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Supramolecular Systems (supramolecular + system)
Selected AbstractsComplexes of 2,6-Disubstituted 1-Oxa-4-thia-3,5-diazine 4,4-Dioxides with Symmetric Triazines as Supramolecular Systems.CHEMINFORM, Issue 36 2005Preparation, Properties. No abstract is available for this article. [source] Processing Energy and Signals by Molecular and Supramolecular SystemsCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2008Vincenzo Balzani Prof. Abstract Any kind of device or machine requires a substrate, energy, and information signals. If we wish to operate at the nanometer scale, we must use molecules as substrates. Energy- and signal-processing at a molecular level relies on cause/effect relationships between the input supplied and the kind of process obtained. We have classified energy- and signal-processing at the molecular level according to the nature of the input (electronic, photonic, or chemical) and the nature of the obtained effect (electronic, photonic, or chemical process that follows). By coupling the three kinds of inputs with the three types of resulting processes, nine types of molecular-based processes (electronic, photonic, chemionic, electrophotonic, electrochemionic, photoelectronic, photochemionic, chemiophotonic, and chemioelectronic) can be identified. In this concept article, looking at molecular transformations in an unconventional way, we have tried to give a flavor of some of the new features that project the old science of chemistry towards novel achievements. [source] Ionic Hydrogen Bonds Controlling Two-Dimensional Supramolecular Systems at a Metal SurfaceCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2007Dietmar Payer Abstract Hydrogen-bond formation between ionic adsorbates on an Ag(111) surface under ultrahigh vacuum was studied by scanning tunneling microscopy/spectroscopy (STM/STS), X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and molecular dynamics calculations. The adsorbate, 1,3,5-benzenetricarboxylic acid (trimesic acid, TMA), self-assembles at low temperatures (250,300,K) into the known open honeycomb motif through neutral hydrogen bonds formed between carboxyl groups, whereas annealing at 420,K leads to a densely packed quartet structure consisting of flat-lying molecules with one deprotonated carboxyl group per molecule. The resulting charged carboxylate groups form intermolecular ionic hydrogen bonds with enhanced strength compared to the neutral hydrogen bonds; this represents an alternative supramolecular bonding motif in 2D supramolecular organization. [source] pH-Controllable Supramolecular SystemsCHEMISTRY - AN ASIAN JOURNAL, Issue 3 2009Ken Cham-Fai Leung Prof. Abstract Proton, all that matters! This Focus Review surveys representative examples of pH-controllable supramolecular systems with interesting features and state-of-the-art applications, which can lead to the construction of meaningful molecular machines for electronic and biological applications that can be controlled by simple perturbation with acid and base. This Focus Review surveys representative examples of pH-controllable supramolecular systems with interesting features and state-of-the-art applications such as 1),conformational changes within individual molecules; 2),folding/unfolding of polymers; 3),simultaneous binding of cations and anions; 4),logic function; 5),ON,OFF switchable colorimetric sensing; 6),translocation of macrocycle-in-rotaxane molecules; 7),large-scale movement within molecules; and 8),regulation of the substrate flow in nanocontainers. In particular, systems will be discussed that involve: pH-induced conformational changes of a resorcinarene cavitand and a bis(iron porphyrin) complex; pH control in assembly and disassembly of supramolecular systems stabilized with different major noncovalent interactions; pH-driven movements of interlocked molecules involving rotaxanes, molecular elevators, and molecular muscles; and, finally, multicomponent supramolecular systems immobilized on solid supports as pH-responsive nanovalves for the controlled release of specific substrates. Recent advances in the understanding of pH-controllable supramolecular systems have led to the construction of meaningful molecular machines for electronic and biological applications that are amenable to control by simple perturbation with acids and bases. [source] Fluorescence Regeneration as a Signaling Principle for Choline and Carnitine Binding: A Refined Supramolecular Sensor System Based on a Fluorescent Azoalkane,ADVANCED FUNCTIONAL MATERIALS, Issue 2 2006H. Bakirci Abstract The fluorescent azoalkane, 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO), forms inclusion complexes with p -sulfonatocalix[4]arene (CX4). The binding constants are on the order of 103,M,1 in water. The addition of CX4 to DBO solutions results in an efficient fluorescence quenching (up to 90,%). This supramolecular system can be used as a truly water-soluble sensor system to signal the binding of organic ammonium ions over a large pH range. Addition of choline and carnitine derivatives and tetraalkylammonium ions results in regeneration of this fluorescence, from which the binding constants (KC,=,103,105,M,1) are calculated by means of a competitive complexation model. Electrostatic effects are observed, namely, a more-than-one order of magnitude weaker binding of the carnitines in neutral solution. [source] Chemical ant colony algorithm with supramolecular coefficient and multivariate calibration to calix[n]arenas(n,=,4, 6, 8) supramolecular systemJOURNAL OF CHEMOMETRICS, Issue 6 2008Yaping Ding Abstract A chemical ant colony algorithm (CACA) with supramolecular coefficient , was put forward. It has successfully solved the multivariate calibration issue of the supramolecule analysis system, and realized the pure spectra fitting and the simultaneous determination of the calix[n]arenas(n,=,4, 6, 8) in a multicomponent supramolecular system. The analyzing errors for calix[4, 6, 8]arenas through Chemical Ant Colony Algorithm with supramolecular coefficient , are within ±3.75%. The errors by CACA are within ±7.50%. The former obviously excels the latter. Copyright © 2008 John Wiley & Sons, Ltd. [source] Order-disorder transitions in self-assembled polymers: A positron annihilation studyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2009Ramasubbu Ramani Abstract We report here the first results of order-disorder transition (ODT) in a self-assembled comb-like polymer-amphiphile supramolecular system as identified from the change in positron lifetime parameters. We have used poly(4-vinyl pyridine) hydrogen bonded with 3-pentadecyl phenol, which upon heating showed a stepwise reduction in o -Ps intensity at the ODT from lamellar self-assembled state to the disordered state. The ODT temperature was confirmed by differential scanning calorimetry and small angle X-ray scattering. The free volume "holes" in this polymer-amphiphile system are proposed to be near the chain ends of the polymer backbones. We suggest that positron lifetime spectroscopy can serve as a technique to identify ODTs in self-assembled lamellar structured supramolecular systems. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Di-,-chlorido-bis[chlorido(4,- p -tolyl-2,2,:6,,2,,-terpyridine-,3N,N,,N,,)nickel(II)]: a supramolecular system constructed by C,H...Cl interactionsACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2009Ying-Lin Chen The title complex, [Ni2Cl4(C22H17N3)2], was synthesized solvothermally. The molecule is a centrosymmetric dimer with the unique NiII centre in a distorted octahedral N3Cl3 coordination environment. The chloride bridges are highly asymmetric. In the 4,- p -tolyl-2,2,:6,,2,,-terpyridine ligand, the p -tolyl group is perfectly coplanar with the attached pyridine ring, and this differs from the situation found in previously reported compounds; however, there are no ,,, interactions between the ligands. The terminal Cl atom forms four intermolecular C,H...Cl hydrogen bonds with one methyl and three methine groups. The methyl group also forms intermolecular C,H..., interactions with a pyridine ring. These nonclassical hydrogen bonds extend the molecule into a three-dimensional network. [source] Allosteric Tuning of the Intra-Cavity Binding Properties of a Calix[6]arene through External Binding to a ZnII Center Coordinated to Amino Side ChainsCHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2007Ulrich Darbost Dr. Abstract Molecular recognition by calix[6]arene-based receptors bearing three primary alkylamino side chain arms (1) is described. Complexation of ZnII ion provides the dinuclear ,-hydroxo complex , XRD characterization of which, together with solution studies, provided evidence of its hosting of neutral polar organic guests G. Treatment of this complex with a carboxylic acid or a sulfonamide (XH) results in the formation of mononuclear species , one of which (X = Cl) has been characterized by XRD. A dicationic complex is obtained upon treatment of with a mixture of an alkylamine and a strong acid. Each of these ZnII complexes features a tetrahedral metal ion bound to the three amino arms of ligand 1 and to an exogenous ligand (either HO,, X,, or RNH2) sitting outside of the cavity. As a result, the metal ion structures the calixarene core, constraining it in a cone conformation suitable for guest hosting. The receptor properties of these compounds have been explored in detail and are compared with those of the trisammonium receptor , based on the same calixarene core, as well as those of the trisimidazole-based dicationic Zn funnel complexes. This study reveals very different host properties, in spite of the common hydrophobic, ,-basic, and hydrogen-bonding acceptor properties of the calixarene cores. A harder external ligand produces a less polarized receptor that is consequently particularly sensitive to the hydrogen-bonding ability of its guest. The less electron-rich the apical ligand, and a fortiori the trisammonium host, the more sensitive the receptor to the dipole moment of the guest. All this stands in contrast with the funnel Zn complexes, in which the coordination link plays a dominant role. It is also shown that the asymmetry of an exo -coordinated enantiopure amino ligand is sensed by the guest. This supramolecular system nicely illustrates how the receptor properties of a hydrophobic cavity can be allosterically tuned by the environment. [source] Thiourea Based Tweezer Anion Receptors for Selective Sensing of Fluoride IonsCHINESE JOURNAL OF CHEMISTRY, Issue 5 2007You-Ming Zhang Abstract Three 3,3,-di(4-substituted-phenyl)-1,1,-isophthaloylbis(thiourea) compounds were designed as novel neutral anion receptors, and synthesized by simple steps in good yields. The single crystal structure of receptor 1 shows that a solvent molecule was captured by the host molecule through intermolecular hydrogen bonding. Moreover, it was self-assembled as a supramolecular system for the presence of abundant inter- and intramolecular hydrogen bonding and ,-, interactions between phenyl groups. Their application as anion receptors has been examined by UV-Vis and 1H NMR spectroscopy, showing that they had a higher selectivity for fluoride than other halides. The host and guest formed a 1:1 stoichiometry complex through hydrogen bonding interactions in the first step, then following a process of deprotonation in presence of an excess of F, in the solvent of DMF. [source] Photoswitches: From Molecules to MaterialsADVANCED MATERIALS, Issue 31 2010Maria-Melanie Russew Abstract Small organic molecules, capable of undergoing efficient and reversible photochemical reactions to switch them between (at least) two (meta)stable isomers associated with markedly different properties, continue to impact the materials world. Such photoswitches are being implemented in a variety of materials for applications ranging from optical devices to "smart" polymers. All approaches exploit the photoswitching molecular entities as gates, which translate an incoming light stimulus to trigger macroscopic property changes of the materials. In this progress report, the most promising recent examples in this field are highlighted and put in perspective. Moving from supramolecular systems in solution to surfaces and finally to bulk materials, important design concepts are discussed, emphasizing both the challenges as well as the great promise of such truly advanced materials. [source] Cumulative ,-, interaction triggers unusually high stabilization of linear hydrocarbons inside the single-walled carbon nanotubeINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 12 2007T. C. Dinadayalane Abstract The interactions of linear hydrocarbons C2nH4 and C2nH2 (n = 1,4) with a finite-length armchair (5,5) single-walled carbon nanotube have been investigated using HF and MP2 methods in conjunction with 6-31G(d) basis set, and molecular mechanics (MM) with MM2 force field. In all cases, the results obtained at MP2/6-31G(d) level show stabilization of these supramolecular systems, contrary to the repulsive interactions obtained with the HF method. The interaction energies computed using MM with MM2 force field are in close agreement with the results obtained using the MP2/6-31G(d) level. They increase gradually as the length of linear hydrocarbon chain increases. The present study indicates that cumulative ,-, interaction is the origin for the exceptionally high stabilization of the long nanotube-hydrocarbon complexes. Mulliken population analysis reveals a very small charge transfer between the nanotube and the guest. Essentially there is no change in HOMO-LUMO energy gap by the insertion of linear hydrocarbons. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Application of standard DFT theory for nonbonded interactions in soft matter: Prototype study of poly- para -phenyleneJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 2 2006Marcelo Alves-Santos Abstract We present a detailed analysis of the application of density functional theory (DFT) methods to the study of structural properties of molecular and supramolecular systems, using as a paradigmatic example three para -phenylene-based systems: isolated biphenyl, single chain poly- para -phenylene, and crystalline biphenyl. We use different functionals for the exchange correlation potential, the local density (LDA), and generalized gradient approximations (GGA), and also different basis sets expansions, localized, plane waves (PW), and mixed (localized plus PW), within the reciprocal space formulation for the hamiltonian. We find that regardless of the choice of basis functions, the GGA calculations yield larger interring distances and torsion angles than LDA. For the same XC approximation, the agreement between calculations with different basis functions lies within 1% (LDA) or 0.5% (GGA) for distances, and while PW and mixed basis calculations agree within 1° for torsion angles, the localized basis results show larger angles by , 8° and a nonmonotonic dependence on basis size, with differences within 6°. The most prominent features, namely the torsion between rings for isolated molecule and infinite chain, and planarity for the molecule in crystalline environment, are well reproduced by all DFT calculations. © 2005 Wiley Periodicals, Inc. J Comput Chem 27: 217,227, 2006 [source] Advanced solid-state nuclear magnetic resonance for polymer scienceJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2004Hans Wolfgang Spiess Abstract Today, solid-state nuclear magnetic resonance (NMR) is one of the most powerful and versatile tools for elucidating the structures and dynamics of molecular, macromolecular, and supramolecular systems. It provides information on molecular and collective phenomena over large length scales and timescales and is particularly suited to handle noncrystalline materials. This report describes how developments in solid-state NMR were triggered by the possibilities that became available about 30 years ago by neutron scattering and synchrotron radiation. Close analogies between NMR spectroscopy and scattering are pointed out to emphasize that the two approaches nicely complement each other. Specific examples applying the new NMR techniques to amorphous polymers and supramolecular systems are described. The findings are related to the mechanical properties of polymers as well as specific functions such as photoconductivity and proton conductivity. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5031,5044, 2004 [source] NMR-based analysis of structure of heteroleptic triple-decker (phthalocyaninato) (porphyrinato) lanthanides in solutionsMAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2010Kirill P. Birin Abstract A novel approach for the structural analysis of heteroleptic triple-decker (porphyrinato)(phthalocyaninato) lanthanides(III) in solutions is developed. The developed approach consists in molecular mechanics (MM+) optimization of the geometry of the complex taking into account the lanthanide-induced shift (LIS) datasets. LISs of the resonance peaks in 1H NMR spectra of a series of symmetric complexes [An4P]Ln[(15C5)4Pc]Ln[An4P], where An4P2, is 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrinato-dianion, [(15C5)4Pc]2, is 2,3,9,10,16,17,24,25-tetrakis(15-crown-5)phthalocyaninato-dianion and Ln = La, Ce, Pr, Nd, Sm, Eu, are analyzed. Analysis of LISs showed two sets of protons in the molecule with opposite signs of shift. Two-nuclei analysis of LISs testifies isostructurality of the whole series of investigated complexes in solution despite contraction of the lanthanide ions. Model-free separation of contact and dipolar contributions of LISs was performed with one-nucleus technique and did not show changes in contact and dipolar terms within the investigated series. MM+ optimization of the molecular structure allowed the interpretation of features of LIS for each particular group of protons. Parameterization of MM + -optimized model of molecule with values of structure-dependent dipolar contributions of LIS allows the development of the precise structural model of the triple-decker complex in solution. This approach allows the determination of the geometry and structure of the sandwich macrocyclic tetrapyrrolic complexes together with conformational analysis of flexible peripheral substituents in solutions. The developed method can be applied with minor modifications for the determination of structural parameters of other types of lanthanides(III) complexes with tetrapyrrolic ligands and also supramolecular systems based on them. Copyright © 2010 John Wiley & Sons, Ltd. [source] Synthesis and Preferred All- syn Conformation of C3 -Symmetrical N -(Hetero)arylmethyl TriindolesCHEMISTRY - A EUROPEAN JOURNAL, Issue 28 2008Abstract A new series of C3 -symmetrical N -(hetero)arylmethyl triindoles has been synthesized in a straightforward procedure. The structure and conformation in the solid state have been determined for three derivatives (3, 4, and 6) by X-ray crystallographic analysis. In all three cases, the molecules adopt a tripodal conformation with all of the flexible arms directed towards the same side, thereby delimiting an inner cavity. Compound 6 crystallizes and forms C3 -symmetric dimeric cagelike complexes. Guest molecules of chloroform and water are confined within the resulting cavities with stabilization by different intermolecular interactions; this highlights the potential of these compounds in the construction of supramolecular systems. A computational analysis has been performed to predict the most stable conformers. As a general trend, a preference for a conformation with all branches directed to the same side has been predicted. Comparison between theoretical and experimental results indicates that the computational level selected for the present study, B3LYP/6-31G*, is able to reproduce both the minimum energy conformations and the rotation barriers about the NCH2 bond. [source] Self-Assembled Ionophores from Isoguanosine: Diffusion NMR Spectroscopy Clarifies Cation's and Anion's Influence on Supramolecular StructureCHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2007Tamar Evan-Salem Abstract Cation-templated self-assembly of the lipophilic isoguanosine (isoG,1) with different monovalent cations (M+=Li+, Na+, K+, NH4+, and Cs+) was studied in solvents of different polarity by using diffusion NMR spectroscopy. Previous studies that did not use diffusion NMR techniques concluded that isoG,1 forms both pentamers (isoG,1)5,M+ and decamers (isoG,1)10,M+ in the presence of alkali-metal cations. The present diffusion NMR studies demonstrate, however, that isoG,1 does not form (isoG,1)5,M+ pentamers. In fact, the diffusion NMR data indicates that both doubly charged decamers of formula (isoG,1)10,2,M+ and singly charged decamers, (isoG,1)10,M+, are formed with lithium, sodium, potassium, and ammonium tetraphenylborate salts (LiB(Ph)4, KB(Ph)4, NaB(Ph)4 and NH4B(Ph)4), depending on the isoG,1:salt stoichiometry of the solution. In the presence of CsB(Ph)4, isoG,1 affords only the singly charged decamers (isoG,1)10,Cs+. By monitoring the diffusion coefficient of the B(Ph)4, ion in the different mixtures of solvents, we also concluded that the anion is more strongly associated to the doubly charged decamers (isoG,1)10,2,M+ than to the singly charged decamers (isoG,1)10,M+. The (isoG,1)10,2,M+ species can, however, exist in solution without the mediation of the anion. This last conclusion was supported by the finding that the doubly charged decamers (isoG,1)10,2,M+ also prevail in 1:1 CD3CN:CDCl3, a solvent mixture in which the B(Ph)4, ion does not interact significantly with the self-assembled complex. These diffusion measurements, which have provided new and improved structural information about these decameric isoG,1 assemblies, demonstrate the utility of combining diffusion NMR techniques with conventional NMR methods in seeking to characterize labile, multicomponent, supramolecular systems in solution, especially those with high symmetry. [source] Triple Hydrogen Bonds Direct Crystal Engineering of Metal-Assembled Complexes: The Effect of a Novel Organic,Inorganic Module on Supramolecular StructureCHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2005Keiichi Adachi Dr. Abstract Novel triply hydrogen bonded suprastructures based on [M(tdpd)2(L)2]2, (H2tdpd=1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarbonitrile, L=solvent) and melamine-analogous cations have been synthesized and characterized. The use of anions containing two AAA sets from [M(tdpd)2(L)2]2, together with cations containing one DDD set (A=hydrogen-bond acceptor, D=hydrogen-bond donor) leads to the formation of complementary triply hydrogen bonded modules in the solid state. In all cases, the building module is further extended via additional hydrogen-bonding interactions to produce a tape, and tapes are assembled into sheets. These results show that a hydrogen-bonded module consisting of different kinds of building blocks, one of which is a metal complex that includes hydrogen-bond acceptor sites and the other is a hydrogen-bond donor molecule, will be attractive for constructing metal-containing supramolecular systems by the self-assembly technique. [source] Direct Assignment of Enantiofacial Discrimination on Single Heterocyclic Substrates by Self-induced CDCHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2005Carsten Siering Abstract The first direct assignment of highly dynamic enantiofacial discrimination acting on a single heterocyclic substrate has been achieved by a combination of experimental and theoretical CD spectroscopy. The interaction of chirally modified hosts based on triphenylene ketals with appropriate prochiral guests can lead to the preferential formation of one diastereomeric host,guest complex. This reversible stereoselective binding transmits the chiral information from remote chiral groups in the host to the strongly absorbing triphenylene chromophore, which gives rise to self-induced CD. This effect was exploited for the determination of the enantiofacial recognition in various host,guest systems. Inversion of the steric demand either of the chiral substituents at the host or of the prochiral guest leads to almost complete inversion of the resulting CD spectra. For the assignment of the absolute stereochemistry of the complexes, a combined molecular dynamics/quantum-chemical approach was successfully employed. Despite the size and the highly dynamic character of the supramolecular systems, fundamental properties of the systems and details of the spectra were simulated accurately, providing access to fast and reliable assignment of the enantiofacial preference. The results are highly consistent with available X-ray data. [source] Supramolecular Photomagnetic Materials: Photoinduced Dimerization of Ferrocene-Based Polychlorotriphenylmethyl RadicalsCHEMISTRY - A EUROPEAN JOURNAL, Issue 3 2004Imma Ratera Abstract New ferrocenyl Schiff-base polychlorotriphenylmethyl radicals have been synthesized and characterized. The imino group of one such radical undergoes an irreversible trans to cis structural isomerization induced by light. Such photoinduced isomerization has been monitored by UV/Vis and ESR spectroscopy and also monitored by HPLC. ESR frozen solution experiments at low temperature revealed that the cis isomer dimerizes, showing a strong antiferromagnetic interaction. Although numerous photochromic supramolecular systems have been described, such a photoinduced self-assembly process represents the first example of a one-way photoswitchable magnetic system in which a conversion between a doublet and a singlet ground state species is promoted by a photoinduced dimerization process driven by the formation of hydrogen bonds. DFT calculations on the minimized structure and on the rotational barriers have been performed to establish the origin of such behavior. The effect of the substituents and the media polarity on the photoisomerization of this imine chromophore have also been studied. It has been observed that the efficiency of the process is markedly dependent on the presence and characteristics of electron-donor and electron-acceptor substituents of the ferrocenyl Schiff-base polychlorotriphenylmethyl radicals as well as on the polarity of the solvent. Han estat sintetitzats i caracteritzats nous radicals policlorotrifenilmetílics connectats a una unitat de ferrocè mitjançant una base de Schiff. El grup imino d,un d,aquests radicals experimenta una isomerització estructural irreversible de trans a cis mitjançant la llum. Aquesta isomerització fotoinduïda ha estat seguida amb les tècniques d, UV/Vis, espectroscòpia de RPE així com també mitjançant cromatografia d, HPLC. L,espectre de RPE d,una solució congelada revel.la que L,isòmer cis dimeritza mostrant una forta interacció antiferromagnètica entre monòmers. Malgrat els nombrosos sistemes supramoleculars fotocròmics que han estat descrits fins ara, aquest procés d,autoassemblatge fotoinduït representa el primer exemple d,interruptor magnètic fotoinduït d,un sol sentit en el qual té lloc una conversió de doblet a singlet de L,espècie en estat fonamental promoguda per un procés d,autoassemblatge mitjançant la formació d,enllaços d,hidrogen. S,han realitzat càlculs de DFT de les estructures minimitzades i de les barreres rotacionals per tal de poder establir L,origen d,aquest comportament. També s,ha estudiat L,efecte dels substituents i de la polaritat del medi en la fotoisomerizació d,aquests cromòfors d,imina. S,ha observat que L,eficiència del procés té una dependència molt marcada amb la presència de substituents electro donadors així com també amb la polaritat del dissolvent. [source] pH-Controllable Supramolecular SystemsCHEMISTRY - AN ASIAN JOURNAL, Issue 3 2009Ken Cham-Fai Leung Prof. Abstract Proton, all that matters! This Focus Review surveys representative examples of pH-controllable supramolecular systems with interesting features and state-of-the-art applications, which can lead to the construction of meaningful molecular machines for electronic and biological applications that can be controlled by simple perturbation with acid and base. This Focus Review surveys representative examples of pH-controllable supramolecular systems with interesting features and state-of-the-art applications such as 1),conformational changes within individual molecules; 2),folding/unfolding of polymers; 3),simultaneous binding of cations and anions; 4),logic function; 5),ON,OFF switchable colorimetric sensing; 6),translocation of macrocycle-in-rotaxane molecules; 7),large-scale movement within molecules; and 8),regulation of the substrate flow in nanocontainers. In particular, systems will be discussed that involve: pH-induced conformational changes of a resorcinarene cavitand and a bis(iron porphyrin) complex; pH control in assembly and disassembly of supramolecular systems stabilized with different major noncovalent interactions; pH-driven movements of interlocked molecules involving rotaxanes, molecular elevators, and molecular muscles; and, finally, multicomponent supramolecular systems immobilized on solid supports as pH-responsive nanovalves for the controlled release of specific substrates. Recent advances in the understanding of pH-controllable supramolecular systems have led to the construction of meaningful molecular machines for electronic and biological applications that are amenable to control by simple perturbation with acids and bases. [source] Chiral Induction, Memory, and Amplification in Porphyrin Homoaggregates Based on Electrostatic InteractionsCHEMPHYSCHEM, Issue 6 2009LiXi Zeng Dr. Abstract Supramolecular chirality in two configurational homoaggregates of anionic meso -tetrakis(4-sulfonatophenyl)porphyrin (TPPS) can be induced by D - and L -alanine in acidic water (see picture). The chirality can be further memorized and enforced through strong electrostatic interactions between TPPS aggregates and achiral poly(allylamine) [PAA]. Supramolecular chirality in two configurational homoaggregates of anionic meso -tetrakis(4-sulfonatophenyl)porphyrin (TPPS) can be induced by D - and L -alanine (Ala) in acidic water, respectively. The induced supramolecular chirality can be further memorized and enforced, even after complete removal of Ala or in the presence of excess Ala with the opposite configuration, through strong electrostatic interactions with achiral poly(allylamine) [PAA]. The ionic chiral interactions between TPPS and Ala or PAA are characterized by means of UV/Vis absorption and circular dichroism spectrometry. Fluorescence spectroscopy and atomic force microscopy are used as complementary techniques. On the basis of the comprehensive experimental results, a possible mechanism for chiral induction, memory, and amplification of TPPS homoaggregates by chiral amino acids and achiral PAA is proposed. Thus, we demonstrate a novel strategy to realize chiral memory in supramolecular systems by polyelectrolytes through hierarchical electrostatic self-assembly. [source] Photo-ionization spectroscopy and mass spectrometry of some molecular and supramolecular asymmetric systems in the isolated stateCHIRALITY, Issue 7 2006Anna Giardini Abstract Asymmetric molecular and supramolecular systems are characterized by: i. the circular dicroism in the angular distribution of valence photoelectrons emitted from randomly oriented chiral molecules by their interaction with circularly polarized VUV light; ii. the different stability and reactivity of diastereomeric aggregates. Both these aspects may have some relationship with the "chiral enrichment mechanism" of chirogenesis, based on the preferential destruction of one enantiomer of a racemate by interaction with a chiral agent, whether a massive species or a circularly polarized photon. The most recent spectroscopic and mass spectrometric studies on this topic are reported in the present mini-review. Chirality 18:562,568, 2006. © 2006 Wiley-Liss, Inc. [source] | ||||||||||||||||||||||||||||