Basis Of Chemical Reactivity Research Articles

Si precursor inhibitors for area selective deposition of Ru

Area-selective atomic layer deposition (AS-ALD) using highly process-compatible precursor inhibitors (PIs) has garnered attention because of the need to overcome three-dimensional nanofabrication bottlenecks. The main advantages of precursor inhibitor (PI) molecules are their high process compatibility and their inherent bifunctionality as inhibitors and precursors. Herein, we examined the inhibition properties, adsorption mechanisms, and adsorption configurations of two PIs, bis(N,N-dimethylamino)dimethylsilane (PI1) and tris(dimethylamino)silane (PI2). Both PIs selectively inhibited the SiO2 surface but not the Cu surface, which enabled the AS-ALD of Ru films on the latter. The inhibition mechanisms were elucidated on the basis of chemical reactivity and steric hindrance considerations using density functional theory calculations and Monte Carlo simulations. PI1 featured a larger areal coverage than PI2 because of the favorable adsorption configuration of the former, inducing a stronger steric hindrance effect and achieving a higher inhibition performance against Ru ALD, although the two PIs had similar chemical reactivities toward the examined surface. Furthermore, PI1 and PI2 formed SiO2 ALD films when ozone was used as a reactant. The differences in the growth characteristics of the corresponding ALD SiO2 films were explained by the different adsorption configurations of PIs. Thus, our work elucidates the adsorption configurations of silane-based PIs and thus paves the way for the more effective utilization of their bifunctionality, inhibition properties, and growth characteristics in future AS-ALD processes.

Observation of the two triplet state conformations of alkyl phenylglyoxylates.

Step-scan time-resolved FT-IR spectra of alkyl phenylglyoxylates in hexane with a 4 cm(-1) spectral resolution reveal splitting of the transient absorption signal near 1650 cm(-1) into two closely located peaks with different lifetimes on the nanosecond time scale. This signal had been previously assigned to the triplet state of the starting material that gives rise to the alpha-hydroxyphenylketene. In the current article, evidence is presented to assign these two peaks to different triplet state conformers only one of which undergoes fast Norrish Type II photoelimination. This assignment was made on the basis of chemical reactivity, steric effects, and kinetic data.

Interaction between the substrate and the high-valent-iron-oxo porphyrin cofactor as a possible factor influencing the regioselectivity of cytochrome P450 catalysed aromatic ring hydroxylation of 3-fluoro(methyl)anilines

In the present study the in vitro and in vivo aromatic ring hydroxylation of a series of amino and/or methyl containing fluorobenzenes, i.e. 3-fluoro(methyl)anilines, was investigated and compared to the calculated density distribution of the reactive frontier π-electrons of the aromatic substrate. This was done (1) to study to what extent the regioselectivity of the aromatic ring hydroxylation of the 3-fluoro(methyl)anilines could be predicted on the basis of the calculated chemical reactivity, as was previously observed for a series of fluorinated benzenes and monofluoroanilines, and (2) to investigate which factors contribute to possible deviations from the predictions on the basis of the calculated chemical reactivity. Results obtained show that the in vitro and in vivo aromatic ring hydroxylation of the series of 3-fluoro(methyl)anilines correlates qualitatively with the calculated frontier orbital density distribution for electrophilic attack by the cytochrome P450(FeO) 3+ species. These results indicate that the HOMO/HOMO-1 frontier orbital densities, i.e. the chemical reactivity of the carbon centres for an electrophilic attack, predict the preferential as well as the non-reactive sites for cytochrome P450 catalysed aromatic ring hydroxylation of the tested model compounds. The absolute values, however, deviated in a systematic way; C4 para hydroxylation being observed to a higher extent than expected on the basis of chemical reactivity and C2 C6 ortho hydroxylation being observed to a lower extent than expected. Additional experiments were performed using different microsomal preparations and microperoxidase-8. The latter is a mini-heme protein of eight amino acids without a substrate binding site. In incubations of the model compounds with different types of microsomal preparations, as well as with MP-8 and purified reconstructed cytochrome P4502B1, similar systematic deviations between the predicted and observed regioselectivity of aromatic hydroxylation were observed. These results show that the regioselectivity of aromatic ring hydroxylation of the 3-fluoro(methyl)anilines cannot be predominantly ascribed to an interaction between the substrate and the substrate binding site of the cytochromes P450 dictating a specific stereoselective positioning of the substrate in the active site. More likely, the systematic deviations between the observed and predicted regioselectivity of hydroxylation of the tested model substrates should be ascribed to an (orienting) interaction between the substrate and the activated cytochrome P450(FeO) 3+ cofactor.

Reassessment of the oceanic residence time of phosphorus

Phosphorus (P) is an essential nutrient for the growth of all organisms and is believed to limit marine productivity, especially on geologic time scales (Holland, 1984; Smith, 1984; Howarth, 1988; Codispoti, 1989). As a result of the link between marine photosynthetic productivity and atmospheric CO2, phosphorus along with other nutrients present in short supply in the euphoric zone have been cited as potential players in the ocean's role in climate change. This link has been referred to as the nutrient-CO2 connection (Broecker, 1982). Model simulations which aim to quantify the role of oceanic nutrient inventories in promoting or enhancing climate change rely on the most currently formulated element budgets for the ocean. In this paper significant modifications to the currently accepted marine phosphorus budget are proposed. The modified P budget presented here requires a reassessment of phosphorus residence time in the ocean, and a concomitant review of the role of P as a potential player in climate change over glacialinterglacial time scales. Element budgets constructed for the oceans consist of a mass balance between inputs and outputs, for which the simplifying assumption is generally made that the ocean is in steady state with the specific element in question. The fluvial P flux constitutes the bulk of the input term for the marine phosphorus budget (atmospheric input is < 10% of the fluvial input: Froelich et al., 1982 ). Burial with sediments is the mechanism for ultimate removal of P from the oceans. For a system at steady state, the input flux equals the output flux. In the present paper, we focus on the output flux, burial with sediments, for two reasons. First, the chemistry of phosphorus buried in sediment cores, from which P burial fluxes are calculated, has not been affected to the same degree as rivers by anthropogenic perturbation. It is therefore simpler to quantify the output term of the P budget which can be extrapolated to pre-anthropogenic times. Second, detailed P speciation data permit us to quantify the burial flux of reactive-P as contrasted with refractory-P in sediments. This distinction is significant because burial of reactive-P constitutes removal of potentially bio-available P from the oceans. Two types of modification to the marine phosphorus budget are proposed here. First, the locus of P burial is addressed. Specifically, the importance of P burial in the deep sea is contrasted with P burial in continental margins. Second, the burial flux is characterized in terms of reactive(potentially bio-available) P vs. refractory-P. This distinction is made possible by obtaining detailed P speciation data from application of the SEDEX method (Ruttenberg, 1992), a selective leaching procedure which separates solid-phase P into five reservoirs on the basis of chemical reactivity: loosely-sorbed P; ferric iron bound-P; authigenic apatite + biogenic apatite + C a C O 3 bound-P; detrital apatite P; and organic-P. Detailed P spe-

Discrimination of C3H3+ structures on the basis of chemical reactivity

Discrimination of C3H3+ structures on the basis of chemical reactivity

Vibrational spectra of trialkylphosphine-carbon disulphide adducts, R3PCS2 (R = n-Bu, C6H11)

Abstract The i.r. and laser Raman spectra of the 1:1 addition compounds, R 3 PCS 2 (R = n -Bu, C 6 H 11 ), have been measured at ambient temperatures. The data are in accord with the zwitterionic formulation, R 3 P + -CS 2 − , which was proposed earlier for related trialkylphosphine—carbon disulphide adducts on the basis of chemical reactivity, dipole moments and i.r. spectra.

Structural effects on the reactivity of substrates and inhibitors in the epoxidation system of Pseudomonas oleovorans

The epoxidation reaction catalyzed by an enzyme system of Pseudomonas oleovorans exhibits a substrate specificity different from that expected on the basis of chemical reactivity in non-enzymatic epoxidation reactions. Cyclic and internal olefins, aromatic compounds and styrene are not epoxidated. The reactivity of straight chain diolefins is maximal for octadiene and falls off rapidly as the carbon chain is shortened, but decreases only slightly as the chain is lengthened. In contrast, methyl group hydroxylation is less sensitive to decreasing chain length. As a consequence, propylene and 1-butene are hydroxylated but not epoxidated by this enzyme system. With the substrate 1-decene, which is capable of undergoing both epoxidation and hydroxylation, the former reaction predominates. Methyl imidoesters were found to be inhibitors of enzymatic epoxidation, and the potency of a homologous series of imidoester inhibitors was examined. The results parallel the substrate specificity patterns observed, and support the conclusion that the mode of substrate binding severely moderates the inherent chemical reactivity of the activated oxygen in this system. The effect of the bifunctional imidoester, dimethyladipimidate, was also examined and the results compared with those obtained in other investigations.

A convenient synthesis of labelled rhodopsin and studies on its active site.

Digitonin solutions of labelled rhodopsin, containing (3)H in the retinyl moiety, were prepared by two related methods. Labelled rhodopsin was also prepared for the first time in cetyltrimethylammonium bromide and purified by column chromatography. It was shown that only certain rhodopsin preparations on denaturation in the dark and the reduction with sodium borohydride gave up to 60% of the radioactivity in a fraction characterized as N-retinylphosphatidylethanolamine. Such preparations also gave a lipid-linked retinyl moiety at the metarhodopsin-I stage, but, as expected, a protein-linked retinyl moiety at the metarhodopsin-II stage. Other preparations however, gave exclusively protein-bound radioactivity at the native-rhodopsin, metarhodopsin-I and metarhodopsin-II stages. It is therefore conceivable that the formation of N-retinylphosphatidylethanolamine is due to a non-enzymic reaction resulting from the transfer of the retinyl moiety from its native site to an amino group of a favourably oriented phospholipid molecule. The only firmly established aspect of the rhodopsin active site remains the demonstration in our previous work that at the metarhodopsin-II stage the retinyl moiety is linked to an in-amino group of lysine. On the basis of chemical reactivity it is argued that the light-induced conversion of rhodopsin into metarhodopsin II involves a profound conformational change resulting in the dislocation of the retinylideneiminium chromophore from a non-polar environment in rhodopsin to a polar environment in metarhodopsin II.

Triglyceride composition of native and rearranged butter and coconut oils

AbstractTriglyceride gas chromatography was used for quantitative fractionation by carbon number of native and rearranged butter and coconut oils. Significant differences in the triglyceride type distributions between the corresponding native and chemically modified fats were found. Increased proportions of both short and long chain triglycerides occurred in the rearranged butterfat. In reconstituted coconut oil there was a shift towards the shorter chain length triglycerides. The natural and the rearranged triglyceride distributions of the two oils were shown to differ from the random distributions calculated for the corresponding fatty acid complements. The butterfat triglyceride compositions showed greater deviations from random than did the coconut oils. The modified oils approached random distributions more closely than did the native ones. In both cases the deviations from truly random populations appeared to be in the direction anticipated on the basis of chemical reactivity.