Gas-Phase Hydration Thermochemistry of Sodiated and Potassiated Nucleic Acid Bases

Hydration reactions of sodiated and potassiated nucleic acid bases (uracil, thymine, cytosine, and adenine) produced by electrospray have been studied in a gas phase using the pulsed ion-beam high-pressure mass spectrometer. The thermochemical properties, ΔH ( o ) ( n ), ΔS ( o ) ( n ), and ΔG ( o ) ( n ), for the hydrated systems were obtained from hydration equilibrium measurement. The structural aspects of the hydrated complexes are discussed in conjunction with available literature data. The correlation between water binding energies in the hydrated complexes and the corresponding metal ion affinities of nucleobases suggests that a significant (if not dominant) amount of the canonical structure of cytosine undergoes tautomerization during electrospray ionization, and the thermochemical values for cationized cytosine probably correspond to a mixture of tautomeric complexes.     

Hydration Energies of Protonated and Sodiated Thiouracils

Hydration reactions of protonated and sodiated thiouracils (2-thiouracil, 6-methyl-2-thiouracil, and 4-thiouracil) generated by electrospray ionization have been studied in a gas phase at 10 mbar using a pulsed ion-beam high-pressure mass spectrometer. The thermochemical data, ΔH ^o n, ΔS ^o n, and ΔG ^o n, for the hydrated systems were obtained by equilibrium measurements. The water binding energies of protonated thiouracils, [2SU]H⁺ and [6Me2SU]H⁺, were found to be of the order of 51 kJ/mol for the first, and 46 kJ/mol for the second water molecule. For [4SU]H⁺, these values are 3–4 kJ/mol lower. For sodiated complexes, these energies are similar for all studied systems, and varied between 62 and 68 kJ/mol for the first and between 48 and 51 kJ/mol for the second water molecule. The structural aspects of the precursors for hydrated complexes are discussed in conjunction with available literature data. Graphical Abstract

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Microhydration of Deprotonated Nucleobases

Hydration reactions of deprotonated nucleobases (uracil, thymine, 5-fluorouracil,2-thiouracil, cytosine, adenine, and hypoxanthine) produced by electrospray have been experimentally studied in the gas phase at 10 mbar using a pulsed ion-beam high-pressure mass spectrometer. The thermochemical data, ΔH ^o , ΔS ^o , and ΔG ^o , for the monohydrated systems were determined. The hydration enthalpies were found to be similar for all studied systems and varied between 39.4 and 44.8 kJ/mol. A linear correlation was found between water binding energies in the hydrated complexes and the corresponding acidities of the most acidic site of nucleobases. The structural and energetic aspects of the precursors for the hydrated complexes are discussed in conjunction with available literature data.

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Graphical Abstract ?

     

Microhydration of Guanine base pairs

We report spectroscopy of clusters of guanine base pairs with one and two water molecules. We recorded the vibronic spectra of the mass-selected GG(H2O) and GG(H2O)2 clusters using resonant two photon ionization (R2PI) and we used IR-UV double resonance spectroscopy to obtain ground state IR spectra of these clusters. We found that a single water molecule stabilizes one of two structures we had previously found for guanine dimers. Addition of a second water molecule causes no further structural change.     

Monosaccharides

Conclusions The synthetic accessibility of higher 3-deoxyglyculosonic acids was shown on the example of the preparation of 3-deoxy-L-gluco- and 3-deoxy-L-manno-octulosonic acid derivatives.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2341–2346, September, 1968.     

Monosaccharides

Summary In the condensation of derivatives of the aldehydo forms of pentoses with malonic acid under the conditions of the Knoevenagel-Döbner reaction good yields were obtained of the corresponding 2,3-dehydro-2,3-dideoxyaldehydoheptonic acids, wriose structures were confirmed by some chemical transformations and also by the ultraviolet and infrared spectra.     

Monosaccharides

Conclusions Condensation of the aldose form of monosaccharides with carboethoxybromomethylenetriphenylphosphorane gives-bromounsaturated aldonic acids, which upon reaction with ammonia and primary amines form trans-aziridine derivatives of the acyclic forms of the sugars.Translated from Ivestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2691–2697, December, 1967.     

Vertical detachment energies of anionic thymidine: Microhydration effects

Density functional theory has been employed to investigate microhydration effects on the vertical detachment energy (VDE) of the thymidine anion by considering the various structures of its monohydrates. Structures were located using a random searching procedure. Among 14 distinct structures of the anionic thymidine monohydrate, the low-energy structures, in general, have the water molecule bound to the thymine base unit. The negative charge developed on the thymine moiety increases the strength of the intermolecular hydrogen bonding between the water and base units. The computed VDE values of the thymidine monohydrate anions are predicted to range from 0.67 to 1.60 eV and the lowest-energy structure has a VDE of 1.32 eV. The VDEs of the monohydrates of the thymidine anion, where the N(1)[Single Bond]H hydrogen of thymine has been replaced by a 2(')-deoxyribose ring, are greater by ～0.30?eV, compared to those of the monohydrates of the thymine anion. The results of the present study are in excellent agreement with the accompanying experimental results of Bowen and co-workers [J. Chem. Phys. 133, 144304 (2010)].     

Thermochemistry of Ketene

A new value, -100±10 kJ mol^{- 1}, was obtained for the enthalpy of formation of gaseous ketene, H _f ⁰(g)(CH₂ = C = O), from the data obtained by the authors in combination with certain published experimental and calculation data. The suggested value is considerably lower than the value accepted in the literature, -48 kJ mol^{- 1}.     

Thermochemistry of lignin

Thermochemical reactions occurring in various stages of structural transformations of native lignin in its thermal treatment in a wide temperature range are considered and classified. Attention is given to the initial state of lignin in its primary isolation without heating. The terminology of lignin products, used in the literature, is put in order to a certain extent. The thermochemical reactions in which lignins are transformed in processing of raw wood materials and the structure of isolated lignins undergoes changes in the course of the target thermal treatment are differentiated. The applied aspect of the directed thermochemical synthesis of new lignin-based low- and high-molecular-mass compounds is discussed.     

Thermochemistry of explosives

The kinetics constants for the decomposition reaction of an explosive can be used to calculate the lowest temperature (critical temperature, T_m) at which any specific size and shape of explosive can self heat to explosion; however, the accuracy of the calculation is in doubt without an independent experimental determination of a critical temperature for a known size and shape of the explosive. A method is presented for the experimental determination of critical temperatures on a routine basis, and it is shown that agreement between calculated and experimental values is excellent for most common explosives.