排序方式: 共有22条查询结果,搜索用时 78 毫秒
1.
Doshi DA Shah PB Singh S Branson ED Malanoski AP Watkins EB Majewski J van Swol F Brinker CJ 《Langmuir : the ACS journal of surfaces and colloids》2005,21(17):7805-7811
Neutron reflectivity (NR) is used to probe the solid, liquid, vapor interface of a porous superhydrophobic (SH) surface submerged in water. A low-temperature, low-pressure technique was used to prepare a rough, highly porous organosilica aerogel-like film. UV/ozone treatments were used to control the surface coverage of hydrophobic organic ligands on the silica framework, allowing the contact angle with water to be continuously varied over the range of 160 degrees (superhydrophobic) to <10 degrees (hydrophilic). NR shows that the superhydrophobic nature of the surface prevents infiltration of water into the porous film. Atomic force microscopy and density functional theory simulations are used in combination to interpret the NR results and help establish the location, width, and nature of the SH film-water interface. 相似文献
2.
Focused-electron-beam-induced processing (FEBIP) for emerging applications in carbon nanoelectronics
Andrei G. Fedorov Songkil Kim Mathias Henry Dhaval Kulkarni Vladimir V. Tsukruk 《Applied Physics A: Materials Science & Processing》2014,117(4):1659-1674
Focused-electron-beam-induced processing (FEBIP), a resist-free additive nanomanufacturing technique, is an actively researched method for “direct-write” processing of a wide range of structural and functional nanomaterials, with high degree of spatial and time-domain control. This article attempts to critically assess the FEBIP capabilities and unique value proposition in the context of processing of electronics materials, with a particular emphasis on emerging carbon (i.e., based on graphene and carbon nanotubes) devices and interconnect structures. One of the major hurdles in advancing the carbon-based electronic materials and device fabrication is a disjoint nature of various processing steps involved in making a functional device from the precursor graphene/CNT materials. Not only this multi-step sequence severely limits the throughput and increases the cost, but also dramatically reduces the processing reproducibility and negatively impacts the quality because of possible between-the-step contamination, especially for impurity-susceptible materials such as graphene. The FEBIP provides a unique opportunity to address many challenges of carbon nanoelectronics, especially when it is employed as part of an integrated processing environment based on multiple “beams” of energetic particles, including electrons, photons, and molecules. This avenue is promising from the applications’ prospective, as such a multi-functional (electron/photon/molecule beam) enables one to define shapes (patterning), form structures (deposition/etching), and modify (cleaning/doping/annealing) properties with locally resolved control on nanoscale using the same tool without ever changing the processing environment. It thus will have a direct positive impact on enhancing functionality, improving quality and reducing fabrication costs for electronic devices, based on both conventional CMOS and emerging carbon (CNT/graphene) materials. 相似文献
3.
A simple, rapid, precise and specific isocratic HPAE‐PAD method for quantification of CGP69669A was developed and validated. CGP69669A is a glycomimetic of sialyl Lewisx and an antagonist of E‐selectin with potential application in the treatment of inflammatory skin disease. Quantification was performed using a Dionex CarboPacTM PA‐200 anion‐exchange column (3 × 250 mm) with 100 mm NaOH solution as mobile phase, a flow rate of 0.50 mL/min and an injection volume of 10 μL. A quadruple potential waveform was used to detect the carbohydrate (+0.1 V from 0.00 to 0.40 s, ?2.0 V from 0.41 to 0.42 s, +0.6 V at 0.43 s and ?0.1 V from 0.44 to 0.50 s with current integrated between 0.20 and 0.40 s for detection) and rafinose was employed as an internal standard. The optimized conditions enabled rapid elution of CGP69669A (at 3.0 min) without interference from solvent peaks or substances present in the skin. The method showed good intra‐ and inter‐day precision and accuracy and the response was linear from 1.0 to 25 µg/mL. This is the first validated direct method for the quantification of CGP69669A. It will now be employed in studies investigating the topical and transdermal delivery of CGP69669A in vitro and in vivo and it should also be of use for other applications of this molecule. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
4.
Prashant T. Mistry Nimesh R. Kamdar Dhaval D. Haveliwala Saurabh K. Patel 《Journal of heterocyclic chemistry》2012,49(2):349-357
A variety of pyrano[2,3‐d]pyrimidine‐5‐one derivatives 5 , 5a , 5b , 5c , 5d , 5e , 5f , 5g , 5h , 5i , 5j , 6 , 6a , 6b , 6c , 6d , 6e , 6f , 6g , 6h , 6i , 6j have been synthesized from 6‐amino‐4‐(substituted phenyl)‐5‐cyano‐3‐methyl‐1‐phenyl‐1,4‐dihydropyrano[2,3‐c]pyrazole derivatives 4a , 4b , 4c , 4d , 4e , 4f , 4g , 4h , 4i , 4j via cyclization using formic acid and acetic acid. All the newly synthesized compounds have been characterized by IR, 1H NMR, 13C NMR, and elemental analysis. All the synthesized compounds have been screened for antibacterial, antifungal and antitubercular activity. J. Heterocyclic Chem., (2012). 相似文献
5.
Doshi DA Gibaud A Goletto V Lu M Gerung H Ocko B Han SM Brinker CJ 《Journal of the American Chemical Society》2003,125(38):11646-11655
It is now recognized that self-assembly is a powerful synthetic approach to the fabrication of nanostructures with feature sizes smaller than achievable with state of the art lithography and with a complexity approaching that of biological systems. For example, recent research has shown that silica/surfactant self-assembly combined with evaporation (so-called evaporation induced self-assembly EISA) can direct the formation of porous and composite thin-film mesostructures characterized by precise periodic arrangements of inorganic and organic constituents on the 1-50-nm scale. Despite the potential utility of these films for a diverse range of applications such as sensors, membranes, catalysts, waveguides, lasers, nano-fluidic systems, and low dielectric constant (so-called low k) insulators, the mechanism of EISA is not yet completely understood. Here, using time-resolved grazing incidence small-angle X-ray scattering (GISAXS) combined with gravimetric analysis and infrared spectroscopy, we structurally and compositionally characterize in situ the evaporation induced self-assembly of a homogeneous silica/surfactant/solvent solution into a highly ordered surfactant-templated mesostructure. Using CTAB (cetyltrimethylammonium bromide) as the structure-directing surfactant, a two-dimensional (2-D) hexagonal thin-film mesophase (p6mm) with cylinder axes oriented parallel to the substrate surface forms from an incipient lamellar mesophase through a correlated micellar intermediate. Comparison with the corresponding CTAB/water/alcohol system (prepared without silica) shows that, for acidic conditions in which the siloxane condensation rate is minimized, the hydrophilic and nonvolatile silicic acid components replace water maintaining a fluidlike state that avoids kinetic barriers to self-assembly. 相似文献
6.
Prashant T. Mistry Nimesh R. Kamdar Dhaval D. Haveliwala Saurabh K. Patel 《Phosphorus, sulfur, and silicon and the related elements》2013,188(5):561-572
Abstract To develop a series of bioactive heterocycles in minimum number of steps, 3-methyl- 4-(substituted phenyl)-1-phenyl-4,8-dihydropyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidine-5,7 (1H,6H)-dithione 2(a–j), 4-(4-substituted phenyl)-5-imino-3-methyl-1,6-diphenyl-4,5,6,8-tetrahydropyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidine-7(1H)-thione 3(a–j), and N-[4-(subs- tituted phenyl)-3-methyl-1-phenyl-7-thioxo-1,4,7,8-hexahydropyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidine-5-yl]thiourea 4(a–j) have been synthesized from amino nitrile functionality 1(a–j). The structures of the compounds were elucidated by IR, 1H NMR, elemental analysis, and some representative 13C NMR and mass spectra. All the title compounds were screened for antimicrobial and antitubercular activities, while some representative compounds were tested for antioxidant activity. Out of synthesized compounds, compounds 1j (4-CH3), 2d (4-F), 4c (4-OH), and 4i (3-Br) exhibited maximum inhibition against Mycobacterium Tuberculosis H37Rv. Compound 3c (4-OH) revealed elevated efficacy against all tested bacterial strain, while compounds 1i (3-Br), 2c (4-OH), and 3h (3-NO2) were found efficacious against Candida albicans as compared to standard drugs. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. 相似文献
7.
Dhaval D. Haveliwala Nimesh R. Kamdar Prashant T. Mistry Saurabh K. Patel 《Helvetica chimica acta》2013,96(5):897-905
A series of functionalized H‐[1]benzopyrano[2,3‐b]pyridine derivatives were synthesized by the Friedländer reaction of 2‐amino‐4‐oxo‐4H‐chromene‐3‐carbonitriles 1 with malononitrile, ethyl cyanoacetate, or acetophenone (Scheme). The synthesized compounds 2 – 4 were screened for their in vitro activity against antitubercular, antibacterial, and antifungal species (Fig., Table). Among the synthesized compounds, 3c and 4f were the most active with 99% inhibition against Mycobacterium tuberculosis H37Rv, while compounds 2f, 3f , and 4d exhibited 69%, 63%, and 61% inhibition, respectively. The 4‐amino‐7,9‐dibromo‐1,5‐dihydro‐2,5‐dioxo‐2H‐chromeno[2,3‐b]pyridine‐3‐carbonitrile ( 3b ) showed the most potent antibacterial activity against Escherichia coli and Pseudomonas aeruginosa. Several chromeno[2,3‐b]pyridine derivatives showed equal or more potency against Staphylococcus aureus and Candida albicans. 相似文献
8.
Dhaval Adjodah Yan Leng Shi Kai Chong P. M. Krafft Esteban Moro Alex Pentland 《Entropy (Basel, Switzerland)》2021,23(7)
A critical question relevant to the increasing importance of crowd-sourced-based finance is how to optimize collective information processing and decision-making. Here, we investigate an often under-studied aspect of the performance of online traders: beyond focusing on just accuracy, what gives rise to the trade-off between risk and accuracy at the collective level? Answers to this question will lead to designing and deploying more effective crowd-sourced financial platforms and to minimizing issues stemming from risk such as implied volatility. To investigate this trade-off, we conducted a large online Wisdom of the Crowd study where 2037 participants predicted the prices of real financial assets (S&P 500, WTI Oil and Gold prices). Using the data collected, we modeled the belief update process of participants using models inspired by Bayesian models of cognition. We show that subsets of predictions chosen based on their belief update strategies lie on a Pareto frontier between accuracy and risk, mediated by social learning. We also observe that social learning led to superior accuracy during one of our rounds that occurred during the high market uncertainty of the Brexit vote. 相似文献
9.
Stefan Andrew Harry Michael Richard Xiang Eric Holt Andrea Zhu Fereshte Ghorbani Dhaval Patel Thomas Lectka 《Chemical science》2022,13(23):7007
We report a photochemically induced, hydroxy-directed fluorination that addresses the prevailing challenge of high diastereoselectivity in this burgeoning field. Numerous simple and complex motifs showcase a spectrum of regio- and stereochemical outcomes based on the configuration of the hydroxy group. Notable examples include a long-sought switch in the selectivity of the refractory sclareolide core, an override of benzylic fluorination, and a rare case of 3,3′-difluorination. Furthermore, calculations illuminate a low barrier transition state for fluorination, supporting our notion that alcohols are engaged in coordinated reagent direction. A hydrogen bonding interaction between the innate hydroxy directing group and fluorine is also highlighted for several substrates with 19F–1H HOESY experiments, calculations, and more. We report a photochemical, hydroxy-directed fluorination that addresses the prevailing challenge of high diastereoselectivity. Numerous motifs showcase a range of regio- and stereochemical outcomes based on the configuration of the hydroxy group.The hydroxy (OH) group is treasured and versatile in chemistry and biology.1 Its ubiquity in nature and broad spectrum of chemical properties make it an attractive source as a potential directing group.2 The exploitation of the mild Lewis basicity exhibited by alcohols has afforded several elegant pathways for selective functionalization (e.g., Sharpless epoxidation,3 homogeneous hydrogenation,4 cross-coupling reactions,5 among others6). Recently, we reported a photochemically promoted carbonyl-directed aliphatic fluorination, and most notably, established the key role that C–H⋯O hydrogen bonds play in the success of the reaction.7 Our detailed mechanistic investigations prompt us to postulate that other Lewis basic functional groups (such as –OH) can direct fluorination in highly complementary ways.8 In this communication, we report a hydroxy-directed aliphatic fluorination method that exhibits unique directing properties and greatly expands the domain of radical fluorination into the less established realm governing high diastereoselectivity.9Our first inclination that functional groups other than carbonyls may influence fluorination regiochemical outcomes was obtained while screening substrates for our published ketone-directed radical-based method (Scheme 1).8a In this example, we surmised that oxidation of the tertiary hydroxy group on substrate 1 cannot occur and would demonstrate functional group tolerance (directing to C11, compound 2). Surprisingly, the two major regioisomers (products 3 and 4) are derivatized by Selectfluor (SF) on C12 and C16 – indicative of the freely rotating hydroxyl directing fluorination. Without an obvious explanation of how these groups could be involved in dictating regiochemistry, we continued the mechanistic study of carbonyl-directed fluorination (Scheme 2A). We established that the regioselective coordinated hydrogen atom abstraction occurs by hydrogen bonding between a strategically placed carbonyl and Selectfluor radical dication (SRD).7 However, we noted that the subsequent radical fluorination is not diastereoselective due to the locally planar nature of carbonyl groups. Thus, we posed the question: are there other directing groups that can provide both regio- and diastereoselectivity? Such a group would optimally be attached to a sp3 hybridized carbon; thus the “three dimensional” hydroxy carbon logically comes to mind as an attractive choice, and Scheme 1 illustrates the first positive hint.Open in a separate windowScheme 1Observed products for the fluorination of compound 1.Open in a separate windowScheme 2(A) Proposed mechanism, (B) β-caryophyllene alcohol hypochlorite derivative synthetic probe, (C) isodesmic relation of transition states showing the general importance of the hydroxy group to reactivity (ωB97xd/6-31+G*), and (D) 1H NMR experiment with Selectfluor and various additives at different concentrations.We began our detailed study with a simple substrate that contains a tertiary hydroxyl group. Alcohol 5 was synthesized stereoselectively by the reaction of 3-methylcyclohexanone, FeCl3, and 4-chlorophenylmagnesium bromide;10 the 4-chlorophenyl substituent allows for an uncomplicated product identification and isolation (aromatic chromophore). We sought to determine optimal reaction conditions by examination of numerous photosensitizers, bases, solvents, and light sources (7 Although we utilize cool blue LEDs (sharp cutoff ca. 400 nm), CFLs (small amount of UVB (280–315 nm) and UVA (315–400 nm)) are useable as well.11 A mild base additive was also found to neutralize adventitious HF and improve yields in the substrates indicated ( Entry Sensitizer 19F yield 1 None 0% 2 Benzil 83% 3 Benzil, no base 63% 4 Benzil, K2CO3 68% 5 Benzil, CFL light source 75% 6 5-Dibenzosuberenone 15% 7 4,4′-Difluorobenzil 63% 8 9,10-Phenantherenequinone 71% 9 Perylene 8% 10 Methyl benzoylformate 42%