5,969 research outputs found
Evaluation and Application of Stationary Phase Selectivity for Drug Analysis
Despite the wide range of HPLC stationary phases available for reversed-phase
high-performance liquid chromatography (RP-HPLC) and the in-depth studies
using probes to highlight differences between them, there is very little in the way of
stationary phases which offer selectivity that is substantially different from that
offered by the very commonly used alkyl-silicas. Therefore, the primary aim of the
research programme was to explore and try to exploit LC stationary phases which
offered genuinely different selectivity to alkyl-silicas for typical drug applications.
Chiral stationary phases (CSP) potentially had different selectivity and in this
context a secondary aim was to explore aspects of the enantioselectivity of CSP
as well as their chemical selectivity.
Claims of orthogonal selectivity had been made for pentafluorophenyl (PFP)
phases and phases exhibiting the hydrophilic interaction liquid chromatography
(HILIC) mode. However, the Ultra PFP phase was found to be very similar in
selectivity to ACE 5 C18 for both amitriptyline and acemetacin related compounds.
The ZIC-HILIC phase was shown to behave as a reversed-phase material at high
aqueous content in the mobile phase. There was some indication of selectivity
orthogonal to that of ACE 5 C18 with low aqueous content in the mobile phase but
this occurred at low retention and with mobile phases unsuitable for use with C18
phases in coupled (column or phase) systems. Nonetheless the work carried out
shed more light on the mechanisms taking place in the HILIC mode which is
currently attracting so much interest. Also it was possible to put ZIC-HILIC to good
use for polar plant metabolites and other applications.
Chiral stationary phases (CSP) also offered the prospect of selectivity orthogonal
to that of C18 phases. Given the proliferation of such phases though and the fact
that it would be useful to use CSP that gave chiral separations for a broad
spectrum of compound classes as well as giving orthogonal separations between
different compounds, it was decided to carry out comparative studies of CSP
classes in order to identify any redundancies and to seek out CSP that were
complementary to one another. The Regis Whelk-O1 CSP was shown to be much
superior to other higher-generation Pirkle-concept CSP such as DACH-DNB and
ULMO. Also it was shown to be complementary to the Chiralcel OD derivatised
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polysaccharide CSP and that both had something to offer alongside the widely
used Chiralpak AD derivatised polysaccharide CSP. It was also found that a series
of Chiralcel OD clones were virtually identical to Chiralcel OD and similarly for
Chiralpak AD clones. Chiralpak IA, an immobilised version of Chiralpak AD, was
not markedly less enantioselective than Chiralpak AD. Chiralcel OJ was less
enantioselective than Chiralpak AD but the gap in performance was not as wide as
between Whelk-O1 and the other Pirkle-concept CSP. The information gathered
during these studies should prove to be of enormous value for further work in
chiral LC method development screening.
Before embarking on applications work utilising the stationary phase selectivity
that had been found, a study was carried out on the effectiveness of the high
efficiencies obtainable with short run times through ultra-performance liquid
chromatography (UPLC). It was found that, for a range of pharmaceutical
applications, that it was still necessary in each case to adjust selectivity before
increasing speed through working at higher temperatures with faster flow rates. In
the course of this work some exceptionally high speed separations for example for
paroxetine and related substances, benzodiazepines and flurbiprofen and related
substances, were developed.
With respect to the evaluation of CSP as orthogonal phases to alkyl silicas under
reversed-phase conditions, the Whelk-O1 CSP showed promise. However on
closer inspection it was found that the Whelk-O1 CSP had very similar selectivity
to the alkyl silica phase, ACE 5 C18, and deviation from this only occurred in
instances when there was interaction with the chiral recognition site to give a
separation of enantiomers. This prompted the notion that, rather than using Whelk-
O1 in a coupled column system with ACE 5 C18, it could be used on its own for
the separation of both trace enantiomer and all other related substances. This was
shown to be possible using (S)-naproxen, laevokalim and (S)-flurbiprofen as
illustrative examples.
The evaluation of the enantioselectivity of CSP led to an optimised resolution
(suitable for scaling up for preparative work) of the enantiomers of the former
‘legal-high’ drug, mephedrone, on Whelk-O1 under normal phase conditions. It
was also shown that the infrequently used Chiralcel OJ derivatised polysaccharide
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CSP was ideal for developing an assay to determine trace amounts of (R)-nicotine
in (S)-nicotine.
Overall, the information obtained on stationary phase selectivity and retentivity
through evaluation and application will be of great value in HPLC and UHPLC
column selection and also selection of orthogonal phases for coupled column
systems but, ultimately, moving forward, most value may be in aiding the design of
two-dimensional LC systems for complex mixture analysis. This would particularly
apply to the use of CSP with reversed-phase eluents in achiral-chiral systems
Availability legibility and adequacy of diagnosis as entered in bed head ticket in a base hospital Sri Lanka: a descriptive cross-sectional study
Introduction: Hospital information storage is done through an internationally accepted coding system. It is very important to have an accurate diagnosis for proper coding. Ministry of Health has issued a circular (No-01-05/99) for the documentation of Bed Head Ticket (BHT) including writing the correct diagnosis. Objective: To assess the availability, legibility, and adequacy of diagnosis as entered in the BHTs of selected wards in a base hospital in Sri Lanka. Methods: Descriptive cross-sectional study was conducted to assess availability, legibility, and adequacy of diagnosis as entered in 384 BHTs of selected wards in a Base Hospital in Sri Lanka. A data Extraction sheet (DES) was used as a study instrument. Results: Out of 384 BHTs diagnosis were not available in 12 (3.13%) BHTs and diagnosis were illegible in 36(6.99%) BHTs. In 244(67.59%) BHTs diagnosis were written as abbreviations. Only in136(37.46%) BHTs, diagnosis were written in block capital letters. Conclusion and recommendation: Documentation diagnosis in the BHTs is not according to the standards. Therefore, medical administrators, policymakers, and clinicians should take urgent actions to improve documentation diagnosis in BHTs
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HCMV Antivirals and Strategies to Target the Latent Reservoir.
Human cytomegalovirus (HCMV) is a ubiquitous human herpesvirus. In healthy people, primary infection is generally asymptomatic, and the virus can go on to establish lifelong latency in cells of the myeloid lineage. However, HCMV often causes severe disease in the immunosuppressed: transplant recipients and people living with AIDS, and also in the immunonaive foetus. At present, there are several antiviral drugs licensed to control HCMV disease. However, these are all faced with problems of poor bioavailability, toxicity and rapidly emerging viral resistance. Furthermore, none of them are capable of fully clearing the virus from the host, as they do not target latent infection. Consequently, reactivation from latency is a significant source of disease, and there remains an unmet need for treatments that also target latent infection. This review briefly summarises the most common HCMV antivirals used in clinic at present and discusses current research into targeting the latent HCMV reservoir
Benchmarking network propagation methods for disease gene identification
In-silico identification of potential target genes for disease is an essential aspect of drug target discovery. Recent studies suggest that successful targets can be found through by leveraging genetic, genomic and protein interaction information. Here, we systematically tested the ability of 12 varied algorithms, based on network propagation, to identify genes that have been targeted by any drug, on gene-disease data from 22 common non-cancerous diseases in OpenTargets. We considered two biological networks, six performance metrics and compared two types of input gene-disease association scores. The impact of the design factors in performance was quantified through additive explanatory models. Standard cross-validation led to over-optimistic performance estimates due to the presence of protein complexes. In order to obtain realistic estimates, we introduced two novel protein complex-aware cross-validation schemes. When seeding biological networks with known drug targets, machine learning and diffusion-based methods found around 2-4 true targets within the top 20 suggestions. Seeding the networks with genes associated to disease by genetics decreased performance below 1 true hit on average. The use of a larger network, although noisier, improved overall performance. We conclude that diffusion-based prioritisers and machine learning applied to diffusion-based features are suited for drug discovery in practice and improve over simpler neighbour-voting methods. We also demonstrate the large impact of choosing an adequate validation strategy and the definition of seed disease genesPeer ReviewedPostprint (published version
DNA adducts in human urinary bladder and other tissues.
Tobacco smoking is associated with an increased risk of cancer in a number of organs, including bladder and lung. Tobacco smoke contains at least 50 known chemical carcinogens that exert their biological effects through their covalent binding to cellular DNA. Examining human DNA for the presence of altered nucleotides is a means of monitoring exposure to genotoxic chemicals. DNA isolated from 73 human bladder biopsies has been analyzed by 32P-postlabeling for the presence of aromatic/hydrophobic adducts. Butanol extraction of DNA digests resulted in up to a 3-fold greater recovery of adducts than nuclease P1 digestion. Among 16 nonsmokers, adduct levels were in the range 3.2-20.8/10(8) nucleotides (mean 9.7). Eight ex-smokers had values in the range 2.6-12.3 (mean 7.1). Thirteen smokers had adduct levels between 1.3 and 26.7 adducts/10(8) nucleotides (mean 9.5, not different from nonsmokers). Six cigar smokers had higher levels of adducts (mean 12.1, range 7.3-15.0), but pipe smokers did not (five samples, mean 8.6, range 2.9-12.7). A further 8 samples from nonsmokers and 17 from smokers were examined in more detail. Although most of the DNA binding appears not to be smoking related, the levels of one adduct were found to be on average 2-fold higher in smokers (p < 0.005, one-tailed t test). Studies on tissues of the respiratory tract demonstrate a correlation between DNA adduct levels and exposure to tobacco smoke. Evidence to date on the influence of smoking on adducts in peripheral blood cells is equivocal; some studies demonstrate a significant effect, whereas others do not.(ABSTRACT TRUNCATED AT 250 WORDS
Simulations of a single membrane between two walls using a Monte Carlo method
Quantitative theory of interbilayer interactions is essential to interpret
x-ray scattering data and to elucidate these interactions for biologically
relevant systems. For this purpose Monte Carlo simulations have been performed
to obtain pressure P and positional fluctuations sigma. A new method, called
Fourier Monte-Carlo (FMC), that is based on a Fourier representation of the
displacement field, is developed and its superiority over the standard method
is demonstrated. The FMC method is applied to simulating a single membrane
between two hard walls, which models a stack of lipid bilayer membranes with
non-harmonic interactions. Finite size scaling is demonstrated and used to
obtain accurate values for P and sigma in the limit of a large continuous
membrane. The results are compared with perturbation theory approximations, and
numerical differences are found in the non-harmonic case. Therefore, the FMC
method, rather than the approximations, should be used for establishing the
connection between model potentials and observable quantities, as well as for
pure modeling purposes.Comment: 10 pages, 10 figure
The Double Pulsar Eclipses I: Phenomenology and Multi-frequency Analysis
The double pulsar PSR J0737-3039A/B displays short, 30 s eclipses that arise
around conjunction when the radio waves emitted by pulsar A are absorbed as
they propagate through the magnetosphere of its companion pulsar B. These
eclipses offer a unique opportunity to probe directly the magnetospheric
structure and the plasma properties of pulsar B. We have performed a
comprehensive analysis of the eclipse phenomenology using multi-frequency radio
observations obtained with the Green Bank Telescope. We have characterized the
periodic flux modulations previously discovered at 820 MHz by McLaughlin et
al., and investigated the radio frequency dependence of the duration and depth
of the eclipses. Based on their weak radio frequency evolution, we conclude
that the plasma in pulsar B's magnetosphere requires a large multiplicity
factor (~ 10^5). We also found that, as expected, flux modulations are present
at all radio frequencies in which eclipses can be detected. Their complex
behavior is consistent with the confinement of the absorbing plasma in the
dipolar magnetic field of pulsar B as suggested by Lyutikov & Thompson and such
a geometric connection explains that the observed periodicity is harmonically
related to pulsar B's spin frequency. We observe that the eclipses require a
sharp transition region beyond which the plasma density drops off abruptly.
Such a region defines a plasmasphere which would be well inside the
magnetospheric boundary of an undisturbed pulsar. It is also two times smaller
than the expected standoff radius calculated using the balance of the wind
pressure from pulsar A and the nominally estimated magnetic pressure of pulsar
B.Comment: 9 pages, 7 figures, 3 tables, ApJ in pres
Heterogeneous Diffusion in Highly Supercooled Liquids
The diffusivity of tagged particles is demonstrated to be very heterogeneous
on time scales comparable to or shorter than the relaxation time
( the stress relaxation time) in a highly supercooled
liquid via 3D molecular dynamics simulation. The particle motions in the
relatively active regions dominantly contribute to the mean square
displacement, giving rise to a diffusion constant systematically larger than
the Einstein-Stokes value. The van Hove self-correlation function is
shown to have a long distance tail which can be scaled in terms of
for t \ls 3\tau_{\alpha}. Its presence indicates heterogeneous diffusion in
the active regions. However, the diffusion process eventually becomes
homogeneous on time scales longer than the life time of the heterogeneity
structure ().Comment: 4 pages, 5 figure
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