Thermal Stability Of Solutions Research Articles

Synthesis, characterization and stability of phosphonium phenolate zwitterions derived from a (diphenylphosphino)phenol derivative and oxiranes

Phosphonium phenolate zwitterions have been synthesized from 2,4-di-tert-butyl-6-(diphenylphosphino)phenol and five different oxirane derivatives. The reaction does not proceed at a detectable rate when the two reactants are combined in dichloromethane at room temperature. Despite the substantial ring strain, the reaction proceeds only with the addition of methanol, which acts as a hydrogen transfer shuttle, allowing a slow conversion to the desired zwitterions. The compounds have been fully characterized and single crystal X-ray crystallography has been performed on the methyloxirane and the phenyl glycidyl ether-derived zwitterion. The phosphonium phenolate units exhibit an ylidic bonding situation as evidenced by spectroscopic and crystallographic analysis. Glycidyl ethers were found to react faster than alkyl and aryloxiranes. Decomposition studies of the zwitterions showed high thermal stability in solution under ambient conditions. Under forced conditions (150 °C, 6 h), decomposition to the corresponding phosphine oxide and secondary aliphatic alcohols, the formally hydrogenated oxirane derivative, was observed.Graphical abstract

Design of complicated all-α protein structures

A wide range of de novo protein structure designs have been achieved, but the complexity of naturally occurring protein structures is still far beyond these designs. Here, to expand the diversity and complexity of de novo designed protein structures, we sought to develop a method for designing ‘difficult-to-describe’ α-helical protein structures composed of irregularly aligned α-helices like globins. Backbone structure libraries consisting of a myriad of α-helical structures with five or six helices were generated by combining 18 helix–loop–helix motifs and canonical α-helices, and five distinct topologies were selected for de novo design. The designs were found to be monomeric with high thermal stability in solution and fold into the target topologies with atomic accuracy. This study demonstrated that complicated α-helical proteins are created using typical building blocks. The method we developed will enable us to explore the universe of protein structures for designing novel functional proteins.

Ruthenium tris(σ-B-H) borate complexes: synthesis, structure, and reactivity.

The coordination of the B-H bond to a transition metal is fundamentally intriguing due to its connection with the transition metal-mediated B-H bond activation mechanism and catalysis. Most of the reported examples are σ-borane/borate complexes containing one or two σ-B-H bonds. However, examples of compounds containing three σ-B-H bonds are still much rarer. Herein, we report a facile approach for the synthesis of rare transition metal tris(σ-B-H) borate complexes by the salt elimination protocol using [Cp*RuCl]4 and lithium trihydroborates Li[ArBH3] containing 2,6-disubstituted aryl groups. These complexes have remarkable thermal stability in solution. In addition, this novel class of compounds has the unusual σ-complex that features three labile σ-B-H bonds. Our studies on these new species demonstrate that the coordination σ-B-H bond can undergo H/D exchange with D2 and ligand substitution reactions with PPh3, PCy3 and IPr2Me2. These results provide new approaches for the synthesis of both tris(σ-B-H) borates and bis(σ-B-H) borates.

Higher stability of metalloid tin clusters obtained via the cation–anion interaction

The reaction of SnCl with the bulky substituents HyptBuMe2 and HypEt3 leads to the formation of two isostructural Sn10-clusters, showing novel coordination polymers in the solid state and high thermal stability in solution.

Deuteration of nonexchangeable protons on proteins affects their thermal stability, side-chain dynamics, and hydrophobicity.

We have investigated the effect of deuteration of non-exchangeable protons on protein global thermal stability, hydrophobicity, and local flexibility using well-known thermostable model systems such as the villin headpiece subdomain (HP36) and the third immunoglobulin G-binding domain of protein G (GB3). Reversed-phase high-performance liquid chromatography (RP-HPLC) measurements as a function of temperature probe global thermal stability in the presence of acetonitrile, while differential scanning calorimetry determines thermal stability in solution. Both indicate small but measurable changes in the order of several degrees. RP-HPLC also permitted quantification of the effect of deuteration of just three core phenylalanine side chains of HP36. NMR dynamics investigation has focused on methyl axes motions using cross-correlated relaxation measurements. The analysis of order parameters provided a complex picture indicating that deuteration generally increases motional amplitudes of sub-nanosecond motion in GB3 but decreases those in HP36. Combined with earlier dynamics measurements at Cα -Cβ sites and backbone sites of GB3, which probed slower time scales, the results point to the need to probe multiple atoms in the protein and variety of time scales to the discern the full complexity of the effects of deuteration on dynamics.

Single-handed supramolecular double helix of homochiral bis(N-amidothiourea) supported by double crossed C\u2212I\xb7\xb7\xb7S halogen bonds

The natural DNA double helix consists of two strands of nucleotides that are held together by multiple hydrogen bonds. Here we propose to build an artificial double helix from fragments of two strands connected by covalent linkages therein, but with halogen bonding as the driving force for self-assembling the fragments to the double helix. We succeed in building such a double helix in both solution and solid state, by using a bilateral N-(p-iodobenzoyl)alanine based amidothiourea which in its folded cis-form allows double and crossed C−I···S halogen bonds that lead to right- or left-handed double helix when the two alanine residues are of the same L,L- or D,D-configuration. The double helix forms in dilute CH3CN solution of the micromolar concentration level, e.g., 5.6 μM from 2D NOESY experiments and exhibits a high thermal stability in solution up to 75 °C, suggesting cooperative and thereby strong intermolecular double crossed halogen bonding that makes the double helix stable. This is supported by the observed homochiral self-sorting in solution.

Backbone resonance assignment for the N-terminal region of bacterial tRNA-(N1G37) methyltransferase.

Bacterial tRNA (guanine37-N1)-methyltransferase (TrmD) is an important antibacterial target due to its essential role in translation. TrmD has two domains connected with a flexible linker. The N-terminal domain (NTD) of TrmD contains the S-adenosyl-L-methionine (SAM) cofactor binding site and the C-terminal domain is critical for tRNA binding. Here we report the backbone NMR resonance assignments for NTD of Pseudomonas aeruginosa TrmD. Its secondary structure was determined based on the assigned resonances. Relaxation analysis revealed that NTD existed as dimers in solution. NTD also exhibited thermal stability in solution. Its interactions with SAM and other compounds suggest it can be used for evaluating SAM competitive inhibitors by NMR.

Development of a technique for psyllium husk mucilage purification with simultaneous microencapsulation of curcumin.

This study focused on evaluating a technique for the psyllium husk mucilage (PHM) purification with simultaneous microencapsulation of curcumin. PHM was extracted with water and purified with ethanol. For the mucilage purification and simultaneous microencapsulation, an ethanolic solution of curcumin was used. After dehydration, the samples were analysed by instrumental techniques and evaluated for thermal stability. The presence of curcumin in the solution did not impair the yield of precipitated polysaccharide. Interactions of the dye and carbohydrates were confirmed by displacement of peaks in FT-IR and FT-Raman spectroscopy. The onset temperature of degradation of microcapsules was superior to that of curcumin. Thermal stability in solution at 90°C also improved. After 300 minutes of heating, the microcapsules had a remnant curcumin content exceeding 70%, while, in standard sample, the remaining curcumin content was 4.46%. Thus, the developed technique was successful on purification of PHM and microencapsulation of curcumin.

Bis(pyrazolyl)carbazole as a Versatile Ligand for Supporting Lutetium Alkyl and Hydride Complexes

Two derivatives of a new bis(pyrazolyl)carbazole pincer ligand H(CzPzR), R = iPr and Me, and their syntheses are reported. Lutetium dialkyl complexes of the ligand (CzPzR)Lu(CH2SiMe3)2, R = iPr and Me, have been prepared and found to exhibit high thermal stability in solution. These organolutetium compounds are Lewis base free, and the solid-state structure of (CzPziPr)Lu(CH2SiMe3)2 revealed that the complex is monomeric with a trigonal-bipyramidal geometry. Hydrogenolysis of (CzPziPr)Lu(CH2SiMe3)2 afforded a trimetallic lutetium hydride complex that possesses five bridging hydride ligands. Notably, intramolecular C–H bond activation of the CzPziPr ligand was found to occur during the formation of this latter hydride complex, with metalation of a pyrazole carbon atom.

Thermally stable rare earth dialkyl complexes supported by a novel bis(phosphinimine)pyrrole ligand

A novel bis(phosphinimine)pyrrole based ligand (HL) and its synthesis are reported. Rare earth dialkyl complexes of the ligand, LLn(CH(2)SiMe(3))(2) (Ln = Er, Lu, Sc), have been prepared and found to exhibit high thermal stability in solution. The protio-ligand and dialkyl lanthanide complexes (Ln = Er, Lu) have been characterised by single crystal X-ray diffraction studies.

Synthesis of copolymer of acrylamide with sodium vinylsulfonate and its thermal stability in solution

The copolymer of acrylamide and sodium vinylsulfonate (PAMSVS) was synthesized by inverse emulsion polymerization and its thermal stability in aqueous and saline solution was investigated. Four samples with different monomer ratio were prepared and the thermal degradation of these samples in aqueous solutions was carried out at 90 °C, 120 °C and 150 °C, respectively. The variation of apparent viscosity during the degradation was investigated. The results indicate that all three PAMSVS samples have better performance of heat endurance than polyacrylamide. Moreover, the sample, which contains 3.4% (molar ratio) sulfonic groups, has the most excellent property of heat endurance. The salt tolerance test of these samples was carried out at 57 °C in 5 mmol/L CaCl2, 5 mmol/L MgCl2 and mineralized water, respectively. The results show that all three PAMSVS samples exhibit better property of Ca2+ ion tolerance than PAM and the best one is the sample, which contains 6.5% (molar ratio) sulfonic groups.

Cover Picture: Unexpected Thermally Stable, Cholesteric Liquid‐Crystalline Helical Polyisocyanides with Memory of Macromolecular Helicity (Chem. Asian J. 6/2007)

A good memory for macromolecular helicity is displayed by the one‐handed helical sodium salt of poly(4‐carboxyphenyl isocyanide) after the complete removal of the optically active amines that induced the helicity. This memory persists even with further modification to the side groups of the amide residues, thus giving designer helical polyisocyanides with outstanding thermal stability in solution, some of which also exhibit liquid crystallinity. To find out more, turn to the Full Paper by E. Yashima et al. on page 755 ff.

Synthesis and structural characterization of the first metal organic thallium antimonide

The first metal organic thallium antimonide, the heterocycle [Me2TlSb(SiMe3)2]3, was synthesized by reaction of [Me2AlSb(SiMe3)2]3 with the Lewis acid-base adduct dmap-TlMe3 (dmap = 4-dimethylaminopyridine). The analogous TlBi heterocycle [Me2TlBi(SiMe3)2]3 couldn't be isolated due to its limited thermal stability in solution.

Helical shifts generate two distinct conformers in the atomic resolution structure of the CheA phosphotransferase domain from Thermotoga maritima.

Helical histidine phosphotransferase (HPt) domains play a central role in many aspects of bacterial signal transduction. The 0.98 A resolution crystallographic structure of the amino-terminal HPt domain (P1) from the chemotaxis kinase CheA of Thermotoga maritima reveals a remarkable degree of structural heterogeneity within a four-helix bundle. Two of the four helices have alternate main-chain conformations that differ by a 1.3-1.7A shift along the bundle axis. These dual conformers were only resolved with atomic resolution diffraction data and their inclusion significantly improved refinement statistics. Neither conformer optimizes packing within the helical core, consistent with their nearly equal refined occupancies. Altered hydrogen bonding within an inter-helical loop may facilitate transition between conformers. Two discrete structural states rather than a continuum of closely related conformations indicates an energetic barrier to conversion between conformers in the crystal at 100K, although many more states are expected in solution at physiological temperatures. Anisotropic atomic thermal B factors within the two conformers indicate modest overall atomic displacement that is largest perpendicular to the helical bundle and not along the direction of apparent motion. Despite the conformational heterogeneity of P1 in the crystal at low temperature, the protein displays high thermal stability in solution (T(m)=100 degrees C). Addition of a variable C-terminal region that corresponds to a mobile helix in other CheA structures significantly narrows the temperature width of the unfolding transition and may affect domain dynamics. Helices that compose the kinase recognition site and contain the phospho-accepting His45 do not have alternate conformations. In this region, atomic resolution provides detailed structural parameters for a conserved hydrogen-bonding network that tunes the reactivity of His45. A neighboring glutamate (E67), essential for phosphotransferase activity hydrogen bonds directly to His45 N(delta1). E67 generates a negative electrostatic surface surrounding the reactive His that is conserved by most CheA kinases, but absent in related phosphotransferase proteins. The P1 conformations that we observe are likely relevant to other helical or coiled-coil proteins and may be important for generating switches in signaling processes.

Two-Dimensional Structure Induced K[sup +] and Na[sup +] Recognition by Self-Assembled Anthraquinone-Polyether Monolayers on Gold Electrodes

Self-assembled monolayer anthraquinone-polyethers on gold electrodes were prepared and characterized by various spectroscopic and electrochemical techniques. The monolayers exhibited better thermal stability in solution, suggesting that multianchoring effects of disulfide moieties improve the integrated adhesion and binding stability of the monolayers. In contrast to solution electrochemistry, the unique structure and packing of the monolayer lead to selective ion binding to ions with the right size and charge, such as potassium and sodium.

Stabilization of the P(CF3)(2)(-) and P(C6F5)(2)(-) ions by coordination to pentacarbonyl tungsten: structures of [18-crown-6-K]P(CF3)2, [18-crown-6-K][W[P(CF3)2](CO)5], and [18-crown-6-K][[W(CO)5]2[mu-P(C6F5)2]].THF.

The stabilization of the P(CF(3))(2)(-) ion by intermediary coordination to the very weak Lewis acid acetone gives access to single crystals of [18-crown-6-K]P(CF(3))(2). The X-ray single crystal analysis exhibits nearly isolated P(CF(3))(2)(-) ions with an unusually short P-C distance of 184(1) pm, which can be explained by negative hyperconjugation and is also found by quantum chemical hybrid DFT calculation. Coordination of the P(CF(3))(2)(-) ion to pentacarbonyl tungsten has only a minor effect on electronic and geometric properties of the P(CF(3))(2) moiety, while a strong increase in thermal stability of the dissolved species is achieved. The hitherto unknown P(C(6)F(5))(2)(-) ion is stabilized by coordination to pentacarbonyl tungsten and isolated as a stable 18-crown-6 potassium salt, [18-crown-6-K][W[P(C(6)F(5))(2)](CO)(5)], which is fully characterized. The tungstate, [W[P(C(6)F(5))(2)](CO)(5)](-), decomposes slowly in solution, while coordination of the phosphorus atom to a second pentacarbonyl tungsten moiety results in an enhanced thermal stability in solution. The single-crystal X-ray analysis of [18-crown-6-K][[W(CO)(5)](2)[mu-P(C(6)F(5))(2)]].THF exhibits a very tight arrangement of the two C(6)F(5) and two W(CO)(5) groups around the central phosphorus atom. NMR spectroscopic investigations of the [[W(CO)(5)](2)[mu-P(C(6)F(5))(2)]](-) ion exhibit a hindered rotation of both the C(6)F(5) and W(CO)(5) groups in solution.

Self-Assembled Monolayers Composed of Aromatic Thiols on Gold: Structural Characterization and Thermal Stability in Solution

Self-assembled monolayers (SAMs) derived from 1,2-bis(mercaptomethyl)-4,5-dialkylbenzene (1), 1-mercaptomethyl-3,4-dialkylbenzene (2), 1-mercaptomethyl-4-alkylbenzene (3), 1-mercapto-4-alkylbenzene (4), and 4-mercaptomethyl-4‘-alkoxybiphenyl (5) were prepared by adsorption from solution onto evaporated gold. The SAMs were characterized by contact angle goniometry, optical ellipsometry, and polarization modulation infrared reflection absorption spectroscopy. Comparison of SAMs generated from 1 and 2 to well-known SAMs generated from normal alkanethiols (6) revealed that the former SAMs are densely packed and highly oriented. The alkyl chains of the SAMs derived from 1 and 2 are, however, less crystalline (i.e., less conformationally ordered) than those derived from 6. The adsorption of compounds 3, 4, and 5 onto gold yielded highly crystalline SAMs. Solution-phase thermal desorption of SAMs 1−6 at temperatures ranging from 60 to 110 °C was monitored using ex situ ellipsometry. The desorption profiles of SA...

Synthesis of Water-Soluble Platinum(II) Complexes Stabilized with Trimethylstibane. Stibane Transfer in Aqueous Solution

Abstract A new series of trimethylstibane-platinum(II) complexes were prepared. They have relatively low thermal stability in solution. The crystal structures of [Pt(SbMe3)4](NO3)2 (where Me = methyl) was determined by X-ray analysis.

Study of the hydrolysis of combined Al3+ and Ga3+ aqueous solutions: Formation of an extremely stable GaO4Al12(OH)24(H2O) polyoxycation

Abstract71Ga and 27Al NMR and clay mineral pillaring studies were used to investigate the hydrolysis of Al(H2O)–Ga(H2O) solutions, mixed in an Al:Ga mole ratio of 12:1, and confirmed the formation of the previously proposed GaO4Al12(OH)24(H2O) polyoxycation. This species has been found to be formed in marked preference to both AlO4Al12(OH)24(H2O) and the previously identified GaO4Ga12(OH)24(H2O) ions, and further to have a much higher thermal stability in solution than either of these. It is suggested that the reason for the increased stability of the ‘GaAl12’ species is that the substitution of a larger metal into the central tetrahedral position has resulted in the formation of a less distorted structure.

Hydrido-organometallic complexes of platinum(II). X-Ray crystal structure of trans-[PtH(C6H4F-p)(PPh3)2

A series of compounds trans-[PtH(R)(PPh3)2][R = C6H4Y-p(Y = Me, OMe, F, or Cl), C6H4Me-o, C6H3Cl2-2,5, C6HCl4-2,3,4,5, C6HCl4-2,3,4,6, C6Cl5, or C6F5], cis-[PtH(C6F5)(PPh3)2], and cis-[PtH(Ph)(dppe)](dppe = Ph2PCH2CH2PPh2) have been obtained by decarboxylation of formate complexes, or by the reaction of the halogeno complexes with NaBH4. The compounds have been characterized by i.r. and n.m.r. (1H, 31P, and 195Pt) spectroscopy. The molecular structure of trans-[PtH(C6H4F-p)(PPh3)2] has been determined by a single-crystal X-ray structural analysis. The crystals are orthorhombic, space group Pcab, with a= 25.304(5), b= 23.963(5), c= 11.530(3)Å, and Z= 8. Dimethyl acetylenedicarboxylate inserts into the Pt–H bond of trans-[PtH(R)(PPh3)2](R = C6H4Cl-p, C6H4Me-p, or C6H4Me-o) to give the corresponding σ-vinyl complexes, but other alkynes and olefins do not react. The thermal stability in solution has also been studied; decomposition takes place via reductive elimination to give RH. The results obtained are explained in terms of the electronegativity and the size of the ligands and the configuration of the complexes.