Ternary copper(II) complexes containing reduced Schiff base ligands (N-(2-hydroxybenzyl)-alpha-amino acid, where alpha-amino acid = glycine (H(2)sgly), L-alanine (H(2)sala) and L-valine (H(2)sval)) and 1,10-phenanthroline (phen) have been synthesized and characterized. The neutral mononuclear Cu-II complexes [Cu(L)(phen)].xH(2)O (L = sgly (1), sala (2), sval (3)) have been prepared from Cu(OAc)(2).H2O, H2L, phen, LiOH in the ratio 1 : 1 : 1 : 2 in H2O-MeOH. The monodeprotonated Cu-II complexes [Cu(HL)(phen)](ClO4).xH(2)O (L = Hsgly (4), Hsala (5), Hsval (6)) have been obtained from Cu(ClO4)(2).6H(2)O, H2L, phen, LiOH in the ratio 1 : 1 : 1 : 1 in H2O-MeOH. The dinuclear Cu-II complexes [Cu-2(L)(phen)(3)](ClO4)(2).xH(2)O (L = sgly (7), sala (8), sval (9)) were the only product isolated instead of 1-3 when Cu(ClO4)(2).6H(2)O was used in the place of Cu(OAc)(2).H2O. The electronic spectral titration experiments indicate that the neutral mononuclear compounds could be converted to protonated 4-6 but not vice versa. The protonated phenolic oxygen is involved in medium to weak interaction with Cu-II-OH distances, 2.446(3) Angstrom in 4, and 2.73(4) and 2.79(4) Angstrom in 5. Compound 4 is a mononuclear cation while 5 is a helical coordination polymer in the solid state with the carboxylate group in anti-anti bridging mode. The structures of 1, 4, 5 and 7 have been determined by X-ray crystallography. Variable temperature magnetic measurements of the helical polymer 5 showed very weak ferromagnetic coupling with mu(eff) per Cu remaining constant at 1.80 BM between 300 and 30 K, then a rapid increase to 2.07 BM at 4 K. Fitting to a Heisenberg S = 1/2 chain model gave a J value of 1.2 cm(-1)
Endogenously bridged binuclear copper(II) and zinc(II) complexes of singly deprotonated 1,2-bis[1,4,7-triazacyclonon-1-yl]propan-2-ol (T2PrOH) have been prepared by reacting the ligand hexabromide salt with appropriate metal salts. An X-ray structural analysis of the Cu(II) complex, [Cu2(T2PrO)Br2]Br·2H2O (1), confirmed the presence of a complex cation, [Cu2(T2PrO)Br2]+, which consists of Cu(II) centres linked by an endogenous alkoxo bridge. Three N donors from the tacn macrocycle and a bromo ligand complete the coordination sphere. The two Cu(II) centres are in slightly different distorted square pyramidal (SPY) Cu(II) geometries. A magnetic susceptibility study of 1 revealed the presence of moderately strong antiferromagnetic coupling between the Cu(II) centres (J = −86 cm−1), as found for other binuclear Cu(II) complexes bridged by endogenous alkoxo groups. The molecular structure of the Zn(II) complex, [Zn2(T2PrO)Br(H2O)2](ClO4)2 (2), apart from confirming that the two Zn(II) were bridged by an endogenous alkoxo group, revealed coordination asymmetry in the two Zn(II) centres. One Zn(II) centre is six-coordinate and pseudo-octahedral with the coordination sphere occupied by three tacn nitrogens, the bridging oxygen, one bromo and one water ligand, while the other is five-coordinate and pseudo-square pyramidal, lacking the bromo ligand.
A new Schiff-base macrocycle is obtained by the lead(II) ion templated [2+2] condensation of 3,5-diacetyl-1H-1,2,4-triazole and 1,4-diaminobutane in the presence of sodium hydroxide. Transmetallation of the resulting dilead complex, Pb2(L2)(ClO4)21, in acetonitrile with two equivalents of CoCl2·6H2O leads to the isolation of an orange, six-coordinate complex, [CoII2(L2)(OH2)3(NCCH3)](ClO4)2·H2O·2CH3CN 2. Subsequent reaction of 2 with two equivalents of NaOCN or NEt4Cl yielded red–purple five-coordinate [CoII2(L2)(NCO)2] 3 and red five-coordinate [CoII2(L2)(Cl)2]·1.5CH3CN 4, respectively. In all three air-stable dicobalt complexes the macrocycles contain two high-spin cobalt(II) centers which are weakly antiferromagnetically coupled (2J = −3.0, −0.4, −3.5 cm−1 for 2, 3 and 4, respectively). Complexes 2–4 have been characterized by X-ray diffraction and are the first structurally characterised complexes of a triazolate-containing macrocycle to date.
From the reaction of [60]fullerene with K2PtF6 at 470 degreesC, we have isolated C60F4, C60F6 (mixed with C60F7CF3), C60F8 and C60F2O. The F-19 NMR spectrum of C60F2O comprises a single line at -69.3 ppm, consistent with it being the simplest oxahomofullerene. The AA'BB' spectrum for C60F4 (double doublets at -141.82 and -142.78 ppm) shows it to be isostructural with C60H4, the addends in each case being in a 1,2,3,4-arrangement. The spectrum for C60F6 consists of doublets at -124.39 and -142.41 and a triplet at -139.78 ppm (coupling confirmed by a 2D spectrum), showing the fluorines to be in a previously-conjectured S-shaped motif, giving the molecule overall C-2 symmetry. The C60F8 spectrum comprises five peaks in a 1 : 2 : 2 : 2 : 1 ratio, so that the molecule has C-s symmetry based on a T-shaped motif, also conjectured previously. The peak couplings and symmetry indicate that the structure is created by addition of three pairs of fluorines across contiguous double bonds, followed by 1,8-addition of the final fluorine pair; this unique latter step is attributed to the ability of a pentagon containing three sp(3) carbons to accommodate a double bond, due to the reduction in strain. The C60F8 structure is part of the motif of C60F16 and C60F18, indicating it to be an intermediate on the pathway to formation of these compounds. The spectrum for C60F7CF3 shows the presence of one major and one minor isomer, the probable structures of which are deduced.
The structures of neutral and ionic 4-cyanophenylpalladium(II) and methylpalladium(II) complexes containing bidentate phosphine ligands were investigated in solution and in the solid state. Diphosphine ligands with a xanthene and a ferrocene backbone were used. New bis(dialkylphosphino) substituted Xantphos ligands were synthesised. H-1 NMR and P-31 NMR spectroscopy, conductivity measurements, UV-Vis spectroscopy, and X-ray crystallography were used to elucidate the structures of the complexes. Subtle changes of the phosphine ligands govern the coordination mode of the ligand. A variety of bidentate cis-, and trans-coordination and terdentate P-O-P, P-S-P and P-Fe-P coordination modes of the ligands were observed.
Ab initio (Hartree Fock), hybrid density functional (B3LYP), and semiempirical SCF (MNDO and AM1) calculations on sumanene (2), trioxa-sumanene (3) and trithia-sumanene (4) show that the C-3v-bowl structure is a minimum in all cases, but show dramatic variations in bowl depths and inversion barriers. Calculations on monosubstituted corannulenes C19XH10 (X = N+, B-, P+ and Si) at various levels predict that isoelectronic substituents possessing large atomic size increase the bowl-to-bowl inversion barrier at the hub position and decrease it at the rim position. Strain is a guiding factor, which accounts for the relative stability of positional isomers, curvature and bowl rigidity. The most stable positional isomer for a given substituent shows the minimum bowl-to-bowl inversion barrier in all cases. Calculations are performed on monosubstituted sumanenes derived by replacing skeletal C by isoelectronic atoms on sumanene (2), C20XH12 for X = N+ and Si. The general strategy of substituting larger atoms at rim positions flattens the bowl, and at the hub position it makes the bowl deeper. The strategy seems to work well. HF/3-21G and B3LYP/6-31G* computations are in very good agreement with each other, both qualitatively and quantitatively, and the central results are reproducible even at semiempirical levels. The performance of MNDO is consistently better than AM1 and becomes the method of choice when ab initio and DFT methods are not practical. Homodesmic equations, used to ascertain the thermodynamic stabilities of the monosubstitutions on corannulenes and sumanenes, show that substitution at appropriate sites imparts stability to the buckybowl framework. Linear correlation is obtained between the curvature, as estimated by the pyramidalization angle (Phi), and the inversion barrier. It is shown that bowl rigidity, curvature and the relative stabilities of positional isomers are controlled by the strain energy build up, which depends on the size of the substituent and the site of substitution.
Cationic liposomes are potential vectors for gene therapy applications. In previous work, our first generation cationic liposome system, formulated from cytofectin 3β-[N-(N′,N′-dimethylaminoethyl)carbamoyl]cholesterol (DC-Chol) and the neutral phospholipid dioleoyl-L-α-phosphatidylethanolamine (DOPE), was shown to transfect the lungs of mice in vivo. More recently, we described second generation cationic liposome systems including one formulated from DOPE and the novel pentaamine cytofectin N15-cholesteryloxycarbonyl-3,7,12-triazapentadecane-1,15-diamine (CTAP). As a result of formulation changes, CTAP–DOPE cationic liposomes are shown here to be approximately 400-fold more efficient at mediating gene delivery to mouse lung in vivo than DC-Chol–DOPE liposomes (2000-fold more effective than plasmid DNA alone). Physico-chemical analyses were performed on CTAP–DOPE, other second generation cationic liposome systems and DC-Chol–DOPE to determine how differences in the structural and physical properties of cytofectins, cationic liposomes and lipoplex mixtures might affect the efficiency of transfection both in vitro and in vivo. The data suggest that CTAP–DOPE cationic liposomes are effective in vivo for two reasons. (1) They are able to efficiently neutralise, condense and encapsulate nucleic acids into lipoplex particles; (2) they present unprotonated amine functional groups (pKa < 8) at neutral pH that could have the capacity for endosome buffering, thereby facilitating nucleic acid escape from endosome compartments into the cytosol following cell entry, like polyethylenimine. Weak, inefficient neutralisation, condensation and encapsulation of nucleic acids and the presence of unprotonated amine functional groups appear to be desirable liposome characteristics for in vitro transfection. The inclusion of “natural” propylene and butylene spacings between the amine functional groups of cytofectin head groups appears to promote efficient neutralisation, condensation and encapsulation. The inclusion of some “unnatural” ethylene spacings appears to be a useful way of lowering amine pKa values.
We have evaluated the allyl, 2-sulfonylethyl (SEC) and 2-thioethyl (TEC) carbamate linker systems for their application in solid supported N-acyliminium ion chemistry. As model reactions the syntheses of both homoallylic amines (via a three component protocol starting from an immobilised primary carbamate) and 2-substituted pyrrolidines (via carbamate bound 4,4-diethoxy-2-phenylbutylamine) were conducted. The required precursor p-nitrophenyl carbonate resins were prepared in high yields from cheap starting materials. All linkers proved to be stable under the required cationic reaction conditions. A serious drawback of the allyl carbamate linker is the tedious work up procedure which is required for the removal of the remains of the cleavage cocktail. The SEC linker is excellently stable to both Lewis and protic acidic conditions combined with a moderate base stability thus allowing the use of amines as reactants or bases in subsequent reactions. Cleavage of SEC linker bound amines was easily effected by treatment of the resins with a cocktail of 1 M NaOMe in THF-MeOH (2:1). The widest synthetic scope was found with the TEC linker which combined a sufficient stability against the cationic conditions required for N-acyliminium ion chemistry with complete stability under basic conditions. Cleavage of TEC linker bound amines could be effected by treatment with strong acid or by oxidation of the sulfide to the sulfone (to give the SEC linker) followed by addition of the basic cleavage cocktail.
Three new co-ordination complexes, [Ag(mu -hmt)(cin)]. 2H(2)O 1</BO>, [Ag-2(mu (3)-hmt)(sal)(2)] 2, and [Ag-2(mu -hmt)(mu (3)-hmt)(ssa)] 3 (hmt = hexamethylenetetramine (1,3,5,7-tetraazatricyclo[3.3.1(3,7)]decane), cin = cinnamate, sal = salicylate and ssa = 5-sulfosalicylate), have been prepared and structurally characterised. All of these complexes contain different new topological motifs of two-dimensional Ag-hmt nets. Among them, 1 has two-dimensional infinite co-ordination layers featuring compressed hexagonal units each consisting of six Ag(I) and four mu -hmt ligands as spacers. 2 has two-dimensional infinite wavy co-ordination layers with decagonal and small hexagonal units; each decagonal unit comprises six Ag(I) and four mu (3)-hmt ligands, and each small hexagonal unit comprises four Ag(I) and two mu (3)-hmt ligands. 3 has two-dimensional infinite highly undulated Ag-hmt layers with irregular decagonal units each consisting of five Ag(I), two mu -hmt and three mu (3)-hmt ligands.
According to previous electronic absorption, resonance Raman and DFT studies the lowest-energy electronic transition of the Ru-II and Os-II complexes trans.cis-[M(SnR3)(2)(CO)(2)(alpha -diimine)] (alpha -diimine = bpy, etc.) has a sigma (Sn-M-Sn) --> pi*(alpha -diimine) or sigma-bond-to-ligand charge-transfer (SBLCT) character. Nanosecond time-resolved step-scan IR (s(2)-TRIR) spectra of a series of these complexes are reported which indicate that the initial SBLCT excitation is followed by a redistribution of the electron density if this transition has an appreciable charge transfer character. This effect is virtually the same for the Ru and Os compounds, but different for the SnMe3 and SnPh3 complexes. s(2)-TRIR spectra of [Os(SnPh3)(2)(CO)(2)(dmb)] showed the occurrence of an infrared rigidochromic effect in a low-temperature glass.
Several substituted beta -amino alcohols 1 were synthesised in a diastereoselective manner via the novel highly versatile intermediate 8b, involving a combination of N-acyliminium ion and Weinreb amide chemistry.
The enantiopure dienes 8 and 24, which have been prepared by chemoenzymatic methods, engage in Diels–Alder cycloaddition reactions with maleic and citraconic anhydride to give adducts (e.g.25–27) embodying the ABC-ring system associated with spinosyns A (1) and D (2).
Conversion of 2-hydroxymethyl- and 2-hydroxyethylaniline with Appel salt 1 into the arylimines 3 and 4 is accompanied by formation of the chloromethyl and chloroethyl derivatives 8 and 9. Triphenylphosphine converts compound 8 into the benzothiazine 6 but the chloroethyl compound 9 gives N-(cyanothioformyl)indoline 10 (55%) rather than the analogous benzothiazepine 12. Indoline 10 is also formed from 9 with sodium hydride (45%), and from the hydroxyethyl compound 4 with mesyl chloride and triethylamine (65%) or with excess of Appel salt 1 (38%). 1H and 13C NMR spectra show that the indoline exists in solution as two rotamers 10a and 10b. Indoline 10 is converted into the known cyanoformylindoline 13 by the nitrile oxide method, and is prepared independently from indoline and 4-chloro-5H-1,2,3-dithiazole-5-thione. Mechanisms are proposed for the new reactions.
A series of unsubstituted (1→3,1→4)-β-D-glucooligosaccharides, designed for subsite mapping in which the number of glucosyl-binding subsites and the subsite-binding/transition state activation affinities at individual subsites of plant and bacterial (1→3,1→4)-β-D-glucan 4-glucanohydrolases (EC 3.2.1.73) can be determined, has been synthesised through chemical and enzymic procedures. A recombinant (1→3,1→4)-β-D-glucan 4-glucanohydrolase from Bacillus licheniformis has been used in organic media to catalyse the condensation of 3-O-β-D-glucopyranosyl-β-D-glucopyranosyl fluoride (Glcβ3GlcβF, compound 1) with cellobiose (Glcβ4Glc, 2), cellotriose (Glcβ4Glcβ4Glc, 3), cellotetraose (Glcβ4Glcβ4Glcβ4Glc, 4) and cellopentaose (Glcβ4Glcβ4Glcβ4Glcβ4Glc, 5), to produce the (1→3,1→4)-β-D-glucooligosaccharides, Glcβ3Glcβ4Glcβ4Glc 6, Glcβ3Glcβ4Glcβ4Glcβ4Glc 7, Glcβ3Glcβ4Glcβ4Glcβ4Glcβ4Glc 8, Glcβ3Glcβ4Glcβ4Glcβ4Glcβ4Glcβ4Glc 9. Synthesised oligosaccharides 6–9 were isolated in yields of 15–45%, compared with compound 1. In a second series of syntheses, a cellodextrin phosphorylase (EC 2.4.1.49) from Clostridium thermocellum was used to sequentially transfer glucosyl residues from α-D-glucopyranosyl phosphate 10 to the 4-position of the non-reducing terminus of the trisaccharide Glcβ3Glcβ4Glc 11, to generate the (1→3,1→4)-β-D-glucooligosaccharides, Glcβ4Glcβ3Glcβ4Glc 12, Glcβ4Glcβ4Glcβ3Glcβ4Glc 13, Glcβ4Glcβ4Glcβ4Glcβ3Glcβ4Glc 14 in 14, 10 and 5% yield, respectively, from compound 11.
A simple, mild and efficient procedure for obtaining N-methyl secondary amines from aldehydes and ketones is reported. Treatment of carbonyl compounds with methylamine hydrochloride, triethylamine and titanium(IV) isopropoxide, followed by in situ sodium borohydride reduction and straightforward aqueous work-up, affords clean products in good to excellent yields.
The reaction of trans-[M(C2H4)(2)(PMe3)(4)] with the tripodal phosphine 1,1,1-tris[(dimethylphosphino)methyl]-ethane (CP3) affords complexes trans-[M(C2H4)(2)(eta(2)-CP3)(PMe3)(2)] (M = Mo 1a or W 1b). A detailed NMR study, including hetero-and homo-nuclear two-dimensional correlations, has been carried out for Ib which allows a complete assignment of signals and a structural spectroscopic determination. In solution, no ethylene rotation is observed at room temperature and the preferential conformer of the six-membered ring W[eta(2)-CH3C(CH2PMe2)(3)] fragment is, on the basis of steric arguments, the skew-boat conformation. Interaction of compounds 1 with CO affords trans-[M(C2H4)(2)(eta(2)-CP3)(CO)(PMe3)] (M = Mo 2a or W 2b), while reaction of 1a with CNBut furnishes the compound trans-[Mo(C2H4)(2)(eta(2)-CP3)(CNBut)(PMe3)] 3. The bidentate co-ordination of CP3 induces chirality at the metal center and compounds 2 and 3 are obtained as a ca. 1:1 mixture of diastereoisomers, identified by the presence of two different patterns of resonances in their P-31-{H-1} NMR spectra at low temperature. At the fast regimen exchange, the isomers are interconverted through bis(ethylene) rotation. A variable-temperature P-31-{H-1} NMR study carried out for 2a gives an approximate value of Delta G(double dagger) for this process of 55 kJ mol(-1) at 298 K.
The major yellow compounds extracted from the mycelium of Cercospora beticola, the beticolins, can be divided into two subgroups, the o- and the p-beticolins. It has been found that crystallogenesis conditions which allowed the X-ray analyses of the first subgroup are unsuccessful for the second. New conditions affording microcrystals for three p-beticolins, B1, B3 and B13 are described, Diffraction experiments have been performed on a synchrotron beam line; the results confirm the proposed structures for B1 and B3 and allow that of B13 to be elucidated.
The inclusion behaviour of mono-6-(N-acetyltyrosinyl)amino-6-deoxy-β-cyclodextrin and mono-6-(N-acetyltryptophanyl)amino-6-deoxy-β-cyclodextrin with regard to borneol, menthol and 5-methoxypsoralen have been investigated by fluorescence spectroscopy, circular dichroism and NMR spectroscopy. For mono-6-(N-acetyltryptophanyl)amino-6-deoxy-β-cyclodextrin, the weakly self-included indole residue is disincluded, and for 5-methoxypsoralen, fluorescence resonant energy transfer is observed. In contrast, for mono-6-(N-acetyltyrosinyl)amino-6-deoxy-β-cyclodextrin the self-inclusion is sufficiently strong that no disinclusion occurs. A binary complex is postulated to arise from hydrogen bonding between borneol and mono-6-(N-acetyltyrosinyl)amino-6-deoxy-β-cyclodextrin.
The oxidation of n-butane at 390 degrees C over a catalyst derived from VO(H2PO4)(2) gives only maleic anhydride and furan as products and no CO or CO2 are formed.
