The Torsional Barriers of 2‐Hydroxy‐ and 2‐Fluorobiphenyl: Small but Measurable

By making use of a novel diastereotopicity probe, namely C(CF₃)₂OH, it has been possible to measure by very low temperature ¹⁹F NMR spectroscopy the elusive aryl–aryl rotation barriers of biphenyls bearing an OH or F group in one ortho position. The experimental values (5.4 and 4.4 kcal mol^?1, respectively) are matched by those from ab initio calculations (5.3 and 4.3 kcal mol^?1, respectively).     

Thermal Properties of Oligo(2-ethyl-2-oxazoline) Containing Comb and Graft Copolymers and their Aqueous Solutions

Summary: The cationic ring opening polymerization of 2-ethyl-2-oxazoline (EtOx) was applied for the synthesis of methacrylate end-functionalized well-defined macromonomers that could be polymerized in a controlled manner using reversible addition-fragmentation chain transfer polymerization. The obtained comb polymers revealed lower critical solution temperature behavior in aqueous solution. The cloud points of these solutions could be tuned in a range from 35 °C to 85 °C by the incorporation of hydrophobic methyl methacrylate comonomer in varying amounts into the graft copolymers whereas copolymerization with methacrylic acid rendered temperature and pH sensitive copolymers. Thermo-gravimetric analysis showed a two-step decomposition of the graft copolymers and differential scanning calorimetry revealed glass transition temperatures that are significantly lowered in comparison to linear PEtOx.     

A convenient decontraction procedure of internally contracted state-specific multireference algorithms

Internally contracted state-specific multireference (MR) algorithms, either perturbative such as CASPT2 or NEVPT2, or nonperturbative such as contracted MR configuration interaction or MR coupled cluster, are computationally efficient but they may suffer from the internal contraction of the wave function in the reference space. The use of a low dimensional multistate model space only offers limited flexibility and is not always practicable. The present paper suggests a convenient state-specific procedure to decontract the reference part of the wave function from a series of state-specific calculations using slightly perturbed zero-order wave functions. The method provides an orthogonal valence bond reading of the ground state and an effective valence Hamiltonian, the excited roots of which are shown to be relevant. The orthogonal valence bond functions can be considered quasidiabatic states and the effective valence Hamiltonian gives therefore the quasidiabatic energies and the electronic coupling among the quasidiabatic states. The efficiency of the method is illustrated in two case problems where the dynamical correlation plays a crucial role, namely, the LiF neutral/ionic avoided crossing and the F(2) ground state wave function.     

Stereoselective synthesis of novel 4,5-epoxy-1,2-oxazin-6-ones and alpha,beta-epoxy-gamma-amino acids from beta-lithiated oxazolinyloxiranes and nitrones

[reaction: see text] A stereoselective synthesis of 9,10-epoxy-1,6-dioxa-4,7-diazaspiro[4,5]decanes has been developed on the basis of the addition of beta-lithiated oxazolinyloxiranes to nitrones. Conversion of these spirocyclic derivatives into 4,5-epoxy-1,2-oxazin-6-ones and successively into alpha,beta-epoxy-gamma-amino acids, alpha-hydroxy-gamma-amino acids, and gamma-butyrolactams is described.     

Study and characterization of mural paintings from XIX Century in a noble Venetian (Italy) palace

The present paper describes the characterization carried out on the roof of a private palace located in the historical center of Venice (Italy). We focused our attention on the studies of original constituent materials (pigments and binders), in order to identify the pictorial technique of the artist and verify the stylistic attribution to Giuseppe Borsato, a Venetian painter operating between 18th and 19th century. Characterization of collected samples was carried on using both conventional and advanced analytical techniques, such as Optical Microscopy and Scanning Electron Microscopy coupled with Energy Dispersive X-Ray (SEM–EDS) microscopy, Fourier Transform Infrared Spectroscopy (FTIR) and High Performance Liquid Chromatography (HPLC) coupled with photodiode array detection (DAD) and Mass Spectrometry (MS). The finding of dating pigments (such as Cobalt blue and Cu–As based green) and of a complex binding's mixture compatible with the considered supposed period, allowed us to confirm the attribution hypothesis.     

Activated peroxide bleaching of regenerated bamboo fiber using a butyrolactam-based cationic bleach activator

Regenerated bamboo fibers are potentially a valuable source of renewable fibers for use in a wide variety of applications. As with almost all natural fibers, inherent yellowness must be reduced or eliminated in order for the fibers to be used effectively in processes such as dyeing. Oxidative bleaching in the form of hot alkaline hydrogen peroxide is the most common method for bleaching cellulosic fibers. However, significant fiber damage results, especially in the case of regenerated bamboo. Recently, more benign oxidative bleaching methods have been developed using so-called bleach activators. Reported is an effective bleaching method using a novel bleach activator, N-[4-(triethylammoniomethyl)benzoyl]butyrolactam chloride (TBBC). The ratio of TBBC to hydrogen peroxide and pH were found to be critical to achieving effective bleaching at low temperature. Using equimolar amounts of TBBC and hydrogen peroxide at pH 7 and 50 °C, comparable whiteness and less fiber damage compared with conventional peroxide bleaching was obtained. However, at pH 11.5, TBBC had no effect on whiteness.     

A theoretical model for the critical micelle concentration of bile salts

Critical micelle concentration (CMC) is a fundamental parameter in the evaluation of the biological activity of natural and synthetic bile salts. The CMC is logarithmically related to the free energy of solute micellization in aqueous solution. Hydrophobic and hydrogen bonding interaction energies were identified as the primary contributors to this free energy and the logarithm of the CMC was modeled as a linear function of relevant chemical group contributions to the solvent accessible molecular surface area of the solute. The structures (three-dimensional atomic coordinates) of 23 mono-, di-, and tri-hydroxyl bile acids were generated and optimized by energy minimization. The accessible surface area for each structure was computed and partitioned according to calculated charge distribution and polar group orientation. Experimental CMC values were fitted to these computed quantities by least squares multiple linear regression. Two regression equations, based on slightly different surface area partition schemes, were derived and compared. Their significance in explaining the aggregation process and in predicting the CMC of new bile salts is discussed.     

Multireference perturbation CI III. Fast evaluation of the one-particle density matrix

Within the frame of multireference perturbation configuration interaction we have developed a fast algorithm, based on diagrammatic techniques, for the calculation of the first-order correction to the one-particle density matrix. As an example of an application we have chosen the evaluation of the dipole moment of the CO molecule, where utilization of the first-order density is shown to corroborate the variational calculation. Received: 4 August 1998 / Accepted: 21 September 1998 / Published online: 16 November 1998     

Evidence for an indirect halogen exchange in the reaction of trans- 2,3-dibromo-2,3-dihydrobenzofuran with chloride ions

Treatment of the title compound with chloride ions in acetonitrile leads mainly to the formation of trans-2,3-dichloro-2,3-dihydrobenzofuran. Since a nucleophilic displacement of bromide anion by chloride anion can be excluded, a mechanism involving the equilibrium 2Cl^? + Br₂ ? 2Br^? + Cl₂ is suggested.