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Yu Liu

Publications and source records attributed to Yu Liu.

At least 253 records · Page 14Linked to original sources
PubMed2002

Dephosphorylation of tau protein by calcineurin triturated into neural living cells.

Alzheimer disease and related dementia are characterized by the presence of hyperphosphorylated tau aggregated into filaments. The role of tau phosphorylation in the fibrillogenesis has not yet been unraveled. Therefore, it is important to know which phosphatases can dephosphorylate tau protein in vivo. The effect of recombinant purified calcineurin (CN(PP2B)) and several calcineurin mutants on tau phosphorylation was studied in two neuronal like cell lines PC12 and SH-SY5Y. The modulation of tau phosphorylation at Serl99/Ser202, Ser396/Ser404, Ser262/Ser356, and Thr181 sites was examined in these cell lines using the phosphorylation state-dependent antitau antibodies Tau 1, PHF1, 12E8, and AT270. The results have shown that CN directly dephosphorylates all of those sites of tau protein. Recombinant calcineurin introduced into cells that have previously been treated with okadaic acid and cyclosporin A, which are inhibitors of phosphatases (PP1/PP2A and PP2B), has a direct effect on the phosphorylation status on all phosphorylation sites studied. We conclude that calcineurin is (besides PP2A) a important modulator of tau phosphorylation in vivo.

Animals↗
PubMed2002

Influence of phenol on cultures of acetate-fed aerobic granular sludge.

AIMS: This paper attempts to investigate the inhibition of phenol on the acetate utilization in acetate-fed aerobic granular sludge culture. METHODS AND RESULTS: Acetate-fed aerobic granules with a mean diameter of 1.0 mm were predeveloped in a column sequencing aerobic sludge blanket reactor. The present study looked into the utilization kinetics of acetate by acetate-fed aerobic granules in the presence of different phenol concentrations ranging from 0 mg l(-1) to 50 mg l(-1). For this purpose, batch experiments were conducted at 25 degrees C, while the initial biomass and acetate concentrations were in a range of 109-186 mg mixed liquor suspended solids (MLSS) l(-1) and 185-300 mg acetate-chemical oxygen demand (COD) l(-1). Results showed that the utilization of acetate in the presence of phenol was subject to a zero-order reaction kinetics. The relative phenol concentration in terms of the ratio of initial phenol concentration (C(p)) to initial biomass concentration (X(0)) was used to describe the real inhibitory strength of phenol imposed on acetate-fed aerobic granules. When the C(p)/X(0) ratio increased from 0 to 0.19 mg phenol mg(-1) MLSS, the zero-order reaction rate constant of acetate dropped from 1.15 mg l(-1) min(-1) to 0.38 mg l(-1) min(-1), and a similar trend was also observed in specific oxygen utilization rate. As compared to the control test without addition of phenol, the acetate-COD removal efficiency was reduced by nearly 50% at a C(p)/X(0) value of 0.19 mg phenol mg(-1) MLSS. It was found that biodegradation of phenol was negligible in acetate-fed aerobic granular sludge batch culture. CONCLUSIONS: It appears that phenol can seriously repress the utilization of acetate in the acetate-fed aerobic granular sludge batch cultures. A simple zero-order reaction model could adequately describe the utilization of acetate by acetate-fed aerobic granules in the presence of phenol. SIGNIFICANCE AND IMPACT OF THE STUDY: It is expected that this study would lead to a better understanding of the behaviour of acetate-fed aerobic granules in the presence of inhibitory organic compounds.

Acetates↗
PubMed2002

A chemically modified tetracycline (CMT-3) is a new antifungal agent.

Several chemically modified tetracycline analogs (CMTs), which were chemically modified to eliminate their antibacterial efficacy, were unexpectedly found to have antifungal properties. Of 10 CMTs screened in vitro, all exhibited antifungal activities, although their efficacies varied. Among these compounds, CMT-315, -3, and -308 were found to be the most potent as antifungal agents. The MICs of CMT-3 against 47 strains of fungi in vitro were determined by using amphotericin B (AMB) and doxycycline as positive and negative controls, respectively. The MICs of CMT-3 were generally found to be between 0.25 and 8.00 microg/ml, a range that approximates the blood levels of this drug when administrated orally to humans. Of all the yeast species tested to date, Candida albicans showed the greatest sensitivity to CMT-3. The filamentous species most susceptible to CMT-3 were found to be Epidermophyton floccosum, Microsporum gypseum, Pseudallescheria boydii, a Penicillium sp., Scedosporium apiospermum, a Tricothecium sp., and Trichophyton rubrum. Growth inhibition of C. albicans by CMT-3, determined by a turbidity assay, indicated a 50% inhibitory concentration of 1 microg/ml. Thirty-nine strains, including 20 yeasts and 19 molds, were used to measure viability (the ability to grow after treatment with a drug) inhibition by CMT-3 and AMB. CMT-3 exhibited fungicidal activity against most of these fungi, especially the filamentous fungi. Eighty-four percent (16 of 19) of the filamentous fungi tested showed more than 90% inhibition of viability by CMT-3. In contrast, AMB showed fungicidal activity against all yeasts tested. However, most of the filamentous fungi (16 of 19) showed less than 50% inhibition of viability by AMB, indicating that AMB is fungistatic against most of these filamentous fungi. To begin to identify the sites in fungal cells affected by CMT-3, C. albicans and a Penicillium sp. were incubated with the compound at 35 degrees C, and then the fluorescence of CMT-3 was observed by confocal laser scanning electron microscopy. CMT-3 appeared to have widespread intracellular distribution throughout C. albicans and the Penicillium sp. The mechanisms of the antifungal activity of CMT-3 are now being explored.

Amphotericin B↗
PubMed2002

Potato dextrose agar antifungal susceptibility testing for yeasts and molds: evaluation of phosphate effect on antifungal activity of CMT-3.

The broth macrodilution method (BMM) for antifungal susceptibility testing, approved by the National Committee for Clinical Laboratory Standards (NCCLS), was found to have deficiencies in testing of the antifungal activity of a new type of antifungal agent, a nonantibacterial chemically modified tetracycline (CMT-3). The high content of phosphate in the medium was found to greatly increase the MICs of CMT-3. To avoid the interference of phosphate in the test, a new method using potato dextrose agar (PDA) as a culture medium was developed. Eight strains of fungi, including five American Type Culture Collection strains and three clinical isolates, were used to determine the MICs of amphotericin B and itraconazole with both the BMM and the PDA methods. The MICs of the two antifungal agents determined with the PDA method showed 99% agreement with those determined with the BMM method within 1 log(2) dilution. Similarly, the overall reproducibility of the MICs with the PDA method was above 97%. Three other antifungal agents, fluconazole, ketoconazole, and CMT-3, were also tested in parallel against yeasts and molds with both the BMM and the PDA methods. The MICs of fluconazole and ketoconazole determined with the PDA method showed 100% agreement within 1 log(2) dilution of those obtained with the BMM method. However, the MICs of CMT-3 determined with the BMM method were as high as 128 times those determined with the PDA method. The effect of phosphate on the antifungal activity of CMT-3 was evaluated by adding Na2HPO4 to PDA in the new method. It was found that the MIC of CMT-3 against a Penicillium sp. increased from 0.5 microg/ml (control) to 2.0 microg/ml when the added phosphate was used at a concentration of 0.8 mg/ml, indicating a strong interference of Na2HPO4 with the antifungal activity of CMT-3. Except for fluconazole, all the other antifungal agents demonstrated clear end points among the yeasts and molds tested. Nevertheless, with its high reproducibility, good agreement with NCCLS proposed MIC ranges, and lack of interference of phosphate, the PDA method shows promise as a useful assay for antifungal susceptibility testing and screening for new antifungal agents, especially for drugs that may be affected by high (supraphysiologic) phosphate concentrations.

Agar↗
PubMed2002

Inhibition of matrix metalloproteinase-mediated periodontal bone loss in rats: a comparison of 6 chemically modified tetracyclines.

BACKGROUND: Chemically modified tetracyclines (CMTs), devoid of antimicrobial activity, inhibit pathologically elevated collagenase activity both in vivo and in vitro. In the current study, doxycycline and 5 different CMTs were tested to prevent matrix metalloproteinase (MMP)-dependent periodontal tissue breakdown in an animal model of periodontitis. METHODS: Adult male rats received intragingival injections with either 10 microl of physiologic saline or Escherichia coli endotoxin (1 mg/ml) every other day for 6 days and were distributed into 8 treatment groups (12 rats/group): saline (S), endotoxin alone (E), E + CMT-1, E + CMT-3, E + CMT-4, E + CMT-7, E + CMT-8, and doxycycline. All animals were treated daily with 1 ml of 2% carboxymethyl cellulose (CMC) alone or containing one of the above-mentioned CMTs (2 mg/day) orally. The gingival tissues were removed, extracted, and assayed for gelatinase (GLSE). Some rat maxillary jaws from each treatment group were fixed in buffered formalin and processed for histology and immunohistochemistry for the cytokines tumor necrosis factor (TNF), interleukin (IL)-1, and IL-6, and MMP-2 and MMP-9. RESULTS: Endotoxin injection induced elevated GLSE activity (functional assay and osteoclast-mediated bone resorption), the former identified as predominantly MMP-9 (92 kDa GLSE) by gelatin zymography. All 6 tetracyclines (2 mg/day) inhibited periodontal breakdown in the following order of efficacy: CMT-8 > CMT- 1 > CMT-3 > doxycycline > CMT-4 > CMT-7. Immunohistochemistry was positive for TNF, IL-1, and IL-6 in the inflammatory cells from untreated endotoxin rat tissues, whereas treatment with CMTs decreased the number of immuno-positive stained cells for cytokines and MMPs. The in vivo efficacy of these drugs varied with CMT structure and was significantly correlated with bone resorption: r2 = -0.77, P<0.01; gelatinase inhibitory activity: r2 = -0.84, P <0.01; and serum drug concentrations. CONCLUSION: Since both conventional (antimicrobial) and non-antimicrobial tetracyclines inhibited periodontal bone resorption induced by endotoxin injection, MMP-mediated bone loss in this model can be prevented by inhibition of MMPs.

Alveolar Bone Loss↗
PubMed2002

[Variations of apolipoprotein A IV gene in Chinese endogenous hypertriglyceridemics].

OBJECTIVE: The aim of this study was to investigate variations of apolipoprotein A IV (apo A IV) gene and its relation to endogenous hypertriglyceridemia(HTG) in Chinese population. METHODS: One hundred and six endogenous hypertriglyceridemics and 171 healthy subjects from a population of Chinese Han nationality in Chengdu area were studied using restriction fragment length polymorphisms (RFLPs) and sequencing of apoA IV gene amplified by polymerase chain reaction (PCR). The polymorphic sites of apo A IV gene studied included codon 9 (A to G, synonymous mutation), codon 347 (A to T, non-synonymous mutation), codon 360 (G to T, non-synonymous mutation), and Msp I polymorphism (CC/TGG) within intron 2. RESULTS: The frequency of G allele at codon 9 in HTG group was higher than that in healthy controls(0.453 vs 0.366, P<0.05). The other polymorphic sites showed no significant differences of the allele frequencies between the two groups. The frequencies of rare alleles, such as G allele at codon 9, T allele at codon 347 and T allele at codon 360 polymorphic site were significantly different from those reported in European Caucasians (0.366 vs 0.032, P<0.001, 0.000 vs 0.160, P<0.001; 0.000 vs 0.070, P<0.001), but no differences were found when compared with those in Japanese, including Msp I site (P>0.05). In the healthy male control group, subjects with genotype G/G of codon 9 had a higher serum mean concentration of apoA I when compared with that of genotype A/A(P<0.01). In the HTG group, subjects with genotype C/T of Msp I site had a higher serum mean concentration of TG with compared with those with genotype C/C and T/T (P<0.05). This difference was only observed in male HTG group when male and female subgroups were further separated. CONCLUSION: These results suggest that Msp I and codon 9 polymorphism in apoA IV gene are associated with endogenous hypertriglyceridemia to some extent in Chinese population.

Adult↗
PubMed2002

[Regulation of cyclin-dependent kinase inhibitors by mitogen-activated protein kinase in angiotensin II-stimulated vascular smooth muscle cell hypertrophy].

OBJECTIVE: To investigate the role of mitogen-activated protein kinase (MAPK) in the regulation of cyclin-dependent kinase inhibitors (CDKI) in the process of vascular smooth muscle cell (VSMC) hypertrophy induced by angiotensin II stimulation. METHODS: The medial layer of male SD rat aorta was isolated for VSMC culture. After cultured in serum-free medium to arrest the cell growth, VSMCs were stimulated with angiotensin II (1x10(-6) mol/L) or/and phorbol myristate acetate (PMA, 20 nmol/L), with the cells cultured in serum-free medium serving as control. MAPK activity of the cells was assayed 90 min after stimulation with immunoprecipitation test, and the expression levels of CDKI p27, p57 and p21 were determined by Western blotting 6 and 24 h after stimulation respectively. RESULTS: Compared with the control level, MAPK activity of the VSMCs was up-regulated by 238% by treatment with angiotensin II alone which, however, did not inhibit p27 expression or induce VSMC proliferation. Costimulation with angiotensin II and PMA slightly inhibited p27 expression but VSMC proliferation was still not observed. CONCLUSION: MAPK pathway is an important channel for extracellular proliferative and hypertrophic signal transduction into the nucleus of VSMCs.

Angiotensin II↗
PubMed2002

Effect of human serum albumin on cell attachment of human gingival epithelial cells.

OBJECTIVE: To investigate the effect of human serum albumin (HSA) on cell attachment of human gingival epithelial cells (HGE). METHODS: HGE were primary cultured with keratinocyte serum-free medium (KSFM) and dispase. The cultured cells were immunohistochemically stained by monoclonal anti-pan cytokeratin. MTT test was employed to investigate the influence of HSA on the cell attachment on polystyrene surface. The cell growth curve of HGE which were cultured in KSFM with 50 g/L HSA was observed. RESULTS: The results showed significant decrease in cell numbers within 8 hours after HGE were inoculated, in which the polystyrene surface was preincubated with 50 g/L HSA. But it did not prove to be the case from 10 hours to 24 hours after HGE were inoculated. There were no significant difference within 24 hours in cell numbers between cultured in KSFM with 50 g/L HSA and control. The cell numbers in cell growth curve of HGE in KSFM with and without 50 g/L HSA did not show significant difference. CONCLUSIONS: HSA preincubation on polystyrene were produce inhibitory effect of HGE attachment in early stage.

Cell Adhesion↗
PubMed2002

[Effects of acute moderate hypoxia on plasma angiotensin II and adrenomedullin in pilots].

Objective. To study the effect of acute moderate hypoxia on plasma angiotensin II (AII) and adrenomedullin (ADM) content in pilots. Method. The concentration of plasma AII and ADM was measured by radioimmunoassay in 16 healthy male pilots in the early morning (6:00), following acute moderate hypoxic exposure (10:00) and 6 h after returned to the ground (16:00). Sixteen healthy male ground crews were set as control group, and their plasma AII and ADM content was assayed at corresponding time. Result. 1) Plasma AII and ADM content of pilot group and that of the control group was not different (P>0.05). 2) Plasma AII and ADM content immediately after acute moderate hypoxic exposure in the pilot group was significantly higher than that of before hypoxia (P<0.05), and it returned to normal level 6 h after hypoxia. Conclusion. Acute moderate hypoxia can induce temporarily increase of plasma AII and ADM in pilots.

Adrenomedullin↗
PubMed2002

[The paraoxonase Gln-Arg 192 polymorphism in patients with endogenous hypertriglyceridemia in Chinese population].

OBJECTIVE: To investigate the 192 Gln-Arg polymorphism of paraoxonase (PON) gene and its relationship with serum lipids and apolipoproteins (apo) levels in patients with endogenous hypertriglyceridemia in Chinese population in Chengdu area. METHODS: The genotype and allele frequencies of paraoxonase gene 192 Gln-Arg polymorphism were assayed by polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP). Serum lipids were measured by enzymatic kits and apolipoproteins AI, A II, B100, C I, C II and E were measured by the RID kits developed by the Apolipoprotein Research Unit of this university in 128 HTG patients whose fasting serum TG levels were > or = 2.26 mmol/L and 129 healthy subjects whose fasting serum TG levels were < 1.82 mmol/L and TC levels < 6.2 mmol/L from a population of Chinese Han nationality in Chengdu area. RESULTS: Both in HTG group and control group, the QR genotype of PON gene was the major one, and the frequencies were 0.515 and 0.581 respectively. No differences were found in PON gene Gln-Arg polymorphism between the HTG group and the control group. In the control group, the QQ genotype of PON gene was found to have higher serum apoA I levels, compared with the RR genotype (P < 0.05). But in the HTG group, when compared with the RR genotype, the QQ genotype was found to have lower serum apoA I and A II levels and higher serum apoE levels. CONCLUSION: These may be an association of the QQ genotype of the paraoxonase 192 Gln-Arg polymorphism with the decrease of serum apoA I level and the increase of serum apoE level in endogenous hypertriglyceridemica.

Aged↗
PubMed2002

[Angiotensinogen and angiotensin-I converting enzyme gene variations in Chinese pregnancy induced hypertension].

OBJECTIVE: This study was designed to observe the genotype and allele frequency of angiotensinogen (AGT) and angiotensin-I converting enzyme (ACE) genes in pregnancy induced hypertension (PIH) and compare them with those in normal pregnant women. METHODS: Eighty-one women with pre-eclampsia (median age 28 years) and 205 normal pregnant women as controls (median age 28 years) from a population of Chinese Han nationality in Chengdu area participated in this study. The pregnant patients whose blood pressure exceeded 140/90 mmHg (or 18.7/12 kPa) were recruited with a rigorous definition of pre-eclampsia. Genotyping was performed using PCR-amplified DNA fragment for ACE I/D and PCR-RFLP for AGT polymorphism. RESULTS: The allele frequencies of AGT235T and ACE D in PIH and normal pregnant women were 0.856 vs. 0.846 and 0.333 vs 0.364, respectively. No significant difference in these allele frequencies was observed between PIH and normal pregnant women. The allele frequencies of ACE D in Caucasians were higher than those in Chinese population (P < 0.001). The allele frequencies of AGT235T in Caucasians (0.350-0.482) and other populations (0.620-0.739) were lower than that in Chinese (0.846) (P < 0.01, P < 0.001). CONCLUSION: There was no evidence in this study for the association of AGT M235T and ACE I/D polymorphism with pre-eclampsia in Chinese population in Chengdu area.

Adult↗
PubMed2002

[Analysis of serum lipid and apolipoprotein levels in pregnancy-induced hypertension and normotensive pregnant women].

OBJECTIVE: To investigate the serum lipid and apolipoprotein levels in pregnancy-induced hypertension (PIH or pre-eclampsia), normotensive pregnant women and non-pregnant women. METHODS: Twenty-eight women with PIH, 31 normatensive and 24 non-pregnant ones were studied, from whom maternal blood samples were collected. Serum lipid levels were measured by enzymatic method and apolipoproteins AI, B100, C II, CIII and E levels by radial immunodiffusion kits developed by our Lab. RESULTS: 1. Serum TG, apoC II and apoC III were highly increased in normotensive pregnant women by 3.5, 2.4 and 2.8 times respectively, when compared with those in non-pregnant ones (P < 0.001); serum TC, nHDL-C and apoAI, B100 and E were also increased in normotensive pregnant women by 21%, 33%, 55%, 79% and 77% respectively, when compared with those in non-pregnant ones (P < 0.001). TG/HDL-C in normotensive pregnant women was also significantly, higher than that in non-pregnant ones(P < 0.01). Serum HDL-C levels remained unchanged in both groups. 2. Serum TG, apoC II and apoC III were highly increased in PIH patients by 2.3, 4.0 and 2.8 times respectively, when compared with those in non-pregnant ones (P < 0.001); serum TC, nHDL-C and apoAI, B100 and E were also increased in PIH patients by 27%, 26%, 52%, 90% and 67% respectively, when compared with those in non-pregnant ones (P < 0.001) TG/HDL-C in PIH patients was also significantly higher than that in non-pregnant ones (P < 0.01). Serum HDL-C levels were increased in PIH patients by 29%, when compared with non-pregnant women. Only serum HDL-C level in PIH patients was higher than that in normotensive pregnant women. No significant differences were seen in other lipid and apolipoprotein levels between PIH patients and normotensive pregnant ones. 3. There was no significant difference in the levels of serum lipid and apolipoprotein between the subgroups of PIH patients according to the severity of the disease. CONCLUSION: The increase of serum lipid and apolipoprotein levels in PIH is probably not the predictor for pre-eclampsia.

Adult↗
PubMed2002

[FTIR investigation on crystal chemistry of CO(2-)3-substituted apatite solid solutions prepared through different methods].

The CO(2-)3-substituted apatite solid solutions were prepared through different methods. The FTIR and XRD measurements were applied to investigate its crystal chemistry properties. The results indicated that the CO(2-)3-substituted sites in the carbonate hydroxyapatite(CHAP) prepared through homogeneous precipitation method are type-B in which [CO3.OH] tetrahedral-coordinations are substituted for [PO4] tetrahedral-coordinations; the ones in the CHAP prepared through solid phase ions exchange method are type-A in which [CO3] triangle-coordinations are substituted for [OH] in column sites; the ones in the carbonate fluorapatite(CFAP) prepared through solid phase reaction method are type-B in which [CO3.F] tetrahedral-coordinations are substituted for [PO4] tetrahedral-coordinations; the ones in the CHAP prepared through sol-gel method are AB mixed-type. The vibrational band psi 3 is splitted into psi 3-1, psi 3-4 and psi 3F. The psi 3F is combined by psi 3-2 (type-A) and psi 3-3 (type-B) in Gaussian function fitting. When Wco(2-)3 < 3.34%, substitution value of type-A increases with the increasing of CO(2-)3 contents. When Wco(2-)3 = 3.34%, substitution value of type-A has maximum. When 3.34% < Wco(2-)3 < 7.52%, substitution value of type-B increases with the increasing of CO(2-)3 contents. When Wco(2-)3 = 7.52%, substitution value of type-B has maximum.

Apatites↗
PubMed2001

Ultrasound-Induced Formation of CdS Nanostructures in Oil-in-Water Microemulsions.

In this study the formation of approximately spherical assemblies of nanocrystalline primary particles of CdS in a CS(2)-water-ethylenediamine (CWE) microemulsion induced by ultrasonic irradiation is described. CS(2) was employed as the sulfur source for CdS and also as the oil phase in the microemulsion. The particles were studied with X-ray powder diffraction, transmission electron microscopy, UV/Vis absorption spectroscopy, and photoluminescence spectroscopy. A blue shift compared to bulk CdS was observed in absorption and photoluminescence spectra. Copyright 2001 Academic Press.

Journal Article↗
PubMed2001

Effect of recombinant human interleukin-10 on the in vitro proliferation of rat vascular smooth muscle cells.

OBJECTIVE: To observe the effects of recombinant human interleukin-10 (rhIL-10) on the proliferation of rat vascular smooth muscle cells (VSMCs) cultured in vitro. METHOD: Aortic VSMCs cultured in vitro were treated with varied doses of rhIL-10 alone or in combination with tumor necrosis factor-alpha (TGF-alpha) or platelet-derived growth factor-BB(PDGF- BB) respectively. The VSMC proliferation was quantified by colormetric assay. RESULTS: Compared with control, both TNF-alpha and PDGF-BB stimulated conspicuous proliferation of VSMCs, but the effect of which was not observed by rhIL-10 treatment alone. In the presence of rhIL-10, the proliferation effects of both TGF-alpha and PDGF-BB on VSMCs were significantly inhibited (P<0.05). CONCLUSION: rhIL-10 can inhibit VSMC proliferation induced by TNF-alpha and PDGF-BB, thus may provide a new therapeutic approach for regulating vascular wall remodeling after vascular injury.

Journal Article↗
PubMed1999

Molecular Recognition Studies on Supramolecular Systems. 22. Size, Shape, and Chiral Recognition of Aliphatic Alcohols by Organoselenium-Modified Cyclodextrins.

A novel cyclodextrin derivative, mono[6-(p-methoxyphenylseleno)-6-deoxy]-beta-cyclodextrin (2), has been synthesized and characterized by elemental analysis and mass, FT-IR, and (1)H NMR spectroscopy. The stability constants (K(S)) of the inclusion complexation of 2 and mono[6-(p-tolylseleno)-6-deoxy]-beta-cyclodextrin (3) with a series acyclic and cyclic alcohols have been determined in phosphate buffer solution (pH 7.20) at 25 degrees C by using the circular dichroism spectral titration method. Although the stability constants obtained for the inclusion complexation of 2 and 3 with aliphatic alcohols are generally smaller than those for native beta-cyclodextrin, the modified cyclodextrins can recognize both the size and chirality of the guest molecules. Interestingly, the complex stability constants (log K(S)), or the Gibbs free energy change (-DeltaG degrees ), increase linearly with increasing number of carbon atoms in the guest molecule (N(C)), irrespective of the topological differences of acyclic, cyclic, and bicyclic guests. The unit increment of complex stability per methylene (-dDeltaG degrees /dN(C)) is not appreciably affected by the difference of the host's substituent but is a critical function of the guest topology, affording distinctly different -dDeltaG degrees /dN(C) values of 2.4 and 2.9 kJ mol(-)(1) for alkanols and cycloalkanols, respectively. In the complexation of chiral guests with 2 and 3, the observed enantioselectivities, as measured by the stability difference (DeltaDeltaG degrees ), are mostly in the range of 1-2 kJ mol(-)(1).

Journal Article↗
PubMed1999

Molecular Recognition Study on Supramolecular Systems. 20. Molecular Recognition and Enantioselectivity of Aliphatic Alcohols by L-Tryptophan-Modified beta-Cyclodextrin.

L-Tryptophan-modified beta-cyclodextrin (L-Trp-beta-CD) has been synthesized and its molecular recognition behavior investigated through fluorescence and circular dichroism spectrometry, as well as fluorescence lifetime measurement in the presence and absence of various alcohols as guest molecules. Employing the indolyl group as a spectral probe, spectrofluorometric and spectropolarimetric titrations have been performed in aqueous phosphate buffer solution at pH 7.20 to calculate the complex stability constants for 1:1 inclusion complexation of L-Trp-beta-CD with several series of alcohols at 25 degrees C. The results obtained indicate that L-Trp-beta-CD can recognize not only size/shape and hydrophobicity but also the enantiomeric and geometrical isomers of the guest alcohols, showing a 230-fold molecular selectivity (13.5 kJ mol(-)(1)) for 2-adamantanol over cyclopentanol among the cyclic alcohols examined. Moderate enantiomeric selectivities of 1.2 and 1.9 for (-)-isomers of borneol and menthol, respectively, and geometrical selectivity of 2.0 for geraniol over nerol have also been observed.

Journal Article↗