Molecular and electronic structures, infrared spectra, and vibrational assignment for ap and sc conformers of hexafluoro-iso-propanol

Comprehensive studies of the molecular structures, vibrational frequencies and infrared intensities of the antiperiplanar (ap) and synclinal (sc) conformers of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) have been performed by the density functional (B3LYP) method using the extended 6-311++G(df,pd) basis set. The detailed natural bond orbital (NBO) analysis has revealed the nature of the hyperconjugative interactions, which stabilize each conformer, in the gas phase. The mid-infrared spectra of HFIP in carbon tetrachloride solution were measured, and the experimental intensities of each conformer were obtained by the curve–resolution procedure. The relative abundance of the two conformers, calculated from the relative intensities, shows nearly equimolar ratio (N_sc/N_ap ≈ 1), in this solution. The DFT-predicted frequencies show very good agreement with the experimental data. The clear-cut vibrational assignment for each conformer is reported on the basis of the calculated potential energy distributions. Several controversies in an earlier assignment of HFIP have been elucidated.     

Easy and hard instances of arc ranking in directed graphs

In this paper we deal with the arc ranking problem of directed graphs. We give some classes of graphs for which the arc ranking problem is polynomially solvable. We prove that deciding whether , where G is an acyclic orientation of a 3-partite graph is an NP-complete problem. In this way we answer an open question stated by Kratochvil and Tuza in 1999.     

Templated crystal nucleation: mixed crystals of very different copper(II) N,N',N'-trimethyltriazacyclononane complexes

Templation of a daughter phase by a parent crystal results from an equilibrating mixture of two very different copper(ii) N,N',N'-trimethyltriazacyclononane complexes.     

Synthesis and characterization of variable-architecture thermosensitive polymers for complexation with DNA

Copolymers of N-isopropylacrylamide with a fluorescent probe monomer were grafted to branched poly(ethyleneimine) to generate polycations that exhibited lower critical solution temperature (LCST) behavior. The structures of these polymers were confirmed by spectroscopy, and their phase transitions before and after complexation with DNA were followed using ultraviolet and fluorescence spectroscopy and light scattering. Interactions with DNA were investigated by ethidium bromide displacement assays, while temperature-induced changes in structure of both polymers and polymer-DNA complexes were evaluated by fluorescence spectroscopy, dynamic light scattering, laser Doppler anemometry, and atomic force microscopy (AFM) in water and buffer solutions. The results showed that changes in polymer architecture were mirrored by variations in the architectures of the complexes and that the overall effect of the temperature-mediated changes was dependent on the graft polymer architecture and content, as well as the solvent medium, concentrations, and stoichiometries of the complexes. Furthermore, AFM indicated subtle changes in polymer-DNA complexes at the microstructural level that could not be detected by light scattering techniques. Uniquely, variable-temperature aqueous-phase AFM was able to show that changes in the structures of these complexes were not uniform across a population of polymer-DNA condensates, with isolated complexes compacting above LCST even though the sample as a whole showed a tendency for aggregation of complexes above LCST over time. These results indicate that sample heterogeneities can be accentuated in responsive polymer--DNA complexes through LCST-mediated changes--a factor that is likely to be important in cellular uptake and nucleic acid transport.     

Theoretical and experimental studies of enflurane. Infrared spectra in solution, in low-temperature argon matrix and blue shifts resulting from dimerization

Theoretical studies are performed on enflurane (CHFCl-CF(2)-O-CHF(2)) to investigate the conformational properties and vibrational spectra. Calculations are carried out at the B3LYP/6-31G(d) level along with a natural bond orbital (NBO) analysis. Experimental infrared spectra are investigated in carbon tetrachloride solution at room temperature and in argon matrix at 12 K. In agreement with previously reported data (Pfeiffer, A.; Mack, H.-G.; Oberhammer, H. J. Am. Chem. Soc. 1998, 120, 6384), it is shown that the four most stable conformers possess a trans configuration of the C-C-O-C skeleton and a gauche orientation of the CHF(2) group (with respect to the central C-O bond). These conformations are favored by electrostatic interaction between the H atom of the CHF(2) group and the F atoms of the central CF(2) group. Hyperconjugation effects from the O lone pairs to the antibonding orbitals of the neighboring C-H and C-F bonds also contribute to the stability of the four conformers. The vibrational frequencies, infrared intensities, and potential energy distributions are calculated at the same level of theory for the most stable conformers. On the basis of the theoretical results, these conformers are identified in an argon matrix. The influence of the concentration on the nu(CH) vibrations suggests the formations of higher aggregates in solution. Theoretical calculations are carried out on the enflurane dimer. The results show that the dimer is formed between two enflurane conformers having the largest stability. The dimer has an asymmetric cyclic structure, the two enflurane molecules being held together by two nonequivalent C-H...F hydrogen bonds, the C-H bond of the CHFCl group acting as a proton donor, and one of the F atoms of the CHF(2) groups acting as a proton acceptor. The theory predicts a contraction of 0.0014-0.0025 A of the two CH bonds involved in the interaction along with a blue shift of 30-38 cm(-1) of the corresponding nu(C-H) bands, in good agreement with the blue shifts of 35-39 cm(-1) observed in an argon matrix.     

A Novel Extension of the Technique for Order Preference by Similarity to Ideal Solution Method with Objective Criteria Weights for Group Decision Making with Interval Numbers

This paper presents an extension of the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method with objective criteria weights for Group Decision Making (GDM) with Interval Numbers (INs). The proposed method is an alternative to popular and often used methods that aggregate the decision matrices provided by the decision makers (DMs) into a single group matrix, which is the basis for determining objective criteria weights and ranking the alternatives. It does not use an aggregation operator, but a transformation of the decision matrices into criteria matrices, in the case of determining objective criteria weights, and into alternative matrices, in the case of the ranking of alternatives. This ensures that all the decision makers’ evaluations are taken into account instead of their certain average. The numerical example shows the ease of use of the proposed method, which can be implemented into common data analysis software such as Excel.     

Preliminary studies on the surface layer of starch

Characterization of the surface layer of starch powder, originated from potato or maize, was carried out applying various experimental techniques: Fourier-transformed infrared internal reflection spectroscopy (FTIR-IRS), inverse gas chromatography (IGC) and scanning electron microscopy (SEM). The main kinds of starch were studied as potential fillers for rubber and results discussed in terms of factors requiring modification to improve starch miscibility and activity towards rubber. Starch of high amylopectine content shows surface enrichment with amylose what makes crystallinity of the surface layer higher than in bulk of the material. Particles of the both kinds of starch have very smooth surface (morphological index, I_m = 0.995), highly resistant to its geometrical development. Dispersive component of the surface energy of starch was found to be similar to that of low energy polymers (γ_s^d = 32.5 mJ/m² at 23°C) and its surface to be of electron-donor character.     

Estimation of platinum in environmental water samples with solid phase extraction technique using inductively coupled plasma mass spectrometry

A solid phase extraction technique for the determination of platinum(IV) at trace levels by inductively coupled plasma mass spectromA solid phase extraction technique for the determination of platinum(IV) at trace levels by inductively coupled plasma mass spectrometry (ICP-MS) was developed. The method was based on retention of platinum in a sample on silica gel modified with aminepropyl groups. The retention of platinum(IV) from the sample solution and the recovery of platinum with 1.0 mol L⁻¹ thiourea solution were quantitative. The relative standard deviation (RSD) was calculated as 5% (n = 7) at the 10 ng L⁻¹ level. The enrichment factor was found to be (50-fold) for 250 mL of water sample. Under optimum conditions, the method detection limit (MDL) was found to be 1 ng L⁻¹ for platinum in water matrices. Recoveries of Pt from spike addition to atmospheric water samples were quantitative (80–95%). The present method was used for the determination of platinum in precipitation, throughfall and runoff water samples.      

Electron ionization mass spectra of 8‐aryl‐3,4‐dioxo‐2H,8H‐6,7‐dihydroimidazo[2,1‐c][1,2,4]triazines. Do they exhibit tautomerism in the gas phase?

The electron ionization mass spectra of the title compounds (1: a R = H, b 2-CH(3), c 4-CH(3), d 2,3-diMe, e 2-OCH(3), f 4-OCH(3), g 2-Cl, h 3-Cl, i 4-Cl, j 3,4-diCl) were recorded at 70 eV to determine the effects of substituents and the possible keto-enol tautomerism. The compounds showed several common fragment ions but also fragment ions which divided them into three classes, namely 1a-1d (parent compound and Me-substituted derivatives), 1e and 1f (MeO-substituted derivatives), and 1g-1j (Cl-substituted derivatives). The presence of the HOCN(+.) ion as well as the exponential dependence of its total ion current in the case of p- and also 3-Cl-substituted compounds (1a, c, f, h-j) on the Hammett sigma constants and the loss of CHO or one or two HOCN moieties can be somewhat easier explained by the presence of the enol form but as a whole the results support the predominance of the keto form, in parallel to the situation in solution.