Orig Life Evol Biosph (2013) 43:207–220 DOI 10.1007/s11084-013-9338-1 PREBIOTIC CHEMISTRY
Interaction of Aromatic Amines with Iron Oxides: Implications for Prebiotic Chemistry Uma Shanker & Gurinder Singh & Kamaluddin
Received: 17 April 2013 / Accepted: 8 June 2013 / Published online: 29 June 2013 # Springer Science+Business Media Dordrecht 2013
Abstract The interaction of aromatic amines (aniline, p-chloroaniline, p-toludine and panisidine) with iron oxides (goethite, akaganeite and hematite) has been studied. Maximum uptake of amines was observed around pH 7. The adsorption data obtained at neutral pH were found to follow Langmuir adsorption. Anisidine was found to be a better adsorbate probably due to its higher basicity. In alkaline medium (pH>8), amines reacted on goethite and akaganeite to give colored products. Analysis of the products by GC–MS showed benzoquinone and azobenzene as the reaction products of aniline while p-anisidine afforded a dimer. IR analysis of the amine–iron oxide hydroxide adduct suggests that the surface acidity of iron oxide hydroxides is responsible for the interaction. The present study suggests that iron oxide hydroxides might have played a role in the stabilization of organic molecules through their surface activity and in prebiotic condensation reactions. Keywords Aromatic amines . Interaction . Goethite . Akaganeite
Introduction Iron oxides are present in almost all the different compartment of global system, including the pedosphere, biosphere, lithosphere, and hydrosphere (Cornell and Schwertmann 2003). The large surface area of goethite (57.40 m2/g) and akaganeite (27.37 m2/g), classify them as strong adsorbents for biomonomers and other species.
Electronic supplementary material The online version of this article (doi:10.1007/s11084-013-9338-1) contains supplementary material, which is available to authorized users. U. Shanker (*) : G. Singh Department of Chemistry, Dr B R Ambedkar National Institute of Technology Jalandhar, Jalandhar 144011 Punjab, India e-mail:
[email protected]
Kamaluddin Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247 667 Uttarakhand, India
208
U. Shanker et al.
The dominant theory of Earth’s earliest atmosphere (Urey 1952) until quite recently predicted that CH4, NH3 and H2 were initially common constituents and consequently that the first phases of chemical evolution and origin of life took place in a highly reducing environment. The general view of the early atmosphere has shifted from a reducing one to a redox ‘neutral’ or slightly oxidizing one (Levine et al. 1982; Towe 1990). A reducing atmosphere would, however, allow the existence of fewer catalytically active minerals on the Earth’s surface, primarily silicates and sulfides, than would a redox neutral one Holland 1984). A more oxidizing early atmosphere increases the chances for the existence of oxidized iron minerals like FeOOH and perhaps even manganates. Braterman and coworkers (1983) showed that the Archean Banded Iron-Formations (BIFs) may have formed in such an atmosphere due to photochemical reactions caused by UV light. Oxidized iron, mainly in the form of hematite (α-Fe2O3) is present in BIF already in the oldest sedimentary sequence on Earth. Thus far the maximum determined age of sedimentary rocks is 3.8 Ga (Moorbath 1977). That age has been measured at Isua on Western Greenland. Obliviously oxidized iron minerals have been abundant through the whole known geologic history of the Earth. The binding and reactions of nucleotides and polynucleotides on iron oxide hydroxide polymorphs has been studied by Holm et al. and it was concluded, these might have adsorbed organics and catalyzed the condensation processes which led to the origin of life (Holm et al. 1993). Synthetic ferrihydrite was found to act as amino acid adsorbent and promoter for peptide bond formation (Matrajit and Blanot 2004). The iron oxide hydroxide minerals, goethite and akaganeite were likely constituents of sediments present in, for instance, geothermal regions of the primitive Earth. Condensation of DL–glyceraldehydes to ketohexoses in the presence of iron (III) oxide hydroxide has also been reported (Weber 1992). Recently iron oxides (Goethite, Akaganeite and Hematite) were proved to catalyze the formation of nucleobases from formamide (Shanker et al. 2011). Amines are one of the important classes of organic compounds which are widely distributed in nature in the form of amino acids, alkaloids and vitamins. The presence of amino acids containing aromatic rings on the primitive Earth has been proposed (Friedmann and Miller 1969). One could, therefore, reasonably postulate the presence of aromatic amines in the primitive Earth environment. During the last few years, experimental studies on the catalytic role of cyano complexes and their possible role in chemical evolution have been carried out. A number of metal hexacyanoferrates (II) have been prepared and their interaction with aromatic amines have been studied by Alam and Kamaluddin (1999 1999, 2000), Alam et al. (2000a, b, 2002) and Viladkar et al. (1994). It has been established by the above study that metal hexacyanoferrates (II) are highly efficient in adsorbing amines in neutral as well as alkaline media (pH~9) to bring about oxidation of the amines. In order to further investigate the importance of various forms of iron oxides during the course of chemical evolution in catalyzing different reactions, aromatic amines were interacted with goethite, akaganeite and hematite. Spectral studies have indicated that surface acidity of iron oxides is responsible for interaction.
Experimental Materials and Methods Ferric nitrate (Merck), potassium hydroxide (Merck), ferric chloride (Merck), Aniline (Merck), p-Anisidine (Merck), p-chloroaniline (Merck), p-toludine (Merck) and all other chemicals used
Interaction of Aromatic Amines with Iron Oxides
209
were of analytical reagent grade. Aniline was distilled and anisidine was recrystallized each time before use. Synthesis and Characterization of the Iron Oxides (Goethite, Akaganeite and Hematite) We prepared appreciable amounts of iron oxides (goethite, akaganeite and hematite) as described by (Shanker et al. 2011). It was characterized as a pure material by X-ray diffraction (XRD), FE-SEM (Field emission scanning electron microscopy) and analytical TEM (Transmission electron microscopy), by comparing the spectra and diffraction lines to the ones already published. Further, details concerning the characterization (XRD spectra, diffraction lines, diffraction rings, FE-SEM and TEM images) are same as reported earlier by Shanker et al. 2011). Adsorption of Aromatic Amines on Iron Oxides Evaluation of Parameters Necessary for Investigating the Sorption Equilibria The conditions which were studied for investigating the adsorption equilibrium for the amine and metal oxides were: i) ii) iii) iv) v)
Concentration of adsorbate Particle size of adsorbent Equilibrium time for adsorbate and adsorbent Quantity of adsorbent Effect of pH and effect of temperature
For determining the adsorption isotherm of amines on iron oxides a moderate concentration range of amines (1×10−4 to 1.5×10−3 M) has been chosen in order to get absorbance of amines in the suitable range of the absorbance scale on the spectrophotometer. Iron oxides of various particle sizes have been tested and it was found that particle size of 80– 100 mesh was the most suitable one. Experiments were performed varying the time of contact (30 min to 24 h) and the amount of iron oxides at a fixed adsorbate concentration (5×10−4 M). It was observed that the maximum adsorption took place when the amount used was 100 mg per 10 ml of adsorbent solution for aniline, p-toluidine, p-anisidine and p-chloroaniline for 24 h. Adsorption of p-chloroaniline on a metal oxide was found to be a slow process and equilibrium was found to be established after 72 h. Effect of pH Adsorption of amine was studied over a wide pH range (4–9) on all iron oxides. Buffers used to maintain pH of adsorption studies were acetate (pH 4 to 7) and Borax (pH~9). It was found that adsorption of aromatic amines on iron oxide was negligible in acidic and basic media. A neutral pH range (6.8–7.12) was found to be suitable for maximum adsorption. Spectral Analysis Electronic spectra of aniline, anisidine, p-toluidine and p-choloroaniline were recorded on a UV spectrophotometer (Model UV-188–240 V, Shimadzu Corporation Kyoto, Japan). The characteristic lmax values for amines (aniline, p-choloroaniline, p-toluidine and p-anisidine
210
U. Shanker et al. p- Chloroaniline p- Toludine Aniline p- Anisidine
Amount Adsorbed (mg-amine/g-mineral)
13 12 11 10 9 8 7 6 5 4 3 2 1 0 0
1
2
3
4
5
6
7
8
9
-4
[Amine] / 10 M
Fig. 1 Adsorption isotherm for adsorption of amines on goethite
are 280 nm, 290 nm, 286 nm and 295 nm, respectively. Infrared spectra of adsorbates, adsorbent, and adsorption adducts were recorded on a Perkin-Elmer 1600 FTIR spectrophotometer using KBr pellets. A series of 50 ml glass test tubes were employed and each tube was filled with 10 ml of amine solution of varying concentration. Goethite, akaganeite and hematite (100 mg) was added to each tube. The pH of the solution was adjusted to the desired value using acetate or borax buffers. Species of these buffers did
Amount Adsorbed (mg-amine/g-mineral)
10
Aniline p- Toludine p- Anisidine p- Chloroaniline
9 8 7 6 5 4 3 2 1 0 0
2
4
6
8 -4
[Amine] / 10 M Fig. 2 Adsorption isotherm for adsorption of amines on akaganeite
10
12
14
Amount Adsorbed (mg-amine/g-mineral)
Interaction of Aromatic Amines with Iron Oxides
211
p- Chloroaniline p- Toludine Aniline p- Anisidine
4
3
2
1
0 0
2
4
6
8
10
12
14
-4
[Amine] / 10 M Fig. 3 Adsorption isotherm for adsorption of amines on Hematite
1.2
Aniline p-Toludine p-Chloroaniline p-Anisidine
Y = 0.13836 X + 0.03299
1.0
Y= 0.05032 X + 0.01232
Ce /Xe
0.8
Y= 0.06132 X + 0.005232 0.6
0.4
Y= 0.02911 X + 0.001232 0.2
0.0 -1
0
1
2
3
4
5
6
7
8
9
10
-4
[Amine] / 10 M Fig. 4 Langmuir isotherms for adsorption of amines on goethite
11
12
13
14
15
212
U. Shanker et al.
Aniline p- Toludine p- Chloroaniline p- Anisidine
5
4
Y= 0.313361 X + 0.3654
Ce /Xe
3
2
Y= 0.15854 X + 0.7488 Y= 0.12174 X + 0.2341
1
Y= 0.6614 X + 0.06341 0
0
2
4
6
8
10
12
14
-4
[Amine] / 10 M Fig. 5 Langmuir isotherms for adsorption of amines on Akaganeite
Aniline p- Toludine p- Chloroaniline Anisidine
10
8
Y= 0.54127 + 1.3704 Y= 0.60021 + 0.8766
Ce /Xe
6
Y= 0.35565 + 0.31475
4
Y= 0.23615 + 0.21752 2
0
-2
0
2
4
6
8
10
-4
[Amine] / 10 M Fig. 6 Langmuir isotherms for adsorption of amines on Hematite
12
14
Interaction of Aromatic Amines with Iron Oxides
Table 1 Percent uptake of amines on iron oxides
213
Amine
Percent binding Goethite
Akaganeite
Hematite
p-anisidine
67.37
50.27
20.32
p-toludine
62.10
44.80
16.92
Aniline
52.26
42.83
11.32
p-chloroaniline
46.11
22.65
7.87
not get adsorbed onto the iron oxide hydroxides surface. This was verified by conductivity measurements as there was no change in the inflection point of buffers with and without iron oxides. The tubes were shaken with a Spinix Vortex shaker initially for 1 h and then allowed to equilibrate at 25 °C with intermittent shaking at fixed time intervals. The equilibrium was attained within 6 h. The equilibrium time and concentration range were, however, decided after a good deal of preliminary investigations. The concentration of aniline, p-choloroaniline, p-toluidine and anisidine was measured spectrophotometrically at 280 nm, 290 nm, 286 nm and 295 nm, respectively. The amount of amine adsorbed was calculated from the difference between the amine concentration before and after adsorption. The equilibrium concentration of amine and the amount adsorbed were fitted in the adsorption isotherm (Figs. 1, 2, and 3). Oxidation of Aromatic Amines in the Presence of Iron Oxides In alkaline medium (pH>8) brown-red colored products were deposited on the goethite and akaganeite surfaces within 24 h. These colored products were concentrated for Gas chromatography Mass spectrometry (GC–MS) analysis by extraction in benzene. Analysis of the reaction products was performed on a Perkin Elmer gas chromatograph coupled directly to a mass spectrometer system. Separation was performed on a fused silica capillary column (Elite-5 model) with composition 5 % diphenyl and 95 % dimethyl polysiloxane. The conditions for GC were as follows: injector temperature, 280 °C; transfer line temperature, 250 °C. The capillary column temperature was programmed as follows: 80 °C for 2 min; from 80 to 260 °C at 10 °C min−1, held at 250 °C for 15 min. Helium was used as a carrier gas with a flow rate of 2 ml min−1. The mass spectrometer conditions were ion source 250 °C and ionization energy 40 eV.
Table 2 Langmuir constants for the adsorption of amines on iron oxides Amine
Aniline
Goethite
Akaganeite
Hematite
Xm(l/mol)
KL(mg/g)
Xm(l/mol)
KL(mg/g)
Xm(l/mol)
KL(mg/g)
7.22
0.23
6.30
0.46
1.87
2.53
p-chloroaniline
19.87
0.24
3.19
1.16
1.66
1.46
p-toluidine
23.14
0.12
8.21
0.19
2.81
0.88
p-anisidine
34.35
0.042
15.11
0.95
4.23
0.92
214
U. Shanker et al.
Fig. 7 Representative FE-SEM photographs of goethite (a), p-anisidine (b) and goethite-p-anisidine adduct (c)
Results and Discussion A wide pH range (3.0–7.0) was selected for preliminary adsorption studies of aromatic amines on iron oxides (goethite, akaganeite and hematite). A remarkable change in the amount of adsorbate was observed by varying the pH of the solution. Subsequent studies were performed at pH~7.0 which was optimum for the maximum sorption of both the amines. Since amines are basic with lone pair of electrons on nitrogen and also assisted by π-electron clouds on aromatic rings, they easily interact with positively charged surface of iron oxide hydroxides. It was observed that at lower pH range aniline showed greater uptake as compared to anisidine. This can be explained on the basis of the fact that in acidic media anisidine has a greater tendency for salt formation and hence a lesser tendency to interact with iron oxides. On the other hand, aniline has a lesser tendency in comparison with anisidine for salt formation resulting in a greater tendency to interact with goethite and akaganeite. At a neutral pH, anisidine has more electrons available to interact with both the iron oxide hydroxides and thus there is a drastic increase in uptake. Adsorption isotherms of aniline, pchloroaniline, p-toluidine and anisidine in the present case show that adsorption is fast
Interaction of Aromatic Amines with Iron Oxides
215
Fig. 8 Proposed mechanism for the formation of azobenzene
in both the cases and the isotherms are regular, positive, and concave to the concentration axis. A typical graph of Ce/Xe vs Ce is a straight line (Where Ce Equilibrium concentration of solute in mole/l and Xe amount of solute adsorbed per gram weight of adsorbent (mg) (Figs. 4, 5, and 6). Adsorption data can be represented through a Langmuir adsorption isotherm which assumes the formation of a monolayer of solute molecules on the surface of the adsorbent and given by method reported by Viladkar et al. 1994. The percent uptake of anisidine, p-chloroaniline, p-toluidine and aniline is represented by (Table 1). The values of Xm and KL were also calculated (Table 2). Xm values also indicate that anisidine adsorption is more in comparison to that of other amines. It is observed from percent binding that anisidine is strongly adsorbed on iron oxides in comparison to aniline. The observed adsorption trend is also related to the basicities of the amines. This indicates that anisidine is a stronger base than other amines which reflects the greater availability of electrons for the interaction.
216
U. Shanker et al.
Fig. 9 Proposed mechanism for the formation of tetramer of aniline and benzoquinone
The infrared spectra of iron oxides before and after adsorption were recorded and analyzed. The results are given in Tables 1–3 (supplementary information). The change in characteristic frequencies of iron oxides after adsorption was not remarkable. The
Interaction of Aromatic Amines with Iron Oxides p
(
)
(
217
) 107
100
N
MeO 77
N
OMe
Dimer of p- anisidine m/z = 242
% 92 64 135 63
242 78
52 57
65
76
108
80 81 91
93
106
121 128
136
115
0 47
57
67
77
87
97
107
117
127
137
147
156 165
147
157
207 171
167
181
177
187
193 199
197
207
219 224
239
217
237
227
243 253
247
257
267
267
2
Fig. 10 Mass spectrum of dimer of p-anisidine
pronounced change in the characteristic frequencies of amino group indicates that the interaction occurred through the iron oxides with an amino group. Field Emission Scanning Electron Microscopic studies of the amine and iron oxide was also performed. Figure 7 represents FE-SEM of anisidine, iron oxide and p-anisidine–iron oxide adduct. FE-SEM photographs of iron oxide-amine adduct shows that surface of iron oxide becomes smooth after adsorption. Energy dispersive X-ray (EDX) pattern also supports the adsorption as percentage of C, N, and O increases in the EDX pattern of adduct. Further it was also observed that in alkaline medium pH >8 all the amines reacted with goethite and akaganeite to give the colored products. Reaction of Aniline with Goethite and Akaganeite Mass spectra of the reaction products corresponding to peaks at retention time (Rt) 3.31, 7.29, 16.62 and 25.51 min are shown in Figures (1–3 in supplementary information). The formation of benzoquinone (Rt 7.29 min) is clearly evidenced by the peaks corresponding to m/z 108, 82, and 54, in accordance with its fragmentation pattern determined by electron bombardment. However, GC–MS study of the peak with Rt 16.62 min showed the formation of azobenzene confirmed by a peak at m/z 182. Some other mass peaks in the fragmentation pattern of the product at m/z 105, 77, and 51 were also observed. Rt 25.51 peak corresponds to tetramer of aniline, confirmed by their fragmentation pattern. A possible mechanism for the formation of azobenzene, benzoquinone, tetramer of aniline and azobenzene has proposed (Figs. 8, and 9) Reaction of Anisidine with Goethite and Akaganeite In the case of anisidine the chromatogram showed two major peaks with Rt 3.81 and 15.72 min corresponding to anisidine and its dimer, respectively. Mass analysis of the product with Rt 15.72 min showed major peaks at m/z 242, 135, and 107 which correspond to fragmentation of anisidine dimer (Fig. 10). A possible mechanism for the formation of dimer of anisidine may be proposed as shown in Fig. 11.
218
U. Shanker et al.
Fig. 11 Proposed mechanism for the formation of dimer of p-anisidine
Reaction of p-Chloroaniline with Goethite and Akaganeite In the case of p-chloroaniline the chromatogram showed two major peaks with Rt 3.87 and 30.72 min. Peak with retention time (Rt) 3.87,corresponding to p-chloroaniline whereas the second peak at retention time (Rt) 30.72 min corresponds to its dimer. Mass analysis of the product with Rt 30.72 min showed major peaks at m/z 139, 111, 92 and 77 which correspond to fragmentation of p-chloroaniline dimer (Fig. 12). Reaction of p-Toluidine with Goethite and Akaganeite The oxidation products of p-toluidine gave well defined and well separated peaks in gas chromatogram with Rt 3.25 and 27.59 min. Mass spectra of the peak with Rt 27.59 min showed molar mass 317 (100 %), which corresponds to trimer of p-toluidine Fig. 13. Some high fragments observed were 300, 226, 211, 107, 91 and 77. Above fragment masses resembled with possible fragments of a trimer. Peak with Rt 3.25 min corresponds to the starting material, i.e. p-toluidine.
Interaction of Aromatic Amines with Iron Oxides
219
Fig. 12 Mass spectrum of dimer of p-chloroaniline
Conclusion In view of present studies it can be suggested that iron oxides, once formed in the prebiotic environment, could have interacted with important biomolecules to protect them from degradation and could have catalyzed their oligomerization.
Fig. 13 Mass spectrum of dimer of p-toludline
220
U. Shanker et al.
Acknowledgments One of the authors, Dr. Uma Shanker is thankful to the Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee India for providing necessary instrumental facilities.
References Alam T, Kamaluddin (1999) Interaction of aminopyridines with metal hexacyanoferrates (II). Bull Chem Soc Jpn 72:1697–1703 Alam T, Kamaluddin (2000) Interaction of 2-amino, 3-amino and 4-aminopyridines with nickel and cobalt ferrocyanides. Colloids Surf 162:89–97 Alam T, Tarannum H, Kumar N, Kamaluddin (2000a) Interaction of 2-amino-, 3-amino-and 4-aminopyridines with chromium and manganese ferrocyanides. J Colloid Interface Sci 224:133–139 Alam T, Tarannum H, Ravi MNV, Kamaluddin (2000b) Adsorption and oxidation of aromatic amines by metal hexacyanoferrate (II). Talanta 51:1097–1105 Alam T, Tarannum H, Ali S, Kamaluddin (2002) Adsorption and oxidation of aniline and anisidine by chromium ferrocyanide. J Colloid Interface Sci 245:251–256 Braterman RS, Cairns-Smith AG, Sloper RW (1983) Photo-oxidation of hydrated Fe 2+ significance for banded iron formations. Nature 303:163–164 Cornell RM, Schwertmann U (2003) The iron oxides: structure, properties, reactions, occurrences and uses, 2nd edn. WILEY-VCH GmbH& Co. KGaA, Weinheim, pp 525–537 Friedmann N, Miller SL (1969) Phenylalanine and tyrosine synthesis under primitive Earth conditions. Science 166:766–767 Holland HD (1984) The chemical evolution of the atmosphere and oceans. Princeton University Press, Princeton, 582p Holm NG, Ertem G, Ferris JP (1993) The binding and reactions of nucleotide and polynucleotide on iron oxide hydroxide polymorphs. Orig Life Evol Biosph 23:195–215 Levine JS, Augustsson TR, Natarajan M (1982) The prebiological paleoatmosphere:stability and composition. Orig Life Evol Biosph 12:245–259 Matrajit G, Blanot D (2004) Properties of synthetic ferrihydrite as an amino acid adsorbent and a promoter of peptide bond formation. Amino acids 26:153–158 Moorbath S (1977) The oldest rocks and the growth of con-tinents. Sci Am 236:92–104 Shanker U, Bhushan B, Bhattacharjee G, Kamaluddin (2011) Formation of nucleobases in the presence of iron oxides: implication in chemical evolution and origin of life. Astrobiology 11:225–233 Towe KM (1990) Aerobic respiration in the Archaean? Nature 348:54–60 Urey HC (1952) On the early chemical history of the Earth and the origin of life. Proc Natl Acad Sci USA 38:351–363 Viladkar S, Alam T, Kamaluddin (1994) Adsorption of aromatic amines on metal ferrocyanides. J Inorg Biochem 53:69–78 Weber AL (1992) Prebiotic sugar synthesis: hexose and hydroxyl acid synthesis from glyceraldehydes catalyzed by Iron (III) hydroxide oxide. J Mol Evol 35:1
