bluuebunny/crossref_metadata_2025 huggingface dataset:
Die Auffassung der Valenz als Elektronenwirkung
Authors: George Falk K. , Nelson J. M.
Published: December 2004

Der Begriff der Valenz als einer gerichteten Kraft, die durch die Ubertragung eines Korpuskels von einem Atom zum anderen hervorgebracht ist, wird als Grundhypothese benutzt (J. J. Thomson).
Zur Lichtabsorption der polycyclischen Komplexverbindungen. 2. Kuprikomplexe der Aldiminreihe
Authors: v. Kiss Á. , Bácskai G. , Csokán P.
Published: December 2004

Es wurden die Extinktionskurven von mehreren polycycli‐schen innerkomplexen Kuprisalze und deren Ausgangsstoffe bei Zimmertemperatur zwischen 700 und 200 mμ genau aus‐gemessen.
Die Darstellung optisch aktiver Aminoacylmercaptane durch Racematspaltung der D, L‐Verbindungen mit Dibenzoyl‐D‐weinsäure
Authors: Losse Günter , Müller Gerhard
Published: December 2004

D,L‐Valinthiophenylester und D, L‐Phenylalanin‐p‐nitrothiophenylester wurden mit Dibenzoyl‐D‐weinsäure über ihre Hydrogentartrate in die optischen Antipoden gespalten und damit aus racemischem Material für Peptidsynthesen direkt verwendbare optisch aktive Bausteine isoliert.
Notiz über die Verwendung von Polyphosphorsäure bei der Reaktion nach DÖBNER‐v. MILLER
Authors: Fiedler Heinz
Published: December 2004

Polyphosphorsäure eignet sich zur Darstellung verschiedener 2‐Methyl‐8‐hydroxy‐chinoline nach Döbner‐v. Miller.
Heterocyclen aus CH‐aciden Nitrilen. V. Gemeinsame Einwirkung von Schwefel und Schwefelkohlenstoff auf methylenaktive Nitrile
Authors: Gewald Karl
Published: December 2004

Nitrile, die in α‐Stellung eine aktive Methylengruppe besitzen, reagieren mit Schwefelkohlenstoff und Schwefel basenkatalysiert zu 5‐Amino‐1,2‐Dithiolthionen‐(3), die sich in Gegenwart von starken Basen in Isothiazolderivate umlagern.
Preparation, Absorption Spectra and Electronic Configuration of some amino complexes of nickel (II) acetate
Authors: Narain Gopal
Published: December 2004

Three hexaco‐ordinated complexes of nickel (II) acetate with ammonia, ethylenediamine and propylenediamine have been prepared. Conductivity measurements indicate the complexes to be non‐electrolytes. Molecular weight measurements confirm this. The visible absorption spectrophotometric measurements show a number of bands corresponding to the various permitted transitions of the metal and a discussion of the structure in the light of these transitions is presented.
Synthese von Diarylschwefeldiimiden durch basische Kondensation von N‐Sulfinyl‐arylaminen
Authors: Hörhold Hans‐Heinrich , Beck Jürgen
Published: December 2004

Durch Umsetzung von N‐Sulfinyl‐arylaminen mit stark basischen Anionen (Alkoholat, Amid, Hydrid) werden in hohen Ausbeuten Diarylschwefeldiimide erhalten. Die Reaktion ist auf eine Vielfalt von substituierten N‐Sulfinyl‐arylaminen anwendbar, wobei die Substituenten sowohl Gruppen mit Elektronendonatorwirkung als auch solche mit Elektronen‐akzeptorwirkung sein können.
Metallorganische Peroxide, VII. Zum Mechanismus der Zersetzung von Bis‐organoantimonyl‐peroxiden. Teil I
Authors: Dahlmann J. , Winsel K.
Published: December 2004

Der Zerfall der Bis‐(halogen‐triphenyl‐antimonyl)‐peroxide1 aundbwurde hinsichtlich der Zersetzungsprodukte, der Kinetik und des Einflusses verschiedener Faktoren untersucht. Es wurde gefunden, daß bei der Zersetzung neben einer heterolytischen Spaltung der O‐O‐Bindung unter 1.2‐Umlagerung bei dem bromhaltigen Peroxid1 aleicht eine Abspaltung von Singulett‐Sauerstoff erfolgt. Der Mechanismus dieser Reaktion wurde aufgeklärt.
Polyhalogenation of nitrogen containing heterocyclic compounds. II. Polychloro‐1,10‐phenanthrolines
Authors: Dénes V. , Chira R. , Fărcăsan M. , Ciurdaru Gh.
Published: December 2004

1,10‐Phenanthroline can be chlorinated directly with sulfuryl and thionyl chloride giving a chromatographically separable mixture of polychloro compounds.
Kristallin‐flüssige Ketoximester
Authors: Weissflog W. , Schubert H. , König S. , Demus D. , Vogel L.
Published: December 2004

Disubstituierte Acetophenonoximbenzoate 1a–q, 2a–j, 3a–d, 4a–b und 5a–b sind nematische Flüssigkristalle mit bemerkenswerter thermischer Stabilität und – unabhängig von den Flügelgruppen — relativ niedrigen Schmelzpunkten. Binäre und ternäre Gemische, deren Schmelztemperaturen auch theoretisch bestimmt wurden, sind weit unterhalb Zimmertemperatur flüssig und im Wechselstromfeld beständig. Der Austausch von CH3 durch C2H5 oder n‐C3H7 führt in 6a–d und 7 zu starken Klärpunktsdepressionen.
Mehrfunktionelle N‐Tenside. I. Nucleophile Substitutionen an Bischlornitrosoverbindungen. 1. Reaktionen mit Aminen, Mercaptanen und Natriumazid
Authors: Berger J. , Luong T. T. , Thielemann C. , Thong P. D.
Published: December 2004

Polyfunctionalized N‐Tensides. I. Nucleophilic Substitutions with Bischloronitrosocompounds. 1. Reactions with Amines, Mercaptans and Sodium Azide

Chloronitrosation of alkenes gives bischloronitrosocompounds 1, which react with amines to α‐aminooximes (2 and 4), with mercaptans to α‐alkylthiooximes 11, and with sodium azide to α‐azidooximes 8. Reduction with LiAlH4 gives vicinal substituted diamines (6, 7, 10) from α‐amino‐or α‐azidooximes (2, 4, 8) and β‐alkylthioamines 13 from α‐alkylthiooximes 11.

The determination of E‐ or Z‐configuration in the α‐substituted oximes is discussed.
Eine Methode zur Quantitativen Verfolgung von Festphasenreaktionen in der Peptidsynthese
Authors: Kaufmann Klaus‐Dieter , Raddatz Frank
Published: December 2004

A Method for the Quantitative Control of Solid Phase Reactions in the Peptide Synthesis

A quantitative control‐method of partial steps of a solid phase peptide synthesis is described, based on a hydrazinolytic cleavage of protected peptides from the solid support. A separation of the peptide hydrazides by gelchromatography on sephadex G 15 in dimethylformamide and a quantitative evaluation of the hydrazide‐content in the elution fractions is reported, which permits the control of the Nα‐deprotection step in the same way as the evaluation of the coupling yields of the desired sequence. The new method is discussed for the example of two solid phase syntheses of the pentapeptide N‐tert.‐butyl‐oxycarbonyl‐L‐valyl‐S‐benzyl‐L‐cysteinyl‐L‐alanyl‐L‐ leucyl‐O‐benzyl‐L‐tyrosine hydrazide.
Nucleophile Substitutionen an Bischlornitrosoverbindungen. III. Reaktionen mit Salzen und Estern der Dithiocarbazinsäure sowie der N‐Phenyldithiocarbazinsäure
Authors: Beger J. , Thielemann C. , Thong P. D.
Published: December 2004

Nucleophilic Substitutions with Bischloronitroso Compounds. III. Reactions with Salts and Esters of the Dithiocarbazinic Acid and the N‐Phenyldithiocarbazinic Acid

Bischloronitroso compounds 1 react with salts of the dithiocarbazinic acid to give S‐(β‐oximinoalkyl)‐esters of the dithiocarbazinic acid. The esters easily cyclise to the corresponding 1,3,4‐thiadiazine‐2‐thiones. Esters of the dithiocarbazinic acid lead to 2‐alkylthio‐1,3,4‐thiadiazines. The structure of possible tautomeres follows from i.r.‐, u.v./vis‐ and n.m.r.‐spectra.
Reaktionen mit N‐Acylimino‐dithiokohlensäurediestern
Authors: Augustin M. , Richter M. , Salas S.
Published: December 2004

Reactions with N‐Acylimino‐dithiocarbonic‐acid‐diesters.

Reactions of N‐acylimino‐dithiocarbonic‐acid‐S,S‐diesters 1 with nucleophilic com‐pounds present new possibilities to synthesize heterocycles. With amines 1a reacts by mono‐ and disubstitution, respectively, of methylthio‐groups to isothioureas 2 and guanidines 3, with 1,2‐bi‐nucleophilic arenes to benzoheterocycles 4, with aliphatic diamines to imidazolidines 5, pyrimidines 6, diazepines 7 and the hexamethylene‐diamine‐derivatives 8. 1a reacts also with hydrazines to 1,2,4‐triazoles 9 and with hydrazides to the thiosemicarbazones 10 or 1,3,4‐oxadiazoles 11. Heterocyclisations of 1 with guanidines, thiourea, salts of thiourea and amidines give the 1,3,5‐triazines 12, 14, 15 and 16. N‐benzoyl‐dithiocarbonic‐acid‐methylester ‐amid reacts with CH‐acidic compounds to thiazoles 17. The structures of the final products are determined by i.r.‐, 1H‐n.m.r.‐, u.v.‐ and mass‐spectras.
Darstellung von trans‐4‐Diphenylphosphinyl‐stilbenen
Authors: Gloyna D. , Alder L. , Henning H.‐G. , Köppel H. , Siegmund M. , Schleinitz K.‐D.
Published: December 2004

Synthesis of trans‐4‐Diphenylphosphinyl Stilbenes

The reaction of 4‐tolyl‐diphenylphosphine oxide with N‐bromosuccinimide results in 4‐diphenylphosphinyl benzylbromide 5 which can be easily converted to (4‐diphenylphosphinyl)‐benzyl triphenylphosphonium bromide 6 and (4‐diphenylphosphinyl)‐benzyl diphenylphosphine oxide 7, respectively. In the presence of strong bases 6 and 7 react with aromatic aldehydes 8 to the 4‐diphenylphosphinyl substituted stilbenes 1. The yields depend on the nature of base and solvent. The trans configuration of 1 is determined by i.r. and 1H‐n.m.r. measurements.
Zur Strukturaufklärung der Bromierungsprodukte von N‐Aryl‐2,4‐dimethyl‐buta‐1,3‐dien‐sultamen‐1,4
Authors: Fanghänel E. , Mohamed H. , Keita Y. , Radeglia R.
Published: December 2004

Structure Elucidation of Bromination Products of N‐Aryl‐2, 4‐dimethyl‐buta‐1,3‐diene‐sultames‐1, 4

The structure of bromination products of N‐aryl‐2, 4‐dimethyl‐buta‐1, 3‐diene‐sultames‐1, 41a–d,fis determined by 13‐C‐n.m.r. spectroscopy. As mono bromination product of N‐phenylsultam1athe 4‐bromomethyl derivative2awas isolated. Dibromination of sultames1yields 1‐brom‐4‐brommethyl‐sultames3and by tribromination 1,3‐dibrom‐4‐brommethyl‐sultames4are obtained.
Anwendungen des Kern‐Overhauser‐Effekts. I. Strukturuntersuchungen an Z/E‐isomeren 2,3‐Diarylazetidin‐3‐olen
Authors: Fuhrmann J. , Köppel H. , Schleinitz K.‐D. , Henning H.‐G.
Published: December 2004

Applications of the Nuclear Overhauser Effect. I. Investigations of the Structure of Z/E Isomeric 2,3‐Diarylazetidin‐3‐oles

The relative configurations of Z/E‐isomeric 2,3‐diaryl‐azetidin‐3‐oles are determined by mass spectrometry and 1H‐n.m.r.‐NOE‐measurements. The increase of the C(2)‐H line intensity by saturation of the OH‐signals demonstrates the Z‐position of the 2,3‐diaryl groups in the isomers 2a.
Eine einfache Synthese von β‐Chlorzimtsäurenitrilen nach einer modifizierten Vilsmeier‐Haack‐Arnold‐Reaktion
Authors: Liebscher JÜRgen , Neumann Bernd , Hartmann Horst
Published: December 2004

A Simple Synthesis of β‐Chlorocinnamonitriles by a Modified Vilsmeier‐Haack‐Arnold‐Reaction

A simple one‐pot synthesis of β‐chloro‐cinnamonitriles 2 can be achieved by treating acetyl arenes 1 first with formamide chlorides and subsequently with hydroxyl amine hydrochloride. The formamide chlorides used are conveniently prepared from an excess of dimethyl formamide and phosphoryl chloride. However it is also possible to employ other N,N‐disubstituted formamides or acid chlorides, respectively. For comparison purposes β‐chloro‐cinnamonitriles 2 have also been synthesized in a two‐step process. Thus 3‐aryl‐3‐chloro‐(2)‐iminium salts 4 are reacted with hydroxyl amine hydrochloride giving rise to 3‐chloro‐cinnamic aldoximes 5. The latter compounds are dehydrated to the corresponding nitriles 2 by refluxing in acetic anhydride following a known procedure.
Thermitase – eine thermostabile Serinprotease. I. Synthese von Alaninpeptidestern als Substrate des Enzyms
Authors: Jahreis Günther , Fittkau Siegfried
Published: December 2004

Thermitase – A Thermostable Serine Protease. I. Synthesis of Alanine Peptide Esters as Substrates of the Enzyme

The synthesis of N‐acetylated and N‐succinylated peptide esters of alanine is described. The peptides are built up from the Z‐

Abkürzung: Z = Benzyloxycarbonyl, Ac = Acetyl, Suc = Succinyl, OMe = Methylester, MA = Mischanhydridmethode, E = Ether, PE = Petrolether, Etac = Ethylacetat, AcOH = Essigsäure, Dibu = n‐Dibutylether, DMSO = Dimethylsulfoxid, DMF = Dimethylformamid, TEA = Triethylamin, Ac2O = Essigsäureanhydrid

protected peptides by liquid phase fragment condensation and by acylation of the deprotected peptide esters. The kinetic parameters K
m
and K
cat
of some compounds are presented.
Tetrathiafulvalene. XXI. Synthese von Tetrathiafulvalenen aus 2‐Alkylthio‐, 2‐Arylthio‐ und 2‐Alkylseleno‐1,3‐dithioliumsalzen
Authors: Fanghänel E. , Richter A. M. , Schukat G.
Published: December 2004

Tetrathiafulvalenes. XXI. Syntheses of Tetrathiafulvalenes from 2‐Alkylthio‐, 2‐Arylthio‐ and 2‐Alkylseleno‐1,3‐dithiolium Salts

In the reaction of 2‐alkylthio‐, 2‐arylthio‐ or 2‐alkylseleno‐1, 3‐dithiolium salts with trivalent phosphorus compounds in acetonitril tetrathiafulvalenes2are formed. As an intermediate we suppose a phosphorane, which reacts with further 1,3‐dithiolium salt to provide the tetrathiafulvalene. By the application of a 2‐alkylthio‐1,3‐dithiolium salt a monomethin dye is formed in a side reaction. When the reaction is carried out in methanol, the phosphorane is trapped by the solvent and a 2H‐1,3‐dithiolium salt is obtained.
Direkte und sensibilisierte Photoisomerisierung der α,δ‐Phenylfulgide
Authors: Ilge H.‐D. , Paetzold R.
Published: December 2004

Direct and Sensitized Photoisomerization of α,δ‐Phenylfulgides

The photoreactions starting from the E‐ and E‐E‐isomers of mono‐, di‐, tri‐ and tetra‐(substituted‐)phenylfulgides are investigated. The phenylfulgides show strong steric interactions in the molecular framework. For that reason internal conversion is the main deactivation process which increases in the series of mono‐, tri‐ and tetraphenylfulgides. The α,δ‐di‐(substituted‐)‐phenylfulgides show the highest photoreactivity. At room temperature in no case luminescence is observed from any E(E‐E)‐, Z(E‐Z, Z‐E)‐ or Z‐Z‐phenylfulgid isomer of the substances under study. Intersystem crossing cannot compete neither with thermal deactivation nor can it be observed by applying both the internal and external heavy atom effect. The phenylfulgides show typical ππ*‐photoreactivity: in the singlet state E‐Z‐isomerization about one double bond competes with electrocyclic ring closure; in the triplet state only simultaneous E‐Z‐isomerization about the two double bonds is observed. The steric and electronic substituent influences on the photoreactivity are interpreted. A first qualitative model of the isomerization reactions of the fulgides in the excited states is established.
Untersuchungen zur Bromierung/Dehydrobromierung von 17α‐Cyanmethyl‐17β‐hydroxy‐östr‐5(10)‐en‐3‐on
Authors: Menzenbach B. , Hübner M. , Ponsold K.
Published: December 2004

Investigations on the Bromination/Dehydrobromination of 17α‐Cyanomethyl‐17β‐hydroxy‐estr‐5(10)‐en‐3‐one

Bromination/dehydrobromination of 17α‐Cyanomethyl‐17β‐hydroxy‐estr‐5(10)‐en‐3‐one 1a in the presence of pyridine leads to 17α‐cyanomethyl‐17β‐hydroxy‐estra‐4, 9‐dien‐3‐one 2a. The reaction was studied in various solvents with several bromination agents. Intermediates and byproducts of the reaction were isolated and their structures elucidated.
Photochemische Untersuchungen an 3‐(9‐anthryl)‐substituierten Isoxazolinderivaten
Authors: Timpe H.‐J. , Lammel U. , Fišera Ľ.
Published: December 2004

Photochemical Investigations on 3‐(9‐Anthryl)‐substituted Isoxazoline Derivatives

The photochemical and photophysical properties of anthryl substituted isoxazolines5a–cand6are caused by the anthracene ring. Absorption and fluorescence spectral data correspond to those of parent anthracene. By irradiation with light of the wavelength λ = 365 nm the products dimerizise at 9,10‐position of the anthracene ring. Excited singlet states of these isoxazolines are donors for an electron transfer to onium compounds.
Pyryliumverbindungen. 38. Zur Ringtransformation von 2,4,6‐Triaryl‐thiopyryliumsalzen mit Essigsäureanhydrid zu Arylbenzenen und Thiobenzophenonen
Authors: Zimmermann Thomas , Fischer Gerhard W.
Published: December 2004

Pyrylium Compounds. 38. About the Ring Transformation of 2,4,6‐Triarylthiopyrylium Salts by Acetic Acid Anhydride to Arylbenzenes and Thiobenzophenones

2,4,6‐Triarylthiopyrylium salts 5 react in the presence of an appropriate condensing agent (sodium acetate, carbonate, methoxide, tert‐butoxide or potassium acetate) with acetic acid anhydride to yield arylbenzenes 3 and thiobenzophenones 6. This ring transformation represents the first example of the conversion of the moiety into the thiocarbonyl group Under the same conditions 3,5‐dimethyl‐2,4,6‐triphenylthiopyrylium perchlorate (13) forms via [1,5]‐sigmatropic rearrangement the thiobenzophenone 15. The structure of the new compounds 6 was proved by spectroscopic methods as well as by degradation reactions. Thus, hydrogen peroxide converts 6a to the known benzophenone 4. Alkaline saponification gives the 2‐hydroxy‐benzophenone 8, whereas heating with hydrochloric acid causes a selective cleavage of the acetoxy group to the 2‐hydroxy‐thiobenzophenone 7.
MO‐LCAO Calculations on Polymethines. XXV [1]. The molecular and electronic structure of 3,3′‐dimethyl‐3,3′‐pyridocyanines and related non‐kekulè polymethine dyes
Authors: Fabian J.
Published: December 2004

Non‐Kelulé polymethines are polymethine dyes that cannot be written by single Kekulé‐type formulae. As demonstrated with 3,3′‐dimethyl‐3,3′‐pyridocyanines (1) the electron distribution and term level ordering of them differ greatly from those of the related simple open‐chain polymethines (streptopolymethines), considering the latter ones as constitutive elements of these dyes according to Dähne's polymethine concept. Non‐Kekulé dyes are, however, closely related to isoconjugated classical polymethine dyes. The peculiar features of the non‐Kekulé polymethines are well understood in terms of simple MO theory. Orbital tracing assisted by MOA (molecular orbital analysis) reveals crossing between the frontier orbitals of these dyes and those of the related open‐chain polymethine substructures. Additional insight into peculiarities of1is gained at the semiempirical level by analyzing the π‐electronic system in terms of the heterocyclic end groups and the interconnecting odd‐alternant hydrocarbon (carbopolymethine) chain. Numerical predictions are made based on MNDO optimum geometries. According to CNDO/S and PPP calculations the non‐Kekulé dyes considered absorb at longer wavelengths than the isoconjugate classical dyes. In the case of the first members of series1the lowest‐energy transition is less determined by the characteristic polymethinin charge redistribution inherent to polymethine dyes than by notable heterocycle‐to‐chain charge transfer (CT). The interfragmental CT upon excitation reduces the transition probability of this electronic transition. Some calculations performed beyond the monoexcitation approximation indicate a certain birdicaloid character of the non‐Kekuléan dye structures. The exceptional position of these dyes is also indicated by the higher heats of formation of1relative to the isomeric classical dyes.
Computer Generation of Caged Frameworks which can be used as synthons for creating high‐energetic materials
Authors: Pivina Tatyana S. , Molchanova Marina S. , Shcherbukhin Vladimir V. , Zefirov Nikolai S.
Published: December 2004

A methodology for computer‐assisted generation of novel highenergetic compounds with the given gross formula is described. On the first step, structures are generated as graphs in the form of connectivity matrices, using the GEM program. Each of these graphs is input into the MOLGEO program, yielding a number of possible stereoisomers in the form of 3D structures. Subsequent optimization by MM2 allowed to evaluate the precise molecular geometry and the enthalpy of formation. On the basis of these data, it is possible to estimate the energy content and the crystal density of the corresponding molecular crystals for each of the structures and. therefore, to evaluate their suitability for practical purposes.
Shaped Charge Jet Initiation on Explosive Charges equipped with barriers made up of various materials
Authors: Held Manfred
Published: December 2004

This paper describes initiation tests on cast TNT/RDX (35/65) explosive charges applying shaped charge jets with test set‐ups on which the HE charge was arranged either in contact to a 50‐mm thick barrier or after a 100‐mm thick barrier in a 15‐mm air gap. A variety of materials was attached to the barrier's rear side which, on one band, resulted in a varying shock wave attenuation and also in different bulging effects that are responsible for the differences in the initiation mechanisms observed on the two test arrangements. Materials with a lower density also provide, due to a less precompression of the IIM charge used on the arrangement “test charge in contact”, shorter buildup distances than materials with a higher density. An exception to this is a high ductile material such as e.g. steel. The build‐up distances, however, remain constant when arranging the explosive charge with an air gap. This backs up the hypothesis that most of all, bulging of the target is responsible for the sensitivity reduction observed on the test HE charges in contact with the barrier.
Safety investigations of trinitrotoluene/water emulsions
Authors: Teipel Ulrich
Published: December 2004

In the disposal of explosives, preparation of the dismantled material is necessary before subjecting it to a breakdown process. Knowledge of the material properties and determination of safety‐related parameters are major prerequirements when designing a disposal facility and increasing handling safety. When TNT is treated using emulsion processing, a desensitization of the TNT melt via the aqueous phase is obtained, in addition to increasing the surface area of the TNT phase. During the entire process of TNT treatment, the system is exposed to a wide range of different stresses as a result of the mechanical energy applied. This study presents the results of an investigation on the sensitivity of pure TNT melts and TNT/water emulsions at different concentrations on exposure to the applied impact or shock energies. It is found that the impact sensitivity of a TNT/water emulsion is lower by a factor of 4 when the TNT concentration has been reduced from 50 wt % to 30 wt %. On exposure to stress from a detonation shock wave, a desensitization of the system due to the aqueous phase is also found, so that the safety of the TNT treatment process can be increased by using a TNT/water emulsion when applying mechanical breakdown methods.
A MO‐SCF study of hydroxyl binding and hydroxyl diffusion in pure and fluorine‐containing hydroxyapatite
Authors: Wahlgren Ulf , Roos Björn , Forslind Erik
Published: December 2004

Hydroxyl diffusion and interhydroxyl binding in hydroxyapatite has been studied. LCGO‐MO‐SCF calculations have been carried out on groups of hydroxyl ions in a perfect and a vacancy‐containing crystal.

Electrostatic crystal effects were accounted for by including the crystal potential field in the SCF calculations. Nearest‐neighbour interactions were calculated to first order. Effects exerted by fluorine impurities were considered for the vacancy‐containing crystal.

The calculations indicate that narrow bandwidths obtained in nmr experiments on biological hydroxyapatite may be caused by a hydroxyl displacement mechanism and that no interhydroxyl hydrogen bonds exist in hydroxyapatite. The suggestion that the caries‐inhibiting properties of fluorine impurities in human dental enamel is caused by a diffusion‐binding mechanism is supported by the results.
Enhanced probability for the photoelectric effect in a Faraday cage
Authors: Avery John S.
Published: December 2004

The cross section for the photoelectric effect is calculated for the case where the photoionization takes place within a Faraday cage held at a constant electrostatic potential. When the geometry has spherical symmetry, and when the potential is repulsive, the cross section is enhanced by a factor E/(E − V0). The predicted effect is a purely quantum mechanical one, since according to classical electrodynamics, no forces due to the potential of the cage will act on a charged particle in the fieldfree region inside it. In quantum theory, the effect arises because the continuum states extend to the region outside the cage.
Ultraviolet carcinogenesis
Authors: Rosen Philip
Published: December 2004

A theory of UV carcinogenesis is described in which damage to DNA in the form of pyrimidine dimers occurs in a critical operator region of the genome that controls the synthesis of divisional proteins. There is a chance that a mutation will occur in the region of the operator either during replication or during postreplication repair, so that unchecked growth will be passed on to daughter cells. Comparison with the experiments of Hart and Setlow (1973) indicates that agreement is semiquantitative.
Quantenchemische untersuchungen zum mechanismus der elektrophilen substitution. I. Zur potentialhyperfläche des systems benzol/h+
Authors: Heidrich D. , Grimmer M.
Published: December 2004

Results of semiempirical calculations (CNDO/2‐FK and MINDO/2 methods) for the σ‐π complex problem on protonated benzene are given and compared with previous ones. The semiempirical methods were chosen according to the agreement of their results with new theoretical energy data (EHF + Ekorrel) concerning the classical–nonclassical problem of protonated ethylene. By these methods the corresponding part of the energy surface of the benzene/H+ system is simulated. The stationary points of this surface are found by a gradient method with complete optimization of the geometry. On the basis of this method we determined the energy profile of a reaction coordinate between the classical (σ‐complex) and nonclassical (π‐complex) cation. The so called strong π‐complex is a saddle point between two σ‐complex minima and can be interpreted as transition state of 1,2‐proton shifts. Hypotheses for possible minimum energy paths of electrophilic attacks in the given region of the surface are discussed.
Direct minimization of the energy by simultaneous variation of parameters in nonorthogonal basis functions. I. Method
Authors: Weltin E. E.
Published: December 2004

A direct method to optimize parameters in nonorthogonal basis orbitals is discussed. The partial derivatives of the energy of the state of interest, not necessarily the ground state, with respect to the orbital parameters are calculated analytically. The required cofactors up to third order of the overlap matrices over spin‐space orbitals in pairs of Slater determinants are calculated by biorthogonalization. All parameters are varied simultaneiously in the direction of the negative gradient (steepest descent). A search logic with dynamically adjusted step‐size is shown, in the example of the minimum basis Ne ground state, to find the energy minimum in an efficient manner.
Ab initioLCAO‐MO‐SCF Calculation of chlorpromazine and promazine
Authors: Popkie Herbert E. , Kaufman Joyce J.
Published: December 2004

Ab initio LCAO‐MO‐SCF Gaussian basis function calculations have been performed for chlorpromazine and promazine. By prescreening for the size of the integrals before calculation, it was only necessary to calculate 12 million out of the possible 38.5 million integrals for chlorpromazine. By a novel procedure of processing the integral tapes for the SCF it was possible to cut down significantly on the amount of time for the SCF. The SCF calculations converged smoothly for both promazine and chlorpromazine. There is a sizeable energy gap between the energy of the highest occupied molecular orbitals in these molecules (which is of the order of −0.3 a.u.) and the lowest unoccupied molecular orbital (which is of the order of + 0.15 a.u.). The gross atomic populations of chlorpromazine and promazine resemble each other and differ only somewhat on the carbon atom to which the substituent is attached and the carbons and their hydrogens adjacent to it.
Ab initio molecular orbital calculations of the cobalt porphine complex. I. LCAO SCF MO calculation of low‐spin, high‐spin, and π‐ionized states of Co‐porphine
Authors: Kashiwagi Hiroshi , Takada Toshikazu , Obara Shigeru , Miyoshi Eisaku , Ohno Kimio
Published: December 2004

Ab initio LCAO SCF MO calculations are carried out on planar Co‐porphine with a basis set of roughly double zeta quality for Co and N and of single zeta quality for C and H. The net charge on Co and N and the overlap population between them are 1.78, −0.57, and 0.06, respectively, in the 2A1g, state, which is known to be the ground state by experiment. The bonding in this complex is thus largely ionic. The first and second calculated ionization potentials are 6.51 and 6.77 eV, respectively, and are in reasonable agreement with the observed ionization potentials of 6.44 and 6.62 eV for Ni‐tetraphenylporphine. CI calculations within the framework of the ligand field theory are also performed. The calculated order of the five lowest states is 4B2g ≈ 4Eg, 4A2g, 2A1g, 4Eg from below and is not in agreement with the semiempirical order of 2A1g ≈ 4B2G, 4A2g, 2Eg, 4Eg determined by Lin.
Conformational changes and excitation energy transfer in myosin–auramine O system
Authors: Bogach P. G. , Zyma V. L. , Shakhovsky A. M. , Danilova V. M.
Published: December 2004

In the myosin–auramine O system 10 or 11 binding sites of auramine O on the rod‐like part of myosin were discovered. The myosin fluorescence decreases with an increase in auramine O concentration. This is evidence of the excitation energy transfer from tryptophanyls situated near the binding sites to auramine O. The effective distance of energy transfer is 35 Å. It is suggested that the light meromyosin has binding sites with periodicities of 77‐86 Å. Every binding site has a negative charge and hydrophobic locus.
Generalization of the second quantization operators: Electron attachment and detachment operators
Authors: Saute M. , Laforgue A.
Published: December 2004

This paper proposes a method for the generalization of the second quantization operators. The method is based on two main hypotheses: (i) the same form of the correlation operator, which is good for closed‐shell systems is chosen and (ii) a system of equations is given to calculate the differences (xk0−xk1), which characterize both attachment and detachment operators.
Effect of low‐molecular impurity on the melting of DNA‐type macromolecules
Authors: Kosevich A. M. , Galkin V. L. , Polyakov M. L.
Published: December 2004

Thermodynamics of the melting of a DNA‐type macromolecule is studied theoretically. Elements of the macromolecule are able to annex a low‐molecular impurity from the solvent (e.g., metal ions). Two models of the annexing of the impurity to the macromolecule are analyzed. It is shown that the concentration dependence of the helix‐coil phase transition temperature is describable by a non‐monotonic function in the case of certain relations between parameters.
Interrelations between electronic structure and spatial geometry of specific ligands in the functioning active site of some pyridoxal‐p‐dependent enzymes
Authors: Almazov V. P. , Morozov Yu. V. , Savin F. A. , Sukhareva B. S.
Published: December 2004

Using a spectrokinetic approach the absorption spectra of the short‐lived transient products in the enzymatic reaction of the glutamate decarboxylase with natural substrate are determined for the first time. The quantum‐chemical calculations of the electronic structure and spectra of various ionic species of numerous vitamin B6 derivatives allowed a hypothesis on the nature of the intermediate products detected to be suggested. A model of the enzyme functioning taking into account the charge equilibria and some electronic–conformational relations is proposed.
Spectroscopic and photochemical studies of model visual pigment chromophores
Authors: Kliger David S.
Published: December 2004

The primary step in the bleaching sequence of visual pigments has been shown to occur in picoseconds, while the isomerization of model visual pigment chromophores, protonated 11‐cis retinylidene Schiff bases, takes place on a time scale several orders of magnitude slower. Thus, the well‐accepted notion that the primary step in visual transduction involves a simple isomerization deserves closer examination. Studies of visual pigments and compounds which mimic visual pigment chromophores are discussed in terms of several alternatives for the nature of the primary step. In addition to discussion of photochemical studies, spectroscopic experiments are discussed. To fundamentally understand the nature of the primary processes in visual transduction it is important to understand the photochemistry, and therefore the electronic structure, of pigment chromophores. Spectroscopic studies aimed at elucidating the electronic structure of polyenic systems are thus discussed.
Electronic structure of the pyrimidine and purine components of nucleic acids in their ground and lower excited singlet and triplet states
Authors: Savin F. A. , Morozov Yu. V. , Borodavkin A. V. , Chekhov V. O. , Budowsky E. I. , Simukova N. A.
Published: December 2004

Quantum‐chemical calculation of the energies of the electronic transitions and the electronic structures of the neutral and ionic species of the nucleic acids components in their ground and lower excited singlet and triplet ππ* and nπ* states has been carried out in the all‐valence‐electron approximation CNDO/S. The results of the calculation allow one to identify the most photoreactive sites of the molecules and to consider the dependence of the location of these sites on the ionic state of the molecules. The calculated data are compared with our previous results obtained in a π‐electron approximation. The individual absorption spectra of various ionic and tautomeric species of the nucleic acids components obtained by us earlier have been decomposed into bands corresponding to separate electronic transitions. As a rule, there is a good agreement between the calculated data in the two approximations and the experimental results.
Torsional isomerization of biologically active bicyclic molecules
Authors: Bolotin Adolph B. , Bolotin Victor A. , Gineityte Victoria L.
Published: December 2004

Rotational isomerization of bipyridines C5H4NC5H4N was studied by CNDO/2, PPP/CI, and CNDO/CI methods. It is shown that CNDO/2 overestimates the angle of rotation ϕ between the pyridine rings ca. two times. The angle ϕ was determined for 2,2′‐bipyridine by means of correlation of the theoretical (CNDO/2) and experimental dipole moment. It was also found from the correlation between the theoretical and experimental UV spectra. It is shown that there is an explicit dependence of the results upon the distance between heteroatoms (PPP/CI). It has been found that the CNDO/CI method correctly predicts the value of the rotational angles and their sequence in bipyridines.
Simulation of intermolecular and intramolecular interactions of nucleic acid subunits by means of atom–atom potential functions
Authors: Poltev V. I.
Published: December 2004

Atom–atom potential functions for calculation of nonbonded interaction energies of nucleic acids are proposed. Quantitative reliability of the obtained results is checked by using the calculations of intermolecular interaction energy in crystals. Based on the calculations of the interaction energy of the nucleic acid bases the molecular mechanisms of spontaneous mutations are suggested.
Mechanisms of charge separation in bacterial photosynthesis
Authors: Kharkyanen V. N. , Khristoforov L. N. , Kukhtin V. V. , Petrov E. G.
Published: December 2004

The physical aspects of the primary charge separation processes in bacterial photosynthesis are discussed. The donor‐acceptor model of electron transfer due to participation of protein current states is used. The kinetics of photosynthetic reaction center (PRC) processes is investigated and the PRC energetic scheme is constructed using the nonequilibrium density matrix method. It is shown that with allowance for the effect of vibrational sublevels of states participating in transitions the theory describes well experimental data.
Orbit–orbit interaction in the NO–Fe(II)Hemoproteins studied by the low‐temperature magnetic circular dichroism: Dynamic Jahn–Teller effect detected by MCD
Authors: Mineyev A. P. , Sharonov Yu. A. , Sharonova N. A. , Figlovsky V. A.
Published: December 2004

This paper analyzes the low‐temperature magnetic circular dichroism of NO–Fe(II)hemoproteins in detail. We include the Jahn–Teller effect in our consideration of the low‐temperature MCD results.
Coordinate measurements and operators
Authors: Broyles A. A.
Published: December 2004

Relativistic quantum‐field theory provides the machinery for calculating wave functions or probability amplitudes depending upon space‐time coordinates. The currently accepted theory, however, fails to provide position operators and a means of measuring particle coordinates that are consistent with Dirac's properties of physical observables. This is because it calls for a space position probability distribution at a specified time. This paper shows, however, that space‐time event coordinate operators, together with a corresponding measurement procedure, can be found that are consistent with Dirac's requirements. This is done through a reinterpretation of the amplitudes computed by field theory and does not involve any change in that mathematical formalism. The measurement of the space‐time coordinates of an event is accomplished by detecting the absorption of a photon by a particle from each of two light pulses designed to overlap at a given point at a given time. If a final emitted photon has an energy whose sum with the final particle energy approximately equals the sum of the mean energies of the pulses, then the absorption of the two pulse photons must certainly have taken place within a distance the order of a Compton wavelength of the small space‐time region of overlapping pulses. This is clear from the fact that the high energy required to confine the pulses to very small volumes must throw a particle absorbing them far off the mass shell. Thus the absorption of the two photons throws the particle into a narrowly confined spatial wave function that must decay extremely rapidly—to within a Compton wavelength, a delta function in space‐time. This delta function is the eigenfunction of space‐time coordinate operators Xμ and is the scalar product of vectors in a Hilbert space spanned by spin–space‐time kets large enough to contain the operators of the Poincaré group. These event operators transform properly under the action of Poincaré operators but do not commute with the mass. If the Compton wavelength is not negligible compared to the accuracy desired in the coordinate measurements, individual coordinate measurements are no longer possible. Nevertheless, a large number of repeated coordinate measurements can be carried out to produce a coordinate probability distribution. This distribution can be unfolded to find a true coordinate probability distribution if the charge form factor is known from basic theory. An analysis of laboratory particle detection techniques shows that they actually determine space coordinates and energy rather than spatial coordinates at a given time. When this fact is included, the Klein–Nishina formula can be derived using the electromagnetic four‐vector potential as the photon probability amplitude wave. To clarify the meaning of the observables, a mass‐momentum measurement is described.
Multiple scattering mass operator method for molecular orbital calculations
Authors: Pavãto A. C. , Braga M. , Fazzio A. , Leite J. R.
Published: December 2004

An exchange‐correlation potential model to be used in connection with the multiple scattering method is presented. Retaining the main advantages of the multiple scattering method with the Xα potential, particularly its low computational requirements, this new formalism does not require any adjustable parameter. Test calculations on the NiF64− system are reported and compared with experimental and ab initio results.
Rydberg states in chemistry
Authors: Sandorfy C.
Published: December 2004

The excited states of molecules can be divided into three categories: valence‐shell, Rydberg, and intermediate. Reasons are given why this classification is important for photochemistry. The photolytic primary steps should be different for excited states falling into these different categories. Rydberg states should be taken into account when the photochemical reaction path is interpreted in terms of orbital symmetry conservation or diradical intermediates. They might play a role in certain photobiological events.
Study of molecular polarizabilities of some amino and polyamino acids
Authors: Gupta V. P. , Gupta V. D. , Mehrotra C.
Published: December 2004

Molecular polarizabilities of glycine,L‐alanine,L‐proline, and polygylcine I and II have been calculated by the Lippincott delta function potential model, the atomic polarization method, and the atom‐dipole interaction model. In the atom‐dipole interaction model the molecular polarizabilities are dependent on atomic (or group) polarizabilities and positional coordinates of the atoms (or groups) constituting the molecule and are conformation dependent. Those obtained from the other two methods are conformation independent and dependent on bond properties only. The results are compared with those obtained from the Kerr effect and molar refraction data.
Electrostatic molecular potential contour maps generated from ab initioMODPOT/VRDDO/MERGE wave functions of carcinogenic 3‐methylcholanthrene and its metabolites
Authors: Hariharan P. C. , Kaufman Joyce J. , Petrongolo Carlo
Published: December 2004

The electrostatic molecular potential contour maps were calculated for carcinogenic 3‐methylcholanthrene (3‐MCA) and a number of its metabolites {3‐MCA 7,8‐oxide and 3‐MCA 9,10‐oxide; 3‐MCA 7,8‐dihydrodiols[several stereoisomers: A trans(equatorial, equatorial) and A cis(equatorial, axial)]; 3‐MCA 9,10‐dihydrodiol–7,8‐epoxide A βββ and 3‐MCA 9,10‐dihydrodiol–7,8‐epoxide A αβα}. The maps were generated from our ab initio MODPOT/VRDDO/MERGE wave functions calculated for these species. The results of these maps for 3‐MCA [similarly to our results for the maps we generated for benzo(a)pyrene (BP)] show that these electrostatic molecular potential contour maps can be used to indicate favored positions of attack for electrophilic species, such as “electrophilic” oxygen to form an epoxide as well as for positive ion attack. The 3‐MCA maps indicate the favored site for attack and the pathways. The maps around 3‐MCA 9,10‐oxide and around 3‐MCA 9,10‐dihydrodiol‐7,8‐epoxide indicate the directional preferences for proton assisted epoxide ring opening. The maps around the 3‐MCA dihydrodiols indicate that while for certain stereoisomers the “electrophilic” oxygen will prefer to attack from below, for other isomers it will prefer to attack from above. This gives great insight into the stereochemical preference for formation of different 3‐MCA 9,10‐dihydrodiol–7,8‐epoxides.
Diagram approach to group algebraic methods
Authors: Black R. J. , Stedman G. E.
Published: December 2004

Class sum theory, the duality with IRREP methods and tensor operators in the group algebra are discussed by generalizing the diagrammatic approach of conventional IRREP theory to include group label manipulation. Concepts such as invariant nodes and Jucys–Levinson–Vanagas reduction theorems generalize straightforwardly. The results are capable of unique simplification for certain nodes, when the group rearrangement theorem is useable or when a class sum is performed. A duality transformation (between IRREP–partner and class–element labels) emerges as an important concept.
Semiempirical molecular orbital calculations on octahedral aquo complexes of transition metal ions: σ‐donor ability of water
Authors: Bhattacharyya Sankar Prasad
Published: December 2004

A comparative analysis is carried out on the strengths of binding of a series of transition metal ions to a water molecule using CNDO type MO theory developed earlier. Comparative features of the energetics of metal–ligand bonds in aquo and amine complexes are also analyzed.
Virial fragments and the Hohenberg–Kohn functional
Authors: Ludeña Eduardo V. , Mujica Vladimiro
Published: December 2004

Starting from the Hohenberg‐Kohn functional we show that when the energy density is given as a function of ρ and ∇ρ, i.e., ξ = ξ(ρ, ∇ρ), the condition ∇ρ · n = 0 (which was found by Bader et al. to define virial fragments), appears as a natural boundary condition for the variation of this functional. We also show that when the energy density includes second order derivatives (∇2ρ) this condition is necessary but not sufficient to guarantee the vanishing of the variation. The implications of these results are discussed in the context of a density functional theory for virial fragments.
Method of recurrent construction of Löuwdin spin‐adapted wave functions. II. Local representation of creation–annihilation operators
Authors: Panin A. I.
Published: December 2004

Some compositions of the addition and subtraction operators and recurrence relations for the Sanibel‐type coefficients cu, v (n, s, M) generated by these compositions are studied. A local representation of the fermion creation–annihilation operators via the addition and subtraction operators is obtained. Operators of single excitations, coupling, and decoupling operators, in terms of which the unitary group generators can be expressed are defined. The resulting representation of the nonelementary unitary group generators is much more simple than in the Gelfand–Tzetlin basis and in the most general case contains only six logically different terms, each of them possessing quite transparent physical significance.
Theoretical analysis of K‐region and bay‐region indicators of carcinogenicity
Authors: Lowe John P.
Published: December 2004

The correlation of the K‐region carcinogenicity indices of Pullman and of Mainster and Memory with bay‐region carbocation delocalization energy (BCDE) is displayed and shown to be maintained at the perturbational molecular orbital (PMO) level. PMO algebraic relations are examined to reveal the underlying relationships. Some correlation between BCDE and K‐region indices exists simply because carbocation formation occurs preferentially on carbons which are bonded to positions α (adjacent) to ring fusion centers. Sampling a K region is synonymous with sampling such α carbons. However PMO analysis shows that a very strong correlation exists between BCDE and indices for a certain type of K region (called “primitive”). It is further shown that high BCDE is favored by a straight‐line chain of benzene rings as one moves away from the bay region. Kinks in the chain will lower the BCDE, and the closer the kink is to the bay region, the greater is its effect. Effects of methylation upon BCDE are shown to correlate with K‐region indices if the methylation occurs at a carbon which is in the opposite class as the carbon to which the bay‐region carbocation is attached.
Calculated properties of some possible vinyl chloride metabolites
Authors: Politzer Peter , Proctor Timothy R.
Published: December 2004

There is considerable evidence indicating that the carcinogenic action of vinyl chloride involves metabolic conversion to the epoxide (chlorooxirane) as the initial step. In order to learn more about its subsequent behavior, we have computed structures, energies and other properties for two different protonated forms of the epoxide, and also for two possible rearrangement products, chloroacetaldehyde and acetyl chloride. An ab initio SCF‐MO procedure (GAUSSIAN 70) was used. Oxygen protonation is found to weaken both CO bonds, the effect being greater for the bond involving the carbon bearing the chlorine. Chlorine protonation leads to a marked weakening of the CCl bond; this suggests a possible loss of HCl, leaving behind a carbonium ion (and possible alkylating agent or rearrangement precursor). Thus, while CO bond breaking is doubtless an important reaction pathway for chlorooxirane, our results indicate that attention should also be focused upon the CCl bond; its rupture may conceivably be a key step in the biological action of vinyl chloride.