Gas-phase Raman spectra of hot bands of fundamentals and combinations associated with the torsional vibration of s-trans-1,3-butadiene and its deuterated isotopologues

The gas-phase Raman spectra of 1,3-butadiene and its 2,3-d₂, 1,1,4,4-d₄, and d₆ isotopologues have been recorded with high sensitivity and resolution of 0.7 cm⁻¹. Hot band series of fundamentals and combinations involving the ν₁₃ torsional vibration of the s-trans rotamer have been observed for each of the isotopologues. Modes studied were ν₁₀ (CH wag), ν₁₂ (CH₂ twist), ν₁₀ + ν₁₂, ν₁₅ (CH₂ wag) + ν₁₆ (CH₂ twist), and ν₂₃ (CH₂ rock) + ν₂₄ (CCC deformation). The spacings of the quantum states of the torsional contribution were found to decrease with additional excitation of this mode (ν₁₃) in the upper vibrational states except for the ν₂₃ + ν₂₄ combination state.     

Experimental investigation of various turbulator inserts in gas-heated channels

This experimental research was focused on the investigation of the heat transfer augmentation by various turbulator inserts in gas-heated channels. The work was conducted directly in a convective part of a two fire-tube boiler. The flue ducts were positioned vertically and horizontally for various design applications. Twisted-tape insert (with the twist ratio y=4.12), the straight-tape insert, and the combined turbulator insert (the internal twisted tape with the twist ratio of 180° y=2.16 and an external tape, which spirally winded on an internal tape, with longitudinal pitch H_360°=110 mm and the relative height of a tape (rib) e/D₀=0.098;0.2) were investigated. The working fluids were the combustion products of light oil fuel and wood pellets. In addition, the experiments were conducted in the two fire-tube boiler without any inserts. Despite of relatively large data scattering obtained in these experiments some qualitative and quantitative conclusions were drawn.     

Basicity Limits of Neutral Organic Superbases

The potential limits of superbasicity achievable with different families of neutral bases by expanding the molecular framework are explored using DFT computations. A number of different core structures of non‐ionic organosuperbases are considered (such as phosphazenes, guanidinophosphazenes, guanidino phosphorus ylides). A simple model for describing the dependence of basicity on the extent of the molecular framework is proposed, validated, and used for quantitatively predicting the ultimate basicities of different compound families and the rates of substituent effect saturation. Some of the considered bases (guanidino phosphorus carbenes) are expected to reach gas‐phase basicity around 370 kcal mol^?1, thus being the most basic neutral bases ever reported. Also, the classical substituted alkylphosphazenes were predicted to reach pK_a values of around 50 in acetonitrile, which is significantly higher than previously expected.     

Equilibrium acidities of superacids

In this paper, we report the most comprehensive equilibrium superacidity scale that is available to date. Contrary to most of the past works, this scale is set up in a medium of constant composition and the obtained acidity values characterize the acidities of molecules rather than acidities of media. The current scale is thus complementary to the well-known H(0) scale in the information that it provides. The solvent used is 1,2-dichloroethane (DCE). DCE has very weak basic properties (but sufficiently high polarity) and is an appropriate solvent for measuring acidities of very strong acids of diverse chemical nature. DCE acidities of well-known superacids (CF(3)SO(2)OH, (CF(3)SO(2))(2)NH, cyanocarbon acids, etc.) as well as common mineral acids (H(2)SO(4), HI, HBr, etc.) are reported. Acidities of altogether 62 acids have been determined from 176 interlinked relative acidity measurements. The scale spans 15 orders of magnitude (from picric acid to 1,1,2,3,3-pentacyanopropene) and is expected to be a useful tool in design, use, and further acidity measurements of superacidic molecules.     

Vibrational spectra, structure, and theoretical calculations of 2-fluoro- and 3-fluoropyridine

The infrared and Raman spectra of liquid and vapor-phase 2-fluoropyridine and 3-fluoropyridine have been recorded and assigned. Ab initio and DFT calculations were carried out to compute the molecular structures and to verify the vibrational assignments. The observed and calculated spectra agree extremely well. The ring bond distances of the fluoropyridines are very similar to those of pyridine except for a shortening of the C-N(F) bond in 2-fluoropyridine. The C-F bond stretching frequencies are similar to that in fluorobenzene reflecting the influence of the ring π bonding.     

Electron Probe Microanalysis of HfO2 Thin Films on Conductive and Insulating Substrates

Quantitative electron probe microanalysis of highly insulating materials is a complicated problem, partially solved by coating samples with grounded thin conductive layers or using novel scanning electron microscopy (SEM) techniques, such as low-voltage and/or variable pressure SEM. In this work, some problems of quantitative X-ray microanalysis of thin HfO₂ films, in particular the possibility to determine mass thickness correlated to the density of the layer material, are discussed. For comparison, Al₂O₃, Ta₂O₅ and TiO₂ films grown onto both semiconductive Si and insulating quartz substrates were also analysed. All the films studied were synthesized by atomic layer deposition method.     

Application of scaling concepts to sedimentation phenomena in semidilute macromolecular solutions

Sedimentation velocity data on polystyrene in a good solvent (toluene) and in a theta solvent (cyclopentane), over a large concentration range are reported. Under good-solvent conditions the exponent β in the apparent scaling law describing the concentration dependence of the sedimentation coefficient (s ∝ c^β) in the semidiiute region is found to be concentration dependent. However, a power law fit to data for the highest molecular weight (M = 20.6 × 10⁶) in the concentration region (c < 2 kg m^?3) yields a value β = ?0.59, somewhat smaller than that (?0.54) predicted theoretically. This discrepancy and the observed curvature in logs vs. logc at higher concentrations are discussed. Under theta-solvent conditions, on the other hand, the concentration dependence of s in the semidilute regime can be represented by a simple power law, with β = ?1.0, in excellent agreement with the theoretical prediction. The crossover concentration c^*, separating the dilute and semidilute concentration regimes, was found to be well defined and located at c = 1/[η]. c^* varies with molecular weight as M^?0.73 and M^?0.50 under good-solvent and theta-solvent conditions, respectively.     

Vibrational spectra, DFT calculations, unusual structure, anomalous CH2 wagging and twisting modes, and phase-dependent conformation of 1,3-disilacyclobutane

Our previously published infrared and Raman spectra of 1,3-disilacyclobutane (13DSCB) and its 1,1,3,3-d4 isotopomer have been reexamined and partially reassigned on the basis of DFT and ab initio calculations. The calculations confirm previous microwave work that the CSiC angles in the ring are unexpectedly larger than the SiCSi angles. This may arise from the partial charges on the ring atoms. The calculations are in excellent agreement with the observed spectra in both frequency and intensity. They also demonstrate that this molecule has CH2 wagging and twisting vibrations with frequencies below 1000 cm-1, about 200 cm-1 lower than expected. These unprecedented low values can be explained by the decreased slope in the potential energy curves for these vibrations as the sideways motions of the CH2 groups result in attractive forces between the positively charged hydrogens on the carbon atoms and the negatively charged hydrogens on the silicon atoms. The theoretical calculations also confirm the previous conclusions that the individual molecules (vapor) have C2v symmetry whereas in the solid the molecules become planar with D2h symmetry. The vibrational coupling between the ring-angle bending mode and the SiH2 in-phase rocking, which is present for the C2v structure, is forbidden for D2h and hence disappears.     

Embedded conformon model of chain folding

The real-space renormalization-group technique is used to study the low lying energy states of a random copolymer composed of hydrophobic (H) and polar (P) beads on a simple cubic lattice. Application of a variety of boundary conditions to parts of the larger chain (embedded conformons) while progressively increasing the length scale gives the lowest energy states in agreement with exact calculations for a 17 bead chain with a random H,P sequence. These results are significant for studying minimalist models of the folding of complex molecules because the computation time is several orders of magnitude less than for other approaches.     

A meanfield approach to the thermodynamics of a protein-solvent system with application to the oligomerization of the tumor suppressor p53

The thermodynamic stability and oligomerization status of the tumor suppressor p53 tetramerization domain have been studied experimentally and theoretically. A series of hydrophilic mutations at Met-340 and Leu-344 of human p53 were designed to disrupt the hydrophobic dimer-dimer interface of the tetrameric oligomerization domain of p53. Meanfield calculations of the free energy of the solvated mutants as a function of interdimer distance were compared with experimental data on the thermal stability and oligomeric state [tetramer, dimer, or equilibrium mixture of both] of each mutant. The calculations predicted a decreasing stability and oligomeric state for the following amino acids at residue 340: Met [tetramer] > Ser Asp, His, Gin, > Glu, Lys [dimer], whereas the experimental results showed the following order: Met [tetramer] > Ser > Gln > His, Lys > Asp, Glu [dimers]. For residue 344, the calculated trend was Leu [tetramer] > Ala > Arg, Gln, Lys [dimer], and the experimental trend was Leu [tetramer] > Ala, Arg, Gln, Lys [dimer]. The discrepancy for the lysine side chain at residue 340 is attributed to the dual nature of lysine, both hydrophobic and charged. The incorrect prediction of stability of the mutant with Asp at residue 340 is attributed to the fact that within the meanfield approach, we use the wild-type backbone configuration for all mutants, but low melting temperatures suggest a softening of the α-helices at the dimer-dimer interface. This initial application of meanfield theory toward a protein-solvent system is encouraging for the application of the theoretical model to more complex systems.