Universal system for liquid stationary phase classification on the basis of thermodynamical data

Summary Equations modifying Rohrschneider's relationship between I and thermodynamical characteristics values are derived. Polarity in chromatography is discussed as a possibility of stationary phases or absorbents to enter into intermolecular interactions and is determined on the basis of the partial molar free energies of solution (G) of six test substances. A simple method for the calculation of stationary phase polarity in terms of G from retention indices and McReynolds constants is given. Equations are presented for the calculation of stationary phase selectivity utilizing G data tabulated for selected test substances. The thermodynamical basis of selecting a reference phase for a unified system expressing the selectivity of stationary phases which can also be applied for adsorbents is suggested. The energy equivalent to an index unit, G_i.u., is discussed.     

Hydrogen bonding and molecular association in methylated 3-hydroxypyridines

Association in derivatives of 3-hydroxypyridine has been examined via the chemical shifts for OH in PMR for equimolar mixtures of the derivatives of pyridine and phenol in CCl₄ and CH₂Cl₂. It is found that spatial screening of the pyridine N and phenol OH by methyl groups has an anomalous effect on the strength of the complex. A possible explanation is that the ionic form NH . . . O is stabilized on account of increased basicity of the N and acidity of the H in the methyl derivatives of pyridine and phenol. Domination by the intermolecular hydrogen bond between OH and N is the distinctive feature of association in 3-hydroxypyridines relative to association in phenol. The temperature dependence of _OH gives the enthalpy and entropy of association for 2, 4, 6-trimethyl-3-hydroxypyridine and of complex formation for various model systems. IR measurements confirm the conclusions.See [1] for the previous communication.We are indebted to G. G. Dvoryantseva for making the IR measurements.     

13C NMR spectra of 3- and 5-substituted flavone derivatives

Summary The¹³C NMR of a number of 3- and 5-hydroxyflavones and of 3- and 5-methoxyflavones have been studied for the first time and all the signals have been assigned. A comparison of the chemical shifts of the¹³C nuclei with the acidity and basicity parameters of the compounds investigated and with the results of calculations of -charge density has been made. It has been shown that the chemical shifts of the individual signals in the¹³C NMR spectra are qualitatively connected with estimates of the reactivities of the compounds studied.Irkutsk Institute of Organic Chemistry, Siberian Branch of the Academy of Sciences of the USSR. A. A. Zhdanov Irkutsk State University. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 513–519, July–August, 1977.     

New Fullerene-Based Stationary Phases for Gas Chromatography

Regularities were revealed for the retention of different classes of organic compounds on stationary phases based on C₆₀ and carbon nanotubes and on phases of mixed composition (C₆₀ and dibenzo-24-crown-8, C₆₀ and dibenzo-30-crown-10, and C₆₀ and -cyclodextrin) in gas chromatography. A synergistic effect was observed for the stationary phases of mixed composition. Quantitative estimation of the dispersion potential demonstrated that the C₆₀-based stationary phase differs significantly from hydrocarbon adsorbents and more closely resembles nonpolar liquid stationary phases. Under the conditions of solid-phase microextraction, an adsorbing element based on fullerene C₆₀ can be used for the preconcentration of aromatic hydrocarbons.     

Selectivity of amino-, cyano- and diol-bonded silica in reversed-phase liquid chromatography

Amino-, cyano- and diol-bonded silica stationary phases were characterized by estimating their characteristic interaction constants in reversed-phase liquid chromatography (RPLC) based on linear solvation energy relationships. Five characteristic interaction constants of the stationary phases, the hydrophobicity (v), polarizability (r), dipolarity (s), hydrogen bond (HB) acceptor basicity (a) and HB donor acidity strength (b) were determined by multiple regression analyses of logarithmic retention factors (k) for a set of test solutes measured on them in 10% (v/v) methanol-water vs. the solute properties represented by characteristic molecular volume (Vx), excess polarization (R2), dipolarity/polarizability (pi*), HB donor acidity (alpha) and HB acceptor basicity (beta). Magnitudes of the five constants for the phases in RPLC were compared with those in normal-phase LC to see the differences in chromatographic selectivity in the two LC modes.     

Characterization of stationary phases in subcritical fluid chromatography by the solvation parameter model. I. Alkylsiloxane-bonded stationary phases

Varied types of alkylsiloxane-bonded and fluoroalkylsiloxane-bonded stationary phases, all commercially available, were investigated with subcritical fluid mobile phase. The effect of the alkyl chain length (from C4 to C18) and of the nature of the bonding (fluorodecylsiloxane, phenyl-C18 and polar-embedded-C18) on the chromatographic behaviour was investigated by the use of a linear solvation energy relationship (LSER), the solvation parameter model. A large set of test compounds provides precise and reliable information on the intermolecular interactions responsible for retention on these stationary phases used with a subcritical mobile phase. First of all, the results underline the close properties between subcritical fluid and organic liquid. The use of non aqueous mobile phases reduces the cavity energy and the mobile phase acidity generally encountered with aqueous liquid phases, allowing other interactions to take a part in retention. As expected, an increase in the alkyl chain length favours the dispersive interactions between the solutes and the stationary phases. Changes in basicity and acidity of the stationary phases are also related to the chain length, but, in this case, mobile phase adsorption onto the stationary phase is supposed to explain these behaviours. The addition of a phenyl group at the bottom of the C18 chain, near the silica, does not induce great modifications in the retentive properties. The fluorodecylsiloxane and the polar-embedded alkylsiloxane phases display very different properties, and can be complementary to the classical alkylsiloxane-bonded phases. In particular, the fluorinated phase does not favour the dispersive interactions, in comparison to hydrogenated stationary phases, when the basicity of the polar-embedded phase is obviously greater than the one of classical alkylsiloxane-bonded phases, due to the amide function. Finally, logk-logk curves plotted between the different phases illustrate the effect of the interaction properties on the retention of different classes of compounds.     

Contribution of adsorption to rentension data in capillary gas chromatography part II. Non-polar stationary phases

Summary The influence of adsorption on the dependence of retention data upon film thickness of the non-polar stationary phases OV-101 and Apiezon L coated on glass (series of capillary columns with non-deactivated and Carbowax 20 M deactivated surface) and fused silica has been studied. Limiting values of Kovats indices, I, of solutes which exhibit tendency to hydrogen bonding are calculated for each series of columns.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Structural Properties Governing Retention Mechanisms on Immobilized Artificial Membrane (IAM) HPLC Columns

The aims of this study were to investigate whether three commercially available immobilized artificial membrane (IAM) HPLC columns yield collinear data for neutral compounds, and whether IAM scales are distinct from the log P_oct (partition coefficient in the octanol/H₂O system) scale. With these objectives, the retention mechanisms on the IAM HPLC columns were analysed by linear solvation free‐energy relationships (LSERs). A set of 68 neutral model compounds with known solvatochromic parameters and log P_oct values was investigated, allowing a regular and broad exploration of property space. The resulting solvatochromic equations clearly indicate that the three IAM stationary phases retain small neutral solutes by a balance of intermolecular forces closely resembling those underlying partitioning in octanol/H₂O and retention on a reversed‐phase LC‐ABZ HPLC column. For all systems, the solute's size and hydrogen‐bond‐acceptor basicity are the two predominant factors, whereas dipolarity/polarisability and hydrogen‐bond‐donor acidity play only minor roles.     

Heterocyclic nitro compounds

The acidity of a number of nitro derivatives of 1,2,4-triazole has been determined. The acidity indices correlate well with Hammett's _I and _meta constants and somewhat less well with the _para constants. The high values of show the great sensitivity of the system to the influence of substituents. The acidities of the conjugate acids of 3-nitro-1,2,4-triazole and its C- and N-methyl derivatives have also been determined. Hammett's postulate is not observed for these compounds, and the amide scale of acidity, H_A, is more suitable for calculating their acidity indices than H_O.For part III, see [1].     

Hydrogen bonding in polymer mixtures

The enthalpy–infrared frequency shift correlation for simple acids and bases is extended to study hydrogen bonding in polymer systems. The acidity of a polymer is calibrated by comparing the shifts in hydroxyl absorption frequency of the acidic polymer when mixed with a series of bases with the corresponding spectral shifts of known acids with the same bases. The basicity of a polymer is calibrated by measuring the hydroxyl frequency shifts of known acids when mixed with the basic polymer. For polymers containing carbonyl groups, the shift in carbonyl absorption is also a measure of basicity. The acidity and basicity constants obtained for polymers are in good agreement with the values for small-molecule analogs. The enthalpies of hydrogen bond formation in polymer mixtures are calculated from the acidity or basicity constants.     

Correlation of the RM-values of some heterocyclic bases,naphthols, naphthylamines and nitroanilines in adsorption and partition chromatography

Summary The correlation between the R_M-values measured in both adsorption and partition chromatography have been investigated for a number of substances such as heterocyclic bases, naphthols, naphthylamines, and isomeric nitroanilines. Aluminium oxide G, silica gel G, and magnesium silicate were used as the adsorbent and formamide, ethylene glycol, and a pH=2.4 buffer as the liquid stationary phase. Eleven solvents served as the mobile phase. It was found that for all compounds investigated the function is represented by a linear relationship corresponding to the equation . The constants a and b are characteristic for a compound in a given system of stationary phases (adsorbent and partitioning liquid). The values of constant a in a given system for a group of compounds are close to each other and the differences are due to differences in the structure of the molecules. Changes in the values of b when changing the adsorbent or the partitioning liquid can be used under certain conditions to characterize the molecular interaction between the sample and the stationary phases. It follows from these investigations that the linear correlation between the R_M-values measured in liquid adsorption and partition chromatography provides new possibilities in analysis as well as in physicochemical investigations.     

Photolabile Protecting Groups for Nucleosides: Mechanistic Studies of the 2‐(2‐Nitrophenyl)ethyl Group

The photochemistry of several 2‐(2‐nitrophenyl)ethyl‐caged compounds including caged thymidine nucleosides was studied by nanosecond laser flash photolysis and stationary illumination experiments with quantitative HPLC analysis for quantum yields and product distribution. Effects of solvent basicity and acidity were investigated by varying the H₂O content and HCl concentration, respectively, in MeCN/H₂O mixtures. For all compounds 1 – 7 investigated, intramolecular H abstraction by the nitro group from the exocyclic α‐position with respect to the aryl moiety was found to be the primary process. The protolytic dissociation equilibrium of the resulting aci‐nitro compound was kinetically characterized in the 0.1 – 10 μs time region. In general, two reaction channels compete for the aci‐nitro compound and its anion: β‐elimination of the caged compound occurs from the anion, while from the undissociated aci‐nitro compound, a nitrosobenzene derivative is formed with no release of the caged compound. The yield ratio of these two reaction channels can be controlled through shifts in the protolytic dissociation equilibrium of the aci‐nitro compound. In solutions with either low basicity (H₂O‐free MeCN) or high acidity (higher concentration of HCl in H₂O/MeCN), two as yet unidentified products are formed, each one specifically for one of the mentioned conditions.     

Retention behaviors of novel ionic liquid stationary phases and their selectivity for capillary gas chromatography

<正>One chloride-terminated ionic liquid(CTIL) and two hydroxyl-terminated ionic liquids(HTILs) were synthesized and used as stationary phases for capillary gas chromatography(CGC).Molecular interactions of these stationary phases were evaluated by Abraham solvation parameter model,indicating that the CTIL exhibits remarkably strong H-bond basicity and the HTILs possess both H-bond basicity and acidity.The molecular interactions were further confirmed by separation of a complex mixture consisting of ketones,aldehydes,esters,alcohols and aromatic compounds.It was found that the obtained solvation parameters correlate well with the chromatographic performances of the analytes in terms of elution order and resolution.The well correlated relationship between the solvation parameters and the selectivity of the CTIL and HTILs stationary phases is quite helpful in predicting and understanding the retention behaviors of different types of analytes on these stationary phases.     

Aminomethylphosphine Oxides: Synthesis,dissociation and stability constants, 31P{1H}-NMR-controlled titrations

The title compounds are prepared via Gabriel-synthesis following known or improved procedures. Novel methods using ³¹P{¹H}-NMR controlled titrations of aminomethylphosphine oxides lead to dissociation constants (given as basicity or acidity constants resp.) and to stability constants. Dynamically averaged and ion specific chemical shifts δ_P were derived.     

End-functionalized polyethylene oxide coated silica particles for packed capillary column supercritical fluid chromatography

Summary Polyethylene oxide (PEO)-based polymers with hydroxy, methoxy, and aminopropoxy terminal groups were coated on diol functionalized and hexamethyldisilazane end-capped silica particles. Proton-donor and proton-acceptor test solutes, including carboxylic acids, hydroxy-containing compounds, arylamines, and alkylamines were used to evaluate the chromatographic performances of these polymer coated particles under SFC conditions with neat CO₂ as mobile phase. It was found that the particles coated with hydroxy-terminated PEO were suitable for the separation of proton-donor compounds such as hydroxy-containing compounds and carboxylic acids, and the particles coated with aminopropoxy-terminated PEO could be used for the separation of amines. That is, the proton-accepting stationary phase is suitable for the separation of proton accepting solutes, including strong basic alkylamines (pK_b4), using neat CO₂ as mobile phase, while the protondonating stationary phase is suitable for the separation of proton-donating compounds such as carboxylic acids (pK_a4). Hydrogen bond basicity was found to be a critical factor for the chromatography of basic amines. Low volatility acidic and basic drugs were chromatographed using the new stationary phases. The stability of the PEO coated particles was determined by measuring the loss of organic carbon under SFC conditions. It was found that approximately 18 % of the coating (average molecular weight of 15,000) was washed out of the particles by supercritical CO₂ after 7 h at 350 atm and 50°C     

A periodic table for all-benzenoid hydrocarbons and enumerations of some polyrex isomers

A polyhex (benzenoid or coronoid) isomer is characterized by the formula C _n H _s , which pertains to the corresponding hydrocarbon. The periodic table for benzenoid hydrocarbons is revisited, and the construction of it is simplified. All-benzenoids are treated with respect to their isomers. A periodic table for all-benzenoid hydrocarbons is proposed, and an easy construction of it is described. It involves the process of super-circumscribing, a new concept. Numerical data are given for a number of isomer classes of benzenoids, all-benzenoids and single coronoids. These data represent a substantial amount of supplements to the previously known numbers of different polyhex isomers.     

Study of the basicity of some alkoxy derivatives of germanium employing infrared spectroscopy

Conclusions The basicity of the oxygen atom in a number of alkoxygermanes was determined. A comparison of the obtained results with the data on the basicity of the silicon and carbon compounds disclosed that germanium forms weaker d—p bonds with oxygen than does silicon.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2329–2331, October, 1971.     

Effect of the concentration of polybasic aminoanilides and aminobenzimidazoles on the acidity functionH 0 of aqueous solutions of HCl

The effect of the concentrations of the reactants and reaction products on the protonating ability of aqueous HCl is investigated in the example of the cyclization of polybasic aminoanilides to aminobenzimidazoles at 25°C and 50°C. It is established that the acidity functionH ₀ ^s of HCl solutions in organic-aqueous solvents of constant composition is equal toH ₀, the acidity function for an aqueous solution with the same concentration of HCl on the mole-ratio scale. This can be utilized for the quantitative prediction ofH ₀ ^s. The decrease in the basicity of indicators in mixed solvents is a consequence of the decrease in the activity coefficient of the unionized form of the base standardized to water _B. It is observed that not onlyH ₀ ^s but also the basicity constant of the reactant may vary during the reaction. The latter depends on the concentration of the reactant, as well as on the effect of the product concentration on the value of _B for the reactant.Deceased April 8, 1991.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 488–491, March, 1993.     

Structural and Catalytic Activity of V2O5-Supported on AlPO4 Catalysts

Summary. A series of AlPO₄-V₂O₅ (APV) systems with various vanadia amounts 1–30mol% were prepared by the impregnation method and calcinated at 400 and 600°C for 4h. The catalysts were characterized by TG/DTG, DSC, IR spectroscopy, XRD, N₂ adsorption, and electrical conductivity measurements. The surface acidity and basicity of the catalysts were studied by the dehydration-dehydrogenation of isopropyl alcohol and the adsorption of pyridine. The catalytic gas phase esterification of acetic acid with ethyl alcohol was carried out at 210°C in a flow system at 1atm using air as a carrier gas. The results showed that the catalysts calcinated at 400°C were active and selective towards the formation of ethyl acetate whereas the calcination of samples at 600°C led to a drastic reduction in both activity and selectivity. Good correlations were obtained between catalytic activities towards ester formation and acidity of the prepared catalysts.