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C Zheng

Publications and source records attributed to C Zheng.

At least 37 records · Page 2Linked to original sources
PubMed2001

Stable three-center hydrogen bonding in a partially rigidified structure.

The three-center hydrogen bond in diaryl amide 1 was examined by IR and 1H NMR spectroscopy, X-ray crystallography, and ab initio calculations. By comparing 1 with its structural isomers 2, 3 and 4, and with its conformational isomers 1a-c, it was found that the two two-center components of the three-center interaction reinforce each other, that is, the enhanced stability of the three-center hydrogen bond is a result of positive cooperativity between the two components. Substituents not involved in hydrogen bonding have little effect on the strength of the two- and three-center hydrogen bonds. To our knowledge, this is the first three-center hydrogen-bonding system that has been shown to exhibit positive cooperativity. Ab initio calculations of the geometries, vibrational modes, and 1H NMR chemical shifts also support the experimental findings. These results have provided a new insight into the three-center intramolecular hydrogen bonding in a partially rigidified structure and have provided a reliable motif for designing stably folded structures.

Amides↗
PubMed2001

Lanthanide coordination with alpha-amino acids under near physiological pH conditions: polymetallic complexes containing the cubane-like [Ln4(mu3-OH)4]8+ cluster core.

Tetranuclear lanthanide-hydroxo complexes of the general formula [Ln(4)(mu(3)-OH)(4)(AA)(x)(H(2)O)(y)](8+) (1, Ln = Sm, AA = Gly, x = 5, y = 11; 2, Ln = Nd, AA = Ala, x = 6, y = 10; 3, Ln = Er, AA = Val, x = 5, y = 10) have been prepared by alpha-amino acid controlled hydrolysis of lanthanide ions under near physiological pH conditions (pH 6-7). The core component of these compounds is a cationic cluster [Ln(4)(mu(3)-OH)(4)](8+) whose constituent lanthanide ions and triply bridging hydroxo groups occupy the alternate vertexes of a distorted cube. The amino acid ligands coordinate the lanthanide ions via bridging carboxylate groups. Utilizing L-glutamic acid as the supporting ligand, a cationic cluster complex (4) formulated as [Er(4)(mu(3)-OH)(4)(Glu)(3)(H(2)O)(8)](5+) has been obtained. Its extended solid-state structure is composed of the cubane-like [Er(4)(mu(3)-OH)(4)](8+) cluster building units interlinked by the carboxylate groups of the glutamate ligands. All compounds are characterized by using a combination of spectroscopic techniques and microanalysis (CHN and metal). Infrared spectra of the complexes suggest the coordinated amino acids to be zwitterionic. The presence of mass (MALDI-TOF) envelopes corresponding to the [Ln(4)(mu(3)-OH)(4)](8+) (Ln = trivalent Sm, Nd, or Er) core containing fragments manifests the integrity of the cubane-like cluster unit. Magnetic studies using Evans' method suggest that exchange interactions between the lanthanide ions are insignificant at ambient temperature. The structural identities of all four compounds have been established crystallographically. The tetranuclear cluster core has been demonstrated to be a common structural motif in these complexes. A mechanism responsible for its self-assembly is postulated.

Amino Acids↗
PubMed2001

Interleukin-10 gene promoter polymorphisms in multiple myeloma.

Multiple myeloma (MM) is a B-cell malignancy characterized by an accumulation of malignant plasma cells in the bone marrow. It is unclear whether genetic background could have an etiological impact on MM or influence the course of the disease. Interleukin-10 (IL-10) has been implicated in the growth and differentiation of normal B cells, and has also been shown to enhance the proliferation of MM cells. To address the putative involvement of IL-10 genetic variation in MM, we analyzed previously defined loci for bi-allelic polymorphism at position -1082 and two microsatellite loci (IL10.G and IL10.R) in the IL-10 promoter region. Seventy-three patients with MM, 27 with monoclonal gammopathy of undetermined significance, and 109 ethnically matched individuals as controls were included in the study. Significantly increased frequencies of the IL10.G genotype 136/136 and the IL10.R genotype 112/114, in addition to a decreased frequency of the IL10.R genotype 114/116, were found among the MM patients. Increased production of IL-10 was detected in the supernatants of lipopolysaccharide-stimulated peripheral blood mononuclear cells from MM patients who were homozygotes (136/136) and heterozygotes (136/non-136) for the IL10.G allele 136, as compared with the other IL10.G genotype carriers (non-136/non-136). These results suggest that the genetic variation in the IL-10 promoter region may play a role in the development of MM.

Adult↗
PubMed2001

Fate of selenium in coal combustion: volatilization and speciation in the flue gas.

In light of Title I of the Clean Air Act Amendments of 1990, selenium will most probably be considered for regulation in the electric power industry. This has generated interest for removing this element from fossil-fired flue gas. This study deals with coal combustion: selenium volatilization and its speciation in the cooled flue gas were investigated to better understand its chemical behavior to validate the thermodynamic approach to such complex systems and to begin developing emission control strategies. Se volatility is influenced by several factors such as temperature, residence time, fuel type, particle size, and Se speciation of the fuels, as well as the forms of the Se inthe spiked coal/coke. Spiked coke and coal samples were burned in a thermobalance, and atomic Se and its dioxide were identified in the cooled combustion flue gas by X-ray photoelectron spectroscopy (XPS). A thermodynamic calculation was applied to a complex system including 54 elements and 3,200 species that describes the coal combustion. Several theoretical predictions concerning Se behavior, such as its speciation in flue gas, agreed well with experiments, which supports using thermodynamics for predicting trace element chemistry in combustion systems.

Air Pollutants↗
PubMed2001

Telomerase activity in plasma cell dyscrasias.

Activation of telomerase is essential for in vitro cellular immortalization and tumorigenesis. In the present study, we investigated telomerase activation and its implications in plasma cell dyscrasias including monoclonal gammopathy of undetermined significance (MGUS), multiple myeloma (MM) and plasma cell leukaemia (PCL). All 5 patients with MGUS exhibited normal levels of telomerase activity in their plasma cells. Elevated telomerase activity was found in the samples from 21/27 patients with MM and 4/4 with PCL. In addition, 4 myeloma cell lines all expressed high levels of telomerase activity. The expression of telomerase reverse transcriptase (hTERT) and telomerase RNA template (hTER) was positively associated with the levels of telomerase activity in MM/PCL. Tankyrase expression was upregulated, concomitant with the induction of hTERT and activation of telomerase in MM/PCL. The present findings indicate that MGUS cells may not be immortalized and that activation of telomerase plays a role in the malignant transformation from MGUS to MM.

Adult↗
PubMed2001

Construction of a generic reaction knowledge base by reaction data mining.

As synthesis by combinatorial chemistry and high throughput screening have become well-established strategies in the drug discovery process, chemists face increased challenges in managing large amounts of data and using these data to design more diverse and focused libraries. As synthesis is an intuitive and empirical process, however, the classical approaches to computer-assisted synthesis planning do not fully satisfy the needs of the synthetic chemist. We describe a novel computational technique for extracting reaction data and building a generic reaction knowledge base (GRKB) to provide chemists with useful and well-organized knowledge. The method consists of three key steps: (1) the automatic recognition of reaction centers, (2) the definition of a hierarchy of reaction patterns, and (3) the organization of the generic reaction knowledge. Significant reaction knowledge has been discovered via mining a subset of the InfoChem Reaction database. A frame system has been constructed to store and retrieve the GRKB. Applications of this GRKB to synthesis planning are illustrated.

Artificial Intelligence↗
PubMed2001

Cytotoxic T-lymphocyte antigen-4 microsatellite polymorphism is associated with multiple myeloma.

Multiple myeloma (MM) is a B-lineage malignancy with unknown aetiology. It has been considered that predisposing genetic factors might be implicated in the disease. In this study, the microsatellite polymorphism in the exon 3 of the cytotoxic T-lymphocyte antigen-4 (CTLA-4) gene was analysed in patients with MM and monoclonal gammopathy of undetermined significance (MGUS), together with ethnically matched healthy controls. The results showed that frequencies of the genotype 86/86 and of the allele 86 were significantly decreased in MM and MGUS compared with matched healthy controls, indicating that the CTLA-4 microsatellite polymorphism might represent a susceptibility locus for MM and MGUS.

Abatacept↗
PubMed2001

Using HSV-thymidine kinase for safety in an allogeneic salivary graft cell line.

Extreme salivary hypofunction is a result of tissue damage caused by irradiation therapy for cancer in the head and neck region. Unfortunately, there is no currently satisfactory treatment for this condition that affects up to 40,000 people in the United States every year. As a novel approach to managing this problem, we are attempting to develop an orally implantable, fluid-secreting device (an artificial salivary gland). We are using the well-studied HSG salivary cell line as a potential allogeneic graft cell for this device. One drawback of using a cell line is the potential for malignant transformation. If such an untoward response occurred, the device could be removed. However, in the event that any HSG cells escaped, we wished to provide additional patient protection. Accordingly, we have engineered HSG cells with a hybrid adeno-retroviral vector, AdLTR.CMV-tk, to express the herpes simplex virus thymidine kinase (HSV-tk) suicide gene as a novel safety factor. Cells were grown on plastic plates or on poly-L-lactic acid disks and then transduced with different multiplicities of infection (MOIs) of the hybrid vector. Thereafter, various concentrations of ganciclovir (GCV) were added, and cell viability was tested. Transduced HSG cells expressed HSV-tk and were sensitive to GCV treatment. Maximal effects were seen at a MOI of 10 with 50 microM of GCV, achieving 95% cell killing on the poly-L-lactic acid substrate. These results suggest that engineering the expression of a suicide gene in an allogeneic graft cell may provide additional safety for use in an artificial salivary gland device.

Artificial Organs↗
PubMed2001

Plasma levels of asymmetrical dimethyl-L-arginine in patients with congenital heart disease and pulmonary hypertension.

Asymmetrical dimethyl-L-arginine (ADMA) is an endogenous inhibitor of nitric oxide synthase. We hypothesized that plasma levels of ADMA could be increased in patients with congenital heart disease and pulmonary hypertension. Cardiac catheterization was performed in 20 children and young adults with congenital heart disease with a median age of 10 years (range, 4 months to 33 years). The patients were assigned to group I (high flow, low pressure; n = 14) when Qp/Qs was 1.5 or greater and the mean PAP was less than 25 mm Hg or to group II (high pressure, high resistance; n = 6) when the mean PAP was greater than 25 mm Hg and Rp/Rs was greater than 0.3. Blood samples were taken from pulmonary vein or left ventricle. ADMA was measured by high-performance liquid chromatography. In addition, levels of ADMA were measured in peripheral venous blood obtained from eight control patients. Levels of ADMA in control patients (median, 0.21 microM/l; range, 0.08-0.27 microM/l) did not differ from levels obtained in group I (median, 0.30 microM/l; range, 0.06-0.49) microM/l). Patients in group II showed increased plasma levels of ADMA (median, 0.55; range, 0.25-0.79) (p < 0.01). Inhibition of nitric oxide synthase by increased levels of ADMA might contribute to pulmonary hypertension in patients with congenital heart disease.

Adolescent↗
PubMed2001

Structures of an unliganded neurophysin and its vasopressin complex: implications for binding and allosteric mechanisms.

The structures of des 1-6 bovine neurophysin-II in the unliganded state and as its complex with lysine vasopressin were determined crystallographically at resolutions of 2.4 A and 2.3 A, respectively. The structure of the protein component of the vasopressin complex was, with some local differences, similar to that determined earlier of the full-length protein complexed with oxytocin, but relatively large differences, probably intrinsic to the hormones, were observed between the structures of bound oxytocin and bound vasopressin at Gln 4. The structure of the unliganded protein is the first structure of an unliganded neurophysin. Comparison with the liganded state indicated significant binding-induced conformational changes that were the largest in the loop region comprising residues 50-58 and in the 7-10 region. A subtle binding-induced tightening of the subunit interface of the dimer also was shown, consistent with a role for interface changes in neurophysin allosteric mechanism, but one that is probably not predominant. Interface changes are suggested to be communicated from the binding site through the strands of beta-sheet that connect these two regions, in part with mediation by Gly 23. Comparison of unliganded and liganded states additionally reveals that the binding site for the hormone alpha-amino group is largely preformed and accessible in the unliganded state, suggesting that it represents the initial site of hormone protein recognition. The potential molecular basis for its thermodynamic contribution to binding is discussed.

Allosteric Regulation↗
PubMed2001

Molecular cloning and sequencing of the circumsporozoite protein gene from Plasmodium falciparum strain FCC-1/HN and expression of the gene in Mycobacteria.

Mycobacterium bovis bacillus Calmette-Guérin (BCG) has been used as a live bacterial vaccine to immunize more than 2 billion people against tuberculosis. In an attempt to use this vaccine strain as a vehicle for protective antigens, the Plasmodium falciparum gene from strain FCC-1/HN encoding circumsporozoite protein (CSP) was amplified from the P. falciparum genome, sequenced, and expressed in M. bovis BCG under the control of an expression cassette carrying the promoter of heat shock protein 70 (HSP70) from Mycobacterium tuberculosis. The recombinant shuttle plasmid pBCG/CSP was introduced into mycobacteria by electroporation, and the recombinant mycobacteria harboring pBCG/CSP could be induced by heating to express CSP; the molecular mass of recombinant CSP was about 42 kDa. This report of expression of the almost-full-length P. falciparum CSP gene in BCG provides scientific evidence for the application of the HSP70 promoter in expressing a foreign gene in BCG and in development of BCG as a multivalent vectoral vaccine for malaria.

Amino Acid Sequence↗
PubMed2001

Vagosympathetic interactions in ischemia-induced myocardial norepinephrine and acetylcholine release.

To elucidate the pathophysiological roles of vagosympathetic interactions in ischemia-induced myocardial norepinephrine (NE) and acetylcholine (ACh) release, we measured myocardial interstitial NE and ACh levels in response to a left anterior descending coronary occlusion in the following groups of anesthetized cats: intact autonomic innervation (INT, n = 7); vagotomy (VX, n = 6); local administration of atropine (Atro, n = 6); transection of the stellate ganglia (TSG, n = 5); local administration of phentolamine (Phen, n = 6); and combined vagotomy and transection of the stellate ganglia (VX+TSG, n = 5). The maximum NE release was enhanced in the VX group (141 +/- 30 nmol/l, means +/- SE, P < 0.05) compared with the INT group (61 +/- 12 nmol/l). Neither the Atro (50 +/- 24 nmol/l) nor VX+TSG groups (84 +/- 25 nmol/l) showed enhanced NE release. The maximum ACh release was unaltered in the TSG and Phen groups compared with the INT group (19 +/- 4, 18 +/- 4, and 13 +/- 3 nmol/l, respectively). These findings indicate that the cardiac vagal afferent but not efferent activity reduced the ischemia-induced myocardial NE release. In contrast, the cardiac sympathetic afferent and efferent activities played little role in the ischemia-induced myocardial ACh release.

Acetylcholine↗
PubMed2001

Differential dynamic baroreflex regulation of cardiac and renal sympathetic nerve activities.

Although regional difference in sympathetic efferent nerve activity has been well investigated, whether this regional difference exists in the dynamic baroreflex regulation of sympathetic nerve activity remains uncertain. In anesthetized, vagotomized, and aortic-denervated rabbits, we isolated carotid sinuses and randomly perturbed intracarotid sinus pressure (CSP) while simultaneously recording cardiac (CSNA) and renal sympathetic nerve activities (RSNA). The neural arc transfer function from CSP to CSNA and that from CSP to RSNA revealed high-pass characteristics. The increasing slope of the transfer gain in the frequencies between 0.03 and 0.3 Hz was significantly greater for CSNA than for RSNA (2.96 +/- 0.72 vs. 1.64 +/- 0.73 dB/octave, P < 0.01, n = 9). The difference was hardly explained by the difference in static nonlinear characteristics of CSP-CSNA and CSP-RSNA relationships or by the difference in conduction velocities in the multifiber recording. These results indicate that the central processing in the brain stem differs between CSNA and RSNA. The neural arc of the baroreflex may exert differential effects on the heart and kidney in response to dynamic baroreflex activation.

Animals↗
PubMed2001

[Research advances of multidimensional reconstruction of ultrasonic heart images].

The methods, present research situation, existing problems, and application foreground of multidimensional reconstruction of ultrasonic heart images are discussed in the present paper. According to the procedure of multidimensional reconstruction of ultrasonic heart images, the discussions are presented in respect to image acquisition, processing, and display. Based on the present situation and existing problems, the future development and application foreground are proposed.

Echocardiography, Three-Dimensional↗
PubMed2001

[Review of filtering algorithms for medical ultrasonic images].

Several kinds of filters for medical ultrasonic images, such as multidimensional filter, adaptive weighted filter (for example, adaptive weighted median filter), adaptive window selecting filter (for example, homogeneous region growing mean filter and adaptive speckle suppression filter) and two-step filter, are introduced. The existing problems and the progress trend are also discussed. Some application instances for medical ultrasonic images of the filters discussed and the performance of the filters presented are based on the present authors' practice.

Algorithms↗
PubMed2001

[Study on abstracting method of high frequency components of ECG].

This paper presents a method to abstract high frequency components from ECG. A new signal averaging method based on vectorcardiographic loop matched alignment is proposed. It improves the crucial estimation of signal averaging and ensures that every one of the cardiographic signals participating in signal averaging comes from the same heart beat, so that each of three leads at least has uniform low pass filter effect. These conclusions have been confirmed by the analysis of ECG in clinical test.

Humans↗
PubMed2001

[Manufacture and study of porous poly(l-lactic acid) (PLLA)/beta-tricalcium phosphate (beta-TCP) composite].

A promising alternative to supply bone substitutes is to develop living tissue substitutes based on biodegradable materials, which is called bone tissue engineering. One of the research high-lights of bone tissue engineering is to design and manufacture scaffolds for cell attaching, migrating, and proliferating. A process which consists of a solvent casting stage, a compression molding stage and a leaching stage has been used to fabricate macroporous composites of poly(l-lactic acid) (PLLA) and beta-tricalcium phosphate (beta-TCP). The effects of the weight fraction of porogen--NaCl, of the weight ratio of PLLA to beta-TCP and of the diameters of beta-TCP on the porosities, the average pore diameters and the compressive yield strength and compressive modulus have been studied. The results showed that the porosities and the average pore diameters increased and the compressive yield strength and modulus decreased when the weight fraction went from 50% to 90%. The compressive yield strength and compressive modulus could be improved by changing the weight ratio of PLLA to beta-TCP and the diameters of beta-TCP in low-porosity composites (lower than 70%). But high-porosity composites (90%) were not reinforced by changing the weight ratio.

Biocompatible Materials↗