Quantitative <Superscript>2</Superscript>H NMR spectroscopy

The selectivity of deuterium distribution between the nonequivalent positions in 3-carene (1), 4-α-acetyl-2-carene (2), and 4-(1-hydroxyethyl)-2-carene (3) has been measured by ²H-{¹H} NMR spectroscopy at the natural abundance of deuterium. These “H/D-isotope portraits” were shown to be typical of terpenes and terpenoids produced in plants via the biosynthetic DXP pathway. The mechanism of acylation of 1 was studied by the density functional theory method (PBE functional, TZ2p basis set). The six-membered ring in compound 1 is planar. However, the endo attack of electrophiles on this ring is more favorable both kinetically and thermodynamically. It was shown both experimentally and theoretically that the elimination of a hydrogen atom in the second reaction step proceeds stereoselectively at the C(2) atom from the anti position with respect to the three-membered ring and occurs with pronounced nucleophilic assistance from the carbonyl group. For Part 2, see Ref. 1. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1657–1664, August, 2008.     

Isomeric Effect on H/D Exchange of Resveratrol Studied by NMR Spectroscopy

Resveratrol (3,5,4′‐trihydroxylstilbene), a phytoalexin in response to injury or fungal attack, is found in grapes and other food products. It has been well documented that the compound has beneficial effects as hypolipidemic, anticancer, antiviral, neuroprotective, antiaging, and anti‐inflammatory natural active principle. It was observed that both trans‐ and cis‐resveratrols undergo hydrogen‐deuterium (H/D) exchange at H‐2,6 and H‐4 positions of the A‐ring. The exchange rates were determined by ¹H NMR spectroscopy. The results reveal that the exchange rates are configuration and pH dependent. Derivative of 2‐O‐β‐D‐glucoside can significantly speed up the H/D exchange reactions for both isomers. The trans‐resveratrol experiences faster H/D exchanging than the cis‐resveratrol. Such isomeric effect is possibly due to the factor that the trans‐resveratrol is in favor of forming larger/super conjugative system and has less spatial interference. Theoretical calculation shows that electronegativity at these positions is in the order of H‐2,6>H‐4, which is in consistent with the exchange rates observed by NMR. The results may be of help in understanding the properties of resveratrol, and in analysis of resveratrol in natural products or body fluids using mass spectroscopy that occasionally requires stable deuterium isotope labeling.     

1D and 2D NMR studies of N-vinylcarbazole/butyl methacrylate copolymers

Copolymers containing N-vinylcarbazole (V) and butyl methacrylate (B) units of different compositions were synthesized and their compositions were determined from quantitative ¹³C{¹H} NMR spectroscopy. The reactivity ratios of the comonomers were estimated using the Kelen-Tudos and non-linear error in variable methods. The complete spectral assignment in terms of compositional and configurational sequences of the overlapping ¹H and ¹³C{¹H} spectra of the copolymers were done with the help of distortionless enhancement by polarization transfer, 2D heteronuclear single quantum correlation and total correlated spectroscopy experiments.     

Investigations of intramolecular hydrogen bonding in three types of Schiff bases by 2H and 3H NMR isotope effects

Hydrogen bonding within the structures of three Schiff bases (1-3), obtained by condensation of 4-methoxy-, 5-methoxy- and 4,6-dimethoxysalicylaldehyde with methylamine, was investigated by measuring deuterium and tritium NMR isotope effects. The primary deuterium and tritium isotope effects (delta(XH)-delta(XD/T)) and secondary one-bond nitrogen deuterium effect appear to be very useful parameters for defining the character of intramolecular hydrogen bonds. The tritium isotope effects were also determined for nitrogen-hydrogen one-bond coupling constants for both 4-methoxy and 4,6-dimethoxy derivatives. These parameters are seen to be highly sensitive to hydrogen bond characteristics and can be used to distinguish localized and tautomeric hydrogen bonds.     

New accessory for studies of isotopic 1H/2H exchange and biomolecular interactions using transmission infrared spectroscopy

We present here a new accessory for IR transmission measurements of ¹H/²H exchange, as an ancillary tool for monitoring structural features of biomolecules in aqueous solution. This new accessory results from the combination of two dialysis membranes and a conventional liquid cell having two cylinders containing ²H₂O buffer. When compared with conventional transmission measurements, carried out either after dissolving lyophilized biomolecules in ²H₂O or after dialyzing the aqueous solution considered against ²H₂O buffer, this accessory shows the following advantages: (1) controlled measurements over the initial steps of this isotopic exchange and absence of molecular aggregation, and (2) smaller sample amounts. This new Fourier transform IR cell can also be used to analyze ligand–biomolecule and drug–cell interactions.      

Infrared spectra (700–200 cm−1) and6Li/7Li and H2O/D2O isotope effects for four isotopically substituted lithium formate monohydrates

The infrared spectra, in the 700–200 cm^–1 region, have been reported for⁶LiHCO₂ · H₂O,⁶LiHCO₂ · D₂O,⁷LiHCO₂ · H₂O and⁷LiHCO₂ · D₂O and the observed fundamental bands have been discussed taking into account the⁶Li/⁷Li and H₂O/D₂O isotope wavenumber shifts on the fundamental vibrations.

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Infrarotspektren (700–200 cm^–1) und⁶Li/⁷Li- und H₂O/D₂O-Isotopeneffekte für vier isotopensubstituierte Lithiumformat-monohydrate

Zusammenfassung Die Infrarotspektren in der Region von 700–200 cm^–1 werden für⁶LiHCO₂ · H₂O,⁶LiHCO₂ · D₂O,⁷LiHCO₂ · H₂O und⁷LiHCO₂ · D₂O angegeben und die beobachteten Grundschwingungen zusammen mit den isotopischen Verschiebungen der Wellenzahlen diskutiert.

     

13C and1H NMR spectra of substituted dihydropyrroles prepared by the reaction of 2-aminooxazoles and maleimide

Substituted dihydropyrroles were characterized by¹³C and¹H NMR spectra. The spectral patterns of these compounds and reversible hydrogen—deuterium exchange are discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 697–700, April, 2000.     

Solvation of Na+ in N,N-dimethylformamide + methanol solutions. A nuclear magnetic relaxation study using dynamic solvent isotope effects

Inter- and intramolecular nuclear magnetic quadrupole relaxation measurements have been used to study the system methanol (CH₃OH)+ N,N-dimethylformamide (DMF)+NaI at 25°C. The dynamic behavior of the solvent molecules was investigated, throughout the composition range of the binary mixtures, by means of ¹⁴ N relaxation of DMF and ² H of methanol-d ₁ (CH ₃ OD). The intermolecular relaxation of ²³ Na⁺ in pure DMF was used to obtain information about the symmetry of the solvent electric dipole arrangement in the solvation sphere of the ion. The investigation of preferential solvation around Na⁺ in the binary mixtures was carried out by means of ²³ Na⁺ relaxation measurements using, for the first time, both the CH ₃ OH/CD ₃ OD and the DMF/DMF-d ₇ dynamic isotope effect. The results show that, throughout the composition range, there is preferential solvation by DMF. Furthermore, the use of the isotope effects of both components allowed for the first time a basic check of the reliability of the method since we obtained two independent sets of data for the composition of the Na⁺ solvation shell in the mixtures. The consistency of the two separate data sets demonstrates that the application of the dynamic isotope effect represents a powerful tool in preferential solvation studies.     

2H Chemical-shift resolution and dipolar2H-1H,2H-15N correlations in solid-state MAS NMR spectroscopy for structure determination and distance measurements in hydrogen-bonded systems

In solid-state NMR, deuteron (²H) spectroscopy can be performed in full analogy to¹H spectroscopy, including²H chemical-shift resolution and²H-X dipolar correlation schemes, when the NMR experiments are conducted in a “rotor-synchronized” fashion under fast magic-angle spinning. Here, 2H-X NMR experiments of this type, including²H-¹⁵N and²H-¹H chemical-shift correlations and distance measurements, are introduced and demonstrated on cytosine monohydrate, whose acidic protons can readily be replaced by deuterons by recrystallization from D₂O. In this way,²H NMR spectroscopy provides information complementary to¹H NMR data, which is particularly useful for studying hydrogen bonds in supra- or biomolecular systems. Electronic supplementary material Supplementary material is available in the online versionof this article atand is accessible for authorized users.     

Nuclear quantum and H/D isotope effects on three-centered bonding diborane: Path integral molecular dynamics simulations

Nuclear quantum and H/D isotope effects of bridging and terminal hydrogen atoms of diborane (B₂H₆) molecules were systematically studied by classical ab initio molecular dynamics (CLMD) and ab initio path integral molecular dynamics (PIMD) simulations with BHandHLYP/6-31++G** level of theory at room temperature (298.15 K). Calculated results clearly show that H/D isotope effect appears in the distribution of hydrogen (deuterium) of B₂H₆ (B₂D₆). Geometry of B₂H₆ also plays a significant role in the nuclear quantum effect proved by PIMD simulations, but slightly deviated from its equilibrium structure when simulated via CLMD simulation. The bond lengths between boron atoms R (B1 … B2) and the bridging hydrogen atoms R_HH (H_B1 … H_B2) of the B₂H₆ molecule obtained from PIMD simulations are slightly longer than those of the deuterated form of the diborane (B₂D₆) molecule. The principal component analysis (PCA) was also employed to distinguish the important modes of bridging hydrogen as related to the nuclear quantum and H/D isotope effects. The highest level of contribution obtained from PCA of PIMD simulations is bending, while various mixed vibrations with less contribution were also found. Therefore, the nuclear quantum and H/D isotope effects need to be taken into account for a better understanding of diborane geometry.     

Conformational study of a strained tolanophane by dynamic 1H NMR spectroscopy and computational methods

The existence of a short C–H ⋯ π (alkyl–alkyne) interaction in the structure of a strained and relatively rigid tolanophane is expected to hinder the rotation about the C–C sp³ single bond. Variable-temperature NMR experiments (performed in three solvents, CDCl₃, THF-d₈, and acetone-d₆) and ab initio density functional calculations were carried out to investigate its dynamic nature. An energy barrier of 48.6 kJ/mol is determined at coalescence (210 K) with acetone-d₆ which is in good agreement with calculation result (54 kJ/mol). Correspondence: Hossein Reza Darabi, Chemistry and Chemical Engineering Research Center of Iran, Pajoohesh Blvd., km 17, Karaj Hwy, 14968-13151 Tehran, Iran.     

1H, 13C,and 14N NMR study of 3-methylfurazans with nitrogen-containing substituents at position 4

3-Methylfurazans with nitrogen-containing substituents at position 4 were studied by ¹H, ¹³C, and ¹⁴N NMR spectroscopy. A correlation between the chemical shifts in ¹³C NMR spectra of these furazans and monosubstituted benzenes with the same substituents was found. The increments for a number of furazan-containing substituents were determined for the first time.     

Invertomers at nitrogen in aziridine carboxylates by mltltinuclear (1H,13C,17O,and15N) NMR study

A confrgurational and conformational study of NH, N-acetyl- and N-sulfonylaziridine carboxylates is performed by¹H ,¹³C,¹⁷O, and¹⁵N NMR spectroscopy. The presence of acetyl and su fonyl groups on the ring nitrogen atom seems to reduce greatly the configurational stability at nitrogen.Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1226–1234, September, 1995.     

Banana-shaped molecules peculiarly oriented in a magnetic field: (2)H NMR spectroscopy and quantum mechanical calculations.

The orientational properties of the banana-shaped liquid crystal 4-chloro-1,3-phenylenebis{4-[4'-(10-undecenyloxy)]benzoyloxy} benzoate (ClPbis11BB) are reported in the nematic phase under the effect of an external magnetic field. A new hypothesis, which states that the central ring of the aromatic core is oriented perpendicularly to the external magnetic field, is proposed. In support of this hypothesis, a series of studies based on (2)H NMR spectroscopy, both in the bulk and in solution, are discussed. (2)H NMR measurements on three selectively deuterium-labelled isotopomers are presented, together with DFT results from B3LYP/cc-pvDz calculations performed on the aromatic core. The rather flat shape of the investigated intramolecular energy surface allows for several different conformations to be populated, the computed magnetic susceptibilities of which are consistent with the proposed hypothesis of peculiar orientation of banana-shaped molecules. Moreover, the orientation of the magnetic susceptibility tensor is shown to be strongly dependent on the internal conformation of the banana-shaped molecules.     

Structure elucidation of a novel group of dithiocarbamate derivatives using 1D and 2D NMR spectroscopy

Compounds 1-7 form a novel group of dithiocarbamates, first synthesized from the reaction of a series of primary amines with carbon disulfide and 3-bromo ethyl pyruvate in the presence of anhydrous potassium phosphate. Structure elucidation of this group of compounds was accomplished using extensive 1D and 2D NMR spectroscopic studies, including (1)H, (13)C, COSY, NOESY, HSQC, and gHMBC experiments. The distinction between the linear structures I, II and the cyclic structure III was made mainly on the basis of the analysis of the cross peak between H-2 and H-4a in the COSY spectra, in combination with the long-range correlation between H-2 and C-4, 6 in the gHMBC spectra.     

13C and1H NMR study of 3-R-substitutedtrans-2-oxadecalins and 1-R-substitutedcis- andtrans-2-oxahydrindans

Previously synthesized 3-substitutedcis- andtrans-2-oxadecalins and 1-substitutedcis- andtrans-2-oxahydrindans were studied by ¹³ C and ¹ H NMR. The structure and configuration of these compounds were established.A. V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, 117912 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 861–865, April, 1992.     

Stereochemicai study of 7-aryl-1,7,8,8a-tetrahydro-3(2H)indolizinones by1H and13C NMR

Stereochemistry of 7-aryl-1,7,8,8a-tetrahydro-3(2H)-indolizinones was studied by¹H and¹³C NMR. Complete assignment of¹H NMR signals and analysis of¹H-¹H coupling constants were performed using the iterative PANIC program. Values of³ J _6,7,³ J _7,8endo, and⁴ J _5,7 allow one to unambiguously identify the correspondingexo- andendo-stereoisomers. For stereoisomers with exo-orientation of H(7), complete assignment of¹³C NMR signals was performed on the basis of analysis of the¹³C-¹H coupling constants using two dimensional heteronuclear shift-correlating spectroscopy.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 591–593, March, 1996.     

Analysis of lipoproteins using 2D diffusion-edited NMR spectroscopy and multi-way chemometrics

This study represents the first application of multi-way calibration by N-PLS and multi-way curve resolution by PARAFAC to 2D diffusion-edited ¹H NMR spectra. The aim of the analysis was to evaluate the potential for quantification of lipoprotein main- and subfractions in human plasma samples. Multi-way N-PLS calibrations relating the methyl and methylene peaks of lipoprotein lipids to concentrations of the four main lipoprotein fractions as well as 11 subfractions were developed with high correlations (R = 0.75-0.98). Furthermore, a PARAFAC model with four chemically meaningful components was calculated from the 2D diffusion-edited spectra of the methylene peak of lipids. Although the four extracted PARAFAC components represent molecules of sizes that correspond to the four main fractions of lipoproteins, the corresponding concentrations of the four PARAFAC components proved not to be correlated to the reference concentrations of these four fractions in the plasma samples as determined by ultracentrifugation. These results indicate that NMR provides complementary information on the classification of lipoprotein fractions compared to ultracentrifugation.     

Fruit juice authentication by <Superscript>1</Superscript>H NMR spectroscopy in combination with different chemometrics tools

To discriminate orange juice from grapefruit juice in a context of fraud prevention, ¹H NMR data were submitted to different treatments to extract informative variables which were then analysed using multivariate techniques. Averaging contiguous data points of the spectrum followed by logarithmic transformation improved the results of the data analysis. Moreover, supervised variable selection methods gave better rates of classification of the juices into the correct groups. Last, independent-component analysis gave better classification results than principal-component analysis. Hence, ICA may be an efficient chemometric tool to detect differences in the ¹H NMR spectra of similar samples, and so may be useful for authentication of foods.     

Extraction and Spectrophotometric Determination of Manganese(VII) with N1-Hydroxy-N1,N2-Diphenylbenzamidine

Abstract

Spectrophotometric determination of manganese(VII) at 614 nm after its extraction with N¹ -hydroxy-N¹,N²-diphenylbenzamidine into amyl alcohol at pH 7–8 is described. Beer's law was obeyed for 0.1–10 μg ml^?1 Mn(VII). The effects of experimental variables and of several diverse ions on the determination of manganese(VII) have been studied. The method has been applied to the determination of manganese in steels and in water extracts of a commercial tea and is found to be simple, precise and highly selective.