Electron Spin Polarization and Time-Resolved Electron Paramagnetic Resonance: Applications to the Paradigms of Molecular and Supramolecular Photochemistry

Most molecular and supramolecular organic photochemical reactions involve paramagnetic reactive intermediates (such as molecular triplet states, triplet radical pairs, and free radicals). In a number of cases these species are created with "anomalous" spin populations which are far from thermal equilibrium. Such paramagnetic species are said to be "spin polarized" and may be observed directly by time-resolved electron paramagnetic resonance (TREPR). The TREPR technique can be applied to exploit spin polarization, which, in addition to providing an enormous signal to noise enhancement, also reveals the mechanisms involved in photochemical reactions. TREPR spectroscopy provides a means of tracking the reaction of radicals with molecules and the nonreactive interactions of radicals with other radicals in real time. The latter interactions provide a systematic investigation of supramolecular interactions of geminate radicals in micelles.     

A new proposed model of aldose reductase enzyme inhibition on the basis of an artificial intelligence approach: A computer automated structure evaluation (case) study

A large number of inhibitors of aldose reductase enzyme were submitted to the CASE (computer automated structure evaluation) program in order to ascertain the topological features relevant to activity. On the basis of the twenty-six biophores (activating fragments) and one biophobe (inactivating fragment), a new proposed interaction model was suggested for an aldose reductase enzyme with the chemical inhibitors. The critical relationship between enzyme inhibition and the structure of inhibitors is believed to depend on the relative positions of subordinate regions within the inhibitor structure.     

Optimizing control of simulated moving beds--experimental implementation

The operation of simulated moving beds (SMBs) at their optimal operating conditions is difficult and not robust. Therefore, it is common practice to operate SMB units far from their economic optimum in order to tolerate uncertainties in the system and minimize the effect of disturbances. Recently, we have proposed an on-line optimization based SMB control scheme that allows to exploit the full economic potential of SMB technology. The goal of this work is two-fold. Firstly, to experimentally evaluate and demonstrate the capability of the controller to optimize and operate the SMB units, thus delivering the products with maximum productivity and minimum solvent consumption. Secondly, to show the suitability of the controller even using a minimum of system information, thus making the detailed isotherm measurements redundant and saving time in the separation design phase. This paper reports and discusses the first experimental implementation of the control concept on a high purity separation of nucleosides (uridine, guanosine) with an eight-column four-section SMB where the species to be separated are retained on the source 30RPC stationary phase according to a linear isotherm.     

DNA sensing on glassy carbon electrodes by using hemin as the electrochemical hybridization label

The electrochemical behavior of hemin, an iron complex of porphyrin, on binding to DNA at a glassy carbon electrode (GCE) and in solution, is described. Hemin, which interacts with covalently immobilized calf thymus DNA, was detected by use of a bare GCE, a double-stranded DNA-modified GCE (dsDNA-modified GCE), and a single-stranded DNA-modified GCE (ssDNA-modified GCE), in combination with differential pulse voltammetry (DPV). The structural conformation of DNA was determined from changes in the voltammetric signals acquired on reduction of hemin. As a result of its large steric structure and anionic substitution on its porphyrin plane, hemin intercalates between the base pairs of dsDNA. A scan-rate study for hemin and the dsDNA-hemin complex were also performed to determine the electrochemical behavior of the complex. The partition coefficient was obtained from the peak currents measured when different concentrations of hemin were in the presence of dsDNA. By observing the oxidation signals of guanine, damage to DNA after reaction with hemin at the GCE surface was also detected. The electrochemical detection of hybridization between the covalently immobilized probe and its target sequence was detected by use of hemin. These results demonstrate the use of DNA biosensors in conjunction with hemin for electrochemical detection of hybridization and damage to DNA.     

The removal of textile dyes by diatomite earth

The adsorption of some textile dyes by diatomite was investigated using Sif Blau BRF (SB), Everzol Brill Red 3BS (EBR), and Int Yellow 5GF (IY). Adsorption of these textile dyes onto diatomite earth samples was studied by batch adsorption techniques at 30 degrees C. The adsorption behavior of textile dyes on diatomite samples was investigated using a UV-vis spectrophotometric technique. The effect of particle size of diatomite, diatomite concentration, the effect of initial dye concentrations, and shaking time on adsorption was investigated. Adsorption coverage over the surface of diatomite was studied using two well-known isotherm models: Langmuir's and Freundlich's. These results suggest that the dye uptake process mediated by diatomite has a potential for large-scale treatment of textile mill discharges. According to the equilibrium studies, the selectivity sequence can be given as IY > SB > EBR. Values of the removal efficiency of the dyes ranged from 28.60 to 99.23%. These results show that natural diatomite holds great potential to remove textile dyes from wastewater.     

1H MAS NMR investigations of ethylene glycol adsorbed in NaX

The application of 1H MAS NMR allows a detailed study of the behavior of ethylene glycol adsorbed in NaX zeolites which may be used to understand the effect of confinement. Typical changes in the chemical shift values for the CH2 and OH groups were found which are very sensitive to interactions between the molecules and the internal surfaces. This allows clear differentiation between molecules within the zeolite cages and those adsorbed at the outer surface of the zeolite grains and also allows study of the dynamics of the different species. Selective 1H T1 measurements were carried out for various pore-filling degrees where large differences were found in the thermal mobility. It is shown that for the molecules inside the supercages, a dynamic heterogeneity occurs which may be related to the competing influences of molecule-internal surface interactions and molecule-molecule interactions within a network of intermolecular hydrogen bonds.     

Synthesis,characterization, optimum reaction conditions,and some polymer–metal complexes of poly(phenoxy-imine)s containing furan ring

In this study, Schiff bases containing azomethine (–HC=N–) compounds were synthesized from the condensation reaction of 4-aminophenol and 2-aminophenol and 5-methyl-2-furaldehyde. Orange-colored Schiff bases, 4-[(5-methyl- 2-furyl) methyleneamino] phenol (4MFMAP) and 2-[(5-methyl-2-furyl) methyleneamino] phenol (2MFMAP) turned to poly-4-[(5-methyl-2-furyl) methyleneamino] phenol (P-4MFMAP) and poly-2-[(5-methyl-2-furyl) methyleneamino] phenol (P-2MFMAP) polyazomethine derivatives by NaOCl oxidant in alkaline aqueous medium. In addition, poly-2-[(5-methyl-2-furyl) methyleneamino] phenol cobalt (II) and copper (II) complexes were synthesized. FTIR and NMR measurements for structural analysis of the synthesized compounds, UV–Vis analysis for optical properties, electrical conductivity measurements, and thermal analysis with the TG–DTA techniques were determined. The yield of P-4MFMAP and P-2MFMAP was found to be 84.6% and 78.6 as follows [4MFMAP] = 0.066, [KOH] = 0.198 [NaOCl] = 0.066 mol L^?1 at 60 °C for 3 h and [2MFMAP] = 0.066, [KOH] = 0.132 [NaOCl] = 0.066 mol L^?1 at 70 °C for 3 h, respectively.     

Site‐Selective C−S Bond Formation at C−Br over C−OTf and C−Cl Enabled by an Air‐Stable,Easily Recoverable,and Recyclable Palladium(I) Catalyst

This report widens the repertoire of emerging Pd^I catalysis to carbon–heteroatom, that is, C?S bond formation. While Pd⁰‐catalyzed protocols may suffer from the formation of poisonous sulfide‐bound off‐cycle intermediates and lack of selectivity, the mechanistically diverse Pd^I catalysis concept circumvents these challenges and allows for C?S bond formation (S–aryl and S–alkyl) of a wide range of aryl halides. Site‐selective thiolations of C?Br sites in the presence of C?Cl and C?OTf were achieved in a general and a priori predictable fashion. Computational, spectroscopic, X‐ray, and reactivity data support dinuclear Pd^I catalysis to be operative. Contrary to air‐sensitive Pd⁰, the active Pd^I species was easily recovered in the open atmosphere and subjected to multiple rounds of recycling.