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DOI: 10.1055/s-0043-1777285
Solvents Influence 1H NMR Chemical Shifts and Complete 1H and 13C NMR Spectral Assignments for Florfenicol
Abstract
Florfenicol (FFC) is an important and widely used veterinary drug, and its structure has been characterized by nuclear magnetic resonance (NMR) spectroscopy. The study aimed to investigate the influences of solvent type, solvent concentration, and temperature on the chemical shifts of the 1H NMR of FFC. The results showed that different types of solvents significantly affected the chemical shifts, especially the chemical shifts of 2-H, 3-H, 5-H, and the active protons. When DMSO-d 6 is used as the solvent, there is no significant difference in the chemical shifts of FFC with a concentration ranging from 20 to 250 mmol/L; however, as the temperature increases, the chemical shifts of the active protons move to a higher field. Besides, the NMR spectroscopic data and structural analysis of FFC were refined by 1H, 13C, distortionless enhancement by polarization transfer-135 (DEPT-135), 1H–1H correlation spectroscopy (1H–1H COSY), phase-sensitive gradient heteronuclear singular quantum correlation (gHSQC), and heteronuclear multiple bond correlation (gHMBC) NMR spectroscopy using DMSO-d 6 as a solvent. The study will help with qualitative and quantitative analysis of FFC in the future.
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Keywords
florfenicol - nuclear magnetic resonance - solvents - solvent concentrations - chemical shiftsIntroduction
Florfenicol (FFC) ([Fig. 1]), a derivative of chloramphenicol, is an important broad-spectrum antibiotic that can diffusely enter into bacterial cells through fat solubility. FFC mainly acts on the 50s subunit of the bacterial 70s ribosome to inhibit peptidyl transferase and subsequent peptide chain elongation by blocking peptidase growth and peptide chain formation, thus, preventing the synthesis of bacterial proteins. FFC is frequently used to treat infectious infections in aquatic, livestock, and poultry, due to its advantages including potent antibacterial action, low risk of drug resistance, good absorption in vivo, high safety, high bioavailability, etc.[1] [2] [3] However, the growing use of FFC may be associated with adverse effects. Hassanin et al found that FFC-treated chickens had a significantly high number of adipocytes in the bone marrow, and the hematopoietic cell lines were moderately atrophied,[4] confirming the influence of FFC in hematopoietic and immune functions. Yun et al demonstrated a negative impact of oral administration of FFC on intestinal mucosal barriers, immune system, and intestinal microbiota.[5] Wang et al suggested a promoting effect of FFC on the oxidative stress response, which plays an important role in inducing kidney injury in broiler chickens.[6]
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To protect food health and safety, the detection of FFC residue in animal and meat-derived foods has been gradually emphasized.[7] [8] [9] [10] [11] [12] [13] [14] Chloramphenicol analogs usually have low residue levels in aquatic products, thus, it is necessary to use high sensitivity and low detection limit assays to detect them. Li et al calculated the total residue levels of FFCs in eggs using an ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method to quantify the metabolite florfenicolamide.[15] Wang et al established a simple, rapid, and novel ultra-performance liquid chromatography with fluorescence detection (UPLC-FLD) method to determine methylsulfonamides, FFC, and its metabolite florfenicolamide residues in poultry eggs.[16] Patyra and Kwiatek used a liquid chromatography and diode array detector to simultaneously determine FFC and methylsulfonamides in medicinal feed.[17]
Nuclear magnetic resonance (NMR) is characterized by its speed and ease of use. NMR uses the relationship between the number of protons of a specific group in the molecule and the corresponding spectral peaks to quickly, accurately, and quantitatively analyze the components without the aid of the standards. With the advancement of NMR techniques in terms of hardware and software, quantitative analysis using NMR techniques has been paid increasing attention and has been used to study the changes in drugs in solvents.[18] [19] [20] [21] [22] [23] [24] [25] In this study, the NMR technique was used to analyze the spectral data and the structure of FFC. Besides, the effects of solvents, FFC concentration, and temperature on the chemical shifts of the FFC 1H NMR spectra were assessed. All 1H and 13C NMR chemical shifts were determined by advanced one-dimensional (1D) and two-dimensional (2D) NMR.
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Experimental
Materials and Reagents
FFC used for spectral measurement was supplied by Zhejiang Hisoar Pharmaceutical Co. Ltd. (Taizhou, Zhejiang) with a purity of 99%. Chloroform-d (CDCl3, 99.9 atom% D), acetonitrile-d 3 (ACN-d 3, 99.8 atom% D), acetic acid-d4 (CD3COOD, 99.5 atom% D), methanol-d 4 (CD3OD, 99.8 atom% D), acetone-d 6 (CD3COCD3, 99.9 atom% D), methyl sulfoxide-d 6 (DMSO-d 6, 99.9 atom% D), N,N-dimethylformamide-d 7 (DMF-d 7, 99.5 atom% D), and pyridine-d 5 (C5D5N, 99.5 atom% D) were purchased from Cambridge Isotope Laboratories Inc.(Cambridge, United States).
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Apparatus and Conditions
The advanced 1D and 2D NMR spectra were recorded at 303 K on a Varian Mercury-Plus 400 MHz spectrometer (Varian, United States) operating at frequencies of 400.13 and 100.62 MHz using 5 mm ID probe for 1H/13C, respectively. Tetramethylsilane (δ 0.00 ppm) and DMSO-d 6 (δ 39.50 ppm) were used as the reference for the measurement of 1H and 13C NMR chemical shifts. Eight solutions in different solvents (CDCl3, ACN-d 3, CD3COOD, CD3OD, CD3COCD3, DMSO-d 6, DMF-d 7, C5D5N) with FFC concentrations at 50 mmol/L, six solutions (20, 50, 100, 150, 200, 250 mmol/L) in DMSO-d 6, and three solutions (20, 100, 250 mmol/L) in DMSO-d 6 at different temperatures (303, 308, 313, 318, 323, 328, 333, 338, 343 K) were prepared for investigating the influences of 1H NMR chemical shifts of FFC. 1H NMR spectra were recorded with acquisition times of 2.5 seconds using a 45-degree pulse and 13C spectra were obtained with acquisition times of 1.2 seconds using a 30-degree pulse. The distortionless enhancement by polarization transfer (DEPT) spectrum was recorded using relaxation delay times of 2 seconds by using a shaped pulse for a 180-degree pulse on the f1 channel with a 135-degree read pulse to give CH, CH3 positive, and CH2 negative. The 2D NMR spectra were recorded with standard pulse sequences supplied with the TopSpin 3.6.5 spectrometer software (Bruker DESKTOP-G4TBOV8). The 1H–1H COSY spectrum was recorded using one transient per t 1 increment with relaxation delay times of 2 seconds, spectral widths of 4587.2 Hz, and acquisition times of 0.223 seconds in t 2 with 128 complex t 1 increments. The phase-sensitive gradient heteronuclear singular quantum correlation (gHSQC) spectrum was obtained with polarization transfer and refocusing delays optimized for 1 J CH = 150 Hz; four transients were recorded for each of 128 complex t 1 increments with relaxation delay times of 2 seconds, spectral widths of 4,587.2/17,094.0 Hz, and acquisition times of 0.223 seconds in t 2. The heteronuclear multiple bond correlation (gHMBC) spectrum was obtained with polarization transfer delays optimized for 1 J CH = 150 Hz, n J CH = 6 Hz; four transients were recorded for each of 400 complex t 1 increments with relaxation delay times of 2 seconds, spectral widths of 4,587.2/24,154.6 Hz, and acquisition times of 0.223 seconds in t 2. All 1D and 2D spectra were processed using Mestrelab's Mnova software, version 7.1.0-9185 (Santiago de Compostela, Spain).
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Results and Discussion
The Influences of Solvents on 1H NMR of FFC
FFC dissolved in different solvents was used to identify changes in chemical shifts in 1H NMR spectra. Approximately 9 mg of FFC was dissolved in 500 μL different pure solvents forming a concentration of 50 mmol/L, respectively, but the solubility of FFC in the CDCl3 was very poor and saturated in the solution. Our data showed that the solvent causes a significant change in 1H NMR chemical shifts ([Fig. 2]). The entire elucidation of the hydrogen protons of the FFC in various solvents is displayed in [Table 1]. When CD3OD and CD3COOD were used, the active hydrogen protons disappeared due to the exchange with the deuterium hydrogen which made 5-H exhibit a doublet peak, while in other solvents (ACN-d 3, CD3COCD3, DMSO-d 6, DMF-d 7), the 5-H showed a doublet of doublet peak due to the coupling with both 4-H and the O–H. As a result, the O–H proton showed a double peak. The signals of O–H, 4-H, and 3-H were overlapping when using C5D5N as a solvent, which led to the difficulty of integration. Moreover, it was strange that the 5-H showed a single peak. The signals of 4-H and 3-H were overlapping when using CD3COOD as a solvent, which made it difficult to determine the coupling constants. When CDCl3 was used as a solvent, the signals of 4-H and 3-H were separated clearly. However, the coupling of 5-H with the O–H proton was not observed, which showed a doublet peak and a broad singlet peak, respectively. The N–H proton coupling with the 4-H was obvious. As far as 2-H was concerned, its chemical shift increased with the solvents' order as follows: CDCl3, ACN-d 3, CD3COOD, CD3OD, CD3COCD3, DMSO-d 6, DMF-d 7, C5D5N, and the chemical shift moved to a low frequency from δ 5.81 to δ 6.81 ppm. All these results substantiate the solvent effect. The solvent effect mainly has the following aspects: firstly, different solvents have different solvent magnetic permeability, so FFCs are subjected to different magnetic field strengths, which affects the δ value. Secondly, the solvent molecules can be close to the solute molecules, which changes the electron cloud density of the solute molecules and produces a deshielding effect. In addition, the magnetic anisotropic effect of solvent molecules leads to shielding and deshielding effects on different parts of the solute molecules. Moreover, solvent molecules form hydrogen bonds with solute molecules, which can also affect the chemical shift of the hydrogen nucleus.[22] [26] In particular, the aromatic solvent, C5D5N, showed the most pronounced changes.
Abbreviation: FFC, florfenicol.
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The Influences of Solvent Concentrations on 1H NMR of FFC
Generally, the concentration will also have a certain effect on the 1H NMR chemical shift, acting mainly on changes in solution viscosity, changes in ion pairs, or changes in aggregation states.[27] In this work, six different concentrations of FFC solutions in DMSO-d 6 (20, 50, 100, 150, 200, 250 mmol/L) were used to further investigate the influence of concentrations on the 1H NMR chemical shifts of FFC; however, no dramatical changes were found ([Fig. 3]).
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The Influences of Temperatures on 1H NMR of FFC
To evaluate the influences of temperature, three solutions at different concentrations (20, 100, 250 mmol/L) of FFC in DMSO-d 6 were prepared for further experiments. The results showed that the samples with different concentrations at different temperatures exhibited similar changes in chemical shifts of active protons. The chemical shift of the O–H proton moved to a high frequency from δ 8.56 to δ 8.32 ppm when the temperature rose from 303 to 343 K. Every 5-degree temperature increase led to a 0.03 ppm chemical shift to the high frequency at the same time, the chemical shift of the N–H proton moved to a high frequency from δ 6.12 to δ 5.95 ppm, with 0.02 ppm of the chemical shift moving to the high field as the temperature increased 5 degrees. At high temperatures the thermal motion of the molecule is intensified, the degree of hydrogen bonding is reduced, and the density of the electron cloud around the hydrogen nucleus is increased making the hydrogen protons move into the higher field, and hence the corresponding chemical shift is reduced. The above changes were only found in active protons, while the chemical shifts of other protons did not significantly exhibit such changes. It was confirmed that the influence of temperature on active protons of FFC was greater than other protons ([Fig. 4]).
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The Structure Elucidation of FFC by Comprehensive NMR Analysis
The structure of FFC was elucidated with DMSO-d 6 as a solvent. Assignments of all 1H NMR chemical shifts are summarized in [Table 2]. Hydrogen and carbon atoms were assigned by using 1H NMR, full decoupling 13C NMR, DEPT-135, 1H–1H COSY, gHSQC, and gHMBC. Among 14 hydrogen proton signals in the 1H NMR spectrum, two active hydrogen protons were found with 1H NMR chemical shifts at δ 6.15 ppm (O–H) and δ 8.62 ppm (N–H). Due to proton exchange, these two active hydrogen protons disappeared with a little D2O added. The obtained signals in the range of δ 4.26 to 4.47 and δ 4.58 to 4.73 ppm corresponding to 3-H and 4-H respectively were multiplets, which seems inconsistent with the general split law due to the fluorine atom coupling with 3-H and 4-H. The 5-H (δ 5.00 ppm) signals were doublet of doublet due to the coupling with 4-H and O–H, which changed into a double signal when the hydrogen–deuterium exchanged. The 2-H was in a lower frequency (δ 6.45 ppm) compared with 4-H due to the deshielding effect of chlorine atoms and oxygen atoms. The 7-H and 11-H are chemically equivalent and have the same chemical shift (δ 7.61 ppm). The 8-H and 10-H are chemically equivalent as well (δ 7.85 ppm).
Abbreviation: FFC, florfenicol.
The 13C NMR spectrum elucidation is shown in [Table 3]. There were 12 carbon signals shown in 13C NMR in addition to the solvent peak, among which one primary carbon, six tertiary carbon, two secondary carbon, and three quaternary carbon atoms were found through the comparison among the DEPT-135 and full decoupling 13C NMR. For the symmetry of the structure, the signal at δ 43.59 ppm in the highest frequency was assigned to 12-C and the signal at δ 163.41 ppm in the lowest frequency was assigned to the carbon in the carbonyl. The 3-C (δ 81.31, 83.00 ppm, 1 J CF = 168.4), 4-C (δ 54.51, 54.71 ppm, 2 J CF = 19.8), and 5-C (δ 69.28, 69.34 ppm, 3 J CF = 5.7) exhibited a double peak due to the coupling with the fluorine atom by their coupling with 3-H, 4-H, and 5-H in gHSQC. The 2-C at δ 66.20 ppm was in a lower frequency compared with 4-C due to the deshielding effect of chlorine atoms and oxygen atoms. The signal at δ 126.26 ppm was assigned to 8-C and 10-C, and the 7-C and 11-C had the same chemical shift in the δ 126.92 ppm. The 9-C at δ 139.32 ppm could be confirmed by its coupling with 12-H in gHMBC. The signal at δ 147.61 ppm was assigned to 6-C by its coupling with 5-H in gHMBC.
Abbreviation: FFC, florfenicol.
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Conclusion
In this study, we elucidated the structure of FFC and demonstrated that different types of solvents made obvious changes in their chemical shifts, especially on 2-H, 3-H, 5-H, and active protons. The clearer 1H NMR spectrum was obtained when using CDCl3 as the solvent, but the poor solubility of FFC in it made it difficult to obtain its 13C NMR and 2D spectra. This is due to the molecular structure of FFC containing several polar groups, such as amide bond, –Cl, and –F, which have strong polarity, so it is difficult to dissolve in the weak polar solvent of CDCl3. Therefore, DMSO-d 6 was eventually used for all the NMR spectra. Different concentrations of FFC in DMSO-d 6 at different temperatures were used to further evaluate the changes of 1H NMR chemical shifts and no significant effects were found except for the active protons. As the temperature increases, the chemical shift of active protons gradually decreases because –OH and –NH form hydrogen bonds to a lesser extent at higher temperatures, and the chemical shift is shifted to a higher field. This investigation provided reasonable reference data for further research, especially the choice of the appropriate solvent and temperature, which can lead to significant changes in the 1H NMR chemical shifts, signal separation, and spin–spin coupling constants.
NMR technology has the advantages of no damage, continuity, high resolution, and strong selectivity, and plays a significant role in compound structure identification, content detection, and dynamic tracking of the chemical reaction process. In future development, NMR can be combined with other analytical equipment, for digital intelligence, and more widely used in various fields.
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Conflict of Interest
None declared.
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References
- 1 Blickwede M, Schwarz S. Molecular analysis of florfenicol-resistant Escherichia coli isolates from pigs. J Antimicrob Chemother 2004; 53 (01) 58-64
- 2 Liu Y, Fang Y, Chen Y. et al. Improving intestinal absorption and antibacterial effect of florfenicol via nanocrystallisation technology. J Microencapsul 2022; 39 (7–8): 589-600
- 3 Fan G, Zhang L, Shen Y. et al. Comparative muscle irritation and pharmacokinetics of florfenicol-hydroxypropyl-β-cyclodextrin inclusion complex freeze-dried powder injection and florfenicol commercial injection in beagle dogs. Sci Rep 2019; 9 (01) 16739
- 4 Hassanin O, Abdallah F, Awad A. Effects of florfenicol on the immune responses and the interferon-inducible genes in broiler chickens under the impact of E. coli infection. Vet Res Commun 2014; 38 (01) 51-58
- 5 Yun S, Guo Y, Yang L. et al. Effects of oral florfenicol on intestinal structure, function and microbiota in mice. Arch Microbiol 2020; 202 (01) 161-169
- 6 Wang X, Han C, Cui Y. et al. Florfenicol induces renal toxicity in chicks by promoting oxidative stress and apoptosis. Environ Sci Pollut Res Int 2021; 28 (01) 936-946
- 7 Feng JB, Ruan HT, Chen HG. et al. Pharmacokinetics of florfenicol in the orange-spotted grouper, epinephelus coioides, following oral administration in warm seawater. J World Aquacult Soc 2018; 49 (06) 1058-1067
- 8 Li W, Guo F, Jiang X, Li Y, Li X, Yu Z. Compound ammonium glycyrrhizin protects hepatocytes from injury induced by lipopolysaccharide/florfenicol through oxidative stress and a MAPK pathway. Comp Biochem Physiol C Toxicol Pharmacol 2019; 225: 108585
- 9 Ma RR, Zhan J, Fang WH. et al. Pharmacokinetics and tissue distribution of bronopol in grass carp, Ctenopharyngodon Idella, at 15 and 20°C. Aquacult Res 2020; 51 (02) 648-654
- 10 Osman K, Zolnikov TR, Badr J. et al. Vancomycin and florfenicol resistant Enterococcus faecalis and Enterococcus faecium isolated from human urine in an Egyptian urban-rural community. Acta Trop 2020; 201: 105209
- 11 Qian MR, Wang QY, Yang H. et al. Diffusion-limited PBPK model for predicting pulmonary pharmacokinetics of florfenicol in pig. J Vet Pharmacol Ther 2017; 40 (06) e30-e38
- 12 Li L. Rapid determination of chloramphenicol, thiamphenicol, and florfenicol residues in aquatic products by UPLC-MS/MS method. China Food Safety Magazine 2022; 363 (34) 67-70
- 13 Wang Y, Li X, Wang Y, Schwarz S, Shen J, Xia X. Intracellular accumulation of linezolid and florfenicol in OptrA-Producing Enterococcus faecalis and Staphylococcus aureus. Molecules 2018; 23 (12) 3195
- 14 Yang F, Yang F, Wang GY. et al. Effects of water temperature on tissue depletion of florfenicol and its metabolite florfenicol amine in crucian carp (Carassius auratus gibelio) following multiple oral doses. Aquaculture 2020; 515: 734542
- 15 Li X, Zhang Y, Sun Q. et al. Determination of extractable and non-extractable florfenicol residues as florfenicol amine in eggs by UPLC-MS/MS. Food Addit Contam Part A Chem Anal Control Expo Risk Assess 2022; 39 (09) 1512-1520
- 16 Wang B, Xie X, Zhao X. et al. Development of an accelerated solvent extraction-ultra-performance liquid chromatography-fluorescence detection method for quantitative analysis of thiamphenicol, florfenicol, and florfenicol amine in poultry eggs. Molecules 2019; 24 (09) 1830
- 17 Patyra E, Kwiatek K. HPLC-DAD analysis of florfenicol and thiamphenicol in medicated feedingstuffs. Food Addit Contam Part A Chem Anal Control Expo Risk Assess 2019; 36 (08) 1184-1190
- 18 Chashmniam S, Tafazzoli M. NMR investigation and theoretical calculations of the solvent effect on the conformation of valsartan. J Mol Struct 2017; 1148: 73-80
- 19 Ghiasi R. Exploration of solvent effects on the spectroscopic properties (Ir and C 13 NMR) in the OsCl3(CCH2CMe3)(PH3)2 carbyne complex. J Struct Chem 2018; 59 (05) 1052-1057
- 20 Kaştaş G, Albayrak Kaştaş Ç, Tabak A. Investigation of molecular structure and solvent/temperature effect on tautomerism in (E)-4,6-dibromo-3-methoxy-2-[(p-tolylimino)methyl]phenol, a new thermochromic Schiff base, by using XRD, FT-IR, UV-vis, NMR and DFT methods. Spectrochim Acta A Mol Biomol Spectrosc 2019; 222: 117198
- 21 Kauch M, Pecul M. Spin-spin artificial DNA intercalated with silver cations: theoretical prediction. ChemPhysChem 2012; 13 (05) 1332-1338
- 22 Korac J, Todorovic N, Zakrzewska J. et al. The conformation of epinephrine in polar solvents: an NMR study. Struct Chem 2018; 29 (05) 1533-1541
- 23 Niwayama S, Hiraga Y, Chaki S. 13C NMR spectroscopic studies for the behaviors of carbonyl compounds in various solvents. Tetrahedron Lett 2017; 58 (50) 4677-4681
- 24 Patel AK, Mishra SK, Krishnamurthy K, Suryaprakash N. Retention of strong intramolecular hydrogen bonds in high polarity solvents in binaphthalene-benzamide derivatives: extensive NMR studies. RSC Advances 2019; 9 (56) 32759-32770
- 25 de Melo Sousa CM, Giordani RB, de Almeida WAM. et al. Effect of the solvent on the conformation of monocrotaline as determined by isotropic and anisotropic NMR parameters. Magn Reson Chem 2021; 59 (05) 561-568
- 26 Kim H, Babu CR, Burgess DJ. Quantification of protonation in organic solvents using solution NMR spectroscopy: implication in salt formation. Int J Pharm 2013; 448 (01) 123-131
- 27 Xu L, Huang B, Hou Z, Huang S, Zhao Y. Solvent effects used for optimal simultaneous analysis of amino acids via 19F NMR spectroscopy. Anal Chem 2023; 95 (05) 3012-3018
Address for correspondence
Publication History
Received: 29 June 2023
Accepted: 31 October 2023
Article published online:
01 December 2023
© 2023. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution License, permitting unrestricted use, distribution, and reproduction so long as the original work is properly cited. (https://creativecommons.org/licenses/by/4.0/)
Georg Thieme Verlag KG
Rüdigerstraße 14, 70469 Stuttgart, Germany
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References
- 1 Blickwede M, Schwarz S. Molecular analysis of florfenicol-resistant Escherichia coli isolates from pigs. J Antimicrob Chemother 2004; 53 (01) 58-64
- 2 Liu Y, Fang Y, Chen Y. et al. Improving intestinal absorption and antibacterial effect of florfenicol via nanocrystallisation technology. J Microencapsul 2022; 39 (7–8): 589-600
- 3 Fan G, Zhang L, Shen Y. et al. Comparative muscle irritation and pharmacokinetics of florfenicol-hydroxypropyl-β-cyclodextrin inclusion complex freeze-dried powder injection and florfenicol commercial injection in beagle dogs. Sci Rep 2019; 9 (01) 16739
- 4 Hassanin O, Abdallah F, Awad A. Effects of florfenicol on the immune responses and the interferon-inducible genes in broiler chickens under the impact of E. coli infection. Vet Res Commun 2014; 38 (01) 51-58
- 5 Yun S, Guo Y, Yang L. et al. Effects of oral florfenicol on intestinal structure, function and microbiota in mice. Arch Microbiol 2020; 202 (01) 161-169
- 6 Wang X, Han C, Cui Y. et al. Florfenicol induces renal toxicity in chicks by promoting oxidative stress and apoptosis. Environ Sci Pollut Res Int 2021; 28 (01) 936-946
- 7 Feng JB, Ruan HT, Chen HG. et al. Pharmacokinetics of florfenicol in the orange-spotted grouper, epinephelus coioides, following oral administration in warm seawater. J World Aquacult Soc 2018; 49 (06) 1058-1067
- 8 Li W, Guo F, Jiang X, Li Y, Li X, Yu Z. Compound ammonium glycyrrhizin protects hepatocytes from injury induced by lipopolysaccharide/florfenicol through oxidative stress and a MAPK pathway. Comp Biochem Physiol C Toxicol Pharmacol 2019; 225: 108585
- 9 Ma RR, Zhan J, Fang WH. et al. Pharmacokinetics and tissue distribution of bronopol in grass carp, Ctenopharyngodon Idella, at 15 and 20°C. Aquacult Res 2020; 51 (02) 648-654
- 10 Osman K, Zolnikov TR, Badr J. et al. Vancomycin and florfenicol resistant Enterococcus faecalis and Enterococcus faecium isolated from human urine in an Egyptian urban-rural community. Acta Trop 2020; 201: 105209
- 11 Qian MR, Wang QY, Yang H. et al. Diffusion-limited PBPK model for predicting pulmonary pharmacokinetics of florfenicol in pig. J Vet Pharmacol Ther 2017; 40 (06) e30-e38
- 12 Li L. Rapid determination of chloramphenicol, thiamphenicol, and florfenicol residues in aquatic products by UPLC-MS/MS method. China Food Safety Magazine 2022; 363 (34) 67-70
- 13 Wang Y, Li X, Wang Y, Schwarz S, Shen J, Xia X. Intracellular accumulation of linezolid and florfenicol in OptrA-Producing Enterococcus faecalis and Staphylococcus aureus. Molecules 2018; 23 (12) 3195
- 14 Yang F, Yang F, Wang GY. et al. Effects of water temperature on tissue depletion of florfenicol and its metabolite florfenicol amine in crucian carp (Carassius auratus gibelio) following multiple oral doses. Aquaculture 2020; 515: 734542
- 15 Li X, Zhang Y, Sun Q. et al. Determination of extractable and non-extractable florfenicol residues as florfenicol amine in eggs by UPLC-MS/MS. Food Addit Contam Part A Chem Anal Control Expo Risk Assess 2022; 39 (09) 1512-1520
- 16 Wang B, Xie X, Zhao X. et al. Development of an accelerated solvent extraction-ultra-performance liquid chromatography-fluorescence detection method for quantitative analysis of thiamphenicol, florfenicol, and florfenicol amine in poultry eggs. Molecules 2019; 24 (09) 1830
- 17 Patyra E, Kwiatek K. HPLC-DAD analysis of florfenicol and thiamphenicol in medicated feedingstuffs. Food Addit Contam Part A Chem Anal Control Expo Risk Assess 2019; 36 (08) 1184-1190
- 18 Chashmniam S, Tafazzoli M. NMR investigation and theoretical calculations of the solvent effect on the conformation of valsartan. J Mol Struct 2017; 1148: 73-80
- 19 Ghiasi R. Exploration of solvent effects on the spectroscopic properties (Ir and C 13 NMR) in the OsCl3(CCH2CMe3)(PH3)2 carbyne complex. J Struct Chem 2018; 59 (05) 1052-1057
- 20 Kaştaş G, Albayrak Kaştaş Ç, Tabak A. Investigation of molecular structure and solvent/temperature effect on tautomerism in (E)-4,6-dibromo-3-methoxy-2-[(p-tolylimino)methyl]phenol, a new thermochromic Schiff base, by using XRD, FT-IR, UV-vis, NMR and DFT methods. Spectrochim Acta A Mol Biomol Spectrosc 2019; 222: 117198
- 21 Kauch M, Pecul M. Spin-spin artificial DNA intercalated with silver cations: theoretical prediction. ChemPhysChem 2012; 13 (05) 1332-1338
- 22 Korac J, Todorovic N, Zakrzewska J. et al. The conformation of epinephrine in polar solvents: an NMR study. Struct Chem 2018; 29 (05) 1533-1541
- 23 Niwayama S, Hiraga Y, Chaki S. 13C NMR spectroscopic studies for the behaviors of carbonyl compounds in various solvents. Tetrahedron Lett 2017; 58 (50) 4677-4681
- 24 Patel AK, Mishra SK, Krishnamurthy K, Suryaprakash N. Retention of strong intramolecular hydrogen bonds in high polarity solvents in binaphthalene-benzamide derivatives: extensive NMR studies. RSC Advances 2019; 9 (56) 32759-32770
- 25 de Melo Sousa CM, Giordani RB, de Almeida WAM. et al. Effect of the solvent on the conformation of monocrotaline as determined by isotropic and anisotropic NMR parameters. Magn Reson Chem 2021; 59 (05) 561-568
- 26 Kim H, Babu CR, Burgess DJ. Quantification of protonation in organic solvents using solution NMR spectroscopy: implication in salt formation. Int J Pharm 2013; 448 (01) 123-131
- 27 Xu L, Huang B, Hou Z, Huang S, Zhao Y. Solvent effects used for optimal simultaneous analysis of amino acids via 19F NMR spectroscopy. Anal Chem 2023; 95 (05) 3012-3018
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