Comparison of various coupling reagents in solid-phase aza-peptide synthesis

Aza-peptides are promising drug leads, however extensive study of their properties is hampered by low yielding aza-peptide bond formation during conventional Fmoc SPPS. The kinetics of aza-peptide bond formation in the model peptide H-Ala-AzAla-Phe-NH₂ was compared with various conventional amino acid activators. The reaction rates and yields were dependent on the activator structure. The reaction time of aza-peptide formation using oxyma-based agents was approximately 30 times longer than in typical peptide synthesis. Therefore, new activators are required to increase the reactivity of the activated amino acid to achieve effective acylation of the semicarbazide moiety during aza-peptide bond formation.     

Big Hankel operators of higher weight

Known results concerning the smoothness and boundedness of «big» Hankel operators (Hankel operators in the sense of Axler) are generalized to the case of higher weight (in the sense of representation theory). The key result is a certain estimate for thes-numbers of a particular such operator, involving a combinatorial sum.     

Effect of strain on gas‐phase basicity of (E)‐1‐methyl‐2‐(1‐methyl‐2‐adamantylidene)adamantane

Steric strain, caused by forced deformation of double bond geometry, has significant impact on alkene reactivity, as was shown by a study of the gas‐phase basicity of (E)‐1‐methyl‐2‐(1‐methyl‐2‐adamantylidene)adamantane. The Gibbs free energy of the strain effect in this compound was 42 kJ/mol. This analysis was made based on adamantylideneadamantane as a congeneric reference compound with a planar double bond. It was concluded that gas‐phase basicity could serve as a valuable alternative indicator for quantification of steric strain in alkenes. Copyright © 2015 John Wiley & Sons, Ltd.     

Ultrasonic detection of hydrophobic interactions: a quantitative approach

Kinetic effects of sonication on ester hydrolysis and tert‐butyl chloride solvolysis, studied in ethanol–water binary solvent, are discussed in terms of quantitative relationships between their magnitude and the hydrophobicity of reagents. A number of conclusions were drawn from the observed linear free‐energy (LFE) relationships. Independent of reaction mechanism, the decrease in reaction rates with increasing ethanol content in the solvent is mainly due to hydrophobic stabilization of the ground state. While hydrophobic species can be hidden in the ethanol clusters present in the region X_EtOH > 0.15, at lower ethanol contents hydrophobic reagents are weakly solvated and the hydrophobic stabilization can be easily overcome by sonication. Copyright © 2008 John Wiley & Sons, Ltd.     

Interpolation of compactness using Aronszajn-Gagliardo functors

We prove that ifT: A ₀ →B ₀ andT: A ₁ →B ₁ both are compact, then is also compact, whereF is the minimal or the maximal functor in the sense of Aronszajn-Gagliardo. We also derive some results for ordered couples. Supported in part by Ministerio de Educación y Ciencia (SAB-87-0172).     

Comparison of two kinds of Hankel type operators

We compare two kinds of Hankel type operators, the “BJP-operators” introduced by Boman—Janson—Peetre and the “Z-operators” considered by Zhang. We show that every BJP-operator comes as an orthogonal sum ofZ-operators.     

A green's function for the annulus

In this paper we find an expression for Green's junction for the operator ² in a planar circular annulus with Dirichlet boundary conditions (clamped elastic plate). We likewise determine the corresponding Poisson type kernels and the harmonic Bergman kernel. These results come in terms of certain new transcendental functions which in a natural way generalize the Weierstrass zeta function. They are analogous to the result of R.Courant D.Hubert (Methoden der Mathematischen Physik I (3. Aufl.), Springer-Verlag, Berlin, Heidelberg, New York (1968), pp. 335-337)and H.Villat (Rend. Circ. Mat. Palermo,33 (1912), pp. 134–175)respectively. As an application we show that, regardless of the size of the ratio of the radii of the bounding circles, the Green's function always assumes negative values, which constitutes another rather striking counter-example to the wellknown Boggio-Hadamard conjecture.Sponsored by the «Civilingenjör Gustaf Sigurd Magnusons fond för främjande av vetenskapen inom ämnet matematik» of the Royal Swedish Academy of Sciences (Kungl. Vetenskapsakademien) and also in part by GA AV R grant No. 119106.     

Modification of the structural and electronic properties of graphene by the benzene molecule adsorption

A survey of the literature data on the adsorption of benzene on graphene or carbon nanotubes indicates that the distance between the graphene sheet and benzene molecule is determined from weak van der Waals forces (∼3.40 Å). In our theoretical study, it was found that the benzene/graphene structure (in a specific configuration with carbon atoms located at the atop positions, stacked directly on the top of each other) forms strong covalent bonds, if the distance between the graphene and benzene is about 1.60 Å. Such a short distance corresponds to about a half of the usual separation between the graphite layers. It was also shown that at such a short distance the carbon atoms of the benzene molecule move towards the graphene sheet, whereas the hydrogen atoms move in a different direction, thus breaking the benzene planar structure.     

Role of water in determining organic reactivity in aqueous binary solvents

Kinetic data for organic reactions in various binary water-organic solvent mixtures were collected and quantitatively analysed in terms of linear-free-energy relationships by using tert-butyl chloride (2-chloro-2-methylpropane) solvolysis as the reference system. Linear similarity plots for these kinetic data were determined for solvent systems ranging from pure water mixtures up to considerable amount of cosolvent, and 161 similarity coefficients were calculated from slopes of these plots. The existence of these linear plots demonstrated that the solvent effects are of some common nature in all analysed reaction mixtures independent of the reaction type and the cosolvent used. Therefore it was concluded that the observed effects could be connected to the specific solvating properties of water, which govern reactivity even in significant dilution of water by an organic cosolvent. This conclusion was supported by the linear interrelationship between the slopes of similarity plots of different reactions, and hydrophobicity parameters log P of the reacting compounds. The relative solvent effects observed in binary water-organic solvent mixtures were for the first time directly related to the structure of reacting compounds.