Infrared Spectroscopic Study of the Solvation of Tetramethylurea in Protic + Aprotic Mixed Solvents

The infrared spectra of tetramethylurea have been measured in mixtures of dimethylsulfoxide or acetonitrile with D₂O or deuterated methanol (CH₃OD). Marked solvatochroism is observed for bands associated with the C=O and C–N stretches of tetramethylurea, with the former moving to lower wavenumber, and the latter to higher, as the concentration of the protic component is increased. The C=O band shows four distinct absorbances, which are attributed to non-, mono, di-, and trihydrogen bonded tetramethylurea. The relative populations of the different hydrogen bonded species were determined from analyses of the C=O band shapes. It is found that the variations in the populations of the different hydrogen bonded species can be accounted for by a simple mass action treatment.     

Search for hydrophobic association between small aprotic solutes from an application of the nuclear magnetic relaxation method

Proton and deuteron magnetic relaxation rates of the four solutes acetone, acetonitrile, trimethylamine, and tetramethylurea in their aqueous mixtures are reported. For the normal and deuterated organic substances the water was D₂O and H₂O, respectively. The intermolecular relaxation rates were determined. Experimental results for the self-diffusion coefficients of trimethylamine and tetramethylurea in their aqueous mixtures are also reported. From these results and literature data the A parameter, A=(1/T₁)_inter·D₁/c_′1 being a criterion for association, was calculated. We obtained the result that only for the largest solute molecule, i.e. tetramethylurea, A showed the typical concentration dependence indicating solute-solute association. For the other three components self-association is not outside the range of the sensitivity of the present method.     

Strong slowing down of water reorientation in mixtures of water and tetramethylurea

We use mid-infrared pump-probe spectroscopy to study the ultrafast dynamics of HDO molecules in mixtures of tetramethylurea (TMU) and water. The composition of the studied solutions ranges from pure water to an equimolar mixture of water and TMU. We find that the vibrational relaxation of the OD-stretching vibration of HDO proceeds via an intermediate level in which the molecule is more strongly hydrogen bonded than in the ground state. As the TMU concentration is increased, the lifetime of the excited state and of the intermediate increase from 1.8 to 5.2 ps and from 0.7 to 2.2 ps, respectively. The orientational relaxation data indicate that the solutions contain two types of water molecules: bulk-like molecules that have the same reorientation time constant as in the pure liquid (taurot = 2.5 ps) and molecules that are strongly immobilized (taurot > 10 ps). The immobilized water molecules turn out to be involved in the solvation of the methyl groups of the tetramethylurea molecule. The fraction of immobilized water molecules grows with increasing TMU concentration, reaching a limiting value of 60% at very high concentrations.     

Bulk viscosity of low-concentration solutions of tetramethylurea in ethylene glycol over the pressure range 0.1–300 MPa

The bulk viscosity of solutions of tetramethylurea in ethylene glycol over the concentration and pressure ranges 0–10 mol % and 0.1–300 MPa, respectively, was measured on a MicroPVT System setup. The results are interpreted in terms of structural changes in the system and solvophobic effects in solutions of the nonelectrolyte.     

Hydrophobic molecules slow down the hydrogen-bond dynamics of water

We study the spectral and orientational dynamics of HDO molecules in solutions of tertiary-butyl-alcohol (TBA), trimethyl-amine-oxide (TMAO), and tetramethylurea (TMU) in isotopically diluted water (HDO:D(2)O and HDO:H(2)O). The spectral dynamics are studied with femtosecond two-dimensional infrared spectroscopy and the orientational dynamics with femtosecond polarization-resolved vibrational pump-probe spectroscopy. We observe a strong slowing down of the spectral diffusion around the central part of the absorption line that increases with increasing solute concentration. At low concentrations, the fraction of water showing slow spectral dynamics is observed to scale with the number of methyl groups, indicating that this effect is due to slow hydrogen-bond dynamics in the hydration shell of the methyl groups of the solute molecules. The slowing down of the vibrational frequency dynamics is strongly correlated with the slowing down of the orientational mobility of the water molecules. This correlation indicates that these effects have a common origin in the effect of hydrophobic molecular groups on the hydrogen-bond dynamics of water.     

Effect of temperature and ionic strength on volumetric and acoustic properties of solutions of urea alkyl derivatives in aqueous NaCl

The present work was undertaken to study volumetric and acoustic properties for diluted solutions of tetramethylurea in pure water and for urea, n-propylurea, n-butylurea and tetramethylurea in 0.5 or 1 mol · dm⁻³ aqueous solutions of sodium chloride. This paper presents measured values of densities and sound velocities at T = (288.15, 298.15 and 308.15) K. From these data the apparent molar volumes, V_Φ, adiabatic compressibilities, κ_S, and apparent molar adiabatic compressions, K_S,Φ, were obtained. The values of apparent molar volumes for infinite dilution and limited apparent adiabatic compressions were calculated from extrapolation of the concentration dependence. Further, the corresponding transfer data as well as hydration number of urea and its derivatives in the studied systems were estimated. The obtained parameters are discussed in terms of various solute-solvent and solute-cosolute interactions.     

Transport of Acids through Polyether-Sulfone Anion-Exchange Membrane

Diffusion dialysis of sulfuric acid and hydrochloric acid into water with a polyether-sulfone anion-exchange membrane was studied. Transport of sulfuric acid and hydrochloric acid through the membrane has been quantified by diffusion coefficients and mass transfer coefficients. The mass transfer coefficients were investigated as a function of the rotational speed of the stirring rate of both sides of the membrane and with different pH ranges. It was observed that the diffusion dialysis seems to be dependent on the rotational speed of the stirrer; in contrast, the membrane mass transfer coefficients are independent of rotational speed, but they are slightly affected by the initial acid concentration in donor phase. Copyright 2001 Academic Press.     

Proton transport in a binary biomimetic solution revealed by molecular dynamics simulation

We report the simulation results of the proton transport in a binary mixture of amphiphilic tetramethylurea (TMU) molecules and water. We identify different mechanisms that either facilitate or retard the proton transport. The efficiency of these mechanisms depends on the TMU concentration. The overall picture is more complicated than a recent suggestion that the presence of amphiphilic molecules suppresses the proton mobility by slowing down the reorientation of the surrounding water molecules. It has also been suggested that the hydronium ion induces local water orientational order, which results in an ordered region that has to move along with the proton potentially slowing down the proton transport as suggested by experiment. We find that water-wire like structures formed at low amphiphile concentrations facilitate proton transfer, and reduction of the hydrogen bond connectivity induced at high concentrations retards it.     

Hydrolysis and polycondensation of ethyl silicates. 2. Hydrolysis and polycondensation of ETS40 (ethyl silicate 40)

The effects of catalysts, pH and reaction conditions on the course of the hydrolysis and condensation of ETS40 (ethyl silicate 40), and on the composition of the reaction products were studied with the aid of gas and gel chromatography, potentiometry and gelation tests. Strong acids (HCl, HClO₄, HNO₃, H₂SO₄, p-toluenesulphonic acid), weak acids (Cl₃, CCOOH, ClCH₂COOH, (COOH)₂, CH₃COOH and HCOOH) and bases (LiOH, NH₄,OH) were used as catalysts.

The hydrolysis rate increased with increasing temperature, catalyst concentration, initial water concentration and initial ethyl silicate concentration, whereas it decreased with increasing number of Si atoms in the ethyl silicate molecules. At pH 0–7 the hydrolysis was acid catalysed, but at pH above 7.0 it was base catalysed. Simultaneously with the hydrolysis, condensation occurred at a rate which increased with increasing temperature, catalyst concentration, ETS40 concentration and, above all, with increasing initial water concentration. The condensation rate depended on the pH. The condensation was at its slowest for pH around 2.0. For pH below 2.0, the condensation increased with increasing hydrogen ion concentration; for pH above 2.0 the condensation increased with decreasing hydrogen ion concentration. Phosphoric acid and hydrofluoric acid increased the rate of condensation considerably. The reaction of ETS40 with water at pH around 2.0 gave rise during the hydrolysis to solutions of ethoxyhydroxysiloxanes with an average of 14–20 Si atoms in a molecule, which displayed long-term stability.     

THE AUTOXIDATION OF TETRAKIS-(DIMETHYLAMINO)-ETHYLENE

Abstract— The reaction of tetrakis-(dimethylamino)-ethylene (I) with oxygen in non-hydroxylic solvents gives tetramethylurea (II), tetramethyloxamide (III), tetramethyl-hydrazine (IV), and bis-(dimethylamino)-methane (V) in yields that are virtually independent of solvent and temperature, or whether chemiluminescence occurs. Autoxidation over water solutions, however, first gives octamethyloxamidinium peroxide (VI) which then hydrolyzes to give III and dimethylamine, and undergoes an alternative demethylation reaction to give tetramethyl 2-(dimethylamino)-2-hydroxy-2-(methylamino)-acetamidinium (VIII) and formate (IX) salts. Both courses of autoxidation are observed in solutions containing lithium chloride, in methanol or in water-dioxane mixtures. A common intermediate is suggested.     

硼对鸡生长的影响

以硼酸的形式在鸡的饮水中添加不同质量浓度的硼，添加量(ρ)分别为0、100、200、400mg/L，比较其增重、成活率和料肉比，观察对鸡生长的影响。结果表明，饮水硼含量(ρ)在100mg/L时，有提高雏鸡成活率和饲料转化率的作用；而当饮水硼含量(ρ)大于或等于200mg/L时，对雏鸡的生长有不利的影响。     

Effect of ureas on the viscometric behavior of water-soluble isotactic poly(2-hydroxyethyl methacrylate)

Isotactic poly(2-hydroxyethyl methacrylate) (PHEMA) is soluble and has the compact random coil structure in water solution. The effect of six ureas (thiourea, urea, methylurea, ethylurea, 1,3-dimethylurea, and tetramethylurea) on the viscometric behavior of aqueous solutions of isotactic PHEMA as a function of urea concentrations at 25°C has been investigated. The compact random coil structure is found to disappear as ureas are added. The result is discussed in terms of water structure breaking and making effect of solutes, and hydrophobic interactions. In addition, experiments were performed with aqueous isotactic PHEMA solutions at four different temperatures. Isotactic PHEMA in pure water has the most compact conformation at 20°C.     

Metal counterion transport in donnan dialysis

A series of crosslinked cation-exchange membranes having graded levels of ion-exchange capacity were prepared by irradiation-induced grafting on polyethylene substrates. A kinetic model was proposed for the transport of metal counterions across the membrane in Donnan dialysis. The transport was found to be adequately described by an equation in which the rate is proportional to the metal concentration. Sulfonated styrene-grafted membranes were more effective than acrylic acid-grafted membranes in Donnan dialysis separation applications. The metal transport rate increased with increasing ion-exchange capacity of the membrane. The metal removal rates were essentially the same with sodium sulfate, sodium chloride, or sulfuric acid as the strip agent; however, the use of chelating trisodium ethylenediaminetetraacetate brought about higher rates of metal removal. The rate of metal transport across a membrane of low ion-exchange capacity and gel water content decreased with increasing size and valence of the metal cation. However, negligible effect was observed concerning the size and valence of a metal cation on the metal's transport across a membrane of high ion-exchange capacity and gel water content.     

A kinetic study of the electron-transfer in the reaction of tribenzylchlorotin with[CoW_(12)O_(40)]~(5-)

A kinetic study of the electron-transfer in the reaction of tribenzylchlorotin with potassium 12-tungsto cobalt(Ⅲ) ate ion, K_5[CoW_(12)O_(40)],abbreviated as Co(Ⅲ)W,has been performed in different solvents.The studies were carried out in methanol, ethanol,acetonitrile and acetic acid/water.The rate constants,reaction rates and activation parameters were calculated. Our findings show that the rate of disappearance of the Co(Ⅲ) is pseudo-first order.The kinetic data is strongly affected by used solvents.T...     

Synthesis and properties of novel dialkylaminocarbenium salts

Novel dialkylaminocarbenium salts with metallocomplex counter ions were prepared by the reaction of phosgene with either DMF or tetramethylurea in the presence of metal chlorides. Reactions of organosilicon amides with phosgene gave corresponding carbenium salts, while organosilicon ureas yielded aminoiminocarbenium salts. Dialkylaminochlorocarbenium salts were reduced with hydrosilanes to give dialkylaminocarbenium, salts and can be easily hydrolyzed to afford either amides or ureas. Pathways of the reaction with water and alcohols depend on the nature of reagent and the reaction conditions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1035–1040, May 1997.     

Hydrolysis of Cellobiose in Dilute Sulpuric Acid and Under Hydrothermal Conditions

The sulfuric acid hydrolysis rate of cellobiose between pH 2 and 3 is directly proportional to the acid concentration. In good agreement with other authors, an activation energy of 133 kJ/Mol was found under these acidic conditions. The relation of the reaction rate constants for the glucose formation and glucose degradation (k₁/k₂) shows, in contrast to the hydrolysis of cellulose, little dependence on the temperature. Hydroxymethylfurfural, and to a lesser extent furfural, are glucose degradation products, which are also consumed but at a lower reaction rate than glucose. At pH values between 3 and 4.7 (pure water) strong deviations of the hydrolysis rates were observed. The formation of organic acids decreases the pH but has no influence on the reaction rate. This fact indicates that hydrothermolysis follows a reaction mechanism different from that of acidic hydrolysis.     

Radiation preparation of PVA-g-NIPAAm in a homogeneous system and its application in controlled release

Thermosensitive PVA-g-NIPAAm copolymers were prepared by graft copolymerization of N-isopropylacrylamide (NIPAAm) onto poly (vinyl alcohol) (PVA) in homogeneous system of dimethyl sulfoxide (DMSO) by ⁶⁰Co-γ irradiation at room temperature. The factors of affecting the grafting yield, such as radiation dose, dose rate, acid concentration, were investigated. It was found that the grafting yield was increased with dose up to 30 kGy, but decreased slightly with dose rate from 61.2 to 50.1 Gy/min. The acid concentration also had influence on the grafting yield. Then the hydrogel of PVA-g-NIPAAm copolymer was made through a freezing–thawing process. The PVA-g-NIPAAm hydrogel exhibited obvious thermal sensitivity, which was observed from the differences of swelling behavior in water at different temperatures (below or above LCST). In addition, the release of Methylene Blue (MB) from this kind of hydrogel was studied. The release rate of MB from PVA-g-NIPAAm copolymer hydrogel at 48°C was faster than that at 15°C due to the shrinkage of the hydrogel at 48°C.     

Empirical investigation of precipitation of hexadecanoic acid from toluene/brine system: Implication to naphthenic acid precipitation from crude oils

Naphthenic acids, due to their tendency to precipitate out of solution when in contact with formation water, present a formidable challenge for the petroleum industry. In this study, precipitation of hexadecanoic acid from an idealized oil-water (toluene/brine) system was investigated. The FTIR results revealed that the acid was mainly precipitated as calcium hexadecanoate. Experiments designed to study the effect of water cut, acid concentration, brine concentration, and pH of the brine on the amount of the precipitate formed revealed that the amount of precipitate formed increased with increase in brine pH, concentration of the acid and calcium ions. Similar effect was observed with respect to water cut but with maximum amount of the precipitate formed at water cut of about 40%, below and above which relatively lower amount of the acid was precipitated irrespective of the levels of the other factors. In general, the observed effects of the factors suggest that precipitation of the naphthenic acid can be minimized with acidic formation water that contains relatively low concentration of calcium ions particularly when the concentration of the acid in the oil is as low as possible.     

The burden borne by urease

At the active site of urease, urea undergoes nucleophilic attack by water, whereas urea decomposes in solution by elimination of ammonia so that its rate of spontaneous hydrolysis is unknown. Quantum mechanical simulations have been interpreted as indicating that urea hydrolysis is extremely slow, compared with other biological reactions proceeding spontaneously, and that urease surpasses all other enzymes in its power to enhance the rate of a reaction. We tested that possibility experimentally by examining the hydrolysis of 1,1,3,3-tetramethylurea, from which elimination cannot occur. In neutral solution at 25 degrees C, the rate constant for the uncatalyzed hydrolysis of tetramethylurea is 4.2 x 10-12 s-1, which does not differ greatly from the rate constants observed for the uncatalyzed hydrolysis of acetamide (5.1 x 10-11 s-1) or N,N-dimethylacetamide (1.8 x 10-11 s-1) under the same conditions. We estimate that the proficiency of urease as a catalyst, (kcat/Km)/knon, is 8 x 1017 M-1, slightly higher than the values for other metalloenzymes (carboxypeptidase b and cytidine deaminase) that catalyze the hydrolysis of similar bonds.     

Interaction of Sulfur Dioxide with Aqueous Solutions of Amides

The interactions in the systems H₂O-Am-SO₂ (Am is formamide, dimethylformamide, acetamide, urea, tetramethylurea, tert-butylurea) at 278 and 293 K were studied pH-metrically. The results suggest formation of intermolecular and ion-molecule associates. The composition and stability of the compounds formed strongly depend on the structure and concentration of the solution components and on temperature.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 5, 2005, pp. 771–777.Original Russian Text Copyright © 2005 by Khoma, Gavrilenko, Nikitin.