RESUMO
A glucopyranose functionalized star-shaped oligomer, N-tris{4,4',4''-[(1E)-2-(2-{(E)-2-[4-(benzo[d]thiazol-2-yl)phenyl]vinyl}-9,9-bis(6-2-amido-2-deoxy-1-thio-ß-D-glucopyranose-hexyl)-9H-fluoren-7-yl)vinyl]phenyl}phenylamine (TVFVBN-S-NH(2)), is synthesized for two-photon fluorescence imaging. In water, TVFVBN-S-NH(2) self-assembles into nanoparticles with an average diameter of â¼49â nm and shows a fluorescence quantum yield of 0.21. Two-photon fluorescence measurements reveal that TVFVBN-S-NH(2) has a two-photon absorption cross-section of â¼1100 GM at 780â nm in water. The active amine group on the glucopyranose moiety allows further functionalization of TVFVBN-S-NH(2) with folic acid to yield TVFVBN-S-NH(2) FA with similar optical and physical properties as those for TVFVBN-S-NH(2). Cellular imaging studies reveal that TVFVBN-S-NH(2) FA has increased uptake by MCF-7 cells relative to that for TVFVBN-S-NH(2), due to specific interactions between folic acid and folate receptors on the MCF-7 cell membrane. This study demonstrates the effectiveness of glycosylation as a molecular engineering strategy to yield water-soluble materials with a large two-photon absorption (TPA) cross-section for targeted cancer-cell imaging.
Assuntos
Fluorescência , Ácido Fólico/química , Glucose/análogos & derivados , Glucose/síntese química , Linhagem Celular Tumoral , Ensaios de Seleção de Medicamentos Antitumorais , Feminino , Glicosilação , Humanos , Estrutura Molecular , FótonsRESUMO
Spider webs are made of silk, the properties of which ensure remarkable efficiency at capturing prey. However, remaining on, or near, the web exposes the resident spiders to many potential predators, such as ants. Surprisingly, ants are rarely reported foraging on the webs of orb-weaving spiders, despite the formidable capacity of ants to subdue prey and repel enemies, the diversity and abundance of orb-web spiders, and the nutritional value of the web and resident spider. We explain this paradox by reporting a novel property of the silk produced by the orb-web spider Nephila antipodiana (Walckenaer). These spiders deposit on the silk a pyrrolidine alkaloid (2-pyrrolidinone) that provides protection from ant invasion. Furthermore, the ontogenetic change in the production of 2-pyrrolidinone suggests that this compound represents an adaptive response to the threat of natural enemies, rather than a simple by-product of silk synthesis: while 2-pyrrolidinone occurs on the silk threads produced by adult and large juvenile spiders, it is absent on threads produced by small juvenile spiders, whose threads are sufficiently thin to be inaccessible to ants.
Assuntos
Formigas/fisiologia , Comportamento Predatório/efeitos dos fármacos , Pirrolidinonas/metabolismo , Seda/química , Aranhas/fisiologia , Animais , Comportamento Animal/fisiologia , Feminino , Comportamento Predatório/fisiologia , Pirrolidinonas/farmacologia , Aranhas/metabolismoRESUMO
1,5- and 1,8-bis(bifluorenyl)anthracene were synthesized and converted to their corresponding bis(bifluorenyl)triptycenes and bis(bifluorenyl)-9,10-dihydroanthracenes. Analysis of their optical properties shows no feature of extended conjugation in the triptycene pair. The electronic spectra of the triptycene and dihydroanthracene pairs are in fact superimposable. There is definite evidence that triptycene displays zero homoconjugation effect.
RESUMO
Triphenylamine derivatives bridged by methylene units afford a near planar molecular platform in a series of one dimer and two oligomers exhibiting increased structural rigidity compared to that of their parent triphenylamines. This series of dendrimers show significantly enhanced two-photon absorptions that are up to 3-fold that of triphenylamines with similar molecular size and structure.
Assuntos
Compostos de Anilina/química , Dendrímeros/química , Fótons , Compostos de Anilina/síntese química , Cristalografia por Raios X , Dendrímeros/síntese química , Fluorescência , Modelos Moleculares , Estrutura Molecular , Fotoquímica , Teoria Quântica , Espectrometria de Fluorescência , EstereoisomerismoRESUMO
A novel class of monodisperse conjugated polymer nanoparticles have been readily prepared by the facile reprecipitation of poly{1,3-bis[2-(3-alkylthienyl)]azulene} or poly{1,3-bis[2-(3-alkoxythienyl)]azulene}. The multicomponent poly(bithiophene-alt-azulene) macromolecules were efficiently self-assembled into a wide range of size-tunable nanoparticles from a few tens to five hundred nanometers via the hydrophobic and pi-stacking effects in the mixed chloroform/methanol solutions. Electronically altered polymer structures with different alkyl or alkoxy substitutes exhibited variable self-assembling behaviors to precisely tune the size and the optical/electronic properties of nanoparticles. A strong size dependence of continuous bathochromic absorption and significant enhanced emission were observed with the increase of particle size. A linear relationship between the absorption or fluorescence intensities and the particle size was demonstrated as well, and this is very useful to probe the intermolecular interactions and the size evolutions of conjugated polymer nanoparticles. After the size-dependent optical and electronic properties are created, they can be further optimized to improve the performance of materials prior to the use in novel organic nanodevices in a cost-effective way.
RESUMO
The well-defined and patterned copper clusters formed on the Si(111)-(7 x 7) surface have been employed as a template for selective binding of 1,4-benzenedimethanethiol (HS-CH2-C6H4-CH2-SH, 1,4-BDMT), to form ordered molecular nanostructures. Scanning tunneling microscopic (STM) studies showed that each 1,4-BDMT molecule preferentially binds to two neighboring copper atoms within one copper cluster through the S-Cu interaction with its molecular plane parallel to the surface, whereas some 1,4-BDMT bond to individually adsorbed copper atoms, resulting in an upright configuration. Large-scale two-dimensional molecular nanostructures can be obtained using this patterned assembly technique. Our experiments demonstrate the feasibility for controllable growth of ordered molecular nanostructures on the Si(111)-(7 x 7) surface.
RESUMO
A synthetic sequence involving dithiametacyclophane --> metacyclophanediene --> dihydropyrene was employed to prepare trans-10b-methyl-10c-(2-naphthyl)- and trans-10b-methyl-10c-(1-naphthyl)-10b,10c-dihydropyrene 5 and 6, respectively. Both exhibit a strong diamagnetic ring current despite the introduction of an internal bulky substituent within the pi-electron cloud. Their electronic spectra suggest interaction between the two near-perpendicular naphthyl and dihydropyrenyl pi systems, resulting in red shift and band broadening. All naphthyl protons are well resolved in their 1H NMR spectra due to a strong shielding effect of the dihydropyrene ring. The most shielded protons in 5 and 6 are H1' and H2' at delta 2.47 and 1.42, respectively, being 5.25 and 5.95 ppm shifted from those of reference protons. There is evidence for free rotation on the NMR time scale of the 2-naphthyl ring in 5 with a preference for a particular conformer, whereas the 1-naphthyl ring in 6 is conformationally rigid with its H2' projecting deeply into the pi-cloud, thus accounting for the most shielded aromatic proton (H2' in 6) reported to date.
RESUMO
We experimentally demonstrated that pyridine/Si(111)-7 x 7 can act as an electron donor/acceptor pair as a result of the charge transfer from the electron-rich N atom of pyridine to the electron-deficient adatom of the Si surface, evidenced by the upshift of 1.8 eV (state A) for the N(1s) core level upon the formation of a datively bonded complex compared to physisorbed molecules. Another state (B) whose N(1s) binding energy downshifts by 1.2 eV was assigned to an adduct through Si-C and Si-N covalent linkages, formed via a [4 + 2]-like addition mechanism on Si(111)-7 x 7. Binding molecules through the formation of the dative bond resulted from significant electron transfer opens a new approach for the creation of Si-based molecular architectures and modification of semiconductor interfacial properties with unsaturated organic molecules.
RESUMO
Direct treatment of azulene-thiophene copolymers with Ru(3)(CO)(12) led to unique examples of coordination of a multinuclear transition metal cluster to conjugated polymers. The polymer-metal cluster formation could be confirmed by (1)H NMR spectroscopic studies, and the coordination mode could be deduced from the crystallographic structure of model compounds. The composition of ruthenium carbonyl cluster could be used as a governing factor to tune the electronic, optical, and morphological properties of the organometallic polymers. [structure: see text]
RESUMO
Ring contraction followed by an elimination reaction on anti-9-methyl-18-trans-2-(10b,10c-dimethyl-10b,10c-dihydropyrenyl)-2,11-dithia[3,3]metacyclophane gave the desired compound 10b-methyl-10c-[2-(10b,10c-dimethyl-10b,10c-dihydropyrenyl)]-10b,10c-dihydropyrene. 1H NMR spectroscopic analysis indicated a ring current effect over a considerable distance from the macro-molecular plane of each of the aromatic rings with the two pi systems freely rotating. Bathochromic shifts and peak broadening in its electronic spectrum clearly supports the presence of through-space pi-pi interactions between the two aromatic rings. This should serve as a good model to verify homo-conjugation effect in such a novel system where the two pi systems are freely revolving.
RESUMO
[structure: see text]. An X-ray crystallographic study of zinc(II) 5,15-di-(2-methoxymethylphenyl)-porphyrin indicates that it forms a coordination polymer through ligation of the ether oxygen atoms on the porphyrin peripheries to the metal centers of two identical adjacent porphyrins. This gives a novel extensively linked, three-dimensional polymeric structure in which the zinc(II) metal forms a six-coordination center. The uniquely structured network has cavities between 4.81 and 9.27 angstroms, which makes it resemble molecular sieve materials.
RESUMO
[structure-see text]A series of fluorene-dithia[3.3]paracyclophane copolymers was synthesized by Suzuki coupling reactions of suitable precursors. Transannular pi-pi interactions altered the electronic and optical properties of the polymer backbone significantly. A large red shift in the emission spectrum of the unsubstituted polymer was accompanied by enhanced photoluminescence (PL) efficiency. Substitution in the cyclophane unit resulted in PL quenching.
RESUMO
[reaction: see text] A series of dithia[n.3.3](1.3.5)crownophanes were synthesized by cesium carbonate-assisted intramolecular cyclization reactions in 10-31% yields. Their complexation behavior exhibits an unusual ion-selectivity preference due to the presence of a "breathing" process of the dithia[3.3]metacyclophane moiety, which indirectly controls the ion selectivity through the adjustment of the cavity size of the crown unit. This breathing mechanism is also supported by observation made in X-ray crystallographic analysis.
RESUMO
The interactions of styrene and phenylacetylene and their isotope substitutions with a Si(111)-7 x 7 surface have been studied as model systems to mechanistically understand the chemical binding of conjugated pi-electron systems to di-radical-like silicon dangling bonds of the adjacent adatom-rest atom pair. Vibrational studies show that styrene mainly binds to the surface through a diradical reaction involving both the external C=C and its conjugated internal C=C of the phenyl ring with an adjacent adatom-rest atom pair, forming a 5-ethylidene-1,3-cyclohexadiene-like skeleton. On the other hand, phenylacetylene was shown to be covalently attached to Si(111)-7 x 7 through the external C[triple bond]C, forming a styrene-like conjugation system. These experimental results are consistent with density functional theory calculations. The different binding mechanisms for styrene and phenylacetylene clearly demonstrate that reaction channels for multifunctional organic molecules are strongly dependent on the chemical and physical properties of the functional groups. The resulting pi-electron conjugation structures may possibly be employed as intermediates for further organic syntheses and fabrication of multilayer organic films on semiconductor surfaces.
RESUMO
[reaction: see text] 1,3-Polyazulene prepared by the chemical polymerization of 1,3-dibromoazulene with Ni(COD)(2) was aptly characterized by spectroscopic analysis. The azulene units remain intact in the isolated polymer. Protonation of 1,3-polyazulene by trifluoroacetic acid was found to exhibit high conductivity and paramagnetic properties via the formation of cation radicals and di- and polycations.
RESUMO
[reaction: see text] The preparation of pyrazoline and isoxazoline derivatives with traceless solid-phase sulfone linker strategy is described. Key steps involved in the solid-phase synthetic procedure include (i) sulfinate S-alkylation, (ii) sulfone anion alkylation, (iii) gamma-hydroxy sulfone --> gamma-ketosulfone oxidation, and (iv) traceless product release via elimination-cyclization. A library of 12 pyrazolines and isoxazolines was synthesized.
RESUMO
Oligothiophene-functionalized 9,9'-spirobifluorene derivatives exhibit good solubility in polar organic solvents, especially compounds 5a-d to 7a-d due to the introduction of the flexible n-hexyl chain. The structures of all compounds studied are characterized and verified by (1)H and (13)C NMR spectra. The results not only show that these organic conjugated materials with no substituents or n-hexyl substituents are successfully synthesized through the corresponding synthetic methodologies, but also prove that chemical shifts of protons and carbons in the aromatic range change with the attachment and the increase of the thiophene ring at the 9,9'-spirobifluorene fragment. The thermal analysis results demonstrate that these compounds are quite stable, and evaporate from 300 to 700 degrees C. Most of these compounds exhibit a stable amorphous state in the solid state. The electrochemical properties of all compounds studied are also investigated. The results indicate that radical cation behaviors of oligothiophene-modified 9,9'-spirobifluorene derivatives are more stable than those of normal oligothiophenes, that oxidative and reductive peak potentials shift cathodically or anodically, and that the HOMO and LUMO energy levels are also tuned with the increase of the thiophene ring owing to the enhanced pi-electron delocalization and the increasing conjugation length. Oxidative potentials of nonsubstituted oligothiophene-functionalized 9,9'-spirobifluorene derivatives are more sensitive to the increase of thiophene rings than those of 9,9'-spirobifluorene derivatives with n-hexyl groups. The energy levels and band gaps of all compounds studied are also calculated from the onset potentials of n-doping and p-doping and are adjusted by varying thiophene oligomers and their attachment patterns to the 9,9'-spirobifluorene ring to make them suitable for the work functions of the electrodes.
RESUMO
[structure: see text] A crownophane consisting of a dithia[3.3]metacyclophane moiety was synthesized by employing a high dilution method. The crystal structure and complexation behavior of this crownophane was studied. A hydrogen-bonded linear supramolecular assembly using anion-Na(+)-crownophane-solvent as a synthon was observed in the solid state. This supramolecular assembly was also stabilized via an intermolecular S.H-C interaction.
RESUMO
Two series of novel fully conjugated oligomers, oligothiophene-functionalized 9,9'-spirobifluorene derivatives, have been developed in this contribution. First, four 9,9'-spirobifluorene bromide derivatives (compounds 1a-d) are prepared through various synthetic routes. Oligothiophene derivatives with or without substituents are synthesized through the Grignard and Suzuki coupling reactions. The Negishi coupling reactions between oligothienylzinc chloride and various 9,9'-spirobifluorene bromides with Pd(PPh(3))(4) as catalyst successfully produce the desired compounds, unsubstituted oligothiophene-functionalized 9,9'-spirobifluorene derivatives, compounds 2 to 4a-d. Since the Negishi coupling reactions afford regioregularly head-to-tail (H-T) oligo(4-n-hexylthiophene)-functionalized 9,9'-spirobifluorene derivatives in poor yields, the Suzuki coupling reactions between sodium 4-n-hexylthienyl-2-boronate 8, and various 9,9'-spirobifluorene-based bromides 1a-d and 9-16 are employed to produce highly regioregular head-to-tail oligothiophene-functionalized 9,9'-spirobifluorene derivatives (compounds 5 to 7a-d) in very high yields. We also investigate the effect of solvents on the Suzuki coupling reactions. The structure and purity of all compounds are verified by FT-IR, (1)H and (13)C NMR, MS, and elemental analysis.
RESUMO
[formula: see text] A spherical host with D2d symmetry consisting of a tetrathia[3.3.3.3]paracyclophane and two 18-crown-6 moieties was synthesized. Its crystal structure shows a central cavity with a diameter of 1.96 A and a depth of 6.75 A. A Na+ ion could rest in the cavity center but prefers core binding to external binding in one of the crown units. An intramolecular kinetic equilibrium was reached with the Na+ ion switching between the two crown units with an energy barrier of 14.1 +/- 3 kcal/mol.