Waterborne 2-component polyurethane coatings based on acrylic polyols with secondary alcohols

Synthesis of waterborne polyurethane using snow as dispersant: Structures and properties controlled by polyols utilization

Phosphatidylinositol-(4,5)-bisphosphate [PI(4,5)P(2)] plays a key role in the modulation of actin polymerization and vesicle trafficking. These processes seem to depend on the enrichment of PI(4,5)P(2) in plasma membrane domains. Here, we show that PI(4,5)P(2) does not form domains when in a fluid phosphatidylcholine matrix in the pH range of 4.8-8.4. This finding is at variance with the spontaneous segregation of PI(4,5)P(2) to domains as a mechanism for the compartmentalization of PI(4,5)P(2) in the plasma membrane. Water/bilayer partition of PI(4,5)P(2) is also shown to be dependent on the protonation state of the lipid.

Interpenetrating polymer networks (IPNs) were prepared from polyurethane (PU)-modified epoxy with different molecular weight of polyol and polyurethanes based on the mixture of polydiol and polytriol by a one-shot method. Two types of PU-modified epoxy: PU-crosslinked epoxy and PU-dangled epoxy were synthesized, and the effects of the different molecular weights of polyol in the PU-modified epoxy/PU IPNs on the dynamic mechanical properties, morphology, and damping behavior were investigated. The results show that the damping ability is enhanced through the introduction of PU-modified epoxy into the PU matrix to form the IPN structure. As the molecular weight of polyol in PU-modified epoxy increases, the loss area (LA) of the two types of the IPNs increases. PU-dangled epoxy/PU IPNs exhibit much higher damping property than that of the PU-crosslinked epoxy/PU IPNs with 20 wt % of PU-crosslinked epoxy. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 328–335, 1999

A novel cyanine 3 (Cy3)-based bio-conjugated sensor has been developed to detect target DNA or extracted RNA from COVID -19 samples using the fluorescence resonance energy transfer (FRET) experiment. A special sequence of the COVID -19 genome was selected as a complementary DNA (target DNA) part. The opposite chain of this target sequence was designed in 2 parts; one part was attached to the Cy3 organic dye (capture DNA or Cy3- DNA), and the other part was attached to the BHQ2 molecule (quencher DNA or BHQ2- DNA). The Cy3 molecule acts as a donor pair, and BHQ2 acts as an acceptor pair in the FRET experiment. The capture DNA and quencher DNA can form a sandwiched complex in the presence of target DNA. The formation of the entitled sandwiched hybrid causes the decrement of emission intensity of the Cy3 donor in bio-conjugated Cy3-DNA via energy transfer from Cy3 (as a donor) to BHQ2 (as an acceptor). Indeed, in the presence of non-complementary DNA, the pairing of DNA strands does not occur, the FRET phenomenon does not exist, and therefore fluorescence intensity of Cy3 does not decrease. Moreover, this biosensor was successfully applied to analyze real samples containing extracted RNA of COVID -19 prepared for the reverse transcriptase-polymerase chain reaction (RT-PCR) test, and the results were promising.

Single molecule fluorescence resonance energy transfer (FRET) experiments are a powerful and versatile tool for studying conformational motions of single biomolecules. However, the small number of recorded photons typically limits the achieved time resolution. We develop a maximum likelihood theory that uses the full information of the recorded photon arrival times to reconstruct nanometer distance trajectories. In contrast to the conventional, intensity-based approach, our maximum likelihood approach does not suffer from biased a priori distance distributions. Furthermore, by providing probability distributions for the distance, the theory also yields rigorous error bounds. Applied to a burst of 230 photons obtained from a FRET dye pair site-specifically linked to the neural fusion protein syntaxin-1a, the theory enables one to distinguish time-resolved details of millisecond fluctuations from shot noise. From cross validation, an effective diffusion coefficient is also determined from the FRET data.

Quantum-dot-assisted fluorescence resonance energy transfer approach for intracellular trafficking of chitosan/DNA complex

PASTICCINO1 (PAS1) is a high molecular weight FK506-binding protein (FKBP) involved in the control of cell proliferation and differentiation during plant development. Mutations in the C-terminal region of PAS1 result in severe developmental defects. We show here that the C-terminal domain of PAS1 controls the subcellular distribution of this protein. We also demonstrated in vitro and in vivo, by Forster resonance energy transfer, that this C-terminal region is required for interaction with FAN (FKBP-associated NAC), a new member of the plant-specific family of NAC transcription factors. PAS1 and FAN are translocated into the nucleus upon auxin treatment in plant seedlings. The nuclear translocation of PAS1 is dependent on the presence of the C terminus of the protein. Finally, we showed that FAN is involved in PAS1-regulated processes because FAN overproduction partly complemented the pas1 phenotype. We suggest that PAS1 regulates the function of this NAC-like transcription factor by controlling its targeting to the nucleus upon plant cell division.

Waterborne polyurethane coatings were prepared using polyhydroxyacrylate dispersion, polyisocyanate, and propylene glycol diacetate (PGDA). The rate of reaction between hydroxyl and NCO groups in film formation and curing processes was studied by FTIR. The influence of PGDA amount on film formation and curing was also studied. Results showed that PGDA content had a significant effect on the curing process. With less than 10% PGDA, the role of PGDA was more to assist diffusion of polyhydroxyacrylate and polyisocyanate resin droplets. This promoted the reaction between hydroxyl groups and NCO. With more than 10% PGDA, its effect as a solvent was more and it inhibited the reaction between hydroxyl and NCO groups. When the amount of PGDA was about 10%, the synergy between both the roles promoted the crosslinking and curing reactions. The extent of the curing reaction of NCO was more than 70% in 4 h, which was significantly higher, compared with that of about 30% without PGDA. The good applicability and appearance of the waterborne polyurethane coating prepared in this study were verified for the application to carbon fiber metro vehicles.

The misfolding and self-assembly of proteins into amyloid fibrils that occurs in several debilitating and age-related diseases is affected by common components of amyloid deposits, notably lipids and lipid complexes. We have examined the effect of the short-chain phospholipids, dihexanoylphosphatidylcholine (DHPC) and dihexanoylphosphatidylserine (DHPS), on amyloid fibril formation by human apolipoprotein C-II (apoC-II). Micellar DHPC and DHPS strongly inhibited apoC-II fibril formation, whereas submicellar levels of these lipids accelerated apoC-II fibril formation to a similar degree. These results indicate that the net negative charge on DHPS, compared with the neutrally charged DHPC, is not critical for either the inhibition or activation process. We also investigated the mechanism for the submicellar, lipid-induced activation of fibril formation. Emission data for fluorescently labeled apoC-II indicated that DHPC and DHPS stimulate the early formation and accumulation of oligomeric species. Sedimentation velocity and equilibrium experiments using a new fluorescence detection system identified a discrete lipid-induced tetramer formed at low apoC-II concentrations in the absence of significant fibril formation. Seeding experiments showed that this tetramer was on the fibril-forming pathway. Fluorescence resonance energy transfer experiments established that this tetramer forms rapidly and is stabilized by submicellar, but not micellar, concentrations of DHPC and DHPS. Several recent studies show that oligomeric intermediates in amyloid fibril formation are toxic. Our results indicate that lipids promote on-pathway intermediates of apoC-II fibril assembly and that the accumulation of a discrete tetrameric intermediate depends on the molecular state of the lipid.

Vapor and gas permeability of polyurethane membranes. Part I. Structure-property relationship

Low molecular weight (MW) polyols are organic osmolytes influencing protein structure and activity. We have intended to investigate the effects of low MW polyols on the optical and the excited-state properties of the light-harvesting complex 2 (LH2) isolated from the photosynthetic bacterium Thermochromatium (Tch.) tepidum, a thermophile growing at ∼50 °C. Steady state spectroscopy demonstrated that, on increasing glycerol or sorbitol fractions up to 60% (polyol/water, v/v), the visible absorption of carotenoids (Crts) remained unchanged, while the near infrared Qy absorption of bacteriochlorophyll a (BChl) at 800 nm (B800) and 850 nm (B850) varied slightly. Further increasing the fraction of glycerol (but not sorbitol) to 80% (v/v) induced distinct changes of the near infrared absorption and fluorescence spectra. Transient absorption spectroscopy revealed that, following the fast processes of BChl-to-Crt triplet energy transfer, rather weak Qy signals of B800 and B850 remained and evolved in phase with the kinetics of triplet excited state Crt (3Crt*), which are attributed to the Qy band shift as a result of 3Crt*-BChl interaction. The steady state and the transient spectral responses of the Qy bands are found to correlate intimately with the water activity varying against polyol MW and mixing ratio, which are rationalized by the change of the hydration status of the C- and N-termini of LH2. Our results suggest that, with reference to the mesophilic purple bacterium Rhodobacter sphaeroides 2.4.1, Tch. tepidum adopts substantially more robust LH2 hydration against the osmotic effects from the low MW polyols.

To the editor: Fluorescence resonance energy transfer (FRET) efficiency between variants of fluorescent protein can be determined by photobleaching the acceptor molecule1. After complete acceptor bleaching, FRET efficiency equals the dequenched donor fluorescence divided by the total donor fluorescence. Recently, Valentin et al.2 reported that photobleaching of yellow fluorescent protein (YFP), Citrine and Venus (commonly used acceptor fluorescent protein tags) produced a species with an emission peak similar to that of cyan fluorescent protein (CFP), a widely-used donor fluorescent protein. This result predicts that FRET efficiency determined by acceptor photobleaching will be overestimated. As this prediction potentially impacts the accuracy of numerous existing studies and raises concerns about the validity of the photobleaching method, we examined the effects of acceptor fluorescent protein photobleaching using several imaging modalities commonly used in FRET experiments. We imaged HeLa cells coexpressing Venus and nuclear-localized CFP one day after transfection (Fig. 1a; Supplementary Methods online). Prolonged illumination through a YFP filter set (excitation: 500 ± 10 nm, emitter: 540 ± 15 nm, dichroic: 520LP) decreased the intensity of Venus fluorescence (YFP filter set) evenly throughout the cell. Conversely, the pattern and intensity of fluorescence detected through a CFP filter (excitation: 436 ± 10 nm, emitter: 480 ± 20 nm, dichroic: 455LP) remained unchanged. Additionally, fixation of cells expressing YFP or Venus with paraformaldehyde followed by photobleaching (50% decrease in YFP channel intensity) did not produce an increase in CFP channel fluorescence intensity (Supplementary Fig. 1 online). We obtained similar results (Supplementary Fig. 1) using CFP excitation (excitation: 406 ± 7.5 nm) similar to that used by Valentin et al.2. We determined the emission spectra of either Venus or YFP before and after photobleaching (514 nm argon ion laser) of fixed HeLa cells expressing these proteins. Photobleaching of Venus or YFP (> 50%) did not alter the shape of the emission spectra acquired with an LSM510 confocal microscope using two-photon excitation between 750 and 940 nm (Fig. 1b, and Supplementary Figs. 1 and 2 online). In particular, we observed no detectable increase in fluorescence intensity from 420–500 nm. This finding is in marked contrast to the result of Valentin et al.2. Our results demonstrate that photobleaching of YFP or Venus, under the conditions stated, does not produce CFP-like fluorescence, and thus FRET efficiency determination using acceptor photobleaching need not be encumbered by the reported phenomenon2. It is unclear why our results deviate from those of Valentin et al.2 as experimental conditions were similar (but not identical).

Let’s Twist (the S4) Again

Materials and methods We generated a transgenic mouse model with cardiomyocyte-specific expression of the highly sensitive fluorescence resonance energy transfer (FRET)-based cGMP biosensor red cGES-DE5. This sensor mouse allows us to performed FRET measurements of cGMP in freshly isolated adult mouse ventricular myocytes, to visulaize realtime dynamics of cGMP. To analyze cAMP and cGMP interactions (cGMP/cAMP signaling crosstalk), FRET experiments were performed in cardiomyocytes isolated from mice, transgenically expressing the FRET-based cAMP sensor Epac1-camps.

Cytosolic delivery of macromolecules: 4. Head group-dependent membrane permeabilization by pH-sensitive detergents