A Potassium Complex of a Fluorine-Containing Macrocyclic Cage Compound: Interactions between Fluorine Atoms and Metal Ions

A new donor , the C−F unit, can be added to the field of host–guest chemistry. The interaction between fluorine atoms and a potassium ion was proven with the fluorine-containing cage compound 1 as a host. The six fluorine atoms of K⁺⊂ 1 are coordinated to K⁺ in a distorted octahedral fashion.     

A New Luminescent Ruthenium(II) Polypyridine‐derived Dipicolylamine Complex as a Sensor for Cu2+ Ions

A chemo‐sensor [Ru(bpy)₂(bpy‐DPF)](PF₆)₂ ( 1 ) (bpy=2,2′‐bipyridine, bpy‐DPF=2,2′‐bipyridyl‐4,4′‐bis(N,N‐di(2‐picolyl))formylamide) for Cu²⁺ using di(2‐picolyl)amine (DPA) as the recognition group and a ruthenium(II) complex as the reporting group was synthesized and characterized successfully. It demonstrates a high selectivity and efficient signaling behavior only for Cu²⁺ with obvious red‐shifted MLCT (metal‐to‐ligand charge transfer transitions) absorptions and dramatic fluorescence quenching compared with Zn²⁺ and other metal ions.     

Poly(arginine)‐Selective Coprecipitation Properties of Self‐Assembling Apoferritin and Its Tb3+ Complex: A New Luminescent Biotool for Sensing of Poly(arginine) and Its Protein Conjugates

The apoferritin protein and apoferritin–Tb³⁺ complex were demonstrated to form oligomeric and polymeric self‐assemblies in neutral aqueous solutions, based on characterization by using luminescence and UV/Vis spectroscopy, dynamic light scattering, and transmission electron microscopy. Addition of a 20‐mer or higher poly(arginine) to the solution resulted in coprecipitation through nanoscale interactions, while biological proteins and other poly(amino acids) rarely yielded precipitates under the conditions employed. The apoferritin–Tb³⁺ complex assembly exhibited a particularly long‐lived green luminescence in aqueous solution, and its poly(arginine)‐selective precipitation behavior was followed by monitoring the changes in luminescence. The poly(arginine)‐tagged albumin precipitated selectively and quantitatively, so that the apoferritin–Tb³⁺ complex can function as a new luminescent biotool for the sensing of poly(arginine) and its protein conjugates.     

Reversal of a Single Base‐Pair Step Controls Guanine Photo‐Oxidation by an Intercalating Ruthenium(II) Dipyridophenazine Complex

Small changes in DNA sequence can often have major biological effects. Here the rates and yields of guanine photo‐oxidation by Λ‐[Ru(TAP)₂(dppz)]²⁺ have been compared in 5′‐{CCGG AT CCGG}₂ and 5′‐{CCGG TA CCGG}₂ using pico/nanosecond transient visible and time‐resolved IR (TRIR) spectroscopy. The inefficiency of electron transfer in the TA sequence is consistent with the 5′‐TA‐3′ versus 5′‐AT‐3′ binding preference predicted by X‐ray crystallography. The TRIR spectra also reveal the differences in binding sites in the two oligonucleotides.     

Two-focus fluorescence correlation spectroscopy: a new tool for accurate and absolute diffusion measurements.

We present a new method to measure absolute diffusion coefficients at nanomolar concentrations with high precision. Based on a modified fluorescence correlation spectroscopy (FCS)-setup, this method is improved by introducing an external ruler for measuring the diffusion time by generating two laterally shifted and overlapping laser foci at a fixed and known distance. Data fitting is facilitated by a new two-parameter model to describe the molecule detection function (MDF). We present a recorded MDF and show the excellent agreement with the fitting model. We measure the diffusion coefficient of the red fluorescent dye Atto655 under various conditions and compare these values with a value achieved by gradient pulsed field NMR (GPF NMR). From these measurements we conclude, that the new measurement scheme is robust against optical and photophysical artefacts which are inherent to standard FCS. With two-focus-FCS, the diffusion coefficient of 4.26 x 10(-6) cm2s(-1) for Atto655 in water at 25 degrees C compares well with the GPF NMR value of 4.28 x 10(-6) cm2s(-1).     

Light Harvesting and Efficient Energy Transfer in Dendritic Systems: New Strategy for Functionalized Near‐Infrared BF2‐Azadipyrromethenes

Bright funnels : A series of dendritic systems, which are capable of funneling energy from the periphery to the core, have been synthesized. The photophysical properties of dendrimers have been determined. Selective excitation of the donor leads to an efficient energy transfer (>90 %) to the acceptor. The approach provides a facile synthesis for the modification of near‐infrared BF₂‐Azadipyrromethenes.

     

A Rotational BODIPY Nucleotide: An Environment‐Sensitive Fluorescence‐Lifetime Probe for DNA Interactions and Applications in Live‐Cell Microscopy

Fluorescent probes for detecting the physical properties of cellular structures have become valuable tools in life sciences. The fluorescence lifetime of molecular rotors can be used to report on variations in local molecular packing or viscosity. We used a nucleoside linked to a meso‐substituted BODIPY fluorescent molecular rotor ( dC^bdp ) to sense changes in DNA microenvironment both in vitro and in living cells. DNA incorporating dC^bdp can respond to interactions with DNA‐binding proteins and lipids by changes in the fluorescence lifetimes in the range 0.5–2.2 ns. We can directly visualize changes in the local environment of exogenous DNA during transfection of living cells. Relatively long fluorescence lifetimes and extensive contrast for detecting changes in the microenvironment together with good photostability and versatility for DNA synthesis make this probe suitable for analysis of DNA‐associated processes, cellular structures, and also DNA‐based nanomaterials.     

Intramolecular [2+2] Photocycloaddition of 3‐ and 4‐(But‐3‐enyl)oxyquinolones: Influence of the Alkene Substitution Pattern,Photophysical Studies,and Enantioselective Catalysis by a Chiral Sensitizer

The intramolecular [2+2] photocycloaddition of four 4‐(but‐3‐enyl)oxyquinolones (substitution pattern at the terminal alkene carbon atom: CH₂, Z‐CHEt, E‐CHEt, CMe₂) and two 3‐(but‐3‐enyl)oxyquinolones (substitution pattern: CH₂, CMe₂) was studied. Upon direct irradiation at λ=300 nm, the respective cyclobutane products were formed in high yields (83–95 %) and for symmetrically substituted substrates with complete diastereoselectivity. Substrates with a Z‐ or E‐substituted terminal double bond showed a stereoconvergent reaction course leading to mixtures of regio‐ and diastereomers with almost identical composition. The mechanistic course of the photocycloaddition was elucidated by transient absorption spectroscopy. A triplet intermediate was detected for the title compounds, which–in contrast to simple alkoxyquinolones such as 3‐butyloxyquinolone and 4‐methoxyquinolone–decayed rapidly (τ≈1 ns) through cyclization to a triplet 1,4‐diradical. The diradical can evolve through two reaction channels, one leading to the photoproduct and the other leading back to the starting material. When the photocycloaddition was performed in the presence of a chiral sensitizer (10 mol %) upon irradiation at λ=366 nm in trifluorotoluene as the solvent, moderate to high enantioselectivities were achieved. The two 3‐(but‐3‐enyl)oxyquinolones gave enantiomeric excesses (ees) of 60 and 64 % at ?25 °C, presumably because a significant racemic background reaction occurred. The 4‐substituted quinolones showed higher enantioselectivities (92–96 % ee at ?25 °C) and, for the terminally Z‐ and E‐substituted substrates, an improved regio‐ and diastereoselectivity.