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C K Larive

Publications and source records attributed to C K Larive.

16 recordsLinked to original sources
PubMed2001

Examination of cadmium(II) complexation by the Suwannee River fulvic acid using 113Cd NMR relaxation measurements.

Aquatic and terrestrial fulvic acids are environmentally important because they affect the bioavailability and transport of metal ions. Prior studies demonstrated that Cd(ll) binds to the oxygen containing functional groups of fulvic acids. The complexation of Cd(II) is further investigated in this study using 113Cd NMR relaxation measurements for solutions of the Suwannee River fulvic acid (SRFA). Spin-lattice (T1) and spin-spin (T2) relaxation times are measured over a range of Cd(II):SRFA ratios. The results clearly indicate two types of Cd(II) binding sites for the SRFA. A series of model ligands was also examined to gain further understanding of the two types of binding motifs present in the fulvic acid. The results for a model compound containing several carboxylate functionalities in near proximity correspond very closely to the results obtained for the strong binding sites of the Cd(II)-SRFA complexes.

Algorithms↗
PubMed2001

Measurement of cadmium(II) and calcium(II) complexation by fulvic acids using 113Cd NMR.

Aquatic and terrestrial fulvic acids are environmentally important in pollution transport because they affect the bioavailability and transport of metal ions. The complexation of the metal ions, Cd(II) and Ca(II), with several fulvic acids is examined in this study using 113Cd NMR. Our results indicate that Cd(II) predominately binds to the oxygen containing functional groups of the fulvic acids. A single 113Cd NMR resonance is observed in NMR spectra of Cd(II)-fulvic acid solutions indicating fast exchange between free and complexed cadmium species. An average association equilibrium constant, K(Cd), is determined from NMR spectra measured for the titration of fulvic acid with Cd(II). The K(Cd) values determined for the four fulvic acids studied range between 1.2 and 3.5 x 10(3) M(-1). Competitive binding between Ca(II) and Cd(II) is used to indirectly determine an average association equilibrium constant, K(Ca), for Ca(II) with each fulvic acid. Overall K(Ca) values range from 4.6 to 7.8 x 10(2) M(-1).

Benzopyrans↗
PubMed2001

1H NMR characterization of the product from single solid-phase resin beads using capillary NMR flow probes.

A capillary NMR flow probe was designed to generate high-resolution (1)H NMR spectra at 600 MHz from the cleaved product of individual 160-microm Tentagel combinatorial chemistry beads. By injecting a dissolved sample sandwiched between an immiscible, perfluorinated organic liquid directly into the probe, NMR spectra of the product cleaved from single beads were acquired in just 1 h of spectrometer time without diffusional dilution. Sample handling efficiency on the single bead scale was comparable to that obtained with a bulk sample. Using the relative intensity of the DMSO-d(5)H versus the analyte signals in a fully relaxed CPMG spectrum, the amount of product cleaved from a single bead was determined to be 540+/-170 pmol in one of the samples. Following the NMR data collection, the samples were examined with electrospray ionization mass spectrometry to provide additional structural information. By coupling with microliter-volume fluidic capabilities, the capillary flow probe described here will enable multidimensional characterization of single solid-phase resin products in an online manner.

Journal Article↗
PubMed2001

Improved spin-echo-edited NMR diffusion measurements.

The need for simple and robust schemes for the analysis of ligand-protein binding has resulted in the development of diffusion-based NMR techniques that can be used to assay binding in protein solutions containing a mixture of several ligands. As a means of gaining spectral selectivity in NMR diffusion measurements, a simple experiment, the gradient modified spin-echo (GOSE), has been developed to reject the resonances of coupled spins and detect only the singlets in the (1)H NMR spectrum. This is accomplished by first using a spin echo to null the resonances of the coupled spins. Following the spin echo, the singlet magnetization is flipped out of the transverse plane and a dephasing gradient is applied to reduce the spectral artifacts resulting from incomplete cancellation of the J-coupled resonances. The resulting modular sequence is combined here with the BPPSTE pulse sequence; however, it could be easily incorporated into any pulse sequence where additional spectral selectivity is desired. Results obtained with the GOSE-BPPSTE pulse sequence are compared with those obtained with the BPPSTE and CPMG-BPPSTE experiments for a mixture containing the ligands resorcinol and tryptophan in a solution of human serum albumin.

Albumins↗
PubMed2001

Evaluation of NMR diffusion measurements for the conformational analysis of flexible peptides.

The use of diffusion coefficients measured with pulsed-field gradient NMR spectroscopy for the determination of the relative population of conformers in solutions of the human Growth Hormone peptide fragment, hGH(9-19), has been studied in aqueous and in trifluoroethanol (TFE)/ water solutions. The peptide is a good model compound for this study because it adopts a predominantly random coil conformation in aqueous solution and is helical in TFE. The results of the diffusion measurements suggest that the peptide exhibits predominantly random coil structures in aqueous solution and adopts a more helical conformation in solutions containing increasing mole fractions of TFE, consistent with the qualitative findings of the standard CD and NMR experiments to probe peptide conformation. These results indicate that diffusion coefficients measured with NMR can provide additional information about temperature- and solvent-induced changes in the extent of the helical conformer for hGH(9-19) in aqueous solution and in solutions containing various mole fraction of TFE, respectively.

Amino Acid Sequence↗
PubMed2001

Correlation of the capacity factor in vesicular electrokinetic chromatography with the octanol:water partition coefficient for charged and neutral analytes.

PURPOSE: The aim of this study was to develop a method based upon electrokinetic chromatography (EKC) using oppositely charged surfactant vesicles as a buffer modifier to estimate hydrophobicity (log P) for a range of neutral and charged compounds. METHODS: Vesicles were formed from cetyltrimethylammonium bromide (CTAB) and sodium n-octyl sulfate (SOS). The size and polydispersity of the vesicles were characterized by electron microscopy, dynamic light scattering, and pulsed-field gradient NMR (PFG-NMR). PFG-NMR was also used to determine if ion-pairing between cationic analytes and free SOS monomer occurred. The CTAB/SOS vesicles were used as a buffer modifier in capillary electrophoresis (CE). The capacity factor (log k') was calculated by determining the mobility of the analytes both in the presence and absence of vesicles. Log k' was determined for 29 neutral and charged analytes. RESULTS; There was a linear relationship between the log of capacity factor (log k') and octanol/water partition coefficient (log P) for both neutral and basic species at pH 6.0, 7.3, and 10.2. This indicated that interaction between the cation and vesicle was dominated by hydrophobic forces. At pH 4.3, the log k' values for the least hydrophobic basic analytes were higher than expected, indicating that electrostatic attraction as well as hydrophobic forces contributed to the overall interaction between the cation and vesicle. Anionic compounds could not be evaluated using this system. CONCLUSION: Vesicular electrokinetic chromatography (VEKC) using surfactant vesicles as buffer modifiers is a promising method for the estimation of hydrophobicity.

Alkanesulfonic Acids↗
PubMed1998

Measurement of peptide aggregation with pulsed-field gradient nuclear magnetic resonance spectroscopy.

Interactions between hydrophobic patches in proteins are often a driving force for denaturation and aggregation. The aggregation of the beta-amyloid peptide fragment, VHHQKLVFFAEDVGSNK (beta(12-28)), has been investigated in aqueous solution at low pH. This peptide contains a central hydrophobic patch spanning residues 17-21. Diffusion coefficients measured with pulsed-field gradient NMR as a function of peptide solution concentration were used to assess the extent of aggregation. Following the hypothesis that hydrophobic interactions are an important driving force in the aggregation of this peptide at low pH, a non-aggregating analog of the beta(12-28) peptide, [Gly19,20]beta(12-28) was synthesized. In the [Gly19,20]beta(12-28) peptide, the replacement of the two phenylalanine residues disrupts the hydrophobic interactions which drive the aggregation of beta(12-28). The diffusion coefficient of the [Gly19,20]beta(12-28) peptide is invariant over the concentration range studied and provides a good estimate of the monomeric diffusion coefficient of beta(12-28). A second peptide analog was synthesized in which the phenylalanine at position 20 was replaced with a cysteine residue. The disulfide-linked dimer, ([Cys20]beta(12-28))2, was formed upon air oxidation of this peptide. The diffusion coefficient of the ([Cys20]beta(12-28))2 peptide was measured and used to estimate the diffusion coefficient of the beta(12-28) dimer. Using the monomeric and dimeric diffusion coefficients measured for the glycine and cysteine analogs, the concentration dependence of the beta(12-28) diffusion coefficient was found to be consistent with a monomer-dimer aggregation model.

Amino Acid Sequence↗
PubMed1998

Copper-binding compounds from Methylosinus trichosporium OB3b.

Two copper-binding compounds/cofactors (CBCs) were isolated from the spent media of both the wild type and a constitutive soluble methane monooxygenase (sMMOC) mutant, PP319 (P. A. Phelps et al., Appl. Environ. Microbiol. 58:3701-3708, 1992), of Methylosinus trichosporium OB3b. Both CBCs are small polypeptides with molecular masses of 1,218 and 779 Da for CBC-L1 and CBC-L2, respectively. The amino acid sequence of CBC-L1 is S?MYPGS?M, and that of CBC-L2 is SPMP?S. Copper-free CBCs showed absorption maxima at 204, 275, 333, and 356 with shoulders at 222 and 400 nm. Copper-containing CBCs showed a broad absorption maximum at 245 nm. The low-temperature electron paramagnetic resonance (EPR) spectra of copper-containing CBC-L1 showed the presence of a copper center with an EPR splitting constant between those of type 1 and type 2 copper centers (g = 2.087, g = 2.42 G, A = 128 G). The EPR spectrum of CBC-L2 was more complex and showed two spectrally distinct copper centers. One signal can be attributed to a type 2 Cu2+ center (g = 2.073, g = 2.324 G, A = 144 G) which could be saturated at higher powers, while the second shows a broad, nearly isotropic signal near g = 2.063. In wild-type strains, the concentrations of CBCs in the spent media were highest in cells expressing the pMMO and stressed for copper. In contrast to wild-type strains, high concentrations of CBCs were observed in the extracellular fraction of the sMMOC mutants PP319 and PP359 regardless of the copper concentration in the culture medium.

Bacterial Proteins↗
PubMed1997

Modified pulsed-field gradient NMR experiments for improved selectivity in the measurement of diffusion coefficients in complex mixtures: application to the analysis of the Suwannee River fulvic acid.

To simplify the complex 1H NMR spectrum of a fulvic acid sample and gain structural and molecular size information, spectral editing techniques were used in conjunction with a general PFG NMR pulse sequence. These editing techniques exploit differences in T1 and T2 relaxation times as well as differences in coupling constants. The experiments were initially performed on a model mixture of glutamic acid and ethyl acetate in order to validate the method as a technique for measurement of diffusion coefficients. The editing experiments were then applied to the International Humic Substances Society Suwannee River fulvic acid standard. These editing techniques allowed more selective measurement of diffusion coefficients for broad classes of components within regions of the 1H NMR spectrum of the fulvic acid solution. The average radii of gyration calculated for the Suwannee River fulvic acid sample from the diffusion coefficients are in good agreement with literature values.

Acetates↗
PubMed1997

Physicochemical characterization of psychosine by 1H nuclear magnetic resonance and electron microscopy.

Krabbe's disease is an autosomal recessive disease that affects the lysosomal enzyme galactosylceramidase. The storage of one of its substrates, psychosine (beta-galactosyl-sphingosine), is thought to be responsible for the induction of pathological changes. Psychosine has a free amine group which is necessary for the mediation of its toxic effects. In the present study, the physicochemical properties of psychosine were investigated. Nuclear magnetic resonance (NMR) detected pH titration was used to determine that the amine group had a pKa of 7.18 +/- 0.05. Pulsed-field gradient NMR spectroscopy was used to determine that the diffusion coefficient of 2.8 mM psychosine in D2O at pD 4.46 or 7.04 is 1.16 +/- 0.02 x 10(-10) m2/s or 0.77 +/- 0.02 x 10(-10) m2/s, respectively. Negative staining electron microscopy (EM) studies of acidic and neutral solutions of psychosine also were performed. At pH 4.5, spherical structures were formed, which were relatively stable between 3, 120, and 216 h following preparation; the diameter ranged from approximately 14 nm at the earliest time point to approximately 18 nm at the last time point. The critical micelle concentration (CMC) was 1.26 mM at pH 4.0. At pH 7.1, the structures changed from spherical structures with a diameter of 15-23 nm, at the earliest time point, to a heterogeneous population of structures ranging from spherical structures, with a diameter of only a few nm, to irregularly shaped oblong structures that had one or more dimensions exceeding 100 nm. The NMR and EM data indicate that the deprotonation of the amine group causes psychosine to form aggregates that are unstable, which prevents a determination of the CMC at a neutral pH. These data indicate that molecular interactions of psychosine at the acidic pH of the lysosome, where it is normally digested, are more orderly than those at the pH of the cytoplasm or extracellular space where psychosine goes during disease.

Diffusion↗
PubMed1997

A mechanistic study of griseofulvin dissolution into surfactant solutions under laminar flow conditions.

The in vivo dissolution of many poorly soluble drugs is enhanced by the action of surfactants secreted into the upper gastrointestinal (GI) tract. These substances may act by solubilizing individual drug molecules into two separate liquid phases: the free aqueous phase and a micellar phase in which the drug is incorporated into a complex of two or more surfactant molecules. This complex process, micellar solubilization, was the subject of this in vitro study, wherein griseofulvin (gris) dissolution was observed in flowing surfactant solutions. Aqueous solutions of sodium dodecyl sulfate (SDS), an anionic surfactant, were pumped over a gris tablet embedded in a laminar flow device to simulate flow in the human upper GI tract. SDS solutions were well above the critical micellar concentration (cmc approximately 6-7 mM), and flow rates ranged from 4 to 7 mL/min. Gris solubility in premicellar (4 mM), near-micellar (6 mM), and micellar (>6 mM) SDS solutions was also determined. The measured solubility of gris increased linearly with SDS concentrations above the cmc. Drug solubility in SDS concentrations below the cmc was also higher than that in water. Gris diffusion coefficients were measured using pulsed-field gradient NMR spectroscopy. To determine the controlling mechanism for surfactant-enhanced dissolution, a mathematical model was developed. The model solution, an equation for drug dissolution rate, was compared with experimental data to demonstrate that drug transport away from the solid surface is the slow step in the process. Measured gris diffusion coefficients and solubility values were used as constants in the mathematical model solution and were combined to calculate an effective gris diffusion coefficient. Using these experimentally determined properties, model-calculated dissolution rates were within 7% of the measured values. As hypothesized, dissolution rates were found to be directly proportional to the transport properties of the system (effective drug diffusion coefficient and fluid flow rate) as well as to the drug solubility. To further verify transport-limited dissolution, the measured dissolution rates were found to be proportional to the surrounding medium flow rate to the 1/3 power, as predicted by the model dissolution rate equation.

Antifungal Agents↗
PubMed1997

Free radical production by Nd:YAG laser photodisruption.

BACKGROUND AND OBJECTIVES: Plasma and cavitation bubble formation during optical breakdown in aqueous media may produce hydroxyl (*OH) radicals. The authors' objectives were to detect *OH produced by a neodymium:yttrium-aluminum-garnet (Nd:YAG) laser photodisruptor and to determine *OH concentration in relation to laser energy. MATERIALS AND METHODS: *OH was assayed by measuring absorbance of triiodide (I3-) in a potassium iodide (KI) solution exposed to optical breakdown by an Nd:YAG laser. The concentration-dependent reduction of radical production in relation to cystamine concentration was evaluated. RESULTS: I3- concentration increased linearly with total irradiation energy and decreased exponentially with increasing cystamine concentration. *OH concentration was calculated using extinction coefficients of I3- and chemical equations relating I3- formation to *OH. CONCLUSIONS: The authors calculated that approximately 4 x 10(-12) moles of *OH are produced in a typical posterior capsulotomy of 100 mJ of total energy. This *OH concentration could produce strand breaks in approximately 0.4% of vitreous hyaluronic acid molecules, but is unlikely to produce clinical effects.

Aqueous Humor↗
PubMed1996

Synthesis and conformational analysis of cyclic pentapeptide endothelin antagonists.

Two endothelin antagonists cyclo(D-Leu-D-Val-Pro-D-Asp-Trp) (IPI-147), and cyclo (D-Trp-D-Asp-Ac3c-D-Val-Leu) (IPI-725) have been synthetized. Their solution conformations have been studied in aqueous solution by NMR spectroscopy and dynamics simulation. Activity studies show that IPI-725 is a strong ETA antagonist, while IPI-147 is a weak ETA antagonist. Comparison of the solution conformations of these two ETA antagonists suggests that the difference in their activities results from their structural differences. IPI-147 contains a type II beta-turn with a hydrogen bond between NH of D-Val and the C = O of D-Asp. IPI-725, on the other hand, contains two turns, a type II beta-turn with a hydrogen bond between NH of D-Asp and C = O of D-Val, as well as a gamma'-turn with a hydrogen bond formed between D-Val NH and D-Asp carbonyl group. Therefore IPI-147 appears to be more flexible than IPI-725. Although both beta-turns contain the same residues, their orders in the turn are reversed. The beta-turn in IPI-725 is formed with D-Val:Leu:D-Trp:D-Asp, while in IPI-147, the beta-turn is formed with D-Asp:Trp:D-Leu:D-Val. The activities and solution conformations of IPI-147 and IPI-725 were also compared with BQ-123 [cyclo(D-Trp-D-Asp-Pro-D-Val-Leu)], a well characterized, highly potent endothelin antagonist.

Endothelins↗
PubMed1995

Detection of insulin aggregates with pulsed-field gradient nuclear magnetic resonance spectroscopy.

Self-association of metal-free human insulin in aqueous solution at pH 9.4 has been studied using pulsed-field gradient (PFG) NMR spectroscopy. The diffusion coefficients were measured for two different insulin concentrations, 0.72 mM in which the dimer is the predominant species and 3 mM which is a mixture of dimer and tetramer. In the more concentrated solution, exchange between the two aggregates is slow on the NMR chemical shift time scale. As a result, the dimer and tetramer give rise to separated resonances in the aromatic region of the 1H NMR spectrum. The diffusion coefficient determined for the tetramer by PFG NMR is 1.07 x 10(-6) cm2 s-1 at 298 K, while that for the dimer is 1.38 x 10(-6) cm2 s-1. The hydrodynamic diameters calculated for the tetramer and dimer are 46 and 36 A, respectively, which are in good agreement with those measured by dynamic light scattering. The advantage of PFG NMR for the measurement of insulin aggregation in these solutions results from the chemical shift selectivity which allows diffusion coefficients to be directly calculated for the different aggregates. The T1 and T2 relaxation times of the dimer and tetramer aromatic protons were also measured in order to optimize the parameters of the PFG NMR experiment and correctly interpret the results of the measured spectra.

Diffusion↗
PubMed1995

Conformational analysis of the beta-amyloid peptide fragment, beta(12-28).

NMR and CD spectroscopy have been used to examine the conformation of the peptide, beta(12-28), (VHHQKLVFFAEDVGSNK) in aqueous and 60% TFE / 40% H2O solution at pH 2.4. In 60% TFE solution, the peptide is helical as confirmed by the CD spectrum and by the pattern of the NOE cross peaks detected in the NOESY spectrum of the peptide. In aqueous solution, the peptide adopts a more extended and flexible conformation. Broadening of resonances at low temperature, temperature-dependent changes in the chemical shifts of several of the CH alpha resonances and the observation of a number of NOE contacts between the hydrophobic side-chain protons of the peptide are indicative of aggregation in aqueous solution. The behavior of beta(12-28) in 60% TFE and in aqueous solution are consistent with the overall conformation and aggregation behavior reported for the larger peptide fragment, beta(1-28) and the parent beta-amyloid peptide.

Amino Acid Sequence↗