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101.
This paper describes the work carried out to investigate the pore pressures occurring in secondary consolidation. A theoretical approach and an experimental technique was developed in order to conduct the study. By considering compression to occur only due to water leaving the soil it was possible to derive an expression for the dissipation of pore pressure in the secondary phase. By further simplified assumptions which are based on experimental observations, the above general solution was reduced to a simple formula which predicted the observed behaviour of pore water pressures during secondary consolidation. 相似文献
102.
Dr. Luca Bondì Dr. Anna L. Garden Prof. Federico Totti Dr. Paul Jerabek Prof. Sally Brooker 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(22):e202104314
The effect of para-substituent X on the electronic structure of sixteen tridentate 4- X -(2,6-di(pyrazol-1-yl))-pyridine ( bppX ) ligands and the corresponding solution spin crossover [FeII( bppX )2]2+ complexes is analysed further, to supply quantitative insights into the effect of X on the σ-donor and π-acceptor character of the Fe- NA (pyridine) bonds. EDA-NOCV on the sixteen LS complexes revealed that neither ΔEorb,σ+π (R2=0.48) nor ΔEorb,π (R2=0.31) correlated with the experimental solution T1/2 values (which are expected to reflect the ligand field imposed on the iron centre), but that ΔEorb,σ correlates well (R2=0.82) and implies that as X changes from EDG → EWG (Electron Donating to Withdrawing Group), the ligand becomes a better σ-donor. This counter-intuitive result was further probed by Mulliken analysis of the NA atomic orbitals: NA (px) involved in the Fe−N σ-bond vs. the perpendicular NA (pz) employed in the ligand aromatic π-system. As X changes EDG → EWG , the electron population on NA (pz) decreases, making it a better π-acceptor, whilst that in NA (px) increases, making it a better σ-bond donor; both increase ligand field, and T1/2 as observed. In 2016, Halcrow, Deeth and co-workers proposed an intuitively reasonable explanation of the effect of the para- X substituents on the T1/2 values in this family of complexes, consistent with the calculated MO energy levels, that M→L π-backdonation dominates in these M−L bonds. Here the quantitative EDA-NOCV analysis of the M−L bond contributions provides a more complete, coherent and detailed picture of the relative impact of M−L σ-versus π-bonding in determining the observed T1/2, refining the earlier interpretation and revealing the importance of the σ-bonding. Furthermore, our results are in perfect agreement with the ΔE(HS-LS) vs. σp+(X) correlation reported in their work. 相似文献
103.
Muhammad Irfan Ashiq Ishtiaq Hussain Sally Dixon Mark E. Light Jeremy D. Kilburn 《Acta Crystallographica. Section C, Structural Chemistry》2010,66(9):o455-o458
The structures of N‐benzyl‐N′‐{6‐[(4‐carboxylatobenzyl)aminocarbonyl]‐2‐pyridylmethyl}guanidinium, C23H23N5O3, (I), and N‐[2‐(benzylaminocarbonyl)ethyl]‐N′‐{6‐[(4‐carboxylatobenzyl)aminocarbonyl]‐2‐pyridylmethyl}guanidinium monohydrate, C26H28N6O4·H2O, (II), both form three‐dimensional supramolecular hydrogen‐bonded networks based on a dimeric primary synthon involving carboxylate–guanidinium linkages. The differences in the geometries and hydrogen‐bonding connectivities are driven by the additional methylpropionamide group and water of crystallization of (II). 相似文献
104.
A family of five new bis-bidentate azole–triazole Rat ligands (1,3-bis(5-(azole)-4-isobutyl-4H-1,2,4-triazol-3-yl)benzene), varying in choice of azole (2-imidazole, 4-imidazole, 1-methyl-4-imidazole, 4-oxazole and 4-thiazole), and the corresponding family of spin-crossover (SCO) and redox active triply bridged dinuclear helicates, [FeII2L3]4+, has been prepared and characterised. X-ray crystal structures show all five Fe(ii) helicates are low spin at 100 K. Importantly, DOSY NMR confirms the intactness of these SCO-active dinuclear helicates in D3-MeCN solution, regardless of HS fraction: γHS(298 K) = 0–0.81. Variable temperature 1H NMR Evans and UV-vis studies reveal that the helicates are SCO-active in MeCN solution. Indeed, the choice of azole in the Rat ligand used in [Fe2L3]4+ tunes: (a) solution SCO T1/2 from 247 to 471 K, and (b) reversible redox potential, Em(FeII/III), from 0.25 to 0.67 V for four helicates, whilst one has an irreversible redox process, Epa = 0.78 V, vs. 0.01 M AgNO3/Ag. For the four reversible redox systems, a strong correlation (R2 = 0.99) is observed between T1/2 and Epa. Finally, the analogous Ni(ii) helicates have been prepared to obtain Δo, establishing: (a) the ligand field strength order of the ligands: 4-imidazole (11 420) ∼ 1-methyl-4-imidazole (11 430) < 2-imidazole (11 505) ∼ 4-oxazole (11 516) < 4-thiazole (11 804 cm−1), (b) that Δo ([NiII2L3]4+) strongly correlates (R2 = 0.87) with T1/2 ([FeII2L3]4+), and (c) interestingly that Δo strongly correlates (R2 = 0.98) with Epa for the four helicates with reversible redox, so the stronger the ligand field strength, the harder it is to oxidise the Fe(ii) to Fe(iii).Choice of non-coordinated diazole heteroatom in five robust triply bridged dinuclear helicates tunes Δo, spin crossover and redox potential. Regardless of fraction high spin (0–0.81), DOSY NMR confirms the helicates are intact in solution. 相似文献
105.
Attempts to use alkylation to introduce a positive charge at the nitrogen atom of the 4‐pyridyl ring in the bis(bidentate) triazole ligand N4‐(4‐pyridyl)‐3,5‐di(2‐pyridyl)‐1,2,4‐triazole ( pydpt ) were made to ascertain what effect a strongly electron‐withdrawing group would have on the magnetic properties of any subsequent iron(II) complexes. Alkylation of pydpt under relatively mild conditions led in some cases to unexpected rearrangement products. Specifically, when benzyl bromide is used as the alkylating agent, and the reaction is carried out in refluxing acetonitrile, the N4 substituent moves to the N1 position. However, when the same reaction is performed in dichloromethane at room temperature, the rearrangement does not occur and the desired product containing an alkylated N4 substituent is obtained. Heating a pure sample of N4‐Bzpydpt?Br to reflux in MeCN resulted in clean conversion to N1Bzpydpt.Br . This is consistent with N4‐Bzpydpt.Br being the kinetic product whereas N1Bzpydpt.Br is the thermodynamic product. When methyl iodide is used as the alkylating agent, the N4 to N1 rearrangement occurs even at room temperature, and at reflux pydpt is doubly alkylated. The observation of the lowest reported temperatures for an N4 to N1 rearrangement is due to this particular rearrangement involving nucleophilic aromatic substitution: a possible mechanism for this transformation is suggested. 相似文献
106.
Two new methods based on FT–Raman spectroscopy, one simple, based on band intensity ratio, and the other using a partial least squares (PLS) regression model, are proposed to determine cellulose I crystallinity. In the simple method, crystallinity in cellulose I samples was determined based on univariate regression that was first developed using the Raman band intensity ratio of the 380 and 1,096 cm?1 bands. For calibration purposes, 80.5% crystalline and 120-min milled (0% crystalline) Whatman CC31 and six cellulose mixtures produced with crystallinities in the range 10.9–64% were used. When intensity ratios were plotted against crystallinities of the calibration set samples, the plot showed a linear correlation (coefficient of determination R 2 = 0.992). Average standard error calculated from replicate Raman acquisitions indicated that the cellulose Raman crystallinity model was reliable. Crystallinities of the cellulose mixtures samples were also calculated from X-ray diffractograms using the amorphous contribution subtraction (Segal) method and it was found that the Raman model was better. Additionally, using both Raman and X-ray techniques, sample crystallinities were determined from partially crystalline cellulose samples that were generated by grinding Whatman CC31 in a vibratory mill. The two techniques showed significant differences. In the second approach, successful Raman PLS regression models for crystallinity, covering the 0–80.5% range, were generated from the ten calibration set Raman spectra. Both univariate-Raman and WAXS determined crystallinities were used as references. The calibration models had strong relationships between determined and predicted crystallinity values (R 2 = 0.998 and 0.984, for univariate-Raman and WAXS referenced models, respectively). Compared to WAXS, univariate-Raman referenced model was found to be better (root mean square error of calibration (RMSEC) and root mean square error of prediction (RMSEP) values of 6.1 and 7.9% vs. 1.8 and 3.3%, respectively). It was concluded that either of the two Raman methods could be used for cellulose I crystallinity determination in cellulose samples. 相似文献
107.
This article explores the use of multivariate techniques to build perceptual maps that show the perceived competitive positions of a set of ethical drugs. The data were drawn from a commercial panel of 283 family doctors working for the UK National Health Service. Factor analysis was applied to identify the main dimensions used by doctors to perceive and evaluate antihypertensive brands. Perceptual maps showing the competitive positions of 14 antihypertensives were produced using the factor scores of the medicines. Multiple regression analysis enabled the relative importance of each perceptual dimension to be determined. The results reveal that doctors use a small number of perceptual dimensions to evaluate competitive antihypertensive drugs, namely: “medical support”, “long term efficacy”, and the “additional beneficial effects” provided by the brand. The implications for marketing managers in the ethical pharmaceutical industry are explained and ways in which the perceptual analysis can be used to guide strategic marketing decisions considered. 相似文献
108.
The Suzuki-Miyaura cross-coupling of sterically hindered and electron-rich ortho,ortho′-substituted aryl halides with potassium vinyltrifluoroborate utilizing microwave irradiation has been conducted while adjusting solvent ratio, irradiation time, and catalyst loading to find optimal conditions. Coupling of benzyl 3,5-bis(benzyloxy)-4-bromobenzoate leads to a mixture of the desired styrene derivative and the reduced product. 4-Bromo-1,3,5-trimethoxybenzene, methyl 4-bromo-3,5-dimethoxybenzoate, and mesitylene bromide were also coupled to test the breadth and scope of this methodology. Of these substrates tested only 4-bromo-1,3,5-trimethoxybenzene was not vinylated successfully, which is believed to be due to the electron-rich nature of this system. 相似文献
109.
Fehring V Knights S Chan MY O'Neil IA Cosstick R 《Organic & biomolecular chemistry》2003,1(1):123-128
The ability of 2'-alpha-C-carboxyalkyl nucleosides to undergo an unusual two-step stereocontrolled nucleobase exchange process has been investigated. Upon silylation a protected 2'-deoxy-2'-alpha-C-(carboxymethyl)uridine derivative can undergo intramolecular displacement of the uracil base, by the 2'-carboxylic acid group, to form a pentofuranosyl gamma-lactone. Under identical conditions the homologous 2'-deoxy-2'-alpha-C-(carboxyethyl)uridine derivative does not yield the corresponding delta-lactone, but undergoes elimination of uracil to give the corresponding glycal. The pentofuranosyl gamma-lactone is a good substrate for nucleoside synthesis by the Vorbrüggen procedures and undergoes completely stereoselective ring opening with either pyrimidine or purine silylated nucleobases to give novel 2'-C-carboxymethyl beta-nucleosides in moderate to high yield. 相似文献
110.
Intelligent control of surface hydrophobicity. 总被引:1,自引:0,他引:1
Sally L Gras Tanveer Mahmud Gary Rosengarten Arnan Mitchell Kourosh Kalantar-Zadeh 《Chemphyschem》2007,8(14):2036-2050
Switchable surfaces are highly useful materials with surface properties that change in response to external stimuli. These surfaces can be employed in both research and industrial applications, where the ability to actively control surface properties can be used to develop smart materials and intelligent surfaces. Herein, we review a range of surfaces in which hydrophobicity can be controlled. We present the principal ideas of surface switching, discuss recent developments, explore experimental issues and examine factors that influence surface switching, including the nature of the stimuli, the underlying material, the morphology of the surface and the surrounding environment. We have categorised switchable surfaces according to the stimuli that trigger changes in surface hydrophobicity. These are electrically, electrochemically, thermally, mechanically, photo- and environmentally inducible surfaces. In addition, we review the use of chemical reactions to modify the properties of switchable surfaces and produce changes in the molecular structure and nanoscale features of the surface. 相似文献