Recent NMR Methodological Developments for Chiral Analysis in Isotropic Solutions

Chiral auxiliaries are used for NMR spectroscopic study of enantiomers. Often the presence of impurities, severe overlap of peaks, excessive line broadening and complex multiplicity pattern restricts the chiral analysis using 1D H-1 NMR spectrum. There are few approaches to resolve the overlapped peaks. One approach is to use suitable chiral auxiliary, which induces large chemical shift difference between the discriminated peaks (Delta delta(R,S)) and minimize the overlap. Another direction of approach is to design appropriate NMR experiments to circumvent some of these problems, viz, enhancing spectral resolution, unravelling the superimposed spectra of enantiomers, and reduction of spectral complexity. Large number of NMR techniques, such as two dimensional selective F-1 decoupling, RES-TOCSY, multiple quantum detection, frequency selective homodecoupling, band selective homodecoupling, broadband homodecoupling, etc. have been reported for such a purpose. Many of these techniques have aided in chiral analysis for molecules of diverse functionality in the presence of chiral auxiliaries. The present review summarizes the recently reported NMR experimental methodologies, with a special emphasis on the work carried out in authors' laboratory.

Transverse single spin asymmetry in e plus p up arrow -> e plus J/psi plus X and Q(2) evolution of Sivers function-II

We present estimates of single spin asymmetry in the electroproduction of J/psi taking into account the transverse momentum-dependent (TMD) evolution of the gluon Sivers function. We estimate single spin asymmetry for JLab, HERMES, COMPASS and eRHIC energies using the color evaporation model of J/psi. We have calculated the asymmetry using recent parameters extracted by Echevarria et al. using the Collins-Soper-Sterman approach to TMD evolution. These recent TMD evolution fits are based on the evolution kernel in which the perturbative part is resummed up to next-to-leading logarithmic accuracy. We have also estimated the asymmetry by using parameters which had been obtained by a fit by Anselmino et al., using both an exact numerical and an approximate analytical solution of the TMD evolution equations. We find that the variation among the different estimates obtained using TMD evolution is much smaller than between these on one hand and the estimates obtained using DGLAP evolution on the other. Even though the use of TMD evolution causes an overall reduction in asymmetries compared to the ones obtained without it, they remain sizable. Overall, upon use of TMD evolution, predictions for asymmetries stabilize.

Charge Transfer Induces Formation of Stimuli-Responsive, Chiral, Cohesive Vesicles-on-a-String that Eventually Turn into a Hydrogel

A charge transfer (CT) mediated two-component, multistimuli responsive supergelation involving a L-histidine-appended pyrenyl derivative (PyHisOMe) as a donor and an asymmetric bolaamphiphilic naphthalene-diimide (Asym-NDI) derivative as an acceptor in a 2: 1 mixture of H2O/MeOH was investigated. Asym-NDI alone self-assembled into pH-responsive vesicular nanostructures in water. Excellent selectivity in CT gel formation was achieved in terms of choosing amino acid appended pyrenyl donor scaffolds. Circular di-chroism and morphological studies suggested formation of chiral, interconnected vesicular assemblies resembling ``pearls-on-a-string'' from these CT mixed stacks. XRD studies revealed the formation of monolayer lipid membranes from these CT mixed stacks that eventually led to the formation of individual vesicles. Strong cohesive forces among the interconnected vesicles originate from the protrusion of the oxyethylene chains from the surfaces of the chiral vesicles.

Chiral discrimination of secondary alcohols and carboxylic acids by NMR spectroscopy

The manuscript reports two novel ternary ion-pair complexes, which serve as chiral solvating agents, for enantiodiscrimination of secondary alcohols and carboxylic acids. The protocol for discrimination of secondary alcohols is designed by using one equivalent mixture each of enantiopure mandelic acid, 4-dimethylaminopyridine (DMAP) and a chiral alcohol. For discrimination of carboxylic acids, the ternary complex is obtained by one equivalent mixture each of enantiopure chiral alcohol, DMAP and a carboxylic acid. The designed protocols also permit accurate measurement of enantiomeric composition. Copyright (C) 2014 John Wiley & Sons, Ltd.

Small signal Nonquasi-Static Model for Common Double-Gate MOSFETs Adapted to Gate Oxide Thickness Asymmetry

We present a physics-based closed form small signal Nonquasi-static (NQS) model for a long channel Common Double Gate MOSFET (CDG) by taking into account the asymmetry that may prevail between the gate oxide thickness. We use the unique quasi-linear relationship between the surface potentials along the channel to solve the governing continuity equation (CE) in order to develop the analytical expressions for the Y parameters. The Bessel function based solution of the CE is simplified in form of polynomials so that it could be easily implemented in any circuit simulator. The model shows good agreement with the TCAD simulation at-least till 4 times of the cut-off frequency for different device geometries and bias conditions.

Disappearance of electron-hole asymmetry in nanoparticles of Nd1-xCaxMnO3(x=0.6, 0.4): magnetization and electron paramagnetic resonance evidence

We study and compare magnetic and electron paramagnetic resonance behaviors of bulk and nanoparticles of Nd1-xCaxMnO3 in hole doped (x = 0.4; NCMOH) and electron doped (x = 0.6; NCMOE) samples. NCMOH in bulk form shows a complex temperature dependence of magnetization M(T), with a charge ordering transition at similar to 250 K, an antiferromagnetic (AFM) transition at similar to 150 K, and a transition to a canted AFM phase/mixed phase at similar to 80 K. Bulk NCMOE behaves quite differently with just a charge ordering transition at similar to 280 K, thus providing a striking example of the so called electron-hole asymmetry. While our magnetization data on bulk samples are consistent with the earlier reports, the new results on the nanoparticles bring out drastic effects of size reduction. They show that M(T) behaviors of the two nanosamples are essentially similar in addition to the absence of the charge order in them thus providing strong evidence for vanishing of the electron-hole asymmetry in nanomanganites. This conclusion is further corroborated by electron paramagnetic resonance studies which show that the large difference in the ``g'' values and their temperature dependences found for the two bulk samples disappears as they approach a common behavior in the corresponding nanosamples. (C) 2015 AIP Publishing LLC.

RNA nucleosides as chiral sensing agents in NMR spectroscopy

The study reports chiral sensing properties of RNA nucleosides. Adenosine, guanosine, uridine and cytidine are used as chiral derivatizing agents to differentiate chiral 1 degrees-amines. A three component protocol has been adopted for complexation of nucleosides and amines. The chiral differentiating ability of nucleosides is examined for different amines based on the H-1 NMR chemical shift differences of diastereomers (Delta delta(R,S)). Enantiomeric differentiation has been observed at multiple chemically distinct proton sites. Adenosine and guanosine exhibit large chiral differentiation (Delta delta(R,S)) due to the presence of a purine ring. The diastereomeric excess (de) measured by using adenosine is in good agreement with the gravimetric values.

Single Spin Asymmetry in Charmonium Production

We present estimates of single spin asymmetry (SSA) in the electroproduction of taking into account the transverse momentum dependent (TMD) evolution of the gluon Sivers function and using Color Evaporation Model of charmonium production. We estimate SSA for JLab, HERMES, COMPASS and eRHIC energies using recent parameters for the quark Sivers functions which are fitted using an evolution kernel in which the perturbative part is resummed up to next-to-leading logarithms accuracy. We find that these SSAs are much smaller as compared to our first estimates obtained using DGLAP evolution but are comparable to our estimates obtained using TMD evolution where we had used approximate analytical solution of the TMD evolution equation for the purpose.

Ag+-induced reverse vesicle to helical fiber transformation in a self-assembly by adjusting the keto-enol equilibrium of a chiral salicylideneaniline

A new chiral amphiphilic salicylideneaniline bearing a terminal pyridine was synthesized. It formed reverse vesicles in toluene. The addition of Ag+, however, reversibly transforms these reverse vesicles into left-handed nanohelices accompanied by spontaneous gel formation at room temperature.

Efficient and practical synthesis of modular chiral beta-organochalcogeno amines, ArYCH2CH(R)NH2, and single crystal structures of (S) - MsOCH2CH(Bz)NH3+ center dot Cl- and (R)-MsOCH2CH(Ph)NH3+ center dot Cl-

Modular chiral I3-organochalcogeno amines, ArYCH2CH(R)NH2 (4a-4g) where R = Me, Bz, Ph; and ArY = PhS, BzSe and 4-MeOC6H4Te respectively have been synthesized and characterized. Compounds 4a-4g were synthesized (Method II) from chiral aminoalkyl 13-methanesulfonate hydrochlorides, MsOCH2CH(R)NH3+ center dot Cl- (2a-2c) through nucleophilic displacement of MsO- with organochalcogenolate (ArY-). In another attempt (Method I) chiral beta-organotelluro amines (4a-4c) were prepared by deprotection of chiral N-boc I3-organotelluro amides, 4-MeOC6H4TeCH2CH(R)NH-Boc (3a-3c), which in turn, 13,-,1 were made from chiral N-boc 13-methanesulfonate amides (la-lc) and ArTeNa. 1H, and FTIR spectra of all the compounds (3a-3c and 4a-4g) were characteristic. The composition of 3a-3c was determined by elemental analysis. The a]TD values of 3b-3c and 4a-4g were determined. The single crystal structures of (S)-2b and (R)-2c were determined by X-Ray diffraction studies. Both (S)-2b and (R)2c were crystallized in orthorhombic system and the Flack parameter x was found 0.08(12) and 0.00(2) respectively. The crystal of (S)-2b contain two asymmetric units with gauche (A) and staggered (B) conformations. There are NH Cl-, NH-O and CH-O intra and intermolecular secondary interactions in (S)-2b and (R)-2c resulting in supramolecular structures. (C) 2015 Elsevier By. All rights reserved.

Electron-hole asymmetry in the electron-phonon coupling in top-gated phosphorene transistor

Using in situ Raman scattering from phosphorene channel in an electrochemically top-gated field effect transistor, we show that phonons with A(g) symmetry depend much more strongly on concentration of electrons than that of holes, wheras phonons with B-g symmetry are insensitive to doping. With first-principles theoretical analysis, we show that the observed electon-hole asymmetry arises from the radically different constitution of its conduction and valence bands involving pi and sigma bonding states respectively, whose symmetry permits coupling with only the phonons that preserve the lattice symmetry. Thus, Raman spectroscopy is a non-invasive tool for measuring electron concentration in phosphorene-based nanoelectronic devices.

Time-Resolved Resonance Raman Spectroscopic Studies on the Radical Anions of Menaquinone and Naphthoquinone

Quinones and their radical ion intermediates have been much studied by vibrational spectroscopy to understand their structure-function relationships in various biological processes. In this paper, we present a comprehensive analysis of vibrational spectra in the structure-sensitive region of both the naphthoquinone (NQ) and 2-methyl-1,4-naphthoquinone (MQ, menaquinone) radical anions using time-resolved resonance Raman and ab initio studies. Specific vibrational mode assignments have been made to all the vibrational frequencies recorded in the experiment. It is observed that the carbonyl and C-C stretching frequencies show considerable coupling in NQ and MQ radical anions. Further, the asymmetric substitution present in MQ with respect to NQ shows important signatures in the radical anion spectrum. It is concluded that assignments of vibrational frequencies of asymmetrically substituted quinones must take into consideration the influence of asymmetry on structure and reactivity.

First donor-acceptor interaction promoted gelation of organic fluids

In recent years there has been considerable interest in developing new types of gelators of organic solvents.1 Despite the recent advances, a priori design of a gelator for gelling a given solvent has remained a challenging task. Various noncovalent interactions like hydrogen-bonding,2 metal coordination3 etc. have been used as the driving force for the gelation process. A special class of cholesterol-based gelators were reported by Weiss,4 and by Shinkai.5 Gels derived from these molecules have been used for chiral recognition/sensing,6 for studying photo- and metal-responsive functions,7 and as templates to make hollow fiber silica.8 Other types of organogels have been used for designing polymerized 9 and reverse aerogels,10 and in molecular imprinting.11 Hanabusa’s group has recently reported organogels with a bile acid derivative.12 This has prompted us to disclose our results on a novel electron donor–acceptor (EDA) interaction mediated two-component13 gelator system based on the bile acid14 backbone.

Constraining the low-energy pion electromagnetic form factor with space-like and phase of time-like data

The Taylor coefficients c and d of the EM form factor of the pion are constrained using analyticity, knowledge of the phase of the form factor in the time-like region, 4m(pi)(2) <= t <= t(in) and its value at one space-like point, using as input the (g - 2) of the muon. This is achieved using the technique of Lagrange multipliers, which gives a transparent expression for the corresponding bounds. We present a detailed study of the sensitivity of the bounds to the choice of time-like phase and errors present in the space-like data, taken from recent experiments. We find that our results constrain c stringently. We compare our results with those in the literature and find agreement with the chiral perturbation-theory results for c. We obtain d similar to O(10) GeV-6 when c is set to the chiral perturbation-theory values.

Enantiospecific total synthesis of ent-10, 11-thapsan-10-ol

First enantiospecific total synthesis of optical antipode of the sesquiterpene 10,11-epoxythapsan-10-ol has been described. (R)-Carvone has been employed as the chiral starting material and a combination of intramolecular alkylation and Criegee fragmentation are employed for intramolecular stereospecific transfer of the chirality. An intramolecular diazoketone cyclopropanation and regioselective cyclopropane ring cleavage reactions have been employed for the creation of the three requisite contiguous quaternary carbon atoms.