PubMed Health⌕ Search

Biomedical subjects

B Widom

Publications and source records attributed to B Widom.

13 recordsLinked to original sources
PubMed2006

Note on the energy density in the solvent induced by a solute.

The question of how far the effect of the presence of a solute molecule propagates into the solvent is studied in a lattice model that had been used earlier to describe hydrophobic interactions. The local energy density in the model solvent is obtained as an explicit function of distance from the solute and is found to decay to its bulk-phase value with the same decay length as that of the solvent-mediated part of the potential of mean force between a pair of solute molecules. The integrated deviation of the energy density from its bulk-phase value is evaluated in Bethe-Guggenheim approximation and shown to be identical to the energy change accompanying the dissolution of the solute as obtained from the temperature dependence of its solubility.

Journal Article↗
PubMed2006

Models of adsorption at a line of three-phase contact.

Two model density distributions at a line of three-phase contact for which the adsorptions are readily calculated are analyzed. One of them provides a numerical illustration of a recently found surprising fact about the thermodynamics of adsorption at such contact lines. A form of the line analogue of the Gibbs adsorption equation is conjectured, and it is noted that the conjecture is in principle testable by computer simulation and by experiment.

Journal Article↗
PubMed2006

Generalized solvation heat capacities.

The partial molar heat capacity associated with a constant-pressure solvation process is extended to define a total of six generalized solvation heat capacities, each of which contain unique physical information. These arise from all the possible cross derivatives of the reversible heat of solvation (with respect to T and N), each evaluated at either constant pressure or constant volume. The resulting quantities may be interconverted using expressions that depend on the solvent equation of state and the solute partial molar volume. Moreover, contributions to each of the solvation heat capacities arising from the temperature dependence of the solute-solvent interaction energy and the solvent-reorganization energy (at either constant pressure or constant volume) are formally identified. For the self-solvation of a molecule in its own pure fluid, the latter quantities may be extracted directly from experimental data, while for more general solvation processes additional input is required, either from computer simulation or from theoretical approximations. The results are used to experimentally quantify the generalized heat capacities pertaining to the self-solvation of xenon, difluoromethane, n-hexane, and water, as well as the hydration of xenon, cyclohexane, and three hard sphere solutes (of about the same size as water, xenon, and cyclohexane).

Journal Article↗
PubMed2004

Geometric view of the thermodynamics of adsorption at a line of three-phase contact.

We consider three fluid phases meeting at a line of common contact and study the linear excesses per unit length of the contact line (the linear adsorptions Lambda(i)) of the fluid's components. In any plane perpendicular to the contact line, the locus of choices for the otherwise arbitrary location of that line that makes one of the linear adsorptions, say Lambda(2), vanish, is a rectangular hyperbola. Two of the adsorptions Lambda(2) and Lambda(3) then both vanish when the contact line is chosen to pass through any of the intersections of the two corresponding hyperbolas Lambda(2)=0 and Lambda(3)=0. There may be two or four such real intersections. It is found most surprisingly, and confirmed in a numerical example, that Lambda(1(2,3)), the adsorption of component 1 in a frame of reference in which the adsorptions Lambda(2) and Lambda(3) are both 0, depends on which intersection of the hyperbolas Lambda(2)=0 and Lambda(3)=0 is chosen for the location of the contact line. This implies that what had long been taken to be the line analog of the Gibbs adsorption equation is incomplete; there must be additional, previously unanticipated terms in the relation, consistent with the invariance of the line tension to choice of location of the contact line. It is then not Lambda(1(2,3)) by itself but a related expression containing it that must be invariant, and this invariance is also confirmed in the numerical example. The presence of the additional terms in the adsorption equation is further confirmed and their origin clarified in a mean-field density-functional model. The supplemental terms vanish at a wetting transition, where one of the contact angles goes to 0.

Journal Article↗
PubMed1997

Contact Angles of Liquid Drops on Low-Energy Solid Surfaces

There have been many experiments that have determined the wetting behavior of liquids on low-energy solid surfaces. These experiments show that, in general, the contact angle, theta, measured through the liquid, increases with increasing liquid-vapor surface tension, sigmalv. Surprisingly, in experiments with some such surfaces, the contact angle of a drop appears to depend almost entirely on the liquid-vapor surface tension and very little on the other properties of the liquid. To gain some insight into this phenomenon, we have used a generalized van der Waals theory to model a diverse series of liquids on a low-energy substrate and to calculate the corresponding surface tensions and contact angles. We find that it is indeed possible to reproduce behavior similar to that seen in experiments, with the data for cos theta plotted versus sigmalv falling in a narrow band which could almost be interpreted as a smooth curve. The width of the band in our calculation depends on the ranges of the model parameters and on the details of the molecular interactions.

Journal Article↗
PubMed1995

Cognitive function in patients with insulin-dependent diabetes mellitus during hyperglycemia and hypoglycemia.

BACKGROUND: To determine the impact of glycemic control, gender, and other relevant parameters on cognitive function during exposure to different blood glucose levels in patients with insulin-dependent diabetes mellitus (IDDM), we examined neuropsychologic function during experimentally induced periods of hyperglycemia and hypoglycemia. METHODS: We studied 20 men and 22 women, aged 18 to 44 years, with IDDM duration of 3 to 14 years and HbA1 values ranging from 5.8% to 18.0% (nondiabetic range 5.4% to 7.4%). We used a controlled experimental setting involving tests of sensory perceptual processing, simple motor abilities, attention, learning and memory, language, and spatial and constructional abilities at plasma glucose levels of 2.2, 5.6, 8.9, 14.4, and 21.1 mmol/L. Patients were blind to the glucose level. Tests used at each glucose level included reaction time (simple and choice), digit vigilance, trail making part B, word recall, digit sequence learning, and verbal fluency. RESULTS: All aspects of neuropsychologic function were diminished at 2.2 mmol/L when compared with basal levels of performance at 8.9 mmol/L, whereas no alterations were observed at 14.4 or 21.1 mmol/L. Tests involving associative learning, attention, and mental flexibility were the most affected during hypoglycemia. Glycemic control was not correlated with neuropsychologic function at any glucose level. Women demonstrated less of an impairment in neuropsychologic function than men at 2.2 mmol/L. CONCLUSIONS: Cognitive function in IDDM patients was generally well-preserved even at substantially elevated blood glucose levels. Deficits in all relevant areas of cognitive function occurred during hypoglycemia (2.2 mmol/L), irrespective of prior glycemic control, and women with IDDM were less cognitively impaired than men with IDDM during hypoglycemia.

Adult↗
PubMed1995

Differential regulation of counterregulatory hormone secretion and symptoms during hypoglycemia in IDDM. Effect of glycemic control.

OBJECTIVE: To determine 1) if there was a differential effect of glycemic control on individual counterregulatory hormone responses to hypoglycemia in patients with insulin-dependent diabetes mellitus (IDDM), 2) whether these modifications affect hypoglycemic symptom perception, and 3) if there was a level of glycemic control below which counterregulatory and symptomatic responses to hypoglycemia become consistently altered. RESEARCH DESIGN AND METHODS: We performed hypoglycemic clamp studies on 38 patients with IDDM and 38 healthy control subjects. Glucose was lowered from 5.0 to 2.2 mmol/l over 3 h in decrements of 0.6 mmol/l each 30 min. Epinephrine, cortisol, growth hormone (GH), glucagon, and symptom score were measured at each glucose plateau. RESULTS: In IDDM patients, HbA1 levels were positively correlated with incremental epinephrine (r = 0.58, P < 0.001) and cortisol (r = 0.52, P < 0.01) responses, but inversely correlated with GH responses (r = -0.31, P < 0.05). The increase in symptom score correlated with the epinephrine response in the IDDM patients (r = 0.57, P < 0.001), but not in the healthy control subjects (r = -0.02, NS). In IDDM patients with HbA1 < or = 7.8% (n = 7), the epinephrine, cortisol, and symptomatic responses to hypoglycemia were blunted, but GH secretion was preserved. CONCLUSIONS: These data suggest that 1) there is differential regulation of counterregulatory hormone secretion that is dependent on the level of glycemic control, 2) epinephrine is an important determinant of symptom perception in IDDM patients, but not in healthy control subjects, and 3) multiple defects in counterregulatory hormone secretion and symptom perception are consistently observed in patients with HbA1 levels < or = 7.8%.

Adult↗
PubMed1994

Stimulus specificity of defects in counterregulatory hormone secretion in insulin-dependent diabetes mellitus: effect of glycemic control.

Counterregulatory hormone responses to hypoglycemia are impaired in subjects with insulin-dependent diabetes mellitus (IDDM) in strict glycemic control. To determine whether these defects are specific for hypoglycemia, we examined counterregulatory hormone responses during a 3-h hypoglycemic hyperinsulinemic clamp (14.4 pmol/kg.min) that lowered plasma glucose from 5.0 to 2.2 mmol/L in 9 well controlled IDDM patients (hemoglobin-A1, 7.5 +/- 0.8%), 9 poorly controlled patients (hemoglobin-A1, 12.5 +/- 1.5%), and 10 healthy volunteers. Counterregulatory hormone secretion was compared with responses to non-glucose secretagogues for epinephrine and norepinephrine (cold pressor test), ACTH (overnight metyrapone test), and GH (L-arginine infusion). During hypoglycemia, epinephrine and cortisol responses were lower in the IDDM group in strict glycemic control than those in the poorly controlled IDDM group or healthy volunteers (P < 0.05). In response to the cold pressor test, the areas under the curve for epinephrine and norepinephrine were also reduced in the well controlled IDDM group (P < 0.05 vs. healthy volunteers). The ACTH response to hypoglycemia was not significantly reduced in the well controlled IDDM, whereas the response to metyrapone was actually greater in this group (P < 0.05 vs. poorly controlled IDDM). GH responses to both hypoglycemia and arginine were highest in the well controlled diabetic patients. These data suggest that 1) the reduced epinephrine responses in well controlled IDDM may not be specific for the hypoglycemic stimulus alone, but may also occur in response to other nonhypoglycemic stimuli; 2) cortisol responses to hypoglycemia are reduced in well controlled IDDM, whereas the ACTH response to a non-hypoglycemic stimulus remains intact; and 3) GH responses to both hypoglycemic and nonhypoglycemic stimuli are preserved in well controlled IDDM. The preservation of ACTH and GH responses to metyrapone and arginine, respectively, suggests adequate pituitary functional reserve in IDDM patients in strict glycemic control in response to nonhypoglycemic stimuli.

Adolescent↗
PubMed1992

Intermittent hypoglycemia impairs glucose counterregulation.

IDDM patients who maintain strict glycemic control have impaired counterregulatory hormone and symptomatic responses to hypoglycemia. To test the hypothesis that intermittent exposure to hypoglycemia plays an etiological role in these defective responses, we produced 4 consecutive daily episodes of hypoglycemia in 10 healthy, nondiabetic volunteers by using the insulin clamp technique. Fasting (5.3 +/- 0.1 vs. 5.4 +/- 0.1 mM) and nadir (2.3 +/- 0.1 vs. 2.4 +/- 0.1 mM) glucose levels achieved during insulin infusion did not differ on study days 1 and 4. In contrast, the glucose levels required to stimulate an increase in EPI (2.8 vs. 3.1 mM), glucagon (2.8 vs. 3.2 mM), cortisol (2.4 vs. 2.9 mM), GH (2.6 vs. 3.0 mM), and autonomic hypoglycemic symptoms (2.2 vs. 2.5 mM) were all significantly lower on study day 4 versus study day 1 (P < 0.005-0.05). Basal levels of EPI and cortisol, but not glucagon, GH, or NE also were reduced on the final study day. We conclude that intermittent hypoglycemia can result in attenuation of the hormonal and symptomatic responses to insulin-induced hypoglycemia and may contribute to the defective counterregulatory responses in patients with well-controlled IDDM.

Adult↗
PubMed1992

Alterations in glucose metabolism during menstrual cycle in women with IDDM.

OBJECTIVE: To examine the hormonal mechanisms underlying the variability in glycemic control during the different phases of the menstrual cycle in women with insulin-dependent diabetes mellitus (IDDM). RESEARCH DESIGN AND METHODS: Hyperglycemic (11.7 +/- 0.1 mM), hyperinsulinemic (24 +/- 3 mU/L) clamp studies were performed in 16 women with IDDM during the follicular (day 8 +/- 1) and luteal (day 23 +/- 1) phases of the menstrual cycle. Seven of the patients (group 1) experienced worsening glucose control during the luteal phase, whereas nine patients (group 2) did not. RESULTS: In group 1, glucose metabolism fell from 30.2 +/- 3.8 mumol.kg-1.min-1 during the follicular phase to 24.5 +/- 2.0 mumol.kg-1.min-1 during the luteal phase (P = 0.09), whereas in group 2 it increased from 18.5 +/- 1.2 to 23.2 +/- 2.3 mumol.kg-1.min-1 (P = 0.03). The decrease in glucose metabolism during the luteal phase in patients in group 1 was associated with a significant rise in the serum estradiol levels from the follicular to luteal phase (164 +/- 39 vs. 352 +/- 59 pM, P = 0.006), whereas this rise was not observed in group 2 (334 +/- 156 vs. 423 +/- 74 pM, NS). Changes in other reproductive hormones (progesterone, testosterone, dihydrotestosterone, androstenedione, luteinizing hormone, follicular-stimulating hormone, or prolactin) were not related to the differences in glucose uptake in the two groups. CONCLUSIONS: 1) Marked heterogeneity in glucose metabolism is seen throughout the menstrual cycle in women with IDDM, 2) a subgroup of patients exhibits worsening premenstrual hyperglycemia and a decline in insulin sensitivity during the luteal phase, and 3) the deterioration in glucose uptake in this subgroup was associated with a greater increment in estradiol levels from the follicular to the luteal phase.

Adult↗
PubMed1990

Glycemic control and neuropsychologic function during hypoglycemia in patients with insulin-dependent diabetes mellitus.

STUDY OBJECTIVE: To evaluate counterregulatory hormone secretion and neuropsychologic function during hypoglycemia in two groups of patients with insulin-dependent diabetes mellitus: those with good and those with poor glycemic control. DESIGN: Cross-sectional physiologic and neuropsychologic evaluation. SETTING: Clinical research unit of a referral-based diabetes clinic. PATIENTS: Eight patients with well controlled diabetes (glycosylated hemoglobin [HgbA1], 8.0% +/- 0.2%), nine patients with poorly controlled diabetes (HgbA1, 11.8% +/- 0.4%), and ten healthy persons. INTERVENTIONS: The insulin clamp technique was used to produce a stepwise decline in plasma glucose from 5.0 to 2.2 mmol/L over 3 hours. Tests of attention, memory, visual-spatial skills, visual-motor skills, and global cognition; a symptom survey; and counterregulatory hormone measurements were done at glucose decrements of 0.6 mmol/L. MEASUREMENTS AND MAIN RESULTS: Patients with well controlled diabetes did not differ statistically from those with poorly controlled diabetes regarding the median glucose threshold for dysfunction in visual-spatial skills, visual-motor skills, or global cognition. In contrast, glycemic thresholds for an increase in adrenergic symptoms and release of epinephrine, norepinephrine, cortisol, and growth hormone were lower in patients with well controlled diabetes than in those with poorly controlled diabetes (P less than 0.05 to 0.005). CONCLUSIONS: Despite alterations in the glucose levels at which adrenergic symptoms of hypoglycemia occur and counterregulation begins, there is no statistically detectable change in the glucose threshold at which cognitive deterioration occurs in diabetic persons with strict glycemic control. This dissociation of neuropsychologic function and counterregulatory hormone secretion suggests that diabetic patients with good glycemic control are at increased risk for developing cognitive impairment before the onset of adrenergic symptoms during hypoglycemia.

Adult↗
PubMed1984

Mechanisms of insulin resistance in cultured fibroblasts from a patient with leprechaunism: impaired post-binding actions of insulin and multiplication-stimulating activity.

The binding and action of insulin and of the insulin-like growth factor, multiplication-stimulating activity (MSA), were studied in cultured skin fibroblasts from an infant with leprechaunism and associated insulin resistance. Three actions of insulin were reduced in the leprechaun cells: activation of glycogen synthase was 30% as great as in control fibroblasts, the increase in 2-deoxyglucose transport was 33% of the control value, and the uptake of alpha-aminoisobutyric acid was sevenfold less sensitive to enhancement. On a molar basis, MSA was at least as effective as insulin in activating glycogen synthase in control fibroblasts; in the patient's cells there was a reduction in activation that paralleled the changes observed with insulin. To localize the site of insulin resistance, the binding of both [125I]-insulin and [125I]-MSA to fibroblasts was measured and found to be reduced in the leprechaun cells. However, the impairment of the actions of insulin and MSA in the patient's cells was not explained solely by the diminished binding of the two polypeptides. Since the hexose transport system and the terminal enzymes studied thus far are intact, the defect is postulated to involve the post-binding coupling mechanism and mediator formation.

Adult↗