Glucoamylase was immobilized on acid
activated montmorillonite clay via two different procedures
namely adsorption and covalent binding. The
immobilized enzymes were characterized by XRD,
NMR and N2 adsorption measurements and the
activity of immobilized glucoamylase for starch
hydrolysis was determined in a batch reactor. XRD
shows intercalation of enzyme into the clay matrix
during both immobilization procedures. Intercalation
occurs via the side chains of the amino acid residues,
the entire polypeptide backbone being situated at the
periphery of the clay matrix. 27Al NMR studies
revealed the different nature of interaction of enzyme
with the support for both immobilization techniques.
N2 adsorption measurements indicated a sharp drop in
surface area and pore volume for the covalently bound
glucoamylase that suggested severe pore blockage.
Activity studies were performed in a batch reactor. The
adsorbed and covalently bound glucoamylase retained
49% and 66% activity of the free enzyme respectively.
They showed enhanced pH and thermal stabilities. The
immobilized enzymes also followed Michaelis–Menten
kinetics. Km was greater than the free enzyme that was
attributed to an effect of immobilization. The immobilized
preparations demonstrated increased reusability
as well as storage stability.
Glucoamylase from Aspergillus Niger was immobilized on montmorillonite clay (K-10) by two procedures, adsorption and covalent binding. The immobilized enzymes were characterized using XRD, surface area measurements and 27Al MAS NMR and the activity of the immobilized enzymes for starch hydrolysis was tested in a fixed bed reactor (FBR). XRD shows that enzyme intercalates into the inter-lamellar space of the clay matrix with a layer expansion up to 2.25 nm. Covalently bound glucoamylase demonstrates a sharp decrease in surface area and pore volume that suggests binding of the enzyme at the pore entrance. NMR studies reveal the involvement of octahedral and tetrahedral Al during immobilization. The performance characteristics in FBR were evaluated. Effectiveness factor (η) for FBR is greater than unity demonstrating that activity of enzyme is more than that of the free enzyme. The Michaelis constant (Km) for covalently bound glucoamylase was lower than that for free enzyme, i.e., the affinity for substrate improves upon immobilization. This shows that diffusional effects are completely eliminated in the FBR. Both immobilized systems showed almost 100% initial activity after 96 h of continuous operation. Covalent binding demonstrated better operational stability.
The effect of residual cations in rare earth metal modified faujasite–Y zeolite has been monitored using magic angle spinning NMR spectral analysis and catalytic activity studies. The second metal ions being used are Na+, K+ and Mg+. From a comparison of the spectra of different samples, it is concluded that potassium and magnesium exchange causes a greater downfield shift in the 29Si NMR peaks. Also, lanthanum exchanged samples show migration behavior from large cages to small cages, which causes the redistribution of second counter cations. It is also observed that Mg2+ causes the most effective migration of lanthanum ions due to its greater charge. The prepared systems were effectively employed for the alkylation of benzene with 1-octene in the vapor phase. From the deactivation studies it is observed that the as-exchanged zeolites possess better stability towards reaction condition over the pure HFAU zeolite.
Suja, H; Deepa, C S; Sreeja Rani, K; Sugunan, S(Indian Journal of Chemistry, August , 2003)
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Abstract:
The present work attempts a systematic examination of the effect of sulphate content on the physico-chemical properties
and catalytic activity of sulphated zirconia and iron promoted sulphated zirconia systems. Sulphate content is estimated by
EDX analysis. The amount of sulphate incorporated has been found to influence the surface area, crystal structure and the
acid strength distribution. Ammonia TPD and adsorption studies using perylene have enabled the determination of surface
acidic properties. The results are supported by the thermodesorption studies using pyridine and 2,6-dimethylpyridine. The
catalytic activity towards benzoylation reaction has been correlated with the surface acidity of the systems.
Cyclohexanol decomposition activity of supported vanadia catalysts is ascribed to the high surface area, total acidity and interaction between supported vanadia and the amorphous support. Among the supported catalysts, the effect of vanadia over various wt% V2O5 (2–10) loading indicates that the catalyst comprising of 6 wt% V2O5 exhibits higher acidity and decomposition activity. Structural characterization of the catalysts has been done by techniques like energy dispersive X-ray analysis, X-ray diffraction and BET surface area. Acidity of the catalysts has been measured by temperature programmed desorption using ammonia as a probe molecule and the results have been correlated with the activity of catalysts.
Invertase was immobilised on microporous montmorillonite K-10 via adsorption and covalent binding. The immobilised enzymes were tested for sucrose hydrolysis activity in a batch reactor. Km for immobilised systems was greater than free enzyme. The immobilised forms could be reused for 15 continuous cycles without any loss in activity. After 25 cycles, 85% initial activity was retained. A study on leaching of enzymes showed that 100% enzyme was retained even after 15 cycles of reuse. Leaching increased with reaction temperature. Covalent binding resisted leaching even at temperatures of 70 °C.
The present work investigates on the applicability of metal promoted sulphated zirconia
catalysts for the hydroxylation of phenol under mild conditions. The percentage conversion
and product distribution was highly sensitive towards the reaction parameters like the catalyst
composition, reaction temperature, H202/ phenol ratio and the solvent used.
Sreekumar, K; Elizabeth, Chirackal Varkey(Springer, January 13, 2010)
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Abstract:
A new class of chiral polyurethanes containing
amido linkages in the polymer backbone have been synthesized
by reacting toluene diisocyanate with isosorbide
(IS) chiral moiety and the chromophores [N,N0-ethane-
1,2-diyl bis(6-hydroxy hexanamide), N,N0-butane-1,4-diyl
bis(6-hydroxy hexanamide) and N,N0-hexane-1,6-diyl bis
(6-hydroxy hexanamide)]. The corresponding chromophores
were obtained by the aminolysis of e-caprolactone by
using the diamines, diaminoethane, diaminobutane and
diaminohexane, respectively. All the polymers were synthesized
according to the symmetry conditions so as to
obtain the non-centrosymmetric environment. A series of
polyurethanes were synthesized by varying the chiral–
chromophore composition. The polyurethanes developed
were characterized by optical and thermal methods.
Description:
J Mater Sci (2010) 45:1912–1920
DOI 10.1007/s10853-009-4177-1
Sugunan, S; Bindhu, J; Disha; Jessey, V(Indian Journal of Chemistry, July , 1997)
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Abstract:
The Lewis acidity of yttrium and dysprosium exchanged
zeolite Y and ZSM-5 has been determined by titration method
using Hammett indicators. The acidity of the Y form increases
with increase in concentration of the rare earth cation in the Y
zeolite. It is independent of the amount of the rare earth ion for
ZSM-5. The data have been correlated with the activity of these
zeolites for the esterification of butanol using acetic acid.
The present work undertakes the preparation and physico-chemical characterisation of iron promoted sulphated zirconia
(SZ) with different amounts of iron loading and their application to Friedel-Crafts benzoylation of benzene, toluene and xylene
under different experimental conditions, XRD and laser Raman techniques reveal the stabilisation of the tetragonal phase of
zirconia and the existence of iron in highly dispersed form as Fe203 on the catalyst surface. The surface acidic properties were
determined by ammonia temperature programmed desorption (TPD) and perylene adsorption, The results were supported by
the TGA studies after adsorption of pyridine and 2,6-dimethylpyridine (2,6-DMP), Strong Lewis acid sites on the surface, which
are evident from TPD and perylene adsorption studies. explain the high catalytic activity of the systems towards benzoylation.
The experimental results provide evidence for the truly heterogeneous nature of the reaction. The studies also establish the
resistance to deactivation in the metal incorporated sulphated systems.
Manju, Kurian; Sugunan, S(Indian Journal of Chemistry, October , 2003)
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Abstract:
Iron, aluminium and mixed iron aluminium pillared clays have been prepared by partial hydrolysis method and doped
with IO% Mo, V and Cr. The samples have been characterised by XRD, FTIR and surface area and pore Volume
measurements. The surface acid site distribution has been determined by temperature programmed desorption of ammonia.
Vanadia incorporated systems show maximum acidity. Benzylation of o-xylene has been done as probe reaction to test
catalytic activity. Benzyl chloride is a superior benzylating agent compared to benzyl alcohol in activity and selectivity.
Cent percent selectivity towards monobenzylated product is obtained in all the cases. Fe pillared systems exhibit maximum
activity. The catalytic activities of the systems can be correlated with the amount of strong add sites. The effects of various
reaction variables on the reaction have been studied. Presence of moisture has a diminishing effect on the reaction rate.
Sugunan, S; Nishamol, K(Indian Journal of Chemistry, May , 2002)
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Abstract:
The liquid-phase Friedel-Crafts acylation of toluene using benzoyl chloride as benzoylating agent has heen carried out over Nix, Mn(l-x)Fe2 O4 (x=O, 0.2, 0.4, 0.6, 0.8 and 1.0) type systems under different reaction conditions. It is observed that the systems with high 'x' values are effective for the conversion of BOC and the selective formation of 4-MBP. Selectivity for 4-MBP over MnFe2O4 is more than 90% under the optimized reaction conditions. Sites of moderate acidity is effective in calalyzing the benzoylation reaction.
Manoj, Easwaran potti; Prathapachandra Kurup, M R; Fun, Hoong-Kun(Elsevier, 2007)
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Abstract:
A novel N4O coordination mode offers carbohydrazone ligands as a building block for interesting frameworks through self-assembly. Bridging mode of oxygen of bis(2-benzoylpyridine ketone) carbohydrazone (H2L) with metal centers facilitates the formation of the macrocyclic molecular square [Zn(HL)]4(BF4)4 · 10H2O, offers wide range of applications for carbohydrazones.
Anantaraman, R; Sugunan, S(Indian Journal of Chemistry, August , 1982)
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Abstract:
Kinetics of mercuric chloride catalysed solvolysis of benzyl chloride have been studied in water. 10% aq. ethanol, 10,20 and
30% aq. acetone and 20% aq. DMSO. The results confirm the operation of a mass law effect.
Sreekumar, K(Taylor and francis, October 20, 2003)
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Abstract:
Polymer materials find application in optical storage technology,
namely in the development of high information density and fast access type
memories. A new polymer blend of methylene blue sensitized polyvinyl alcohol
(PVA) and polyacrylic acid (PAA) in methanol is prepared and characterized
and its comparison with methylene blue sensitized PVA in methanol and
complexed methylene blue sensitized polyvinyl chloride (CMBPVC) is presented.
The optical absorption spectra of the thin films of these polymers
showed a strong and broad absorption region at 670-650 nm, matching the
wavelength of the laser used. A very slow recovery of the dye on irradiation was
observed when a 7:3 blend of polyvinyl alcohol/polyacrylic acid at a pHof 3.8
and a sensitizer concentration of 4.67 10 5 g/ml were used. A diffraction
efficiency of up to 20% was observed for the MBPVA/alcohol system and an
energetic sensitivity of 2000 mJ/cm2 was obtained in the photosensitive films
with a spatial frequency of 588 lines/mm.
Prathapachandra Kurup, M R; Sheeja, S R; Neema, Ani Mangalam(Elsevier, 2010)
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Abstract:
Mn(II) complexes derived from a set of acylhydrazones were synthesised and characterized by elemental
analyzes, IR, UV–vis and X-band EPR spectral studies as well as conductivity and magnetic susceptibility
measurements. In the reported complexes, the hydrazones exist either in the keto or enolate form, as evidenced
by IR spectral data. Crystal structures of two complexes are well established using single crystal
X-ray diffraction studies. In both of these complexes two equivalent monoanionic ligands are coordinated
in a meridional fashion using cis pyridyl, trans azomethine nitrogen and cis enolate oxygen atoms positioned
very nearly perpendicular to each other. EPR spectra in DMF solutions at 77 K show hyperfine sextets
and in some of the complexes the low intensity forbidden lines lying between each of the two
hyperfine lines are also observed
The influence of the chemical composition and silylation of mesoporous MCM-41 materials on the photochromic
behaviour of adsorbed spiropyran (BIPS) and 6-nitrospiropyran was studied. Upon incorporation, the spiropyrans
underwent ring opening to form either zwitterionic merocyanine or its corresponding O-protonated form. In all
silica MCM-41 or in the MCM-41 containing aluminium, the O-protonated merocyanine was predominantly
formed. In the case of MCM-41 modified by silylation of the OH groups, a mixture of zwitterionic merocyanine
and spiropyran was present. The photochromic response was studied by means of steady-state irradiation and by
laser flash photolysis. Steady-state irradiation (λ > 450 nm) of the solid samples gives rise in all cases to an intensity
decrease of the absorption bands corresponding to either the protonated or the unprotonated merocyanine form
(reverse photochromism). In contrast, laser flash photolysis at 308 nm of spiropyrans supported on silylated
MCM-41 allows observation of the photochemical ring opening of residual spiropyran to the corresponding
zwitterionic form (normal photochromism).
Prathapachandra Kurup, M R; Jessy, Emmanuel; Sithambaresan, M(November 3, 2011)
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Abstract:
The title compound, C11H9N3O2, exists in the E conformation
with respect to the azomethane C N bond, and has the keto
form. There are two independent molecules in the asymmetric
unit and each of these features a slight slanting of the pyridine
and furan rings, which form a dihedral angle of 14.96 (10) in
one of the molecules and 5.53 (10) in the other. The crystal
structure is stabilized by N—H O and N—H N hydrogen
bonds, weak C—H O and C—H N hydrogen bonds and
C—H interactions and – interactions [shortest
centroid–centroid distance = 3.7864 (15) A ° ].
Mohammed Yusuff, K K; Leeju, P; Arun,V; Manju, Sebastian; Varsha, Gopalakrishnan; Digna, Varghese(Crystallography Journals,Acta Crystallographica Section E ,Structure Reports, July 15, 2009)
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Abstract:
In the title molecule, C16H11N5, the mean planes of the
quinoxaline and indazole fragments form a dihedral angle of
10.62 (5). In the crystal, weak intermolecular N—H..........N
hydrogen bonds link the molecules into zigzag chains
extending in the [001] direction. The crystal packing also
exhibits pye interactions [centroid–centroid distances of
3.7080 (2) and 3.8220 (5) A ˚ ], which form stacks of the
molecules parallel to the a axis