C3-symmetrical self-assembled structures investigated by vibrational circular dichroism

We demonstrate by using vibrational circular dichroism (VCD) spectroscopy that it is possible to investigate the chirality of a supramolecular polymeric system in relatively dilute solutions. Chiral C(3)-symmetrical discotic molecules, based on a trialkylbenzene-1,3,5-carboxamide, form supramolecular columnar stacks with a right-handed helical structure in solution due to intermolecular hydrogen bonds. The handedness of the supramolecular chirality is determined using electronic spectroscopy measurements. Under dilute conditions (at 10(-3) M concentrations), it was also possible to probe the hydrogen bonding moieties with IR and VCD spectroscopy on these self-assembled structures. In combination with density functional theory (DFT) calculations, we could verify the preference for a right-handed chirality in the helical stacks and the nonplanar orientation of the carbonyl groups present in the molecule. This chiral arrangement is in agreement with the structure determined for a related benzene-1,3,5-tricarboxamide by X-ray diffraction. Chirality, 2008. (c) 2008 Wiley-Liss, Inc.     

Supramolecular platinum complexes for cancer therapy

The rise of supramolecular chemistry offers new tools to design therapeutics and delivery platforms for biomedical applications. This review aims to highlight the recent developments that harness host-guest interactions and self-assembly to design novel supramolecular Pt complexes as anticancer agents and drug delivery systems. These complexes range from small host-guest structures to large metallosupramolecules and nanoparticles. These supramolecular complexes integrate the biological properties of Pt compounds and novel supramolecular structures, which inspires new designs of anticancer approaches that overcome problems in conventional Pt drugs. Based on the differences in Pt cores and supramolecular structures, this review focuses on five different types of supramolecular Pt complexes, and they include host-guest complexes of the FDA-approved Pt(II) drugs, supramolecular complexes of nonclassical Pt(II) metallodrugs, supramolecular complexes of fatty acid-like Pt(IV) prodrugs, self-assembled nanotherapeutics of Pt(IV) prodrugs, and self-assembled Pt-based metallosupramolecules.     

New Pd(II) and Pt(II) complexes with N,S-chelated pyrazolonate ligands: molecular and supramolecular structure and preliminary study of their in vitro antitumoral activity

New Pd(II) and Pt(II) complexes [ML2] (HL=a substituted 2,5-dihydro-5-oxo-1H-pyrazolone-1-carbothioamide) have been synthesized by reacting K2MCl4 (M=Pd, Pt) or Pd(OAc)2 with beta-ketoester thiosemicarbazones. The structures of seven of these complexes were determined by X-ray diffraction. Although all exhibit a distorted square-planar coordination with trans- or (in one case) cis-[MN2S2] kernels, their supramolecular arrangements vary widely from isolated molecules to 3D-networks. The in vitro antitumoral assays performed with two HL ligands and their metal complexes showed significant cytostatic activity for the latter, with the most active [ML2] derivative (a palladium complex) being about sixteen times more active than cis-DDP against the cisplatinum-resistant cell line A2780cisR.     

Synthesis and structural characterization of three hydrogen-bonding connected supramolecular complexes of nickel, zinc and copper with 1,3-diphenyl-4-(salicylidene hydrazide)-acetyl-pyrazolone-5 and 2,2′-bipyridine

A new set of supramolecular complexes, [Ni(DPAP-SHZ)(2,2′-bipy)CH₃OH] (1), [Zn(DPAP-SHZ)(2,2′-bipy)CH₃OH] (2) and [Cu(DPAP-SHZ)(2,2′-bipy)] · 2CH₂Cl₂ (3) (DPAP-SHZ = 1,3-diphenyl-4-(salicylidene hydrazide)-acetyl-pyrazolone-5, 2,2′-bipy = 2,2′-bipyridine) have been synthesized and characterized by elemental analysis, TG-DTA, IR spectroscopy and X-ray crystallography. The X-ray diffraction analyses of the complexes show that the Ni(II) ion and Zn(II) ion centers are six-coordinated while the Cu(II) ion center is five-coordinated. The three supramolecular complexes contain the same ligands, namely DPAP-SHZ and 2,2′-bipy. However, their hydrogen bonds are significantly different, and this variation apparently is responsible for the dissimilar structures of the three supramolecular complexes.     

Copper(II) and cadmium(II) complexes of 2-pyridinyl-4-pyridinylmethanone: Supramolecular architectures consolidated by hydrogen bonding and π-π interaction

2-Pyridinyl-4-pyridinylmethanone (L) has been shown to behave as a monodentate ligand via its 4-pyridyl ring in three new metal(II) complexes, all of which exhibit supramolecular architectures assembled through weak interactions including hydrogen bonding and π-π stacking. Effects of the inorganic anions on the structure of the Cd(II) complexes of L are also discussed.     

Spermine-DNA complexes build up metastable structures. Small-angle X-ray scattering and circular dichroism studies.

Spermine-DNA complexes have been examined by small-angle and wide-angle X-ray scattering as well as by circular dichroism studies. Condensed complexes are building up below a critical ionic strength. We have found that at one and the same ionic strength condensed complexes having two different supramolecular structures (Type I and Type II) can coexist. The structure of the condensates depends on the method of condensate formation. Phase transitions between these structures can be induced by thermal treatment. We conclude from these facts that with polyamine-DNA condensates metastable structures are of importance.     

Coordination chemistry of di-2-pyridylamine-based bridging heterocyclic ligands: A structural study of coordination polymers and discrete dinuclear complexes

Four new bridging ligands containing two di-2-pyridylamine subunits have been synthesised. The coordination chemistry of these, along with one previously reported ligand, has been investigated through reactions with various silver(I), copper(II) and palladium(II) reactants. Typically, reaction of these ligands with silver(I) salts gave 1-D coordination polymers, within which the ligands act as divergent bridging units, while reaction with copper(II) and palladium(II) precursors provided discrete dinuclear complexes with chelating bidentate subunits. The complexes were characterised by a combination of elemental analysis, NMR spectroscopy and X-ray crystallography. The silver coordination polymers displayed interesting variations in supramolecular architecture, attributed to weak secondary interactions, such as Ag?π-bonding.     

A systematic study of ligand intermolecular interactions in crystals of copper(II) complexes of bidentate guanidino derivatives

The synthesis and X-ray structures of copper(II) complexes of the bidentate ligands, N-(4-oxo-5,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-N′-phenylguanidino, 2-uanidinobenzimidazolo and N-(4-oxo-3-phenyl-1,3-diazaspiro[4.4]non-1-en-2-yl)guanidino, are reported. These complexes, which possess potential doublet (DA) or triplet (DAD) hydrogen bonding motifs, can form supramolecular structures based on synthons involving hydrogen bonding or phenyl embraces. The changes in supramolecular structure resulting from small changes in ligand structure, as well as from the use of different solvents for their crystallisation, are examined. The structures adopted are compared with others reported previously for complexes of related ligands.     

Preparation and characterization of two supramolecular complexes with 5-amino-2,4,6-triiodoisophthalic acid under N-donor auxiliary ligand intervention

Assemblies of 5-amino-2,4,6-triiodoisophthalic acid (H₂ATIBDC) with Cd(II) and Zn(II) in the presence of N-donor auxiliary ligand, 1,4-bis(1,2,4-triazol-1-yl)butane (btb), at ambient conditions yield two new supramolecular complexes, [Cd(ATIBDC)(btb)(H₂O)₂]·3H₂O (1), and [Zn(ATIBDC)(btb)]·2H₂O (2). Generally, these two complexes display 1D ATIBDC²⁻-bridged coordination arrays. Distinct extended 3D network architectures are further constructed with the help of weak secondary interactions especially aromatic stacking, halogen bonding, and hydrogen bonding as supramolecular driving forces. It is worthy to mention that halogen bonds (C-I?π and C-I?N/O) play important roles in the supramolecular assembly. The pentameric cluster (H₂O)₅ in 1 assembles into highly ordered helical infinite chains. Complex 2 exhibits the fascinating single-walled tube-like chain structure. It loses crystallinity rapidly in the air and leads to the formation of [Zn(ATIBDC)(btb)]·H₂O (2A). Thermal stabilities and solid state fluorescent properties of complexes 1 and 2A have been studied.     

Platinum(II) complexes with 2-acetyl pyridine thiosemicarbazone. Synthesis, crystal structure, spectral properties, antimicrobial and antitumour activity

An interesting series of new platinum complexes has been synthesized by the reaction of Na(2)PtCl(4) with 2-acetyl pyridine thiosemicarbazone, HAcTsc. The new complexes, [Pt(AcTsc)Cl], [Pt(HAcTsc)(2)]Cl(2) and [Pt(AcTsc)(2)], have been characterized by elemental analyses and spectroscopic studies. The crystal structure of the complex [Pt(AcTsc)Cl] has been solved by single-crystal X-ray diffraction. The anion of HAcTsc coordinates in a planar conformation to the central platinum(II) through the pyridyl N, azomethine N and thiolato S atoms. Double intermolecular hydrogen bonds (NH-Cl), pi-pi and weak Pt-Pt and Pt-pi contacts lead to aggregation and to a two-dimensional supramolecular assembly. The antibacterial and antifungal effect of the novel platinum(II) complexes and the related palladium(II) complexes, [Pd(AcTsc)Cl], [Pd(HAcTsc)(2)]Cl(2) and [Pd(AcTsc)(2)], were studied in vitro. The complexes were found to have a completely lethal effect on Gram+ bacteria, while the same complexes showed no bactericidal effect on Gram- bacteria. Additionally, the complexes [Pt(AcTsc)(2)] and [Pd(AcTsc)(2)] showed effective antifungal activity towards yeast. Among these compounds [33], the most effective in inducing antitumour and cytogenetic effects are the complexes [Pt(AcTsc)(2)] and [Pd(AcTsc)(2)] while the rest, display marginal cytogenetic and antitumour effects.     

Experimental and theoretical study on the 1:1 supramolecular complexes of formamide with adrenaline

The electron transfer properties were investigated for supramolecular complexes of formamide (FA) with adrenaline (Ad) at graphite electrode and paraffine soaked graphite electrode using cyclic voltammetry (CV). The experimental results show that FA affected the electron transfer properties of Ad. The formed supramolecular complexes by hydrogen bond (H-bond) interaction between FA and Ad slowed down the diffusion ability of adrenaline, which makes it hard to donate electron and be oxidized. The H-bond interaction energies calculation for the supramolecular complexes of FA with Ad at MP2/6-311+G(d,p)//B3LYP/6-311+G(d,p) level have also been performed. The calculational results confirm the experimental fact that FA can form stable supramolecular complexes with Ad.     

Using Lewis acidity differences in chelating ligands to control molecular structure and supramolecular assembly of Cu(II) complexes

The electronic effects of the fluorine atoms in hfacac (hexafluoroacetylacetonato) compared with acac (acetylacetonato) in Cu(II) complexes are used to control the molecular and supramolecular structure of Cu(II) compounds. While bis(acac)Cu(II) (acac = acetylacetonato) is known to be able to have a fifth-position coordination, bis(hfacac)Cu(II), (hfacac = hexafluoroacetylacetonato) may have two extra ligands. This, together with the reliable “supramolecular reagent” isonicotinamide, as the additional ligand, are used to go from a zero-dimension structure, with Cu-acac, to an extended supramolecular two-dimension network, with Cu-hfacac. The molecular and crystal structure of bis(acetylacetonato-O,O′)-(isonicotinamide-N) copper(II), 1, and bis(hexafluoroacetylacetonato-O,O′)-trans-bis(isonicotinamide-N) copper(II), 2, are reported.     

Recognition promoted by Zn2+ between phenanthroline bridging polyaza ligands and nucleotides--Zn2+ acts as 'messenger' between the receptor and substrate

The stability constants of the supramolecular complexes formed between L ((a,b,c,d)) or their Zn(2+) complexes, and adenosine 5'-triphosphate (ATP) in aqueous solution were determined by potentiometric titrations (25 degrees C, I = 0.1 mol dm(-3) KNO(3)). The results show that protonated aliphatic-substituted L (a,d) and aromatic-substituted L (b,c) ligands and/or Zn(II) ion can efficiently recognition the substrate, ATP. All of the equilibrium studies, (1)H and (31)P nuclear magnetic resonance spectra indicate that multiple interactions, including coordination, pi-stacking, ion-pairing, H-bonding, and possible ion-pi-donor, hydrophobic and even van der Waals interactions exist in the Zn(II)-L-ATP systems. On the other hand, the recognition of the substrates by the protonated ligands was significantly promoted by the addition of Zn(II), which leads to coordination competition between the mixed ligands, L and nucleotide. In Zn(II)/L/ATP systems the tendency for phosphate chain to receive proton and metal ion increases, facilitating the cleavage of the phosphate chain of the nucleotide.     

The conjugates of uracil-cyclen Zn(II) complexes: synthesis, characterization, and their interaction with plasmid DNA

As an important nucleobase in RNA, uracil was introduced into the side chain of cyclen (1,4,7,10-tetraazacyclododecane) by using phenylene dimethylene group as bridge. The target compounds 5 were obtained in high yields. Subsequent experiments demonstrated that the uracil-cyclen conjugates can bind Zn(2+) cation rapidly in water, and the catalytic activities of their Zn(II) complexes 6 in DNA cleavage were also studied. The results showed that Zn(II) complexes can catalyze the cleavage of supercoiled DNA (pUC 19 plasmid DNA) (Form I) to produce nicked DNA (Form II and Form III) with high selectivity. In water solution, complex 6b may form a unique and stable supramolecular structure, which benefits the DNA cleavage process.     

冷冻透射电镜:从分子到系统

单颗粒电镜结合其他方法能够在(近)原子水平提供结构模型,已经成为一种研究大蛋白复合物的有效方法。该文将以两个大的蛋白裂解复合物——tripeptidyl peptidaseII(6MDa)和26S蛋白酶体(2.5MDa)举例说明。低温电子层析能进行非重复的超分子结构分析,如多核糖体和全细胞;能够为超分子组织提供前所未有的信息(可视化蛋白质组学)。     

The role of chlorophyll-protein complexes in the function and structure of chloroplast thylakoids

Summary The photosynthetic pigments of chloroplast thylakoid membranes are complexed with specific intrinsic polypeptides which are included in three supramolecular complexes, photosystem I complex, photosystem II complex and the light-harvesting complex. There is a marked lateral heterogeneity in the distribution of these complexes along the membrane with photosystem II complex and its associated light-harvesting complex being located mainly in the stacked membranes of the grana partitions, while photosystem I complex is found mainly in unstacked thylakoids together with ATP synthetase. In contrast, the intermediate electron transport complex, the cylochrome b-f complex, is rather uniformly distributed in these two membrane regions. The consequences of this lateral heterogeneity in the location of the thylakoid complexes are considered in relation to the function and structure of chloroplasts of higher plants.     

Supramolecular complexes of polyethylene glycol-alpha-Chymotrypsin covalent and noncovalent adducts with polyoxyethylene-modified cyclo dextrins

Complexes of covalent and noncovalent adducts of polyethylene glycol (PEG) and alpha-chymotrypsin (ChT), PEG-ChT, were generated in the presence of beta-cyclodextrin derivatives of polyoxyethylene (beta CD-PEO), and their thermal stability was studied. The covalent [PEG-ChT]c conjugates were obtained by chemical modification of the protein amino groups with the monoaldehyde derivatives of monomethoxypolyethylene glycol. The noncovalent [PEG-ChT]n complexes were obtained by the treatment of ChT-PEG mixtures with increasing pressure (1.1-400 MPa). Supramolecular structures resulting from complex formation between PEG chains of the PEG-ChT adducts (PEGad) and beta CD-PEO were studied. The decrease in the rate constant of the slow stage of ChT thermal inactivation in PEG-ChT adducts (k2) can serve as confirmation of complex formation between beta CD-PEO and PEGad. The stoichiometric composition of our supramolecular structures was determined from the k2 dependence on the molar ratio of beta CD-PEO to PEGad. It was shown that each polymeric chain in the [PEG-ChT]c conjugates forms an inclusion complex with beta CD-PEO, whereas only half of the PEGad polymeric chains participate in the formation of supramolecular structures in the case of [PEG-ChT]n complexes. Although covalent and noncovalent PEG-ChT adducts of the same composition significantly differ in their thermal stability, the maximal values of the k2 rate constants for [PEG-ChT]c and [PEG-ChT]n adducts in the triple system attainable at the (beta CD-PEO) to (PEGad) ratio corresponding to the stoichiometry of the resulting ternary systems are practically the same (k2 = 0.007 c-1 at 45 degrees C in 0.02 M Tris-HCl buffer solution, pH 8.0). Structures for the supramolecular dendrite-like ensembles formed upon the interaction of covalent and noncovalent PEG-ChT adducts with beta CD-PEO were suggested.     

Syntheses, characterization and antimicrobial activity of the first complexes of Zn(II), Cd(II) and Co(II) with N-benzyloxycarbonylglycine: X-ray crystal structure of the polymeric Cd(II) complex

For the first time, complexes of Zn(II), Cd(II) and Co(II) (1-3) with N-benzyloxycarbonylglycine have been synthesized and characterized. The complexes adopt tetrahedral, pentagonal-bipyramidal and octahedral geometry, respectively. The structure of the polymeric cadmium complex was resolved by single crystal X-ray analysis. The cadmium ion has a distorted pentagonal-bipyramidal coordination formed by two water molecules and two N-benzyloxycarbonylglycinato ligands (N-Boc) coordinated in different fashions, one as bidentate and the second connecting three cadmium atoms. In a rather complicated 2D supramolecular structure, the phenyl rings interact mutually exclusively by the CH?π interactions.Investigation of the antimicrobial activity of the obtained complexes and N-benzyloxycarbonylglycine revealed that the ligand does not inhibit the growth of Candida albicans, whereas the newly synthesized complexes suppress the growth of this human fungal pathogen.     

A new tripodal poly-imine indole-containing ligand: Synthesis, complexation, spectroscopic and theoretical studies

A novel flexible tripodal ligand derived from 3-methylindole, (“InTREN” L), and its mononuclear Zn(II), Cu(II), Ni(II), Hg(II) and Pd(II) complexes are described. All compounds gave analytically pure solid samples. Characterisation of the compounds was accomplished by ¹H NMR, IR and absorption spectroscopies, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and elemental analysis and their geometry optimized using density functional theory (DFT).Time-dependent-density functional theory (TD-DFT) calculations have been used to assign the lowest energy absorption bands of the free ligand and the Zn(II) complex. The system is a very good candidate for in situ recognition/coordination effects by MALDI-TOF-MS spectrometry and absorption spectroscopy. The presence of three indole groups in InTREN opens up the possibility to synthesize new three-dimensional self-assembly supramolecular structures.