A convenient preparative method for cyclic triphosphenium bromide and chloride salts

Analytically pure chloride and bromide salts of two different cyclic triphosphenium cations are prepared by the reaction of PX3 (X=Cl, Br) in the presence of the halogen-scavenging reagent cyclohexene. For the brominated species, the neutral, volatile 1,2-dibromocyclohexane byproduct is readily removed under reduced pressure, and the desired salts are obtained in high yield. Reactions involving phosphorus trichloride are complicated by the formation of salts containing both chloride and hydrogen dichloride anions. Reactivity experiments on potential undesired halogenated diphosphine byproducts suggest that the formation of such species can be prevented by increasing the concentration of cyclohexene employed in the reaction.     

On the sobriety of the inverse topology

An algebraic frame L with the finite intersection property (FIP) on compact elements is said to be polarised if every minimal prime element in it is complemented. In this note, we give a necessary and sufficient condition for the inverse topology on the set of minimal prime elements of such a frame to be sober. We also establish some sufficient conditions for sobriety when the polarisation condition is relaxed.     

Growth of first generation dendrons on SiO2: controlling chemisorption of transition metal coordination complexes

We have investigated the growth of first generation branched polyamidoamine dendrons on silicon dioxide as a way to tailor and control the subsequent chemisorption of transition metal coordination complexes. Beginning with straight-chain alkyl, amine-terminated self-assembled monolayers as anchors, we find that the efficiency of the dendritic branching step depends on the length of the anchor, it being nearly perfect on a 12-carbon chain anchor. The reaction of these layers, both the anchor layers and the first generation dendrons, with Ta[N(CH3)2]5 and Ti[N(CH3)2]4 have been examined in ultrahigh vacuum using X-ray photoelectron spectroscopy. We find that the saturation coverage increases with the density of terminal -NH2 groups; thus, the branching step has effectively amplified the chemisorptive capacity of the surface. Concerning the spatial extent of reaction we find that it depends on the thickness and structure of the organic layer. The thinnest layer cannot prevent penetration of the metal complex to the organic/SiO2 interface, where it can react with residual -OH, whereas, on the longer straight chain anchor, reaction occurs exclusively at the terminal -NH2 group. On the branched dendrons, the situation is more complex, and reaction occurs not only with the terminal -NH2 group but also likely with functional groups, such as -NH-(C=O)-, on the backbone of the branched dendron.     

5-Aminolevulinic acid-induced protoporphyrin-IX accumulation and associated phototoxicity in macrophages and oral cancer cell lines

Studies were carried out on 5-aminolevulinic acid (ALA)-induced protoporphyrin (PpIX) synthesis in mice peritoneal macrophages and two human oral squamous cell carcinoma (OSCC) cell lines NT8e and 4451. Cells were treated with 200 microg/ml ALA for 15 h and PpIX accumulation was monitored by spectrofluorometry and phototoxicity to red light (630+/-20 nm) was measured by MTT assay. PpIX accumulation was higher in macrophages as compared to OSCC cells under both normal serum concentration (10%) and conditions of serum depletion. The results on phototoxicity measurements correlated well with the levels of PpIX accumulation in both macrophages and cancer cells. While red light caused 20% phototoxicity in macrophages, no phototoxicity was seen in 4451 cells at 10% serum. Decrease in serum concentration to 5% and 1% led to higher phototoxicity corresponding to 40% and 70% in macrophages and 10% and 15% in 4451 cells. Similar results were obtained in NT8e cell line. Propidium iodide staining followed by fluorescence microscopic observations on photodynamically treated co-culture of murine or human macrophages and cancer cells showed selective damage to macrophages. These results suggest that in OSCC, macrophages would contribute more to tumor PpIX level than tumor cells themselves and PDT may lead to selective killing of macrophages at the site of treatment. Since macrophages are responsible for production and secretion of various tumor growth mediators, the effect of selective macrophage killing on the outcome of PDT would be significant.     

Raman scattering study of high-pressure phase transition in thiourea

A high-pressure Raman spectroscopic study of phase transitions in thiourea is reported. The changes in the Raman spectra with increasing and decreasing pressure have been followed to a maximum pressure of approximately 11 GPa. We observe several changes in the spectra including splitting of modes, appearance of new modes, and sudden change in the slope of the frequency-pressure curve at several pressures. On the basis of this study, we propose the existence of three more transitions in this system to phases VII, VIII, and IX at approximately 1, 3, and 6.1 GPa, respectively, in addition to the V-VI phase transition at 0.35 GPa reported earlier. All the transitions have been found to be completely reversible. We interpret these changes in terms of symmetry-lowering phase transitions.     

Tuning the Ground and Excited State Dynamics of Hemithioindigo Molecular Motors by Changing Substituents

Efficiency and performance of light triggered molecular motors are crucial features that need to be mechanistically understood to improve the performance and enable conscious property tailoring for specific applications. In this work, three different hemithioindigo-based molecular motors are investigated and all four steps in their complete unidirectional rotation are unraveled fully quantitatively. Transient absorption spectroscopy across twelve orders of magnitude in time is used to probe the fs nuclear motions up to the ms thermal kinetics, covering the timeframe of the whole motor rotation. The newly known full mechanisms allow simulation of the motor systems to scrutinize their performance at realistic illumination conditions. This highlights the importance of photoisomerization quantum yields for the rotation speed. The substitution pattern in close proximity to the rotation axle influences the excited and ground state properties. Reduction of electron donation and concomitant increase of steric hindrance leads to faster photoisomerization reactions with quasi-ballistic behavior, but also to a slight decrease in the quantum efficiency. The expected decelerating effects of increased sterics are primarily manifested in the ground state. A promising approach for next-generation hemithioindigo motors is to elevate electron donation at the rotor fragment followed by an increase of steric hindrance.     

A broader view of the almost Lindelöf property

By first finding necessary and sufficient conditions for the realcompact coreflection, νL, and the regular Lindelöf coreflection, λL, of a completely regular frame L to be isomorphic, we define a frame L to be almost Lindelöf if it is Lindelöf or λL → L is a one-point extension. This agrees with the condition “νL is Lindelöf and L is realcompact or νL is a one-point extension”, which would be a frame version of what are called almost Lindelöf spaces. Thus, the condition “νX is Lindelöf”, which is added in the definition of almost Lindelöf spaces, serves only to compensate for the lack of the regular Lindelöf reflection in Top, and can be dispensed with by concentrating on the frame \({\mathfrak {O}X}\) instead of the space X.     

Stereoselective cascade reactions for construction of polyfunctionalised octahydroquinolines via [2C+2C+1C,1N] cyclisation

A conceptually unifying approach for a highly enantio- and diastereoselective synthesis of polyfunctionalised octrahydroquinolines incorporating three contiguous chiral centres is reported. The synthesis involves diphenylprolinol silyl ether-catalysed Michael addition of 1,3-cyclohexanedione to nitroalkenes followed by potassium carbonate-promoted aza-Henry reaction with N-tosyl aldimines, intramolecular hemiaminalisation and dehydration reaction cascade in a one-pot operation.     

Stable physically adsorbed coating of poly-vinyl alcohol for the separation of basic proteins

In aqueous capillary electrophoresis, the electroosmotic flow can be strongly suppressed by coating the inner surface of the capillary. In the present work hydrophilic coating of 4% polyvinyl alcohol (PVA) has been used for the analysis of basic proteins. The coating is simple and easy to obtain. The separation of ribonuclease and α-chymotrypsin has been uniquely done with other three basic proteins (lysozyme, cytochrome-c and trypsin) using a buffer 11.60 mM sodium acetate and 18.40 mM acetic acid at pH 4.5 in addition to positive power supply of 20 kV at 25°C. Detection was performed using UV detector at 230 nm. The proposed PVA coated capillary provides reproducible separation of five basic proteins within 10 min with RSD values for mobility bellow 1.4% (n = 6) for all the five basic proteins. The stability of coated capillary has been checked up to 40 runs. The viscosity measurement for 4% PVA have been studied and scanning electron microscope (SEM) images obtained to make it compatible with future micro-chip applications.