Optimization of ammonium nitrate concentration in single-stage continuous cultures of Aspergillus niger with biomass retention

The effect of ammonium nitrate concentration in the citric acid biosynthesis by Aspergillus niger NC-12 in single-stage continuous cultures with biomass retention was investigated. Experiments were carried out in a BIOMER laboratory fermenter with 5 dm³ working volume. At the initial stage of each cultivation, the substrate in the bioreactor contained 1.5 g NH₄NO₃ dm⁻³. After 120 h onwards, the bioreactor was fed continuously at a constant dilution rate of 0.009 h⁻¹. NH₄NO₃ concentration in the feed was varied from one culture to another, ranging between 0.5 g dm⁻³ and 2.5 g dm⁻³. Promising results were obtained when NH₄NO₃ concentration of 1.5 g dm⁻³ was used. The observed concentration of citric acid (c _P) and yield of citric acid with respect to the introduced sucrose (Y _P/S) were 117.88 g dm⁻³ and 78.59 %, respectively. The efficiency coefficient of citric acid biosynthesis (K _ef) was very high, amounting to 83.38. Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May 2006.     

Disclosing Interfaces of ZnO Nanocrystals Using Dynamic Nuclear Polarization: Sol‐Gel versus Organometallic Approach

The unambiguous characterization of the coordination chemistry of nanocrystal surfaces produced by wet‐chemical synthesis presently remains highly challenging. Here, zinc oxide nanocrystals (ZnO NCs) coated by monoanionic diphenyl phosphate (DPP) ligands were derived by a sol‐gel process and a one‐pot self‐supporting organometallic (OSSOM) procedure. Atomic‐scale characterization through dynamic nuclear polarization (DNP‐)enhanced solid‐state NMR (ssNMR) spectroscopy has notably enabled resolving their vastly different surface‐ligand interfaces. For the OSSOM‐derived NCs, DPP moieties form stable and strongly‐anchored μ₂‐ and μ₃‐bridging‐ligand pairs that are resistant to competitive ligand exchange. The sol‐gel‐derived NCs contain a wide variety of coordination modes of DPP ligands and a ligand exchange process takes place between DPP and glycerol molecules. This highlights the power of DNP‐enhanced ssNMR for detailed NC surface analysis and of the OSSOM approach for the preparation of ZnO NCs.     

A kinetic study of the oxidation of 2-(2-hydroxyethyl)pyridine by chromium(VI) in strongly acidic aqueous solutions of HClO4

Oxidation of 2-(2-hydroxyethyl)pyridine (pyeol) to 2-pyridylacetaldehyde (pyeal) by Cr^VI has been studied in the 0.5–2.0M HClO₄ range at I=2.2M and in super acidic media within the 3–7M HClO₄ range. In all cases the reaction has been examined under pseudo-first order conditions keeping the alcohol and H⁺ _aq in excess. Cr^III-complexes formed during reduction of Cr^VI by pyeol at different molar ratios of the reactants, were isolated chromatographically and identified as [Cr(H₂O)₆]³⁺ and [Cr(pyeac)(H₂O)₄]²⁺ ions (pyeac=2-pyridylacetic acid). Free 2-pyridylacetaldehyde (pyeal) was separated and determined as its 2,4-dinitro-phenylhydrazone derivative. A dependence of the rate constants on [pyeol] and [H⁺] has been established at I=1.2M and I=2.2M. The apparent activation parameters at [H⁺]=1 and 2M have been determined. A rate law of the form d[Cr^VI]/dt= (k ₁[H ⁺]+k ₂[H ⁺]²)[pyeol][Cr^VI] is proposed. A linear dependence of log k _obs on H₀ in the super acidic media is obeyed. A rate decrease is observed if oxygen instead of argon is in the reaction cell. The reaction mechanism has been discussed.     

Rapid and Accurate Approach for Honeybee Pollen Analysis Using ED-XRF and FTIR Spectroscopy

Since honeybee pollen is considered a “perfectly complete food” and is characterized by many beneficial properties (anti-inflammatory, antioxidant, anti-bacterial, etc.), it has begun to be used for therapeutic purposes. Consequently, there is a high need to develop methods for controlling its composition. A thorough bee pollen analysis can be very informative regarding its safety for consumption, the variability of its composition, its biogeographical origin, or harvest date. Therefore, in this study, two reliable and non-destructive spectroscopy methods, i.e., ED-XRF and ATR–FTIR, are proposed as a fast approach to characterize bee pollen. The collected samples were derived from apiaries located in west-central Poland. Additionally, some commercially available samples were analyzed. The applied methodology was optimized and combined with sophisticated chemometric tools. Data derived from IR analyses were also subjected to two-dimensional correlation spectroscopy. The developed ED-XRF method allowed the reliable quantification of eight macro- and micro-nutrients, while organic components were characterized by IR spectroscopy. Principal component analysis, cluster analysis, and obtained synchronous and asynchronous maps allowed the study of component changes occurring dependently on the date and location of harvest. The proposed approach proved to be an excellent tool to monitor the variability of the inorganic and organic content of bee pollen.     

Towards Organized Hybrid Nanomaterials at the Air/Water Interface Based on Liquid‐Crystal/ZnO Nanocrystals

The ability to self‐assemble nanosized ligand‐stabilized metal oxide or semiconductor materials offers an intriguing route to engineer nanomaterials with new tailored properties from the disparate components. We describe a novel one‐pot two‐step organometallic approach to prepare ZnO nanocrystals (NCs) coated with deprotonated 4‐(dodecyloxy)benzoic acid (i.e., an X‐type liquid‐crystalline ligand) as a model LC system (termed ZnO‐LC1 NCs ). Langmuir and Langmuir–Blodgett films of the resulting hybrids are investigated. The observed behavior of the ZnO NCs at the air/water interface is rationalized by invoking a ZnO‐interdigitation process mediated by the anchored liquid‐crystalline shell. The ordered superstructures form according to mechanism based on a Z nO‐ i nterdigitation p rocess mediated by l iquid c rystals (termed ZIP‐LC). The external and directed force applied upon compression at the air/water interface and the packing of the ligands that stabilize the ZnO cores drives the formation of nanorods of ordered internal structure. To study the process in detail, we follow a nontraditional protocol of thin‐film investigation. We collect the films from the air/water interface in powder form ( ZnO‐LC1 LB ), resuspend the powder in organic solvents and utilize otherwise unavailable experimental techniques. The structural and physical properties of the resulting superlattices were studied by using electron microscopy, atomic force microscopy, X‐ray studies, dynamic light scattering, thermogravimetric analysis, UV/Vis absorption, and photoluminescence spectroscopy.     

Stereoselective formation of a P-P bond in the reaction of 2-alkoxy-2-thio-1,3,2-oxathiaphospholanes with O,O-dialkyl H-phosphonates and H-thiophosphonates

A new method for the formation of organohypophosphates containing a P-P bond under mild conditions, based on the DBU-assisted reaction of 2-alkoxy-2-thio-1,3,2-oxathiaphospholanes with O,O-dialkyl H-phosphonates or H-thiophosphonates, has been elaborated. The resulting triesters of P(1)-thio- and P(1),P(2)-dithiohypophosphoric acids, respectively, having O-methyl or O-ethyl groups, can be selectively dealkylated to form the corresponding di- or monoesters. Appropriately protected 2'-deoxyguanosine-3'-O-(2-thio-1,3,2-oxathiaphospholane) was converted into the corresponding P(1)-thio- and P(1),P(2)-dithiohypophosphate esters in a highly stereoselective manner (98%+ and 90%+, respectively).     

Preparation of the HgCr2(SexS1−x)4 type compounds and the X ray control of the process of formation of their spinel structures

Compounds of the HgCr₂(Se_xS_1?x)₄ type were prepared for 0.750 ? x ? 0.250 by thermal synthesis from parent elements. Individual reaction stages were controlled röntgenographically. The values of electrical conductivity activation energy of the compounds have been calculated and chemical analyses of the substances prepared have been developed.