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Pham Van Quyet Bernice Mei Jin Tan Celine Valeria Liew Lai Wah Chan Quan Sing Ng 《Drug development and industrial pharmacy》2018,44(4):624-631
L-NG-nitroarginine (LNNA), an analog of L-arginine, is a competitive inhibitor of nitric oxide synthase which causes the selective reduction of blood flow to tumor cells. Despite the potential of LNNA to function as an adjuvant in cancer therapies, its poor solubility and stability have hindered the development of an injectable formulation of LNNA that is suitable for human administration. This work, for the first time, details a systematic study on the determination of equilibrium Ka constants and the rate law of LNNA degradation. The four Ka values of LNNA were determined to be 1.03, 1.10?×?10?2, 2.51?×?10?10, and 1.33?×?10?13 M. From the kinetic and equilibrium studies, we have shown that the deprotonated form of LNNA is the main form of LNNA that undergoes degradation in aqueous media at room temperature. The rate law of LNNA degradation was found to be first order with respect to OH? concentration and first order with respect to LNNA? concentration. The rate constant at 25?°C and 1?atm was determined to be 0.04453 M?1min?1. A base catalyzed mechanism of LNNA degradation was proposed based on the kinetic study. The mechanism was found to be very useful in explaining the discrepancies and changes of the rate law at different pH values. It is thus recommended that LNNA should be formulated as a concentrated solution in acidic conditions for maximum chemical stability during storage and be diluted with a basic solution to near physiological pH just before administration. 相似文献
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This article focuses on controlling the morphology of regenerated cellulose aerogel (RCA) and its application as a template for the preparation of functional cellulose nanoparticles (FCNPs). RCA is prepared by lyophilizing cellulose hydrogel which is fabricated through a sol–gel method in sodium hydroxide (NaOH)/urea aqueous solution. The morphology of RCA is adjusted by varying the gelation temperature and time. With the gelation temperature and time increasing, lamellar RCA transforms into strings of cellulose nanoparticles. Subsequently, RCA with the morphology of "strings of nanoparticles" is modified through the bulk condensation of l -lactic acid and RCA. Eventually, the prepared functionalized RCA (FRCA) is dispersed in an organic solvent to obtain purified FCNPs. The results demonstrate that single FCNP can be obtained by dispersing FRCA in dimethyl sulfoxide. Moreover, the prepared FCNPs have uniform size, good thermal-stability, and increasing hydrophobicity, which are ideal candidates for polymer composites in terms of fillers. 相似文献
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为了研究大气条件下,正焦移距离对冲量耦合系数的影响,采用能量为15.7(16%)J 的激光脉冲聚焦于铝靶前端,通过改变激光焦点距离靶面的位置,获得了冲量耦合系数与正焦移距离的对应关系。结果表明脉冲激光在与大气环境中的铝靶相互作用时,靶面通过能量转移获得的冲量耦合系数与激光焦点距离靶面的位置呈非单调性变化。焦移距离在从0~20 mm 之间变化时,获得的冲量耦合系数从4.4810-5 Ns/J 连续下降到1.6810-5Ns/J,随着焦移距离的进一步增大,冲量耦合系数在20~35 mm 间呈缓慢上升趋势,在35 mm 处升至2.2110-5 Ns/J 后转而下降,在45 mm 处降至1.9110-5Ns/J。文中采用大气中激光支持爆轰波与固体靶面相互作用的二维模型对上述物理过程进行理论计算,获得了与实验结果较为一致的结论。 相似文献
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Polarization and related properties in the M‐type lead hexaferrite (PbFe12O19) are reported for the first time. The remnant polarization of PbFe12O19 exhibits a maximum value of 104 μC/cm2, as well as large spontaneous polarization at room temperature. Annealing of PbFe12O19 in oxygen plays a key role in the saturation of its polarization hysteresis loop because it greatly enhances the ceramic's electric resistance. Two current peaks in the I–V curve reveal a polarization switch, providing effective evidence for the ferroelectricity of PbFe12O19. Its temperature‐dependent dielectric constant undergoes colossal change in the vicinity of two temperatures (322°C and 518°C), which are assigned to the transitions from ferro‐ to antiferro‐ and antiferro‐ to paraelectric phases, respectively. The plots of logarithm of (1/ε–1/εm) as a function of logarithm of (T–Tm) obey a modified Curie–Weiss law, verifying the relaxor ferroelectric characterization of PbFe12O19. The ceramic also exhibits a strong magnetic hysteresis loop. These combined functional responses of ferroelectricity and ferromagnetism in PbFe12O19 ceramic present an opportunity to create electric devices that actively couple the magnetic and ferroelectric orders. 相似文献
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