Identification Of Positional Isomers Research Articles

Identification and quantification of bipyridyl dicarboxylic acid isomers by ion mobility spectrometry

The identification of positional isomers is of interest because different isomers have different chemical or biological functions and applications. The analysis of positional isomers is sometimes challenging since they have similar chemical structures and properties. For example, the analysis of mass cannot identify different positional isomers because they have identical mass-to-charge ratios and show a single mass peak in mass spectrometry. In this study, an efficient and simple qualitative and quantitative analytical method for differentiating 2,2′-bipyridine-3,3′-dicarboxylic acid (3,3′-BDA), 2,2′-bipyridine-4,4′-dicarboxylic acid (4,4′-BDA), and 2,2′-bipyridine-5,5′-dicarboxylic acid (5,5′-BDA) was developed by using ion mobility spectrometry (IMS). The results revealed that the three BDA isomers formed non-covalent complexes with cyclodextrins (CDs) and Mg2+ ions in the gas phase: [β-CD+3,3′/4,4′/5,5′-BDA+Mg]2+ and [γ-CD+3,3′/4,4′/5,5′-BDA+Mg]2+, which were distinguished by measuring the mobility of the complexes because of their spatial conformational differences. The peak-to-peak resolution (Rp-p) values of the three isomers of [γ-CD+3,3′/4,4′/5,5′-BDA+Mg]2+ reached 2.983 and 2.892, respectively. The conformations of the ternary complexes simulated by the theoretical calculations revealed the different interactions and shapes of the stereoisomers, and the predicted results agreed with the experimental results. Simultaneously, further studies on the collisional dissociation of the ternary complexes revealed that the dissociation energies of the different complex ions varied were different owing to the diverse different conformations. Finally, the relative quantitative analysis of the different isomers in mixed samples was performed and satisfactory linearity results (R2 > 0.99) were obtained. Thus, an effective analytical method was proposed for the identification and quantification of BDA isomers without chemical derivatization, offering a promising approach for the identification of similar derivatives or positional isomers that could be applied in various fields including chemicals and pharmaceuticals.

Separation of ortho, meta and para isomers of methylmethcathinone (MMC) and methylethcathinone (MEC) using LC-ESI-MS/MS: Application to forensic serum samples.

Separation and identification of positional isomers is an important issue in forensic toxicology, particularly in the context of new psychoactive substances (NPS). Despite the structural similarity, positional isomers often show different pharmacological properties and thus can exhibit dramatic differences with respect to their toxicity. Additionally, besides these pharmacological and toxicological effects, the legal status is also of great importance. We present a sensitive and selective LC-MS/MS method to separate the ortho, meta and para isomers of methylmethcathinone (MMC) and methylethcathinone (MEC) using a core-shell biphenyl analytical column. Reliability of the method was confirmed under consideration of the validation parameters selectivity, linearity, accuracy and precision, analytical limits, processed sample stability, matrix effects and recovery. Linearity was demonstrated over the entire calibration range from 5 to 250ng/ml with the use of a 1/x2 weighting. Appropriate quantification and detection limits (LLOQ=5ng/ml, LOD<2ng/ml) could be achieved. Application of the method to real serum samples collected between June 2014 and August 2016 revealed the proof of a recent MMC or MEC consumption, respectively, in eight cases. Isomers of MMC could be detected in three of these eight cases, of which two were positive for 3-MMC and one was positive for 2-MMC. The other samples were tested positively for 3-MEC. In none of the samples 4-MMC, 2-MEC or 4-MEC could be detected. Only substances that were not governmentally controlled at that time could be detected, reflecting the rapid response of the recreational drug market to newly enacting drug laws.

Identification of position isomers by energy-resolved mass spectrometry.

This study reports an energy-resolved mass spectrometric (ERMS) strategy for the characterization of position isomers derived from the reaction of hydroxyl radicals ((●)OH) with diphenhydramine (DPH) that are usually hard to differentiate by other methods. The isomer analogues formed by (●)OH attack on the side chain of DPH are identified with the help of a specific fragment ion peak (m/z 88) in the collision-induced dissociation (CID) spectrum of the protonated molecule. In the negative ion mode, the breakdown curves of the deprotonated molecules show an order of stability (supported by density functional theory (DFT) calculations) ortho > meta > para of the positional isomers formed by the hydroxylation of the aromatic ring. The gas phase stability of the deprotonated molecules [M - H](-) towards the benzylic cleavage depends mainly on the formation of intramolecular hydrogen bonds and of the mesomeric effect of the phenol hydroxyl. The [M - H](-) molecules of ortho and meta isomers result a peak at m/z 183 with notably different intensities because of the presence/absence of an intramolecular hydrogen bonding between the OH group and C9 protons. The ERMS approach discussed in this report might be an effective replacement for the conventional methods that requires very costly and time-consuming separation/purification methods along with the use of multi-spectroscopic methods.

Analytical Methods in Quality Control of Scientific Publications

Plagiarism, fake or even falsified presentation has become a major plague for scientific publications. This paper is a response to personal appeal by David JW Lane the Editor-in-Chief of Research and Reports in Biodiversity Studies to support and promote the international author standards as developed by COPE for authors and editors-in-chief posted to me April 3rd 2012 (International standards for editors and authors http://www.dovepress.com/rrbscope.t9699812). As corresponding author for more than 100 scientific papers, dozens of scientific reviews, several chapters in scientific books, and author and editor of a book Historical Overview of Chromatography and Related Techniques in Analysis of Antimalarial Drug Primaquine, and as a reviewer of Journal of Chromatography, Journal of Chromatography A, Journal of Chromatography B: Biomedical Sciences and Applications, Lipids, Journal of General Microbiology, Journal of Clinical Microbiology, Journal of Microbiological Methods, Oral Microbiology and Immunology, Analytica Chimica Acta, Mycological Research and Journal of Pharmaceutical and Biomedical Analysis, and member of editorial board of Electronic Components and Systems, American Journal of Analytical Chemistry, ISRN Chromatography and Open Journal of Clinical Diagnostics I was adhered to a new ethical and moral standards in scientific publications. The presented paper is an example of use the analytical methods in visualizing of plagiarism and falsification in the published scientific literature. It is obvious that some of scientific publications need careful quality control. Some papers should have been rejected but were not. These papers clearly pollute the field of scientific information. It is not always easy to demonstrate inappropriate presentation even when many supporting facts are available. The facts should be obvious; there should be no hesitation about the quality or value of a paper presented for consideration to be published. Plagiarism is most common and harmful phenomenon in scientific publications. The plagiarism is based on an original discovery or reproduction of the results from the other authors. The analytical methods used in the quality control of the data can disclose plagiarism. An example is the publication under scrutiny “Applications of GC-EI-MS for the Identification of Positional Isomer in Primaquine, an Antimalarial Drug” by Dongre et al. (2005) Journal of Pharmaceutical and Biomedical Analysis 39, No. 1-2, 111-116.

Identification of alkylarene chloromethylation products using gas-chromatographic retention indices

Gas-chromatographic retention indices on standard nonpolar polydimethylsiloxane stationary phases allow identification of products formed by known organic reactions even without using mass-spectrometric data. The efficiency of this approach was demonstrated by the example of identification of previously uncharacterized chloromethyl derivatives of alkylarenes, including structural isomers of compounds containing several chloromethyl groups, directly in reaction mixtures. Chromatographic analysis of such reaction mixtures allows identification of positional isomers of the starting alkylarenes even when they are present simultaneously. The retention indices were determined for the first time for more than 50 alkyl-(chloromethyl)arenes, by-products of chloromethylation, and chloromethyl derivatives of the simplest alkyl phenyl ketones.

Structure analysis of triacylglycerol positional isomers using atmospheric pressure chemical ionisation mass spectrometry

Fragmentation of triacylglycerols by atmospheric pressure ionisation allows identification of positional isomers. The relative intensities of the [M-RCO 2] + ions provide information on the position of fatty acids within an ABC type triacylglycerol and enable ABA and AAB type molecules to be distinguished.

Application of Quantum Chemical Calculations to the Identification of Positional Isomers of Polysubstituted Alkylbenzenes

The problem of assignment of positional isomers of alkylbenzenes to chromatographic peaks is addressed. Probable structures are attributed based on the correlation of stabilities of the isomers, which are expressed as the total molecular energies calculated by the MINDO/3 semiempirical quantum chemical method, and the proportions of the isomers in the reaction mixture. Multicomponent alkylbenzene mixtures were prepared and separated by capillary gas chromatography, and the identity of the isomers was confirmed by the gas chromatography-mass spectrometry combination.

Borazines. VI. Reaction of unsymmetrically 1,3,5-substituted borazines with Grignard reagents. Identification of position isomers

Borazines. VI. Reaction of unsymmetrically 1,3,5-substituted borazines with Grignard reagents. Identification of position isomers