Synthesis and dynamic NMR studies of the 3,7-diazabicyclo[4.1.0]heptane system

A new bicyclic system, 3,7-diazabicyclo[4.1.0]heptane, has been prepared from 3-(ethoxycarbonyl)-7,3-oxazabicyclo[4.1.0]heptane by reaction with sodium azide and reduction of the resulting tosyloxy azide with lithium aluminum hydride. The molecule can exist in four stereoisomeric half-chairs, depending on the configuration of the two nitrogen atoms. Half-chair ring reversal and piperidine nitrogen inversion are fast on the NMR time scale at all observed temperatures. Inversion of the secondary aziridine nitrogen becomes slow as the temperature is lowered (T_c= ?10°C). Complete analysis of the ¹H spectrum was possible with the 1,5,5-trideuteriated analog. At slow exchange, two aziridine invertomers are present with an exo/endo ratio of approximately 0.7 in toluene-d₈, 0.7 in CH₂Cl₂ and 1.7 in CHCl₃/CH₂Cl₂. The free energy of activation for nitrogen inversion is 13.2 kcal mol^?1 at ?10°C in CHCl₃/CH₂Cl₂.     

Morphological characteristics of modified freeze-dried poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide) microspheres studied by optical microscopy,SEM, and DLS

Influence of the initiator and additional hydrophobic copolymer on the morphology of thermosensitive poly(N-isopropylacrylamide) (pNIPAM) microspheres, and their presumed application for the stabilization of biologically active molecules were evaluated in this study. Three different types of pNIPAM were synthesized, applying various components: PN1 is a polymer with terminal anionic groups resulting from potassium persulfate initiator; PN2 was synthesized with a 2,2′-azobis(2-methylpropionamidine) dihydrochloride initiator introducing cationic amidine terminal groups; in the PN3 polymer, anionic terminals were implemented, however, increased hydrophobicity was maintained using N-tert-butyl functional groups. Turbidity measurements of the obtained dispersions confirmed specific thermosensitivity of synthesized microspheres in the range of 32–33°C. The polymerization course was proved by infrared spectroscopy and ¹H NMR assessments, whereas the size of the synthesized microspheres, expressed as planar area, was evaluated by dynamic light scattering (DLS), scanning electron microscopy (SEM) and optical microscopy (OM). The respective surface patterns of the freeze-dried microspheres were evaluated by SEM. Planar area of the synthesized macromolecules was in the range between 0.41–3.22 μm, depending on the substrates composition and the method applied for the measurements. The assessments performed in the dry stage gave higher values of the diameter and planar area of the observed microspheres. The measured diameter and planar area increased in the following order for the PN3 microspheres: DLS, OM, SEM. In the case of PN1 and PN2, the observed diameters were positioned as: DLS, SEM, OM. These differences were assigned both to varied intramolecular hydrophobic-hydrophilic interactions of the polymer chains and to the environment, i.e. low pressure in the SEM conditions and aqueous solvent in the DLS measurements. The observed gaps in the freeze-dried PN2 polymer resulted in an attempt to evaluate the application of this polymer for mechanical stabilization of certain macromolecules or nanocrystals in the size range between 10 nm and 20 nm.     

Etude des reactions pericycliques sous pression—IV: Cyclodimerisation thermique de l'acroleine et de la methylvinylcetone

The thermal cyclodimerization of acrolein with methyl vinyl ketone gives selectively only one substituted dihydropyran. The rate is only slightly sensitive to the nature of the solvent; however a slight decrease of the reaction rate with increasing solvent polarity was observed. Effects of high pressure give strong support for a one-step mechanism and the formation of a transition state more compact than the adduct.     

Transannular interactions insyn- andanti- [2.2](1,4) napthalenophanes andsyn- andanti- [2.2](1,4) anthracenophanes

The UV spectra of the title compounds were interpreted as a result ofPPP-CI-1 calculations of excitation energies and oscillator strengths for the singlet—singlet transitions. A good agreement of the theoretical transitions with the experimental spectrum was found. A strong transannular effect was characteristic for thesyn isomers, the effect decreased in the order:syn-ring anthracenophane,syn-ring naphtalenophane,anti-ring naphthalenophane,anti-ring anthracenophane. Also the influence of a pseudo-substituent effect was found and discussed.     

Interplay between cation-pi, anion-pi and pi-pi interactions.

The interplay between three important noncovalent interactions involving aromatic rings is studied by means of high level ab initio calculations. They demonstrate that very strong synergic effects are present in complexes where either cation–π or anion–π and π‐‐π interactions coexist. These strong synergic effects have been studied using the “atoms in molecules” theory and the physical nature of the interactions investigated by means of the molecular interaction potential with polarization (MIPp).     

Separation of beta2-microglobulin conformers by high-field asymmetric waveform ion mobility spectrometry (FAIMS) coupled to electrospray ionisation mass spectrometry

An investigation into the use of high-field asymmetric waveform ion mobility spectrometry (FAIMS) coupled to electrospray ionisation mass spectrometry (ESI-MS) for the differentiation of co-populated protein conformers has been conducted on the amyloidogenic protein beta(2)-microglobulin (beta(2)m). Accumulation of beta(2)m in vivo can result in the deposition of insoluble fibrils whose formation is thought to originate from partially folded protein conformers; hence, the folding properties of beta(2)m are of significant interest. We have analysed beta(2)m using ESI-FAIMS-MS under a range of pH conditions and have studied the effect of the ion mobility spectrometry parameters on the behaviour of the various protein conformers. The data show that different protein conformers can be detected and analysed by ESI-FAIMS-MS, the results being consistent with observations of pH denaturation obtained using complementary biophysical techniques. A variant of beta(2)m with different folding characteristics has been analysed for comparison, and the distinctions observed in the data sets for the two proteins are consistent with their folding behaviour. ESI-FAIMS-MS offers significant opportunities for the study of the conformational properties of proteins and thus may present valuable insights into the roles that different conformers play in diseases related to protein folding.     

Isobaric vapor–liquid equilibria for acetone + methanol + lithium nitrate at 100 kPa

Isobaric vapor–liquid equilibria for the ternary system acetone + methanol + lithium nitrate have been measured at 100 kPa using a recirculating still. The addition of lithium nitrate to the solvent mixture produced an important salting-out effect and the azeotrope tended to disappear for small contents of salt. The experimental data sets were fitted with the electrolyte NRTL model and the parameters of the Mock's model were estimated. These parameters were used to predict the ternary vapor–liquid equilibrium which agreed well with the experimental one.     

Spreading of viscous liquids at high temperature: silicate glasses on molybdenum

The spreading of Si-Ca-Al-Ti-O glasses on molybdenum has been investigated. By controlling the oxygen activity in the furnace, spreading can take place under reactive or nonreactive conditions. As the nucleation of the reaction product under reactive conditions is slow in comparison to the spreading kinetics, in both cases the glass front moves on the metal surface with similar spreading velocities. Spreading can be described using a molecular dynamics model where the main contribution to the wetting activation energy comes from the viscous interactions in the liquid. Enhanced interfacial diffusions in low-oxygen activities (reactive cases) form triple-line ridges that can pin the wetting front and cause a stick-slip motion.