ATR-IR spectroscopy of pendant NH2 groups on silica involved in the Knoevenagel condensation

The liquid-phase Knoevenagel condensation between benzaldehyde and ethyl cyanoacetate catalyzed by aminopropyl-modified silica has been investigated using in situ attenuated total reflection infrared (ATR-IR) spectroscopy. The aim of the work was to demonstrate the different levels of information on the reaction mechanism that can be achieved by operating the spectroscopic cell in the absence and in the presence of a solvent, in flow-through and stop-flow modes and in combination with concentration modulation spectroscopy. The reaction mechanism involves the formation of an imine intermediate whose existence has been verified in situ by combining in one experiment continuous and stop-flow operations. Identical information has been gained more elegantly using concentration modulation spectroscopy, which additionally provided information on the possible origin of the solvent effect observed in the Knoevenagel reaction. Faster production and consumption of the imine intermediate was observed in cyclohexane solvent than in toluene. Identification of other species evolving on the catalyst surface and monitoring of the effluents of the spectroscopic cell provided some insight in possible catalyst deactivation.     

Cupreines and cupreidines: an emerging class of bifunctional cinchona organocatalysts

In the steadily expanding field of organocatalysis, cinchona alkaloids play a prominent role. Until the late 1990s, bifunctional catalysts based on this scaffold relied exclusively on the C9-hydroxy group as the hydrogen-bond donor. Recently, new cinchona catalysts have been developed that feature a phenolic OH group in the C6' position-a structural feature that allows a diverse set of reactions to be catalyzed in a highly stereoselective fashion. This Minireview describes the scope and modes of action of this new class of asymmetric bifunctional organocatalysts.     

Polycationic calix[8]arenes able to recognize and neutralize heparin

A mutual induced fit mechanism is responsible for the exceptional complexation performances exhibited by calix[8]arene polycations towards heparin. The recognition process was studied in comparison with two other heparin antagonists: protamine and polylysine. The arrangement of multiple functional groups on the flexible macrocyclic scaffold of calix[8]arene, with respect to the conformationally rigid protamine and low ordered polylysine, allowed a mutual adaptability between calixarene polycations and heparin, significantly enhancing the recognition performances. Fluorescence, NMR titration, and activated partial thromboplastin time (aPTT) experiments confirmed that these calixarene derivatives have a very high specificity and affinity towards heparin neutralization as in aqueous solution as in blood. Analogous results were obtained with low molecular weight heparin (LMWH) whose effect protamine is unable to completely reverse.     

Total synthesis of (-)-spongidepsin

[structure: see text] A convergent and rapid stereoselective synthesis of (-)-spongidepsin has been achieved from the Roche ester in 14 steps with an overall yield of 13%.     

Theoretical study on the circular dichroism in core and valence photoelectron angular distributions of camphor enantiomers

In the present work the photoelectron circular dichroism of camphor has been theoretically studied using B-spline and continuum multiple scattering-Xalpha methods, and comparisons are made with available experimental data. In general, rather large dichroism effects have been found for both valence and core (O 1s, C 1s) photoionizations. The agreement between the two calculations reported here and previous experimental measurements for core C 1s data is essentially quantitative. For valence ionization satisfactory agreement between theory and experiment has been obtained and the discrepancies have been attributed to both exchange-correlation potential limitations and the absence of response effects in the adopted formalism. The calculations predict, moreover, important features in the cross-section profiles, which have been discussed in terms of dipole-prepared continuum orbitals.     

Two-step synthesis of per-O-acetylfuranoses: optimization and rationalization

A simple two-step procedure yielding peracetylated furanoses directly from free aldoses was implemented. Key steps of the method are (i) highly selective formation of per-O-(tert-butyldimethylsilyl)furanoses and (ii) their clean conversion into acetyl ones without isomerization. This approach was easily applied to galactose and structurally related carbohydrates such as arabinose, fucose, methyl galacturonate and N-acetylgalactosamine to give the corresponding peracetylated targets. The success of this procedure relied on the control of at least three parameters: (i) the tautomeric equilibrium of the starting unprotected oses, (ii) the steric hindrance of both targeted furanoses and silylating agent, and finally, (iii) the reactivity of each soft nucleophile during the protecting group interconversion.     

2‐Starters,Graceful Labelings,and a Doubling Construction for the Oberwolfach Problem

Every 1‐rotational solution of a classic or twofold Oberwolfach problem (OP) of order n is generated by a suitable 2‐factor (starter) of or , respectively. It is shown that any starter of a twofold OP of order n gives rise to a starter of a classic OP of order (doubling construction). It is also shown that by suitably modifying the starter of a classic OP, one may obtain starters of some other OPs of the same order but having different parameters. The combination of these two constructions leads to lots of new infinite classes of solvable OPs. Still more classes can be obtained with the help of a third construction making use of the possible gracefulness of a graph whose connected components are cycles and at most one path. As one of the many applications, Hilton and Johnson's [J London Math Soc, 64 (2001) 513–522] bound about the solvability of OP is improved to in the case of r even. © 2012 Wiley Periodicals, Inc. J. Combin. Designs 20: 483‐503, 2012     

15N magnetic resonance hyperpolarization via the reaction of parahydrogen with 15N-propargylcholine

(15)N-Propargylcholine has been synthesized and hydrogenated with para-H(2). Through the application of a field cycling procedure, parahydrogen spin order is transferred to the (15)N resonance. Among the different isomers formed upon hydrogenation of (15)N-propargylcholine, only the nontransposed derivative contributes to the observed N-15 enhanced emission signal. The parahydrogen-induced polarization factor is about 3000. The precise identification of the isomer responsible for the observed (15)N enhancement has been attained through a retro-INEPT ((15)N-(1)H) experiment. T(1) of the hyperpolarized (15)N resonance has been estimated to be ca. 150 s, i.e., similar to that reported for the parent propargylcholine (144 s). Experimental results are accompanied by theoretical calculations that stress the role of scalar coupling constants (J(HN) and J(HH)) and of the field dependence in the formation of the observed (15)N polarized signal. Insights into the good cellular uptake of the compound have been gained.     

On the comparison principle for unbounded solutions of elliptic equations with first order terms

We prove a comparison principle for unbounded weak sub/super solutions of the equation

$\lambda u?\text{div}(A(x)Du)=H(x,Du)\text{ in }\mathrm{\Omega }$

where $A(x)$ is a bounded coercive matrix with measurable ingredients, $\lambda \ge 0$ and $\xi ?H(x,\xi )$ has a super linear growth and is convex at infinity. We improve earlier results where the convexity of $H(x,?)$ was required to hold globally.