Interaction of aromatic amino acids with metal hexacyanochromate(III) complexes: A possible role in chemical evolution

Article abstract of DOI:10.1246/bcsj.79.1541

Metal cyanogen complexes have been proposed to be efficient prebiotic catalysts. Insoluble metal cyanogen complexes are thought to have concentrated biomonomers from dilute prebiotic soup which facilitated a class of prebiotic reactions. Thus, large biopolymers were able to form during the course of chemical evolution and the origin of life. Based on this hypothesis, the interaction of two naturally occurring α-aromatic amino acids, tryptophan and phenylalanine, with cobalt(II), copper(II), and cadmium(II) hexacyanochromate(III) has been studied, and the interaction was found to be strongest at neutral pH (≈7:0). Cobalt(II) hexacyanochromate(III) adsorbed the largest amount of both amino acids while tryptophan had a stronger affinity than phenylalanine. Infrared spectral studies of the metal hexacyanochromate( III) complexes, amino acids and metal hexacyanochromate(III)-amino acid adducts indicated the involvement of NH₂ as well as COO^- groups of amino acids and surface metal ions present in the lattice of the metal hexacyanochromate(III) complexes.

Full text of DOI:10.1246/bcsj.79.1541

Ó 2006 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 79, No. 10, 1541–1546 (2006) 1541
Interaction of Aromatic Amino Acids with
Metal Hexacyanochromate(III) Complexes:
A Possible Role in Chemical Evolution
ꢀ
Shah Raj Ali and Kamaluddin
Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247 667, India
Received November 25, 2005; E-mail: kamalfcy@iitr.ernet.in
Metal cyanogen complexes have been proposed to be efficient prebiotic catalysts. Insoluble metal cyanogen com-
plexes are thought to have concentrated biomonomers from dilute prebiotic soup which facilitated a class of prebiotic
reactions. Thus, large biopolymers were able to form during the course of chemical evolution and the origin of life.
Based on this hypothesis, the interaction of two naturally occurring ꢀ-aromatic amino acids, tryptophan and phenyl-
alanine, with cobalt(II), copper(II), and cadmium(II) hexacyanochromate(III) has been studied, and the interaction
was found to be strongest at neutral pH (ꢁ7:0). Cobalt(II) hexacyanochromate(III) adsorbed the largest amount of both
amino acids while tryptophan had a stronger affinity than phenylalanine. Infrared spectral studies of the metal hexa-
cyanochromate(III) complexes, amino acids and metal hexacyanochromate(III)–amino acid adducts indicated the in-
volvement of NH2 as well as COOꢂ groups of amino acids and surface metal ions present in the lattice of the metal
hexacyanochromate(III) complexes.
Besides their potential applications as adsorbents, ion ex-
changers, molecular sieves, catalysts, and pigments, metal cya-
nogen complexes have been proposed to play an important
role in prebiotic synthesis, which is a matter of active research
among the scientists from different disciplines. From the mid-
dle of the last century, a vast number of workers have focused
their attention on tracing out the various steps involved in
chemical evolution and the origin of life on Earth.
It is assumed that some of the important biomonomers, such
as amino acids, purine and pyrimidine nitrogen bases, nucleo-
tides, pentose sugars, etc., were synthesised in a prebiotic en-
vironment1 and subsequently polymerized into large biopoly-
mers during the course of chemical evolution and origin of life.
Since it is unlikely that the prebiotic synthesis of biomonomers
would have yielded high concentrations of these biomolecules
in primeval seas, the mechanisms and the reagents through
which biomonomers were concentrated from their dilute aque-
ous solutions and polymerized into large biopolymers have
received growing interest. Adsorptive interaction processes
and the solid surfaces of inorganic minerals, respectively, have
been proposed to play important roles in concentrating the
biomonomers from a dilute prebiotic soup.2–4 The adsorptive
interaction processes could have brought the organic mole-
cules closer to each other which would accelerate the kinetics
of a series of prebiotic chemical reactions.
ꢂ acceptors, act as strong field ligands and easily coordinate to
transition-metal ions, it is, therefore, reasonable to assume that
cyanide ions might have complexed with transition-metal ions
present in primeval seas forming a number of soluble and
insoluble metal cyanogen complexes. As most of the metal
cyanogen complexes are insoluble in water, they may have
locally settled at the bottom of primeval sea or on its shore.
It is proposed that biomonomers present in the prebiotic soup
might have interacted on the solid surfaces of metal cyanogen
complexes, and thus, they were concentrated from dilute aque-
ous solutions in primeval seas. The biomonomers would have
been protected from degradation and undergone a class of
reactions, such as condensation, dimerisation, oligomerisation,
redox reactions, etc., to afford the essential materials needed to
form the first living cell. In view of this hypothesis, the inter-
action of organic molecules, including amino acids, nucleoti-
des, amino pyridines, and aromatic amines, with different met-
al cyanogen complexes have been studied, and the results sug-
gest that they have active role in chemical evolution.7–16 In this
paper, we report the results of our study on the interaction of
tryptophan and phenylalanine with cobalt(II), copper(II), and
cadmium(II) hexacyanochromate(III) exploring their possible
role in chemical evolution. Existence of aromatic amino acids
on primitive Earth has been proposed by Friedmann and
Miller.17
Cyanide has been reported as a product in some of the simu-
lated prebiotic experiments and is thought to have been readily
available in prebiotic environments. Use of cyano compounds
as precursors for biological compounds, including amino acids,
purine and pyrimidines has been reviewed by Ferris and
Hagan.5 Synthesis of 2,30-cAMP starting from cyano-derived
compounds has also been demonstrated by Ferris et al.6 Since
cyanide ions are negatively charged, good ꢁ donors and good
Experimental
Chemicals.
Potassium dichromate (B.D.H.), acetic acid
(E. Merck), potassium cyanide (Loba Chemie), cobalt(II) nitrate
(E. Merck), copper(II) nitrate (E. Merck), cadmium(II) nitrate
(E. Merck), tryptophan (E. Merck), and phenylalanine (E. Merck)
were used as received. All other chemicals were of analytical
reagent grade.
Published on the web October 10, 2006; doi:10.1246/bcsj.79.1541

1542 Bull. Chem. Soc. Jpn. Vol. 79, No. 10 (2006)
Amino Acid–Hexacyanochromate(III) Interaction
Preparation of Metal Hexacyanochromates(III). All three
metal hexacyanochromates(III) were synthesized from potas-
sium hexacyanochromate(III), which was synthesized using
Christensen’s method.18 To synthesize potassium hexacyanochro-
mate(III), 25 grams of potassium dichromate was dissolved in
500 mL of water, and SO2 gas was passed through the solution to
reduce Cr6þ to Cr3þ. This solution was then boiled to remove the
excess SO2. To the above boiling solution, liquid ammonia was
added slowly with vigorous stirring to precipitate chromium(III)
hydroxide. The chromium(III) hydroxide was collected by filtera-
tion, washed with hot water, and then, kept in a casserole in order
to prevent its conversion to insoluble chromium(III) oxide through
the loss of water molecules. The wet chromium(III) hydroxide
was dissolved in 100 mL of glacial acetic acid, and this solution
was evaporated to near dryness and was taken up with 180 mL
of water. It was then poured into a flask containing a boiling solu-
tion of 75 grams of potassium cyanide in 300 mL of water. The
reaction mixture was cooled, filtered, concentrated to 300 mL and
filtered again while still hot. On cooling the solution, pale-yellow
needles of potassium hexacyanochromate(III) formed, were col-
lected and washed with a little cold water. Finally, it was recrys-
tallized from water at ca. 5 ꢃC.
precipitate. The reaction mixtures were kept as such for 24 h.
The precipitate was collected by filteration, washed thoroughly
with water and dried. The dried products were ground and sieved
to 100-mesh size. CHN analyses, X-ray diffraction, thermogravi-
metric analyses, differential thermal analyses and infrared spectral
studies of all three metal hexacyanochromates(III) were per-
formed in order to test the purity of the complexes.
Elemental Analyses. The percentage of carbon, nitrogen, and
hydrogen in all the three metal hexacyanochromate(III) was deter-
mined with an Elementar Vario ELHI CHN analyzer. The percent
composition of the metals in the complexes was determined using
a Perkin-Elmer 3100 Atomic Absorption Spectrophotometer. The
data are summarized in Table 1.
Thermogravimetric and Differential Thermal Analyses.
Thermogravimetric analysis of all three metal hexacyanochro-
mate(III) was carried out using a Perkin-Elmer Thermogravimet-
ric Analyzer (Model:Pyris Diamond). The heating rate was 10
ꢃC minꢂ1. All measurements were carried out in a static air atmo-
sphere using Al2O3 as a reference. The thermogravimetric and
differential thermal spectra showed a mass loss corresponding to
14, 6, and 14 water molecules in cobalt(II), copper(II), and cad-
mium(II) hexacyanochromate(III), respectively.
Cobalt(II), copper(II), and cadmium(II) hexacyanochromate(III)
were prepared using the double decomposition method. 167 mL of
a 0.1 M solution of potassium hexacyanochromate(III) was added
to 500 mL of a 0.1 M solution of cobalt(II) nitrate or copper(II)
nitrate or cadmium(II) nitrate, respectively, with constant stirring.
The excess metal salts were used to improve the coagulation of
X-ray Diffraction Studies. The X-ray diffraction analyses of
all three powdered metal hexacyanochromate(III) complexes was
carried out using a Philips PW-1140/90 X-ray diffractometer. The
relative-intensity data and interplaner spacing (d) values were in
good agreement with the reported values,19 Table 2.
Spectral Studies. Electronic spectra of tryptophan and phen-
Table 1. Elemental Analysis of the Metal Hexacyanochromate(III) ComplexesaÞ
Metal hexacyanochromate(III)
C%
N%
H%
M%
M0%bÞ
Cobalt(II) hexacyanochromate(III)
16.78
(17.04)
16.51
(16.89)
13.95
(14.34)
18.43
(18.88)
18.79
(19.01)
15.83
(16.11)
3.44
(3.31)
2.22
(1.98)
2.76
(2.79)
21.00
(20.95)
26.13
(26.67)
34.13
(33.47)
12.56
(12.31)
13.00
(13.56)
10.44
(10.36)
Copper(II) hexacyanochromate(III)
Cadmium(II) hexacyanochromate(III)
a) Bracket values represent the theoretical values. b) M0 is exchangeable transition metal.
Table 2. X-ray Diffraction Data for the Metal Hexacyanochromate(III) ComplexesaÞ
Cobalt(II)
hexacyanochromate(III)
˚
Copper(II)
hexacyanochromate(III)
˚
Cadmium(II)
hexacyanochromate(III)
˚
d/A
I=Io
d/A
I=Io
d/A
I=Io
5.16
(5.18)
3.67
(3.66)
2.59
78
(80)
100
(100)
82
5.14
(5.14)
3.65
(3.66)
3.15
100
(100)
97
(100)
11
6.24
(6.22)
5.41
(5.47)
3.83
61
(60)
100
(100)
98
(2.59)
2.32
(2.31)
(80)
61
(60)
(3.14)
2.56
(2.58)
2.34
(2.33)
(10)
83
(80)
61
(3.88)
3.28
(3.30)
2.73
(2.73)
2.44
(100)
59
(60)
82
(80)
81
(60)
(2.44)
2.23
(2.24)
(80)
48
(50)
a) Bracket values represent the reported values.

S. R. Ali et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 10 (2006) 1543
ylalanine were recorded on a Beckman DU-6 Spectrophotometer.
The characteristic values of ꢃmax for tryptophan and phenylala-
nine were observed as 278 and 258 nm, respectively. Infrared
spectra of the amino acids, metal hexacyanochromate(III) com-
plexes and amino acid–metal hexacyanochromate(III) adducts
were recorded as KBr discs on a Perkin-Elmer F.T.I.R. Spetropho-
tometer.
Adsorption Studies. Adsorption of tryptophan and phenyl-
alanine on all three metal hexacyanochromate(III) complexes
was studied by adding 10 mL aliquots of amino acids solutions
to 50 mg metal hexacyanochromate(III) complex. The pH was
adjusted by adding small volumes of concentrated solutions of
HCl or NaOH depending on the pH. The suspensions were shaken
using an Expo Shaker initially for 1 h and then allowed to equili-
brate at 25 ꢃC with intermittent shaking. The suspensions were
centrifuged after 24 h and the supernatant liquid was decanted.
The amino acid concentration was determined spectrophotometri-
cally. The amount of the amino acids adsorbed was calculated
from the difference between the concentrations before and after
adsorption. The equilibrium concentration of amino acids and
their amount adsorbed were used to obtained adsorption iso-
therms. The pH of the supernatant liquids was recorded with a
pH meter (model CP-90, manufactured by Toshniwal Instruments
Manufacturer Pvt. Ltd., Ajmer).
(a)
Results
CHN analyses, atomic absorption spectrophotometric stud-
ies, thermogravimetric and differential thermal analyses was
used to verify that the structural formulae of the synthesized
complexes was similar to the reported formulae, i.e., Co3[Cr-
(CN)6]2 14H2O, Cu3[Cr(CN)6]2 6H2O, and Cd3[Cr(CN)6]2
ꢄ
ꢄ
ꢄ
14H2O. Further, X-ray diffraction studies confirmed the purity
of the synthesized complexes as there was no significant differ-
ence in the observed and reported relative-intensity and inter-
planar spacing (d) values19 as shown in Table 2.
(b)
Fig. 1. (a) Adsorption of tryptophan (4:0 ꢅ 10ꢂ3 M) on
metal hexacyanochromates(III) with a particle size less
than 100 mesh at room temperature as a function of pH.
(b) Adsorption of phenylalanine (1:6 ꢅ 10ꢂ3 M) on metal
hexacyanochromates(III) with a particle size less than
100 mesh at room temperature as a function of pH.
The effect of pH on the interaction of amino acids with all
three metal hexacyanochromate(III) complexes was studied
over a wide pH range (5.0–9.0). 10 mL of the amino acid solu-
tions with fixed concentrations (4:0 ꢅ 10ꢂ3 M for tryptophan
and 1:60 ꢅ 10ꢂ3 M for phenylalanine) were used to study their
adsorption onto all three metal hexacyanochromate(III) com-
plexes as a function of pH. The change in the amount of amino
acids adsorbed on different metal hexacyanochromate(III)
complexes and at different pH values are shown in Figs. 1a
and 1b. Results indicate a maximum adsorption at neutral
pH and less adsorption under acidic as well as basic conditions
in each case. Tryptophan showed more adsorption than phen-
ylalanine towards all three metal hexacyanochromate(III)
complexes. Adsorption data obtained at a neutral pH and wide
concentration range of amino acids (0:5 ꢅ 10ꢂ3–4:0 ꢅ 10ꢂ3 M
in case of tryptophan, 2:0 ꢅ 10ꢂ4–1:6 ꢅ 10ꢂ3 M in case of
phenylalanine) were fitted as Langmuir Adsorption Isotherms
as shown in Figs. 2a and 2b. The isotherms indicate that the
adsorption is fast, regular, positive and concave to the concen-
tration for both amino acids studied. The adsorption data fol-
lowed the equation:
(KLꢀeꢂꢀH=RT ), Xe is the amount (mg) of amino acid adsorbed
per gram weight of metal hexacyanochromate(III) and Xm is
the amount (mg) of the amino acid required per gram weight
of the metal hexacyanochromate(III) complexes for a complete
monolayer to form. The KL and Xm values were determined
and are shown in Table 3. The percent binding of tryptophan
and phenylalanine is listed in Table 4. The values of Xm and
percent binding data means that the interaction with trypto-
phan is greater than phenylalanine towards all three metal hexa-
cyanochromate(III) complexes. Cobalt(II) hexacyanochro-
mate(III) showed the maximum uptake capacity among the
three metal hexacyanochromate(III) complexes studied. The
order of uptake capacity was found as follow:
Cobalt(II) hexacyanochromate(III)
> Copper(II) hexacyanochromate(III)
Ceq=Xe ¼ 1=KLXm þ Ceq=Xm;
ð1Þ
> Cadmium(II) hexacyanochromate(III)
ð2Þ
where Ceq is equilibrium concentration of the amino acids; KL
is a constant related to enthalpy (ꢀH) of the adsorption
The infrared spectra of metal hexacyanochromate(III) com-
plexes, amino acids, and metal hexacyanochromate(III)–amino

1544 Bull. Chem. Soc. Jpn. Vol. 79, No. 10 (2006)
Amino Acid–Hexacyanochromate(III) Interaction
Table 3. Langmuir Constants for Adsorption of Aromatic Amino Acids on the Metal Hexacyanochro-
mate(III) Complexes
Tryptophan
Phenylalanine
Metal
hexacyanochromate(III)
KL/dm3 molꢂ1
Xm/mg gꢂ1
KL/dm3 molꢂ1
Xm/mg gꢂ1
Cobalt(II)
hexacyanochromate(III)
Copper(II)
hexacyanochromate(III)
Cadmium(II)
hexacyanochromate(III)
2.67
2.21
1.87
69.44
0.57
25.25
64.52
54.65
0.48
0.28
24.98
23.92
Table 4. Percent Binding of Aromatic Amino Acids on the
Metal Hexacyanochromate(III) Complexes
Percent binding
Metal hexacyanochromate(III)
Tryptophan Phenylalanine
Cobalt(II) hexacyanochromate(III)
Copper(II) hexacyanochromate(III)
Cadmium(II) hexacyanochromate(III)
41.7
38.6
33.0
36.2
32.9
27.0
action with the metal hexacyanochromate(III) complexes.
Typical frequencies of amino acids corresponding to ꢄ(NH )
2
and ꢄ(assymCOOH) increase due to the interaction with all three
metal hexacyanochromate(III) complexes. Minor changes
were observed in the infrared frequencies corresponding
to ꢄ(symCOOH). The results are shown in Table 5. Negligible
changes were observed in characteristic frequencies of the
(a)
metal hexacyanochromate(III) complexes (ꢄCr{C and ꢄC{N
after interaction with both the amino acids.
)
Discussion
Due to their solid surfaces, various clay minerals have been
proposed to play important role in concentrating the biomole-
cules from dilute prebiotic soup in the primeval seas during the
course of chemical evolution. Interaction with a wide variety
of organic molecules including amino acids, peptides, nucleic
acids and sugars with clays and clay minerals have been stud-
ied suggesting their possible role in chemical evolution.2–5
Since most of the metal cyanogen complexes have solid sur-
faces that are microporous20 in nature, they might have inter-
acted with biomolecules in such a way as to concentrate them
from dilute aqueous solutions in primeval seas.
The molecular formula of the metal hexacyanochromate(III)
complexes has been reported as M3[Cr(CN)6]2 nH2O, where
ꢄ
(b)
M represents an exchangeable divalent transition-metal ion
and n represents the number of water molecules present in
the interstitial site of the lattice. The structure of hexacyano-
chromate(III) complexes of divalent transition metals is analo-
gous to that of Prussian blue. Shriver21 has studied the system-
atics of the lattice parameters for the Prussian blue analogues.
The face-centered cubic lattice structure of Prussian blue is the
characteristic of many other metal hexacyanometalate. Ferrari
et al.19 reported that the three metal hexacyanochromate(III)
complexes have cubic symmetry. The lattice parameters for
the cobalt(II), copper(II), and cadmium(II) hexacyanochro-
mate complexes have been reported19 as 10.36, 10.32, and
Fig. 2. (a) Adsorption of tryptophan on metal hexacyano-
chromates(III) with a particle size less than 100 mesh at
neutral pH and room temperature. (b) Adsorption of phen-
ylalanine on metal hexacyanochromates(III) with a parti-
cle size less than 100 mesh at neutral pH and room tem-
perature.
acid adducts were recorded and analysed. Metal hexacyano-
chromate(III)–amino acid adducts were washed thoroughly
with water, dried and then study by using IR spectroscopy.
A pronounced change was observed in the characteristic
frequencies of both the amino acids after and before the inter-
˚
10.95 A, respectively. The transition-metal hexacyanochro-

S. R. Ali et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 10 (2006) 1545
Table 5. Typical Infrared Spectral Frequencies (cmꢂ1) of Tryptophan and Phenylalanine before and after
Adsorption on the Metal Hexacyanochromate(III) ComplexesaÞ
Metal
hexacyanochromate(III)
Characteristic frequencies/cmꢂ1
Phenylalanine Tryptophan
ꢂ
ꢂ
ꢂ
ꢂ
ꢄs(COO
)
ꢄN{H
ꢄas(COO
ꢄs(COO
ꢄN{H
ꢄas(COO
)
)
)
Cobalt(II)
hexacyanochromate(III)
Copper(II)
3390
(3400)
3390
1596
(1608)
1596
1404
(1400)
1404
3409
(3441)
3409
1590
(1606)
1590
1408
(1395)
1408
hexacyanochromate(III)
Cadmium(II)
hexacyanochromate(III)
(3404)
3390
(3399)
(1606)
1596
(1602)
(1398)
1404
(1400)
(3441)
3409
(3430)
(1609)
1590
(1601)
(1392)
1408
(1392)
a) Bracket values represent frequencies after adsorption.
mate(III) complexes generally have a polymeric lattice struc-
ture with [Cr(CN)6]3ꢂ anions, in which the other transition-
metal ions are coordinated by the nitrogen atom of the cyanido
ligand. Detailed structural studies of the metal hexacyanochro-
Conclusion
The results of the present study reveal that insoluble metal
hexacyanochromate(III) complexes present at the bottom of
shores of primeval seas could have interacted with aromatic
amino acids in such a way as to concentrate them from the di-
lute prebiotic soup during the course of chemical evolution and
the origin of life. Biomonomers, thus concentrated, are thought
to have been protected from degradation and undergone a class
of reactions of prebiotic relevance producing biopolymers es-
sential for the formation of first living cell on this planet.
mate(III) complexes with the general formula M3[Cr(CN)6]2
nH2O were carried out by Ludi and Gudel.22 Attempts are
being made to determine the structures of other metal cyano-
ꢄ
´
gen complexes. Recently, Gomez and Reguera reported the
structure of cadmium hexacyanoferrate(II).23
At lower pH, the lower adsorption of amino acids on the
metal hexacyanochromate(III) complexes may be due to the
protonation of the amino acid molecules. In alkaline medium,
lower adsorption may be due to the interaction between OHꢂ
and the metal hexacyanochromate(III) complexes. The greater
adsorption of tryptophan than phenylalanine by all three metal
hexacyanochromate(III) complexes may be due to additional
interaction through the tryptophan indole ring. The indole ring
of tryptophan may interact with surface metal ions present in
the lattice of complexes through the donation of ꢂ electrons
present in the dꢂ orbitals of the outer metal ion to the anti-
bonding molecular orbitals of indole ring. The greater adsorp-
tion of tryptophan than phenylalanine is consistent with our
previous studies.8 The effect of pH on the amount of amino
acids adsorbed could not only be because of the change in
the ionic form of amino acids but also due to the change in sur-
face characteristics of the metal hexacyanochromate(III) com-
plexes. The surface conditions of the metal hexacyanochro-
mate(III) complexes due to pH seem to affect the amount of
amino acids adsorbed more than the ionic forms of amino
acids. It is likely because both amino acids, i.e., tryptophan
and phenylalanine, exist as zwitterions over a wide pH range
with respect to their isoelectric pH. For intance, the pKa values
for tryptophan are 2.20 and 9.55, so that at pH 4.20 and 7.55,
approximately 99% of the tryptophan exists as a zwitterion.
Since no significant change was observed in the IR spectra
of the metal hexacyanochromate(III) complexes before and af-
ter adsorption, the amino acid molecules do not appear to enter
into the inner sphere of the metal hexacyanochromate(III)
complexes by replacing CNꢂ ligands. Moreover, the replace-
ment of CNꢂ ligands by other ligands is highly improbable.24
Thus, it is suggested that the amino acid molecules are adsorb-
ed onto the metal hexacyanochromate(III) complexes through
interaction between the metal ions of the corresponding metal
hexacyanochromate(III) complexes and COOꢂ as well as NH2
groups of amino acid molecules.
This research work was sponsored by Indian Space Re-
search Organization, Bangalore (India).
References
1
S. L. Miller, L. E. Orgel, The Origins of Life on Earth,
Prentice Hall, Inc., Englewood Cliffs, N.J., 1974, pp. 83–117.
D. J. Greenlands, R. H. Laby, J. P. Quirk, Trans Faraday
Soc. 1965, 61, 2013.
2
3
1986, 17, 69.
J. P. Ferris, W. J. Hagan, Origins Life Evol. Biosphere
4
5
6
S. C. Bondy, M. E. Harrington, Science 1979, 203, 1243.
J. P. Ferris, W. J. Hagan, Tetrahedron 1984, 40, 1093.
J. P. Ferris, C. H. Huang, W. J. Hagan, Origins Life Evol.
Biosphere 1988, 18, 121.
7 Kamaluddin, M. Nath, S. W. Deopujari, A. Sharma,
Origins Life Evol. Biosphere 1990, 20, 259.
8
Biosphere 1994, 24, 469.
9
Jpn. 1996, 69, 95.
Kamaluddin, M. Nath, A. Sharma, Origins Life Evol.
S. Viladkar, A. Rachana, Kamaluddin, Bull. Chem. Soc.
10 T. Alam, Kamaluddin, Bull. Chem. Soc. Jpn. 1999, 72,
1697.
11 T. Alam, Kamaluddin, Colloids Surf. 1999, 162, 89.
12 S. R. Ali, J. Ahmad, Kamaluddin, Colloids Surf. 2004, 236,
165.
13 S. R. Ali, Kamaluddin, Astrobiology 2004, 4, 420.
14 S. R. Ali, T. Alam, Kamaluddin, Bull. Chem. Soc. Jpn.
2004, 77, 1681.
15 S. R. Ali, T. Alam, Kamaluddin, J. Colloid Interface Sci.
2002, 245, 51.
16 T. Alam, H. Tarannum, R. M. N. V. Kumar, Kamaluddin,
Talanta 2000, 51, 1097.
17 N. Friedmann, S. L. Miller, Science 1969, 166, 766.
18 S. Christensen, Potassium Hexacyanochromate(III) in

1546 Bull. Chem. Soc. Jpn. Vol. 79, No. 10 (2006)
Amino Acid–Hexacyanochromate(III) Interaction
porous Mesoporous Mater. 2002, 54, 285.
21 D. F. Shriver, Struct. Bonding 1966, 1, 32.
22 A. Ludi, H.-U. Gudel, Struct. Bonding 1973, 14, 1.
´
23 A. Gomez, E. Reguera, Inorg. Mater. 2001, 3, 1045.
24 S. I. Ohno, Bull. Chem. Soc. Jpn. 1967, 40, 1765.
Inorganic Syntheses, ed. by W. C. Fernelius, Mc Graw-Hill
Company Inc., New York, 1946, Vol. 2, pp. 203–205.
19 A. Ferrari, M. E. Tani, E. Morisi, Gazz. Chim. Ital. 1961,
91, 1142.
20 J. Balmaseda, E. Reguera, A. Gomez, B. Diaz, Micro-