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Research Article | | Peer-Reviewed

Azo-Imino Tautomerism in Sudan Red 7B/Cyclodextrin Coated ZnO Nanocomposites: Evidence by Spectral and Microscopic Perspectives

Palanichamy Ramasamy,  Narayanasamy Rajendiran*,  Ayyadurai Mani,  Govindaraj Venkatesh,  Albert Antony Muthu Prabhu
Published in Science Journal of Chemistry (Volume 13, Issue 3)
Received: 9 May 2025     Accepted: 23 May 2025     Published: 23 June 2025
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Abstract

Sudan Red-7B/Cyclodextrin doped ZnO nanocomposites are synthesized and analyzed by various spectral and microscopic methods. The doping effect of SR7B/CD on ZnO nano investigated by UV-visible, fluorescence, FTIR, DTA, XRD, FE-SEM and TEM methods. The effect of different polarities of the solvents, α-cyclodextrin (α-CD) and β-cyclodextrin (β-CD), on MV was studied by various spectral methods. The inclusion behaviour of SR7B on both CDs was determined by PM3 method. The solvent and CD studies show that the azo-imino tautomer is present in the SR7B molecule and that, depending upon the polarity of the solvents, absorbance and emission intensities of the azo-imino tautomer is varied. With increasing CD concentrations, the shorter wavelength emission intensity of the SR7B regularly increased while the longer wavelength emission intensity decreased. The horizontal bond length of SR7B is longer than the CD cavities; hence, this molecule is partially encapsulated in the CD cavity. HOMO-LUMO gap for MV/β-CD inclusion complex was more negative, which supports that this complex is more stable than MV/α-CD inclusion complex. Red or blue shifted absorption and fluorescence maxima were seen in SR7B/CD/ZnO nanocomposites than SR7B/CD inclusion complex. Nanoparticle size was measured by TEM-EDS and X-RD methods. TEM image showed that nanosheets are formed in SR7B/CD/ZnO.

Published in Science Journal of Chemistry (Volume 13, Issue 3)
DOI 10.11648/j.sjc.20251303.13
Page(s) 65-75
Creative Commons

This is an Open Access article, distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution and reproduction in any medium or format, provided the original work is properly cited.

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Copyright © The Author(s), 2025. Published by Science Publishing Group
Previous article
Keywords

Sudan Red-7B, Tautomer, Zinc Oxide Nano, Cyclodextrin, Inclusion Complex

1. Introduction
The azo (A)-hydrazone (H) tautomerism of the phenyl azo naphthols was observed in the case of 1-phenylazo-4-naphthol by Zince and Bindenwald
[1]
over one century ago and has been explained by the existence of a `movable' proton in the molecule
[2]
. Unfortunately, due to the high proton exchange rate, both tautomeric forms cannot be separated experimentally, and therefore it was, for some time, impossible to investigate exactly tautomer-solvent interactions
[3, 22]
. The spectrophotometric analysis of tautomeric equilibria
[5-22]
and the solvent influence on the A-H tautomerism of some derivatives of 1 were investigated quantitatively, and it was found that the tautomeric ratio increases from non-polar to polar solvents. This general trend is also valid in the case of the isomeric 1-phenylazo-2-naphthol and 2-phenylazo-1-naphthol, but the solvent effect is not so pronounced because of the stabilizing intramolecular hydrogen bonding
[6, 19-21]
. From the above cited results, it is clear that there is no relation between KT and the dielectric constants of the solvents, suggesting specific interactions.
Proton tautomerism plays an important role in many fields of chemistry and especially biochemistry
[1-22]
. It is well known that the proton transfer can occur in the ground and/or excited state, but only during the last decade has the excited state proton transfer been the subject of substantial interest
[3-9]
. Molecules giving rise to excited state tautomer’s by intramolecular proton transfer (IPT) are often used as laser dyes, in higher energy radiation detectors and molecular memory storage devices, as fluorescent probes, and polymer protectors
[10, 11]
.
Zinc oxide nanoparticles are low in toxicity and have high UV absorption are used in various fields like the ceramic industry, biomedical, etc, because they act as a good surface material.
[23-37]
. It has a hard, rigid structure and is naturally known to have a strong resistance to microbes
[23]
. Due to these reasons, zinc oxide nanoparticles are extensively used for biological labeling, biological sensing, drug delivery, gene delivery, and nanomedicine
[24]
. The Food and drug administration has approved zinc oxide as a safe material. Zinc oxide can also be solubilized in an acidic environment; therefore, this allows the material to be discovered as multifunctional nanocarriers to ease the drug delivery and release processes. Because of the above reasons, this manuscript focuses on: a) analyzing the type of tautomer present in the Sudan Red-7B, b) synthesizing and characterizing ZnO, CD/ZnO, SR7B/ZnO, and SR7B/CD/ZnO nanomaterials using various spectral and microscopic techniques, and c) studying the doping effect of the SR7B/CD on ZnO nanoparticles.
2. Experimental
2.1. Preparation of Drug/CD Inclusion Complex in Solution
Different concentrations of α-CD or β-CD solution (0.1 to 1.0×10-2 M) were taken in 10 ml standard measuring flask. SR7B stock solution has a concentration of 2×10-2 M. 0.2 ml of the SR7B stock solution was added to the above flasks. The mixed solution was made up to 10 ml with triple-distilled water and shaken very well. The final SR7B concentration in each flask was 4×10-4 M and 298 K temperature was used for the experiments.
2.2. Preparation of ZnO and ZnO /SR7B/CD Nanomaterials
0.01 M of zinc sulphate dissolved in 100 ml of deionized water was to heated 50 - 60°C for 20 to 30 minutes. ZnSO4 and NaOH (1%) solution with a molar ratio of 1: 2, which was carried out under vigorous stirring for 12 h at room temperature. The obtained white ZnO precipitate was washed several times and separated by centrifugation
[36-42]
and dried in an oven at 100°C for 6h. The prepared ZnO nanoparticles showed a size distribution of about 25-50 nm.
SR7B (2×10-3 M) was dissolved in 20 ml of ethanol and gradually added to the CD (1×10-2 M in 80 ml) in deionized water. Then this SR7B/CD solution was added to the 0.01 M zinc sulphate (100 ml) Using a hot plate with a magnetic stirrer, this mixture was heated to 50°C for one hour. With vigorous stirring, one to two ml of 1% sodium hydroxide was added and stirred for one to two hours. After that, the above solution was frozen and dried (mini-lyophilized) at -80°C. The powder SR7B/CD/ZnO sample was collected and used for further analysis.
2.3. Molecular Modeling Studies
Using the molecular modeling software Spartan 08, the molecular geometry of SR7B, CD and its inclusion complexes were analyzed. The most stable complexation energy was determined theoretically after the structural assembly of two orientation inclusion complexes using the semi-empirical PM3 method in the gas phase and Gaussian 09W software.
Figure 1. Chemical structure of sudan red-7B [SR7B].
Figure 2. Absorption and fluorescence spectra of SR7B in different solvents at 303 K: 1) cyclohexane 2) 1, 4-dioxane 3) ethyl acetate 4) acetonitrile 5) 2-propanol 6) ethanol 7) water.
Figure 3. Absorption and fluorescence spectra of SR7B in different α-CD concentrations (M): (1) 0, (2) 0.001, (3) 0.002, (4) 0.004, (5) 0.006, (6) 0.008, (7) 0.01. Insert figure: absorbance/IF vs [α-CD].
3. Result and Discussion
3.1. Effect of Solvents and Cyclodextrins
The absorption and emission spectra of sudan red-7B (N-Ethyl-1-{
[4
-(phenyl diazenyl) phenyl] diazenyl}naphthalen-2-amine, SR7B, Figure 1) were examined in different solvents and α-CD and β-CD solutions (Table 1, Figures 2 and 3). In all the solvents, α-CD and β-CD solutions, three absorption and two emission spectral maxima are observed in SR7B (Table 1) which is similar to that observed in other azo compounds
[16-22]. 
The absorption and emission maxima of SR7B are red shifted from nonpolar (cyclohexane: λabs~ 521, 367, 247 nm, λemi~591, 410 nm) to polar solvents, however, large red shift is observed in water (λabs~ 565, 368, 244, 224 nm, λemi~584, 364 nm). The data reveal that the location of both bands is relatively influenced by the nature of the substituent and the polarity of the solvents. The absorption and emission spectral shifts of SR7B in all the solvents are different from the CD solution, suggesting that SR7B molecule is encapsulated in the CD cavity. The bathochromic or hypsochromic shifts in the ground and excited state reflect increased delocalization of the N=N group and π-cloud of the aromatic ring
[16-22]
.
Table 1. Absorption and fluorescence spectral maxima of SR7B with different Solvents and cyclodextrins.

Solvents

abs

log

flu

Cyclohexane

521

3.27

591

367

3.17

410

247

3.46

1, 4-Dioxane

534

3.48

591

369

3.34

412

248

3.64

Ethyl acetate

534

3.52

597

365

3.39

414

250

3.61

Acetonitrile

534

3.20

595

364

3.05

414

247

3.33

2-Propanol

533

3.47

414

366

3.34

598

246

3.63

Ethanol

536

3.12

593

366

2.98

414

246

3.28

Water

565

2.88

584

368

3.13

364

244

3.32

224

3.25

α-CD -0.01 M

562

3.18

584

365

3.39

362

242

3.57

222

3.57

β-CD 0.01 M

563

3.17

584

366

3.35

363

243

3.53

223

3.53

α-CD K (1: 1) x105 M-1

54

-

139

β-CD K (1: 1) x105 M-1

144

-

176

α-CD G (kcalmol-1)

-11.0

-

-13.4

β-CD G (kcalmol-1)

-13.5

-

-14.0

Excitation wavelength (nm)

-

-

320
Upon increasing the CD concentrations, i) the absorption appear in water (565, 368, 244, 222 nm) slightly blue shifted and the absorbance regularly increased, ii) in the excited state dual emission noted at 584, 366 nm, iii) the shorter wavelength emission maxima regularly increased with slight blue shift, whereas the longer wavelength emission intensity decreased at the same wavelength, and iv) the CD cavity provide a non-polar environment and restrict the free rotation of the guest molecules, hence, the absorption and emission intensities of the SR7B molecule was changed
[16-22]
. The absorption and emission spectral shifts and shape of SR7B with α-CD or β-CD are the same indicating that both CDs form a similar type of inclusion complex. Binding constant (Table 1) for the inclusion complexes was determined from the slope and intercept of the plot 1/(A-A0) vs 1/[CD] and 1/(I-I0) vs 1/[CD]. The straight line of the plot and the presence of an isosbestic point in the absorption spectrum suggest the formation of a 1: 1 inclusion complex
[16-22]
.
3.2. Molecular Modeling
The ground state geometries of SR7B, α-CD, β-CD and their inclusion complexes were optimized by the PM3 method. HOMO, LUMO (Figure 4), energy, enthalpy, entropy, free energy, dipole moment and zero-point vibrational energy values for SR7B, α-CD, β-CD and the inclusion complexes are all listed in Table 2. When SR7B entered the CD cavity, the polarity and the above parameter values for SR7B, α-CD, and β-CD significantly changed in the inclusion complexes. The internal diameter of the α-CD and β-CD is approximately 5.6 and 6.5 Å and the height is 7.8 Å respectively. In SR7B, the horizontal bond length is 15.58 Å and the vertical bond distance is 8.63 Å (Table 2 and Figure 4). In SR7B, horizontal bond length and the vertical bond length of the N-ethyl naphthalen-2-amine ring is longer than the α-CD and β-CD cavity size, hence, this molecule is partially encapsulated in the CD cavity
[43-50].
The ΔE, ΔG and ΔH values for the SR7B/β-CD inclusion complex are more negative than SR7B/α-CD and the cavity. The negative Gibbs energy and enthalpy of the inclusion complexes indicate that the formation of the complex is spontaneous and exothermic. The negative entropy (ΔS) value suggests the disorder of the system. The energy gap between HOMO and LUMO of the complexes suggest that there will be a significant change in the electronic structures of the guest molecules while molecular recognition and binding. The red color in the molecular electrostatic potential's (MEP) figure (Figure 4) shows that the electronegative charge of the atoms is greater than that of other atoms. HOMO-LUMO gap for SR7B/β-CD inclusion complex was more negative, which supports that this complex is more stable than SR7B/α-CD inclusion complexes.
Figure 4. PM3 optimized structures of (a) SR7B, (b) HOMO, LUMO and (c) MEP of SR7B. The blue color indicates for nitrogen atom, while in HOMO-LUMO, the green and red colors denote negative and positive phases of the molecules.
Table 2. Energetic features, thermodynamic parameters and HOMO-LUMO energy calculations for SR7B and its inclusion complexes by semiempirical PM3 method.

Properties

SR7B

α-CD

β-CD

SR7B/α-CD

SR7B/β-CD

EHOMO (eV)

-8.29

-10.37

-10.35

-8.42

-8.44

ELUMO (eV)

-1.02

1.26

1.23

-1.22

-1.32

EHOMO – ELUMO (eV)

7.26

-11.63

-11.58

7.19

7.12

Dipole (D)

1.46

11.34

12.29

10.96

10.56

E (kcal mol-1)

-170.91

-1247.62

-1457.63

-1083.08

-1295.89

ΔE (kcal mol-1)

-

-

-

-6.37

-9.17

G (kcal mol-1)

-266.73

-676.37

-789.52

-945.25

-1002.41

ΔG (kcal mol-1)

-

-

-

-2.15

-53.84

H (kcal mol-1)

-210.97

-570.84

-667.55

-796.77

-852.93

ΔH (kcal mol-1)

-

-

-

-14.96

-25.59

S (kcal/mol-Kelvin)

0.187

0.353

0.409

0.498

0.561

ΔS (kcal/mol-Kelvin)

-

-

-

0.042

0.035

ZPE

250.16

635.09

740.56

886.52

941.11
kcal/mol; **kcal/mol-Kelvin; ZPE = Zero-point vibration energy
Figure 5. FE-SEM images for (a) ZnO, (b) ZnO/β-CD, (c) SR7B, (d) ZnO/SR7B/β-CD inclusion complexes.
3.3. Doping Effect of SR7B/ CD on ZnO Nanoparticles
In the solution phase, the absorption and emission spectra of the ZnO, ZnO/SR7B, ZnO/β-CD, SR7B/CD/ZnO nanoparticles are determined. The ground and excited state bands of ZnO nanoparticles appear at 320 nm and 420, 355 nm, respectively
[36-38]
. When SR7B solution was added to the ZnO nanoparticle solution, the above ground and excited state bands red shifted to 588, 377 nm and 435 nm, respectively. With the addition of β-CD solution to the ZnO nano, the ground and excited state band shifted to 250 and 398 nm, respectively. When SR7B/β-CD solution was added to the ZnO nanoparticles, the ground and excited state bands shifted to 350, 240 nm and 405 nm, respectively. The above red or blue shifts in the ground and excited state spectra suggest that SR7B and CD are doped on ZnO nanoparticles. Generally, if other nano doped/covered the ZnO nanoparticles, the intensity tends to increase or decrease and the interaction is supported by spectral variations.
3.4. FE-SEM and TEM Images
ZnO nano, SR7B, ZnO/β-CD and SR7B/CD/ZnO nanomaterials were examined by FE-SEM and EDAX (Figure 5). ZnO particles form small size balls present in cluster shape, ZnO/β-CD is appear in sheet shape, SR7B is present in microrod shape and SR7B/CD/ZnO present in marble rod shape image. FE-SEM-EDAX data shows (a) ZnO nano contains 57.34% zinc nano and 42.66% oxygen, (b) ZnO/β-CD nano comprises 19.67% zinc, 54.42% oxygen and 25.91% carbon, (c) SR7B dye contains 79.17% carbon, 20.83% nitrogen, and (d) SR7B/CD/ZnO contains 2.72% zinc, 66.15% carbon, 13.70% nitrogen, and 17.44% oxygen. FE-SEM pictures and the atom composition of the nano ZnO, SR7B are different from SR7B/CD/ZnO, confirming the formation of new nanomaterials.
Figure 6. HR-TEM images for (a-c) ZnO, (d-f) ZnO/β-CD, (g-i) ZnO/SR7B/β-CD.
TEM images of ZnO, ZnO/β-CD and SR7B/CD/ZnO are displayed in Figure. 6. Nanosheet like structures found in the ZnO nanomaterials, while nanorod like structure is formed in ZnO/β-CD. TEM image of ZnO nanosheet showed uniformly spherical particles between 20 and 44 nm in size and ZnO/β-CD nano, the particles size between 20 and 40 nm. The SR7B/CD/ZnO nano-sheet image was displayed between 14-16 nm. The formation of nanoparticles is supported by TEM-EDX data: (a) ZnO nano contains 69.84% zinc nano and 30.16% oxygen, (b) ZnO/β-CD nano comprises 8.79% zinc, 44.59% oxygen and 46.61% carbon, (c)) The composition of SR7B/CD/ZnO is 25.11% zinc, 24.46% carbon, 46.86% oxygen, and 3.57% nitrogen. The presence of ZnO along with SR7B/β-CD is confirmed by the EDX data for the metallic nanoparticles.
The nanoparticle size is analyzed by X-RD and HR TEM methods. In XRD method, Scherer equation is used and the particle size is given below: ZnO nano – 19.30 nm, β-CD – 23.84, SR7B- 20.29 nm, ZnO/β-CD - 20.69 nm, and SR7B/CD/ZnO Nano – 14.92 nm. In HR-TEM, the particle size is measured by using IMAGE-J software and the average particle size is calculated by origin software. ZnO nano– 24.98 nm, ZnO/β-CD– 23.98 nm, SR7B/CD/ZnO nano– 19.31 nm. Compared to XRD method, the 5-7 nm particle size is varied in HR-TEM method.
3.5. Powder X-RD
XRD method provided additional confirmation of the formation of nanomaterials. With the use of the JCPDS: 03-065-3411 data, the mineral name (3C) and the development of the hexagonal closely packed (HCP) structure have been confirmed. The JCPDS card number 800-075 was used to index and all the diffraction peaks conformed with its standard ZnO face-centered cubic peaks. The values of the hkl plane are found at (100), (002), (101), (102), (103), (110), (112) and (201) reflection planes of the hexagonal structure of ZnO.
In ZnO, eight diffraction peaks located at 31.80, 34.51, 36.21, 47.52, 56.61, 62.90, 67.91, 69.92 correspond to the reflection planes of hexagonal structure of ZnO. In β-CD, eight peaks were observed at 13.39, 19.93, 23.50, 27.65, 31.96, 35.54, 40.58, 48.90, while in ZnO/β-CD ten peaks formed at 10.15, 15.18, 25.41, 28.38, 34.92, 42.29, 49.77, 59.16, 63.32, 70.33. In SR7B, seven peaks formed at 14.21, 15.55, 19.20, 24.46, 25.94, 27.69, whereas in SR7B/CD/ZnO eleven peaks were noted at 8.30, 16.80, 21.64, 26.62, 28.51, 33.10, 35.15, 42.40, 49.94, 58.90, 63.50. Compared to isolated SR7B, the XRD patterns of the SR7B/CD/ZnO nanomaterials showed a different diffraction pattern and different peak intensities, suggesting that inclusion complex nanomaterials were formed. Further, several prominent peaks appeared from 10 to 80 degree range, supporting the formation of SR7B/CD/ZnO inclusion complex nanomaterials.
3.6 Infrared Spectral Studies
FTIR spectra of ZnO nano, SR7B, ZnO/SR7B, ZnO/β-CD and SR7B/CD/ZnO were analysed. Due to the conversion of Zn+2 to ZnO nanoparticles, the FTIR frequencies of the ZnO nanoparticles were observed at 3325, 1587, 1450, 592, and 513 cm-1. The frequencies appear at 3325 cm−1 indicate the presence of ZnO and the peaks seen at 592, and 513 cm-1 suggest the presence of Zn nanoparticles. It is already reported, the FTIR spectrum of pure ZnO nanoparticles peaks at 595 cm−1, which is characteristic of ZnO band and the broad band peak noted at 3507 cm−1 can be attributed to the characteristic absorption of O-H group. When zinc oxide nano added to β-CD, the 3325 cm−1 frequency shifted to 3280 cm−1, while 1587, 1450 cm-1 frequencies moved to 1614, 1514 cm-1 and 592, 513 cm-1 peaks shifted to 594, 526 cm-1. The above variation in the FTIR frequencies indicates that the CD is covered on ZnO nanoparticles.
In SR7B, NH group stretching frequency appears at 3051 cm−1, azo group stretching frequency seen at 1365 cm-1, aromatic ring stretching frequency appears at 2970, 1433 cm-1. C-NH frequency appears at 1122 cm-1, and CH out of plane bending frequency looks at 738, 684 cm-1. Out of plane bending frequency seems at 850, 808 cm-1 and C-N-C bending frequency appear at 532 cm-1. When SR7B/β-CD doped on ZnO nano particles, the above frequencies are shifted to lower or higher wave numbers. In ZnO/SR7B/CD, NH group stretching frequency appears at 3292 cm−1, azo group stretching frequency appears at 1367 cm-1, aromatic ring stretching frequency seems at 2973, 1435 cm-1. C-NH frequency looks at 1118 cm-1, and CH out of plane bending frequency appears at 738, 682 cm-1. Out of plane bending frequency seems at 958, 846 cm-1 and C-N-C bending frequency looks at 597 cm-1. Compared to SR7B and ZnO/β-CD, the SR7B/CD/ZnO nanomaterials showed a marked change in the frequencies, suggesting that the SR7B/β-CD was doped on ZnO nanoparticles.
3.7. DTA Thermogram
DTA profiles of pure ZnO nano, SR7B, ZnO/β-CD and SR7B/CD/ZnO are analyzed. In ZnO nano, two exothermic and three endothermic peaks were noticed at 226.1, 546.7°C and 272.6, 731.1, 19.2°C, respectively. SR7B exhibits one exothermic and one endothermic peak at 240.6°C and 597.8°C, respectively. β-CD exhibits four exothermic peaks at 230.3, 515.6, 657.4, 761.8°C. In ZnO/β-CD, two exothermic and four endothermic peaks appear at 224.3, 932.4°C and 265.2, 354.6, 749.8, 884.1°C, respectively. In SR7B/CD/ZnO, two endothermic and three exothermic peaks appear at 280.5, 898.8°C, and 236.7, 745.3, 966.8°C, respectively. The endothermic peaks in the nanomaterials are caused by the loss of water from the CDs. In contrast to the pure SR7B and ZnO, a new peak arises in SR7B/CD/ZnO, indicating the formation of the new nanomaterials.
4. Conclusion
Sudan Red-7B/Cyclodextrin doped ZnO nanocomposites are synthesized and analysed by various spectral and microscopic methods. The solvent and CD studies show that the azo-imino tautomer is present in SR7B molecule and depend upon the polarity of the solvents, the absorbance and emission intensities of the azo-imino tautomer are varied. Horizontal bond length of SR7B is longer than the CD cavities, hence, this molecule is partially encapsulated in the CD cavity. HOMO-LUMO gap for SR7B/β-CD inclusion complex is more negative than SR7B/α-CD, suggesting the previous inclusion complex is more stable than the latter. Red or blue shifted absorption and fluorescence maxima were seen in SR7B/CD/ZnO nanocomposites than SR7B/CD. TEM image showed that nanosheets are formed in SR7B/CD/ZnO. Compared to the XRD method, the 5-7 nm particle size of SR7B/CD/ZnO is varied in HR-TEM method.
Abbreviations

FTIR

Fourier Transform Infrared Spectroscopy

DTA

Differential Thermal Analysis

XRD

X-ray Diffraction

SEM

Scanning Electron Microscopy

TEM

Transmission Electron Microscopy

HOMO

Highest Occupied Molecular Orbital

LUMO

Lowest Unoccupied Molecular Orbital

SR7B

Sudan Red 7B

ZnO NPs

Zinc Oxide Nanoparticles

α-CD

Alpha Cyclodextrin

β-CD

Beta Cyclodextrin

PM3

Parametric Method 3

ΔE

Internal Energy Change

ΔH

Enthalpy Change

ΔG

Free Energy Change

ΔS

Entropy Change
Author Contributions
The authors confirm contributions to the paper as follows: P. Ramasamy - Experimental study: A. Mani, - Calculation, Analysis, Data Collection, A. Antony Muthu Prabhu, G. Venkatesh – PM3 calculation, Data interpretation, Manuscript draft preparation, Supervisor-N. Rajendiran.
Acknowledgments
This work was supported by the Rashtriya Uchchatar Shiksha Abhiyan (RUSA) Phase -2.0 [No. 128/A1/ RUSA 2.0, Health and Environment] New Delhi, India.
Data Availability
No data was used for the research described in the article.
Conflicts of Interest
The authors declare no conflicts of interest.
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    Ramasamy, P., Rajendiran, N., Mani, A., Venkatesh, G., Prabhu, A. A. M. (2025). Azo-Imino Tautomerism in Sudan Red 7B/Cyclodextrin Coated ZnO Nanocomposites: Evidence by Spectral and Microscopic Perspectives. Science Journal of Chemistry, 13(3), 65-75. https://doi.org/10.11648/j.sjc.20251303.13

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    Ramasamy, P.; Rajendiran, N.; Mani, A.; Venkatesh, G.; Prabhu, A. A. M. Azo-Imino Tautomerism in Sudan Red 7B/Cyclodextrin Coated ZnO Nanocomposites: Evidence by Spectral and Microscopic Perspectives. Sci. J. Chem. 2025, 13(3), 65-75. doi: 10.11648/j.sjc.20251303.13

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    AMA Style

    Ramasamy P, Rajendiran N, Mani A, Venkatesh G, Prabhu AAM. Azo-Imino Tautomerism in Sudan Red 7B/Cyclodextrin Coated ZnO Nanocomposites: Evidence by Spectral and Microscopic Perspectives. Sci J Chem. 2025;13(3):65-75. doi: 10.11648/j.sjc.20251303.13

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  • @article{10.11648/j.sjc.20251303.13,
  author = {Palanichamy Ramasamy and Narayanasamy Rajendiran and Ayyadurai Mani and Govindaraj Venkatesh and Albert Antony Muthu Prabhu},
  title = {Azo-Imino Tautomerism in Sudan Red 7B/Cyclodextrin Coated ZnO Nanocomposites: Evidence by Spectral and Microscopic Perspectives
},
  journal = {Science Journal of Chemistry},
  volume = {13},
  number = {3},
  pages = {65-75},
  doi = {10.11648/j.sjc.20251303.13},
  url = {https://doi.org/10.11648/j.sjc.20251303.13},
  eprint = {https://article.sciencepublishinggroup.com/pdf/10.11648.j.sjc.20251303.13},
  abstract = {Sudan Red-7B/Cyclodextrin doped ZnO nanocomposites are synthesized and analyzed by various spectral and microscopic methods. The doping effect of SR7B/CD on ZnO nano investigated by UV-visible, fluorescence, FTIR, DTA, XRD, FE-SEM and TEM methods. The effect of different polarities of the solvents, α-cyclodextrin (α-CD) and β-cyclodextrin (β-CD), on MV was studied by various spectral methods. The inclusion behaviour of SR7B on both CDs was determined by PM3 method. The solvent and CD studies show that the azo-imino tautomer is present in the SR7B molecule and that, depending upon the polarity of the solvents, absorbance and emission intensities of the azo-imino tautomer is varied. With increasing CD concentrations, the shorter wavelength emission intensity of the SR7B regularly increased while the longer wavelength emission intensity decreased. The horizontal bond length of SR7B is longer than the CD cavities; hence, this molecule is partially encapsulated in the CD cavity. HOMO-LUMO gap for MV/β-CD inclusion complex was more negative, which supports that this complex is more stable than MV/α-CD inclusion complex. Red or blue shifted absorption and fluorescence maxima were seen in SR7B/CD/ZnO nanocomposites than SR7B/CD inclusion complex. Nanoparticle size was measured by TEM-EDS and X-RD methods. TEM image showed that nanosheets are formed in SR7B/CD/ZnO.
},
 year = {2025}
}

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  • TY  - JOUR
T1  - Azo-Imino Tautomerism in Sudan Red 7B/Cyclodextrin Coated ZnO Nanocomposites: Evidence by Spectral and Microscopic Perspectives

AU  - Palanichamy Ramasamy
AU  - Narayanasamy Rajendiran
AU  - Ayyadurai Mani
AU  - Govindaraj Venkatesh
AU  - Albert Antony Muthu Prabhu
Y1  - 2025/06/23
PY  - 2025
N1  - https://doi.org/10.11648/j.sjc.20251303.13
DO  - 10.11648/j.sjc.20251303.13
T2  - Science Journal of Chemistry
JF  - Science Journal of Chemistry
JO  - Science Journal of Chemistry
SP  - 65
EP  - 75
PB  - Science Publishing Group
SN  - 2330-099X
UR  - https://doi.org/10.11648/j.sjc.20251303.13
AB  - Sudan Red-7B/Cyclodextrin doped ZnO nanocomposites are synthesized and analyzed by various spectral and microscopic methods. The doping effect of SR7B/CD on ZnO nano investigated by UV-visible, fluorescence, FTIR, DTA, XRD, FE-SEM and TEM methods. The effect of different polarities of the solvents, α-cyclodextrin (α-CD) and β-cyclodextrin (β-CD), on MV was studied by various spectral methods. The inclusion behaviour of SR7B on both CDs was determined by PM3 method. The solvent and CD studies show that the azo-imino tautomer is present in the SR7B molecule and that, depending upon the polarity of the solvents, absorbance and emission intensities of the azo-imino tautomer is varied. With increasing CD concentrations, the shorter wavelength emission intensity of the SR7B regularly increased while the longer wavelength emission intensity decreased. The horizontal bond length of SR7B is longer than the CD cavities; hence, this molecule is partially encapsulated in the CD cavity. HOMO-LUMO gap for MV/β-CD inclusion complex was more negative, which supports that this complex is more stable than MV/α-CD inclusion complex. Red or blue shifted absorption and fluorescence maxima were seen in SR7B/CD/ZnO nanocomposites than SR7B/CD inclusion complex. Nanoparticle size was measured by TEM-EDS and X-RD methods. TEM image showed that nanosheets are formed in SR7B/CD/ZnO.

VL  - 13
IS  - 3
ER  -

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Author Information

  • Palanichamy Ramasamy

    Department of Chemistry, Annamalai University, Annamalai Nagar, Tamilnadu, India

  • Narayanasamy Rajendiran

    Department of Chemistry, Annamalai University, Annamalai Nagar, Tamilnadu, India

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  • Ayyadurai Mani

    Center for Advanced Energy Materials, SRM TRP Engineering College, Tiruchy, India

  • Govindaraj Venkatesh

    Department of Chemistry, Knowledge Institute of Technology (Autonomous), Salem, India

  • Albert Antony Muthu Prabhu

    Department of Chemistry, Aditanar College of Arts and Science, Tiruchendur, India

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    1. 1. Introduction
    2. 2. Experimental
    3. 3. Result and Discussion
    4. 4. Conclusion
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  • Abbreviations
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  • Acknowledgments
  • Data Availability
  • Conflicts of Interest
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  • Cite This Article
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