bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spectroscopic Probes Incorporated into Specific Substrates and Inhibitors of Papain for the Study of Acylenzyme Formation
Authors: Smolarsky Moshe 
Published: November 2013

Abstractα‐β‐Unsaturated aromatic amino acids such as β‐phenyldehydroalanine (PDA) or β‐styryldehydroalanine (SDA) can serve as spectroscopic probes of acylpapain formation. The spectral changes observed upon acylation of the enzyme are a large red shift of 49 nm (277 nm to 326 run) in the case of PDA, and of 59 run (318 nm to 377 nm) in the case of SDA. Using these chromophores, the following specific substrates were synthesized: Ac‐Phe‐PDA‐OEt, Ac‐Phe‐PDA‐NH2, Ala‐Ala‐Phe‐SDA‐OMe, and Ala‐Ala‐Phe‐SDA‐NH2. Similarly, the specific competitive inhibitors Ac‐Phe‐PDA (\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm (\bar K}_{\rm i} = 1.9 \times 10^5 {\rm M}^{ - 1} ) $$\end{document}) and Ala‐Ala‐Phe‐SDA (\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm (\bar K}_{\rm i} = 3.5 \times 10^4 {\rm M}^{ - 1} ) $$\end{document}) were prepared. By this method acylenzyme formation by inhibitors and substrates is demonstrated qualitatively. To make possible the independent observation of the physical binding of substrates and inhibitors to papain, an additional chromophorep(p′‐dimethylaminophenylazo)‐phenylalanine (DAP) was introduced as a second probe into the peptide. The spectrum of this chromophore is known to depend on its environment. Thus, binding to papain of the competitive inhibitor Ala‐Ala‐DAP‐SDA (\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm (\bar K}_{\rm i} = 4 \times 10^5 {\rm M}^{ - 1} ) $$\end{document}) and its corresponding amide and methylester can be observed qualitatively and quantitatively by following either the increase in absorption at 480 nm or the decrease at 550 nm. The simultaneous formation of the acylenzyme can be followed at 377 nm. The extent of acylenzyme formation was found to decrease in a sigmoidal way with increasing pH, with a transition point around pH 5.5.
Studies on the C–H/C–D Exchange in Imidazolium (Pilocarpinium) and in 2‐ and 4‐Hydroximinomethyl Pyridinium Compounds
Authors: Ben‐Bassat A. A. , Lavie D. 
Published: November 2013

AbstractThe H–D exchange of methylene protons in a side‐chain when situated between a positively charged N‐atom (α–CH2) and a ketone function was studied in various pilocarpinium (N‐methyl imidazolium) and hydroximinomethyl pyridiniums using NMR measurements. Structural factors which determine the course of the exchange are reported, and the role of the solvent was examined. Mass‐spectra of nondeuteriated and deuteriated 4‐hydroximinomethyl‐1‐phenacyl‐pyridinium chloride confirmed the fast exchange of the α–CHa. An alternative H–D exchange of the C2–H in the imidazolium moiety of certain pilocarpinium compounds without a ketone in the N‐chain was detected. Mechanisms for the two types of exchanges involving an ylid as intermediate and attack of a deuteron were proposed.
Photochemistry of α,α′‐Disubstituted Azoalkanes. I. Photosolvolytic Inversion and Substitution of α,α′‐Dichloro‐ and α,α′‐Dialkoyloxyazoalkanes
Authors: Levi Nissim , Malament Donald S. 
Published: November 2013

AbstractA series of α,α′‐dichloro (α DClA), α,α′‐dialkoyloxy‐ (αDAlA) and α,α′‐dibenzoxy‐azoalkanes (αDBeA) without α‐aryl substituents was found to undergo meso ⇄ dl photointerconversion upon direct irradiation through Pyrex in the presence of oxygen in a number of solvents. Furthermore, irradiation of α,α′‐dipropionoxy‐azoalkanes in benzene in the presence of excess acetic acid leads to substitution of the propionoxy groups by acetoxy groups in addition to meso ⇄ dl photointerconversion. Similar irradiation in the presence of CH3CO2D does not lead to deuterium substitution of the β‐hydrogens. The presence of benzenethiol radical scavenger does not affect the course of these photoreactions. Photosolvolysis schemes involving heterolysis (in the case of αDAlA and αDBeA) or an unstable intermediate (in the case of αDClA) are proposed.
Tautomerism and Ionisation of 6‐Thioxopurin‐8‐Ones. A Contribution to the Behaviour of 6‐Thiopurines
Authors: Rahat Miriam , Bergmann Felix , Tamir Ilana 
Published: November 2013

AbstractThe neutral molecules of 6‐thioxopurin‐8‐ones are present in aqueous solution as lactams‐thiolactams. However, 6‐SH‐tautomers may be present in the anions of the 1‐ and 9‐methyl derivatives. The sequence of dissociation of the NH‐groups is 1 → 9 → 7. Ionisation of the 9‐NH‐group is greatly facilitated in the 3‐methyl derivatives, leading to pK values of about 5. Protonation of the 3‐methyl derivatives takes place predominantly at N‐1 with the formation of “fixed”, amidinium‐like, cations. In all other members of the series, protonation involves mainly the 8‐oxo group. In 3,9‐dimethyl derivatives, the NMR signals of both methyl substituents are markedly deshielded. The behavior of 6‐thioxopurin‐8‐ones resembles that of 6‐thiopurines and 6‐thioxanthines.
Laser Raman Spectra and Structure of Halogen Nitrates (FONO2 and ClONO2)
Authors: Shamir J. , Yellin D. , Claassen H. H. 
Published: November 2013

AbstractThe laser Raman spectra of halogen nitrates were recorded and polarization measurements performed. Out of the nine expected fundamentals, eight were observed and the ninth deduced from its overtone. From the number of depolarised lines and their width, it was concluded that these molecules are of a non‐planar structure of C1v symmetry.
Topochemistry. Part XXXVII. The Crystal Structure of Dibenzoyldiimide
Authors: Bart J. C. J. , Schmidt G. M. J. 
Published: November 2013

AbstractThe crystal and molecular structures of dibenzoyldiimide, C6H5CO–N = N–COC6H5, have been determined by SEARCH as part of a study of the solid state photochemistry of α‐carbonyl‐azo‐compounds. Partial three‐dimensional data were refined with anisotropic temperature factors of the heavy atoms to r = 0.031 and R = 0.080. The bond lengths and angles have been measured with estimated standard deviations of 0.01 A and 0.6°. As the result of rotation around the C–N bonds, the interplanar distance of the parallel benzoyl groups of the (centro‐symmetric) trans‐molecule is 1.02 Å. Photochemical rearrangement paths are discussed in terms of contact geometry.
Alkyl Inductive Effects on Molecular Ionization Potentials. XIV. Amides
Authors: Widing H. F. , Levitt B. W. , Levitt L. S. 
Published: November 2013

AbstractCorrelation of molecular ionization potentials, EI, with Taft's alkyl inductive substituent constants, σI(R), has now been extended to include the amides. It is found that two series of amides, the formamides and acetamides, fall on two separate straight lines in accord with the general equation EI = Eo + aI σI(R), where Eo is the intercept (EI for the parent compound), and aI the slope. Evidence is deduced for the site of electron expulsion and a prediction is made concerning the site of vapor phase protonation of the amides.
The Action of Atomic Hydrogen on Bovine Carbonic Anhydrase in Aqueous Solution
Authors: Lanir A. 
Published: November 2013

AbstractThe action of atomic hydrogen on bovine carbonic anhydrase in aqueous solution has been investigated at different total doses of H atoms. The rate of inactivation of the enzyme is (5.0 ± 0.5) × 107 liter mole−1 s−1. Concurrent with the inactivation of the enzyme, specific changes in the ultraviolet absorption spectrum have been observed. The observed decrease of the 280 nm absorption peak is consistent with attack on the tryptophan residues. H atoms were found to react faster with apocarbonic anhydrase than with the native enzyme. Sulfonamide inhibitor did not protect the tryptophan residues in the enzyme from the action of hydrogen atoms.
The Reaction of Bacterial Catalase with H2O2
Authors: Kremer M. L. 
Published: November 2013

AbstractThe kinetics of the reaction of bacterial catalase with H2O2 has been examined. By applying a non‐steady state analysis, the formation curve of the transient intermediate and the kinetics of its formation have been explained. The discussion has been based on the peroxidatic model of catalase action. The rate constants of the reaction are

The (corrected) spectrum of the transient intermediate has been evaluated.
The Nature of the Ionic Dissociation of Salicylhydroxamic Acid
Authors: Bergmann Ernst D. , Tashma Zeev , Katzhendler Jehoshua 
Published: November 2013

AbstractThe double ionization of salicylhydroxamic acid has been studied. Kinetic and spectrophotometric experiments show that the first dissociation originates from the phenolic OH group, the second dissociation is related to the –CONHOH group.
An Orbital Interaction Rationale for Organic Molecules and Reactions
Authors: Fukui Kenichi 
Published: November 2013

AbstractThe important role of the interaction of particular molecular orbitals (MO), the highest occupied (HO) and the lowest unoccupied (LU)MO's, in the problem of the molecular structure and the chemical reaction is well authenticated. The rationale of the HOMO‐LUMO interaction between two molecules is extended to the case of the three‐molecule interaction and to the theory of intermediate action of the third species as a catalyst in the two molecule reaction. The favourable modes of orbital interaction in three systems can simply be represented by the schemesmagnified imagein which—signifies an in‐phase overlapping and—means an out‐of‐phase overlapping. The theoretical basis for this conclusion and various examples of applications are given including the stabilization of a molecule by intramolecular orbital interactions, the process of simultaneous shift of three or more bonds, and the catalysis by transition metal complexes.
On the Stereochemistry of Energy Transfer — the Dual Phosphorescence of 1‐Indanones
Authors: Schaffner Kurt , Amrein Walter , Larsson Inga‐Mai 
Published: November 2013

AbstractThe results of a stereochemical study of the intramolecular triplet energy transfer between indanone (donor) and naphthalene (acceptor) groups are discussed. Two diastereoisomeric spatial arrangements were chosen in which the donor occupies the endo and exo configuration, respectively, on conformationally rigid bicyclic frames 1,8‐ and 2,3‐annelated to naphthalene. In the endo geometry a transfer route via a triplet donor‐acceptor exciplex specific to through‐space interaction between the two π systems (providing for additional radiationless T → S deactivation) is proposed to compete with an efficient through‐α‐bond exchange transfer mechanism operative in both the endo and exo arrangements. In connection with this study the dual phosphorescence phenomenon of 1‐indanone was reinvestigated. It was found that the favored intersystem crossing routes are S1 (n, π*) → T(n, π*) and S2,3 (π,π*n) → T(π,π*) and that internal conversion to S1 competes efficiently with S(π,π*) → T(π,π*) intersystem crossing only from higher vibrational levels of the S2 and S3 states.
Recent Development in the Chemotherapy of Mycobacterial Infections
Authors: Sensi P. , Terenzi E. 
Published: November 2013

AbstractIn the past three decades, several drugs have been proved to be highly effective in the therapy of the mycobacterial infections (tuberculosis, leprosy, atypical mycobacteriosis). In spite of these successes, mycobacterial infections are still a world health problem. The search for new antimycobacterial agents is necessary due to the increasing resistance of mycobacteria to the available drugs, the increasing frequency of atypical mycobacteriosis, the unsatisfactory status of leprosy treatment and the various and sometimes serious side effects of the available drugs. Most of the presently used antitubercular agents represent the result of a large screening program leading to the selection of active compounds, followed generally by chemical modification of the selected substances, in order to optimize their therapeutic efficacy. There is no doubt that this approach, so fruitful in the past, will be also followed in the future. In the case of antileprous drugs, their selection was generally done among antitubercular substances, the screening and evaluation tests for antileprous activity being too time consuming. Recent studies on specific constituents of the mycobacterial cell, such as the mycolic acids, the toxic principles (cord factor), the growth factors (mycobactins) and specific enzymes might give the possibility of a rational approach to new antimycobacterial drugs. Also the studies on the mechanism of action of the main drugs already used in therapy and on the mycobacterial resistance to them could possibly give leads for the search for new products overcoming the resistance mechanisms.
Formation of Reactive Drug Metabolites as a Basis of Drug Action and Toxicity
Authors: Gillette James R. 
Published: November 2013

AbstractMost drugs are converted by diverse reactions to various metabolites before they are eliminated from the body. Many of these metabolites cause pharmacologic or toxicologic effects, some of which may differ from those of the parent drug. Some metabolites are chemically inert and, therefore, exert their effects by combining reversibly with specific receptor sites in target organs. But some drug metabolites are chemically reactive and exert their effects by combining covalently with various macromolecules in tissues. The formation of chemically reactive metabolites is important because they frequently cause a number of different toxicities, including tumorogenesis, mutagenesis, tissue necrosis, and hypersensitivity reactions. For example, my colleagues have discovered that the liver necrosis caused by halogenated benzene derivatives, paracetamol, furosemide, and isoniazid is mediated by chemically reactive metabolites of these substances. In assessing the effects of various treatments that alter drug metabolism on the magnitude of covalent binding, we have found it useful to think of the incidence of toxicity as the product of several ratios, i.e., Incidence = Dose AB …. MP. When the foreign compound is converted directly to a chemically reactive metabolite, (A) is the proportion of the dose that is converted to the reactive metabolite, (B) is the proportion of the reactive metabolite that becomes covalently bound, (M) is the proportion of the covalently bound metabolite that combines with “target macromolecules”, and (P) is the probability that a given amount of covalently bound metabolite attached to target macromolecule will result in toxicity. With this concept it becomes evident that the magnitude of covalent binding depends on the rate of formation of the reactive metabolite, on the rate at which the parent drug is eliminated from the body by other processes, on the rate at which the reactive metabolite is covalently bound, and on the rate at which it is inactivated by other processes.
Waste Exchange as a Solution to Industrial Waste Problems
Authors: Müller Ilse , Schottelius Dieter 
Published: November 2013

AbstractThe waste exchange systems, very popular in Europe and in Japan, are important as centres for exchanging industrial residues and information. Through their activity they promote the re‐use and recycling of substances which otherwise would be disposed of as wastes, and thus help to reduce the waste volume. The European waste exchange centres are described and the problems arising in the re‐use and recycling of residues discussed. It turns out that recycling is counteracted by the careless mixing of different residues as well as by the increasing tendency to more heterogenous products and materials. In modern waste economy the technical and economical factors are decisive factors involved in reducing the waste volume, sparing resources and protecting the environment. Accordingly, industry should be left enough room in this field to develop new means and concepts in free enterprise.
Adsorption and Molecular Structuring at the Solid/Liquid Interface
Authors: Everett D. H. 
Published: November 2013

AbstractAdsorption at the solid/liquid interface plays a decisive role in a wide range of phenomena including the stabilisation of colloidal dispersions, clarification and purification of liquid media (e.g., oil, sugar, liquors, wine), lubrication, and crystal habit modification. Not only the extent of adsorption but the chemical nature and the structure of the adsorbed layer is important. In recent years increasing interest has been attached to the study of molecular structuring phenomena in adsorbed layers. In aqueous media adsorption studies are complicated by the simultaneous influence of elecrical double layer effects, so that, so far, most progress has been made in nonaqueous media. This paper surveys briefly the general problems, and discusses in particular the structuring of n‐alkanes, n‐alkanols and n‐alkanoic acids from the pure liquids and from solution at carbon surfaces. Consideration is given to the possibility that similar phenomena may occur at the aqueous solution/solid interface.
Chiroptical Properties of Optically Active (−)Poly [N‐(sec‐Butyl)‐N‐Methyl Acrylamide] with Regard to Amide Chromophores
Authors: Braud Christian , Vert Michel 
Published: November 2013

AbstractUV, ORD and CD spectra of (−)poly[N‐(sec‐butyl)‐N‐methyl acrylamide] (II) in methanol, dioxane and hexafluoro iso‐propanol were investigated. CD spectra were resolved into gaussian Cotton bands. Three Cotton effects were found in the 185–250 nm spectral range, a small one at about 230 nm which was assigned to a n → π* transition and two larger ones, of opposite signs, respectively located at ≃ 205 and ≃ 195 nm. For such a non‐stereoregular and non‐rigid polymer, exciton splitting cannot be taken into consideration to explain the presence of two opposite sign Cotton effects in the usual π → π* transition spectral range. Chiroptical properties of polymer (II) were compared to those of (+)N‐(sec‐butyl)‐N‐methyl iso‐butyramide taken as a suitable model for the monomeric unit of the polymer. The corresponding secondary amide, (+)N‐(sec‐butyl)iso‐butyramide, was also considered in order to show the effect of the nitrogen atom substitution on the UV and CD spectra and thus on the electronic transitions of the amide chromophore. According to the chiroptical properties of the model compounds and to a discussion based on the literature, the negative Cotton effect found at about 205 nm in the three solvents was assigned to the π1 → π* transition. The positive one found at about 195 nm was considered as resulting from either the π2 → π* or a n → σ* transition usually located at shorter wavelengths in the far UV but red‐shifted in the present case by the disubstitution of the nitrogen atom of the amide chromophores and by the bulkiness of the polymer chain.
Chiroptical Properties of Phorbol‐12, 13, 20‐triacetate and Some Other Phorbol Derivatives
Authors: Snatzke Günther , Hruban Ladislav , Snatzke Feliksa , Schmidt Rainer , Hecker Erich 
Published: November 2013

AbstractThe CD spectra of phorbol and of some of its derivatives, such as its 12, 13, 20‐triacetate 1, show at least four bands. Three of them (called I, III, and IV) correspond to the R‐, K‐, and (perhaps) second n → π*‐transition, respectively, of the enone system; the fourth band around 260 nm (band II) is of π → π*‐origin and could be ascribed to an interaction of the lone pair of electrons on the oxygen atom at C(4) with the C=C‐C=O system. The signs of the R‐band as well as the K‐band Cotton effects are very sensitive to chemical modifications around the chromophoric system in the cyclopentenones investigated. The absolute configuration of phorbol may be derived from the CD spectra of some of its derivatives, and, in particular, from the application of the “dibenzoate rule” to 12, 13‐di‐O‐benzoyl phorbol‐20‐acetate (4).
Ligand Field Parameters
Authors: Bertini Ivano , Gatteschi Dante , Scozzafava Andrea 
Published: November 2013

AbstractThe more common Ligand Field parameterizations have been reviewed and the conditions under which the various schemes are equivalent have been discussed. The relations among equivalent sets of parameters have been tabulated. Attempts to give a physical meaning to the parameters as they derive from the characterization of various physical properties of related compounds have been critically reviewed.
21,20‐Anhydromelianone and Melianone from Simarouba amara (Simaroubaceae); Carbon‐13 NMR Spectral Analysis of Δ7‐Tirucallol‐Type Triterpenes
Authors: Polonsky Judith , Varon Zoia , Rabanal Rosa M. , Jacquemin Henry 
Published: November 2013

AbstractFurther examination of the hexane extract of the root bark of Simarouba amara (Simaroubaceae) has led to the isolation of two side chain oxygenated Δ7‐tirucallol‐type triterpenes in addition to the already reported compounds 4 and 5. One has been found to be identical with the known melianone 8 and the second is a new compound and has been shown to be 21,20‐anhydromelianone 11. The 13C‐NMR spectra of nine Δ7‐tirucallol derivatives have been analysed and the data obtained have been applied to the confirmation of the structure of the new substance 11.
Coherent Transient Excitation and Superposition of Adiabatic States
Authors: Friedmann H. , Wilson‐Gordon A. D. 
Published: November 2013

AbstractDouble resonance, resonance Raman and resonance fluorescence are discussed in terms of a superposition of adiabatic states. The adiabatic states are the instantaneous eigenstates of a two‐level Hamiltonian which includes the interaction with a near‐resonant coherent pulse and which has been transformed by a unitary transformation so that its only time‐dependence is that of the field envelope of the pulse. Resonance Raman results from spontaneous transitions to a third, lower state from the adiabatic following state which reduces to the initial (lower) state of the two‐level system in the absence of radiation. Resonance fluorescence is produced by spontaneous transition to the lower third state from the upper adiabatic state which reduces to the upper state of the two‐level system in the absence of radiation. Differential equations allowing the calculation of the probability amplitudes of the adiabatic states are given and a method of solving these equations by successive approximation is proposed. Saturation effects such as dynamic Stark shift and splitting (Autler—Townes effect) and optical nutation are interpreted in terms of perturbation of adiabatic energy levels and interference effects between adiabatic states. The possibility of observing optical nutation in a two‐level system by using time‐resolved double resonance experiments is suggested. Decay of the states of the two‐level system is taken into account leading to extended adiabaticity conditions which show that adiabatic following becomes possible even at resonance. For weak fields it is shown that adiabatic following at resonance can produce light scattering narrower than the linewidth as predicted by Heitler. The adiabatic states theory has also been extended to near‐resonance multiphoton interaction for systems that can be described by an effective two‐level Hamiltonian.