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121.
Mazhar Ul-Islam Waleed Ahmad Khattak Minkyung Kang Sang Min Kim Taous Khan Joong Kon Park 《Cellulose (London, England)》2013,20(1):253-263
Physicochemical properties of materials can be amended by altering their physical structure through different processing conditions. The present study was conducted to investigate the post-synthesis structural variations and physico-mechanical properties of bacterial cellulose (BC) sheets prepared using different drying methods. Wet BC sheets of the same origin were freeze dried (BC-FD), dried at room temperature (25 °C) (BC-DRT), and dried at elevated temperature (50 °C) (BC-DHT). FE-SEM micrographs revealed that BC-DRT and BC-DHT had a more tightly packed and compact structure than the loosely held fibrils of BC-FD. XRD analysis revealed the relative crystallinity of the BC sample to be 64.60, 59.16, and 47.20 % for BC-DHT, BC-DRT and BC-FD, respectively. The water holding capacity (WHC) of the BC-FD was higher than that of the other two samples. Four consecutive drying and rewetting cycles demonstrated that the WHC of all samples decreased with each cycle. The WHC of BC-DRT and BC-DHT was reduced to almost 0 after the first drying cycle, but the BC-FD samples were able to regain some of their WHC. The tensile strength and elongation modulus were in the order of BC-DHT > BC-DRT > BC-FD. Overall, the results of this study revealed that the post-synthetic processing conditions had a strong effect on the structure and physico-mechanical properties of BC. 相似文献
122.
Solvent-free reactions were used for the synthesis of a series of imidazolium-based ionic salts: 3,3′-[pyridine-2,6-diylbis(methylene)]bis(1-R-1H-imidazol-3-ium)chloride; (R = methyl, ethyl, butyl, isobutyl, hexyl, and benzyl). A simple and effective filtration process was used to isolate all the products in high purity and with yields ?93% within a 24 h period. The highly pure ionic compounds which are precursors to N-heterocyclic carbene ligands used in catalysis were fully characterized as gray-white hygroscopic salts. 相似文献
123.
Ullah Irfan Baloch Musa Kaleem Ullah Imran Mustaqeem Muhammad 《Journal of solution chemistry》2014,43(8):1360-1373
Journal of Solution Chemistry - The development of a meaningful dissolution procedure for drug products with limited water solubility has been a challenge to both the pharmaceutical industry and... 相似文献
124.
Haladhara Naik Ashok Goswami Guinyun Kim Kwangsoo Kim Sung-Chul Yang Muhammad Sahid Muhammad Zaman Manwoo Lee Sung-Gyun Shin Moo-Hyun Cho 《Journal of Radioanalytical and Nuclear Chemistry》2014,299(3):1335-1343
The independent isomeric-yield ratios of 89m,gNb for the 93Nb(γ, 4n) 89m,gNb reaction with bremsstrahlung energies of 45-, 50-, 55-, 60-, and 70-MeV were measured by the activation and the off-line γ-ray spectrometric technique at 100 MeV electron linac of the Pohang accelerator laboratory. The isomeric-yield ratios of 89m,gNb for the natZr(p, xn) 89m,gNb and the 89Y(α, 4n) 89m,gNb reactions were measured by using a stacked-foil activation technique with the proton energies of 19–45 MeV and alpha energies of 38.9-, 40.5-, and 42.5-MeV at the MC-50 cyclotron of Korea Institute of Radiological and Medical Sciences. The measured isomeric-yield ratio of 89m,gNb from the 93Nb(γ, 4n), natZr(p, xn), and 89Y(α, 4n) reactions were compared with the similar literature data in the 89Y(3He, 3n) reaction. It was found that the isomeric yield ratio of 89m,gNb increases with projectile energy, which indicate the effect of excitation energy. However, for the similar compound nucleus with the same excitation energy, the isomeric-yield ratios of 89m,gNb in the 89Y(α, 4n) and 89Y(3He, 3n) reactions are higher than those in the 93Nb(γ, 4n) and natZr(p, xn) reactions, which indicates the role of input angular momentum. The isomeric-yield ratios of 89m,gNb in the 93Nb(γ, 4n), natZr(p, xn), 89Y(α, 4n), and 89Y(3He, 3n) reactions were also calculated theoretically using computer code TALYS 1.4. The theoretical isomeric-yield ratios of 89m,gNb from four reactions increase with excitation energy. However, the theoretical value are significantly higher than the experimental data in the 93Nb(γ, 4n) and natZr(p, xn) reactions but slightly lower or comparable in the 89Y(α, 4n) rand 89Y(3He, 3n) reactions. 相似文献
125.
Muhammad Imran Malik Tooba Mahboob Shakil Ahmed 《Analytical and bioanalytical chemistry》2014,406(25):6311-6317
Poly(2-vinylpyridine)s (P2VPs) are important polymers with extensive applications in modern day material science. P2VP is an exceptional case for liquid chromatography because of certain polar interactions with most of the stationary phases. In the present study, we established the critical adsorption point (CAP) of P2VP for the first time. The effectiveness of the method is demonstrated by analyses of blends and block copolymers of P2VP and PMMA. The CAP of PMMA is established for determination of molar mass of P2VP component of above mentioned blends and block copolymers. The methods successfully demonstrate the separation of both types of homopolymers from the rest of the samples in conjunction with the determination of molar mass distribution of noncritical block or component. Graphical Abstract
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126.
Muhammad Tariq Saqib Ali Muhammad Nawaz Tahir Nasir Khalid Jafir Hussain Shirazi 《Journal of the Iranian Chemical Society》2014,11(3):839-846
A series of six organotin(IV) carboxylates [Me2SnL2] (1), [n-Bu2SnL2] (2), [n-Oct2SnL2] (3), [Me3SnL] (4), n-Bu3SnL (5) and [Ph3SnL] (6), where L = 3-(4-cyanophenyl) acrylic acid have been synthesized and characterized by elemental analysis, FT-IR and NMR (1H, 13C). The complex (4) was also analyzed by single crystal X-ray analysis which showed distorted trigonal bipyramidal geometry with polymeric bridging behavior. The complexes 1–6 were screened for antimicrobial activities and cytotoxicity. The results showed significant activity with few exceptions. The catalytic activity of complexes was assessed in transesterification reaction of Brassica campestris oil (triglycerides) to produce biodiesel (fatty acid methyl esters). The results showed that triorganotin(IV) complexes exhibited good catalytic activity than their di-analogues. 相似文献
127.
Yetkin Gök Senem Akkoç Mehmet Akkurt Muhammad Nawaz Tahir 《Journal of the Iranian Chemical Society》2014,11(6):1767-1774
The nine new heteroaryl-substituted imidazolidinium (1a–c), pyrimidinium (2a–c) and diazepinium (3a–c) salts as N-heterocyclic carbene (NHC) precursors were synthesized in good yields and entirely characterized using elemental analyses and conventional spectroscopic methods. In situ formed complexes from heterocyclic salts (1–3), Pd(OAc)2 and in the presence of KOBu t as a base were tested as catalysts for the Mizoroki–Heck coupling reaction in an aqueous media and very high yields were achieved. 1,3-Di(5-methylthiophen-2-ylmethyl)pyrimidinium hexafluorophosphate salt (2b) was structurally characterized by single-crystal X-ray diffraction. In the 2b compound (C16H21N2S2)+[PF6]?, the terminal thiophene rings are twisted with a dihedral angle of 72.8(3)°. In the pyrimidine ring, the three successive C atoms between the N atoms are disordered over two positions [occupancy ratio 0.753(12):0.247(12)]. In the crystal, neighboring molecules are linked by C–H…F hydrogen bonds, running along the b axis. 相似文献
128.
Zia‐ur‐ Rehman Muhammad Moazzam Naseer Afzal Shah Saqib Ali Auke Meetsma 《Heteroatom Chemistry》2015,26(2):123-133
A fascinating ligand, 4‐formylpiperazinium 4‐formylpiperazine‐1‐carbodithioate (L‐salt) has been reacted with two electronically and sterically different trimethyltin(IV) chloride and triphenyltin(IV) chloride. The complexes 1 and 2 were characterized by elemental analysis, spectroscopic techniques, and X‐ray single crystal analysis. The latter technique confirmed the polymeric and monomeric nature of 1 and 2 , respectively. Both 1 and 2 showed intriguing molecular packing properties in the solid state. However, the packing of 1 is more interesting and unique where one‐dimensional polymer chains self assemble in two‐over‐two saltire‐shaped fashion to provide an overall multilayered structure. The different behavior of L toward two different tin(IV) compounds can be attributed to different electronic and steric environments around metal center. 相似文献
129.
Sadiq‐ur‐Rehman Bilal Ahmad Khan Muhammad Aziz Chaudhary Khawaja Ansar Yasin Saqib Ali 《Heteroatom Chemistry》2015,26(6):417-425
Di‐ and triorganotin(IV) carboxylates, RnSn(OCOC(R2)=CHR1)4–n (n = 2 and 3; R = Me, Et, n‐Bu, Ph; R1 = 3‐CH3O‐4‐OHC6H3, R2 = C6H5) were prepared by reacting the corresponding organotin(IV) chloride with the silver salt of the (E)‐3‐(4‐hydroxy‐3‐methoxyphenyl)‐2‐phenylpropenoic acid. The title compounds were investigated and characterized by elemental analysis, infrared (FT‐IR), multinuclear (1H, 13C, 119Sn) NMR, and mass spectrometry, and possible structures were proposed. The complexes and ligand acid ( HL ) have been evaluated in vitro against various bacteria and fungi. The results noticed during the biocidal activity screenings proved their in vitro biological potential. They were also tested for cytotoxicity. 相似文献
130.
Motivated by the high potential of shape memory alloys (SMA) in several industrial applications, we investigate the material response under cyclic loading. In particular, the focus is set on the modelling of functional fatigue, which results in the deterioration of the specific features of SMA. In fact, functional fatigue restricts SMA in terms of its applicability for real structures and workpieces. This necessitates the development of material models which take this phenomenon into account. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献