REGULAR ARTICLE

Carbonyl releasing Schiff base complex of Fe (III): synthesis,physicochemical characterization, antimicrobial and anticancerstudies

R V KUPWADE and V J SAWANT*

Department of Chemistry, Smt. Kasturbai Walchand College, Sangli, Maharashtra 416 416, India

E-mail: v11131@rediffmail.com

MS received 20 August 2019; revised 14 October 2019; accepted 15 October 2019

Abstract. The carbonyl releasing Schiff base chelate derived Fe(III) complex has been synthesized fol-

lowing the simple wet chemical method. The rhombohedral packing of ligands with the metal ion in the

complex was confirmed by its XRD pattern and FTIR spectrum. Compounds were characterized by UV-Vis.,

PL, FTIR, XRD and TEM techniques. Better biocompatibility of the complex than that of the pure Schiff base

had been elaborated on gram-positive and gram-negative bacteria by Agar well disc-diffusion antibacterial

screening. The complex also displayed pH-responsive in vitro anticancer therapy on MCF-7 breast cancer

cells as revealed by MTT assay. The release of CO and Schiff base as well as the interaction of Fe(III) with

the mitochondria inside the cell are the key factors of cell biocompatibility. This CORM complex had

exhibited higher anticancer activity on MCF-7 cells than the Schiff base and thus potential candidate for the

future biomedical applications.

Keywords. Carbonyl releasing; Schiff base; chelate; anticancer.

1. Introduction

Carbonyl releasing complexes and molecules

(CORM) are gaining more interest due to their ver-

satile properties in biomedical fields, such as antimi-

crobial, anticancer, antioxidant and anti-proliferative

agents.1 Alike the NO, carbonyl (CO) ligand is also

cell signalling species which exhibits vasodilatory,

anti-inflammatory and anti-proliferative activities.2

Carbonyl releasing species are generally

supramolecular complex agents which pass through

the cell barriers. When their uptake takes place by

lysosomes in cells at acidic pH, the release of CO

molecule takes place and ROS (Reactive Oxygen

Species) get generated by cell proton efflux. Hence,

such complexes act as an antimicrobial and anticancer

agent with better biocompatibility. Schiff bases are

generally chelating ligands containing carbimide

bonds formed after refluxing aldehydes with amines

in synthetic protocols. These ligands are the best

antimicrobial agents and form better complexes with

a variety of transition and inner transition metals with

good biocompatibility.

When such ligands combine together in a chelate of

bioactive metals like Fe(III), these complexes play

significant roles in bio signalling inside cells and give

effects of biocompatibility or cytotoxicity. Hence,

Schiff base complexes along with carbonyl ligands

result in fast endocytosis and release of ligands inside

cells to effect into ROS production at pH gradient of

cells. This ROS produced into cells leads to antimi-

crobial, anticancer or cytotoxic and biocompatible

effects on cells. Parallel effects of biocompatibility

have been shown by antibiotic ligand complexes with

special biocompatible metals.3 ROS-based antimicro-

bial activity of Pd(II) complex has been reported by W

Guerra et al.4 Recent work on heterocyclic and Schiff

base ligand complexes have been not only reported the

antimicrobial properties but also DNA cleavage

activities in cells leading to the production of ROS in

cells and biomedical interface mechanisms.5–7 Similar

research of heterocyclic and carbimide containing

Schiff base type ligands and their metal complexes

have been reported for their biomedical applica-

tions.8–12 According to recent work on such hetero-

cyclic species and Schiff bases along with their

complexes with transition metals, these complexes

have exhibited the supramolecular nature to pass from*For correspondence

J. Chem. Sci. (2020) 132:44 � Indian Academy of Sciences

https://doi.org/10.1007/s12039-020-1746-y Sadhana(0123456789().,-volV)FT3](0123456789().,-volV)

cell membranes easily and produce effects of bio-

compatibility and DNA interactions to realize poten-

tial effects on cell divisions and proliferations.13–17

In continuation of these ideas, we had synthesized

new carbonyl releasing Schiff base complex of Fe(III).

In addition to physicochemical characterization of the

simple Schiff base and its carbonyl complex with

Fe(III), the antimicrobial biocompatibility and anti-

cancer potentials have been tested by in vitro assay.

The higher antimicrobial and anticancer potential of

the complex as compared to Schiff base has been

elaborated on special MCF-7 human breast cancer

cells by in vitro MTT assay. Complex exhibited

increased endocytosis inside negatively charged cell

membranes of bacteria and cancer cells and produced

higher amount of ROS at acidic pH than Schiff base,

CO, implying the effect of Fe(III) species towards

intrinsic apoptosis of cancer cells.18–20 Thus, carbonyl

releasing Schiff base complex of Fe(III) can be con-

sidered as a potential candidate for future biomedical

applications.

2. Experimental

2.1 Materials and cell cultures

All the chemicals used for the synthesis of Schiff base and

its carbonyl complex with Fe(III) and their in vitro bio-

logical screening such as Ferric nitrate, P-nitro aniline,

Benzaldehyde, Zinc powder, Calcium carbonate, Conc.

HCl, Ethanol were of A. R. grade. These chemicals were

purchased from S. D. Fine Chem. Ltd. and Merck Ltd. and

were used without further purification. The cell culture

medium such as agar growth broth and bacterial culture,

fetal bovine serum, trypsin buffer were obtained from

Himedia Ltd. and NCCS cell repository center, Pune, India.

The human breast cancer cells MCF-7 were purchased from

this cell repository. The double-distilled water was obtained

from Millipore system and used throughout the synthesis

and in vitro biological screening tests.

2.2 Synthesis of Schiff base ligand

The simple Schiff base ligand was synthesized by refluxing

P-nitroanilline and Benzaldehyde at 250 �C on the constant

flame in R.B. flask with condenser for 3 h. The yellow

product formed water-washed with ethanol to remove

unreacted organic precursors and dried in the oven below

80 �C. The Schiff base powder then subjected to physico-

chemical the complex using UV-Vis., PL, FITR spectrom-

etry. The formation of the product was confirmed on the

basis of physical constant and TLC (see protocol in

Scheme 1).

2.3 Wet chemical synthesis of CORM, carbonyl -

Schiff base complex of Fe(III)

The carbonyl-containing Schiff base metal complex of

Fe(III) was synthesized by bubbling CO into the flask

containing Schiff base and Fe(III) nitrate precursor using a

wet chemical method (Scheme 1). In detail, the Schiff base

with Fe(III) in 2:1 mM proportion in the ethanol-water

solvent system were refluxed in R. B. flask for 3 h and the

precursor was then added in the flask with double distilled

water. The gaseous CO ligand was produced in separate

flask by the reaction of conc. HCl with calcium carbonate

and zinc powder mixture. Then the CO ligands produced

separately in another flask was passed and bubbled in ligand

and metal precursor mixture to get carbonyl releasing

CORM complex of Fe(III) containing CO ligands and

Schiff base. The complex formed thus was washed with

ethanol-water solvent system and dried in the oven.

2.4 Structural and morphological

characterization of CORM-Fe(III) complex

The structure, morphology, particle diameter range and

types of bonding of functionalities in the CORM complex

of Fe(III) was determined based on physicochemical char-

acterization using UV-Vis., PL, FTIR, XRD spectrometry

OH

CHO

+ NH2 NO2

3h reflux in ethanol- H2O

CH

N NO2

OH

CO bubbling Fe(NO3)3 stirred with ligand

N

NO2

ON

NO2

OFe

CO

CO

(NO3)3

Salicyladehyde P-nitro aniline

Schiff base ligand

CORM Fe (III) Schiff base complex

Scheme 1. Synthesis protocol of Schiff base ligand andcarbonyl-schiff base Fe(III) complex.

44 Page 2 of 12 J. Chem. Sci. (2020) 132:44

techniques and TEM microscopic analysis. The spectronics

double beam UV-Vis. spectrometer with water as blank was

used to determine the absorption spectrum of complex to

compare with Schiff base. To confirm functionalities pre-

sent in complex and a with Schiff base, Perkin Elmer series

FTIR spectrometer was used with KBr pellet technique. The

PL emission spectrum of complex and Schiff base were

determined using Jasco type spectrofluorometer with exci-

tation identity of complex and Schiff base in ethanol solvent

with the same ppm. Concentrations. The X-ray diffraction

pattern of the complex was determined using X-ray spec-

trometer by powder diffraction technique to elaborate the

packing of ligands with metal in complex, hybridization and

crystal system of complex. The particle range of complex to

pass cell through membranes was determined using TEM

microscopic analysis and SAED patterns were matched with

XRD data to confirm the powder crystal system of complex.

2.5 Antimicrobial screening on gram-positive

and gram-negative bacteria by agar well disc

diffusion method

The cell-particle interactions of materials and complexes

demonstrating their reactivity and biocompatibility can be

elaborated using simple in vitro antibacterial screening in

buffer solutions to maintain physiological mimicking pH at

material cell interactions. As cell pH affects the biocom-

patibility of molecules. Here in this work 15, 20 and

25 ppm concentrations of Schiff base and CORM complex

were dosed on bacterial cell cultures grown in agar broth on

discs, inside the wells bored on plates. The gram-positive

bacteria Staph. Aurues, and gram-negative bacteria E. Coli,

Kleb. were grown on culture plates and inhibited by dosing

of Schiff base and complex solutions in buffer dispersions

with physiological pH = 7.4 by use of phosphate buffer. The

culture plates were incubated and zones of inhibition were

measured, and biocompatibility/antimicrobial property of

Schiff base and complex were compared.

2.6 In vitro MTT cell line anticancer assay

on MCF-7 human breast cancer cells

The anticancer potential of Schiff base and complex were

estimated and compared on the basis on in vitro MTT,

MCF-7cellline spectrometric assay. Cytotoxicity of Schiff

base and CORM complex were elaborated into MCF-7

(Human Breast cancer cells) with MTT assays. Cells (1 9

103/mL) were seeded in 96-well plates and then incubated

for 24 h at 37 �C and 5% CO2 atmosphere in an incubator

with 100 lL of DMEM medium supplemented with 10%

fetal bovine serum (FBS) as a growth medium and 1%

penicillin-streptomycin solution per well. This medium was

then replaced with 200 lL of the PBS, phosphate buffer

saline (pH=7.4) medium containing either Schiff bases or

complex doses (concentration 5, 10, 15, 20 and 25 lg/mL).

Cells without treatment were considered as a control as well

to evaluate its cytotoxicity. Cells were further incubated for

48 hours, and relative anticancer activity was assessed with

MTT assays. After 48 h, MTT assay was carried out. In

brief, MTT solutions (20 lL of 5 mg/mL) were added after

treatment and cell culture were again incubated for an

additional 4 h. Dimethyl sulphoxide (150 lL solution) was

added to each well to solubilize the blue formazan crystals,

and optical density at 492 nm was recorded for culture

medium. Cell viability (%) for exposure of Schiff base and

complex doses were calculated as follows,

%Cell viability ¼ Optical density at 492 nm in test cells

Optical density at 492 nm in control cells� 100

The anticancer activities of Schiff base and complex

doses were elaborated in terms of cell viability and plotted

as a function of concentrations to compare the effects.

Finally, these cultures were subjected to DAPI staining to

elaborate internalization of the complex into cancer cells,

and determine the mechanism of cell deaths or apoptosis by

interactions from the complex by the production of inter-

anions/inter-cations or release of ligands and metal ion

inside cell fluids.

2.7 DAPI staining and imaging of cancer cells

after MTT assay

After the incubation with Schiff base/complex doses and

further MTT interactions, the cells were washed with PBS

(phosphate buffer saline) solution and fixed with 4%

paraformaldehyde for 30 min, then cells were added with

20 lL of DAPI and were incubated for 20 min; finally, after

spreading on slides, the cell were examined under a fluo-

rescent microscope. The internalization of complex higher

than Schiff base was examined by the staining and mech-

anism of anticancer effects and biocompatibility/ cytotoxi-

city was demonstrated.

3. Results and Discussion

3.1 Morphological and structural characterization

of Schiff base ligand and the CORMFe(III) complex

3.1a UV-Vis. absorption and PL emission

spectrum: UV-Vis. and PL spectrum of

Schiff/complex were determined to study the

structural characteristics, metal to ligand charge

transfer transitions, bonding within the molecule and

absorption/emission property. Here UV-Vis, the

absorption spectrum of the complex (Figure 1)

explains the charge transfer transition of Fe(III)

metal ion with Schiff base and carbonyl ligand, to

elaborate the bonding interactions in the complex. The

J. Chem. Sci. (2020) 132:44 Page 3 of 12 44

spectrum exhibits the diffused broad absorption peaks

at 235 nm and 355 nm for the MLCT transitions from

Fe(III) d electrons to CO and carbimide bond of Schiff

base ligand respectively (metal to ligand charge

transfer take place probably due to non bonded and

Pi electrons of Schiff base and CO ligands and d

electrons of Fe(III) in the complex). The Schiff base

shows higher O.D. for a single peak near at same

absorption wavelength of the complex at 365 nm. (Not

shown), but dampening and peak shifting take place

for absorption maxima of Schiff base after bonding

interaction of carbimide bond with Fe(III) ions in the

complex. Hence, UV-Vis spectrum of complex

elaborates the bonding of ligands with Fe(III) and

gives the idea of probable chelate type structure of the

complex. The PL spectrum of Schiff base and complex

determined separately explain the quenching of peak

signal of Schiff base after bonding of Fe(III) with

carbimide bonds in the complex. In Figures 2A and 2B

the PL emission peaks of Schiff base and CORM

complex respectively show the quenching of signal.

PL spectra of Schiff base and complex support for

the bonding, structure and nature of complex con-

taining Schiff base and CO ligand simultaneously

linked with Fe(III) ions to give more stability for the

chelate. According to PL spectra, the PL intensity of

Schiff base at 815 nm. due to non bonded and Pi

electrons was quenched by Fe(III) bonding in complex

proving MLCT transition and coordinate/covalent

linkages of carbimide bonds with a metal ion. Overall

these spectra elaborate chelate nature of complex

containing CO ligand liked with planer Schiff base

ligand with Fe(III) ion in the complex. So the spectra

support for CO releasing nature of the complex, as

Schiff base is firmly linked by coordinate bonds and

CO electrons are representing different absorption

maxima in UV-Vis spectrum of the complex at

235 nm representing more non-bonding free electrons

over it. This elaborated the free site of CO ligands for

easy release from complex to behave as CORM

complex for better cell biocompatibility. Table 1

supports for MLCT transition identities in Schiff base

and CORM complex determined from UV-Vis and PL

spectrum.

The composition of the complex for its elements and

ions C, H, O, N, Fe (III) along with functionalities of

carbimide, carbonyl bonds to metal are confirmed by

using UV-Vis and PL electron transitions and peaks in

respective spectra. These evidence are supported by

FTIR signals as per spectral studies in works of B. Sinha

et al.,21 hence these analyses of Schiff base and CORM

complex not only prove the composition but also

probable structure and functionalities in the complex.

3.1b FTIR spectrum of Schiff base and CORM

complex: FTIR spectrum of Schiff base and

complex were determined to estimate the

functionalities present inside the molecules and to

confirm the formation of CORM complex on the basis

of signals represented by functional groups in

fingerprint and functional regions of spectra.

Figure 3A represents the FTIR spectrum of Schiff

base, in this spectrum presence of carbimide bond –

C=N- was elaborated due to signal at 1918 and

2 0 0 3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0

0

1

2

3

4

5

d 5 F e ( II I) M L C T w ith C O a n d c a rb im id e

Abso

rban

ce

W a v e le n g th n m

U V -V IS a b s o rp t io n s p e c tra o f s c h if f b a s e c o m p le x

Figure 1. UV-Visible absorption spectrum of CORM Schiff base complex of Fe(III).

44 Page 4 of 12 J. Chem. Sci. (2020) 132:44

Figure 2. (A) PL emmission spectrum of schiff base. (B) PL emmission spectrum of complex.

Table 1. MLCT transitions of non bonded/Pi electrons of ligands and d electrons of Fe(III).

Absorption or emissionpeak shown in UV-Vis. OrPL spectrum Schiff base transition Metal CORM complex charge transfer transition

UV-Vis. Absorption at 355nm.

n to Pi absorption maxima A1g to T2g and A1g to A2g from d5 state of Fe(III) for splittingfrom bonding of carbimide and CO species

PL quenching at 815 nm. n to Pi relaxation-no quenching

Pi to Pi relaxation – quenching due to Fe(III) and carbimidelinkage

J. Chem. Sci. (2020) 132:44 Page 5 of 12 44

1971 cm-1. The signals at 531, 665 and 805 cm-1

represent the fingerprint identity of aromatic groups

from benzaldehyde and nitroaniline. Signals at 2555

and 2673 cm-1 are attributed towards the aromatic

nitro and nitrile entity of Schiff base. Signals from

3034 to 3379 cm-1 are raised in the spectrum due to

the presence of aromatic –OH and carbimide hydroxyl

side interactions in Schiff base. In Figure 3B FTIR

spectrum proves functionalities present in CORM

Fe(III) complex elaborates the presence of carbimide

metal bond and side CO ligands over the metal ion.

Signals at 1760 and 1822 cm-1 elaborates the

presence CO groups over Fe(III) metal ion in the

complex. The signals at 1936 and 1969 cm-1 are

attributed to Fe(III) bonded with carbimide linkage in

the complex. The broadening of signals in complex

FTIR spectrum at 2585 and 2884 cm-1 is attributed to

carbimide and CO linkages at Fe(III) ion and covalent

aromatic-O linkage to Fe(III) from Schiff base near to

carbimide metal bond. Overall all these observations

lead to prove the chelate nature of the complex and

octahedral site of Schiff base with metal ion and free

carbonyl groups over it. Table 2 throws light on

specific signals of the FTIR spectrum for the

functionalities in the Schiff base and the complex.

3.1c XRD (X-ray diffraction) pattern

of complex: As per XRD pattern of the complex in

Figure 4, the complex evidenced to rhombohedra

crystalline packing for metal ion and ligands, it

elaborates the structure and morphology for CORM

complex. The diffraction pattern gives signals for

metal ion planes in an octahedral environment of

Schiff base and carbonyl ligands, Fe(III) of the

complex are in octahedral sites of packing with

ligands in complex, hence phase purity of complex

crystal have been proved by XRD patterns. The XRD

data is determined using miller indices of pattern,

FTIR spectra of Schiff base

4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 40088.90

89.2

89.4

89.6

89.8

90.0

90.2

90.4

90.6

90.8

91.0

91.2

91.4

91.6

91.8

92.00

Frequency cm-1

%T

FTIR spectra of CORM complex

4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 40033.034

36

38

40

42

44

46

48

50.0

Frequency cm-1

%T

A

B

Figure 3. (A) FTIR spectrum of Schiff base ligand. (B) FTIR spectrum of CORM complex.

44 Page 6 of 12 J. Chem. Sci. (2020) 132:44

Scherer’s formula and packing of planes and it was

matched with octahedral Fe(III) data in JCPDS card

no. 85-3854. As per Table 3, the crystal parameters of

rhombohedral packing of complex clearly represented

the octahedral packing of the metal ion with ligands

producing rhombohedral crystal. Hence, XRD data

proved the phase purity, crystal packing, geometry,

chelate octahedral nature of CORM complex.

3.1d TEM image and SAED pattern

of Complex: The TEM image of the complex in

Figure 5A throws light on spherical elongated

morphology and some aggregation of complex

molecules due to supramolecular neighbouring

bonding interactions. The particle sizes of complex

crystals ranged from 60 nm to 75 nm. But most of the

particles of complex molecules exhibited average size

08060402

0

2000

4000

6000

8000

10000

12000

[Fe(III) in rhom bohedra ]

[111 ]

[002 ]

[121 ]

[001 ]

[020 ]F e(III) ion in carb im ide and C O ligand env ironm ent O ctahedra l rhom bohedra l crysta l sym m etry

Inte

nsity

2 T he ta

X R D spectra o f com plex

Figure 4. XRD pattern of the Complex.

Table 2. Matching of FTIR signals elaborating the functionalities of Schiff base and CORM complex.

Signal in FTIR spectrum Schiff base functionality CORM complex functionality

1969 cm-1 Carbimide bond -C=N- Carbimide linked to Fe(III)1760 cm-1 Absence of CO Presence of linked CO ligands over Fe(III)3034 cm-1 Aromatic -OH Ether aromatic-O- linkage with Fe(III)1790 and 1824 cm-1 Presence of an aromatic nitro group Out of plane nitro groups2555 and 2585 cm-1 Presence of nitrile entity Presence of linked nitrile entity

Table 3. Crystal parameters of CORM Fe(III) complex matched with standard Fe(III) octahedral JCPDS card.

Crystallite planes(Miller Indices)(h,k,l)Rhombohedra ofoctahedral chelate phase

d Calculated A0

d = a/H(h2?k2?l2)or

2dSinh = nk

d Standard A0

JCPDS card no.- 89-3854Fe(III)

Lattice Constanta and b A0 from main XRD peak

at theta = 37.5 of CORM complex crystalfrom rhombohedra

001 5.088 5.089 a standard = 3.249b standard = 5.266121 4.032 4.045

020 7.039 7.043002 3.089 3.083 a calculated = 3.251 and

b calculated = 5.272111 6.334 6.329

J. Chem. Sci. (2020) 132:44 Page 7 of 12 44

range 60 nm which can pass through cell membranes

by supramolecular interactions easily. The TEM

results were matched with XRD data and proved the

chelate octahedral nature of complex with the

crystalline state for good water solubility and further

biocompatibility. The SAED patterns greatly matched

with XRD data with crystalline dot patterns as per

Figure 5B. Overall TEM image and SAED pattern of

the complex had proved the morphology of the

complex for further water-loving nature and

biomedical applications.

3.2 Antimicrobial properties Schiff base

and complex for better biocompatibility

As per the images of bacterial cultures and zones of

inhibition exhibited by Schiff base and complex on

Figure 5. (A) TEM image of complex. (B) SAED pattern of complex.

Figure 6. (A) to (C) Anti microbial effects of schiff base ligand at 25 ppm. on (A) E-Coli.-Gram negative bacteria,(B) Kleb.- Gram negative bacteria, (C) Staph. aureus- Gram positive bacteria.

44 Page 8 of 12 J. Chem. Sci. (2020) 132:44

gram-positive and gram-negative bacteria in Fig-

ures 6A to 6C and 7A to 7C, it clearly indicated that

the Schiff base and complex show better antimicrobial

activities. The CORM complex shows higher activity

than Schiff base and as per Table 4, especially on

gram-positive bacteria, higher activity was estimated

than gram-negative bacteria. So the CORM complex

exhibit higher biocompatibility than Schiff base, due

to release of CO, Schiff base ligand and Fe(III) metal

ion inside bacterial cells causing interactions with

DNA. So, the complex show higher cell compatibility

and internalization due to its chelate supramolecular

nature proving its applicability in biomedical fields.

3.3 Anticancer potential of Schiff base

and complex by in vitro MTT assay on MCF-7 cells

As per Figure 8, pH stimulated higher anticancer

activity had been shown by complex than Schiff base

compared with free control cells on the basis of

in vitro MTT assay on MCF-7 breast cancer cells. The

cell viabilities determined are related to cytotoxicity

and anticancer effects on these cancer cells at 5, 10,

15, 20, 25 ppm. Concentrations of doses of Schiff base

and CORM complex. Higher cell line apoptosis was

observed at 25 ppm. Giving dose-dependent and pH

triggered cytotoxicity of CORM complex. About 77%

Table 4. Anti-microbial activities of Schiff base and complex compared for gram-positive and gram-negative bacteria.

Type/name of bacterial culture in Agar broth[as per Figures 6A to 6C and 7A to 7C]

Zones of inhibition for gram-positive bacteria/gram-negative bacteria aszone diameter in mm. for concentrations of drug/dose of complex or Schiff

base 25 lg/mL (ppm.) in vitro on bacterial cells

For Schiff base For CORM complex

E. Coli (gram -ve) 10 mm. 35 mm.Kleb.(gram -ve) 5 mm. 15 mm.Staph aureus(gram ?ve) 8 mm. 48 mm.

Figure 7. (A) to (C) Anti microbial effects of CORM complex at 25 ppm. on (A) E-Coli.-Gram negative bacteria,(B) Kleb.-Gram negative bacteria, (C) Staph. aureus- Gram positive bacteria.

J. Chem. Sci. (2020) 132:44 Page 9 of 12 44

apoptosis was given by CORM complex at 25 ppm

dose, hence, the complex show good cytotoxicity on

cancer cells and proved its potential application in the

biomedical area. Supramolecular chelate nature to

pass from cell barriers, presence key signaling CO

ligand and Schiff base with electron providing Fe(III)

ion and pH triggered action on cancer cell endocytosis

and apoptosis are the main entities which play role in

anticancer effects of this new CORM complex. These

all observations are supported and proved by DAPI

staining image of MCF-7 cells after the action of

CORM complex by MTT assay. In Figure 9, it was

observed that the complex after endocytosis shrinks

cancer cells fastly after incubation and show DAPI

fluorescence at center of cells under a microscope.

This observation indicates the action of released spe-

cies with DNA producing pH-sensitive ROS flux

inside cancer cells from CORM complex resulting in

intrinsic apoptosis of MCF-7 cells.

3.4 Mechanism for antimicrobial activity

and anticancer potentials of the CORM complex

As per Scheme 2, when CORM complex enters into

bacterial or cancer cells with production of ROS (re-

active oxygen species) like O2, OH, OOH and H2O2

after endocytosis and lysosomal digestion at acidic pH,

it causes prominent biocompatible effects on these

cells. CORM complex release CO ligand, Schiff base

and dissociate Fe(III) inside acidic pH of cells, so by

pH trigger it releases proton flux, CO, intercations

inside cell organelles. The ROS produced inside bac-

terial cells by these species on the basis of cell

molecule interaction enters into rough organelles and

mitochondria of cells disturbing membrane potentials

of cell organelles and damage DNA or mutated DNA.

The free electrons from Fe(III) ions, CO ligand, Schiff

base activity, inter cation and proton flux are key

factors disturbing the cancer cell mitochondria and

mutated DNA. Overall these intrinsic pathways of

apoptosis by CORM complex cause higher anticancer

effects than Schiff base on MCF-7 cells with probable

ROS-lipid peroxidation mechanism which are pH-re-

sponsive and CO signaling affecting biomedical

activities.19,22,23 Hence, this new CORM complex

5 10 15 20 250

10

20

30

40

50

60

70%

cel

l via

bilit

y fo

r MC

F-7

cells

afte

r MTT

ass

ay

Concentrations of dosing for complex and schiff base in ppm.

action of CORM complex action of Schiff base

Figure 8. Anticancer activities of schiff base and CORMcomplex by MTT assay on MCF-7 cells.

Figure 9. DAPI staining image of internalization ofcomplex for apoptosis of MCF-7 cells.

pH trigger CORM Complex (Excitation at 385 nm.) emission at 815 nm.

[Release of H+ / Fe3+/ CO and Schiff base at acidic pH in lysosome]

Fe(III) to Schiff base CT transition VB+ + e- to CB in Fe(III) - (free electrons)

Dissociation-mitochondrial disruption

[CO] and Schiff base releasing at lysosomes pH change --- ROS in cells- O2., OH., .OOH

Mitochondrial cyt.-c destruction and caspase activation Apoptosis of cancer cell

Scheme 2. Mechanism for antimicrobial and anticancer activities of complex.

44 Page 10 of 12 J. Chem. Sci. (2020) 132:44

clearly indicates potential biomedical applications for

antimicrobial and anticancer activities.

4. Conclusions

The new carbonyl-Schiff base CORM complex of

Fe(III) exhibited rhombohedral packing and chelate

nature with an octahedral site of ligands. The complex

had exhibited 60 nm mean particle diameter and

crystalline oval morphology as confirmed by XRD

pattern and TEM analysis. This chelate with CO

releasing ability has the potential to pass cell barrier

with supramolecular nature and hence show better

biocompatibility than Schiff base. The quenching of

signal in PL spectrum elaborated the bonding of

Fe(III) ion with Schiff base and CO ligand. Further-

more, the complex exhibits ROS in bacterial and

cancer cells after the release of the Schiff base, Fe(III)

and CO by pH trigger. The CORM complex shows

better biocompatibility by in vitro than Schiff base.

The synergic effects of the release of CO, Schiff base

and interaction of Fe(III) with mitochondria inside the

cells are the key factors for cell biocompatibility.

Hence, this CORM complex of Fe(III) exhibits an

intrinsic pathway for apoptosis of cancer cells. Overall

this CORM complex has potential application in

biomedical fields for cytotoxicity and

biocompatibility.

Acknowledgements

The author is thankful to analytical instrumentation labo-

ratory, Jaysingpur College, Jaysingpur, India for providing

some spectroscopic characterizations of samples, and to the

Biotechnology laboratory of Smt. K. W. College, Sangli for

providing cell cultures and in vitro testing facilities.

Compliance with ethical standards

Conflict of interest The authors declare that they have no

conflict of interest.

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