Search

Interdisciplinary teamwork is essential for the rehabilitation of patients with cleft lip and palate, and therefore, the application of treatment techniques for velopharyngeal insufficiency, both surgical and prosthetic, depends on the experience of each rehabilitation team. For this reason, the following study consisting of the cooperation between interdisciplinary cleft lip and palate teams from Chile and Argentina, which succeeded in correcting velopharyngeal insufficiency in an adolescent, initially using a pharyngeal bulb prosthesis and speech therapy, and finally through pharyngeal flap surgery, is presented. This shows that international cooperation is a valuable tool for training, implementation, and follow-up of different treatment techniques for teams in formation., Competing Interests: The authors report no conflicts of interest., (Copyright © 2023 by Mutaz B. Habal, MD.)

Experimental and theoretical data have been revisited to shed light onto the aspects of hydration and chain expansion of pectic acid (galacturonan) upon charging. The prediction of the variation of the number of solvation water molecules between the two limit ionization states from theoretical calculations was confirmed to a very high accuracy by the corresponding number evaluated form dilatometric measurements. The relevance of hydration to the mechanism of bonding of calcium ions by sodium pectate is discussed. Characterization of polymer expansion has been obtained by calculating the values of the characteristic ratio and/or the persistence length on the respective populations and comparing the theoretical predictions with experimental data. The results show that a charged chain in typical conditions of ionic strength is more expanded than its neutral counterpart, whereas the ideal limit (3 1 and 2 1 ) helical conformations in the uncharged and totally charged conditions, respectively, share the same value of the linear advance of the helical repeat, when the ionic strength tends to infinite. Total divergence between theoretical predictions and experimental evidence rules out the possibility that carboxylate charge reduction by protonation and by methyl esterification are equivalent in determining the solution behavior of galacturonan., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Pectic acid/sodium pectate is one of the most widespread hydrocolloid used in the food industry. It is able to form strong ionotropic gels by the addition of ions, in particular, calcium ions. The initial steps of binding Ca 2+ ions to a sample of sodium pectate with a composition close to 90% of ideal Na + -poly(galacturonate) were investigated by means of circular dichroism (CD), microcalorimetry, dilatometry, viscosity, and membrane osmometry, as a function of increasing R j , R j being the ratio of the molar concentrations of Ca 2+ and pectate repeating units. Data were collected in aqueous NaClO 4 at 25 °C. The key instrument of interpretation has been the counterion condensation theory (CCT) of linear polyelectrolytes, modified to include the presence of both specific affinity of the divalent counterion for the polysaccharide ("territorial binding"), and, very importantly, strong chemical bonding (not a covalent bonding, though) of Ca 2+ on conformationally well-defined sites on the polymer, with local charge annihilation. Intrinsic viscosity and number-average molar mass data as a function of R j showed that calcium bonding brings about chain association right from the beginning of addition to pectate. The analysis of the microcalorimetric curve using the modified CCT revealed two types of bonding. In the order of development as a function of R j , the first mode (type 1) could be reconciled with the "tilted egg-box" type, recently proposed for Ca 2+ binding to alginate and the second mode (type 2) with the "shifted egg-box" proposed for calcium pectate on the basis of conformational analysis investigation. Likewise, the two types of bonding turned out to be superimposable with similar bonding categories proposed for alginate and low-methoxyl pectin (LMP), on the one side, and for the association of semiflexible polyelectrolytes, on the other. The analysis allowed us to obtain standard Gibbs free energy, enthalpy, entropy, and volume molar values both for the affinity and the chemical bonding processes. Interestingly, the analysis of the dependence of the gelation temperatures, T g , of LMP upon increasing additions of calcium ions provided the values of T g and standard Gibbs free-energy of calcium-to-pectate association coinciding with those obtained from calorimetry for the type-2 bonding process. This finding corroborated previously reported evidence on the enthalpic nature of the elasticity of Ca 2+ -pectate gels. Finally, comparative analysis of different techniques, but of CD in particular, enabled proposing a "loose-2 1 -helix" as the starting conformation of sodium pectate in aqueous solution.

Chitosan and its highly hydrophilic 1-deoxy-lactit-1-yl derivative (Chitlac) are polysaccharides with increasing biomedical applications. Aimed to unravel their conformational properties we have performed a series of molecular dynamics simulations of Chitosan/Chitlac decamers, exploring different degrees of substitution (DS) of lactitol side chains. At low DS, two conformational regions with different populations are visited, while for DS ≥ 20% the oligomers remain mostly linear and only one main region of the glycosidic angles is sampled. These conformers are (locally) characterized by extended helical "propensities". Helical conformations 3 2 and 2 1, by far the most abundant, only develop in the main region. The accessible conformational space is clearly enlarged at high ionic strength, evidencing also a new region accessible to the glycosidic angles, with short and frequent interchange between regions. Simulations of neutral decamers share these features, pointing to a central role of electrostatic repulsion between charged moieties. These interactions seem to determine the conformational behavior of the chitosan backbone, with no evident influence of H-bond interactions. Finally, it is also shown that increasing temperature only slightly enlarges the available conformational space, but certainly without signs of a temperature-induced conformational transition., (© 2018 Wiley Periodicals, Inc.)

Chitlac is a biocompatible modified polysaccharide composed of a chitosan backbone to which lactitol moieties have been chemically inserted via a reductive N-alkylation reaction with lactose. The physical-chemical and biological properties of Chitlac that have been already reported in the literature suggest a high accessibility of terminal galactose in the lactitol side chain. This finding may account for its biocompatibility which makes it extremely interesting for the production of biomaterials. The average structure and the dynamics of the side chains of Chitlac have been studied by means of NMR (nuclear Overhauser effect and nuclear relaxation) and molecular dynamics to ascertain this hypothesis. A complete assignment of the (1)H and (13)C NMR signals of the modified polysaccharide has been accomplished together with the determination of the apparent pKa values of the primary and secondary amines (6.69 and 5.87, respectively). NMR and MD indicated a high mobility of Chitlac side chains with comparable average internuclear distances between the two techniques. It was found that the highly flexible lactitol side chain in Chitlac can adopt two distinct conformations differing in the orientation with respect to the polysaccharide chain: a folded conformation, with the galactose ring parallel to the main chain, and an extended conformation, where the lactitol points away from the chitosan backbone. In both cases, the side chain resulted to be highly hydrated and fully immersed in the solvent.

A model, developed within the framework of the counterion condensation theory of linear polyelectrolytes, is presented in this paper to describe the acid-base properties of linear polyelectrolytes, consisting of several types of functional ionizable groups. This formalism has been successfully applied to Fluka humic acid under salt-free conditions, as well as in the presence of supporting simple 1:1 salt (KNO3) at three different concentrations. As part of this approach, the charge density of the humic acid is obtained from the activity coefficient measurements of potassium counterions at different humic acid concentrations at a constant degree of dissociation of the polyelectrolyte. The humic acid average charge density was found to be 0.80 +/- 0.05. Using the present model, we are able to satisfactorily describe the experimental data obtained from acid-base potentiometric titrations. Four main functional groups making up the polymer are determined through their fractional abundances (Xi) and intrinsic pK (pK0i) values. The fractional abundances remained constant and independent of the ionic strength, indicating that the humic acid constitution does not depend on the concentration of excess salts. The pK0i values show a small change with ionic strength, which can be explained by the polyelectrolytic behavior of the solution.

A formal development of the Counterion Condensation theory (CC) of linear polyelectrolytes has been performed to include specific (chemical) affinity of condensed counterions, for polyelectrolyte charge density values larger than the critical value of condensation. It has been conventionally assumed that each condensed counterion exhibits an affinity free-energy difference for the polymer, (DeltaG(aff)). Moreover, the model assumes that the enthalpic and entropic contributions to DeltaG(aff), i.e., DeltaH(aff) and DeltaS(aff), are both independent of temperature, ionic strength and polymer concentration. Equations have been derived relative to the case of the thermally induced, ionic strength dependent, conformational transition of a biopolyelectrolyte between two conformations for which chemical affinity is supposed to take place. The experimental data of the intramolecular conformational transition of the ionic polysaccharide kappa-carrageenan in dimethylsulfoxide (DMSO) have been successfully compared with the theoretical predictions. This novel approach provides the enthalpic and entropic affinity values for both conformations, together with the corresponding thermodynamic functions of nonpolyelectrolytic origin pertaining to the biopolymer backbone change per se, i.e., DeltaH(n.pol) and DeltaS(n.pol), according to a treatment previously shown to be successful for lower values of the biopolyelectrolyte linear charge density. The ratio of DeltaH(n.pol) to DeltaS(n.pol) was found to be remarkably constant independent of the value of the dielectric constant of the solvent, from formamide to water to DMSO, pointing to the identity of the underlying conformational process., (Copyright 1999 John Wiley & Sons, Inc.)

Voltammetric speciation data for the potassium/zinc/polymethacrylate system, recently obtained for various charge densities of the polyelectrolyte (Díaz-Cruz et al., Anal. Chim. Acta, 264 (1992) 163) and for different concentrations of monovalent counterions (van den Hoop and van Leeuwen, Anal. Chim. Acta, 273 (1993) 275), are compared with theoretical predictions computed according to a new thermodynamic model developed by Paoletti et al. (Biophys. Chem., 41 (1991) 73) and recently extended by Benegas and Paoletti (in preparation). The model allows: (i) the simultaneous condensation of both monovalent and divalent counterions and (ii) can account for a certain specific affinity of the polyelectrolyte for one type of the counterion over the other. For various charge densities of the polyelectrolyte, experimentally obtained speciation data for the K/Zn/PMA system agree well with theoretical predictions by considering an extra reduced molar affinity energy of -4RT for the Zn(2+) polyelectrolyte binding. The agreement between experimental and theoretical values for the distribution of Zn(2+) ions over the free and bound state becomes less perfect for relatively high concentrations of monovalent counterions.

The competitive binding of monovalent and divalent counterions (M+ and M2+, respectively) has been studied by a conductometric procedure as described by De Jong et al. (Biophysical Chemistry 27 (1987) 173) for aqueous solutions of alkali metal polymethacrylates in the presence of Ca (NO3)2 or Mg(NO3)2. The experimentally obtained fractions of conductometrically free counterions are compared with theoretical values computed according to a new thermodynamic model recently developed by Paoletti et al. (Biophysical Chemistry, 41 (1991) 73). For the systems studied, the fractions of free monovalent and divalent counterions can be fairly well described by the theory. In fact, the results support the assumption that under the present conditions the conductometrically obtained distribution parameters (l) and (2) approximate the equilibrium fractions of free monovalent and divalent counterions. For a degree of neutralization of 0.8 and a molar concentration ratio of divalent counterions and charged groups on the polyion up to 0.25, the mean M+/M2+, exchange ratio nu has been found to be 1.39 +/- 0.03 and 1.33 +/- 0.03 for the alkali metal/Ca/PMA and alkali metal/Mg/PMA systems, respectively. These values agree well with the theoretical value, which for this particular case is 1.38.

An extension of the counterion-condensation (CC) theory of linear polyelectrolytes has been developed for the case of a system containing a mixture of counterions of different valency, i and j. The main assumption in the derivation of the model is that the relative amount of the condensed counterions of the type i and j is strongly correlated and it is determined by the overall physical bounds of the system. The results predicted by the model are consistent, in the limiting cases of single species component, with those of the original CC theory. The most striking results are obtained for the cases of low charge density and excess of counterion species: in particular, an apparent positive "binding" cooperativity of divalent ions is revealed for small, increasing additions of M2+ ions to a solution containing a swamping amount of monovalent salt and a polyelectrolyte of low charge density. Apparent "competitive binding" of mono- and divalent ions derives as a bare consequence of the electrostatic interactions. Theoretical calculations of experimentally accessible quantities, namely single-(counter) ion activity coefficients, confirm the surprising predictions at low charge density, which qualitatively agree with the measured quantities.

An analysis is given of the theoretical approach to the quantitative description of proton dissociation curves for weak polyacids. The basic model of the counterion condensation theory has been used, with the modification reported in the preceding study (S. Paoletti, A. Cesàro, C. Arce Samper and J.C. Benegas, Biophys. Chem. 34 (1989) 301). In this paper we demonstrate the effect of relaxing the hypothesis of a rigid conformation on the polyelectrolytic properties of weak polyacids. As an application of the present approach, a description is given of the titration curves for two weak polyacids, poly(DL-glutamic acid) (PDLGA) and poly(L-aspartic acid) (PLAA).

The cooperative conformational transition of poly(L-glutamic acid) induced by pH is monitored by the titration curves from literature. The polyelectrolytic approach described in the preceding article (A. Cesàro, S. Paoletti and J.C. Benegas, Biophys. Chem. 39 (1991) 1) is used to fit the experimental curves under various conditions of ionic strength and temperature, with the sole assumption that each polymeric state is characterized by a proper conformational flexibility. The helix-coil transition of the system becomes molecularly defined by the balance between the non-ionic conformational energy and the repulsive electrostatic energy of the two forms. Implications of the results of the theoretical model on the energetics of the cooperative order-disorder transition are discussed.

We describe a 41-year-old man with an unusual presentation of tuberculous joint disease involving 3 peripheral joints: right knee, wrist and first metatarsophalangeal. Periarticular "cold" tuberculous abscesses were observed in the ulnar aspect of his right hand and on the lateral aspect of his first right metatarsal bone. Mycobacterium tuberculosis was isolated from his knee and both abscesses. Synovial biopsies taken from these 3 joints showed typical tuberculous granulomata. M. tuberculosis was also isolated from 3 urine samples. Neither immunodeficiency, or a predisposing condition for tuberculosis could be demonstrated. Combined surgical and antibiotic treatment was effective.

The charge-induced conformational transition of poly(alpha-L-glutamic acid) (PLGA) is considered in this paper from the point of view of proton dissociation. Equations for the excess electrostatic Gibbs energy of dissociation (i.e., delta pKa) are derived as a function of the degree of ionization, alpha. These analytical equations are used to describe some experimental dissociation curves at different polymer and salt concentrations. The dependence of the calculated delta pKa with respect to the ionic strength for the two conformational states, alpha-helical and extended coil, respectively, is rather satisfactorily explained. Even more interesting are the predictions which are derived from this approach for the transition point, alpha tr which is found to be ionic-strength dependent, in full agreement with the experimental results.

A statistical model is presented in which an ionic polymer is taken as a linear arrangement of flexible segments (similar to the spring-bead model). This model is used to represent semi-flexible linear ionic polysaccharides in solution. The distribution of end-to-end distances is taken from Monte Carlo calculations of the amylosic chain conformation and combined with Manning's counterion condensation theory of linear polyelectrolytes. The excess thermodynamic properties are then calculated as a function of the degree of ionization and of a number of physical variables. The results show that the statistical average of thermodynamic functions taken over the conformational states is not equivalent to the thermodynamic function of the average conformation. This has important implications for the correct comparison of theoretical prediction with the experimental results.