Theoretical studies of the oxidative addition of PhBr to Pd(PX3)2 and Pd(X2PCH2CH2PX2) (X = Me, H, Cl)

The density functional theory calculations were used to study the influence of the substituent at P on the oxidative addition of PhBr to Pd(PX₃)₂ and Pd(X₂PCH₂CH₂PX₂) where X = Me, H, Cl. It was shown that the C_ipso-Br activation energy by Pd(PX₃)₂ correlates well with the rigidity of the X₃P-Pd-PX₃ angle and increases via the trend X = Cl < H < Me. The more rigid the X₃P-Pd-PX₃ angle is, the higher the oxidative addition barrier is. The exothermicity of this reaction also increases via the same sequence X = Cl < H < Me. The trend in the exothermicity is a result of the Pd(II)-PX₃ bond strength increasing faster than the Pd(0)-PX₃ bond strength upon going from X = Cl to Me. Contrary to the trend in the barrier to the oxidative addition of PhBr to Pd(PX₃)₂, the C_ipso-Br activation energy by Pd(X₂PCH₂CH₂PX₂) decreases in the following order X = Cl > H > Me. This trend correlates well with the filled d_π orbital energy of the metal center. For a given X, the oxidative addition reaction energy was found to be more exothermic for the case of X₂PCH₂CH₂PX₂ than for the case of PX₃. This effect is especially more important for the strong electron donating phosphine ligands (X = Me) than for the weak electron donating phosphine ligands (X = Cl).     

Molecular logic circuits and a security keypad lock based on a novel colorimetric azo receptor with dual detection ability for copper(II) and fluoride ions

A novel azoimine dye-based colorimetric chemosensor (1) has been designed and synthesised for dual recognition of copper(II) and fluoride ions in aqueous media. Significantly, the outstanding dual-ion recognition properties along with the excellent reversibility prompted us to consider 1 as an ideal candidate for fabrication of multiple logic circuits. According to the response profile of 1 towards Cu²⁺ and F^? inputs, we developed a unique tunable system integrated with one INHIBIT logic gate as well as one OR gate. Also, 1 behaved as a molecular keypad lock with sequential addition of Cu²⁺ and F^? inputs. In accession, a reversible ‘Write–Read–Erase–Read’ function with complementary ‘IMP/INH’ logic gate has been demonstrated through a feedback loop using F^? and trifluoroacetic acid as two chemical inputs. To the best of our knowledge, this is the first report where the symmetrical bis azo-azomethine dye has been exploited as a molecular keypad lock.     

Diastereoselective synthesis of chloro‐ and fluoro‐aniline containing phosphonate esters in a three‐component condensation

New phosphonate ester derivatives were obtained by in situ stereo‐specific reaction between triphenyl phosphite and dialkyl acetylenedicarboxylates in the presence of a series of halogenated anilines. Spectroscopic data and X‐ray crystallography analysis are in agreement with the gauche arrangement for the two vicinal protons in the structures. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:222–227, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20600     

Theoretical study on ionic liquids based on DBUH+: Molecular engineering and hydrogen bond evaluation

The new generation of the ionic liquids (ILs) based on 1,8-diazobicylo [5,4,0] undec-7-ene (DBU) are applied as the solvent in organic reactions. In this work, by using a theoretical procedure, the most probable interactions between the ion pairs of DBUH⁺ based ILs, including 10 functionalized imidazole anions were investigated. For this purpose, the electrostatic potential surfaces were analyzed to detect the most probable interaction sites of DBUH⁺. On the basis of the obtained results, hydrogen bond formation between the anions and DBUH⁺ is influenced by the electronic effect of the substituted functional groups. This means that electron donating groups, such as phenyl has a stabilizing effect on the ion pairs, while electron-withdrawing groups, such as nitro, induces a destabilizing effect. These behaviors are described based on the interaction energy values (ΔE_int). To investigate the dispersion interaction effects in ILs formation, M06-2X-D3 functional was applied in energy analysis. The solvent reaction field was investigated by the polarizable continuum model in ethanol and chloroform as the solvent. The results showed that ethanol has a greater effect on the interaction energy of the ILs. Finally, to have a comprehensive understanding of the charge transfer effect on the stability of the studied ILs and to characterize the most probable interactions, natural bond orbital and quantum theory of atoms in molecules analyses were applied and the obtained results were analyzed.     

Investigating the effects of precursor concentration and gelling parameters on droplet-based generation of Ca-Alginate microgels: identifying new stable modes of droplet formation

Droplet-based microfluidics is an attractive approach for producing microgels due to its high potential to control the size and shape of the particles and precisely entrap the substances within the hydrogel matrix. However, the microfluidic generation of monodisperse microgels with desired structures is still challenging. Indeed, the rheological and interfacial properties of the immiscible fluids, as well as the adopted gelling strategy, play important roles in microfluidic methods. Herein, sodium alginate droplets with different concentrations are generated via a microfluidic device with a flow-focusing unit. Besides, a combined in situ and ex situ strategy is optimized to crosslink sodium alginate droplets in the presence of calcium ions. The effects of alginate concentration and junction width in the flow focusing unit are investigated on droplet size and droplet formation regimes. It is observed that by increasing the alginate concentration, the dripping regime of droplet formation may be transformed to one of the binary dripping or quasijetting regimes. In the binary dripping regime, two successive different-sized droplets are generated in each period of droplet formation, which leads to low monodispersity in the collected droplets. However, the droplets produced in the quasijetting regime are interestingly monodisperse and also smaller than those of the dripping and binary dripping regimes. The breakup dynamics of the alginate thread is also analyzed with a computational fluid dynamics (CFD) code. This analysis discloses that the viscous stresses, as well as the viscous dissipation, have important roles in controlling the stable modes of droplet formation.     

Synthesis of 1‐(Cyclohexylamino)‐2‐(aryl)pyrrolo[1,2‐a]quinoline‐3‐carbonitrile Derivatives Using a Mild,Four‐Component Reaction

1‐(Cyclohexylamino)‐2‐(aryl)pyrrolo[1,2‐a]quinoline‐3‐carbonitrile derivatives were synthesized in an efficient method from four‐component condensation reaction between cyclohexyl isocyanide, quinoline, malononitrile, and aromatic aldehydes in the presence of a catalytic amount of titanium dioxide (TiO₂) in CH₂Cl₂ at ambient temperature in good yields. Silica gel column chromatography was employed for HCN elimination and then 1, 3 hydrogen shift was led to form final products 5a , 5b , 5c , 5d , 5e .     

On the number of distinct elliptic curves in some families

We give explicit formulas for the number of distinct elliptic curves over a finite field (up to isomorphism over the algebraic closure of the ground field) in several families of curves of cryptographic interest such as Edwards curves and their generalization due to D. J. Bernstein and T. Lange as well as the curves introduced by C. Doche, T. Icart and D. R. Kohel.     

Batch and flow measurement of hydrogen ions in highly acidic media using 2-(4-methoxy phenyl) 6-(4-nitrophenyl)-4-phenyl-1,3-diazabicyclo [3.1.0] hex-3-ene as an H-selective ionophore

A hydrogen ion-selective poly(vinyl chloride) (PVC) membrane electrode was developed using 2-(4-methoxy phenyl) 6-(4-nitrophenyl)-4-phenyl-1,3-diazabicyclo [3.1.0] hex-3-ene as ionophore. Effects of experimental parameters such as membrane composition, nature and amount of plasticizer, and the amount of additive on the potential response of pH sensor were investigated. This H⁺-selective membrane electrode gave a linear response over the pH range 0-4 (10⁻⁴ to 1 mol L⁻¹ HCl) with slope of 57.4 ± 0.3 mV pH⁻¹ and limit of detection 6.3 × 10⁻⁵ mol L⁻¹ at 20 °C. Also, hydrofluoric acid did not influence the surface of this electrode and thus it was maintained without showing any changes in potentials after being used in a hydrofluoric acid solution. The equilibrium water content of the electrode was determined in the presence of two different plasticizers as membrane solvent. The alkaline cation binding affinity of ionophore was very low that prove these cations do not have specific interaction with this ionophore. The electrode had fairly low electrical resistance, good potential stability and reproducibility. It has a rapid potential response to changes of pH (10 s), easily used in a single channel wall-jet flow injection system with good reproducibility (RSD% = 1.67%) and high reversibility. It was used as indicator electrode in potentiometric determination of pH in real samples.