Proton-donor Capacity Research Articles

Cooperativity between hydrogen bonds and beryllium bonds in (H2O)nBeX2 (n = 1–3, X = H, F) complexes. A new perspective

The interaction of BeX(2) (X = H, F) with water molecules has been analyzed at the B3LYP/6-311+G(3df,2p)//B3LYP/6-311+G(d,p) level of theory. The formation of strong beryllium bonds between water molecules and the BeX(2) derivative triggers significant electron density redistribution within the whole system, resulting in significant changes in the proton donor and proton acceptor capacity of the water molecules involved. Hence, significant cooperative and anti-cooperative effects are present, explaining why there is no case in which the global minimum corresponds to a tetracoordinated beryllium atom. In fact, the most stable clusters can be viewed as the result of the attachment of BeX(2) to the water trimer and the water dimer, respectively, and not as the result of the solvation of the BeX(2) molecule. We have also shown that the decomposition of the interaction energy into atomic components is a reliable quantitative tool to describe all the closed-shell interactions present in the clusters investigated herein, namely hydrogen bonds, beryllium bonds and dihydrogen bonds. Indeed, we have shown that the changes in the atomic energy components are correlated with the changes in the strength of these interactions, and they provide a quantitative measure of cooperative effects directly in terms of energies.

Assesment of the Proton Donor Capacity as a Marker of Anti-Oxidative Defense in Premature New Borns

Aim: The aim of this study was to determine the antioxidative defense in preterm by measuring the levels of proton donors (PD). Material and methods: We conducted a prospective non-randomized study between March 2003 and December 2006. The study cohort was represented by twenty four premature newborns with diferent types of respiratory distress syndrome( RDS), asphyxia, cerebral hemorrhage. The control was represented by 13 healthy term newborns. For each newborn in the study group we determined the PD in the first and third days, while only on day one of life. Hatano's method was used to determine the PD. The statistical analysis was done using the “Statistica” program Ex- SPSS. Results: In the study group median values of PD in the study group were 45.59%[ 41.37-49.80] on day one and 49.01%[44.18-53.85] on day three with significant difference at corelation matrix(p< 0.05). The PD value on day one was significantly higher in premature newborns with medium RDS than in prematures with mild form of RDS(p = 0.0065). The PD values on day one were significantly higher in the presence of cerebral hemorrhage (p=0.20). On day one, the median PD in controls was significantly higher than that of the study group (p=0,032699). There were no significant correlations between the values of the PD and the types of asphyxia. Conclusions: The PD values increase on the first day life with RDS severity and presence of cerebral hemorrhage. At term newborns the PD value is significantly higher then in preterms with different patologies.

Modeling of continental weathering under high-CO2atmospheres during Precambrian times

Batch experiments were conducted to simulate abiotic weathering of the continental crust under high-CO2 atmospheric conditions during Precambrian times, i.e., corresponding to the general Archaean conditions as well as to the immediate aftermath of the Neoproterozoic Snowball Earth ice ages. Three types of rock (basalt, granodiorite and tonalite) representative of the Archaean to Proterozoic continental crust were reacted in the form of powders for 1 year at 40°C with pure water under various water/rock ratios, in oxic and anoxic atmospheres containing 10% CO2, that is, under conditions assumed to characterize the greenhouse effect which prevailed at that time. Chemical and mineralogical data collected during the course of the experiments reflect alteration phenomena occurring in two steps: (1) rapid leaching of the fresh surfaces, probably related to the proton-donor capacity of the CO2 and (2) a steady state reaction under near-neutral conditions. These observed dissolution rates can be satisfactorily modeled by kinetic data available in the literature. Using a 1-D weathering model reproducing the two steps, we evaluate the atmospheric CO2 consumption rate at the Snowball Earth aftermath, focusing on the relative contribution of surface leaching versus steady state reaction. The results show that the process is dominated by surface exchange.

Concerning the color change of pyrromethene 650 dye in electron-donor solvents

This paper studies the change in the color from violet to green of pyrromethene 650 (PM650) dye observed in certain N, N′-dialkyl-amides characterized by their high electron-donor ability and low proton-donor capacity. For this purpose, the photophysical properties of PM650 are registered in diluted solutions of several amides, including dimethylformamide/dioxane mixtures. The color change of PM650 is discussed on the basis of the formation of new hypsochromic absorption and fluorescence bands, which are assigned to the formation of new chromophoric species as consequence of a specific reaction between PM650 and the amide solvents. The influence of the ageing time of the sample and the temperature on the color change is also discussed. In some cases the ageing leads to the bleaching of the dye.

Protolytic properties of cyanic and thiocyanic acids and their isoforms

The electronic structure of HOCN, HSCN, HNCO, and HNCS molecules and [OCN]− and [SCN]− anions has been studied by ab initio calculations at HF/6-31G(d), HF/6-31G(d, p), MP2/6-31G(d)//HF/6-31G(d), and MP2/6-31G(d, p)//HF/6-31G(d, p) levels of theory. The HNCO and HNCS molecules are shown to have higher thermodynamic stability than HOCN and HSCN, respectively. The protolyte strength series are substantiated: HSCN > HOCN, HNCS > HNCO, HOCN > HNCO, HSCN > HNCS. Computations including electron correlation [MP2/6-31G(d)//HF/6-31G(d) and MP2/6-31G(d, p)//HF/6-31G (d, p)] reproduce the general sequence of proton-donor properties: HSCN > HOCN > HNCS > HNCO, which coincides with the hydrophobicity series for the compounds. The relative proton-donor capacity of these acids in water solutions is generally governed by the electronic structure and by the size of their molecules and [OCN]− and [SCN]− anions, but not by medium effects.

Theoretical study of the protonation and deprotonation of cytosine. Implications for the interaction of cytosine with water

The geometries, harmonic vibrational frequencies and energies of the two stable cyclic structures of the keto tautomer of cytosine complexed with water are computed using density functional theory (B3LYP) combined with the 6-31++G(d,p) basis set. The effect of complex formation with water on the pyramidalization of the amino group is discussed. The proton affinities of the oxygen and nitrogen atoms and the deprotonation enthalpies of the three NH bonds of cytosine are computed at the same level of theory. The deprotonation enthalpies of the two NH bonds of the amino group differ by 23 kJ mol −1 from each other and this reflects the asymmetric deformation of the amino group. The most stable hydrogen bond between cytosine and water is formed at the acceptor atom characterized by the lowest proton affinity and at the NH group having the highest acidity. The results are compared with data obtained at the same level of theory for the uracil– and thymine–water complexes. For the three nucleobases, the intermolecular distances and the energies of the hydrogen bonds formed at the different sites depend on the proton affinity and the deprotonation enthalpy of these sites. The dominance of the proton donor capacity in determining the hydrogen-bond energies and the cooperativity in the cyclic structures are discussed.

Chemical rescue of the catalytically disabled clostridial glutamate dehydrogenase mutant D165S by fluoride ion

The catalytically disabled Asp165-->Ser mutant of clostridial glutamate dehydrogenase shows 100000-fold less activity than the wild-type (WT) enzyme in a standard glutamate oxidation assay and 1000-fold less activity in the reductive-amination reaction. The large reduction in the rate has been attributed to removal of the negative charge and the postulated proton-donor capacity of the aspartate carboxyl group. However, fluoride ion (1 M NaF) causes a 1000-fold activation of the mutant enzyme while simultaneously inhibiting WT activity by 20-fold in the forward reaction. For the reverse reaction, F- (1 M) activates the mutant 4-fold and inhibits WT activity to approx. 64%. The net result when 1 M F- is present is a decrease in the WT:mutant activity ratio from 100000 to 5 for the forward reaction. None of the other halides tested, nor NO3(-), CHCOO- or HCOO-, give comparable activation. Re-activation took 15-30 s under assay conditions, suggesting the possibility of conformational change; CD spectroscopy, however, provided no evidence of a substantial change and kinetics of modification using 5,5'-dithiobis(2-nitrobenzoic acid) suggested only subtle structural rearrangement. This phenomenon is discussed in the light of available information about the structure of the mutant enzyme. It is suggested that the F- ion provides a fixed negative charge at the position of the missing aspartate carboxyl group. Therefore, this appears to be an example of 'chemical rescue'.

Investigation of silica surface chemistry by the method of the luminescence probes

The state of hydroxyl coverage, the presence of admixtures, defects, coadsorbates and also the values of adsorption are shown in electron spectra of the adsorbed luminescence molecules. In the present work we have studied the luminescence spectra of molecules with different electron structures (polyacenes, their N-heteroaromatic analogues, dyes), absorbed on the surface of SiO 2 pure modifications by steady-state and kinetic measurements with UV and selective laser excitation at 300, 77 and 4.2 K. The existence of silica gel and aerosil electron acceptor sites which can form molecular complexes with polyacenes is shown. The number of these sites has been determined. A discussion of their nature is given. The proton—donor capacity of silica hydroxyl groups has been determined at every stage of heat treatment. Adsorption complex geometry on silica surfaces is discussed.

Influence of solute size and the non-polar interaction term on the selection of test solutes for the classification of stationary phase selectivity in gas chromatography

A new parameter Δ G S INT (X) is introduced for the determination of the capacity of a stationary phase to enter into orientation and hydrogen-bonding interactions. Δ G S INT (X) is defined as the component of the free energy of solution that is equivalent to the solute—solvent interactions of solute (X) that exceeds those interactions typified by an n-alkane of identical volume in solvent S reduced by the identical interactions of solute (X) in a hydrocarbon solvent (squalane). Δ G S INT (X) provides a quantitative scale of orientation and proton donor—acceptor interactions that is independent of solute size and non-polar solute—solvent interactions. Multivariate analysis of Δ G S INT (X) values for 21 test solutes on 20 stationary phases was used to identify acceptable test solutes for characterizing specific intermolecular interactions and to classify the stationary phases based on their capacity for these interactions. Several highly correlated solutes were identified as suitable for determining orientation and solvent proton acceptor capacity of which nitrobenzene and n-octanol, respectively, are recommended as the preferred solutes. Benzene and dioxane were identified as the most favorable test solutes for solvent proton donor capacity within the data set. It seems likely that a more appropriate solute could be found for this interaction. The classification of stationary phases by Δ G S INT (X) is informative and shows a logical clustering of phases of similar type and a linearly related change in properties for the homologous series of poly(methylphenylsiloxane) solvents as the mole percentage of phenyl groups is increased.

Experimental protocol for the assessment of solvent strength and selectivity of liquid phases used in gas chromatography

A thermodynamic approach to the practical characterization of solvent strength and selectivity of a wide range of molecular and ionic stationary phases for gas chromatography is discussed. The experimenal protocol is outlined in detail and the principal sources of error with their magnitude identified. The solvent strength parameter (the partial molar Gibbs free energy of solution for a methylene group per unit solvent volume) is proposed as a universal parameter for measuring solvent strength although it is indicated that in the general ranking of liquid phases anomalous positioning of ionic phases and perfluorocarbon phases may occur. The partial molal Gibbs free energy of solution for selected test solutes is proposed as a scale of solvent selectivity. Nitrobenzene and n-octanol are demonstrated to be acceptable test solutes to characterize solvent orientation and proton acceptor capacity, respectively. Benzodioxan is shown to be an unacceptable test solute for assessing solvent proton donor capacity and dibutylformamide is tentatively identified as a promising replacement. Tabulation of the above constants provides new insight into the solvent properties of the most common liquid phases used in gas chromatography. In particular, it is demonstrated that the liquid organic salts provide enhanced orientation and proton acceptor capacity compared to non-ionic liquids and represent an important class of new solvents for extending the selectivity range of solvents used in gas chromatography. A need for new phases with strong proton donor capacity is also identified.

Acid-base reaction of fluorinated aliphatic alcohols with triethylamine

1. IR spectroscopy showed that fluorinated alcohols H(CF2CF2)nCH2OH with n=1–5 are in the dimeric form; in mixtures with triethylamine, they form complexes; dimer + 2(amine)=2(complex). The complexing equilibrium constant is constant in a wide range of [alcohol]/ [amine] ratios. 2. An increase in n in the molecule of the alcohol results in an increase in the protondonor capacity with respect to triethylamine.

Acid-base properties of 2-(?-carbinol)norbornadiene-cyclopentadienylrhodium complexes

1. IR spectroscopy has been employed to compare the proton-donor properties of a series of carbonyl complexes and the proton-acceptor properties of their methyl ethers. It has been found that the proton-donor capacity of the OH group in the alcohols decreases in the sequence (CO)3MnC5H4CH2OH > C5H5FeC5H4CH2OH > C5H5Rh·C7H7-2-CH2OH, and the proton-acceptor ability of the oxygen atom in the ethers RCH2OMe — in the reverse order: R=C5H5RhC7H7-2 > C7H7-2 > C5H5FeC5H4 > CH2=CH(CO)3MnC5H4. 2. The results obtained show that 2-(hydroxymethyl)norbornadienecyclopentadienyl-rhodium exhibits increased basicity (reduced acidity), in accordance with the concept of the powerful positive inductive effect of the C5H5RhC7H7-2 group and with the general electron-donor effect of the η5-C5H5Rh group.

Spectral study of association of nitroamines

This paper reports on the study of the thermodynamic parameters of association carried out by a spectral investigation of CC14 solutions of nitroamines, whose proton-donor capacity in the H bond has already been investigated. Here the series of nitroamines is somewhat shortened since, because of the low solubility of some of the nitroamines in CC14, a measurable concentration of the associated form could not be obtained.

Infrared spectroscopic study of proton-donor capacity of ch bonds of C- and B-ethynylcarboranes

1. In the B- and C-ethynylcarboranes the ethynyl CH bond has a greater proton-donor capacity than the carborane CH bond. 2. The insertionof an ethynyl group into the carborane nucleus hardly changes the proton-donor capacity of the carborane CH bond when compared with the unsubstituted carboranes. 3. The carboranyl group increases the proton-donor capacity of the acetylenic CH bond when compared with butylacetylene, in which connection this effect decreases in the order 1->2-, 3->9-carboranyl groups, i.e., with decrease in the electron-acceptor effect of the carboranyl group.

Investigation of the proton donor capacity of aliphatic N-nitroamines by the method of IR spectroscopy. Thermodynamic parameters of complexes with a hydrogen bond

Investigation of the proton donor capacity of aliphatic N-nitroamines by the method of IR spectroscopy. Thermodynamic parameters of complexes with a hydrogen bond

Spectral characteristics of the bands of NH groups and structure of 2-thioxobenzazolines in solvents with low polarities

The IR spectra of five 2-thioxo-benzazolines in carbon tetrachloride (2500–3500 cm−1) and chloroform (3200–3500 cm−1) are examined. Analysis of the spectral parameters of the absorption band of the unassociated NH groups showed that the high proton-donor capacity of the hydrogen atom of the thioamide group of 2-thioxobenzoxazoline is evidently associated with the high electronegativity of the oxygen atom. The existence of intermolecular hydrogen bonds with a degree of dissociation of 0.3 in carbon tetrachloride and 0.1 in chloroform was established by means of the concentration dependence of the spectra. A change with time in the integral coefficient of the absorption band of the unassociated NH groups was observed in solutions in carbon tetrachloride; this is explained by interaction of the 2-thioxobenzazolines with carbon tetrachloride. The IR spectra, a table of the spectral characteristics, the dependence of the relative integral intensity on the concentration, and the dependence of the optical density of the absorption band of free NH groups on time are presented.

A polarographic study of aliphatic nitro compounds 10. Electroreduction of nitrolic acid intermediates in the reduction of gem-dinitroalkanes and their analogs

1. A study of the polarographic behavior of methylnltrolic, ethylnitrolic, and cyanomethylnitrolic acids has shown that: a) reduction is a two-step process in solutions with low proton-donor capacity, the first of these steps corresponding to reversible one-electron transfer; b) the first step in reduction in acidic solution involves a four-electron transfer with the formation of a nitrolic acid oxime. 2. A mechanism for nitrolic acid reduction, applicable in both acid and alkaline solutions, has been proposed.

ChemInform Abstract: STUDY OF THE PROTON‐DONOR CAPACITY OF 4‐SUBSTITUTED 1,5‐DIPHENYLPENTADIENOLS BY THE IR SPECTROSCOPIC METHOD

Chemischer InformationsdienstVolume 7, Issue 13 Physical Organic Chemistry ChemInform Abstract: STUDY OF THE PROTON-DONOR CAPACITY OF 4-SUBSTITUTED 1,5-DIPHENYLPENTADIENOLS BY THE IR SPECTROSCOPIC METHOD N. S. PIVNENKO, N. S. PIVNENKOSearch for more papers by this authorO. V. LAVRUSHINA, O. V. LAVRUSHINASearch for more papers by this authorL. M. GRIN, L. M. GRINSearch for more papers by this authorV. F. LAVRUSHIN, V. F. LAVRUSHINSearch for more papers by this author N. S. PIVNENKO, N. S. PIVNENKOSearch for more papers by this authorO. V. LAVRUSHINA, O. V. LAVRUSHINASearch for more papers by this authorL. M. GRIN, L. M. GRINSearch for more papers by this authorV. F. LAVRUSHIN, V. F. LAVRUSHINSearch for more papers by this author First published: March 30, 1976 https://doi.org/10.1002/chin.197613060AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume7, Issue13March 30, 1976 RelatedInformation

Complex formation of trinitromethane and 1,1-dinitroethane with etheetype solvents

1. C-H acids of a number of polynitroalkanes with ether-type solvents form intermolecular hydrogen bonds, forming stable complexes with a 1∶1 composition. 2. The replacement of the methyl group in the α-position of C-H acids by a nitro group increases their proton donor capacity and the energy of the hydrogen bond, 3. The change in the structure of the investigated ethers-hydrogen acceptors — leads to a change in the value of the dissociation constant of the complexes and does not affect the shift of the C-D band and, consequently, the energy of the hydrogen bond.