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101.
Ahmad Firdaus B. Lajis Mahiran Basri Rosfarizan Mohamad Muhajir Hamid Siti Efliza Ashari Nurazwa Ishak Azulia Zookiflie Arbakariya B. Ariff 《Chemical Papers》2013,67(6):573-585
In this paper, enzymatic methods for the synthesis of 5-hydroxy-2-(hydroxymethyl)-4H-pyran-4-one (kojic acid) esters are reviewed. Important process parameters related to the synthesis of kojic acid esters such as the type of immobilized lipase, solvent, temperature, initial water activity, water content, pH, metal salts, enzyme loading, substrates mole ratio, and acyl donors are highlighted and discussed. The properties of kojic acid esters related to their solubility, stability, cytotoxicity, depigmenting activity, tyrosinase inhibitory, metal-chelating, anti-oxidant, and other biological activities are also highlighted. At present, kojic acid and its esters are widely used in cosmetic and skin health industries as skin whitening agents. The advantages and disadvantages of various kojic acid esters are compared and possible industrial applications of these derivatives are also discussed. 相似文献
102.
Hua Nong Ting See Yan Chia Badrulzaman Abdul Hamid Siti Zamratol-Mai Sarah Mukari 《Journal of voice》2011,25(6):e305
The acoustic characteristics of sustained vowel have been widely investigated across various languages and ethnic groups. These acoustic measures, including fundamental frequency (F0), jitter (Jitt), relative average perturbation (RAP), five-point period perturbation quotient (PPQ5), shimmer (Shim), and 11-point amplitude perturbation quotient (APQ11) are not well established for Malaysian Malay young adults. This article studies the acoustic measures of Malaysian Malay adults using acoustical analysis. The study analyzed six sustained Malay vowels of 60 normal native Malaysian Malay adults with a mean of 21.19 years. The F0 values of Malaysian Malay males and females were reported as 134.85 ± 18.54 and 238.27 ± 24.06 Hz, respectively. Malaysian Malay females had significantly higher F0 than that of males for all the vowels. However, no significant differences were observed between the genders for the perturbation measures in all the vowels, except RAP in /e/. No significant F0 differences between the vowels were observed. Significant differences between the vowels were reported for all perturbation measures in Malaysian Malay males. As for Malaysian Malay females, significant differences between the vowels were reported for Shim and APQ11. Multiethnic comparisons indicate that F0 varies between Malaysian Malay and other ethnic groups. However, the perturbation measures cannot be directly compared, where the measures vary significantly across different speech analysis softwares. 相似文献
103.
Phase behavior and crystal morphology in poly(ethylene succinate) biodegradably modified with tannin
Siti Nurkhamidah Eamor M. Woo I-Han Huang Chean C. Su 《Colloid and polymer science》2011,289(14):1563-1578
Specific interactions, growth kinetics, and dendritic morphology in poly(ethylene succinate) (PESu) biodegradably modified
with various contents of tannic acid (TA) were characterized using differential scanning analysis, Fourier-transform infrared
(FTIR) spectroscopy, polarized-light optical microscopy, and atomic force microscopy. Strong interactions and highly retarded
growth between PESu and a macromolecular ester with polyphenol groups, TA, interaction-induced highly retarded growth rates
for the PESu/TA (80:20) composition are proven to lead to single-crystal-like dendrites when crystallized at high crystallization
temperature (T
c). At T
c = 70 °C, the growth rate for neat PESu is 12 μm/min while it is dramatically depressed to one tenth-fold at 1.5 μm/min with
20 wt.% TA in the blend. Strong specific interactions between the carbonyl group of polyesters and the phenolic hydroxyl group
of TA are confirmed by (1) the blend’s glass transition temperature (T
g)–composition relationship exhibits a sigmoidal curve, well fitted by the Kwei T
g model for miscible blends with large negative q = −90; (2) thermal analysis on crystal melting revealed an interaction parameter χ = −0.64 between PESu and TA; and (3) IR peak shifting analyzed using two-dimensional FTIR technique. A comparative blend
of another polyester poly(hexamethylene sebacate) with TA, lacking the specific interactions, does not exhibit such single
crystals upon similar melt crystallization. 相似文献
104.
Y. Abu Muhanna Rosihan M. Ali Zhen Chuan Ng Siti Farah M. Hasni 《Journal of Mathematical Analysis and Applications》2014
The class consisting of analytic functions f in the unit disk satisfying f+αzf′+γz2f″ subordinated to some function h is considered. The Bohr radius for this class is obtained when h is respectively convex or starlike. The Bohr radius for analytic functions mapping the unit disk into a concave-wedge domain as well as for bounded harmonic mappings are also established. 相似文献
105.
106.
Yana Cahyana Yunita Safriliani Eka Putri Dian Siti Solihah Farrah Shabira Lutfi Randah Miqbil Alqurashi Herlina Marta 《Molecules (Basel, Switzerland)》2022,27(22)
Pickering emulsions are emulsion systems stabilized by solid particles at the interface of oil and water. Pickering emulsions are considered to be natural, biodegradable, and safe, so their applications in various fields—such as food, cosmetics, biomedicine, etc.—are very promising, including as a vehicle for essential oils (EOs). These oils contain volatile and aromatic compounds and have excellent properties, such as antifungal, antibacterial, antiviral, and antioxidant activities. Despite their superior properties, EOs are prone to evaporation, decompose when exposed to light and oxygen, and have low solubility, limiting their industrial applications. Several studies have shown that EOs in Pickering emulsions displays less sensitivity to evaporation and oxidation, stronger antibacterial activity, and increased solubility. In brief, the application of Pickering emulsions for EOs is interesting to explore. This review discusses recent progress in the application of Pickering emulsions, particularly as EO carriers, drug carriers, antioxidant and antimicrobial carriers, and in active packaging. 相似文献
107.
Siti Sarah Abdul Rahman Daisuke Kawaguchi Daisaku Ito Atsushi Takano Yushu Matsushita 《Journal of Polymer Science.Polymer Physics》2009,47(22):2272-2280
The phase behavior of statistical copolymers composed of (4‐tert‐butylstyrene) (B) and (4‐tert‐butoxystyrene) (O), abbreviated as s‐BO, with polyisoprene (I) was investigated by optical microscopic (OM) observation and small‐angle neutron scattering (SANS) measurements. It has been known that B/I blend shows lower critical solution temperature (LCST) type phase diagram, while O/I blend has upper critical solution temperature (UCST) type one. Several blends of s‐BOs having mol fraction of B, mB, comparable to 0.50, with I showed both UCST and LCST type phase diagram. Furthermore, UCST type phase behavior was observed for blends having small mB, while LCST type one was for that of large mB at all used temperatures. Hence, the phase behavior of s‐BO/I blend can be understood as a result of the competition of two interactions having opposite temperature dependence. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2272–2280, 2009 相似文献
108.
Siti Aminah Omar Thahira B. S. A. Ravoof M. Ibrahim M. Tahir K. A. Crouse 《Transition Metal Chemistry》2014,39(1):119-126
Four new Schiff bases containing N and S heteroatoms (HL1–HL4) have been prepared and characterized, including determination of the X-ray crystal structures of HL1 and HL3. Spectroscopic evidence indicates that these Schiff bases behave as uninegatively charged tridentate NNS ligands in complexes of general formula [Cu(Ln)sac] (Ln is the anionic form of NNS, and sac represents saccharinate anion). Crystals of both HL1 and [Cu(L4)sac)(H2O)]·Hsac crystallized in triclinic system with P $ \bar{1} $ space group, while HL3 crystallized in monoclinic system with P 21/c space group. [Cu(L4)sac)(H2O)]·Hsac has a distorted square-pyramidal structure with a non-bonded saccharin molecule present in the outer coordination sphere. The tridentate NNS ligands are coordinated to Cu through pyridine nitrogen, azomethine nitrogen and thiolate sulfur atoms, while the fourth and fifth coordination positions are occupied by the N-bonded saccharinate anion and a water ligand, respectively. 相似文献
109.
110.
Suvik Assaw Muhammad Isyraq Hazim Mohd Amir Tyng Tyng Khaw Kamariah Bakar Siti Aisha Mohd Radzi 《Natural product research》2020,34(16):2403-2406
Abstract Mangrove plants are endowed with various biologically active compounds which have potent antibacterial and antioxidant properties. In present study, a bioactivity-guided fractionation for antibacterial and antioxidant active metabolites from the twigs of Avicennia officinalis collected from Kuala Selangor Nature Park, Selangor, Malaysia gave 13 major fractions. The antibacterial activity of A. officinalis fractions using well-diffusion showed strong selectivity on the Gram-positive bacteria (Staphylococcus epidermidis, S. aureus and Bacillus subtilis) with minimum inhibition concentration (MIC) values of 0.156-5.00?mg/mL. However, no antibacterial activities were observed on the Gram-negative bacteria (Vibrio cholera, Enterobacter cloacae and Escherichia coli). The active antibacterial fractions were further isolated using several chromatographic techniques to give two naphthofuranquinones, namely, avicenol C (1) and stenocarpoquinone B (2). Meanwhile, the antioxidant activity of A. officinalis fractions were evaluated using DPPH radical scavenging assay exhibited low antioxidant activities. Molecular structure of the naphthofuranquinones was elucidated using 1?D and 2?D NMR spectroscopy. 相似文献