A new carboxyl-copper-organic framework and its excellent selective absorbability for proteins

Article abstract of DOI:10.1016/j.jssc.2014.05.019

One-pot solvothermal treatments of CuCl₂·2H₂O, H₂L (5-(3-methyl-5-(pyridin-4-yl)-4H-1,2,4-triazol-4-yl) isophthalic acid) and Sm(NO₃)₃·6H₂O in water yielded a rare carboxyl-copper-organic framework, [Cu(HL)]_n· nH₂O (1). The existence of carboxyl groups in compound 1 may be due to the interference of Sm(NO₃)₃·6H₂O at the relatively high temperature and autogenous pressure of the reaction. Compound 1 has been characterized by single-crystal X-ray diffraction, PXRD, IR, and elemental analysis. Compound 1 is a 3D coordination polymer, and an xfe-4-Fddd, (4².6.8³) topology in 1 is created. In addition, the optical properties have been investigated. Rhodamine B dyeing experiments exhibited that there were residual carboxyl groups on the surface of compound 1. UV-vis results showed that more lysozyme was adsorbed onto the surface of compound 1 than BSA at pH 7.4. At the same time, XPS spectra were also investigated to verify the results.

Full text of DOI:10.1016/j.jssc.2014.05.019

Journal of Solid State Chemistry 218 (2014) 64–70
Contents lists available at ScienceDirect
Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
A new carboxyl-copper-organic framework and its excellent selective
absorbability for proteins
Linyan Yang a, Liangliang Xin b, Wen Gu a,c, Jinlei Tian a,c, Shengyun Liao a, Peiyao Du a,
Yuzhang Tong a, Yanping Zhang a, Rui Lv a, Jingyao Wang a, Xin Liu a,c,
n
a Department of Chemistry, Nankai University, Tianjin 300071, China
b School of Science, Tianjin University, Tianjin 300072, China
c Tianjin Key Laboratory of Metal and Molecule Based Material Chemistry, Tianjin 300071, China
a r t i c l e i n f o
a b s t r a c t
Article history:
One-pot solvothermal treatments of CuCl2 ꢀ 2H2O, H2L (5-(3-methyl-5-(pyridin-4-yl)-4H-1,2,4-triazol-4-yl)
isophthalic acid) and Sm(NO3)3 ꢀ 6H2O in water yielded a rare carboxyl-copper-organic framework, [Cu
(HL)]n ꢀ nH2O (1). The existence of carboxyl groups in compound 1 may be due to the interference of Sm
(NO3)3 ꢀ 6H2O at the relatively high temperature and autogenous pressure of the reaction. Compound 1 has
been characterized by single-crystal X-ray diffraction, PXRD, IR, and elemental analysis. Compound 1 is a
3D coordination polymer, and an xfe-4-Fddd, (42.6.83) topology in 1 is created. In addition, the optical
properties have been investigated. Rhodamine B dyeing experiments exhibited that there were residual
carboxyl groups on the surface of compound 1. UV–vis results showed that more lysozyme was adsorbed
onto the surface of compound 1 than BSA at pH 7.4. At the same time, XPS spectra were also investigated to
verify the results.
Received 5 February 2014
Received in revised form
19 May 2014
Accepted 24 May 2014
Available online 16 June 2014
Keywords:
Carboxyl-copper-organic framework
Luminescent
Protein adsorption
XPS
& 2014 Elsevier Inc. All rights reserved.
1. Introduction
could be exploited to separate specific chemical mixtures [11–13].
In view of free carboxylic acids from the surface of MOF, we have
Considerable attention has been paid to the study of transition
metal coordination polymers not only because of non-linear optics
[1,2], gas absorption [3–5], luminescence [6,33], magnetism [34],
medicine [35], and catalytic properties [36,37], but also their
fascinating architectures [38,39]. Many chemical functionalities
are incompatible with the conditions for MOF assembly, and
cannot be obtained covalently attached within MOF cavities via
traditional synthetic routes. For example, MOFs with struts con-
taining free carboxylic acids [7] or pyridines [8] remain rare, as
these moieties often serve as the key coordinating elements of the
MOF frameworks. This can be explained by the tendency of such
reactive groups to engage in framework building through coordi-
nation or hydrogen bonding. The appeal of MOF materials that
have free carboxylic acids is clear: they can be further modified
using a wide range of reactions to afford new MOFs with different
capabilities [9]. For example, such a MOF could be functionalized
with a variety of metals, generating a series of new MOF materials
with metal carboxylates in their pores, where each one can be
used for a particular catalytic reaction [8,10]. Alternatively, the varying
affinities that metal carboxylates have for different chemical species
considered the possibility of protein adsorption. In physiological
media, most proteins carry a net charge, with the sign and magnitude
of the net charge depending on the isoelectric point of the protein (pI).
Electrostatic interactions between proteins and charged surfaces,
therefore, often play a major role in the adsorption behavior of
proteins [14–16]. Herein, we present a novel copper-based MOF [Cu
(HL)]n ꢀ nH2O (1; H2L¼5-(3-methyl-5-(pyridin-4-yl)-4H-1,2,4-triazol-
4-yl) isophthalic acid). The ligand H2L, which can be obtained from
cheap starting materials by a two-step synthesis in good yield,
combines carboxylate, triazole, and pyridine functions and is adopted
from a recently presented series of linkers. We investigated the
amounts of bovine serum albumin (BSA, negatively charged at pH
7.4) and lysozyme (positively charged at pH 7.4) adsorbed onto
negatively MOF to monitor the effect of electrostatic attraction and
repulsion on the amount of adsorbed proteins. At the same time, XPS
spectra were also investigated to verify the results.
2. Experimental section
2.1. Materials and physical measurements
n
Corresponding author at: Department of Chemistry, Nankai University, Tianjin
Lysozyme was purchased from Sigma-Aldrich. Bovine serum
albumin (BSA) was obtained from Amresco Inc. (Solon, OH).
300071, China. Tel.: þ86 13512865 360; fax: þ86 22 2350 2779.
E-mail address: liuxin64@nankai.edu.cn (X. Liu).
http://dx.doi.org/10.1016/j.jssc.2014.05.019
0022-4596/& 2014 Elsevier Inc. All rights reserved.

L. Yang et al. / Journal of Solid State Chemistry 218 (2014) 64–70
65
All commercially available chemicals and solvents were of reagent
grade and used without further purification. The ligand 5-(3-methyl-
5-(pyridin-4-yl)-4H-1,2,4-triazol-4-yl) isophthalic acid (H2L) was
synthesized according to the method reported previously [17].
X-ray powder diffraction (PXRD) intensities were measured on
(hv¼1486.6 eV). The vacuum in the main chamber was kept above
3 ꢃ 10ꢁ6 Pa during XPS data acquisitions. General survey scans
(binding energy range: 0–1200 eV; pass energy: 160 eV) and high-
resolution spectra (pass energy: 40 eV) in the regions of N1s were
a Rigaku D/max-IIIA diffractometer (Cu-Kα, λ¼1.54056 Ǻ). The
single crystalline powder samples were prepared by crushing
the crystals and scanned from 31 to 601 with a scanning speed
of 0.021/s. Thermogravimetric analysis (TGA) were performed on a
NETZSCH TG 209 instrument with a heating rate of 10 1C/min in
the N2 atmosphere. Flourescence spectroscopy data were recorded
on HORIBA Jobin Yvon HJY-FL3-221-TCSPC spectrophotometer.
Table 1
Crystal data and structure refinements for compound 1.
Identification
Compd 1
Empirical formula
Formula weight
T (K)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
C16H13CuN4O5
404.84
293(2)
Monoclinic
C2/c
17.035(3)
10.172(2)
19.396(4)
90
113.62(3)
90
2.2. Preparation of coordination polymers
2.2.1. Synthesis of [Cu(HL)]n ꢀ nH2O
CuCl2 ꢀ 2H2O (0.1 mmol, 0.017 g), H2L (0.2 mmol, 0.0648 g) and
Sm(NO3)3 ꢀ 6H2O (0.1 mmol, 0.0444 g) were dissolved in 15 mL
water, reacted for 20 min under the 100 W of ultrasound, trans-
ferred to a 25 mL Teflon-lined pot, and the reaction mixture was
heated within 2 h up to 140 1C. The temperature was kept on a
constant level for 3 days, and then the autoclave was cooled
rapidly to room temperature. Brown block crystals of 1 were
collected with a yield of 78% (based on Cu). Anal. calcd for
α (1)
β (1)
γ (1)
Z
8
ρcalc (g cmꢁ3
)
1.747
1.458
1648
4.58 to 50.021
12,530
0.1068
2705
240
1.093
μ (mmꢁ1
F(0 0 0)
)
2θ scan range
Reflections collected
Rint
C
16H13N4O5Cu: C, 47.47; H, 3.24; N, 13.84. Found: C, 47.52;
H, 3.14; N, 13.90. IR data (KBr pellet,
ν
[cmꢁ1]): 3419.61, 2362.76,
Independent reflections
Parameters
2342.41, 2026.88, 1619.15, 1544.96, 1373.96, 1306.30, 1251.18,
1132.83, 879.04, 840.91, 623.85, 488.66.
Goodness-of-fit on F2
R1,wR2[I42σ(I)]
R1,wR2[all data]
0.0428, 0.0975
0.0491, 0.1036
2.3. Analysis of the residual carboxyl groups of compound 1
Compound 1 was first immersed in rhodamine B (0.1 wt%) in
sodium phosphate buffer (0.1 M, pH 8) for 5 min. After rinsing
with DI water and drying in a stream of nitrogen, the rhodamine B
stained compound 1 was imaged using fluorescent microscopy
(excitation 540720 nm, emission 625720 nm) [14].
Table 2
Selected bond lengths [Å] and angles [1] for 1
Selected bonds (Å) and angles (1)
N(3)–Cu(1)#1
Cu(1)–N(2)
Cu(1)–N(3)#2
Cu(1)–N(4)#3
Cu(1)–O(3)#4
N(4)–Cu(1)#3
O(3)–Cu(1)#5
1.970(2)
1.965(2)
1.970(2)
2.068(2)
2.220(2)
2.068(2)
2.220(2)
N(2)–Cu(1)–N(3)#2
131.60(9)
113.23(9)
110.50(9)
90.87(9)
109.30(9)
89.60(8)
N(2)–Cu(1)–N(4)#3
N(3)#2–Cu(1)–N(4)#3
N(2)–Cu(1)–O(3)#4
N(3)#2–Cu(1)–O(3)#4
N(4)#3–Cu(1)–O(3)#4
N(2)–N(4)–Cu(1)#3
N(4)–N(2)–Cu(1)
2.4. Protein adsorption analysis
Protein adsorption assay was performed following the method
previously reported [14]. Protein solutions were freshly prepared
by dissolving BSA or lysozyme in phosphate-buffered saline (PBS,
0.01 mol/L, pH 7.4) to give a final concentration of 20 mg/mL.
Compound 1 (40 mg) was placed in 5 mL centrifugal tubes, to
which 2 mL of the freshly prepared BSA or lysozyme was added.
Adsorption was allowed to proceed at 37 1C for 2 h under gentle
shaking. The suspension was then centrifuged and washed with
PBS five times. The supernatant was collected together, filtered
through a membrane of 0.45 mm pore diameter, and diluted to
500 mL with PBS buffer. The supernatant was analyzed by ultra-
violet absorbance at 280 nm to determine the adsorption amount
of protein. Three repetitions were performed for all samples. The
adsorption of protein, P (mg/g), on compound 1 was calculated
according the following formula:
114.46(16)
122.61(17)
Symmetry transformations used to generate equivalent atoms: #1xꢁ1/2, yꢁ1/2, z;
#2xþ1/2, yþ1/2, z; #3 ꢁxþ3/2, ꢁyþ1/2, ꢁz; #4 x, ꢁy, zꢁ1/2; #5 x, ꢁy, zþ1/2.
½CiꢂVi ꢁ½CrꢂVr
P ¼
m
where [Ci] is the protein concentration in the initial solution
(mgProtein/mLsolution), [Cr] is the residual concentration of protein
in solution (mgProtein/mLsolution), and m is the mass of compound
1 (g).
2.5. X-ray photoelectron spectroscopy (XPS) analysis
XPS spectra were recorded using a Kratos Axis Ultra DLD
spectrometer employing a monochromated Al-K
α
X-ray source
Scheme 1. Coordination Modes of the ligand HLꢁ in compound 1.

66
L. Yang et al. / Journal of Solid State Chemistry 218 (2014) 64–70
Fig. 1. (a) Coordination environment of the CuI ion. (b) 3D MOF of 1 running along the bc-plane. (c) The topology in 1 along the ac-plane (All hydrogen atoms are omitted for
clarity).

L. Yang et al. / Journal of Solid State Chemistry 218 (2014) 64–70
67
recorded. Binding energies were referenced to the C1s binding
energy at 284.60 eV.
coordination mode. So a 3D pts topology is generated in com-
pound 1 [18]; while an xfe-4-Fddd, (42.6.83) topology was formed
in compound 1 here.
2.6. X-ray crystallography
Diffraction data for compound 1 was collected with a Bruker
SMART APEX CCD instrument with graphite monochromatic MoK
α
radiation (
λ
¼0.71073 Å). The data were collected at 293(2)K.
The absorption corrections were made by multi-scan methods.
The structure was solved by charge flipping methods with the
program Olex2 and refined by full-matrix least-squares methods
on all F2 data with Olex2. The crystallographic details are provided
in Table 1, and selected bond lengths and angles for 1 are given in
Table 2.
3. Results and discussion
3.1. Crystal structure
In compound 1, the HLꢁ ligand presents only one coordination
mode (see Scheme 1: configuration
μ
4 for HLꢁ). In compound 1,
crystallizing in the monoclinic system, with the C2/c space group.
As shown in Fig. 1a, the asymmetric unit of 1 consists of one
crystallographically independent CuI ions, one HLꢁ ligand, and
one lattice water molecule. Cu1 is four-coordinated, four donors
are one N2 atom near to methyl group of the triazole ring from one
HLꢁ ligand, one N4C atom near to pyridyl group of the triazole
ring from another HLꢁ ligand, one N3B atom of the 4-pyridine ring
from the third HLꢁ ligand, and one O3D atom of the fourth HLꢁ
ligand. The Cu–N distances range between 1.965(2) and 2.068(2) Å,
and the Cu–O bonds are 2.220(2) Å. Thus, CuI site has a tetrahedral
geometry, which is indicated by the bond angles: N(2)–Cu(1)–N(3)
B¼131.60(9)1, N(2)–Cu(1)–N(4)C¼113.23(9)1, N(3)B–Cu(1)–N(4)
C¼110.50(9)1, N(2)–Cu(1)–O(3)D¼0.90.87(9)1. In Fig. 1b, a three-
dimensional network structure could be formed by the HLꢁ ligands
and CuI ions along bc-plane. The remaining carboxyl groups could
be seen from the 3D skeleton. The CuI centers could be viewed as
4-c nodes, and the HLꢁ ligands could be viewed as linkers. An xfe-
4-Fddd, (42.6.83) topology in 1 is created (Fig. 1c).
Fig. 3. Solid state emission spectra for compound 1 (red) and the H2L ligand (black)
at room temperature upon excitation at 370 nm (The insert image is the enlarged
view of compound 1). (For interpretation of the references to color in this figure
legend, the reader is referred to the web version of this article.)
3
Compared to 1[Cu(Me-4py-trz-ia)] from Lässig et al. [18], a
microporous MOF was formed by the CuII centers and Me-4py-trz-
ia2ꢁ ligands. While in compound 1 here, the HLꢁ ligands and CuI
ions connected to 3D sheet; on the other hand, residual carboxyl
groups were formed in compound 1 here, and no big holes were
found (a calculated porosity of about 1.1% according to PLATON).
In compound 1, the CuII centers presents two coordination modes
[18], but in compound 1 here, the CuI centers presents only one
Fig. 4. (a) Fluorescence image of non-stained compound 1. (b) Fluorescence image
of the rhodamine B-stained compound 1 (both are magnified by four times).
Fig. 2. TG curve of compound 1.

68
L. Yang et al. / Journal of Solid State Chemistry 218 (2014) 64–70
3.2. Phase purity and thermal analysis
131 1C to 238 1C (4.78% contrast to theoretical 4.45%), which is
attributed to the release of the guest water molecule. The second
stage of weight loss occurs from 298 1C to 368 1C (62.14%), which is
attributed to the partial decomposition of the organic ligands. The
third stage of weight loss occurs from 368 1C to 800 1C (9.75%),
which is attributed to the partial decomposition of the organic
ligands. The degradation of compound 1 is incomplete (17.67%
base on the Cu2O).
The purity of the powder samples was confirmed by PXRD. The
PXRD pattern of compound 1 is illustrated in Fig. S1, which is in an
agreement with the simulated one, confirming the phase purity of
the as-synthesized product. The TGA were carried out on the
crystalline samples in the N2 atmosphere with a heating rate of
10 1C/min in the temperature range 25–800 1C.
The TG curve of compound 1 is illustrated in Fig. 2. The TG
curve of compound 1 exhibits three main weight loss steps. The TG
curve of compound 1 shows the first stage of weight loss from
3.3. Emission properties
The fluorescence emission spectrophotometry of compound 1
and the ligand was studied in the solid state at room temperature
(Fig. 3). The free ligand H2L shows luminescence with the emission
maximum at 441 nm and 492 nm, upon excitation at 370 nm.
Compound 1 shows luminescence with the emission maximum at
441 nm and 491 nm, upon excitation at 370 nm, which is attrib-
uted to the internal transitions of the ligands. In contrast with the
H2L ligand, compound 1 shows decreased luminescence, which
could be caused by the presence of free water molecules [19–22].
3.4. Analysis of the residual carboxyl groups of compound 1
At pH 8, carboxyl groups of compound 1 could be changed to
negatively-charged carboxyl anions. Rhodamine B has positively-
charged amino groups and could adsorb to the negatively-charged
carboxyl anions of compound 1 [23]. Stronger intensity of red fluore-
scence could be seen from the rhodamine B-stained compound 1, in
Fig. 5. Comparison of amount of lysozyme and BSA adsorption on the surface of
compound 1.
Fig. 6. (a) XPS wide scan spectra of compound 1 (non-dealed with PBS buffer), BSA-stained and lysozyme-stained compound 1. (b) High-resolution XPS N1s spectra of
compound 1 (non-dealed with PBS buffer). (c) High-resolution XPS N1s spectra of BSA-stained compound 1. (d) High-resolution XPS N1s spectra of lysozyme-stained
compound 1.

L. Yang et al. / Journal of Solid State Chemistry 218 (2014) 64–70
69
contrast with non-stained compound 1. The results (Fig. 4) exhibited
that there were residual carboxyl groups on the surface of compound
1, compared with the control (i.e., non-stained compound 1).
An xfe-4-Fddd, (42.6.83) topology in 1 is created. Compound 1
shows decreased luminescence, in contrast with the H2L ligand,
which could be caused by the presence of free water molecules.
There were residual carboxyl groups on the surface of compound
1. BSA was significantly less adsorbed onto the carboxylic acid-rich
surface; charge–charge attraction could be responsible for the
increased adsorption of lysozyme. XPS spectra were also investi-
gated to verify the results.
3.5. Protein adsorption analysis
In physiological media, most proteins carry a net charge. There is
a pH, at which a net charge is zero on the surface of each protein,
that is, the isoelectric point of the protein (pI). Electrostatic
interactions between proteins and charged surfaces, therefore, often
play a major role in the adsorption behavior of proteins. Therefore,
BSA and lysozyme were selected for protein adsorption assay in the
current study. The amounts of protein adsorbed onto the surface of
compound 1 are shown in Fig. 5a, which indicates that compound 1
tends to reduce BSA adsorption; but increase lysozyme adsorption.
As mentioned above, compound 1 maintained residual carboxylic
acid groups on the surface. At pH 7.4, the carboxylic acid of
compound 1 was converted to a negatively-charged carboxylate
ion. The pI value of BSA is 4.7. At pH 7.4, the net charge of BSA is
negative. Therefore, BSA (pI 4.7), a carboxylic acid-rich protein was
significantly less adsorbed onto the carboxylic acid-rich surface,
possibly due to charge–charge repulsion [24]. On the other hand,
lysozyme (pI 11), contains a large number of –NH2 groups. Therefore,
it is positively-charged at pH 7.4. Charge–charge attraction could be
responsible for the increased adsorption of lysozyme. The results from
this study seem to fit well with a previous report on the study of the
charge interaction of protein and polyelectrolyte films [14].
Acknowledgment
This work was supported by the National Natural Science
Foundation of China (nos. 21371103, 21071083 and 20771062).
Appendix A. Supporting information
CCDC 951567 for compound 1 contains the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from the Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
Supplementary data associated with this article can be found in
the online version at http://dx.doi.org/10.1016/j.jssc.2014.05.019.
References
[1] Cheng Wang, Teng Zhang, Wenbin Lin, Chem. Rev. 112 (2012) 1084–1104.
[2] Z.G. Guo, R. Cao, X. Wang, H.F. Li, W.B. Yuan, G.J. Wang, H.H. Wu, J. Li, J. Am.
Chem. Soc. 131 (2009) 6894–6895.
[3] H.H. Wu, R.S. Reali, D.A. Smith, M.C. Trachtenberg, J. Li, Chem. Eur. J 16 (2010)
13951–13954.
3.6. X-ray photoelectron spectroscopy (XPS) analysis
Fig. 6a shows the low-resolution XPS survey spectra of these
surfaces, all of which are semiquantitative. The XPS spectrum of
compound 1 (non-dealed with PBS buffer) exhibited a ratio of 0.11
between the N1s and C1s photoemissions. A different N1s:C1s
ratio of 0.16 was observed for BSA-stained compound 1, 0.23 for
lysozyme-stained compound 1, indicating that protein adsorption
changed the surface chemical compositions and more nitrogen
was introduced. The low-resolution XPS survey spectrum of BSA-
stained compound 1 has a peak of Cu 2p [25], which could be also
showed in the pictures (Fig. S2, in supporting information). PBS
buffer has changed the carboxylic acid to a negatively charged
carboxylate ion. And part of compound 1 has been dissolved into
PBS buffer and the color of solution has been changed to brown
[4] J.R. Li, J. Sculley, H.C. Zhou, Chem. Rev. 112 (2012) 869–932.
[5] H.H. Wu, Q.H. Gong, D.H. Olson, J. Li, Chem. Rev. 112 (2012) 836–868.
[6] A. Lan, K. Li, H. Wu, D.H. Olson, T.J. Emge, W. Ki, M.C. Hong, J. Li, Angew. Chem.
Int. Ed. 48 (2009) 2334–2338.
[7] R. Custelcean, M.G. Gorbunova, J. Am. Chem. Soc. 127 (2005) 16362–16363.
[8] J.S. Seo, D. Whang, H. Lee, S.I. Jun, J. Oh, Y.J. Jeon, K. Kim, Nature 404 (2000)
982–986.
[9] T. Gadzikwa, O.K. Farha, K.L. Mulfort, J.T. Hupp, S.T. Nguyen, Chem. Commun.
(2009) 3720–3722.
[10] M.J. Ingleson, J.P. Barrio, J.B. Guilbaud, Y.Z. Khimyak, M.J. Rosseinsky, Chem.
Commun. (2008) 2680–2682.
[11] E.I. Basaldella, J.C. Tara, G.A. Armenta, M.E. Patiño Iglesias, J. Porous Mater. 14
(2007) 273–278.
[12] S. Uchida, R. Kawamoto, H. Tagami, Y. Nakagawa, N. Mizuno, J. Am. Chem. Soc.
130 (2008) 12370–12376.
[13] J.P. Zhang, S. Kitagawa, J. Am. Chem. Soc. 130 (2008) 907–917.
[14] L.Y. Yang, L. Li, Q. Tu, L. Ren, Y.R. Zhang, X.Q. Wang, Z.Y. Zhang, W.M. Liu,
L.L. Xin, J.Y. Wang, Anal. Chem. 82 (2010) 6430–6439.
[15] A. Vinu, K.Z. Hossian, P. Srinivasu, M. Miyahara, S. Anandan,
N. Gokulakrishnan, T. Mori, K. Ariga, V.V. Balasubramanian, J. Mater. Chem.
17 (2007) 1819–1825.
[16] J.W. Shim, S.J. Park, S.K. Ryu, Carbon 39 (2001) 1635–1642.
[17] D. Lässig, J. Lincke, H. Krautscheid, Tetrahedron Lett. 51 (2010) 653–656.
[18] D. Lässig, J. Lincke, J. Moellmer, C. Reichenbach, A. Moeller, R. Gläser, G. Kalies,
K.A. Cychosz, M. Thommes, R. Staudt, H. Krautscheid, Angew. Chem. Int. Ed. 50
(2011) 10344–10348.
in non-stained compound
1 (dealed with PBS buffer) and
BSA-stained compound 1. But for lysozyme-stained compound 1,
no obvious dissolution happened and the solution was still
transparent. This phenomenon could be better explained by more
adsorption of lysozyme than that of BSA.
The high-resolution N1s XPS spectra (Fig. 6b) of compound 1
(non-dealed with PBS buffer) have peaks at 399.00 eV (C–N–Me)
and 400.43 eV (–NH– groups, and perhaps, to a lesser extent,
involvement in intermolecular hydrogen bonding interactions)
[26,27]. High-resolution N1s XPS spectra (Fig. 6c) of BSA-stained
[19] J.J. Wang, C.S. Liu, T.L. Hu, Z. Chang, C.Y. Li, L.F. Yan, P.Q. Chen, X.H. Bu, Q. Wu,
L.J. Zhao, Z. Wang, X.Z. Zhang, CrystEngComm 10 (2008) 681–692.
[20] D.X. Xue, W.X. Zhang, X.M. Chen, H.Z. Wang, Chem. Commun. (2008)
1551–1553.
compound
1 have peaks at 399.27 eV (–NH2 groups) and
[21] T. Sun, J.P. Ma, R.Q. Huang, Y.B. Dong, Acta Crystallogr., Sect. E: Struct. Rep.
Online 62 (2006) o2751–o2752.
[22] L.Y. Yang, L.F. Zeng, W. Gu, J.L. Tian, S.Y. Liao, M. Zhang, X.H. Wei, L.L. Xin, X. Liu,
Inorg. Chem. Commun. 29 (2013) 76–81.
[23] Y.L. Wang, M. Bachman, C.E. Sims, G.P. Li, N.L. Allbritton, Langmuir 22 (2006)
2719–2725.
[24] V. Tangpasuthadol, N. Pongchaisirikul, V.P. Hoven, Carbohydr. Res. 338 (2003)
937–942.
399.88 eV (amide groups from BSA) [28–32]. High-resolution N1s
XPS spectra (Fig. 6d) of lysozyme-stained compound 1 have peaks
at 399.50 eV (–NH2 groups), and 399.94 eV (amide groups from
lysozyme). After protein adsorption, the skeleton of compound 1
did not change, which could be seen from PXRD patterns (Fig. S3,
in Supporting information).
[25] M.D. Silva Pinto, C.A. Sierra-Avila, J.P. Hinestroza, Cellulose 19 (2012)
1771–1779.
[26] C.M. Whelan, F. Cecchet, R. Baxter, F. Zerbetto, G.J. Clarkson, D.A. Leigh,
P. Rudolf, J. Phys. Chem. B 106 (2002) 8739–8746.
[27] O. Olivares, N.V. Likhanova, B. Go´mez, J. Navarrete, M.E. Llanos-Serrano,
E. Arce, J.M. Hallen, Appl. Surf. Sci. 252 (2006) 2894–2909.
[28] I. Frateur, J. Lecoeur, S. Zanna, C.O.A. Olsson, D. Landolt, P. Marcus, Electrochim.
Acta 52 (2007) 7660–7669.
4. Conclusions
In conclusion,
a rare carboxyl-copper-organic framework,
[Cu(HL)]n ꢀ nH2O (1) has been hydrothermally synthesized.

70
L. Yang et al. / Journal of Solid State Chemistry 218 (2014) 64–70
[29] A. Ithurbide, I. Frateur, A. Galtayries, P. Marcus, Electrochim. Acta 53 (2007)
[34] W. Zhang, R.G. Xiong, Chem. Rev. 112 (2012) 1163–1195.
[35] P. Horcajada, R. Gref, T. Baati, P.K. Allan, G. Maurin, P. Couvreur, G. Férey, R.
E. Morris, C. Serre, Chem. Rev. 112 (2012) 1232–1268.
[36] S.E.H. Etaiw, S.A. Amer, M.M. El-Bendary, J. Inorg. Organomet. Polym. 21
(2011) 662–672.
[37] S.E.H. Etaiw, A.S. Elsherbiny, A.S. Badr El-din, Chin. J. Chem 29 (2011)
1401–1410.
[38] H.L. Jiang, T.A. Makala, H.C. Zhou, Coord. Chem. Rev. 257 (2013) 2232–2249.
[39] N. Stock, S. Biswas, Chem. Rev. 112 (2012) 933–969.
1336–1345.
[30] S. Premathilaka, M. Hyland, X. Chen, B. Bansal, Food Bioprod. Process. 84 (C4)
(2006) 265–273.
[31] C.M. Pradier, D. Costa, C. Rubio, C. Compere, P. Marcus, Surf. Interface Anal. 34
(2002) 50–54.
[32] G. Iucci, G. Polzonetti, G. Infante, L. Rossi, Surf. Interface Anal. 36 (2004)
724–728.
[33] Y. Cui, Y. Yue, G. Qian, B. Chen, Chem. Rev. 112 (2012) 1126–1162.