A two‐stage surface treatment for the long‐term stability of hydrophilic SU‐8

The use of SU‐8 photoresist as a structuring material for portable capillary‐flow cytometry devices has been restricted by the near‐hydrophobic nature of the SU‐8 surface. In this work, we evaluate the use of chemical and plasma treatments to render the SU‐8 surface hydrophilic and characterise the resulting surface utilising a combination of techniques including contact angle goniometry, atomic force microscopy and X‐ray photoelectron spectroscopy. In particular, for low‐power plasma treatments, we find that the chemistry of the plasma used to modify the SU‐8 surface and the incorporation of O₂ on that modified surface are paramount for improved surface wettability, whilst plasma‐induced surface roughness is not a necessary requirement. We demonstrate a technique to obtain a hydrophilic SU‐8 surface with contact angle as low as 7° whilst controlling and significantly reducing the level of surface roughness generated via the applied plasma. An additional chemical treatment step is found to be essential to stabilise the activated SU‐8 surface, and incubation of the samples with ethanolamine is demonstrated as an effective second‐stage treatment. Application of the optimised two‐stage surface treatment to cross‐linked SU‐8 is shown to result in a smooth hydrophilic surface that remains stable for over 3 months. Copyright © 2015 The Authors Surface and Interface Analysis Published by John Wiley & Sons Ltd.     

The origin of thermodynamic stability of microemulsions

The adsorption of surfactant and cosurfactant on the surface of the globules decreases the interfacial tension between oil and water to very low values. In addition, the decrease of the bulk concentrations of the surfactant and cosurfactant decreases their chemical potential both in the bulk and at the interface, thus decreasing the free energy of the system (dilution effect). The thermodynamic stability of microemulsions is due to the fact that the total free energy change caused by these effects can become negative. The theory can explain the occurence of stable microemulsions for both non-ionic and ionic surfactants.     

A kinetic stability study of MN (MBe,Mg, Ca,Sr, and Ba)

This work describes a structure and kinetic stability study of some complexes with the general formula MN, where M are the alkaline earth metal atoms, Be, Mg, Ca, Sr, and Ba. A complex (A) with two points of attachment to the N₅ ring is the most energetically favored for all metals considered here. Except for Be, structure (B) containing a mono‐coordinated metal atom is a transition state corresponding to the metal atom transfer around the N₅ ring. Pyramidal structure (C) is kinetically unstable with the low isomerization barrier height, ranging from 0.9 to 6.7 kcal/mol. The dissociation barrier heights for the lowest energy isomers (A) are predicted to be 1.2–18.7 kcal/mol (Be to Ba), indicating that kinetic stability increases from lighter to heavier metal atoms. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

fac‐Trichloro(quinolin‐8‐ylimido‐N,N′)(triphenylphosphine‐P)rhenium(V)

The Re atom in [Re(C₉H₆N₂)Cl₃(C₁₈H₁₅P)] is octahedrally coordinated by three Cl atoms in facial positions, two N atoms from 8‐imido­quinoline (imq) and one P atom from tri­phenyl­phosphine. The Re—N(imido) distance [1.760 (9) and 1.772 (8) Å] for imq is very short and implies double‐bond character. The trans influence of the P atom is indicated. Intra‐ and intermolecular π–π interactions between the π‐rings in the complex are also observed.     

NMR study of O and N,O‐substituted 8‐quinolinol derivatives

The ¹H and ¹³C NMR spectral study of several biologically active derivatives of 8‐quinolinol have been made through extensive NMR studies including homodecoupling and 2D‐NMR experiments such as COSY‐45°, NOESY, and HeteroCOSY. Electron donating resonance and electron withdrawing inductive effect of several groups showed marked changes in chemical shifts of nuclei at the seventh positions of O‐substituted quinolinols (2–15). Although in N‐alkyl, 8‐alkoxyquinolinium halides (16–21), ring A rightly showed low frequency chemical shift values. Copyright © 2013 John Wiley & Sons, Ltd.     

Selective Functionalization of P4 by Metal‐Mediated CP Bond Formation

A new and selective one‐step synthesis was developed for the first activation stage of white phosphorus by organic radicals. The reactions of NaCp^R with P₄ in the presence of CuX or FeBr₃ leads to the clean formation of organic substituted P₄ butterfly compounds Cp^R₂P₄ (Cp^R: Cp^BIG=C₅(4‐nBuC₆H₄)₅ ( 1 a ), Cp′′′=C₅H₂tBu₃ ( 1 b ), Cp*=C₅Me₅ ( 1 c ) und Cp^4iPr=C₅HiPr₄ ( 1 d )). The reaction proceeds via the activation of P₄ by Cp^R radicals mediated by transition metals. The newly formed organic derivatives of P₄ have been comprehensively characterized by NMR spectroscopy and X‐ray crystallography.     

A TD‐DFT study on the cyanide‐chemosensing mechanism of 8‐formyl‐7‐hydroxycoumarin

Proton transfer (PT) and excited‐state PT process are proposed to account for the fluorescent sensing mechanism of a cyanide chemosensor, 8‐formyl‐7‐hydroxycoumarin. The time‐dependent density functional theory method has been applied to investigate the ground and the first singlet excited electronic states of this chemosensor as well as its nucleophilic addition product with cyanide, with a view to monitoring their geometries and spectrophotometrical properties. The present theoretical study indicates that phenol proton of the chemosensor transfers to the formyl group along the intramolecular hydrogen bond in the first singlet excited state. Correspondingly, the nucleophilic addition product undergoes a PT process in the ground state, and shows a similar structure in the first singlet excited state. This could explain the observed strong fluorescence upon the addition of the cyanide anion in the relevant fluorescent sensing mechanism. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011     

Synthesis of 8‐Desoxythunberginol A and (±)‐8‐Desoxy‐3,4‐Dihydrothunberginol A

A two step synthesis of title isocoumarin isolated from Homalium longifolium and its conversion into corresponding 3,4‐dihydroisocoumarin has been described. 3,4‐Dimethoxybenzoyl chloride on condensation with homophthalic acid afforded 3‐(3′,4′‐dimethoxyphenyl)isocoumarin which was demethylated to furnish the 8‐desoxythunberginol A, whereas its sequential saponification, reduction and demethylation yielded the (±)‐8‐desoxy‐3,4‐dihydrothunberginol A. The synthesized compounds were examined in vitro for antibacterial activity.     

AB initio study of thermodynamic stability and structure of cage molecules B4N4H8 and Be4O4H8

Stable molecular structures of heterocubane systems B₄N₄H₈ 2 and Be₄O₄H₈, isoelectronic to the cubane molecule, are investigated by ab initio (RHF/6-31G**, MP2(full)/6-31C**, and MP2(full)/6-311+ + G**) methods and are shown to be highly thetmodynamically stable. Decomposition of structure 2 into two 1,3,2,4-diazadiboroethidine molecules 6 or four iminobomne NBNH molecules 11 is an endothermal process taking 10.1 (RHF/6-31G**), 39.6 (MP2(full)/6-31G**) kcaUmole and 140.6 (RHF/6-31G**), 161.4 (MP2(full)/6-31G**) kcal/mole, respectively. Decomposition of structure 3 into two 1,3,2,4-dioxydi-beryllothidine molecules 12 or four molecules 13 is also an endothermal reaction taking 22.1 (RHF/6-31G**), 39.8 (MP2(full)/6-31G**) kcal/mole and 127.1 (RHF/6-31G**), 155.2 (MP2(full)/631G**) kcal/mole, respectively. The geometrical characteristics of simple molecules BeH₂ 15, Be₂ 16 and 17, Be₂H₂ 18, Be₂H₄ 19, BeO 20, and Be₂O₂ 21 are calculated. Translated from Zhumal Struktumoi Khim ii, Vol. 41, No. 1, pp. 3-13, January–February, 2000     

Generalized P,Q and G conditions

The N-Representability Problem entails characterizing the set of second order reduced states that are contractions of N-electron states of the Fermion Fock algebra. This problem is formulated in the form of finding the conditions that a positive linear functional defined on a subspace of this algebra must satisfy in order to be extended to the whole algebra. As this algebra is a w*-algebra one can utilize a theorem by Kadison that shows it is sufficient to consider the values of linear functionals on projectors contained in the subspace in order to determine whether they have positive extensions. Thus we find the form of projectors belonging to the subspace of one and two particle operators and subsequently show that the extension conditions needed in the N-Representability Problem correspond to generalized P, Q and G conditions plus the additional constraints that the functionals be dispersion free on the number operator and their values on one particle operators determined by their values on two particle operators.     

A structural and theoretical study of the intermolecular interactions in 8‐hydroxyquinolinium‐7‐carboxylate monohydrate

In the title compound, C₁₀H₇NO₃·H₂O, the zwitterionic organic molecules and the water molecules are connected by N—H...O and O—H...O hydrogen bonds to form ribbons, and π–π stacking interactions expand these ribbons into a three‐dimensional net. The energies of these hydrogen bonds adopt values typical for mildly weak interactions (3.33–7.75 kcal mol⁻¹; 1 kcal mol⁻¹ = 4.184 kJ mol⁻¹). The total π–π stacking interactions between aromatic molecules can be classified as mildly strong (energies of 15.3 and 33.9 kcal mol⁻¹), and they are made up of multiple constituent π–π interactions between six‐membered rings. The short intermolecular C—H...O contact between two zwitterionic molecules is nonbonding in character.     

The stability of titania‐silica interface

Silica is very often the catalyst support of choice for transition metal oxides such as titania, and specially anatase. Titania is an excellent absorber and photocatalyst for many organic molecules degradation. In order to understand the chemical nature of the interaction between titania and silica, we have performed a theoretical study using density functional theory aiming to elucidate the role on the stability of the interface of the specific type of interactions, H‐bonding, covalent bonding of the pristine surfaces, and covalent bonding after silicon and titanium ions interdiffusion. The calculations were carried out for hydrogen and oxygen terminated surface, comparing the bonding types and the forces acting along the interface. The interface dynamics was studied for interfaces under applied stress in order to elucidate their stability and failure limits. The shearing forces and the mechanisms of interface failure were determined. Interfaces with interdiffused Si and Ti ions were studied to improve the interface stabilization. The results demonstrate that high‐temperature treatment leading to formation of Si O Ti bonds at the interface is responsible for the formation of strong and flexible binding interaction between both oxides. At high strains, the Si O Ti interface failure is observed due to lattice mismatch between the SiO₂ and TiO₂. The failure is a result of forces acting orthogonal to the interface shearing. In case of hydrogen terminated surface, the interface binding is a result of hydrogen bond network. Such interface is fragile at moderate shearing forces along the applied strain. The hydrogen bond network decreases the elastic properties and flexibility of the interface. The SiO₂/TiO₂ interface is further stabilized by Si/Ti ion interdiffusion. The ionic interdiffusion process also increases the interface flexibility. Thus, in order to obtain more stable anatase photocatalyst supported on silica, the synthetic routes should favor silicon and titanium ions interdiffusion along the interface.     

Substituent effects on the stability of 1,4‐benzodiazepin‐2‐one tautomers: A density functional study

The relative stability of 1,4‐benzodiazepin‐2‐one tautomers in the gas phase and model solvents was calculated at the M06 and ωB97XD levels of theory. The two density functionals were benchmarked earlier and demonstrated as excellent models to study tautomerism in a vast array of chemical systems. A number of commercially available 1,4‐benzodiazepin‐2‐ones were investigated computationally for the first time. In addition, some biologically active and newly devised benzodiazepines were considered, which may be important in designing structures with desired (bio)chemical features. Special attention was paid to determine substituent effects on the Gibbs free energies of keto, enol, and iminol forms for each respective benzodiazepine. It was demonstrated that (i) the replacement of the benzene ring by the heterocyclic ring in the benzodiazepine system may stabilize the iminol tautomer, and (ii) the electron‐withdrawing substituent at the C3‐position of the respective benzodiazepine may stabilize the enol tautomer relative to the parent keto form. It is concluded that substituent effects may govern the chemical reactivity and biological properties of selected benzodiazepines.     

A locked derivative of 8‐aza‐7‐deazaadenosine

The title compound [systematic name: (1S,3S,4R,7S)‐3‐(4‐amino‐1H‐pyrazolo[3,4‐d]pyrimidin‐1‐yl)‐1‐hydroxymethyl‐2,5‐dioxabicyclo[2.2.1]heptan‐7‐ol], C₁₁H₁₃N₅O₄, belongs to a family of nucleosides with modifications in both the sugar and nucleobase moieties: these modifications are known to increase the thermodynamic stability of DNA and RNA duplexes. There are two symmetry‐independent molecules in the asymmetric unit that differ significantly in conformation, and both exhibit a high‐anti conformation about the N‐glycosidic bond, with χ torsion angles of −85.4 (3) and −87.4 (3)°. The sugar C atom attached to the nucleobase N atom is −0.201 (4) and 0.209 (4) Å from the 8‐aza‐7‐deazaadenine skeleton plane in the two molecules. The molecules are assembled into layers via hydrogen bonds and π–π stacking interactions between the modified nucleobases.