Localized avidin/biotin derivatization of glassy carbon electrodes using SECM

Different forms of the microreagent mode of SECM were used to attach biotin or make "clean" spots on micron-sized regions on the surface of a carbon electrode. In the direct-write mode, the SECM probe tip is used as an electrochemical "pen" depositing biotin in micron-sized lines on the carbon substrate as it is scanned across its surface. In the negative microreagent mode, the SECM probe tip is used as an electrochemical "eraser" cleaning of the surface attached molecules and leaving clean spots on the surface of a globally derivatized carbon surface. This type of simple micromodification of the surface of a carbon electrode will allow the fabrication of biosensors that can potentially be tailor-made for a variety of applications.     

Electron transfer kinetics at a biotin/avidin patterned glassy carbon electrode

STUDY DESIGN: Comparison of findings in plain radiography and conventional tomography with findings in plain radiography and magnetic resonance imaging of the upper cervical spine in consecutive patients with rheumatoid arthritis and with known or suspected abnormalities of the cervical spine. OBJECTIVES: To determine whether plain radiography and magnetic resonance imaging provide enough information to dispense with tomography in investigations of cervical spine involvement in rheumatoid arthritis. SUMMARY OF BACKGROUND DATA: With the recent advances in magnetic resonance imaging technology and the proliferation of magnetic resonance imaging techniques for specific clinical conditions. METHODS: Twenty-eight patients with rheumatoid arthritis and with known or suspected abnormalities of the cervical spine underwent a clinical neurologic examination; plain radiography, including full flexion lateral radiography; anteroposterior and lateral tomography at C1-C2; and magnetic resonance imaging at the same level in neutral position and in flexion. Two radiologists evaluated one image set consisting of plain radiography and conventional tomographic images and another image set consisting of plain radiography and magnetic resonance images, for each patient. RESULTS: Compared with conventional tomography and plain radiography, magnetic resonance imaging and plain radiography showed cystic lesions and erosions of the odontoid process and vertical atlantoaxial subluxation more often, showed anterior subluxation as often, and showed lateral atlantoaxial subluxation less often. CONCLUSION: Magnetic resonance imaging produces sufficiently distinct images of destruction of the odontoid and subluxations for it to replace conventional tomography in investigations of upper cervical spine involvement in rheumatoid arthritis.     

Pharmacokinetics and biodistribution of radiolabeled avidin, streptavidin and biotin

The extraordinary high affinity of avidin and streptavidin for biotin may be exploited in a two-step approach for delivering radiolabeled biotin derivatives suitable for imaging and therapy to target-bound streptavidin or avidin conjugated monoclonal antibodies (MAbs). The in vivo pharmacokinetics and biodistribution of radiolabeled avidin, streptavidin (SA) and DTPA-biocytinamide (DTPA-biotin) were studied in the rabbit and dog. SA circulated in the blood similar to other 60 kDa proteins, avidin cleared immediately and DTPA-biotin exhibited plasma clearance by glomerular filtration.     

Brain delivery of biotin bound to a conjugate of neutral avidin and cationized human albumin

The delivery of pharmaceuticals through the brain capillary endothelial wall, which makes up the blood-brain barrier (BBB) in vivo, may be facilitated by conjugation of therapeutics to brain drug delivery vectors. Since cationized albumin has been shown to undergo absorptive-mediated transcytosis through the BBB in vivo, cationized human serum albumin (cHSA) is a potential brain drug delivery vector in humans. Conjugation of biotinylated therapeutics to brain drug delivery vectors is facilitated by the preparation of vector/avidin conjugates. Therefore, the present studies describe the preparation of a cHSA-avidin conjugate and the delivery of 3H-biotin bound to this conjugate through the BBB in vivo in anesthetized rats. Since the cationic nature of avidin (AV) accelerates the removal of avidin-based conjugates from blood in vivo, the present studies also describe the preparation and the pharmacokinetics of 3H-biotin bound to a conjugate of cHSA and neutral avidin (NLA). The bifunctional nature of the conjugate was retained: the cHSA/NLA conjugate contained 2.8 to 6.8 biotin binding sites per conjugate, and the BBB permeability-surface area (PS) product for 3H-biotin bound to cHSA/NLA was at least 7-fold greater than the BBB PS product for 3H-biotin bound to a conjugate of NLA and native HSA (nHSA). The systemic clearance of the cHSA conjugate was reduced 10-fold by the use of NLA as opposed to AV. The increased area under the plasma concentration curve (AUC) of the cHSA-NLA conjugate correlated with an increase in brain delivery of 3H-biotin as compared to the brain delivery achieved with the cHSA/AV conjugate.(ABSTRACT TRUNCATED AT 250 WORDS)     

Formation of coatings with nanostructures and amorphous structures

A technique for spraying coatings as thick as 10 mm (one-point spraying technique) is designed to analyze the changes in the structure of rapidly quenched coatings of nickel-and iron-based eutectic alloys at high heating and cooling rates. Zones with amorphous, nano-, and microcrystalline structures form across the coatings. The microhardness of the coating of a grade 12496 nickel-based alloy (Ni-0.8% C-15% Cr-4.1% Si-3.1% B) is maximal in the zone with nanophases, and the microhardness increases from 11351.3 ± 461 to 16372 ± 2066 MPa as the load decreases from 0.2 to 0.01 N. This scale dependence is explained by the effect of microporosity at the boundaries of the sprayed particles. The microhardness of the initial grade 12496 alloy powder with strengthening microphases at a load of 0.01 N is 11572.9 ± 1996 MPa, which is lower than the maximum microhardness of the coating by a factor of 1.41. Thermoplastic treatment of the grade 12496 alloy coating increases its microhardness at a load of 0.05 N from 12372.8 ± 1226.8 to 13287 ± 612.5 MPa due to the strong cohesion of the particles in the coating and the formation of strengthening nanophases in it.     

Interaction of biotin with streptavidin. Thermostability and conformational changes upon binding

The effect of biotin binding on streptavidin (STV) structure and stability was studied using differential scanning calorimetry, Fourier transform infrared spectroscopy (FT-IR), and fluorescence spectroscopy. Biotin increases the midpoint temperature Tm, of thermally induced denaturation of STV from 75 degrees C in unliganded protein to 112 degrees C at full ligand saturation. The cooperativity of thermally induced unfolding of STV changes substantially in presence of biotin. Unliganded STV monomer has at least one domain that unfolds independently. The dimer bound to biotin undergoes a single coupled denaturation process. Simulations of thermograms of STV denaturation that take into account only the thermodynamic effects of the ligand with a Ka approximately 10(15) reproduce the behavior observed, but the estimated values of Tm are 15-20 degrees C lower than those experimentally determined. This increased stability is attributed to an enhanced cooperativity of the thermal unfolding of STV. The increment in the cooperativity is as consequence of a stronger intersubunit association and an increased structural order upon binding. FT-IR and fluorescence spectroscopy data reveal that unordered structure found in unliganded STV disappears under fully saturating conditions. The data provide a rationale for previous suggestions that biotin binding induces an increase in protein tightness (structural cooperativity) leading, in turn, to a higher thermostability.     

Electrochemical preparation and characterization of brain-like nanostructures of Y2O3

Nanostructured Y2O3 was successfully prepared via a two-step and template-free method.Firstly,yttrium hydroxide precursor was galvanostatically grown on the steel substrate from chloride bath by direct and pulse current deposition modes.Direct current deposition was carried out at the constant current density of 0.1 A/dm2 for 600 s.The pulse current was also performed at a typical on-time and off-time(ton=1 s and toff=1 s)with an average current density of 0.05 A/dm2(Ia=0.05 A/dm2)for 600 s.The obtained hydroxide films were then scraped from the substrates and thermally converted into final oxide product via heat-treatment.Thermal behaviors and phase transformations during the heat treatment of the hydroxide powder samples were investigated by differential scanning calorimetry(DSC)and thermogravimetric analysis(TGA).The final oxide products were characterized by means of X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR)and scanning electron microscopy(SEM).The results showed that the well-crystallized Y2O3 with brain-and sphere-like morphology were achievable via pulse and direct deposition modes,respectively.It was concluded that pulse current cathodic electrodeposition offered a facile route for preparation of nanostructured Y2O3.     

Spin-label studies on the anchoring and lipid-protein interactions of avidin with N-biotinylphosphatidylethanolamines in lipid bilayer membranes

The specific binding of hen egg white avidin to phosphatidylcholine lipid membranes containing spin-labeled N-biotinylphosphatidylethanolamines (biotin-PESLs) was investigated by using ESR spectroscopy. Spin-labeled biotin-PEs were prepared with the nitroxide group at position C-5, C-8, C-10, C-12, or C-14 of the sn-2 chain and were incorporated at 1 mol % in lipid bilayer membranes of dimyristoylphosphatidylcholine. Binding of avidin produced a strong and selective restriction of the biotin-PE lipid mobility at all positions of chain labeling, as shown by the ESR spectra recorded in the fluid lipid phase. The spectral components of the fraction of the biotin-PESLs that were not complexed by avidin indicated that the mobility of the bulk membrane lipids was unperturbed by binding avidin, as demonstrated by difference spectroscopy. Comparison of the positional profiles and temperature dependences of the outer hyperfine splittings from the biotin-PESLs suggests that the C-12 and C-14 positions of the avidin-bound biotin-PEs are in register with the C-5 and C-7/C-6 positions, respectively, of the chains of the bulk membrane lipids. This indicates that the biotin-PEs are partially withdrawn from the membrane, with a vertical displacement of ca. 7-8 A, on complexation with avidin. In addition, the specific lipid-protein interaction with avidin results in a selective reduction in the rates of lipid chain motion, as shown by the increased ESR line widths. These data define the way in which avidin is anchored to lipid membranes containing biotin-PEs.     

Structure and function of PCD/DCoH, an enzyme with regulatory properties

AIMS/BACKGROUND: The intentions of this study were to estimate agreement between two different autorefractors and standard subjective refraction techniques and to evaluate the clinical implications of relying on the autorefractor measurements. METHODS: Subjective refraction was carried out on 448 cycloplegic eyes and compared with cycloplegic readings with the Allergan Humphrey 500 autorefractor (448 eyes) and the Nidek AR-1000 autorefractor (160 eyes). Each refraction was followed by clinical visual acuity measurement. The study population comprised 224 healthy students, 107 men and 117 women, with a mean age of 20.6 (SD 1.1) years. RESULTS: Both the Nidek and Humphrey autorefractors measured more negative or less positive refractive values compared with subjective refraction and these biases were statistically significant (Humphrey right eye -0.23 D, p = 0.0001, left eye -0.20 D, p = 0.0001), (Nidek right eye -0.13 D, p = 0.0001, left eye -0.11 D, p = 0.0002). Comparing the results of autorefraction with subjective refraction, the Nidek was better than the Humphrey autorefractor in several ways: a smaller mean difference, better agreement between spherical equivalent values, narrower limits of agreements, and better visual acuity obtained with the autorefraction. On the other hand, the Humphrey autorefractor agreed better with subjective refraction concerning cylinder axis. CONCLUSION: The results show that both autorefractors represent a valuable complement to subjective refraction, but cannot be used as a replacement.     

Thermoelectric properties of LaFe_3CoSb_(12) skutterudite materials with different nanostructures

Nanostructures with different morphologies could profoundly influence the electron and phonon transport in thermoelectric materials and thus their properties could be improved by tuning the nanostructures.The LaFe3CoSb12 skutterudite nano powders with differentmorphologies were fabricated via a hydro/solvo thermal route.The microstructures of the hot-pressed LaFe3CoSb12 bulks were characterizedthrough X-ray diffraction(XRD) and scanning electron microscopy(SEM) and the effects of the nanostructures on the thermoelectric properties were investigated by measuring the electrical conductivity,the Seebeck coefficient and the thermal conductivity.The results suggestedthat the mixed morphology of nanorods and nanospheres could enhance the electrical conductivity largely although the Seebeck coefficientwas decreased and the thermal conductivity was increased slightly.Differently,a higher Seebeck coefficient,a lower thermal conductivity anda lower electrical conductivity could be obtained for the LaFe3CoSb12 bulk with a single morphology of nanospheres.Consequently,the figure of merit of LaFe3CoSb12 bulk with a mixed morphology of nanorods and nanospheres could be increased by about 59% as compared tothat with a single morphology of nanospheres.     

新一代信息技术尽在2011年中国国际信息通信展览会

“十一五”时期,我国信息通信产业建设在发展中取得了辉煌的成绩,2011年是“十二五”规划开局之年,我国将着力推动信息通信产业的整体性突破和跨越式发展,推动信息网络和信息技术的广泛应用。     

燃气发电在济钢的发展前景

预计2003年济钢富裕的各种煤气总量将达到307982 Nm3/h,为提高能源利用率,设计了燃气蒸汽联合发电工艺方案.该方案采用燃气轮机发电技术,高温废气进余热锅炉,预计达产后将提供电104700kW、10.5kV,每年为济钢降低电耗83760×104kW·h.     

提高烧结余热发电量的实践

马钢二铁烧结废气余热发电项目自2005年9月投入运行后,由于种种原因,余热发电生产极不稳定,发电量较低.为此,通过稳定烧结工艺操作,改进带冷密封提高烟气温度,以及优化余热发电系统等,大幅度提高了发电量.     

Kinetics of enzyme systems with unstable suicide substrates

We have designed and implemented a system to carry out cross-genome comparisons of open reading frames (ORFs) from multiple genomes. This implementation includes a genome profiling system that allows us to explore pairwise comparisons at different levels of match similarity and ask biologically motivated queries involving number and identity of ORFs, their function, functional category, distribution in genomes or in biological domains, and statistics on their matches and match families. This analysis required precise definition of new classification terms and concepts. We define the terms genomic signature, summary signature, biologic domain signature, domain class, match level, match family, and extended match family, then use these terms to define concepts, including genomically universal proteins and proteins characteristics of sets of genomes. We initiate an analysis based on automated FASTA (Pearson, 1996) comparison of 22,419 conceptually translated protein sequences from nine microbial genomes.     

Au／ZnO，Pd／ZnO和Au-Pd／ZnO催化剂甲醇部分氧化制氢性能的研究

采用PVP保护乙醇还原法制备Au/ZnO,Pd/ZnO和Au-Pd/ZnO催化剂,研究了Au,Pd和Au-Pd负载ZnO催化荆对甲醇部分氧化制氢性能的影响,并运用XRD,TPR和TPD等手段对催化剂进行了表征.结果表明,与Au/ZnO和Pd/ZnO催化剂相比,Au-Pd/ZnO双金属催化剂显示出较高的催化活性和氢气选择性、较低的CO选择性以及较好的稳定性.表征结果表明,Pd的加入抑制了Au粒子的烧结,使Au粒子变小,生成了富Au型Aux,Pdy合金,且Au-Pd与载体之间发生了一定的协同作用,从而提高了催化刺的活性和稳定性.     

I/D polymorphism of angiotensin converting enzyme gene and myocardial infarction

The DD genotype of angiotensin converting enzyme gene has been reported to be a risk factor for myocardial infarction. However, this association has not been confirmed in some study populations. We hypothesized that the discrepancies between these studies may be due to variations in the definition of ischemic heart diseases. According to the genotype of the ACE gene, we analyzed the profiles of 320 patients who underwent coronary angiography for suspected ischemic heart disease. We found that the II genotype of the ACE gene was associated with a longer period of time between the first anginal pain and the onset of myocardial infarction. Because higher ACE has been reported to be associated with higher plasminogen activator inhibitor-1 activity, our observation suggests that the genotype of the ACE gene is a marker of fibrinolytic activity.     

Insertion/deletion polymorphism in the angiotensin-converting enzyme gene associated with macroangiopathy and blood pressure in patients with non-insulin-dependent diabetes mellitus

In the search for new risk factors for diabetic macroangiopathy the insertion/deletion (I/D) polymorphism in the angiotensin-converting enzyme gene was studied in 237 consecutive patients (125 men and 112 women) with non-insulin-dependent diabetes. The female population showed an excess of ischemic electrocardiographic changes or definite myocardial infarctions in the patients homozygous for the deletion [D/D; odds ratio (OR) 2.8; 95% confidence interval (CI) 1.4-5.3] and in the insertion/deletion heterozygotes (I/D; OR 1.8; CI 1.1-3.1) compared with the patients homozygous for the insertion (I/I). In the total series coronary heart disease, cerebrovascular disease, and claudication were more often observed in the patients with I/D (OR 1.5; CI 1.0-2.2) or the D/D genotype patients (OR 1.7; CI 1.1-2.6) than in those with the genotype I/I. The systolic blood pressure was lower in patients with genotype I/I (138 +/- 19 mmHg) than in those with the genotype I/D (149 +/- 22 mmHg) or D/D (150 +/- 21 mmHg; P < 0.02). The prevalence of hypertension and the median urinary albumin excretion rate also tended to be lowest in the I/I genotype patients. Multiple logistic analysis revealed that in women the angiotensin-converting enzyme D/D genotype is independently associated with coronary heart disease. Our findings suggest that variation at the angiotensin-converting enzyme gene locus is one of the factors involved in the predisposition of diabetic patients to the development of arterial disease and hypertension.