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Chang-Cheng You

Publications and source records attributed to Chang-Cheng You.

14 recordsLinked to original sources
PubMed2006

Modulation of the catalytic behavior of alpha-chymotrypsin at monolayer-protected nanoparticle surfaces.

Amino-acid-functionalized gold clusters modulate the catalytic behavior of alpha-chymotrypsin (ChT) toward cationic, neutral, and anionic substrates. Kinetic studies reveal that the substrate specificity (k(cat)/K(M)) of ChT-nanoparticle complexes increases by approximately 3-fold for the cationic substrate but decreases by 95% for the anionic substrate as compared with that of free ChT, providing enhanced substrate selectivity. Concurrently, the catalytic constants (k(cat)) of ChT show slight augmentation for the cationic substrate and significant attenuation for the anionic substrate in the presence of amino-acid-functionalized nanoparticles. The amino acid monolayer on the nanoparticle is proposed to control both the capture of substrate by the active site and release of product through electrostatic interactions, leading to the observed substrate specificities and catalytic constants.

Catalysis↗
PubMed2006

Light-harvesting metallosupramolecular squares composed of perylene bisimide walls and fluorescent antenna dyes.

The fluorescent dye 4-dimethylamino-1,8-naphthalimide was incorporated at the bay area of N,N'-bispyridyl perylene bisimide to afford a fourfold-functionalized perylene bisimide ligand. Through self-assembly directed by metal-ion coordination, a multichromophore supramolecular entity composed of sixteen dimethylaminonaphthalimide antennas and a perylene bisimide-walled square core was subsequently constructed from this linear ditopic ligand and 90 degrees metal corner [Pd(dppp)](OTf)2 (dppp=1,3-bis(diphenylphosphino)propane; OTf=trifluoromethanesulfonate) in good yield. The isolated metallosupramolecular square was characterized by elemental analysis and 1H, 13C, and 31P{1H} NMR and UV/Vis spectroscopy. Furthermore, by means of 1H NMR diffusion-ordered spectroscopy (DOSY) the dimension of this assembly was evaluated by employing a previously reported perylene bisimide ligand and its square assembly as references. The results obtained confirm the square framework of the current assembly. The optical properties of this multichromophore dye assembly were investigated by UV/Vis and steady-state and time-resolved fluorescence spectroscopy. It was revealed that light captured by dimethylaminonaphthalimide antennas could be efficiently transported to the perylene bisimide core by a fluorescence resonance mechanism (energy-transfer efficiency E=95%), and this resulted in almost exclusive detection of intense perylene bisimide emission, irrespective of the excitation wavelength applied. The present square scaffold containing aminonaphthalimide antenna dyes exhibits more than seven times higher fluorescence quantum yield (Phifl=0.37) than a previously reported pyrene-bearing perylene bisimide-walled square (Phifl=0.05). Thus, this multichromophore square assembly with aminonaphthalimide antenna dyes is an artificial model for the cyclic light-harvesting complexes in purple bacteria.

Fluorescent Dyes↗
PubMed2005

Contrasting effects of exterior and interior hydrophobic moieties in the complexation of amino acid functionalized gold clusters with alpha-chymotrypsin.

[chemical structure: see text]. A series of L-amino acid functionalized gold nanoparticles with oligo(ethylene glycol) (OEG) tethers of varying length are prepared. These studies show that the hydrophobic side chains of amino acids facilitate the structural retention of alpha-chymotrypsin (ChT) but the interior alkyl chains promote its denaturation. An 80-fold range of denaturation rate constants were obtained for ChT in the presence of various nanoparticles. Thus, the tunable denaturation of protein could be achieved by rational combination of amino acid side chains and OEG tethers.

Amino Acids↗
PubMed2005

Monolayer-protected nanoparticle-protein interactions.

Monolayer-protected nanoparticles provide an appealing artificial receptor scaffold for targeting proteins and related biomacromolecules. During the past two years, multiple efforts have focused on the engineering and application of nanoparticle-protein interactions. These investigations include the molecular recognition of proteins with nanoparticles in aqueous media, self-assembly of proteins and nanoparticles either in solution or on surface, and construction of nanoparticle-based protein sensors.

Models, Biological↗
PubMed2005

Tunable inhibition and denaturation of alpha-chymotrypsin with amino acid-functionalized gold nanoparticles.

Water-soluble gold nanoparticles bearing diverse l-amino acid terminals have been fabricated to probe the effect of receptor surface on protein surface binding. The interaction of these nanoparticles with alpha-chymotrypsin (ChT) was investigated by activity assay, gel electrophoresis, zeta-potential, circular dichroism, and fluorescence spectroscopy. The results show that both electrostatic and hydrophobic interactions between the hydrophobic patches of receptors and the protein contribute to the stability of the complex. The microscopic binding constants for these receptor-protein systems are 10(6)-10(7) M(-1), with the capacity of the nanoparticle receptors to bind proteins determined by both their surface area and their surface charge density. Furthermore, it is found that the hydrophilic side chains destabilize the ChT structure through either competitive hydrogen bonding or breakage of salt bridges, whereas denaturation was much slower with hydrophobic amino acid side chains. Significantly, correlation between the hydrophobicity index of amino acid side chains and the binding affinity and denaturation rates was observed.

Amino Acids↗
PubMed2004

Supramolecular p-n-heterojunctions by co-self-organization of oligo(p-phenylene vinylene) and perylene bisimide dyes.

Comparative studies on hydrogen-bonded versus covalently linked donor-acceptor-donor dye arrays obtained from oligo(p-phenylene vinylene)s (OPVs) as donor and bay-substituted perylene bisimides (PERYs) as acceptor dyes are presented. Both systems form well-ordered J-type aggregates in methylcyclohexane, but only hydrogen-bonded arrays afford hierarchically assembled chiral OPV-PERY dye superstructures consisting of left-handed helical pi-pi co-aggregates (CD spectroscopy) of the two dyes that further assemble into right-handed nanometer-scale supercoils in the solid state (AFM study). In the case of hydrogen-bonded arrays, the stability of the aggregates in solution increases with increasing conjugation length of the OPV unit. The well-defined co-aggregated dyes presented here exhibit photoinduced electron transfer on subpicosecond time scale, and thus, these supramolecular entities might serve as valuable nanoscopic functional units.

Journal Article↗
PubMed2004

Porphyrin-perylene bisimide dyads and triads: synthesis and optical and coordination properties.

[structure: see text] Novel porphyrin perylene dyad and triad dyes have been prepared by the coupling of aminophenyltrisphenylporphyrin and tetraphenoxy-substituted perylenetetracarboxylic acid bisanhydrides in a one-step synthesis. Fluorescence spectra of these compounds reveal features that are attributable to emission of perylene bisimides as well as porphyrin excited states. The self-assembly behavior of zinc-metalated compounds with 4,4'-bipyridine and diazabenzoperylene has been investigated by (1)H NMR spectroscopy in CDCl(3), showing that oligomeric zigzag assemblies are formed.

Journal Article↗
PubMed2004

Metallosupramolecular squares: from structure to function.

Metallosupramolecular squares have been successfully evolved over the past years as versatile substitutes of the conventional organic macrocycles owing to the development of reliable synthetic protocols and abundant structural variability (metals and ligands). In this review we have presented the fundamental aspects of metallosupramolecular squares such as the strategies for their construction (self-assembly vs. kinetically controlled macrocyclization) and characterization. The major emphasis of this tutorial review lies on the function of metallosupramolecular squares. Thus, the introduction of functionality into these systems has been discussed in detail by highlighting the recent progress toward application in various fields, including molecular recognition, enantioselective sensing, photoluminescence, redox activity and electrochemical sensing, and homogeneous catalysis.

Biosensing Techniques↗
PubMed2003

Self-assembly of ferrocene-functionalized perylene bisimide bridging ligands with PtII corner to electrochemically active molecular squares.

Ferrocenyl-substituted N,N'-di(4-pyridyl)perylene bisimide ligands have been synthesized by the coupling reaction of hydroxyphenoxy-perylene bisimides with ferrocenyl carboxylic acids. By means of metallosupramolecular self-assembly, hitherto unprecedented multiredox active dendritic molecular squares with 16 ferrocene groups positioned in the bridging ligands are prepared from the perylene bispyridyl imide ligands and [Pt(dppp)][(OTf)(2)] (dppp = 1,3-bis(diphenylphosphano)propane; OTf = trifluoromethanesulfonate) corner in high yield. The isolated metallosupramolecular squares were characterized by elemental analysis, (1)H, (31)P[(1)H] NMR, and UV/vis spectroscopy. The electrochemical properties of the ligands and squares are investigated by cyclic voltammetry as well as spectroelectrochemistry. The results obtained show that the redox behavior of ferrocene units is influenced by the square superstructure. Furthermore, redox titration of free ligand and corresponding molecular square with the one-electron oxidant thianthrenium pentachloroantimonate reveals that ferrocene groups in these structures may be oxidized completely by this oxidant, and highly charged species generated through oxidation of ferrocenyl groups in molecular square cause decomposition of the assembly due to pronounced Coulombic repulsion.

Journal Article↗
PubMed2002

Calix[4]arene-functionalized naphthalene and perylene imide dyes.

[reaction: see text] Calix[4]arenes bearing one, two, or four 1,8-naphthyl imide groups at the wide rim and bis-calix[4]arenes connected via perylene-bisimide dye spacers have been synthesized. The low-temperature NMR spectrum of the tetranaphthylimide suggests, in agreement with a crystal structure, a C2-symmetrical pinched cone conformation stabilized via face-to-face pi-pi interactions between opposite naphthylimide groups. UV-vis and fluorescence studies have been carried out for the perylene bis-calix[4]arene dyes.

Calixarenes↗
PubMed1999

Molecular Recognition Studies on Supramolecular Systems. 22. Size, Shape, and Chiral Recognition of Aliphatic Alcohols by Organoselenium-Modified Cyclodextrins.

A novel cyclodextrin derivative, mono[6-(p-methoxyphenylseleno)-6-deoxy]-beta-cyclodextrin (2), has been synthesized and characterized by elemental analysis and mass, FT-IR, and (1)H NMR spectroscopy. The stability constants (K(S)) of the inclusion complexation of 2 and mono[6-(p-tolylseleno)-6-deoxy]-beta-cyclodextrin (3) with a series acyclic and cyclic alcohols have been determined in phosphate buffer solution (pH 7.20) at 25 degrees C by using the circular dichroism spectral titration method. Although the stability constants obtained for the inclusion complexation of 2 and 3 with aliphatic alcohols are generally smaller than those for native beta-cyclodextrin, the modified cyclodextrins can recognize both the size and chirality of the guest molecules. Interestingly, the complex stability constants (log K(S)), or the Gibbs free energy change (-DeltaG degrees ), increase linearly with increasing number of carbon atoms in the guest molecule (N(C)), irrespective of the topological differences of acyclic, cyclic, and bicyclic guests. The unit increment of complex stability per methylene (-dDeltaG degrees /dN(C)) is not appreciably affected by the difference of the host's substituent but is a critical function of the guest topology, affording distinctly different -dDeltaG degrees /dN(C) values of 2.4 and 2.9 kJ mol(-)(1) for alkanols and cycloalkanols, respectively. In the complexation of chiral guests with 2 and 3, the observed enantioselectivities, as measured by the stability difference (DeltaDeltaG degrees ), are mostly in the range of 1-2 kJ mol(-)(1).

Journal Article↗