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191.
We studied the thermal diffusion behavior of the nonionic surfactant solutions C 12E 6/water and C 12E 5/water at different concentrations and temperatures using thermal diffusion forced Rayleigh scattering (TDFRS). Two different types of TDFRS setups have been applied. In the classical TDFRS, we use an argon laser to write the optical grating into the sample by using a small amount of ionic dye to convert the optical grating into a temperature grating. In the other setup, called IR-TDFRS, we use an infrared laser as the writing beam, which utilizes the water absorption band to convert the optical grating into a temperature grating. The measurements by IR-TDFRS show a one-mode signal for all concentrations and temperatures, while the signal in the classical TDFRS consists of two modes for higher temperatures and lower surfactant concentrations (Ning, H.; et al. J. Phys. Chem. B 2006, 110, 10746). We find good agreement between the Soret coefficient determined in the IR-TDFRS and the one derived from the first fast mode in the previous studies. The Soret coefficient of the nonionic solutions is positive and enhanced at the critical point. In general, the Soret coefficient of the micelles tends to increase with temperature. We found that the presence of the second mode observed in the classical TDFRS is related to the addition of the ionic dye, but even with the ionic dye it is not possible to observe a second mode in the IR-TDFRS. The origin of the second mode is discussed in terms of charged micelles and an inhomogenous dye distribution in the temperature gradient. 相似文献
192.
In this work thermal stability and tensile strength of polyurethanes obtained from glycolysates was investigated. The glycolysates
were produced via glycolysis of waste polyurethane foam (PUR) in the reaction with 1,3-propylene glycol (PG). Polyurethanes
were synthesized from the obtained intermediates by the prepolymer method using diisocyanate (MDI) and glycolysis product
of molecular mass ranging from 700 to 1000, while 1,4-butylene glycol (BDO) was used as a chain elongation agent. The influence
of NCO group concentration in prepolymer on tensile strength and elongation at break of polyurethanes was investigated using
Zwick universal tensile tester.
Thermal decomposition of the obtained glycolysates and polyurethanes was followed by TG coupled with FTIR spectroscopy. The
main products of thermal decomposition have been identified. 相似文献
193.
A high-yield straightforward conversion of lactams to lactim ethers is shown by the conversion of (10H)-dipyrrin-1-ones to (11H)-dipyrrin-1-ol methyl and ethyl ethers in 90% yield from heating in neat trimethyl or triethyl phosphite at 160°C. Unlike
the parent dipyrrinones, which form intermolecularly hydrogen-bonded dimers in CHCl3, their lactim ethers are shown to be monomeric by vapor pressure osmometry. The latter react with boron trifluoride etherate
to N,N′-bridged BF2 derivatives that exhibit strong fluorescence (φF 0.6–0.8) near 535 nm. X-Ray crystal structures were obtained of the lactim ethyl ether of kryptopyrromethenone and the BF2 derivative of the lactim ethyl ether 2,3-diethyl-7,8-dimethyl-(10H)-dipyrrin-1-one.
Correspondence: David A. Lightner, Department of Chemistry, University of Nevada, Reno, Nevada 89557-0020 USA. 相似文献
194.
T. Mathew R. N. Datta W. K. Dierkes J. W. M. Noordermeer W. J. van Ooij 《Plasma Chemistry and Plasma Processing》2008,28(2):273-287
Carbon black is widely used as an active filler in the rubber industry to improve the physical properties of rubber. The surface
energy of carbon black is high compared to that of various elastomers like styrene–butadiene rubber (SBR), butadiene rubber
(BR) and ethylene–propylene–diene rubber (EPDM). The work aims at reducing the surface energy of carbon black by modifying
its surface for application especially in rubber blends. The present paper looks into the possibility of using plasma polymerisation
of acetylene as a surface modification technique for carbon black in comparison with silica. Thermogravimetric analysis, wetting
behaviour with various liquids of known surface tension and time of flight secondary ion mass spectrometry (ToF-SIMS) were
used to characterise the carbon black before and after surface modification. The study shows that surface modification of
carbon black by plasma polymerisation is difficult in comparison with silica, unless treated for long duration. The mechanistic
aspects of the surface modification and the importance of active sites on the carbon black surface for effective modification
are discussed in the paper. 相似文献
195.
Piyali Datta Chaudhuri 《Journal of organometallic chemistry》2008,693(3):567-573
Stable pallada(II)cycles featuring Csp2-Pd and Csp3-Pd bonds reacted with vinyl- and alkynyl(phenyl)iodonium salts to generate two new geminal carbon-carbon bonds to the terminal carbon of the vinyl and alkynyl substituents providing benzofuran and dihydrobenzofuran heterocycles. The new annulation process was rationalized by the involvement of Pd(IV) intermediates arising via an initial oxidative addition of hypervalent iodonium electrophiles to the Pd(II) center. Reaction monitoring via low temperature 1H NMR spectroscopy was performed, and organopalladium(II) intermediates featuring a new Csp2-Csp2 or Csp2-Csp bond were isolated and characterized, providing insights into the regiochemical course of the proposed mechanistic pathway. 相似文献
196.
Amipurimycin, a member of the complex peptidyl nucleoside family of antibiotics, is a Streptomyces-derived potent antifungal agent. The mechanism of action of amipurimycin, however, remains undetermined. Additionally, there are no reports on the total synthesis or structure-activity relationships (SAR) of this potentially useful bioactive compound. In a study aimed at the total synthesis and SAR studies of this natural product, the present research reports the development of a synthetic route to the central pyranosyl amino acid core of amipurimycin and its further elaboration, culminating in the synthesis of a unique thymine analogue. Utilizing a d-serine-derived dihydroaminopyrone as a strategic building block, the synthesis involves de novo construction of the fully functionalized C-3-branched carbohydrate amino acid core, followed by glycosidic attachment of thymine at C-1, and peptidic linking of the C-6 amine with the 1,2-aminocyclopentane carboxylic acid side chain. 相似文献
197.
Satyajit Banerjee Atish Datta Chowdhury Subhas Kumar Ghosh 《Mathematics in Computer Science》2008,1(4):673-688
Obtaining a matching in a graph satisfying a certain objective is an important class of graph problems. Matching algorithms
have received attention for several decades. However, while there are efficient algorithms to obtain a maximum weight matching,
not much is known about the maximum weight maximum cardinality, and maximum cardinality maximum weight matching problems for
general graphs. Our contribution in this work is to show that for bounded weight input graphs one can obtain an algorithm
for both maximum weight maximum cardinality (for real weights), and maximum cardinality maximum weight matching (for integer
weights) by modifying the input and running the existing maximum weight matching algorithm. Also, given the current state
of the art in maximum weight matching algorithms, we show that, for bounded weight input graphs, both maximum weight maximum
cardinality, and maximum cardinality maximum weight matching have algorithms of similar complexities to that of maximum weight
matching. Subsequently, we also obtain approximation algorithms for maximum weight maximum cardinality, and maximum cardinality
maximum weight matching.
相似文献
198.
Dr. Manju P. Maman Dr. Tamilselvi Gurusamy Dr. Arun K. Pal Dr. Rajkumar Jana Dr. Kothandaraman Ramanujam Dr. Ayan Datta Dr. Sukhendu Mandal 《Angewandte Chemie (International ed. in English)》2023,62(27):e202305462
The fixing of N2 to NH3 is challenging due to the inertness of the N≡N bond. Commercially, ammonia production depends on the energy-consuming Haber-Bosch (H−B) process, which emits CO2 while using fossil fuels as the sources of hydrogen and energy. An alternative method for NH3 production is the electrochemical nitrogen reduction reaction (NRR) process as it is powered by renewable energy sources. Here, we report a tiara-like nickel-thiolate cluster, [Ni6(PET)12] (where, PET=2-phenylethanethiol)] as an efficient electro-catalyst for the electrochemical NRR at ambient conditions. Ammonia (NH3: 16.2±0.8 μg h−1 cm−2) was the only nitrogenous product over the potential of −2.3 V vs. Fc+/Fc with a Faradaic efficiency of 25%±1.7. Based on theoretical calculations, NRR by [Ni6(PET)12] proceeds through both the distal and alternating pathways with an onset potential of −1.84 V vs. RHE (i.e., −2.46 V vs. Fc+/Fc) which corroborates with the experimental findings. 相似文献
199.
DFT calculations, including the effects of small curvature tunneling, have been performed on the reductive elimination of methane from hydridomethylbis(trimethylphosphine)platinum (1d). The calculations find that at 250 K tunneling results in an increase in the rate constant for reductive elimination by a factor of 4, a lowering of Ea by 1.7 kcal/mol, and a decrease in A by a factor of nearly 10. Tunneling is also calculated to increase the primary H/D kinetic isotope effect (KIE) from k(1d)/k(1f) = 2.26 to k(1d)/k(1f) = 4.12 and to result in a large secondary KIE of k(1d)/k(1e) = 1.35. In addition, tunneling is predicted to result in a violation of the rule of the geometric mean, so that the secondary KIE for reductive elimination of methane-d1 from 1f is calculated to be k(1f)/k(1g) = 1.06, which is much smaller than the secondary KIE of k(1d)/k(1e) = 1.35 for reductive elimination of methane from 1d. Comparison of the measured values of k(1d)/k(1e) and k(1f)/k(1g) is therefore proposed as an experimental test of the prediction that tunneling plays an important role in the reductive elimination of methane from 1d. 相似文献
200.
Datta A Hooker JM Botta M Francis MB Aime S Raymond KN 《Journal of the American Chemical Society》2008,130(8):2546-2552
High relaxivity macromolecular contrast agents based on the conjugation of gadolinium chelates to the interior and exterior surfaces of MS2 viral capsids are assessed. The proton nuclear magnetic relaxation dispersion (NMRD) profiles of the conjugates show up to a 5-fold increase in relaxivity, leading to a peak relaxivity (per Gd3+ ion) of 41.6 mM(-1) s(-1) at 30 MHz for the internally modified capsids. Modification of the exterior was achieved through conjugation to flexible lysines, while internal modification was accomplished by conjugation to relatively rigid tyrosines. Higher relaxivities were obtained for the internally modified capsids, showing that (i) there is facile diffusion of water to the interior of capsids and (ii) the rigidity of the linker attaching the complex to the macromolecule is important for obtaining high relaxivity enhancements. The viral capsid conjugated gadolinium hydroxypyridonate complexes appear to possess two inner-sphere water molecules (q = 2), and the NMRD fittings highlight the differences in the local motion for the internal (tauRl = 440 ps) and external (tauRl = 310 ps) conjugates. These results indicate that there are significant advantages of using the internal surface of the capsids for contrast agent attachment, leaving the exterior surface available for the installation of tissue targeting groups. 相似文献