Methods for identifying and characterizing interactions involving RNA

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Sequential Injection/Mid-Infrared Spectroscopic Analysis of an Acetone‐Butanol‐Ethanol Fermentation: Analyte Cross‐Correlation Effects

Mid‐infrared spectroscopy together with sequential injection analysis (SIA) and partial least squares (PLS) regression analysis was used to monitor acetone‐butanol‐ethanol (ABE) fermentations under different fermentation conditions. Five analytes were simultaneously predicted (acetone, acetate, butyrate, n‐butanol, and glucose). In order to compare the overall model prediction ability, a relative average of the root mean square error of prediction (RMSEP) across all five analytes was employed. To form a PLS model devoid of any cross‐correlations between analytes, a synthetic calibration data set was created by the SIA system. As a test of their robustness, PLS models from synthetic samples and those from real fermentation samples were compared and used to predict samples from the opposite data set and from independent “acid‐crash” fermentations. The PLS model developed from the synthetic samples proved to be far more robust and accurate and used fewer factors than PLS models from the real fermentations, which were found to contain analyte cross‐correlations. The use of synthetic data enabled more accurate selection of factors and showed the importance of investigating spectral regression coefficients plots to aid and confirm appropriate factor selection. In addition, an alternative method of factor selection was proposed, using a “similarity measure” between the regression coefficient plots of factors for certain analytes and their standard spectra. Predictions using this method of factor selection over the common “minimum from an error vs. factor” plot proved to be more accurate and used far fewer factors.     

Chemical analysis of acoustically levitated drops by Raman spectroscopy

An experimental apparatus combining Raman spectroscopy with acoustic levitation, Raman acoustic levitation spectroscopy (RALS), is investigated in the field of physical and chemical analytics. Whereas acoustic levitation enables the contactless handling of microsized samples, Raman spectroscopy offers the advantage of a noninvasive method without complex sample preparation. After carrying out some systematic tests to probe the sensitivity of the technique to drop size, shape, and position, RALS has been successfully applied in monitoring sample dilution and preconcentration, evaporation, crystallization, an acid–base reaction, and analytes in a surface-enhanced Raman spectroscopy colloidal suspension. Figure We have systematically investigated the analytical potential of Raman spectroscopy of samples in acoustically levitated drops.     

Neutron-deutron differential cross section at 26.5 MeV

The angular distributions of 26.5 MeV neutrons scattered elastically by deuterons between 90° and 166° (C.M.) were measured by using charged particle telescopes. The absolute n-d cross section ( of ≈ 5% precision ) was obtained by normalizing to the precision n-p cross section. Within the errors, the magnitude of the minimum cross section was found to be in agreement with that of the proton-deuteron differential cross section at the same energy and in disagreement with some recent results.     

High resolution FTIR spectroscopy of pentafluoroethane: perturbations in the Coriolis doublet of ν4 and ν13

The FTIR spectrum of pentafluoroethane (R125) was measured in the mid infrared region from 900 to 4000 cm⁻¹. Vibrational assignments for R125 are revised by comparison of previous and current experimental data with ab initio calculations at both the MP2/6-311+(d,p) and B3LYP/TZV+(3df,3p) levels of theory. High resolution FTIR spectra were recorded at room temperature and in an enclosive flow cell at a rotational temperature of 140 K. The cold spectrum was sufficiently resolved to enable rovibrational analyses of the overlapping ν₄ (1200.7341 cm⁻¹) and ν₁₃ (1223.3 cm⁻¹) bands, which have a/c hybrid and b-type character, respectively. Ground state combination differences were used to confirm assignment of 2375 lines to ν₄ (J_max = 86, K_{a max} = 50) and 2921 lines to ν₁₃ (J_max = 60, K_{a max} = 54). Effective rotational and centrifugal distortion constants were determined for ν₄, and the polarization ratio was found to be . Severe Coriolis perturbations prevent any satisfactory fit to the ν₁₃ band.     

The relative stabilities of tetrafluoroethylene and Hexafluoro-2-butyne adducts of fluoro- or chlorobis- triphenylphosphine)carbonyliridium

Tetracyanoethylene, tetrafluoroethylene and hexafluoro-2-butyne form 1/1 adducts with trans-IrF(CO)(PPh₃)₂. Enthalpies of dissociation for the reactions:

(X = F or Cl; L = C₂F₄ or C₄F₆) have been measured. More stable adducts are formed when X = F.     

Determination of the molecular structure of diacetylene from high-resolution FTIR spectroscopy

The high-resolution infrared absorption spectra of eight²H or¹³C substituted isotopomers of diacetylene have been recorded, and the bands corresponding to thev ₄ fundamental andv ₆ combination of the major isotopomer have been analyzed using a Loomis-Wood-type program. Effective ground-state rotational constants have been obtained from ground-state combination differences. A number ofr ₀,r _s,r _m , and (r _m )_corr structures have been calculated from the available data and are compared to those obtained by ab initio methods. The (r _m )_corr structure, which is a reliable near-equilibrium structure of diacetylene, isr _C–H=106.131(13) pm;r _C–C=137.081(16) pm;r _C-C=120.964(14). (r _m )_corr structures of the related molecules cyanogen, cyanoacetylene, and cyanodiacetylene have been calculated, and near-equilibrium structures of triacetylene and dicyanoacetylene have been predicted.