Sequential Order of the Secondary Structure Transitions of Proteins under External Perturbations: Regenerated Silk Fibroin under Thermal Treatment

Whether the process of protein folding/unfolding is fully cooperative or it contains sequential elements has long been a fundamental issue in protein science. This issue seemingly became straightforward since the appearance of generalized two-dimensional (2D) correlation spectroscopy in 1990s, because 2D correlation analysis has been considered as a convenient and powerful analytical tool to determine the sequential order of events under external physical or chemical perturbations. In this work, the sequential order of the secondary structure transitions of regenerated silk fibroin under thermal treatment from 130 to 220 °C was first studied using generalized 2D correlation spectroscopy, but an apparently doubtful sequential order was obtained; β-sheet was the first one to change at low temperature, then the random coil, followed by the nonamide CO and, finally, the α-helix. A subsequent detailed in situ infrared spectral analysis showed that the main secondary structures of silk fibroin, including α-helix, β-turn, random coil and β-sheet (high-wavenumber component), all changed with a fully cooperative manner at a relatively low temperature of 150 °C. But the low-wavenumber component of β-sheet started to change at a higher temperature of 180 °C. Besides, it has also been found that, before 200 °C, the loss of α-helix and random coil was transformed into β-turn, β-sheet, and nonamide CO. After 200 °C, some β-turn structure was also disruptured and transformed into β-sheet and nonamide CO

Construction of Lanthanide–Organic Frameworks from 2-(pyridine-3-yl)-1<i>H</i>-4,5-imidazoledicarboxylate and Oxalate

Three novel isostructural lanthanide organic frameworks, |(H₂O)­(H₃O)|[Ln­(HPyImDC)­(OX)_0.5Cl] (Ln = Pr (<b>1</b>), Nd (<b>2</b>), and Sm (<b>3</b>), H₃PyImDC = 2-(pyridine-3-yl)-1<i>H</i>-4,5-imidazoledicarboxylic acid, H₂OX = oxalic acid) have been prepared under hydrothermal conditions and characterized by single crystal X-ray diffraction, elemental analysis, IR spectra, and thermogravimetric analysis. The results of crystal structural analysis indicate that three compounds are isomorphous 3D frameworks, which are constructed by lanthanide polyhedral {LnNClO₆}, 4-connected HPyImDC^2– ligand and bridging OX^2– ligand. The HPyImDC^2– ligand offering its four oxygen atoms and one nitrogen atom of the pyridyl group, and the OX^2– ligand offering all its four oxygen atoms coordinate with the lanthanide ions, which is a key essential for constructing the 3D frameworks. Topological analysis reveals that the 3D framework can be simplified into a 5-connected network with the lanthanide ion as a unique node, possessing the rare <b>sqp</b> topology. Meanwhile, the luminescent properties of three compounds in the solid state at room temperature are also investigated

Construction of Lanthanide–Organic Frameworks from 2-(pyridine-3-yl)-1<i>H</i>-4,5-imidazoledicarboxylate and Oxalate

Three novel isostructural lanthanide organic frameworks, |(H₂O)­(H₃O)|[Ln­(HPyImDC)­(OX)_0.5Cl] (Ln = Pr (<b>1</b>), Nd (<b>2</b>), and Sm (<b>3</b>), H₃PyImDC = 2-(pyridine-3-yl)-1<i>H</i>-4,5-imidazoledicarboxylic acid, H₂OX = oxalic acid) have been prepared under hydrothermal conditions and characterized by single crystal X-ray diffraction, elemental analysis, IR spectra, and thermogravimetric analysis. The results of crystal structural analysis indicate that three compounds are isomorphous 3D frameworks, which are constructed by lanthanide polyhedral {LnNClO₆}, 4-connected HPyImDC^2– ligand and bridging OX^2– ligand. The HPyImDC^2– ligand offering its four oxygen atoms and one nitrogen atom of the pyridyl group, and the OX^2– ligand offering all its four oxygen atoms coordinate with the lanthanide ions, which is a key essential for constructing the 3D frameworks. Topological analysis reveals that the 3D framework can be simplified into a 5-connected network with the lanthanide ion as a unique node, possessing the rare <b>sqp</b> topology. Meanwhile, the luminescent properties of three compounds in the solid state at room temperature are also investigated

Highly Sensitive Two-Photon Sensing of Thrombin in Serum Using Aptamers and Silver Nanoparticles

Thrombin plays an important role in pathological conditions. It is important, however challenging, to detect thrombin in complex biological media for clinical practice and diagnostic applications. Here we demonstrate a label-free, fast, highly sensitive and selective two-photon sensing scheme for detection of thrombin on the picomolar level. The assay is based on interactions between thrombin and a DNA aptamer, which induce aggregation of silver nanoparticles to display significantly enhanced two-photon photoluminescence. The limit of detection (LOD) of this two-photon sensing assay is as low as 3.1 pM in the buffer solution, more than 400 times lower than that of the extinction method (1.3 nM). The dynamic range of this method covers more than 4 orders of magnitude. Furthermore, this two-photon sensing assay can be applied to detection of thrombin in 100% fetal bovine serum with LOD of 1.8 nM. In addition to the unique advantages of two-photon sensing such as deep penetration and localized detection, this method could be potentially integrated with two-photon microscopy to offer additional advantages of 3D detection and mapping for potential in vivo applications

A 52-year-old woman with papillary thyroid carcinoma.

<p>Longitudinal sonogram showing a 45-mm, ill-defined, hypoechoic solid nodule in the right thyroid lobe. A linear echogenic focus with reverse-triangle artifact (solid arrow), and a round echogenic focus with fine artifact (arrowhead), and a punctate echogenic foci (faint arrow) are seen (Type 3).</p

Construction of Lanthanide–Organic Frameworks from 2-(pyridine-3-yl)-1<i>H</i>-4,5-imidazoledicarboxylate and Oxalate

Three novel isostructural lanthanide organic frameworks, |(H₂O)­(H₃O)|[Ln­(HPyImDC)­(OX)_0.5Cl] (Ln = Pr (<b>1</b>), Nd (<b>2</b>), and Sm (<b>3</b>), H₃PyImDC = 2-(pyridine-3-yl)-1<i>H</i>-4,5-imidazoledicarboxylic acid, H₂OX = oxalic acid) have been prepared under hydrothermal conditions and characterized by single crystal X-ray diffraction, elemental analysis, IR spectra, and thermogravimetric analysis. The results of crystal structural analysis indicate that three compounds are isomorphous 3D frameworks, which are constructed by lanthanide polyhedral {LnNClO₆}, 4-connected HPyImDC^2– ligand and bridging OX^2– ligand. The HPyImDC^2– ligand offering its four oxygen atoms and one nitrogen atom of the pyridyl group, and the OX^2– ligand offering all its four oxygen atoms coordinate with the lanthanide ions, which is a key essential for constructing the 3D frameworks. Topological analysis reveals that the 3D framework can be simplified into a 5-connected network with the lanthanide ion as a unique node, possessing the rare <b>sqp</b> topology. Meanwhile, the luminescent properties of three compounds in the solid state at room temperature are also investigated

Aqueous Synthesis of Multidentate-Polymer-Capping Ag₂Se Quantum Dots with Bright Photoluminescence Tunable in a Second Near-Infrared Biological Window

A new strategy for fabricating water-dispersible Ag₂Se quantum dots (QDs) is presented. A multidentate polymer (MDP) was synthesized and used as a capping agent for Ag₂Se QDs. The MDP-capping Ag₂Se QDs were synthesized in aqueous solution at room temperature, which are highly photoluminescent in a second near-infrared (NIR-II) biological window and possess good photostability. These readily prepared NIR-II fluorescent nanoprobes have great potential for biomedical applications, especially useful for in vivo imaging

Highly Sensitive CO₂‑Responsive Polymeric Microgels That Respond Within Seconds

In this work, polymeric microgels with swift response to CO₂ are synthesized by polymerization of tertiary-amine containing methacrylate monomers (<i>N</i>,<i>N</i>-diethylaminoethyl methacrylate, DEAEMA) and polyethylene glycol monomethyl ether acrylate (PEGMA) as stabilizers. The obtained microgels are stable but very sensitive to CO₂, which can rapidly swell and further collapse within 5 s upon bubbling of CO₂, or within minutes in an atmosphere of gaseous CO₂. The protonation of the tertiary amine groups in the presence of CO₂ induces sensitive swelling and further irreversible collapse of the microgels due to the internal charge repulsion and relatively low cross-linking density in the core area of microgels. This rapid response to CO₂ may find further applications in the fields of sensitive detection or responsive loading and release upon CO₂ stimulus

Ratiometric and Time-Resolved Fluorimetry from Quantum Dots Featuring Drug Carriers for Real-Time Monitoring of Drug Release in Situ

An effective ratiometric and time-resolved fluorimetry was described. On the basis of Förster resonance energy transfer (FRET) between semiconductor quantum dots (QDs) and fluorescent drugs, poly­(ethylene glycol)-modified QDs were successfully prepared and further developed as QDs featuring carriers for real-time monitoring of drug release in situ

Construction of Lanthanide–Organic Frameworks from 2-(pyridine-3-yl)-1<i>H</i>-4,5-imidazoledicarboxylate and Oxalate

Three novel isostructural lanthanide organic frameworks, |(H₂O)­(H₃O)|[Ln­(HPyImDC)­(OX)_0.5Cl] (Ln = Pr (<b>1</b>), Nd (<b>2</b>), and Sm (<b>3</b>), H₃PyImDC = 2-(pyridine-3-yl)-1<i>H</i>-4,5-imidazoledicarboxylic acid, H₂OX = oxalic acid) have been prepared under hydrothermal conditions and characterized by single crystal X-ray diffraction, elemental analysis, IR spectra, and thermogravimetric analysis. The results of crystal structural analysis indicate that three compounds are isomorphous 3D frameworks, which are constructed by lanthanide polyhedral {LnNClO₆}, 4-connected HPyImDC^2– ligand and bridging OX^2– ligand. The HPyImDC^2– ligand offering its four oxygen atoms and one nitrogen atom of the pyridyl group, and the OX^2– ligand offering all its four oxygen atoms coordinate with the lanthanide ions, which is a key essential for constructing the 3D frameworks. Topological analysis reveals that the 3D framework can be simplified into a 5-connected network with the lanthanide ion as a unique node, possessing the rare <b>sqp</b> topology. Meanwhile, the luminescent properties of three compounds in the solid state at room temperature are also investigated