Fermentative bioconversion in a horizontal rotating tubular bioreactor

The performance of a horizontal rotating tubular bioreactor (HRTB) was investigated with a biological system under non-sterile conditions. A spontaneously developed microbial culture was cultivated in a simple glucose/yeast extract medium. A fermentative bioconversion was examined by different combinations of process parameters (bioreactor rotation speed 5–30 min⁻¹ and medium inflow rate 1–10 l h⁻¹). Bioconversion dynamics in HRTB was monitored by withdrawing the samples from five positions along the bioreactor. Investigation in HRTB showed a rapid and an efficient glucose conversion into different products of metabolism. Glucose consumption rate along the HRTB depended on medium inflow rate, while bioreactor rotation speed did not have a significant influence. Complete glucose conversion in HRTB was observed at inflow rates of up to 6.5 l h⁻¹. The pH gradient along the HRTB was detected at higher medium inflow rates (6.5 and 10 l h⁻¹), but did not significantly influence substrate conversion efficiency. A discussion of its potential use and a comparison of HRTB with other bioreactors are also presented.     

Synthesis, characterization and antitumor studies of Mn(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) complexes of N-salicyloyl-N'-o-hydroxythiobenzhydrazide

A new ligand N-salicyloyl-N'-o-hydroxythiobenzhydrazide (H2Sotbh) forms complexes [Mn(HSotbh)2], [Fe(Sotbh-H)(H2O)2], [M(Sotbh)] [M=Co(II), Cu(II) and Zn(II)] and [Ni(Sotbh)(H(2)O)2], which were characterized by various physico-chemical techniques. M?ssbauer spectrum of [Fe(Sotbh-H)(H2O)2] reveals the quantum admixture of 5/2 and 3/2 spin-states. Mn(II), Cu(II) and Ni(II) complexes were observed to inhibit the growth of tumor in vitro, whereas, Fe(III), Co(II), Zn(II) complexes did not. In vivo administration of Mn(II), Cu(II) and Ni(II) resulted in prolongation of survival of tumor bearing mice. Tumor bearing mice administered with Mn(II), Cu(II) and Ni(II) complexes showed reversal of tumor growth associated induction of apoptosis in lymphocytes. The paper discusses the possible mechanisms and therapeutic implication of the H2Sotbh and its metal complexes in tumor regression and tumor growth associated immunosuppression.     

Studies on mixing in horizontal rotating tubular bioreactor

In previous investigations on mixing in a horizontal rotating tubular bioreactor (HRTB) the structured “spiral flow” model was developed which contained four adjustable parameters [1, 2]. In order to incorporate the mixing model in a semifundamental scale-up procedure it was necessary to make a relation between the adjustable model parameters and process parameters of the bioreactor expressed as dimensionless numbers. Mathematical equations which relate adjustable model parameters with dimensionless numbers were developed by non-linear and surface regression methods. These equations were applied to develop the prediction systems for adjustable model parameters. In total, nine systems of equations for the prediction of the adjustable model parameters were established and examined by simulation. Three of them (SC-2, SC-6 and SC-9) were selected as adequate to describe the mixing performance of HRTB in a wide range of process conditions.     

Microbial acetate oxidation in horizontal rotating tubular bioreactor

The aim of this work was to investigate the possibility of conducting a continuous aerobic bioprocess in a horizontal rotating tubular bioreactor (HRTB). Aerobic oxidation of acetate by the action of a mixed microbial culture was chosen as a model process. The microbial culture was not only grown in a suspension but also in the form of a biofilm on the interior surface of HRTB. Efficiency of the bioprocess was monitored by determination of the acetate concentration and chemical oxygen demand (COD). While acetate inlet concentration and feeding rate influenced efficiency of acetate oxidation, the bioreactor rotation speed did not influence the bioprocess dynamics significantly. Gradients of acetate concentration and pH along HRTB were more pronounced at lower feeding rates. Volumetric load of acetate was proved to be the most significant parameter. High volumetric loads (above 2 g acetate l⁻¹ h⁻¹) gave poor acetate oxidation efficiency (only 17 to 50%). When the volumetric load was in the range of 0.60–1.75 g acetate l⁻¹ h⁻¹, acetate oxidation efficiency was 50–75%. At lower volumetric loads (0.14–0.58 g acetate l⁻¹ h⁻¹), complete acetate consumption was achieved. On the basis of the obtained results, it can be concluded that HRTB is suitable for conducting aerobic continuous bioprocesses.     

Studies on mixing in horizontal rotating tubular bioreactor

A horizontal rotating tubular bioreactor (HRTB) is a combination of a “thin-layer bioreactor” and a “biodisc” reactor. Its interior is divided by O-ring shaped partition walls. Mixing properties of this new type of the bioreactor were investigated by using a temperature step method. The mixing simulations were done by Runge-Kutta-Fehlberg numerical integration. Adjustable parameters of the “spiral flow” model were optimised by Monte-Carlo method. In this investigation, the structured “spiral flow” model (containing four adjustable parameters) was tested in a wide range of experimental conditions. The results show that the structured “spiral flow” model is capable to describe the mixing in HRTB in the whole range of both bioreactor operational parameters (n and D).     

Studies on mixing in horizontal rotating tubular bioreactor

Mixing studies in the horizontal rotating tubular bioreactor (HRTB) were done to explore the influences of the liquid level (H _M =0.050.08 m) and the distance between the partition walls (D _S =0.020.07 m) on the mixing performance in the bioreactor described by the “spiral flow” model. The optimised adjustable parameters of the model were correlated with the process parameters of the bioreactor expressed as dimensionless numbers: Reynolds rotation number (Re _N ) and Reynolds axial flow number (Re _D ). The polynomial coefficients of the correlations were correlated further with the liquid level in the bioreactor (H _M ) and the distance between the partition walls (D _S ). In that way, three modified prediction systems (SC-2A, SC-6A and SC-9A) were established. The analysis based on different criteria selected the prediction system SC-9A as the most suitable to describe the mixing performance of HRTB.     

Mathematical modeling of a horizontal tubular loop bioreactor for biomass production from natural gas

In this study, mathematical modeling of a horizontal tubular loop bioreactor (HTLB) was considered for biomass production from natural gas. Gas inlet segments, static mixers, gas–liquid separator, and liquid pump of the HTLB were mathematically modeled according to the ideal stirred reactors, and the horizontal parts, riser, and down-comer sections were modeled in line with the dispersed plug-flow reactors as well. The set of ordinary and partial differential equations were coupled to calculate the oxygen and methane concentrations in the liquid through the length of bioreactor and time. Moreover, the tuned kinetic and hydrodynamic parameters of SCP process in the HTLB were determined based on the mathematical model at various operational conditions. The model was validated by considering experimental dissolved oxygen, methane, and biomass concentrations in liquid at different ratios of air to methane and liquid flow rates. The results showed satisfactory agreement between the developed model and the experimental data.     

Adsorption of Cu(II), Ni(II) and Zn(II) on modified jute fibres

The potential of a lignocellulosic fibre, jute, was assessed for adsorption of heavy metal ions like Cu(II), Ni(II) and Zn(II) from their aqueous solutions. The fibre was also used as adsorbent after chemically modifying it by two different techniques viz, loading of a dye with specific structure, C.I. Reactive Orange 13, and oxidising with hydrogen peroxide. Both the modified jute fibres gave higher metal ion adsorption. Thus, the dye loaded jute fibres showed metal ion uptake values of 8.4, 5.26 and 5.95 mg/g for Cu(II), Ni(II) and Zn(II), respectively, while the corresponding values for oxidised jute fibres were 7.73, 5.57 and 8.02 mg/g, as against 4.23, 3.37 and 3.55 mg/g for unmodified jute fibres. Adsorption isotherm models indicated best fit for Langmuir model for the modified jute fibres. The adsorption values decreased with lowering of pH. The desorption efficiency, regenerative and reuse capacity of these adsorbents were also assessed for three successive adsorption-desorption cycles. The adsorptive capacity was retained only when the caustic soda regeneration is carried out as an intermediate step after desorption. Possible mechanism has been given.     

Heterotrophic cultivation of Paracoccus denitrificans in a horizontal rotating tubular bioreactor

In this work, the heterotrophic cultivation of bacterium Paracoccus denitrificans has been studied in a horizontal rotating tubular bioreactor (HRTB). After development of a microbial biofilm on the inner surface of the HRTB, conditions for one-step removal of acetate and ammonium ion were created. The effect of bioreactor process parameters [medium inflow rate (F) and bioreactor rotation speed (n)] on the bioprocess dynamics in the HRTB was studied. Nitrite and nitrogen oxides (NO and N₂O) were detected as intermediates of ammonium ion degradation. The biofilm thickness and the nitrite concentration were gradually reduced with increase of bioreactor rotation speed when the medium inflow rate was in the range of 0.5–1.5 l h⁻¹. Further increase of inflow rate (2.0–2.5 l h⁻¹) did not have a significant effect on the biofilm thickness and nitrite concentration along the HRTB. Complete acetate consumption was observed when the inflow rate was in the range of 0.5–1.5 l h⁻¹ at all bioreactor rotation speeds. Significant pH gradient (cca 1 pH unit) along the HRTB was only observed at the highest inflow rate (2.5 l h⁻¹). The results have clearly shown that acetate and ammonium ion removal by P. denitificans can be successfully conducted in a HRTB as a one-step process.     

Transition metal-saccharide chemistry: d-glucose complexes of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II)

Metal complexes of d-glucose (d-Glc) from large cation containing dibromo-dichloro salts of dipositive metals [NEt₄]₂[MBr₂Cl₂] (M = Mn, Co, Ni, Cu and Zn) and the disodium salt of glucose were synthesized from a MeOH:MeCN mixture. The complexes were characterized by UV-vis absorption, circular dichroism, IR and proton magnetic resonance spectroscopies, and by elemental analysis, and were found to be Na[M(d-Glc)(OMe)Cl]. Cyclic voltammetric studies of these complexes, in the acidic to neutral pH range, indicated no dissociation, even in highly acidic conditions.This paper is dedicated to Professor Richard H. Holm (Harvard University) on the occasion of his 60th birthday.     

Antibacterial Co(II), Ni(II), Cu(II) and Zn(II) Complexes of Schiff bases Derived from Fluorobenzaldehyde and Triazoles

Antibacterial Schiff bases derived from 1,2,4-triazoles as well as their metal complexes incorporating cobalt(II), nickel(II), copper(II) and zinc(II) have been synthesized and characterized. Physico-chemical studies suggest that an octahedral geometry for the cobalt(II), nickel(II) and zinc(II)and square-planer geometry for the copper(II) complexes. These complexes have been screened for antibacterial activity against three Gram-positive (Staphylococcus aureus, Staphylococcus epidermidis and Bacillus subtilis) and two Gram-negative (Salmonella typhi and Pseudomonas aeruginosa) bacterial strains, and results compared with the activity of the free ligands. The metal complexes were found to be more potent against one or more bacterial strains than the free ligands.     

Antibacterial Co(II), Ni(II), Cu(II) and Zn(II) complexes of Schiff bases derived from fluorobenzaldehyde and triazoles

Antibacterial Schiff bases derived from 1,2,4-triazoles as well as their metal complexes incorporating cobalt(II), nickel(II), copper(II) and zinc(II) have been synthesized and characterized. Physico-chemical studies suggest that an octahedral geometry for the cobalt(II), nickel(II) and zinc(II)and square-planer geometry for the copper(II) complexes. These complexes have been screened for antibacterial activity against three Gram-positive (Staphylococcus aureus, Staphylococcus epidermidis and Bacillus subtilis) and two Gram-negative (Salmonella typhi and Pseudomonas aeruginosa) bacterial strains, and results compared with the activity of the free ligands. The metal complexes were found to be more potent against one or more bacterial strains than the free ligands.     

Preparation, characterization and pH-metric measurements of 4-hydroxysalicylidenechitosan Schiff-base complexes of Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Ru(III), Rh(III), Pd(II) and Au(III)

The 4-hydroxysalicylidenechitosan Schiff-base (2CS-Hdhba) was prepared by the condensation of 2,4-dihydroxybenzaldehyde with chitosan, and its metal complexes, [M(2CS-dhba)Cl₂(H₂O)₂] (M(III) = Fe, Ru, Rh), [M′(2CS-dhba)(AcO)(H₂O)₂] (M′(II) = Co, Ni, Cu, Zn), [Pd(2CS-dhba)Cl(H₂O)] and [Au(2CS-dhba)Cl₂], are reported. These complexes were characterized by elemental analysis, by spectral data (FTIR, solid-phase ¹³C NMR, UV–vis and ESR spectroscopy), by morphological observations (SEM and XRD), and by magnetic and thermal measurements. The Schiff base (2CS-Hdhba) behaves as a bidentate chelate with a single negative charge. The azomethine nitrogen and the deprotonated 2-hydroxy centres with the pendant glucosamine hydroxy functionality play no role in coordination. The dissociation constants of 2CS-Hdhba and the stability constants of some of its metal complexes have been determined pH-metrically.     

Complexes of a macrocyclic ligand having both mono- and binucleating capability: binuclear Mn(II), Fe(II), Co(II), Ni(II), Zn(II) complexes

Bi-nuclear complexes of 28- atom membered macrocycles derived from 2,6-diacetyl pyridine and the amines 3,3′-diamino dipropylamine or 3,3′-diamino-N-methyl dipropylamine have been prepared by template synthesis on Ag⁺ or Pb²⁺. Template synthesis can also be accomplished, in the case of 3,3′-diamino dipropylamine, but not its N-methyl derivative, on Gp(II) metal ions, with accompanying rearrangement of the macrocycle. All the complexes produced by template synthesis can be transmetallated with the first transition series metal ions M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II) to give binuclear and in some cases, mononuclear, derivatives. The binuclear complexes show no evidence of magnetic exchange interaction from magnetic susceptibility measurements in the range 93-300 K. The cyclovoltammetric behaviour of mono- and bi-nuclear Fe(II) complexes is compared.     

Equilibrium and structural studies on Co(II), Ni(II), Cu(II) and Zn(II) complexes with N-(2-benzimidazolyl)methyliminodiacetic acid: crystal structures of Ni(II) and Cu(II) complexes

Combined pH-metric, UV-Vis, ¹H NMR and EPR spectral investigations on the complex formation of M(II) ions (M=Co, Ni, Cu and Zn) with N-(2-benzimidazolyl)methyliminodiacetic acid (H₂bzimida, hereafter H₂L) in aqueous solution at a fixed ionic strength, I=10⁻¹ mol dm⁻³, at 25 ± 1 °C indicate the formation of M(L), M(H₋₁L)⁻ and M₂(H₋₁L)⁺ complexes. Proton-ligand and metal-ligand constants and the complex formation equilibria have been elucidated. Solid complexes, [M(L)(H₂O)₂] · nH₂O (n=1 for M = Co and Zn, n=2 for M = Ni) and {Cu (μ-L) · 4H₂O}_n, have been isolated and characterized by elemental analysis, spectral, conductance and magnetic measurements and thermal studies. Structures of [Ni(L)(H₂O)₂] · 2H₂O and {Cu(μ-L) · 4H₂O}_n have been determined by single crystal X-ray diffraction. The nickel(II) complex exists in a distorted octahedral environment in which the metal ion is coordinated by the two carboxylate O atoms, the amino-N atom of the iminodiacetate moiety and the pyridine type N-atom of the benzimidazole moiety. Two aqua O atoms function as fifth and sixth donor atoms. The copper(II) complex is made up of interpenetrating polymeric chains of antiferromagnetically coupled Cu(II) ions linked by carboxylato bridges in syn-anti (apical-equatorial) bonding mode and stabilized via interchain hydrogen bonds and π-π stacking interactions.     

The synthesis and characterisation of polyene complexes with divalent metal ions: Mg(II), Ca(II), Ni(II), Cu(II) and Zn(II)

Metal ion (Mg(II), Ca(II), Zn(II), Cu(II), Ni(II)) complexes of nystatin and amphotericin B (polyene antibiotics) have been prepared as solids. The stoichiometry of the complexes has been established. IR, ESR investigation indicates the metal-ligating sites in the polyene molecules. The existence of such complexes is discussed in the light of polyene mode- of-action theories.     

Antibacterial Co(II), Cu(II), Ni(II) and Zn(II) complexes of thiadiazole derived furanyl,thiophenyl and pyrrolyl Schiff bases

2-Amino-1,3,4-thiadiazole undergoes a condensation reaction with furane-, thiophene- and pyrrole-2-carboxaldehyde to form tridentate NNO, NNS and NNN donor Schiff bases. These Schiff bases were further used to obtain complexes of the type [M(L)2]X, where M = Co(II), Cu(II), Ni(II) or Zn(II), L = L1, L2 or L3 and X = Cl2. The new compounds described here have been characterized by their physical, spectral and analytical data, and have been screened for antibacterial activity against several bacterial strains such as Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. The antibacterial potency of the Schiff bases increased upon chelation/complexation in comparison to the uncomplexed Schiff bases against the tested bacterial species thus, opening new approaches to find new ways in the fight against antibiotic-resistant strains.     

Antibacterial Co(II), Cu(II), Ni(II) and Zn(II) Complexes of Thiadiazole Derived Furanyl,Thiophenyl and Pyrrolyl Schiff Bases

2-Amino-1,3,4-thiadiazole undergoes a condensation reaction with furane-, thiophene- and pyrrole-2-carboxaldehyde to form tridentate NNO, NNS and NNN donor Schiff bases. These Schiff bases were further used to obtain complexes of the type [M(L) 2] X, where M=Co(II), Cu(II), Ni(II) or Zn(II), L=L 1, L 2 or L 3 and X=Cl 2. The new compounds described here have been characterized by their physical, spectral and analytical data, and have been screened for antibacterial activity against several bacterial strains such as Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. The antibacterial potency of the Schiff bases increased upon chelation/complexation in comparison to the uncomplexed Schiff bases against the tested bacterial species thus, opening new approaches to find new ways in the fight against antibiotic-resistant strains.     

Iminodiacetyl-hydroxamate derivatives as metalloproteinase inhibitors: equilibrium complexation studies with Cu(II), Zn(II) and Ni(II)

Two new iminodiacetyl-hydroxamate derivatives, the N-benzyl-N-carboxymethyl-iminoacetohydroxamic acid (H(2)L(1)) and the N-benzyl-N'-hydroxypiperazine-2,6-dione (HL(2)), have been recently reported as very effective inhibitors against a set of zinc-containing matrix metalloproteinases (MMPs). Herein, aimed at understanding that inhibitory function, these compounds are studied in their complex formation equilibria with three biologically relevant first-row transition M(2+) metal ions (M=Cu, Zn, Ni) by using potentiometric and spectroscopic techniques. At physiological conditions, complexation of these metal ions by H(2)L(1) mostly occurs with formation of 1:1 species by tridentate co-ordination (O,N,N) (carboxylate-amino-hydroxamate), whereas complexation with HL(2) mainly involves the formation of 1:2 (M:L) species with normal (O,O) hydroxamate coordination. Moreover, at higher pH, H(2)L(1) is able to form a pentanuclear tetrameric copper complex with an interesting 12-metallacrown-4 structure.