Reply to the Comments on Planar Tetracoordinate Hydrogen: Pushing the Limit of Multicentre Bonding

Recently, Huo et al. has commented on our communication (Angew. Chem. Int. Ed. 2024, 63, e202317312, DOI: 10.1002/anie.202317312), regarding the multireference character (MRC) of our proposed cluster. Their argument is based on small HOMO-LUMO gap, fractional occupation density (FOD) and CASPT2(12,13) calculations. They also proposed that the singlet planar In4H+ cluster cannot be observed. We present our calculations which reveals that some of their arguments are based on wrong interpretation of data and inadequate use of methodology. While we certainly agree with the strong physical ground of FOD, CASSF and CASPT2 methodology, we believe that such analysis for clusters is not adequate.

Manganese Complex Catalyzed Sequential Multi-component Reaction: Enroute to a Quinoline-Derived Azafluorenes

The development of innovative synthetic strategies for constructing complex molecular structures is the heart of organic chemistry. This significance of novel reactions or reaction sequences would further enhance if they permitted the synthesis of new classes of structural motifs, which have not been previously created. The research on the synthesis of heterocyclic compounds is one of the most active topics in organic chemistry due to the widespread application of N-heterocycles in life and material science. The development of a new catalytic process that employs first-row transition metals to produce a range of heterocycles from renewable raw materials is considered highly sustainable approach. This would be more advantageous if done in an eco-friendly and atom-efficient manner. Herein we introduce, the synthesis of various new quinoline based azafluorenes via sequential dehydrogenative multicomponent reaction (MCR) followed by C(sp3)-H hydroxylation and annulation. Our newly developed, Mn-complexes have the ability to direct the reaction in order to achieve a high amount of desired functionalized heterocycles while minimizing the possibility of multiple side reactions. We also performed a series of control experiments, hydride trapping experiments, reaction kinetics, catalytic intermediate and DFT studies to comprehend the detailed reaction route and the catalyst's function in the MCR sequence.

Planar tetracoordinate fluorine atom: global minimum with viable possibility

Planar hypercoordinate structures are emerging tremendously. Most of the second-row elements from the periodic table exhibit this remarkable structural feature. Planar tetracoordinate fluorine (ptF) atoms were also predicted in group 13 supported clusters. However, high-level ab initio calculations nullified the fact and established that all these ptFs were not minimum energy structures on the potential energy surface. Thus, a true ptF is still scarce in the literature. Herein, we propose the unprecedented ptF as the global minimum of the C2V symmetric H3Li4F- cluster. Heavier alkali metals (Na and K) showed similar results. Both density functional theory (DFT) and ab initio calculations revealed that the ptF structure is a real minimum and indeed, the global minimum. Bonding analysis indicates that the central fluorine atom is stabilized by multicentre bonding with four surrounding Li atoms. Natural charge analysis reveals that the fluorine atom is negatively charged, which is strongly attracted by the positively charged surrounding lithium centres, thereby imparting significant electrostatic attraction. Aromaticity has no role to play here. The cluster is dynamically stable and is expected to be detected in the gas phase.

Fluoride ion detection in aqueous medium: Colorimetric and turn-off fluorescent Schiff base chemosensor

The work described is focused on a newly developed colorimetric Schiff base fluorescent sensor that exhibits a "turn-off" response when detecting fluoride ions (F-) in an aqueous environment. The confirmation of the recognition event is accomplished through fluorescence titration, absorbance titration, and Density Functional Theory (DFT) calculation study. From the results, it is determined that the detection limit of F- is 2.35 × 10-8 M which is much lower than the World Health Organization (WHO) permissible limit for drinking water while the binding constant was obtained to be 0.1 × 106 M-1 indicating a moderate affinity for the fluoride ions. Furthermore, the binding stoichiometry between the Probe L and F- was found to be 1:1 which is evidenced by the Job's plot and DFT calculation study. Overall, the novel sensor's impressive sensitivity and selectivity make it a promising candidate for the detection of fluoride ions in aqueous media, particularly for monitoring drinking water quality to ensure compliance with WHO guidelines.

Planar Tetracoordinate Hydrogen: Pushing the Limit of Multicentre Bonding

Among the list of planar tetracoordinate atoms, the smallest element hydrogen is missing. No experimental and theoretical evidence have ever been put forwarded. Herein, we introduce the first planar tetracoordinate hydrogen atom (ptH) in the global minimum geometry of In4 H+ cluster. Bonding analysis indicates that the central hydrogen atom is acting like a proton and significant charge transfer from the surrounding In4 framework results in a negative charge of the central hydrogen atom. The proposed global minimum geometry possesses σ-aromaticity and the central hydrogen atom forms unusual multicentre bond with more than three centres.

Can Dative Bond Between Two Anions Possible?

Formation of a genuine chemical bond between two similarly charged fragments is beyond expectation. Any such interaction generally lies in the realm of non-covalent interaction. Herein, formation of a strong dative covalent bond between two anionic fragments is reported for the first time. Calculation using ab initio coupled cluster theory reveals the formation of an unprecedented strong H3 Be- ←X- (X- =CH3 - , CN- , OH- , F- ) dative covalent bond. The calculated bond dissociation energies in polar solvents are significant, which indicates the possibility of their experimental realization.

Comment on "Strong Be-Be bonds in double-aromatic bridged Be2(μ-SO) molecules" by F. Rezaie and S. Noorizadeh, Dalton Transactions, 2022, 51, 12596

Metal-metal interactions have always fascinated chemists. One such interesting example is the Be-Be interaction. Recently, a strong Be-Be interaction in a bridged Be2(μ-SO) cluster has been proposed by Rezaie et al. I, hereby, challenge their view. Detailed calculations reveal that there is no Be-Be interaction in the proposed cluster. In fact, the proposed bridged structure is energetically very high on the potential energy surface. The global minimum has completely different geometry from that reported by Rezaie et al. and features no Be-Be interaction at all.

Heterogeneous iron catalyst for C(1)-H functionalization of 2-naphthols with primary aromatic alcohols

An iron oxide nanocatalyst supported on a potassium exchanged zeolite-Y (Fe₂O₃-KY) is an efficient and reusable catalyst that promotes the selective α-H functionalization of 2-naphthols with various aromatic primary alcohols. The reaction occurs at 110 °C in dichloroethane and requires 6 h for completion. The product yields were found to vary with respect to the nature of the substituents. Benzyl alcohols with electron-donating groups gave the highest yields of up to 90%.

Inter-Alkali-Metal Dative Bond in the MMN3 - (M=Alkali Metal) Cluster

Alkali metals are generally Lewis acids. On the contrary, Lewis basic character of alkali metals forming donor - acceptor complexes is a very rare phenomenon. In this contribution, I have theoretically designed an anionic cluster MMN₃ ^- (M=alkali metals) on the basis of experimentally known reagent, alkali salt of azide ion MN₃ , which shows unprecedented M:^- →M donor-acceptor interaction. To the best of author's knowledge, the characterization of such donor-acceptor interaction among alkali metals is unprecedented. Formation of the 2c-2e donor-acceptor bonds have been confirmed by quantum theory of atoms in molecules and electron localization function analyses. The calculated bond dissociation energies are significant suggesting their possible spectroscopic identification.

Ultra High Reversible Hydrogen Storage Capacity of Li4B2 Cluster: A Quantum Chemical Study

Quantum chemical calculations have been carried out to investigate the hydrogen adsorption characteristics of Li4B2 cluster. Calculations reveal that the cluster can adsorb a maximum of thirteen H2 molecules reaching...

Dual colorimetric sensing of ascorbic acid and thyroxine using Ag-EGCG-CTAB via a DFT approach

In this work, a colorimetric approach for the detection of ascorbic acid (AA) and thyroxine (TH) was developed by synthesizing cost-effective silver nanoparticles (AgNPs) decorated with epigallocatechin gallate (EGCG) and CTAB. EGCG is the major bioactive chemical constituent that played a significant role in this study. The environment around the nanoparticle (NP) was controlled by adding CTAB surfactants. The synthesized NPs were characterized by different advanced techniques including XRD, XPS, SEM, and TEM. UV-visible spectra were thoroughly analyzed for sensing of AA and TH and the colour change of the solution can be visually monitored. The change in the localized surface plasmon resonance (LSPR) properties was used as an asset for the detection of AA and TH. A good linear relationship was obtained in both the sensing schemes with a limit of detection (LoD) of 0.67 μM and 0.33 μM for AA and TH respectively. Furthermore, the nanoparticles (NP) were implemented for real-sample analysis (pharmaceutical tablets). A cost-effective filter paper strip-based method coupled with smartphone scanning sensing was developed for the detection of AA. The interaction of AA and TH with the probe was depicted by a density functional theory (DFT) analysis. The synthesized NPs show tremendous selectivity towards AA and TH and excellent potential for practical applications.

Selective detection of fluoride via amplified donor-acceptor interaction of 6H-indolo[2,3-b]quinoline

In this report, 6H-indolo[2,3-b]quinoline (hereafter 2a) was synthesized and employed as an optical chemosensor for fluoride. The sensitivity of 2a towards fluoride was established from the change in both the absorption and emission signals. The various in-situ¹H NMR, UV-Vis, and density functional studies indicate that the 1:2 binding interaction between 2a and fluoride followed by deprotonation to its corresponding di-anion (2a^2-), which in turn boosted the donor-acceptor interaction between indole and quinoline moiety in 2a^2-via expansion of torsion angle by 10.2° as compared to 2a. Consequently the significant changes in both the absorption and emission signal of 2a allow us to detect and estimate the concentration of fluoride up to 0.2 μM from the mixture of different anions.

Protonation of Verkade bases: a theoretical study

The dilemma of favorable protonation at less basic phosphorus rather than more basic nitrogen in Verkade bases has been resolved.

A theoretical study on antioxidant activity of ferulic acid and its ester derivatives

Phenolic compounds play a very crucial role as antioxidant that can prevent various diseases caused by free radicals in human body. Although, lots of natural phenolic compounds having antioxidant activity are available nowadays, the modeling of compounds with naturally available phenolics as building blocks is very important in order to get enhanced antioxidant activity. In this study, Ferulic acid (FA), one natural phenolic acid present in coffee, apples, orange, etc., is taken as building block and its ester derivatives with different alkyl groups are subjected to measure the antioxidant activity by using density functional theory (DFT). Various parameters like bond dissociation enthalpy (BDE), vertical ionization potential (IP[Formula: see text]), reactivity descriptors, metal chelation ability, etc. are used to measure the antioxidant activity. All the parameters suggest that the ester derivatives are superior antioxidants to the parent FA. Since FA has been reported to be present as esters in many herbs and plants, hence our study provides a route to study the structure activity relationship of this class of natural phenolics with antioxidant activity.

A selective ratiometric fluoride ion sensor with a (2,4-dinitrophenyl)hydrazine derivative of bis(indolyl) methane and its mode of interaction

An easy-to-synthesis chemosensor was synthesized and employed as a selective optical chemosensor for fluoride through naked eye detection, which allow us to detect and estimate the concentration of fluoride ion accurately up to 2 μM via ratiometric responses.

Effect of substituent and solvent on cation-π interactions in benzene and borazine: a computational study

A DFT and ab initio quantum chemical study has been carried out at different theoretical levels to delve into the role of the cation-π interaction within the main group metal cations (Li(+), Na(+) and K(+)), substituted benzene and borazine. The effects of electron withdrawing and electron donating groups on these non-covalent forces of interaction were also studied. The excellent correlation between Hammett constants and binding energy values indicates that the cation-π interaction is influenced by both inductive and resonance effects. Electron donating groups (EDG) such as -CH3 and -NH2 attached to benzene at the 1, 3 and 5 position and the three boron atoms of borazine were found to strengthen these interactions, while electron withdrawing groups (EWG) such as -NO2 did the reverse. These results were further substantiated by topological analysis using the quantum theory of atoms in molecules (QTAIM). The polarized continuum model (PCM) and the discrete solvation model were used to elucidate the effect of solvation on the cation-π interaction. The size of the cations and the nature of the substituents were found to influence the enthalpy and binding energy of the systems (or complex). In the gas phase, the cation-π interaction was found to be exothermic, whereas in the presence of a polar solvent the interaction was highly endothermic. Thermochemical analysis predicts the presence of thermodynamic driving forces for borazine and benzene substituted with EDG. DFT based reactivity descriptors, such as global hardness (η), chemical potential (μ) and the electrophilicity index (ω) were used to elucidate the effect of the substituent on the reactivity of the cation-π complexes.

A study on biochemical changes during cultivation of Rhizopus oryzae in deproteinized whey medium in relation to chitosan production

The kinetics of cultivation of zygomycete filamentous fungus Rhizopus oryzae in deproteinized whey medium in relation to chitosan production was studied here to optimize chitosan production from R. oryzae as well as utilize whey, a by-product of sweetmeat industry as a cheap source of sugar in the cultivation process. Chitosan content of R. oryzae biomass was found to be increased with time during cultivation and reached maximum (13·6%) after 72 h and then declined steadily. Maximum 1·13 g of chitosan was obtained from one litre of deproteinized whey medium. Concentration of lactose in the medium was observed to be reduced from 45·0 to 11·7 g l(-1) during cultivation resulting in decrease in biochemical oxygen demand (BOD) of whey by approx. 60%, and this was important from environmental point of view before discharging whey into any water body. However, no significant change in pH or titratable acidity was noted during the entire course of cultivation, probably due to good buffering capacity of the medium. Molecular weight of chitosan varied from 130 to 230 kDa depending on the time of cultivation, but no significant change in degree of deacetylation of chitosan (approx. 87%) was found during cultivation.

SIGNIFICANCE AND IMPACT OF THE STUDY

Whey is the largest by-product of dairy industries, and its disposal is a big environmental issue because of its high biological oxygen demand (BOD) value. This study will help to lower BOD value of whey by using it as a cultivation medium for fungus R. oryzae that contains chitosan, a very commercially important material on its cell wall. Moreover, the study on biochemical changes in whey during cultivation process with R. oryzae will help to understand the exact changes occurring in the medium and optimize cultivation process to isolate chitosan in larger extent with better and uniform physicochemical properties.

Pd(ii) coordinated deprotonated diphenyl phosphino amino pyridine: reactivity towards solvent, base, and acid

The reactivity and stability of P(iii)–N and P(iii)≈N bonds will be different towards various solvents, bases, and acids because of their difference in bond strength due to different N-pπ–P-dπ donor bonding.

Optimization of fermentation conditions for green pigment production from Bacillus cereus M¹ 16 (MTCC 5521) and its pharmacological application

Optimal culture conditions for the production of green pigment was investigated. The optimal culture condition for the production of an extracellular green pigment by growing Bacillus cereus M(1) 16 (MTCC 5521) in a complex medium containing (g l(-1) ) Peptone-4.0, Beef Extract-9.0, NaCl-7.0, MgSO4 .7H2 O-1.0 and KH2 PO4 -5.0 was as follows pH-7.0 at 30°C for 72 h in a 5 l fermenter. Aeration rate and agitator speed had no effect on the pigment production. Thin layer chromatogram of the pigment extracted from the fermented broth with chloroform on silica gel GF254 using ethyl acetate and hexane (1 : 1) as solvent showed three fractions. The major fraction (C3 ) was separated out and identified as 9-methyl-1, 4, 5, 8-tetra-azaphenanthrene. Acute toxicity test revealed the nontoxic nature upto a dose of 2000 mg kg(-1) , b.wt., of mice. MTT assay showed the cytotoxic nature in HL60 cells having an IC50 of 2.47 mmol. So, this biopigment may have application in food, textile colorant and pharmaceutical industry.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrated the optimum production of a biopigment (9-methyl-1, 4, 5, 8-tetra-azaphenanthrene) by fermentation of a complex medium with Bacillus cereus M(1) 16 (MTCC 5521) in submerged fermentation. This is the first investigation of toxicity and cytotoxicity activities of this biopigment. The study showed that the purified pigment had no toxicity to healthy albino mice but a high cytotoxicity activity in HL60 cancer cell line in vitro. The biopigment had further displayed dyeing capability to both solidified agar and cotton cloth. Therefore, it may represent a nontoxic and natural alternative to chemical dyes and pigments.

Tracing the route to ammonia: a theoretical study on the possible pathways for dinitrogen reduction with tripodal iron complexes

The chemistry of nitrogen fixation has been the subject of considerable research with a view to gaining a proper understanding of the mechanistic details. In this article, density functional calculations are performed on all the mechanistic possibilities for dinitrogen reduction mediated by the tripodal iron complexes [(SiP(Me)3)Fe(I)] ([Fe(Si)]) and [(BP(Me)3)Fe(0)] ([Fe(B)]). Dinitrogen addition to the neutral bare complex is found to be thermodynamically more favorable than that to the anionic one. Both symmetric and asymmetric pathways, along with the possible intermediates and transition states, are considered in this study. For both systems, the symmetric path is found to be more likely, although the prospect of the asymmetric path cannot be ignored. Moreover, interconversions between these two pathways are found to be less likely. This study corroborates most experimental observations and provides theoretical insight into the possible existence of some hitherto unknown intermediates such as multiple-bonded Fe-N species in a trigonal bipyramidal geometry. Furthermore, in agreement with experimental observations, this study also highlights the possibility of hydrogen and hydrazine evolution during the complete reduction of dinitrogen.