共查询到20条相似文献,搜索用时 15 毫秒
1.
Blends of bacterial poly((R)-3-hydroxybutyrate) (PHB) and poly(l-lactic acid) (PLLA) synthesized by polycondensation of l-lactic acid or by ring-opening polymerization of l-lactide were studied. Miscibility was investigated through both conventional differential scanning calorimetry (DSC) and
temperature-modulated DSC (TMDSC). PHB and low-molar mass PLLA were miscible in a whole concentration range, and a single
glass transition temperature was observed. On the other hand, PHB/high-molar mass PLLA mixtures phase separate, giving rise
to two glass transition temperatures corresponding to PHB and PLLA. A treatment of blends at 190 °C leads to formation of
block/multiblock/random copolymers, and blends become miscible. 相似文献
2.
Jorge Luis Escobar Ivirico Manuel Salmerón-Sánchez José Luis Gómez Ribelles Manuel Monleón Pradas 《Colloid and polymer science》2009,287(6):671-681
A poly(l-lactide) diol was obtained through ring opening polymerization of l-lactide, using 1,6 hexanediol and tin(II) 2 ethylhexanoate as a catalyst. In the second step, the poly(l-lactide) macromer (mLA) was obtained by the reaction of poly(l-lactide) diol with methacrylic anhydride. The effective incorporation of the polymerizable end groups was assessed by Fourier
transform infrared spectroscopy and nuclear magnetic resonance (1H NMR). Besides, poly(l-lactide) networks (pmLA) were prepared by photopolymerization of mLA. Further, the macromer was copolymerized with 2-hydroxyethyl
acrylate seeking to tailor the hydrophilicity of the system. A set of hydrophilic copolymer networks were obtained. The phase
microstructure of the new system and the network architecture was investigated by differential scanning calorimetry, infrared
spectroscopy, dynamic mechanical spectroscopy, thermogravimetry, and water sorption studies. 相似文献
3.
Hasegawa H Fukushima T Lee JA Tsukamoto K Moriya K Ono Y Imai K 《Analytical and bioanalytical chemistry》2003,377(5):886-891
d-Lactic and l-lactic acids were simultaneously determined by means of a column-switching high-performance liquid chromatography (HPLC) with fluorescence detection. As a fluorescence reagent, 4-nitro-7-piperazino-2,1,3-benzoxadiazole (NBD-PZ) was employed for the fluorescence derivatization of lactic acid. The proposed HPLC system adopted both octylsilica (Cadenza CD-C8) and amylose-based chiral columns (CHIRALPAK AD-RH), which proved to give a sufficient enantiomeric separation of the lactic acid derivatives with a separation factor () of 1.32 and a resolution (Rs) of 1.98. Moreover, the features of the first elution of d-lactic acid peak in the proposed HPLC were convenient for the determination of trace amount of serum d-lactic acid, which is known to increase under diabetes. Intra-day and inter-day accuracies were in the range of 90.5–101.2 and 89.0–100.7%, and the intra-day and inter-day precisions were 0.3–1.2 and 0.4–4.8%, respectively. The proposed method was applied to determine d-lactic and l-lactic acids in human serum of normal subjects and diabetic patients, showing that both d-lactic and l-lactic acid concentrations were significantly increased in the serum of diabetic patients (n=31) as compared with normal subjects (n=21). This fact was found for the first time owing to the development of the proposed HPLC method which is able to determine d-lactic and l-lactic acid simultaneously. Finally, serum d-lactic acid concentrations determined by the proposed HPLC method were compared with those from a reported enzymatic assay, and the smaller p value between normal subjects and diabetic patients was shown by the proposed HPLC method. 相似文献
4.
C. G. Mothé A. D. Azevedo W. S. Drumond S. H. Wang 《Journal of Thermal Analysis and Calorimetry》2010,101(1):229-233
Samples of poly(l,l-lactide)-block-poly(ethylene glycol)-block-poly(l,l-lactide) (PLLA-PEG-PLLA) were synthesized from l,l-lactide polymerization using stannous 2-ethylhexanoate, Sn(Oct)2 as initiator and di-hydroxy-terminated poly(ethylene glycol) (PEG) (M
n
= 4000 g mol−1) as co-initiator. The chemical linkage between the PEG segment and the PLA segments was characterized by Fourier transform
infrared spectroscopy (FTIR). Thermogravimetry analysis (TG) revealed the copolymers composition and was capable to show the
deleterious effect of an excess of Sn(Oct)2 in the polymer thermal stability, while Differential Scanning Calorimetry (DSC) allowed the observation of the miscibility
between the PLLA and PEG segments in the different copolymers. 相似文献
5.
Ya-Ting Hsieh Nai-Tzu Kuo Eamor M. Woo 《Journal of Thermal Analysis and Calorimetry》2012,107(2):745-756
Abstract
Thermal behavior, miscibility, and crystalline morphology in blends of low-molecular-weight poly(l-lactic acid) (LMw-PLLA) or high-molecular-weight PLLA (HMw-PLLA) with various polyesters such as poly(butylene adipate) (PBA), poly(ethylene adipate) (PEA), poly(trimethylene adipate) (PTA), or poly(ethylene succinate) (PESu), respectively, were explored using differential scanning calorimeter (DSC), and polarized-light optical microscopy (POM). Phase behavior in blends of PLLA with other polyesters has been intriguing and not straight forward. Using a low- and high molecular weight PLLA, this study aimed at mainly using thermal analyses for probing the phase behavior, phase diagrams, and temperature dependence of blends systems composed of PLLA of two different molecular weights (low and high) with a series of aliphatic polyesters of different structures varying in the (CH2/CO) ratio in main chains. The blends of LMw-PLLA/PEA and LMw-PLLA/PTA show miscibility in melt and amorphous glassy states. Meanwhile, the LMw-PLLA/PESu blend is immiscible with an asymmetry-shaped upper critical solution temperature (UCST) at 220–240 °C depending on the blend composition. In contrast to miscibility in LMw-PLLA/PTA and LMw-PLLA/PEA blends, HMw-PLLA with polyesters are mostly immiscible; and HMw-PLLA/PTA blend is the only one showing an asymmetry-shaped UCST phase diagram with clarity points at 195–235 °C (depending on composition). Reversibility of UCST behavior, with no chemical transreactions, in these blends was proven by solvent recasting, gel permeation chromatography, and Fourier transform infrared spectroscopy (FT-IR). Crystalline morphology behavior of the LMw-PLLA/PEA and LMw-PLLA/PTA blends furnishes addition evidence for miscibility in the amorphous phase between LMw-PLLA and PTA or PEA. 相似文献6.
Endo H Hayashi Y Kitani Y Ren H Hayashi T Nagashima Y 《Analytical and bioanalytical chemistry》2008,391(4):1255-1261
l-Lysine (l-Lys) in living bodies is critical for metabolism; therefore, determination of its levels in food is important. Most enzymatic
methods for l-Lys analysis are performed using l-lysine oxidase (LyOx), but commercially manufactured LyOx is generally not highly selective for l-Lys among amino acids. We previously isolated LyOx as an antibacterial protein secreted from the skin of the rockfish Sebastes schlegeli. In the present study, we developed an optical enzyme sensor system for rapid and continuous determination of l-Lys using this LyOx. The system comprised an immobilized LyOx membrane, an optical oxygen probe, a flow system, and a personal
computer. The amount of l-Lys was detected as a decrease in the oxygen concentration due to the LyOx reaction. The specificity of the sensor was examined
against various amino acids. The sensor response was specific for l-Lys. Good reproducibility was obtained in 58 assays. The response of the sensor using commercially prepared LyOx was unstable
compared with the response using LyOx isolated in our laboratory. Our sensor system could be used for 5 weeks without our
having to change the enzyme membrane. The calibration curve for a standard l-Lys solution was linear from 0.1 to 3.0 mmol L−1. One assay could be completed within 2 min. The sensor was applied to determine the l-Lys content in food samples such as bonito cooking water and scallop hepatopancreas. The values obtained using the sensor
and conventional high-performance liquid chromatography methods were well correlated. 相似文献
7.
Hatanaka T Usuki H Arima J Uesugi Y Yamamoto Y Kumagai Y Yamasato A Mukaihara T 《Applied biochemistry and biotechnology》2011,163(7):836-844
l-Asparaginase (ASNase) has proved its use in medical and food industries. Sequence-based screening showed the thermophilic
Streptomyces strain Streptomyces thermoluteus subsp. fuscus NBRC 14270 (14270 ASNase) to positive against predicted ASNase primary sequences. The 14270 ASNase gene and four l-asparaginase genes from Streptomyces coelicolor, Streptomyces avermitilis, and Streptomyces griseus (SGR ASNase) were expressed in Streptomyces lividans using a hyperexpression vector: pTONA5a. Among those genes, only 14270 ASNase and SGR ASNase were successful for overexpression and detected in culture supernatants
without an artificial signal peptide. Comparison of the two Streptomyces enzymes described above demonstrated that 14270 ASNase was superior to SGR ASNase in terms of optimum temperature, thermal
stability, and pH stability. 相似文献
8.
The structural transition of the l- and dl forms of poly(N-(1- hydroxymethyl)propylmethacrylamide (PHMPMA) in aqueous solution was studied by measuring the pressure dependence of the apparent scattering intensity, differential scanning calorimetry (DSC), and circular dichroism (CD). The thermodynamic implications of the results are discussed in relation to the chiral structure of the side chain, and differences in the thermal and barometric transitions. T-P diagrams of the transition showed characteristic ellipsoid features. Antagonism of the temperature and pressure effects was observed only for P(dl-HMPMA). For P(l-HMPMA), the transition temperature (T
tr) decreased with increasing pressure, and the highest T
tr was observed at atmospheric pressure (0.1 MPa). For both polymers, the highest P
trs were observed at the lowest temperatures. The l polymer showed a specific negative peak in its CD spectrum at around 220 nm in the lower temperature region and the temperature dependence was reproduced by a single-step transition, with the midpoint corresponding to the T
tr obtained from the scattering measurements. Coupled with the results from the DSC, the different behavior between the P(l-HMPMA) and P(dl-HMPMA) could be explained in terms of the chain states before and after the transition. The cooperative factors derived from the DSC measurement revealed that about 4 to 5 polymers of the present size were necessary to perform a thermal transition for P(l-HMPMA), and that P(dl-HMPMA) underwent its transition as an almost single molecular event.This revised version was published online in June 2005 with correction to the article category. 相似文献
9.
Désirée L. Röhlen Johanna Pilas Michael J. Schöning Thorsten Selmer 《Applied biochemistry and biotechnology》2017,183(2):566-581
Three amperometric biosensors have been developed for the detection of l-malic acid, fumaric acid, and l -aspartic acid, all based on the combination of a malate-specific dehydrogenase (MDH, EC 1.1.1.37) and diaphorase (DIA, EC 1.8.1.4). The stepwise expansion of the malate platform with the enzymes fumarate hydratase (FH, EC 4.2.1.2) and aspartate ammonia-lyase (ASPA, EC 4.3.1.1) resulted in multi-enzyme reaction cascades and, thus, augmentation of the substrate spectrum of the sensors. Electrochemical measurements were carried out in presence of the cofactor β-nicotinamide adenine dinucleotide (NAD+) and the redox mediator hexacyanoferrate (III) (HCFIII). The amperometric detection is mediated by oxidation of hexacyanoferrate (II) (HCFII) at an applied potential of + 0.3 V vs. Ag/AgCl. For each biosensor, optimum working conditions were defined by adjustment of cofactor concentrations, buffer pH, and immobilization procedure. Under these improved conditions, amperometric responses were linear up to 3.0 mM for l-malate and fumarate, respectively, with a corresponding sensitivity of 0.7 μA mM?1 (l-malate biosensor) and 0.4 μA mM?1 (fumarate biosensor). The l-aspartate detection system displayed a linear range of 1.0–10.0 mM with a sensitivity of 0.09 μA mM?1. The sensor characteristics suggest that the developed platform provides a promising method for the detection and differentiation of the three substrates. 相似文献
10.
Only a single type of circular circumferential crack is conventionally reported for poly(l-lactic acid) (PLLA). In this study, PLLA samples were found to exhibit as many as four crack types of different directions
and patterns, which cannot be feasibly explained simply by the directional difference in coefficients of thermal expansion.
Depending on crystallization temperature (T
c), PLLA crystallizes into ringless or ring-banded spherulites, whereas the crack patterns are dramatically different in these
two types of spherulites. In ring-banded spherulites of PLLA crystallized at intermediate T
c, two uniquely different crack types are present: (1) twin circumferential cracks coinciding with the dark–bright and bright–dark
boundary and (2) radial short-segmental voids coinciding on the bright bands in spherulites. The radial short-segmental cracks
on the bright band of ring-banded spherulites may be caused by PLLA crystals of radial direction with various twisting that
contract laterally upon cooling. Only circumferential cracks are present in PLLA crystallized into ringless spherulites, where
concentric continuous circumferential cracks are present in the ringless spherulites at low T
c with finer lamellae, but discontinuous and irregular circumferential cracks are present in the ringless spherulites at high
T
c with coarse lamellae. Although all cracks are triggered by cooling from T
c, all evidences indicate that the crack patterns and types are highly associated with the lamellar orientation, patterns,
and coarseness in spherulites. 相似文献
11.
Shadpour Mallakpour Samaneh Soltanian Mohammad R. Sabzalian 《Colloid and polymer science》2011,289(1):93-100
A series of biodegradable functional amino-acid-based poly(ester-imide)s (PEI)s were designed and synthesized by the direct
polycondensation reaction of chiral diacids composed of naturally occurring α-amino acids with 4,4′-thiobis(2-tert-butyl-5-methylphenol) in the presence of tosyl chloride, pyridine, and N,N-dimethylformamide as a condensing agent. These new chiral polymers were characterized with respect to chemical structure
and purity using specific rotation experiments, FT-IR, 1H-NMR, techniques, and elemental analysis. The surface morphology of these polymers was investigated by field emission scanning
electron microscopy. The result indicated nanoscale morphology of the obtained polymers. Thermal stability and the weight
loss behavior of the resulting PEIs were studied by TGA techniques. All PEIs showed no significant weight loss below 400 °C
in a N2 environment. The monomers and prepared polymers were co-cultivated with airborne fungal spores in culture media to study
their biological activity. Soil burial test was also used for evaluation of their biodegradation behavior. The results showed
that the synthesized monomers and their derived polymers are biologically active and that their degradation products are probably
nontoxic to microbial growth. 相似文献
12.
Béatrice Nicolaï Nathalie Mahé René Céolin Ivo B. Rietveld Maria Barrio Josep-Lluis Tamarit 《Structural chemistry》2011,22(3):649-659
l-Tyrosine alkyl esters are used as prodrugs for l-tyrosine. Although prodrugs are often designed for their behavior in solution, understanding their solid-state properties is the first step in mastering drug delivery. The crystal structure of l-tyrosine methyl ester has been determined and compared to published structures of l-tyrosine and its ethyl and n-butyl esters. It is almost isostructural with the other esters: it crystallizes in the orthorhombic chiral space group P212121, a = 5.7634(15) Å, b = 12.111(2) Å, c = 14.3713(19) Å, V = 1003.1(4) Å3 with Z′ = 1. Their main packing motif is a C(9) infinite hydrogen-bond chain, but the conformation of l-tyrosine methyl ester is different from the other two: eclipsed versus U-shaped, respectively. The published structure of the ethyl ester, which was incomplete, has been confirmed by X-ray powder diffraction data. Because l-tyrosine methyl ester is very stable (28 years stored at room temperature), and its hydrolysis rate is relatively low, it should be one of the better prodrugs among the alkyl esters of tyrosine. 相似文献
13.
The integral enthalpies of dissolution Δsol
H
m of l-cysteine and l-asparagine in mixtures of water with acetonitrile and dimethyl sulfoxide at the concentration of organic solvent up to 0.32
molar fractions were measured by means of dissolution calorimetry. The standard enthalpies of dissolution (Δsol
H°) and transfer (Δtrans
H°) of the amino acids from water to a mixed solvent were calculated. The enthalpy coefficients of pair interactions for L-cysteine
and L-asparagine with cosolvent molecules are positive, except for the L-asparagine-water-acetonitrile system. The concepts
on the prevailing effect of specific interactions in solutions and the influence of the nature of the cosolvents and lateral
substituents of the amino acids on the thermochemical characteristics of dissolution were used to explain the data obtained. 相似文献
14.
P. A. Demakov S. A. Sapchenko D. G. Samsonenko D. N. Dybtsev V. P. Fedin 《Russian Chemical Bulletin》2018,67(3):490-496
Three new metal-organic coordination polymers were obtained namely, [Mn3(chdc)3-(NMP)2(DMF)2] (1, chdc2– is trans-1,4-cyclohexanedicarboxylate, NMP is N-methylpyrrolidone, DMF is N,N-dimethylformamide), [Zn3(chdc)3(NMP)2]?2NMP (2), and [Zn3(chdc)3(ur)-(DMF)0.5]?DMF (3, ur is the urotropine). The crystal structures of polymers 1, 2, and 3 were determined by single-crystal X-ray crystallography. All three compounds were found to contain a trinuclear secondary building unit {M3(OOC)6}. Coordination polymers 1 and 2 have a layered structure, while polymer 3 has a three-dimensional coordination framework with isolated pores formed due to the presence of urotropine bridging molecules. Compounds 1 and 3 were characterized by IR spectroscopy, thermogravimetric and elemental analysis data, powder X-ray diffraction. Compound 3 was also characterized by UV-Vis diffuse reflectance spectrum. 相似文献
15.
C. Alosious Gonsago Helen Merina Albert P. Malliga A. Joseph Arul Pragasam 《Journal of Thermal Analysis and Calorimetry》2012,107(3):1231-1235
A novel nonlinear optical semi-organic single crystal of l-histidine methyl ester dihydrochloride was grown by slow evaporation solution growth method at an ambient temperature. The
grown crystal was characterized by single crystal X-ray diffraction. Functional groups and the modes of vibrations were identified
by FT–IR spectroscopy. The chemical composition of the crystal was confirmed by Energy dispersive X-ray analysis. The optical
behavior of the crystal was examined by UV spectral analysis, which shows the absence of absorption between the wavelengths
ranging from 230 to 1000 nm. The optical band gap of the grown crystal was estimated and is found to be 5.35 eV. The thermal
behavior of the crystal was investigated by thermogravimetric and differential thermal analyses. The nonlinear optical property
of the grown crystal was confirmed by the powder technique of Kurtz and Perry. 相似文献
16.
A polychelate with poly(dl-aspartic acid) was prepared in order to study the influence of the polymer ligands on the copper(II) acetate monohydrate.
This compound was characterized by elemental analysis, magnetic susceptibility measurements, spectroscopy and thermal analysis.
It is suggested that in the unit Cu2(acetate)4 the breakage of two acetate groups occurs by the effect of polymer ligand group coordination. It coordinates through a carboxylate
group, keeping the water molecules coordinated to CuII. A magnetic moment of the polychelate is observed which presents a value of 1.74 M.B, which corresponds to uncorrelated Cu2+ (S = 1/2) spins, separated by large Cu–Cu distances.
According to the suggested structure, PM3 semi-empirical calculations of the polychelate of CuII were done. 相似文献
17.
A. A. Titov A. F. Smol´yakov A. N. Rodionov I. D. Kosenko E. A. Guseva Ya. V. Zubavichus P. V. Dorovatovskii O. A. Filippov E. S. Shubina 《Russian Chemical Bulletin》2017,66(9):1563-1568
New tri- and tetranuclear macrocyclic silver(i) and copper(i) 3-ferrocenyl-5-(trifluoromethyl)pyrazolates were prepared: [{(3-((η5-C5H4)Fe(η5-C5H5))-5-(CF3)-Pz}M]3 (M = Cu (1), Ag (2)) and [{(3-(( η5-C5H4)Fe(η5-C5H5))-5-(CF3)-Pz}Cu]4 (3). The structures of compounds were established by X-ray diffraction analysis. In the crystalline state, a planar trinuclear silver-containing macrocycliс pyrazolate and a saddle-shaped tetranuclear copper-containing macrocycle are formed. The introduction of a bulky substituent, ferrocene, into the pyrazole ligand results in complete shielding of the acidic metal sites, which precludes the coordination of base molecules. 相似文献
18.
Ni-Ning Hong Guang Yang Jian Li Yao-Ping Zhang 《Applied biochemistry and biotechnology》2009,158(2):398-407
A genetically engineered Escherichia coli was developed as the source of enzyme for rapidly quantifying glutamine. E. coli BL21 (DE3) cells overexpressing a glutamine synthetase from Bacillus subtilis were prepared as tube aliquots and used in a small volume of nontoxic mixture. The current method was compared to high performance
liquid chromatography analysis, Sigma kit (GLN-1) and Mecke method. The method is applicable to a wide range of glutamine
concentrations (0.05–2.5 mM) and correlates well to the detection results obtained from high performance liquid chromatography
(Pearson correlation is 0.978 at the 0.01 level). Moreover, the whole assay procedure takes less than 15 min and uses nontoxic
reagents, so it can be applied to monitor glutamine production and utilization conveniently. 相似文献
19.
Yodthong Baimark Mangkorn Srisa-ard Jirasak Threeprom Nual-Anong Narkkong 《Colloid and polymer science》2007,285(13):1521-1525
Nanoparticle colloids of methoxy poly(ethylene glycol)-b-poly(D,L-lactide) (MPEG-b-PDLL) diblock copolymer were prepared by a modified spontaneous emulsification solvent diffusion method using acetone/ethanol
as the mixture organic solvents. The MPEG-b-PDLL was synthesized by ring-opening polymerization of D,L-lactide using stannous octoate and MPEG with molecular weight of 5,000 g/mol as the initiating system. The MPEG-b-PDLL obtained was an amorphous polymer with molecular weight of 73,600 g/mol. Influences of acetone/ethanol (v/v) ratios
and Tween 80 surfactant concentrations on characteristics of the colloidal nanoparticles were investigated and discussed.
Light-scattering analysis showed that average diameters of the surfactant-free colloidal nanoparticles were in the range of
86–124 nm. The nanoparticle sizes decreased as the ethanol ratio increased. The Tween 80 did not show the significant effect
on the nanoparticle sizes. Scanning electron micrographs of dried nanoparticles that demonstrated the aggregation of most
particles suggested they were the soft nanoparticles. However, the dried nanoparticle morphology can be observed from scanning
electron microscopy as having a spherical shape and smooth surfaces. 相似文献
20.
l-asparaginase (LA) catalyzes the degradation of asparagine, an essential amino acid for leukemic cells, into ammonia and aspartate. Owing to its ability to inhibit protein biosynthesis in lymphoblasts, LA is used to treat acute lymphoblastic leukemia (ALL). Different isozymes of this enzyme have been isolated from a wide range of organisms, including plants and terrestrial and marine microorganisms. Pieces of information about the three-dimensional structure of l-asparaginase from Escherichia coli and Erwinia sp. have identified residues that are essential for catalytic activity. This review catalogues the major sources of l-asparaginase, the methods of its production through the solid state (SSF) and submerged (SmF) fermentation, purification, and characterization as well as its biological roles. In the same breath, this article explores both the past and present applications of this important enzyme and discusses its future prospects. 相似文献