Regression data processing methods for parallel zero- and first-order processes applied to lactate dehydrogenase subunit determinations

Multipoint data-processing methods developed for parallel zero-order and first-order processes have been evaluated for the simultaneous determination of the heart and muscle subunits of lactate dehydrogenase. Conditions are adjusted such that pyruvate inhibition of heart and muscle subunits of the enzyme follows pseudo-first-order kinetics with apparent rate constants of k_H? 0.7 s^-1 and k_M? 1.4 s^-1 for the heart and muscle subunits, respectively. The influence of these first-order inhibition processes on the zero-order catalytic reaction is used to determine the two subunits in single- and two-component samples. Stopped-flow mixing is used and 250 data points collected during the early part of the reaction are fitted to four different mathematical models for the parallel process in order to determine initial velocity components resulting from each subunit present, and these velocity components are related to enzyme concentration. Enzymes in synthetic samples are determined in the 0–80 nmol l^-1 range with uncertainties of about 1 nmol l^-1 for single- and two-component samples prepared from purified preparations for the enzymes.     

Ultraweak Photon Emission from the Seed Coat in Response to Temperature and Humidity—A Potential Mechanism for Environmental Signal Transduction in the Soil Seed Bank

Seeds beneath the soil sense the changing environment to time germination and seedling emergence with the optimum time of year for survival. Environmental signals first impact with the seed at the seed coat. To investigate whether seed coats have a role in environmental sensing we investigated their ultraweak photon emission (UPE) under the variable temperature, relative humidity and oxygen conditions they could experience in the soil seed bank. Using a custom‐built luminometer we measured UPE intensity and spectra (300–700 nm) from Phaseolus vulgaris seeds, seed coats and cotyledons. UPE was greatest from the internal surface of the seed coat. Seed coat UPE increased concomitantly with both increasing temperature and decreasing relative humidity. Emission was oxygen dependent and it was abolished by treatment with dinitrophenylhydrazine, demonstrating the key role of seed coat carbonyls in the phenomenon. We hypothesize that beneath the soil surface the attenuation of light (virtual darkness: low background noise) enables seeds to exploit UPE for transducing key environmental variables in the soil (temperature, humidity and oxygen) to inform them of seasonal and local temperature patterns. Overall, seed coats were found to have potential as effective transducers of key fluctuating environmental variables in the soil.     

Optical activity in mixed-ligand terbium complexes containing 5-sulfosalicyclic acid and chiral hydroxycarboxylic acids

The optical activity associated with the f-f; emission bands of Tb(III) complexes which contain chiral hydroxycarboxylic acids has been studied by means of circularly polarized luminescence (CPL) spectroscopy. Complexes having the general formula Tb(SSA)₂(L) were studied (where SSA signifies 5-sulphosalicylic acid), with the chiral ligand (L) being L-lactic acid, L-mandelic acid, L-aspartic acid, and L-malic acid. The CPL spectra were found to be sensitive to the mode of bonding between the metal and the chiral ligand and therefore allowed predictions to be made regarding how the hydroxycarboxylic acid ligands attach to the Tb(III) ion. Also, the degree of optical activity varied systematically with the concentration of chiral ligand, and we have used this dependence to calculate formation constants for the addition of a hydroxycarboxylic acid ligand to the Tb/SSA complex. Finally, the line shape and magnitudes of the CPL spectra provide information regarding the type of chirality experienced by the Tb(III) ion.     

Automated,Accelerated Nanoscale Synthesis of Iminopyrrolidines

Miniaturization and acceleration of synthetic chemistry is an emerging area in pharmaceutical, agrochemical, and materials research and development. Herein, we describe the synthesis of iminopyrrolidine‐2‐carboxylic acid derivatives using chiral glutamine, oxo components, and isocyanide building blocks in an unprecedented Ugi‐3‐component reaction. We used I‐DOT, a positive‐pressure‐based low‐volume and non‐contact dispensing technology to prepare more than 1000 different derivatives in a fully automated fashion. In general, the reaction is stereoselective, proceeds in good yields, and tolerates a wide variety of functional groups. We exemplify a pipeline of fast and efficient nanomole‐scale scouting to millimole‐scale synthesis for the discovery of a useful novel reaction with great scope.     

Hydrogels based on schiff base formation between an amino‐containing polyphosphazene and aldehyde functionalized‐dextrans

Hydrogels generated by the interaction of two different water‐soluble polymers offer access to a new group of soft materials. A prototype amino‐functionalized polyphosphazene with both tyramine and ferulic acid‐based side groups was coupled to aldehyde functionalized‐dextrans to form hydrogels crosslinked via Schiff base chemistry. Synthesis of the polyphosphazene was accomplished by macromolecular substitution and protection‐deprotection chemistry, with characterization by ¹H NMR, ³¹P NMR, solid state ¹³C NMR, and DSC techniques. Combination of the aqueous polyphosphazene and aldehyde functionalized‐dextran solutions at room temperature caused gelation with different gelation times and crosslink densities dependent on the aldehyde content of the dextran. The hydrogel properties were evaluated using rheology, thermal characterization, and cryo‐microscopy. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2984–2991     

ENDOR Spectroscopy — A Promising Technique for Investigating the Structure of Organic Radicals

The name “ENDOR” has been known since biblical times and denotes a small town close to the Sea of Galilee (ca. 1000 B.C., 1 Sam. 28 : 7 ff). The acronym “ENDOR” (Electron Nuclear DOuble Resonance) characterizes the extension of electron spin resonance to electron-nuclear double resonance spectroscopy, a method that has opened up new dimensions for the investigation of complicated paramagnetic molecules. Only ENDOR spectoscopy, which has achieved technical perfection in the last decade, overcomes the resolution limitations of EPR spectroscopy, thus allowing interesting applications in the field of biochemistry. ENDOR investigations of the primary process of photosynthesis, of the mode of action of derivatives of vitamin E and K, and of the mechanism of the enzymatic catalysis of flavoenzymes in biological redox-chains have opened up new vistas. ENDOR and its extension to the triple resonance experiment TRIPLE offer, for example, the potential for a precise determination of hyperfine coupling constants, including their signs, which are frequently especially interesting. In addition to protons, a multiple of magnetic nuclei can be studied by ENDOR, such as e.g. ²H, ¹³C, and ¹⁴N. The ENDOR techniques is not restricted to monoradicals, but can also be applied to polyradicals in spin states of higher multiplicities (triplet, quartet, or quintet state). The experimental data accessible from ENDOR yield information about spin and charge density distributions, and about the geometrics of radicals and their internal dynamics; they also provide an excellent test for the accuracy of quantum mechanical calculations.     

Novel polycyclic heterocycles. VII. Synthesis of tetracyclic ketones and derivatives from tricyclic 5,11-dihydrodibenz[b,e][1,4] oxazepines

Michael addition of 5,11-dihydrodibenz[b,e][1,4]oxazepines to acrylonitrile gave 5,11-di-hydrodibenz[b,e][1,4]oxazepine-5-propionitriles, which were converted to the corresponding methyl 5-propionates. Mild alkaline hydrolysis of these esters furnished the key intermediates, the 5,11-dihydrodibenz[b,e] [1,4]oxazepine-5-propionic acids. In the preferred procedure, these propionic acids were cyclized to the tetracyclic ketones in yields of 60-90%, by the action of one equivalent of trifluoroacetic anhydride in benzene. When ring C was involved in cylcization, 1,2-dihydro-3H,7H-quino[8,1-cd][1,5]benzoxazepin-3-ones were obtained, and when ring A was involved, 1,2-dihydro-3H,8H-quino[1,8-ab] [4,1]benzoxazepin-3-ones were formed. With 1c , both modes of cyclization were observed. In an alternative procedure that gave lower yields, the propionic acids were first converted to the corresponding acid chlorides, and these were cyclized by means of anhydrous stannic chloride; as anticipated, the products by this method were identical with those obtained via the trifluoroacetic anhydride method. Several reactions of these tetra-cylcic ketones, e.g., their ease of oxime formation, and dehydrogenation to the α,β-unsaturated ketones, are described. The α,β-unsaturated ketones do not form oximes. The structures assigned to the ketones are based on interpretations of their pmr, uv, and ir spectra. These assignments were confirmed by an X-ray analysis of a single crystal of one representative ketone, 2b ; the X-ray study was also useful in indicating the thermodynamically preferred conformation of 2b . The structures of all the other compounds followed from similar spectral interpretations. The mass spectra of a few compounds are also discussed.