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41.
The reaction of a transition metal coordination complex, Ti[N(CH(3))(2)](4), with self-assembled monolayers (SAMs) possessing-OH, -NH(2), and -CH(3) terminations has been examined using supersonic molecular beam techniques. The emphasis here is on how the reaction probability varies with incident kinetic energy (E(i)=0.4-2.07 eV) and angle of incidence (theta(i)=0 degrees -60 degrees ). The most reactive surface is the substrate underlying the SAMs-SiO(2) with a high density of -OH(a) (>5 x 10(14) cm(-2)), "chemical oxide." On chemical oxide, the dynamics of adsorption are well described by trapping, precursor-mediated adsorption, and the initial probability of adsorption depends only weakly on E(i) and theta(i). The dependence of the reaction probability on substrate temperature is well described by a model involving an intrinsic precursor state, where the barrier for dissociation is approximately 0.2-0.5 eV below the vacuum level. Reaction with the SAMs is more complicated. On the SAM with the unreactive, -CH(3), termination, reactivity decreases continuously with increasing E(i) while increasing with increasing theta(i). The data are best interpreted by a model where the Ti[N(CH(3))(2)](4) must first be trapped on the surface, followed by diffusion through the SAM and reaction at the SAMSiO(2) interface with residual -OH(a). This process is not activated by E(i) and most likely occurs in defective areas of the SAM. On the SAMs with reactive end groups, the situation is quite different. On both the-OH and -NH(2) SAMs, the reaction with the Ti[N(CH(3))(2)](4) as a function of E(i) passes through a minimum near E(i) approximately 1.0 eV. Two explanations for this intriguing finding are made-one involves the participation of a direct dissociation channel at sufficiently high E(i). A second explanation involves a new mechanism for trapping, which could be termed penetration facilitated trapping, where the Ti[N(CH(3))(2)](4) penetrates the near surface layers, a process that is activated as the molecules in the SAM must be displaced from their equilibrium positions. 相似文献
42.
Themba Dube 《Topology and its Applications》2010,157(14):2159-2331
Given a completely regular frame L, let, as usual, βL, λL and υL denote, respectively, the Stone-?ech compactification, the universal Lindelöfication and the Hewitt realcompactification of L. Let γ denote any of the functors β, λ or υ. It is well known that any frame homomorphism h:L→M has a unique “lift” to a frame homomorphism hγ:γL→γM such that σM⋅hγ=h⋅σL, where the σ-maps are effected by join. We find a condition on h such that if h satisfies it, then h is open iff its lift hγ is open. Furthermore, the same condition ensures that hγ is nearly open iff h is nearly open. This latter result is, in fact, a special case of a more general phenomenon. In the last part of the paper we investigate when hυ is surjective. The instances when hβ or hλ is surjective are known. It turns out that the surjectivity of the lifted map hυ:υL→υM captures Blair's notion of υ-embedding in the sense that a subspace S of a Tychonoff space X is υ-embedded iff the lifted map υ(Oi):υ(OX)→υ(OS) is surjective, where i:S→X is the subspace embedding. 相似文献
43.
In a topological spaceX, a T2-distinct pointx means that for anyyX xy, there exist disjoint open neighbourhoods ofx andy. Similarly, T0-distinct points and T1distinct points are defined. In a Ti-distinct point-setA, we assume that eachxA is a T
i
-distinct point (i=0, 1, 2). In the present paper some implications of these notions which localize the T
i
-separation axioms (i=0, 1, 2) requirement, are studied. Suitable variants of regularity and normality in terms of T2-distinct points are shown hold in a paracompact space (without the assumption of any separation axioms). Later T0-distinct points are used to give two characterizations of the R
D
-axiom.1 In the end, some simple results are presented including a condition under which an almost compact set is closed and a result regarding two continuous functions from a topological space into a Hausdorff space is sharpened. A result which relates a limit pointv to an -limit point is stated. 相似文献
44.
Vishnu J. Ram Vidyottama Dube Luc A. C. Pieters Arnold J. Vlietinck 《Journal of heterocyclic chemistry》1989,26(3):625-628
Various bis[4-aryl/alkyl-1, 2, 4-triazoline-5-thione-3-yl]alkanes ( 3 ) were prepared from base cyclization of bis thiosemicarbazide 2 and transformed into sulphides by reaction with different alkyl halides in alkaline medium. These compounds were further oxidised to sulphones 5 with acidic potassium permanganate. 1-Aryl-3-[4-(4-aryl/alkyl-1, 2, 4-triazoline-3-thione-5-yl)phenyl]thioureas ( 8 ) were prepared in two steps from p-aminophenylhydrazide ( 6 ) and aryl/alkylisothiocyanates. Alkylation of 8 with different alkyl halides yielded exclusively sulphides 9 . Some sulphides 12 and Mannich bases 13 from 5-(p-fluorophenyl)-1, 3, 4-oxadiazol-2-thione ( 11 ) were also prepared to evaluate their pesticidal activities. All the prepared compounds were screened for pesticidal activities but none of them exhibited any significant activity. 相似文献
45.
Thomas Bartelmann Frederik Gnannt Max Zitzmann Peter Mayer Henry Dube 《Chemical science》2021,12(10):3651
Introducing responsive elements into supramolecular recognition systems offers great advantages for the control of intermolecular interactions and represents an important stepping stone towards multi-purpose and reprogrammable synthetic systems. Of particular interest is implementation of light-responsiveness because of the unique ease and precision of this signal. Here we present visible light responsive hemithioindigo-based molecular tweezers that bear a highly polar sulfoxide function as an additional recognition unit inside their binding site. Sulfur oxidation allows to simultaneously enhance all crucial properties of this receptor type i.e. photoswitching capability, thermal stability of individual switching states, binding affinity, and binding modulation upon switching. With a novel titration method the thermodynamic binding parameters were determined using reduced sample amounts. Employing these strongly enhanced molecular tweezers allowed to demonstrate photocontrol of intermolecular charge transfer in a reversible manner.Hemithioindigo based molecular tweezers with a comprehensively improved property profile are obtained by simple oxidation of the sulfur atom. 相似文献
46.
Summary The separation of charged analytes by electrochromatography has been examined on porous-layer open tubular capillaries prepared
using the sol gel method. An electroosmotic flow of about 2.10×104 cm2V1s1 was obtained using between 10 and 30% acetonitrile in the mobile phase. Acidic diuretic drug compounds were successfully
separated at high pH as were theN-alkylanilines in their basic and neutral forms. The limitation of open tubular columns was observed on separating some basic
pharmaceutical drugs. These components showed severe peak tailing and were not resolved on a 20 μm i.d. porous silica layer
open tubular column. Strongly acidic components could not be detected on these columns due to their higher counter electromobilities.
The successful separation of neutral aryl alkyl ketones with an efficiency of 101,533 plates m1 for butyrophenone was an indication of the improved phase ratio on this type of open tubular columns. 相似文献
47.
G. Dube 《Accreditation and quality assurance》2001,6(1):3-7
The importance of analytical chemistry is increasing in many public fields, and the demand for reliable measurement results
is growing accordingly. A measurement result will be reliable only if its uncertainty has been quantified. This can be achieved
only by tracing the result back to a standard realizing the unit in which the measurement result is expressed. The National
Metrology Institutes (NMIs) can contribute to the reliability of the measurement results by developing measuring methods,
and by providing reference materials and standard measuring devices. In fields in which the comparability of measurement results
is of particular importance, they establish traceability structures. Responding to the globalization of trade and industry
the International Committee for Weights and Measures (CIPM) agreed on an arrangement on the mutual recognition of calibration
certificates (CIPM MRA) issued by the NMIs.
Received: 19 April 2000 / Accepted: 28 July 2000 相似文献
48.
Themba Dube 《Algebra Universalis》2008,58(2):181-202
If a frame satisfies a property which is some variant of realcompactness, then certain types of its subframes inherit the
property. Conversely, there are instances where a frame has a subframe satisfying some such property only if the frame itself
satisfies the property. We analyze these phenomena for the case of realcompactness, almost realcompactness, a-realcompactness, c-realcompactness and weak realcompactness vis-a-vis perfect subframes and flat subframes.
Received September 19, 2006; accepted in final form March 10, 2007. 相似文献
49.