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PubMed1999

Conformational equilibria of alkanes in aqueous solution: relationship to water structure near hydrophobic solutes.

Conformational free energies of butane, pentane, and hexane in water are calculated from molecular simulations with explicit waters and from a simple molecular theory in which the local hydration structure is estimated based on a proximity approximation. This proximity approximation uses only the two nearest carbon atoms on the alkane to predict the local water density at a given point in space. Conformational free energies of hydration are subsequently calculated using a free energy perturbation method. Quantitative agreement is found between the free energies obtained from simulations and theory. Moreover, free energy calculations using this proximity approximation are approximately four orders of magnitude faster than those based on explicit water simulations. Our results demonstrate the accuracy and utility of the proximity approximation for predicting water structure as the basis for a quantitative description of n-alkane conformational equilibria in water. In addition, the proximity approximation provides a molecular foundation for extending predictions of water structure and hydration thermodynamic properties of simple hydrophobic solutes to larger clusters or assemblies of hydrophobic solutes.

Alkanes↗
PubMed1996

A double-blind clinical trial comparing World Health Organization oral rehydration solution with a reduced osmolarity solution containing equal amounts of sodium and glucose.

OBJECTIVE: To compare the safety and efficacy of an oral rehydration solution (ORS) containing 75 mmol/L of sodium and glucose each with the standard World Health Organization (WHO) ORS among Egyptian children with acute diarrhea. METHODS: One hundred ninety boys, aged 1 to 24 months, who were admitted to the hospital with acute diarrhea and signs of dehydration were randomly assigned to receive either standard ORS (311 mmol/L) or a reduced osmolarity ORS (245 mmol/L). Intake and output were measured every 3 hours. RESULTS: In the group treated with reduced osmolarity ORS, the mean stool output during the rehydration phase was 36% lower (95% confidence interval, 1%, 100%) than in those treated with WHO ORS. The relative risk of vomiting during the rehydration phase was significantly lower in children treated with reduced osmolarity ORS (relative risk, 2.4; 95% confidence interval, 1.2, 4.8). During the maintenance phase, stool output, mean intake of food and ORS, duration of diarrhea, and weight gain were similar in the treatment groups. The relative risk of treatment failure (need for unscheduled administration of intravenous fluids) was significantly increased in children receiving standard WHO ORS (relative risk, 7.9; 95% confidence interval, 1.1, 60.9). The mean serum sodium concentration at 24 hours was significantly lower in children receiving the reduced osmolarity ORS solution (134 +/- 6 mEq/L) than in children receiving the standard WHO ORS (138 +/- 7 mEq/L) (p < 0.001). The relative risk of the development or worsening of hyponatremia was not increased in children given the reduced osmolarity ORS, and urine output was similar in the treatment groups. CONCLUSION: The reduced osmolarity ORS has beneficial effects on the clinical course of acute diarrhea in children by reducing stool output, and the proportion of children with vomiting during the rehydration phase, and by reducing the need for supplemental intravenous therapy. These results provide support for the use of a reduced osmolarity ORS in children with acute noncholera diarrhea.

Acute Disease↗
PubMed2000

A comparison of the relative efficacy and clinical performance of olopatadine hydrochloride 0.1% ophthalmic solution and ketotifen fumarate 0.025% ophthalmic solution in the conjunctival antigen challenge model.

OBJECTIVE: The purpose of this study was to compare the relative efficacy and clinical performance of olopatadine hydrochloride 0.1% ophthalmic solution and ketotifen fumarate 0.025% ophthalmic solution in the conjunctival antigen challenge model. METHODS: This was a prospective, randomized, double-masked, contralaterally controlled, single-center, antigen challenge study. Of the 53 subjects screened, 32 were enrolled and completed the study. The study comprised 3 visits. Primary efficacy variables were ocular itching (assessed at visits 2 and 3) and subject satisfaction (assessed at visit 3). Tolerability variables were slit-lamp findings (all visits), visual acuity (all visits), ocular comfort after drug instillation (visit 3), and adverse events (visits 2 and 3). At visit 1, the antigen concentration that elicited a positive ocular allergic response was determined, and this concentration was confirmed at visit 2. Subjects graded itching on a 5-point scale at 3, 5, and 10 minutes postchallenge. The scores from this visit were used as baseline scores and compared with scores from visit 3 to determine drug efficacy. At visit 3, subjects were randomly assigned to 2 treatment groups. Group A received 1 drop of olopatadine in the right eye and I drop of ketotifen in the left eye. Group B received 1 drop of olopatadine in the left eye and 1 drop of ketotifen in the right eye. Following drug instillation, the subjects assessed the comfort level in each eye. Twelve hours after instillation, subjects were challenged with the antigen concentration that elicited a positive response at the previous visits. Itching was subjectively graded at 3, 5, and 10 minutes postchallenge. Subjects were asked to choose which therapy they were more satisfied with. RESULTS: Twelve hours after administration, efficacy scores for olopatadine were significantly higher than those for ketotifen at 3 and 5 minutes postchallenge (1.84 and 1.75 vs 1.25 and 1.34; P < 0.05). Olopatadine-treated eyes were rated significantly more comfortable than those treated with ketotifen immediately after drug instillation (1.25 vs 2.09; P < 0.05) and 12 hours later, as measured by patient ratings of ocular comfort. Of the 22 subjects who had a preference, 16 (73%) were more satisfied with olopatadine than with ketotifen. CONCLUSIONS: Olopatadine is more effective than ketotifen in reducing the itching associated with allergic conjunctivitis in the antigen challenge model. Olopatadine caused less ocular discomfort than ketotifen and was preferred by approximately 3 times as many patients as was ketotifen.

Allergens↗
PubMed2000

Comparison of the clinical efficacy and comfort of olopatadine hydrochloride 0.1% ophthalmic solution and nedocromil sodium 2% ophthalmic solution in the human conjunctival allergen challenge model.

BACKGROUND: Mast cell stabilizers, such as the ocular antiallergic agent nedocromil sodium 2% ophthalmic solution, are not rapid acting and often require a loading period of > or =2 weeks for maximal efficacy. Olopatadine hydrochloride 0.1% ophthalmic solution is a member of a new class of topical antiallergic agents that have combined antihistaminic and mast cell-stabilizing properties. OBJECTIVE: The purpose of this study was to compare the clinical efficacy and comfort of olopatadine with those of nedocromil in the conjunctival allergen challenge model. METHODS: This was a single-center, 3-visit, randomized, double-masked, contralaterally controlled study. Seventy-five subjects with a history of allergic conjunctivitis were screened, and the 52 who responded to conjunctival allergen challenge at visits I and 2 were randomized by eye to receive olopatadine, nedocromil, or placebo (a "natural tears" lubricant eye drop). Because nedocromil may require a 2-week loading period for maximal efficacy, the eyes assigned to that agent received nedocromil for 14 days (between visits 2 and 3), whereas the eyes assigned to olopatadine or placebo received placebo during this period. Throughout the loading phase, subjects instilled 1 drop of the assigned masked medication in each eye twice daily. At the assessment visit (visit 3), subjects received I drop of masked olopatadine, nedocromil, or placebo in each eye and were asked to rate the comfort of each drop on a scale from 0 to 8. Fifteen minutes after instillation of medication, subjects were challenged with the allergen concentration that had elicited a positive conjunctival allergic response at the previous visits. Subjects then scored their itching on a scale from 0 to 4 at 3, 5, and 10 minutes after challenge. Mean itching scores for all eyes were compared by treatment. Paired t tests were performed on the mean itching and ocular comfort scores at each time point. At the end of the study, subjects were asked which treatment they preferred in terms of comfort and efficacy. RESULTS: Forty-nine subjects completed the study. Forty eyes received olopatadine, 36 received nedocromil, and 22 received placebo. Olopatadine was clinically and statistically superior to nedocromil at reducing itching in the conjunctival allergen challenge model (mean unit difference: -1.60 at 3 minutes, -1.68 at 5 minutes, -1.19 at 10 minutes; P < 0.001). One drop of olopatadine was more efficacious than 29 drops of nedocromil. Olopatadine-treated eyes were rated as being significantly more comfortable than nedocromil-treated eyes (0.73 vs 1.55; P = 0.034). Of the 14 subjects treated with olopatadine and nedocromil who stated a preference, 10 (71%) were more satisfied with olopatadine than with nedocromil. CONCLUSION: In the conjunctival allergen challenge model, olopatadine was more efficacious and comfortable than nedocromil in reducing the itching associated with allergic conjunctivitis.

Conjunctivitis, Allergic↗
PubMed2001

Evaluation of the efficacy of olopatadine hydrochloride 0.1% ophthalmic solution and azelastine hydrochloride 0.05% ophthalmic solution in the conjunctival allergen challenge model.

BACKGROUND: Olopatadine hydrochloride 0.1% ophthalmic solution and azelastine hydrochlofide 0.05% ophthalmic solution are 2 topical antiallergic agents indicated for the treatment of itching of the eye associated with allergic conjunctivitis. Olopatadine has recently received US Food and Drug Administration (FDA) approval for an expanded indication for the treatment of signs and symptoms of allergic conjunctivitis, including itching, tearing, eyelid swelling, redness, and chemosis. OBJECTIVE: The purpose of this study was to compare the efficacy of olopatadine hydrochloride versus azelastine hydrochloride and placebo (artificial tears) in the conjunctival allergen challenge (CAC) model. METHODS: This was a prospective, randomized, double-masked, contralaterally controlled, multicenter, allergen-challenge study. Itching was chosen as the primary efficacy variable since it is the only FDA-approved indication these 2 agents have in common. Subjects with a history of allergic conjunctivitis who responded to the CAC at screening visits 1 and 2 were randomized to 1 of 3 treatment groups: olopatadine in 1 eye and azelastine in the other eye; olopatadine in 1 eye and placebo in the other eye; or azelastine in 1 eye and placebo in the other eye. At the assessment visit (visit 3), subjects received masked study medication according to the randomization scheme. After 5 minutes, subjects were bilaterally challenged with the allergen concentration that had elicited a positive conjunctival allergic response at visits 1 and 2. Immediately after challenge, subjects gave itching assessments (scale, 0 = no itching to 4 = severe itching) every 30 seconds for a total period of 20 minutes. Mean itching scores for all eyes were compared by treatment. Mean itching scores at each time point were compared between treatments using 2 sample t tests. RESULTS: Of the 180 subjects screened, 111 responded to the CAC at visits 1 and 2 and completed the study; 65% (72/111) of patients were female, 87% (97/111) were white, and 49% (54/111) had brown irides. The mean age was approximately 40 years. Seventy-three eyes were treated with olopatadine, 75 with azelastine, and 74 with placebo. A single dose of 1 of the 3 study medications per eye was well tolerated by all subjects. Both treatments were significantly more effective than placebo at reducing itching postchallenge. Olopatadine was significantly more effective than azelastine in reducing itching at 3.5 minutes through 20 minutes postchallenge (average mean unit difference of -0.31; P < 0.05) in the CAC model. CONCLUSION: In this population, olopatadine was significantly more effective than azelastine in the management of itching associated with allergic conjunctivitis in the CAC model.

Adult↗
PubMed2002

Randomized, double-masked, placebo-controlled comparison of the efficacy of emedastine difumarate 0.05% ophthalmic solution and ketotifen fumarate 0.025% ophthalmic solution in the human conjunctival allergen challenge model.

BACKGROUND: Emedastine difumarate 0.05% ophthalmic solution and ketotifen fumarate 0.025% ophthalmic solution are 2 topical antiallergic agents available in the United States and other countries. Emedastine is indicated for the temporary relief of the signs and symptoms of allergic conjunctivitis. Ketotifen is indicated for the temporary relief of ocular itching caused by allergic conjunctivitis. OBJECTIVE: The purpose of this study was to compare the efficacy of these agents in the temporary relief of ocular itching due to allergic conjunctivitis. The 2 agents were compared with each other and with placebo (artificial tears) using the conjunctival allergen challenge (CAC) model. METHODS: This was a single-center, randomized, double-masked, placebo-controlled study. At visit 1, CAC was performed on eligible subjects to identify the dose required to elicit a positive allergic reaction. Subjects returned after 7 days for visit 2 to confirm the allergen dose. On day 14 (+/-3) of the study, enrolled subjects were randomized to 1 of 3 treatment groups: emedastine in I eye and placebo in the other, ketotifen in 1 eye and placebo in the other, or emedastine in 1 eye and ketotifen in the other. In 25 subjects, bilateral CAC was performed 5 minutes after study medication instillation. In a second group of 20 subjects, CAC was performed 15 minutes after medication instillation. Itching was graded according to a standardized 5-point scale (0 = none to 4 = severe itching) at 3, 5, and 10 minutes postchallenge. Differences in efficacy scores between treatments and versus placebo were compared using 2-sample t tests of equal variance. RESULTS: A total of 45 patients (mean age, 41.2 years) received treatment: 16 received emedastine in 1 eye and ketotifen in the other; 14 received emedastine in 1 eye and placebo in the other; and 15 received ketotifen in 1 eye and placebo in the other. Both emedastine and ketotifen significantly inhibited itching (P < 0.05) compared with placebo at all time points after the 5- and 15-minute CAC. Mean raw scores for the active treatments were not statistically different. The mean itching efficacy scores were also not statistically different between active treatments. No adverse events were reported in this study. CONCLUSION: The results of this study suggest that emedastine and ketotifen are not significantly different with respect to anti-itching efficacy in the CAC model of acute allergic conjunctivitis.

Allergens↗
PubMed2003

A phase III clinical trial of 0.5% levofloxacin ophthalmic solution versus 0.3% ofloxacin ophthalmic solution for the treatment of bacterial conjunctivitis.

OBJECTIVE: To compare the efficacy and safety of 0.5% levofloxacin ophthalmic solution (QUIXIN) with 0.3% ofloxacin ophthalmic solution for the treatment of bacterial conjunctivitis. DESIGN: Prospective, randomized, active-controlled, double-masked, multicenter study. PARTICIPANTS: Four hundred twenty-three patients with a clinical diagnosis of bacterial conjunctivitis were enrolled. METHODS: Patients were randomly assigned to receive either 0.5% levofloxacin (n = 211) or 0.3% ofloxacin (n = 212) for 5 days (every 2 hours on days 1 and 2 and every 4 hours on days 3-5). Conjunctival cultures were obtained, and ocular signs and symptoms were evaluated on day 1 (baseline), days 3 to 5 (interim), and days 6 to 10 (final). End point was defined as the last evaluable observation. MAIN OUTCOME MEASURES: Primary microbial and clinical outcomes were based on culture results and resolution of cardinal signs, respectively. Secondary efficacy assessments included evaluations of ocular signs and symptoms. RESULTS: Two hundred eight patients (levofloxacin, n = 109; ofloxacin, n = 99) were evaluated for efficacy. Microbial eradication rates were significantly greater in the 0.5% levofloxacin treatment group compared with the 0.3% ofloxacin group at both the final visit (89% vs. 80%, P = 0.034) and at end point (90% vs. 81%; P = 0.038). Treatment with 0.5% levofloxacin was significantly more effective in resolving photophobia than was 0.3% ofloxacin treatment (94% vs. 73%, P = 0.006). Both study medications were well tolerated, with a low incidence of adverse events. CONCLUSIONS: Although clinical cure rates in the 0.5% levofloxacin and 0.3% ofloxacin treatment groups were similar, a 5-day treatment regimen with 0.5% levofloxacin achieved microbial eradication rates that were statistically superior to those attained with 0.3% ofloxacin. Despite the higher concentration of active drug in 0.5% levofloxacin versus 0.3% ofloxacin, there was no difference between treatment groups in the incidence of treatment-related adverse events.

Adolescent↗
PubMed1997

Structure and thermodynamics of nonideal solutions of colloidal particles: investigation of salt-free solutions of human serum albumin by using small-angle neutron scattering and Monte Carlo simulation.

The understanding of the structural and thermodynamic properties of moderately or highly concentrated solutions is fundamental, e.g., in medicine and biology and also in many technical processes. In this work, we have used the small-angle neutron scattering method (SANS), in combination with Monte Carlo simulation, to study salt-free solutions of human serum albumin (HSA) in the concentration range up to 0.26 g ml-1. The model calculations of the theoretical SANS intensities are quite general, thus avoiding the approximation that the relative positions and orientations of the particles are independent of each other. The computation of the theoretical intensities also includes the calculation of a "thermodynamic' intensity scattered at zero angle, which is obtained via the nonideal part of the chemical potential. The latter quantity is obtained by applying the test particle method during the Monte Carlo simulations. It is found that the SANS data can be explained by a model where the HSA molecules behave as hard ellipsoids of revolution with semiaxes a = 6.8 nm, b = c = 1.9 nm. In addition to the hard core interaction, the particles are also surrounded by a soft, repulsive rectangular-shaped potential which is spherically oriented around the particles. The combination of SANS and statistical thermodynamics also allows a determination of the nonideal part of the chemical potential and the activity coefficient of HSA. As expected the activity coefficient deviates strongly from the value one (several powers of ten) already at fairly low concentrations: the effects are comparable to, or even larger than, for instance hydrophobic or van der Waals interaction.

Chemical Phenomena↗
PubMed2003

Solution-state dynamics of sugar-connected spin probes in sucrose solution as studied by multiband (L-, X-, and W-band) electron paramagnetic resonance.

A multiband (L-band, 0.7GHz; X-band, 9.4GHz; and W-band, 94GHz) electron paramagnetic resonance (EPR) study was performed for two glycosidated spin probes, 4-(alpha,beta-D-glucopyranosyloxy)-TEMPO (Glc-TEMPO) and 4-(alpha,beta-D-lactopyranosyloxy)-TEMPO (Lac-TEMPO), and one non-glycosylated spin probe, 4-hydroxy-TEMPO (TEMPOL), where TEMPO=2,2,6,6-tetramethyl-1-piperidinyloxyl, to characterize fundamental hydrodynamic properties of sugar-connected spin probes. The linewidths of these spin probes were investigated in various concentrations of sucrose solutions (0-50wt%). The multiband approach has allowed full characterization of the linewidth parameters, providing insights into the molecular shapes of the spin probes in sucrose solution. The analysis based on the fast-motional linewidth theory has yielded anisotropy parameters of rho(x) approximately 2.6 and rho(y) approximately 0.9 for Glc-TEMPO, and rho(x) approximately 4.2 and rho(y) approximately 0.9 for Lac-TEMPO. These values indicate that the glycosidated spin probes have a prolate-type molecular shape elongated along the x-axis (NO(rad) axis) with Lac-TEMPO elongated more remarkably, consistent with their molecular structures. The interaction parameters k (the ratios of the effective hydrodynamic volumes to the real ones) corrected for the difference in molecular shape have been estimated and found to have the relation k(TEMPOL)<k(Glc-TEMPO) approximately k(Lac-TEMPO). This agrees with the expectation that glycosidated spin probes can have stronger hydrogen bonding to water. Glycosidated spin probes are expected to be useful for probing sugar-involving interactions, which commonly occur in biological systems. Thus this study will provide an indispensable basis for such spin-probe studies.

Anisotropy↗
PubMed2004

Solution structure of the two-iron rubredoxin of Pseudomonas oleovorans determined by NMR spectroscopy and solution X-ray scattering and interactions with rubredoxin reductase.

Here we provide insights into the molecular structure of the two-iron 19-kDa rubredoxin (AlkG) of Pseudomonas oleovorans using solution-state nuclear magnetic resonance (NMR) and small-angle X-ray scattering studies. Sequence alignment and biochemical studies have suggested that AlkG comprises two rubredoxin folds connected by a linker region of approximately 70 amino acid residues. The C-terminal domain (C-Rb) of this unusual rubredoxin, together with approximately 35 amino acid residues of the predicted linker region, was expressed in Escherichia coli, purified in the one-iron form and the structure of the cadmium-substituted form determined at high-resolution by NMR spectroscopy. The structure shows that the C-Rb domain is similar in fold to the conventional one-iron rubredoxins from other organisms, whereas the linker region does not have any discernible structure. This tandem "flexible-folded" structure of the polypeptide chain derived for the C-Rb protein was confirmed using solution X-ray scattering methods. X-ray scattering studies of AlkG indicated that the 70-amino acid residue linker forms a structured, yet mobile, polypeptide segment connecting the globular N- and C-terminal domains. The X-ray scattering studies also showed that the N-terminal domain (N-Rb) has a molecular conformation similar to that of C-Rb. The restored molecular shape indicates that the folded N-Rb and C-Rb domains of AlkG are noticeably separated, suggesting some domain movement on complex formation with rubredoxin reductase to allow interdomain electron transfer between the metal centers in AlkG. This study demonstrates the advantage of combining X-ray scattering and NMR methods in structural studies of dynamic, multidomain proteins that are not suited to crystallographic analysis. The study forms a structural foundation for functional studies of the interaction and electron-transfer reactions of AlkG with rubredoxin reductase, also reported herein.

Amino Acid Sequence↗
PubMed1998

Three-dimensional solution structure of alpha-conotoxin MII by NMR spectroscopy: effects of solution environment on helicity.

alpha-Conotoxin MII, a 16-residue polypeptide from the venom of the piscivorous cone snail Conus magus, is a potent and highly specific blocker of mammalian neuronal nicotinic acetylcholine receptors composed of alpha3 beta2 subunits. The role of this receptor type in the modulation of neurotransmitter release and its relevance to the problems of addiction and psychosis emphasize the importance of a structural understanding of the mode of interaction of MII with the alpha3 beta2 interface. Here we describe the three-dimensional solution structure of MII determined using 2D 1H NMR spectroscopy. Structural restraints consisting of 376 interproton distances inferred from NOEs and 12 dihedral restraints derived from spin-spin coupling constants were used as input for simulated annealing calculations and energy minimization in the program X-PLOR. The final set of 20 structures is exceptionally well-defined with mean pairwise rms differences over the whole molecule of 0.07 A for the backbone atoms and 0.34 A for all heavy atoms. MII adopts a compact structure incorporating a central segment of alpha-helix and beta-turns at the N- and C-termini. The molecule is stabilized by two disulfide bonds, which provide cross-links between the N-terminus and both the middle and C-terminus of the structure. The susceptibility of the structure to conformational change was examined using several different solvent conditions. While the global fold of MII remains the same, the structure is stabilized in a more hydrophobic environment provided by the addition of acetonitrile or trifluoroethanol to the aqueous solution. The distribution of amino acid side chains in MII creates distinct hydrophobic and polar patches on its surface that may be important for the specific interaction with the alpha3beta2 neuronal nAChR. A comparison of the structure of MII with other neuronal-specific alpha-conotoxins provides insights into their mode of interaction with these receptors.

Amino Acid Sequence↗
PubMedDate not supplied

Reorganization of dynamic self-assemblies of cellulose diacetate in solution: dynamical critical-like fluctuations in the lower critical solution temperature system.

Dynamics of cellulose diacetate (CDA, the total degree of substitution (TDS) = 2.44) in dimethylacetamide (DMAc) in dilute solution was investigated at 2, 10, 20, 30, 40, 49.7, and 61.5 degrees C through dynamic light scattering in the quiescent state. The following three facts were made clear. First, CDA existed in three types of structures in the polar solvent, DMAc; one is a single CDA chain, and the others are dynamic structures, or self-assemblies, which were formed temporarily and locally by the solvent-mediated hydrogen bonding between the intermolecular C-6 position hydroxyls of the anhydroglucose units in the CDA backbone. Second, CDA showed a nature of low-temperature solubility in DMAc, that is, CDA is expected to dissolve molecularly below -12 degrees C but to take a phase separation above 65 degrees C, where two structures such as collapses of a single CDA chain and an aggregate appear. Third, a reorganization in the dynamic structures was detected at the temperature T = 33.8 degrees C. At this temperature, two dynamic structures showed the discontinuity in their correlation lengths, whereas the single CDA realized an uncorrelated chain state in the dynamical sense. In view of the low-temperature solubility of CDA in DMAc, this abnormal behavior around T was explained by dynamical critical-like fluctuations if T were treated as a kind of lower critical solution temperature (LCST) in the CDA/DMAc system. Here, the self-assemblies arise as the dynamical fluctuations under the spinodal decomposition situation and the competition between the hydrogen bonding (HB) and the hydrophobic interaction (HPhI) makes the conformation of CDA chains change drastically. In this scheme, the solvent-mediated HB and HPhI play important roles in the structure reorganization of cellulose derivatives in strong electronegative solvents, though HB and HPhI cooperate with the inherent chain helicality.

Cellulose↗
PubMedDate not supplied

Flory temperature and upper critical solution temperature of gelatin solutions.

The Flory temperatures (theta) measured by turbidity experiments performed on gelatin solutions were found to be 12 +/- 0.3, 13 +/- 0.3, 14 +/- 0.3, 14.5 +/- 0.3, and 15 +/- 0.3 degrees C for salt concentrations 0.1, 0.075, 0.05, 0.025, and 0 M (NaCl), respectively. Estimated persistence length (l(p)) of this weakly charged polyelectrolyte could be deduced from the Benoit and Doty (J. Phys. Chem. 1953, 57, 958) relationship with the approximation that this biopolymer assumes a compact near-globular shape at Flory temperature, implying l(p) = 9(R(h))(2)/(5L(m)), where L(m) is the contour length and R(h) is the hydrodynamic radius. It was found that l(p) approximately 2.2 +/- 0.2 nm at room temperature (20 degrees C), invariant of salt concentration. The Flory expansion factor (alpha= R(h)(T)/R(h)(theta) = 1.5+/-0.2) was found to be almost constant. theta-Composition for this biopolymer was deduced from turbidimitric titration of aqueous gelatin solutions with the alcohols methanol, ethanol, 2-propanol, and tert-butyl alcohol. It appears that hydrophobic interactions play a crucial role in causing chain collapse at theta-temperature and composition.

Gelatin↗
PubMed2006

Quantitating the dynamics of NBD hexanoic acid in homogeneous solution and in solutions containing unilamellar vesicles.

We report here on the motional and fluorescence lifetime dynamics of the chromophore NBDHA (6-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)hexanoic acid) in neat solvents and in aqueous solutions containing unilamellar vesicles of varying composition. We measure the transient response of this chromophore by time-correlated single-photon counting, using one- and two-photon excitation to resolve the Cartesian components of the rotational diffusion constant, D. Our experimental data for NBDHA in selected solvents of varying viscosity demonstrate that one- and two-photon excitation probe different components of the rotational diffusion constant and that this chromophore reorients as a prolate rotor with an aspect ratio of approximately 2. For NBDHA in aqueous solutions containing unilamellar vesicles of varying composition, we recover the same reorientation behavior regardless of vesicle composition. Fluorescence lifetime and steady-state fluorescence data show the chromophore to reside in a polar environment that is different from neat water. We understand these data in the context of the chromophore residing in close proximity to the unilamellar vesicle polar headgroups in all cases.

Caproates↗
PubMed2006

Temperature dependence of excited-state proton transfer in water electrolyte solutions and water-methanol solutions.

The reversible proton dissociation and geminate recombination of a photoacid is studied as a function of temperature in water electrolyte solutions and binary water-methanol mixtures, containing 0.1 and 0.2 mole fractions of methanol. 8-Hydroxypyrene-1,3,6-trisulfonate trisodium salt (HPTS) is used as the photoacid. The experimental data are analyzed by the reversible geminate recombination model. We found that the slope of the logarithm of the proton-transfer rate constant as a function of the inverse of temperature (Arrhenius plot) in the liquid phase of these samples are temperature-dependent, while in the solid phase, the slope is nearly constant. The slope of the Arrhenius plot in frozen electrolyte solution is larger than that of the water-methanol mixtures, which is about the same as in pure water. Careful examination of the time-resolved emission in ice samples shows that the fit quality using the geminate recombination model is rather poor at relatively short times. We were able to get a better fit using an inhomogeneous kinetics model assuming the proton-transfer rate consists of a distribution of rates. The model is consistent with an inhomogeneous frozen water distribution next to the photoacid.

Electrolytes↗
PubMed1991

Stability of interleukin 1 beta (IL-1 beta) in aqueous solution: analytical methods, kinetics, products, and solution formulation implications.

The thermal stability of IL-1 beta in aqueous solution as a function of temperature (5-60 degrees C), pH (2-9), buffer (acetate, citrate, tris, and phosphate), and cyroprotectants (sugars, HSA) was investigated in this study. The analytical methodologies included RP-HPLC, SEC, ELISA, IEF-PAGE, SDS-PAGE, and bioassay. The degradation and inactivation of IL-1 beta at or above 39 degrees C were attributed to autoxidation of the two cysteine residues in the denatured protein, followed by hydrophobic/covalent aggregation and precipitation. At or below 30 degrees C, IEF- and SDS-PAGE results suggest a possible deamidation reaction. The difference in mechanism of degradation precludes the prediction of formulation shelf life from accelerated temperature data. Nonetheless, the good stability observed at 5 degrees C suggests that a solution formulation may be feasible for IL-1 beta.

Drug Stability↗
PubMed1995

Cereal-based oral rehydration solutions in Sudanese children with diarrhoea: a comparative clinical trial of rice-based and sorghum-based oral rehydration solutions.

A randomized controlled study was carried out at the Children's Emergency Hospital, Khartoum to evaluate the acceptability, safety and efficacy of (rice or sorghum) cereal-based oral rehydration solutions (ORS) relative to that of the standard WHO ORS formulation in children with acute diarrhoea. Ninety-six children whose ages ranged from 6 to 40 months were enrolled in the study. Thirty-two of them were allocated to the rice-based ORS group, 34 to the sorghum-based ORS group and 30 to the control group. Cereal-based ORS solutions were found to shorten the duration of diarrhoea and to reduce both the stool volume and the frequency of diarrhoea and vomiting as well as the mean total ORS intake. These effects were more marked with the sorghum-based ORS than with the rice-based ORS. By the end of day 3, 50% of patients in the rice ORS group and 67.6% in the sorghum ORS group had recovered compared with 40% from the standard ORS group.

Child, Preschool↗
PubMed1977

Effect of salt solutions on radiosensitivity of mammalian cells. II. Treatment with hypotonic solutions.

Chinese hamster (V79) cells were treated with hypotonic NaCl, NaCl-ouabain, KCl, LiCl, NH4Cl, NaNO3 or sucrose solutions and irradiated at various times during exposure to the solution. The extreme increase in the radiosensitivity of these cells, mainly characterized by changes in DO, could be attributed to increases in the cell water-content and possibly the decrease in total cell water structure. The various ions may exert their specific effects on radiosensitivity by influencing the above water-related factors.

Ammonium Chloride↗