Intramolecular and Intermolecular Schmidt Reactions of Alkyl Azides with Aldehydes

Despite recent advances in the use of alkyl azides in ring expansion reactions of ketones, there has been little work done on the corresponding chemistry of aldehydes. In the present study, the Lewis acid-promoted reactions of alkyl azides with aldehydes were studied in both intermolecular and intramolecular contexts. The intramolecular reactions of azidoalkyl aldehydes in which the azide and carbonyl groups were separated by 2-5 carbons were examined. Although the examples having the shortest tether failed (3-azidopropanals), each of the other systems gave good yields of either NH-substituted lactams (resulting from hydride migration in the initially formed azidohydrin adduct) or formamides (alkyl migration). The product formed was dependent on the chain length of the starting azido aldehyde. The intermolecular reactions were less efficient, requiring TiCl₄ promotion for even moderate yields, and in each case gave mixtures of products resulting from hydride and alkyl migration.     

Foam Separation of Anions: Hydration,Entropy, and Selectivity

Abstract

A selectivity coefficient for the foam separation of Fe(CN)₆ ^4-, Ag(S₂0₃)₂ ^3-, Cr₂0₇ ^2-, Cr0₄ ^2-, S₂0₃ ^2-, HP0₄ ^2-, and I^? from solutions containing ethylhexadecyldimethylammonium bromide is related to the absolute partial molal entropy of each ion. The entropy, which correlates well with the degree of hydration, enables an estimate of the selectivity of an ion flotation or foam fractionation by a surfactant.     

3-Pyrrolidinones: Michael Addition and Schmidt Rearrangement Reactions

Various spiro-pyrano[3,2-b]pyrrolo-2-oxoindolines 3a–d and dicyano-pyrano[3,2-b]pyrroles 5a–e have been synthesized in the present study by Michael addition of 3-pyrrolidinones 1 to isatin-3-ylidenes 2 and arylidenemalononitrile 4. Hexahydro-4-oxo-1-aryl-pyrimidine-5-carboxylic acids 7a,b were synthesized from 1 by Schmidt rearrangement.     

Selectivity in consecutive heterogeneous catalytic reactions: Case of polyatomic molecules

Consecutive catalytic reaction mechanism of type A^(+B)C^(+B)D is considered and the polyatomic nature of adsorbed molecules is taken into account. The equations for the selectivity are presented and compared with ones for consecutive reactions with monoatomic reagents.     

Inter- and Intramolecular Hetero Diels-Alder Reactions, 49[1] Kinetics and Selectivity of the Intramolecular Hetero Diels-Alder Reaction of 1-Oxa-1,3-butadienes using a Benzylidenebarbituric Acid Derivative Effect of Pressure,Temperature, and Solvent

The intramolecular hetero Diels-Alder reaction of the benzy-lidenebarbituric acid derivative 1 to give the ortho and meta products 2 and 3 is studied under high pressure up to 6 kbar in various solvents. The kinetics is measured by on-line FT-IR spectroscopy up to 3 kbar. The cycloaddition shows a pressure-dependent increase in regioselectivity in favour of the ortho adduct 2. The activation volumes, ΔV, are determined to be -(33.1· 1.2) and -(34.2· 1.5) cm³· mol⁻¹ for the reactions in dichloromethane and tetrahydrofuran at 100°C, respectively. For the cycloaddition in toluene and acetonitrile the activation volumes are found to be -(13.4· 1.5) and -(17.0· 4.1) cm³· mol⁻¹, respectively. Contrary to the large solvent effect on the activation volume, only a minor effect on the activation volume differences, ΔΔV, is observed. Measurement of the molar volumes of 1 and the cycloadducts 2 and 3 show a strong solvent dependency.     

Salt‐Induced Adaptation of a Dynamic Combinatorial Library of Pseudopeptidic Macrocycles: Unraveling the Electrostatic Effects in Mixed Aqueous Media

Dynamic combinatorial libraries are powerful systems for studying adaptive behaviors and relationships, as models of more complex molecular networks. With this aim, we set up a chemically diverse dynamic library of pseudopeptidic macrocycles containing amino‐acid side chains with differently charged residues (negative, positive, and neutral). The responsive ability of this complex library upon the increase of the ionic strength has been thoroughly studied. The families of the macrocyclic members concentrating charges of the same sign showed a large increase in its proportion as the ionic strength increases, whereas those with residues of opposite charges showed the reverse behavior. This observation suggested an electrostatic shielding effect of the salt within the library of macrocycles. The top‐down deconvolution of the library allowed us to obtain the fundamental thermodynamic information connecting the library members (exchange equilibrium constants), as well as to parameterize the adaptation to the external stimulus. We also visualized the physicochemical driving forces for the process by structural analysis using NMR spectroscopy and molecular modeling. This knowledge permitted the full understanding of the whole dynamic library and also the de novo design of dynamic chemical systems with tailored co‐adaptive relationships, containing competing or cooperating species. This study highlights the utility of dynamic combinatorial libraries in the emerging field of systems chemistry.     

Addition Reactions of Me3SiCN with Aldehydes Catalyzed by Aluminum Complexes Containing in their Coordination Sphere O,S, and N Ligands

The reaction of one equivalent of LAlH₂ ( 1 ; L=HC(CMeNAr)₂, Ar=2,6‐iPr₂C₆H₃, β‐diketiminate ligand) with two equivalents of 2‐mercapto‐4,6‐dimethylpyrimidine hydrate resulted in LAl[(μ‐S)(m‐C₄N₂H)(CH₂)₂]₂ ( 2 ) in good yield. Similarly, when N‐2‐pyridylsalicylideneamine, N‐(2,6‐diisopropylphenyl)salicylaldimine, and ethyl 3‐amino‐4,5,6,7‐tetrahydrobenzo[b]thiophene‐2‐carboxylate were used as starting materials, the corresponding products LAl[(μ‐O)(o‐C₆H₄)CN(C₅NH₄)]₂ ( 3 ), LAlH[(μ‐O)(o‐C₄H₄)CN(2,6‐iPr₂C₆H₃)] ( 4 ), and LAl[(μ‐NH)(o‐C₈SH₈)(COOC₂H₅)]₂ ( 5 ) were isolated. Compounds 2 – 5 were characterized by ¹H and ¹³C NMR spectroscopy as well as by single‐crystal X‐ray structural analysis. Surprisingly, compounds 2 – 5 exhibit good catalytic activity in addition reactions of aldehydes with trimethylsilyl cyanide (TMSCN).     

Effects of Electrostatic Interactions on the Translocation of Polymers Through a Narrow Pore Under Different Solvent Conditions: A Dissipative Particle Dynamics Simulation Study

Polymer translocation through a narrow pore is investigated using a particle‐based dissipative particle dynamics (DPD) method. A rigid core is included in each particle to avoid particle interpenetration problems based on the original DPD method. Electrostatic interactions of charged particles are simply represented via screened Coulombic interactions. The average translocation time τ versus polymer length N satisfies the scaling law τ ∼ N^β. The scaling exponent β depends on solvent quality. The results demonstrate that solvent quality exerts a considerable influence on the dynamics of translocation of polymers. The findings may help facilitate understanding of the dynamic behaviors of various polymer and DNA molecules during translocation processes.

     

Nucleic Acid Templated Reactions: Consequences of Probe Reactivity and Readout Strategy for Amplified Signaling and Sequence Selectivity

Making the right signals : Reactions in which the DNA target acts as a catalyst allow amplified signaling in the detection of DNA. The reactivity of the peptide nucleic acid (PNA) probes determines whether a given probe set provides high sensitivity or high selectivity. The careful adjustment of reactivity, probe affinity, and the use of a product‐selective readout method allows improvements in the sensitive analyses of single‐base mutations in DNA with little background interference.

     

Ammonium across a Selective Polymer Inclusion Membrane: Characterization,Transport, and Selectivity

The recovery of ammonium from urine requires distinguishing and excluding sodium and potassium. A polymer inclusion membrane selective for ammonium is developed using an ionophore based on pyrazole substituted benzene. The interactions of the components are studied, as well as their effect on transport and selectivity. Spectroscopic and thermogravimetric measurements show no extensive physical interactions of the components, and that the plasticizer reduces the intermolecular forces (rigidity) of the membrane. The ionophore turns the membrane more rigid, although it increases its swelling degree and therefore the affinity of cations. A ratio of plasticizer (DEHP) and polymer (PVC) of 1:3 in mass gives the highest ammonium flux. Tested contents of ionophore (2 and 5 wt%) show that the higher the content of the ionophore, the fastest the flux is (7.5 × 10⁻³ mmol cm⁻² h⁻¹). Selectivity of NH₄⁺ over Na⁺ and over K⁺ is reduced from 13.07 to 9.33 and from 14.15 to 9.57 correspondingly.

     

Enantioselectivity in Ruthenium-Catalyzed Propargylic Substitution Reactions of Propargylic Alcohols with Acetone: A DFT Study

The enantioselectivity in the propargylic substitution reactions of propargylic alcohols with acetone catalyzed by optically active thiolate-bridged diruthenium complexes was examined via ωB97X-D level DFT calculations. Some structures with intramolecular dispersion interactions between ligands were found for the ruthenium-allenylidene complex, which is the key intermediate in the catalytic reaction, and it was determined that the structure corresponding to the X-ray crystal structure, which had provided the transition state model for the enantioselectivity in previous studies, was not the most stable among the obtained structures. Then, a variety of transition-state structures for the nucleophilic attack of prop-1-ene-2-ol, which is the enol isomer of acetone, on the γ-carbon of the ruthenium-allenylidene complex were explored. Among the transition-state structures with lower energies, the number of structures leading to the major (R) product was found to be larger than that of structures leading to the minor (S) product, providing enantioselectivity in terms of probability distributions. The introduction of a phenyl group in the thiolate ligand was suggested to increase the selectivity. Thus, we propose the novel transition state model for the asymmetric catalytic reaction system.     

Substrate and Positional Selectivity in Electrophilic Substitution Reactions of Pyrrole, Furan, Thiophene, and Selenophene Derivatives

The relative reactivity (substrate selectivity) of five-membered heterocycles on electrophilic substitution (pyrrole >> furan > selenophene > thiophene) and their positional selectivity (furan > selenophene thiophene > pyrrole) are not consistent. The indicated differences in positional selectivity ( : ratios) of the parent heterocycles show up essentially in orientation on electrophilic substitution reactions of their derivatives and the corresponding benzannelated systems. It was shown that the positional selectivity was reduced in a sequence corresponding to the change in relative stability of the onium states of the elements (O⁺ < Se⁺ S⁺ < N⁺) and reflects the predominant role of the heteroatoms in stabilizing the -complexes formed on -substitution, in which the positive charge is distributed between the heteroatom and one -carbon atom (in -isom ers four atoms of the ring participate in delocalization of the charge). This interpretation was confirmed by quantum-chemical calculations carried out by the RHF/6-31G(d), MP2/6-31G(d)//RHF(6)-31G(d), and B3LYP/6-31G(d) ab initio methods.     

Cofilin-Membrane Interactions: Electrostatic Effects in Phosphoinositide Lipid Binding

The actin cytoskeleton interacts with the cell membrane primarily through the indirect interactions of actin-binding proteins such as cofilin-1. The molecular mechanisms underlying the specific interactions of cofilin-1 with membrane lipids are still unclear. Here, we performed coarse-grain molecular dynamics simulations of cofilin-1 with complex lipid bilayers to analyze the specificity of protein-lipid interactions. We observed the maximal interactions with phosphoinositide (PIP) lipids, especially PIP₂ and PIP₃ lipids. A good match was observed between the residues predicted to interact and previous experimental studies. The clustering of PIP lipids around the membrane bound protein leads to an overall lipid demixing and gives rise to persistent membrane curvature. Further, through a series of control simulations, we observe that both electrostatics and geometry are critical for specificity of lipid binding. Our current study is a step towards understanding the physico-chemical basis of cofilin-PIP lipid interactions.     

Charged Semi-Permeable Shell with Encapsulated Polyions: Concentration Profile,Surface Potential,and Electrostatic Pressure

Summary: We study theoretically the electrostatic equilibrium for a charged shell filled with a suspension of polyions (e.g., colloids, polyelectrolytes, etc.) and immersed in an infinite salt-free reservoir. The shell is impermeable for polyions, but allows free diffusion of counterions. From the solution of the linearized Poisson-Boltzmann equation we obtain the distribution of the potential and concentration profiles for polyions. We then derive explicit formulas for the electrostatic pressure exerted by the shell. If the overall charge of the filled shell has the same sign as the surface alone the pressure on the shell increases with increase of the surface charge density. Otherwise the surface charge density suppresses the electro-osmotic pressure due to the electrostatic attraction between the oppositely charged polyions and shell.     

Nonbonding pairs in cyclic thioethers: Electrostatic modeling and ab initio calculations for complexes of 2,5-dihydrothiophene,thietane, and thiirane with hydrogen fluoride

Electrostatic potential energies V(ϕ) of a non-perturbing, protonic charge at fixed distances r from the S atom in three cyclic thioethers were examined as functions of the angles ϕ made by the r-vector with the C₂ axis (thiirane and 2,5-dihydrothiophene) or the local C₂ axis (thietane). The electrostatic PE V_HF(ϕ) of HF (HF modelled as an extended electric dipole) was also calculated and the results compared with geometries of the thioether⋯HF complexes calculated at the CCSD(T)-F12c/cc-pVTZ-F12 level. The latter reveal angular deviations θ ∼10-20° of the S⋯H F nuclei from collinearity in directions suggesting secondary interactions of F with H atom(s) of the rings. Angles ϕ made by the S⋯H hydrogen bond with the C₂ (or local C₂) axes in the complexes are systematically larger (∼4-9°) than indicated by the V_HF(ϕ) functions. Minima in the simple V(ϕ) versus ϕ functions occur at values smaller (∼5-10°) than those in the V_HF(ϕ) curves.     

Expanding the Use of Dynamic Electrostatic Repulsion Reversed-Phase Chromatography: An Effective Elution Mode for Peptides Control and Analysis

Bioactive peptides are increasingly used in clinical practice. Reversed-phase chromatography using formic or trifluoroacetic acid in the mobile phase is the most widely used technique for their analytical control. However, sometimes it does not prove sufficient to solve challenging chromatographic problems. In the search for alternative elution modes, the dynamic electrostatic repulsion reversed-phase was evaluated to separate eight probe peptides characterised by different molecular weights and isoelectric points. This technique, which involves TBAHSO₄ in the mobile phase, provided the lowest asymmetry and peak width at half height values and the highest in peak capacity (about 200 for a gradient of 30 min) and resolution concerning the classic reversed-phase. All analyses were performed using cutting-edge columns developed for peptide separation, and the comparison of the chromatograms obtained shows how the dynamic electrostatic repulsion reversed-phase is an attractive alternative to the classic reversed-phase.     

Theoretical study on selectivity trends in (N‐heterocyclic carbene)‐Pd catalyzed mizoroki–heck reactions: Exploring density functionals methods and molecular models

The regioselectivity of the NHC‐Pd catalyzed Heck coupling reaction between phenyl bromide and styrene has been investigated using the density functional theory, wave‐function (WF)‐based methods and two different sizes of model ligands. In addition to the WF methods, the TPSS‐D3, B97X‐D, BP86‐D3, and M06‐L density functionals were reliable approaches to be applied, independently of the basis set. Moreover, the NCI analysis showed that weak interactions are important forces to be taken into account when exploring the regioselectivity of this reaction, mainly when a crowded NHC ligand is present. © 2017 Wiley Periodicals, Inc.