Biomedical subjects

Xin Li

Publications and source records attributed to Xin Li.

At least 325 records · Page 18Linked to original sources

PubMed2002

Vaccines for Proteus mirabilis in urinary tract infection.

Proteus mirabilis is a documented cause of urinary tract infection (UTI) in the complicated urinary tract. Urease-mediated urea hydrolysis is responsible for both virulence of the organism and the ability to cause urolithiasis. A urease-negative mutant of P. mirabilis is unable to initiate stone formation and colonizes the kidney at a significantly lower rate. The considerable pathology caused by P. mirabilis warrants the development of a vaccine. We have initiated the advancement of vaccine studies and have determined that the MR/P fimbria, a surface adhesin of P. mirabilis, is a promising vaccine candidate. Successful vaccination would be expected both to prevent colonization by P. mirabilis and urolithiasis.

Bacterial Vaccines↗

PubMed2002

Treatment of occluded central venous catheters with alteplase: results in 1,064 patients.

PURPOSE: Thrombosis of central venous access devices (CVADs) is a relatively frequent complication. Alteplase (tissue plasminogen activator) has been used to salvage dysfunctional devices. The purpose of this study was to analyze the safety and efficacy of alteplase after administration of a maximum of two 2-mg/2-mL doses to thrombosed CVADs. MATERIALS AND METHODS: A combined analysis was performed of two pivotal prospective phase-III clinical trials (Cardiovascular thrombolytic to Open Occluded Lines [COOL] Trials) involving 80 centers enrolling patients from November 1999 through December 2000. Patients 2 years of age or older (with body weights >10 kg) with dysfunctional nondialysis CVADs were eligible, including those with peripherally inserted central catheters, apheresis catheters, and ports. Alteplase (2 mg/2 mL) was instilled into the lumen of the central venous catheter and allowed to dwell for as long as 120 minutes. For patients with body weights of 10-30 kg, 110% of the internal lumen volume of alteplase (2 mg/2 mL) was administered. If the device was still occluded after a maximum of 120 minutes, a second alteplase dose was given and allowed to dwell for as long as 120 minutes. The primary efficacy endpoint was designated as restored function after a maximum of two doses. The primary safety endpoint was intracranial hemorrhage (ICH) within 5 days. RESULTS: A total of 1,064 patients (465 men, 599 women; mean age, 50.7 y; range, 2-91 y) with dysfunctional catheters were treated. After alteplase administration, function was restored in 798 patients (75.0%; 95% CI: 72.3%, 77.6%) after one dose and 905 (85.1%; 95% CI: 82.8%, 87.2%) after two doses. Efficacy rates were similar among catheter types (single-, double-, and triple-lumen catheters, and ports). Serious adverse events monitored within 30 days of treatment included ICH (0.0%), embolic events (0.0%), gastrointestinal bleeding (0.3%), thrombosis (0.3%), and sepsis (0.4%). One event (fever) was attributed to the study drug. Efficacy was independent of age, sex, body weight, and catheter type. CONCLUSION: A regimen of as many as two 2-mg doses of alteplase is safe and effective for restoring flow to occluded central venous access devices.

Adolescent↗

PubMed2002

Identification of MrpI as the sole recombinase that regulates the phase variation of MR/P fimbria, a bladder colonization factor of uropathogenic Proteus mirabilis.

Proteus mirabilis is a common cause of urinary tract infection (UTI) in individuals with structural abnormalities or long-term catheterization. The expression of mannose-resistant/Proteus-like (MR/P) fimbria is phase variable because of the inversion of a 251 bp DNA fragment that carries the promoter for the mrp operon. Previous studies have shown that mrpI, which is transcribed divergently from the mrp operon, encodes a recombinase capable of switching the orientation of this invertible element. In this study, we constructed isogenic mrpI null mutants from a clinical isolate of P. mirabilis, HI4320. A polymerase chain reaction (PCR)-based invertible element assay revealed that the isogenic mrpI null mutants were locked in one phase, either expressing (locked on) MR/P fimbriae or not (locked off), which indicated that MrpI was the sole recombinase that regulated the phase variation of MR/P fimbria. The locked-on and locked-off mutants were evaluated for virulence in the CBA mouse model of ascending UTI by co-challenges with each other and with the wild-type strain. Results from these experiments demonstrated conclusively that the MR/P fimbria was a critical bladder colonization factor of uropathogenic P. mirabilis and also suggested that the ability to switch off the expression of MR/P fimbria might be important for kidney colonization.

Animals↗

PubMed2002

Visualization of Proteus mirabilis within the matrix of urease-induced bladder stones during experimental urinary tract infection.

The virulence of a urease-negative mutant of uropathogenic Proteus mirabilis and its wild-type parent strain was assessed by using a CBA mouse model of catheterized urinary tract infection. Overall, catheterized mice were significantly more susceptible than uncatheterized mice to infection by wild-type P. mirabilis. At a high inoculum, the urease-negative mutant successfully colonized bladders of catheterized mice but did not cause urolithiasis and was still severely attenuated in its ability to ascend to kidneys. Using confocal laser scanning microscopy and scanning electron microscopy, we demonstrated the presence of P. mirabilis within the urease-induced stone matrix. Alizarin red S staining was used to detect calcium-containing deposits in bladder and kidney tissues of P. mirabilis-infected mice.

Animals↗

PubMed2002

SNARE expression and localization in renal epithelial cells suggest mechanism for variability of trafficking phenotypes.

The apical- and basolateral-specific distribution of target soluble N-ethylmaleimide-sensitive factor attachment protein receptors (t-SNAREs) of the syntaxin family appear to be critical for polarity in epithelial cells. To test whether differential SNARE expression and/or subcellular localization may contribute to the known diversity of trafficking phenotypes of epithelial cell types in vivo, we have investigated the distribution of syntaxins 2, 3, and 4 in epithelial cells along the renal tubule. Syntaxins 3 and 4 are restricted to the apical and basolateral domains, respectively, in all cell types, indicating that their mutually exclusive localizations are important for cell polarity. The expression level of syntaxin 3 is highly variable, depending on the cell type, suggesting that it is regulated in concert with the cellular requirement for apical exocytic pathways. While syntaxin 4 localizes all along the basal and lateral plasma membrane domains in vivo, it is restricted to the lateral membrane in Madin-Darby canine kidney (MDCK) cells in two-dimensional monolayer culture. When cultured as cysts in collagen, however, MDCK cells target syntaxin 4 correctly to the basal and lateral membranes. Unexpectedly, the polarity of syntaxin 2 is inverted between different tubule cell types, suggesting a role in establishing plasticity of targeting. The vesicle-associated (v)-SNARE endobrevin is highly expressed in intercalated cells and colocalizes with the H(+)-ATPase in alpha- but not beta-intercalated cells, suggesting its involvement in H(+)-ATPase trafficking in the former cell type. These results suggest that epithelial membrane trafficking phenotypes in vivo are highly variable and that different cell types express or localize SNARE proteins differentially as a mechanism to achieve this variability.

Animals↗

PubMed2002

Cloning of cytochrome P-450 2C9 cDNA from human liver and its expression in CHL cells.

AIM: Using bacterial, yeast, or mammalian cell expressing a human drug metabolism enzyme would seem good way to study drug metabolism-related problems. Human cytochrome P-450 2C9(CYP2C9) is a polymorphic enzyme responsible for the metabolism of a large number of clinically important drugs. It ranks among the most important drug metabolizing enzymes in humans. In order to provide a sufficient amount of the enzyme for drug metabolic research, the CYP2C9 cDNA was cloned and expressed stably in CHL cells. METHODS: After extraction of total RNA from human liver tissue, the human CYP2C9 cDNA was amplified with reverse transcription-polymerase chain reaction (RT-PCR), and cloned into cloning vector pGEM-T. The cDNA fragment was identified by DNA sequencing and subcloned into a mammalian expression vector pREP9. A transgenic cell line was established by transfecting the recombinant vector of pREP9-CYP2C9 into CHL cells. The enzyme activity of CYP2C9 catalyzing oxidation of tolbutamide to hydroxy tolbutamide in S9 fraction of the cell was determined by high performance liquid chromatography(HPLC). RESULTS: The amino acid sequence predicted from the cDNA segment was identical to that of CYP2C9*1, the wild type CYP2C9. However, there were two base differences, i.e. 21T>C, 1146C>T, but the encoding amino acid sequence was the same, L7, P382. The S9 fraction of the established cell line metabolizes tolbutamide to hydroxy tolbutamide; tolbutamide hydroxylase activity was found to be 0.465 +/- 0.109 micromol.min(-1).g(-1) S9 protein or 8.62 +/- 2.02mol.min(-1).mol(-1) CYP, but was undetectable in parental CHL cell. CONCLUSION: The cDNA of human CYP2C9 was successfully cloned and a cell line of CHL- CYP2C9, efficiently expressing the protein of CYP2C9, was established.

Animals↗

PubMed2002

Establishment of a transgenic cell line stably expressing human cytochrome P450 2C18 and identification of a CYP2C18 clone with exon 5 missing.

AIM: The human cytochrome P-450 2C18(CYP2C18) has been characterized. However, the protein has not been purified from liver and very little is known regarding the specific substrate of CYP2C18. In order to study its enzymatic activity for drug metabolism, the CYP2C18 cDNA was cloned and a stable CHL cell line expressing recombinant CYP2C18 was established. METHODS: The human CYP2C18 cDNA was amplified with reverse transcription-polymerase chain reaction (RT-PCR) from total RNAs extracted from human liver and cloned into pGEM-T vector. The cDNA segment was identified by DNA sequencing and subcloned into a mammalian expression vector pREP9. A transgenic cell line was established by transfecting the recombinant plasmid of pREP9-CYP2C18 to Chinese hamster lung (CHL) cell. The enzyme activity of CYP2C18 catalyzing oxidation of tolbutamide to hydroxytolbutamide in postmitochondrial supernant(S9) fraction of the cell was determined by high performance liquid chromatography(HPLC). RESULTS: The amino acid sequence predicted from the cloned cDNA segment was identical to that of reported by Romkes et al (GenBank accession number: M61856, J05326). The S9 fraction of the established cell line metabolizes tolbutamide to hydroxytolbutamide. Tolbutamide hydroxylase activity was found to be 0.509+/-0.052 micromol x min(-1) x g(-1) S9 protein or 8.82+/-0.90 mol x min(-1) x mol(-1) CYP, but was undetectable in parental CHL cell. In addition, we have identified a CYP2C18 cDNA clone with exon 5 missing. CONCLUSION: The cDNA of human CYP2C18 was successfully cloned and a cell line, CHL-CYP2C18, efficiently expressing the protein of CYP2C18, was established. A spliced variant of CYP2C18 with exon 5 missing was identified in the cloning process.

Alternative Splicing↗

PubMed2002

An implantable rat liver tumor model for experimental transarterial chemoembolization therapy and its imaging features.

AIM: To establish an ideal implantable rat liver tumor model for interventional therapy study and examine its angiographic signs and MRI, CT features before and after embolization. METHODS: Forty male Wistar rats were implanted with Walker-256 tumor in the left lateral lobe of liver. Digital subtraction angiography (DSA) and transarterial chemoembolization were performed on day 14 after implantation. Native computer tomography (CT, n=8) and native magnetic resonance (MR, n=40) were performed between the day 8 and day 21 after implantation. The radiological morphological characteristics were correlated with histological findings. RESULTS: Successful implantation was achieved in all forty rats, which was confirmed by CT and MRI. MR allowed tumor visualization from day 8 while CT from day 11 after implantation. The tumors were hypodensity on CT, hypointense on MR T1-weighted and hyperintense on T2-weighted. The model closely resembled human hepatocarcinoma in growth pattern and the lesions were rich in vasculature on angiography and got its filling mainly from the hepatic artery. Before therapy, tumor size was 211.9+/-48.7 mm(3). No ascites, satellite liver nodules or lung metastasis were found. One week after therapy, tumor size was 963.6+/-214.8 mm(3) in the control group and 356.5+/-78.4mm(3) in TACE group. Ascites (4/40), satellite liver nodules (7/40) or lung metastasis (3/40) could be seen on day 21. CONCLUSION: Walker-256 tumor rat model is suitable for the interventional experiment. CT and MRI are helpful in animal optioning and evaluating experimental results.

Animals↗

PubMed2002

[The clinical study of adhesion prevention of sodium hyaluronate in flexor tendon surgery].

OBJECTIVE: To evaluate the effects of sodium hyaluronate on adhesion prevention after flexor tendon surgery. METHODS: In 47 cases with the flexor tendon surgery, two kinds of sodium hyaluronate jelly preparations were injected into the tendon sheath before suture. Preparation I (20 mg/2 ml) was for group A (17 patients) and preparation II (20 mg/2 ml) was for group B (16 patients). The control group (group C, 14 patients) were treated in the same way except injection of sodium hyaluronate. The functions of afflicted fingers including flexibility, pain and swelling were measured immediately, at the first, second and the third month after operation. RESULTS: All 47 patients were followed up 1 to 3 months. 64.71% patients in group A and 68.75% in group B showed significant improvement. There were significant difference compared with group C (P < 0.05). There were no significant adverse reactions were observed in all groups. CONCLUSION: Two sodium hyaluronate preparations have effects in adhesion prevention after flexor tendon surgery with safety and expedience.

Adolescent↗

PubMed2002

[Transforming growth factor-beta superfamily in the regulation of new bone formation].

OBJECTIVE: To review the recent advances in transforming growth factor-beta(TGF-beta) superfamily study and its role in new bone formation. METHODS: The latest original articles related to this subject were retrieved extensively, especially the effect of TGF-beta, bone morphogenetic proteins(BMPs) and activin(ACT) on distraction osteogenesis. RESULTS: TGF-beta, BMPs and ACT play important roles in prompting new bone formation and each of them has different effects. Among them, TGF-beta can stimulate the proliferation of osteoblast and synthesis of extra cellular medium; BMPs can initiate the differentiation of interstitial cell to osteocyte; then ACT displays the combine effect of above two factors. CONCLUSION: TGF-beta superfamily can regulate new bone formation and thus shorten the course of mandibular distraction osteogenesis.

Activins↗

PubMed2002

[Simultaneous determination of trace Ni2+, Mn2+, Zn2+ and Cu2+ with microwave derivatization/ion-pair high performance liquid chromatography/meso-tetra(4-sulfophenyl)-porphyrin spectroscopy].

The best conditions for the reaction of meso-tetra(4-sulfophenyl)-porphyrin (TPPS4) with Mn2+, Ni2+, Zn2+ and Cu2+ have been investigated. A method for the fast determination of Ni2+, Mn2+, Zn2+ and Cu2+ has been developed: microwave derivatization at 750 W for 3 min, C18 column, acetonitrile-water(22.5:77.5, volume ratio) as mobile phase with tetraethylammonium bromide (TEABr) as ion-pair reagent and detection wavelength of 415 nm. The detection limits for Zn2+, Cu2+, Ni2+ and Mn2+ were 0.05 microgram/L, 0.01 microgram/L, 0.10 microgram/L and 0.40 microgram/L, respectively. This method has been applied to analyze the concentrations of these four metal ions in marketed tea.

Chromatography, High Pressure Liquid↗

PubMed2002

[Treatment of simple renal cysts with small incision].

OBJECTIVE: To analyze the operative characteristics and indications small incision for treating simple renal cysts. METHODS: 19 patients with simple renal cyst were treated by ablation with small incision from January. 1995 to September. 2001 at our institute. Surgical technique, curative effect and indications were analyzed. RESULTS: In the 19 patients the operative procedure took 34 +/- 15 min (20-80 min) on average and the mean hospitalization was 4.4 +/- 1.5 d (3-8 d). Neither complication nor recurrence occurred from 3 to 6 months during the follow-up. CONCLUSIONS: Ablation with small incision is significantly advantageous for operation, recovery, short hospital stay, and lower cost. This operation is indicated for simple renal cyst in the lower, middle pole of the kidney.

Adult↗

PubMed2002

[The effects of cytokines mediated ex vivo expansion on the cell adhesion molecule expression of cord blood hematopoietic stem and progenitor cells].

OBJECTIVE: To compare the expression of cell adhesion molecules (CAMs) among VLA-4 (CD49 d), VLA-5 (CD49e), LFA-1 (CD11a), L-selectin (CD62L), and PECAM-1 (CD31) which are more related to the homing of hematopoietic stem and progenitor cells (HSPC) on the ex vivo expanded CD34+ subset with that of fresh isolated AC133+ cells. METHODS: AC133+ cells selected from fresh cord blood (CB) samples were cultured in QBSF-60 serum-free media in the presence of Flt-3 ligand + SCF + TPO (FST), with initial addition of IL-3 for up to 2 week. Expansion potential and the expression of above CAMs were evaluated at day 0, day 7, day 10 and day 14. RESULTS: (1) Simultaneously numerical expansion of various HSPC was constantly observed during the culture, and the fold expansion of AC133+ cells and CD34+ cells on day 14 were 33.50 and 64.56 respectively; (2) The number of CD34+ subsets expressing the above adhesions were all increased at different degrees (from 20 fold to 160 fold). (3) The expressions of CD11a, CD49d, and CD49e on ex vivo expanded CD34+ cells were increased as compared to their baseline levels, but the percentage of CD62L+ and CD31+ subpopulations in CD34+ cells were decreased. CONCLUSIONS: Our short-term culture system can not merely support the simultaneous expansion of CB derived AC133+ cells, but the expanded hematopoietic progenitors may well sustained the expression of homing-related adhesion molecules.

AC133 Antigen↗

PubMed2002

[Study on the difference in DNA damage of human lymphocyte caused by arsenicals].

OBJECTIVE: To explore whether there is difference in arsenicals-induced DNA damage of human lymphocyte. METHODS: Lymphocyte were sterilely collected from healthy donor and exposed to sodium arsenite (AsIII), sodium arsenate(AsV) and methyl sodium arsenate(MAsv) at 1,5,10,20 and 50 mumol/L. After incubation of 24 hours, cells were collected by centrifugation and DNA damage was detected by single cell gel electrophoresis (SCGE). RESULTS: The comet frequency distribution of all groups except 1 mumol/L group of MAsV were significantly different from that of control. The comet length of all groups except 1 mumol/L group of AsV and 1.5 mumol/L groups of MAsV were significantly higher than that of control. There were correlations between the doses of arsenicals and the ratios of comet cell or length of comet(rAsIII = 0.8134, rAsV = 0.8734, rMAsV = 0.8994). CONCLUSION: DNA damage in human lymphocyte were induced by all the three arsenicals. A dose-effect relationship was observed between exposure doses of the same arsenical and DNA damage. With different arsenicals but the same exposure dose, the DNA damage level was as follow: AsIII > AsV > MAsV.

Arsenates↗

PubMed2000

Stereoselective propranolol metabolism in two drug induced rat hepatic microsomes.

AIM:To study the influence of inducers BNF and PB on the stereoselective metabolism of propranolol in rat hepatic microsomes.METHODS:Phase I metabolism of propranolol was studied by using the microsomes induced by BNF and PB and the non induced microsome as the control.The enzymatic kinetic parameters of propranolol enantiomers were calculated by regression analysis of Lineweaver-Burk plots. Propranolol concentrations were assayed by HPLC.RESULTS:A RP-HPLC method was developed to determine propranolol concentration in rat hepatic microsomes. The linearity equations for R(+)propranolol and S(-) propranolol were A = 705.7C+311.2C (R = 0.9987) and a = 697.2C+311.4C (R = 0.9970) respectively. Recoveries of each enantiomer were 98.9%, 99.5%, 101.0% at 60&mgr;mol/L, 120&mgr;mol/L, 240&mgr;mol/L respectively. At the concentration level of 120&mgr;mol/L, propranolol enantiomers were metabolized at different rates in different microsomes. The concentration ratio R(+)/S(-) of control and PB induced microsomes increased with time, whereas that of microsome induced by BNF decreased. The assayed enzyme parameters were: 1. Km. Control group: R(+)30 plus minus 8, S(-)18 plus minus 5; BNF group: R(+)34 plus minus 3, S(-)39 plus minus 7; PB group: R(+)38 plus minus 17, S(-)36 plus minus 10. 2. Vmax. Control group: R(+)1.5 plus minus 0.2, S(-)2.9 plus minus 0.3; BNF group: R(+)3.8 plus minus 0.3, S(-)3.3 plus minus 0.5; PB group: R(+)0.07 plus minus 0.03, S(-)1.94 plus minus 0.07. 3. Clint. Control group: R(+)60 plus minus 3, S(-)170 plus minus 30; BNF group: R(+)111.0 plus minus 1, S(-) 84 plus minus 5; PB group: R(+)2.0 plus minus 2, S(-)56.0 plus minus 1. The enzyme parameters compared with unpaired t tests showed that no stereoselectivity was observed in enzymatic affinity of three microsomes to enantiomers and their catalytic abilities were quite different and had stereoselectivities.Compared with the control, microsome induced by BNF enhanced enzyme activity to propranolol R(+)enantiomer, and microsome induced by PB showed less enzyme activity to propranolol S(-)enantiomer which remains the same stereoselectivities as that of the control.CONCLUSION:Enzyme activity centers of the microsome were changed in composition and regioselectivity after the induction of BNF and PB, and the stereoselectivities of propranolol cytochrome P450 metabolism in rat hepatic microsomes were likely due to the stereoselectivities of the catalyzing function in enzyme.CYP1A subfamily induced by BNF exhibited pronounced contribution to propranolol metabolism with stereoselectivity to R(+)enantiomer.CYP2B subfamily induced by PB exhibited moderate contribution to propranolol metabolism, but still had the stereoselectivity of S(-)enantiomer.

Journal Article↗

PubMed1999

Identification of protease and rpoN-associated genes of uropathogenic Proteus mirabilis by negative selection in a mouse model of ascending urinary tract infection.

Proteus mirabilis, a motile gram-negative bacterium, is a principal cause of urinary tract infections in patients with functional or anatomical abnormalities of the urinary tract or those with urinary catheters in place. Thus far, virulence factors including urease, flagella, haemolysin, various fimbriae, IgA protease and a deaminase have been characterized based on the phenotypic traits conferred by these proteins. In this study, an attempt was made to identify new virulence genes of P. mirabilis that may not have identifiable phenotypes using the recently described technique of signature-tagged mutagenesis. A pool of chromosomal transposon mutants was made through conjugation and kanamycin/tetracycline selection; random insertion was confirmed by Southern blotting of chromosomal DNA isolated from 16 mutants using the aphA gene as a probe. From the total pool, 2.3% (9/397) auxotrophic mutants and 3.5% (14/397) swarming mutants were identified by screening on minimal salts agar and Luria agar plates, respectively. Thirty per cent of the mutants, found to have either no tag or an unamplifiable tag, were removed from the input pool. Then 10(7) c.f.u. from a 96-mutant pool (approximately 10(5) c.f.u. of each mutant) were used as an input pool to transurethrally inoculate seven CBA mice. After 2 d infection, bacteria were recovered from the bladders and kidneys and yielded about 10(5) c.f.u. as an output pool. Dot blot analysis showed that two of the 96 mutants, designated B2 and B5, could not be hybridized by signature tags amplified from the bladder output pool. Interrupted genes from these two mutants were cloned and sequenced. The interrupted gene in B2 predicts a polypeptide of 37.3 kDa that shares amino acid similarity with a putative protease or collagenase precursor. The gene in B5 predicts a polypeptide of 32.6 kDa that is very similar to that encoded by ORF284 of the rpoN operon controlling expression of nitrogen-regulated genes from several bacterial species. The virulence of the two mutants was tested further by co-challenging CBA mice with each mutant and the parental strain. After 1 week of infection, the B2 and B5 mutants were recovered in numbers 100-fold and 1000-fold less than the parental strain, respectively. Using an in vitro assay, it was shown that the B2 mutant had significantly less (P = 0.0001) extracellular protease activity than the wild-type strain. These findings demonstrate that signature-tagged mutagenesis is a viable approach to identify bacterial genes associated with the ability to infect the urinary tract.

Amino Acid Sequence↗

PubMedDate not supplied

Molecular imprinting of nitrophenol and hydroxybenzoic acid isomers: effect of molecular structure and acidity on imprinting.

Three nitrophenol isomer-imprinted polymers were prepared under the same conditions using 4-vinylpyridine as a functional monomer. Different recognition capacities for template molecules were observed for the three polymers. Another imprinting system with stronger acidity than nitrophenol isomers, 2-hydroxybenzoic acid (salicylic acid) and 4-hydroxybenzoic acid, was imprinted using 4-vinylpyridine or acrylamide as functional monomer respectively. Both 4-hydroxybenzoic acid-imprinted polymers using the two monomers showed recognition ability for the template molecule. However, when acrylamide was chosen as functional monomer, the salicylic acid-imprinted polymer showed very weak recognition for the template molecule, whereas strong recognition ability of the resultant polymer for salicylic acid was observed with 4-vinylpyridine as functional monomer. It seems that the structure and acidity of template molecules is responsible for the difference in recognition, by influencing the formation and strength of interaction between template molecule and functional monomer during the imprinting process. An understanding of the mechanism of molecular imprinting and molecular recognition of MIPs will help to predict the selectivity of MIPs on the basis of template molecule properties.

Chromatography, High Pressure Liquid↗

PubMedDate not supplied

Application of cross-linked beta-cyclodextrin polymer for adsorption of aromatic amino acids.

Beta-cyclodextrin (beta-CyD) was cross-linked by hexamethylene diisocyanate and the polymer was investigated for adsorption of aromatic amino acids (AAA) from phosphate buffer. High adsorption rates were observed at the beginning and the adsorption equilibrium was then gradually achieved in about 45 min. The adsorption of AAA decreased with the increase of initial concentration and also temperature. Under the same conditions, the adsorption efficiencies of AAA were in the order of L-tryptophan (L-Trp) > L-phenylalanine (L-Phe) > L-tyrosine (L-Tyr). Much higher adsorption values, up to 52.4 and 43.0 mg/g for L-Trp and L-Phe, respectively, at 50 mmol/L and 3.2 mg/g for L-Tyr at 2 mmol/L, were obtained with the beta-CyD polymer at 37 degrees C. It was shown that the adsorption of AAA on the beta-CyD polymer was consistent with the Freundlich isotherm equation. The adsorption of mixed aromatic amino acids and branched-chain amino acids (BCAA) showed that AAA were preferentially adsorbed with adsorption efficiencies 10-24%, while those of BCAA were lower than 2%. It seems that the structure and hydrophobicity of amino acid molecules are responsible for the difference in adsorption, by influencing the strength of interactions between amino acid molecule and the polymer.

Adsorption↗