Positional Isomers Research Articles

Characterization of Odor-Active 2-Ethyldimethyl-1,3,6-trioxocane Isomers in Polyurethane Materials

Polyurethane materials, widely used in indoor environments, occasionally exhibit unpleasant odors. An important source of polyurethane odorants is polyether polyols. Previous studies identified odorous 2-ethyldimethyl-1,3,6-trioxocanes in polyurethane materials and polyols but did not investigate the odor activity of the individual isomers. In the present work, an isomer mixture of the precursor dipropylene glycol was fractionated through preparative high-performance liquid chromatography. After the conversion to the corresponding trioxocanes, gas chromatography-olfactometry analyses revealed that just one positional isomer, namely 2-ethyl-4,7-dimethyl-1,3,6-trioxocane, was odor active. Moreover, we observed clear differences in the odor threshold concentrations among its stereoisomers. Only two out of eight isomers displayed an odor, both with an earthy smell and one being approximately 60 times more potent than the other. These insights contribute to a better understanding of polyurethane odor on a molecular level and provide a basis for effective odor control.

Isomer Differentiation by UHPLC-Q-Exactive-Orbitrap MS led to Enhanced Identification of Daphnane Diterpenoids in Daphne tangutica.

Liquid chromatography-mass spectrometry (LC-MS) has enhanced the rapid, accurate analysis of complex plant extracts, eliminating the need for extensive isolation. Tandem mass spectrometry (MS/MS) further enhances this process by providing detailed structural information. However, differentiating structural isomers remains a challenge due to their minor spectral and structural differences. This study aimed to extend the applicability of LC-MS/MS for the structural identification of daphnane diterpenoids, with a particular focus on distinguishing functional isomers. LC-MS analyses were performed using an UHPLC-Q-Exactive-Orbitrap MS. The MS conditions for distinguishing isomers were optimized using in-source CID and HCD modes with reference compounds. A qualitative analysis was then conducted on the extract of Daphne tangutica. The chemical structures of the detected daphnane diterpenoids were estimated by analyzing the fragmentation patterns in both the mass spectra and product ion spectra. These identifications were further validated by isolation and comparison with an in-house daphnane diterpenoid library. By optimizing MS conditions, especially in the negative ion mode, it was possible to accurately distinguish structural isomers such as yuanhuajine and gniditrin. Qualitative analysis of D. tangutica identified a total of 28 daphnanes, including seven previously unreported compounds. Furthermore, a novel geometric isomer of gniditrin was isolated by conducting isolation on the crude diterpenoid fraction. This study demonstrated that LC-MS/MS analysis can effectively distinguish functional isomers of daphnane diterpenoids, thereby enhancing the identification of daphnanes in plant extracts and highlighting its potential as a powerful tool for phytochemical analysis.

Differential Mobility Spectrometry Acoustic Ejection Mass Spectrometer System for Screening Isomerization-Mediating Enzyme Drug Targets.

We report the first implementation of ion mobility mass spectrometry combined with an ultrahigh throughput sample introduction technology for high-throughput screening (HTS). The system integrates differential mobility spectrometry (DMS) with acoustic ejection mass spectrometry (AEMS), termed DAEMS, enabling the simultaneous quantitation of structural isomers that are the substrates and products of isomerase-mediated reactions in intermediary metabolism. We demonstrate this potential by comparing DAEMS to a luminescence assay for the isoform of phosphoglycerate mutase (iPGM) distinctively present in pathogens, offering an opportunity as a drug target for a variety of microbial and parasite borne diseases. The metabolome consists of many structural isomers that require for separation a mobility resolving power of more than 300. Resolving powers measured in collision cross-section space of 1588 and 1948 for 2- and 3-phosphoglycerate and the citrate/isocitrate isomeric pairs, respectively, are shown. These are the highest reported ion mobility resolving powers for molecules from the metabolome reported to date. The potential for DAEMS as a generalized screening tool is demonstrated with the separation of the substrates and products of two additional isomerases that present as potential therapeutic targets, chorismate mutase and triosephosphate isomerase. The separations are achieved at speeds compatible with the sample introduction rates of AEMS providing sufficient data points to integrate the peaks for quantitation without the use of internal standards. DMS hyphenated with acoustic sample ejection MS provides a unique solution to high-throughput mass spectrometry applications where separation of isomers and other types of isobaric overlaps are required.

Migratory Aryl Cross-Coupling.

A fundamental property of cross-coupling reactions is regiospecificity, meaning that the site of bond formation is determined by the leaving group's location on the electrophile. Typically, achieving a different substitution pattern requires the synthesis of a new, corresponding starting-material isomer. As an alternative, we proposed the development of cross-coupling variants that would afford access to multiple structural isomers from the same coupling partners. Here, we first demonstrate that a bulky palladium catalyst can facilitate the efficient, reversible transposition of aryl halides by temporarily forming metal aryne species. Despite the nearly thermoneutral equilibrium governing this process, combining it with the gradual addition of a suitable nucleophile results in dynamic kinetic resolution of the isomeric intermediates and high yields of unconventional product isomers. The method accommodates a range of oxygen- and nitrogen-centered nucleophiles and tolerates numerous common functional groups. A Curtin-Hammett kinetic scheme is supported by computational and experimental data, providing a general mechanistic framework for extending this migratory cross-coupling concept.

Antimicrobial Activity of Naphthyridine Derivatives

To combat the problem of the increasing drug resistance of microorganisms, it is necessary to constantly search for new medicinal substances that will demonstrate more effective mechanisms of action with a limited number of side effects. Naphthyridines are N-heterocyclic compounds containing a fused system of two pyridine rings, occurring in the form of six structural isomers with different positions of nitrogen atoms, which exhibit a wide spectrum of pharmacological activity, in particular antimicrobial properties. This review presents most of the literature data about the synthetic and natural naphthyridine derivatives that have been reported to possess antimicrobial activity.

A highly sensitive UHPLC-MS/MS method for determining 15 designer LSD analogs in biological samples with application to stability studies.

In recent years, the rise in the synthesis and distribution of LSD analogs in illicit drug markets, commonly referred to as "designer psychedelics", has contributed to increased recreational use. This trend has resulted in a rising number of global reports, with law enforcement increasingly detecting these compounds in blotter papers and biological samples. In the presented paper, an UHPLC-QqQ-MS/MS method was developed for trace determination (fg mL-1) of LSD, its designer analogs (ALD-52, AL-LAD, LAMPA, LSM-775, LSZ, MiPLA, 1B-LSD, 1cP-LSD, 1cP-MiPLA, 1P-LSD, 1P-MiPLA, 1V-LSD and 2-Bromo-LSD) and its metabolite (2-oxo-3-OH-LSD) with simultaneous separation of structural isomers. Biological samples were prepared using liquid-liquid extraction (LLE) at pH 9 (with ethyl acetate); quantification was performed in multiple reaction monitoring (MRM) mode. LSD-d3 was used as an internal standard. The limit of quantification (LOQ) for all substances was 0.5 pg mL-1. Precision and accuracy did not exceed 15.8% and ±14.4%, respectively. Recovery and matrix effect values were 80.6-118.6% and ±19.4%. A stability study was conducted over 30 days under different storage conditions (25 °C, 4 °C and -20 °C) for blood, urine, plasma, and serum, collected in various test tube configurations and with different preservative agents. It was found that the collection of samples in NaF can effectively stabilize LSD analogs and minimize the conversion of N1-substituted compounds to LSD or MiPLA. The presented method is the most sensitive to date for analyzing designer LSD analogs in biological samples, with potential for routine clinical and forensic use, enhancing detection of emerging illicit compounds. By examining the mass spectra (QTOF-MS/MS) obtained in this study and reviewing the literature on analytical characterization of LSD analogs, we proposed fragmentation patterns to aid in future identification of new designer LSD analogs (NPS).

Role of molecular packing in RTP features of positional isomers: The case study of triimidazo-triazine functionalized with ethynyl pyridine moieties

Organic materials characterized by multi-component emissive behavior including RTP features are extremely desirable for various applications. Frequently, long lasting emissions of solids are originated from intermolecular interactions whose role is far from being fully understood. In this context, positional isomers with similar molecular properties but different packing arrangement can be a useful tool to get a deeper comprehension of the mechanisms involved in the solid state emissive behavior. Here, the results obtained on two derivatives of cyclic triimidazole (TT) functionalized with a pyridin-2-yl or 4-yl ethynyl group are presented and interpreted through spectroscopical, structural and computational studies. The two isomers are hardly emissive in solution but become good emitters in blended PMMA films displaying almost overlapping fluorescence and phosphorescence. In solid-state, two additional lower energy phosphorescences are activated through the establishment of either π-π stacking or synergic π-π/hydrogen bond interactions. Stronger aggregated RTP features are observed in the pyridin-2-ylethynyl derivative which displays tighter π-π stacking interactions.

Combined Gas Chromatography–Mass Spectrometry, Gas Chromatography–Infrared, and Computational Approach to Differentiate Constitutional Isomers of Methylpyridine Derivatives

Methylpyridine derivatives serve as crucial components and intermediates in agrochemical products, particularly synthetic auxin herbicides. Accurate structural elucidation of these compounds is required for regulatory compliance and successful product registration. While mass spectrometry (MS) techniques are commonly employed for structural analysis, their effectiveness decreases when dealing with isomeric compounds. In this study, we propose an integrated workflow that combines gas chromatography–infrared spectroscopy (GC-IR) and density functional theory (DFT) calculations to enable structural elucidation of methylpyridine derivatives. GC-IR provides temporally resolved infrared (IR) spectra, enabling qualitative and quantitative analysis without compound isolation. GC-IR can effectively distinguish isomeric compounds by comparing IR spectra of energy-minimized structures calculated using DFT, even when the spectral differences are subtle. Our comprehensive approach leverages GC-MS, GC-IR, and DFT calculations, facilitating robust structural characterization of methylpyridine derivatives utilized in the production of diverse agrochemical products.

Soot particle morphology and polycyclic aromatic hydrocarbons formation molecular dynamics during diffusion combustion of three pentanol biofuels

Soot particles constitute a major pollutant in engine diffusion combustion, posing a serious threat to human health and the atmospheric environment. The employment of carbon-neutral biofuel, pentanol, in engines contributes to reducing soot emissions; however, its effectiveness is contingent upon the position of the OH functional group. This work investigated the soot morphology and microstructural parameters evolution of three pentanol isomers, and explored the influence mechanism of OH functional group positional isomerism on the entire process of PAHs formation at the atomic level. The results showed that the peak of primary particle size and soot volume fraction in pentanol flames showed a trend of 2-pentanol>3-pentanol>1-pentanol, and the initial formation time of soot in 1-pentanol flame is the latest, and the particle aggregate size is the smallest. The entire process of pentanol isomers soot formation can be divided into four stages: fuel pyrolysis forming initial ring, PAHs growing into initial soot, soot chain growth and structural evolution, soot morphology transformation and maturation. Among the three isomers, 2-pentanol has the fastest initial ring formation rate, the highest peak C-number in the largest molecule, and ultimately forms a more mature fullerene-like structure. 1-pentanol has the slowest initial ring formation rate, the lowest peak C-number in the largest molecule, ultimately forms a lower maturity layered structure. In terms of reaction pathways, H-atom abstraction and dehydroxylation reactions jointly dominate the initial decomposition pathway in 1-pentanol combustion, while in 2-pentanol, dehydroxylation becomes the main initial decomposition pathway due to the high stability of H atoms on β‑carbon. The dehydroxylation reaction tends to generate olefins, promoting the generation of C1-C4 hydrocarbon. The oxygen atom bonded on the α‑carbon site exhibits a stronger carbon fixation ability, and C1-C4 hydrocarbons are more inclined to participate in oxidation to form CO rather than promote the soot production.

Practically complementary size exclusion chromatography and reversed-phase liquid chromatography for the preparative separation of structurally similar flavone-C-glycosides

In this study, a practicably complementary size exclusion chromatography and reversed-phase liquid chromatography method was constructed and applied to efficiently separate and purify structural analogs or isomers from natural products. First, a ternary styrene–divinylbenzene matrix CHP20P medium–pressure elution system was applied for Ligustrum qianluoenenst leaf crude sample pretreatment, with a recovery of 91.2 %, and 13.0 g of the target fraction Fr4 was obtained. A complementary HW-40C SEC and ReproSil-Pur C18 AQ RPLC system was subsequently constructed by optimizing the HW-40C separation conditions and ReproSil-Pur C18 AQ analysis. Finally, the established complementary SEC and RPLC method was used for the separation and purification of compounds from Ligustrum qianluoenenst leaf target fraction Fr4, and 12 flavone-C-glycosides were successfully prepared with purities exceeding 95 %. The overall methodologies established for flavone-C-glycoside preparative isolation have the potential to maximize the possibility of discovering more structural analogs, including new structural analogs or isomers from natural products.

Coordination geometry flexibility driving supramolecular isomerism of Cu/Mo pillared-layer hybrid networks.

Hydrothermal synthesis led to four novel 3D pillared-layer metal-organic frameworks: [Cu4(4,4'-bipy)4(MoO4)4·0.3H2O]n (1), [Cu(4,4'-bipy)0.5(MoO4)·0.25H2O]n (2), [Cu(4,4'-bipy)(MoO4)·0.1H2O]n (3), and [{Cu(4,4'-bipy)}2(Mo8O26)0.5]n (4). These compounds exhibit diverse supramolecular isomerism within their 3D coordination networks, each incorporating bimetallic {CuMoO} layers linked by 4,4'-bipyridine, demonstrating a remarkable structural diversity. Compound 1 features a 3D network derived from conformational supramolecular isomerism. Its bimetallic layer comprises fused 16-membered {Cu4Mo4O8} and eight-membered {Cu2Mo2O4} rings, with varying O-Cu-O bond angles affecting the network puckering and Cu-Cu distances. In contrast, the coordination networks observed in 2, 3, and 4 correspond to structural supramolecular isomers from the earlier stated networks. In 2, centrosymmetric Cu2+ dimers with distorted square-pyramidal geometry are linked along the c axis by 4,4'-bipyridine, forming 1D {Cu2(4,4'-bipy)}n chains with a Cu-Cu distance of 2.95 Å. Its oxide substructure comprises bilayers of fused 12-membered {Cu3Mo3O6} rings. Crystal structures 3 and 4 are particularly notable for their construction at the Cu+ centers. In compound 4, this isomerism is further influenced by the interplay between the distortion of the coordination geometry of both the Cu and Mo ions. The propensity to form these supramolecular isomers primarily stems from the flexible coordination environment of copper ions. Electron paramagnetic resonance measurements corroborated the structural descriptions of the paramagnetic compounds 1 and 2.

Studying Structural Details in Complex Samples: II. High Field Asymmetric Waveform Ion Mobility Spectrometry (FAIMS) Coupled to High Resolution Tandem Mass Spectrometry (MS/MS).

The elucidation of structural motifs in extremely complex mixtures is very difficult since the standard methods for structural elucidation are not capable to provide significant information on a single molecule. The best method for the analysis of complex mixtures is ultrahigh resolution mass spectrometry, but the utilization of this method alone does not provide significant information about structural details. Here, a combination with a separation method is necessary. While chromatography is a well-established technique, it has some disadvantages in regard to the separation of complex mixtures, as often no separation of individual isomers is possible. Therefore, here the combination of an ion mobility separation with ultrahigh resolution mass spectrometry is evaluated. As a sample matrix, crude oil is used because it is an excellent matrix to develop new analytical techniques on complex samples. Crude oil is the most complex natural sample known, but only little information is available on the structural identity or functionalities due to a high number of structural isomers or isobars. A lab-built APPI/APLI-FAIMS source was revised to optimize ion transmission and used to follow up on the ion mobility of crude oil constituents after photoionization. An MS/MS approach using collision-induced dissociation (CID) was used to elucidate structural motifs of the transmitted isomers.

Side Chain Phenyl Isomerization-Induced Spatial Conjugation for Achieving Efficient Near-Infrared II Phototheranostic Agents.

The contradiction of near-infrared II (NIR-II) emission and photothermal effects limits the development of phototheranostic agents (PTAs) in many emerging cutting-edge applications. Organic aggregates present a promising opportunity for the balance of competitive relaxation processes through the manipulation of molecular structure and packing. Herein, side chain phenyl isomerization-induced spatial conjugation was proposed for constructing A-D-A type NIR-II PTAs with simultaneous enhancement of fluorescence brightness and photothermal properties. Three pairs of mutually isomeric fluorophores, whose phenyls respectively located at the outside (o-series) and inside (i-series) of the side chain, were designed and synthesized. The positional isomerization of the phenyl endows the o-series crystals with strong spatial conjugation between the phenyl group on the side chain and the backbone, as well as interlocked planar network, which is different to that observed in the i-series. Thus, all o-series nanoparticles (NPs) exhibit red-shifted absorption, enhanced NIR-II emission, and superior photothermal properties than their i-series counterparts. A prominent member of the o-series, o-ITNP NPs, demonstrated efficacy in facilitating NIR-II angiography, tumor localization, and NIR-II imaging-guided tumor photothermal therapy. The success of this side chain phenyl isomerization strategy paves the way for precise control of the aggregation behavior and for further development of efficient NIR-II PTAs.

Side Chain Phenyl Isomerization‐Induced Spatial Conjugation for Achieving Efficient Near‐Infrared II Phototheranostic Agents

AbstractThe contradiction of near‐infrared II (NIR‐II) emission and photothermal effects limits the development of phototheranostic agents (PTAs) in many emerging cutting‐edge applications. Organic aggregates present a promising opportunity for the balance of competitive relaxation processes through the manipulation of molecular structure and packing. Herein, side chain phenyl isomerization‐induced spatial conjugation was proposed for constructing A‐D‐A type NIR‐II PTAs with simultaneous enhancement of fluorescence brightness and photothermal properties. Three pairs of mutually isomeric fluorophores, whose phenyls respectively located at the outside (o‐series) and inside (i‐series) of the side chain, were designed and synthesized. The positional isomerization of the phenyl endows the o‐series crystals with strong spatial conjugation between the phenyl group on the side chain and the backbone, as well as interlocked planar network, which is different to that observed in the i‐series. Thus, all o‐series nanoparticles (NPs) exhibit red‐shifted absorption, enhanced NIR‐II emission, and superior photothermal properties than their i‐series counterparts. A prominent member of the o‐series, o‐ITNP NPs, demonstrated efficacy in facilitating NIR‐II angiography, tumor localization, and NIR‐II imaging‐guided tumor photothermal therapy. The success of this side chain phenyl isomerization strategy paves the way for precise control of the aggregation behavior and for further development of efficient NIR‐II PTAs.

One pot synthesis of donor-acceptor carbon nitride with distinct thiophene rings accelerate photocatalytic hydrogen evolution

Graphitic carbon nitride (g-CN) with a donor-acceptor structure was synthesized by urea and cross-linking thiophene precursors at the terminal sites, achieved through calcination of urea with four different thiophene-based precursors under atmospheric conditions. Among these, UDB-2-1, which incorporates dibenzothiophene-2-carboxyaldehyde (DB-2) 1 mg, demonstrated a hydrogen evolution activity of 650 μmol/g·h, approximately six times higher than pristine graphitic carbon nitride (U). The apparent quantum yield (AQY) was measured to be 4.01 %, 4.89 %, and 3.72 % at 400 nm, 420 nm, and 450 nm, respectively, in the presence of potassium hydrogen phosphate (KPH). This enhanced performance is attributed to increased visible light absorption from the n-π∗ transition introduced by the thiophene ring and enhanced charge separation due to the donor-acceptor (DA) structure, with DB-2 acting as an electron donor. Prepared photocatalysts were characterized by XRD, XPS, FTIR, SEM, TEM, BET, ESR, EIS, Mott-Schottky, DRS, PL, and TRPL measurement. This study provides a simple and effective strategy to improve carbon nitride performance and underscores the importance of functional group positioning and structural isomers in molecular design for solar-energy applications.

Alkali cation-π interactions in aqueous systems, modulating supramolecular stereoisomerism of nanoscopic metal-organic capsules

Contrary to common chemical intuition, cation-π interactions can persist in polar, aqueous reaction solutions, rather than in dry non-coordinative solvent systems. This account highlights how alkali ion-π interactions impart distinctive structure-influencing supramolecular forces that can be exploited in the preparation of nanoscopic metal-organic capsules. The incorporation of alkali ions from polar solutions into molecular pockets promotes the assembly of otherwise inaccessible capsular entities whose structures are distinctive to those of common polyoxovanadate clusters in which {V=O} moieties usually point radially to the outside, shielding the molecular entities. The applied concept is exemplified by homologous {V20} and {V30} cages, composed of inverted, hemispherical {V5O9} units. The number and geometrical organization of these {V5O9} sub-units in these cages are associated with prevailing cation-π\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\pi$$\\end{document} interactions and competing steric effects. The stereoisomers of these resulting nano-sized objects are comparable to Alfred Werner-type structural isomers of simple mononuclear complexes in-line with fundamental coordination chemistry principles.

Ingenious design of novel layered double hydroxide/conjugated microporous polymer modified silica gel for diversified chromatographic applications

The development of novel stationary phases with specific functionalities for multitudinous separations has far-reaching implications in the field of chromatography. Layered double hydroxide (LDH) shows great potential for application in separation science, and the composite use of LDH with other materials is an effective way to increase its application potential. Herein, an attempt has been made for the first time to combine LDH nanosheets with full exposure of active sites and porous conjugated microporous polymer (CMP) with π-conjugated backbones and large aperture cavity for the preparation of a novel separation material. Compositing of 2D-LDH nanosheets with CMP can achieve synergistic effects, coupling the coordination, hydrogen bonding and electrostatic interactions provided by LDH with the hydrophobic and π-conjugation properties of CMP, which is expected to enhance the separation capabilities. In this work, 2D-LDH/CMP@SiO2 composites were first developed as liquid chromatographic stationary phases, in which CMP was coordinated with metal ions on LDH nanosheets, and meanwhile, immobilized on the thiolated silica microspheres via thiol-yne click reaction. This facile strategy not only reduces the particle aggregation of LDH, but also increases its opportunity to interact with analytes, thus endowing the composites with more interaction sites. The synthesized novel 2D-LDH/CMP@SiO2 possesses superior separation efficiency and selectivity to the CMP@SiO2 and commercialized columns, which shows good separation for various hydrophilic/ionic/hydrophobic analytes, including polycyclic aromatic hydrocarbons, steroid hormones, bisphenols, phthalates, alkylphenols and positional isomers. The separation process is determined by multiple interactions resulting from the synergistic function of CMP and 2D-LDH materials. In summary, this work confirms the promising application of 2D-LDH/CMP@SiO2 composites in the separation of multicomponent samples, providing new possibilities for the use of LDH/CMP as functional materials for liquid chromatographic separation.

Phosphonate-Based Aza-Macrocycle Ligands for Low-Temperature, Stable Chelation of Medicinally Relevant Rare Earth Radiometals and Radiofluorination.

Radioisotopes of fluorine (18F), scandium (43/44Sc, 47Sc), lutetium (177Lu), and yttrium (86Y, 90Y) have decay properties ideally suited for targeted nuclear imaging and therapy with small biologics, such as peptides and antibody fragments. However, a single-molecule strategy to introduce these radionuclides into radiopharmaceuticals under mild conditions to afford inert in vivo complexes is critically lacking. Here, we introduce H4L2 and H4L3, two small-cavity macrocyclic chelator structural isomers bearing a single phosphonate functional group. Potentiometry and spectrophotometry were employed to determine H4L2 and H4L3's ability to form a single [M(L)]- species with metals of different sizes (Sc3+, Lu3+, and Y3+) under physiologically relevant conditions. NMR spectroscopy and density functional theory (DFT) calculations suggest modulation of H4L2 and H4L3's inner-sphere hydration across the Sc3+/Lu3+/Y3+ series. Radiochemical labeling experiments with 18F, 44Sc, 177Lu, and 86Y reveal that H4L2 selectively chelates radioscandium at room temperature with high apparent molar activity (AMA, 462 mCi/μmol), while radiofluorination remains inaccessible. In contrast, H4L3 enables room temperature radiochelation 44Sc, 177Lu, and 86Y (AMA: 96-275 mCi/μmol) and incorporates 18F via the Sc-18F methodology to form [18F][ScF(L3)]2-. In vivo biodistribution analysis at 1 h postinjection confirms the broad utility of H4L3: all four radiochemical complexes clear off-target organs and remain >98% intact in urine metabolite analyses. The scope of room temperature radiochemical labeling, paired with facile 18F incorporation, to afford in vivo compatible complexes exceeds the clinical gold standard chelator DOTA and previously reported acyclic chelators, rendering H4L3 promising for prospective radiopharmaceutical applications.

Revisiting Butafulvene Formation by Thermal Dimerization of Fluorene-Based Dialkynes - Effects of Aromatic Substituents.

Butafulvenes, together with pentafulvenes and [3]radialenes, form a series of constitutional benzene isomers in which aromaticity changes significantly and can be strongly substituent dependent. Butafulvene, as a member of this series, is frequently proposed to be antiaromatic. Based on butafulvenes Hopf, Zimmerman and coworkers first time described, derivatives thereof were synthesized and the effects of substituents on both the stability of the intermediate isobenzenes and on their optoelectronic and (anti)aromatic properties are discussed.

Some isomers of boron-nitrogen doped phenanthrene – DFT treatment

Phenanthrene is an even alternant aromatic hydrocarbon. In adjacent positions simultaneously boron and nitrogen doped phenanthrene and some of their derivatives have found some technological applications. In the present study, isomers of phenanthrene perturbed as mentioned above have been considered within the restrictions of density functional theory at the level of B3LYP/6-311++G(d,p) level. All the isomeric structures presently considered are thermally favored and electronically stable at the standard states. Various structural and quantum chemical data have been collected and discussed, including UV-VIS spectra. Also the NICS (0) data have been obtained for the isomers.