In situ formation of AuNPs using fatty N-acylamino hydrazide organogelators as templates

Article abstract of DOI:10.1039/C8NJ04127J

This work reports, for the first time, the synthesis of new fatty N-acylamino hydrazides and demonstrates the activity of these compounds as low-molecular-weight organic gelators and templates for preparation of gold nanoparticles (AuNPs). Initially, we evaluated the gelation properties of fatty N-acylamino hydrazides in various nonpolar and polar solvents (n-hexane, toluene, benzene, cyclohexane, and ethanol). Fatty N-acylamino hydrazide derived of the glycine and stearic acid (C18:0) did not form gels in any of the tested solvents. All other hydrazides did form gels in at least two of the organic solvents tested. The morphology of each gel was observed via scanning electron microscopy. The organogels derived from alanine, valine, and phenylalanine had translucid properties, while the serine organogels were opaque. Afterwards, the synthesis of AuNPs in the presence of the organogelator using microwave irradiation was realized. Organogelator agents reduced HAuCl₄ showing plasmon band peaks between 530 and 543 nm. In addition, the method does not require a reducing agent, which is typically a potential source of contamination and toxicity. Therefore, this work confirms the importance of the hydrazide group of the new fatty N-acylamino hydrazides in gel formation and as organogelator agents for preparation of AuNPs.

Full text of DOI:10.1039/C8NJ04127J

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In situ formation of AuNPs using fatty
N-acylamino hydrazide organogelators as
templates†
Cite this: New J. Chem., 2019,
43, 295
Renata Ongaratto,a Naiane Conte,a Caroline R. Montes D’Oca,a
Rafael C. Brinkerhoff,a Caroline Pires Ruas,b Marcos Alexandre Geleskyb and
a
Marcelo G. Montes D’Oca
*
This work reports, for the first time, the synthesis of new fatty N-acylamino hydrazides and
demonstrates the activity of these compounds as low-molecular-weight organic gelators and templates
for preparation of gold nanoparticles (AuNPs). Initially, we evaluated the gelation properties of fatty
N-acylamino hydrazides in various nonpolar and polar solvents (n-hexane, toluene, benzene, cyclohexane,
and ethanol). Fatty N-acylamino hydrazide derived of the glycine and stearic acid (C18:0) did not form gels
in any of the tested solvents. All other hydrazides did form gels in at least two of the organic solvents
tested. The morphology of each gel was observed via scanning electron microscopy. The organogels
derived from alanine, valine, and phenylalanine had translucid properties, while the serine organogels were
opaque. Afterwards, the synthesis of AuNPs in the presence of the organogelator using microwave
irradiation was realized. Organogelator agents reduced HAuCl4 showing plasmon band peaks between
530 and 543 nm. In addition, the method does not require a reducing agent, which is typically a potential
source of contamination and toxicity. Therefore, this work confirms the importance of the hydrazide
group of the new fatty N-acylamino hydrazides in gel formation and as organogelator agents for
preparation of AuNPs.
Received 13th August 2018,
Accepted 15th November 2018
DOI: 10.1039/c8nj04127j
rsc.li/njc
Introduction
Fatty N-acylamino acid, ester, and amine derivatives are noted
for their ability to gelatinize organic solvents1–5 and their role
in important biological activities (Fig. 1).6,7 Moreover, these
gelators selectively form gels in water8 and they are biodegrad-
able, making them compatible with biological systems.9
These compounds belong to a class of materials called low-
molecular-weight organic gelators (LMOGs), which include
derivatives of long-chain hydrocarbons, salts of organic compounds,
steroids, metallic complexes, and derivatives of fatty ureas and
amino acids.8 N-Acylamino acids and their fatty derivatives harden
Fig. 1 Fatty organogel agents.
organic solvents at the supramolecular level, resulting in a network interactions between gelator molecules such as dipole–dipole
of three-dimensional structures. The role of these compounds in and van der Waals forces, p-stacking, and hydrogen bond
the gelation of organic solvents originates from intermolecular interactions.9 However, it is unclear how and why an organo-
gelator gelatinizes one particular solvent over another.
LMOGs have attracted interest from technicians as well as
a
´
´
ˆ
Laboratorio Kolbe de Sıntese Organica, Universidade Federal do Rio Grande,
academics because they are present in many commercial
products (e.g., cosmetics, foods, and medicines) and are used
in tissue engineering and effluent treatment.8,9 N-Acylamino
acid derivatives and fatty derivatives are also used in the
pharmacological field as carriers of drugs.10–13 A subcutaneous
implant made from the organogelator N-stearyl alanine methyl
´
Av. Italia Km 08 s/n, 96203-000, Rio Grande, RS, Brazil.
E-mail: dqmdoca@furg.br; Fax: +55 53 32336961; Tel: +55 53 32336964
b
´
´
´
ˆ
Laboratorio de Catalise e Sıntese Inorganica, Universidade Federal do Rio Grande,
´
Av. Italia Km 08 s/n, 96203-000, Rio Grande, RS, Brazil
† Electronic supplementary information (ESI) available: NMR 1H and 13C spectra
and TEM and SEM micrographs. See DOI: 10.1039/c8nj04127j
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ester showed advantages over a known polymeric matrix for magnetic resonance (NMR) and infrared (IR) spectroscopic
delivering drugs, as it was easier to prepare and nontoxic.11
In the literature, obtained nanoparticles have different
applications in many fields, such as electrochemistry, electronic
techniques and data were consistent with the expected structures.
Formation of physical gels
magnetic storage, sensors, catalysis, biotechnology and optical Compounds 16b and 17–20a, b were tested for their ability
devices.14–16 In addition, LMOGs are also employed as templates to gelatinize different organic solvents. A total of 10 mg of each
to obtain nanoparticles.4
compound was heated in 1 mL solvent (n-hexane, toluene,
In this work, we describe the synthesis of new fatty N-acylamino benzene, cyclohexane, or ethanol) until total dissolution of
hydrazides from fatty acids with saturated chains and commercial the compound. Then the vial containing the mixture was cooled
amino acids. The gelation properties of the new compounds were to 25 1C. After a few minutes, the vial was inverted to allow for
evaluated using non-polar and polar organic solvents, namely, the observation of the gelation effect.3,10 Table 1 show the
n-hexane, toluene, benzene, cyclohexane, and ethanol. In addition, gelation abilities of the new fatty N-acylamino hydrazides 16b
the obtained LMOGs were tested to develop a new method to and 17–20a, b in organic solvents at 25 1C.
obtain gold nanoparticles, using microwave irradiation.
Structure–activity relationship
The gelation ability was highly influenced by structural changes
in the compounds, specifically the number of carbons present
Results and discussion
in the lipophilic chains and the nature of the substituents
The structural design of the new fatty N-acylamino hydrazides
present in the amino acid moieties of the tested hydrazides.
was based on the natural availability of amino acids and fatty
The glycine derivative 16b, with a C18:0 chain, was insoluble in
acids, considering their biodegradability and ability to solidify
the major solvents tested (n-hexane, toluene, benzene and
organic solvents based on previous work.5 A large number of
cyclohexane) and did not form a gel in ethanol (Table 1, entry 1).
derivatives were considered, to better clarify the mechanism of
All the other compounds synthesized (17–20a, b) in this work
gelation and to determine the structural motifs required by
formed gels in some tested solvents, and all of those compounds
these systems to exhibit efficient gelation behavior. Previous
had stereogenic centers. This finding is already described in the
results have indicated that unsaturated chains are not favorable
literature and confirms that the presence of a stereogenic center is
for the formation of gels. Thus, in this study, we synthesized
essential for the gelation ability and molecular organization.5,18
new fatty N-acylamino hydrazide derivatives from saturated
The number of carbons in lipophilic chains showed a relation-
lipophilic chains.
ship with the gelation properties. The fatty N-acylamino hydra-
zide 17a, derived from valine and C16:0, formed gels in n-hexane
and cyclohexane (Table 1, entry 2). The homologue 17b, from
Organic synthesis
Initially, the fatty N-acylamino esters 11–15a, b were synthe-
C18:0, formed gels in toluene, n-hexane, and cyclohexane
sized from a reaction between palmitic (C16:0) and stearic
(Table 1, entry 6). The same behavior was observed for the
(C18:0) acids with amino esters, according to previous work.5
Next, the new fatty N-acylamino hydrazides were synthesized by
compound 19a, a derivative of phenylalanine and C16:0; it also
formed a partial gel in benzene (Table 1, entry 4). Compound 19b
reacting fatty N-acylamino esters with an excess of hydrazine in
formed gels in toluene, benzene, n-hexane, and ethyl alcohol and
acetonitrile (as the solvent) under reflux for 4 h (Scheme 1). The
a partial gel in cyclohexane (Table 1, entry 8). These results
solids formed were washed with water to afford the compounds
suggest the influence of the carbon atom number on gelation.
16b and 17–20a, b without the need for chromatographic
The experiments also demonstrated the influence of the
polarity and planarity of each solvent on the compounds’
columns. All compounds were analyzed by H and 13C nuclear
1
gelation ability. In all cases involving apolar solvents was
observed a similar behavior between planar solvents (benzene
and toluene) and between nonplanar solvents (n-hexane and
cyclohexane). Previous studies that used fatty N-acylamino
esters and fatty N-acylamino acids derived from alanine, valine,
phenylalanine, and serine demonstrated gelation properties
only for palmitic or stearic N-acylamino acids from alanine in
toluene and phenylalanine or from serine in hexane.5
In this work, replacing the ester and acid groups with a
hydrazide group led to superior gelation of different solvents.
The results showed that all the new fatty N-acylamino hydrazides
synthesized which were derived from palmitic (C16:0) and stearic
(C18:0) acids, with the exception of glycine derivatives, were able
to form gels in at least two of the organic solvents tested.
Scheme 1 Synthesis of fatty N-acylamino hydrazides 16b and 17–20a, b
An explanation for this might be the effective intermolecular
hydrogen bond interactions made possible with hydrazides.
from amino acids 1–5 and palmitic (21a, C16:0) and stearic (21b, C18:0)
acids.
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Table 1 Gelation ability of new fatty N-acylamino hydrazides 16b and 17–20a, b in different organic solvents
Physical characteristics
Entry Fatty N-acylamino hydrazide Toluene
Benzene
n-Hexane
Cyclohexane
Insoluble
Ethanol
Soluble
1
2
Insoluble Insoluble
Insoluble
Soluble
Gel
Soluble
Gel
Gel
Gel
Insoluble
3
4
Insoluble
Immediate precipitation Gel
Gel
Immediate precipitation Gel
Gel
Soluble
5
6
7
Gel
Gel
Gel
Gel
Gel
Gel
Insoluble
Insoluble
Insoluble
Insoluble
Gel
Insoluble
Immediate precipitation Immediate precipitation Gel
8
9
Gel
Gel
Gel
Gel
Gel
Immediate precipitation Gel
Insoluble
Insoluble
Insoluble
These interactions are more efficient than the effects of bulkier L-serine amphiphiles have also been used to produce gels in
substituents attached to amino acid portions, such as the CHCl3, water, and in hexane.17 Therefore, the balance between
isopropyl group in derivatives of valine. Such bulky substituents gelator structure, intermolecular interactions, and gelation
prevent gel formation with fatty ester or fatty acid valine properties is very important for good formation of gels.
derivatives, in contrast to that observed using hydrazide valine
IR spectroscopy was carried out to understand the role of the
derivatives 17a and 17b (Table 1, entries 2 and 6, respectively). hydrazine residue and fatty chains in gelation of organic solvents.
In the previous study using serine derivatives, the presence Samples of gel produced in toluene were dried under a vacuum,
of a polar substituent in the stereogenic center is crucial for the and the resulting solids were examined by IR spectroscopy as KBr
gelation of hydrocarbons.5 This polar substituent establishes pellets. The same compounds had previously been dissolved in
strong intermolecular interactions during the self-assembly of 1 mL chloroform (in conditions in which they were not able to
gelators in the derivative segment of this amino acid. The fatty form a gel) to observe the changes in absorption bands related to
N-acylamino esters used in earlier studies derived from serine intermolecular interactions (Fig. 2). IR spectra of the gel derived
were able to form gels in hexane. In the present study, fatty from fatty N-acylamino hydrazide 18a showed a strong inter-
N-acylamino hydrazides 20a and 20b, derivatives of serine, did action between the groups able to form hydrogen bonds, namely
not form gels with hexane, cyclohexane, or ethanol but did strong stretches of hydrazine N–H at 3284 cmÀ1 and carbonyl
form gels with toluene and benzene. According to the literature, groups CQO at 1627 and 1541 cmÀ1. Moreover, the analysis of
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Fig. 4 Organogels from compounds 20b, 17a, and 18b in toluene.
Fig. 2 Infrared spectra: compound 18a in CHCl3 (red), and compound
18a in gel form (black).
These observations indicate that the different morphologies
of compounds 17–20b, derived from stearic acid (C18:0),
depended of the structural changes in the amino acid moiety,
because all were derived from the same fatty acid. In addition,
compounds derived from different fatty alkyl chains and the
same amino acid portion resulted in a similar morphology of
the xerogel. This is confirmed by the SEM image of compound
18a derived from valine and palmitic acid (C16:0), that showed
a morphology similar to 18b (Fig. 5b). In the morphological
analyses conducted via SEM differences in the 3D arrangement
of the materials with opaque and translucid properties were
also observed (Fig. 6).
the IR spectra of compound 18a in CHCl3 revealed that the profile
underwent great changes, showing the weakening of the inter-
molecular hydrogen bonds.
Fig. 3 shows the importance of intermolecular interactions
of hydrogen bonds in the hydrazide and amide groups for the
auto-organization of three-dimensional structures of the fatty
N-acylamino hydrazide organogelators.5
Fig. 4 shows gels obtained from toluene with fatty organogel
agents 17a, 18b and 20b. According to experimental results the
organogels 17–19a, b from alanine, valine, and phenylalanine
had translucid properties, while the serine organogels 20a and
20b were opaque.
In situ preparation of AuNP containing new organogels
The new organogel fatty N-acylamino hydrazides were employed
as templates for the in situ preparation of gold nanoparticles
(AuNPs) using a microwave-assisted method and the resulting
SEM observation of xerogels
To investigate the morphologies of the organogels, SEM was nanoparticles were studied using UV-visible absorption and
performed on the corresponding xerogels (air-dried gels). Gel TEM.4 The synthesized fatty compounds were employed as
samples were slowly evaporated to dryness, and then the resultant stabilizing agents for the nanoparticle syntheses due to the
xerogels were examined. As shown in Fig. 5, the ‘preferable’ presence of long chains, derived from the fatty acids, and of
morphology adopted by the gels was tapes for compounds the free terminal hydrazine (–NH–NH2) group that could act as a
17b and 18b derived from alanine and valine, respectively ligand towards gold, capping the AuNPs.
(Fig. 5a and b), and a more fibrous morphology for compounds According to the literature, gold nanoparticles can be pre-
19b and 20b derived from phenylalanine and serine, respectively pared in a simple one-pot process employing fatty alkylamine
(Fig. 5c and d).
oleyl amine (OLA), where the amine group acts as a reducing
Fig. 3 Physical gelation of organic solvents by fatty N-acylamino hydrazides.
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Fig. 7 In situ preparation of gold nanoparticles in the presence of the
organogelator 19b catalyzed by microwave irradiation.
after the reduction the gelator peptides keep their gelation
properties intact.
Fig. 5 SEM images of air-dried organogels in toluene obtained from 17b
(a), 18b (b), 19b (c), and 20b (d).
Thus, after the formation of the gel in the presence of the
organogelators 18–20a, b in toluene the metal precursor HAuCl4
was added. The mixture was placed in a microwave and after
15 min with a power of 150 W the diffusion of the salt complex
in the gel matrix occurred, with a change in the coloration of the
mixture to pink, indicating the formation of gold metallic
nanoparticles. In all cases, a small amount of HAuCl4 salt in the
organogel matrix afforded the AuNPs after exposure to microwave
irradiation and the method does not require a reducing agent,
which is typically a potential source of contamination and toxicity.
Fig. 7 shows the preparation of the gold nanoparticles carried out
with organogelator 19b.
In addition, an experiment to form AuNPs was also carried
out, using the same protocol, in toluene using fatty N-acylamino
esters and N-acylamino acids as organogelators derived from
palmitic (C16:0) and stearic (C18:0) acids and alanine. However,
in this case the formation of gold nanoparticles was not observed.
Thus, this result shows that the free terminal hydrazine group
(RC(O)–NH–NH2) of the organogelator could act as a ligand toward
gold, capping the metal, and this derivative can be employed as
Fig. 6 Different morphologies observed in opaque and translucid gels.
agent and then subsequently stabilizes the gold particles.19 The
authors suggest that the gold–amine complex is formed in stabilizing agents of the synthesized nanoparticles due to the
the reaction procedure and its reactivity strongly depends on presence of long chains. The –NH–NH2 group could initially capture
the nature of the amine indicating that the gold nanoparticles the metal, for example, to form gold hydrazide complexes of type
[RC(O)NH–NH2]/[Au(III)], followed by electron loss, involving the
transfer of electrons between the –NH–NH2 group and gold ions
in each step, and finally Au(0), under microwave irradiation.
are produced via the Au–amine complex.
Monosubstituted fatty urea has been used for in situ pre-
paration of gold nanoparticles. Vemula and John developed
fatty urea-based aryl derivatives as gelators, which showed
excellent gelation ability in a broad range of solvents from
UV-vis spectra of AuNPs
water to cyclohexane.20 Afterward, these gelators were success- The reduction of transition metals in the presence of a stabilizer
fully used in the synthesis of AuNPs as reducing and capping for the formation of metallic nanoparticles can be monitored
agents, showing the essential nature of the free NH2 group for through the spectrum in the UV-vis region. According to the
the reduction and further capping process. In these experiments literature, UV-vis absorption spectroscopy is the most widely used
fatty urea derivatives were added to the HAuCl4 solution; after method for characterizing the optical properties and electronic
heating the yellow coloured solution became colourless [Au(III) structure of nanoparticles as the absorption bands are related to
to Au(I)] and then turned a pink hue, indicating the reduced the diameter and aspect ratio of metal nanoparticles. The nano-
form of gold. After, at room temperature a pink coloured gel meter dimensions can oscillate on the particle surface and
with embedded AuNPs formed.
absorb electromagnetic radiation at a particular energy. This
In another study, in situ preparation of gold and silver resonance, known as surface plasmon resonance (SPR) or
nanoparticles into a gel network structure using tyrosine con- plasmon absorbance, of nanoparticles is a consequence of their
taining oligopeptide based organogelators was investigated.21 small size. It is well reported that the size and shape of metal
The tyrosine residue of peptides were successfully utilized to reduce nanoparticles determine the spectral position of the plasmon
Au(III)/Ag(I) into colloid Au(0)/Ag(0) nanoparticles. In addition, band, as well as its width.22,23
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The UV-vis spectra of AuNPs employing as templates the
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organogel agents fatty N-acylamino hydrazides are shown in
Fig. 8–10. According to the results the UV-vis spectra of AuNPs
using organogelators 18b, 18b and 20b in toluene have plasmon
Fig. 11 SEM images of air-dried organogels in toluene with nanoparticles
of gold from: (a) 19b and (b) 18b.
bands at 532, 530 and 543 nm, respectively. The plasmon band
width of agents 19b and 20b is larger than that of agent 18b
indicating a higher aggregation state of nanoparticles in the
presence of organogelators 19b and 20b. The characteristic SPR
absorption peak indicates a larger size particle in the organogel
agent 20b compared to 19b and 18b.
SEM observation of xerogels with AuNPs
Fig. 8 The plasmon absorbance of AuNPs in the presence of the
organogelator 18b.
SEM analysis was performed to verify the morphology of the
obtained gels in the presence of gold nanoparticles. Fig. 11
shows that the morphology was not altered.
TEM observation of xerogels with AuNPs
Fig. 12 shows the electron micrographs of gold nanoparticles
obtained in the new organogelator fatty N-acylamino hydrazide
18b and toluene. The obtained gold nanoparticles were spheres
and the average particle size was equal to 28.5 nm. Fig. 13
displays the corresponding particle size distribution of formed
AuNPs obtained from the toluene gel of 18b.
Thus, we found that, in principle, AuNPs with a narrow
particle size distribution can be prepared in the organogels, due
to the presence of long chains and of the free terminal hydrazine,
after exposure to microwave irradiation in the absence of a
reducing agent.
Fig. 9 The plasmon absorbance of AuNPs in the presence of the
organogelator 19b.
Fig. 12 TEM micrographs showing the Au(0) nanoparticles obtained in
toluene organogels of 18b observed at 100 kV.
Fig. 10 The plasmon absorbance of AuNPs in the presence of the
organogelator 20b.
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and the coupling constants ( J ) are reported in hertz (Hz). Melting
points were measured on a Fisatom 430D and are uncorrected.
Infrared (IR) spectra were obtained on a Shimadzu-IR PRESTIGE-21.
A sample of each gel produced was dried in a vacuum and the
resulting solid was examined as a KBr pellet. The morphology of the
materials was analyzed by FE-SEM using a JEOL model JSM 6610 at
20 kV. Reactions were monitored by TLC with Merck silica gel
60 GF254r plates and n-hexane/EtOAc (7 : 3 v/v) eluents. The
products were purified using column chromatography with
ACROS silica gel 60A, 0.035–0.070 mm, and gradients of n-hexane/
EtOAc eluents.
Synthetic procedure
Fatty N-acylamino hydrazides: the N-acylamino acid methyl
ester (1 mmol) previously synthesized was added to a flask with
10 mL CH3CN. After, the hydrazine monohydrate (5 mmol) was
added into the mixture of N-acylamino acid methyl ester and
was refluxed for 4 hours. The product was purified by filtration
and washed with water.
Fig. 13 Histogram illustrating the particle size distribution of AuNPs
obtained in the toluene gel of 18b.
Conclusions
N-(Acyl-stearyl)glicinyl hydrazide (16b). Yield 89%. White
solid. M.p.: 74–75 1C. IR (KBr) cmÀ1: 3296, 3194, 2916, 2848,
This study reports the synthesis of new fatty N-acylamino
hydrazides from renewable fatty acids with saturated chains
and amino acids. The gelation properties of compounds were
evaluated using five different organic solvents. Our results
demonstrate the importance of including groups that form
hydrogen bonds, such as hydrazides, to obtain new compounds
with gelling properties. In addition, our findings further emphasize
the importance of a stereogenic center to gelling, because even with
the insertion of a hydrazide group, derivatives of glycine did not
form gels. SEM analyses showed that the morphologies of the new
compounds depended on the chemical structure, where those
derived from lower fatty chains showed more compact and regular
morphologies. These findings are very important for a better under-
standing of the gelation mechanism. In addition, the microwave-
assisted synthesis of gold nanoparticles (AuNPs) using organogelator
agents as templates was demonstrated. Organogelator agents
reduced HAuCl4 in the absence of reducing agents, resulting in
nanoparticles which showed the plasmon absorbance peak. The
average size of particles was about 29 nm. Therefore, this work
confirms the importance of the hydrazide group of the new fatty
N-acylamino hydrazides in gel formation and as organogelator
agents for preparation of AuNPs. This methodology could also
be applicable for producing other metal nanoparticles.
1
1647, 1554, 981. H NMR (400 MHz, DMSO-d6): d 0.87 (t, 3H,
J = 6.8 Hz), 1.25 (m, 28H), 1.49 (m, 2H), 2.11 (t, 2H, J = 7.4 Hz),
4.32 (d, 2H, J = 5.5 Hz), 5.8 (m, 1H), 8.16 (m, 1H). 13C NMR
(100 MHz, DMSO-d6): d 9.9, 14.3, 22.4, 25.5, 29.0, 29.1, 29.2,
29.3, 31.7, 33.2, 35.5, 152.9, 173.1.
(S)-N-(Acyl-palmitoyl)alaninyl hydrazide (17a). Yield 82%.
White solid. M.p.: 117–124 1C. IR (KBr): 3307, 2918, 2848,
1737, 1639, 1573 cmÀ1 1H NMR (400 MHz, CDCl3): d 0.89
.
(t, 3H, J = 6.8 Hz), 1.27 (m, 28H), 1.38 (m, 3H), 1.63 (m, 2H),
2.20 (t, 2H, J = 7.6 Hz), 3.91 (m, 2H), 4.51 (m, 1H), 6.17 (d, 1H,
J = 6.8 Hz), 7.79 (m, 1H). 13C NMR (100 MHz, CDCl3): d 10.3,
14.1, 22.6, 25.6, 29.2, 29.3, 29.4, 29.5, 31.9, 49.1, 155.6, 156.8.
(S)-N-(Acyl-stearyl)alaninyl hydrazide (17b). Yield 96%.
White solid. M.p.: 139–142 1C. IR (KBr): 3307, 2918, 2848,
1737, 1639, 1573 cmÀ1 1H NMR (400 MHz, CDCl3): d 0.89
.
(t, 3H, J = 7.6 Hz), 1.29 (m, 28H), 1.38 (d, 3H, J = 6.9 Hz), 1.63 (m,
2H), 2.20 (t, 2H, J = 7.6 Hz), 3.89 (m, 2H), 4.51 (m, 1H), 6.17 (d, 1H,
J = 6.8 Hz), 7.94 (m, 1H). 13C NMR (100 MHz, CDCl3): d 14.0, 17.9,
22.6, 25.5, 29.2, 29.3, 29.4, 29.6, 29.6, 31.9, 36.5, 47.2, 173.0, 173.3.
(S)-N-(Acyl-palmitoyl)valinyl hydrazide (18a). Yield 80%.
White solid. M.p.: 124–131 1C. IR (KBr): 3284, 2918, 2848,
1629, 1541, 1465 cmÀ1 1H NMR (400 MHz, CDCl3): d 0.89
.
Finally, our results show that these LMOGs can be synthesized
very easily from naturally occurring sources (e.g., fatty acids and
common amino acid substrates in the chemical industry), which
makes them excellent materials for use in various applications.
(t, 3H, J = 6.3 Hz), 0.96 (d, 6H, J = 5.2 Hz), 1.29 (m, 24H), 1.64
(m, 2H), 2.06 (m, 1H), 2.23 (t, 2H, J = 7.2 Hz), 3.91 (m, 2H), 4.25
(t, 1H, J = 7.9 Hz), 6.20 (d, 1H, J = 7.2 Hz), 7.92 (m, 1H). 13C NMR
(100 MHz, CDCl3): d 14.0, 18.4, 19.2, 22.6, 25.6, 29.3, 29.4, 29.6,
30.7, 31.9, 36.6, 57.0, 172.0, 173.3.
(S)-N-(Acyl-stearyl)valinyl hydrazide (18b). Yield 88%. White
solid. M.p.: 164–169 1C. IR (KBr): 3386, 2916, 2848, 1633, 1544,
1462 cmÀ1. 1H NMR: (400 MHz, CDCl3): d 0.89 (t, 3H; J = 6.6 Hz),
Experimental section
Materials and methods
All solvents and reagents were obtained from commercial 0.96 (d, 6H, J = 5.3 Hz), 1.27 (m, 28H), 1.67 (m, 2H), 2.07 (m, 1H),
1
suppliers (Synth, Brazil; Sigma Aldrich, United States). H and 2.23 (t, 2H, J = 6.9 Hz), 3.95 (m, 2H), 4.24 (t, 1H, J = 7.8 Hz), 6.15
13C NMR spectra were recorded on a Varian VNMRS at 400 and (d, 1H, J = 7.4 Hz), 7.78 (m, 1H). 13C NMR: (100 MHz, DMSO-d6):
100 MHz, respectively, using CDCl3 and DMSO-d6 as a solvent. d 14.3, 18.8, 19.5, 22.4, 25.7, 29.0, 29.20, 29.28, 29.3, 30.8, 31.7,
The chemical shifts (d) are reported in parts per million (ppm), 35.6, 56.9, 170.0, 172.5.
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(S)-N-(Acyl-palmitoyl)phenylalanyl hydrazide (19a). Yield at an accelerating voltage of 20 kV. The gel was placed on a
95%. White solid. M.p.: 156–161 1C. IR (KBr): 3294, 3059, cover slip and dried for 48 h under vacuum before imaging.
1
3030, 2916, 2848, 1641, 1604, 1537 cmÀ1. H NMR: (400 MHz,
TEM observation of gold nanoparticles. The morphology of
CDCl3): d 0.89 (t, 3H; J = 6.8 Hz), 1.26 (m, 24H), 1.54 (m, 2H), the reported organogels and gold nanoparticles (AuNPs) was
2.15 (t, 2H, J = 7.3 Hz), 3.06 (m, 2H), 3.84 (m, 2H), 4.71 (q, 1H, observed using TEM. Samples were prepared by depositing a
J = 7.5 Hz), 6.33 (d, 1H, J = 8.0 Hz), 7.22 (m, 5H), 7.84 (m, 1H). drop of the gel phase gelators or AuNPs dispersed in MeOH on
13C NMR: (100 MHz, CDCl3): d 14.1, 22.6, 25.5, 29.1, 29.35, a TEM copper grid (200 mesh) coated with a carbon film. The
29.36, 29.4, 29.64, 29.66, 31.9, 36.5, 38.3, 52.9, 127.0, 128.6, grid was then dried under vacuum at room temperature over-
129.1, 136.4, 171.7, 173.3.
night. Images were obtained using a JEOL JEM-1400 electron
(S)-N-(Acyl-stearyl)phenylalanyl hydrazide (19b). Yield 97%. microscope operating at 100 kV. The histograms of the nano-
White solid M.p.: 160–163 1C. IR (KBr): 3317, 3277, 3080, 3030, particle size distribution were obtained from measurements of
2918, 2848, 1645, 1589, 1529 cmÀ1. 1H NMR: (400 MHz, CDCl3): around 300 diameters and reproduced in different regions of
d 0.89 (t, 3H; J = 6.7 Hz), 1.26 (m, 28H), 1.54 (m, 2H), 2.15 (t, 2H, the Cu grid assuming spherical shapes.
J = 7.4 Hz), 3.06 (m, 2H), 3.85 (m, 2H), 4.72 (q, 1H, J = 7.5 Hz),
6.37 (d, 1H, J = 8.0 Hz), 7.24 (m, 5H), 7.90 (m, 1H). 13C NMR
(100 MHz, CDCl3): d 14.1, 22.6, 25.5, 29.1, 29.34, 29.36, 29.4,
Conflicts of interest
29.64, 29.67, 31.9, 36.5, 38.3, 52.9, 127.0, 128.6, 129.1, 136.3,
171.7, 173.3.
The authors declare no conflict of interest.
(S)-N-(Acyl-palmitoyl)serinyl hydrazide (20a). Yield 89%.
White solid. M.p.: 161–163 1C. IR (KBr): 3298, 3271, 2916, Acknowledgements
2848, 1643, 1624, 1462 cmÀ1. H NMR: (400 MHz, DMSO-d6):
1
˜
The authors are thankful for financial support from Fundaçao
d 0.87 (t, 3H, J = 6.8 Hz), 1.27 (m, 24H), 1.50 (m, 2H), 2.14 (t, 2H,
J = 7.4 Hz), 3.52 (m, 2H), 4.27 (m, 1H), 7.43 (d, 1H, J = 7.8 Hz),
8.79 (m, 1H). 13C NMR (100 MHz, DMSO-d6): d 14.2, 22.4, 25.5,
29.0, 29.1, 29.2, 29.34, 29.37, 31.6, 35.8, 39.7, 39.9, 40.7, 40.9,
54.3, 62.3, 169.9, 172.6.
(S)-N-(Acyl-stearyl)serinyl hydrazide (20b). Yield 92%. White
solid. M.p.: 164–166 1C. IR (KBr): 3298, 3273, 2916, 2848, 1645,
1544, 1462 cmÀ1. 1H NMR (400 MHz, DMSO-d6): d 0.82 (m, 3H),
1.18 (m, 28H), 1.47 (m, 2H), 2.13 (m, 2H), 3.44–3.51 (m, 2H),
4.28 (m, 1H), 7.55 (m, 1H), 8.89 (m, 1H). 13C NMR (100 MHz,
DMSO-d6): d 14.3, 22.4, 24.8, 25.5, 25.8, 29.0, 29.1, 29.2, 31.7,
33.7, 35.7, 48.0, 54.2, 62.2, 169.9, 172.6.
`
de Amparo a Pesquisa do Estado do Rio Grande do Sul
(FAPERGS/PRONEM 11/2069-0 and PRONEX 16/2551-0000481-1),
and Conselho Nacional de Desenvolvimento Cientıfico e Tecnologico
(CNPq). Fellowships from CNPq and Coordenaçao de Aperfeiçoa-
´
´
˜
mento de Pessoal de Nivel Superior (CAPES) are also acknowledged.
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