An Operative Electrostatic Slipping Mechanism along Macrocycle Flexibility Accelerates Guest Sliding during pseudo-Rotaxane Formation

A pseudo-rotaxane is a host−guest complex composed of a linear molecule encircled by a macrocyclic ring. These complexes can be assembled by sliding the host over the guest terminal groups. If there is a close match between the molecular volume of the flanking groups on the guest and the cavity size of the macrocycle, the slipping might occur slowly or even become completely hindered. We have previously shown that it is possible to overcome the restraints imposed by steric effects on the sliding process by integrating electrostatic attractive interactions during the slipping step. In this work, we extend our electrostatically assisted slipping approach (EASA) to a new host−guest system featuring a flexible macrocyclic ring and a series of asymmetric guests containing a cyclic tertiary ammonium group. Compelling evidence for pseudo-rotaxane formation is presented, along with thermodynamic and kinetic data. Experimental results suggests that the higher conformational flexibility of 24-crown-8 significantly increases the sliding rate, compared with the more rigid dibenzo-24-crown-8, without affecting complex stability. Furthermore, by combining the EASA and macrocycle flexibility, we were capable to slip a large eight-membered cyclic group across the 24-crown-8 annulus, setting a new limit on the ring molecular size that can pass through a 24-membered crown ether.     

Antioxidant, hemolytic and cytotoxic activities of Senecio species used in traditional medicine of northwestern Argentina

Senecio nutans Sch. Bip., S. viridis var. viridis Phill. and S. spegazzinii Cabrera are native species used in traditional medicine of northwestern Argentina. The total phenolics, flavonoids and caffeoylquinic acids contents, as well as radical scavenging, antioxidant, hemolytic and cytotoxic activities of aqueous extracts (infusion and decoction) of all three species were determined. S. nutans was the most active. The extracts did not show antibacterial activity. Alkaloids were not detected in any of the aqueous extracts of the three studied species.     

Signaling advertising by multiproduct firms

We consider the use of advertising expenses as quality signals in multiproduct firms, extending previous results on single product firms. In our model, a firm introduces sequentially two products whose qualities are positively correlated. We investigate whether there exist information spillovers from the first to the second market. We show that, when correlation is high, the equilibrium in market 2 depends on the quality reputation the firm has gained in market 1. Moreover, if a firm with a high-quality product 1 wants to separate from its low-quality counterpart, it needs to advertise more in this market than if the qualities of the two products are unrelated. This advertising level signals not only high quality in the first market, but also the likely quality of the second product. Thus, advertising in the first market has information spillovers in the second market.     

New acyclic diterpenic acids from yacon (Smallanthus sonchifolius) leaves

Two new acyclic diterpenoids, smaditerpenic acid E (1a) and F (2a), along with nineteen melampolide-type sesquiterpene lactones, six of them not previously reported in yacon, were isolated from the methylene chloride leaf rinse extract. Their structures were elucidated from 1D and 2D NMR experiments and gas chromatography coupled to mass spectrometry.     

Identification of bioactive peptides in hypoallergenic infant milk formulas by capillary electrophoresis-mass spectrometry

In this study, we use capillary electrophoresis-mass spectrometry (CE-MS) for the identification of bioactive peptides in hypoallergenic infant milk formulas (IF), which are complex bovine milk protein hydrolysates. A sample clean-up pretreatment with a citrate buffer containing dithiothreitol and urea followed by solid-phase extraction (SPE) with different reversed-phase commercial cartridges was investigated to achieve optimum detection sensitivity in CE-MS. SPE with C18, StrataX and Oasis HLB cartridges allowed detection of the largest number of low molecular mass components, but combination of C18 and StrataX results was enough to achieve an excellent coverage of the studied IF. The monoisotopic molecular mass values of the low molecular mass components obtained by capillary electrophoresis ion-trap mass spectrometry (CE-IT-MS) allowed the tentative identification of nine bioactive sequences. Only the identification of five of them could be confirmed when accurate mass measurements were performed by capillary electrophoresis time-of-flight mass spectrometry (CE-TOF-MS), namely LKP, IPY, ALPM, PGPIHN and VAGTWY, which were reported to present angiotensin-converting enzyme (ACE) inhibitory and antimicrobial activity (only VAGTWY).     

A theoretical study on the protonation of benzamide

We have performed an ab initio study of the protonation of benzamide, using a STO-3G minimal basis set. According to our results, benzamide is an oxygen-base in the gas-phase. Rotation of the -CONH₂ group respect to the aromatic ring does not affect the basicity of the molecule. If the presence of the solvent causes pyrimidization of the -NH₂ group, the intrinsic basicity of the O atom decreases, while that of the N atom increases and the interaction of this center with the solvent is stronger, favoring nitrogen protonation in solution.     

On the ordering of the first two excited electronic states in all-trans linear polyenes

Reported experimental evidence of the relative position of the first two excited electronic states in linear polyenes was carefully examined and compared with that derived from time dependent density functional theory (TDDFT) theoretical calculations performed at the B3LYP level on optimized geometries. The energy values for the first two triplet states 3Bu and 3Ag, obtained from TDDFT calculations, were found to be highly strongly correlated with the experimental values. Also, the theoretical calculations for the electronic transition 1 1Ag --> 1 1Bu were also extremely well correlated with their experimental counterparts; even more important, the three reported experimental data for 1 1Ag --> 2 1Ag transitions in these systems conformed to the correlation for the TDDFT 1 1Ag --> 1 1Bu transition. The first excited electronic state in the linear polyenes studied (from ethene to the compound consisting of 40 ethene units, P40) was found to be 1Bu. The energy gap between the excited states 2 1Ag and 1 1Bu decreased with increasing length of the polyene chain, but not to the extent required to cause inversion, at least up to P40. In the all-trans linear polyenes studied, the widely analyzed energy gap from the ground electronic state to the first excited singlet state for infinitely long chains may be meaningless as, even in P40, it is uncertain whether the ground electronic state continues to be a singlet.