The nature of active centers in cyclotrimerization of isocyanates catalyzed by the tertiary amine—α-oxide—proton donor system 1. The role of the proton donor

The rate of cyclotrimerization of phenyl isocyanate in chlorobenzene at 120 °C in the presence of the tertiary amine--oxide-proton donor (PD) ternary catalytic system has been studied using a dual calorimeter and a series of phenols with various acidities as the PD. In the presence of weakly acidic phenols, complexes of quaternary ammonium type bases are formed in the ternary catalytic systems. Acidic phenols afford salt complexes with the transfer or a proton from phenol to the tertiary amine in a quantitative yield, while the -oxide present remains unaffected. The structures of the complexes were studied by IR and by IR and¹H NMR spectroscopy.DeceasedTranslated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1382–1385, lune, 1996.     

Revising the proton affinity scale of the naturally occurring α-amino acids

The proton affinities (PA) of the 20 naturally occurring alpha-amino acids (AA) have been determined computationally by means of density functional theory (DFT) and high-level G2(MP2) calculations. These theoretical PAs, together with data that have appeared since 1997 in the literature, are used to validate the most reasonable currently available PA scale for AAs (Harrison, A. G. Mass Spectrom. Rev. 1997, 16, 201-217.). Significant scatter is observed for the PAs of Ser, Asp, Phe, Asn, Met, Pro, Gln, Glu, Trp, His, Lys, and Arg, many of which have a basic side-chain functionality. Critical review of the available data leads to new consensus PAs for Asn, Gln, Met, and Arg of 222.4, 230.5, 223.7, and 250.2 kcal/mol, respectively.     

Influence of π-stacking on the N7 and O6 proton affinity of guanine

The influence of π-stacking interactions between guanine (G) and the side chain of tyrosine (Tyr) on the N7 and O6 proton affinities of guanine and on the capability of these sites to act as hydrogen bond acceptors is analyzed at the B3LYP-D, M05-2X and MP2 levels of theory. With all methods, results from full geometry optimizations indicate that stacking interactions increase the N7 and O6 proton affinities by about 5–6 kcal mol^?1, the increase being slightly larger for N7. Consistently with these results, hydrogen bond distances between guanine and one water molecule decrease in the stacked system. Moreover, interaction energy between H₂O and (G-Tyr) is found to be 2–3 kcal mol^?1 larger than in G···H₂O. This strengthening arises from the additional Tyr–H₂O stabilizing interactions and from a cooperative interplay between stacking and hydrogen bond forces.     

Theoretical study of proton transfer in ammonia–hydrogen halides in the presence of methanol

In this work, the effect of solvent (methanol, CH₃OH) molecules on proton transfer (PT) between ammonia and hydrogen halides was studied. We performed MP2 and B3LYP calculations on HX–NH₃–(CH₃OH) _n clusters for three hydrogen halides, HF, HCl, and HBr, with the number of methanol molecules varying from none to three (n = 0–3). The results showed that stepwise association of methanol molecules with the gas-phase complex can eventually facilitate ionization within the complex, producing the $ {\text{NH}}_{4}^{ + } {\text{X}}^{ - } - \left( {{\text{CH}}_{ 3} {\text{OH}}} \right)_{\text{n}} $ cluster. We found that PT occurs on addition of from one (for HBr) to three (for HF) methanol molecules. The interaction energy $ E_{\text{int}} $ and $ \Updelta E_{\text{add}} $ for the complexes were calculated and basis set superposition error (BSSE) correction was also performed. Atoms-in-molecule and natural-bond-orbital analysis were used to study the properties of the hydrogen bonds in the complexes.     

Theoretical study of intramolecular proton transfer of perylenequinone

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Pressure and isotope effects on the proton jump of the hydroxide ion at 25°C

The limiting molar conductances Λ⁰ of potassium deuteroxide KOD in D₂O and potassium hydroxide KOH in H₂O were determined at 25°C as a function of pressure to disclose the difference in the proton-jump mechanism between an OH^? (OD^?) and a H₃O⁺ (D₃O⁺) ion. The excess conductance of the OD^? ion in D₂O λ _E ^O (OD ^-), as estimated by the equation $$\lambda _E^O (OD^ - ) = \Lambda ^O (KOD/D_2 O) - \Lambda ^O (KCl/D_2 O)$$ increases a little with pressure as well as the excess conductance of the OH^? ion in H₂O $$\lambda _E^O (OH^ - ) = \Lambda ^O (KOH/H_2 O) - \Lambda ^O (KCl/H_2 O)$$ However, their rates of increase with pressure are much smaller than those of the excess deuteron and proton conductances, λ _E ^O (D ⁺) and λ _E ^O (H ⁺). With respect to the isotope effect on the excess conductance, λ _E ^O (OH ^-)/λ _E ^O (D ⁺) decreases with presure as in the case of λ _E ^O (H ⁺)/λ _E ^O (D ⁺), but the value of λ _E ^O (OH ^-)/λ _E ^O (OD ^-) itself is much larger than that of λ _E ^O (H ⁺)/λ _E ^O (D ⁺) at each pressure. These results are ascribed to the difference in the pre-rotation of water molecules, which is brought about by the difference in the intial orientation of the rotating water molecule adjacent to the OH^? (OD^?) or the H₃O⁺ (D₃O⁺) ion.     

The quantitative determination of the S0—T1 absorption in pyrene with the use of intracavity absorption spectroscopy

The spin-forbidden S₀—T₁ transition of pyrene was quantitatively investigated by applying intracavity absorption spectroscopy. The measurements were carried out in benzolic solutions. The molar decadic extinction coefficient of the 0—0 transition was determined to 6.0 × 10⁻⁴ dm³mol⁻¹ cm⁻¹. The integral absorptivity was calculated to 2.94 × 10⁻² dm³ mol⁻¹ cm⁻¹ and yielded an intrinsic phosphorescence lifetime of 55.4 s. The intracavity absorptions were measured in a cavity-dumped Rhodamine 6G dye laser. Absorbances were recorded in the range between 8 × 10⁻⁴ and 5 × 10⁻⁶.     

Synthesis of Nafion~-stabilized Pt nanoparticles to improve the durability of proton exchange membrane fuel cell

Nafion-stabilized Pt nanoparticle colloidal solution is synthesized through ethylene glycol reduction.Pt/Nafion added with carbon black as electric conduction material(labeled Pt/Nafion-XC72) shows excellent electrochemical property compared with Pt/C.After a 300-cycle discharging durability test,the cell performance of membrane electrode assembly(MEA) with the Pt/Nafion-XC72 and Pt/C catalysts indicates a 29.9% and 92.2% decrease,respectively.The charge transfer resistances of Pt/Nafion-XC72 and Pt/C increase by 27.2% and 101.9%,respectively.The remaining electrochemically active surface area of Pt is about 61.7% in Pt/Nafion-XC72 and about 38.1% in Pt/C after the durability test.The particle size of Pt/C increases from about 5.1 nm to about 10.8 nm but only from 3.6 nm to 5.8 nm in the case of Pt/Nafion-XC72.These data suggest that Pt/Nafion-XC72 as a catalyst can enhance the durability of PEMFCs compared with Pt/C.     

Thermodynamic analysis of the interaction of proflavin with the deoxytetraribonucleotide 5′-d(GpCpGpC) according to proton magnetic resonance data

The temperature dependences of the chemical shifts of the proflavin protons in a mixture with the deoxytetraribonucleoside diphosphate 5-d(GpCpGpC) in aqueous solution were investigated on a pulse NMR spectrometer (500 MHz). A procedure is proposed for calculating the mole fractions of various associates in solution as a function of the temperature. The Gibbs free energies, enthalpies, and entropies of the reactions forming the 11, 12, 21, and 22 complexes of proflavin with the tetranucleotide were determined. The results are evidence of a vital role of hydrophobic interactions in the formation of complexes of the dye with the duplex of the tetramer.Translated from Teoreticheskaya i Éksperimental' naya Khimiya, Vol. 28, Nos. 5–6, pp. 430–435, September–December, 1992.     

Approximation of the electron–proton mass ratio as a series in powers of $$\uppi $$

Eddington in 1923, first identified four dimensionless numbers, derived from combinations of the basic physical constants, which are known as the “Eddington constants”. In formulating these dimensionless numbers, Eddington, a leading physicist of his time, claimed that they are characteristic of the structure and dynamics of the Universe at large, on the microscopical scale and at the macroscopical scale. Recently, there has been suggested a possible way of accounting for the magnitude of one of these four dimensionless constants, indicated as the “fine structure constant”, \(\upalpha \), that first emerged from studies of the atomic line spectrum of H. A simple power series in the product \(\hbox {e}\cdot \uppi \) has been proposed, that fits the measured value of the fine structure constant to better than 9999 parts in 10,000. Following along these lines, the authors here propose a simple power series expansion in \(\uppi \) that agrees with the currently accepted measurement of the value of the electron–proton mass ratio (m/M), or \(\upbeta \), to better than 999 parts in 1000.     

Energies of OH⋯X− hydrogen bonds in the gas phase and proton affinities

The energies of hydrogen-bond formation (−ΔH⁰_HX) between hydroxy derivatives and halide ions in the gas phase obey the following relationship: −ΔH⁰_HX = 0 (ΔPA > 0)+32 e^{−0.0156&mid;ΔPA&mid;}, or −ΔH⁰_HX = −ΔPA (ΔPA < 0) + 32 e^{−0.0156∣ΔPA∣}, where ΔPA is the difference between the heterolytic dissociation energy of the -OH and HX bonds. This relation is discussed as a function of the different factors (electrostatic, repulsion, polarization and charge transfer) contributing to the protonation reaction or hydrogen-bond formation.     

The impact of dihydrogen phosphate anions on the excited-state proton transfer of harmane. Effect of β-cyclodextrin on these photoreactions

Photoinduced proton transfer reactions of harmane (1-methyl-9H-pyrido[3,4-b]indole) (HAR) in the presence of a proton donor/acceptor such as dihydrogen phosphate anions in aqueous solution have been studied by stationary and time-resolved fluorescence spectroscopy. The presence of high amounts of dihydrogen phosphate ions modifies the acid/base properties of this alkaloid. Thus, by keeping the pH constant at pH 8.8 and by increasing the amount of NaH(2)PO(4) in the solution, it is possible to reproduce the same spectral profiles as those obtained in high alkaline solutions (pH >12) in the absence of NaH(2)PO(4). Under these conditions, a new fluorescence profile appears at around 520 nm. This result could be related to the results of a recent investigation which suggests that a high intake of phosphates may promote skin tumorigenesis. The presence of β-cyclodextrin (β-CD) avoids the proton transfer reactions in this alkaloid by means the formation of an inclusion complex between β-CD and HAR. The formation of this complex originates a remarkable enhancement of the emission intensity from the neutral form in contrast to the cationic and zwitterionic forms. A new lifetime was obtained at 360 nm (2.5 ns), which was associated with the emission of this inclusion complex. At this wavelength, the fluorescence intensity decay of HAR can be described by a linear combination of two exponentials. From the ratio between the pre-exponential factors, we have obtained a value of K = 501 M for the equilibrium of formation of this complex.     

The use of Transwells™ improves the rates of differentiation and growth of cultured 3T3L1 cells

The use of Transwells? for routine cultures of 3T3L1 cells results in a much improved rate of differentiation of fibroblasts to adipocytes (100 % in 9 of 10 tests) compared with bottom-well layer cultures. Mean size of cells was not different, but the cell number and overall cell mass was 3× larger in transwell in spite of a smaller surface area. The difference between both models was the accessibility in transwells of both sides of the cells to the medium (and oxygen). Cells were counted, and their size estimated using a handheld cell counter, Scepter?, designed for blood cells, but adjusted to the larger size of adipocytes. Finally, the effect of nitric oxide was tested using spermineNONOate, a nitric oxide (NO·) donor. The product was released to cultures at a constant 1 μl/h rate for up to 3 days using osmotic Alzet? minipumps held in wells with water and discharging their contents to the cultured cell-laden wells through a short capillary tube. A rate of 0.3 pmol/min/ml of medium did not affect the cells’ size, but 0.4 pmol/min/ml significantly increased cell mass. The methodological improvements presented here allow for more uniform cultured cell yields and a more flexible environment for control of cell size and administration of signaling agents.

Kinetic study for the formation of microcrystalline “disks” of204T1I in gelatin medium

This paper presents a radiochemical study of the appearance of²⁰⁴T1I microcrystals and their development as disks resembling Liesegang rings, in gelatin, under different experimental conditions. Thus, kinetic diagrams have been traced, from which gel diffusion rate constants for radioactive ions were calculated, as well as reaction rate constants between reactant species:²⁰⁴T1⁺ and I^–, in colloidal medium, followed by the development of concentrated microcrystals under form of one or more disks. There is an interconnection between gelatin concentration of the colloidal medium, on one hand, and²⁰⁴T1I microcrystal disks number and dimensions, on the other hand, disks which appeared in gel as a result of the global process of nucleation.     

The pρT behaviour of the lactate family

The densities of methyl lactate, ethyl lactate and butyl lactate have been measured using a high-pressure, high-temperature vibrating tube densimeter system over a temperature range from T = (283.15 to 338.15) K and a pressure range from p = (0.1 to 60.0) MPa. The experimental densities have been satisfactorily correlated with temperature and pressure using the TRIDEN equation. Finally, from the experimental densities, properties such as isobaric expansibility and isothermal compressibility have been calculated.     

Are complete metal-organic frameworks really responsible for improving the performance of high-temperature proton exchange membranes?

Constructing continuous proton transfer channels used metal-organic frameworks (MOFs), which can effectively improve proton conductivity of proton exchange membrane, have recently attracted a lot of attentions. MOFs have relatively harsh operating environment in phosphoric acid-doped (PA-doped) high-temperature proton exchange membranes (HTPEMs). However, there are few reports on the stability and state of MOFs in HTPEMs after PA doping. In this work, a series of MOFs (UIO-66, UIO-66-COOH, UIO-66-NH₂, UIO-66-SO₃H, MIL-101(Cr), and MIL-53(Al)) are selected to investigate their stability via simulating the operating environment for the first time. Composite membranes based on the MOFs are prepared to explore the influence of the stability and state of MOFs on HTPEMs properties. These results indicate that proton transfer channels are constructed in two different styles. After soaking in PA of UIO-66, UIO-66-COOH, MIL-101(Cr), and MIL-53(Al) at 160 °C, metal ions leave the ligands and dissolve, while the ligands are kept in the membranes. These ligands can provide proton transport sites in the membranes and help to construct proton transfer channels. UIO-66-NH₂ and UIO-66-SO₃H are dissolved completely in PA, leading to continuous nanopores. The proton transfer channels are constructed using the nanopores. From the results, we can infer that constructing proton transfer channels is an effectively method to improve the membranes performance, but the transmission mechanism needs to be revealed carefully.     

Mononuclear rearrangements of heterocycles in water/β-CD: information on the real site of reaction from structural modifications of substrates and from proton concentration dependence of the reactivity

The effect of β-cyclodextrin (β-CD) on the reactivity in the base-catalyzed pathway for the rearrangement in water of some (Z)-hydrazones of 3-benzoyl-1,2,4-oxadiazoles (1b-f) into the relevant triazoles (2b-f) was investigated, finding different behavior as a function of the proton concentration. ESIMS and ¹H NMR data evidence the formation of host-guest complexes. The whole of the experimental and calculated (MM2) data enabled us to draw some intriguing conclusions concerning the influence of the structures of the substrates and the nature of the formed host-guest complexes on the real site of the reaction.     

Toward the synthesis of 1′E-isomer of ent-hyptenolide

A short total synthesis of a diacetoxylated E,E-diene lactone ent-hyptenolide, was achieved involving from Phosphonate and cis-butene 1,4-diol. Brown Asymmetric allylation, Acrylation, Acetylation, Ring-closing metathesis as the key steps has been described. Moreover, the biological activity of ent-hyptenolide was evaluated on HeLa, A549, IMR32, and MDA-MB231 cancer cell lines. The ent-hyptenolide selectively and potently inhibited the growth of IMR32 cell line.