Carbon-13 Nuclear Magnetic Resonance Spectra Research Articles

Cross-Modal Retrieval Between 13C NMR Spectra and Structures Based on Focused Libraries.

Library matching by comparing carbon-13 nuclear magnetic resonance (13C NMR) spectra with spectral data in the library is a crucial method for compound identification. In our previous paper, we introduced a deep contrastive learning system called CReSS, which used a library that contained more structures. However, CReSS has two limitations: there were no unknown structures in the library, and a redundant library reduces the structure-elucidation accuracy. Herein, we replaced the oversize traditional libraries with focused libraries containing a small number of molecules. A previously generative model, CMGNet, was used to generate focused libraries for CReSS. The combined model achieved a Top-10 accuracy of 54.03% when tested on 6,471 13C NMR spectra. In comparison, CReSS with a random reference structure library achieved an accuracy of only 9.17%. Furthermore, to expand the advantages of the focused libraries, we proposed SAmpRNN, which is a recurrent neural network (RNN). With the large focused library amplified by SAmpRNN, the structure-identification accuracy of the model increased in 70.0% of the 30 random example cases. In general, cross-modal retrieval between 13C NMR spectra and structures based on focused libraries (CFLS) achieved high accuracy and provided more accurate candidate structures than traditional libraries for compound identification.

Construction and Single-Crystal Structures of N-Isoxazolin-5-ylcarbonylindole Derivatives, and Their Pesticidal Activities and Toxicology Study.

To explore natural product-based pesticide candidates, a series of indole derivatives containing the isoxazoline skeleton at the N-1 position were synthesized by 1,3-dipolar [2 + 3] cycloaddition reaction. Their structures were characterized by melting points (mp), infrared (IR) spectra, proton nuclear magnetic resonance spectra (1H NMR), carbon-13 nuclear magnetic resonance spectra (13C NMR), and high resolution mass spectrometry (HRMS). The single-crystal structures of five compounds were presented. Against Tetranychus cinnabarinus Boisduval, compound 3b showed greater than 3.8-fold acaricidal activity of indole and good control effects under glasshouse conditions. Against Aphis citricola Van der Goot, compounds 3b and 3q exhibited 48.3- and 36.8-fold aphicidal activity of indole and 6-methylindole, respectively. Particularly, compound 3b showed good bioactivities against T. cinnabarinus and A. citricola. Against Eriosoma lanigerum Hausmann, compound 3h and 3i showed 2.1 and 1.9 times higher aphicidal activity compared to indole. Furthermore, the construction of the epidermal cuticle layer of 3b-treated carmine spider mites was distinctly damaged, which ultimately led to their death.

Preparation of polyurethane coating formulation based on dihydropyridine derivatives as an insecticide and antifungal additives for surface coating applications

Pyridine derivatives are prepared and evaluated before being incorporated into polyurethane coating formulations to create antifungal and insecticidal coating compositions. Different analyses, including Fourier transform infrared (FTIR), mass, proton nuclear magnetic resonance (1HNMR), and carbon-13 nuclear magnetic resonance (13C NMR) spectra, were used to confirm the synthesized compounds. The material has been coated using a polyurethane coating mixture. Gloss, scratch resistance, flexibility, and adhesion are some of the coating attributes investigated; mechanical capabilities include impact resistance and shore hardness, and physicochemical properties such as chemical resistance of coated polyurethane (PU) samples are also investigated. PU coatings were applied to substrates to measure coating properties. The mechanical properties of the PU cast films were measured. The results of the experiments revealed that all PU coatings based on dihydropyridine derivatives had good scratch resistance which varied from > 1.5 to > 2 kg. While reducing gloss value varied from 65 to 85, there is no effect of the prepared compounds in the other mechanical test. These PU coatings have excellent chemical resistance except the alkali resistance as evidenced by their physicochemical properties. The observed antifungal and insecticide activities indicated that dry wood coated with PU based on dihydropyridine derivatives is promising for resistance to these insects and fungi, in comparison with the paint as blank. The results revealed that the inhibition zones diameter by compound 2 were 25.1 ± 0.69, 23.2 ± 0.94, 20.16 ± 0.62, 20 ± 0.80, and 18 ± 0.81 mm against A. terreus, A. niger, A. flavus, C. albicans, and A. fumigatus, respectively, whereas the inhibition zones (IZ) diameter by compound 3 were 22.56 ± 0.30, 21.03 ± 0.49, 21.03 ± 0.61, 21 ± 0.66, and 20 ± 0.78 mm versus A. niger, A. fumigatus A. flavus, C. albicans, and A. terreus, respectively. The ordering activity against insects increased as the dose concentration of the pyridine derivatives was increased.

An initial investigation of accuracy required for the identification of small molecules in complex samples using quantum chemical calculated NMR chemical shifts

The majority of primary and secondary metabolites in nature have yet to be identified, representing a major challenge for metabolomics studies that currently require reference libraries from analyses of authentic compounds. Using currently available analytical methods, complete chemical characterization of metabolomes is infeasible for both technical and economic reasons. For example, unambiguous identification of metabolites is limited by the availability of authentic chemical standards, which, for the majority of molecules, do not exist. Computationally predicted or calculated data are a viable solution to expand the currently limited metabolite reference libraries, if such methods are shown to be sufficiently accurate. For example, determining nuclear magnetic resonance (NMR) spectroscopy spectra in silico has shown promise in the identification and delineation of metabolite structures. Many researchers have been taking advantage of density functional theory (DFT), a computationally inexpensive yet reputable method for the prediction of carbon and proton NMR spectra of metabolites. However, such methods are expected to have some error in predicted 13C and 1H NMR spectra with respect to experimentally measured values. This leads us to the question–what accuracy is required in predicted 13C and 1H NMR chemical shifts for confident metabolite identification? Using the set of 11,716 small molecules found in the Human Metabolome Database (HMDB), we simulated both experimental and theoretical NMR chemical shift databases. We investigated the level of accuracy required for identification of metabolites in simulated pure and impure samples by matching predicted chemical shifts to experimental data. We found 90% or more of molecules in simulated pure samples can be successfully identified when errors of 1H and 13C chemical shifts in water are below 0.6 and 7.1 ppm, respectively, and below 0.5 and 4.6 ppm in chloroform solvation, respectively. In simulated complex mixtures, as the complexity of the mixture increased, greater accuracy of the calculated chemical shifts was required, as expected. However, if the number of molecules in the mixture is known, e.g., when NMR is combined with MS and sample complexity is low, the likelihood of confident molecular identification increased by 90%.

Characterization of liquefied products from corn stalk in the presence of polyhydric alcohols with acid catalysis

Atmospheric liquefaction technology has been used widely and is an effective way of biomass component utilization. In this paper, the liquefied products obtained from corn stalk using polyhydric alcohols 1,2-propanediol (PG) mixed diethylene glycol (DEG) through acid catalysis under atmosphere pressure were characterized by various analytical technologies. The results indicated that 39 kinds of organic compounds were present in bio-oil, among which alcohols were the most, phenols were the second, and their relative contents were 70.7% and 25.6%, respectively. There were also some organic acids, ethers, esters, and ketones. More than 80% of these compounds had a carbon number less than 25. Carbon nuclear magnetic resonance spectra (13C-NMR) showed that different chemical shifts  (ppm) corresponded to various carbon types. The chemical composition of the residue from liquefaction was complex and contained a certain amount of large molecular substances that were difficult to degrade. It required more severe pyrolysis conditions than those of corn stalk. Results from X-Ray Diffraction (XRD) indicated the destruction of crystalline structure of carbohydrates and the cellulose molecules were cracked, indicating that the cellulose was degraded and the degree of liquefaction was high.

Cross-Modal Retrieval between 13C NMR Spectra and Structures for Compound Identification Using Deep Contrastive Learning.

Library matching using carbon-13 nuclear magnetic resonance (13C NMR) spectra has been a popular method adopted in compound identification systems. However, the usability of existing approaches has been restricted as enlarging a library containing both a chemical structure and spectrum is a costly and time-consuming process. Therefore, we propose a fundamentally different, novel approach to match 13C NMR spectra directly against a molecular structure library. We develop a cross-modal retrieval between spectrum and structure (CReSS) system using deep contrastive learning, which allows us to search a molecular structure library using the 13C NMR spectrum of a compound. In the test of searching 41,494 13C NMR spectra against a reference structure library containing 10.4 million compounds, CReSS reached a recall@10 accuracy of 91.64% and a processing speed of 0.114 s per query spectrum. When further incorporating a filter with a molecular weight tolerance of 5 Da, CReSS achieved a new remarkable recall@10 of 98.39%. Furthermore, CReSS has potential in detecting scaffolds of novel structures and demonstrates great performance for the task of structural revision. CReSS is built and developed to bridge the gap between 13C NMR spectra and structures and could be generally applicable in compound identification.

Synthesis and Characterization of a Trifunctional Photoinitiator Based on Two Commercial Photoinitiators with α-Hydroxyl Ketone Structure.

A trifunctional photoinitiator based on commercial photoinitiators 2-hydroxy-2-methylpropiophenone (Irgacure1173) and 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone (Irgacure2959) was synthesized by an esterization reaction. Its structure was characterized by UV-Vis spectrometry, Infrared Transformed Fourier, Proton Nuclear Magnetic Resonance Spectra, 13 Carbon Nuclear Magnetic Resonance Spectra, Mass Spectrometry, and Thermogravimetry. In addition, its photoinitiating activity was investigated. The results showed that the novel photoinitiator had good photoinitiating activity and thermal stability compared to commercial photoinitiators. The migration of the residual photoinitiator in the cured film was lower than that of 1173 and 2959.

A hepatic sinusoids-based microtube reactor for (Z)-5-(4-hydroxybenzylidene)thiazolidine-2,4-dione intermediate drug synthesis

Microreactor technology is considered a breakthrough technology that can replace regular reactors systems as microreactors deliver proper mixing and reaction performance which satisfy both industry and research demands. This drives researchers to develop several microreactor systems with improved characteristics for plenty of applications, including medicine and pharmaceutical applications. In the present study, a microtube reactor system is constructed to produce (Z)-5-(4-hydroxybenzylidene)thiazolidine-2,4-dione intermediate drug with a hepatic sinusoids-based micromixer used as the part responsible of mixing the reactants in early stages. (Z)-5-(4-hydroxybenzylidene)thiazolidine-2,4-dione is an intermediate drug that belongs to glitazones. A batch reactor system is also constructed for the purpose of comparison. Thiazolidine-2,4-dione (TZD) and p-hydroxybenzaldehyde are used as the main reactants while two compounds are used as catalysts; diethylamine and piperdine. Effects of different parameters such as initial reactants concentration, catalyst concentration, and flow rate and residence time on the product yield and the pressure drop across the micromixer are investigated. Analysis of the collected samples is done using different characterization methods such as High Pressure Liquid Chromatography, Thermogravimetric/Differential Thermal Analysis, X-ray diffraction spectroscopy, Fourier Transform Infrared spectroscopy, and carbon and proton Nuclear magnetic resonance spectra. The microtube reactor system has proven to be more efficient than the batch system. The maximum yield obtained from the microtube reactor system is 97% with a residence time of only 22 min using diethylamine as a catalyst compared with 92% obtained from the batch system using piperdine as a catalyst after 12 hr run. The yield obtained from the microtube reactor system spans from 77% to 97% using diethylamine as a catalyst and from 56% to 84% using piperdine as a catalyst while the pressure drop across the micromixer ranges from 0.9 to 12 kPa.

Elucidation of the structure, spectroscopic techniques and quantum chemical investigations on nonlinear optical material 2‑hydroxy-5-methylbenzaldehyde

First and second order hyperpolarizabilities of, 2‑hydroxy-5-methylbenzaldehyde (HMB) and its related three molecules 2, 6‑hydroxy-3-methyl acetophenone (HMA), 5-ethyl-2-hydroxybenzaldehyde (HBA) and 2, 6-Dihydroxy-4-methyl benzaldehyde (DMB) were calculated by employing MP2 (Moller-Plesset) method. The vibrational behavior of the title molecule was extracted by using Fourier transform infrared, Fourier transform-Raman analysis. The UltraViolet-visible spectrum recorded and analyzed using ethanol solvent, reveals the optical and electronic transition properties. Hydrogen and carbon nuclear magnetic resonance spectra were also recorded. Kurtz and Perry powder technique was utilized to examine the second harmonic generation effectiveness. The third-order nonlinear optical performances and optical limiting threshold are investigated by Z-scan techniques. The experimental results of SHG and Z-scan strongly proved the NLO behavior of the HMB molecule. The optical limiting value is 19.64 Jcm−2 indicating that the HMB molecule could be a promising candidate for optical limiting materials. Potential energy surface scanning has been performed to discover the stability of the molecules which leads to the nonlinear optical activity. The geometry optimization has been performed to analyze the nonlinear optical active site with bonding features. Natural bond orbital analysis, Hirshfeld surface analysis, density of energy states, Frontier molecular orbital analysis, molecular electrostatic potential, Fukui function and global reactivity descriptor have also been carried out to verify the nonlinear optical activity. The natures of intramolecular hydrogen bonds are analyzed using QTAIM and RDG analysis.

Carbonization mechanisms of polyimide: Methodology to analyze carbon materials with nitrogen, oxygen, pentagons, and heptagons

Carbonization process of pyromellitic dianhydride (PMDA)-4,4′-diaminodiphenyl ether (ODA)-type polyimide has been studied for decades. However, various reaction mechanisms have been proposed and the detailed mechanisms are still controversial. It is essential to understand the carbonized structures of PMDA-ODA-type polyimide before analyzing the defect structures in graphite. In this work, the carbonization mechanisms of polyimide heated at 1273 K or lower were unveiled and the methodology to analyze carbon materials containing nitrogen, oxygen, pentagons, and heptagons using computational spectral analysis combined with molecular dynamics simulation (ReaxFF) are exhibited. For example, the formations of isoimide and cyclic ether were estimated by ReaxFF, and the presence was supported by experimental and calculated X-ray photoelectron spectroscopy (XPS) and carbon-13 nuclear magnetic resonance (13C NMR) spectra of polyimide heated between 813 and 873 K. The formations of pentagons and heptagon, suggested by ReaxFF, were also supported by Raman and 13C NMR spectra of polyimide heated between 833 and 1273 K. This work also revealed that the previously reported structures were unstable and that amine in the basal plane was the most plausible structure in polyimide heated at 1073 K or higher, as clarified by XPS, ReaxFF, and the energy calculation.

Electronic structure and spectroscopy of C60 nitroaryl radical adducts

In this study, density functional theory (DFT) calculations were applied to study electronic structure and spectroscopy of C60 nitroaryl radical adducts with 2-nitrophenyl, 4-nitrophenyl, 2,4-dinitrophenyl and up to six 2,4,6-trinitrophenyl substituents. The structural parameters for optimized geometries were measured, and polarity of molecules was compared to nitrobenzene derivatives. The atomic charges and charge distribution map of these compounds were calculated based on electrostatic potential (ESP) and natural population analysis (NPA). The distribution of unpaired electron in opened shell molecules was visualized by spin density profiles. The calculated thermochemical constants for reactions of nitroaryl radicals with C60 were reported. The wave function analysis was performed to study molecular orbital (MO) and density of states (DOS) diagrams. The aromaticity index of molecules was estimated by nucleus-independent chemical shift (NICS) method. The infrared (IR) and carbon-13 nuclear magnetic resonance (13C NMR) spectra of these compounds were also investigated. It was found that addition of nitroaryl radicals to C60 is exothermic and occurs with decreasing entropy and Gibbs free energy. These compounds exhibit higher aromatic character and smaller band gap compared to C60.

ATP Analogues for Structural Investigations: Case Studies of a DnaB Helicase and an ABC Transporter.

Nucleoside triphosphates (NTPs) are used as chemical energy source in a variety of cell systems. Structural snapshots along the NTP hydrolysis reaction coordinate are typically obtained by adding stable, nonhydrolyzable adenosine triphosphate (ATP) -analogues to the proteins, with the goal to arrest a state that mimics as closely as possible a physiologically relevant state, e.g., the pre-hydrolytic, transition and post-hydrolytic states. We here present the lessons learned on two distinct ATPases on the best use and unexpected pitfalls observed for different analogues. The proteins investigated are the bacterial DnaB helicase from Helicobacter pylori and the multidrug ATP binding cassette (ABC) transporter BmrA from Bacillus subtilis, both belonging to the same division of P-loop fold NTPases. We review the magnetic-resonance strategies which can be of use to probe the binding of the ATP-mimics, and present carbon-13, phosphorus-31, and vanadium-51 solid-state nuclear magnetic resonance (NMR) spectra of the proteins or the bound molecules to unravel conformational and dynamic changes upon binding of the ATP-mimics. Electron paramagnetic resonance (EPR), and in particular W-band electron-electron double resonance (ELDOR)-detected NMR, is of complementary use to assess binding of vanadate. We discuss which analogues best mimic the different hydrolysis states for the DnaB helicase and the ABC transporter BmrA. These might be relevant also to structural and functional studies of other NTPases.

Stripping and mechanical properties of water-based polyacrylate stripper and its application in art masking fluid

A long chain polyacrylate which was a functional composition of a new water-based stripper (WLOAC) for art masking fluid was prepared using azobisisobutyronitrile under the solution polymerization method. The WLOAC was mixed with natural latex to form an art masking fluid (WACN). The optimized preparation conditions, i.e., reaction time 4 h, reaction temperature 80 °C, and stirring rate 200 r/min were selected by the orthogonal experimental design method. The proton (1H NMR) and carbon (13C NMR) nuclear magnetic resonance spectra of polyacrylate were recorded. There were no peaks at 6.5–5.5 ppm in 1H NMR and at 128.3 ppm and 130.2 ppm in 13C NMR, which indicated that the radical polymerization was indeed occurred. The rheological properties of the WLOAC emulsions were investigated by a rheometer, and the rheology tests indicated that the WLOAC emulsion is a pseudoplastic fluid. The surface tension, peel strength, tensile strength and scanning electron microscopy (SEM) of WACN were all determined. The results showed that the surface tension decreased by the addition of WLOAC. The peel strength decreased from 0.58 to 0.29 N/mm with WLOAC increased from 5 to 12.5 wt%. With the addition of WLOAC, the tensile stress increased from 10.56 to 22.36 MPa. The SEM results showed that WACN coatings could be detached without causing any damage to the paper substrate.

Designing quinone-dopamine-based conjugates as six electron system for high-performance hybrid electrode

The development of electrode materials for supercapacitors is a necessary research and development work to address the present-day energy crises. The improvement of productive pseudo-capacitors requires quick and reversible kinetics of redox-molecules. In the development of pseudo-capacitors, quinone/hydroquinone redox couples are one of the promising molecules. Graphite sheet, along with quinone molecules with an increased number of carbonyl groups, is expected to give higher performance hybrid supercapacitors. In this direction, a simple one-step reaction of p-benzoquinone and dopamine hydrochloride to 2,5-bis((3,4-dihydroxyphenethyl)amino)cyclohexa-2,5-diene-1,4-dione molecule (BQ-DP) is carried and confirmed the formation from Fourier-transform infrared, high-resolution mass, proton and carbon nuclear magnetic resonance spectra. This molecule is used as a redox system along with a graphite sheet as active electrode material for supercapacitor, wherein a redox system consists of three quinone groups with six electrons transfer reaction. Cyclic voltammetry and charge-discharge graphs, and two constant phase elements obtained from EIS measurement clearly show the contribution of both electrochemical double layer and pseudo-capacitor components. Both benzoquinone and dopamine groups are involved in the redox reaction. The values of specific capacitance for this electrode are 910 F g−1 at 5 mV s−1 and 1180 F g−1 at 9.5 A g−1, respectively. This cell is subjected to 10,000 charge-discharge cycles, which underwent decay in specific capacitance from 416 to 209 F g−1 up to 1000 cycles and then remains constant up to 7000 cycles. In the case of a negligible contribution of EDLC, the supercapacitor cell could be treated as a battery cell. The battery gives an initial specific capacity of 115–58 mAh g−1 at 1000 cycles. This quinone molecule showed higher electrochemical performance compared to the earlier reports on quinone molecules for supercapacitors. An alternative strategy to increase the performance of the quinone-graphite electrode is made by making holes on graphite sheet and accommodated more amount of electro-active quinone molecule and used as an electrode in symmetric cell configuration in coin cell and subjected for 5000 cycles in the voltage range from 0 to 1 V at 9.5 F g−1. The value of specific capacitance for the symmetric cell obtained from charge-discharge measurement for the electrode (419 F g−1) is found to be higher than that of the electrode without holes (324 F g−1).

Synthesis of Bio-Nanomagnetite Using Poly(butylene adipate) and Poly(butylene adipate-co-terephthalate)

Nano-scale magnetite presents fascinating opportunities in various fields. For example, they are used for removing pollution from water bodies as they can bind electrochemically to suspended particles so that they are settled as sludge. Applying biodegradability property to these nanomagnetites improves their usage. In this study, bio-nanomagnetite is synthesized using co-precipitation reaction in which nanoparticles are used as a base for mounting two biodegradable polymers, i.e. poly(butylene adipate) (PBA) and poly(butylene adipate-co-terephthalate) (PBAT). Proton nuclear magnetic resonance (1HNMR) and carbon nuclear magnetic resonance (13CNMR) spectra of synthesized polymers are presented. Fourier transform infrared spectroscopy (FTIR) of nano-particles is also presented. Biodegradation tests of bio-polymers including degradation under UV (ultraviolet) rays and in phosphate buffer show they can be degraded in biological conditions. Curves showing the progression of degradation are also presented. Relative size of the particles based on Debye–Scherrer relation is also obtained through X-ray powder diffraction (XRD) test and it is 9.12 nm.

High Molecular‐Weight Cyclic Polyesters from Solvent‐Free Ring‐Opening Polymerization of Lactones with a Pyridyl‐Urea/MTBD

Abstract(Thio)urea/base systems have been widely used in the ring‐opening polymerization (ROP) of lactones based on their superior performance in activity and selectivity. Herein, a pyridyl‐urea (6C‐PU)/7‐methyl‐1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene catalytic system is used to prepare the polyesters with cyclic topology via the ROP of lactones in the absence of initiator under solvent‐free conditions. The catalytic system shows high activity in the ROP of δ‐valerolactone (δ‐VL) and cyclic polyvalerolactones (PVLs) with high molecular weights and narrow molecular weight distribution are obtained despite the existence of some linear products generated during the precipitation process. The structure of the resulting polymers is determined by proton and carbon nuclear magnetic resonance spectra, matrix assisted laser desorption/ionization time of flight mass spectrometry, and intrinsic viscosity studies. A possible mechanism is proposed on the basis of NMR analysis and characteristics of polymerization. Thermal and mechanical properties of cyclic PVLs are investigated through differential scanning calorimetry, thermogravimetric analysis, and tensile test.

Solid state nuclear magnetic resonance studies of hydroxypropylmethylcellulose acetyl succinate polymer, a useful carrier in pharmaceutical solid dispersions.

Hydroxypropylmethylcellulose (HPMC) acetyl succinate (HPMC-AS) is a key polymer used for the enablement of amorphous solid dispersions (ASDs) in oral solid dosage forms. Choice of the appropriate grade within the material is often made empirically by the manufacturer of small-scale formulations, followed by extensive real time stability. A key factor in understanding and predicting the performance of an ASD is related to the presence of hydrogen (or other) bonds between the polymer and active pharmaceutical ingredient (API), which will increase stability over the parameters captured by miscibility and predicted by the Gordon-Taylor equation. Solid state nuclear magnetic resonance (NMR) is particularly well equipped to probe spatial proximities, for example, between polymer and API; however, in the case of HPMC-AS, these interactions have been sometimes difficult to identity as the carbon-13 NMR spectra assignment is yet to be firmly established. Using feedstock, selectively substituted HPMC polymers, and NMR editing experiments, we propose here a comprehensive understanding of the chemical structure of HPMC-AS and a definitive spectral assignment of the 13 C NMR spectra of this polymer. The NMR data also capture the molar ratios of the acetate and succinate moieties present in HPMC-AS of various grades without the need for post treatment required by chromatography methods commonly use in pharmacopoeia. This knowledge will allow the prediction and measurement of interactions between polymers and APIs and therefore a rational choice of polymer grade to enhance the solid state stability of ASDs.

What is the form of muscimol from fly agaric mushroom (Amanita muscaria) in water? An insight from NMR experiment supported by molecular modeling

The biologically active alkaloid muscimol is present in fly agaric mushroom (Amanita muscaria), and its structure and action is related to human neurotransmitter γ -aminobutyric acid (GABA). The current study reports on determination of muscimol form present in water solution using multinuclear 1 H and 13 C nuclear magnetic resonance (NMR) experiments supported by density functional theory molecular modeling. The structures of three forms of free muscimol molecule both in the gas phase and in the presence of water solvent, modeled by polarized continuous model, and nuclear magnetic isotropic shieldings, the corresponding chemical shifts, and indirect spin-spin coupling constants were calculated. Several J-couplings observed in proton and carbon NMR spectra, not available before, are reported. The obtained experimental spectra, supported by theoretical calculations, favor the zwitterion form of muscimol in water. This structure differs from NH isomer, previously determined in dimethyl sulfoxide (DMSO) solution. In addition, positions of signals C3 and C5 are reversed in both solvents.

NMR & Electronic Spectra, NLO, FMO, NBO and Thermodynamic Properties of Pentachlorophenol: An Experimental and Theoretical Investigation

Proton (1H) and Carbon-13 (13C) nuclear magnetic resonance spectra of pentachlorophenol were measured. Corresponding chemical shifts were generated using Gauge Independent Atomic Orbital (GIAO) approach, as a part of density functional theory (DFT) application. UV-visible spectrum was measured in the spectral range 200-400 nm and compared with its simulated counterpart generated, using time-dependent density functional theory (TD-DFT). Frontier molecular orbital (FMO) approach was used to understand origin of UV-visible spectrum and chemical reactivity of the molecule. The non-linear (NLO) behaviour was studied by evaluating the values of dipole moment, polarizability and hyperpolarizability. Molecular electrostatic potential (MESP) surface was drawn to locate reactive sites of pentachlorophenol. Natural bond orbital (NBO) analysis of the molecule was made to examine stability of the molecule arising from charge delocalization. Thermodynamic parameters of the molecule were also calculated.

Molecular analyses using FT-IR, FT-Raman and UV spectral investigation; quantum chemical calculations of dimethyl phthalate

Dimethyl phthalate C6H4 (COOCH3)2 (DIMPHT) has been synthesized. To characterize molecular functional groups FT-IR and FT-Raman spectrum were recorded and wavenumbers were assigned accordingly. The optimized geometrical parameters, vibrational assignments, chemical shifts and thermodynamic properties of title compound were computed by ab-initio calculations at Density Functional Theory (DFT/B3LYP) method with 6–311++G(d,p) as basis set. The potential energy curve expresses that DIMPHT molecule has three stable structures. The computational results diagnose the most stable conformer of the DIMPHT as the conformer 2 of the compound. The calculated harmonic wavenumbers of compound were then analyzed in comparison to experimental FT-IR and Raman spectrum. Gauge independent atomic orbital (GIAO) method was used for determining, (1H) and carbon (13C) nuclear magnetic resonance (NMR) spectra of the molecule. Molecular parameters were calculated along with its periodic boundary conditions calculation (PBC) analysis supported by X-ray diffraction studies. The frontier molecular orbital (HOMO, LUMO) analysis describes charge distribution and stability of the molecule which concluded that nucleophilic substitution is more preferred and the mullikan charge analysis also confirmed the same. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) complements with the experimental findings. In addition, molecular electrostatic potential, nonlinear optical and thermodynamic properties of the title compound were performed. Mulliken and natural charges of the title molecule were also calculated and interpreted. The effects of the computations were applied to theoretical spectra of the title compound, which show excellent agreement with observed spectra. The scaled B3LYP/6-311++G(d,p) results show the best arrangement with the experimental values over the other method.