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Biomedical subjects

R P Singhal

Publications and source records attributed to R P Singhal.

At least 19 recordsLinked to original sources
PubMed1998

Urban air pollution monitoring: laser-based procedure for the detection of carbon monoxide gas.

Urban air quality is of considerable importance in many cities throughout Europe and the USA. In particular, current EU legislation has driven an expansion of monitoring of more pollutants at more sites. At present in the UK, real time readings are now available for benzene, buta-1,3-diene and other volatile organic compounds, airborne fine dust (PM10), CO, 03, SO2, and NOX. Carbon monoxide is produced to varying degrees in all combustion processes but more than 90% is caused by emissions from petrol vehicle exhausts. The World Health Ogranisation guidelines for exposure to the gas is < 10 ppm for 8 h and 85 ppm for periods not exceeding 15 min. All the pollutants mentioned above are monitored by different detection techniques and it has been the authors' philosophy to develop instrumentation which can monitor all the different pollutants using a single detector. To this end, a multiphoton laser based procedure, using simple ionization chambers, has been developed to detect the different pollutants with different wavelengths. For CO, a 2 + 1 resonance enhanced multiphoton ionization (REMPI) scheme at 230 nm can be used with detection limits of about 1 ppm.

Air Pollutants↗
PubMed1992

Separation of dideoxyribonucleosides in trace amounts by automated liquid chromatography and capillary electrophoresis.

No satisfactory high-performance liquid chromatographic (HPLC) method is currently available for the separation of the major dideoxyribonucleosides (ddNs) and their derivatives. A method involving HPLC has been developed for the separation of five major ddNs [ddA, ddC, ddI, azT and 2',3'-dideoxy-2',3'-didehydrothymidine (d4T)]. Elution of the common and modified components of DNA was also examined under the selected separation conditions of HPLC. The elution characteristics of these compounds were studied using serum plasma samples spiked with ddN derivatives. In addition, capillary electrophoresis (CE) was investigated for the separation of ddNs and their derivatives. Picomolar amounts of the five major ddNs and the metabolic product of azT [5'-O-glucuronide-3'-azido-3'-deoxythymidine (Glo-azT)] were satisfactorily resolved in 10 min by using a modification of CE. The spectral properties of the ddNs were characterized under different pH conditions and compared with those of their parent deoxyribonucleosides (dNs) because these compounds are commonly measured in HPLC by their spectral properties. The spectra of ddC and ddT derivatives resemble very closely those of dC and dT, but those of ddA and ddI differ to some extent from their parent dNs. The HPLC method was extensively examined for satisfactory resolutions of these compounds. For example, an isocratic elution method, although simple, failed to resolve these compounds and ion-pair chromatography did not offer any advantage. Gradient elution involving buffered solutions and increasing amounts of an organic modifier yielded satisfactory results. Methanol appeared to be the organic modifier of choice. A reversed-phase matrix with smaller than octadecyl alkyl chains did not produce the necessary interactions. Uniform spherical beads of smaller diameter produced superior resolutions. The separation of these compounds on three commercially available columns is discussed. The separation of human plasma samples spiked with dideoxynucleoside derivatives by HPLC was accomplished in ca. 16 min. The presence of the dNs did not interfere in their separations.

Capillary Action↗
PubMed1988

High-performance liquid chromatographic analysis of DNA composition and DNA modification by chloroacetaldehyde.

The separation of common and modified deoxyribonucleosides derived from DNA hydrolyzates was examined under different chromatographic conditions on silica-based octadecyl (C18) columns, involving hydrophobic interactions with the matrix. A novel method for the analysis of the DNA composition is described. It involves the removal of RNA contaminants and enzymatic hydrolysis of DNA, first to deoxyribonucleoside monophosphates and then dephosphorylation of the latter to deoxyribonucleosides. Hydrolysis conditions were sought to avoid deamination of dA and dC residues to dI and dU contaminants, respectively. Elution of these contaminants and the artifacts (ribonucleosides derived from RNA) is described in relation to the elution of deoxyribonucleosides. Chromatographic separation of the hydrolyzate derived from a 15-micrograms sample of DNA under selected separation conditions and on one high-performance liquid chromatographic column is achieved in 18 min at room temperature. Detection of modified components (and contaminants) present in minute amounts is enhanced with the use of a diode-array detector. The power of this technique lies in its ability to characterize and quantitate accurately the amount of modified species present in the DNA structure (less than 2% of all the other residues). Examples of the composition analysis of DNA derived from a prokaryote (Escherichia coli B) and a eukaryote (salmon sperm) are described. Details of quantitation (calibration graphs) of different nucleosides are furnished for peak-area integration by commercially available software, and spectral properties of the nucleoside in the elution buffer are described for quantitation by other means. Application of the composition analysis is shown here for probing the DNA conformation in solution by chemical means, while using chloroacetaldehyde as the modifying agent.

Acetaldehyde↗
PubMed1987

DNA methylation in aging of mice.

Methylation of cytidine residues of DNA appears to be involved in the control of gene expression; therefore, hypomethylation of the DNA can be considered to be an active rather than a passive process. Previous studies of mammalian DNA methylation during aging have produced an assortment of results. In this study, we have examined the change in DNA base composition, including the change in 5-methyldeoxycytidine (m5dC) contents with age of mice. Livers pooled from 6 mice from each of six age groups between 6 and 31 months have been subjected to a sensitive analytical technique (HPLC). The DNA composition of different age groups is very consistent in most aspects. The ratio of (dA + dT)/(dG + dC + m5dC) as well as the sum of dC and m5dC remain constant throughout the animal's lifespan. However, a consistent gradual decline in m5dC content is noted as the age increases to 24 months. Thus, the 6-month-old animal pool exhibits the largest amount of m5dC (1.67 +/- 0.2%), which is reduced consistently as the animal's age reaches 24 months. This decrease in m5dC is accompanied by an increase in dC. No further decrease in m5dC occurs after 24 months; in fact, the data could indicate an increase after that age. No dTs are apparently produced by deamination of m5dC.

Aging↗
PubMed1983

High-performance liquid chromatography of transfer RNAs. Separation of transfer RNAs from mammalian sources.

A survey of recent advances in high-performance liquid chromatography (HPLC) of tRNA is presented here. The polystyrene and reversed-phase anion exchangers are discussed for their ability to resolve tRNAs without loss of the aminoacyl-tRNA bond. The HPLC of a tRNA of choice, based on the affinity principle, is studied. Both chemical (boronate) and biological (plant lectins) affinity groups for the tRNA interaction are described. A comprehensive scheme is presented for the separation of four mammalian tRNAs. Scope of future research in this area is also discussed.

Amino Acids↗
PubMed1983

The role of queuine in the aminoacylation of mammalian aspartate transfer RNAs.

Can a queuine-specific tRNA function normally without replacement of G by Q in its structure? To answer this, kinetics of aspartate queuine-containing tRNA (Q-tRNA) is compared with its queuine-deficient counterpart (G-tRNA). The results indicate that Asp Q-tRNA is a more effective substrate than the Asp G-tRNA. The Asp Q-tRNA exhibits a higher reaction velocity (Vmax greater than 30%) and a higher reaction rate (Km less than 55%) than its counterpart. The Asp tRNAs derived from human tumor lines and grown in athymic mice contain a full complement of queuine. This tumor tRNA exhibits aminoacylation kinetics similar to a normal liver tRNA. Reasons for observing the lack of a G-to-Q modification in cancer tRNAs by others are hypothesized. Two purified Asp isoacceptors from liver are compared for the aminoacylation reaction; small differences are noted in the Vmax, but none in the Km values.

Animals↗
PubMed1982

Computer program for storage and retrieval of the nucleic acid structures: storing and updating of transfer RNA sequences - drawing of the secondary structure for transfer RNA by computer.

The availability of a large number of tRNA sequences has created a need for computer programs to store the data. A program written in FORTRAN language allows one to store tRNA sequences and to retrieve information. The data are stored in such a way that it allows a direct comparison of various tRNA sequences. Moreover, the program draws the 'cloverleaf' structure of any stored tRNA sequence and also provides the characteristics of minor, modified nucleosides and major references. Additions and corrections to the program and stored data can be made easily and an individual does not need computer programming skills to use the program.

Base Sequence↗