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L R Snyder

Publications and source records attributed to L R Snyder.

At least 55 records · Page 3Linked to original sources
PubMed1990

Computer simulation (based on a linear-elution-strength approximation) as an aid for optimizing separations by programmed-temperature gas chromatography.

If the dependence of retention on temperature is specified for the various components of a sample in isothermal gas chromatography (GC), it is possible to predict retention, bandwidth, and resolution for programmed-temperature GC separations as a function of experimental conditions. The use of a linear-elution-strength (LES) approximation for isothermal retention allows these predictions to be carried out more easily and conveniently, in turn facilitating rapid simulations with a personal computer. This approach to GC method development appears promising, especially if segmented-temperature programs are used. The LES approximation also provides added insight into how different factors affect separation in programmed-temperature GC.

Chromatography, Gas↗
PubMed1988

Preparative separation of peptide and protein samples by high-performance liquid chromatography with gradient elution. I. The Craig model as a basis for computer simulations.

The Craig model (assuming a Langmuir isotherm) has been used by us previously to successfully simulate isocratic high-performance liquid chromatographic (HPLC) separation in a mass-overload mode. Here we have extended this approach to the case of gradient elution for large samples. These simulations support our earlier conclusion that so-called "corresponding" isocratic and gradient separations provide similar sample resolution when the sample size is the same. "Corresponding" separations refer to the case where isocratic retention k' is equal to average gradient retention k, and where other conditions (column, flow-rate, etc.) are the same. Craig simulations reported here also provide further insight into the factors that affect preparative HPLC separations under mass-overload conditions.

Chromatography, High Pressure Liquid↗
PubMed1988

Preparative separation of peptide and protein samples by high-performance liquid chromatography with gradient elution. II. Experimental examples compared with theory.

Craig simulations of mass-overloaded gradient elution reported in the preceding paper have been extended to the case of non-Langmuir isotherms. Isotherms were selected that appear to be characteristic of peptide and protein samples in reversed-phase high-performance liquid chromatography. The dependence of bandwidth on sample size and gradient conditions was examined by Craig simulation and compared with experimental data for 13 different experimental systems involving four different proteins. There is a good correspondence between simulations and experimental data, and it seems possible to quantitatively predict bandwidth and resolution as a function of small-sample retention data, experimental conditions, and sample size. A systematic approach for designing the preparative or process-scale separation of protein mixtures by reversed-phase gradient elution is proposed.

Chemical Phenomena↗
PubMed1988

Separation of proteins by reversed-phase high-performance liquid chromatography. I. Optimizing the column.

In the process of developing a new analytical technology (the chromatophoresis process) which couples reversed-phase high-performance liquid chromatography (HPLC) to sodium dodecyl sulfate polyacrylamide gel electrophoresis in a real-time automated system, it was apparent that improvements in resolving power for the first-dimension (HPLC) separation were necessary. The present paper describes the optimization of the column for our initial work on reversed-phase HPLC separations. Polymeric (polystyrene) packings having particle diameters of 5 micron and pore diameters of 300 A were generally superior in terms of resolution, sample recovery and minimization of "ghosting". Optimum column dimensions were 50 x 1.0 mm I.D. for the flow-rates required in our system (10-100 microliter/min).

Chromatography, High Pressure Liquid↗
PubMed1988

Separation of proteins by reversed-phase high-performance liquid chromatography. II. Optimizing sample pretreatment and mobile phase conditions.

The effects of separation variables such as temperature, pH and composition of the mobile phase (including additives such as chaotropes, ion-pairing agents and surfactants), sample size and sample pretreatment for reversed-phase high-performance liquid chromatography (RP-HPLC) of proteins is examined. Experimental optimization of these parameters using the preferred instrumental and column conditions described previously lead to well behaved chromatographic performance for most proteins. This allowed us to achieve the required level of performance for the first dimension (RP-HPLC) separation of most protein samples by the chromatophoresis process.

Bacterial Proteins↗
PubMed1987

Predicting bandwidth in the high-performance liquid chromatographic separation of large biomolecules. I. Size-exclusion studies and the role of solute stokes diameter versus particle pore diameter.

Column plate numbers, N, were measured for 12 different proteins as a function of mobile phase flow-rate in two gel filtration systems (either denaturing or non-denaturing conditions). These data were used to extend a previous model that predicts bandwidths in reversed-phase and ion-exchange chromatography. Restriction of diffusion of large molecules within column packing pores is now defined more precisely, with a single relationship describing this effect for both reversed-phase and size-exclusion chromatography (SEC) (and presumably other high-performance liquid chromatography systems). Separations by gel filtration (SEC) are now included in our general model. A total of 17 flow-rate studies were carried out, involving different proteins, columns and/or mobile phase conditions (denaturing or non-denaturing). Comparisons of plate numbers predicted by the model with experimental values were satisfactory in 15 out of 17 cases. The remaining two cases appear to represent "non-well-behaved" systems, where experimental bandwidths were higher than predicted values by more than 20%. Initial attempts at understanding the origin of these non-ideal effects are described.

Animals↗
PubMed1987

Predicting bandwidth in the high-performance liquid chromatographic separation of large biomolecules. II. A general model for the four common high-performance liquid chromatography methods.

A general model for describing gradient elution separations of peptides and proteins by reversed-phase high-performance liquid chromatography (HPLC) has been presented previously. This model has now been modified so that it can be applied to any of the four HPLC methods used for separating biological macromolecules: reversed-phase, ion-exchange, hydrophobic-interaction and size-exclusion chromatography, carried out in either an isocratic or gradient elution mode. The role of sample molecule structure and the particular column used has been further studied, so that previous empirical parameters for different column/sample choices can now be estimated from three physical properties of the sample and the column: sample molecular weight, native vs. denatured sample, column packing pore diameter. This eliminates much of the empiricism of our preceding model, and minimizes the number of experimental runs now required in order to apply the model in practice. The final model has been tested for several hundred runs involving peptides and proteins in the molecular weight range 600-162,000, all four of these HPLC methods, in both isocratic and gradient elution modes, and using data from several different laboratories (including our own). The model is able to predict bandwidth in HPLC separations of proteins and peptides with an accuracy of +/- 17% (1 standard deviation), for the case of "well-behaved" separations. Separations that are not "well-behaved" will give wider bands than predicted by the model.

Chemical Phenomena↗
PubMed1987

The molecular organization of the beta-globin complex of the deer mouse, Peromyscus maniculatus.

Recombinant DNA clones have been isolated that contain 80 kb of the beta-globin complex from the deer mouse, Peromyscus maniculatus. Comparisons of this complex with that from the laboratory mouse, Mus domesticus (with an order 5'-Hbby, Hbb-bhO, Hbb-bhl, Hbb-bh2, Hbb-bh3, Hbb-bl, Hbb-b2 3') highlight organizational trends in the beta-globin complex since the two species diverged. Unlike other mammals studied thus far, the deer mouse possesses three adult genes. Partial sequence analysis indicates that each of the three adult genes is intact and hence may be functional. Hybridization of one of the two Mus pseudogenes, Hbb-bh3, to genomic blots from Peromyscus reveals that it has a homologous counterpart in Peromyscus. Homologous genes to the two gamma-like Mus genes, Hbb-bhO and Hbb-bhl, are also found in Peromyscus. The strong hybridization between the Hbb-bhl genes and significant nucleotide similarity between the Hbb-bhO genes suggest that both pairs are important for the ontogeny of these mice although no known product has been identified for the Hbb-bhO genes. The presence of Hbb-bhO and Hbb-bhl in Peromyscus suggests that the duplication that created this related gene set occurred before the two lineages diverged. A single gene for Hbb-y has been isolated from Peromyscus. The adult region in Peromyscus has undergone significant divergence from the same region in Mus, having three rather than two adult genes, the acquisition of at least 15 kb of extra DNA relative to Mus, and possibly the loss of the Hbb-bh2 pseudogene. The nonadult region of the complex, in contrast, contains the same set of genes apparently distributed over the same amount of DNA as in the Mus beta-globin complex. This observation suggests that the embryonic region of the complex is more evolutionarily stable than the adult region.

Animals↗
PubMed1986

Model of protein conformation in the reversed-phase separation of interleukin-2 muteins.

Thirty muteins* of interleukin-2 were studied by reversed-phase high-performance liquid chromatography in a gradient mode. Values of the stoichiometry-factor Z [from Geng and Regnier, J. Chromatogr., 296 (1984) 15] varied over a 2.5-fold range for these proteins of similar molecular weight and composition. It is proposed that the more hydrophobic and/or more stable proteins have smaller values of Z while the larger Z-values correspond to a higher degree of protein unfolding during reversed-phase retention. The practical utility of this approach was demonstrated when these Z values were used to predict correctly a reversal in elution order for two closely related interleukin-2 muteins, when shallower gradients were used.

Amino Acids↗
PubMed1985

Comparison of reversed-phase columns for the separation of tryptic peptides by gradient elution. Correlation of experimental results and model prediction.

A total of 10 reversed-phase columns obtained from different suppliers were evaluated for their ability to separate typical peptide mixtures: tryptic digests of cytochrome c, lysozyme and collagen. Each column was tested in a standard gradient elution using phosphate buffer (pH 2.85) as the A-solvent and acetonitrile as the B-solvent. Some differences in band spacing for the various peptides were observed from column to column. More important differences were observed in the ability of these various columns to provide narrow peaks and good resolution, as measured by column peak capacity. These differences in column peak capacity were related to differences in column dimensions and particle size; it also appeared that C8 bonded phases were somewhat more efficient than were C18 phases. The recovery of cytochrome c digest from four of the columns was also assessed. Summed peak areas were proportional to sample size, as the latter was varied from 1 to 100 micrograms. The apparent recovery from each column did not vary by more than +/- 5%. From this it was concluded that these columns gave essentially quantitative recovery for this particular sample. Limited data on column life were obtained for some of these columns.

Animals↗
PubMed1985

Low P50 in deer mice native to high altitude.

Whereas it is widely believed that animals native to high altitude show lower O2 partial pressures at 50% hemoglobin saturation (P50) than do related animals native to low altitude, that "fact" has not been well documented. Consequently, P50 at pH 7.4, PCO2(7.4), the CO2 Bohr effect, and the buffer slope (delta log PCO2/delta pH) were determined via the mixing technique in Peromyscus maniculatus native to a range of altitudes but acclimated to 340 or 3,800 m. PCO2(7.4) and buffer slope were substantially lower at high altitude. The change in P50(7.4) between acclimation altitudes was minimal (0.8% increase at 3,800 m), because of counterbalancing changes in PCO2, 2,3-diphospho-D-glycerate concentration, and perhaps other factors. At both acclimation altitudes there was a highly significant negative correlation between P50(7.4) and native altitude. Since pH in vivo probably increases slightly at high altitude, the data on P50 corrected to pH 7.4 are probably underestimates of the difference in in vivo P50 at low vs. high altitude. Hence these results corroborate theoretical predictions that low P50 is advantageous under severe hypoxic stress.

Acclimatization↗
PubMed1984

Automated analysis of antiepileptic drugs in serum by column-switching high-performance liquid chromatography.

An automated high-performance liquid chromatographic column-switching system is presented for the analysis of antiepileptic drugs in serum. Initial results show that a reversed-phase extraction column works best overall when fitted with screens versus frits, and when packed with porous 30-micron particles as opposed to a pellicular packing of similar size or with smaller porous particles. The continuous analysis of primidone for over 2000 serum samples is achieved at a rate of twelve samples per hour with a single analytical column. An analogous boxcar high-performance liquid chromatographic system is also assembled and used to analyze two of four injected antiepileptic drugs at a rate of 40 samples per hour. For 1000 of these analyses, the coefficient of variation is 1% without an internal standard.

Anticonvulsants↗
PubMed1984

Biochemical and physiological correlates of deer mouse alpha-chain hemoglobin polymorphisms.

The alpha-hemoglobin chains in adult deer mice are usually encoded by two tightly linked loci. Because of strong linkage disequilibrium, almost all alpha-globin haplotypes fall into just two classes. The a0c0 class predominates in high-altitude populations, whereas the a1c1 class is generally fixed in low-altitude populations. Here we show that the alpha-globin genotype has effects at both the biochemical level [on blood oxygen affinity (P50)]and at the level of whole-animal physiology [on maximum rate of oxygen consumption (VO2max) during both exercise and cold exposure]. The a1c1/a1c1 genotype mice have the highest P50 values and show the highest Vo2max values at low altitude (340 m) but the lowest VO2max values at high altitude (3800 m). The a0c0/a0c0 mice have the lowest P50, and show the highest VO2max at high altitude but usually have the lowest VO2max at low altitude. The a0c0/a1c1 heterozygotes have an intermediate P50 and are generally intermediate in VO2max at both altitudes. Since high VO2max is advantageous for aerobic exercise and thermogenesis, the physiological data provide a potential explanation for the correlation of haplotype frequencies with altitude.

Animals↗
PubMed1983

Inbreeding effects on reproductive traits in the ring-necked pheasant.

Ten inbred lines of Ring-necked pheasants were established in 1978 and mated for four generations using a system of repeated backcrossing of daughters to a common sire. In the event the old sire died, the surviving daughters were mated to a surviving brother or half-brother of the same generation. Only 4 of 10 original inbred lines survived four generations of backcrossing; two involved matings with the original sire and two with brothers or half-brothers of Generations 1 and 3, respectively. Egg production, hatchability, and viability were the three traits most affected by inbreeding depression. For 4 generations of inbreeding, the coefficients of regression for all inbred lines on a 10% increase in inbreeding were -5.89, -.42, -1.73, and -3.04 for egg production, egg weight, fertility, and hatchability, respectively. Inbreeding had less severe effects on reproductive traits in two of the four surviving lines. There is evidence that intense early selection among lines for high performance after one generation of inbreeding F = .250 will enhance the success of establishing highly viable inbred lines of pheasants.

Animals↗
PubMed1982

Blood oxygen affinity in high- and low-altitude populations of the deer mouse.

There is little solid evidence for specific genetic adaptations in animal populations native to high altitude. There is also continuing debate over what oxygen transport characteristics are truly adaptive at high altitude. We have attempted to elucidate both problems through population genetic and physiological studies of the deer mouse, Peromyscus maniculatus. That species is noteworthy because it inhabits the widest range of altitudes of any North American mammal, and it shows a high degree of genetic variation in hemoglobins. Deer mice were collected from 35 populations representing ten nominal subspecies covering a broad geographical range of the United States. The mice were acclimated to low altitude (340 m); then a mixing method was used to determine P50 and other blood gas parameters on samples pooled from individuals of representative hemoglobin genotypes. When the data from all subspecies wee combined, there was a highly significant negative correlation between P50 and the native altitude of the population. Tests on progeny reared at low altitude indicated that the differences in P50 were primarily genetic. Part of the clinal variation in P50 could be attributed to 2,3-DPG effects; high-altitude populations showed lower baseline DPG/Hb ratios. Surprisingly, within those subspecies which inhabit a wide range of altitudes, there was no correlation between P50 and native altitude. Our tentative conclusion from these data and data presented elsewhere is that deer mouse populations do show genetic adaptations to high altitude. However, because of gene exchange between populations, the genetic characteristics of a population reflect the average altitude over a relatively broad geographic area.

2,3-Diphosphoglycerate↗
PubMed1982

2,3-diphosphoglycerate in high- and low-altitude populations of the deer mouse.

Erythrocyte DPG concentrations were studied in populations of Peromyscus maniculatus native to different altitudes. Deer mice native to, and resident at, high altitude showed higher DPG/Hb ratios than did deer mice native to, and resident at, low altitude. However, after prolonged acclimation to low altitude, the high-altitude natives showed lower DPG/Hb ratios than did low-altitude natives. The differences in baseline DPG levels appear to be determined primarily by genetic factors. The heritability (h2) of DPG/Hb ratios was estimated by two independent methods to be 0.51 and 0.66, but those values are inflated to an unknown extent by environmental correlations between relatives. Mild cold stress did not elicit an increase in DPG/Hb ratios. DPG levels tended to decrease with age, but the aging effect was not consistently observed in all samples. Neither sex nor alpha-globin genotype influenced DPG levels. The adaptive significance of the genetic differences in DPG metabolism between high- and low-altitude populations remains problematic.

2,3-Diphosphoglycerate↗