Six-fold-symmetry internal rotation in toluenes: the low barrier challenge of 2,6-and 3,5-difluorotoluene

Pure six-fold symmetry (V6) internal rotation poses significant challenges to experimental and theoretical determination, as the very low torsional barriers result in huge tunneling splittings difficult to identify and to model. Here we resolved the methyl group internal rotation dynamics of 2,6- and 3,5-difluorotoluene using a newly developed computer code especially adapted to V6 problems. The jet-cooled rotational spectra of the title molecules in the 5–25 GHz region revealed internal rotation tunneling doublings of up to 3.6 GHz, which translated in methyl group potential barriers of V6 = 0.14872(24) and 0.0856(10) kJ mol−1, respectively, in the vibrational ground-state. Additional information on Stark effects and carbon isotopic species in natural abundance provided structural data and the electric dipole moments for both molecules. Ab initio calculations at the MP2 level do not reproduce the tiny torsional barriers, calling for experiments on other systems and additional theoretical models.DFGMINECO/CTQ2012-39132-C02-0

Conformational steering in dicarboxy acids: the native structure of succinic acid

Succinic acid, a dicarboxylic acid molecule, has been investigated spectroscopically with computational support to elucidate the complex aspects of its conformational composition. Due to the torsional freedom of the carbon backbone and hydroxy groups, a large number of potentially plausible conformers can be generated with an indication that the gauche conformer is favored over the trans form. The microwave and millimeter wave spectra have been analyzed and accurate spectroscopic constants have been derived that correlate best with those of the lowest energy gauche conformer. For an unambiguous conformational identification measurements were extended to the monosubstituted isotopologues, precisely determining the structural properties. Besides bond distances and angles, particularly the dihedral angle has been determined to be 67.76(11)°, confirming the anomalous tendency of the methylene units to favor gauche conformers when a short aliphatic segment is placed between two carbonyl groups.Spanish Ministry of Science and Innovation/CTQ2011-22923Spanish Ministry of Science and Innovation/CGL2011-2244

Subcellular trafficking of the substrate transporters GLUT4 and CD36 in cardiomyocytes

Cardiomyocytes use glucose as well as fatty acids for ATP production. These substrates are transported into the cell by glucose transporter 4 (GLUT4) and the fatty acid transporter CD36. Besides being located at the sarcolemma, GLUT4 and CD36 are stored in intracellular compartments. Raised plasma insulin concentrations and increased cardiac work will stimulate GLUT4 as well as CD36 to translocate to the sarcolemma. As so far studied, signaling pathways that regulate GLUT4 translocation similarly affect CD36 translocation. During the development of insulin resistance and type 2 diabetes, CD36 becomes permanently localized at the sarcolemma, whereas GLUT4 internalizes. This juxtaposed positioning of GLUT4 and CD36 is important for aberrant substrate uptake in the diabetic heart: chronically increased fatty acid uptake at the expense of glucose. To explain the differences in subcellular localization of GLUT4 and CD36 in type 2 diabetes, recent research has focused on the role of proteins involved in trafficking of cargo between subcellular compartments. Several of these proteins appear to be similarly involved in both GLUT4 and CD36 translocation. Others, however, have different roles in either GLUT4 or CD36 translocation. These trafficking components, which are differently involved in GLUT4 or CD36 translocation, may be considered novel targets for the development of therapies to restore the imbalanced substrate utilization that occurs in obesity, insulin resistance and diabetic cardiomyopathy

Proton inversion tunneling in the rotational spectrum of acetone cyanohydrin

International audienceRotational transitions of gauche-acetone cyanohydrin are measured in the microwave range between 5 and 23 GHz. Results from quantum chemical calculations indicate that the hydrogen atom of the hydroxyl group undergoes a tunneling motion connecting two equivalent structures. The observed signals are assigned to the two lowest tunneling substates 0+ and 0-, which belong to either a- or c-type transitions exhibiting Coriolis splittings of a few MHz. Additional hyperfine structure arises from the quadrupole coupling 14N nucleus. The energy separation between the 0+ and 0- states is predicted to be around 50 GHz. The molecular structure and internal dynamics are discussed in terms of their spectral signatures

MW SPECTROSCOPY COUPLED WITH ULTRAFAST UV LASER VAPORIZATION: SUCCINIC ACID IN THE GAS PHASE

Author Institution: Departamento de Quimica Fisica, Facultad de Ciencia y Tecnologia, Universidad del Pais Vasco (UPV/EHU), Ap.644, E-48940, Bilbao, Spain; School of Chemistry, Box 23 Victoria 3800 Monash University, Australia; Institut fur Physikalische Chemie und Elektrochemie, Gottfried-Wilhelm-Leibniz-Universitat, 30167 Hannover, GermanyRecent lab and field measurements have indicated critical roles of organic acids in enhancing new atmospheric aerosol formation. In order to understand the nucleation process, here we report an experimental and theoretical investigation of chemical structure of succinic acid. We have used the technique of Fourier Transform Microwave Spectroscopy (FTMW). Succinic acid was vaporized by UV ultrafast laser ablation to suppress thermal decomposition processes$^a$ and seeded into an expanding stream of Ne forming a supersonic jet. The rotational spectrum detected the presence of a single most stable conformation in the cm- mm- wave regions for which accurate rotational and centrifugal distortion parameters have been determined. The study was extended to all monosubstituted isotopic species ($^{13}C$, $^{18}O$, $D(O)$), which were positively identified, leading to an accurate determination of the effective and substitution structures of the molecule. The experimental study was supplemented by \emph{ab initio} (MP2) and DFT (M06-2X and B3LYP) calculations. $^{a}$ E. J. Cocinero, A. Lesarri, P. Ecija, F. J. Basterretxea, J. U. Grabow, J. A. Fernandez and F. Casta\~{n}o, \emph{Angew. Chem. Int. Ed.}, 51, 3119-3124, 2012

Rotational Spectra of Bicyclic Decanes: The Trans Conformation of (−)-Lupinine

The conformational and structural properties of the bicyclic quinolizidine alkaloid (−)-lupinine have been investigated in a supersonic jet expansion using microwave spectroscopy. The rotational spectrum is consistent with a single dominant trans conformation within a double-chair skeleton, which is stabilized by more than 10.4 kJ mol^–1 with respect to other conformations. In the isolated conditions of the jet, the hydroxy methyl side chain of the molecule locks in to form an intramolecular O–H···N hydrogen bond to the electron lone pair at the nitrogen atom. Accurate rotational constants, centrifugal distortion corrections, and ¹⁴N nuclear quadrupole coupling parameters are reported and compared to ab initio (MP2) and DFT (M06-2X) calculations. The stability of lupinine is further compared computationally with epilupinine and decaline in order to gauge the influence of intramolecular hydrogen bonding, absent in these molecules

Accurate Semiexperimental Structure of 1,3,4-Oxadiazole by the Mixed Estimation Method

In order to determine an accurate equilibrium structure for 1,3,4-oxadiazole, microwave transitions and ground-state rotational constants are reported for the parent species and for the ¹⁸O isotopologue measured in natural abundance. These rotational constants along with those of the ¹³C, ¹⁵N, and D₁ species were used together with vibration–rotation constants calculated from a cubic force field calculated at the B3LYP/6-311+G­(3df,2pd) level of theory to derive a semiexperimental equilibrium structure. However, the results of this fit were not satisfactory; therefore, the structure was later significantly improved by the mixed estimation method. In this method, internal coordinates from good-quality quantum chemical calculations (with appropriate uncertainties) are fitted simultaneously with moments of inertia of the full set of isotopologues. The accuracy of this structure has been confirmed by using an extrapolation technique. All elements of the ¹⁴N nuclear quadrupole coupling tensor have been determined