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51.
The purpose of this study was to examine the suitability of polystyrene-coated (PS-coated) microcapsules of drug-resin complex
for achieving prolonged release of diltiazem-HCl, a highly water-soluble drug, in simulated gastric and intestinal fluid.
The drug was bound to Indion 254, a cation-exchange resin, and the resulting resinate was microencapsulated with PS using
an oil-in-water emulsion-solvent evaporation method. The effect of various formulation parameters on the characteristics of
the microcapsules was studied. Mean diameter and encapsulation efficiency of the microcapsules rose with an increase in the
concentration of emulsion stabilizer and the coat/core ratio, while the same characteristics tended to decrease with an increase
in the volume of the organic disperse phase. The desorption of drug from the uncoated resinate was quite rapid and independent
of the pH of the dissolution media. On the other hand, the drug release from the microcapsules was prolonged for different
periods of time depending on the formulation parameters and was also found to be independent of the pH of the dissolution
media. Both the encapsulation efficiency and the retardation of drug release were found to be dependent on the uniformity
of coating, which in turn was influenced by the formulation parameters. Kinetic studies revealed that the desorption of drug
from the resinate obeyed the typical particle diffusion process, whereas the drug release from the microencapsulated resinate
followed the diffusion-controlled model in accordance with the Higuchi equation. PS appeared to be a suitable polymer to provide
prolonged release of diltiazem independent of the pH of the dissolution media. 相似文献
52.
Generally less glycosylation or deglycosylation has a detrimental effect on enzyme activity and stability. Increased production and secretion of cellobiase was earlier obtained in the presence of the glycosylation inhibitor 2-deoxy-d-glucose in filamentous fungus Termitomyces clypeatus [Mukherjee, S.; Chowdhury, S.; Ghorai, S.; Pal, S.; Khowala, S. Biotechnol. Lett.2006, 28, 1773-1778]. In this study the enzyme was purified from the culture medium by ultrafiltration and gel-permeation, ion-exchange and high-performance liquid chromatography, and its catalytic activity was six times higher compared to the control enzyme. Km and Vmax of the purified enzyme were measured as 0.187 mM and 0.018 U mg−1, respectively, using pNPG as the substrate. The enzyme had temperature and pH optima at 45 °C and pH 5.4, respectively, and retained full activity in a pH range of 5-8 and temperatures of 30-60 °C. Interestingly less glycosylated cellobiase was resistant towards proteolytic as well as endoglycosidase-H digestion and showed higher stability than native enzyme due to increased aggregation of the protein. The enzyme also showed higher specific activity in the presence of cellobiose and pNPG and less susceptibility towards salts and different chemical agents. The β-glucosidase can be considered as a potentially useful enzyme in various food-processing, pharmaceutical and fermentation industries. 相似文献
53.
Partial or complete dentures are more commonly constructed for the elderly group of the population. Teeth debonding from the dentures can be frustrating to the patients as well as the dentist. Research has been carried out and is continuing to study the issue of bonding acrylic teeth to the denture base resin. The present review takes into account the majority of research papers published in the last five decades for determining the bond strength. Selection of more compatible combinations of denture base resins and acrylic teeth may reduce the number of prosthesis fractures and the resultant repairs. 相似文献
54.
Integrated antiherbivore, antidesiccant and ultraviolet screening properties of creosotebush resin 总被引:2,自引:0,他引:2
David F. Rhoades 《Biochemical Systematics and Ecology》1977,5(4):281-290
The surface leaf resin of creosotebush, Larrea spp. (Zygophyllaceae) exhibits antiherbivore, antidesiccant and UV screening properties. Composed mainly of monomeric phenolic aglycones, the resin absorbs most radiation of wavelength shorter than 410 nm, reduces the rate of evaporative water loss across cellulose membrane and exhibits tannin-like protein-complexing and digestibility-reducing properties. Leaf-chewing insects prefer mature leaves which have a lower resin content than young leaves. A phenoloxidaes system present in the leaves probably enhances the digestibility-reducing action of resin on in vitro proteolysis and growth-rates of Astroma quadrilobatum (Orthoptera: Proscopiidae) are negatively correlated with resin-phenoloxidase activity as measured by macerated leaf oxygen demand. Non-ideal behaviour of the resin is suggestive of cooperative action between components. 相似文献
55.
doi: 10.1111/j.1741‐2358.2011.00573.x Effect of long‐term water immersion on the fracture toughness of denture base and reline resins purpose: This study evaluated the fracture toughness (FT) of one denture base (Lucitone 550 – L) and four hard reline resins [Ufi Gel Hard (UH), Tokuyama Rebase II (TR), New Truliner (NT) and Kooliner (K)], and the effect of long‐term water storage on this property. Materials and methods: Forty specimens (40 × 8 × 4 mm) of each material were made, and FT was assessed after polymerisation (control of reliners), after 48 ± 2 h in water at 37°C (control of denture base resin) and after storage in water at 37°C for 7, 90 or 180 days (all materials). Data (MPa.m1/2) were analysed by two‐way anova and Games–Howell test (p = 0.05). Results: Resin L exhibited the highest FT mean values. After 180 days of storage, FT mean values of L (3.37), UH (1.53) and K (1.20) were higher than those of the other periods. FT mean values of NT decreased from control (1.63) to 7 days (1.30) and then remained constant. FT mean values of TR (1.13) were similar in all periods of analysis. Conclusion: The denture base resin L showed higher FT mean values than the reline resins. Long‐term water storage increased the FT of L, UH and K, reduced the FT of NT and did not influence the FT of TR. 相似文献
56.
doi: 10.1111/j.1741‐2358.2010.00473.x Influence of artificial accelerated ageing on the colour stability of paints used for ocular prosthesis iris painting Objectives: To evaluate the colour stability of paints used for ocular prosthesis iris painting submitted for accelerated artificial ageing (AAA). Materials and methods: Forty specimens of acrylic resin for sclera (16 × 2 mm) were made and separated into eight groups (n = 10) according to the type of paint (gouache, GP; oil, OP; acrylic AP; and composite resin for characterisation, CR) and the colours used (blue/brown). After drying (72 h), a new layer of colourless acrylic resin was applied and the initial colour readout was performed (Spectrophotometer PCB 6807). New colour readouts were performed after AAA, and ΔE was calculated. Results: Statistical analysis (two‐way anova –Bonferroni, p < 0.05) demonstrated that the brown colour showed lower ΔE means in comparison with the blue colour, with statistically significant difference for AP only. Blue colour showed no statistically significant difference with regard to the type of paint used. Brown AP showed lower ΔE than the other groups, with significant difference for OP and GP. GP showed greater alteration in ΔE for the brown colour, being statistically similar only to OP. Conclusions: Only the AP group for brown pigment shows clinically acceptable values for colour stability after AAA. 相似文献
57.
doi: 10.1111/j.1741‐2358.2010.00397.x Prevention of trauma to edentulous ridge from opposing natural teeth Objective: To suggest a technique to prevent trauma of the edentulous ridge from opposing natural or restored teeth. Background: The prevalence of the condition where one edentulous arch opposes a natural or restored dentition is quite common. In most of cases, the maxillary arch is completely edentulous and either all teeth or only anterior teeth are present in the mandibular arch. These remaining teeth may continuously cause trauma to the opposing edentulous ridge during the night when a removable prosthesis is kept out of the mouth. Materials and methods: A thermoplastic acrylic resin mouthguard was fabricated on a cast of the remaining teeth dentition. Conclusion: This article presents a simple and inexpensive procedure to prevent self‐induced trauma of the edentulous ridge from opposing natural teeth by using a thermoplastic acrylic resin mouthguard. 相似文献
58.
Claudia U. Hjørringgaard Andreas Brust Paul F. Alewood 《Journal of peptide science》2012,18(3):199-207
Benzotriazole‐based coupling reagents have dominated the last two decades of solid phase peptide synthesis. However, a growing interest in synthesizing complex peptides has stimulated the search for more efficient and low‐cost coupling reagents, such as COMU which has been introduced as a nonexplosive alternative to the classic benzotriazole coupling reagents. Here, we present a comparative study of the coupling efficiency of COMU with the benzotriazole‐based HBTU and HCTU for use in in situ neutralization Boc‐SPPS. Difficult sequences, such as ACP(65–74), Jung–Redeman 10‐mer, and HIV‐1 PR(81–99), were used as model target peptides on polystyrene‐based resins, as well as polyethylene glycol‐based resins. Coupling yields obtained using fast in situ Boc‐SPPS cycles were determined with the quantitative ninhydrin test as well as via LC‐MS analysis of the crude cleavage products. Our results demonstrate that COMU coupling efficiency was less effective compared to HBTU and HCTU with HCTU ≥ HBTU > COMU, when polystyrene‐based resins were employed. However, when the PEG resin was employed in combination with a safety catch amide (SCAL) linker, more comparable yields were observed for the three coupling reagents with the same ranking HCTU ≥ HBTU > COMU. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd. 相似文献
59.
对海洋真菌Xylariasp.(No.2508)生产xyloketa]B的摇瓶发酵过程进行了初步优化。结果表明,Xylariasp.(No.2508)在培养120h时xyloketalB产量最高,当培养168h后菌体进入衰亡期且xyloketalB迅速降解,因此Xylariasp.(No.2508)生产xyloketalB的最适发酵周期为120h;Xylariasp.(No.2508)合成xyloketalB的过程及用乙酸乙酯萃取xyloketalB的过程对pH非常敏感,其中最适xyloketalB生产的发酵液初始pH为5.7,利用乙酸乙酯萃取xyloketalB时的发酵液最适pH为3。0;最适接种量为10%(v/v);接种前发酵液中加入10g/L的大孔树脂XAD-16可以降低某些代谢产物对xyloketalB合成的抑制作用,从而使产量提高2倍左右,而菌体进入稳定期以后加入大孔树脂XAD-16对产物产量没有影响。 相似文献
60.
阴离子交换晶胶层析分离质粒DNA 总被引:1,自引:0,他引:1
质粒DNA(pDNA)作为重要的基因治疗药物载体,其广泛应用受纯度和产量的限制。为了获得高纯度的pDNA,首先制备超大孔连续床晶胶基质,接枝二乙氨基乙基葡聚糖得到阴离子交换型晶胶介质;然后以pUC19质粒为例,将目标质粒转化至大肠杆菌,培养收集,碱液裂解和离心;最后用阴离子交换型晶胶介质从离心上清液中一步法层析分离pDNA。通过优化层析过程的pH值和洗脱条件,最终在pH值为6.6时,用0.5 mol/L的NaCl溶液洗脱,得到较高纯度的pDNA。整个分离过程中不使用动物源性酶,也不需常规分离中的高毒试剂,使获得pDNA的过程和产物更加安全。 相似文献