scispace - formally typeset

Journal ArticleDOI

Proton-conductive materials formed by coumarin photocrosslinked ionic liquid crystal dendrimers

01 Feb 2018-Journal of Materials Chemistry C (The Royal Society of Chemistry)-Vol. 6, Iss: 5, pp 1000-1007

AbstractIn this work, we have successfully examined for the first time the use of ionic dendrimers as building blocks for the preparation of 1D and 2D proton conductive materials. For this purpose, a new family of liquid crystalline dendrimers has been synthesized by ionic self-assembly of poly(amidoamine) (PAMAM) dendrimers bearing 4, 8, 16, 32 or 64 NH2 terminal groups and a coumarin-containing bifunctional dendron. The noncovalent architectures were obtained by the formation of ionic salts between the carboxylic acid group of the dendron and the terminal amine groups of the PAMAM dendrimer. The liquid crystal properties have been investigated by polarized optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). All the compounds exhibited mesogenic behavior with smectic A or hexagonal columnar mesophases depending on the generation of the dendrimer. Coumarin photodimerization was used as a crosslinking reaction to obtain liquid crystalline polymer networks. All the materials showed good proton conductive properties as the LC arrangement leads to the presence of ionic nanosegregated areas (formed by the ion pairs) that favor proton conduction.

Topics: Dendrimer (60%), Ionic liquid (58%), Liquid crystal (53%), Ionic bonding (53%), Mesogen (51%)

Summary (1 min read)

Introduction

  • Ion transport is an important phenomenon in biological processes, batteries and separation technologies.
  • LCs showing columnar mesophases can be used to create 1D ion conductors, with ion conduction taking place in the direction of the columnar axes.
  • Crosslinking of polymerizable LC monomers in their mesophase can yield nanostructured, thermally and mechanically stable membrane materials with permanent pathways for ion transport.

Synthesis and Characterization of Ionic dendrimers

  • The carboxylic acid dendron was prepared by the synthetic route and the experimental details given in the Supporting Information.
  • The mixture was ultrasonicated for 5 min, then the THF was slowly evaporated at room temperature and the sample was dried in vacuum at 40 ᵒC until the weight remained constant.
  • The formation of ionic interactions between the PAMAM dendrimer and the dendron acids was studied by infrared spectroscopy (IR) and by nuclear magnetic resonance (NMR).
  • In the spectrum of PAMAM16-ChCou the signals at 1686 and 1741 were replaced by two new bands at around 1550 and 1400 cm1 due to the asymmetric and symmetric stretching modes of the carboxylate group.

Proton Conduction Properties

  • The proton conductivity was measured using electrochemical impedance spectroscopy in samples consisting of films sandwiched between ITO-coated electrodes.
  • The typical impedance response (Nyquist plots) consisted of a suppressed semicircle in the high-frequency region and an incline straight line in the low-frequency range .
  • (b) FTIR spectra of PAMAM16-ChCou before (blue) and after (red) coumarin photodimerization.
  • (b) Proton conduction through the nanochannels generated in the ionic dendrimers.

Conclusions

  • A new strategy for the preparation proton conductive materials has been developed using ionic LC dendrimers combined with a crosslinking reaction based on coumarin photodimerization.
  • 1D and 2D ionic nanosegregated assemblies can be obtained in a modular approach using different generation dendrimers.
  • The use of coumarin photodimerization impart a new tool to fabricate mechanical stable ionic materials.
  • All ionic materials showed good proton conductivity and it is expected that macroscopic alignment will enhance this.
  • The proton conduction in these ionic LC dendrimers may open a new path in the search of electrolyte materials for the preparation of electrochemical devices.

Did you find this useful? Give us your feedback

...read more

Content maybe subject to copyright    Report

Proton-conductive materials formed by coumarin
photocrosslinked ionic liquid crystal dendrimers
Citation for published version (APA):
Concellon, A., Liang, T., Schenning, A. P. H. J., Luis Serrano, J., Romero, P., & Marcos, M. (2018). Proton-
conductive materials formed by coumarin photocrosslinked ionic liquid crystal dendrimers.
Journal of Materials
Chemistry C
,
6
(5), 1000-1007. https://doi.org/10.1039/c7tc05009g
DOI:
10.1039/c7tc05009g
Document status and date:
Published: 07/02/2018
Document Version:
Accepted manuscript including changes made at the peer-review stage
Please check the document version of this publication:
• A submitted manuscript is the version of the article upon submission and before peer-review. There can be
important differences between the submitted version and the official published version of record. People
interested in the research are advised to contact the author for the final version of the publication, or visit the
DOI to the publisher's website.
• The final author version and the galley proof are versions of the publication after peer review.
• The final published version features the final layout of the paper including the volume, issue and page
numbers.
Link to publication
General rights
Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners
and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.
• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.
• You may not further distribute the material or use it for any profit-making activity or commercial gain
• You may freely distribute the URL identifying the publication in the public portal.
If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license above, please
follow below link for the End User Agreement:
www.tue.nl/taverne
Take down policy
If you believe that this document breaches copyright please contact us at:
openaccess@tue.nl
providing details and we will investigate your claim.
Download date: 10. Aug. 2022

This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
Accepted Manuscript
rsc.li/materials-c
Journal of
Materials Chemistry C
Materials for optical, magnetic and electronic devices
www.rsc.org/MaterialsC
ISSN 2050-7526
PAPER
Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
the Hofmeister e ects
~
Volume 4 Number 1 7 January 2016 Pages 1–224
Journal of
Materials Chemistry C
Materials for optical, magnetic and electronic devices
View Article Online
View Journal
This article can be cited before page numbers have been issued, to do this please use: A. Concellon, T.
Liang, A. Schenning, J. L. Serrano, P. Romero and M. Marcos, J. Mater. Chem. C, 2017, DOI:
10.1039/C7TC05009G.

Journal Name
ARTICLE
This journal is © The Royal Society of Chemistry 20xx J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins
Please do not adjust margins
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Proton-conductive materials formed by coumarin
photocrosslinked ionic liquid crystal dendrimers
Alberto Concellón,
a
Ting Liang,
b
Albertus P. H. J. Schenning,
b,c
José Luis Serrano,
d
Pilar Romero,*
a
and Mercedes Marcos*
a
In this work, we have successfully examined for first time the use of ionic dendrimers as building blocks for the preparation
of 1D and 2D proton conductive materials. For this purpose, a new family of liquid crystalline dendrimers have been
synthesized by ionic self-assembly of poly(amidoamine) (PAMAM) dendrimers bearing 4, 8, 16, 32 or 64 NH
2
terminal
groups and a coumarin-containing bifunctional dendron. The noncovalent architectures were obtained by the formation of
the ionic salts between the carboxylic acid group of the dendron and the terminal amine groups of the PAMAM dendrimer.
The liquid crystal properties have been investigated by polarized optical microscopy (POM), differential scanning
calorimetry (DSC) and X-ray diffraction (XRD). All the compounds exhibited mesogenic behavior with smectic A or
hexagonal columnar mesophases depending on the generation of the dendrimer. Coumarin photodimerization was used
as crosslinking reaction to obtain liquid crystalline polymer networks. All the materials showed good proton conductive
properties as the LC arrangement leads to the presence of ionic nanosegregated areas (formed by the ion pairs) that favor
proton conduction.
Introduction
Ion transport is an important phenomenon in biological
processes, batteries and separation technologies. The use of
ionic liquid crystals (LCs) has been found to be a versatile
approach for the development of ion transporting materials.
1-2
In fact, LC materials can self-organize into various
nanostructured phases, such as nematic, smectic or columnar.
These nanosegregated structures provide well-organized
channels for the transport of electrons, holes or ions.
3-6
Columnar and smectic arrangements may lead to the
formation of 1D and 2D channels (respectively) capable of
transporting ions. As with all LC properties, ion transport is
highly anisotropic thus, the orientation of the 1D and 2D
channels on the macroscopic scale is an important and
challenging feature. Smectic LCs can be considered as 2D ion
conductors with ion conduction in the directions within the
layer plane. However, LCs showing columnar mesophases can
be used to create 1D ion conductors, with ion conduction
taking place in the direction of the columnar axes.
7-8
Therefore, LC materials have potential as new functional
electrolytes for electrochemical devices; for example, in
lithium-ion batteries (transport of Li
+
ion), dye-sensitized solar
cells (transport of the I
-
/I
3
-
redox couple) or fuel cells (proton
transport).
9-18
Nanostructured LC phases can be stabilized by
photopolymerization to maintain the anisotropic ion transport
over a longer period of time. Crosslinking of polymerizable LC
monomers in their mesophase can yield nanostructured,
thermally and mechanically stable membrane materials with
permanent pathways for ion transport.
19-23
Over the last few years, we have been working on LC
dendrimers with the aim of combining the inherent properties
of the dendrimer scaffold with the anisotropic properties
provided by the LC state.
24-25
LC dendrimers are generally
prepared by the introduction of promesogenic units at the
periphery of a preformed dendrimer. However, it is possible
the design of LC dendrimers without any promesogenic unit.
Ionic LC dendrimers are the most interesting example,
nanosegregation between polar and apolar regions was the
driving force for the formation of the observed mesophases.
26-
31
In addition, the structural versatility of dendrimers allows
the introduction of different functional units on the periphery,
obtaining materials with potential applications in targeted
drug-delivery, optoelectronics, light harvesting and sensors.
32-
35
Page 1 of 9 Journal of Materials Chemistry C
Published on 21 December 2017. Downloaded by UNIVERSIDAD DE ZARAGOZA on 21/12/2017 16:46:53.
View Article Online
DOI: 10.1039/C7TC05009G

ARTICLE Journal Name
2 | J. Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins
Please do not adjust margins
Figure 1. Schematic representation of the ionic self-assembly process to prepare the ionic LC dendrimers and the nomenclature of the ionic dendrimers.
To date, proton conductivity has been reported with low-
molecular-weight mesogenic compounds that were stabilized
by photocrosslinking to maintain the ionic conductivity over a
longer period of time. In the present study, to develop 1D and
2D proton-conductive materials, we have examined the
supramolecular LC organization of ionic dendrimers. A new
family of ionic hybrid dendrimers were synthesized from
poly(amidoamine) (PAMAM) dendrimer generations 0 to 4
(bearing 4, 8, 16, 32 or 64 NH
2
terminal groups) (
Figure 1
).
PAMAM was surrounded by carboxylic acid dendrons
bifunctionalized with a promesogenic unit (cholesteryl
hemisuccinate) and coumarin moieties. Coumarin derivatives
have been widely used as fluorophores in material science.
36-42
In this work coumarin was chosen as reactive group for the
crosslinking reaction. Upon UV irradiation, coumarins undergo
[2+2] cycloaddition to yield cyclobutane dimers. It doesn’t
require an initiator or catalyst and side reactions may be
avoided.
Results and discussion
Synthesis and Characterization of Ionic dendrimers
The carboxylic acid dendron (
Ac-ChCou
,
Figure 1
) was
prepared by the synthetic route and the experimental details
given in the Supporting Information.
Ionic dendrimers were prepared by mixing a tetrahydrofuran
(THF) solution of
Ac-ChCou
with a solution of the
corresponding generation of PAMAM dendrimer in the
stoichiometry necessary to functionalize all terminal amine
groups. The mixture was ultrasonicated for 5 min, then the
THF was slowly evaporated at room temperature and the
sample was dried in vacuum at 40 ᵒC until the weight
remained constant. The formation of ionic interactions
between the PAMAM dendrimer and the dendron acids was
studied by infrared spectroscopy (IR) and by nuclear magnetic
resonance (NMR).
As a representative example that demonstrates the
formation of the ionic salts, the FTIR spectra of
Ac-ChCou
,
PAMAM16
and the corresponding ionic dendrimer is shown in
Figure 2
. In the spectrum of
Ac-ChCou
, three C=O stretching
bands appeared at 1683, 1730 and 1741 cm
-1
. The band at
1730 cm
-1
is assigned to the ester groups, whereas the bands
at 1686 and 1741 cm
-1
correspond to the dimeric and free
form of the carboxylic acid group, respectively. In the
spectrum of
PAMAM16-ChCou
the signals at 1686 and 1741
were replaced by two new bands at around 1550 and 1400 cm
-
1
due to the asymmetric and symmetric stretching modes of
the carboxylate group.
Figure 2.
FTIR spectra (C=O st. region) of
PAMAM16
(black line),
Ac-
ChCou
(blue line), and
PAMAM16-ChCou
(red line). (See
Figure S1
for
the FTIR spectra in the complete frequency range)
1900 1800 1700 1600 1500 1400 1300
Absorbance (a.u.)
Wavenumber (cm
-1
)
ester
acid (free)
acid (dimer)
carboxylate
Page 2 of 9Journal of Materials Chemistry C
Published on 21 December 2017. Downloaded by UNIVERSIDAD DE ZARAGOZA on 21/12/2017 16:46:53.
View Article Online
DOI: 10.1039/C7TC05009G

Journal Name ARTICLE
This journal is © The Royal Society of Chemistry 20xx J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins
Please do not adjust margins
Figure 3.
1
H (left) and
13
C (right) NMR spectra in CDCl
3
solution at 25 ᵒC of: (a) Ac-ChCou, (b) ionic dendrimer PAMAM32-ChCou, and (c) PAMAM32.
The
1
H NMR spectra recorded in CDCl
3
clearly show the
formation of the ionic assemblies. As a representative example
the
1
H NMR spectra of the dendron
Ac-ChCou
, the third
generation PAMAM dendrimer (
PAMAM32
) and the ionic
dendrimer
PAMAM32-ChCou
complex are shown in
Figure 3
.
In the initial dendron, the acid proton signal was very broad
and barely visible in the
1
H spectrum, thus this signal could not
be used to determine the formation of the salt. The protons
close to the ionic pairs experienced the highest chemical shifts.
For instance, the proton signals of the diastereotopic
methylene (H
P
and H
P’
) moved to higher field after the
formation of the salts. In the same way, quantitative
protonation of terminal amine groups of PAMAM dendrimer
was confirmed by the absence of the NH
2
proton signal at 7.91
ppm and the appearance of the NH
3
+
broad signal at 5.20-4.00
ppm. The absence of the CH
2
CH
2
-NH
2
(H
α
, δ= 2.77 ppm) and
CH
2
CH
2
-NH
2
(H
β
, δ= 3.22 ppm) signals and the appearance of
the CH
2
CH
2
-NH
3
+
(H
α
, δ= 3.13 ppm) and CH
2
CH
2
-NH
3
+
(H
β
, δ=
3.52 ppm) signals, also confirms the quantitative protonation
of terminal amine groups.
1
H-
1
H NOESY experiments were also employed to study the
formation of these ionic dendrimers in solution. The main
feature of NOESY is their ability to provide in a single
experiment all the correlations between nuclei which are
physically close in space, thus making it a very valuable tool for
determining whether supramolecular interactions were
established between
Ac-ChCou
dendron and
PAMAM
dendrimer. The
1
H-
1
H NOESY spectrum of
PAMAM32-ChCou
is
shown in
Figure S2
(Supporting Information). Significant cross-
peaks were observed between the diastereotopic protons of
Ac-ChCou
(H
P
and H
P’
) and H
α
and H
β
protons of the terminal
branches of PAMAM, indicating that these groups were close
in space because of the ionic pair formation. Besides of this, H
P
and H
P’
docked closely with the terminal NH
3
+
groups of
PAMAM.
In the
13
C NMR spectra (
Figure 3
) the carboxyl group signal
(C
S
) of the acid shifts from 176.98 to 178.18, indicating the
formation of the carboxylate (COO
). Likewise, the
deprotonation of the carboxylic acid was also corroborated by
the displacement of the methylic carbon (C
Q
), the methyl (C
R
)
carbon and the methylene carbons (C
P
and C
P’
) to lower field.
In addition, when terminal amine groups of PAMAM are
protonated, the methylene carbons (C
α
and C
β
) move from
41.6/42.4 to 39.7/37.7, respectively (data confirmed by
1
H-
13
C
HSQC experiments,
Figure S3
).
Figure 4.
13
C CPMAS NMR spectra of:
(a)
Ac-ChCou
,
(b)
ionic dendrimer
PAMAM16-ChCou
, and
(c)
ionic dendrimer
PAMAM16-ChCou
after
photodimerization.
Page 3 of 9 Journal of Materials Chemistry C
Published on 21 December 2017. Downloaded by UNIVERSIDAD DE ZARAGOZA on 21/12/2017 16:46:53.
View Article Online
DOI: 10.1039/C7TC05009G

Citations
More filters

Journal ArticleDOI
Abstract: We have prepared nanoporous polymers from columnar hexagonal hydrogen-bonded complexes, whose order is fixed by coumarin photoinduced [2 + 2] cycloaddition (photodimerization). Two different hydrogen-bonded complexes were used and consisted of a melamine (M) or tris(triazolyl)triazine (T) derivative acting as central templates and three peripheral carboxylic acids containing coumarin units. These coumarin units were employed for the cross-linking process by photodimerization in order to fix the LC arrangement. Template removal leads to the formation of self-standing nanoporous polymers keeping the columnar hexagonal order. Two nanoporous polymers with different pore diameters were obtained depending on size of the utilized template. These polymers with carboxylic acids at the pore surface demonstrate the ability to selectively adsorb certain molecules depending on their size. Moreover, after base treatment of the nanoporous polymers, they are able to adsorb cationic dyes over anionic and larger cations, d...

25 citations


Journal ArticleDOI
Abstract: ARG and AMF thank the financial support of the Generalitat Valenciana, through the Grisolia and Forteza programs, and the Spanish Ministry of Science and Innovation, through the Research Projects ENE2007-67584-C03 and UPOVCE-3E-013 and the awarding of two FPI and FPU pre-doctoral grants. AMF and NFKA would like to thank the Royal Academy of Engineering for the award of the Newton Research Collaboration Programme grant NRCP1516/4/61. AMF acknowledges the School of Engineering of the University of Aberdeen for financial support.

19 citations


Journal ArticleDOI
Abstract: We report a new family of liquid crystalline porphyrin-core dendrimers with coumarin units at the periphery of the dendrimer. These compounds have been prepared by copper-catalyzed azide–alkyne “click” cycloaddition (CuAAC). The mesomorphic properties have been investigated via polarized optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The peripheral coumarin units play a key role in the liquid crystal behavior, contributing to the appearance of discotic nematic mesophases with hole mobility values among the highest values reported for discotic liquid crystals (of the order of 1 cm2 V−1 s−1). It has also been demonstrated that excitation of the coumarin moieties leads to energy transfer (antenna effect) to the luminescent porphyrin core. Therefore, this strategy, which involves ‘click’ chemistry, has been proven to be a powerful and elegant synthetic tool for the preparation of optoelectronic materials based on complex dendritic architectures.

18 citations


Journal ArticleDOI
TL;DR: The PRLDA method provides new insight into programmed gel property control and has excellent potential for biomaterial and optoelectronic applications.

18 citations


Journal ArticleDOI
14 Sep 2020-Langmuir
TL;DR: The applications of ionic liquid crystals are overviewed in a comprehensive manner, finding various applications including host frameworks for guest binding, separation membranes, reaction media, and optoelectronic materials.
Abstract: Ionic liquid crystals have emerged as a new class of functional soft materials in the last two decades, and they exhibit synergistic characteristics of ionic liquids and liquid crystals such as mac...

17 citations


References
More filters

MonographDOI
26 Feb 1998
Abstract: This four-volume reference aims to provide information on the basic principles of both low- and high-molecular weight materials, as well as the synthesis, characterization, modification, and applications (such as in computer displays or as structural materials) of all types of liquid crystals. Volume 1, for example, deals with the basic physical and chemical principles of liquid crystals, including structure-property relationships, nomenclature, phase behaviour, characterization methods, and general synthesis and application strategies.

1,670 citations


Journal ArticleDOI
TL;DR: Dendritic Fluorescent Sensors and Supramolecular Assemblies between Dendrimers and Surfactants or Polymers 1885 4.8.1.
Abstract: 3.15. Miscellaneous Photophysical Studies 1874 3.16. Dendritic Fluorescent Sensors 1875 3.17. Nonlinear Optical Properties 1875 4. Supramolecular Properties 1876 4.1. Concepts and Pioneering Studies 1876 4.2. H-Bonding 1877 4.3. Electrostatic Binding 1877 4.4. Combined H-Bonding/Ionic Bonding 1879 4.5. Coordination of Metal Ions 1880 4.6. Intradendritic π-π Interactions 1880 4.7. Encapsulation of Neutral Guest Molecules 1881 4.8. Interdendritic Supramolecular Associations 1883 4.8.1. Liquid Crystals 1883 4.8.2. Other Dendritic Self-Assemblies 1884 4.9. Supramolecular Assemblies between Dendrimers and Surfactants or Polymers 1885

1,530 citations


Journal ArticleDOI
TL;DR: New approaches to the functionalization of liquid crystals are described and it is shown how the design ofliquid crystals formed by supramolecular assembly and nano-segregation leads to the formation of a variety of new self-organized functional materials.
Abstract: In the 21st century, soft materials will become more important as functional materials because of their dynamic nature. Although soft materials are not as highly durable as hard materials, such as metals, ceramics, and engineering plastics, they can respond well to stimuli and the environment. The introduction of order into soft materials induces new dynamic functions. Liquid crystals are ordered soft materials consisting of self-organized molecules and can potentially be used as new functional materials for electron, ion, or molecular transporting, sensory, catalytic, optical, and bio-active materials. For this functionalization, unconventional materials design is required. Herein, we describe new approaches to the functionalization of liquid crystals and show how the design of liquid crystals formed by supramolecular assembly and nano-segregation leads to the formation of a variety of new self-organized functional materials.

1,335 citations


Journal ArticleDOI
29 Mar 2002-Science
Abstract: Modern crystal engineering has emerged as a rich discipline whose success requires an iterative process of synthesis, crystallography, crystal structure analysis, and computational methods. By focusing on the molecular recognition events during nucleation and growth, chemists have uncovered new ways of controlling the internal structure and symmetry of crystals and of producing materials with useful chemical and physical properties.

1,070 citations


Journal ArticleDOI
Abstract: Dendron-mediated self-assembly, disassembly, and self-organization of complex systems have been investigated. The most ideal building blocks would need to display shape persistence in solution and in the solid state, since only this feature provides access to the use of complementary methods of structural analysis. Most supramolecular dendrimers are chiral even when they are constructed from nonchiral building blocks and are equipped with mechanisms that amplify chirality. This poses additional challenges associated with the understanding of the structural origin of chirality in different supramolecular structures through combinations of structural analysis methods. While many supramolecular structures assembled from dendrimers and dendrons resemble some of the related morphologies generated from block-copolymers, they are much more complex and are not determined by the volume ratio between the dissimilar parts of the molecule.

1,007 citations


Frequently Asked Questions (1)
Q1. What are the contributions in "Proton-conductive materials formed by coumarin photocrosslinked ionic liquid crystal dendrimers" ?

• A submitted manuscript is the version of the article upon submission and before peer-review. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher 's website. The final author version and the galley proof are versions of the publication after peer review. The final published version features the final layout of the paper including the volume, issue and page numbers.