Reversible Hydrophobic Barriers Introduced by Microcontact Printing: Application to Protein Microarrays

Microcontact printing (µCP) has been used to introduce temporary hydrophobic barriers on carboxymethylated dextran (CMD) hydrogels on gold. Among the investigated types of inks, tetraoctadecylammonium bromide (TOAB), electrostatically bound to the CMD layer, provided the most well-defined features both with respect to pattern-definition and reversibility upon exposure to a regeneration solution. The printed patterns were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), microscopic wetting and imaging null ellipsometry to explore the influence of concentration of ink solution and contact time on the appearance of the printed layer. AFM revealed that the printed TOAB molecules aggregated into clusters rather than into a homogeneous mono- or multilayer on the CMD hydrogel. It was also observed that printed areas of TOAB that are larger than 25µm are inhomogeneous most likely because of an edge transfer lithography (ETL) mechanism. A protein model system based on Protein A-rabbit antimouse Fc was used to evaluate the potential of the patterned surface as a protein microarray chip by means of surface plasmon microscopy (SPM). Moreover, non-specific adsorption of several proteins onto TOAB barriers was also studied using surface plasmon resonance (SPR), and it is evident that undesired adsorption can be eliminated by removing barriers after ligand immobilization, but prior to analyte exposure, by treating the patterned surface with a simple salt regeneration solution.     

Development of dextran-derivative arrays to identify physicochemical properties involved in biofouling from serum

To control protein adsorption on surfaces, low-fouling polymer coatings such as poly(ethylene oxide) (PEG or PEO) and polysaccharides are used. Their ability to resist protein adsorption is related to the layer structure, hence the immobilization mode. A polymer array technology was developed to study the structural diversity of carboxymethyl dextran (CMD) layers, whose immobilization conditions were varied. CMD arrays were analyzed by X-ray photoelectron spectroscopy (XPS) and by atomic force microscopy (AFM) colloidal probe force measurements. Serum protein adsorption was studied directly on the CMD arrays using surface plasmon resonance (SPR) microscopy. Physicochemical characterization revealed that pinning density regulates surface coverage and the amount of adsorbed molecules, and that salt concentration influences the surface structure of the charged polymer, forming extended or short layers. Protein adsorption experiments from serum showed that repulsive CMD layers are dense, with extended flexible chains. The present study underlines the usefulness of polymer arrays to study structural diversity of thin graft layers and to relate their physicochemical properties to their resistance to nonspecific protein adsorption.     

Novel properties of molecular assemblies of isoprenoid surfactants

Unlike micelles of straight hydrocarbon chain-surfactants, isoprenoid surfactants, CH₃ [CH(CH₃)CH₂CH₂CH₂]₃ CH(CH₃)CH₂–R (R=CH₂N⁺ (CH₃)₃ Br^–, CH₂OPO₃H^– Na⁺, CH₂OSO ₃ ^– Na⁺, CO ₂ ^– Na⁺), gave large globular and cellular assemblies in water which could be observed directly by transmission electron microscopy; critical micelle concentration of 0.31.4×10^–3 M at 20°C, aggregation number of 215×10⁴, and diameter of 200–2000 Å. A basic structure of the assemblies was a thin layer with a thickness (about 30 Å) which was close to the molecular length of the surfactants. The assemblies were decomposed during gel column chromatography; viz., they were not as stable as the liposomes of lecithins. The morphology was discussed in conjunction with a steric effect of the isoprenoid chain.     

Sterisch behinderte Rotation in monosubstituierten Ansa-Verbindungen

The barriers to rotation about the pivot bonds in with n = 8 or 10 and R = CH₂C₆H₅, CH₂COOH, CH₂COOCH₃ or CH(CH₃)₂ were studied. ΔG^≠ values were found to be > 24 kcal. mol^?1. The solvent, the temperature, and the concentration dependence of the double magnetically non-equivalent methylenic protons and methyl groups were studied.     

Direct electrochemistry of hemoglobin on an ionic liquid carbon electrode modified with zinc tungstate nanorods

We have constructed a new electrochemical biosensor by immobilization of hemoglobin (Hb) and ZnWO₄ nanorods in a thin film of chitosan (CTS) on the surface of carbon ionic liquid electrode. UV–vis and FT-IR spectra reveal that Hb remains in its native conformation in the film. The modified electrode was characterized by scanning electron microscopy, electrochemical impedance spectroscopy and cyclic voltammetry. A pair of well-defined redox peaks appears which indicates direct electron transfer from the electrode. The presence of CTS also warrants biocompatibility. The electron transfer coefficient and the apparent heterogeneous electron transfer rate constant were calculated to be 0.35 and 0.757 s^?1, respectively. The modified electrode displays good electrocatalytic activity for the reduction of trichloroacetic acid with the detection limit of 0.613 mmol L^?1 (3σ). The results extend the protein electrochemistry based on the use of ZnWO₄ nanorods.

Effect of pressure on the solubility of naphthalene in water at 25°C

Solubility of naphthalene in water was measured at 25°C and pressures up to 200 MPa. The solubility decreased with increasing pressure. From the pressure coefficient of the solubility, the volume change V accompanying the dissolution was estimated as 13.8±0.4 cm ³ -mol ^–1 . Further we estimated the volume change V _CH accompanying hydrophobic hydration as –0.1±0.6 cm ³ -mol ^–1 using the V value, the molar volume of crystalline naphthalene, and the partial molar volume of naphthalene in n-heptane. This V _CH is much larger (i.e., less negative) than that for hydrophobic hydration of alkyl-chain compounds and suggests that the hydration structure of naphthalene differs from that of alkyl-chain compounds.     

Three new isomers of [C2H6O]+˙: The radical cations [CH3O(H)CH2]+˙, [CH3CHOH2]+˙ and a low-energy isomer of unassigned structure

Three new [C₂H₆O]⁺˙ ions have been generated in the gas phase by appropriate dissociative ionizations and characterized by means of their metastable and collisionally induced fragmentations. The heats of formation, ΔH_f⁰, of the two ions which were assigned the structures [CH₃O(H)CH₂]⁺˙ and [CH₃CHOH₂]⁺˙ could not be measured. The third isomer, to which the structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 2} = \mathop {\rm C}\limits^{\rm .} {\rm H} \cdot \cdot \cdot \mathop {\rm H}\limits^ + \cdot \cdot \cdot {\rm OH}_{\rm 2} $\end{document} is tentatively assigned, was measured to have ΔH_f⁰ = 732±5 kJ mol^?1, making it the [C₂H₆O]⁺˙ isomer of lowest experimental heat of formation. It was found that the exothermic ion–radical recombinations [CH₂OH]⁺+CH₃˙→[CH₃O(H)CH₂]⁺˙ and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm C}\limits^{\rm + } {\rm HOH + H}^{\rm .} $\end{document}→[CH₃CHOH₂]⁺˙ have large energy barriers, 1.4 and ?0.9 eV, respectively, whereas the recombinations yielding [CH₃CH₂OH]⁺˙ have little or none.     

Synergic extraction of Pr(III), Ho(III) and Er(III) with a mixture of 2-thenoylltrifluoroacetone and tribenzylamine

Synergic solvent extraction of Pr(III), Ho(III) and Er(III) was carried out at pH3.5 with a mixture of 2-thenoyltrifluoroacetone (HTTA) and tribenzylamine (TBA) from perchlorate media, having ionic strength 0.1M(H⁺, ClO ₄ ^– ). The stoichiometmric composition of all three synergic adducts was established to be Pr(TTA)₃·3TBA, Ho(TTA)₃·3TBA and Er(TTA)₃·3TBA. The formation constants K_TTA and K_syn and stability constant ±_syn were also computed and found to be in the order ErHo>Pr. The effect of various anions on the extraction has also been studied.     

Structures and mutual transformations of isomers of germylium ions (CH<Subscript>3</Subscript>)H<Subscript>2</Subscript>Ge<Superscript>+</Superscript> and (CH<Subscript>3</Subscript>)<Subscript>2</Subscript>HGe<Superscript>+</Superscript> and their silicon analogs

The potential energy surfaces of the (CH₃)_nH_3?n M⁺ ions, where n = 1, 2; M = Si, Ge, were scanned using the B3LYP method with 6–31G* and aug-cc-pVDZ basis sets. The major attention was given to isomeric species having the form of complexes of the HM⁺ and CH₃M⁺ ions with hydrogen, methane, and ethane molecules. These species were characterized previously neither by experimental nor by theoretical methods. It was found that these species become more stable in going from Si to Ge; the complex [CH₃Ge⁺CH₄] is the second isomer in the energy after (CH₃)₂HGe⁺. However, the heights of the activation barriers to formation of these complexes from the most stable isomer, though decreasing in going from Si to Ge, remain relatively high and, what is particularly important, somewhat exceed the activation barrier to formation of the complex [H₃Ge⁺·C₂H₄].     

Thermal and MS studies of silver(I) 2,2-dimethylbutyrate complexes with tertiary phosphines and their application for CVD of silver films

[Ag₂(CH₃CH₂C(CH₃)₂COO)₂] (1), [Ag₂(CH₃CH₂C(CH₃)₂COO)₂(PMe₃)₂] (2) and [Ag₂(CH₃CH₂C(CH₃)₂COO)₂(PEt₃)₂] (3) were prepared and characterized by MS-EI; ¹H, ¹³C, ³¹P NMR, variable temperature IR (VT-IR) spectroscopy and thermal analysis. MS and VT-IR data analysis suggests bidentate bridging carboxylates and monodentately bonded phosphines in the solid phase. The same methods used for gas phase analysis of 1–2 proved [(CH₃CH₂C(CH₃)₂COO)Ag₂]⁺ as the main ion, which could be transported in the gas phase during the CVD process. In the case of 3, similar intensity to the latter ion revealed [Ag{P(C₂H₅)}]⁺ and it is responsible for the CVD performance of 3. Thermal analysis results revealed that decomposition of 1–3 proceed in one endothermic process, with metallic silver formation between 197 and 220 °C. In the case of 1, VT-IR studies of the gaseous decomposition products demonstrate the presence of ester molecules and CO₂, whereas for 2 the main gaseous product appeared to be acid anhydride. Therefore, 2 was not used as a silver CVD precursor. Metallic layers were produced from 3 in hot-wall CVD experiments, (between 200 and 280 °C), under a total reactor pressure of 2.0 mbar, using argon as a carrier gas. Thin films deposited on Si(1 1 1) substrate were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Silver films obtained at moderate temperature (220–250 °C) revealed a thickness below 50 nm, and were whitish colored and slightly matt.     

Nucleophilic assistance in methane activation by superelectrophiles with halogen-centered cationic sites

Simulation of fragments of potential energy surface for systems CH₄ + CBr ₃ ⁺ , CH₄ + CBr ₃ ⁺ AlBr ₄ ^? , CH₄ + CCl ₃ ⁺ AlCl ₄ ^? , and CH₄ + CCl ₃ ⁺ Al₂Cl ₇ ^? was performed by DFT-B3LYP and DFT-PBE methods. The important role of nucleophilic assistance in methane halogenation by these superelectrophiles was confirmed. These reactions occur with a synchronous hydride transfer from methane to the electrophile within the cyclic transition states in linear C-H-C fragment of the rings and a generation of a C-Hlg bond between the carbon atom of the arising methyl group and the halogen atom of the electrophile. The nucleophilic assistance from the unshared electron pair of this halogen atom provides the lowering of the potential barriers to methane halogenation by complexes CBr ₃ ⁺ AlBr ₄ ^? , CCl ₃ ⁺ AlCl ₄ ^? , and CCl ₃ ⁺ Al₂Cl ₇ ^? to the values of the order of 20 kcal mol^?1. These essential features of the mechanism of methane halogenation are independent of the halogen nature and are retained on going from the model electrophiles to the real ones.     

A photoionization study of the ion-neutral complexes CH3CH +CH 3 · CH2CH3] and CH3CH2CH+CH 3 · CH3 in the gas phase: Formation,H-transfer and C—C bond formation between partners,and channeling of energy into dissociation

Photoionization mass spectrometry was used to investigate the dynamics of ion-neutral complex-mediated dissociations of the n-pentane ion (1). Reinterpretation of previous data demonstrates that a fraction of ions 1 isomerizes to the 2-methylbutane ion (2) through the complex CH₃CH⁺CH ₃ ^· CH₂CH₃ (3), but not through CH₃CH⁺CH₂CH ₃ ^· CH₃ (4). The appearance energy for C₃Hin ₇ ⁺ formation from 1 is 66 kJ mol^?1 below that expected for the formation of n-C₃H ₇ ⁺ and just above that expected for formation of i-C₃H ₇ ⁺ . This demonstrates that the H shift that isomerizes C₃H ₇ ⁺ is synchronized with bond cleavage at the threshold for dissociation to that product. It is suggested that ions that contain n-alkyl chains generally dissociate directly to more stable rearranged carbenium ions. Ethane elimination from 3 is estimated to be about seven times more frequent than is C-C bond formation between the partners in that complex to form 2, which demonstrates a substantial preference in 3 for H abstraction over C-C bond formation. In 1 → CH₃CH⁺CH₂CH₃ + CH₃ by direct cleavage of the C1–C2 bond, the fragments part rapidly enough to prevent any reaction between them. However, 1 → 2 → 4 → C4H ₈ ⁺ + CH₄ occurs in this same energy range. Thus some of the potential energy made available by the isomerization of n-C₄H₉ in 1 is specifically channeled into the coordinate for dissociation. In contrast, analogous formation of 3 by 1 → 3 is predominantly followed by reaction between the electrostatically bound partners.     

Interaction of Plasma Proteins with Tri‐quaternary Ammonium Salt Cationic Surfactant Studied by QCM‐D

A tri‐quaternary ammonium salt cationic surfactant was synthesized. Its structure was confirmed by using Fourier‐transform infrared spectroscopy, ¹H nuclear magnetic resonance spectroscopy, and X‐ray photoelectron spectroscopy analyses. Three model surfaces, including Au‐CH₃, Au‐OH and Au‐COOH, were fabricated. Adsorptions of surfactant on the three model surfaces and subsequent plasma proteins adsorption were investigated by quartz crystal microbalance with dissipation (QCM‐D). The mass of surfactant on the Au‐COOH surface was the largest, followed by that on the Au‐CH₃ surface, and that on the Au‐OH surface. These results suggested that the main driving force of surfactant immobilization was electrostatic interaction followed by hydrophobic interaction. Based on the results obtained, we concluded that the protein mass adsorbed on Au‐CH₃‐ S , Au‐OH‐ S , and Au‐COOH‐ S surfaces depended on the protein size and orientation. The mass and thickness of S on the Au‐COOH surface is the largest and the protein adsorption capacity of Au‐COOH‐ S surface is inferior to that of Au‐CH₃‐ S . The Au‐COOH‐ S surface could inhibit lysozyme adsorption, maintain the adsorption balance of bovine serum albumin, and induce fibrinogen‐binding protein adsorption.     

Isomeric ion-neutral complexes generated from ionized 2-Methylpropanol and n-Butanol: the effect of the polarity of the neutral partner on complex-mediated reactions

Photoionization was used to characterize the energy dependence of C₃H ₇ ⁺ , C₃H ₆ ⁺ , CH₃OH ₂ ⁺ and CH₂=OH⁺ formation from (CH₃)₂)CHCH₂OH^+? (1) and CH₃CH₂CH₂CH₂OH^+? (2). Decomposition patterns of labeled ions demonstrate that close to threshold these products are primarily formed through [CH ₃ ⁺ CHCH₃ ^?CH₂OH] (bd3) from 1 and through [CH₃CH₂CH₂ ^?CH₂=OH⁺] (9) from 2. The onset energies for forming the above products from 1 are spread over 85 kJ mol^?1, and are all near thermochemical threshold. The corresponding onsets from 2 are in a 19 kJ mol^?1 range, and all except that of CH₂=OH⁺ are well above their thermochemical thresholds. Each decomposition of 3 occurs over a broad energy range (> 214 kJ mol^?1), This demonstrates that ion-permanent dipole complexes can be significant intermediates over a much wider energy range than ion-induced dipole complexes can be. H-exchange between partners in the complexes appears to be much faster than exchange by conventional interconversions of the alcohol molecular ions with their distonic isomers. The onsets for water elimination from 1 and 2 are below the onsets for the complex-mediated processes, demonstrating that the latter are not necessarily the lowest energy decompositions of a given ion when the neutral partner in the complex is polar.     

Theoretical Study of Intradimer Mechanism for Diamond Growth over Diamond (100)

The study of the energetics of the accepted intradimer diamond growth mechanism over (100) diamond surface is presented. The calculations were made in a density functional approach with the DGauss code using a DZVP2 basis set and a BLYP interchange and correlation potential. A simple 9-carbon cluster modeling the (100) diamond surface was used; its validity is discussed in relation with other calculations that used larger model clusters. The mechanism, presented in six steps, is based in the Harris and Garrison's work that considers the methyl radical as the main growth precursor agent and the breaking of the dimer surface bond with the corresponding methylene radical formation as a prior step to the formation of a CH₂-bridge structure, which is a feasible step; in contrast to these molecular dynamics results, Huang and Frenklach, using semiempirical methods, consider the breaking of the dimer surface bond and the formation of a CH₂-bridge structure as one step and this step as the energetically determinant of the mechanism. They also found an activation energy barrier for the interaction between a radical surface center with a H and CH₃. The present work tries to discern between these two ideas by calculating the activation barriers and the reaction energies for each step of the Harris and Garrison's mechanism in a density functional approach and comparing them to the results of Huang and Frenklach. The energy calculations point toward the scission of the dimer bond (step 4) as the determinant step; this step is endothermic, with an energy barrier of 50.43 kcal-mol^–1. On the other hand, the formation of the CH₂-bridge structure (step 5) is a feasible step with an energy barrier of 13.57 kcal-mol^–1. The adsorption of CH₃ (step 2) and H (step 6) species over radical surface sites did not involve any energy barriers, as it would be hoped. These steps were strongly exothermic and are close to the thermodynamic values for C—C and C—H bond energies. The removal of methylic hydrogen (step 3) did not show any problem because the activation barrier is only 3.68 kcal-mol^–1 less than the removal of a surface hydrogen (step 1), which has an energy barrier of 19.59 kcal-mol^–1. All steps, except number 4, were exothermic.     

Structures and relative energies of gas phase [C3H7O]+ ions

Ab initio molecular orbital calculations have been carried out for 17 possible isomeric [C₃H₇O]⁺ structures. Optimized geometries have been obtained with a split-valence basis set and improved relative energies determined with polarization basis sets and with incorporation of electron correlation. The results agree well with available experimental data. In particular, (CH₃)₂COH⁺, CH₃CH₂CHOH⁺, CH₃CHOCH₃⁺, CH₃CH₂OCH₂⁺, and have been confirmed as low-energy isomers. Six additional structures appear to be energetically accessible and to offer a reasonable prospect for experimental observation. These are CH₂CHCH₂OH₂⁺, CH₂C(CH₃)OH₂⁺, CH₃CHCHOH₂⁺, CH₂CHOHCH₃⁺, and .     

Synergic extraction of nickel/II/ by 2-thenoyltrifluoroacetone and tribenzylamine in chloroform from perchlorate media

Synergic extraction of Ni/II/ at pH 1 to 10 was studied using a mixture of 2-thenoyltrifluoroacetone /HTTA/ and tribenzylamine /TBA/ in chloroform. The synergist TBA enhances the extraction of Ni/II/ by an order of 5 from pH 3 to 5 having ionic strength 0.1M /H⁺, ClO ₄ ^– /. The synergic adduct was found to be Ni/TTA/₂.2TBA. The equilibrium constants K_2,0 and K_2,2 and stability constant ₂,2 have been ascertained radiometrically. The influence of various cations and anions on the extraction of Ni/II/ has been examined under optimal conditions. Back extraction of the adduct species in different acids of varying concentrations has been studied.     

Gas‐phase intramolecular anion rearrangements of some trimethylsilyl‐containing systems revisited. A theoretical approach

Ab initio calculations at the CCSD(T)/6‐311++G(2d,p)//B3LYP/6‐311++G(d,p) level of theory have been carried out for three prototypical rearrangement processes of organosilicon anion systems. The first two are reactions of enolate ions which involve oxygen–silicon bond formation via three‐ and four‐membered states, respectively. The overall reactions are: The ΔG (reaction) values for the two processes are +175 and +51 kJ mol^?1, with maximum barriers (to the highest transition state) of +55 and +159 kJ mol^?1, respectively. The third studied process is the following: (CH₃O)C(?CH₂)Si(CH₃)₂CH → (CH₃)₂(C₂H₅)Si^? + CH₂CO, a process involving an S_Ni reaction between ‐CH and CH₃O‐ followed by silicon–carbon bond cleavage. The reaction is favourable [ΔG(reaction) = ?39 kJ mol^?1] with the barrier for the S_Ni process being 175 kJ mol^?1. The previous experimental and the current theoretical data are complementary and in agreement. Copyright © 2009 John Wiley & Sons, Ltd.     

Barriers to internal rotation in neopentylbenzenes substituted on the benzyl group. A 13C NMR band shape study

Two series of neopentylbenzenes with one or two substituents on the benzyl group have been synthesized. In one series the substituents were H, F, Cl, Br, I, OCH₃, OCOCH₃, OSi(CH₃)₃ CH₃ and CH₂CH₃, and in the other OH and R [R ? H, CH₃, CH₂CH₃, (CH₂)₃CH₃, CH(CH₃)₂ and C(CH₃)₃]. Barriers to internal C? C and C? C rotation have been estimated by ¹³C NMR band shape methods. Estimated barriers were found to increase as the size of the substituent increases. The results are discussed in terms of possible initial and transition states, based on summations of results from molecular mechanics (MM) calculations, using the Allinger MMP1 program. Barriers estimated experimentally are compared with results from other systems found in the literature.     

Silanol group effect in C18 bonded phases in HPLC

Summary If any residual (free) silanol groups remain at the surface of silica gel after bonding treatment, they may affect the retention of solutes since the dissociated groups (SiO^–) will attract cations. The silanol group effect on the retention of cationic solutes will increase with increasing pH of the mobile phase but the effect will decrease with increasing hydrophobic-ion concentration at the C₁₈ surface because such ions can mask the residual silanol groups. A method for the separation of metal complexes with 2-(5-bromo-2-pyridylazo)-diethylaminephenol (5-Br-PADAP) has been developed. The hydrophobic ion in the MeOH/H₂O mobile phase was tetrabutylammonium (TBA).