ADVANCED FUNCTIONAL MATERIALS, Issue 2 2009
Dimas G. de Oteyza
Abstract Self-assembly of functional supra-molecular nanostructures is among the most promising strategies for further development of organic electronics. However, a poor control of the interactions driving the assembling phenomena still hampers the tailored growth of designed structures. Here exploration of how non-covalent molecule-substrate interactions can be modified on a molecular level is described. For that, mixtures of DIP and F16CuPc, two molecules with donor and acceptor character, respectively are investigated. A detailed study of their structural and electronic properties is performed. In reference to the associated single-component layers, the growth of binary layers results in films with strongly enhanced intermolecular interactions and consequently reduced molecule-substrate interactions. This new insight into the interplay among the aforementioned interactions provides a novel strategy to balance the critical interactions in the assembly processes by the appropriate choice of molecular species in binary supra-molecular assemblies, and thereby control the self-assembly of functional organic nanostructures. [source]

Intermolecular , -dimer of oxoverdazyl radicals with long-distance multicenter (2e/8c) bonding via nitrogen atoms

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2010
Sergiy V. Rosokha
Abstract The 1,5-dimethyl-6-oxoverdazyl radical's solid-state structure shows distinct , -dimeric units with close interplanar separations (3.10,Å) between the head-over-tail cofacial moieties and several interatomic contacts shorter than the sums of the van der Waals radii. Evaluations of the frontier orbitals of monomeric oxoverdazyl and its , -dimer reveal that interaction of the radical SOMOs (concentrated on the nitrogen atoms) leads to the formation of the supramolecular orbital involving four equivalent bonding (N,N) segments between two oxoverdazyl moieties. As such, this , -dimer represents a rare example of nitrogen-based multicenter (2e/8c) long-distance bonding and emphasizes the universal character of this phenomenon in organic (ion-) radical systems. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Ruthenium-catalyzed carbonylative cycloaddition reactions involving carbonyl and imino groups as assembling units

THE CHEMICAL RECORD, Issue 4 2008
Naoto Chatani
Abstract This paper describes carbonylative cycloaddition reactions catalyzed by Ru3(CO)12. Ru3(CO)12 was found to catalyze an intramolecular Pauson,Khand-type reaction. Carbonylative cycloaddition reactions involving a carbonyl group in aldehydes, ketones, and esters as a two-atom assembling unit were also achieved in the presence of Ru3(CO)12 as the catalyst. The reaction of 5-hexyn-1-al and 6-heptyn-1-al derivatives with CO in the presence of Ru3(CO)12 resulted in cyclocarbonylation from which bicyclic ,, ,-unsaturated lactones were obtained. Intermolecular [2,+,2,+,1] carbonylative cycloaddition of alkenes, ketones, and CO was also catalyzed by Ru3(CO)12 as the catalyst to give saturated ,-lactone derivatives. Simple ketones were not applicable, but ketones having a CO or CN group at the ,-position served as a good substrate. These reactions could be extended to carbonylative cycloaddition of the corresponding imines leading to ,-butyrolactam derivatives. The [4,+,1] carbonylative addition of ,,,-unsaturated imines leading to unsaturated ,-lactams was achieved with Ru3(CO)12. © 2008 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 8: 201,212; 2008: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.20149 [source]

Intermolecular ,-stacking and F...F interactions of fluorine-substituted meso -alkynylporphyrin

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2010
Yuta Marushima
Two C2-symmetric meso -alkynylporphyrins, namely 5,15-bis[(4-butyl-2,3,5,6-tetrafluorophenyl)ethynyl]-10,20-dipropylporphyrin, C50H42F8N4, (I), and 5,15-bis[(4-butylphenyl)ethynyl]-10,20-dipropylporphyrin, C50H50N4, (II), show remarkable ,,, stacking that forms columns of porphyrin centers. The tetrafluorophenylene moieties in (I) show intermolecular interactions with each other through the F atoms, forming one-dimensional ribbons. No significant ,,, interactions are observed in the plane of the phenylene and tetrafluorophenylene moieties in either (I) or (II). The molecules of both compounds lie about inversion centers. [source]

(1,3-Dimethylimidazolidine-2-selone-,Se)bis(1,10-phenanthroline-,2N,N,)copper(II) bis(perchlorate) and bis(2,2,-bipyridyl-,2N,N,)(imidazolidine-2-thione-,S)copper(II) bis(perchlorate)

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2007
Alexander J. Blake
In the first title salt, [Cu(C12H8N2)2(C5H10N2Se)](ClO4)2, the CuII centre occupies a distorted trigonal,bipyramidal environment defined by four N donors from two 1,10-phenanthroline (phen) ligands and by the Se donor of a 1,3-dimethylimidazolidine-2-selone ligand, with the equatorial plane defined by the Se and by two N donors from different phen ligands and the axial sites occupied by the two remaining N donors, one from each phen ligand. The Cu,N distances span the range 1.980,(10),2.114,(11),Å and the Cu,Se distance is 2.491,(3),Å. Intermolecular ,,, contacts between imidazolidine rings and the central rings of phen ligands generate chains of cations. In the second salt, [Cu(C10H8N2)2(C3H6N2S)](ClO4)2, the CuII centre occupies a similar distorted trigonal,bipyramidal environment comprising four N donors from two 2,2,-bipyridyl (bipy) ligands and an S donor from an imidazolidine-2-thione ligand. The equatorial plane is defined by the S donor and two N donors from different bipy ligands. The Cu,N distances span the range 1.984,(6),2.069,(7),Å and the Cu,S distance is 2.366,(3),Å. Intermolecular ,,, contacts between imidazolidine and pyridyl rings form chains of cations. A major difference between the two structures is due to the presence in the second complex of two N,H...O hydrogen bonds linking the imidazolidine N,H hydrogen-bond donors to perchlorate O-atom acceptors. [source]

The Holy Grail of Organocatalysis: Intermolecular ,-Alkylation of Aldehydes

CHEMCATCHEM, Issue 4 2009
Andrea-Nekane Alba
This is the cup of a chemist: Organocatalytic intermolecular ,-alkylation has been accomplished. The groups of Melchiorre and Cozzi have recently reported the realization of this long-time goal in organocatalysis, by the crucial use of stabilized carbocations. Alkylated products are obtained in good yields and with moderate to good enantioselectivities. [source]

ChemInform Abstract: Gold-Catalyzed Intermolecular [4C + 3C] Cycloaddition Reactions.

CHEMINFORM, Issue 31 2010
Benjamin W. Gung
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

ChemInform Abstract: Synthesis of Isoxazole Conjugates of 1,4-Benzodioxane Moiety via Intermolecular 1,3-Dipolar Cycloaddition.

CHEMINFORM, Issue 14 2010
Vipraja V. Vaidya
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

ChemInform Abstract: Crossed Intermolecular [2 + 2] Cycloadditions of Acyclic Enones via Visible Light Photocatalysis.

CHEMINFORM, Issue 9 2010
Juana Du
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

ChemInform Abstract: Regioselective Rhodium-Catalyzed Intermolecular [2 + 2 + 2] Cycloaddition of Alkynes and Isocyanates to Form Pyridones.

CHEMINFORM, Issue 44 2009
Kevin M. Oberg
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

ChemInform Abstract: Lewis Acid-Catalyzed Intermolecular [4 + 2] Cycloaddition of 3-Alkoxycyclobutanones to Aldehydes and Ketones.

CHEMINFORM, Issue 2 2009
Jun-ichi Matsuo
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

ChemInform Abstract: Enantioselective Synthesis of Spirocyclic Benzopyranones by Rhodium-Catalyzed Intermolecular [4 + 2] Annulation.

CHEMINFORM, Issue 47 2008
Daiki Hojo
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Intermolecular 1,5-Dipolar Cycloaddition Reaction of Tungsten-Containing Vinylazomethine Ylides Leading to Seven-Membered Heterocycles.

CHEMINFORM, Issue 28 2006
Hiroyuki Kusama
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]

Rhodium-Catalyzed Regio- and Enantioselective Intermolecular [4 + 2] Carbocyclization of 4-Alkynals with N,N-Dialkyl Acrylamides.

CHEMINFORM, Issue 10 2006
Ken Tanaka
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]

Stille Reactions Catalytic in Tin: A "Sn,F" Route for Intermolecular and Intramolecular Couplings.

CHEMINFORM, Issue 25 2005
William P. Gallagher
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

Stereoselective Synthesis of Cycloheptanone Derivatives via an Intermolecular [5 + 2] Cycloaddition Reaction.

CHEMINFORM, Issue 44 2002
Keiji Tanino
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

ChemInform Abstract: Photochemistry of Benzotriazole: An Unprecedented Tautomer-Selective Intermolecular [2 + 2] Photocycloaddition.

CHEMINFORM, Issue 37 2002
Kevin I. Booker-Milburn
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Palladium-Catalyzed Cyclopropanation of Alkenyl Silanes by Diazoalkanes: Evidence for a Pd0 Mechanism

CHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2009
Guillaume Berthon-Gelloz Dr.
Abstract Pd0does the trick! Alkenyl silanes are efficiently cyclopropanated by diazoalkanes at low Pd loadings (see scheme). Clear evidence for the involvement of a Pd0 resting state for this reaction is given. Alkenyl silanes are efficiently converted to the corresponding silyl cyclopropanes in the presence of a slight excess of diazomethane (2,4,equiv) and a low loading of Pd(OAc)2 (<0.5,mol,%). Diazoethane and diazobutane can also be employed and yield silyl cyclopropanes with diastereoselectivities of up to 10:1 for the trans isomer. When conducted on a 4,g scale, the reaction only required a catalyst loading of 5×10,3,mol,%, which corresponds to a turnover frequency of 40,000,h,1. Competition experiments revealed that vinyl silanes can be selectively cyclopropanated in the presence of an aliphatic terminal alkene and styrene. The complex [Pd02(DVTMS)3] (38, DVTMS=divinyltetramethyldisiloxane) proved to be an exceptionally active catalyst for the cyclopropanation reaction, giving complete conversion at ,35,°C in 1,min. Intermolecular and intramolecular competition experiments with DVTMS (36), both with Pd(OAc)2 and 38, provided strong evidence for a Pd0(alkenyl silane)3 resting state. Detailed density functional calculations on the reaction pathways for the cyclopropanation of trimethylvinylsilane and DVTMS by diazomethane with Pd0 corroborated the experimental observations. [source]

Carbohydrate-derived alkylcobalt carbonyl: {[(1,2:5,6-Di-O,O-isopropylidene-,-D-glucofuranos-3-yl)oxycarbonyl]methyl}cobalt tricarbonyl triphenylphosphine

CHIRALITY, Issue 8 2001
Claudia Zucchi
Abstract A carbohydrate-derivative alkylcobalt carbonyl, {[(1,2:5,6-di-O,O-isopropylidene-,-D-glucofuranos-3-yl)oxycarbonyl]methyl}cobalt tricarbonyl triphenylphosphine (3) was prepared and characterized by IR, NMR, and CD spectra, as well as by X-ray diffraction. The supramolecular chemistry in the crystalline P212121 (chiral) phase and in solution was analyzed and compared. The bulky carbohydrate-based ligand stabilized one chiral conformation, which, however, is less ordered than for analogous compounds with more flexible and less bulky chiral groups. Intermolecular, H-bond interactions are more important in the P212121 phase of complex 3 than at other analogous compounds. Chirality 13:458,464, 2001. © 2001 Wiley-Liss, Inc. [source]

Glycobiology: The sweet language of life, complexity, and morphogenesis: Syntax for Intermolecular and Intercellular Communication

COMPLEXITY, Issue 6 2007
Lokesh Joshi
No abstract is available for this article. [source]

The embedded ion method: A new approach to the electrostatic description of crystal lattice effects in chemical shielding calculations

CONCEPTS IN MAGNETIC RESONANCE, Issue 5 2006
Dirk Stueber
Abstract The nuclear magnetic shielding anisotropy of NMR active nuclei is highly sensitive to the nuclear electronic environment. Hence, measurements of the nuclear magnetic shielding anisotropy represent a powerful tool in the elucidation of molecular structure for a wide variety of materials. Quantum mechanical ab initio nuclear magnetic shielding calculations effectively complement the experimental NMR data by revealing additional structural information. The accuracy and capacity of these calculations has been improved considerably in recent years. However, the inherent problem of the limitation in the size of the systems that may be studied due to the relatively demanding computational requirements largely remains. Accordingly, ab initio shielding calculations have been performed predominantly on isolated molecules, neglecting the molecular environment. This approach is sufficient for neutral nonpolar systems, but leads to serious errors in the shielding calculations on polar and ionic systems. Conducting ab initio shielding calculations on clusters of molecules (i.e., including the nearest neighbor interactions) has improved the accuracy of the calculations in many cases. Other methods of simulating crystal lattice effects in shielding calculations that have been developed include the electrostatic representation of the crystal lattice using point charge arrays, full ab initio methods, ab initio methods under periodic boundary conditions, and hybrid ab initio/molecular dynamics methods. The embedded ion method (EIM) discussed here follows the electrostatic approach. The method mimics the intermolecular and interionic interactions experienced by a subject molecule or cluster in a given crystal in quantum mechanical shielding calculations with a large finite, periodic, and self-consistent array of point charges. The point charge arrays in the EIM are generated using the Ewald summation method and embed the molecule or ion of interest for which the ab initio shielding calculations are performed. The accuracy with which the EIM reproduces experimental nuclear magnetic shift tensor principal values, the sensitivity of the EIM to the parameters defining the point charge arrays, as well as the strengths and limitations of the EIM in comparison with other methods that include crystal lattice effects in chemical shielding calculations, are presented. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A 28A: 347,368, 2006 [source]

Dinuclear Iridium(III) Complexes Linked by a Bis(,-diketonato) Bridging Ligand: Energy Convergence versus Aggregation-Induced Emission

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2010
Chang Hwan Shin
Abstract Novel iridium(III)/iridium(III) and iridium(III)/platinum(II) dinuclear complexes, [{Ir(ppyFF)2}2(,2 - L)] (4) and [{Ir(ppyFF)2}(,2 - L){Pt(ppy)}] (5) [ppyFF = 2-(2,4-difluorophenyl)pyridine, ppy = 2-phenylpyridine, L = 1,3-bis(3-phenyl-3-oxopropanoyl)benzene], linked by an L bridging ligand were prepared, and their photophysical properties were investigated in solution and in the solid state. The photophysical properties of mononuclear iridium(III) and platinum(II) complexes, [Ir(ppyFF)2(dbm)] (1) and [Pt(ppy)(dbm)] (2) bearing a dibenzoylmethane (dbm) ligand were also compared. Whereas the UV/Vis absorption spectra of 4 and 5 show independent light absorption at each metal-centered moiety, the photoluminescence spectra of 4 and 5 display almost identical features, but very weak emissions in solution at both room temperature and 77 K. The weak emission in solution is found to mainly originate from a 3LX state of the L bridging ligand, which reflects the occurrence of efficient energy convergence from the triplet states of the Pt(ppy) and Ir(ppyFF) moieties to the 3LX state of L. By contrast, intense orange-red emission, that is, aggregation-induced emission, is produced in the solid state of 4 and 5. Inspection of the crystal-packing structures of 5 reveals that strong intermolecular ,,, interactions between the adjacent pyridine rings of ppyFF ligands in the Ir-centered moieties are responsible for the emissive metal-to-ligand,ligand charge-transfer [3M(LL)CT] state of the solid-state dinuclear systems. The electrochemical properties of 4 and 5 further indicate that the first two reductions occur at the dbm moieties of the L bridging ligand linked to each metal center, which is consistent with the fact that the lowest-energy excited state of the L bridging ligand dominates the excited-state properties of 4 and 5 in solution. [source]

Synthesis, Structural, Thermal and Magnetic Characterization of a Pyrophosphato-Bridged Cobalt(II) Complex

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2008
Oluwatayo F. Ikotun
Abstract The reaction in water of CoII sulfate heptahydrate with 1,10-phenanthroline (phen) and sodium pyrophosphate (Na4P2O7) in a 2:4:1 stoichiometric ratio resulted in the crystallization of a neutral dinuclear CoII complex, {[Co(phen)2]2(,-P2O7)}·6MeOH (1), as revealed by a single-crystal X-ray diffraction study. The bridging pyrophosphato ligand between the two [Co(phen)2]2+ units in a bis(bidentate) coordination mode places the adjacent metal centers at 4.857 Å distance, and its conformation gives rise to intramolecular ,,, stacking interaction between adjacent phen ligands. Indeed, intermolecular ,,, stacking interactions between phen ligands from adjacent dinuclear complexes create a supramolecular 2D network in 1. Magnetic susceptibility measurements on a polycrystalline sample of 1 in the temperature range 1.9,295 K are typical of an overall antiferromagnetic coupling with a maximum of the magnetic susceptibility at 3.0 K. The analysis of the magnetic data in the whole temperature range allows the determination of the value of the intramolecular magnetic coupling (J = ,1.23 cm,1). The ability of the pyrophosphato ligand to mediate magnetic interactions between different first-row transition-metal ions when adopting the bis(bidentate) bridging mode is analyzed and discussed in the light of the small number of magneto-structural reports on this type of compound, bearing in mind the number of unpaired electrons and type of magnetic orbitals on each metal center. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

Non-Covalent Aggregation of Discrete Metallo-Supramolecular Helicates into Higher Assemblies by Aromatic Pathways: Structural and Chemical Studies of New Aniline-Based Neutral Metal(II) Dihelicates

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2005
Miguel Vázquez
Abstract Neutral manganese(II), iron(II), cobalt(II), nickel(II), zinc(II) and cadmium(II) complexes with an N -tosyl-substituted N4 -donor Schiff base containing a 4,4'-methylenedianiline residue as spacer [H2La: N,N' -bis(2-tosylaminobenzylidene)-4,4'-methylenedianiline], and the zinc(II) complex with an analogous ligand [H2Lb: N,N' -bis(2-tosylaminobenzylidene)-4,4'-oxodianiline] have been prepared by an electrochemical procedure. FAB and ESI mass spectra of the complexes show peaks due to species corresponding to a general formula [M2(La,b)2 + H]+, thereby suggesting their dinuclear nature. A detailed study of the crystal packing in the unit cell of the zinc(II) complex with H2La shows that the helicates aggregate to form discrete prismatic moieties containing three molecules held together by ,,, and ,,, interactions. Moreover, the ZnII neutral dihelicate with H2Lb forms a 3D network in the solid state due to intermolecular ,-stacking interactions. 1H NMR studies of the diamagnetic compounds reported herein have been performed. Finally, the ligand H2La and its ZnII and CdII complexes have been studied by spectrophotometric and spectrofluorimetric techniques in order to get a better understanding of the formation mechanisms of the complexes and of the nature of their fluorescence emission. Emission studies show that the ZnII and CdII dihelicates with H2La display a green fluorescence in acetonitrile solution (, = 473 nm, , = 0.03 and , = 476 nm, , = 0.01, respectively). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Synthesis and Physicochemical Characterization of Bis(macrocycles) Involving a Porphyrin and a meso -Substituted Corrole , X-ray Crystal Structure of a [(Free-base porphyrin),corrole]bis(pyridine)cobalt Complex

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 6 2005
Jean-Michel Barbe
Abstract A very efficient, simple synthesis of face-to-face porphyrin,corrole free-bases bearing substituents at the meso positions of the corrole ring is reported. Starting from the (porphyrin,aldehyde)zinc species 1Zn, porphyrin,corrole free-bases (3M, 3C) are obtained in two steps, in fairly good yields (40,43,%), compared to 11 steps for their corrole ,-pyrrole-substituted counterparts. Moreover, the possibility to directly synthesize the free-base (porphyrin,corrole)cobalt complex (5M or 5C) allows for the further preparation of heterodimetallic derivatives. Crystals of the bis(pyridine) adduct of 5M have been grown; the molecular structure clearly shows that the two pyridine molecules are coordinated to the cobalt ion in endo and exo positions, leading to an open-mouth geometry of the bis(macrocycle). The structure of 5M(py)2also shows intermolecular ,,, interactions along the [1,0,0] direction, leading to stacking of the complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Stable Non-Covalent Large Area Patterning of Inert Teflon-AF Surface: A New Approach to Multiscale Cell Guidance,

ADVANCED ENGINEERING MATERIALS, Issue 6 2010
Francesco Valle
Micro- and nano-patterning of cell adhesion proteins is demonstrated to direct the growth of neural cells, viz. human neuroblastoma SHSY5Y, at precise positions on a strongly antifouling substrate of technolological interest. We adopt a soft-lithographic approach with oxygen plasma modified PDMS stamps to pattern human laminin on Teflon-AF films. These patterns are based on the interplay of capillary forces within the stamp and non-covalent intermolecular and surface interactions. Remarkably, they remain stable for several days upon cell culture conditions. The fabrication of substrates with adjacent antifouling and adhesion-promoting regions allows us to reach absolute spatial control in the positioning of neuroblastoma cells on the Teflon-AF films. This patterning approach of a technologically-relevant substrate can be of interest in tissue engineering and biosensing. [source]

Sequence-Selective Peptide Recognition with Designed Modules

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 1 2006
Mark Wehner
Abstract A concept for the rational design of sequence-selective peptide receptors has been extended: in addition to recognition modules for polar, aromatic and basic amino acids, the series has now been completed with new receptor units for apolar and acidic amino acids. The underlying strategy uses the intermolecular ,-sheet stabilization of a dipeptide as a prerequisite to bind its N-terminal amino acid side chain through a strategically placed recognition tip at the end of a U-turn protruding from the receptor moiety. Thus, a diaminopyrazole has been covalently attached to Kemp's triacid by way of a cyclic imide, while a meta -substituted aniline was coupled as an amide to the pendant third carboxylate arm, bringing the two aromatic units into a sub-van der Waals distance in a tight conformational lock. NMR titrations, Karplus analyses and Monte-Carlo simulations demonstrate the effective sequence-selective recognition of alanine-containing dipeptides. No example of such a rationally designed set of peptide receptors had existed previously. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Transgalactosylation by thermostable ,-glycosidases from Pyrococcus furiosus and Sulfolobus solfataricus

FEBS JOURNAL, Issue 16 2000
-glycosides during lactose conversion, Binding interactions of nucleophiles with the galactosylated enzyme intermediate make major contributions to the formation of new
The hyperthermostable ,-glycosidases from the Archaea Sulfolobus solfataricus (Ss,Gly) and Pyrococcus furiosus (CelB) hydrolyse ,-glycosides of d -glucose or d -galactose with relaxed specificities pertaining to the nature of the leaving group and the glycosidic linkage. To determine how specificity is manifested under conditions of kinetically controlled transgalactosylation, the major transfer products formed during the hydrolysis of lactose by these enzymes have been identified, and their appearance and degradation have been determined in dependence of the degree of substrate conversion. CelB and Ss,Gly show a marked preference for making new ,(1,3) and ,(1,6) glycosidic bonds by intermolecular as well as intramolecular transfer reactions. The intramolecular galactosyl transfer of CelB, relative to glycosidic-bond cleavage and release of glucose, is about 2.2 times that of Ss,Gly and yields ,- d -Galp- (1,6)- d -Glc and ,- d -Galp- (1,3)- d -Glc in a molar ratio of ,,1 : 2. The partitioning of galactosylated Ss,Gly between reaction with sugars [kNu (m,1·s,1)] and reaction with water [kwater (s,1)] is about twice that of CelB. It gives a mixture of linear ,- d -glycosides, chiefly trisaccharides at early reaction times, in which the prevailing new glycosidic bonds are ,(1,6) and ,(1,3) for the reactions catalysed by Ss,Gly and CelB, respectively. The accumulation of ,- d -Galp- (1,6)- d -Glc at the end of lactose hydrolysis reflects a 3,10-fold specificity of both enzymes for the hydrolysis of ,(1,3) over ,(1,6) linked glucosides. Galactosyl transfer from Ss,Gly or CelB to d -glucose occurs with partitioning ratios, kNu/kwater, which are seven and >,170 times those for the reactions of the galactosylated enzymes with 1-propanol and 2-propanol, respectively. Therefore, the binding interactions with nucleophiles contribute chiefly to formation of new ,-glycosides during lactose conversion. Likewise, noncovalent interactions with the glucose leaving group govern the catalytic efficiencies for the hydrolysis of lactose by both enzymes. They are almost fully expressed in the rate-limiting first-order rate constant for the galactosyl transfer from the substrate to the enzyme and lead to a positive deviation by ,,2.5 log10 units from structure,reactivity correlations based on the pKa of the leaving group. [source]

Customized Electronic Coupling in Self-Assembled Donor,Acceptor Nanostructures

ADVANCED FUNCTIONAL MATERIALS, Issue 22 2009
Dimas G. de Oteyza
Abstract Charge transfer processes between donor,acceptor complexes and metallic electrodes are at the heart of novel organic optoelectronic devices such as solar cells. Here, a combined approach of surface-sensitive microscopy, synchrotron radiation spectroscopy, and state-of-the-art ab initio calculations is used to demonstrate the delicate balance that exists between intermolecular and molecule,substrate interactions, hybridization, and charge transfer in model donor,acceptor assemblies at metal-organic interfaces. It is shown that charge transfer and chemical properties of interfaces based on single component layers cannot be naively extrapolated to binary donor,acceptor assemblies. In particular, studying the self-assembly of supramolecular nanostructures on Cu(111), composed of fluorinated copper-phthalocyanines (F16CuPc) and diindenoperylene (DIP), it is found that, in reference to the associated single component layers, the donor (DIP) decouples electronically from the metal surface, while the acceptor (F16CuPc) suffers strong hybridization with the substrate. [source]

Substituent Effects on Crosslike Packing of 2,,7,-Diaryl- spiro(cyclopropane-1,9,-fluorene) Derivatives: Synthesis and Crystallographic, Optical, and Thermal Properties,

ADVANCED FUNCTIONAL MATERIALS, Issue 2 2007
Z. Wang
Abstract A series of 2,,7,-diarylspiro(cyclopropane-1,9,-fluorene) derivatives are efficiently synthesized and characterized to determine the reason for the "green-light" emission of these compounds. These compounds exhibit bright-violet to blue photoluminescence (PL) (,PLmax,=,353,419,nm) with excellent PL quantum efficiencies (,PL,=,83,100,%) in solution and show high thermal stabilities (Td,=,267,474,°C). The variation of the optical properties of these molecules in the solid state depends on the different stacking modes of these compounds containing different substituents, which are revealed by crystallographic analysis. CH,, hydrogen bonds instead of intermolecular ,,, interactions act as the driving force between adjacent fluorenes, even though a very small dialkyl group (cyclopropane) is introduced at the C-9 position of fluorene. The crosslike molecular stacking efficiently reduces the energy transfer between the herring-like aggregates and therefore results in the absence of a "green-light" emission tail. In order to determine the cause of the "green-light" emission tails, the fluorescence spectra of the films annealed in N2 or in air are recorded. Broad green-light emission tails were observed for the films annealed in air, which might be caused by fluorenone defects generated during processing or during the course of the photophysical analysis by reaction with residual oxygen. [source]