Mayokofod7742

On Earth water plays an active role in the cellular life, over several scales of distance and time. At the nanoscale, water drives macromolecular conformation through hydrophobic forces and at short times acts as proton donor/acceptor providing charge carriers for signal transmission. At longer times and larger distances water controls osmosis, transport and protein mobility. Neutron diffraction experiments augmented by computer-simulation, show that the three-dimensional shape of the hydration shell of carboxyl and carboxylate groups belonging to different molecules is characteristic of each molecule. Different hydration shells identify and distinguish specific sites with the same chemical structure. These experimental evidence suggests an active role of water also at controlling, modulating, and mediating chemical reactions involving carboxyl and carboxylate groups.The ability to control crystallization is of central importance to many technologies and pharmaceutical materials. Electric fields have been shown to impact crystallization, but little is known about the mechanism of such effects. Here we report on our observations of how the frequency of an external electric (ac) field changes the crystallization rate and the partitioning into distinct polymorphs of vinylethylene carbonate. We find that the field effects are pronounced only for frequencies below a certain threshold, which is orders of magnitude below that characterizing molecular orientation but consistent with the reorientation of polar crystal nuclei of radius r less then 3 nm. We conclude that the electric field opens an additional nucleation pathway by lowering the free-energy barrier to form a polymorph that melts at a temperature ∼20 K below that of the ordinary crystal. This lower melting polymorph is not obtained at zero electrical field.Gadolinium-based contrast agents are widely used in magnetic resonance imaging procedures to enhance image contrast. Despite their ubiquitous use in clinical settings, gadolinium is not an innocuous element, as suggested by several disorders associated with its use. Therefore, novel analytical technologies capable of tracking contrast agent excretion through urine are necessary for optimizing patient safety after imaging procedures. Here, we describe an assay to detect and quantify contrast agents in urine based on the luminescence quenching of a metal chelate probe, Eu3+-3,4,3-LI(1,2-HOPO), which only requires 10 min incubation before measurement. Gadolinium-based contrast agents prevent the formation of the Eu3+-3,4,3-LI(1,2-HOPO) complex, subsequently decreasing the luminescence of the assay solution. Three commercial contrast agents, Magnevist, Multihance, and Omniscan, were used to demonstrate the analytical concept in synthetic human urine, and subsequent quantification of mouse urine samples. To the best of our knowledge, this is the first assay capable of detecting and quantifying gadolinium-based contrast agents in urine without sample preparation or digestion.Diagnostic and predictable gas-phase ion-molecule reactions have emerged as a potential alternative to collision-activated dissociation in tandem mass spectrometry (MS2) experiments performed to gain structural information for unknown organic compounds, such as drug metabolites, in complex mixtures. However, the applicability of this approach for analyzing metabolites at physiologically relevant concentrations has not been determined. In this study, HPLC/MS2 experiments based on gas-phase ion-molecule reactions of protonated model compounds were successfully conducted at nanomolar and picomolar analyte concentrations. UNC8153 As the analyte concentration decreased, the signal-to-noise ratio of the HPLC peaks decreased more than the signal-to-noise ratio of the mass spectrometer peaks. Therefore, the HPLC part of this analysis was the primary limiting factor for each analyte (rather than the ion-molecule reactions). The ion-molecule reaction limits of detection ranged from 50 pM to 250 nM with the average being 50-100 nM. Since all compounds had ion-molecule reaction detection limits below 500 nM, the detection limits are within the physiologically relevant range for in vivo studies of drugs and drug metabolites. When considering only mass spectrometry, the number of ion isolation events (one in MS2 experiments involving ion-molecule reactions or two in MS3 experiments involving CAD of products formed upon ion-molecule reactions) and the subsequent CAD in the MS3 experiments were the most important limiting factors. Indeed, the limit of detection for the MS3 experiments was 250 nM, about three times higher than the average ion-molecule reaction detection limit of 75 nM but still within physiologically relevant concentrations.Gelation of starch is a process during short-term retrogradation. However, long-term retrogradation always leads to the quality deterioration of starch-based food. In this work, a new type of modified tapioca starch (MTS) gel with maintained short-term gelation strength and retarded long-term retrogradation was prepared using a novel recombinantly produced and characterized 4-α-glucanotransferase (TuαGT). In the resulting MTS, the exterior chains of the amylopectin part were elongated and the content of amylose was reduced because of the disproportionation activity of TuαGT. The retrogradation analysis demonstrated that the MTS possessed highly weakened long-term retrogradation characteristics as compared to the native starch. Most importantly, the strength of the gel formed by regelatinized MTS is very close to that of gelatinized native tapioca starch when storing below 30 °C. These findings provide a starting point for developing a novel method for the enzymatic modification of the starch-based gels.We present an efficient, analytical, and simple route to approximating tunneling splittings in multidimensional chemical systems, directly from ab initio computations. The method is based on the Wentzel-Kramers-Brillouin (WKB) approximation combined with the vibrational perturbation theory. Anharmonicity and corner-cutting effects are implicitly accounted for without requiring a full potential energy surface. We test this method on the following three systems a model one-dimensional double-well potential, the isomerization of malonaldehyde, and the isomerization of tropolone. The method is shown to be efficient and reliable.