Tetramethylurea Molecules Research Articles

Molecular Aggregation Behavior and Microscopic Heterogeneity in Binary Osmolyte-Water Solutions.

Osmolytes, small organic compounds, play a key role in modulating the protein stability in aqueous solutions, but the operating mechanism of the osmolyte remains inconclusive. Here, we attempt to clarify the mode of osmolyte action by quantitatively estimating the microheterogeneity of osmolyte-water mixtures with the aid of molecular dynamics simulation, graph theoretical analysis, and spatial distribution measurement in the four osmolyte solutions of trimethylamine-N-oxide (TMAO), tetramethylurea (TMU), dimethyl sulfoxide, and urea. TMAO, acting as a protecting osmolyte, tends to remain isolated with no formation of osmolyte aggregates while preferentially interacting with water, but there is a strong aggregation propensity in the denaturant TMU solution, characterized by favored hydrophobic interactions between TMU molecules. Taken together, the mechanism of osmolyte action on protein stability is proposed as a comprehensive one that encompasses the direct interactions between osmolytes and proteins and indirect interactions through the regulation of water properties in the osmolyte-water mixtures.

Thermodynamics of TMU-TMU interaction in water, ethylene glycol and formamide – From pair solvophobic interaction to cluster formation

This paper focuses on the interaction between tetramethylurea (TMU) molecules in liquid water, ethylene glycol (Eg) and formamide (FA) which form the H-bond network on a supramolecular level. The virial enthalpic, heat capacity, entropic and free energy parameters of solute–solute interaction have been extracted from the experimental thermodynamic data in a wide temperature range. The second virial coefficients of the TMU-TMU pair interaction and their temperature changes have been computed both in aqueous and non-aqueous systems. Our comparative analysis indicates that the strong solvophobic interaction between two TMU molecules does exist and increases with the temperature, the effect being much stronger pronounced in aqueous solutions. This strong attraction between methyl groups of TMU leads to formation of labile clusters containing both solute and solvent molecules.

Comparative Characteristics of the Enthalpy Parameters of Interaction between Urea and Tetramethylurea Molecules in Formamide, Ethylene Glycol, and Water at 298.15 K

Comparative Characteristics of the Enthalpy Parameters of Interaction between Urea and Tetramethylurea Molecules in Formamide, Ethylene Glycol, and Water at 298.15 K

Thermodynamics of tetramethylurea solutions in ethylene glycol: The evidence of pairwise solvophobic interaction

This paper focuses on the solute – solute interactions in dilute solutions of a typically hydrophobic solute tetramethylurea (TMU) in ethylene glycol (EG) which forms the three-dimensional hydrogen-bond network at the supramolecular level. The results of our experimental efforts based on dilution calorimetry and phase partition techniques are able to make a conclusion that thermodynamics of the TMU – TMU pairwise interaction in EG is to a great extent similar to that occurs in liquid water. All effects, however, are weaker expressed in the non-aqueous medium. In particular, the integrand of the potential of mean force, i.e. the second virial coefficient, between two TMU molecules becomes negative only at elevated temperatures indicating the appearance of a rather weak solvophobic interaction in EG. Since C=O-groups of TMU are well-incorporated into the H-bond network of EG, it is reasonable to assume that the attraction observed should be mainly induced by apolar methyl groups. The correlation between the enthalpy- and volume-related parameters of pairwise interaction provides the additional confirmation of the existence of the solvent-induced solvophobic interaction between TMU molecules in EG.

Are N-methyl groups of Tetramethylurea (TMU) Hydrophobic? A composition and temperature-dependent fluorescence spectroscopic investigation of TMU/water binary mixtures

This paper reports results from temperature and composition dependent steady state UV-Visible absorption and fluorescence measurements and time-resolved fluorescence experiments, using a dipolar probe coumarin 153 (C153), in TMU/water binary mixtures. Both steady state and time-resolved spectroscopic data indicate, much like in water/alcohol mixtures, TMU-induced structural stiffening and transition of the tetrahedral H-bond network of water. The structural transition referred to above means cosolvent-induced transition of three dimensional tetrahedral H-bond network to two dimensional zig-zag chain-like structure often found in alcohols. A comparison to the results obtained for aqueous alcohol solutions suggests that the cosolvent concentration at which the structural transition occurs depends both on the polarity of the cosolvent and the size of the cosolvent molecules. UV-Visible absorption measurements reveal aggregation among TMU molecules at lower TMU concentration which shows a temperature maximum. In addition, red edge excitation effects have been observed at very dilute TMU concentration suggesting distribution of C153 among heterogeneous environments. All these results indicate hydrophobic interaction-induced aggregation of TMU in dilute aqueous solutions which corroborate well with the existing simulation observation. Temperature dependence of absorption spectral red-shift of dipolar probe coumarin 153 in TMU/Water binary mixtures has been shown here. The redshift grows up with increase of temperature from 278K and it reaches maximum at 293K.

Structure of associates in tetramethylurea aqueous solutions from the data of Raman scattering spectroscopy

The results from investigating interactions between tetramethylurea (TMU) and water molecules by means of Raman light scattering spectroscopy (RS) are presented. It is established that spectroscopic manifestations of association of TMU and H2O molecules are observed for the TMU molecule valence vibration band ν(CO) 1638 cm−1. By means of quantum-chemical calculations, it is shown that the band sensitivity to molecular environment is defined by the number of 5–6 H2O molecules. It is found that in a pure TMU medium, chain dimers are formed due to the interactions of molecular dipoles arranged in parallel and hydrogen bonds of the C-H…O type. Ground state geometries of TMU, TMU-TMU, H2O molecules and TMU · (H2O)n complexes (n = 1−14) are optimized by the density functional B3LYP procedure, using the 6–31++G(d, p) basis set. The main vibration frequencies are calculated in the harmonic approximation. Associate formation energies are calculated with allowance for the basis set superposition error (BSSE).

Hydrophobic Solvation: A 2D IR Spectroscopic Inquest

For decades, the enigma of the hydrophobic force has captured the imagination of scientists. In particular, Frank and Evans' idea that the hydrophobic effect was mainly due to some kind of "iceberg" formation around a hydrophobic solute stimulated many experiments and molecular dynamics simulation studies. A better understanding of hydrophobic interactions will aid understanding in many contexts including protein structural dynamics and functioning in biological systems. In this Account, we present results of two-dimensional infrared (2D IR) spectroscopy experiments on the OH-stretch vibrational mode of water molecules near hydrophobic groups in concentrated solutions with tetramethylurea (TMU). The frequency of the OH vibration is a sensitive probe for environmental dynamics and, in particular, for the strength of the hydrogen bond. Two-dimensional IR spectroscopy can trace time correlations of the vibrational frequency at the scale of hundreds of femtoseconds and thus provides valuable insight into the effect of hydrophobic solutes on the dynamics of a hydrogen-bond network. We compare the 2D spectroscopic results with molecular dynamics (MD) simulations to obtain a microscopic picture of hydrophobic solvation. We observe two different types of hydrogen-bond dynamics in the water/TMU mixtures. We attribute the "fast" ( approximately 100 fs) dynamics to highly coordinated water molecular-jump reorientations and assigned the "slow" (>1 ps) dynamics to water translational motions that are strongly suppressed by the TMU molecules. Molecular dynamics simulations demonstrate a clear correlation between the slowed dynamics and the translational mobility of water. This finding indicates that the molecular-jump reorientations are switched off near hydrophobic groups. The fifth water molecule, which is required to form a defect state in the tetrahedral surroundings, cannot approach the hydrogen-bonded pair to initiate the molecular jump. As a result, the rate of the jumping events sharply decreases, which, in turn, strongly slows the rotation of the water molecules. Our findings suggest that water molecules in the hydrophobic solvation shell do not exhibit an increased tetrahedral ordering compared with the bulk but that the hydrogen-bond dynamics in the two cases are different. This result also indicates that consideration of a hydrogen bond's dynamics could be critical for its definition.

Polysulfonylamine, CLXXXVI [1]. Strukturvielfalt in sechs Cokristallen von Tetramethylharnstoff mit Di(4-X-benzolsulfonyl)aminen (X = F, Cl, Br, I, CH3, NO2) / Polysulfonylamines, CLXXXVI [1]. Structural Diversity in Six Tetramethylurea Di(4-X-benzenesulfonyl) amine Cocrystals (X = F, Cl, Br, I, CH3, NO2)

Abstract Cocrystallization of tetramethylurea (TMU) with one equivalent of either di(4-fluorobenzenesulfo- nyl)amine (FAH), di(4-chlorobenzenesulfonyl)amine (CAH), di(4-bromobenzenesulfonyl)amine (BAH). di(4-iodobenzenesulfonyl)amine (IAH), di(4-methylbenzenesulfonyl)aniine (MAH>, ordi(4- nitrobenzenesulfonyDamine (NAH), using dichloromethane/petroleum ether as the solvent, afforded the molecular complexes (FAH)2 · TMU (1. monoclinic. P21/c,Z' = 1. structure previously reported), CAHTMU, BAH-TMU and IAH-TMU (2-4, isomorphic series, triclinic, P1̅,Z' = 1), MAH · TMU (5, monoclinic. P21, Z' = 1). and the uranium salt TMUH+NA- (6, monoclinic. P21/c,Z' = 2). The structural results obtained by X-ray crystallography at low temperatures indicate that the varying p- substituents of the di(arenesulfonyl)amines exert a decisive influence on (i) the stoichiometry of the cocrystallization reaction (2:1 for 1 vs. 1:1 for 2-6), (ii) the degree of proton transfer between the strongly acidic (SO2)2NH moieties and the basic carbonyl function of TMU (molecular complexes assembled via N-H···O=C hydrogen bonds in 1 -5 vs. two independent ion pairs based upon charge- assisted C-O-H+ ···N- interactions in 6). and (Hi) the conformation of the disulfonylamineZ-amide units as defined by rotations about the S-N bonds (extended forms displaying anticlinal C-S ··· S'- C' torsions for the two molecules in 1 and the two anions in 6 vs. folded forms featuring synperi- planar C-S ···S'-C torsions for the molecules in 2-5). The packing modes of 1-4 underline the well-known correlation between the atomic number of halogen atoms and their propensity to form halogen bonds. Thus, the structure of 1 is devoid of short F···O contacts, whereas the isomorphic co- crystals 2-4 consist of lamellar layers in which the inner lamellae include the TMU molecules and the peripheral regions are built up from CAH, BAH or IAH molecules associated into catemers via C-Hal ··· O=S bonds. The lamellar layers of the non-isomorphic methyl congener 5. although topological^' similar to those of 2-4, are stacked according to a herringbone pattern that does not arise in the structures of 2-4. The most prominent packing feature of the uranium salt 6 are intimate dimers of two independent NA- ions, stabilized by dipolar nitro-nitro interactions and C-H ··· O=S contacts and further connected into monolayers through C-H ··· Onitro contacts. The uranium ions are inserted between these layers and bonded to the anion dimers by the strong hydrogen bonds mentioned above and numerous C-H ··· Onitro contacts. The presence of two independent formula units appears to arise from frustration between several competing interactions, e. g. dipolar nitro attractions, weak hydrogen bonding to sulfonyl and nitro acceptors and π/π stacking of aromatic rings.

Crystal structure of an yttrium nitrate complex with tetramethylurea

An X-ray diffraction study of Y(NO3)3 · 3TMU crystals is performed (heavy-atom method, difference electron-density maps, H atoms in calculated positions, full-matrix anisotropic-isotropic (H) least-squares refinement). The crystals are monoclinic, a = 9.353(1) A, b = 15.966(3) A, c = 18.805(8) A, β = 95.41(2)°, Z = 4, and space group P21/c. The structural units of the crystals are molecular complexes. The coordination number of the Y atom is nine due to three bidentate NO3 groups and three monodentate tetramethylurea molecules. The mean Y-O bond lengths are 2.464 and 2.274 A for NO3 and tetramethylurea, respectively.

Urea and methylurea dipole-bound anions

We report experimental (Rydberg electron transfer) and theoretical results on dipole-bound anions of urea, deuterated urea, 1,1- and 1,3-dimethylureas and tetramethylurea. For the 1,1-dimethylurea and tetramethylurea molecules, which possess only one low-lying energy conformer, the experimental excess electron energies are found to be in good agreement with neutral structure quantum chemistry calculations and semi-empirical model calculations of the corresponding dipole-bound anions. For 1,3-dimethylurea two low-lying energy conformers (trans–trans and cis–trans) should contribute to the dipole-bound anion formation behaviour but cannot fully account for it. The large-amplitude motion, associated with the anti/syn conformations of urea molecules, has been studied by performing experiments on the deuterated species and by calculating the potential energy surfaces, for both the neutral and the dipole-bound anion, along the corresponding coordinate. Even if this low-frequency mode is very likely to be involved in the anomalous anion formation behaviour, a full understanding of this process could only come from a dynamic theory, beyond the Born–Oppenheimer approximation, of both the electron and the large-amplitude nuclear motions which possess similar characteristic frequencies.

Effect of urea, dimethylurea, and tetramethylurea on the phase behavior of dioleoylphosphatidylethanolamine

The phase behavior of dioleoylphosphatidylethanolamine in aqueous solutions of urea, N, N′-dimethylurea (DMU), and N, N, N′, N′-tetramethylurea (TMU) has been characterized by synchrotron X-ray diffraction and differential scanning calorimetry. All three solutes stabilize the lamellar liquid-crystalline phase at the expense of lamellar-gel phase and inverted hexagonal phase of the phospholipid when present in concentrations up to 3 M. X-ray diffraction data demonstrated that the repeat spacing of DOPE increased with increasing urea concentration, but decreased as the DMU and TMU concentrations increased. The repeat spacing of DOPE in the liquid-crystal phase dispersed in the three solutes is d(urea)> d(DMU)> d(TMU). The molecular mechanisms underlying these observations are discussed in terms of either membrane Hofmeister effect, where urea acts as a water structure breaker, or a direct insertion effect of the amphiphilic DMU and TMU molecules into the lipid head groups in the interfacial region of the phospholipid bilayer.

Structure and dynamics of aqueous solutions of tetramethylurea

Some microscopic properties of a tetramethylurea (TMU) water solution were investigated using neutron scattering methods. It was established that over the concentration range investigated a remarkable attractive contribution arises due to hydrophobic interaction. Orientational perturbation of the solvent around the TMU molecules was observed. All types of diffusional motion are inhibited and their concentration dependence is rather small.

The Adsorption of Tetramethylurea at the Mercury/Water Interface

Abstract The adsorption of tetramethylurea (TMU) at the mercury/water interface was studied by means of differential capacity measurements. TMU was found to take three different orientations, depending on the surface excess and the charge sign of the electrode. These orientations could not be explained simply by the orientation of the TMU dipole in the electric field or by the hydrophobic interaction between the methyl groups of TMU and the electrode, but it was explained on the basis of interactions between TMU and water molecules, and on the basis of the TMU molecules themselves in the adsorption layer and an electronic polarization effect of the nitrogen atoms in TMU. A few water-adsorption models were compared in an attempt to estimate the dipole moment of the TMU molecule at the interface.

Thermochemical Studies on the Lanthanoid Complexes of N,N,N′,N′-Tetramethylurea

Abstract The techniques of thermogravimetry (TG) and differential thermal analysis (DTA) were applied to the study of the thermal decomposition of the lanthanoid (Ln) complexes of N,N,N′,N′-tetramethylurea (TMU), Ln(TMU)6X3 (X=ClO4, PF6, or BPh4). In general, the ease of decomposition increases in the order of BPh4<ClO4<PF6; in the latter two cases, the release (and, in the case of ClO4, partial oxidation) of the coordinated TMU molecules takes place together with the decomposition of the anions, leading finally to the formation of LnCl3 or LnF3, respectively. The data were also discussed on the basis of the effects of the lanthanoid contraction.