183 research outputs found
Shrinking droplets in electrospray ionization and their influence on chemical equilibria
We investigated how chemical equilibria are affected by the electrospray process, using simultaneous in situ measurements by laser-induced fluorescence (LIF) and phase Doppler anemometry (PDA). The motivation for this study was the increasing number of publications in which electrospray ionization mass spectrometry is used for binding constant determination. The PDA was used to monitor droplet size and velocity, whereas LIF was used to monitor fluorescent analytes within the electrospray droplets. Using acetonitrile as solvent, we found an average initial droplet diameter of 10 µm in the electrospray. The PDA allowed us to follow the evolution of these droplets down to a size of 1 µm. Rhodamine B-sulfonylchloride was used as a fluorescent analyte within the electrospray. By spatially resolved LIF it was possible to probe the dimerization equilibrium of this dye. Measurements at different spray positions showed no influence of the decreasing droplet size on the monomer-dimer equilibrium. However, with the fluorescent dye pair DCM and oxazine 1 it was shown that a concentration increase does occur within electrosprayed droplets, using fluorescence resonance energy transfer as a probe for the average pair distanc
Statistical mechanics of semiflexible polymers
We present the statistical-mechanical theory of semiflexible polymers based
on the connection between the Kratky-Porod model and the quantum rigid rotator
in an external homogeneous field, and treatment of the latter using the quantum
mechanical propagator method. The expressions and relations existing for
flexible polymers can be generalized to semiflexible ones, if one replaces the
Fourier-Laplace transform of the end-to-end polymer distance, ,
through the matrix , where and are
related to the spectrum of the quantum rigid rotator, and considers an
appropriate matrix element of the expression under consideration. The present
work provides also the framework to study polymers in external fields, and
problems including the tangents of semiflexible polymers. We study the
structure factor of the polymer, the transversal fluctuations of a free end of
the polymer with fixed tangent of another end, and the localization of a
semiflexible polymer onto an interface. We obtain the partition function of a
semiflexible polymer in half space with Dirichlet boundary condition in terms
of the end-to-end distribution function of the free semiflexible polymer, study
the behaviour of a semiflexible polymer in the vicinity of a surface, and
adsorption onto a surface.Comment: 30 pages, 7 figures, changed conten
A MAFG-lncRNA axis links systemic nutrient abundance to hepatic glucose metabolism
Obesity and type 2 diabetes mellitus are global emergencies and long noncoding RNAs (lncRNAs) are regulatory transcripts with elusive functions in metabolism. Here we show that a high fraction of lncRNAs, but not protein-coding mRNAs, are repressed during diet-induced obesity (DIO) and refeeding, whilst nutrient deprivation induced lncRNAs in mouse liver. Similarly, lncRNAs are lost in diabetic humans. LncRNA promoter analyses, global cistrome and gain-of-function analyses confirm that increased MAFG signaling during DIO curbs lncRNA expression. Silencing Mafg in mouse hepatocytes and obese mice elicits a fasting-like gene expression profile, improves glucose metabolism, de-represses lncRNAs and impairs mammalian target of rapamycin (mTOR) activation. We find that obesity-repressed LincIRS2 is controlled by MAFG and observe that genetic and RNAi-mediated LincIRS2 loss causes elevated blood glucose, insulin resistance and aberrant glucose output in lean mice. Taken together, we identify a MAFG-lncRNA axis controlling hepatic glucose metabolism in health and metabolic disease
A MAFG-lncRNA axis links systemic nutrient abundance to hepatic glucose metabolism
Obesity and type 2 diabetes mellitus are global emergencies and long noncoding RNAs (lncRNAs) are regulatory transcripts with elusive functions in metabolism. Here we show that a high fraction of lncRNAs, but not protein-coding mRNAs, are repressed during diet-induced obesity (DIO) and refeeding, whilst nutrient deprivation induced lncRNAs in mouse liver. Similarly, lncRNAs are lost in diabetic humans. LncRNA promoter analyses, global cistrome and gain-of-function analyses confirm that increased MAFG signaling during DIO curbs lncRNA expression. Silencing Mafg in mouse hepatocytes and obese mice elicits a fasting-like gene expression profile, improves glucose metabolism, de-represses lncRNAs and impairs mammalian target of rapamycin (mTOR) activation. We find that obesity-repressed LincIRS2 is controlled by MAFG and observe that genetic and RNAi-mediated LincIRS2 loss causes elevated blood glucose, insulin resistance and aberrant glucose output in lean mice. Taken together, we identify a MAFG-lncRNA axis controlling hepatic glucose metabolism in health and metabolic disease
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