Aromatic Donor Research Articles

Co-Crystallization of Sym-Triiodo-Trifluorobenzene with Bipyridyl Donors: Consistent Formation of Two Instead of Anticipated Three N···I Halogen Bonds

The potential triple-halogen-bond acceptor, sym-triiodo-trifluorobenzene IFB (1), has been co-crystallized with a series of bipyridyl derivatives (2−4) to gain insight to the factors controlling formation of multiple halogen bonds with a single aromatic system. Co-crystals 5−7 were obtained that consistently contained two N···I halogen bonds. The reluctance to the formation of a supramolecular assembly having a third N···I halogen bond does not depend on the size of the bispyridine donor systems (2−4). Apparently, there are limitations to the number of halogen bonds that can be formed with a single aromatic halogen donor. The solid-state structure of co-crystal (5) contains short I···F contacts of 2.96 and 3.05 A. DFT calculations were performed at the PBE0/(apc1-aSDBDZ)//PBE0/(pc1-SDBDZ) level of theory to investigate the nature of the interaction between the pyridine nitrogen and IFB (1). These calculations reveal a weakening of N···I interactions as more pyridine moieties coordinate to the IFB (1), whi...

Template Effects in the Formation of [2]Pseudo-rotaxanes Containing Diazapyrenium Units

The template effects exerted by guests 14 and 15 in the ring closure reaction of 3 have been quantitatively evaluated. The rate largely increases in the presence of the two templates. The results are compared with those relative to the ring closure reaction of 1 yielding cyclobis(paraquat-p-phenylene), 2. The comparison indicates that the formation of tetracationic aromatic cycles templated by aromatic donors benefits from the use of extended pi surfaces both in the acceptor and in the donor components.

Insights into the binding properties of a cuprous ion embedded in the tren cap of a calix[6]arene and supramolecular trapping of an intermediate

Coordination of Cu(I) to a tren unit that is covalently linked to a calix[6]arene has been explored. The resulting complex revealed itself very stable in solution under an inert atmosphere, but extremely sensitive to O2 in solution as well as in the solid state. Therefore, its binding properties towards non-redox ligands have been studied in detail. The electron-rich metal center displays moderate affinity for nitrilo ligands compared to the calix[6]tris-pyridine ligand. Indeed, the binding enthalpy with acetonitrile is only -30 kJ mol(-1), whereas it is -72 kJ mol(-1) with the tris-pyridine system. In contrast, CO binding is relatively strong due to important pi-back donation from the metal center, as evidenced by the CO stretch, which was found to be less energetic (2075 cm(-1)) than that measured for ligands based on aromatic donors such as imidazole or pyridine. The conformational and dynamic properties of this calix-system have also been studied in detail. With an empty cavity or with the very small CO guest-ligand, the calix-core undergoes partial self-inclusion leading to dissymmetrical conformations. In contrast, nitrilo ligands act as "shoe-trees" that maintain the calix-core in a C(3v) symmetrical cone conformation. Very interestingly, the variable T study relative to the ligand exchange process highlighted a two-step dissociative pathway, where Cu-N bond cleavage/formation is differentiated from the nitrilo guest expulsion/inclusion from/into the calixarene cavity.

Design of a depside with a lipophilic adamantane moiety: Synthesis, crystal structure and molecular conformation

New adamantane depsides, ethyl 2-(1-adamantyl)-3- O-[( S)-Boc-Phe]butanoate ( R, R, S)- 1a and ( S, S, S)- 1b were prepared and characterized by spectroscopic data. The crystal structures and the stereochemistry of rac-( R, R, S)- 1a and threo-2-(1-adamantyl)-3-hydroxybutanoic acid rac-( R, R)- 4a were determined by X-ray structure analysis. In the racemic crystal, the molecules of 1a form centrosymmetric dimers through hydrogen bonds involving a double acceptor function of the depside carbonyl oxygen, and donors of the amino group and aromatic C–H atoms. The dimers are connected through an infinite chain of C–H⋯O interactions, where C–H is an aromatic donor and the ester carbonyl oxygen is an acceptor. In the solid state, amphiphilic molecules 1a and 4a exhibit pronounced hydrophilic and hydrophobic bilayers.

Pre-Shaped Aromatic Picket Porphyrins Bearing Neutral Oxygen Donors and their Bismuth Complexes: Synthesis and Coordination Studies

Pre-Shaped Aromatic Picket Porphyrins Bearing Neutral Oxygen Donors and their Bismuth Complexes: Synthesis and Coordination Studies

Femtodynamics Reflected in Nanoseconds: Bimolecular Free Electron Transfer in Nonpolar Media

The (free) electron transfer (FET) from electron donor molecules to parent solvent radical cations of alkanes and alkyl chlorides exhibits mechanistic peculiarities that are conditioned by the low polarity of these solvents. Because of the negligible solvation of ions in such systems and the almost complete lack of an activation barrier, the electron jump takes place at the very first encounter of the reactants and, as such, in extremely short times of <or=10(-15) s. Molecular oscillations (deformation, bending) occurring within the femtosecond time domain result directly in significant changes of the pi- or n-electron distribution in the HOMO ground state of the donor molecule, thereby generating a distribution of conformers. This is considered to be a rationale for a possible generation of different product radical cations in the free electron transfer, which exhibit different spin and charge distribution and, consequently different stability. Experimentally, the latter has been verified for aromatic donors, substituted with mobile, i.e., not rigidly fixed heteroatom-centered groups (various phenol type compounds, thiophenols, aromatic amines, benzyltrimethylsilanes etc.). The individually characteristic product distribution could be visualized and quantified by time-resolved spectroscopy in the nanosecond time domain. On the basis of a manifold of experimental data and supported by quantum-chemical calculations, the free electron transfer phenomenon is analyzed and discussed in detail in this summarizing report. The results presented here stand also for a, seemingly paradox, situation in which the products of a diffusion-controlled bimolecular reaction are governed by femtosecond events.

Using Aromatic Donor Acceptor Interactions to Affect Macromolecular Assembly

ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTUsing Aromatic Donor Acceptor Interactions to Affect Macromolecular AssemblyJoseph J. Reczek and Brent L. IversonView Author Information Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, Texas Cite this: Macromolecules 2006, 39, 17, 5601–5603Publication Date (Web):July 29, 2006Publication History Received23 May 2006Revised13 July 2006Published online29 July 2006Published inissue 1 August 2006https://doi.org/10.1021/ma0611669Copyright © 2006 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1478Altmetric-Citations62LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (435 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Aromatic compounds,Chemical structure,Fibers,Noncovalent interactions,Polymers Get e-Alerts

Photoinduced intermolecular electron transfer and energy transfer of C60 dendrimers

Abstract Photoinduced intermolecular electron-transfer and energy-transfer processes of the fullerodendrimers with two poly(amidoamine)dendron groups of 0.5-th, 1.5-th and 2.5-th generations have been investigated by laser flash photolysis. The rate constants and quantum yields of photoinduced electron transfer with the added aromatic amine donors in PhCN tend to decrease with the dendron generation, indicating that the bulky dendron groups act as barriers for the donor molecules to approach the C60 moiety in the center of the dendrimers. The decreases in the rate constants of triplet energy transfer processes vs. O2 and β-carotene with the dendron generation are smaller than those of electron-transfer process, probably because effective encounter radii for energy transfer are larger than those for electron transfer; hence, less sensitive to dendrimer generation. A kinetic model for intermolecular electron-transfer and energy-transfer of fullerodendrimers was proposed. To cite this article: Yasuyuki Araki et al., C. R. Chimie 9 (2006).

Exciplex fluorescence emission from simple organic intramolecular constructs in non-polar and highly polar media as model systems for DNA-assembled exciplex detectors

Organic intramolecular exciplexes, N-(4-dimethylaminobenzyl)-N-(1-pyrenemethyl)amine (1) and N'-4-dimethylaminonaphthyl-N-(1-pyrenemethyl)amine (2), were used as model systems to reveal major factors affecting their exciplex fluorescence, and thus lay the basis for developing emissive target-assembled exciplexes for DNA-mounted systems in solution. These models with an aromatic pyrenyl hydrocarbon moiety as an electron acceptor appropriately connected to an aromatic dimethylamino electron donor component (N,N-dimethylaminophenyl or N,N-dimethylaminonaphthyl) showed strong intramolecular exciplex emission in both non-polar and highly polar solvents. The effect of dielectric constant on the maximum wavelength for exciplex emission was studied, and emission was observed for 1 and 2 over the full range of solvent from non-polar hydrocarbons up to N-methylformamide with a dielectric constant of 182. Quantum yields were determined for these intramolecular exciplexes in a range of solvents relative to that for Hoechst 33,258. Conformational analysis of 1 was performed both computationally and via qualitative 2D NMR using (1)H-NOESY experiments. The results obtained indicated the contribution of pre-folded conformation(s) to the ground state of 1 conducive to exciplex emission. This research provides the initial background for design of self-assembled, DNA-mounted exciplexes and underpins further development of exciplex-based hybridisation bioassays.

Unligated Diruthenium(II,II) Tetra(trifluoroacetate): The First X-ray Structural Study, Thermal Compressibility, Lewis Acidity, and Magnetism

The title compound, [Ru(2)(O(2)CCF(3))(4)] (1), has been obtained without any exogenous ligands and crystallized by deposition from the gas phase at 170 degrees C. Its crystal structure has been determined for the first time to confirm an infinite chain motif built on axial Ru...O interactions of the diruthenium(II,II) units. The X-ray diffraction studies at variable temperatures showed no phase transitions in the range of 295-100 K but revealed a significant decrease in the volume per atom from 14.2 to 13.3 A(3). This noticeable thermal compressibility effect is discussed in connection with the solid-state packing of the [Ru(2)(O(2)CCF(3))(4)](infinity) chains. The highly electrophilic character of the diruthenium(II,II) units has been shown by the gas-phase deposition reaction of [Ru(2)(O(2)CCF(3))(4)] with an aromatic donor substrate, namely [2.2]paracyclophane (C(16)H(16)). As a result of the above reaction, a new arene adduct [Ru(2)(O(2)CCF(3))(4).C(16)H(16)] (2) has been isolated in crystalline form. It has an extended one-dimensional (1D) chain structure comprised of alternating building units and based on the rare bridging mode of [2.2]paracyclophane, [Ru(2)(O(2)CCF(3))(4).(mu(2)-eta(2):eta(2)-C(16)H(16))](infinity). The magnetic susceptibility of 1 and 2 has been measured and compared in the range of 1.8-300 K. In addition, in the course of synthesis of 1 by the carboxylate exchange reactions, a new mixed-carboxylate diruthenium(II,II) core complex [Ru(2)(O(2)CCF(3))(3)(O(2)CC(2)H(5))] (3), bearing no exogenous ligands, has also been isolated and structurally characterized. It exhibits an interesting polymeric structure in which the ruthenium(II) centers selectively form axial interdimer contacts with the O-atoms of the propionate groups only.

Reactions of [Ru(CO)3Cl2]2 with aromatic nitrogen donor ligands in alcoholic media

AbstractThe reactions of mono‐ and bidentate aromatic nitrogen‐containing ligands with [Ru(CO)3Cl2]2 in alcohols have been studied. In alcoholic media the nitrogen ligands act as bases promoting acidic behaviour of alcohols and the formation of alkoxy carbonyls [Ru(N–N)(CO)2Cl(COOR)] and [Ru(N)2(CO)2Cl(COOR)]. Other products are monomers of type [Ru(N)(CO)3Cl2], bridged complexes such as [Ru(CO)3Cl2]2(N), and ion pairs of the type [Ru(CO)3Cl3]− [Ru(N–N)(CO)3Cl]+ (N–N = chelating aromatic nitrogen ligand, N = non‐chelating or bridging ligand). The reaction and the product distribution can be controlled by adjusting the reaction stoichiometry. The reactivity of the new ruthenium complexes was tested in 1‐hexene hydroformylation. The activity can be associated with the degree of stability of the complexes and the ruthenium–ligand interaction. Chelating or bridging nitrogen ligands suppresses the activity strongly compared with the bare ruthenium carbonyl chloride, while the decrease in activity is less pronounced with monodentate ligands. A plausible catalytic cycle is proposed and discussed in terms of ligand–ruthenium interactions. The reactivity of the ligands as well as the catalytic cycle was studied in detail using the computational DFT methods. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Structural Aspects of 1,2-Dioxetanes Active toward Intramolecular Charge-Transfer-Induced Chemiluminescent Decomposition

Abstract Simple 1,2-dioxetanes decompose thermally to produce mainly triplet-excited carbonyl fragments, whereas 1,2-dioxetanes bearing an aromatic electron donor display intramolecular charge-transfer-induced decomposition with accompanying effective emission of light. This type of 1,2-dioxetanes has been extensively studied with a view to understanding the mechanisms of bioluminescence and chemiluminescence and applying them to modern biochemical and biomedical analyses. In this account, recent developments of dioxetane-based chemiluminescent substrates are described from the viewpoint of relationships between the structure of dioxetanes and the properties of chemiluminescence, namely, chemiluminescent efficiency, singlet-chemiexcitation efficiency, color, and the rate of chemiluminescent decomposition.

C [dbnd6]O…H–C interactions as packing motifs in crystals. Part 1. Structure and conformation of N-(methyl)-benzyl-3-spiro-cycloalkylopyrrolidine-2,5-diones

A set of six N-benzyl-3-spiro-succinimides with evaluated anticonvulsant activity has been crystallographically studied. In all crystals, in the absence of strong H-bond donors, only weak H-bonds of C–H…O C have been found as intermolecular interactions. For six crystals, two main packing motifs of the strongest interactions of C(sp 3)–H…O C have formed two alternative supramolecular synthons. Additionally in all crystals, interactions with aromatic donors have been identified. The analogy in the chemical formulas of the studied species has been complemented by the similarity in the H-bonding patterns in the crystals. However, no relationship between molecular conformation and packing motif variations has been found.

Bifunctional chelates with mixed aromatic and aliphatic amine donors for labeling of biomolecules with the {Tc(CO) 3} + and {Re(CO) 3} + cores

A series of tridentate ligands consisting of mixed aromatic and aliphatic amine derivatives of single amino acid chelates and phenylpiperazine have been developed, and their reactions with [NEt 4] 2[ReBr 3(CO) 3] have been investigated. The compounds [Re(CO) 3{(NC 5H 4CH 2)NCH 3(C 2H 4)NHCH 3}]Br ( 4), [Re(CO) 3{(NC 5H 4CH 2)NCH 3(C 2H 4)NCH 3(CH 2) x COOC 2H 5}]Br ( x = 1, 5; x = 4, 6) [Re(CO) 3{(NC 5H 4CH 2)NH(C 2H 4)N(CH 3) 2}]Br ( 7), [Re(CO) 3{(NC 5H 4CH 2)N(CH 2COOC 2H 5)(C 2H 4)N(CH 3) 2}]Br ( 8) and [Re(CO) 3(NC 5H 4CH 2)(C 2H 4NH 2)N(CH 2) 3–CH 3Ophenpip]Br ( 9) (phenpip: phenylpiperazine, –C 6H 4–(CH 2CH 2) 2N–) were prepared and characterized by elemental analysis, NMR, IR, HSMS and X-ray crystallography. All complexes exhibit fac-{Re(CO) 3N 3} coordination geometry in the cationic molecular unit. Crystal data for C 13H 17BrN 3O 3Re ( 4): orthorhombic, Pbca, a = 13.4510(8) Å, b = 10.5728(6) Å, c = 22.5378(13) Å, V = 3205.2(3) Å 3, Z = 8; C 17H 23BrN 3O 5Re ( 5): orthorhombic, Pcca, a = 16.5907(7) Å, b = 14.8387(6) Å, c = 16.7075(7) Å, V = 4113.1(3) Å 3, Z = 8; C 13H 25BrN 3O 7Re ( 7 · 4H 2O): monoclinic, P2 1/ n, a = 14.0698(17) Å, b = 9.6760(12) Å, c = 15.6099 (19) Å, β = 114.930(2)°, V = 1927.1(4) Å 3, Z = 4; C 17H 23BrN 3O 5Re ( 8): monoclinic, P2 1/ n, a = 7.5312(5) Å, b = 16.0366(10) Å, c = 16.8741(10) Å, β = 98.9990(10)°, V = 2012.9(2) Å 3, Z = 4.

Synthetic Ion Channels with Rigid-Rod π-Stack Architecture that Open in Response to Charge-Transfer Complex Formation

We describe the design, synthesis, and evaluation of synthetic ion channels with a new rigid-rod pi-stack architecture that open in response to guest binding by aromatic electron donor-acceptor interactions. Highly cooperative and highly selective ligand gating is shown to yield anion selective, small ion channels that have the characteristic plum color of the charge-transfer complexes formed between the dialkoxynaphthalene ligands and the stacked naphthalenediimide acceptors of the channel.

Isolation, X-ray Structures, and Electronic Spectra of Reactive Intermediates in Friedel−Crafts Acylations

[reaction: see text] Reactive intermediates in the Friedel-Crafts acylation of aromatic donors are scrutinized upon their successful isolation and X-ray crystallography at very low temperatures. Detailed analyses of the X-ray parameters for the [1:1] complexes of different aliphatic and aromatic-acid chlorides with the Lewis acids antimony pentafluoride and pentachloride, gallium trichloride, titanium and zirconium tetrachlorides provide unexpected insight into the activation mechanism for the formation of the critical acylium carbocations. Likewise, the X-ray-structure examinations of aliphatic and aromatic acylium electrophiles also isolated as crystalline salts point to the origins of their electrophilic reactivity. Although the Wheland intermediates (as acylium adducts to arene donors) could not be isolated in crystalline form owing to their exceedingly short lifetimes, transient (UV-vis) spectra of benzenium adducts of acylium carbocations with hexamethylbenzene can be measured and directly related to Wheland intermediates with other cationic electrophiles that have been structurally established via X-ray studies.

Exploitation of the unusual thermodynamic properties of human myeloperoxidase in inhibitor design

Myeloperoxidase plays a fundamental role in oxidant production by neutrophils. It uses hydrogen peroxide and chloride to catalyze the production of hypochlorous acid (HOCl), which contributes to both bacterial killing and oxidative injury of host tissue. Thus, MPO is an interesting target for anti-inflammatory therapy. Here, based on the extraordinary and MPO-specific redox properties of its intermediates compound I and compound II, we present a rational approach in selection and design of reversible inhibitors of HOCl production mediated by MPO. In detail, indole and tryptamine derivatives were investigated for their ability to reduce compounds I and II and to affect the chlorinating activity of MPO. It is shown that these aromatic one-electron donors bound to the hydrophobic pocket at the distal heme cavity and were oxidized efficiently by compound I ( k 3), which has a one-electron reduction potential of 1.35 V. By contrast, compound II ( E°′ of the compound II/ferric couple is 0.97 V) reduction ( k 4) was extremely slow. As a consequence compound II, which does not participate in the halogenation cycle, accumulated. The extent of chlorinating activity inhibition (IC 50) was related to the k 3/ k 4 ratio. The most efficient inhibitors were 5-fluorotryptamine and 5-chlorotryptamine with IC 50 of 0.79 μM and 0.73 μM and k 3/ k 4 ratios of 386,000 and 224,000, respectively. The reversible mechanism of inhibition is discussed with respect to the enzymology of MPO and the development of drugs against HOCl-dependent tissue damage.

Crystal structures and spectroscopic properties of polycyano–polycadmate host clathrates including a CT complex guest of methylviologen dication and aromatic donor

A series of polycyano-polycadmate (PCPC) host clathrates including a CT complex of methylviologen dication (MV2+) and an aromatic donor as a guest were synthesized, and their crystal structures and spectroscopic properties were investigated. The PCPC host has a framework structure built with Cd2+ ions as coordination centres and cyanides as bridging ligands. This framework host has negative charge and includes a cationic guest together with an ordinary neutral guest. MV2+, which is a strong acceptor, was included as a cationic guest and an aromatic compound, which works as a donor, was included as a neutral guest. Crystal structures of seven clathrates, whose neutral guests were o-cresol, m-cresol, p-cresol, 1-methylnaphthalene, 1,2,4-trimethoxybenzene, pyrrole and aniline, were determined by single crystal X-ray diffraction methods. In all cases MV2+ and the neutral guest formed a CT complex with a face to face stacking structure and were included as a CT complex guest. However, depending on each clathrate the ratio of aromatic donor to MV2+ was different and several variations were found in their PCPC host structures. The clathrates had their own colour depending on their neutral guest. The plot of the CT transition energies estimated from optical CT bands against the ionization potentials of the neutral guests satisfied a linear relationship predicted by Mulliken theory. However, the CT transition energies observed in the clathrates showed a shift to lower energy by ca. 0.6 eV compared with those observed in corresponding acetonitrile solutions.

Hydrogen-bonding and protonation effects on the formation of charge transfer complex between para-benzoquinone and 2,6-dimethoxy phenol

Formation of CT complex of series of quinines of increasing basicity (chloranil to duroquinone) were checked systematically in methylenechloride with different aromatic donors in presence of hydroxylic additives of increasing hydrogen-bonding power (tetra-butyl-alcohol to hexafluoro-2-propanol) or acidity. The effect of the basic additives of increasing basicity (pyridine to 4- N, N-dimethylaminopyridine) was also observed. The formation constant ( K CT) of CT complex between para-benzoquinone and 2,6-dimthoxyphenol was enhanced approximately 50 times by TFA and approximately two times by HFIPA due to protonation and strong hydrogen-bonding interaction of BQ with TFA and HPIPA, respectively. Similarly, K CT increased approximately six times by DMAPy due to hydrogen-bonding with DMOPh.

Cation–π Bonding: A New Perspective on the Sorption of Polycyclic Aromatic Hydrocarbons to Mineral Surfaces

Recent molecular modeling and spectroscopic studies have suggested that relatively strong interactions can occur between aromatic pi donors and metal cations in aqueous solutions. The objective of this study was to characterize potential cation-pi interactions between pi donors and exchangeable cations accumulated at mineral surfaces via both spectroscopic and batch sorption methods. Quadrupolar splitting in deuterium nuclear magnetic resonance ((2)H NMR) spectroscopy for d(2)-dichloromethane, d(6)-benzene, and d(8)-toluene (C(6)D(5)- moiety) in aqueous suspensions of a Na-saturated reference montmorillonite unambiguously indicated the ordering of solute molecules with respect to the clay surface. The half line broadening (Delta nu(1/2)) of (2)H NMR of d(6)-benzene in montmorillonite suspensions showed that soft exchangeable cations generally resulted in more benzene sorption compared with harder cations (e.g., Ag(+) > Cs(+) > Na(+) > Mg(2+), Ba(2+)). In batch sorption experiments, saturating minerals (e.g., porous silica gels, kaolinite, vermiculite, montmorillonite) with a soft transition metal or softer base cations generally increased the polycyclic aromatic hydrocarbon (PAH) sorption relative to harder cations (e.g., Ag(+) >> Cs(+) > K(+) > Na(+); Ba(2+) > Mg(2+)). Sorption of phenanthrene to Ag(+)-saturated montmorillonite was much stronger compared with 1,2,4,5-tetrachlorobenzene, a coplanar non-pi donor having slightly higher hydrophobicity. In addition, a strong positive correlation was found between the cation-dependent sorption and surface charge density of the minerals (e.g., vermiculite, montmorillonite >> silica gels, kaolinite). These results, coupled with the observations in (2)H NMR experiments with montmorillonite, strongly suggest that cation-pi bonding forms between PAHs and exchangeable cations at mineral surfaces and affects PAH sorption to hydrated mineral surfaces.