A criterion for the confluence of two seams of conical intersection in triatomic molecules

It is shown that the cross product t ^{I J} (R _x )≡g ^{I J} (R _x )×h ^{I J} (R _x ), where g _τ ^{I J} (R)=(c ^I (R _x )−c ^J (c ^I (R _x )+c ^J (R _x )), h _τ ^{I J} (R)=c ^I (R _x )^† c ^J (R _x ), τ is an internal nuclear coordinate, the c ^I (R) satisfy [H(R)−E _I (R)]c ^I (R)=0 and H(R) is the electronic Hamiltonian matrix, is a unique property of a conical intersection at R _x . t ^{I J} (R _x )=0 when R _x is located at the intersection of two (or more) seams of conical intersection. This criterion for an intersection of two seams of conical intersection has important implications for algorithms that seek to locate such points. Here it␣is␣used to analyze the trifurcation of a generic C_2v ^2S+1 A−^2S+1 B seam of conical intersection, analogous to those recently found in AlH₂ and CH₂. Received: 31 July 1997 / Accepted: 27 August 1997     

Synthetic Ionophores. Part 20: Synthesis and Ionophore Character of 2-Aminothiophenol and 1,3-/1,4-Phenylene Based Silver Selective Receptors

Nucleophilic displacements of 1,3- and 1,4-bis(bromomethyl)benzenes with 2-aminothiophenol provide 1,3- and 1,4- bis(2-aminophenylthiomethyl)benzenes 3 and 11 which undergo intermolecular cyclodehydrochlorination with thiodiglycolyl dichloride and isophthaloyl dichloride to give respectively 6, 8 and 12,13. The diamine 3 and its N,N'-dibenzyl derivative 4 with pyridine-2,6-dicarbonyl dichloride give 7 and 5, respectively. The extraction and transport behaviour of these receptors have been determined towards alkali (Li⁺, Na⁺, K⁺),alkaline earth (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺), Tl⁺, Ag⁺ and Pb²⁺ picrates.The participation of various ligating sites in binding have been evaluated through ¹³ NMR studies. The acyclic receptors 3, 4 and 11 show higher Ag⁺ selectivity than the cyclic analogs 6 and 12. In the case of acyclic receptor 3 the organisation induced by the 1,3-phenylene spacer and 2-aminophenylthio units and its flexibility generates optimal binding and selectivity towards Ag⁺. However, in cyclicreceptors 3 and 12 though the three thioether unitsare better organised, the inward placement of the NH_amide units restricts the entry of Ag⁺ into the cavity and lowers both the order of binding and selectivity. The lack of binding ability in 7due to an intramolecular NH_amide–-N_py H-bond isrestored in the N-benzyl derivative 5.     

Synthesis,coordination properties and DFT studies of novel trans-disubstituted hexaaza-macrocycles containing pyridine and/or ethyldioxolane arms

Abstract

Novel trans-disubstituted hexaaza-macrocyclic ligands L¹ and L² were successfully prepared by the alkylation of the trans secondary amines presented in L with pyridine and ethyldioxolane groups, respectively. The coordination properties of compounds L¹ and L² towards different transition, post-transition and lanthanoid metal ions were explored. Colorless crystals of [NaL¹]I and L^2´Br₂, suitable for X-ray diffraction, were obtained by slow evaporation of an acetonitrile solution of compounds L¹ or L², showing an anti conformation between the methyl groups and the pendant arms in trans positions. The [ML¹]ⁿ⁺ (M?=?Ni²⁺, Cu²⁺, Zn²⁺) systems were investigated by DFT calculations (B3LYP model).     

Synthesis,crystal structure,redox behavior and DNA-binding properties of a series of copper(II) complexes with two new carboxamide derivatives

Four mononuclear copper(II) complexes of two new carboxamide derivatives formulated as [Cu(L¹)₂](ClO₄)₂ (1a), [Cu(L¹)₂](NO₃)₂ (1b), [Cu(L²)₂(H₂O)₂](ClO₄)₂ (2a), and [Cu(L²)₂(H₂O)](NO₃)₂ (2b) have been isolated in pure form from the reaction of L¹ and L² [where L¹ = N-(furan-2-ylmethyl)-2-pyridinecarboxamide and L² = N-(thiophen-2-ylmethyl)-2-pyridinecarboxamide] with copper(II) salts of perchlorate and nitrate. All the complexes were characterized by physicochemical and spectroscopic tools along with single-crystal X-ray diffraction studies. The structural analyses showed that 1 is monomeric of square planar geometry with copper(II) chelated by two L¹ ligands. Complex 2 differs in coordination geometry, being octahedral and distorted square pyramidal. Two L² ligands occupy the equatorial positions of the octahedral 2a and the basal sites of the pyramidal 2b, with water molecules that complete the coordination sphere in each case. Electrochemical studies using cyclic voltammetry showed a reversible redox behavior of the copper(II) in 1 and 2. The electronic spectroscopic behavior and the trend of one electron equivalent redox potential corresponding to a Cu^II/Cu^I couple have also been confirmed by density functional theory calculations. The spectroscopic and viscosity measurement study in tris–HCl buffer suggested an intercalative interaction of 1a and 2 with calf thymus DNA likely due to the stacking between the non-coordinated furan and thiophene chromophore with the base pairs of DNA.     

Supramolecular dyad derived from a buckybowl series of O2N2-donor naphthodiaza-crowns coordinated to C60: photophysical,NMR and theoretical studies

Supramolecular complexation of C₆₀ with L¹-L⁵ were studied in toluene, chloroform and 1,2-dichlorobenzene solvents using UV–vis, fluorescence, ¹H, ¹³C NMR spectroscopy as well as density functional theory (DFT) calculations. The Job’s plot of continuous variation method established 1:1 stoichiometry for L¹-L⁵/C₆₀. Binding constants (K) calculated for L¹-L⁵/C₆₀ were also determined employing UV–vis and fluorescence spectroscopy. Both steady-state and time-resolved fluorescence spectroscopic surveys showed remarkable fluorescence quenching phenomenon for L¹-L⁵ in the presence of C₆₀ which was primarily attributed to involvement of a static process. The observed fluorescence quenching in L¹–L⁵ was described in terms of both π–π and n–π interactions of the naphthalene moieties and the nitrogen donor groups on the aza-crown macrocyclic ligands with C₆₀, respectively. Moreover, DFT calculations using B₃LYP/6-31G* basis set confirmed on the aforesaid π–π interaction of naphthalene groups on the aza-crowns with C₆₀. The DFT calculations also established significant distributions of charge between C₆₀ and L¹-L⁵ in according to the electronic structure and geometry of L¹-L⁵/C₆₀, very similar to phthalocycnine/C₆₀ systems.     

Theoretical study on structures and stability of HC2P isomers

 The structures and isomerization pathways of various HC₂P isomers in both singlet and triplet states are investigated at the B3LYP/6-311G(d,p), QCISD/6-311G(d,p) (for isomers only) and single-point CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p) levels. At the CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p) level, the lowest-lying isomer is a linear HCCP structure ³ 1 in the ³∑⁻ state. The second low-lying isomer has a CPC ring with exocyclic CH bonding ¹ 5 in a singlet state at 10.5 kcal/mol. The following third and fourth low-lying isomers are a singlet bent HCCP structure ¹ 1 at 20.9 kcal/mol and a bent singlet HPCC structure ¹ 3 at 35.8 kcal/mol, respectively. Investigation of the HC₂P potential-energy surface indicates that in addition to the experimentally known isomer ³ 1, the other isomers ¹ 1, ¹ 3 and ¹ 5 also have considerable kinetic stability and may thus be observable. However, the singlet and triplet bent isomers HCPC ¹ 2 and ³ 2 as well as the triplet bent isomer HPCC ³ 3 are not only high-lying but are also kinetically unstable, in sharp contrast to the situation of the analogous HCNC and HNCC species that are both kinetically stable and that have been observed experimentally. Furthermore, the reactivity of various HC₂P isomers towards oxygen atoms is briefly discussed. The results presented here may be useful for future identification of the completely unknown yet kinetically stable HC₂P isomers ¹ 1, ¹ 3 and ¹ 5 either in the laboratory or in interstellar space. Received: 5 November 2000 / Accepted: 25 November 2001 / Published online: 8 April 2002     

A Convenient Synthesis of New Macrocyclic Thioether-Esters and Ether-Esters: Extraction Properties of These Esters for Alkali,Alkaline Earth,and Transition Metal Cations

Macrocyclic thioether-esters and ether-esters have been prepared by treating 2,2′-dithiobenzoic acid dichloride and 1,2-benzendicarboxylic acid dichloride with appropriate glycols or dithiol. The complexing ability of these thioether-esters and ether-esters toward Li⁺, Na⁺, K⁺, Mg ^{2 +} , Ca ^{2 +} , Sr ²⁺ , Ba ^{2 +} , Co ^{2 +} , and Ni ^{2 +} has been measured by the solvent extraction method. The extraction data indicate that compound 2 exhibits stronger selectivity toward Li⁺, 3 toward Ba ^{2 +} , 4 toward K⁺, 5 toward Mg ^{2 +} , 6 toward Ba ^{2 +} and Sr ^{2 +} , and 7 toward Co ^{2 +} and Ni ^{2 +} when compared with other cations.     

Imides of 2-Trifluoroacetylphenol and other Trifluoracetic acid Esters: Novel Reactions with Phosphorus(III) Derivates

Abstract

The imido derivates of 2-trifluoroacetylphenol, 1 (R¹=H, Me, iPr) react with the isocyanatophosphites (R²O)₂PNCO, 2 (R²[dbnd]Et, R²-R²[dbnd]CMe₂-CMe₂) to yield the bicyclic compounds 3, wheras in case of 1 (R¹[dbnd](CH₂)₂NMe2) the λ³σ³P compounds 4 are found. The phosphorus(III) chlorides R3PC12 (R³[dbnd]Ph, OEt) and 1 (R¹[dbnd]H, Me) give rise to furnish the tricyclic phosphoranes 5. However with 1 (R¹[dbnd]iPr) phosphite 6 is obtained, which adds hexafluoracetone to give the 1,3,2λ⁵σ⁵-dioxaphospholane 7. 2-(Trifluoracetoxy)pyridine 8. reacts with Tris(trimethylsily1)phosphite to yield the bis(phosph0nate) 10. Some molecular structures are discussed on the basis of x-ray diffraction results.     

Synthesis of deuterium-labelled substrates for the study of oleuropein biosynthesis in Olea europaea callus cultures

We propose the cell culture approach to investigate oleuropein (1) biogenesis in Olea europaea L. We suggest employing olive callus cultures to identify the iridoidic precursor of oleuropein. In fact, we confirmed that callus cells from olive shoot explants are able to produce key secoiridoid as 1. To enable this approach, we synthesised and characterised deuterium-labelled iridoidic precursors belonging both to the loganin and the 8-epiloganin series. These iridoids are [7,8-²H₂]-7-deoxy-8-epi-loganin (2^D), [8,10-²H₂]-8-epi-loganin (4^D) and [7,8-²H₂]-7-deoxy-loganin (3^D).     

Synthesis and Characterization of New Metal-free and Metallophthalocyanines Substituted with Tetrathiadiazamacrobicyclic Moieties

New metal-free (5, 8) and metallophthalocyanines (6, 9) containing four diazatetrathiamacrobicycles or crosswise-disubstituted attached with two nitro and two macrobicyclic groups were synthesized by cyclotetramerization of 7,8-dicyano-4,11,22,23-tetrathia-1,14-diazapentacyclo[12.10.10.0^5,10.0^16,21.0^26,31]tetratriconta-5,7,12,19,20,21,28,30,32-nonane (3), 8,10-dihydro-8,11-diimino-4,14,24,34,-tetrathia-1,17-diazapentacyclo[15.13.13.0^5,13.0^19,23.0^28,33]tetratriconta-5,7,12,19,20,22,28,30,32-nonaisoiminoindoline (4) or 6-nitro-1,3,3-trichloroisoindolenine (7) in the presence of the corresponding metal salt or a strong organic base. The new compounds were characterized by a combination of elemental analysis and ¹H NMR, ¹³C NMR, IR, UV–Vis and MS spectral data.     

Synthesis of Anellated Pyranose Derivatives on the Basis of Levoglucosenone

ABSTRACT

1,6-Anhydro-2-(dicyanomethylene)-2,3-dideoxy-4-S-ethyl-4-thio-β-D-erythro-hexopyranose (1) reacted with tosyl azide or sulfur and triethylamine to furnish the 5-aza-10, 11-dioxatricyclo[6.2.1.0^2,6]undeca-2(6),3-diene-3-carbonitrile 2 and the 10,11-dioxa-5-thiatricyclo[6.2.1.0^2,6]undeca-2(6),3-diene-3-carbonitrile 3, respectively. The reactions of 1 with arylisothiocyanates furnished the 11,12-dioxa-5-thiatricyclo[7.2.1.0^2,7]dodeca-2(7),3-diene-3-carbonitriles 4 and 5. 3 underwent cyclization with triethyl orthoformate and ammonia or hydrazine hydrate to afford the 5,7-diaza-14,15-dioxa-9-thiatetracyclo[10.2.1.0^2,10.0^3.8]pentadecatetra(tri)enes 7 and 8, respectively.     

Synthesis of mixed-ligand complexes of VO2+ and VO3+ incorporating hydrazone, 1,10-phenanthroline and 8-hydroxyquinoline

2-Aminobenzoylhydrazide (abh) reacts with equimolar amounts of either [V^IVO(acac)₂] or [V^IVO(bzac)₂] (where acac^? and bzac^? are the monoanionic forms of acetylacetone (Hacac) and benzoylacetone (Hbzac), respectively) in the presence of equimolar amounts of 1,10-phenanthroline (phen) to form the octahedral mixed-ligand complexes [V^IVO(L¹)(phen)] (1) and [V^IVO(L²)(phen)] (2), where (L¹)^2? and (L²)^2? are the dianionic forms of the 2-aminobenzoylhydrazone of acetylacetone (H₂L¹) and benzoylacetone (H₂L²). Upon substituting phen by 8-hydroxyquinoline (Hhq), pentavalent [V^VO(L¹)(hq)] (3) and [V^VO(L²)(hq)] (4) complexes were instead obtained. In the crystal structures of 3 and 4, the hydrazone ligands coordinate to the vanadium center through the enolic-O, one imine-N and amide-O in a mer geometry. The amine and the second imine nitrogen form intramolecular hydrogen bonds. Complexes 1 and 2 display quasi-reversible one-electron oxidation peaks near +0.60 V, while the pentavalent 3 and 4 exhibit quasi-reversible one-electron reduction peaks near ?0.18 V versus Ag/AgCl in CH₂Cl₂ solution. EPR spectroscopic studies on 1 and 2 suggest that the unpaired electron is present in the d_xy orbital. DFT studies for 3 indicate that the d_xy orbital of vanadium is the main contributor to the LUMO.     

Synthesis and structural characterization of nitrite-coordinating CoII and CoIII complexes as models for the reaction center of Co-substituted nitrite reductase

Co^II and Co^III complexes containing nitrite and tridentate aromatic amine compounds [bis(6-methyl-2-pyridylmethyl)amine (Me₂bpa) and bis(2-pyridylmethyl)amine (bpa)] have been prepared as models of the catalytic center in Co-substituted nitrite reductase: [Co^II(Me₂bpa)(NO₂)Cl]₂ · acetone (2), Co^II(Me₂bpa)(NO₂)₂ (3), Co^II(bpa)(NO₂)Cl (4), Co^II(bpa)(NO₂)₂ (5), Co^III(Me₂bpa)(NO₂)(CO₃) (6), and Co^III(bpa)(NO₂)₃ (7). The X-ray crystal structure analyses of these Co^II and Co^III complexes indicated that the geometries of the cobalt centers are distorted octahedral and the Me₂bpa and bpa with three nitrogen donors exhibit mer- (2, 3, and 7) and fac-form (4 and 6). The coordination mode of nitrite depends on the cobalt oxidation state, to Co^II through the oxygen (nitrito coordination, O- and O,O-coordination) and to Co^III through nitrogen (nitro coordination, N-coordination mode). These findings are consistent with the results of their IR spectra, except that another oxygen of the O-coordinated nitrito group in 3 might interact weakly with Co^II according to its IR spectrum. Reductions of the nitrite in 2, 3, 4, and 5 to nitrogen monoxide were not accelerated in the presence of proton, perhaps due to the nitrito coordination in these Co^II complexes.     

Electroanalytical and spectral investigation of organic receptors as colorimetric and absorption ratiometric anion chemosensor

Colorimetric receptors R1 and R2 have been designed and synthesized by Schiff base condensation and characterised by standard spectroscopic techniques. Anion binding ability of the receptors have been investigated quantitatively through optical, electrochemical and ¹HNMR titration studies. UV-vis spectra of receptor R1 and R2 exhibited a significant red shift for F^? and AcO^? ions with a visual color response. Receptor R1 exhibited selective response towards AcO^? ion in the presence of HEPES buffer media. Incremental color change of receptor R2 with the higher equivalence of AcO^? ions clearly represent the ratiometric response. Cyclic voltammetric studies of R1 and R2 exhibits shift in oxidation and reduction peak with successive addition of AcO^? ions indicating the anion induced oxidation of -NH and reduction of the keto group and nitro species. Electrooptical and ¹H NMR titration studies of R2 collectively reflects the anion induced change of chromophore from C=N to N=N indicative of azo-hydrazone tautomeric signaling in the presence of AcO^? ions. Lower detection limit of 2.1 and 0.41 ppm achieved with sodium salt of AcO^? ion with R1 and R2 reflects their utility as colorimetric chemosensor.     

Synthesis of the [<Superscript>2</Superscript>H,<Superscript>15</Superscript>N]-labeled antiviral drug “triazavirine”

Selective methods for the incorporation of stable isotopes ¹⁵N and ²H into the structure of antiviral medicine “triazavirine” 1 were developed. The synthesized isotopically modified “triazavirine” 1– ² H ₃ , ¹⁵ N ₃ contained the labeled atoms in both the azole and the azine rings. ¹³C and ¹⁵N NMR spectra of the isotope-containing sample 1– ² H ₃ , ¹⁵ N ₃ were thoroughly analyzed.     

C60-吡咯烷衍生物的合成及非线性光学性质的研究

通过富勒烯C₆₀与肌氨酸和有机醛化合物的1,3-偶极环加成反应, 获得了九种含不同有机功能基团的C₆₀吡咯烷衍生物1～9, 用¹H NMR, ¹³C NMR, FTIR, UV-vis和FAB-MS进行了结构表征; 利用皮秒激光光源, 采用z扫描技术测定了分子的三阶非线性超极化率γ⁽³⁾, 结果显示: 化合物3 (γ⁽³⁾＝4.14×10^－33 esu)具有最大的三阶非线性光学系数, 说明增加噻吩共轭链的长度, 使三阶非线性活性增加; 对具有相同共轭链的C₆₀-噻吩吡咯烷衍生物(2, 5, 1和4), 吸电子取代基减小了三阶光学非线性活性, 给电子基增大了三阶光学非线性活性; 同时发现喹啉环2-位键联(7)比4-位(8)有更好的三阶光学非线性活性.     

13C, 15N and 113Cd NMR and Molecular Orbital Studies of Novel Bile Acid N-(2-aminoethyl)amides and Their Cd2+-complexes

Lithocholic acid N-(2-aminoethyl)amide (1) and deoxycholic acid N-(2-aminoethyl)amide(2) have been prepared and characterized by¹H, ¹³C and ¹⁵N NMR. The accurate molecular masses of 1 and 2 have been determined by ESI MS. The formation of the Cd²⁺-complexes (1+Cd and 2+Cd) in CD₃OD solution have been detected by ¹H,¹³C, ¹⁵N and ¹¹³Cd NMR. The ¹³C NMR chemical shift assignments of 1 and 2 and their Cd²⁺-complexes are based on DEPT-135 and z-GS ¹H,¹³C HMQC experiments as well as comparison with the assignments of the related structures. The ¹⁵N NMR chemical shiftassignments of the ligands and theirCd²⁺-complexes are based on z-GS¹H,¹⁵N HMBC experiments. ¹³C NMR chemical shift differences between 1and its 1:1 Cd²⁺-complex based on ab initiocalculations at Hartree-Fock SCI-PCM level using3-21G(d) basis set are in agreement with theexperimental shift changes observed onCd²⁺-complexation.     

Metal binding selectivity of oxa-aza macrocyclic ligand: a DFT study of first- and second-row transition metal for four coordination systems

A detailed theoretical study of the 1,7,1l,17-tetraoxa-2,6,12,16-tetraaza-cycloeicosane ligand ([20]AneN₄O₄) coordinated to Fe²⁺, Co²⁺, Ni²⁺, Ru²⁺, Rh²⁺, and Pd²⁺ transition metal ions was carried out with the B3LYP method. Two different cases were performed: when nitrogen is the donor atom (1a _q ) and also with the oxygen as the donor atom (1b _q ). For all the cases performed in this study 1a _q structures were always more stable than the 1b _q ones. Considering each row is possible to see that the energy increases with the increase of the atomic number. The M²⁺ cation binding energies for the 1a _q complexes increase with the following order: Fe²⁺ < Ru²⁺ < Co²⁺ < Ni²⁺ < Rh²⁺ < Pd²⁺.

     

Synthesis of Lewis a and Lewis X Pentasaccharides Based on N-Trichloroethoxycarbonyl Protection 1

Abstract

Thexyldimethylsilyl 4,6-O-benzylidene-2-deoxy-2-trichloroethoxycarbonylamino-β-D- glucopyranoside (4), having the 3-hydroxy group unprotected, is a versatile starting material for the synthesis of glucosamine containing oligosaccharides. Thus, reaction with galactosyl donor 5 or fucosyl donor 6 afforded the desired β(1-3)- and α(1-3)-linked disaccharides 7 and 8, respectively, in high yields. Reductive opening of the benzylidene moieties in 7 and 8 gave access to the 4-hydroxy groups in 9 and 10. Ensuing fucosylation of 9 or galactosylation of 10 led to Lewis A (Le^a) and Lewis X (Le^x) trisaccharide building blocks 13 and 14, respectively. Their transformation into glycosyl donors 19 and 20 and subsequent reaction with 3b-O-unprotected lactose derivative 23 as acceptor furnished the Le^a? and Le^x pentasaccharide precursors 24 and 25. Exchange of the N-trichloroethoxycarbonyl group for an N-acetyl group and removal of the O-benzyl and O-acetyl protective groups afforded the desired Le^a? and Le^x? pentasaccharides 1 and 2.

     

New Look into the Synthesis of Polyhalogenoarylphosphanes

The present study shows new aspects of the synthesis of polyhalogenoarylphosphanes. The sterically hindered anions Ph(R)P-Y^? (1a–c, Y = O, lone pair; R = Ph, Bu^t) have been used to show the complexity of the reaction between phosphorus nucleophiles and hexahalogenobenzenes or 9-bromofluorene (E3). The Ph(Bu^t)P-O^? (1a) anion reacts with hexachlorobenzene (E1), hexafluorobenzene (E2), or E3 to give Ph(R)P(O)X (4a–c, X = F, Cl, Br) with the release of the corresponding carbanion as a nucleofuge, followed by side reactions. In contrast, the lithium phosphides Ph(R)PLi (1b,c) react with hexahalogenobenzenes to give the corresponding diphosphanes 5a,b as the main product and traces of P-arylated products, i.e., Ph(R)P-C₆X₅ (10a,b, X = Cl, F). Unexpectedly, Ph(Bu^t)PLi (1b) reacts with an excess of 9-bromofluorene to give only halogenophosphane Ph(Bu^t)P-X.