Thermodynamic Evaluation of Solid-State Reactions in which a Volatile Product is Formed

The use of equilibrium thermodynamics in describing interfacial reactions between non-ionic inorganic solids is demonstrated using examples of high-temperature interactions in the Ti–Si–N and Mo–Si–N systems. In the case of a diffusion-controlled process, solid-state reactions can be interpreted with chemical potential (activity) diagrams. The role of volatile reaction products formed during interaction in developing the diffusion zone morphology is analysed. The interfacial phenomena in systems based on dense Si₃N₄ and non-nitride forming metals can be explained by assuming a nitrogen pressure build-up at the contact surface. This pressure determines the chemical potential of Si at the interface and, hence, the reaction products in the diffusion zone.     

Hydration of the amylopectin branch point. Evidence of restricted conformational diversity of the alpha-(1-->6) linkage

The hydration behavior of a model compound for the amylopectin branch point, methyl 6'-alpha-maltosyl-alpha-maltotrioside, was investigated by combining molecular dynamics simulations in explicit water, 500 MHz NMR spectroscopy, including pulsed field gradient diffusion measurements, and exploratory multivariate data analysis. In comparison with results on a tetrasaccharide analogue, the study reveals that the conformational diversity of the three-bond alpha-(1-->6) linkage becomes quite limited in aqueous solution upon the addition of a fifth glucose residue that elongates the alpha-(1-->6) branch. This investigation reveals two plausible starch branch point structures, one that permits the formation of double helices and one that is adapted for interconnection of double helices. The apparent rigidity of the former is explained by the presence of water pockets/bridges in the vicinity of the branch point that lock the pentasaccharide structure into one conformational family that is able to accommodate the creation of the double-helical amylopectin structure.     

Photoinduced electron transfer in a rigid first generation triphenylamine core dendrimer substituted with a peryleneimide acceptor

The electron-transfer process of a first generation dendrimer with a triphenylamine core substituted with one peryleneimide chromophore at the rim (N1P1) was investigated by steady-state and time-resolved spectroscopic techniques in two different solvents of medium and low polarity. Single photon counting experiments showed a fast charge separation and a thermally activated back reaction, which is uncommon for a polyaryl bridge or long-distance through-space electron transfer. The four exponential fluorescence decay can be traced to the presence of two subsets of molecules, which are constitutional isomers of N1P1. Although formally N1P1 resembles a donor-bridge-acceptor compound, detailed analysis of the data shows that the electron transfer occurs by a through-space mechanism. This amine core dendrimer has peculiar and unique characteristics resulting in the observation of efficient back transfer and delayed peryleneimide fluorescence in diethyl ether at 293 K and very long-lived charge recombination luminescence at 77 K.     

Extensive migration of Ni and Mn by lithiation of ordered LiMg0.1Ni0.4Mn(1.5)O4 spinel

Li(x)Mg(0.1)Ni(0.4)Mn(1.5)O(4) spinel (P4(3)32) was chemically and electrochemically lithiated in the range 1 < x 相似文献   

3H-benzophosphepine complexes: versatile phosphinidene precursors

The synthesis of a variety of benzophosphepine complexes [R = Ph, t-Bu, Me; ML(n )()= W(CO)(5), Mo(CO)(5), Cr(CO)(5), Mn(CO)(2)Cp] by two successive hydrophosphinations of 1,2-diethynylbenzene is discussed in detail. The first hydrophosphination step proceeds at ambient temperature without additional promoters, and subsequent addition of base allows full conversion to benzophosphepines. Novel benzeno-1,4-diphosphinanes were isolated as side products. The benzophosphepine complexes themselves serve as convenient phosphinidene precursors at elevated, substituent-dependent temperatures (>55 degrees C). Kinetic and computational analyses support the proposal that the phosphepine-phosphanorcaradiene isomerization is the rate-determining step. In the absence of substrate, addition of the transient phosphinidene to another benzophosphepine molecule is observed, and addition to 1,2-diethynylbenzene furnishes a delicate bidentate diphosphirene complex.     

Polarized emission of individual self-assembled oligo(p-phenylenevinylene)-based nanofibers on a solid support

We have prepared 5 nm diameter, micrometer long tetra(p-phenylenevinylene) (OPV)-based nanofibers on a graphite surface. The fluorescence emission of an individual fiber shows a profound polarization over its entire length that directly corresponds to its orientation on the substrate. Quantitative analysis of the fluorescence polarization, including the depolarizing effect of the underlying graphite, evidences the high degree of organization within chiral fibers with the OPV molecules perpendicular to the fiber axis. The control of the internal order within self-assembled fibers, and the ability to measure it, is a crucial step to obtain uniform organic fibers that can be applied in nanosized electronics at room temperature.     

Synthesis and optical properties of polyphenylene dendrimers based on perylenes

A series of polyphenylene-dendronized perylenes have been synthesized, and their physical and mesoscopic properties have been investigated. The attached polyphenylene dendrons have significant effects on the physical properties of the perylenes. They increase the solubility of perylenes in common organic solvents, suppress significantly the aggregation of the perylene core, and lead to red-shifted absorption and emission. The polyphenylene dendrons give rise to a strong absorption band in the UV region and exhibit efficient intramolecular energy transfer to the perylene moiety. The functionalization of perylenes with polyphenylene dendrons allows the preparation of films by spin-coating.     

Confidence limits for contribution plots in multivariate statistical process control using bootstrap estimates

In Multivariate Statistical Process Control, when a fault is expected or detected in the process, contribution plots are essential for operators and optimization engineers in identifying those process variables that were affected by or might be the cause of the fault. The traditional way of interpreting a contribution plot is to examine the largest contributing process variables as the most probable faulty ones. This might result in false readings purely due to the differences in natural variation, measurement uncertainties, etc. It is more reasonable to compare variable contributions for new process runs with historical results achieved under Normal Operating Conditions, where confidence limits for contribution plots estimated from training data are used to judge new production runs. Asymptotic methods cannot provide confidence limits for contribution plots, leaving re-sampling methods as the only option. We suggest bootstrap re-sampling to build confidence limits for all contribution plots in online PCA-based MSPC. The new strategy to estimate CLs is compared to the previously reported CLs for contribution plots. An industrial batch process dataset was used to illustrate the concepts.     

Multiple-timescale dynamics of side-chain carboxyl and carbonyl groups in proteins by 13C nuclear spin relaxation

Side-chain carboxyl and carbonyl groups play a major role in protein interactions and enzyme catalysis. A series of (13)C relaxation experiments is introduced to study the dynamics of carboxyl and carbonyl groups in protein side chains on both fast (sub-ns) and slower (micros-ms) time scales. This approach is illustrated on the protein calbindin D(9k). Fast dynamics features correlate with hydrogen- and ion-binding patterns. We also identify chemical dynamics on micros time scales in solvent-exposed carboxyl groups, most probably due to exchange between the carboxylate and carboxylic acid forms.     

Giant molecular spoked wheels in giant voids: two-dimensional molecular self-assembly goes big

We present here the formation of giant pores in surface-confined molecular networks of a triangular-shaped dehydrobenzo-[12]annulene derivative: the diameter of the pores reaches over 7 nm and the giant pores are used as templates to accommodate a giant molecular spoked wheel, which allows us to observe rotational and adsorption-desorption dynamics of single guest molecules.