• Volume 127, Issue 6

June 2015,   pages  978a-1144

• Editorial Board

• Notes on the preparation of papers

• A mixed-valent cyclodiphosphazane: Transition metal chemistry and cis/trans isomerisation

The hydrolysis of cis-{ClP(𝜇-N$^t$Bu)2P(NH$^t$Bu)} (1) produced a mixed PIII/PV derivative of cyclodiphosphazane, cis-{($^t$BuNH)P(𝜇-N$^t$Bu)2P(O)H} (2). The treatment of 2 with elemental selenium resulted in the formation of the monoselenide, trans-{($^t$BuNH)P(Se)(𝜇-N$^t$Bu)2P(O)H} (3) in good yield. The reactions of two equivalent of 2 with [Pd(𝜇-Cl)(𝜂3-C3H5)]2 or [Ru(𝜂6-𝑝-cymene)(𝜇-Cl)Cl]2 in dichloromethane afforded corresponding mononuclear complexes, [(𝜂3-C3H5)PdCl{($^t$BuNH)P(𝜇-N$^t$Bu)2P(O)H}] (4) and [((𝜂6-𝑝-cymene)RuCl2){($^t$BuNH)P(𝜇-N$^t$Bu)2P(O)H}] (5). The treatment of 2 with M(COD)Cl2 (M = Pd and Pt) in dichloromethane at room temperature gave [MCl2{($^t$BuNH)P(𝜇-N$^t$Bu)2P(O)H}2] (6 M = Pd; 7 M = Pt) in good yield. Owing to the cis/trans isomerisation of the cyclodiphosphazane rings, the complexes 6 and 7 exist as a mixture of two isomers. Various NMR spectroscopic techniques were employed for structural elucidation. The molecular structures of 5 and 7 were established by single crystal X-ray crystallographic studies.

• SiO2-Diphenic acid: An efficient and recyclable heterogeneous catalyst for one-pot synthesis of bis-(indolyl)methane derivatives in liquid phase

An eco-friendly and expedient procedure for one-pot synthesis of is-(indolyl)methane derivatives via electrophilic substitution reaction at C-3 position of indole with various aldehydes has been developed by using silica-diphenic acid as a novel heterogeneous catalyst. This method has various promising features such as short reaction time, easy work-up procedure, good yield of products and remarkable activity and selectivity of the catalyst.

• A comprehensive study of the structure, tautomeric properties, and conformational flexibility of 3-Hydroxy-propeneselenal

In the present work, a conformational analysis of 3-Hydroxy-propeneselenal is performed using several computational methods, including HF, DFT (B3LYP), and G2MP2 levels of theory. The relative electronic energies, the molecular structure, and intramolecular hydrogen bond energies are reported. Twenty different conformers were obtained, the most stable ones being planar. The conformational preference of this molecule was found to be mainly determined by the formation of Se…H-O and Se-H…O intramolecular hydrogen bonds, which are assisted by 𝜋-electron resonance. The atoms in molecules (AIM) theory of Bader, which is based on topological properties of the electron density, was used to analyze critical points and to study the nature of hydrogen bonds in these systems. NMR and natural bond orbital (NBO) analyses were also performed for a better understanding of the nature of intramolecular interactions in 3-Hydroxy-propeneselenal. Furthermore, calculations for all the possible conformations of the title compound in solution were also carried out at the B3LYP/6-311++G(d,p) level of theory (in three models such as polarizable continuum model (PCM), IEFPCM, and self−consistent isodensity polarized continuum model (SCIPCM).

• A theoretical study of solvent effects on the characteristics of the intramolecular hydrogen bond in Droxidopa

The molecular structures and intramolecular hydrogen bond of Droxidopa have been investigated with density functional theory. It is found that strong hydrogen bonds (O–H…N and O…H–O) exist in the title compound. These hydrogen bonds play essential roles in determining conformational preferences and energy, which would have important effects in biological activity mechanisms that will strongly influence its characteristics in solution. A computational study of a representative number of actual and model structures was carried out in five solvents with different polarities and different types of interactions with solute molecules: water, ethanol, carbon tetrachloride, dimethyl sulfoxide, and tetrahydrofuran, utilizing the polarizable continuum model (PCM) model. The calculations were performed at the B3LYP/6-311++G(d,p) level of theory. In addition, the topological properties of the electron density distributions for O–H…N(O) intramolecular hydrogen bond were analyzed in terms of the Bader’s theory of atoms in molecules. Furthermore, the analyses of different hydrogen bonds in this molecule by quantum theory of natural bond orbital (NBO) methods support the density functional theory (DFT) results.

• Theoretical study on mechanism, kinetics, and thermochemistry of the gas phase reaction of 2,2,2-trifluoroethyl butyrate with OH radicals at 298 K

A theoretical investigation has been carried out on the mechanism, kinetics, and thermochemistry of gas-phase reaction of 2,2,2-trifluoroethyl butyrate (TFEB, CH3CH2CH2C(O)OCH2CF3) with OH radicals using a modern DFT functional. The involvement of pre- and post-reactive complexes was explored and the reaction profiles were modeled. Energetic calculations were performed using the M06-2X/6-31+G(d,p) method. The intrinsic reaction coordinate (IRC) calculation has been performed to confirm the smooth transition from the reactant to product through the respective transition state. It has been found that the dominant path of the H-atom abstraction takes place from the –CH2- position, which is attached with the methyl group at the one end of TFEB. Theoretically calculated rate constant at 298 K using canonical transition state theory (CTST) is found to be in reasonable agreement with the experimental data. Using group-balanced isodesmic procedure, the standard enthalpy of formation for TFEB is reported for the first time. The branching ratios of the different reaction channels are also determined. The atmospheric lifetime of TFEB is determined to be 6.8 days.

• Mathematical description of the nonlinear chemical reactions with oscillatory inflow to the reaction field

In this paper the arduous attempt to find a mathematical solution for the nonlinear autocatalytic chemical processes with a time-varying and oscillating inflow of reactant to the reaction medium has been taken. Approximate analytical solution is proposed. Numerical solutions and analytical attempts to solve the non-linear differential equation indicates a phase shift between the oscillatory influx of intermediate reaction reagent 𝑋 to the medium of chemical reaction and the change of its concentration in this medium. Analytical solutions indicate that this shift may be associated with the reaction rate constants 𝑘1 and 𝑘2 and the relaxation time 𝜏. The relationship between the phase shift and the oscillatory flow of reactant 𝑋 seems to be similar to that obtained in the case of linear chemical reactions, as described previously, however, the former is much more complex and different. In this paper, we would like to consider whether the effect of forced phase shift in the case of nonlinear and non-oscillatory chemical processes occurring particularly in the living systems have a practical application in laboratory.

• ${\rm X-H}\cdots {\rm C}$ hydrogen bonds in 𝑛-alkane-${\rm HX} ({\rm X} = {\rm F, OH})$ complexes are stronger than ${\rm C-H}· · ·{\rm X}$ hydrogen bonds

Computational study of ${\rm X-H}\cdots {\rm C}$ and ${\rm C-H}\cdots{\rm X}$ hydrogen bonds in n-alkane-${\rm HX}$ complexes (${\rm X} = {\rm F,OH}$, alkane=propane, butane, pentane) has been carried out in this work. Ab initio and density functional theories were used for this study. For $n$-alkane-${\rm H}$2${\rm O}$ complexes both ${\rm O} \cdots {\rm H-C}$ and ${\rm O-H}\cdots {\rm C}$ hydrogen bonded complex have been found, while for 𝑛-alkane-${\rm HF}$ complexes, our attempt to optimize ${\rm F}\cdots {\rm H-C}$ ${\rm H}$-bond was not successful. Like most of the hydrogen bonded systems, strong correlation between binding energy and stretching frequency of ${\rm H-F}$ and ${\rm O-H}$ stretching mode was observed. The values of electron density and Laplacian of electron density are within the accepted range for hydrogen bonds. In all these cases, ${\rm X-H}\cdots {\rm C}$ hydrogen bonds are found to be stronger than ${\rm C-H}\cdots {\rm X}$ hydrogen bonds.

• B(C6F5)3 catalyzed one-pot three-component Biginelli reaction: An efficient and environmentally benign protocol for the synthesis of 3,4-dihydropyrimidin-2(1𝐻)-ones/thiones

Tris(pentafluorophenyl)borane catalyzed, one-pot, simple, efficient and environmentally benign protocol for the synthesis of dihydropyrimidinones/thiones via Biginelli reaction has been described. The main highlights of the present protocol is low catalyst loading, low toxicity, compatibility with acid-labile-protecting groups, short reaction time, consistently excellent yields and simple reaction/workup procedure. Moreover, the applicability of the present methodology for large-scale synthesis of monastrol highlights its potential for bulk synthesis.

• Solvothermal synthesis of high molecular weight dithienogermole containing conjugated polymers

Dithienogermole-diphthalimide, a new molecule, and dithienogermole-dithiadiazole alternate polymers were synthesized by the solvothermal method. Optical properties and molecular weight were investigated by UV–Vis absorption spectroscopy and Gel Permeation Chromatography. Compared with the results achieved by the previously reported normal heating method, these polymers reported here exhibited similar optical properties and possess higher molecular weight.

• N, N′-Olefin functionalized Bis-Imidazolium Pd(II) chloride N-Heterocyclic carbene complex builds a supramolecular framework and shows catalytic efficacy for C–C' coupling reactions

The ligand 3,3′-(𝑝-phenylenedimethylene)bis{1-(2-methylallyl)} imidazolium bromide (1) and its Palladium(II) N-heterocyclic carbene (NHC) complex (3) has been synthesized and characterized by several spectroscopic techniques and the solid-state structure of 3 has been determined by single crystal X-ray diffraction studies. The Pd(II) complex possesses ring head to tail 𝛱–𝛱 stacking interactions (3.767 A$^{\circ}$) through imidazole rings. Complex 3 catalyzes Suzuki-Miyaura C–C' coupling reaction. DFT calculations have been used to understand the HOMO/LUMO energy and hence the stability and reactivity of Pd(II) complex in syn and anti-configuration.

• Thermodynamic modeling of naringenin protonation equilibria in NaClO4 aqueous solutions by specific ion interaction theory and Pitzer equations

The protonation equilibria for the flavonoid naringenin were studied at 25$^{\circ}$C using combined multiwavelength spectroscopic and pH-potentiometric methods as a function of the ionic strength. Over a wide range of ionic strengths, 0.10–3.00 mol dm$^{−3}$, the investigation was performed in different aqueous solutions of NaClO4 as the background electrolyte. The dependence on ionic strength of protonation constants was modeled by the Brönsted–Guggenheim–Scatchard Specific Ion Interaction Theory (SIT) and Pitzer approaches. Apart from the values of SIT interaction coefficients and Pitzer parameters, the protonation constants at infinite dilution (zero ionic strength) were obtained. On the basis of these results, it was found that Pitzer mode l gives more satisfactory results rather than the SIT method.

• Linear sweep anodic stripping voltammetry: Determination of Chromium (VI) using synthesized gold nanoparticles modified screen-printed electrode

A highly sensitive electrochemical sensor has been constructed for determination of Cr(VI) with the lowest limit of detection (LOD) reported to date using gold nanoparticles (AuNPs) modified screen-printed electrode (SPE). The modification of SPE by casting pure AuNPs increases the sensitivity for detection of Cr(VI) ion using anodic stripping voltammetry. Cr(VI) ions are reduced to chromium metal on SPE-AuNPs by applying deposition potential of –1.1 V for 180 s. Afterwards, the oxidation peak current of chromium is obtained by linear sweep voltammetry in the range of −1.0 V to 0.2 V. Under the optimized conditions (HClO4, 0.06 mol L$^{−1}$; deposition potential, –1.1 V; deposition time, 180s; scan rate, 0.1 V s$^{−1}$), the limit of detection (LOD) was 1.6 pg mL$^{−1}$. The fabricated electrode was successfully used for detection of Cr(VI) in tap and seawater.

• Observation of the Unusual Aggregation Kinetics of Colloidal Minerals in Acidic Solutions

Hofmeister (Specific ion) effects have been considered as important to chemical science as Mendel’s work was to genetics. In this work, the aggregation kinetics of montmorillonite colloids in H+, Ag+, NH$^+_4$, K+ and Na+ solutions were measured in situ, detecting the unusual kinetics and ion specificity for H+. Activation energies that can quantitatively estimate the underlying specific ion effects change in the order of H+ &lt; Ag+ &lt; NH$^+_4$ &lt; K+ &lt; Na+. Meanwhile, it was found that although the aggregation of montmorillonite colloids with lower particle densities results in higher activation energies, Hofmeister series will not be affected. It was sufficiently testified that interaction energies of colloidal particles with adsorbed ions show fine correlation with activation energies for colloidal aggregation, and larger interaction energy corresponds to lower activation energy. An attempt was made to quantitatively estimate the ion specificity for H+, and it was substantialized that the unusual ion specificity of H+ is caused by steric effect.

• Simultaneous acquisition of three NMR spectra in a single experiment for rapid resonance assignments in metabolomics

NMR-based approach to metabolomics typically involves the collection of two-dimensional (2D) heteronuclear correlation spectra for identification and assignment of metabolites. In case of spectral overlap, a 3D spectrum becomes necessary, which is hampered by slow data acquisition for achieving sufficient resolution. We describe here a method to simultaneously acquire three spectra (one 3D and two 2D) in a single data set, which is based on a combination of different fast data acquisition techniques such as G-matrix Fourier transform (GFT) NMR spectroscopy, parallel data acquisition and non-uniform sampling. The following spectra are acquired simultaneously: (1) $^{13}$C multiplicity edited GFT (3,2)D HSQC-TOCSY, (2) 2D [$^1$H-$^1$H] TOCSY and (3) 2D [$^{13}$C-$^1$H] HETCOR. The spectra are obtained at high resolution and provide high-dimensional spectral information for resolving ambiguities. While the GFT spectrum has been shown previously to provide good resolution, the editing of spin systems based on their CH multiplicities further resolves the ambiguities for resonance assignments. The experiment is demonstrated on a mixture of 21 metabolites commonly observed in metabolomics. The spectra were acquired at natural abundance of $^{13}$C. This is the first application of a combination of three fast NMR methods for small molecules and opens up new avenues for high-throughput approaches for NMR-based metabolomics.

• Computational studies on 1,2,4-Triazolium-based salts as energetic materials

The results of the computational studies performed on 1,2,4-triazolium cation-based salts designed by pairing it with energetic nitro-substituted 5- membered N-heterocyclic anions such as 5-nitrotetrazolate, 3,5-dinitrotriazolate, and 2,4,5 trinitroimidazolate are reported. Condensed phase heats of formation of the designed ionic salts and their thermodynamic and energetic properties have also been calculated. The results show that these salts are potential energetic materials and possess high positive heats of formation. The detonation velocity, D, and detonation pressure, P, have been calculated using the Kamlet-Jacobs equation and found to be 7–8 km/s and 25–29 GPa, respectively. These values fall in the range of the criteria to designate them as high-energy-density materials. Nucleus independent chemical shift (NICS) studies performed on the designed molecules show that these salts are stable in nature.

• Effect of external electric field on Cyclodextrin-Alcohol adducts: A DFT study

Effect of external electric fields on the interaction energy between cyclodextrin and alcohol was analyzed in the light of density functional theory (DFT) and density functional reactivity theory (DFRT). Stability of the cyclodextrin-alcohol adducts was measured in terms of DFT based reactivity descriptor, global hardness, electrophilicity, and energy of the HOMO. Stability of adducts was observed to be sensitive towards the strength as well as direction of the applied external electric field. In addition, reactivity pattern follows the maximum hardness and minimum electrophilicity principles.

• Designing pH-responsive and dielectric hydrogels from cellulose nanocrystals

We report the fabrication and characterization of a pH-responsive hydrogel with improved mechanical and dielectric properties from cellulose nanocrystals. X-ray diffraction and SEM observations were used to analyze the sample morphology. The resulting pH detector exhibits a pronounced change in their swelling index in response to variation in pH. It was used singly and in combination with other nanomaterials to optimize smart material designs. The applications of the developed material are anticipated in chemical, environmental and biological systems.

• Intramolecular hydrogen bond: Can it be part of the basis set of valence internal coordinates in normal mode analysis?

It has been shown earlier1 that the relaxed force constants (RFCs) could be used as a measure of bond strength only when the bonds form a part of the complete valence internal coordinates (VIC) basis. However, if the bond is not a part of the complete VIC basis, its RFC is not necessarily a measure of bond strength. Sometimes, it is possible to have a complete VIC basis that does not contain the intramolecular hydrogen bond (IMHB) as part of the basis. This means the RFC of IMHB is not necessarily a measure of bond strength. However, we know that IMHB is a weak bond and hence its RFC has to be a measure of bond strength. We resolve this problem of IMHB not being part of the complete basis by postulating `equivalent’ basis sets where IMHB is part of the basis at least in one of the equivalent sets of VIC. As long as a given IMHB appears in one of the equivalent complete VIC basis sets, its RFC could be used as a measure of bond strength parameter.

• Half-sandwich pentamethylcyclopentadienyl group 9 metal complexes of 2-aminopyridyl ligands: Synthesis, spectral and molecular study

Thereaction of [Cp*M(𝜇-Cl)Cl]2 (M = Rh, Ir) with 2-aminopyridyl based ligands lead to the formation of mononuclear neutral complexes of general formula [Cp*MCl2(L)] {where L1= 2-aminopyridine, L2= 2-amino-3-picoline, L3= 2-amino-3-nirtopyridine, and L4= 2-amino-3-pyridine carboxyaldehyde}. The complexes have been characterized by FT-IR, UV-Vis, $^1$H-$^{13}$C NMR and mass spectroscopic methods. X-ray crystallographic studies of the complexes have shown typical piano-stool geometry around the metal centre in which 2-aminopyridyl ligand acts as an N-monodentate ligand and the amino functionality is not involved in metal coordination. The intra/intermolecular arrangement is due to hydrogen bonding.

• # Journal of Chemical Sciences

Volume 132, 2019
All articles
Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019