Thermal stability of ester linkage in the presence of 1,2,3‐Triazole moiety generated by click reaction

The copper(I)‐catalyzed alkyne‐azide cycloaddition (CuAAC), so‐called “click” reaction, is one of most useful synthetic strategies to connect two polymer chains. 1,2,3‐Triazole ring (TA) produced by the click reaction has good thermal and chemical stability. However, we observed that block copolymers synthesized by the click reaction showed thermal degradation to give homopolymers when they are thermally annealed at high temperature, which is required for obtaining equilibrium microdomain structure. To investigate the origin of thermal instability of block copolymers, we synthesized model polystyrenes (PSs) using systematically designed bi‐functional atom transfer radical polymerization (ATRP) initiators containing TA. PS including both ester and TA groups showed thermal decomposition at relatively low temperature (e.g., 140 °C). MALDI‐TOF analysis clearly demonstrated that the cleavage site is the ester group adjacent to TA. We also found that the bromine group located at the polymer chain end plays an important role in pyrolysis of ester groups at low temperature. The pyrolysis occurs by syn‐elimination of the ester group. This result implies that the phase behavior of block copolymer synthesized by click reaction should be carefully investigated when high temperature thermal annealing is required. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 427–436     

Polyurethane Ionomers from Cycloaliphatic Diisocyanate and Polytetramethylene Glycol

Abstract

Segmented polyurethane (PU) ionomers were prepared from cycloaliphatic diisocyanate [methylene bis(4-cyclohexyl isocyanate) (H₁₂MDI) and isophoron diisocyanate (IPDI)] and polytetramethylene glycol (PTMG) by using an anionic-type chain extender, viz., dimethylol propionic acid (DMPA). The effect of ionic content and butanediol (BD) on the state of dispersion and physical properties of emulsion-cast film was determined using Autosizer, transmission electron microscopy (TEM), Instron, and Rheovibron. With increased incorporations of DMPA in PU, particle size of emulsion decreased asymptotically, tensile modulus and strength increased, and the glass transition temperature (T _g) moved toward the higher temperature. On the other hand, with increased incorporation of BD in PU, particle size of emulsion, tensile modulus, and strength of the emulsion cast film increased, and the major transition of soft segment moved toward higher temperature. With regard to the structural effect of the isocyanate, H₁₂MDI gave finer dispersion and better mechanical properties over IPDI.     

Quantitative LC–MS/MS method in urine for the detection of drugs used to reverse the effects of chemical castration

The chemical castration law, which targets child molesters with recidivism, was introduced in Korea in 2011. For this, leuprolide, a gonadotropin-releasing hormone agonist, is used to decrease testosterone production and suppress libido. In order to achieve efficient law enforcement, it is necessary to monitor intentional ingestion of drugs that antagonize the effect of leuprolide. Therefore, an analytical method for the simultaneous detection of mirodenafil, sildenafil, tadalafil, udenafil, vardenafil, icariin, alprostadil, and yohimbine, which are the major impotence treatment drugs, legitimately or otherwise, in Korea, as well as their selected metabolites, in human urine was established and validated using liquid chromatography–tandem mass spectrometry (LC–MS/MS). First, different sample preparation methods, two solid-phase extractions with different cartridges and protein precipitation, were compared and protein precipitation was chosen for the entire study because it showed better matrix effects and recoveries. Thus, the drugs and metabolites in urine were extracted by protein precipitation and then filtered and analyzed by LC–MS/MS with polarity switching electrospray ionization. The validation results of selectivity, matrix effect, recovery, linearity, intra- and inter-assay precision and accuracy were satisfactory. The limits of detection ranged from 0.25 to 10 ng/mL, and the limits of quantification were 2.5 to 50 ng/mL. The drugs and metabolites in urine did not show any degradation under storage for 7 and 15 days at 4 and ?20 °C as well as after three freeze–thaw cycles. The developed method will be very useful for monitoring the illegal use of impotence treatment drugs.     

Synthesis and properties of near IR induced self-healable polyurethane/graphene nanocomposites

A series of self-healable polyurethane (SHPU)/modified graphene (MG) nanocomposites were synthesized from poly(tetramethylene glycol) (PTMG) and 4,4′-methylene diphenyl diisocyanate (MDI) with minute amounts (0–1 wt%) of MG which was chemically modified graphene oxide (GO) with phenyl isocyanate and reduced in the presence of phenylhydrazine.     

Determination of micro‐RNA in cardiomyoblast cells using CE with LIF detection

Micro‐RNAs (miRNAs) are small, endogenous, singlestranded, and noncoding RNAs. The miRNAs have been found to perform important functions in many cellular processes, such as development, proliferation, differentiation, and apoptosis. Circulating miRNAs have been proposed as emerging biomarkers in diseases such as cancer, diabetes, and cardiovascular disease including acute myocardial infarction (AMI). In this study, we developed CE with LIF (CE‐LIF) using fluorescence‐labeled DNA probe for determination of low abundance miRNA in cell extracts. The target miRNA is miRNA‐499, a biomarker candidate of AMI with low abundance in biological samples. In order to measure the trace level of miRNA, we optimized the hybridization conditions such as hybridization time, temperature, and buffer solution. The highest fluorescence intensity of the hybridized miRNA‐499 was found when hybridization was conducted at 40°C in 50 mM Tris‐acetate (pH 8.0) buffer containing 50 mM NaCl, and 10 mM EDTA for 15 min. The hybridized miRNA‐499 was detected in cultured H9c2 cardiomyoblast cells and the analysis of miRNA‐499 was completed within 1 h using CE‐LIF. These results showed the potential of CE for fast, specific, and sensitive high‐throughput analysis of low‐abundance miRNAs in cell extracts, biofluids, and tissues.     

Rapid and sensitive detection of lower respiratory tract infections by stuffer‐free multiplex ligation‐dependent probe amplification

Lower respiratory tract infection is one of the most common infectious diseases. However, conventional methods for detecting infectious pathogens are time‐consuming, and generally have a limited impact on early therapeutic decisions. We previously reported a rapid and sensitive method for detecting such pathogens using stuffer‐free multiplex ligation‐dependent probe amplification coupled with high‐resolution CE‐SSCP. In this study, we report an application of this method to the detection of respiratory pathogens. As originally configured, this method was capable of simultaneously detecting seven bacterial species responsible for lower respiratory tract infections, but its detection limit and assay time were insufficient to provide useful information for early therapeutic decisions. To improve sensitivity and shorten assay time, we added a target‐specific preamplification step, improving the detection limit from 50 pg of genomic DNA to 500 fg. We further decreased time requirements by optimizing the hybridization step, enabling the entire assay to be completed within 7 h while maintaining the same detection limit. Taken together, these improvements enable the rapid detection of infectious doses of pathogens (i.e. a few dozen cells), establishing the strong potential of the refined method, particularly for aiding early treatment decisions.     

Exploring the Role of Surface States in Emissive Carbon Nanodots: Analysis at Single-Particle Level

Fluorescent carbon nanodots (CDs) have been highlighted as promising semiconducting materials due to their outstanding chemical and optical properties. However, the intrinsic heterogeneity of CDs has impeded a clear understanding of the mechanisms behind their photophysical properties. In this study, as-prepared CDs are fractionated via chromatography to reduce their structural and chemical heterogeneity and analyzed through ensemble and single-particle spectroscopies. Many single particles reveal fluorescence intensity fluctuations between two or more discrete levels with bi-exponential decays. While the intrinsic τ₁ components are uniform among single particles, the τ₂ components from molecule-like emissions spans a wider range of lifetimes, reflecting the inhomogeneity of the surface states. Furthermore, it is concluded that the relative population and chemical states of surface functional groups in CDs have a significant impact on emissive states, brightness, blinking, stability, and lifetime distribution of photoluminescence.     

Transplantation of betacellulin-transduced islets improves glucose intolerance in diabetic mice

Type 1 diabetes is an autoimmune disease caused by permanent destruction of insulin-producing pancreatic β cells and requires lifelong exogenous insulin therapy. Recently, islet transplantation has been developed, and although there have been significant advances, this approach is not widely used clinically due to the poor survival rate of the engrafted islets. We hypothesized that improving survival of engrafted islets through ex vivo genetic engineering could be a novel strategy for successful islet transplantation. We transduced islets with adenoviruses expressing betacellulin, an epidermal growth factor receptor ligand, which promotes β-cell growth and differentiation, and transplanted these islets under the renal capsule of streptozotocin-induced diabetic mice. Transplantation with betacellulin-transduced islets resulted in prolonged normoglycemia and improved glucose tolerance compared with those of control virus-transduced islets. In addition, increased microvascular density was evident in the implanted islets, concomitant with increased endothelial von Willebrand factor immunoreactivity. Finally, cultured islets transduced with betacellulin displayed increased proliferation, reduced apoptosis and enhanced glucose-stimulated insulin secretion in the presence of cytokines. These experiments suggest that transplantation with betacellulin-transduced islets extends islet survival and preserves functional islet mass, leading to a therapeutic benefit in type 1 diabetes.