Crystal growth and characterisation of new organic nonlinear optical materials: 6-cyano and 6-nitro-2,2-dimethyl-3,4-epoxychroman

Two chiral organic nonlinear optical materials, (3S,4S)-(−)-6-cyano-2,2-dimethyl-3,4-epoxychroman (1) and (3R,4R)-(+)-6-nitro-2,2-dimethyl-3,4-epoxychroman (2), have been grown into single crystals of cm³-size. Although both compounds crystallise in the orthorhombic P2₁2₁2₁ space group, they are not isomorphous and their crystal packings are quite different. Angle tuned type II phase-matched second harmonic generation between 0.8 and 1.064 μm has been evidenced, with effective nonlinear coefficients d_eff of 1 and 5 pm/V at 0.96 μm for 1 and 2, respectively. These values are in agreement with those estimated in the oriented gas model approximation using EFISH first order hyperpolarisability values (β₀=2.6 and 4.0×10⁻³⁰ esu for 1 and 2, respectively).     

The synthesis of [Fe(CO)3(η1-dppm) {Sn(n-Bu)2}]2 by silicon-tin exchange,its crystal structure and its use as a metallodiphosphine ligand

The reaction of the siloxyl containing ferrate [Fe(CO)₃( ¹-dppm){Si(OMe)₃}]^–,1 (dppm = Ph₂PCH₂PPh₂) with Sn(OAc)₂(n-Bu)₂ has yielded the new dimeric complex [Fe(CO)₃( ¹-dppm){µ-Sn(n-Bu)₂}]₂, 3 in 89% yield. Compound3 was characterized crystallographically and was found to be a centrosym-etrical molecule with a rhomboidal Fe₂Sn₂ cluster at the center. Each iron atom contains me ¹-dppm ligand. Compound3 was found to react with [Pd(dmba) (µ-Cl)]₂ (dmba=dimethylbenzylamine) to yield the new complexmer-[Fe(CO)₃{Sn(n-Bu)₂}(µ-dppm)Pd(dmba)Cl]₂, 4 by attachment of a palla-dium grouping to each of the uncoordinated phosphorus atoms in 3. Crystal data for 3: space groupP ,a=11.399(2) Å, 6=15.98(3) Å, c=10.869(3) Å, =94.10(2)°.=100.56(2)°, =69.35(1)°,Z=2, 3533 reflections,R=0.034.     

Potent inhibitors of the hepatitis C virus NS3 protease: design and synthesis of macrocyclic substrate-based beta-strand mimics

The virally encoded NS3 protease is essential to the life cycle of the hepatitis C virus (HCV), an important human pathogen causing chronic hepatitis, cirrhosis of the liver, and hepatocellular carcinoma. The design and synthesis of 15-membered ring beta-strand mimics which are capable of inhibiting the interactions between the HCV NS3 protease enzyme and its polyprotein substrate will be described. The binding interactions between a macrocyclic ligand and the enzyme were explored by NMR and molecular dynamics, and a model of the ligand/enzyme complex was developed.     

Synthesis of Secondary α-Methylene γ-Lactams

N-trimethylsilyl aldimines, on reaction with the isolated organozinc derivative of ethyl α-(bromomethyl) acrylate, afford secondary α-methylene γ-lactams with quite quantitative yields.     

Synthesis, structures, optical properties, and TD-DFT studies of donor-π-conjugated dipicolinic acid/ester/amide ligands

A series of 2,6- and 4-functionalized dipicolinic acid, ester, or amide featuring π-conjugated substituents such as donor-(phenyl or fluorenyl)-acetylene groups have been synthesized. Four crystallographic structures are reported. The influence of the substituent position, the nature of the donor group, and the conjugated backbone as well as the role of the pyridinic side arms on the absorption and emission properties are studied and discussed on the basis of TD-DFT calculations.     

Structures and spectral properties of heteroleptic copper (I) complexes: A theoretical study based on density functional theory

The structures and electronic absorption spectra of newly synthesized heteroleptic copper (I) complexes [CuL₁L₂]⁺ (L₁ = phen-imidazole and/or L₂ = dipyrido [3,2-a:2’,3’-c] phenazine derivatives) are analyzed under the light of density functional theory (DFT) and time-dependent DFT (TD-DFT). The ground states geometries, characterized by π-stacking interactions, have been optimized using PBE-D functional taking into account dispersion correction. The UV-visible theoretical absorption spectra have been calculated using B3LYP functional in vacuum and taking into account solvent corrections by means of the polarized continuum model (PCM). Whereas the PBE-D functional is well adapted to the determination of the structures, it does underestimate drastically the transition energies. The spectra are characterized by high density of states, mainly metal-to-ligand-charge-transfer (MLCT) and intra-ligand (IL), between 600 nm and 250 nm. Most of the complexes show an intense band in the near-UV energy domain (～320 nm) corresponding to an IL transition. The lowest part of the absorption spectra, starting at 600 nm, corresponds to MLCT transitions leading to a shoulder observed experimentally between 400 and 500 nm. The upper part of the spectra, beyond 300 nm, puts in evidence strong mixing between ligand-to-ligand-charge-transfer (LLCT), IL and MLCT states.     

Prediction of spectroscopic constants for diatomic molecules in the ground and excited states using time-dependent density functional theory

Spectroscopic constants of the ground and next seven low-lying excited states of diatomic molecules CO, N2, P2, and ScF were computed using the density functional theory SAOP/ATZP model, in conjunction with time-dependent density functional theory (TD-DFT) and a recently developed Slater type basis set, ATZP. Spectroscopic constants, including the equilibrium distances r(e), harmonic vibrational frequency omega(e), vibrational anharmonicity omega(e)x(e), rotational constant B(e), centrifugal distortion constant D(e), the vibration-rotation interaction constant alpha(e), and the vibrational zero-point energy E(n)0 were generated in an effort to establish a reliable database for electron spectroscopy. By comparison with experimental values and a similar model with an established larger Slater-type basis set, et-QZ3P-xD, it was found that this model provides reliably accurate results at reduced computational costs, for both the ground and excited states of the molecules. The over all errors of all eight lowest lying electronic states of the molecules under study using the effective basis set are r(e)(+/-4%), omega(e)(+/-5% mostly without exceeding +/-20%), omega(e)x(e)(+/-5% mostly without exceeding 20%, much more accurate than a previous study on this constant of +/-30%), B(e)(+/-8%), D(e)(+/-10%), alpha(e)(+/-10%), and E(n)0(+/-10%). The accuracy obtained using the ATZP basis set is very competitive to the larger et-QZ3P-xD basis set in particular in the ground electronic states. The overall errors in r(e), omega(e)x(e), and alpha(e) in the ground states were given by +/-0.7, +/-10.1, and +/-8.4%, respectively, using the efficient ATZP basis set, which is competitive to the errors of +/-0.5, +/-9.2, and +/-9.1%, respectively for those constants using the larger et-QZ3P-xD basis set. The latter basis set, however, needs approximately four times of the CPU time on the National Supercomputing Facilities (Australia). Due to the efficiency of the model (TD-DFT, SAOP and ATZP), it will be readily applied to study larger molecular systems.     

Self-assembled monolayers based on phenanthroline-gold(111) bonding

The self-assembly of long-alkyl-chain substituted phenanthroline derivatives on highly oriented pyrolitic graphite (HOPG) and gold(111) is compared. Whereas the adsorption on HOPG is controlled by the affinity of alkyl chains for the substrate, which leads to flat-lying adsorbed molecules, alignments of upright-oriented molecules are formed on gold(111). This situation is explained by the bonding of chelating species with gold(111) surfaces and by the pi-stacking interaction between conjugated moieties. This intermediate situation between strong thiol-like chemical bonding and the weak n-alkane-like physical adsorption opens the route toward laterally organized functional molecular assemblies.     

Modification of the wettability of a polymeric substrate by pH effect. Determination of the surface acid dissociation constant by contact angle measurements

The wetting properties of a substrate can be changed by chemical reaction. Here, we studied simple materials with acid-base properties, by preparing poly(vinyl chloride) films containing lauric acid. These substrates constitute simple polymeric surfaces the wettability of which can be easily controlled by the acid-base equilibrium. The roughness of the material was then varied by adding Aerosil (hydrophobic fumed silica). We then studied the wettability of these materials toward aqueous buffer solutions between pH 2 and 12 from contact angle measurements. The variation of the contact angle of a droplet of buffer solution with the pH of the solution was described by a simple thermodynamic model requiring only two parameters. Thus, we could characterize the acid polymer by an effective surface acid dissociation constant the value of which was consistent with those obtained with a similar surface. We showed that the behavior of any substrate could be described even if the surface geometry was not well-known.     

Path factors and parallel knock-out schemes of almost claw-free graphs

An H₁,{H₂}-factor of a graph G is a spanning subgraph of G with exactly one component isomorphic to the graph H₁ and all other components (if there are any) isomorphic to the graph H₂. We completely characterise the class of connected almost claw-free graphs that have a P₇,{P₂}-factor, where P₇ and P₂ denote the paths on seven and two vertices, respectively. We apply this result to parallel knock-out schemes for almost claw-free graphs. These schemes proceed in rounds in each of which each surviving vertex eliminates one of its surviving neighbours. A graph is reducible if such a scheme eliminates every vertex in the graph. Using our characterisation, we are able to classify all reducible almost claw-free graphs, and we can show that every reducible almost claw-free graph is reducible in at most two rounds. This leads to a quadratic time algorithm for determining if an almost claw-free graph is reducible (which is a generalisation and improvement upon the previous strongest result that showed that there was a O(n^5.376) time algorithm for claw-free graphs on n vertices).