Osmometric Method Research Articles

Development of a human milk concentrate with human milk lyophilizate for feeding very low birth weight preterm infants: A preclinical experimental study.

Breast milk is considered the gold standard nutritional resource for very low birth weight (VLBW) infants in terms of nutrients and protective factors. If mother's milk is not available, the second choice is donated and fortified human milk (HM) from the Human Milk Bank (HMB). This study hypothesized that HM could be lyophilized and used as an additive to increase the levels of macronutrients and micronutrients available to VLBW infants. This study aimed to constitute a lyophilized HM concentrate and determine the osmolality and the concentration of macronutrients and micronutrients in HM samples at “baseline” and in “HM concentrates”, analyzed immediately (HMCI), and after 3 (HMC3m) and 6 (HMC6m) months of freezing. Osmolality was verified using the freezing point osmometric method. Macronutrient quantification was performed using the MIRIS Human Milk Analyzer. Micronutrients were determined by Flame Atomic Absorption Spectrophotometry and by the automated colorimetric method. Bayesian linear mixed effect models were adjusted using OpenBUGS to estimate mean differences and 95% credibility intervals (CrI) of osmolality and of macro- and micronutrients between the types of HM samples. A comparison of dosage values showed a significant increase between HM baseline and HMCI, HMC3m, and HMC6m. Comparing HM baseline and HMCI highlighted the increase in energy content and the concentration of carbohydrates and total lipids. The Ca and P contents increased and the levels of energy, total lipids, and Cu were reduced in HMC3m compared to HMCI. Ca, Mg, K, Zn, and P increased and the levels of energy, total lipids, and Cu were reduced in HMC6m, compared to HMCI. The present study confirms the possibility of formulation and utilization of the immediate concentrate. Partial stability of HM concentrates generated from freeze-drying of donated milk do not recommend storage.

Apoplastic water fraction and rehydration techniques introduce significant errors in measurements of relative water content and osmotic potential in plant leaves.

Relative water content (RWC) and the osmotic potential (π) of plant leaves are important plant traits that can be used to assess drought tolerance or adaptation of plants. We estimated the magnitude of errors that are introduced by dilution of π from apoplastic water in osmometry methods and the errors that occur during rehydration of leaves for RWC and π in 14 different plant species from trees, grasses and herbs. Our data indicate that rehydration technique and length of rehydration can introduce significant errors in both RWC and π. Leaves from all species were fully turgid after 1-3 h of rehydration and increasing the rehydration time resulted in a significant underprediction of RWC. Standing rehydration via the petiole introduced the least errors while rehydration via floating disks and submerging leaves for rehydration led to a greater underprediction of RWC. The same effect was also observed for π. The π values following standing rehydration could be corrected by applying a dilution factor from apoplastic water dilution using an osmometric method but not by using apoplastic water fraction (AWF) from pressure volume (PV) curves. The apoplastic water dilution error was between 5 and 18%, while the two other rehydration methods introduced much greater errors. We recommend the use of the standing rehydration method because (1) the correct rehydration time can be evaluated by measuring water potential, (2) overhydration effects were smallest, and (3) π can be accurately corrected by using osmometric methods to estimate apoplastic water dilution.

Interactions of the Osmolyte Glycine Betaine with Molecular Surfaces in Water: Thermodynamics, Structural Interpretation, and Prediction of m-Values

Noncovalent self-assembly of biopolymers is driven by molecular interactions between functional groups on complementary biopolymer surfaces, replacing interactions with water. Since individually these interactions are comparable in strength to interactions with water, they have been difficult to quantify. Solutes (osmolytes, denaturants) exert often large effects on these self-assembly interactions, determined in sign and magnitude by how well the solute competes with water to interact with the relevant biopolymer surfaces. Here, an osmometric method and a water-accessible surface area (ASA) analysis are developed to quantify and interpret the interactions of the remarkable osmolyte glycine betaine (GB) with molecular surfaces in water. We find that GB, lacking hydrogen bond donors, is unable to compete with water to interact with anionic and amide oxygens; this explains its effectiveness as an osmolyte in the Escherichia coli cytoplasm. GB competes effectively with water to interact with amide and cationic nitrogens (hydrogen bonding) and especially with aromatic hydrocarbon (cation-pi). The large stabilizing effect of GB on lac repressor-lac operator binding is predicted quantitatively from ASA information and shown to result largely from dehydration of anionic DNA phosphate oxygens in the protein-DNA interface. The incorporation of these results into theoretical and computational analyses will likely improve the ability to accurately model intra- and interprotein interactions. Additionally, these results pave the way for development of solutes as kinetic/mechanistic and thermodynamic probes of conformational changes and formation/disruption of molecular interfaces that occur in the steps of biomolecular self-assembly processes.

Association of model peptides and dehydropeptides: N-acetyl- l-alanine- and dehydroalanine N′, N′-dimethylamides

The comparative studies on the association of Ac-ΔAla-NMe 2 and Ac- l-Ala-NMe 2 in carbon tetrachloride were performed by the analysis of their average molecular weight, dipole moments and FTIR spectra. To aid spectroscopic interpretation and gain some deeper insight into the nature of associates, the geometries of the minimum energy of the dimers of Ac-ΔAla-NMe 2 and Ac- l-Ala-NMe 2 were calculated by the B3LYP/6-31+G** method. The average molecular weight in the studied concentration range, for the ΔAla and l-Ala peptide, as determined by the osmometric method, did not exceed 1.5 and 1.2 of the monomeric mass, respectively. Accordingly, the percentage of the monomeric form (α) decreased as concentration was increased more significantly for the ΔAla analogue than for its saturated counterpart. In the studied concentrations, the dipole moment of the unsaturated compound decreases and that of its counterpart is almost constant. We identified a wider range of dimeric forms of Ac-ΔAla-NMe 2 than those of Ac- l-Ala-NMe 2. While Ac-ΔAla-NMe 2 mainly forms cyclic dimers, built of open conformers H/F, specific for α,β-dehydroamino acids, Ac- l-Ala-NMe 2 forms cyclic and linear dimers, characteristic for the usual amino acids. Ac-ΔAla-NMe 2 has a greater tendency to associate than its saturated variant, which is the result of stronger hydrogen bonds.

Molecular Weight Studies on Hydroxypropyl Methylcellulose I. Osmometry

Osmometry was employed to measure number-average molecular weight Mn of hydroxypropyl methylcellulose (HPMC) using membranes with different permeability for the solute (polymer or electrolyte) and solvent (water) in such a way that no pretreatment of the polymer solution was required to remove electrolyte impurities, thereby eliminating the risk of sample alteration. A novel osmometric method was developed, based on measurements of the kinetics of the pressure over the membrane, which allows the use of membranes permeable even to the polymer. It was shown that such membranes initially, at time t = 0, approaches the physics of a perfectly semipermeable membrane provided that the ratio of the solute/solvent permeability is sufficiently low (i.e., when the molecular weight cut-off, MWCO, of the membrane does not exceed Mn of the polymer). The obtained Mn for a range of viscosity grades of HPMC2910 (3 cP to 10,000 cP) compares favorably with previous estimates, based on analogy with methylcellulose.

Attempts to Study a Water Evaporation Retardation by Soluble Surfactants

The effect of a soluble surfactant adsorption layer on the water evaporation was studied using an osmometric method. It was proved that Knauer's osmometer after appropriate modification of the measuring cell can be successfully used for a qualitative detection of the evaporation retardation. The osmometric behavior of the system was explained taking into account the adsorption properties of the surfactants and the heat effects accompanying the evaporation process. A measurable evaporation hindrance was registered only in case of sodium salts of myristic and palmitic acids at concentrations (close to the solubility limit) at which densely packed adsorption layers are formed. At the same time the latent heat of evaporation may cause a freezing of the higher density adsorption layer which is formed on the supersaturated solution drop.

Beef muscle osmotic pressure as assessed by differential scanning calorimetry (DSC)

SummaryOsmotic pressure, an important physiological characteristic of plant and animal tissues, is difficult to measure, and no convenient and efficient method is so far available. In the present work we developed a differential scanning calorimetry (DSC) method, and estimated the physiological osmotic pressure of intact bovine muscle and post‐mortem variation during the conversion of muscle into meat. We also examined the major role of sample pH in this variation. This method, based on the determination of the melting onset point of frozen muscle's indigenous water, was compared to a freezing point osmometric method and a soaking method. It was concluded that the DSC method appeared more practical and reliable than other methods and could be applied to various animal and plant tissues and fluids.

Osmotic pressure measurements of the ligand-linked dissociation equilibrium of human oxyhemoglobin.

The tetramer/dimer equilibrium of human oxyhemoglobin has been measured by an osmometric method as a function of pH, chloride and 2,3-bisphosphoglycerate concentrations at 21 degrees C. The binding constants of chloride and 2,3-bisphosphoglycerate to the tetramer and the dimer were thus evaluated at various pH values. 2,3-Bisphosphoglycerate is bound to the dimer more strongly than to the tetramer. The dimer has a second binding site for 2,3-bisphosphoglycerate. The data for 2,3-bisphosphoglycerate binding were corroborated by direct binding measurements with the ultrafiltration method.

Metal complexes of polyesters

Polyesters obtained from 2,5-dihydroxyterephthalic acid and 1, n-alkanediols were used to complexate the metal ions Mg 2+, Ca 2+, Sn 2+, Pb 2+, Ga 3+, In 3+, Bi 3+, Si 4+, Ce 3+, UO 2 2+, Mn 2+, Mn 3+, Co 2+, Ni 2+, Cu 2+, Zn 2+ and Cd 2+. The metal ions are always six-coordinated with additional ligands (mostly H 2O) besides the four from the polyester system. The H 2O-ligands can be removed by heating in vacuum, as was proven for the complexes of Mn 2+, Co 2+, Ni 2+ and Cu 2+, and are added again in moist air. For the waterfree Ni 2+-complex a tetrahedral surrounding is suggested by magnetic measurements. Polymerization degrees of the polyesters were found to be 30–70 by the membrane osmometric method. Thermal stabilities of the metal complexes (200– 300 °C) are less than those of the polyesters themselves (300–350 °C).

Investigation of asphaltenes association by a vapour pressure osmometric method

AbstractThe number average molecular weights of asphaltenes have been studied by vapour pressure osmometry using benzene and tetrahydrofuran as solvents at three different temperatures, viz. 37, 45 and 60°C. The degree of association in each solvent at each temperature was determined and is found to be dependent on the nature of solvent and temperature. Results indicated that asphaltenes could be similar to macromolecules structurally.

The Composition of Tungsten(VI) Species Extracted with Trioctylamine from Aqueous Oxalate Solution

トリオクチルアミン(TOA,R3N)によるシュウ酸イオン水溶液からのタングステン(VI)の抽出挙動を検討し,抽出物をゲル浸透クロマトグラフィー(GPC)により分析した。さらに,モル比(C2O42-/WO42-)1.06 と 4.78 における抽出物から, GPC により,それぞれ,TOA のポリタングステン酸(VI)塩 2 種類と TOA のオキサラトタングステン酸(VI)塩を分取した。単離した化学種の化学分析と元素分析の結果から,それぞれの組成式を(R3NH)2W5O16,(R3NH)HW3O10。および(R3NH)2WO2(C2O4)2 と推定した。これらの組成式はIRスペクトル,熱分析の結果とも一致した。また,TOAのオキサラトタングステン酸(W)塩のR3NH+:オキサラトタングステン酸(VI)イオンの比を検討した結果,その値は2:1となった。GPCによる分子量の測定結果は,それぞれの化学種の式量とほぼ一致した。また,蒸気圧浸透法による(R3NH)2W5O16,(R3NH)2WO2(C2O4)2に対する分子量は,それぞれ,1.85×103 および 1.10×103 となり,それぞれの式量と非常によく一致した。しかしながら,(R,NH)HW3O10 に対する値は,10×103 となり,その二量体の式量と一致した。分子量測定の結果は,TOA のポリタングステン酸(VI)塩がベンゼンおよびクロロホルム中で二量体,三量体などの会合体を形成しやすいことを示した。

An osmometric method for measurement of total CO2

We describe a rapid and accurate osmometric method for the measurement of total CO 2 1 which is considerably simpler than techniques previously and currently used [1–7].

Copper(I) and copper(III) diselenocarbamates

(Received 13 J ~ e 1~2) It is known that the reaction of thiuram disulfide with excess of copper powder yields the copper(I)dithiocarbamate tetramer, [Cu(S2CNEt2)]4(I ). Due to the non-existence of the analogous selenuram diselenide (2) the reaction of copper with a mixture of selenuram monoand triselenide, (Et2NCSe)2Se and (Et2NCSe)2Se], was carried out. In this way copper(I) N,Ndiethyldiselenocarbamate, Cu(Se2CNEt2) , was obtained as a diamagnetic yellow complex, stable in dry air. The preparation however, has to be carried out in an inert atmosphere, for this copper(I) complex is easily oxidized. When the yellow solution of copper(I) diselenocarbamate in dichloromethane is exposed to air, this darkens rapidly and in the ultra-violet absorption spectrum band maxima appearwhich can be ascribed to the copper(II) bis(N,N-diethyldiselenocarbamate). A molecular weight determination (osmometric method: found 307, calc~. 306) revealed Cu(Se2CNEt2) to be monomeric in benzene solutions, which is in contrast with the reported (I) polymeric character of the analogous sulfur compounds [Cu(S2CNR2)] n (n = 2.9-4.6, in various solvents).

Determination of the molecular weight of polymethacrylate

1. The relation was established between the characteristic viscosity of polymethacrylate (in benzene at 27°C) and the average molecular weight, determined by the osmometric method [η]=2.95·10−3·¯M n 0.52 The formula was found for the polymethacrylates with hydrocarbon radicals R from C7 to C12 and with average molecular weights from 3 · 103 to 3 · 104. 2. The molecular weight distribution was determined for two samples of a viscosity additive-polymethacrylate.

Osmometric study of the degradation of fluorine-containing polymers

IN STUDIES of the influence of various chemical, physicochemica], and mechanical processes on the properties of polymers, it is frequently necessary to obtain information on the degradation of the polymer and the change in its polydispersity. The most widely used method [1] of determining the change in the molecular weight and polydispersity of a polymer due to degradation is the measurement of its intrinsic viscosity in dilute solutions. This method, however, only permits an estimation of the over-all change in the molecular weight of the polymer and does not enable the amount of low-molecular-weight fraction (molecular weights from 25,000 to 20,000) in the polymer formed by degradation to be determined or to be separated from the bulk of the polymer. These problems can be solved by using the osmometric method, which is widely employed at the present time to determine the molecular weights of polymers. In determining the molecular weight of a polymer having a high degree of polydispersity, the low-molecularweight fraction of the polymer may pass through the membrane; of course, this fact is reflected in the value of the number-average molecular weight and is negative. However, the diffusion of the low-molecular-weight fraction through the membrane may be used to obtain information on the increase in the content of low-molecular-weight fractions as a result of various influences on the polymer. We have used this circumstance in an investigation of the thermal-oxidative degradation of the fluorine-containing polymer Ftorlon.

On the rate of water exchange across the surface of animal cells

The two methods for determination of water permeability, the osmometric method, and the isotope exchange method are discussed, particularly with respect to the sources of error. In the latter method the exchange across the surface barrier is generally so fast that correction for the diffusion in the cytoplasm is required. The presence of cortical layers of considerable mechanical strength may often invalidate results obtained with the former method. In agreement with views advanced previously in the literature, it is concluded that the permeability coefficients obtained by the two different methods only under very special conditions are identical. However, the ratio cannot be expected to deviate much from unity, and it is shown that the large ratios reported in some cases do not represent the ratio between two permeability coefficients.

Capillary pressure and distribution of vascular resistance in isolated lung.

Isolated lobes of dogs' lungs were perfused with constant nonpulsatile blood flow and expanded by negative external pressure. The pressure under which Ringer solution was absorbed through the visceral pleura was measured by an osmometric method. From this pressure and the plasma colloid osmotic pressure, the pressure in the subpleural capillaries was calculated. The average value of the latter was 8.8 mm Hg when the pulmonary artery and vein pressures were 13.4 and 1.8 mm Hg, respectively. Assuming that the pressure in the intrapulmonary capillaries is similar to that in the subpleural capillaries, the vascular resistance on the arterial and venous side of the effective midpoint of pulmonary capillaries could be calculated. The average vascular resistance on the venous side was found to be 60% of the total intrapulmonary vascular resistance. Notwithstanding the limitations of the method this result suggests that in the pulmonary vascular bed the resistance on the arterial side and that on the venous side of the effective midpoint of capillaries are similar.

A critical study of the direct method of measuring the osmotic pressure of hœmoglobin

A solution of hœmoglobin and salts may be considered as a colloidal system. Since the work of Thomas Graham, it has been recognized that such systems are unstable, for they are liable to undergo gradual changes in their state of aggregation. When the chief colloid is a protein, there may be in addition actual chemical breakdown. When, the chemical instability is associated with the lag normal to the colloidal state the application of the direct osmometric method becomes peculiarly difficult, because, if the experimenter elects to wait for the system to obtain equilibrium he is likely to encounter chemical breakdown, and if he accepts the first approximately steady readings and relies upon extrapolation to give the absolute values, his conclusions can never have the finality which would alone justify the use of so difficult a method. These disadvantages can be partly met by using osmometers designed to reach equilibrium rapidly (see Section 4), but they can be wholly overcome only by discovering conditions which ensure chemical stability. Of these the most important is a low temperature, and therefore all the critical measurements described in this paper and the papers which follow were made at 0° C.