Changes in thermodynamic interactions at highly immiscible polymer/polymer interfaces due to deuterium labeling

Deuterium labeling has been shown previously to affect thermodynamic interactions at polymer surfaces, polymer/polymer heterogeneous interfaces, and in bulk (away from a surface or interface). However, the changes in polymer-polymer interactions due to deuterium labeling have not been thoroughly investigated for highly immiscible systems. It is shown here that deuterium labeling can influence polymer-polymer interactions at heterogeneous interfaces with highly immiscible systems, namely, polystyrene/poly(2-vinylpyridine) (PS/P2VP), polystyrene/poly(4-vinylpyridine) (PS/P4VP), and polystyrene/poly(methyl methacrylate) (PS/PMMA). Using secondary ion mass spectrometry, segregation of deuterium labeled polystyrene (dPS) in a dPS + unlabeled PS (dPS:hPS) blend layer was observed at the dPS:hPS/hP2VP, dPS:hPS/hP4VP, and dPS:hPS/hPMMA heterogeneous interfaces. However, a reference system involving PS on a PS brush shows no segregation of dPS to the interface.     

Deuterium quantification through deuterium-induced remote 1H and 13C NMR shifts

Partial labeling by deuterium may be quantified through simple integrations of those (1)H (200 or 400?MHz) and (13)C (100.6?MHz) NMR resonances that are split into pairs by chemical shifts (n)Δ = δ(deuterated) - δ(nondeuterated) as induced by deuterium across n>2 chemical bonds. The relative intensities of the two components of a pair are shown to be influenced to practically equal degrees by relaxation effects, so that a deuterium fraction may be determined from (1)H and (13)C integral pairs at more remote molecular positions under the routine conditions of fast accumulative spectral acquisition.     

A reactive conjugated allene involved in the biosynthesis of volatile oxylipins in the moss Dicranum scoparium

We addressed the role of the unusual acetylenic fatty acid dicranin as a precursor for volatile oxylipins in the moss Dicranum scoparium. Dicranin is transformed immediately after mechanical wounding of moss tissue to volatile C5- and C6-oxylipins. The transformation of synthetic deuterium labeled dicranin was monitored using LC/MS analysis and multivariate statistics to identify polar metabolites produced during volatile formation. Among the newly formed oxylipins is a highly reactive conjugated C13 allene with similar degrees of labeling compared to the C5 volatiles suggesting that it results as second cleavage product from the biosynthesis of pentenal and pentenone.     

Polymer dynamics in hydrogenous systems by neutron reflectivity

Neutron reflectivity is a powerful tool for exploring polymer dynamics above the glass-transition temperature at short diffusion times in layered thin-film systems. Recent studies of membrane-mediated interdiffusion in deuterium-labeled systems have shown that ultrathin membranes can track the position of the interface in binary polymeric diffusion couples and also can discriminate between perdeuterated and hydrogenous polymers of the same molecular weight. This report shows that similar dynamic information can be obtained for binary hydrogenous polystyrene (hPS) diffusion couples separated by an ultrathin (6-nm) isopentylcellulose cinnamate (IPCC) membrane on Si wafers (air//hPS/IPCC/hPS//Si, where “//” represents an interface between obviously different phases and “/” represents a dynamic interface between polymeric species). In particular, the air//hPS/IPCC/hPS//Si system provides the same information as perdeuterium-labeled polystyrene (dPS) diffusion couples separated by the same IPCC membrane (air//dPS/IPCC/dPS//Si). This technique has potential applications for the study of confinement effects on thin-film dynamics and macromolecular transport across membranes. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3248–3257, 2004     

Effets isotopiques du deutérium en RMN 13C,measure du marquage isotopique des alcools allylques.

Primary and secondary deuterium isotope effects on ¹³C NMR chemical shifts for trigonal carbons are reported for twelve allylic alcohols. The secondary DIECCS is used for an accurate measurement of the deuterium labeling of variously substituted allylic alcohols.     

Deuterium Quantification through Deuterium‐Induced Remote 1H and 13C NMR Shifts

Partial labeling by deuterium may be quantified through simple integrations of those ¹H (200 or 400 MHz ) and ¹³C (100.6 MHz ) NMR resonances that are split into pairs by chemical shifts ⁿΔ=δ(deuterated)?δ(nondeuterated) as induced by deuterium across n>2 chemical bonds. The relative intensities of the two components of a pair are shown to be influenced to practically equal degrees by relaxation effects, so that a deuterium fraction may be determined from ¹H and ¹³C integral pairs at more remote molecular positions under the routine conditions of fast accumulative spectral acquisition.     

Tautomerism of sterically hindered schiff bases. Deuterium isotope effects on 13C chemical shifts

A series of sterically hindered o-hydroxy Schiff bases derived from o-hydroxyaceto- and benzophenones with very short intramolecular hydrogen bonds were described qualitative and quantitatively by deuterium isotope effects on (13)C chemical shift, (n)DeltaC(XD), (n)DeltaF(XD), (1)J(N,H) coupling constants, deltaNCH(3) chemical shifts and UV spectra. All the investigated compounds are found to be tautomeric. The tautomeric character is described by the signs of the deuterium isotope effects on the (13)C chemical shifts. For the 3-nitro-5-chloro derivatives at low temperature, the equilibrium is shifted almost fully toward the proton transferred form in CD(2)Cl(2). Intrinsic deuterium isotope effects on chemical shifts of these compounds as well as (1)J(N,H) coupling constants suggest that a zwitterionic resonance form is dominant for the proton transferred form. Structures, (1)H, (19)F, and (13)C chemical shifts, and deuterium isotope effects on (13)C chemical shifts are calculated by ab initio methods. The potential energy functions and the total deuterium isotope effects are calculated, and they are shown to correspond well with the experimental findings.     

Deuterium isotope effects in 13C NMR spectroscopy: Stereochemical assignment of monodeuteriated allylic alcohols.

Vicinal deuterium isotope effects on 13C NMR chemical shifts, ³ΔC (Φ) are given for ten monodeuteriated allylic alcohols. The relationship found for nine of them: 3ΔC(0°) ≅ 5/3 x ³ΔC(180°) allows the stereochemical assignement of their deuterium labeling. This assignment is in agreement with that from the Karplus-type relationship of vicinal coupling constants, ³J_C-D(Φ).     

Gas-phase reactions of protonated tryptophan

The gas phase reactions of protonated tryptophan have been examined in a quadrupole ion trap using a combination of collision induced dissociation, hydrogen-deuterium exchange, regiospecific deuterium labeling and molecular orbital calculations (at the B3LYP/6-31G* level of theory). The loss of ammonia from protonated tryptophan is observed as the primary fragmentation pathway, with concomitant formation of a [M + H - NH(3)](+) ion by nucleophilic attack from the C3 position of the indole side chain. Hydrogen-deuterium exchange and regiospecific deuterium labeling reveals that scrambling of protons in the C2 and C4 positions of the indole ring, via intramolecular proton transfer from the thermodynamically preferred site of protonation at the amino nitrogen, precedes ammonia loss. Molecular orbital calculations have been employed to demonstrate that the activation barriers to intramolecular proton transfer are lower than that for NH(3) loss.     

Isotope-labeling of the fibril binding compound FSB via a Pd-catalyzed double alkoxycarbonylation

We have synthesized two isotopically labeled variants of the β-amyloid binding compound FSB possessing (13)C-labels on the two terminal aryl carboxylic acid moieties. One of these was also fully deuterated on the olefinic spacers. The (13)C-isotope labeling was achieved applying a Pd-catalyzed methoxycarbonylation of the corresponding aryl chlorides with externally (ex situ) generated (13)C-labeled CO. Application of the Shirakawa-Hayashi protocol for the Pd-catalyzed reduction of a dialkyne intermediate using D(2)O allowed for the selective deuterium labeling of the two trans-C,C double bonds of FSB.     

Aggregation, adsorption, and surface properties of multiply end-functionalized polystyrenes

The properties of polystyrene blends containing deuteriopolystyrene, multiply end-functionalized with C8F17 fluorocarbon groups, are strikingly analogous to those of surfactants in solution. These materials, denoted FxdPSy, where x is the number of fluorocarbon groups and y is the molecular weight of the dPS chain in kg/mol, were blended with unfunctionalized polystyrene, hPS. Nuclear reaction analysis experiments show that FxdPSy polymers adsorb spontaneously to solution and blend surfaces, resulting in a reduction in surface energy inferred from contact angle analysis. Aggregation of functionalized polymers in the bulk was found to be sensitive to FxdPSy structure and closely related to surface properties. At low concentrations, the functionalized polymers are freely dispersed in the hPS matrix, and in this range, the surface excess concentration grows sharply with increasing bulk concentration. At higher concentrations, surface excess concentrations and contact angles reach a plateau, small-angle neutron scattering data indicate small micellar aggregates of six to seven F2dPS10 polymer chains and much larger aggregates of F4dPS10. Whereas F2dPS10 aggregates are miscible with the hPS matrix, F4dPS10 forms a separate phase of multilamellar vesicles. Using neutron reflectometry (NR), we found that the extent of the adsorbed layer was approximately half the lamellar spacing of the multilamellar vesicles. NR data were fitted using an error function profile to describe the concentration profile of the adsorbed layer, and reasonable agreement was found with concentration profiles predicted by the SCFT model. The thermodynamic sticking energy of the fluorocarbon-functionalized polymer chains to the blend surface increases from 5.3kBT for x = 2 to 6.6kBT for x = 4 but appears to be somewhat dependent upon the blend concentration.     

No intrinsic depletion layer on a polystyrene thin film at a water interface

Using neutron reflectivity, we found that there is no intrinsic depletion layer at a deuterated polystyrene (dPS) film and deuterium oxide (D(2)O) interface. A spun-cast film is susceptible to contamination on its surface from its surroundings during sample preparation. A contamination layer of hydrogenated organic material will be detected as a reduced scattering length density layer at the interface. We demonstrate that, by careful treatment of the film, contamination would be the primary cause of the reduced scattering length density layer at the interface.     

ToF‐SIMS studies of the oxidation of Fe by D2O vapour: comparison with XPS

The oxidation of iron (Fe) by water (D₂O) vapour at low pressures and room temperature was investigated using time‐of‐flight (ToF) SIMS. The results supported those found previously using XPS and the QUASES^? program in that a duplex oxide structure was found containing a thin outer surface hydroxide (Fe(OD)₂) layer over an inner oxide (FeO) layer. The extraordinary depth resolution of the ToF‐SIMS profiles assisted in identifying the two phases; this resolution was achieved by compensation for surface roughness. A substantial concentration of deuterium was found in the subsurface oxide layer. This observation confirmed previous assessments that the formation of FeO was from the reaction of Fe(OD)₂ with outward‐diffusing Fe, leaving deuterium as a reaction product. Copyright © 2005 John Wiley & Sons, Ltd.     

Iridium-Catalyzed Formyl-Selective Deuteration of Aldehydes

We report the first direct catalytic method for formyl-selective deuterium labeling of aromatic aldehydes under mild conditions, using an iridium-based catalyst designed to favor formyl over aromatic C−H activation. A good range of aromatic aldehydes is selectively labeled, and a one-pot labeling/olefination method is also described. Computational studies support kinetic product control over competing aromatic labeling and decarbonylation pathways.     

Investigating Inner-Sphere Reorganization via Secondary Kinetic Isotope Effects in the C-H Cleavage Reaction Catalyzed by Soybean Lipoxygenase: Tunneling in the Substrate Backbone as Well as the Transferred Hydrogen

This work describes the application of NMR to the measurement of secondary deuterium (2° (2)H) and carbon-13 ((13)C) kinetic isotope effects (KIEs) at positions 9-13 within the substrate linoleic acid (LA) of soybean lipoxygenase-1. The KIEs have been measured using LA labeled with either protium (11,11-h2-LA) or deuterium (11,11-d2-LA) at the reactive C11 position, which has been previously shown to yield a primary deuterium isotope effect of ca. 80. The conditions of measurement yield the intrinsic 2° (2)H and (13)C KIEs on k(cat)/K(m) directly for 11,11-d2-LA, whereas the values for the 2° (2)H KIEs for 11,11-h2-LA are obtained after correction for a kinetic commitment. The pattern of the resulting 2° (2)H and (13)C isotope effects reveals values that lie far above those predicted from changes in local force constants. Additionally, many of the experimental values cannot be modeled by electronic effects, torsional strain, or the simple inclusion of a tunneling correction to the rate. Although previous studies have shown the importance of extensive tunneling for cleavage of the primary hydrogen at C11 of LA, the present findings can only be interpreted by extending the conclusion of nonclassical behavior to the secondary hydrogens and carbons that flank the position undergoing C-H bond cleavage. A quantum mechanical method introduced by Buhks et al. [J. Phys. Chem. 1981, 85, 3763] to model the inner-sphere reorganization that accompanies electron transfer has been shown to be able to reproduce the scale of the 2° (2)H KIEs.     

Quantitative analysis of deuterium using the isotopic effect on quaternary C NMR chemical shifts

Quantitative analysis of specifically deuterated compounds can be achieved by a number of conventional methods, such as mass spectroscopy, or by quantifying the residual ¹H NMR signals compared to signals from internal standards. However, site specific quantification using these methods becomes challenging when dealing with non-specifically or randomly deuterated compounds that are produced by metal catalyzed hydrothermal reactions in D₂O, one of the most convenient deuteration methods. In this study, deuterium-induced NMR isotope shifts of quaternary ¹³C resonances neighboring deuterated sites have been utilized to quantify the degree of isotope labeling of molecular sites in non-specifically deuterated molecules. By probing ¹³C NMR signals while decoupling both proton and deuterium nuclei, it is possible to resolve ¹³C resonances of the different isotopologues based on the isotopic shifts and the degree of deuteration of the carbon atoms. We demonstrate that in different isotopologues, the same quaternary carbon, neighboring partially deuterated carbon atoms, are affected to an equal extent by relaxation. Decoupling both nuclei (¹H, ²H) resolves closely separated quaternary ¹³C signals of the different isotopologues, and allows their accurate integration and quantification under short relaxation delays (D1 = 1 s) and hence fast accumulative spectral acquisition. We have performed a number of approaches to quantify the deuterium content at different specific sites to demonstrate a convenient and generic analysis method for use in randomly deuterated molecules, or in cases of specifically deuterated molecules where back-exchange processes may take place during work up.     

Surface and interfacial segregation in blends of polystyrene with functional end groups and deuterated polystyrene

The effect of chain-end chemistry on surface and interfacial segregation in symmetric blends of polystyrene (hPS)/deuterated polystyrene (dPS) has been investigated by X-ray photoelectron and secondary ion mass spectroscopy in conjunction with neutron reflectivity measurements. Alpha,omega-fluoroalkyl- and alpha,omega-carboxy-terminated polystyrenes (alpha,omega-hPS(Rf)2 and alpha,omega-hPS(COOH)2) were used as end-functionalized polymers; the former possesses chain ends with lower surface energies, and the latter possesses higher surface energies compared with that of the main chain. In the case of an alpha,omega-hPS(Rf)2/dPS blend film, alpha,omega-hPS(Rf)2 was enriched at the surface owing to the surface localization of the Rf groups, although the surface energy of the hPS segments was slightly higher than that of the dPS ones. On the contrary, in the case of an alpha,omega-hPS(COOH)2/dPS blend film, dPS was preferentially segregated at the surface. This may be due to a surface depletion of COOH ends and an apparent molecular weight increase of alpha,omega-hPS(COOH)2 produced by a hydrogen-bonded intermolecular association of COOH ends in addition to the surface energy difference between hPS and dPS segments. Interestingly, both Rf and COOH chain ends were partitioned to the substrate interface for the alpha,omega-hPS(Rf)2/dPS and alpha,omega-hPS(COOH)2/dPS blend films, resulting in the segregation of the hPS component at the substrate interface for both blends. The results presented imply that surface and interfacial segregation in polymer blends could be regulated by incorporating functional groups into the end portions of one component.     

Rutheniun-catalyzed cycloisomerization of o-(ethynyl)phenylalkenes to diene derivatives via skeletal rearrangement

Treatment of a series of 2',2'-disubstituted (o-ethynyl)styrenes with TpRu(PPh(3))(CH(3)CN)(2)PF(6) (10 mol %) in benzene (80 degrees C, 12-18 h) efficiently gave 2-alkenyl-1H-indene derivatives. This catalytic reaction represents an atypical enyne cycloisomerization with skeletal rearrangement of starting enyne, where the C=C bond is completely cleaved and inserted by the terminal alkynyl carbon. The reaction mechanism was elucidated by a series of deuterium and (13)C labeling experiments, as well as by changing the substituents at the phenyl moieties. The mechanism is proposed to involve the following key steps: 5-endo-dig cyclization of ruthenium-vinylidene intermediate, a nonclassical ion formation, and the "methylenecyclopropane-trimethylenemethane" rearrangement.     

Iridium‐Catalyzed Formyl‐Selective Deuteration of Aldehydes

We report the first direct catalytic method for formyl‐selective deuterium labeling of aromatic aldehydes under mild conditions, using an iridium‐based catalyst designed to favor formyl over aromatic C−H activation. A good range of aromatic aldehydes is selectively labeled, and a one‐pot labeling/olefination method is also described. Computational studies support kinetic product control over competing aromatic labeling and decarbonylation pathways.     

ToF-secondary ion mass-spectrometric study of copper deposition and stripping on directly heated screen-printed gold electrodes

We report about a new kind of directly heated gold electrode. All electrodes including a directly heated gold loop electrode, a Ag pseudo reference, and a carbon counter electrode have been screen-printed on a ceramic alumina substrate. Thermal behaviour was studied by potentiometry using either an external or the integrated reference electrode. Stripping voltammetric copper signals were greatly improved at elevated deposition temperature. Secondary ion mass spectrometric studies (ToF-SIMS) revealed that different negative ionic species of copper complexes can be found on the gold electrode surface as a result of ion bombardment during SIMS analysis like Cu^?, CuCl^? and CuCl₂ ^?. SIMS surface imaging using a fine focussed ion beam over the surface allowed us to obtain ion images (chemical maps) of the analyzed sample. SIMS depth profile analysis of the gold loop electrode was performed after copper deposition at room temperature (23 °C) and at 60 °C. CuCl₂ ^? ion was used for the depth profile studies as it has shown the highest intensity among other observed species. Surface spectroscopic analysis, surface imaging and depth profile analysis have shown that the amount of deposited copper species on the gold loop electrode was increased upon increasing electrode temperature during the deposition step. Therefore, the presence of chloride in the solution will hinder underpotential deposition of Cu(0) and lead to badly defined and resolved stripping peaks.