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At least 1,423 records · Page 79Linked to original sources
PubMed1997

Psychometric properties of the Depression Anxiety Stress Scales (DASS) in clinical samples.

The psychometric properties of the Depression Anxiety Stress Scales (DASS) were evaluated in two studies using large clinical samples (N = 437 and N = 241). In Study 1, the three scales comprising the DASS were shown to have excellent internal consistency and temporal stability. An exploratory factor analysis (principal components extraction with varimax rotation) yielded a solution that was highly consistent with the factor structure previously found in nonclinical samples. Between-groups comparisons indicated that the DASS distinguished various anxiety and mood disorder groups in the predicted direction. In Study 2, the conceptual and empirical latent structure of the DASS was upheld by findings from confirmatory factor analysis. Correlations between the DASS and other questionnaire and clinical rating measures of anxiety, depression, and negative affect demonstrated the convergent and discriminant validity of the scales. In addition to supporting the psychometric properties of the DASS in clinical anxiety and mood disorders samples, the results are discussed in the context of current conceptualizations of the distinctive and overlapping features of anxiety and depression.

Adolescent↗
PubMed1986

Determination of urapidil and its metabolites in human serum and urine: comparison of liquid-liquid and fully automated liquid-solid extraction.

Direct injection of biological fluids into an automated pre-column system for high-performance liquid chromatographic quantitation of urapidil and its metabolites was compared with sample preparation by liquid-liquid extraction. On-line sample purification and enrichment proved to be a superior method for quantitation of the parent compound and its metabolites in serum, plasma, and urine. The automatic procedure circumvents the disadvantages of conventional sample work-up by extraction, such as time-consuming and complicated sample preparation, the need for large samples, poor recovery, and formation of artefacts. Injection of 100 microliters of serum into the automated pre-column system, followed by high-performance liquid chromatography with electrochemical detection, gave a detection limit for urapidil and metabolites in serum of 5 ng/ml. For urine samples with injection of 50 microliters the detection limit for the same compounds was 100 ng/ml using UV detection, which is adequate for evaluating renal excretion. Accuracy as well as precision of the analyses were better than 10% for concentrations above 100 ng/ml. In contrast to the direct injection method, liquid-liquid extraction requires 1-2 ml of serum, plasma, or urine for clean-up. Moreover, the extraction yield for the main human metabolite is significantly lower, and its stability after extraction is inadequate for using an autosampler. The direct injection method was applied in studying the pharmacokinetics and metabolism of urapidil in healthy volunteers and patients. So far, ca. 15 000 urapidil samples (both serum or plasma and urine) have been analysed by this technique.

Antihypertensive Agents↗
PubMed2003

Di-diabody: a novel tetravalent bispecific antibody molecule by design.

The clinical development of bispecific antibodies (BsAb) as therapeutics has been hampered by the difficulty in preparing the materials in sufficient quantity and quality by traditional methods. In recent years, a variety of recombinant methods have been developed for efficient production of BsAb, both as antibody fragments and as full-length IgG-like molecules. These recombinant antibody molecules possess dual antigen-binding capability with, in most cases, monovalency to each of their target antigens. Here, we describe an efficient approach for the production of a novel tetravalent BsAb, with two antigen-binding sites to each of its target antigens, by genetically fusing a bispecific/divalent diabody to, via the hinge region, the N-terminus of the CH(3) domain of an IgG. The novel BsAb, which we termed "di-diabody", represents a tetravalent diabody dimer resulting from dimerization between the hinge region and the CH(3) domains. A di-diabody was constructed using two antibodies directed against the two tyrosine kinase receptors of vascular endothelial growth factor, expressed both in a single Escherichia coli host and in mammalian cells, and purified to homogeneity by a one-step affinity chromatography. Compared to the bispecific/divalent diabody, the tetravalent di-diabody binds more efficiently to both of its target antigens and is more efficacious in blocking ligand binding to the receptors. The di-diabody retained good antigen-binding activity after incubation at 37 degrees C in mouse serum for 72 h, demonstrating good product stability. Finally, expression of the di-diabody in mammalian cells yielded higher level of production and better antibody activity. This design and expression for BsAb fragments should be applicable to any pair of antigen specificities.

Angiogenesis Inducing Agents↗
PubMed2006

Fixational eye movements and motion perception.

Small eye movements are necessary for maintained visibility of the static scene, but at the same time they randomly oscillate the retinal image, so the visual system must compensate for such motions to yield the stable visual world. According to the theory of visual stabilization based on retinal motion signals, objects are perceived to move only if their retinal images make spatially differential motions with respect to some baseline movement probably due to eye movements. Motion illusions favoring this theory are demonstrated, and psychophysical as well as brain-imaging studies on the illusions are reviewed. It is argued that perceptual stability is established through interactions between motion-energy detection at an early stage and spatial differentiation of motion at a later stage. As such, image oscillations originating in fixational eye movements go unnoticed perceptually, and it is also shown that image oscillations are, though unnoticed, working as a limiting factor of motion detection. Finally, the functional importance of non-differential, global motion signals are discussed in relation to visual stability during large-scale eye movements as well as heading estimation.

Afterimage↗
PubMed2002

Mechanical conditions in the internal stabilization of proximal tibial defects.

OBJECTIVES: The goal was to design a method which would permit an assessment of the suitability of a newly developed implant under physiological-like loading conditions. Information obtained from such an analysis is expected to delineate more clearly the indications for a new device prior to clinical utilization. DESIGN: In vitro mechanical stiffness testing and finite element analysis. METHODS: From in vitro testing of proximal tibiae with defects, the stiffness of an internal stabilization system was determined. Using a finite element model, the loading of both the implant and bone was analyzed including all muscle forces. The variation in implant loading and interfragmentary strain for different defect locations was also investigated. RESULTS: Conventional stiffness testing demonstrated the comparability of the experimental findings with the finite element predictions. Under physiological-like loading the implant experienced high bending and von Mises stresses if defects in the region of the shaft were stabilized. A short working length increased implant loading up to the yield strength of the material. CONCLUSIONS: The finite element analysis illustrated the appropriateness of this new device for proximal defects of the tibia, but the implant should be used with hesitation in fractures or defects extending into the diaphyseal region of the bone. RELEVANCE: This new analytical approach helped to identify clinical indications for the implant in which its mechanical attributes would prove advantageous.

Biomechanical Phenomena↗
PubMed1999

Microencapsulation of lipophilic drugs in chitosan-coated alginate microspheres.

Chitosan-coated alginate microspheres containing a lipophilic marker dissolved in an edible oil, were prepared by emulsification/internal gelation and the potential use as an oral controlled release system investigated. Microsphere formation involved dispersing a lipophilic marker dissolved in soybean oil into an alginate solution containing insoluble calcium carbonate microcrystals. The dispersion was then emulsified in silicone oil to form an O/W/O multiple phase emulsion. Addition of an oil soluble acid released calcium from carbonate complex for gelation of the alginate. Chitosan was then applied as a membrane coat to increase the mechanical strength and stabilize the microspheres in simulated intestinal media. Parameters studied included encapsulation yield, alginate concentration, chitosan molecular weight and membrane formation time. Mean diameters ranging from 500 to 800 micron and encapsulation yields ranging from 60 to 80% were obtained. Minimal marker release was observed under simulated gastric conditions, and rapid release was triggered by transfer into simulated intestinal fluid. Higher overall levels of release were obtained with uncoated microspheres, possibly due to binding of marker to the chitosan membrane coat. However the slower rate of release from coated microspheres was felt better suited as a delivery vehicle for oil soluble drugs.

Alginates↗
PubMed2001

Stand-off tissue-based biosensors for the detection of chemical warfare agents using photosynthetic fluorescence induction.

Tissue biosensors made from immobilized whole-cell photosynthetic microorganisms have been developed for the detection of airborne chemical warfare agents and simulants. The sensor read-out is based on well-known principles of fluorescence induction by living photosynthetic tissue. Like the cyanobacteria and algae from which they were constructed, the sensors are robust and mobile. The fluorescence signal from the sensors was stable after 40 days, storage and they can be launched or dropped into suspected danger zones. Commercially available hand-held fluorometric detector systems were used to measure Photosystem II (PSII) photochemical efficiency of green algae and cyanobacteria entrapped on filter paper disks. Toxic agents flowing in the gas stream through the sensors can alter the characteristic fluorescence induction curves with resultant changes in photochemical yields. Tabun (GA), sarin (GB), mustard agent, tributylamine (TBA) (a sarin stabilizer), and dibutyl sulfide (DBS) (a mustard agent analog) were tested. Upper threshold limits of detectability for GA, TBA, and DBS are reported. With additional research and development, these biosensors may find application in stand-off detection of chemical and perhaps biological warfare agents under real-world conditions.

Biosensing Techniques↗
PubMedDate not supplied

Enzyme reaction engineering: effect of methanol on the synthesis of antibiotics catalyzed by immobilized penicillin G acylase under isothermal and non-isothermal conditions.

The effect of methanol on the kinetically controlled synthesis of cephalexin by free and immobilized penicillin G acylase (PGA) was investigated. Catalytic and hydrophobic membranes were obtained by chemical grafting, activation, and PGA immobilization on hydrophobic nylon supports. Butyl methacrylate (BMA) was used as graft monomer. Increasing concentrations of methanol were found to cause a greater deleterious effect on the activity of free than on that of the immobilized enzyme. Methanol, however, improved the kinetic stability of cephalexin synthesized by free PGA, resulting in higher maximum yields. By contrast, immobilized PGA reached 100% yields even in the absence of the cosolvent. Cephalexin synthesis by the catalytic membrane was also performed in a non-isothermal bioreactor. Under these conditions, a 94% increase of the synthetic activity and complete conversion of the limiting substrate to cephalexin were obtained. The addition of methanol reduced the non-isothermal activity increase. The physical cause responsible for the non-isothermal behavior of the hydrophobic catalytic membrane was identified in the process of thermodialysis.

Anti-Bacterial Agents↗
PubMed2006

Immobilization of angiotensin-converting enzyme on glyoxyl-agarose.

The assay of angiotensin-converting enzyme (ACE) inhibition by food-derived peptides is usually carried out by using soluble ACE in a batch process. The purification of this enzyme from tissues is not an easy task, and the resulting preparation loses activity very fast. In addition, ACE commercial preparations are very expensive. In this work the immobilization of ACE, through lysine amino groups, to 4% beads cross-linked (4 BCL) glyoxyl-agarose is described. The amount of immobilized enzyme increased with increasing concentrations of enzyme and with incubation time until a saturation point was reached at 50 mg protein/mL gel and 3.5 hours, respectively. The IC50 values for a noncompetitive sunflower peptide inhibitor were similar for the soluble (30.56 microM) and immobilized (32.7 microM) enzymes. An immobilized derivative was obtained that was 60 times more stable than the soluble enzyme at 60 degrees C. This procedure yields a derivative that can be reused and has increased thermal stability compared to that of the soluble enzyme. Thus, ACE immobilization is a good alternative to using soluble freshly prepared or commercial preparations because of economical and practical reasons.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed2005

Inhibition of carboxylesterases by benzil (diphenylethane-1,2-dione) and heterocyclic analogues is dependent upon the aromaticity of the ring and the flexibility of the dione moiety.

Benzil has been identified as a potent selective inhibitor of carboxylesterases (CEs). Essential components of the molecule required for inhibitory activity include the dione moiety and the benzene rings, and substitution within the rings affords increased selectivity toward CEs from different species. Replacement of the benzene rings with heterocyclic substituents increased the K(i) values for the compounds toward three mammalian CEs when using o-nitrophenyl acetate as a substrate. Logarithmic plots of the K(i) values versus the empirical resonance energy, the heat of union of formation energy, or the aromatic stabilization energy determined from molecular orbital calculations for the ring structures yielded linear relationships that allowed prediction of the efficacy of the diones toward CE inhibition. Using these data, we predicted that 2,2'-naphthil would be an excellent inhibitor of mammalian CEs. This was demonstrated to be correct with a K(i) value of 1 nM being observed for a rabbit liver CE. In addition, molecular simulations of the movement of the ring structures around the dione dihedral indicated that the ability of the compounds to inhibit CEs was due, in part, to rotational constraints enforced by the dione moiety. Overall, these studies identify subdomains within the aromatic ethane-1,2-diones, that are responsible for CE inhibition.

Animals↗
PubMed2002

1,2-dioxines as masked cis gamma-hydroxy enones and their versatility in the synthesis of highly substituted gamma-lactones.

Addition of highly stabilized ester nucleophiles to 1,2-dioxines affords good to high yields of gamma-lactones with high diastereoselectivity. Heterolytic or homolytic cleavage of the 1,2-dioxines under appropriate conditions generates the key reactive cis gamma-hydroxy enones, which ultimately afford the observed gamma-lactones. Diastereoselectivity is installed as a result of anti 1,4-addition by the ester enolate to the cis enones followed by intramolecular cyclization. The reaction is tolerant of a range of substitution patterns on the 1,2-dioxine while a broad range of esters are also accommodated. In addition to the synthesis of racemic gamma-lactones, highly enantioenriched gamma-lactones can also be synthesized when chiral cobalt(II) catalysts are employed for the initial homolytic ring-opening of the 1,2-dioxine.

Journal Article↗
PubMed2006

Diboron and triboron compounds based on linear and star-shaped conjugated ligands with 8-hydroxyquinolate functionality: impact of intermolecular interaction and boron coordination on luminescence.

New 8-R-quinoline functionalized linear and star-shaped conjugated molecules have been synthesized using Suzuki-Miyaura coupling methods (R = MeO, L1-L5; R = CH3OCH2O, L1'-L5'). When treated with HCl, L1'-L5' are converted readily to the corresponding 8-hydroxyquinoline compounds L(OH)1-L(OH)5 which react readily with BPh3 in refluxing THF to produce the corresponding polyboron chelate compounds B1-B5 in good yields. L1-L5 and B1-B5 display similar thermal stability with Td at approximately 300 degrees C. Experimental and molecular orbital calculation results showed that the chelation by boron stabilizes the LUMO level of the ligand and narrows the HOMO-LUMO gap, resulting in the blue emission of the ligands and the green or orange emission of the boron compounds. Crystal structures of L1, L3, and L5 showed that these molecules have layered arrangements in the solid state with significant intermolecular pi-pi interactions. The linear diboron B5 displays concentration and temperature-dependent emission in solution, attributable to intermolecular interactions. The properties of a monoboron compound BPh2(5-Ph-8-MeO-q) (B0) and its corresponding free ligand L0 were investigated and compared to the closely related diboron compound B1 and the ligand L1, which revealed that the increase of the number of chromophores linked by an aromatic group has a significant impact on thermal stability and the HOMO and LUMO energy levels.

Journal Article↗
PubMed1996

Novel Syntheses of N-Pivot Lariat Diaza-Crown Ethers from 4,13-Bis(benzotriazolylmethyl)-4,13-diaza-1,7,10,16-tetraoxacyclooctadecane.

4,13-Bis(benzotriazolylmethyl)-4,13-diaza-1,7,10,16-tetraoxacyclooctadecane (6) was synthesized as a versatile intermediate in the preparation of bis(lariats) of diaza-18-crown-6. N,N'-Bis(umbelliferon-8-ylmethyl) derivative 8, bis(lariats) with terminal unsaturated groups (11c,e), ester functionalities (11d), N,N'-di-beta-aralkyl derivatives (11a,b), and gamma-oxy-substituted (13, 14) and gamma-amino-substituted (17-19) propylene-side-armed derivatives were thus prepared in moderate to excellent yields. The X-ray structure of bis(lariat) 6 and stability constants for several of the complexes of bis(lariats), derivatives of 6, with metal cations are discussed.

Journal Article↗
PubMed2005

Charge transfer processes in conjugated triarylamine-oligothiophene-perylenemonoimide dendrimers.

The synthesis and charge transfer properties of triarylamine-oligothiophene-perylenemonoimide dendrimers, TPA(T2-PMI)3 and TPA(T4-PMI)3, are described. The fluorescence quantum yields indicate strong emission quenching by electron transfer [phi(THF) = 0.004 for TPA(T2-PMI)3, phi(THF) = 0.003 for TPA(T4-PMI)3, and phi(THF) = 0.8 for PMI]. Moreover, with the increase of the solvent polarity, the quantum yields decrease indicating that the A+* D-* (acceptor/donor) couple is more stabilized. The femtosecond transient absorption spectra show a very fast charge separation process (approximately 2 ps; k(cs) approximately 5 x 10(11) s(-1)) and a charge recombination of more than 1 order of magnitude slower (approximately 50 ps; k(cr) approximately 2 x 10(10) s(-1)), as observed from the rise time and decay of the radical anion and radical cation absorption bands. The analysis of the transient absorption spectroscopy and of the energetics of the process using Marcus theory indicates that in the electron transfer process the thiophene unit is the first electron donor. The triarylamine is not functioning as a second electron donor, as also substantiated by the absence of an effect of the addition of acid on the emission intensity of the dendrimers. The presence of the triarylamine and/or the proximity of the oligothiophenes does improve the donor capabilities of the oligothiophene unit slightly and enhances its conjugation as seen in the absorption spectra and the transients of the radial cations. These results can be used for a better design of molecular materials for, e.g., photovoltaic applications.

Journal Article↗
PubMed2006

Kinetics of the hydrogen abstraction OH + alkane --> H2O + alkyl reaction class: an application of the reaction class transition state theory.

This paper presents an application of the reaction class transition state theory (RC-TST) to predict thermal rate constants for hydrogen abstraction reactions of the type OH + alkane --> HOH + alkyl. We have derived all parameters for the RC-TST method for this reaction class from rate constants of 19 representative reactions, coupling with linear energy relationships (LERs), so that rate constants for any reaction in this class can be predicted from its reaction energy calculated at either the AM1 semiempirical or BH&HLYP/cc-pVDZ level of theory. The RC-TST/LER thermal rate constants for selected reactions are in good agreement with those available in the literature. Detailed analyses of the results show that the RC-TST/LER method is an efficient method for accurately estimating rate constants for a large number of reactions in this class. Analysis of the LERs leads to the discovery of the beta-carbon radical stabilization effect that stabilizes the transition state of any reaction in this class that yields products having one or more beta-carbons, and thus leads to the lower barrier for such a reaction.

Journal Article↗
PubMed2004

Total synthesis of (+)-discodermolide: an improved endgame exploiting a Still-Gennari-type olefination with a C1-C8 beta-ketophosphonate fragment.

[structure: see text] An improved, third-generation, total synthesis of (+)-discodermolide, a potent microtubule-stabilizing anticancer agent of marine sponge origin, is achieved in 11.1% yield over 21 steps. Key steps include a Still-Gennari HWE olefination, performed using NaH as the base, between C1-C8 beta-ketophosphonate 7 and C9-C24 aldehyde 8, introducing the (8Z)-alkene with 10:1 selectivity, and K-Selectride reduction of the derived enone 16, installing the (7S)-configuration.

Aldehydes↗