Spectroscopic studies on the protonation of Schiff bases

This short review concerns the protonation of Schiff bases by halogenic or carboxylic acids with a bias toward the chromophore of visual and bacterial rhodopsins. It is pointed out that the weak acids available in these pigments could not protonate the retinyl Schiff base 100% and that a supporting mechanism is needed to achieve full protonation. Our Fourier transform infrared studies both at room and low temperatures relating to this problem are summarized, and the propable role of water is emphasized.     

Influence of interparticle interactions on the kinetics of self-assembly and mechanical strength of nanoparticulate aggregates

Computer simulations based on Discrete Element Method have been performed in order to investigate the influence of interparticle interactions on the kinetics of self-assembly and the mechanical strength of nanoparticle aggregates.Three different systems have been considered.In the first system the interaction between particles has been simulated using the JKR (Johnson,Kendall and Roberts) contact theory,while in the second and third systems the interaction between particles has been simulated using van der Waals and electrostatic forces respectively.In order to compare the mechanical behaviour of the three systems,the magnitude of the maximum attractive force between particles has been kept the same in all cases.However,the relationship between force and separation distance differs from case to case and thus,the range of the interparticle force.The results clearly indicate that as the range of the interparticle force increases,the self-assembly process is faster and the work required to produce the mechanical failure of the assemblies increases by more than one order of magnitude.     

THE EFFECT OF ACIDS ON THE INFRARED SPECTRA OF SCHIFF BASES—II. IMINES CONTAINING THE C=C-C=N AND C=C-C=C-C=N UNITS

Abstract— The Fourier-transform infrared spectra of chloroform-d solutions of conjugated imines CH₃CH=CHCH=NCH(CH₃)₂ and CH₃CH₂CH=CHCH=CHCH=NCH(CH₃)₂ and the related protonated species with HCl, HBr, HI, trichloro, dichloro, monobromo and monochloroacetic acids or propionic acid are presented. The effects of conjugation and protonation are examined. The results show that conjugation slightly increases the basicity of the Schiff bases. HCl, HBr and HI protonate the Schiff bases completely. The carboxylic acids protonate partially depending on their p K _a, values. When the Schiff base contains two (or more) C=C bonds conjugated with C=N, the main C=C stretching band undergoes a strong intensification showing that sizeable dipole moment variations occur along the conjugated chain.     

THE EFFECT OF ACIDS ON THE INFRARED SPECTRA OF SCHIFF BASES—I. NON-CONJUGATED IMINES

The Fourier-transform infrared spectra of CHCl₃ solutions containing a non-conjugated imine, R₁HC=NR₂ and an acid of the series HCl, HBr, HI, trichloro-, dichloro-, monochloro-, monobromo acetic acids and propionic acid have been recorded. Both the N⁺H and double bond stretching regions are examined. The results show that HCl, HBr and HI protonate the imine completely, trichloroacetic acid to about 90-95%, the other haloacetic acids to 55-80% and propionic acid to <10%. Considered as model studies for the problem of protonation in rhodopsins our results lead to the conclusion that with the relatively weak acids available in the pigments full protonation requires a stabilization mechanism which should be further investigated.     

Performance of slotted pores in particle manufacture using rotating membrane emulsification

This paper addresses the use of different slotted pores in rotating membrane emulsification technology.Pores of square and rectangular shapes were studied to understand the effect of aspect ratio (1-3.5) and their orientation on oil droplet formation.Increasing the membrane rotation speed decreased the droplet size,and the oil droplets produced were more uniform using slotted pores as compared to circular geometry.At a given rotation speed,the droplet size was mainly determined by the pore size and the fluid velocity of oil through the pore (pore fluid velocity).The ratio of droplet diameter to the equivalent diameter of the slotted pore increased with the pore fluid velocity.At a given pore fluid velocity and rotation speed,pore orientation significantly influences the droplet formation rate: horizontally disposed pores (with their longer side perpendicular to the membrane axis) generate droplets at double the rate of vertically disposed pores.This work indicates practical benefits in the use of slotted membranes over conventional methods.     

Synthesis and Structure of Uranium-Silylene Complexes

While carbene complexes of uranium have been known for over a decade, there are no reported examples of complexes between an actinide and a „heavy carbene.“ Herein, we report the syntheses and structures of the first uranium-heavy tetrylene complexes: (CpSiMe₃)₃U-Si[PhC(NR)₂]R’ (R=tBu, R’=NMe₂ 1 ; R=iPr, R’=PhC(NiPr)₂ 2 ). Complex 1 features a kinetically robust uranium-silicon bonding interaction, while the uranium-silicon bond in 2 is easily disrupted thermally or by competing ligands in solution. Calculations reveal polarized σ bonds, but depending on the substituents at silicon a substantial π-bonding interaction is also present. The complexes possess relatively high bond orders which suggests primarily covalent bonding between uranium and silicon. These results comprise a new frontier in actinide-heavy main-group bonding.     

PI3K-δ and PI3K-γ Inhibition by IPI-145 Abrogates Immune Responses and Suppresses Activity in Autoimmune and Inflammatory Disease Models

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