Ligand effects on the structural dimensionality and antibacterial activities of silver-based coordination polymers.

Dalton Transactions View Article Online

Published on 14 April 2014. Downloaded by University of Washington on 25/10/2014 03:38:34.

PAPER

Cite this: Dalton Trans., 2014, 43, 10104

View Journal | View Issue

Ligand effects on the structural dimensionality and antibacterial activities of silver-based coordination polymers† Xinyi Lu, Junwei Ye,* Yuan Sun, Raji Feyisa Bogale, Limei Zhao, Peng Tian and Guiling Ning* Four Ag-based coordination polymers [Ag(Bim)] (1), [Ag2(NIPH)(HBim)] (2), [Ag6(4-NPTA)(Bim)4] (3) and [Ag2(3-NPTA)(bipy)0.5(H2O)] (4) (HBim = 1H-benzimidazole, bipy = 4,4’-bipyridyl, H2NIPH = 5-nitroisophthalic acid, H2NPTA = 3-/4-nitrophthalic acid) have been synthesized by hydrothermal reaction of Ag(I) salts with N-/O-donor ligands. Single-crystal X-ray diffraction indicated that these coordination polymers constructed from mononuclear or polynuclear silver building blocks exhibit three typical structure features from 1-D to 3-D frameworks. These compounds favour a slow release of Ag+ ions leading to excellent and long-term antimicrobial activities, which is distinguished by their different topological struc-

Received 24th January 2014, Accepted 12th April 2014

tures, towards both Gram-negative bacteria, Escherichia coli (E. coli) and Gram-positive bacteria, Staphylococcus aureus (S. aureus). In addition, these compounds show good thermal stability and light

DOI: 10.1039/c4dt00270a

stability under UV-vis and visible light, which are important characteristics for their further application in

www.rsc.org/dalton

antibacterial agents.

Introduction In the past few decades, mankind has suffered many tribulations with regard to certain microorganisms, such as the infections with pathogenic Escherichia coli O-157 in Japan in 1996, the foot-and-mouth disease (FMD) crisis in Europe in 2001, severe acute respiratory infection syndrome (SARS) pandemic in China between November 2002 and July 2003, and the near spread of avian influenza virus around the world.1,2 Great attention has been focused on the design and synthesis of new antibacterial materials.3,4 Silver and silver-based compounds have been shown to have strong biocidal effects on many species of bacteria, including Gram-negative and Grampositive bacteria, which have been widely used in many fields, such as cosmetics, ceramics, catheters, surgical devices and wound dressings.5,6 A recent review by S. Eckhardt, K. M. Fromm and co-workers7 summarized the interaction of silver and its compounds with peptides and bacteria, giving an

State Key Laboratory of Fine Chemicals and School of Chemical Engineering, Faculty of Chemical, Environmental and Biological Science and Technology, Dalian University of Technology, 2 Linggong Road, Dalian 116024, P. R. China. E-mail: [email protected], [email protected]; Fax: +86-411-84986065; Tel: +86-411-84986065 † Electronic supplementary information (ESI) available: IR data, XRD data, extensive figures, tables of selected bond distances and angles, and hydrogen bonds of 1–4. CCDC 917391, 917394, 917393 and 960781. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4dt00270a

10104 | Dalton Trans., 2014, 43, 10104–10113

integrated view of antibacterial materials from the microscopic to molecular scale. However, existing silver ointments, dressings and coatings containing high loadings of silver could lead to a large excess of silver ions in wounds and surrounding tissue, resulting in skin discoloration, tissue toxicity, allergic reaction and immune response to the human body.8,9 Meanwhile, the low light–thermal stability of silver-based materials still limit their development in disinfection.10,11 On the other hand, coordination polymers are a novel class of inorganic–organic hybrid materials with tunable compositions and fascinating structures, which have been extensively exploited for many functional properties such as catalysis, selective absorption, separation, gas storage, ion exchange, luminescence, magnetism and so on.12,13 In our continuing research on synthesis and properties of coordination polymers constructed from polycarboxylic ligands,14,15 we focused our study on ligand-directed assembly of antibacterial silver-based coordination polymers. Some silver-based coordination polymers were synthesized,16,17 and their antibacterial properties were analyzed as well.18,19 K. Nomiya and co-workers20 first presented the argument that Ag(I)–N bonding compounds had potential applications in antibacterial materials against bacteria, yeast and mold. Y. Cui21 showed that Ag-based compounds constructed from (4-pyridylduryl)borane exhibited strong antimicrobial properties, although their antibacterial mechanisms were unclarified. Recently, P. Smoleński et al.22 reported silver polypyridine derivatives of 1,3,5-triaza-7-phos-

This journal is © The Royal Society of Chemistry 2014

View Article Online


Dalton Transactions

Scheme 1

Synthesis of Ag-based coordination polymers 1–4.

phaadamantane with antimicrobial and antiproliferative activities. C. Pettinari et al.23 demonstrated that antibacterial action of 4,4′-bipyrazolyl-based silver coordination polymers could be embedded in PE disks. It has been reported that the bactericidal action of silver-based materials arises from the release of biocidal Ag+ ions.21,24 Structural silver ions in coordination polymers can be easily diffused into the bacterial membrane and disrupt cell membrane proteins. Meanwhile, the organic ligand of coordination polymers may play an assistant effect on increasing the cell lipid solubility, which can give a convenient way for silver ions to penetrate into the cell.25,26 However, it is still a great challenge to design and prepare new silver-based materials with high activity and durability as an ideal potential source to control the release of Ag+ ions for bactericidal applications. In order to improve the development of silver-based coordination polymers as excellent disinfection agents, the structural-directed effect on antibacterial activities of silver-based coordination polymers should be investigated urgently. In this paper, four silver-based coordination polymers with interesting topological evolution from one-dimensional (1-D) chains to three-dimensional (3-D) frameworks were constructed by controlling the structural isomerism of the organic ligands, namely, [Ag(Bim)] (1), [Ag2(NIPH)(HBim)] (2), [Ag6(4NPTA)(Bim)4] (3) and [Ag2(3-NPTA)(bipy)0.5(H2O)] (4) (HBim = 1H-benzimidazole, bipy = 4,4′-bipyridyl, H2NIPH = 5-nitroisophthalic acid, H2NPTA = 3-/4-nitrophthalic acid) (Scheme 1). The results of the minimal inhibitory concentration (MIC), the growth inhibition curves of bacteria, the zone of inhibition technique and morphological changes of the bacteria indicate that these compounds have excellent antibacterial capability and long-lasting effectiveness on different types of microorganisms including Gram-negative bacteria, Escherichia coli (E. coli) and Gram-positive bacteria, Staphylococcus aureus (S. aureus). The releasing ability of Ag+ ions, thermal stability and light stability of these compounds are presented as well.

Experimental section General methods Elemental analysis was performed on a Perkin-Elmer 240C elemental analyzer. FT-IR spectra were recorded on a Bruker


Paper

IFS 66 V interferometer. Thermogravimetric analysis (TGA) was performed on a Perkin-Elmer TGA 7 unit with a heating rate of 10 °C min−1. The samples were characterized by X-ray Diffraction (XRD) (Rigaku-DMax 2400) in reflection mode (Cu Kα radiation). The shapes and structures of samples were observed by scanning electron microscopy (SEM, JEOL-6360LV). The morphological changes of the bacteria were observed by transmission electron microscopy (TEM, Tecnai F30, made by FEI Company), operated at 20 kV. The release ratio of Ag+ ions was performed on an Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES) (Optima 200 DV, made by Perkin Elmer Company). Synthesis and characterization [Ag(Bim)] (1). A mixture of AgNO3 (0.16 g, 1 mmol), HBim (0.06 g, 0.5 mmol), and H2O (10 mL) was sealed in a 25 mL Teflon-lined stainless steel autoclave and heated at 120 °C for 72 h. After cooling to room temperature, the colorless crystals were obtained in a yield of 35% based on Ag. Elemental analysis calcd (%) for C7H5N2Ag (225.00): C, 37.33; H, 2.22; N, 12.44. Found (%): C, 37.39; H, 2.27; N, 12.31. IR (KBr, cm−1) data: 3074 (w), 1599 (vs), 1453 (m), 1295 (m), 1231 (vs), 742 (s). [Ag2(NIPH)(HBim)] (2). A mixture of AgNO3 (0.16 g, 1 mmol), H2NIPH (0.08 g, 0.4 mmol), HBim (0.06 g, 0.5 mmol) and H2O (10 mL) was sealed in a 25 mL Teflon-lined stainless steel autoclave and heated at 120 °C for 72 h. After cooling to room temperature, the colorless crystals were obtained in a yield of 56% based on Ag. Elemental analysis calcd (%) for C15H9Ag2N3O6 (542.99): C, 33.15; H, 1.66; N, 7.73. Found (%): C, 33.19; H, 1.68; N, 7.79. IR (KBr, cm−1) data: 3086 (w), 2826 (w), 1617 (m), 1505 (vs), 1389 (vs), 740 (s). [Ag6(4-NPTA)(Bim)4] (3). A mixture of AgNO3 (0.16 g, 1 mmol), HBim (0.06 g, 0.5 mmol), 4-H2NPTA(0.05 g, 0.23 mmol) and H2O (10 mL) was sealed in a 25 mL Teflonlined stainless steel autoclave and heated at 140 °C for 72 h. After cooling to room temperature, the colorless crystals were obtained in a yield of 60% based on Ag. Elemental analysis calcd (%) for C36H23Ag6N9O6 (1324.85): C, 32.61; H, 1.74; N, 9.51. Found (%): C, 32.65; H, 1.77; N, 9.54. IR (KBr, cm−1) data: 3074 (w), 1607 (m), 1450 (vs), 1367 (vs), 988 (w), 742 (s). [Ag2(3-NPTA)(bipy)0.5(H2O)] (4). A mixture of AgNO3 (0.1 g, 0.6 mmol), 3-NPTA (0.05 g, 0.2 mmol), bipy (0.05 g, 0.2 mmol) and H2O (10 mL) was sealed in a 25 mL Teflon-lined stainless steel autoclave and heated at 100 °C for 72 h. After cooling to room temperature, the colorless crystals were obtained in a yield of 48% based on Ag. Elemental analysis calcd (%) for C13H9Ag2N2O7 (520.96): C, 29.94; H, 1.73; N, 5.37. Found (%): C, 29.90; H, 1.78; N, 5.33. IR (KBr, cm−1) data: 3365 (w), 3091 (w), 1599 (m), 1530 (m), 1370 (vs), 716 (s). Synthesis of particles of 1–4. A mixture of reactant with high concentration (the concentration is about 10 times that for synthesizing single crystals) was sealed in a 25 mL Teflonlined stainless steel autoclave and heated for 2 h at 120 °C, 120 °C, 140 °C and 100 °C for 1–4, respectively. The products were washed and centrifuged by water and ethanol three times, respectively, and dried in air.

Dalton Trans., 2014, 43, 10104–10113 | 10105

View Article Online

Paper

Dalton Transactions


Single-crystal X-ray crystallography The crystal structures of 1–4 were determined by single-crystal X-ray diffraction. The reflection data were collected on a Bruker-AXS SMART CCD area detector diffractometer. Data collections were carried out at 293 K using a ω-scan and Mo-Kα radiation. Empirical absorption correction was applied for all the data. The structures were solved by direct methods and further refined by full-matrix least-square refinements on the basis of F2 using the SHELXTL program.27 All non-hydrogen atoms were refined anisotropically. The hydrogen atoms of 1–4 were calculated by geometrical models. Experimental details for the structure analysis of 1–4 are given in Table 1. The selected bond distances and angles for 1–4 are listed in Table S1,† and the hydrogen bonds for 1–4 are listed in Table S2.† Antibacterial test The antibacterial activities of the compounds were tested against E. coli (F 1693) and S. aureus (F 1557) by determining the minimal inhibitory concentration, growth inhibition assay and zone of inhibition technique. All bacterial routine handling was conducted with Luria Bertani (LB) broth at 37 °C, and long-term storage was performed in glycerol stock stored at −20 °C. The media were made up by dissolving agar and LB broth in distilled water. Minimal inhibitory concentration (MIC). The stock solutions of the synthesized samples were prepared in aqueous solution, and graded quantities of the test samples were incorporated in a specified quantity of sterilized liquid medium. The bacteria were maintained in general LB liquid media and shaken at 37 °C overnight. Diluted overnight bacteria and LB liquid cultures were treated with serial dilutions of metal complexes for 24 h while shaking at 37 °C. And the optical density was measured at 600 nm (OD600) to determine the MIC values. Table 1

Release concentration of Ag+ ions The samples of commercial Ag-NPs and compounds 1–4 were immersed in distilled water in concentrations of 1000 ppm for 5 days. The supernatant fluids were taken to test every 4 h in the first 24 h, after that, it was measured once a day. The Ag+ ion concentrations of the solutions were measured by ICP-AES.

Results and discussion Description of the crystal structures Single crystal X-ray diffraction studies revealed that 1–4 could be classified into three types of frameworks constructed from mononuclear or polynuclear silver building blocks: 1-D chains for 1 and 2, a 2-D layer for 3, and a 3-D framework for 4. These

Crystallographic data and structure refinements for 1–4

Empirical formula Formula weight Crystal system Space group a (Å) b (Å) c (Å) β (°) Volume (Å3) Z DCalc (mg m−3) μ (mm−1) F(000) Rint GOF on F2 R1 [I > 2σ(I)]a wR2 [I > 2σ(I)]a R1 (all data)a wR2 (all data)a a

Growth inhibition assay. Diluted bacteria and LB liquid cultures were treated with graded quantities of commercial Agnanoparticles (Ag-NPs) and compounds 1–4 for 48 h while shaking at 37 °C, respectively. OD600 was measured for all samples through a UV-vis spectrometer at predetermined time intervals to draw the growth curves of the bacteria. The growth curves of E. coli and S. aureus without antibacterial agents were also measured as blanks. Zone of inhibition technique. The mixture of dissolving agar and LB broth was autoclaved for 15 min at 121 °C and then dispensed into sterilized Petri dishes, which were allowed to solidify and used for inoculation. The target microorganism cultures were prepared separately in 100 mL of liquid LB broth media for activation. 50 μL of activated strain was placed onto the surface of an agar plate, and spread evenly over the surface by means of a sterile, bent glass rod. Then the neutral filters (diameter of 10 mm) filtrating the compound solutions were put into each plate. The diameters of the inhibition zones were measured by vernier callipers.

1

2

3

4

C7H5N2Ag 225.00 Monoclinic P21/c 4.5170(6) 12.3513(15) 11.6129(12) 106.550(4) 621.05(13) 4 2.406 3.145 432 0.0239 1.002 0.0193 0.0509 0.0208 0.0519

C15H9N3O6Ag2 542.99 Monoclinic P21/c 13.9448(7) 5.4968(3) 19.9779(9) 96.892(3) 1520.28(13) 4 2.372 2.618 1048 0.0181 1.040 0.0211 0.0522 0.0237 0.0537

C36H23N9O6Ag6 1324.85 Monoclinic P21/c 14.4128(5) 17.2474(5) 14.1954(5) 94.508(2) 3517.8(2) 4 2.502 3.338 2528 0.0416 1.042 0.0555 0.1542 0.0907 0.1761

C13H9N2O7Ag2 520.96 Monoclinic C2/c 12.526(2) 7.8162(14) 28.984(5) 96.117(2) 2821.5(8) 8 2.453 2.819 2008 0.0246 1.054 0.0285 0.0676 0.0339 0.0704

R1 = ∑||Fo| − |Fc||/∑|Fo|; wR2 = {∑[w(Fo2 − Fc2)2]/∑[w(Fo2)]2}1/2.

10106 | Dalton Trans., 2014, 43, 10104–10113


View Article Online


Dalton Transactions

different structural features may be attributed to the ligand effects and different coordination environments of silver centers. Fig. S1 and S2† summarize the coordination modes of ligands. 1-D chains of [Ag(Bim)] (1) and [Ag2(NIPH)(HBim)] (2). The asymmetric unit of 1 contains one Ag(I) ion and one Bim ligand. The geometry around the Ag1 center can be described as linear formed by two N atoms from two different Bim ligands (Fig. 1a). The average distance of Ag–N bonds is 2.093 Å and the bond angle of N1–Ag1–N2 is 166.33°, which are similar to that in reported Ag-based compounds.28,29 As a μ2-bridge, Bim ligands link Ag atoms to form a distorted chain, in which the distance between two adjacent Ag(I) centers is 6.266 Å (Fig. 1b). The adjacent chains are packed into a 2-D network based on π⋯π interactions between the Bim ligands (Fig. S3†). In order to investigate the effect of organic ligands on the architecture of Ag-based coordination polymers, the H2NIPH ligand was introduced to synthesize [Ag2(NIPH)(HBim)] (2). The asymmetric unit of 2 consists of three Ag(I) ions, one NIPH ligand and one HBim ligand, in which the atomic occupancy of both Ag2 and Ag3 are 0.5. If the Ag–Ag contacts are neglected, the local coordination environment around Ag1 can be described as a line formed by one O atom from one NIPH ligand and one N atom from one terminal HBim ligand, while both Ag2 and Ag3 are two-coordinated with two O atoms from two different NIPH ligands (Fig. 2a). The average distances of Ag–O and Ag–N bonds are 2.145 Å and 2.098 Å, respectively. Two crystallographically equivalent Ag1 atoms and one Ag2 atom are bridged by two carboxylic groups to give a trinuclear silver unit [Ag3N2(CO2)2] with a shorter Ag⋯Ag separation of 3.109 Å, which is slightly shorter than twice the van der Waals’ radius of the Ag+ ion.30–33 The trinuclear units are connected with mononuclear [AgO2] units by bridging NIPH ligands, resulting in the formation of a 1-D belt chain (Fig. 2b). The

Fig. 1 (a) View of the coordination environment of the Ag center in 1. (b) View of a one-dimensional chain structure in 1.


Paper

Fig. 2 (a) View of the coordination environment of Ag centers in 2. (b) View of a one-dimensional chain structure in 2.

terminal HBim ligands decorate alternately at two sides of the chains, in which the N–H group of HBim as a donor forms N–H⋯O hydrogen bonds with a carboxyl-oxygen atom (N2–H2⋯O3, 2.741(3) Å). All linear chains are assembled into a 2-D supramolecular architecture based on hydrogen bonds (Fig. S4†). 2-D framework of [Ag6(4-NPTA)(Bim)4] (3). Single crystal X-ray analysis reveals that 3 crystallizes in a monoclinic setting with space group P21/c. The asymmetric unit of 3 consists of six Ag(I) ions, one 4-NPTA ligand and four Bim ligands. 3 is a 2-D framework with two types of Ag(I) double-stranded looplike chains (Fig. 3a). For the type-(I) chain, Ag3, Ag4 and Ag6 are linked by Bim ligands as a building unit, in which Ag4 and Ag6 exhibit a similar distorted plane triangle geometry with one oxygen atom from the 4-NPTA ligand, one nitrogen atom and one carbon atom from two different Bim ligands, while Ag3 also exhibits a distorted plane triangle geometry with one oxygen atom from one 4-NPTA ligand and two N atoms from

Fig. 3 View of the coordination environment of Ag centers and two types of chains (a) and a two-dimensional layer structure (b) in 3.

Dalton Trans., 2014, 43, 10104–10113 | 10107

View Article Online


Paper

two different Bim ligands. The building units are positioned to form an infinite chain by linked carboxylic groups from 4-NPTA ligands. There are three kinds of Ag(I) centers in the type-(II) chain. Ag1 has a triangle environment coordinated with one oxygen atom from the 4-NPTA ligand, one nitrogen atom and one carbon atom from two different Bim ligands. Ag2 is surrounded by one oxygen atom from the 4-NPTA ligand and two nitrogen atoms from the two different Bim ligands, while Ag5 has tetrahedral geometry coordinated by two oxygen atoms from two different 4-NPTA ligands, one nitrogen atom and one carbon atom from two different Bim ligands. The symmetrical Ag1, Ag1A, Ag2 and Ag2A are circled by four Bim ligands to form a cycle unit, which is connected with symmetrical Ag5 and Ag5A by carboxylic groups of 4-NPTA ligands and Bim ligands to form a double-stranded loop-like chain. Ag1, Ag4, Ag5 and Ag6 are all bonded to C atoms from different Bim ligands with Ag–C bond distances ranging from 2.151(6) to 2.705(8) Å.34–37 Finally, two types of chains are connected by bridged 4-NPTA ligands to form a 2-D layer (Fig. 3b). These 2-D layers are further stacked in a parallel fashion (Fig. S5†). 3-D framework of [Ag2(3-NPTA)(bipy)0.5(H2O)] (4). The X-ray diffraction study reveals that the asymmetric unit of 4 consists of two Ag(I) ions, one 3-NPTA ligand, a half bipy ligand and one coordinated water molecule. The interesting aspect in bonding patterns of 4 is its high coordination number of Ag centers. As shown in Fig. 4a, Ag1 is five coordinated by four oxygen atoms from three 3-NPTA ligands and one μ2-O atom from coordinated water molecule in the distorted octahedral geometry. Ag2 occupies a distorted tetragonal geometry by two oxygen atoms from two 3-NPTA ligands, one μ2-O atom from the water molecule and one N atom from the bipy ligand. The Ag–O bond distances are in the range of 2.214(2)–2.603(3) Å, and the Ag–N bond distance is 2.189(3) Å. The symmetrical Ag1 and Ag2 atoms are bridged by two μ2-O atoms from two co-

Fig. 4 Ball-and-stick, and polyhedral representation of the tetranuclear unit (a), a 2-D layer structure (b) and a three-dimensional framework (c) in 4.

10108 | Dalton Trans., 2014, 43, 10104–10113

Dalton Transactions

ordinated water molecules and two carboxyl groups from two 3-NPTA ligands to generate a tetranuclear [Ag4O2(CO2)2] building unit (Fig. 4a). Each tetranuclear unit is linked by six 3-NPTA ligands resulting in the formation of a 2-D layer structure (Fig. 4b). These layers are further connected by bipy ligands to form the 3-D framework with a 1-D channel along the b direction (Fig. 4c). To better understand the 3-D framework of 4, a topological analysis approach was employed.38 Each tetranuclear [Ag4O2(CO2)2] secondary building unit serves as an eightconnected node, while 3-NPTA ligand can act as a threeconnected node and bipy can act as a bridging ligands (Fig. 5a). On the basis of this simplification, the structure of 4 can be described as a (3,8)-connected 3-D network with the Schläfli symbol (43)2(46·618·84) (Fig. 5b and c). Structural comparison of the frameworks 1–4 To date, a large number of silver(I) coordination polymers with diverse topologies and dimensionalities have been constructed based on abundant coordination geometries of Ag+ ions.39 In particular, Ag(I) N-heterocyclic carbene complexes have received great attention,40 and various N-donor ligands, such as imidazole,41 4,4′-bipyridine,42 4,4′-bipyrazolyl,23 were used to assemble coordination frameworks with outstanding functional properties such as luminescence and antibacterial activity. For four coordination polymers 1–4 reported in this study, the common structural feature is that they belong to the same crystal system of Monoclinic, but in different space groups (P21/c for 1–3 and C2/c for 4). In this case, the organic ligands adopt different coordinated modes (Fig. S1 and S2†). For example, Bim ligands exhibits three coordination modes including μ2-bridge in 1, terminal ligand in 2 and μ3-bridge in 3. Three polycarboxylic organic ligands with structural isomerism exhibits three different kinds of coordination modes: the monodentate and bridging bis-monodentate modes for NIPH, the μ4-bridging tetradentate and μ3-bridging tridentate modes

Fig. 5 (a) Ball-and-stick, and polyhedral representations of the 8-connected tetranuclear unit and 3-connected ligand in 4. Schematic representations of (3, 8)-connected framework of 4 for 2-D layer (b) and 3-D frameworks (c).


View Article Online


Dalton Transactions

for 4-NPTA, and the μ3-bridging tridentate and chelating modes 3-NPTA. The four frameworks can be divided into three sets constructed from mononuclear or polynuclear silver building blocks: 1-D chains for 1 and 2, 2-D layer for 3, and 3-D framework for 4. The 1-D chain of 1 is formed by mononuclear [AgN2] building units and bridging Bim ligands, while that of 2 is constructed by trinuclear [Ag3N2(CO2)2], mononuclear [AgO2] building units and bridging NIPH ligands. The 2-D layer of 3 is composed of two kinds of polynuclear silver chains and bridging 4-NPTA and Bim ligands. The 3-D framework of 4 is formed by tetranuclear [Ag4O2(CO2)2] building units and 3-NPTA and bipy bridging ligands. The structural evolution of 1–4 demonstrates the effect of organic ligands on the architecture of coordination polymers. Morphology and thermal–light stability of 1–4 Compared with the bulk crystals of coordination polymers, coordination polymers micro- and nanoparticles are suitable for use in the antibacterial field due to their large specific surface area and highly stable suspensions in aqueous medium without aggregation or precipitation. The morphologies of particles were characterized by scanning electron microscopy (SEM). It can be shown that 1–4 possess similar rod structures at the micrometer-size (Fig. S6†). The diameter of sample 1 is about 0.5 μm, and the length is in the range of 8–10 μm. The diameter and length of sample 2 are about 0.3 μm and 10 μm, respectively. Samples 3 and 4 are similar in size with diameter and length ranging from 1–2 μm and 3–10 μm, respectively. These particles are stable in aqueous solution. Taking sample 4 as an example, the XRD pattern of sample 4 immersed in aqueous solution for 48 h is in good agreement with that of crystals of 4 (Fig. S7†). The thermal stabilities of 1–4 were studied by thermogravimetric analysis (TGA) under an air atmosphere (Fig. S8†). 1 begins to decompose from 360 °C. 2 is stable up to 206 °C, and then it underwent two weight losses. For 3, the weight loss of 46.35% corresponds to Bim and 4-NPTA (calcd 45.82%) from 339–468 °C. The TGA curve of 4 was presented to characterize the water and bipy loss of 18.88% (calcd 18.42%) from 225 °C. Furthermore, the sample 4 was treated at different temperatures and the XRD patterns were measured at 20 °C, 50 °C, 100 °C, 150 °C and 200 °C, respectively. The XRD patterns show that the framework of 4 is stable within the temperature ranging from 20 to 200 °C (Fig. S9†). The powder XRD measurements agreed with the single crystal structural results. Light stabilities of 1–4 were analyzed under visible light and UV-vis light at room temperature in an air atmosphere. From the aesthetic point of view, the white powders of 1–4 are suitable for coating materials compared with black Ag-NPs. For example, the appearance and chemical structure of white powder for 4 is not significantly changed under visible light and UV-vis light for a long period of time (Fig. 6). Compounds 1–3 show similar stability properties under visible light and UV-vis light (Fig. S10†). Furthermore, the light stability of 4 was tested according to the reported literature.43 Filter papers (diameter of 10 mm) were impregnated with aqueous solutions


Paper

Fig. 6 Solid ultraviolet spectrum of 4 under visible light (a) and UV-vis light (b).

of AgNO3 and 4, respectively. The filter papers were dried at room temperature. And then they were exposed to air and irradiated with visible light for 3 days. The color of the filter paper impregnated with 4 showed no significant change, but that with AgNO3 was clearly blackened (Fig. S11†). The excellent thermal and light stabilities of the coordination polymers are of benefit to their further applications in antibacterial materials. The antibacterial activities of silver-based coordination polymers Among the numerous silver and silver-based compounds,44 Ag-NPs and Ag(I) compounds have emerged as the principal disinfection agent with minimal inhibition concentrations (MIC) values ranging from 10 to 40 ppm. The MIC was determined by using an optical density method as previously described.45 The MIC values of compounds 1–4 are shown in Table 2, and all of them are in the range of 5–15 ppm against E. coli and 10–20 ppm against S. aureus. It reveals that silverbased coordination polymers 1–4 exhibit higher antibacterial activities than most of the commonly used chemical disinfectants.46 The time-dependent antimicrobial activity of compounds 1–4 in different concentrations against E. coli and S. aureus are shown in Fig. 7 and 8. The inhibitory effects of 1, 2 and 4 against E. coli started at less than 20 ppm, and the growth of S. aureus was inhibited at over 20 ppm. In comparison with the antibacterial behavior of these coordination polymers, the antibacterial activities of 3 towards E. coli and S. aureus are better at lower concentrations. Furthermore, the antimicrobial activities of 1–4 were analyzed by inhibition zone testing. For comparison, commercial Ag-NPs and ligands (H2NPTA and HBim) were also assessed. By contrast, 1–4 show excellent antimicrobial behaviors with diameters of inhibition zones being 17–20 mm for E. coli and

Table 2

E. coli S. aureus

MIC values of 1–4 against E. coli and S. aureus ( ppm)

1

2

3

4

10–15 15–20

10–15 15–20

5–10 10–15

10–15 15–20

Dalton Trans., 2014, 43, 10104–10113 | 10109

View Article Online


Paper

Dalton Transactions

Fig. 7 Growth curves of E. coli in 1 (a), 2 (b), 3 (c) and 4 (d) solutions with different concentrations (10–40 ppm). Fig. 9 (a) Images of inhibition zones for 1–4, Ag-NPs, H2NPTA and HBim; (b) Diameters of inhibition zones against E. coli and S. aureus.

The antibacterial mechanism of silver-based coordination polymers In order to understand the morphological changes of the bacteria (E. coli and S. aureus) upon using silver-based coordination polymers as disinfectants, the high-resolution transmission electron microscope (HRTEM) was employed. Intact bacteria having a distinct outer membrane suggest that the bacterial cell structure was well-preserved even under a high vacuum and an energy electron beam (Fig. 10). After coincubation with compound 3, cellular cohesion was lost with the outer membranes being heavily damaged. The cytoplasm of bacteria flowed out, and the bacteria died. Since the cell wall of Gram-positive bacteria is thicker than that of Gram-

Fig. 8 Growth curves of S. aureus in 1 (a), 2 (b), 3 (c) and 4 (d) solutions with different concentrations (10–40 ppm).

14–16 mm for S. aureus, respectively (Fig. 9). The diameters of inhibition zones for compounds 1–4 are ranked: 3 > 4 > 2 > 1. The diameters of inhibition zones of Ag-NPs are 12 and 11 mm against E. coli and S. aureus, respectively. It was observed that the antibacterial activities of Ag-based coordination polymers are higher than Ag-NPs. It has been reported that there are rarely antibacterial activities for organic antibacterial agents under the concentration of 16 ppt.47 As a result, the diameters of inhibition zones for pure ligands H2NPTA and HBim are both 10 mm, which are the same as that of neutral filters. It also indicated that these compounds have a broad antibacterial capabilities and long-lasting effectiveness for different types of microorganisms.

10110 | Dalton Trans., 2014, 43, 10104–10113

Fig. 10 TEM morphological images of intact and damaged E. coli (a and b) and S. aureus (c and d).


View Article Online


Dalton Transactions

Fig. 11 (a) Concentrations of Ag+ ions in 1–4 and Ag-NPs aqueous solution within the first 24 h. (b) The average concentrations of Ag+ in 1–4 and Ag-NPs aqueous solution within 5 days.

negative bacteria, the morphology damaged level of S. aureus is lower than that of E. coli.48,49 It is well established that only silver in its ionic or compound forms has antimicrobial activity. Some literature has suggested that the antibacterial properties of Ag-based materials arises from the release of Ag+ ions.21,24 The release abilities of Ag+ ions for 1–4 and commercial Ag-NPs were tested by ICP-AES. It was found that the concentrations of Ag+ ions released from the coordination polymers significantly increased during the first 24 h (Fig. 11a), and then they remained stable over the subsequent 5 days. The average concentration of Ag+ ions in Ag-NPs solutions was 5.02 ppm and the concentrations of Ag+ ions in Ag-based coordination polymers solutions ranged from 8.41 to 27.1 ppm (Fig. 11b), which indicated Ag+ ion release capacities of silver-based coordination polymers in aqueous solutions are better than those of commercial Ag-NPs. Compared with other silver-based coordination polymers,20–24 compounds 1–4 have an intermediate rate of Ag+ ions release. This result also indicated that all four compounds could give a steady and prolonged release of Ag+ ions in biocidal concentration. Based on our experimental results, the possible antibacterial mechanism of silver-based coordination polymers materials is to change the potential and concentration difference of the cell environment. Ag-based particles diffuse to the bacteria surface and give a sustained release of Ag+. Aggregation of particles and Ag+ could change the surrounding environment of bacterial cells, i.e. the ion balance would be broken and the ion channels destroyed.50,51 The observed changes of cell structures (Fig. 10) have already documented the damage to the membrane when bacteria were treated with Ag-based coordination polymers. As a result, the outflow of cytoplasm and rupture of the cell membrane caused the death of the bacteria. Our experiments proved that the antibacterial activities of Ag-based coordination polymers can easily be regulated by controlling the release ratio of Ag+ ions, which are closely related with the stoichiometric frameworks.

Conclusions In summary, four silver-based coordination polymers [Ag(Bim)] (1), [Ag2 (NIPH)(HBim)] (2), [Ag6(4-NPTA)(Bim)4] (3)


Paper

and [Ag2(3-NPTA)(bipy)0.5(H2O)](4) have been synthesized by the hydrothermal reaction of Ag(I) salts with N-/O-donor ligands. Single-crystal X-ray diffraction analysis revealed that different coordination modes of the organic ligands could promote different topology structures of 1–4, which are constructed from mononuclear or polynuclear silver building blocks. Coordination polymers 1 and 2 possess 1-D chain structures, while 3 is a 2-D layer and 4 is a (3,8)-connected 3-D framework. All of the Ag-based coordination polymers 1–4 can regulate the sustained release of Ag+ ions leading to excellent antibacterial activities towards both Gram-negative bacteria, E. coli and Gram-positive bacteria, S. aureus. These compounds show good thermal stability and light stability under UV-vis and visible light. Such antibacterial behaviors demonstrate that Ag-based coordination polymers could be regarded as potential materials for bactericidal agents.

Acknowledgements This work was supported by National Natural Science Foundation of China (21276046 and 51003009), the ministry of education science and technology research project, and the Fundamental Research Funds for the Central Universities of China (DUT14LK32).

Notes and references 1 M. G. Pawlicka, J. Uradziński, A. M. Calik and M. P. Frak, J. Microbiol. Res., 2013, 7, 361; A. E. Segarra and J. M. Rawson, CRS Report for Congress, April 16, 2001. 2 Z. Zhao, F. Zhang and M. Xu, J. Med. Microbiol., 2003, 527, 15; N. S. Zhong, B. J. Zheng and Y. M. Li, Lancet, 2003, 362, 1353. 3 R. A. Minear and G. L. Amy, in Water Disinfection and Natural Organic Matter: Characterization and Control, 1996, vol. 649, p. 1. 4 J. Snow, Br. J. Anaesth., 1955, 27, 42; H. J. Chick, J. Hyg., 1910, 10, 237; E. A. Cooper, Biochem. J., 1912, 6, 362. 5 J. W. Alexander, Surg. Infect., 2009, 10, 289. 6 J. W. Wiechers, N. Musee and J. Biomed, Nanotechnology, 2010, 6, 408. 7 S. Eckhardt, P. S. Brunetto, J. Gagnon, M. Priebe, B. Giese and K. M. Fromm, Chem. Rev., 2013, 113, 4708. 8 A. Agarwal, K. M. Guthrie, C. J. Czuprynski, M. J. Schurr, J. F. McAnulty, C. J. Murphy and N. L. Abbott, Adv. Funct. Mater., 2011, 21, 1863; E. Ozkaya, Contact Dermatitis, 2009, 61, 120. 9 M. J. Mohungoo and J. D. Gawkrodger, Br. J. Dermatol., 2009, 161, 79; J. B. Wright, K. Lam and R. E. Burrell, Am. J. Infect. Control, 1998, 26, 572. 10 W. K. Jung, H. C. Koo, K. W. Kim, S. Shin, S. H. Kim and Y. H. Park, Appl. Environ. Microbiol., 2008, 74, 2171. 11 H. Y. Song, K. K. Ko, L. H. Oh and B. T. Lee, Eur. Cells Mater., 2006, 11, 58.

Dalton Trans., 2014, 43, 10104–10113 | 10111

View Article Online


Paper

12 S. Noro, S. Kitagawa, M. Kondo and K. Seki, Angew. Chem., Int. Ed., 2000, 39, 2081; X. Lin, I. Telepeni, A. J. Blake, A. Dailly, C. M. Brown, J. M. Simmons, M. Zoppi, G. S. Walker, K. M. Thomas, T. J. Mays, P. Hubberstey, N. R. Champness and M. Schroder, J. Am. Chem. Soc., 2009, 131, 2159; D. J. Tranchemontagne, M. O’Keeffe and O. M. Yaghi, Angew. Chem., Int. Ed., 2008, 47, 5136; K. M. Thomas, Dalton Trans., 2009, 1487; S. K. Das, M. K. Bhunia, M. M. Seikh, S. Dutta and A. Bhaumik, Dalton Trans., 2011, 40, 2932. 13 Y. Cui, Y. Yue, G. Qian and B. Chen, Chem. Rev., 2012, 112, 1126; J. R. Li, J. Sculley and H. C. Zhou, Chem. Rev., 2012, 112, 869; B. Manna, A. K. Chaudhari, B. Joarder, A. Karmakar and S. K. Ghosh, Angew. Chem., Int. Ed., 2013, 52, 998; S. A. Sapchenko, D. G. Samsonenko, D. N. Dybtsev, M. S. Melgunov and V. P. Fedin, Dalton Trans., 2011, 40, 2196; K. B. Wang, Z. R. Geng, Y. X. Yin, X. Y. Ma and Z. L. Wang, CrystEngComm, 2011, 13, 5100. 14 X. Y. Lu, J. W. Ye, W. Li, W. T. Gong, L. J. Yang, Y. Lin and G. L. Ning, CrystEngComm, 2012, 14, 1337. 15 J. W. Ye, J. Y. Zhang, G. L. Ning, G. Tian, Y. Chen and Y. Wang, Cryst. Growth Des., 2008, 8, 3098. 16 F. Sun, Z. Y. Zhou, M. S. Liu, X. X. Zhou and Y. P. Cai, Acta Crystallogr., Sect. E: Struct. Rep. Online, 2007, 63, m2227; Effendy, F. Marchetti, C. Pettinari, R. Pettinari, A. Pizzabiocca, B. W. Skelton and A. H. White, Inorg. Chim. Acta, 2006, 359, 1504. 17 L. Mirolo, T. Schmidt, S. Eckhardt, M. Meuwly and K. M. Fromm, Chem. – Eur. J., 2013, 19, 1754; K. Nomiya, S. Takahashi, R. Noguchi, S. Nemoto, T. Takayama and M. Oda, Inorg. Chem., 2000, 39, 3301. 18 T. V. Slenters, J. L. Sagué, P. S. Brunetto, S. Zuber, A. Fleury, L. Mirolo, A. Y. Robin, M. Meuwly, O. Gordon, R. Landmann, A. U. Daniels and K. M. Fromm, Materials, 2010, 3, 3407; T. V. Slenters, I. H. Gerspach, A. U. Danielsc and K. M. Fromm, J. Mater. Chem., 2008, 18, 5359. 19 A. M. Kirillov, S. W. Wieczorek, A. Lis, M. F. C. G. da Silva, M. Florek, J. Krol, Z. Staroniewicz, P. Smolenski and A. J. L. Pombeiro, Cryst. Growth Des., 2011, 11, 2711. 20 K. Nomiya, K. Tsuda, T. Sudoh and M. Oda, J. Inorg. Biochem., 1997, 68, 39. 21 Y. Liu, X. Xu, Q. C. Xia, G. Z. Yuan, Q. Z. He and Y. Cui, Chem. Commun., 2010, 46, 2608. 22 P. Smoleński, S. W. Jaros, C. Pettinari, G. Lupidi, L. Quassinti, M. Bramucci, L. A. Vitali, D. Petrelli, A. Kochel and A. M. Kirillov, Dalton Trans., 2013, 42, 6572. 23 A. Tăbăcaru, C. Pettinari, F. Marchetti, C. di Nicola, K. V. Domasevitch, S. Galli, N. Masciocchi, S. Scuri, I. Grappasonni and M. Cocchioni, Inorg. Chem., 2012, 51, 9775. 24 M. Berchel, T. L. Gall, C. Denis, S. L. Hir, F. Quentel, C. Elléouet, T. Montier, J. M. Rueff, J. Y. Salaün, J. P. Haelters, G. B. Hix, P. Lehnb and P. A. Jaffrès, New J. Chem., 2011, 35, 1000.

10112 | Dalton Trans., 2014, 43, 10104–10113

Dalton Transactions

25 K. B. Wang, Y. X. Yin, C. Y. Li, Z. R. Geng and Z. L. Wang, CrystEngComm, 2011, 13, 6231; A. Bhan and E. Iglesia, Acc. Chem. Res., 2008, 41, 559. 26 S. Noro, S. Kitagawa, M. Kondo and K. Seki, Angew. Chem., Int. Ed., 2000, 39, 2081; X. Lin, I. Telepeni, A. J. Blake, A. Dailly, C. M. Brown, J. M. Simmons, M. Zoppi, G. S. Walker, K. M. Thomas, T. J. Mays, P. Hubberstey, N. R. Champness and M. Schroder, J. Am. Chem. Soc., 2009, 131, 2159. 27 G. M. Sheldrick, SHELXS-97, Program for Crystal Structure Solution, University of Göttingen, Göttingen, 1997. 28 P. Halder, E. Zangrando and T. K. Paine, Dalton Trans., 2009, 5386; C. D. Nicola, Effendy, F. Marchetti, C. Nervi, C. Pettinari, W. T. Robinson, A. N. Sobolev and A. H. White, Dalton Trans., 2010, 39, 908; K. B. Nilsson, I. Persson and V. G. Kessler, Inorg. Chem., 2006, 45, 6912. 29 Z. X. Lian, J. W. Cai, C. H. Chen and H. B. Luo, CrystEngComm, 2007, 9, 319; J. Wang, S. Hu and M. L. Tong, Eur. J. Inorg. Chem., 2006, 2069. 30 M. Hong, D. Wu, H. Q. Liu, C. W. Thomas, Z. Y. Zhou, D. B. Wu and S. L. Li, Polyhedron, 1997, 16, 1957. 31 H. V. R. Diasa, S. A. Polacha and Z. Y. Wang, J. Fluorine Chem., 2000, 103, 163. 32 K. Bavelaar, R. Khalil, I. Mutikainen, U. Turpeinen, M. G. Patricia, M. Kraaijkamp, G. A. Albada and G. Haasnoot, Inorg. Chim. Acta, 2011, 366, 81. 33 A. J. Bondi, J. Phys. Chem., 1964, 68, 441. 34 R. Bashiri, K. Akhbari, A. Morsali and M. Zeller, J. Organomet. Chem., 2008, 693, 1903. 35 K. Akhbari and A. Morsali, Cryst. Growth Des., 2007, 7, 2024. 36 K. Akhbari, A. Morsali and M. Zeller, J. Organomet. Chem., 2007, 692, 3788. 37 N. B. Jayaratna, D. B. Pardue, S. Ray, M. Yousufuddin, K. G. Thakur, T. R. Cundari and H. V. R. Dias, Dalton Trans., 2013, 42, 15399. 38 V. A. Blatov, Struct. Chem., 2012, 23, 955. 39 C. L. Chen, B. S. Kang and C. Y. Su, Aust. J. Chem., 2006, 59, 3; K. M. Fromm, J. L. Sagué and A. Y. Robin, Inorg. Chim. Acta, 2013, 403, 2. 40 J. C. Garrison and W. J. Youngs, Chem. Rev., 2005, 105, 3978. 41 K. Nomiya, K. Tsuda, T. Sudob and M. Oda, J. Inorg. Biochem., 1997, 68, 39; G. W. Eastland, M. A. Mazid, D. R. Russell and M. C. R. Symons, J. Chem. Soc., Dalton Trans., 1980, 1682; P. Liu and D. S. Deng, Acta Crystallogr., Sect. E: Struct. Rep. Online, 2008, 64, m556. 42 A. Chen, S. Meng, J. F. Zhang and C. Zhang, Z. Anorg. Allg. Chem., 2014, 640, 974; X. Huang, Z. F. Li, Q. H. Jin, Q. M. Qiu, Y. Z. Cui and Q. R. Yang, Polyhedron, 2013, 65, 129; J. F. Guo, B. X. Guo, J. Y. Wu and G. P. Yan, Acta Crystallogr., Sect. C: Cryst. Struct. Commun., 2013, 69, 742. 43 T. Dorn, K. M. Fromm and C. Janiak, Aust. J. Chem., 2006, 59, 22. 44 K. Chamakura, R. P. Ballestereo, S. Bashir, Z. Luo and J. Liu, MRS Fall, 2010, Boston December 02 2010.


View Article Online


Dalton Transactions

45 M. Liong, B. France, K. A. Bradley and J. I. Zink, Adv. Mater., 2009, 21, 1684; S. G. Chen, Y. J. Guo, S. J. Chen, H. M. Yu, Z. C. Ge, X. Zhang, P. X. Zhang and J. N. Tang, J. Mater. Chem., 2012, 22, 9092; K. M. Hindi, T. J. Siciliano, S. Durmus, M. J. Panzner, D. A. Medvetz, D. V. Reddy, L. A. Hogue, C. E. Hovis, J. K. Hilliard, R. J. Mallet, C. A. Tessier, C. Cannon and W. J. Youngs, J. Med. Chem., 2008, 51, 1577. 46 K. Chamakura, R. P. Ballestero, Z. P. Luo, S. Bashir and J. B. Liu, Colloids Surf., B, 2011, 84, 88. 47 J. Liu, K. Chamakura, R. Perez-Ballestero and S. Bashir, ACS Symp. Ser., 2012, 1119, 129. 48 O. Takeuchi, K. Hoshino, T. Kawai, H. Sanjo, H. Takada, T. Ogawa, K. Takeda and S. Akira, Immunity, 1999, 11, 443.


Paper

49 A. J. Harrop, M. D. Hocknult and M. D. Lilly, Biotechnol. Lett., 1989, 11, 807. 50 E. L. Baldwin, J. A. Byl and N. Osheroff, Biochemistry, 2004, 43, 728; E. Kopera, T. Schwerdtle, A. Hartwig and W. Bal, Chem. Res. Toxicol., 2004, 17, 1452; C. P. Moorhouse, B. Halliweil, M. Grootveld and J. M. C. Gutteridge, Biochim. Biophys. Acta, Gen. Subj., 1985, 843, 261; K. Kilinc and R. Rouhani, Biochim. Biophys. Acta, Lipids Lipid Metab., 1992, 1125, 189; K. Biradha, A. Ramanan and J. J. Vittal, Cryst. Growth Des., 2009, 9, 2969. 51 M. A. Youssef, R. Dey, Y. Gohar, A. A. Massoud, L. Ohrstrom and V. Langer, Inorg. Chem., 2007, 46, 5893; M. A. Youssef, V. Langer and L. Ohrstrom, Dalton Trans., 2006, 2542; R. Singleton, J. Bye, J. Dyson, G. Baker, R. M. Ranson and G. B. Hix, Dalton Trans., 2010, 39, 6024.

Dalton Trans., 2014, 43, 10104–10113 | 10113

Co-ligand and solvent effects on the spin-crossover behaviors of PtS-type porous coordination polymers.

Controlling the dimensionality of on-surface coordination polymers via endo- or exoligation.

Three Mn(II) coordination polymers with a bispyridyl-based quinolinate ligand: the anion-controlled tunable structural and magnetic properties.

Structural diversities and related properties of four coordination polymers synthesized from original ligand of 3,3',5,5'-azobenzenetetracarboxylic acid.

Structural Design Parameters for Highly Birefringent Coordination Polymers.

Dependence of adsorption-induced structural transition on framework structure of porous coordination polymers.

Single-crystal X-ray diffraction studies on structural transformations of porous coordination polymers.

Solvent-regulated assemblies of 1D lanthanide coordination polymers with the tricarboxylate ligand.

Photocurrent-generating properties of bulk and few-layered Cd(ii) coordination polymers based on a rigid dicarboxylate ligand.

Synthesis, crystal structures and characterizations of two homochiral coordination polymers based on a chiral reduced Schiff base ligand.

A family of lanthanide-based coordination polymers with boronic Acid as ligand.

Ultrasonic-assisted synthesis and structural characterization of two new nano-structured Hg(II) coordination polymers.

Structural diversity and photoluminescent properties of zinc benzotriazole-5-carboxylate coordination polymers.

Computational screening of structural and compositional factors for electrically conductive coordination polymers.

Linear alkaline earth metal phosphinate coordination polymers: synthesis and structural characterization.

On the coordination chemistry of phosphinecarboxamide: assessing ligand basicity.

Luminescent mechanochromic porous coordination polymers.

Structural diversity and photocatalytic properties of Cd(II) coordination polymers constructed by a flexible V-shaped bipyridyl benzene ligand and dicarboxylate derivatives.

Introducing a semi-coated model to investigate antibacterial effects of biocompatible polymers on titanium surfaces.

New Zn²⁺ coordination polymers constructed from acylhydrazidate molecules: synthesis and structural characterization.

Coligand and solvent effects on the architectures and spin-crossover properties of (4,4)-connected Iron(II) coordination polymers.

Synergistic effects of nanoparticles and polymers on depletion and structural interactions.

Coordination polymers of uranium(IV) terephthalates.

Bio-sensitive activities of coordination compounds containing 1,10-phenanthroline as co-ligand: synthesis, structural elucidation and dna binding properties of metal(II) complexes.