bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic Patterns in Active Transport
Authors: Blumenthal Robert P.
Published: November 2013

A model for active transport is presented based on experiments of sugar uptake across bacterial membranes. The transport proteins in the membrane are assumed to undergo cooperative conformational changes, while mediating the active transport. When the nonlinear active transport flow is kinetically coupled to other flow processes such as passive diffusion or metabolic reactions, the system will exhibit interesting dynamically patterned behavior: multiple steady state transitions, overshoots with respect to the build up of the concentration within the cell resembling action potentials in nerve membranes, and spatial patterns of the transported species along the surface of the membrane. Some consequences of these dynamic processes are discussed.
Unusual Features of the Structure of the Major RNA Component of the Larger Subribosomal Particle of the Rabbit Reticulocyte
Authors: Cox Robert A. , Hüvös Piroska , Godwin Elizabeth A.
Published: November 2013

The major RNA moiety of the larger subribosomal particle of the rabbit reticulocytes was subjected to partial hydrolysis by RNase T1. The fragments were separated first by gel filtration and then by zonal centrifugation. The fractions so obtained were analysed for molecular weight, nucleotide composition and for “melting” properties (E vs. temperature). The largest fragments (ca. 400,000 daltons) that were obtained had a high G + C content (ca. 78%). Fragments of this size appear to account for most of ca. 78% G·C basepairs which comprises ca. 40% of the intact molecule. Melting properties of reticulocyte RNA were compared with those of rRNA of the larger subribosomal particle Escherichia coli, Bacillus stearothermophilus and Xenopus laevis. The possible evolutionary significance of the unusual distribution of nucleotides within the polynucleotide chain of the RNA moiety of the larger subribosomal particle of reticulocytes is discussed.
Synthesis and Conformational Studies of Model Histones: II Sequential and Random Polypeptides with the Composition L‐Lysyl:L‐Alanyl:L‐Proline
Authors: Cernosek Stanley F. , Wells Margarete , Fasman Gerald D.
Published: November 2013

The sequential polytripeptide (Lys‐Ala‐Pro)n and the random polypeptide (Lys36.2 Ala32.5 Pro31.3)n were synthesized as model histones to be used in studying the structure and interactions of nucleohistone complexes. The CD spectra of (Lys‐Ala‐Pro)n in aqueous solutions, at both pH 7 and 11, as well as in HFIP, TFA, and 1 M SDS (pH 7), indicated that this polytripeptide only assumed the random coil conformation under all these conditions. In aqueous solution, the CD spectra of the random sequence polypeptide indicated that this polymer undergoes a pH‐dependent random coil‐helix transition as the pH is raised from 7 to 11. This polymer was also partially helical in TFE. The observation that the random polymer can assume a regular, asymmetric structure may be due to a clustering of lysyl and alanyl residues at one end of the polymer because of the faster incorporation of Pro than Lys or Ala, as indicated by their respective kinetics of polymerization. The random conformation of the sequential polypeptide, (Lys‐Ala‐Pro)n, is probably determined by the presence of Pro at regular intervals. It is concluded that the sequential polymer (Lys‐Ala‐Pro)n is a plausible model histone for use in studying the influence of amino acid sequence and composition on the structure and interactions of nucleohistone complexes.
Conformational Stability, Partial Specific Volumes and Spectroscopic Properties of Poly‐L‐Proline, Poly‐L‐Hydroxyproline and Some of Its O‐Acyl‐Derivatives in Various Solvent Systems
Authors: Knof Siegward , Engel Jürgen
Published: November 2013

Circular dichroism spectra indicate that poly(Pro), poly(Hyp), poly(O‐acetyl Hyp), poly(O‐benzoyl Hyp) and poly(O‐phenacetyl Hyp) form the polyproline‐II‐conformation (all peptide bonds trans) in solvents that form hydrogen bonds with the peptide carbonyl groups. With the exception of poly(Hyp) the I‐helix of these derivatives is stable in more inert solvents like pyridine, di‐ and trichloromethane, dimethylformamide, and N‐methyl‐2‐pyrrolidone. Whereas the CD spectrum of poly (O‐benzoyl Hyp) is governed by large aromatic contributions, poly(O‐pehnacetyl Hyp) shows the same spectrum as poly(O‐acetyl Hyp). This is explained by the high conformational freedom of the phenacetyl groups in contrast to the preferential orientation imposed on the benzoyl groups by steric hindrance. Accurate measurements of partial specific volumes ρdocumentclass{article}ρpagestyle{empty}ρbegin{document}$$ {\rm \bar v} $$ρend{document} were possible in trifluoroethanol and dichloromethane the densities of which are near the reciprocal values of ρdocumentclass{article}ρpagestyle{empty}ρbegin{document}$$ {\rm \bar v} $$ρend{document}. Therefore the usually large errors in polymer concentration have little influence. A remarkable dependence of ρdocumentclass{article}ρpagestyle{empty}ρbegin{document}$$ {\rm \bar v} $$ρend{document} on solvent, large deviations from values calculated from increments, and negative temperature coefficients of ρdocumentclass{article}ρpagestyle{empty}ρbegin{document}$$ {\rm \bar v} $$ρend{document} were observed.
The Acquisition of Functions During Sub‐Unit Assembly of Proteins
Authors: Gutfreund H.
Published: November 2013

The self assembly of subunits of enzymes is an important feature in the evolution of a number of their capabilities. Many oligomeric enzymes have identical subunits that act quite independently. In such cases the quaternary structure appears to act principally to stabilize the correct conformation of the subunit. They offer an interesting field of study of the factors that control the correct folding of enzymes. In enzyme systems where the quaternary structure serves to add control functions, the study of subunit association gives information about the changes in interaction responsible for information transfer. Some examples are given of each of the two fields of investigation and the outstanding problems are discussed.
Color, Conformation, and Catalysis
Authors: Bernhard Sidney A. , Malhotra O. P.
Published: November 2013

The spectra of active‐site specific chromophoric acyl enzymes are discussed in terms of both the chemical (electronic) nature of the acyl‐enzyme bond and the protein conformation. The evidence presented demonstrates the following: (1) The acyl‐enzyme bond is perturbed with regard to both reactivity and electronic spectrum. (2) The perturbation is intimately related to the native enzyme conformation. (3) Such extreme perturbation, although a ubiquitous property of native monomeric acyl enzymes, is lacking in an oligomeric enzyme (glyceraldehyde‐3‐PO4 dehydrogenase). (4) In the presence of a positive effector (NAD+), the same perturbation is evident. (5) NADH, the reverse reactant, is also an effector. Noncovalent binding of NADH results in a new electronic configuration for the acyl enzyme which can undergo hydrogen transfer. This configuration of the thiol ester is nonexistent in the absence of an effector.
Studies on the Mechanism of Action of Collagenase: Inhibition by Cysteine and Other Chelating Agents
Authors: Harper Elvin , Seifter Sam
Published: November 2013

Under specific conditions cysteine inhibits collagenase (Clostridiopeptidase A and B (EC 3.4.4.19)) irreversibly. Neither collagenase A or B contains cysteinyl or cystinyl residues, so that the inhibition cannot proceed either by disulfide reduction, formation, or exchange. By use of [35S]cysteine, cysteine has been shown to bind to collagenase A in the ratio of about two moles to one mole of protein, and to collagenase B in the ratio of approximately one mole to one mole of protein. After cysteine binds to the enzyme, the sulfhydryl group can no longer be titrated with p‐mercuribenzoate or 5,5′‐dithiobis‐(2‐nitrobenzoic acid). Cysteine inhibits the low‐temperature binding of collagenase to a collagen substrate (ichthyocol). Histidine inhibits the activity of collagenases A and B, but this inhibition, in contrast to that produced by cysteine, is readily reversible by dialysis against water or passage through a DEAE cellulose column. 2,3‐Dimercaptopropanol also inhibits both collagenases. The order of the inhibitor efficacy on collagenase by cysteine, histidine, imidazole and 2,3‐dimercaptopropanol appears to be consistent with the order of stability constants of these chelating agents with zinc. The suggestion made previously that zinc may be an intrinsic component of collagenase is thereby reinforced. Indeed preliminary experiments are reported in which the incorporation of 65Zn into collagenases A and B is demonstrated.
An Enzyme with Collagenolytic Activity from Dog Pancreatic Juice
Authors: Takahashi Shizuko , Seifter Sam
Published: November 2013

A purified collagenase has been isolated from the pancreatic juice of dogs prepared with pancreatic fistulae and stimulated to secrete the enzyme by injection of high quality pancreozymin. The purification steps included the use of affinity chromatography employing a Sepharose‐collagen column. The isolated enzyme had relatively high specific activity, was able to digest extracted, undenatured collagen to peptides of relatively small size, and could act on so‐called insoluble beef tendon collagen. Unlike clostridial collagenases, and most tissue collagenases, but resembling the collagenase of the hepatopancreases of crab and crayfish, the canine pancreatic collagenase was inhibited by diisopropylphosphorofluoridate, albeit in relatively high concentrations. Resembling the bacterial collagenase and tissue collagenases, but differing from the collagenase of crab hepatopancreas, the canine pancreatic collagenase was inhibited by cysteine. Resembling other pancreatic proteases, the pancreatic collagenase was inhibited by glycoproteins, human serum, or to a small extent by soy bean trypsin inhibitor. Apparently, just as carnivorous mammals have evolved with a specific elastase homologous with trypsin and chymotrypsin, they also have evolved in some instances with a specific collagenase; its homology with the other serine proteases is not yet established, although it appears to have properties intermediate between those of a serine protease and those of most tissue collagenases. The latter group of enzymes have been considered to be metallo‐enzymes. One may speculate that non‐carnivores would not have had selective pressure to evolve with a digestive collagenase, and that even the selective pressure to develop with a digestive collagenase in non‐carnivores would not be so great since the other serine proteases can digest denatured collagen. Finally, a new radioactive method of assay for collagenases is described.
Spectroscopic Probes Incorporated into Specific Substrates and Inhibitors of Papain for the Study of Acylenzyme Formation
Authors: Smolarsky Moshe
Published: November 2013

α‐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.
Chemical Approaches to the Mode of Action of Carboxypeptidase B
Authors: Sokolovsky Mordechai , Zisapel Nava
Published: November 2013

The present report presents and summarizes new data on the specificity (kinetics and metal replacement) of porcine carboxypeptidase B and the role of phenolic and carboxylic amino acid residues in the function of this enzyme.
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

The 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

A 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

The 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

The 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

The 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

Correlation 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

The 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

The 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

The 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

The 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 schemes

magnified image

in 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

The 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

In 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

Most 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

The 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

Adsorption 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

UV, 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

The 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).
Quasi‐Racemic Clathrates: The Absolute Configuration of Dianin's Compound
Authors: Collet André , Jacques Jean
Published: November 2013

Examples of quasi‐racemic clathrates involving resolved Dianin's compound and some of its analogues are described.
Ligand Field Parameters
Authors: Bertini Ivano , Gatteschi Dante , Scozzafava Andrea
Published: November 2013

The 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

Further 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.
XVI. Representations of the Electron Density and its Topographical Features
Authors: Smith Vedene H. , Price Peter F. , Absar Ilyas
Published: November 2013

The various ways of presenting the topographical features of electron densities and difference densities are discussed and illustrated with graphical examples. A systematic terminology is introduced.
Coherent Transient Excitation and Superposition of Adiabatic States
Authors: Friedmann H. , Wilson‐Gordon A. D.
Published: November 2013

Double 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.
Photoformation of “Z” (cis) Isomers in Diaryl‐ and Triaryl‐ Azomethines, Part II.1 Electronic and NMR Spectra of Methyl Derivatives of Benzylideneaniline (C6H5—CH=N—C6H5)
Authors: Maeda Koko , Fischer Ernst
Published: November 2013

UV irradiation of benzylideneaniline, A, and its methyl derivatives B–E in aliphatic hydrocarbon solvents or CH2Cl2 results in extensive conversion into the corresponding “Z” (cis) isomers. The process is reversible both photochemically and thermally, and no pronounced side reactions were observed. At temperatures below about — 70° the Z modifications are thermally stable and their electronic and NMR spectra were measured by static methods. The extent of photoisomerization was estimated by means of the NMR spectra. The changes in electronic and NMR spectra resulting from the E → Z conversion were compared with those observed in the corresponding derivatives of stilbene and azobenzene. Photosensitized Z ← E at below — 70° was observed with biacetyl, but not with dye sensitizers having triplet energies below about 50 kcal · mol−1. Quantum yields for the direct photoisomerization in both directions were calculated, and are in the range of 0.1—0.6. As distinct from stilbenes and azobenzene derivatives, no appreciable temperature dependence of these yields was found, in the range — 70° to – 180°.
Photoreactions of Aromatic Compounds. XXXVII.1 Photosubstitution Reactions of Nitronaphthalene Derivatives
Authors: Lammers J. G. , Cornelisse J.
Published: November 2013

A systematic investigation was made of the photochemical properties of 12 fluoronitronaphthalenes and some methoxynitronaphthalenes in the presence of hydroxide ions, methoxide ions and methylamine. Results show that photosubstitution of fluorine in fluoronitronaphthalenes by methoxide or hydroxide must be a consequence of the activating effect of the nitro group. This effect is also clearly present when the nitro group and the fluorine atom are in different rings.
Photoreactions of Aromatic Compounds. XXXVIII.1 Kinetics of the Photohydrolysis and Photoamination of 1‐Fluoro‐3‐nitronaphthalene, 1‐Fluoro‐6‐nitronaphthalene and 1‐Methoxy‐3‐nitronaphthalene
Authors: Lammers J. G. , Tamminga J. J. , Cornelisse J. , Havinga E.
Published: November 2013

Nucleophilic photosubstitution reactions of some naphthalene derivatives have been studied in order to establish new data on rate constants and other quantitative aspects of nucleophilic aromatic photosubstitution reactions. Results show that the photoreactions of the meta substituted fluoronitro‐ and methoxynitronaphthalenes with hydroxide ion and methylamine are SN2 (3Ar*) processes. In addition, it is shown that the lifetimes of the excited species in aromatic photosubstitution may be a decisive factor in determining the nature and the quantum yield of the reaction at moderate and low nucleophile concentration.
Topochemistry. Part XXXIX. The Solid‐state Photochemistry of some 2′‐Nitrochalcones
Authors: Jungk Axel E. , Luwisch Moshe , Pinchas Shraga , Schmidt Gerhard M. J.
Published: November 2013

It is shown that the specific pathway of a complex photochemical reaction in the solid state is governed by the molecular conformation and its retention, and by the molecular packing. 2′‐Nitrochalcone and those of its derivatives which are isomorphous with it display the s‐trans conformation in the solid state and yield indigos upon irradiation. However, this conformation is not sufficient to ensure photoreactivity: thus the s‐trans‐4‐bromo‐derivative does not yield indigo. The same derivative in the s‐cis conformation (in a second crystal form) has a crystal structure similar to that of the parent compound, and also does not yield indigo.
Thermodynamics of Power and Dissipation
Authors: Kafri O. , Levine R. D.
Published: November 2013

Can one provide a thermodynamic theory for processes which occur with finite rates? We discuss a possible approach based on expressing the first and second laws as rate equations. The result is a first law formulated in terms of power and a second law in terms of rate of energy dissipation. We argue that such an approach introduces a distinction between passive systems which are devoid of memory and cannot store energy and systems with a facility of recall (e.g. a coiled spring). The second possibility, that of systems capable of recall, allows for short term deviations from the overall restrictions imposed by the second law, illustrating the maxim that knowledge is power.
Oxyfluoro Compounds of Bromine
Authors: Gillespie Ronald J. , Spekkens Paul H.
Published: November 2013

Recent research on oxyfluorides of bromine is reviewed. This work is the first on the subject since 1963 when BrO2F was the only known oxyfluoride of bromine. Since then a number of other oxyfluoro compounds have been prepared, and a considerable amount of information on the structure and properties of all these compounds including additional information on BrO2F has been obtained. This review attempts to summarize all the data reported up to mid‐1977.
Fluorohalogenates: Preparation, Properties and Structure
Authors: Shamir Jacob
Published: November 2013

Recent advances in the field of fluorohalogenate chemistry are reviewed. Areas considered include their preparation, properties and structure. It is concluded that while many of the expected anions formed by the various halogen fluorides can be isolated and identified, full understanding of their structures is hindered by their extremely reactive properties and the fact that their existence is mostly limited to the solid state.
Application of Fluoroxy Compounds to Organic Synthesis: Electrophilic Fluorination of Unsaturated Molecules
Authors: Hesse R. H.
Published: November 2013

Fluoroxy reagents are versatile and useful electrophilic fluorinating reagents. Having wide applicability in a variety of solvents they display great potential for the synthesis of specifically fluorinated analogs of bioactive molecules.
Reactions of Organic Compounds with Xenon Fluorides
Authors: Filler Robert
Published: November 2013

Xenon fluorides, especially XeF2 and the intercalates of XeF4 and XeF6 in graphite, react with a broad range of aromatic compounds to provide a convenient direct route to fluoroaromatic compounds, many of which are otherwise difficult to prepare. Some of the products are of medicinal and biological interest. Highly colored radical cations are generated in the reactions by one‐electron oxidation. XeF2 also serves as a useful source of fluorine by reacting readily with carbon‐carbon double and triple bonds to yield difluoro‐ and tetrafluoro‐ addition products, as well as products resulting from rearrangements (especially in the case of norbornene).
Photochemistry of Fluorosubstituted Aromatic and Heteroaromatic Molecules
Authors: Zupan Marko , Šket Boris
Published: November 2013

The photochemistry of fluoro‐substituted aromatic and heteroaromatic molecules is reviewed. Investigations in this field of organic fluorine chemistry are summarized and some recent observations are presented. It is concluded that the fluorine atom is a convenient substituent for the elucidation of the reaction pathways of photochemical transformations of aromatic and heteroaromatic molecules.
Spirophosphoranes Containing the Perfluoropinacolyl Ring System
Authors: Röschenthaler Gerd‐Volker , Sauerbrey Karl , Schmutzler Reinhard
Published: November 2013

A series of spirophosphoranes, [C6H4O2][OC(CF3)2C(CF3)2O]‐PR (R = F, Me, Bu1, Ph, and OMe) containing the catechol and perfluoropinacolyl ring system have been prepared. Characterization was by NMR and IR spectroscopy, mass spectrometry, and by elemental analysis. In some cases temperature dependent effects were observed in the 19F‐NMR spectra; the findings are rationalized in terms of a “high‐energy” ligand exchange process. Hydrolysis of the phosphorane with R = F may proceed along two different pathways, with formation of phosphoryl compounds.
The Influence of Fluorine Substitution on the Aromaticity of Carbocyclic Systems
Authors: Hess B. A. , Schaad L. J.
Published: November 2013

Hückel integral parameters were evaluated for F and Cl by fitting calculated to observed heats of atomization. With these, empirical C‐F and C‐Cl bond energy terms were obtained from Hückel calculations on a set of 34 halogen‐substituted acyclics. The effect of fluorine substitution on the resonance energy per π electron (REPE) of cyclic compounds was then examined. Both F and Cl were found to act as electron donors in affecting REPE with F being the stronger.
Field Ionization Mass Spectrometry. II. FD Spectra of Nucleotides — Analysis of Methylation Products of Dinucleoside Phosphates
Authors: Linscheid M. , Feistner G. , Budzikiewicz H.
Published: November 2013

The analysis of reaction products in methylation of four dinucleoside monophosphates (ApA, UpU, ApU, UpA) by FDMS is reported. Both the relative amounts of the various methylation products and the sites of methylation could be determined, the latter from the fragmentation patterns. The results are explained by the different reaction rates of the nucleoside moieties.
The Diurnal Rhythms in Plasma Glycine Pool Sizes and Turnover Rates: 15N‐Glycine Single Dose Experiments Employing Gas Chromatographic — Mass Spectrometric Analysis
Authors: Lapidot A. , Nissim I. , Irving C. S.
Published: November 2013

Gas liquid chromatography–mass spectrometry of trifluoroacetyl n‐butyl ester derivatives of plasma amino acids has been used to determine directly the 15N‐enrichment of plasma glycine in rabbits, following the intravenous administration of a single dose of 15N‐glycine. The isotope enrichment time decay curves of plasma glycine were linear over the course of the measurements (5–45 min). Glycine pool sizes and turnover rate constants were obtained from the intercepts and slopes of non weighted least‐squares lines, describing the isotope enrichment time decay curve. In fed animals, glycine pool sizes showed only modest variations over a 24 h period, while glycine turnover rate constants showed a statistically significant daily variation with a minimum at 10 PM. In fasted animals, the glycine pool sizes decreased and turnover rate constants increased with the duration of the fast. The turnover rate constants appeared to represent the utilization of glycine, as an energy or nitrogen source in the liver, rather than uptake of glycine into the free amino acid pool of muscle. These data indicate that physiologically significant variations in amino acid dynamics can be obtained from single dose tracer experiments, when GC‐MS is used to determine directly the isotope enrichments of plasma amino acids.
Analysis of Human Vaginal Secretions by Gas Chromatography–Mass Spectrometry
Authors: Preti George , Huggins George R. , Bares Jana
Published: November 2013

Vaginal secretions from 14 ovulating females were analyzed by gas chromatography (GC) and gas chromatography‐mass spectrometry (GC–MS) during 50 ovulatory cycles. The day of ovulation was documented in each case by charting of basal body temperature and/or determining hormonal profiles for estrogens, progesterone and luteinizing hormone. The secretions were found to contain a complex mixture of acids, alcohols and aromatic compounds. Two distinct types of vaginal environment were found with six subjects displaying large amounts of C2–C5 aliphatic acids in secretions and the remaining showing only acetic acid by GC–MS analysis. Predominant concentrations of these acids occur both at midcycle and in the luteal phase of the menstrual cycle. Lactic acid and urea were present in the secretions of all subjects and underwent cyclic variations in concentration with maxima occurring around midcycle. The effect of sexual arousal on the organic compounds in the secretions is also discussed.
13C‐Kinetic Isotope Effects in Photosynthetic Carboxylation Reactions and δ13C‐Values of Plant Material
Authors: Schmidt H.‐L. , Winkler F. J. , Latzko E. , Wirth E.
Published: November 2013

The influence of different parameters on δ13C‐values in plants in vivo and on the 13C‐isotope effect of the carboxylation reactions in vitro were examined using isotope ratio mass spectrometry.
Solvent Caused Quaternization as a Possible Source of Error in the Mass Spectral Quantitation of Tertiary Amines. I. Methylene Chloride Quaternization
Authors: Vincze Adam , Gefen Leon
Published: November 2013

Basic tertiary amines such as atropine, derivatives of N‐methylpiperidine and quinuclidine, tend to quaternize in methylene chloride at room temperature. The quaternary ammonium salts formed undergo various dequaternization reactions in the heated direct inlet probe of the mass spectrometer, giving rise to volatile tertiary amines — different from the starting material and usually having higher molecular weights. Recorded spectra of such samples are a superposition of those of the various tertiary amines constituting the mixture. If just a few relevant and abundant ions in the mass spectrum of the original tertiary amine are monitored, as in quantitative fragmentography, rather low results might be obtained. Moreover, the operator may be quite unaware of the fact that he is measuring only part of the sample.