Fast estimation of hydrogen-bonding donor and acceptor propensities: a GMIPp study

The suitability of the GMIPp energy functional as a fast, efficient method for estimating the hydrogen-bond donor and acceptor propensities of a wide variety of organic compounds is examined. Comparison of the GMIPp values is made with two experimental hydrogen-bond scales: i) the hydrogen-bond basicity scale for N-heteroaromatics in carbon tetrachloride, and ii) the hydrogen-bond acidities for NH/OH donors and hydrogen-bond basicities of N/O acceptors determined in 1,1,1-trichloroethane. Attention is paid to i) the reliability of semiempirical versus ab initio treatments of the quantum mechanical molecule, ii) the role of solvation, and iii) the effect of including the polarization energy component in the calculation of the GMIPp functional. The statistical analysis of the results reveals that the GMIP functional, which combines electrostatic and steric energy components, predicts with reasonable accuracy and computational efficiency the hydrogen-bond strength for a wide variety of compounds.     

Spectral analysis of naringenin deprotonation in aqueous ethanol solutions

The deprotonation of 5,7-dihydroxy-2-(4-hydroxyphenyl)chroman-4-one (naringenin) was studied in aqueous solutions of ethanol and 0.1 mol L^?1 sodium perchlorate at 25°C. The chemical species that contributed to deprotonation were evaluated together with their pure spectral characteristics and concentration profiles by some chemometric methods. The deprotonation constants assigned by pK ₁, pK ₂, and pK ₃ were determined by multivariate curve analysis of spectral data at different pcH values. The pure spectral analysis concordant with the theoretical prediction of deprotonation constants indicates that the acidity of hydroxyl groups in naringenin decreases in the order: 7-OH, 4′-OH, 5-OH. The effects of the solvent on deprotonation were analysed in terms of the linear solvation energy relationships using the model of Kamlet, Abboud, and Taft (KAT). Multiple linear regressions were aimed towards correlating the deprotonation constants with the microscopic parameters containing hydrogen-bond acidity (α), dipolarity/polarisability (π*), and hydrogen-bond basicity (β). The most significant parameter was found to be the hydrogen-bond acidity of binary mixtures.     

Solvatochromic relationship: Prediction of distribution of ionic solutes in aqueous two-phase systems

Partition ratios of several ionic compounds in 20 different polymer/polymer aqueous two-phase systems (ATPS) containing 0.15 M NaCl in 0.01 M phosphate buffer, pH 7.4, were determined. The differences between the electrostatic properties of the phases in all the ATPS were estimated from partitioning of the homologous series of dinitrophenylated-amino acids. Also the solvatochromic solvent parameters characterizing the solvent dipolarity/polarizability (π*), solvent hydrogen-bond donor acidity (α), and solvent hydrogen-bond acceptor basicity (β) of aqueous media were measured in the coexisting phases of the ATPS. The solute-specific coefficients for the compounds examined were determined by the multiple linear regression analysis using the modified linear solvation energy relationship equation. The minimal number of ATPS necessary for determination of the coefficients was established and 10 ATPS were selected as a reference ATPS set. The solute-specific coefficients values obtained with this reference set of ATPS were used to predict the partition ratios for the compounds in 10 ATPS not included in the reference set. The predicted partition ratios values were compared to those determined experimentally and found to be in good agreement. It is concluded that the presented model of solute–solvent interactions as the driving force for solute partitioning in polymer/polymer ATPS describes experimental observations with 90–95% accuracy.     

Chiral 2-(2-hydroxyaryl)alcohols (HAROLs) with a 1,4-diol scaffold as a new family of ligands and organocatalysts

Efficient and modular syntheses of chiral 2-(2-hydroxyaryl)alcohols (HAROLs), novel 1,4-diols carrying one phenolic and one alcohol hydroxyl group, have been developed which led to generation of a small library of structurally diverse HAROLs in enantiomerically pure form. Of the different HAROLs examined, a HAROL based on the indan backbone exhibited the highest activity and enantioselectivity in the 1,2-addition of certain organometallic compounds to aldehydes in the presence of Ti(OⁱPr)₄ (up to 97% y, 88% ee) and performed as a hydrogen-bond donor organocatalyst in the Morita-Baylis-Hillman reaction, promoted by trialkylphosphines.     

Nearcritical and supercritical ethanol as a benign solvent: polarity and hydrogen-bonding

Nearcritical (NC) and supercritical (SC) ethanol may offer novel media for both chemical reactions and separations as a replacement for environmentally undesirable organic solvents. We investigated the dipolarity/polarizability, hydrogen-bond donating acidity and accepting basicity in terms of Kamlet–Taft solvatochromism parameters π¹, α and β in saturated liquid ethanol from 25 to 225 °C and in gaseous and SC ethanol at 250 °C as a function of pressure. Reichardt’s E_T(30) scale was determined for ethanol under the same conditions. NC and SC ethanol has a wide range of solvent strength, which can be readily and continuously tuned by temperature and pressure. Liquid ethanol becomes nearly nonpolar as the temperature increases towards its critical point. The dipolarity/polarizability for SC ethanol ranges from gas-like to nonpolar liquid-like with increasing pressure. On the other hand, ethanol maintains significant hydrogen-bond donating acidity even under the supercritical conditions at 250 °C and at pressures up to 18.7 MPa. The hydrogen-bond accepting basicity, however, is considerably weakened at elevated temperatures. These well-established solvent parameters greatly improve our understanding of hot compressible ethanol, and allow us to explore the feasibility of using it in a variety of benign processes.     

R-基团相似性的比较

介绍了对化学取代基(R-基团)进行相似性比较的工作．每个R-基团主要依赖一些对反应影响较为明显,同时又便于计算的结构描述符来进行描述,例如电负性、氢键受体、氢键给体等参数．由于与反应核心相距过远的环境对反应的影响较小,R-基团相似性比较对象,就由每个R-基团截取从它与母体连接的位点出发向外扩展6层的子结构组成．在确立了对R-基团描述和距离限制的基础上,提出了用一个45维向量表示一个R-基团,并由化学结构的比较,转化为向量比较来实现R-基团相似性比较的方法．采用这一方法,成功地对大量的R-基团进行了相似性的区分,并实现了对未知化合物进行相似性预测的目标．     

Effect of pressure on the dimerization of benzoic acid in n-heptane

Ultraviolet absorption spectra of benzoic acid in n-heptane were measured at 25°C and up to 640 MPa. The reaction volume for the cyclic dimerization of benzoic acid was estimated as 0.4 ±0.9 cm³ mol⁻¹ from the pressure dependence of the dimerization constant. This is much more positive than those for noncylic hydrogen-bond formations which are from −3 to −6 cm³ mol⁻¹. It is ascribed to a compensation between a reduction in the volume accompanying the hydrogen-bond formation and an increase accompanying the cyclization. These two contributions to the reaction volume are estimated quantitatively.     

Establishing linear solvation energy relationships between VOCs and monolayer-protected gold nanoclusters using quartz crystal microbalance

Linear solvation energy relationships (LSERs) have been recognized as a useful model for investigating the chemical forces behind the partition coefficients between vapor molecules and absorbents. This study is the first to determine the solvation properties of monolayer-protected gold nanoclusters (MPCs) with different surface ligands. The ratio of partition coefficients/MPC density (K/ρ) of 18 volatile organic compounds (VOCs) for four different MPCs obtained through quartz crystal microbalance (QCM) experiments were used for the LSER model calculations. LSER modeling results indicate that all MPC surfaces showed a statistically significant (p < 0.05) preference to hydrogen-bond acidic molecules. Through dipole-dipole attraction, 4-methoxythiophenol-capped MPCs can also interact with polar organics (s = 1.04). Showing a unique preference for the hydrogen bond basicity of vapors (b = 1.11), 2-benzothiazolethiol-capped MPCs provide evidence of an intra-molecular, proton-shift mechanism on surface of nano-gold.     

Hybrid density functional theory investigation of a series of alloxan-based thiosemicarbazones and semicarbazones

Recently, the synthesis and the NMR characterization of a series of eight alloxan-based thiosemicarbazones and semicarbazones were reported. These compounds exhibit a strongly hydrogenbonded hydrazinic proton that is a part of a characteristic six-membered ring. This proton is highly deshielded and resonates far downfield in the proton NMR spectra. In this report, mPW1PW91/6-31+G(d,p) calculations have been used to investigate the structure and other molecular properties of this series of eight compounds. The relationship between the ¹H and ¹³C NMR chemical shifts and various geometric parameters was investigated, and linear relationships for proton peaks that are involved in hydrogen-bond interactions were found.     

Insight into the Way the Content of Biologically Active Compounds in Meadowsweet Inflorescences (Filipendula ulmaria (L.) Maxim.) Is Shaped by Phytosociological Habitats

A collection of herbs from the natural environment remains not only a source of raw material but also provides evidence of chemical differentiation of the local populations. This work aimed at performing a phytosociological analysis of seven different stands of meadowsweet (Filipendula ulmaria (L.) Maxim.) occurrence. A determination of total phenolic compounds and salicylates and the antioxidant activity of dried meadowsweet inflorescences (Flos ulmariae) was also performed. Active chemical compounds in F. ulmaria inflorescences were related to chemotype and diversified between investigated populations. Geographical distance and variation in phytosociological locations affected chemical composition in different ways, shaping the content of biochemical compounds crucial for herbal material quality. The obtained results can be a valuable indicator for Nexo and Baligród populations, which are good genetic material for research, breeding, and cultivation due to their biochemical composition, especially with respect to salicylates, as major compounds of determining market quality of Flos ulmariae.     

Car-Parinello molecular dynamics simulations of thionitroxide and S-nitrosothiol in the gas phase, methanol, and water—A theoretical study of S-nitrosylation

A dilemma about whether thionitroxide radical (RSNHO) or S-nitrosothiol (RSNO) is observed in protein S-nitrosylation has arisen recently. To illustrate the effect of chemical environment on these structures, this paper presents quantum mechanical molecular dynamics of thionitroxide, and cis-and trans-S-nitrosothiols in the gas phase, methanol, and water. By using Car-Parrinello molecular dynamics (CPMD), we have observed that there is free rotation about the S-N bond at 300 K in thionitroxide, but no such rotation is observed for S-nitrosothiol. The C-S-N-O torsion angle distribution in thionitroxide is s-ignificantly dependent upon the surrounding environment, leading to either gauche-, cis-, or trans-conformation. In the case of S-nitrosothiol the C-S-N-O plane is twisted slightly by 5°-15° in the cis-isomer, while the periplanar structure is well-retained in the trans-isomer. The calculated results are in agreement with the X-ray crystallographic data of small molecular RSNO species. Interestingly, for both compounds, the CPMD simulations show that solvation can cause a decrease in the S-N bond length. Moreover, the oxygen atom of thionitroxide is found to be a good hydrogen-bond acceptor, forming an oxyanion-hole-like hydrogen bonding network.     

Vibrational spectroscopic study of o-, m- and p-hydroxybenzylideneaminoantipyrines

Three structurally similar antipyrine derivatives of o-hydroxybenzylideneaminoantipyrine (o-HBAP), m-hydroxybenzylideneaminoantipyrine (m-HBAP) and p-hydroxybenzylideneaminoantipyrine (p-HBAP) were characterized by FT-IR, FT-Raman experimental techniques and density functional theoretical (DFT) calculations. The comparisons between the calculated and experimental results covering molecular structures, assignments of fundamental vibrational modes and thermodynamic properties were investigated. The optimized molecular geometries agree well with the corresponding experimental values by comparing with the XRD data. The comparisons and assignments of the vibrational frequencies indicate that the experimental spectra also coincide satisfactorily with those of theoretically simulated spectrograms except the hydrogen-bond coupling infrared vibrations, and compounds can be distinguished by the IR and Raman spectra due to the differences of the hydroxyl-substituted positions and molecular packing, and the strong Raman scattering activities of the compounds are tightly relative to the molecular conjugative moieties linked through the Schiff base imines. The thermodynamic functions and their correlations with temperatures were also obtained from the theoretical harmonic frequencies.