INNOVATIVE SYNTHESIS AND MULTIFACETED EXPLORATION OF HYDRAZINE-DERIVED SALTS: STRUCTURAL INSIGHTS, BIOACTIVITY, AND CARBON DOT CATALYSIS FOR ENVIRONMENTAL APPLICATIONS.

Abstract

The research highlights the synthesis and comprehensive analysis of novel compound derived from hydrazine derivatives, specifically benzyl carbazate (BCZ, C8H10N2O2) and 2-thiobarbituric acid (2-TBA, C4H4N2O2S). The reaction between BCZ and 2-TBA produced a crystalline compound with the molecular formula [(C4H3N2O2S)-(C8H11N2O2)+]. Various analytical techniques, including FTIR, UV-Vis, 1H NMR, and 13C NMR, were employed to investigate the structural and spectral properties of the compound. Single-crystal X-ray diffraction (S-XRD) analysis confirmed the monoclinic crystal system with a P b c a space group. To gain further insight into the electronic structure, stability, and reactivity of the compound, theoretical studies using density functional theory (DFT) were conducted. Hirshfeld surface analysis was used to examine the solid-state behavior, while fingerprint plots provided detailed insights into the crystal packing motifs. The compound displayed significant biological activity, including strong antibacterial and antioxidant properties, along with toxicity against brine shrimp. In addition, it exhibited catalytic activity by reducing nitrobenzene to aniline with 82.05% degradation efficiency and the rate constant was found to be 0.05412 min⁻¹. The compound was subjected to pyrolysis at 260°C for 12 hours, resulting in highly pure carbon dots. Characterization of these carbon dots using UV-Vis, photoluminescence (PL), X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM) revealed that they had an average size of around 5 nm. Raman spectroscopy showed characteristic D (1355 cm⁻¹) and G (1560 cm⁻¹) bands, corresponding to sp3 and sp2 carbon, respectively. PL analysis displayed a broad blue emission when excited at 300 nm. These carbon dots demonstrated excellent optical properties, making them highly effective for sensing toxic heavy metal ions Ni2+, Cu2+, and Hg2+, respectively. Additionally, they showed enhanced catalytic performance in nitrobenzene reduction, achieving 84.94% degradation with the rate constant of 0.0978 min⁻¹.

Specification

Description:[02] The BCZ salts of 2-TBA were prepared by combining stoichiometric quantities of 2-TBA [0.144 g (1 mmol)] and BCZ [0.166 g (1 mmol)] in 1:1 ratio in an aqueous medium (20 mL). The resulting mixture was stirred until clear solutions with pH=4 was obtained. The resulting solution was then heated at 60°C in a water bath for 4 h and subsequently subjected to slow evaporation at room temperature. After one-week, light pink crystals suitable for single-crystal X-ray diffraction (SC-XRD) analysis were obtained. The compounds was subjected to washing with absolute alcohol and then dried under vacuum. [03] The carbon dot was synthesized using the pyrolysis method. A sample of 5 g of compound was placed in a covered silica crucible and heated in hot air oven. The temperature was gradually increased to 260°C and maintained for 12 h. After the heating process, the crucible was allowed to cool to room temperature, yielding a stable carbon dot powder, which was then subjected to various characterization studies. [04] The Single crystal -XRD analysis reveals that the proton transfer compound crystallizes in the monoclinic crystal system with the P b c a space group (Z = 8). The asymmetric unit of the compound comprises one 2-Thiobarbiturate anions, one protonated BCZ cation moiety (CCDC number: 2334943). [05] The structure of the compound is confirmed through various 1H and 13C NMR signals. The proton signal from the OCH2 group of BCZ is observed at δ 5.09 ppm. The CH proton of 2-TBA exhibits signal at δ 3.17 ppm. The NH and NH2 protons of BCZ are detected at δ 8.86 ppm and δ 1.15 ppm, respectively. The peak at 83.03 ppm was assigned to the CH carbon of 2-TBA. The carbon signals of OCH2 moiety of BCZ appeared at 66.26 ppm from the 13C NMR spectra. [06] The 2D fingerprint plots were generated to determine the percentage of contributions from each type of intermolecular interaction to the total Hirshfeld surface area. The percentages of each contact type contributing to the total Hirshfeld surface are as follows: H…H (31.5%), H…O (13.2%), O…H (14.1%), S…H (9.1%), C…H (6.5%), H…S (5.1%), C…C (4.9%), H…C (4.5%), N…H (2.3%), H…N (1.9%), C…O (1.4%), C…N (1.3%), N…C (1.3%), O…C (1.1%), S…H (9.1%) and C…C 4.9%), S…O (0.3%), C…S (0.1%), O…S (0.2%), O…O (0.2%), S…C (0.2%). H-H interactions constitute 38.4% of the total surface, indicating their prominent role in the crystal packing of compound. [07] The compound demonstrated the highest LC50 value of 1154 μg/mL towards brine shrimp toxicity analysis. Compared to potassium dichromate, the reduced lethality of these synthesized compounds suggests lower risk to aquatic ecosystems, indicating better ecological safety. [08] The carbon dot was synthesized using the pyrolysis method from the above proton transfer precursor. In the solid state, the photoluminescence (PL) spectra of the carbon dots exhibited two characteristic emissions around 440 nm and 550 nm, corresponding to blue and green emission. When dissolved in solvents, the emission wavelength in the blue region dominates, resulting in characteristic blue emission. [09] TEM images of the carbon dots, clearly showing their spherical shape and narrow size distribution, with the average size of the carbon dots ranging from 5.2 to 5.5 nm. [10] The interaction between carbon dots (CDs) and various metal cations was analyzed using fluorescence spectrometry. The fluorescence quenching was particularly pronounced in the presence of Cu²⁺ and Ni²⁺ ions. The order of sensing ability for the carbon dots is Cu2+ > Ni2+ > Fe3+> Ca2+ > Hg2+ > Zn2+ > Cd2+ > Al 3+> Bi3+ > Mg2+ > Mn2+ > Ba2+ > Co2+ > Sr2+, demonstrating broad range of sensing capabilities, including for toxic heavy metal ions like Hg2+ and Cd2+. [11] The antibacterial effects of the precursor and carbon dot against two types of bacteria, namely Gram positive (S. aureus) and Gram negative (E. coli), were assessed using the Kirby-Bauer technique. As a result, the synthesized carbon dot exhibited superior activity towards S. aureus in comparison to E. coli. [12] The carbon dots exhibit strong catalytic activity in the reduction of nitrobenzene, achieving an 84.94% reduction, with a rate constant of 0.0978 min⁻¹ in comparison to its precursor with 82.05% catalytic degradation and rate constant of 0.05412 min⁻¹. , Claims: A novel proton transfer compound combining 2-thiobarbituric acid and benzyl carbazate has been reported for the first time.
 Until now, only Schiff bases of benzyl carbazate have been reported. We are the first to explore and discover proton transfer compounds involving benzyl carbazate.
 The compound exhibited significant biological activity, as confirmed through antibacterial, antioxidant, and brine shrimp cytotoxicity assays.
 The compound served as a novel precursor for the synthesis of carbon dots through pyrolysis.
 The carbon dots demonstrated enhanced antibacterial activity compared to their precursor, attributed to their nanoscale size.
 The carbon dots have been applied in chemosensing and the reduction of nitrobenzene.

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