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P Ratio (p + ratio)
Selected AbstractsNitrogen and Phosphorus Release from Decomposing Leaves under Sub-Humid Tropical Conditions,BIOTROPICA, Issue 2 2001A. B. Kwabiah ABSTRACT For many soils of the tropics, inputs of organic materials are essential to sustain soil fertility and crop production. Research in the quality of organic inputs, a key factor controlling rates of decomposition and nutrient release, continues to guide selection and use of organic materials as nutrient sources. The relationship between decomposition patterns and the quality parameters of the fresh leaves of six agroforestry species: Sesbania sesban, Croton megalocarpus, Calliandra calothyrsus, Tithonia diversifolia, Lantana camara, and Senna spectabilis, was investigated in a litterbag study over a period of 77 days in the highlands of western Kenya. The litterbags were buried 1 cm below the soil surface and covered with soil of ca 1 cm thickness. Percent leaf mass and total N and P that remained with time strongly correlated with total P and C/P ratio (R2= 0.60-0.90) during the first 35 days of study; but afterwards, correlation was stronger with the initial soluble polyphenolics (Pp)/P ratio (R2= 0.69-0.92) than with total P and C/P ratio. Loss of leaf mass and release of N and P followed the exponential function, yt= y0* e- kt, from which the specific decay rate constants (k) were calculated for loss of leaf mass (kB) and release of N (kN) and P (Kp). Among the plant species, the k values were lowest in Calliandra with kB= 0.012/d, kN= 0.017/d and kp= 0.044/d. Lantana had the highest K values with kg= 0.067/d and kp= 0.119/d, but the highest kN value of 0.109/d occurred in Tithonia. The kB values for all organic materials were lower than their corresponding kN and kp values, suggesting that leaching of N and P from litters may have augmented the microbial mineralization of N and P. There was a strong correlation between the kB, kN, and kp values and total P (r = 0.82-0.96; P 0.01), but not total N, lignin (LIG), or Pp. Rates of N and P release followed the general trend: Tithonia > Senna > Lantana > Sesbania > Croton > Calliandra. The results indicated that, among the quality parameters studied, total P is the most important factor controlling rate of decomposition and N and P release from organic inputs in the area of study. [source] Precipitation of Carbonated Calcium Phosphate Powders from a Highly Supersaturated Simulated Body Fluid SolutionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2007Ingo Hofmann Carbonated hydroxy apatite (CHA) powders were prepared by precipitation from a modified simulated body fluid (5 × M-SBF). The ionic concentrations were five times higher than in human blood plasma with the exception of Mg2+ and HCO3, concentrations that were reduced in order to accelerate crystal growth. Spheroaggregates of CHA platelets with molar (Ca+Mg)/P ratios ranging from 1.44 to 1.56 were obtained after precipitation at 50°C. The crystallite size in the c direction was approximately 31 nm and depending on the precipitation time, a CO32, content of 1.8,5.2 wt% was determined. Using this low-temperature precipitation method, CHA powders with a high specific surface area of 83 m2/g and a composition and crystallite size close to those of the mineral phase of human bone were obtained. [source] ChemInform Abstract: Cotemplating Ionothermal Synthesis of a New Open-Framework Aluminophosphate with Unique Al/P Ratio of 6/7.CHEMINFORM, Issue 42 2008Hongzhu Xing Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Effects of influent C/N ratio, C/P ratio and volumetric exchange ratio on biological phosphorus removal in UniFed SBR processJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 12 2008Chen-hong Zhao Abstract BACKGROUND: UniFed SBR is a novel process that can achieve high levels of nitrogen and phosphorus removal simultaneously in a simple single SBR tank. In this study, effects of influent C/N ratio, influent C/P ratio and volumetric exchange ratio on biological phosphorus removal in UniFed SBR process were investigated in a lab-scale UniFed apparatus treating real domestic wastewater. RESULTS: The results showed that phosphorus removal efficiency increased as C/N ratio increased from 27% at 2.8 to 88% at 5.7. For C/N ratios 6.5 and above, complete phosphorus removal could be achieved. When C/N ratios and volumetric exchange ratio were fixed at 6 and 33%, respectively, phosphorus removal efficiency remained at 100% for C/P ratios higher than 33; effluent phosphate concentration was below the detection limit. For C/P ratios lower than 33, phosphorus removal efficiency decreased linearly with C/P ratio. Under the same influent C/N ratio and C/P ratio, the following factors all contributed to better phosphorus removal performance: greater volumetric exchange ratio; more organic substrate for PAOs to utilize, less inhibition by NOx, of phosphorus release during the feed/decant period; more PHB synthesized; and more aerobic phosphate uptake. CONCLUSION: High influent C/N ratio, high C/P ratio and high volumetric exchange ratio were beneficial to phosphorus removal in this process. Copyright © 2008 Society of Chemical Industry [source] Nitrogen and Phosphorus Release from Decomposing Leaves under Sub-Humid Tropical Conditions,BIOTROPICA, Issue 2 2001A. B. Kwabiah ABSTRACT For many soils of the tropics, inputs of organic materials are essential to sustain soil fertility and crop production. Research in the quality of organic inputs, a key factor controlling rates of decomposition and nutrient release, continues to guide selection and use of organic materials as nutrient sources. The relationship between decomposition patterns and the quality parameters of the fresh leaves of six agroforestry species: Sesbania sesban, Croton megalocarpus, Calliandra calothyrsus, Tithonia diversifolia, Lantana camara, and Senna spectabilis, was investigated in a litterbag study over a period of 77 days in the highlands of western Kenya. The litterbags were buried 1 cm below the soil surface and covered with soil of ca 1 cm thickness. Percent leaf mass and total N and P that remained with time strongly correlated with total P and C/P ratio (R2= 0.60-0.90) during the first 35 days of study; but afterwards, correlation was stronger with the initial soluble polyphenolics (Pp)/P ratio (R2= 0.69-0.92) than with total P and C/P ratio. Loss of leaf mass and release of N and P followed the exponential function, yt= y0* e- kt, from which the specific decay rate constants (k) were calculated for loss of leaf mass (kB) and release of N (kN) and P (Kp). Among the plant species, the k values were lowest in Calliandra with kB= 0.012/d, kN= 0.017/d and kp= 0.044/d. Lantana had the highest K values with kg= 0.067/d and kp= 0.119/d, but the highest kN value of 0.109/d occurred in Tithonia. The kB values for all organic materials were lower than their corresponding kN and kp values, suggesting that leaching of N and P from litters may have augmented the microbial mineralization of N and P. There was a strong correlation between the kB, kN, and kp values and total P (r = 0.82-0.96; P 0.01), but not total N, lignin (LIG), or Pp. Rates of N and P release followed the general trend: Tithonia > Senna > Lantana > Sesbania > Croton > Calliandra. The results indicated that, among the quality parameters studied, total P is the most important factor controlling rate of decomposition and N and P release from organic inputs in the area of study. [source] Effects of influent C/N ratio, C/P ratio and volumetric exchange ratio on biological phosphorus removal in UniFed SBR processJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 12 2008Chen-hong Zhao Abstract BACKGROUND: UniFed SBR is a novel process that can achieve high levels of nitrogen and phosphorus removal simultaneously in a simple single SBR tank. In this study, effects of influent C/N ratio, influent C/P ratio and volumetric exchange ratio on biological phosphorus removal in UniFed SBR process were investigated in a lab-scale UniFed apparatus treating real domestic wastewater. RESULTS: The results showed that phosphorus removal efficiency increased as C/N ratio increased from 27% at 2.8 to 88% at 5.7. For C/N ratios 6.5 and above, complete phosphorus removal could be achieved. When C/N ratios and volumetric exchange ratio were fixed at 6 and 33%, respectively, phosphorus removal efficiency remained at 100% for C/P ratios higher than 33; effluent phosphate concentration was below the detection limit. For C/P ratios lower than 33, phosphorus removal efficiency decreased linearly with C/P ratio. Under the same influent C/N ratio and C/P ratio, the following factors all contributed to better phosphorus removal performance: greater volumetric exchange ratio; more organic substrate for PAOs to utilize, less inhibition by NOx, of phosphorus release during the feed/decant period; more PHB synthesized; and more aerobic phosphate uptake. CONCLUSION: High influent C/N ratio, high C/P ratio and high volumetric exchange ratio were beneficial to phosphorus removal in this process. Copyright © 2008 Society of Chemical Industry [source] Calcium-phosphate surface coating by casting to improve bioactivity of titaniumJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 5 2001Taiji Sohmura Abstract In order to improve the bioactivity of titanium, an original surface treatment was attempted with the use of a casting technique was attempted. Pure titanium was cast into a special graphite mold in which the cavity wall was coated with hydroxyapatite (HA) powder. According to analyses of X-ray diffraction and EDX, the existence of HA and CaO and uptake of Ca and P on the surface of the titanium castings were identified. By immersing the specimen in Hank's solution, the concentrations of Ca and P on the surface increased with immersion time, and the formation of a thin layer with characteristics of spherical HA precipitates was observed after 1 week. The concentrations of Ca and P elements and the Ca/P ratio on the HA layer increased with immersion time. The formation of the HA layer on the titanium cast by this treatment was significantly accelerated compared with pure titanium. The present surface treatment of Ti is expected to improve early bone fixation of Ti implants. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 58: 478,485, 2001 [source] Hydroxyapatite Coating on Thermally Oxidized Titanium SubstratesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2001Minkmas Vatanatham Titanium substrates were oxidized in oxygen or air at temperatures of 600°,800°C, then immersed in solutions of 2.0mM, 20.7mM CaCl2 and 1.2mM,12.4mM KH2PO4 for aging periods of 0.5,10 d. The titanium surface was successfully coated with hydroxyapatite (HAP) when the substrates were oxidized in oxygen gas at 610°C for 1 h and then aged in a solution of 2.00mM Ca2+ and 1.20mM PO43,. The Ca/P ratio of the surface coating increased toward its stoichiometric HAP value (return 10/6) as the aging time increased; the Ca/P ratio attained a value of 1.66 after 10 d. [source] A solid-state NMR investigation of the structure of nanocrystalline hydroxyapatiteMAGNETIC RESONANCE IN CHEMISTRY, Issue 6 2006Christian Jäger Abstract Nanocrystalline hydroxyapatite (HAp) prepared by a precipitation route was investigated. The X-ray diffraction (XRD) powder patterns of the elongated nanocrystals with a typical diameter of about 10 nm and length of 30,50 nm (by transmission electron microscopy (TEM)) revealed the presence of HAp with significantly broadened XRD reflections. However, Ca deficiency was found, as the Ca/P ratio was 1.5 only (so-called calcium-deficient hydroxyapatite (CDHA)), and not 1.67. This Ca deficiency of nanocrystalline HAp is explained using NMR. It is shown unambiguously that (i) the nanocrystals consist of a crystalline core and a (disordered) surface region with a relative phosphate content of about 1:1, (ii) the crystalline core is HAp, and (iii) the surface region is dominated by hydrogen phosphate anions (with no hydroxyapatite-like structural motif) and structural water (hydrate). From the relative phosphate content and taking into account the crystal shape, the thickness of the surface layer along the main crystal axis could be estimated to be about 1 nm, and the average chemical composition of the surface layer has been determined. Finally, a Ca/P ratio of 1.52 was estimated from the NMR data that compares well with the value of 1.51 from chemical analysis. The important consequences are that the surface of nanocrystalline HAp has nothing in common with the bulk composition and that the chemistry of such materials (e.g. the binding of protein molecules to phosphate surfaces) must be reconsidered. Copyright © 2006 John Wiley & Sons, Ltd. [source] Phosphorus requirements and optimum calcium/phosphorus ratio in the diet of mrigal Cirrhinus mrigala (Ham.) fingerlingsJOURNAL OF APPLIED ICHTHYOLOGY, Issue 4 2004B. N. Paul Summary An experiment was conducted to investigate phosphorus requirements and the optimal calcium/phosphorus (Ca/P) ratio on growth and carcass tissue composition of mrigal Cirrhinus mrigala (c. 6 g). Five purified diets were formulated to contain Ca/P ratios of 1 : 0 (0.35 : 0), 1 : 1 (0.35 : 0.35), 1 : 2 (0.31 : 0.63), 1 : 3 (0.24 : 0.71), and 1 : 4 (0.19 : 0.75), respectively. Growth performance and feed conversion ratio of mrigal responded significantly (P < 0.01) to the Ca =0.19 : P = 0.75 diet. Carcass protein, lipid, and P percentage also increased significantly with the higher P level. Based on this study, it may be concluded under the given conditions that the optimum Ca : P ratio in mrigal feed is 0.19 : 0.75. [source] Natural and Prosthetic Heart Valve Calcification: Morphology and Chemical Composition CharacterizationARTIFICIAL ORGANS, Issue 4 2010Raquel F. Weska Abstract Calcification is the most common cause of damage and subsequent failure of heart valves. Although it is a common phenomenon, little is known about it, and less about the inorganic phase obtained from this type of calcification. This article describes the scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy and Ca K -edge X-ray absorption near edge structure (XANES) characterization performed in natural and bioprosthetic heart valves calcified in vivo (in comparison to in vitro-calcified valves). SEM micrographs indicated the presence of deposits of similar morphology, and XANES results indicate, at a molecular level, that the calcification mechanism of both types of valves are probably similar, resulting in formation of poorly crystalline hydroxyapatite deposits, with Ca/P ratios that increase with time, depending on the maturation state. These findings may contribute to the search for long-term efficient anticalcification treatments. [source] Reproductive hormonal changes and catamenial pattern in adolescent females with epilepsyEPILEPSIA, Issue 9 2008Hamed A. El-Khayat Summary Purpose: We aimed to evaluate the effect of epilepsy on the reproductive hormones levels among female patients, and to investigate the frequency of catamenial pattern of seizures. Methods: A total of 42 female patients with epilepsy and 21 healthy females (control group) were included. Subjects were at least 2 years postmenarche with regular cycles. Symptoms of premenstrual syndrome (PMS) were assessed using calendar of premenstrual experience scoring. Patients were evaluated for catamenial pattern of seizures. Levels of FSH, LH, estradiol (E), and progesterone (P) were assessed for all subjects in the three phases of the cycles. Pelvi-abdominal ultrasound was performed near time of ovulation, to follow up size of mature follicle. Results: Symptoms of PMS were not different in patients and controls, or in patients with and those without catamenial tendency. In both perimenstrual (M) and midluteal phases, FSH and P levels were lower and E/P ratio higher in patients group. There was a catamenial pattern of seizures in 31% of patients (53.8% M C1; 46.15% inadequate luteal phase C3pattern). Patients with C3pattern showed lower P levels in the midluteal phase compared to patients with noncatamenial pattern, to those with C1pattern or to controls. Patients with C1pattern had lower P levels than controls in the M phase. Conclusion: There was evident disruption in the reproductive hormones in female patients with epilepsy with lower FSH and P levels and higher E/P ratio. A total of 31% of patients showed catamenial pattern of seizures (C1and C3patterns) that was significantly related to P withdrawal. [source] Benthic secondary production and biomass of insects emerging from a northern German temperate streamFRESHWATER BIOLOGY, Issue 2 2000Rainer Poepperl Summary 1Secondary production and emergence of aquatic insects were examined in the outlet of Lake Belau, Northern Germany, by means of benthic samples and emergence traps. 2At three stream sections annual larval secondary production varied between 4.9 and 10.8 gDM (dry mass) m -2 year -1. Insects contributed with 3.4, 8.9, and 8.7% to the total macroinvertebrate production that varied between 56.5 and 215.1 gDM m -2 year -1. Emerged biomass was between 1.0 and 2.0 gDM m -2 year -1. At all three stream sections Diptera dominated with a larval production of 3.0,l6.1 gDM m -2 year -1, followed by Trichoptera with 1.0,2.1 and Ephemeroptera with up to 0.9 gDM m -2 year -1. 3Average larval production amounted to 9.0 gDM m -2 year -1 and emerged biomass to 1.7 gDM m -2 year -1. Larvae of insects amounted to 7.0% of total macroinvertebrate production. 4The ratio of annual emerged biomass to secondary production (E/P) varied among individual taxa. At the stream sections the ratio ranged from 15.9% to 20.1% with an average of 18.3% for the stream. 5Relative constancy of the E/P ratio suggests that the determination of emerged biomass can be used as a method for estimating the secondary production of aquatic insects. The composition of functional feeding groups clearly differs between emerged biomass and total macroinvertebrate production. Therefore, the method does not allow conclusions on the level of production of the whole benthic community. However, composition of functional feeding groups at emergence roughly reflects composition of these groups in the benthic insect community. [source] Performance of calibration standards for antigen quantitation with flow cytometry in chronic lymphocytic leukemiaCYTOMETRY, Issue 6 2007Eva D. Rossmann Abstract Background: The fluorescence intensities of CD3, CD4 on T cells and CD20, CD22 molecules on B cells were quantitatively measured on lymphocytes from chronic lymphocytic leukemia (CLL) patients and healthy donors. Methods: The performance of three different types of microbeads was compared, i.e. Quantum molecules of equivalent soluble fluorochrome (Q-MESF), Quantum simply cellular (QSC), and QuantiBRITEÔ (QB). As all PE-conjugates had a F/P ratio of 1:1, the MESF units represented also the antibody binding capacity (ABC). Results: The ABCs of CD4 and CD20 antigens estimated with QSC (ABCQSC) were higher than those assigned with QB (ABCQB) with an average difference 49%. Higher numbers of antigenic sites were obtained with Q-MESF than with QSC for CD20 antigen. On the contrary, CD4 antigenic sites numbers estimated with QSC were higher than those estimated with Q-MESF. ABC values estimated with Quantum MESF PE (ABCQ-MESF) were ,15% higher than ABCQSC, whereas ABCQ-MESF was ,49% higher than ABCQB. Statistically significant correlations were found between the values obtained using various standards. The present study is the first to report down-regulation of CD3 antigen on T cells from patients with CLL. Conclusions: This study emphasizes the relevance of quantitative measurement of fluorescence intensity by flow cytometry as a standardized approach to measure and interpret the expression of some CLL markers and reduce variability of results obtained at different sites in multi-center clinical studies. © 2007 Clinical Cytometry Society [source] Pancreas volumes in humans from birth to age one hundred taking into account sex, obesity, and presence of type-2 diabetesCLINICAL ANATOMY, Issue 8 2007Y. Saisho Abstract Our aims were (1) by computed tomography (CT) to establish a population database for pancreas volume (parenchyma and fat) from birth to age 100 years, (2) in adults, to establish the impact of gender, obesity, and the presence or absence of type-2 diabetes on pancreatic volume (parenchyma and fat), and (3) to confirm the latter histologically from pancreatic tissue obtained at autopsy with a particular emphasis on whether pancreatic fat is increased in type-2 diabetes. We measured pancreas volume in 135 children and 1,886 adults (1,721 nondiabetic and 165 with type-2 diabetes) with no history of pancreas disease who had undergone abdominal CT scan between 2003 and 2006. Pancreas volume was computed from the contour of the pancreas on each CT image. In addition to total pancreas volume, parenchymal volume, fat volume, and fat/parenchyma ratio (F/P ratio) were determined by CT density. We also quantified pancreatic fat in autopsy tissue of 47 adults (24 nondiabetic and 23 with type-2 diabetes). During childhood and adolescence, the volumes of total pancreas, pancreatic parenchyma, and fat increase linearly with age. From age 20,60 years, pancreas volume reaches a plateau (72.4 ± 25.8 cm3 total; 44.5 ± 16.5 cm3 parenchyma) and then declines thereafter. In adults, total (,32%), parenchymal (,13%), and fat (,68%) volumes increase with obesity. Pancreatic fat content also increases with aging but is not further increased in type-2 diabetes. We provide lifelong population data for total pancreatic, parenchymal, and fat volumes in humans. Although pancreatic fat increases with aging and obesity, it is not increased in type-2 diabetes. Clin. Anat. 20:933,942, 2007. © 2007 Wiley-Liss, Inc. [source] Anatoxin-a toxin in the cyanobacterium Planktothrix rubescens from a fishing pond in northern ItalyENVIRONMENTAL TOXICOLOGY, Issue 3 2004Emanuela Viaggiu Abstract A heavy algal bloom occurring in a fishing pond in northern Italy full of Salmo trutta was examined for algae taxonomy and toxic production. The dominant algal species (98%) was identified as the cyanobacterium Planktothrix rubescens (D.C. ex GOMONT) Komarek Anagnostidis, based on morphological examination, and it was revealed to be toxic in mouse and Vibrio fischeri bioassays. The toxin was identified as anatoxin-a using high-performance liquid chromatography and confirmed using liquid chromatography,mass spectrometry (LC-MS). The mouse bioassay gave signs of poisoning, as previously reported for anatoxin-a. The LC-MS confirmed the presence of an anatoxin-a peak at m/z 166 (M+H+). The content of toxin in the field population was estimated at 12.13 ,g/g of fresh cells. The bloom was sustained by the very high N/P ratio in the water. This is the first report in Italy of an anatoxin-a-producing Planktothrix rubescens population. © 2004 Wiley Periodicals, Inc. Environ Toxicol 19: 191,197, 2004. [source] Preparation of monomethyl poly(ethylene glycol)- g -chitosan copolymers with various degrees of substitution: Their ability to encapsulate and condense plasmid DNAJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Wei Zhang Abstract Chitosan (CS) has great potential as a nonvirus gene delivery vector, but its application is limited because of poor water solubility. Monomethyl poly(ethylene glycol) (mPEG)- graft -CS copolymers were synthesized by the reaction of mPEG,aldehyde (oxidized mPEG) with amino groups on CS chains; they showed enhanced solubility in water. Copolymers with various mPEG degrees of substitution (DS) and CS molecular weights were obtained, and their capabilities of DNA encapsulation were compared through gel retardation assay and particle size and , potential measurements. The effects of different ratios of primary amines on CS to the phosphate groups on DNA (N/P ratios), DS, and molecular weights on particle size and encapsulation efficiency were investigated. The results show that high N/P ratios and proper DS were necessary for the formation of well-distributed complex particles. Among all of these samples, mPEG (3.55),CS (50 kDa)/DNA complexes [where the parentheses following mPEG indicate DS (%), and the parentheses following CS indicate the molecular weight of CS] raised the , potential from negative to positive most quickly, yielded the smallest particle size, and were retarded in agarose gel at the lowest N/P ratio; this indicated the best efficiency of DNA encapsulation. On the contrary, mPEG (0.80),CS (50 kDa)/DNA complexes raised the , potential to positive most slowly, fluctuated around the value 0 from N/P ratios of 15 : 1 to 30 : 1, and were retarded in agarose gel at the highest N/P ratio; this indicated the lowest efficiency of encapsulating plasmids. Copolymers with desirable efficiencies of DNA encapsulation could be promising gene carriers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Studies on the condensation of depolymerized chitosans with DNA for preparing chitosan-DNA nanoparticles for gene delivery applicationsJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2009Viola B. Morris Abstract High molecular weight chitosan (CS) was depolymerized by oxidative degradation with NaNO2 at room temperature to get 11 samples of CS derivatives of varying molecular weights with a view to assessing their effective molecular weight range for gene delivery applications. Viscosity studies indicated that the molecular weight of the depolymerized CS was proportional to the CS/NaNO2 ratio. The condensation behavior of DNA/CS complexes at various charge ratios was studied using UV spectroscopy, FTIR, CD, SEM, and AFM. The results indicated that CSs having very low molecular weights and high charge density exhibited strong binding affinity to DNA compared to high molecular weight CSs. However, the very low molecular weight (1.9,7.7 kDa) CSs were found to form aggregates easily even at very low charge ratios. On the other hand, CSs having medium molecular weight (49,51 kDa) and high degree of deacetylation (DD) gave stable uniform-sized nanoparticles. Biological studies carried out with the spherical nano-sized polyplexes formed between CS of 50 kDa (DD of 94%) and pEGFP plasmid DNA at N/P ratio of 5.0 showed excellent gene transfection efficiency at pH 6.5 in HeLa cells without cytotoxicity indicating their potential as genedelivery carriers. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009 [source] Improving Gene Delivery Efficiency of Bioreducible Poly(amidoamine)s via Grafting with Dendritic Poly(amidoamine)sMACROMOLECULAR BIOSCIENCE, Issue 4 2010Ya-Nan Xue Abstract Dendritic poly(amidoamine)s (PAMAM)s were introduced into the side chains of disulfide-containing poly(amidoamine)s via repetitive Michael addition and amidation. The bioreducible poly(amidoamine)s grafted with dendritic polyamidoamines showed high buffer capacity, low cytotoxicity and strong DNA binding ability at low N/P ratio. They were able to condense DNA into small sized polycation/DNA complexes, which degraded and released the incorporated DNA under reductive conditions. In comparison to the original disulfide-containing poly(amidoamine) with aminoethyl side chain, the grafting of the bioreducible poly(amidoamine) with dendrimer greatly improved the transfection efficiencies of 293T and HeLa cells with foreign DNA at various N/P ratios. The structure,gene delivery property relations of dendrimer-grafted polycations will provide valuable insight into the design of highly efficient and less toxic polycationic gene carriers. [source] Functionalization of Chitosan via Atom Transfer Radical Polymerization for Gene DeliveryADVANCED FUNCTIONAL MATERIALS, Issue 18 2010Yuan Ping Abstract It is of crucial importance to modify chitosan-based polysaccharides in the designing of biomedical materials. In this work, atom transfer radical polymerization (ATRP) was employed to functionalize chitosan in a well-controlled manner. A series of new degradable cationic polymers (termed as PDCS) composed of biocompatible chitosan backbones and poly((2-dimethyl amino)ethyl methacrylate) (P(DMAEMA)) side chains of different length were designed as highly efficient gene vectors via ATRP. These vectors, termed as PDCS, exhibited good ability to condense plasmid DNA (pDNA) into nanoparticles with positive charge at nitrogen/phosphorus (N/P) ratios of 4 or higher. All PDCS vectors could well protect the condensed DNA from enzymatic degradation by DNase I and they displayed high level of transfectivity in both COS7, HEK293 and HepG2 cell lines. Most importantly, in comparison with high-molecular-weight P(DMAEMA) and ,gold-standard' PEI (25 kDa), the PDCS vectors showed considerable buffering capacity in the pH range of 7.4 to 5, and were capable of mediating much more efficient gene transfection at low N/P ratios. At their own optimal N/P ratios for trasnsfection, the PDCS/pDNA complexes showed much lower cytotoxicity. All the PDCS vectors were readily to be degradable in the presence of lysozyme at physiological conditions in vitro. These well-defined PDCS polymers have great potentials as efficient gene vectors in future gene therapy. [source] Preparation of monomethyl poly(ethylene glycol)- g -chitosan copolymers with various degrees of substitution: Their ability to encapsulate and condense plasmid DNAJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Wei Zhang Abstract Chitosan (CS) has great potential as a nonvirus gene delivery vector, but its application is limited because of poor water solubility. Monomethyl poly(ethylene glycol) (mPEG)- graft -CS copolymers were synthesized by the reaction of mPEG,aldehyde (oxidized mPEG) with amino groups on CS chains; they showed enhanced solubility in water. Copolymers with various mPEG degrees of substitution (DS) and CS molecular weights were obtained, and their capabilities of DNA encapsulation were compared through gel retardation assay and particle size and , potential measurements. The effects of different ratios of primary amines on CS to the phosphate groups on DNA (N/P ratios), DS, and molecular weights on particle size and encapsulation efficiency were investigated. The results show that high N/P ratios and proper DS were necessary for the formation of well-distributed complex particles. Among all of these samples, mPEG (3.55),CS (50 kDa)/DNA complexes [where the parentheses following mPEG indicate DS (%), and the parentheses following CS indicate the molecular weight of CS] raised the , potential from negative to positive most quickly, yielded the smallest particle size, and were retarded in agarose gel at the lowest N/P ratio; this indicated the best efficiency of DNA encapsulation. On the contrary, mPEG (0.80),CS (50 kDa)/DNA complexes raised the , potential to positive most slowly, fluctuated around the value 0 from N/P ratios of 15 : 1 to 30 : 1, and were retarded in agarose gel at the highest N/P ratio; this indicated the lowest efficiency of encapsulating plasmids. Copolymers with desirable efficiencies of DNA encapsulation could be promising gene carriers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Improving Gene Delivery Efficiency of Bioreducible Poly(amidoamine)s via Grafting with Dendritic Poly(amidoamine)sMACROMOLECULAR BIOSCIENCE, Issue 4 2010Ya-Nan Xue Abstract Dendritic poly(amidoamine)s (PAMAM)s were introduced into the side chains of disulfide-containing poly(amidoamine)s via repetitive Michael addition and amidation. The bioreducible poly(amidoamine)s grafted with dendritic polyamidoamines showed high buffer capacity, low cytotoxicity and strong DNA binding ability at low N/P ratio. They were able to condense DNA into small sized polycation/DNA complexes, which degraded and released the incorporated DNA under reductive conditions. In comparison to the original disulfide-containing poly(amidoamine) with aminoethyl side chain, the grafting of the bioreducible poly(amidoamine) with dendrimer greatly improved the transfection efficiencies of 293T and HeLa cells with foreign DNA at various N/P ratios. The structure,gene delivery property relations of dendrimer-grafted polycations will provide valuable insight into the design of highly efficient and less toxic polycationic gene carriers. [source] Brush-Like Amphoteric Poly[isobutylene- alt -(maleic acid)- graft -oligoethyleneamine)]/DNA Complexes for Efficient Gene TransfectionMACROMOLECULAR RAPID COMMUNICATIONS, Issue 13 2010Majad Khan Abstract Synthetic gene delivery vectors, especially cationic polymers have attracted enormous attention in recent decades because of their ease of manufacture, targettability, and scaling up. However, certain issues such as high cytotoxicity and low transfection efficiency problems have hampered the advance of nonviral gene delivery. In this study, we designed and synthesized brush-like amphoteric poly[isobutylene- alt -(maleic acid)- graft -oligoethyleneamine] capable of mediating highly efficient gene transfection. The polymers are composed of multiple pendant oligoethyleneimine molecules with alternating carboxylic acid moiety grafted onto poly[isobutylene- alt -(maleic anhydride)]. The polymer formed from pentaethylenehexamine {i.e., poly[isobutylene- alt -(maleic acid)- graft -pentaethylenehexamine)]} was able to condense DNA efficiently into nanoparticles of size around 200,nm with positive zeta potential of about 28,30,mV despite its amphoteric nature. Luciferase expression level and percentage of GFP expressing cells induced by this polymer was higher than those mediated with polyethyleneimine (branched, 25,kDa) by at least one order of magnitude at their optimal N/P ratios on HEK293, HepG2, and 4T1 cells. In vitro cytotoxicity testing revealed that the polymer/DNA complexes were less cytotoxic than those of PEI, and the viability of the cells after being incubated with the polymer/DNA complexes at the optimal N/P ratios was higher than 85%. This polymer can be a promising gene delivery carrier for gene therapy. [source] Phosphorus and nitrogen in a monomictic freshwater lake: employing cyanobacterial bioreporters to gain new insights into nutrient bioavailabilityFRESHWATER BIOLOGY, Issue 6 2010OSNAT GILLOR Summary 1. It is an uncontested paradigm that an adequate supply of the macronutrients nitrogen (N) and phosphorus (P) is critical for maintaining phytoplankton primary production in aquatic ecosystems; it has also been suggested that there is an optimal total N : total P ratio for this globally significant process. 2. This ratio, normally assessed by chemical determination of the major dissolved N and P species, poses a dilemma: do chemical measurements actually reflect the bioavailable fraction of these nutrient pools? Accurate determination of the various N and P species and their fluxes into phytoplankton cells is notoriously difficult. 3. To provide a possible solution to this difficulty, we engineered strains of the cyanobacterium Synechococcus sp. strain PCC 7942 that ,report' on N and P bioavailability via a bioluminescent signal. These strains were used to quantify, for the first time, bioavailable concentrations of these essential macronutrients in a freshwater lake. 4. Only a small fraction (0.01,1%) of the chemically determined P may actually be bioavailable to this unicellular cyanobacterium and, by inference, to the phytoplankton community in general. In contrast, bioavailable N comprises most of the dissolved N pool. Consequently, bioavailable N : P ratios based on these assays are higher then those based on chemical determinations, indicating that P limitation in Lake Kinneret is more extensive then previously thought. [source] Calcium balance in Daphnia grown on diets differing in food quantity, phosphorus and calciumFRESHWATER BIOLOGY, Issue 11 2009XUE-JIA HE Summary 1.,The influences of dietary phosphorus (P) and food concentration on the calcium (Ca) balance in Daphnia magna were examined in this study at two different ambient Ca concentrations (0.5 and 10 mg Ca L,1). Daphnia were grown by feeding the young adults differentially under contrasting dietary P conditions [molar C : P ratio = c. 900 and c. 90 as low P (LP) and high P (HP), respectively], ambient Ca concentrations [0.5 mg and 10 mg Ca L,1 as low Ca (LCa) or high Ca (HCa), respectively] and food levels [0.15 or 1.5 mg C L,1 as low food (LF) or high food (HF), respectively] for 5 days. 2.,The specific Ca contents of daphniids (1.9,6.5% of dry weight,1) increased with increasing Ca concentration, food level and dietary P content, although the food level did not affect the Ca content in the HPHCa treatment. A radioactive tracer method showed that the food level did not affect the influx of Ca from the water under LP conditions, but the Ca influx under HP conditions doubled with a HF level. A LP condition also led to a decrease in Ca influx with a HF level. 3.,During the 3 days of efflux, generally only a small proportion of Ca (2.6,3.3%) was retained by the daphniids, but this retention increased (14,23%) under low ambient Ca concentrations and under P-limitation. Excretion was the most important pathway for Ca loss (accounting for 50,60% of body Ca), followed by moulting (20,47%), but the relative contribution of these two pathways (excretion and moulting) did not vary among all the different treatments. The absolute loss of Ca through excretion and moulting, on the contrary, differed with different ambient Ca concentrations and dietary P conditions. A HF level led to an increase in the loss rates in most cases. 4.,Our study strongly suggested that there is an interaction between an essential metal (Ca) and macronutrients (C and P) in freshwater crustaceans with HCa and P contents. The results imply that variation in environmental nutrient conditions may change the Ca budget in crustaceans and may affect the dynamics of Ca in the epilimnion of freshwaters. [source] Sources and transport of algae and nutrients in a Californian river in a semi-arid climateFRESHWATER BIOLOGY, Issue 12 2007NOBUHITO OHTE Summary 1. To elucidate factors contributing to dissolved oxygen (DO) depletion in the Stockton Deep Water Ship Channel in the lower San Joaquin River, spatial and temporal changes in algae and nutrient concentrations were investigated in relation to flow regime under the semiarid climate conditions. 2. Chlorophyll- a (chl- a) concentration and loads indicated that most algal biomass was generated by in-stream growth in the main stem of the river. The addition of algae from tributaries and drains was small (c.15% of total chl- a load), even though high concentrations of chl- a were measured in some source waters. 3. Nitrate and soluble-reactive phosphorus (SRP) were available in excess as a nutrient source for algae. Although nitrate and SRP from upstream tributaries contributed (16.9% of total nitrate load and 10.8% of total SRP load), nutrients derived from agriculture and other sources in the middle and lower river reaches were mostly responsible (20.2% for nitrate and 48.0% for SRP) for maintaining high nitrate and SRP concentrations in the main stem. 4. A reduction in nutrient discharge would attenuate the algal blooms that accelerate DO depletion in the Stockton Deep Water Ship Channel. The N : P ratio, in the main stem suggests that SRP reduction would be a more viable option for algae reduction than nitrogen reduction. 5. Very high algal growth rates in the main stem suggest that reducing the algal seed source in upstream areas would also be an effective strategy. [source] Essential fatty acids and phosphorus in seston from lakes with contrasting terrestrial dissolved organic carbon contentFRESHWATER BIOLOGY, Issue 1 2007KELLY GUTSEIT Summary 1. It is often assumed that lakes highly influenced by terrestrial organic matter (TOM) have low zooplankton food quality because of elemental and/or biochemical deficiencies of the major particulate organic carbon pools. We used the biochemical [polyunsaturated fatty acids, especially eicosapentaenoic acid (EPA) , 20:5,3] and elemental (C : P ratio) composition of particulate matter (PM) as qualitative measures of potential zooplankton food in two categories of lakes of similar primary productivity, but with contrasting TOM influence (clear water versus humic lakes). 2. C : P ratios (atomic ratio) in PM were similar between lake categories and were above 400. The concentration (,g L,1) and relative content (,g mg C,1) of EPA, as well as the particulate organic carbon concentration, were higher in the humic lakes than in the clear-water lakes. 3. Our results show high fatty acid quality of PM in the humic lakes. The differences in the biochemical quality of the potential zooplankton food between lake categories can be attributed to the differences in their phytoplankton communities. 4. High biochemical quality of the food can result in high efficiency of energy transfer in the food chain and stimulate production at higher trophic levels, assuming that zooplankton are able to ingest and digest the resource available. [source] Threshold elemental ratios for carbon versus phosphorus limitation in DaphniaFRESHWATER BIOLOGY, Issue 12 2005THOMAS R. ANDERSON Summary 1. The transition from carbon (C) to phosphorus (P) limited growth in Daphnia depends not only on the C : P ratio in seston, i.e. food quality, but also on food quantity. Carbon is commonly believed to be limiting at low food because of the energetic demands of basal metabolism. The critical C : P ratio in seston (otherwise known as the threshold elemental ratio, TER) above which P is limiting would then be high when food is scarce. 2. A new model that differentiates between the C : P requirements for growth and maintenance is presented that includes terms for both C and P in basal metabolism. At low food the calculated TERs for Daphnia of around 230 are only slightly higher than values of 200 or so at high intake. Seston C : P often exceeds 230, particularly in oligotrophic lakes where phytoplankton concentration is low and detritus dominates the diet, indicating the potential for limitation by P. 3. The analysis highlights the importance of P, as well as C, in maintenance metabolism and the overall metabolic budget, such that food quality is of importance even when intake is low. Further measurements of C and P metabolism at low food, in particular basal respiration and excretion rates, are needed in order to improve our understanding of the interacting roles of food quantity and quality in zooplankton nutrition. [source] Low algal carbon content and its effect on the C : P stoichiometry of periphytonFRESHWATER BIOLOGY, Issue 11 2005PAUL C. FROST Summary 1. We examined the contribution of algal cells to periphytic organic carbon and assessed the effects of variable biomass composition on the carbon : phosphorus (C : P) ratio of periphyton. We compiled more than 5000 published and unpublished observations of periphytic carbon : chlorophyll a (C : Chl) ratios, an index of algal prevalence, from a variety of substrata collected from lake and low-salinity coastal habitats. In addition, we converted estimates of algal biovolume into algal C to obtain an independent measure of cellular algal carbon in periphyton. This information was used in a model relating periphyton C : P ratio to algal cellular carbon, the algal C : P ratio, and the C : P ratio of non-algal organic matter in periphyton. 2. The mean C : Chl ratio of periphyton (405) was relatively high with values in >25% of the samples exceeding 500. On average, 8.4% of total periphyton C was accounted for by C in algal cells. Only 15% of samples were found to have more than 15% periphyton C in cellular algal carbon. Our model showed a nonlinear relationship between periphytic C : P ratios and the C : P ratio of algal cells in the periphyton when non-algal organic matter was present. However, even at relatively low cellular algal C (<10% of total C), algal C : P ratios can strongly affect the C : P ratio of periphyton as a whole (i.e. algal cells plus other organic matter). 3. The high C : Chl ratios and the low biovolume-derived algal C of periphyton samples in our data set indicate that algal cells are typically a minor component of organic carbon in periphyton, However, this minor contribution would not preclude algal cellular stoichiometry from notably influencing periphyton C : P ratios. [source] Preparation of phosphorus and carbohydrate microcapsules for manipulating dietary C : P ratio for aquatic suspension-feedersFRESHWATER BIOLOGY, Issue 2 2003Daniel A. Kreeger SUMMARY 1.,Dietary phosphorus can be limiting for aquatic animals such as suspension-feeders. However, our understanding has been limited by the difficulty of manipulating dietary P without altering other aspects of food quality. We microencapsulated various forms of bioavailable P with carbohydrate to manipulate dietary C : P ratio for suspension-feeders. 2.,Calcium phosphate, sodium hexametaphosphate, sodium tripolyphosphate and tetrasodium pyrophosphate were each mixed with a concentrated solution of a carbohydrate base (either maltodextrin or potato starch) and microencapsulated using an interfacial polymerisation technique. Each of the 10 types of capsules produced had a particle size ideal for suspension-feeders (3,10 ,m). 3.,Leakage rates were low (<12% of capsule weight per day). Relative enzymatic breakdown in vitro by carbohydrases (amylase or cellulase) was similar among the 10 capsule types and was always at least 15 times the comparable leakage rate. 4.,Release of dissolved P from enzyme-treated capsules varied depending on capsule P content. Liberation of P from capsules prepared from 20% w/w sodium hexametaphosphate in maltodextrin (molar C : P = 1.8) was three times greater than all other types, and this combination appears most suitable as a dietary supplement for zooplankton. 5.,Although P content and capsule integrity were greatly influenced by choice of carbohydrate, choice of P compound, and the mixing ratio of the two, P-rich artificial microparticles can be produced that have low leakiness, high digestibility, and a physical size suitable for aquatic suspension-feeders. Therefore, microcapsules represent promising tools for manipulating dietary C : P for suspension feeders. [source] | ||||||||||||||||||||||||||||||||||||||||||||||