We report the synthesis and characterization of a new DNA-templated gold nanocluster (AuNC) of ∼1 nm in diameter and possessing ∼7 Au atoms. When integrated with bilirubin oxidase (BOD) and single ...walled carbon nanotubes (SWNTs), the AuNC acts as an enhancer of electron transfer (ET) and lowers the overpotential of electrocatalytic oxygen reduction reaction (ORR) by ∼15 mV as compared to the enzyme alone. In addition, the presence of AuNC causes significant enhancements in the electrocatalytic current densities at the electrode. Control experiments show that such enhancement of ORR by the AuNC is specific to nanoclusters and not to plasmonic gold particles. Rotating ring disk electrode (RRDE) measurements confirm 4e– reduction of O2 to H2O with minimal production of H2O2, suggesting that the presence of AuNC does not perturb the mechanism of ORR catalyzed by the enzyme. This unique role of the AuNC as enhancer of ET at the enzyme-electrode interface makes it a potential candidate for the development of cathodes in enzymatic fuel cells, which often suffer from poor electronic communication between the electrode surface and the enzyme active site. Finally, the AuNC displays phosphorescence with large Stokes shift and microsecond lifetime.
A chromophore–catalyst dyad assembly of ruthenium polypyridyl complexes has been prepared, structurally and electronically characterized, and its proton‐coupled multielectron photooxidation ...reactivity demonstrated by the visible sunlight‐driven catalytic oxidation of aliphatic and benzyl alcohols into their corresponding aldehydes or ketones with high selectivities and over 100 turnover cycles in water, at ambient conditions.
We report the discovery of a DNA sequence that templates a highly stable fluorescent silver nanocluster. In contrast to other DNA templated silver nanoclusters that have a relatively short ...shelf-life, the fluorescent species templated in this new DNA sequence retains significant fluorescence for at least a year. Moreover, this new silver nanocluster possesses low cellular toxicity and enhanced thermal, oxidative, and chemical stability.
The dinuclear complexes (tpy)Ru(tppz)Ru(bpy)(L)n+ (where L is Cl− or H2O, tpy and bpy are the terminal ligands 2,2′:6′,2′′‐terpyridine and 2,2′‐bipyridine, and tppz is the bridging backbone ...2,3,5,6‐tetrakis(2‐pyridyl)pyrazine) were prepared and structurally and electronically characterized. The mononuclear complexes (tpy)Ru(tppz)2+ and (tppz)Ru(bpy)(L)m+ were also prepared and studied for comparison. The proton‐coupled, multi‐electron photooxidation reactivity of the aquo dinuclear species was shown through the photocatalytic dehydrogenation of a series of primary and secondary alcohols. Under simulated solar irradiation and in the presence of a sacrificial electron acceptor, the photoactivated chromophore–catalyst complex (in aqueous solutions at room temperature and ambient pressure conditions) can perform the visible‐light‐driven conversion of aliphatic and benzylic alcohols into the corresponding carbonyl products (i.e., aldehydes or ketones) with 100 % product selectivity and several tens of turnover cycles, as probed by NMR spectroscopy and gas chromatography. Moreover, for aliphatic substrates, the activity of the photocatalyst was found to be highly selective toward secondary alcohols, with no significant product formed from primary alcohols. Comparison of the activity of this tppz‐bridged complex with that of the analogue containing a back‐to‐back terpyridine bridge (tpytpy, i.e., 6′,6′′‐bis(2‐pyridyl)‐2,2′:4′,4′′:2′′,2′′′‐quaterpyridine) demonstrated that the latter is a superior photocatalyst toward the oxidation of alcohols. The much stronger electronic coupling with significant delocalization across the strongly electron‐accepting tppz bridge facilitates charge trapping between the chromophore and catalyst centers and therefore is presumably responsible for the decreased catalytic performance.
Driven by sunshine: A tppz‐bridged Ru complex was prepared, structurally and electronically characterized, and its proton‐coupled multi‐electron photooxidation reactivity was demonstrated through the photocatalytic dehydrogenation of aliphatic and benzylic alcohols. Under simulated solar irradiation, the photoactivated catalyst (in water, at ambient conditions) can perform the visible‐light‐driven conversion of the alcohols into their aldehydes or ketones with very high selectivity and several tens of turnover cycles per day.
We use a combined, theoretical and experimental, approach to investigate the spectroscopic properties and electronic structure of three ruthenium polypyridyl complexes, Ru(tpy)22+, ...Ru(tpy)(bpy)(H2O)2+, and Ru(tpy)(bpy)(Cl)+ (tpy = 2,2′:6′,2′′-terpyridine and bpy = 2,2′-bipyridine) in acetone, dichloromethane, and water. All three complexes display strong absorption bands in the visible region corresponding to a metal-to-ligand-charge-transfer (MLCT) transition, as well as the emission bands arising from the lowest lying 3MLCT state. Ru(tpy)(bpy)(Cl)+ undergoes substitution of the Cl− ligand by H2O in the presence of water. Density functional theory (DFT) calculations demonstrate that the triplet potential energy surfaces of these molecules are complicated, with several metal-centered (3MC) and 3MLCT states very close in energy. Solvent effects are included in the calculations via the polarizable continuum model as well as explicitly, and it is shown that they are critical for proper characterization of the triplet excited states of these complexes.
Polystyrene-
-polyethylene glycol (PS-
-PEG) amphiphilic block copolymers featuring a terminal tridentate
-ligand (terpyridine) were synthesized for the first time through an efficient route. In this ...approach, telechelic chain-end modified polystyrenes were produced via reversible addition-fragmentation chain-transfer (RAFT) polymerization by using terpyridine trithiocarbonate as the chain-transfer agent, after which the hydrophilic polyethylene glycol (PEG) block was incorporated into the hydrophobic polystyrene (PS) block in high yields via a thiol-ene process. Following metal-coordination with Mn
, Fe
, Ni
, and Zn
, the resulting metallo-polymers were self-assembled into spherical, vesicular nanostructures, as characterized by dynamic light scattering and transmission electron microscopy (TEM) imaging.
Polythiophenes in biological applications Sista, Prakash; Ghosh, Koushik; Martinez, Jennifer S ...
Journal of nanoscience and nanotechnology
14, Številka:
1
Journal Article
Polythiophene and its derivatives have shown tremendous potential for interfacing electrically conducting polymers with biological applications. These semiconducting organic polymers are relatively ...soft, conduct electrons and ions, have low cytotoxicity, and can undergo facile chemical modifications. In addition, the reduction in electrical impedance of electrodes coated with polythiophenes may prove to be invaluable for a stable and permanent connection between devices and biological tissues. This review article focuses on the synthesis and some key applications of polythiophenes in multidisciplinary areas at the interface with biology. These polymers have shown tremendous potential in biological applications such as diagnostics, therapy, drug delivery, imaging, implant devices and artificial organs.
We report the engineering of a new reversibly switching chromogenic protein, Dathail. Dathail was evolved from the extremely thermostable fluorescent proteins thermal green protein (TGP) and eCGP123 ...using directed evolution and ratiometric sorting. Dathail has two spectrally distinct chromogenic states with low quantum yields, corresponding to absorbance in a ground state with a maximum at 389nm, and a photo-induced metastable state with a maximum at 497nm. In contrast to all previously described photoswitchable proteins, both spectral states of Dathail are non-fluorescent. The photo-induced chromogenic state of Dathail has a lifetime of ~50min at 293K and pH7.5 as measured by UV–Vis spectrophotometry, returning to the ground state through thermal relaxation. X-ray crystallography provided structural insights supporting a change in conformation and coordination in the chromophore pocket as being responsible for Dathail's photoswitching. Neutron crystallography, carried out for the first time on a protein from the green fluorescent protein family, showed a distribution of hydrogen atoms revealing protonation of the chromophore 4-hydroxybenzyl group in the ground state. The neutron structure also supports the hypothesis that the photo-induced proton transfer from the chromophore occurs through water-mediated proton relay into the bulk solvent. Beyond its spectroscopic curiosity, Dathail has several characteristics that are improvements for applications, including low background fluorescence, large spectral separation, rapid switching time, and the ability to switch many times. Therefore, Dathail is likely to be extremely useful in the quickly developing fields of imaging and biosensors, including photochromic Förster resonance energy transfer, high-resolution microscopy, and live tracking within the cell.
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•Dathail will be useful in imaging and biosensors, particularly pcFRET, high-resolution microscopy, and live cell tracking.•Dathail is a reversibly switching chromoprotein with two spectrally distinct chromogenic states with low quantum yields.•X-ray crystallography shows changes in conformation and coordination of the chromophore during Dathail's photoswitching.•Crystallography suggests photo-induced proton transfer from the chromophore with water-mediated proton relay to bulk solvent.•The first time that neutron crystallography has been used for a protein in the GFP family provides surprising new insights.
Multiple intervalence‐transfer (IT) absorptions (see picture) appear in the near‐IR/IR spectra of the mixed‐valence complex Cl3RuII(tppz)RuIIICl3− (tppz=tetrakis(2‐pyridyl)pyrazine), whose X‐ray ...crystal structure and electronic and vibrational spectroscopic features indicate localized‐to‐delocalized (Class II–III) behavior.
A new trinuclear oxo-centered chromium(III) complex with formula Cr3O(CH3CO2)6(L)(H2O)2 (L = 5-hydroxyflavone, known as primuletin) was synthetized and characterized by ESI mass spectrometry, ...thermogravimetry, and 1H-NMR, UV-Vis, and FTIR spectroscopies. In agreement with the experimental results, DFT calculations indicated that the flavonoid ligand is coordinated to one of the three Cr(III) centers in an O,O-bidentate mode through the 5-hydroxy/4-keto groups. In a comparative study involving the uncoordinated primuletin and its corresponding complex, systematic reactions with the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) showed that antiradical activity increases upon complexation.
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