent, by the components of the reaction medium, which control the relative reaction rates in the process. The inference is made that an alcohol-ammonia medium is the most optimum for alkaline synthesis. This medium provides good preparation of the initial components for the reaction and the high rate of hydrolysis of pore walls, minimizes the osmotic effects during hydrothermal treatment, and, eventually, favors the formation of a highly structured hydrothermally stable material.

Synthesis and optical properties of (a)chiral terpyridine–ruthenium complexes

Chiral terpyridine ligands have been synthesized and characterized. By applying Ru(III)/Ru(II) chemistry, symmetrical as well as asymmetrical bis-terpyridine ruthenium(II) complexes were obtained. These materials were fully characterized and their optical properties investigated. While the chiral metal complexes revealed no Cotton effect in good solvents such as chloroform, CD-measurements in dodecane showed an effect in both ligand and MLCT regions, suggesting chirality transfer from the lateral alkyl chains to the complex core. This behavior points to the formation of supramolecular aggregates in dodecane. Furthermore, the analogous achiral ligand and its corresponding ruthenium(II) complexes were prepared.

Two azurins with unusual redox and spectroscopic properties isolated from the Pseudomonas chlororaphis strains DSM 50083 T and DSM 50135

Two azurins (Az624 and Az626) were isolated from the soluble extract of two strains of Pseudomonas chlororaphis, DSM 50083 T and DSM 50135, respectively, grown under microaerobic conditions with nitrate as final electron acceptor. The azurins, purified to electrophoretic homogeneity in three chromatographic steps, exhibit several peculiar properties. They have high reduction potentials and lower p I than most azurins described in the literature. As previously observed for Pseudomonas aeruginosa azurin, their reduction potentials are pH-dependent, but the p K values of their oxidized forms are lower, which suggests that deeper structural changes are associated with the oxidation process of these novel azurins. A hitherto undescribed pH-dependence of the diffusion coefficient was observed in Az624, that could be caused either by conformational changes, or by the formation of supramolecular aggregates associated with a protonation process. Both azurins exhibit axial X-band electron paramagnetic resonance spectra in frozen solution showing a typical hyperfine with the copper nucleus ( I=3/2) and a well-resolved superhyperfine structure with two equivalent 14N nucleus ( I=1), which is not usually observed for azurins from other species.

Modeling of supramolecular ordering in mixtures: Structure, dynamics and properties

The results on modeling supramolecular ordering in molecular mixtures, selforganized by H-bonding and the unified description of their thermodynamic, dielectric, optic, and kinetic properties have been reviewed. The hierarchy of the models of supramolecular species mixtures in thermodynamics of non-ideal solutions has been analyzed. New models of polyvariable supramolecular species as regards structure and composition, taking into account the cooperativity on H-bonding, as well as the description of their structure, composition, electric (dipole moment) and optical (polarizability tensor) properties, are discussed. The interrelations between thermodynamic functions (Gibbs energy, enthalpy, entropy), dielectric (permittivity), optic (refractive index and its fluctuation derivatives, defining Rayleigh light scattering) and kinetic properties of mixtures and microscopic characteristics of supramolecular species are presented. The dynamic models for describing supramolecular reorganization, intermolecular transitions, and energy transfer during thermal molecular motion, as well as fluctuation and relaxation (acoustic, dielectric, optic) phenomena in liquids on the basis of thermodynamic models with internal variables of the different tensor dimension have been considered. Expressions for fluctuation and relaxation contributions for both equilibrium and kinetic properties of nonideal mixtures are obtained. Contributions to integral Rayleigh light scattering due to fluctuation of the scalar parameters have been established. The methods for obtaining both integral and differential parameters of aggregation have been developed. The applications as to individual liquids (alcohols, N-amides, etc.) as well to binary mixtures with directed attractional molecular forces like H-bonds and both negative (e.g. acetone-chloroform) and positive (e.g. hydrocarbon-alcohol, chloroform-alcohol, ketone-alcohol) deviations from ideal solution behaviour are presented. The data on the structure and thermodynamics (equilibrium constant, Gibbs energy, enthalpy, and entropy) of supramolecular aggregation due to H-bonding in liquids and mixtures were obtained. The supramolecular assemblies in molecular liquids, selforganized by H-bonding, consisting of tens Thus the different forms of supramolecular ordering, characterizing the multiformity of aggregates both to structure and composition, differently manifest the macroscopic properties of liquids and mixtures. It's clear from the data obtained, that in associated mixtures with their common parameters of the state there is formation of supramolecular aggregates, consisting of tens of molecules, due to attractional directed molecular interactions like H-bonding, here the distribution functions of the aggregates on the size are quite wide. This is the evidence on the long-range translational and orientational molecular correlations in mixtures containing labile supramolecular aggregates due to the selforganisation processes through H-bonding. These supramolecular aggregates of nanosizes play an important role in the physicochemical properties of liquid systems.

The effect of spermine on plasmid condensation and dye release observed by fluorescence correlation spectroscopy.

We demonstrate that fluorescence correlation spectroscopy (FCS) can be employed to follow the conformational changes of DNA molecules induced by the addition of a cationic condensing compound (spermine). In our experiments the plasmid pHbetaAPr-1-neo (10 kbp; contour length 3.4 microm) was labeled with propidium iodide (PrIo) and then titrated with spermine to induce its condensation. When spermine was applied at concentrations above 5 microM (spermine/DNAphosphate=0.375), the diffusion time of the labeled plasmid dropped from 15 ms down to 3 ms (its diffusion coefficient, D, increased from 1.0x10(-12) m2/s to 6.0x10(-12) m2/s). The application of spermine was also accompanied by decreasing count rate and particle number, reflecting the dye's dissociation. The data presented show that FCS may become a valuable tool in studying supramolecular aggregate formation, especially when association is followed by a change in the hydrodynamic size of the resulting complex.

Single crystals of an ionic anthracene aggregate with a triplet ground state

Crystalline supramolecular aggregates consisting of charged organic molecules, held together through metal-cluster-mediated Coulomb interactions, have attracted interest owing to their unusual structural, chemical and electronic properties. Aggregates containing metal cation clusters 'wrapped' by lipophilic molecular anions have, for example, been shown to be kinetically stable and soluble in nonpolar liquids such as saturated hydrocarbons. The formation of supramolecular aggregates can even be exploited to generate aromatic hydrocarbons that carry four negative charges and crystallize in the form of organic poly(metal cation) clusters or helical polymers. Here we report the anaerobic crystallization of an ionic organic aggregate--a contact ion septuple consisting of a fourfold negatively charged 'tripledecker' of three anthracene molecules bridged by four solvated potassium cations. Its electronic ground state is shown experimentally, using temperature-dependent electron paramagnetic resonance spectroscopy, to be a triplet. Although the spins in this biradical ionic solid are separated by a considerable distance, density functional theory calculations indicate that the triplet ground state is 84 kJ mol(-1) more stable than the first excited singlet state. We expect that the successful crystallization of the ionic solid we report here, and that of a covalent organic compound with a triplet ground state at room temperature, will stimulate further attempts to develop new triplet-ground-state materials for practical use.

Substituent-Dependent Formation of Supramolecular Aggregates of 6-Hydroxy-trans-3-hexenoic Acids in the Solid State

Substituent-Dependent Formation of Supramolecular Aggregates of 6-Hydroxy-trans-3-hexenoic Acids in the Solid State

Substituent-Dependent Formation of Supramolecular Aggregates of 6-Hydroxy-trans-3-hexenoic Acids in the Solid State

The substituted 6-hydroxy-trans-3-hexenoic acids 2-4 have been prepared by a template coupling reaction between (butadiene)zirconocene, W(CO)6, and cyclobutanone, cyclodecanone, or cyclododecanone, respectively, followed by hydrolytic/oxidative demetallation of the resulting metallacyclic zirconoxycarbene tungsten complexes. The hydroxyalkenoic acids 2-4 have been found to form two novel fundamental types of associated supramolecular structural arrays in the solid state through intermolecular hydrogen bonding, which have been characterized by X-ray diffraction analysis. The cyclobutanone-derived compound 2 exhibits an infinitely extending sheet-like structure, which is composed of symmetrically alternating interconnected 12- and 36-membered rings, each being constructed from the functional groups or frameworks of four individual molecules of 2. In contrast, the cyclodecanone-derived compound 3 adopts a ribbon-type structure composed of C2-symmetrically arranged symmetry-equivalent 15-membered rings, each containing the functionalities from three individual molecules of 2. On the basis of scanning force microscopy studies, the cyclododecanone-derived compound 4 would appear to have a similar structure in the solid state. The structural features of the molecular assemblies that are formed by intermolecular hydrogen bonding of compounds 2-4 in the solid state are selectively controlled by the size and favoured conformations of the spiro-anellated carbocyclic rings at C6 of the 6-hydroxy-trans-3-hexenoic acid carbon chain.

Synthesis, Mass Spectrometry, and Spectroscopic Properties of a Dinuclear Ruthenium Complex Comprising a 20 Å Long Fully Aromatic Bridging Ligand

The luminescent dinuclear ruthenium complex [(bpy)2Ru(bqpy)Ru(bpy)2]4+ (1) comprising the 20 Å long fully aromatic bridging ligand bqpy has been synthesized by successive reactions from suitable precursor complexes. Investigations in electrospray mass spectrometry and 1H NMR spectroscopy have indicated the formation of supramolecular aggregates by strong π-stacking of the large aromatic parts. Despite the extended aromatic character of the bqpy bridging ligand, electrochemical and spectroscopic studies of the dinuclear complex have shown that the complex is composed of four noninteracting parts: two Ru(bpy)32+-type units bridged by two bqpy-localized fragments similar to two fused phenazine moieties.