EPR study of some irradiated food enzymes

The EPR spectra of three types of amylases (microbial and fungal α-amylase E.C. 3.2.1.1; gluco-amylase E.C. 3.2.1.3) and one type of pectinase irradiated with gamma-rays and 7 MeV electrons are presented and discussed. For all enzymes, a positive correlation (r = 0.991 to 0.994) between the EPR signal amplitude and absorbed dose has been observed, while, between EPR spectra amplitudes and enzyme in vitro activity, in terms of enzymatic activity a negative correlation (r = -0.987 to -0.995), has been noticed. These facts recommend that enzyme damage during irradiation can be monitored by means of the free radicals detected by EPR spectroscopy. This revised version was published online in July 2006 with corrections to the Cover Date.     

Compound I in heme thiolate enzymes: a comparative QM/MM study

This study directly compares the active species of heme enzymes, so-called Compound I (Cpd I), across the heme-thiolate enzyme family. Thus, sixty-four different Cpd I structures are calculated by hybrid quantum mechanical/molecular mechanical (QM/MM) methods using four different cysteine-ligated heme enzymes (P450(cam), the mutant P450(cam)-L358P, CPO and NOS) with varying QM region sizes in two multiplicities each. The overall result is that these Cpd I species are similar to each other with regard to many characteristic features. Hence, using the more stable CPO Cpd I as a model for P450 Cpd I in experiments should be a reasonable approach. However, systematic differences were also observed, and it is shown that NOS stands out in most comparisons. By analyzing the electrical field generated by the enzyme on the QM region, one can see that (a) the protein exerts a large influence and modifies all the Cpd I species compared with the gas-phase situation and (b) in NOS this field is approximately planar to the heme plane, whereas it is approximately perpendicular in the other enzymes, explaining the deviating results on NOS. The calculations on the P450(cam) mutant L358P show that the effects of removing the hydrogen bond between the heme sulfur and L358 are small at the Cpd I stage. Finally, Mossbauer parameters are calculated for the different Cpd I species, enabling future comparisons with experiments. These results are discussed in the broader context of recent findings of Cpd I species that exhibit large variations in the electronic structure due to the presence of the substrate.     

A comparative study of some hydroxyanthraquinones as acid-base indicators

Alizarin, Alizarin S, quinizarin and quinalizarin have been compared as acid-base indicators with Bromocresol Green and Methyl Orange as reference indicators. The chromaticity co-ordinates, complementary chromaticity co-ordinates, pK(a) values, transition pH-range, pH of maximum colour change, optimum concentration for titrations and the quality of colour change were determined. The results show all four to be good indicators with a colour change quality similar to that of Bromocresol Green.     

Labelling of castor oil for myocardial study

The labelling of castor oil, hydrolyzed castor oil and oleic acid by iodine monochloride and chloramine-T has been investigated. The effect of iodinating agent and concentration of castor oil on labelling yield has been studied. A comparative pharmacological study with analogous aliphatic fatty acids was caried out. Castor oil labelled with iodine monochloride concentrates in heart and liver in good proportion, better than other natural fatty acids and nearly equal to analogous fatty acids. Infrared study revealed that the OH group in ricinoleic acid may protect the¹²⁵I added across the double bond with minor changes in biochemical properties and better extraction by the muscle of the heart.     

A comparative study of the photosensitizing characteristics of some cyanine dyes

The present work has been carried out to explore the potential application of cyanines in photodynamic therapy. After photosensitization, the in vitro cytotoxic and antiproliferative activity on HeLa cells of a total of 35 cyanines belonging to several chemical subgroups is explored. Most of these cyanines have never been used before in similar experimental work. From a first set of experiments, it is found that none of the krypto-, oxa- and imidacyanines is photobiologically active on HeLa cells. Conversely, five thiacyanines (Thiacl-5), one rhodacyanine (Rhodac) and four indocyanines (Indoc2, Indoc4, Indoc5, Indoc7) show photodependent cytotoxicity or antiproliferative effects. A more detailed study shows that out of the ten selected compounds, eight cyanines feature significant photodependent cytotoxic and antiproliferative effects. All possess maximum absorption ranges between 545 and 824 nm. In particular, Rhodac, a tetramethinemeromonomethine rhodacyanine dye with an absorption maximum of 655 nm (ethanol) and a molar absorption coefficient epsilon = 108000 shows very promising photo-dependent biological activity. In general, the measured singlet oxygen quantum yield of the selected cyanines is low (< 0.08) and does not correlate with the degree of photosensitization. Furthermore, the present study shows that cyanines with a partition coefficient close to 1.5 accumulate to the highest extent in HeLa cells, while the more hydrophobic compounds (e.g., indocyanines) concentrate less intracellularly.     

A comparative study of the dipole polarizability of some Zn clusters

We have employed a hierarchy of basis sets and computational techniques in order to approach the polarizability (alpha) of Zn(m), m = 2-20, in a systematic way. This procedure allows the proper approximate results to be selected and validated. More specifically, we have developed in a systematic way a series of basis sets that have been employed for the computation of the polarizability of the Zn atom. Comparison of the computed with the experimental and the best theoretical results allows us to comment on the quality of the basis sets, and to select some of the more successful ones in order to compute the polarizabilities of Zn(m), m = 2-20. We have employed a series of methods to take into account the correlation contribution. These include the following techniques: MP2, CC2, CCSD, CCSD(T), and DFT(B3LYP). We have used two effective core potentials, one small (3s2 3p6 3d10 4s2) and one large (4s2) core. The relativistic contribution to the properties is found to be significant. Thus we have studied in detail the relativistic effects on the polarizability of some small zinc clusters, by employing the Douglas-Kroll approximation in connection with the polarized basis sets developed by Kell? and Sadlej and the methods HF, CC2, and CCSD. Most of the polarizability values are static, but some frequency-dependent properties have also been computed in order to find out the difference between the dynamic and static ones. It is considered that the sharp changes of alpha(Zn(m))/m vs m may be correlated with the change of bonding, from van der Waals to covalent and finally to metallic bonding, in Zn(m). The present comprehensive study of the polarizabilities of Zn(m) includes a limited number of results for the first and second hyperpolarizability of some of the considered zinc clusters.     

Protection and Labelling of Thymidine by a Fluorescent Photolabile Group

A fluorescent photolabile group including coumarin and MeNPOC moieties was synthesized to protect 5′‐OH terminal function of thymidine (T). Its photochemical and photophysical properties were studied, in particular the photocleavage (photodeprotection under a 365‐nm irradiation) is only lowered by a factor of two by addition of the fluorophore. Fluorescence properties of the coumarin probe are not changed upon irradiation, which is satisfactory for the application required, i.e., in situ synthesis of DNA microarrays.     

A comparative study of some oxygen and sulphur substituted alkyl radicals

Several sulphur containing alkyl radicals have been generated and their ESR spectra and hyperfine coupling constants compared with those of the oxygen analogues. Deviations from planarity are smaller when a tervalent carbon atom is bonded to sulphur than when bonded to oxygen. Moreover greater delocalization of the unpaired electron is apparent in the sulphur radicals and this leads to higher barriers to internal rotation in radicals of the form H₂SR compared with H₂OR.     

An unusual rearrangement in the iodination of some 1-allyl- and 1-benzylcyclopropenes

Iodination of selected 1-allyl- or 1-benzyl-cyclopropenes with electron-donating groups on the substituent leads to 2-iodo-1-iodomethyl-1 -vinyl or 1-arylcyclopropanes.     

A comparative study of the histones of some varieties of cotton plant

Tetraploid varieties of the cotton plant belonging to the medium- and thin-fibered types have been studied with respect to their histone/DNA ratio, their content of histone fractions, and the amino acid composition of the total histones. It has been shown that these varieties differ with respect to their contents of the lysine-rich histone fraction Hl, and also by the amounts of certain amino acids in the total histone.V. I. Nikitin Institute of Chemistry, Academy of Sciences of the TadzhSSR, Dushanbe. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 99–102, January–February, 1985.     

A comparative study on the thermal decomposition of some transition metal carboxylates

Thermal decomposition of transition metal malonates, MCH₂C₂O₄?xH₂O and transition metal succinates, M(CH₂)₂C₂O₄?xH₂O (M=Mn, Fe, Co, Ni, Cu, Zn) has been studied employing TG, DTG, DTA, XRD, SEM, IR and Mössbauer spectroscopic techniques. After dehydration, the anhydrous metal malonates and succinates decompose directly to their respective metal oxides in the temperature ranges 310–400 and 400–525°C, respectively. The oxides obtained have been found to be nanosized. The thermal stability of succinates have been found to be higher than that of the respective malonates.     

One- and two-photon spectra of some selected molecules: A comparative study

The complementarity of one- and two-photon spectroscopy has been utilised for throwing light on the following problems of chemical interest: (1) Weak interaction between identical chromophores separated by insulating bridges gives rise to split states of different symmetries. Two-photon spectroscopy (TPA), in conjunction with one-photon absorption (OPA), has been used to identify the states and hence to estimate the magnitude of interaction in bimolecules and trimolecules. From the shifts between the one- and the two-photon spectra, the splittings have been estimated. Calculations confirm that the dominant interaction is the through-bond one. (2) The second type of problem is the identification ofg andu vibrations in molecules. We have initiated studies on three molecules in jet-cooled conditions: 9,10-dihydro-anthracene (DHA). 9,10-dihydro-phenanthrene (DHP) and octa-fluoronaph-thalene (OFN). Only the one-photon fluorescence excitation spectra have so far been obtained by us and the TPA spectra are under investigation. (3) The third class of molecules discussed here are the Ln³⁺ complexes wheref ⁿ⇒ fⁿ transitions are intrinsically two-photon allowed. We have studied two GD³⁺ single crystals. The CF-splittings, observed clearly in TPA, have been fitted with a parametric model. Some of our observations on the variations of TPA intensity patterns from crystal to crystal, such as circular:linear polarisation ratios, relative intensities of transitions to differentJ-states, do not quite fit in with the Axe-Judd-Downer model. The discrepancies call for a reappraisal of the role of ligand in the TPA process.     

Differential electrolytic potentiometric determination of some amino acids in dosage forms

The application of direct-current differential electrolytic potentiometry to the nonaqueous titration of amino acids was investigated. The basic character of amino acids in acetic acid was enhanced to permit their direct titration with perchloric acid. A pair of antimony electrodes was used as an indicating system. The shapes of the titration curves obtained were almost symmetrical with sharp peaks. The optimum current density for those titrations was found to be 1-2 microA/cm2. The procedure was applied successfully to the determination of certain amino acids in drug formulations, and the results were favorably compared statistically with those obtained by official methods.     

Structure activity relationship by NMR and by computer: a comparative study

There has recently been considerable interest in using NMR spectroscopy to identify ligand binding sites of macromolecules. In particular, a modular approach has been put forward by Fesik et al. (Shuker, S. B.; Hajduk, P. J.; Meadows, R. P.; Fesik, S. W. Science 1996, 274, 1531-1534) in which small ligands that bind to a particular target are identified in a first round of screening and subsequently linked together to form ligands of higher affinity. Similar strategies have also been proposed for in silico drug design, where the binding sites of small chemical groups are identified, and complete ligands are subsequently assembled from different groups that have favorable interactions with the macromolecular target. In this paper, we compare experimental and computational results on a selected target (FKBP12). The binding sites of three small ligands ((2S)1-acetylprolinemethylester, 1-formylpiperidine, 1-piperidinecarboxamide) in FKBP12 were identified independently by NMR and by computational methods. The subsequent comparison of the experimental and computational data showed that the computational method identified and ranked favorably ligand positions that satisfy the experimental NOE constraints.     

Bioelectrochemical application of some PQQ-dependent enzymes.

This paper focuses on the use of PQQ-dependent enzymes (PQQ enzymes) in amperometrical biosensors and gives emphasis on their innovative designs and applications. The study covers some aspects in the evolution of biosensors based on PQQ enzymes. Main attention is focused on the electrochemical properties of PQQ enzymes as very promising materials for the formation of electrochemical biosensors. Immobilization approaches and redox mediators recently used in PQQ enzymes based biosensors are reviewed. The acceptance of polypyrrole as a very promising immobilization matrix for some PQQ enzymes is discussed.     

Interactions between carbonic anhydrase and some decarboxylating enzymes as studied by a new bioelectrochemical approach.

This work presents the results of a study, carried out by recently developed amperometric bioelectrodes, on the interactions between carbonic anhydrase (CA) and the decarboxylating enzymes arginine decarboxylase (ADC), L-lysine decarboxylase (LDC), and L-ornithine decarboxylase (ODC). These are all pyridoxal-phosphate dependent enzymes and catalyze the decarboxylation reaction of the respective amino acids, to give carbon dioxide and the corresponding diamine (agmatine, cadaverine, and putrescine, respectively). The rate of each decarboxylase catalyzed reaction was measured by monitoring the production of the respective diamine by a plant tissue diamino oxidase (DAO) based bioelectrode. DAO is the enzyme which catalyzes the oxidation of agmatine, cadaverine, and putrescine with the production of NH and H2O2. DAO-based bioelectrodes consist of an amperometric H2O2 electrode, coupled to the biocatalytic membrane formed by a whole plant tissue (lentil cotyledon) containing the enzyme DAO, immobilized on a dialysis membrane by polyazetidine prepolymer (PAP). The bioelectrodes were calibrated and characterized in standard solutions of agmatine, cadaverine, and putrescine. Kinetic studies to measure decarboxylase activity were performed in the presence of different concentrations of ADC, LDC, and ODC, resulting in a lowest detection limit of 10, 25, and 10 U l(-1), respectively. The effect of bovine CA II (bCAII) was evaluated in the presence of 500 U l(-1) of each decarboxylase, showing a marked increase of the rate of the decarboxylation reaction. These results suggest that (i) CA can be used to enhance the performance of decarboxylase-based biosensors, and (ii) it possibly plays further physiological roles, acting synergistically, at specific cellular and subcellular sites, with low-activity decarboxylating enzymes.     

A comparative study of the aromaticity in some typical conjugated six-membered rings by the method of localized molecular orbital

The localized molecular orbitals and energy levels for four typical conjugated six-membered ring systems C₆H₆, C₃N₃H₃, B₂N₈H₄, and (B₂O₄)^3- as well as a non-aromatic reference molecule P_a-N₃Cl₆ have been calculated by using Edmiston- Ruedenberg energy localization technique under the CNDO / 2 approximation in order to investigate the nature of aromaticity or quasi-aromaticity of the six-membered ring systems studied. The contour maps for x-type localized MO's (LMO) have been plotted to illustrate the bonding characteristics of the five ring systems studied. These LMO calculations show that for all the conjugated six-membered ring systems considered there exists local delocalization of x-bonds or three-centered and occasionally four-centered two-electron x-bonds in our terminology, and the cooperative effect among these x-bonds leading to the formation of a closed continuous x-conjugation system around the ring, which is necessary for the creation of aromaticity in the systems studied. We have been able to discuss the properties of these three-centered x-bonds in terms of the constituent atoms and electrons and the relevant orbitals involved.     

Electronic structure of Li-intercalated oligopyridines: a comparative study by photoelectron spectroscopy

The role of nitrogen in the charge transfer and storage capacity of lithium-intercalated heterocyclic oligophenylenes was investigated using photoelectron spectroscopy. The development of new occupied states at low binding energies in the valence band region, as well as core level chemical shifts at both carbon and nitrogen sites, demonstrates partial charge transfer from lithium atoms to the organic component during formation of the intercalated compound. In small compounds, i.e., biphenyl and bipyridine derivatives, the position of the nitrogen heteroatom significantly affects the spacing between gap states in the Li-intercalated film; yet it has minimal effects on the charge storage capacity. In larger, branched systems, the presence of nitrogen in the aromatic system significantly enhances the charge storage capacity while the Li-N bond strength at high intercalation levels is significantly weakened relative to the nitrogen-free derivative. These observations have strong implications towards improved deintercalation processes in organic electrodes in lithium-ion batteries.