Distinct Fluorescence Properties Research Articles

Synthesis of 3‐Formylfurans via a Silver(I)‐Catalyzed Epoxide Ring‐Opening/1,2‐Acyl Migration/Cyclization Cascade

AbstractBy the design of suitable starting materials, a silver(I)‐catalyzed epoxide ring‐opening/1,2‐acyl migration/cyclization cascade has been developed, which allowed us to systematically prepare unsymmetrical 3‐formylfurans. Various 3‐formylfurans were prepared in good to excellent yields. In addition, the distinct fluorescence properties of 3‐formylfurans in solution and the solid state are disclosed.magnified image

Apolipoprotein C-III Nanodiscs Studied by Site-Specific Tryptophan Fluorescence.

Apolipoprotein C-III (ApoC-III) is found on high-density lipoproteins (HDLs) and remodels 1,2-dimyristoyl-sn-glycero-3-phosphocholine vesicles into HDL-like particles known as nanodiscs. Using single-Trp-containing ApoC-III mutants, we have studied local side chain environments and interactions in nanodiscs at positions W42, W54, and W65. Using transmission electron microscopy and circular dichroism spectroscopy, nanodiscs were characterized at the ultrastructural and secondary conformational levels, respectively. Nearly identical particles (15 ± 2 nm) were produced from all proteins containing approximately 25 ± 4 proteins per particle with an average helicity of 45-51% per protein. Distinct residue-specific fluorescence properties were observed with W54 residing in the most hydrophobic environment followed by W42 and W65. Interestingly, time-resolved anisotropy measurements revealed that Trp side chain mobility is uncorrelated to the polarity of its surroundings. W54 is the most mobile compared to W65 and W42, which are more immobile in a nanodisc-bound state. On the basis of Trp spectral comparisons of ApoC-III in micellar and vesicle environments, ApoC-III binding within nanodiscs more closely resembles a bilayer-bound state. Despite the nanodiscs being structurally similar, we found marked differences during nanodisc formation by the Trp variants as a function of temperature, with W42 behaving the most like the wild-type protein. Our data suggest that despite the modest mutations of Trp to Phe at two of the three native sites, the interfacial location of W42 is important for lipid binding and nanodisc assembly, which may be biologically meaningful as of the three Trp residues, only W42 is invariant among mammals.

Controllable self-assembly of NaREF4 upconversion nanoparticles and their distinctive fluorescence properties

The paper presents the growth of hexagonal NaYF4:Yb3+, Tm3+ nanocrystals with tunable sizes induced by different contents of doped Yb3+ ions (10%–99.5%) using the thermal decomposition method. These nanoparticles, which have different sizes, are then self-assembled at the interface of cyclohexane and ethylene and transferred onto a normal glass slide. It is found that the size of nanoparticles directs their self-assembly. Due to the appropriate size of 40.5 nm, 15% Yb3+ ions doped nanoparticles are able to be self-assembled into an ordered inorganic monolayer membrane with a large area of about 10 × 10 μm2. More importantly, the obvious short-wave (300–500 nm) fluorescence improvement of the ordered 2D self-assembly structure is observed to be relative to disordered nanoparticles, which is because intrinsic absorption and scattering of upconversion nanoparticles leads to the self-loss of fluorescence, especially the short-wave fluorescence inside the disordered structure, and the relative emission of short-wave fluorescence is reduced. The construction of a 2D self-assembly structure can effectively avoid this and improve the radiated short-wave fluorescence, especially UV photons, and is able to direct the design of new types of solid-state optical materials in many fields.

ChemInform Abstract: Synthesis of Dibenzo[f,h][1,2,4]triazolo[3,4‐b]quinazolines via a Two‐Step Route with Water as the only By‐Product.

Microwave-promoted cyclocondensation of isoflavones with 3-amino[1,2,4]triazole gave 6-phenyl-7-(2-hydroxyphenyl)-1,2,4triazolo[4,3- a ]pyrimidines as intermediates. Subsequent photocyclization of these intermediates delivered dibenzo[ f , h ][1,2,4]triazolo[3,4- b ]quinazolines as final products. Water was the only by-product in this two-step procedure. The products showed distinct fluorescence properties both in solution and in the solid state .

Asymmetric Rhodamine-Based Fluorescent Probe for Multicolour In Vivo Imaging.

To achieve rapid and sensitive detection of cancer, activatable fluorescent probes targeting proteases that are overexpressed in various types of cancer have been developed, based on the hydroxymethyl rhodamine green (HMRG) scaffold. However, to visualize altered activities of multiple enzymes in cancer sites, other scaffolds with distinct fluorescence properties from those of HMRG are needed. A novel asymmetrically modified rhodamine with suitable absorption/emission, brightness and equilibrium constant of intramolecular spirocyclization, working in the yellow/orange region, is introduced. As a proof of concept, a probe targeting γ-glutamyl transpeptidase (gGlu-HMJCR) was developed on the basis of the new scaffold. Simultaneous visualization and discrimination of tumours expressing γ-glutamyl transpeptidase (with gGlu-HMJCR) and cathepsins (with Z-Phe-Arg-HMRG) by colour were achieved in a mouse model in vivo.

An insight into the optical properties of a sub nanosize glutathione stabilized gold cluster.

In this study, gold quantum clusters with distinct fluorescence properties were developed and their structural and physical behaviour was evaluated. The clusters were prepared by etching gold nanoparticles with glutathione. Three different Au33 clusters with emission profiles in the NIR region and one blue emitting cluster, Au8 were developed by varying the geometrical arrangement of atoms within the cluster. These clusters having sizes in the range of 0.7 to 2 nm were synthesized by choosing different reaction temperatures from 0 °C to 70 °C and pH between 1.5 and 10. In the three cases, formation of self assembled atoms within the cluster and the corresponding changes in optical properties were observed. A detailed evaluation of the number of atoms and the core-ligand ratio using MALDI-MS and a change in the binding energy as seen in the XPS study confirmed this finding. The study demonstrates that the self assembly of atoms and their arrangement is an important factor in determining the characteristics of the cluster. In this communication, we put forward a new concept where the number of atoms and their arrangement within the clusters play a crucial role in tuning their optical properties.

A Palette of Fluorescent Thiophene-Based Ligands for the Identification of Protein Aggregates.

By replacing the central thiophene unit of an anionic pentameric oligothiophene with other heterocyclic moities, a palette of pentameric thiophene-based ligands with distinct fluorescent properties were synthesized. All ligands displayed superior selectivity towards recombinant amyloid fibrils as well as disease-associated protein aggregates in tissue sections.

Synthesis of Dibenzo[f,h][1,2,4]triazolo[3,4-b]quinazolines via a Two-Step Route with Water as the Only By-Product

Microwave-promoted cyclocondensation of isoflavones with 3-amino[1,2,4]triazole gave 6-phenyl-7-(2-hydroxyphenyl)-1,2,4triazolo[4,3-<i>a</i>]pyrimidines as intermediates. Subsequent photocyclization of these intermediates delivered dibenzo[<i>f</i>,<i>h</i>][1,2,4]triazolo[3,4-<i>b</i>]quinazolines as final products. Water was the only by-product in this two-step procedure. The products showed distinct fluorescence properties both in solution and in the solid state .

A non-amplified FISH protocol to identify simultaneously different bacterial groups attached to eukaryotic phytoplankton

Eukaryotic phytoplankton and bacteria form complex trophic interactions in nature and cultures. The interaction will depend on the spatial arrangement but the architecture of these arrangements has been little investigated. Here we modified a protocol to identify and localize multiple bacterial taxa attached to phytoplankton cells in culture and natural samples, including sensitive dinoflagellates. Samples were embedded in agarose and hybridized simultaneously with different probes of distinct fluorescence properties. Embedding avoided losses or damage of host cells and preserved the attached bacteria during hybridization and washing. Embedding still allowed efficient hybridization and identification of intact host cells. After fluorescence in situ hybridization of the bacteria the phytoplankton host cells, including dinoflagellates were still intact. Digital image stacks taken with a wide field epifluorescence microscope using different excitation–emission wavelength combinations allow the location of the different bacterial groups on the host cell surface and the spatial relationship of the different bacterial groups.

General Synthetic Approach toward Geminal-Substituted Tetraarylethene Fluorophores with Tunable Emission Properties: X-ray Crystallography, Aggregation-Induced Emission and Piezofluorochromism

A general approach to the design and synthesis of a new series of geminal-substituted tetraarylethene (g-TAE) chromophores with aggregation-induced emission (AIE) properties has been developed via Corey–Fuchs reaction and subsequent Suzuki/Stille coupling reactions. To demonstrate the synthetic simplicity and versatility of this approach, fluorophores with diverse electronic characteristics have been synthesized. The validation of the geminal structure and bulky steric effect on the bond lengths and dihedral angles is further confirmed by the X-ray crystallography of three chromophores. With respect to single crystals of 2,2′-(2,2-diphenylethene-1,1-diyl)-dinaphthalene (DPDN2), 1,1′-(2,2-diphenylethene-1,1-diyl)-dinaphthalene (DPDN1), and 9,9′-(2,2-diphenylethene-1,1-diyl)dianthracene (DPDAn), intensive cofacial π–π stacking is absent in their molecular packing. The pseudopolymorphism of DPDAn crystals associated with different photoluminescence properties is investigated. In comparison to the solvent-free DPDAn crystal, the solvated DPDAn with embedded methanol or dichloromethane leads to some non-negligible conformational and packing alterations, which accounts for its distinct fluorescence properties. The AIE phenomena and optical properties of g-TAEs are probed with respect to steric and electronic effects. Along with their electrochemical characteristics and piezofluorochromism, our work has elucidated that this general approach can be utilized to develop a promising class of TAE materials for systematic investigations of its optoelectronic properties and crystal engineering.

Cover Picture: Hydroxyphenyl‐Substituted Benzophosphole Oxides: Impact of the Intramolecular Hydrogen Bond on the Fluorescence Properties (Asian J. Org. Chem. 2/2014)

A molecule that has distinct fluorescence properties that are dependent on the environment of the sample has emerged as a basis of the environment-responsive luminescent materials. In their Communication on page 122 ff., Shigehiro Yamaguchi and co-workers designed and synthesized 2-(o-hydroxyphenyl)-substituted benzophosphole oxides, which can form an intramolecular hydrogen bond between the hydroxy group and the phosphine oxide moiety. A 3-phenylated derivative fluoresces in several specific solvents that have hydrogen-bond-accepting abilities, whereas it is virtually non-emissive in toluene, CH2Cl2, and MeCN. Switching of the hydrogen bonds can be a mechanism for controlling the fluorescence properties of phosphole-oxide-based π-electron systems.

Hydroxyphenyl‐Substituted Benzophosphole Oxides: Impact of the Intramolecular Hydrogen Bond on the Fluorescence Properties

AbstractAiming at a molecule that has distinct fluorescence properties dependent on the environment of the sample, we designed and synthesized 2‐(o‐hydroxyphenyl)‐substituted benzophosphole oxides, which can form an intramolecular hydrogen bond between the hydroxy group and the phosphine oxide moiety. A 3‐phenylated derivative fluoresces in several specific solvents that have hydrogen‐bond‐accepting abilities, whereas it is virtually non‐emissive in toluene, CH2Cl2, and MeCN. Experimental and theoretical studies indicate that this trend likely results from the switching of the excited‐state character. When in weak hydrogen‐bonding solvents, the compound forms a non‐emissive excited state that results from excited‐state intramolecular proton transfer (ESIPT). In hydrogen‐bonding solvents the compound forms an emissive excited state with an intermolecular hydrogen bond between the hydroxy group and the solvent. Switching between the intramolecular and intermolecular hydrogen bonds can be a mechanism for controlling the fluorescence properties of the phosphole‐oxide‐based π‐electron systems.

Blinking Statistics of Small Clusters of Semiconductor Nanocrystals

Individual and small clusters of CdSe/ZnS core/shell semiconductor nanocrystals are studied with single-molecule, time-correlated, single-photon counting confocal fluorescence microscopy to obtain fluorescence intermittency (blinking) statistics and correlations. Clusters were distinguished from individual nanocrystals using intensity autocorrelations and decay histograms. Because clusters do not exhibit on/off blinking, we have constructed objective prescriptions to distinguish between high and low emission intervals using lifetime as well as intensity data. The high/low blinking of clusters is statistically similar to the on/off blinking of individual nanocrystals. These results support a model for the distinctive fluorescence properties of small nanocrystal clusters based on nonradiative energy transfer, in which the high/low blinking of a cluster is a consequence of on/off blinking of the “acceptor” (smallest energy gap) nanocrystal in the cluster.

Highly fluorescent silver nanoclusters stabilized by glutathione: a promising fluorescent label for bioimaging

A panel of silver nanoclusters (Ag NCs) protected by glutathione has been produced by collecting them on a plastic surface during an interfacial etching process. Blue-green, yellow and red emitting Ag NCs with size smaller than 2 nm exhibited distinct fluorescence properties (both emission and lifetime). In particular, the yellow emitting Ag NCs were found to reach a very high quantum yield of over 60% with a monoexponential fluorescence lifetime. These labels show no bleaching and high photostability over time and a high stability for a wide range of pH values. Cytotoxicity tests demonstrated the viability in the presence of of these luminescent probes even at high concentration (1 mg/mL). Cell studies confirmed the uptake of Ag NCs in epithelial lung cancer cells by an endocytotic process. These results show the high potential of fluorescent noble metal nanoclusters for biolabeling and imaging as alternatives to the standard fluorescent probes such as quantum dots or organic dyes.

Silver Nanomaterials Regulated by Structural Competition of G-/C-Rich Oligonucleotides

Silver nanomaterials with distinct fluorescent properties are synthesized with a series of G-rich/C-rich DNA templates, and the influence of DNA conformational structures on the size and the fluorescence of silver nanomaterials was investigated through varying the sequence composition and the ratio of complementary sequences, using CD, UV–vis, fluorescence spectroscopy, and TEM. It is intriguing to find out that G-rich templates at acidic conditions are capable of generating red emitters that are susceptible to the G-quadruplex structures associated with the number of 5′-terminal guanines. C-rich sequences can produce red silver clusters at either acidic or neutral conditions, and the emission is dramatically regulated by the number of 3′-end cytosines. It is the first time to report that double-stranded DNA templates can generate distinct fluorescent nanosilver modulated by the predominance among the structural competition of the Watson–Crick duplex, G-quadruplex, and i-motif. These results provide a pro...

Microflow Cytometer for optical analysis of phytoplankton

Analysis of the intrinsic fluorescence profiles of individual marine algae can be used in general classification of organisms based on cell size and fluorescence properties. We describe the design and fabrication of a Microflow Cytometer on a chip for characterization of phytoplankton. The Microflow Cytometer measured distinct side scatter and fluorescence properties of Synechococcus sp., Nitzschia d., and Thalassiosira p.; measurements were confirmed using the benchtop Accuri C6 flow cytometer. The Microflow Cytometer proved sensitive enough to detect and characterize picoplankton with diameter approximately 1 μm and larger phytoplankton of up to 80 μm in length. The wide range in size discrimination coupled with detection of intrinsic fluorescent pigments suggests that this Microflow Cytometer will be able to distinguish different populations of phytoplankton on unmanned underwater vehicles.

The Photochemistry of Bacteriophytochrome: Key to its Use as a Deep-Tissue Fluorescence Probe

Bacteriophytochromes (Bphs) are red-light photoreceptors that regulate a variety of bacterial responses. Their photosensory core consists of PAS, GAF and PHY domains and covalently binds biliverdin (BV). The Bph light activation mechanism involves isomerization around the BV C15=C16 double bond, resulting in a flip of its D-ring. In an important recent development, PAS-GAF variants were engineered for use as near-infrared fluorescent markers in mammalian tissues (Shu et al. Science 2009). Here, we report the photochemistry of two Bphs from Rps. palustris, RpBphP2 (P2) and RpBphP3 (P3) that have distinct photoconversion and fluorescence properties. We applied ultrafast spectroscopy on P3 and P2 PAS-GAF proteins and the P3 D216A and P2 D202A PAS-GAF-PHY proteins. In these mutants a conserved aspartate which connects BV with the PHY domain through extensive hydrogen-bond networks, was replaced by alanine. The excited-state lifetime of P3 and P2 PAS-GAF was significantly larger than their PAS-GAF-PHY counterparts. Mutation of the conserved Asp to Ala in PAS-GAF-PHY had a similar but larger effect. In particular, the fluorescence quantum yield of the P3 D216A mutant was 0.066, higher than that of wild type P3 (0.043) and similar to the engineered Bph of Shu et al. We conclude that elimination of a key hydrogen-bond interaction between Asp and a conserved Arg in the PHY domain is responsible for the excited-state lifetime increase. H/D exchange resulted in a 1.5 - 1.7 fold increase of excited-state lifetime. The results are rationalized with a reaction model where excited-state deactivation of BV proceeds via excited-state proton transfer from the BV pyrrole nitrogens to the backbone of the conserved Asp or a bound water. This work may aid in rational structure- and mechanism-based conversion of P3 and other BPhs into efficient near-IR fluorescent markers.

Fluorescence quantum yield and photochemistry of bacteriophytochrome constructs

Bacteriophytochromes (Bphs) are red-light photoreceptor proteins with a photosensory core that consists of three distinct domains, PAS, GAF and PHY, and covalently binds biliverdin (BV) to a conserved cysteine in the PAS domain. In a recent development, PAS-GAF variants were engineered for use as a near-infrared fluorescent marker in mammalian tissues (Tsien and co-workers, Science, 2009, 324, 804-807). Here, we report the fluorescence quantum yield and photochemistry of two highly-related Bphs from Rps. palustris, RpBphP2 (P2) and RpBphP3 (P3) with distinct photoconversion and fluorescence properties. We applied ultrafast spectroscopy to wild type P3 and P2 PAS-GAF proteins and their P3 D216A, Y272F and P2 D202A PAS-GAF-PHY mutant proteins. In these mutants hydrogen-bond interactions between a conserved aspartate (Asp) which connects the BV chromophore with the PHY domains are disrupted. The excited-state lifetime of the truncated P3 and P2 PAS-GAF proteins was significantly longer than in their PAS-GAF-PHY counterparts that constitute the full photosensory core. Mutation of the conserved Asp to Ala in the PAS-GAF-PHY protein had a similar but larger effect. The fluorescence quantum yields of the P3 D216A and Y272F mutants were 0.066, higher than that of wild type P3 (0.043) and similar to the engineered Bph of Tsien and co-workers. We conclude that elimination of a key hydrogen-bond interaction between Asp and a conserved Arg in the PHY domain is responsible for the excited-state lifetime increase in all Bph variants studied here. H/D exchange resulted in a 1.4-1.7 fold increase of excited-state lifetime. The results support a reaction model in which deactivation of the BV chromophore proceeds via excited-state proton transfer from the BV pyrrole nitrogens to the backbone of the conserved Asp or to a bound water. This work may aid in rational structure- and mechanism-based conversion of constructs based on P3 and other BPhs into efficient near-IR, deep tissue, fluorescent markers.

Primary Reactions of Bacteriophytochrome Observed with Ultrafast Mid-Infrared Spectroscopy

Phytochromes are red-light photoreceptor proteins that regulate a variety of responses and cellular processes in plants, bacteria, and fungi. The phytochrome light activation mechanism involves isomerization around the C(15)═C(16) double bond of an open-chain tetrapyrrole chromophore, resulting in a flip of its D-ring. In an important recent development, bacteriophytochrome (Bph) has been engineered for use as a fluorescent marker in mammalian tissues. Bphs covalently bind a biliverdin (BV) chromophore, naturally abundant in mammalian cells. Here, we report an ultrafast time-resolved mid-infrared spectroscopic study on the Pr state of two highly related Bphs from Rps. palustris , RpBphP2 (P2) and RpBphP3 (P3) with distinct photoconversion and fluorescence properties. We observed that the BV excited state of P2 decays in 58 ps, while the BV excited state of P3 decays in 362 ps. By combining ultrafast mid-IR spectroscopy with FTIR spectroscopy on P2 and P3 wild type and mutant proteins, we demonstrate that the hydrogen bond strength at the ring D carbonyl of the BV chromophore is significantly stronger in P3 as compared to P2. This result is consistent with the X-ray structures of Bph, which indicate one hydrogen bond from a conserved histidine to the BV ring D carbonyl for classical bacteriophytochromes such as P2, and one or two additional hydrogen bonds from a serine and a lysine side chain to the BV ring D carbonyl for P3. We conclude that the hydrogen-bond strength at BV ring D is a key determinant of excited-state lifetime and fluorescence quantum yield. Excited-state decay is followed by the formation of a primary intermediate that does not decay on the nanosecond time scale of the experiment, which shows a narrow absorption band at ∼1540 cm(-1). Possible origins of this product band are discussed. This work may aid in rational structure- and mechanism-based conversion of BPh into an efficient near-IR fluorescent marker.

Diverse structural assemblies and variable conductivities of silver-hexamethylenetetramine coordination polymers with 2-, 3-, and 4-sulfobenzoate ligands

Self-assembly reactions of sulfobenzoates and Ag(I)-hmt system resulted in the formation of one previously reported complex, {[Ag4(hmt)2(2-sb)2(H2O)]·2H2O}n (1), and two new silver-sulfobenzoate complexes {[Ag4(hmt)2(3-sb)2(H2O)2]·2H2O}n (2), and {[Ag3(hmt)2(4-sb)(NO3)(H2O)]·3H2O}n (3) (sb = sulfobenzoate and hmt = hexamethylenetetramine). These coordination polymers were characterized by single-crystal X-ray analyses, elemental analyses, IR spectra, TG analyses, fluorescence studies, and electric conductivity. Complexes 2 and 3 are 3D coordination networks having novel topologies with different channels, where the Ag–Ag bonds play vital roles. In these complexes, hmt ligands act as μ3- and μ4- bridges in 1 and 3, and just μ4- in 2. The configurations of the Ag-hmt units in 1–3 are different: chair types in 1 and 2, and boat type in 3. The disparately relative positions of carboxylate and sulfonate groups on benzyl rings of 2, 3, and 4-sulfobenzoate ligands and the different coordination modes of sulfobenzoates lead to the different dimensionalities and networks. The different packing environments of Ag–Ag bonds in 1–3 (no Ag–Ag interaction in 1 and the strongest Ag–Ag interactions in 2) result in the distinct fluorescence properties and electric conductivity. There is no any study of electric conductivity for Ag-hmt complexes in the references so far, and the complex 2 has the best electric conductivity in all our reported Ag-sulfobenzoate complexes.