Water‐stable copolymers containing isocyanate moiety protected by hydrophobic styrene segment and their reaction with amines

Reactive isocyanate groups were protected and stabilized by the hydrophobic styrene segment and acquired high tolerance toward water. Copolymers containing isocyanate groups were synthesized by a radical copolymerization of 2‐propenyl isocyanate (2PI) and styrene (St). The stability of the obtained copolymers on water was examined to find that isocyanate groups were protected by the hydrophobic polystyrene segment and were stable on water and these isocyanates reacted with primary amines including amino acids to form urea selectively on water. Primary amines with a higher octanol‐water partition coefficient or smaller steric hindrance were more reactive to the isocyanate groups in the side chain of the copolymer. The protection of reactive isocyanate groups using the hydrophobic styrene segment did not give side products which are produced in the usual chemical protection/deprotection process. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1934–1940     

Highly sensitive simultaneous quantification of indoxyl sulfate and 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid in human plasma using ultra-high-performance liquid chromatography coupled with tandem mass spectrometry

Indoxyl sulfate and 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid are uremic toxins that accumulate in renal failure and have been reported to decrease the activities of the drug-metabolizing enzyme cytochrome P450 3A and the drug transporter organic anion transporting polypeptides 1B, respectively. In this study, we established and validated an assay for simultaneous quantification of indoxyl sulfate and 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid in human plasma. The samples were pretreated by solid-phase extraction, and measured by ultra-high-performance liquid chromatography–tandem mass spectrometry. The validation results for this assay were within the acceptable limits recommended by the US Food and Drug Administration, with a lower limit of quantitation of 0.05 μg/mL for both indoxyl sulfate and 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid. Recovery rates of indoxyl sulfate and 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid corrected by internal standard were 100.7–101.9 and 100.2–101.3%, respectively. Matrix effects of indoxyl sulfate and 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid corrected by internal standard were 101.1–105.5 and 97.0–103.8%, respectively. The validated assay was used to analyze indoxyl sulfate and 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid concentrations in the plasma samples of healthy volunteers and patients with chronic kidney disease. All the measured plasma indoxyl sulfate and 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid concentrations were within the calibration ranges. This novel method may contribute to predicting the activities of drug-metabolizing enzymes and drug transporters in individual patients.     

Converting an Esterase into an Epoxide Hydrolase

Entering the fold : A common structural motif in hydrolytic enzymes is the α,β‐hydrolase fold. The interconversion of one enzyme into another by introduction of mechanistically important residues is not enough; only substitution of a loop allows epoxide hydrolase activity in the esterase scaffold to be formed (see picture; structure comparison of epoxide hydrolases (green) with the esterase (orange)). The result is an enantioselective chimeric enzyme.

     

Preparation and evaluation of a chiral stationary phase covalently bound with a chiral pseudo-18-crown-6 ether having a phenolic hydroxy group for enantiomer separation of amino compounds

In order to develop a chiral stationary phase (CSP), which has even higher separation ability than the corresponding commercially available crown ether based CSP (OA-8000 having a pseudo-18-crown-6 ether with an OMe group as a selector), chemically bonded type CSP having a phenolic OH group on a crown ring was developed. Normal mobile phases with or without acid additive can be used with this OH type CSP in contrast to the conventional OMe type CSP which has a neutral chiral selector. Enantiomers of 25 out of 27 amino compounds, including 20 amino acids, 5 amino alcohols, and 2 lipophilic amines, were efficiently separated on a column with this CSP. Nine amino compounds out of 27 were separated with better separation factors than the corresponding OMe type CSP. It is noteworthy that the chromatography on this CSP exhibited excellent enantiomer-separations for amines and amino alcohols when triethyl amine was used as an additive in the mobile phase. Comparison of enantiomer separation ability on this OH type of CSP and on the OMe type of CSP and correlation between the enantioselectivity in chiral chromatography and that of the corresponding model compounds in solution imply that the chiral separation arose from chiral recognition in host guest interactions.     

A dual transformation between SO(n + 1) and SO(n, 1) and its geometric applications

There is a dual transformation between SO(n + 1)?{(00-component) = 0} and SO(n, 1). This transformation makes clear the relations how orthogonal axes look like in two spaces, Euclidean space and Minkowski space.     

Stabilities and isomeric equilibria in solutions of monomeric metal-ion complexes of guanosine 5'-triphosphate (GTP4-) and inosine 5'-triphosphate (ITP4-) in comparison with those of adenosine 5'-triphosphate (ATP4-)

Under experimental conditions in which the self-association of the purine-nucleoside 5'-triphosphates (PuNTPs) GTP and ITP is negligible, potentiometric pH titrations were carried out to determine the stabilities of the M(H;PuNTP) and M(PuNTP)2-complexes where M2+ = Mg2+, Ca2+, Sr2+. Ba2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, or Cd2+ (I = 0.1 M, 25 degrees C). The stabilities of all M(GTP)2- and M(ITP)2- complexes are significantly larger than those of the corresponding complexes formed with pyrimidine-nucleoside 5'-triphosphates (PyNTPs), which had been determined previously under the same conditions. This increased complex stability is attributed, in agreement with previous 1H MNR shift studies, to the formation of macrochelates of the phosphate-coordinated metal ions with N7 of the purine residues. A similar enhanced stability (despite relatively large error limits) was observed for the M(H;PuNTP) complexes, in which H+ is bound to the terminal y-phosphate group, relative to the stability of the M(H;PyNTP)- species. The percentage of the macrochelated isomers in the M(GTP)2- and M(ITP)2- systems was quantified by employing the difference log KMM(PuNTP)-log KMM(PyNTP); the lowest and highest formation degrees of the macrochelates were observed for Mg(ITP)2- and Cu(GTP)2- with 17 +/- 11% and 97 +/- 1%, respectively. From previous studies of M(ATP)2- complexes, it is known that innersphere and outersphere macrochelates may form; that is, in the latter case a water molecule is between N7 and the phosphate-coordinated M2+. Similar conclusions are reached now by comparisons with earlier 1H MNR shift measurements, that is, that Mg(GTP)2- (21 +/- 11%), for example, exists largely in the form of an outersphere macrochelate and Zn(GTP)2- (68 +/- 4%) as an innersphere one. Generally, the overall percentage of macrochelate falls off for a given metal ion in the order M(GTP)2- > M(ITP)2- > M(ATP)2-; this is in accord with the decreasing basicity of N7 and the steric inhibition of the (C6)NH2 group in the adenine residue. Furthermore, although the absolute stability constants of the previously studied M(GMP), M(IMP), and M(AMP) complexes differ by about two to three log units from the present M(PuNTP)2- results, the formation degrees of the macrochelates are astonishingly similar for the two series of nucleotides for a given metal ion and purine-nucleobase residue. The conclusion that N7 of the guanine residue is an especially favored binding site for metal ions is also in accord with observations made for nucleic acids.     

Photosensitized NADH formation system with multilayer TiO2 film

A TiO(2)/polymer film on a quartz plate fabricated by a layer-by-layer method was employed for NADH production from NAD(+) with lipoamide dehydrogenase and methyl viologen in Tris-HCl buffer on irradiation with UV light, and the ultra thin film prevented from enzyme deactivating effectively.     

Radical cation and dication of fluorene fully annelated with bicyclo[2.2.2]octene units: importance of the quinoidal resonance structure in the cationic fluorene

Fluorene 1 fully annelated with bicyclo[2.2.2]octene units was newly synthesized and oxidized to stable cationic species. The structure of radical cation salt 1(.+)SbCl(6)(-) was determined by X-ray crystallography, while the first fluorene dication 1(2+) was characterized by (1)H and (13)C NMR at -80 degrees C. Combined with the results of theoretical calculations, an important contribution of a quinoidal structure to the resonance hybrid was demonstrated in both 1(.+) and 1(2+). [structure: see text]     

A rapid and sensitive analysis of diphenylarsinic acid in water by gas chromatography/mass spectrometry.

A rapid and sensitive analytical method using pentafluorothiophenol (PFTP) derivatization was applied to detect diphenylarsinic acid (DPAA) in water. In this study, the optimum derivatization conditions, such as acid concentration, reaction time and reaction temperature, were investigated to develop a suitable procedure for DPAA determination. After extracting the derivatives into benzene, the determination was carried out by gas chromatography/mass spectrometry (GC/MS) with selected ion monitoring (SIM). The detection limit of the method was 9.4 microg/l, and the overall recoveries obtained from real environmental samples were 88.9 - 104.7% and coefficient variations were 5.1 - 13.9%.