Application research of pyridine-4-boronic acid

Introduction

Pyridine-4-boronic acid is a kind of boronic acid derivative, of which appearance is white granular powder(Figure 1). It is useful building blocks in crystal engineering. It can also be used as a catalyst to act as a dehydrative condensation agent to synthesize amides using carboxylic acid and amines as raw materials. Its derivative, polystyrene-bound-4-pyridineboronic acid, is a useful catalyst for amidation reaction and esterification of alpha-hydrocarboxylic acids.It was already reported that 4-pyridinyl boronic acid is a zwitterionic species. In particular, the chemical shift of the pyridine protons were shifted remarkably upfield in basic medium (pH≥9), confirming that deprotonation of pyridine occurs at these pH values, and at neutral pH, pyridine-4-boronic acid exists in aqueous solution mostly in the zwitterionic form.[1]

Synthesis of Pyridine-4-boronic acid

The synthesis of pyridine-4-boronic acid by reaction of n-butyllithium with 4-Br-pyridine and successive addition of trimethoxyborane at -60℃has been previously described, but with this procedure obtained a very low yield. Furthermore, to our knowledge, the compound has not yet been fully characterized. The main problems in the synthesis arose from nucleophilic additions to 4-BrPy, which are competitive with the halogen metal exchange reaction at the relatively high temperature of -60℃,and from the low reactivity of 4-pyLi toward trimethoxyborane. To avoid these drawbacks, authors lowered the temperature to -110℃ and added TMEDA (N,N,N′,N′tetramethyl-1,2-ethylendiamine) as an activating agent. Both elemental analysis and mass spectra indicated that pyridine-4-boronic acid was isolated in the neutralform, NC₅H₄B(OH)₂.[1]

Synthesis of [HNC₅H₄B(OH)₂-4][PtCN₄] (1)

[HNC₅H₄B(OH)₂-4][PtCN₄] (1) was synthesized by mixing of pyridine-4-boronic acid hydrochloride (34.7 mg, 0.21mmol) in 5 ml of water and K₂PtCN₄(0.82mg, 0.21mmol) in 10ml of water. The resulting precipitate was obtained, collected by filtration and dried. Single crystal of 1 was obtained by slow diffusion of in stoichiometric quantities of pyridine-4-boronic acid hydrochloride and [Pt(CN)₄] salt reagent. 71%Yield. Elemental analysis (%). Found: C, 30.74; H, 2.58; N, 15.36. Calculated: C, 29.40; H, 2.64; N, 14.80. The structure of [HNC₅H₄B(OH)₂-4][PtCN₄] (1) compound contains the expected planar anions of [PtCN₄] and pyridine-4-boronic acid cations. On the other hand, the hydrogen atoms of the boronic acids in 1 is syn-anti conformation, which is convenient for the formation of a pair of charge-assisted hydrogen bonds with the N-atoms of [PtCN4] anion.The compound (1) crystallizes in monoclinic, space group P2₁/c, a=5.6159(11) Å, b=14.656(3) Å, c=11.619(2) Å, α=90°, β= 110.35(3), γ=90°, V= 896.6(3) Å3, Z=2. The optimum molecular geometry parameters have been investigated with the DFT/B3LYP method. All geometric parameters are found in good agreement with crystallographic and computational results. Contributions of fragments molecular orbitals (HOFO-LUFO) to frontier molecular orbitals (HOMO-LUMO) are calculated charge transferred from Pt moiety to other fragments.[2]

Synthesis of boron-doped carbon nitride derived from pyridine-4-boronic acid

Two-dimensional g-C₃N₄ nanosheets have attracted tremendous attention owing to their specific surface area,high electron transport ability, significantly reduced triplet–triplet annihilation process,and potential applications.To enhance their electrochemical activity, non-metal heteroatoms,i.e., boron(B), phosphor and sulfur, were doped into g-C₃N₄. In particular, B and C belong to the same period and are located at an adjacent location on the periodic table, so they have many similar properties. In addition, functional groups with a B–C bond can act as Lewis acid sites. Based on this advantage, B-doped-C₃N₄ (BCN) has been reported by various research groups.However,these studies needed to utilize other substances (such as H₃BO₃ and B₂O₃) as a boron source and then the as-prepared precursor was calcinated to obtain the B-doped-C₃N₄ materials. Therefore,a convenient and simple synthesis method needs further development. The application of BCN to food quality testing has not been reported.In this work, researchers synthesized BCN nanosheets using pyridine-4-boronic acid as both a boron source and a nitrogen source, and extra impurities were not introduced through the self-doped process. This work aims to provide an innovative material to specifically detect traces of targeted analytes. There are currently three benefits to this approach: (i) BCN nanosheets are non-metallic materials with low toxicity and high stability; (ii) BCN nanosheets are successfully synthesized via one-step calcination treatment; and (iii) BCN-800 exhibits high sensitivity, selectivity, and stability in both antibody and antigen recognition.

In summary, authors suggested a facile strategy to fabricate a series of BCN composites by controlling the calcination temperature (700, 800, 900℃), which serve as an immunosensing system for detecting vomitoxin. This strategy uses pyridine-4-boronic acid as the only boron and nitrogen source. In this simple synthetic strategy, BCN-800 preserves the advantages of the non-metallic, B-doped, and unique layered structure and enhances antibody adsorption and antigen detection. Compared with the other two samples, the defect density and disorder degree of BCN-800 are between those of BCN-700 and BCN-900, which will not cause a higher defect density or higher disorder degree.In addition, the ratio of C, N, and B contents of BCN-800 is also between that of BCN-700 and BCN-800. It is because of the existence of this intermediate state that the BCN-800 material shows better electrochemical performance. Moreover, the layered stacked BCN-800 ultrathin nanosheets show excellent selectivity and sensitivity for detecting as little as 1.0 pg/mL vomitoxin. This approach may provide a new strategy for improving the synthesis of B-doped-C₃N₄.[3]

References

[1] Dreos R , Nardin G , Randaccio L ,et al.A Molecular Box Derived from Cobaloxime Units Held Together by 4-Pyridinylboronic Acid Residues[J].Inorganic Chemistry, 2001, 40(22):5536.DOI:10.1021/ic0102034.

[2] Elif Güngr, Sevinek R ,Hülya Kara Subasat.New Compound of Pyridine-4-Boronic Acid Cation and Pt(CN)4 Anion Salt: Synthesis, Structural Properties, Hirshfeld Surface Analysis and Density Functional Theory Calculations[J].Journal of the Institute of Science and Technology, 2021(3).DOI:10.21597/JIST.859627.

[3] Li X , Zhu P , Liu C , Pang H . One step synthesis of boron-doped carbon nitride derived from 4-pyridylboronic acid as biosensing platforms for assessment of food safety. Chem Commun (Camb). 2019;55(62):9160-9163. doi:10.1039/c9cc03787j

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