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At least 127 records · Page 7Linked to original sources
PubMed2007

Ring-opening cross-metathesis (ROCM) as a novel tool for the ligation of peptides.

The development of ring-opening cross-metathesis (ROCM) as a novel tool for the site-specific ligation of peptide units is reported. The resulting structural units at the site of ligation resulting from ROCM resemble proline as well as other known beta-turn stabilising structural units. ROCM under mild reaction conditions between a variety of peptides bearing a cyclic olefin with amino acids or peptides results in high yields. The peptidic cross-partners for metathesis are equipped with double bonds via the N and the C terminus and the side chain, respectively, to allow the synthesis of linear as well as non-linear and branched peptides. The ligation in this manner succeeds with low catalyst loadings, with no need for any excess of one reaction partner and with a high compatibility with a wide range of functional groups. Furthermore, the stereochemical outcome of the ROCM can easily be controlled by using a Hoveyda-type chiral catalyst. Fluorescence labelling of peptides is possible in the same manner when using a cyclic olefin equipped with a fluorescence marker.

Cycloparaffins↗
PubMed2006

Carbon nanorings: A challenge to theoretical chemistry.

High-level quantum-chemical methods show that the binding in the inclusion complex of hexamethylbenzene (HMB) in 6-cycloparaphenilacetylene (6-CPPA) cannot be explained only in terms of electrostatic interactions-caused by the polarization associated to curved pi-conjugated systems-and the inclusion of dispersion forces is definitely needed. The theoretical description of van der Waals interactions is notoriously complicated and in fact some DFT methods cannot even predict the existence of the relatively small supramolecular nanoring studied here. However, ab initio MP2 calculations agree with experimental data and show that, in the considered complex, the HMB fragment is placed at the center of the 6-CPPA ring. The binding energy, which is not available experimentally, is calculated to be around -14 kcal mol(-1) with a lower limit of -19 kcal mol(-1).

Benzene Derivatives↗
PubMed2005

The zeta potential of cyclo-olefin polymer microchannels and its effects on insulative (electrodeless) dielectrophoresis particle trapping devices.

While cyclo-olefin polymer microchannels have the potential to improve both the optical detection sensitivity and the chemical resistance of polymer microanalytical systems, their surface properties are to date not thoroughly characterized. These surface properties dictate, among other things, electrokinetic effects when electric fields are present. Here, we report the measurement of the zeta potential of cyclo-olefin polymers (injection-molded and hot-embossed Zeonor 1060R and 1020R) microchannels as a function of pH, counter-ion concentration, storage conditions, and chemical treatment in aqueous solutions both with and without EOF-suppressing additives. In contrast with previous reports, significant surface charge is measured, consistent with titration of charged sites with pK(a) = 4.8. Storage in air, acetonitrile, or aqueous solutions has relatively minor effects. While the source of the surface charge is unclear, chemical functionalization has shown that carboxylic acid groups are not present at the surface, consistent with the chemical structure of Zeonor. EOF-suppressing additives (hydroxypropylmethylcellulose) and conditioning in perchloric acid allow the surface charge to be suppressed. We demonstrate dielectrophoretic particle trapping devices in Zeonor 1060R substrates that show reduced trapping voltage thresholds as compared to previous implementations in glass.

Cycloparaffins↗
PubMed2005

Isoelectric focusing in cyclic olefin copolymer microfluidic channels coated by polyacrylamide using a UV photografting method.

As an alternative material to glass or silicon, microfluidic devices made from a cyclic olefin copolymer (COC) were fabricated. This material is of interest because of the relative ease of fabrication, low costs, and solvent resistance. However, as a result of the strong hydrophobic interactions normally present, COC surfaces are not suitable for protein separations. To reduce the protein adsorption and make COC suitable for protein separations, UV-initiated grafting of polyacrylamide was used to coat the surface of COC devices. The change in surface properties caused by different graft times was studied. The surface hydrophilicity and electroosmotic mobility were characterized by contact angle and electroosmosis measurements. Isoelectric focusing was performed to test protein separations in polyacrylamide-coated COC microchannels. A single protein, carbonic anhydrase, was used to analyze the focusing effects and peak capacities in uncoated and polyacrylamide-coated COC devices. Peak capacities ranging from 75 to 190 were achieved with a polyacrylamide-coated surface. A mixture of two proteins, conalbumin labeled with Alexa Fluor 488 and beta-lactoglobulin A labeled with Alexa Fluor 546, was used to test protein separations. Linear and rapid separation of proteins was achieved in the polyacrylamide-coated COC microfluidic device.

Acrylic Resins↗
PubMed2005

Poly(methylmethacrylate) and Topas capillary electrophoresis microchip performance with electrochemical detection.

A capillary electrophoresis (CE) microchip made of a new and promising polymeric material: Topas (thermoplastic olefin polymer of amorphous structure), a cyclic olefin copolymer with high chemical resistance, has been tested for the first time with analytical purposes, employing an electrochemical detection. A simple end-channel platinum amperometric detector has been designed, checked, and optimized in a poly-(methylmethacrylate) (PMMA) CE microchip. The end-channel design is based on a platinum wire manually aligned at the exit of the separation channel. This is a simple and durable detection in which the working electrode is not pretreated. H(2)O(2) was employed as model analyte to study the performance of the PMMA microchip and the detector. Factors influencing migration and detection processes were examined and optimized. Separation of H(2)O(2) and L-ascorbic acid (AsA) was developed in order to evaluate the efficiency of microchips using different buffer systems. This detection has been checked for the first time with a microchip made of Topas, obtaining a good linear relationship for mixtures of H(2)O(2) and AsA in different buffers.

Ascorbic Acid↗
PubMed1979

The respiratory effects of dezocine and pentazocine in man.

The respiratory effects of dezocine and pentazocine were studied in five volunteers. Based on their effects over a 3-hour period, it was found that dezocine was 8.6 times as potent as pentazocine in terms of their respiratory depressant effects. The clinical significance of these findings remains to be determined.

Analgesics↗
PubMed1979

A double-blind study of dezocine in cancer pain.

A double-blind crossover comparison of intramuscularly administration of 10 mg dezocine (Wy 16225), 10 mg morphine, and placebo in ten patients with cancer pain has shown that a dezocine single dose is superior to placebo in producing relief of moderate to severe pain. No side effects were observed.

Analgesics↗
PubMed1986

Intravenous dezocine for postoperative pain: a double-blind, placebo-controlled comparison with morphine.

Dezocine, a new mixed agonist-antagonist opioid analgesic, and morphine were compared in a double-blind study in 206 patients with postoperative pain. The analgesic efficacy of single intravenous injections of dezocine (2.5, 5.0, and 10.0 mg), morphine (5.0 mg), and placebo was assessed by verbal and visual scales at regular intervals for six hours after administration. All active treatments provided greater pain relief than placebo. Pain relief with dezocine 5 and 10 mg was significantly greater (P less than .05) than with placebo for up to four and five hours, respectively, and with morphine up to one hour. Pain relief scores were significantly higher (P less than .05) with morphine than with placebo at all observations except that of the fifth hour, and higher with dezocine 2.5 mg than with placebo for the first 30 minutes. Doses of 5 and 10 mg of dezocine produced approximately the same peak analgesic effect, with the larger dose having a longer duration of effect. All active treatments produced mild to moderate sedation. Side effects were few and mild or moderate with all of the treatments. The physician's and the patients' evaluations favored dezocine in a dose-dependent order, with morphine 5 mg rated lower than dezocine 5 mg and higher than dezocine 2.5 mg.

Adolescent↗
PubMed1995

Single- and multiple-dose pharmacokinetics of dezocine in patients with acute or chronic pain.

The pharmacokinetic properties of dezocine were examined in 15 patients with acute or chronic pain. In 3 groups of 5 patients each, serum levels were determined at various intervals after single intravenous doses of 5, 10, and 20 mg. After these single doses, dezocine was very rapidly distributed (mean t1/2 alpha less than 2 minutes), and then rather rapidly eliminated (mean t1/2 beta about 4 hours); the apparent volume of distribution was large (mean Vz beta about 6 L/kg) as was the total clearance (mean CL about 1.5 L/h/kg). In 2 groups of 5 patients each, serum levels were determined after the first and third of 3 intravenous doses of 5 or 20 mg given at 3-hour intervals. The pharmacokinetic parameters after these multiple doses were consistent with those after the single doses. Although some observations were suggestive, there was no unequivocal evidence that the pharmacokinetics were dose-related. In 7 serum samples containing dezocine at concentrations ranging from 12.8 to 522 ng/mL, the mean (+/- SE) proportion of dezocine bound to protein was 91.6 +/- 0.8%.

Acute Disease↗
PubMed2003

Tork: Conformational analysis method for molecules and complexes.

A conformational search method for organic molecules and bimolecular complexes is presented. The method, termed Tork, uses normal-mode analysis in bond-angle-torsion coordinates and focuses on a key subset of torsional coordinates to identify natural molecular motions that lead the initial conformation to new energy minima. New conformations are generated via distortion along these modes and their pairwise combinations, followed by energy minimization. For complexes, special treatment is accorded to the six coordinates that specify the position and orientation of one molecule relative to the other. Tests described here show that Tork is highly efficient for cyclic, acyclic, and mixed single molecules, as well as for host-guest complexes.

Algorithms↗
PubMed2006

Application of standard DFT theory for nonbonded interactions in soft matter: prototype study of poly-para-phenylene.

We present a detailed analysis of the application of density functional theory (DFT) methods to the study of structural properties of molecular and supramolecular systems, using as a paradigmatic example three para-phenylene-based systems: isolated biphenyl, single chain poly-para-phenylene, and crystalline biphenyl. We use different functionals for the exchange correlation potential, the local density (LDA), and generalized gradient approximations (GGA), and also different basis sets expansions, localized, plane waves (PW), and mixed (localized plus PW), within the reciprocal space formulation for the hamiltonian. We find that regardless of the choice of basis functions, the GGA calculations yield larger interring distances and torsion angles than LDA. For the same XC approximation, the agreement between calculations with different basis functions lies within 1% (LDA) or 0.5% (GGA) for distances, and while PW and mixed basis calculations agree within 1 degrees for torsion angles, the localized basis results show larger angles by approximately 8 degrees and a nonmonotonic dependence on basis size, with differences within 6 degrees. The most prominent features, namely the torsion between rings for isolated molecule and infinite chain, and planarity for the molecule in crystalline environment, are well reproduced by all DFT calculations.

Biphenyl Compounds↗