High Incorporation Ratios Research Articles

The Thermal Energy Storage Characteristics of Oleic Acid Modified ZnO‐Decorated Polymer Matrix‐Supported Composite Phase Change Materials: Synthesis and Characterization

AbstractIn this study, modified nano zinc oxide (ZnO)‐reinforced polymer‐supported novel thermally enhanced form‐stable composite phase change materials (PCMs) are presented, which are prepared via water in oil emulsion polymerization and following impregnation process steps. First, ZnO nanoparticles are modified with oleic acid (OA) to obtain lipophilic structures for emulsion stability, which are designed to take a role as a heat transfer activator. To ensure the shape stabilization of n‐hexadecane used as organic PCM, polymeric support materials are synthesized in the presence of modified ZnO nanoparticles (ZnO@OA). The polymeric frameworks exhibit open porous morphology, and the thermal stability of the support matrix improves with the addition of ZnO nanofiller. In the second step, composite PCMs are prepared by incorporation of n‐hexadecane with the solvent‐assisted vacuum impregnation method into polymer composites. The 1.0% ZnO@OA incorporated composite PCM has the highest incorporation ratio and exhibits a thermal storage capability (η) of 100%. According to the T‐history and thermal conductivity tests, it is observed that the heat conduction rate is enhanced with the addition of ZnO@OA nanofiller. The conclusion is that the obtained ZnO@OA integrated composite PCMs have a remarkable potential for latent heat storage applications requiring low temperature in the range of 5–25 °C.

A hybrid steric ligand modification strategy promotes propylene (co)polymerization

Recently, a Hybrid Steric Ligand Modification (HSLM) strategy has been shown to significantly increase the polymerization activity and the branching degree of the resulting (co)polymers in the ethylene (co)polymerization via α-diimine catalysts. In this study, the HSLM strategy was employed for propylene (co)polymerization using a group of α-diimine Pd(II) catalysts with bulky hybrid ligands. The HSLM catalysts (Pd1-4) produced polypropylene with high molecular weights (45.4–156.9 kg/mol) and resulted in significantly high levels of activity (105 g mol−1 h−1). Additionally, nearly half of the propylene underwent chain straightening (1,3-enchainment = 43–46 %). Our findings suggest that Pd1-4 catalysts are more effective than the symmetrical catalysts Pd5-6 in producing high molecular weight polypropylene with high activity. Among all the catalysts tested, Pd4 with 4-tert-butylphenyl displayed the highest polymerization activity and molecular weight, although with lowest branching densities. It is suggested that the HSLM may provide a more open spatial configuration around the metal center, which facilitates the coordination and insertion of propylene molecules as well as chain walking. The hybrid Pd(II) catalysts showed moderate activity during the copolymerization of propylene with MA. The copolymers produced had low molecular weights (3.1–11.2 kg/mol), high branching densities (120–211/1000C), and high incorporation ratios (8.82–18.08 mol%). The copolymerization activity was highest with 4-tert-butylphenyl Pd4. The resulting P-MA copolymers had the highest molecular weight, the largest branching degree, and the lowest incorporation ratios.

Systematic investigations of ortho-aryl substitution effect on chain microstructure in nickel-catalyzed long chain α-olefin polymerization and copolymerization with methyl undecenoate

The tuning of branching density and branch-type distribution of the polyolefin through the ligand modification in “chain-walking”-type late transition metal catalysts is highly desired but remains a significant challenge in olefin polymerization. Herein, we performed a systematic investigation on the (co)polymerization of long chain α-olefin (1-octene and 1-decene) by a series of α-diimine Ni(II) catalysts with the varied ligand sterics arising from the number of the ortho-aryl (4-methylphenyl) substituents. The effects of structural variations, mainly including the steric tuning on the ortho-position of N-aryl ring and ligand backbone, steric distribution (ligand symmetry) tuning and electronic tuning, and polymerization conditions on catalytic activities, polymer molecular weight, polymer branching density, and branch-type distribution were described. The steric effect of ortho-methylphenyl substituents played a major role rather than the electronic effect in determining the preference of insertion fashion (1,2-insertion or 2,1-insertion) and chain walking in long chain α-olefin polymerization. As the bulk and number of ortho-methylphenyl substituents increased, the preferred 2,1-insertion and 1, ω-enchainment (chain straightening) were observed even at high monomer concentrations, thus leading to the decrease of branching density as well as the percentage of methyl branches, and eventually affording the semicrystalline “polyethylene-like” polymer with high Tm up to 121 °C and good mechanical properties. Moreover, the tuning of chain microstructure can be achieved over a very wide range through the modification of ligand sterics. Most importantly, these Ni(II) catalysts could copolymerize long chain α-olefin and polar monomer methyl undecenoate (MU) to generate the various functionalized semicrystalline copolymers with high incorporation ratios of MU up to 11% and Tm in a wide range of 5.6–93 °C.

Preparation of branched oligoethylene and polar functionalized oligoethylene using unsymmetrical arylamine based cationic Ni(II) and Pd(II) iminopyridyl catalysts

In this contribution, three unsymmetrical arylamine based pyridine-imine ligands and the corresponding nickel and palladium complexes were prepared and used for ethylene oligomerization. The nickel complexes are highly active (level of 106 g·mol−1·h−1) in catalyzing ethylene oligomerization to produce highly branched (66–89/1000C) oligoethylenes (1.4–3.2 kg/mol). The corresponding palladium complexes presented moderate catalytic activities (level of 104 g·mol−1·h−1) and low molecular weight (0.4–0.6 kg/mol) oligoethylenes with high branching densities (103–126/1000C) were yielded in ethylene oligomerization. Moreover, high incorporation ratio (6.86–14.16 mol%) ester functionalized oligoethylenes with low molecular weights (ca. 0.4 kg/mol) were yielded with these palladium complexes in ethylene–methyl acrylate co-oligomerization. Methyl branching comprises the majority of all the branching for the oligoethylenes yielded by nickel complexes and branching of C3+ comprises the majority with palladium ones. Hyperbranched architecture was identified for all the produced oligoethylenes and ester functionalized oligoethylenes. Most interestingly, compared with the reported pyridine-imine catalysts with fully substituted benzothiophenes, the partially benzothiophene substituted ones exhibited significantly higher activity and yielded much higher molecular weight oligoethylenes.

Direct Synthesis of Partially Chain-Straightened Propylene Oligomers and P-MA Co-Oligomers Using Axially Flexible Shielded Iminopyridyl Palladium Complexes.

In this study, a series of partially chain-straightened propylene oligomers and functional propylene−methyl acrylate (P-MA) co-oligomers were synthesized with 8-alkyl-iminopyridyl Pd(II) catalysts. The molecular weight and polar monomer incorporation ratio could be tuned by using Pd(II) catalysts with various 8-alkyl-naphthyl substituents (8-alkyl: H, Me, and n-Bu). In propylene oligomerization, all the 8-alkyl-iminopyridyl Pd(II) catalysts convert propylene to partially chain-straightened (119−136/1000 C) oligomers with low molecular weights (0.3−1.5 kg/mol). Among the catalysts, Pd1 with non-substituent (H) on the ligand showed the highest activity of 5.4 × 104 g/((mol of Pd) h), generating oligomers with the lowest molecular weight (Mn: 0.3 kg/mol). Moreover, polar-functionalized propylene-MA co-oligomers with very high incorporation ratios (22.8−36.5 mol %) could be obtained in the copolymerization using these 8-alkyl-iminopyridyl Pd(II) catalysts. Additionally, Pd1 exhibited the best performance in propylene-MA copolymerization as it displayed the highest MA incorporation ratio of up to 36.5 mol%. All the three catalysts are capable of generating partially chain-straightened P-MA co-oligomers and the activities decrease gradually while the molecular weight increases with the increasing steric hindrance of the alkyl substituent (H < Me < n-Bu). Compared to Pd4 with the rigid 8-aryl substituent, the flexible 8-alkyl-iminopyridyl Pd(II) catalysts (Pd1-3) not only showed much higher activities in the propylene oligomerization, but also yielded P-MA co-oligomers with significantly higher incorporation ratios in the propylene co-oligomerization.

SiO2‐Supported Ni(II) and Fe(II) Catalysts Bearing Sodium‐Sulfonate Group for Olefin Polymerization†

Comprehensive SummaryHeterogeneous catalysts have been dominant for industrial polyolefin production, offering many distinct advantages, such as controlling the morphology of the polymer and preventing reactor fouling. In this contribution, we designed several types of imine ligands bearing sodium‐sulfonate ionic groups and the corresponding nickel/iron catalysts. These catalysts could be immobilized on SiO2 with strong affinity and high catalyst loadings. The SiO2‐supported catalysts behaved better than their homogeneous counterparts during ethylene polymerization with extremely high activity (2.6 × 104 kg·mol−1·h−1) and high thermal stability. In addition, the supported nickel catalysts generated free‐flowing polyethylene with high molecular weight (Mn up to 2.65 × 103 kg·mol–1) and excellent morphology control, indicating no reactor fouling due to the leaching of catalyst. Moreover, for copolymerization, immobilized nickel catalysts showed a higher tolerance of polar monomers, and the efficient copolymerization of ethylene with undecylenic acid was achieved with high activity (450 kg·mol−1·h−1) and a high incorporation ratio (up to 12.3%).

Synthesis of highly branched polyethylene and ethylene-MA copolymers using hybrid bulky α-diimine Pd(II) catalysts

The types and sizes of N-o-aryl substituents in the α-diimine ligands strongly influence the ethylene (co)polymerization. Also, the combination of different substituents may play an unexpected role. A new class of bulky unsymmetrical acenaphthene-based α-diimine Pd(II) catalysts utilizing bulky “hybrid” anilines were designed, synthesized and characterized in this study. In ethylene polymerization, the α-diimine Pd(II) catalysts exhibited moderate activities, generating highly branched polyethylene with reasonable molecular weight. Moreover, these Pd(II) catalysts were also capable of preparing polar functionalized E-MA copolymers with moderate molecular weights and high incorporation ratios in the copolymerization of ethylene with methyl acrylate. Notably, compared to symmetrical bulky Pd(II) catalysts, the “hybrid” unsymmetrical system produced highly branched polyethylene and E-MA copolymers significantly.

Direct synthesis of various polar functionalized polypropylene materials with tunable molecular weights and high incorporation ratios

As compared with the classical α-diimine catalyst, iminopyridyl catalysts were observed to be highly efficient for the direct synthesis of polar functionalized polypropylene with tunable molecular weights and high incorporation ratios.

Highly efficient incorporation of polar comonomers in copolymerizations with ethylene using iminopyridyl palladium system

Given that high-molecular-weight functionalized polyethylene with high polar monomer incorporation ratio are often difficult to achieve, the development of highly efficient catalysts for ethylene and polar monomer copolymerization is still an urgent need in the field of olefin polymerization. In this contribution, we developed a series of highly sterically hindered iminopyridyl Pd(II) catalysts bearing the 8-aryl naphthyl substituents or/and dibenzosuberyl substituents. These substituents can provide an effective shield on the axial sites of the active center, thus allowing for the formation of high-molecular-weight polyethylene or functionalized polyethylene. Unexpectedly, these catalysts were also highly efficient for ethylene and various polar monomers copolymerization, giving access to high-molecular-weight functionalized polyethylene with very high incorporation ratio (up to 24%). The unique structure of the iminopyridyl ligand, especially its ability to shield the axial binding sites, may lead to permitting an adequate incorporation of polar monomers in our system.

Optimizing the economic, environmental and technical performance of concrete mixes with fly ash and recycled concrete aggregates

This study answers an important question that may arise when selecting a sustainable concrete, namely “concrete mixes containing low cement and recycled aggregates are a sustainable solution?” To answer this question, this study shows how to optimize concrete mixes in terms of technical performance, and economic and environmental life cycle. Firstly, the weight to be considered for each of these dimensions of performance depends on the concrete application (e.g. residential house and high-rise building) and on the consumer’s requirements (e.g. business as usual, green, strength, service life and cost scenarios). In this study, concrete mixes containing recycled concrete aggregates (RCA) and/or fly ash (FA) are optimized to be used in sustainable residential houses. For that purpose, the CONCRETop methodology (developed by the same authors of this study) was applied to these concrete mixes by considering a “green scenario”. The results show that, for sustainable residential houses, the concrete mixes made with high incorporation ratios of FA and RCA are considered the best option.

Carbonation of concrete made with high amount of fly ash and recycled concrete aggregates for utilization of CO2

This paper mainly focuses the effect of high incorporation ratios of fly ash (FA) and recycled concrete aggregates (RCA) on the carbonation resistance of concrete. The aim of using high volumes of these non-traditional materials is to decrease the use of natural resources and capture CO2. For that purpose, the carbonation resistance of low- and high-strength concrete mixes produced with various incorporation ratios of FA, fine RCA and coarse RCA, jointly and individually, is obtained and related with compressive strength, water absorption and chloride ion penetration. The results show that the carbonation depth of concrete increased up to 3 and 6 times when incorporating 30% and 60% of FA, respectively, and 100% of RCA led to up to 2.7 times increment. Therefore, the concrete cover for mixes made with FA and/or RCA should be increased in order to obtain an equivalent service life to that of conventional concrete. In spite of this fact, it is recommended to incorporate FA in RCA concrete because, in most concrete mixes, the carbonation depth due to the combined effect of both RCA and FA was lower than the sum of the values due to each effect. Additionally, the results show that, although the carbonation rate of concrete mixes containing high volumes of FA and RCA is high, their service life is also relatively high and the concrete reinforcement can be protected for up to 50 years.

Ultrasonic Pretreatment Combined with Dry-State Glycation Reduced the Immunoglobulin E/Immunoglobulin G-Binding Ability of α-Lactalbumin Revealed by High-Resolution Mass Spectrometry.

Bovine α-lactalbumin (α-LA) is one of major food allergens in cow's milk. The present work sought to research the effects of ultrasonic pretreatment combined with dry heating-induced glycation between α-LA and galactose on the immunoglobulin E (IgE)/immunoglobulin G (IgG)-binding ability and glycation extent of α-LA, determined by inhibition enzyme-linked immunosorbent assay and high-resolution mass spectrometry, respectively. The IgE/IgG-binding ability of glycated α-LA was significantly decreased as a result of ultrasonic pretreatment, while the average molecular weight, incorporation ratio (IR) value, location and number of glycation sites, and degree of substitution per peptide (DSP) value were elevated. When the mixtures of α-LA and galactose were pretreated by ultrasonication at 150 W/cm2, glycated α-LA possesses seven glycation sites, the highest IR and DSP values, and the lowest IgE/IgG-binding ability. Therefore, the decrease in the IgE/IgG-binding ability of α-LA depends upon not only the shielding effect of the linear epitope found to be caused by the glycation of K13, K16, K58, K93, and K98 sites but also the intensified glycation extent, which reflected in the increase of the IR value, the number of glycation sites, and the DSP value. Moreover, allergenic proteins and monosaccharides pretreated by ultrasonication and then followed by dry-state glycation were revealed as a promising way of achieving lower allergenicity of proteins in food processing.

Highly Active Copolymerization of Ethylene and N-Acetyl-O-(ω-Alkenyl)-l-Tyrosine Ethyl Esters Catalyzed by Titanium Complex.

A series of N-acetyl-O-(ω-alkenyl)-l-tyrosine ethyl esters were synthesized by the reaction of vinyl bromides (4-bromo-1-butene, 6-bromo-1-hexene, 8-bromo-1-octene and 10-bromo-1-decene) with N-acetyl-l-tyrosine ethyl ester. 1H NMR, elemental analysis, FT-IR, and mass spectra were performed for these N-acetyl-O-(ω-alkenyl)-l-tyrosine ethyl esters. The novel titanium complex can catalyze the copolymerization of ethylene and N-acetyl-O-(ω-alkenyl)-l-tyrosine ethyl esters efficiently and the highest catalytic activity was up to 6.86 × 104 gP·(molTi)−1·h−1. The structures and properties of the obtained copolymers were characterized by FT-IR, (1H)13C NMR, GPC, DSC, and water contact angle. The results indicated that the obtained copolymers had a uniformly high average molecular weight of 2.85 × 105 g·mol−1 and a high incorporation ratio of N-acetyl-O-(but-3-enyl)-l-tyrosine ethyl ester of 2.65 mol % within the copolymer chain. The units of the comonomer were isolated within the copolymer chains. The insertion of the polar comonomer into a copolymer chain can effectively improve the hydrophilicity of a copolymer.

In vitro evaluation of radiolabeled (125I) methanol extracts of yarrow in cell lines of MCF-7, PC-3, A-549 and Caco-2

Nowadays, cancer is still the second leading cause of death all over the world. Therefore, natural products which have anticancer and antitumor properties are come into prominence. Achillea family is known with anticancer and antitumor activity. Yarrow which has over a hundred bioactive compounds is a member of Achillea family. In current study; components of yarrow which was obtained after methanol extraction and purification were radiolabeled with 125I and effects of these radiolabeled components on the cells were examined with using Caco-2, MCF-7, A-549, PC-3 cell lines. As a result of these studies, seven peaks were obtained and the highest radiolabeling yield was calculated for 125I radiolabeled Peak 7 (95.00 ± 7.07, n = 4). To screen the biological properties of these radiolabeled peaks at determined cell lines, our ongoing effort was to evaluate incorporation percentage with time dependent. Furthermore, 125I-Peak 7 had highest incorporation ratio for whole cell lines and its incorporation percentage was increased with time dependent. Results of these in vitro studies were compatible with previous in vivo studies and traditional use of yarrow plants.

A simple protocol for amino acid type selective isotope labeling in insect cells with improved yields and high reproducibility

An easy to use and robust approach for amino acid type selective isotope labeling in insect cells is presented. It relies on inexpensive commercial media and can be implemented in laboratories without sophisticated infrastructure. In contrast to previous protocols, where either high protein amounts or high incorporation ratios were obtained, here we achieve both at the same time. By supplementing media with a well considered amount of yeast extract, similar protein amounts as with full media are obtained, without compromising on isotope incorporation. In single and dual amino acid labeling experiments incorporation ratios are consistently ≥90% for all amino acids tested. This enables NMR studies of eukaryotic proteins and their interactions even for proteins with low expression levels. We show applications with human kinases, where protein-ligand interactions are characterized by 2D [(15)N, (1)H]- and [(13)C, (1)H]-HSQC spectra.

A new nanomedicine based on didanosine glycerolipidic prodrug enhances the long term accumulation of drug in a HIV sanctuary

New nanomedicines could improve drug accumulation in HIV sanctuaries and ameliorate their antiretroviral efficiency. In this view, we propose herein a combined strategy based on a biomimetic prodrug of ddI and its formulation in well-characterized lipid nanoobjects. The glycerolipidic prodrug of ddI (ProddINP) has been synthesized and its bulk structure was characterized. An appropriate formulation of this prodrug has been designed using a rational approach combining different physicochemical techniques. The high incorporation ratio of the prodrug into dipalmitoylphosphatidylcholine (DPPC) bilayers was determined by DSC. Then two liposome preparation methods were compared, with respect to size, incorporation yield and molecular/supramolecular organization of vesicles. The best liposomal formulation of ProddINP has been checked to keep intact the anti-HIV activity of ddI. This formulation was finally compared to ddI after oral route in rat. The animal experiments evidenced the increase of ddI blood half life (3-fold) and its enhanced accumulation as prodrug form at 24 h in numerous organs and especially intestine after administration of ProddINP in comparison with free drug. Finally, the tested liposomal formulation of ProddINP seems to be a promising approach to eradicate HIV infection from intestinal sanctuaries where the virus can concentrate.

Chloroaniline/Lignin Conjugates as Model System for Nonextractable Pesticide Residues in Crop Plants

In vitro lignins formed by the peroxidase/H2O2-mediated polymerization of coniferyl alcohol in the presence of 3,4-dichloroaniline or [15N]aniline were studied by 1H, 13C, and 15N NMR spectroscopy. The anilines were >95% bound to the benzylic α-position of lignin side chains. Mild acid hydrolysis under simulated stomach conditions (0.1 M HCl, 37 °C) was studied as a first estimate of animal bioavail ability. The two extremes of facile or slow acid hydrolysis that are known for chloroaniline/lignin complexes could be reproduced by using low or high incorporation ratios of aniline to coniferyl alcohol (10 or 40 mol %, respectively). The case of facile acid hydrolysis and high animal bioavailability may be due to the high mole ratios used and may not be relevant for pesticidal crop plant residue levels of 3,4-dichloroaniline. The latter are typically in the parts per million range. On the basis of 15N NMR spectral fine structure, we propose that the acid-labile linkage may be due to anchimeric assistance in ...

Incorporation of 5-Iodo-2′-deoxyuridine and 5-Bromo-2′-deoxyuridine into Rodent DNA as Determined by Neutron Activation Analysis

Using 5-iodo-2′-deoxyuridine (IdU) and 5-bromo-2′deoxyuridine (BrdU) as DNA precursors, neutron activation analysis (NAA) of iodine and Br was developed as a quantitative method for determining DNA synthesis. Endogenous rodent tissue concentrations of bromine (Br) and iodine ranged 100-fold from a low of 0.06 μg of iodine/g of rat gastrointestinal tract (GIT) to a high of 5.99 μg of Br/g of rat kidney. All 10 rodent tissues had concentrations of Br 4 to 76 times higher than those of iodine. Rat hepatic Br concentrations could be reduced 17-fold by dietary and pharmacological methods. Female Fischer 344 rats and male C57BL/6 mice were given 4-8 intraperitoneal injections of either IdU or BrdU as a DNA precursor. Tissue clearance of iodine in IdU-treated rodents was both faster and more complete (in mice 4 h and in rats 17 h or less) than Br clearance from BrdU-treated rodents (at 162 h nonincorporated Br label still remains). In rat liver, lung, and kidney, the iodine label incorporated from IdU into DNA was stable for at least 162 h. The incorporation ratio is defined as the μg halogen/g tissue for either IdU- or BrdU-treated rodents divided by the μg halogen/g tissue of untreated rodents. NAA-based studies of DNA synthesis gave high incorporation ratios in rat liver (5.3), rat lung (6.7), rat GIT (19.0), rat spleen (24.0), mouse GIT (10.1), and mouse spleen (25.8).

Timely and topologically defined protein synthesis in the peri-implanting mouse endometrium revealed by light and electron microscopic radioautography.

Many efforts have been made to correlate the morphological and biochemical evidences with changes on physiological state of the uterus during activation of the implantation window. However, the exact mechanism involved in such a phenomenon remains to be determined. The present experiment used the radioautographic approach to determine whether, chronological and/or topological variations of proteins synthesis occur in the peri-implanting endometrium. Pregnant mice submitted to ovariectomy, received exogenous supply of nidatory estradiol. After 0 to 18 hrs. of time-lapsed estradiol effects, each animal received intraperitoneally, 1 hr. pulse 3H-leucine. The uterine fragments embedded in epoxy resin, were processed for light and electron microscope radioautography. The pattern of 3H-leucine incorporation in the luminal epithelium varied according to their relation with the blastocyst present in the uterine lumen. The highest incorporation ratio was seen in the epithelium just around the conceptus 6 hrs. after estradiol treatment, while in the cells localized at interimplantation site no peak of incorporation was seen. At ultrastructural level, cell organelles involved in protein synthesis were found to be labelled. Accumulation of silver grains occurred at apical portion of the epithelial cells showed accumulation of silver grains after 6 hrs. of estradiol treatment, but not on cell surface. The endometrial stromal cells localized around the blastocyst also showed a peak of 3H-leucine incorporation 6 hrs. after estradiol, but not in the cells localized at interimplantation sites. No increased labeling was seen on the components of extra-cellular matrix at ultrastructural level. The present radioautographic experiment showed that epithelial and stromal cells localized in the endometrium of implantation chamber, changed their pattern of protein synthesis under nidatory estradiol effects. This evidence suggests that the phenomenon of implantation window induced by estradiol, is not a systemic response of the whole pregnant endometrium. The activation involves only a specific population of the endometrial cells localized just around the conceptus.

Direct radioimmunoassay procedure for plasma dexamethasone with a sensitivity at the picogram level.

A simple radioimmunoassay (RIA) for the direct quantitation of plasma dexamethasone (DEX) at the picogram level has been developed. An antiserum with high specificity and avidity was obtained by the immunization of a carefully synthesized dexamethasone-21-succinyl-thyroglobulin with a high incorporation ratio. As little as 1 pg of DEX in 50 microL of plasma sample can be detected directly by this RIA without extraction and other purification procedures. Intra- and interassay coefficients of variation were 2.1 and 3.3% for plasma levels at 2.93 ng/mL or 2.3 and 7.2% for plasma levels at 0.88 ng/mL. Blank values for plasma of normal or pre-DEX patients were always under the detection limit (20 pg/mL). Excellent linearity (r = 0.9991-0.9999) was demonstrated between the serial dilutions of six plasma samples and their corresponding DEX concentrations. In single-dose DEX (0.25-1 mg) pharmacokinetic studies, plasma DEX was consistently detectable up to 24 h post dose. Compared with existing methods, this direct RIA demonstrates superior performance with regard to simplicity, sensitivity, specificity, and reproducibility. It also enables high sample throughput and has proven robust in our hands. This assay should be readily transferable to other laboratories for clinical or research purposes.