Effect of gamma rays irradiation on ferroelectric phase transition and domain defect interaction in lead meta niobate single crystal

The objective of our study is to identify the role of gamma rays to control the existing limit of ferroelectric nature of lead meta niobate (PbNb₂O₆) single crystals in terms of domain-defect interaction. The critical value of density of oxygen vacancy sites and average distance between two successive oxygen vacancies, which are responsible for ferroelectric nature in lead niobate single crystal have been calculated. The disappearance of Ferro electricity, which is associated with domain-defect interaction as well as an absence of obeying the Curie-Weiss law have been discussed in gamma rays irradiated lead meta niobate single crystal.     

The mechanism of N-alkylation of weak N-H-acids by phase transfer catalysis

The alkylation of aromatic amines in the presence of inorganic bases is accelerated by a PT catalyst $\text{even}$ if KHCO₃ is the base. ArNR^θ ions seem not to be involved. A novel type of mechanism for a PTC process is proposed.     

Sarcophine,a new epoxy cembranolide from marine origin

From the soft bodied coral Sarcophytum glaucum a crystalline compound-sarcophine (1), which is believed to be one of the repellents protecting the coral against predators, was isolated. The functional groups of 1 have been deduced from detailed NMR study and the whole molecular structure has been determined by a single-crystal 3-dimensional X-ray diffraction study proceeding from direct methods. The compound crystallizes in orthorhombic crystals, space group P2₁2₁2₁, and there are four molecules in each unit cell of dimensions a = 12·429(3), b = 13·766(3) and c = 10·750(1). The structure was found to be a new epoxy cembranolide. The mass spectrum and CD of 1 and several simple derivatives as well as the conformation of 1 in solution are discussed.     

Long-chain ammonium fluoride salts as universal analytical reagents for total anion determination

Lipophilic quaternary ammonium cations are insoluble in water when paired with any anion except fluoride or hydroxide. This phenomenon is the basis for a novel method for total anion determination. Tetra-n-octylammonium fluoride (TOAF) is used for the direct titration of any anion or mixture of anions with the exception of hydroxide. Anions for which no direct analytical method exists, e.g., nitrate or hydrogenfluoride (HF₂^?), are simply assayed by conductimetric titration with TOAF reagent.     

7-hydroxy (and acetoxy)-α-mullolene from the soft-coral heteroxenia fuscescens

The isolation and structural determination of three cadalane type sesquiterpenes from a soft coral is reported. The ¹³C NMR of these compounds namely (+)-α-murrolene, 7-hydroxy, and 7-acetoxy-α-murrolene is discussed.     

Barrenazine A and B; two new cytotoxic alkaloids from an unidentified tunicate

[structure: see text] Two novel compounds, barrenazine A (1) and B (2), were isolated from an unidentified tunicate collected at Barren Islands, Madagascar. The two new compounds are of an unprecedented heterocyclic skeleton, namely 1,3,4,6,8,9-hexahydrodipyridino[3,4-b:3',4'-e]pyrazine. The structures of the two alkaloids were elucidated by interpretation of MS, COSY, HMQC, HMBC, NOESY, and (15)N-HMBC data. Barrenazine A exhibits mild cytotoxicity against LOVO-DOX colon carcinoma (with a GI(50) value of 0.9 g/mL)     

The synthesis of a phosphadecalone system

The 2-phosphabicyclo[4.4.0]decan-5-onic system (2) was synthesized by a double Michael addition of phenylphosphine to propenylcyclohexenyl ketone (1). This dienone (1) can be prepared starting from either cyclohexanone by a known method, or from cyclohexene by its acylation with crotonic anhydride in the presence of SnCl₄. The NMR of the phosphine and several of its derivatives in comparison with the aza analog, as well as the Mass spectra fragmentation pattern, are discussed,     

New polyacetylenes from the sponge Siphonochalina sp.

Six new compounds, characterized by a long unsaturated alkyl chain (nC₂₂), were isolated from a marine sponge. All compounds except for one, possess an enyne terminus on one side of the molecule and either a terminal acetylene (in four) or a propargyl alcohol on the other end. Four of the compounds were unequivocally identified mainly by spectroscopic methods.Acetylenic compounds are well-known constituents of plants: only few, however, are known from marine organisms and to our knowledge only one group of compounds contains more than a single triple bond. Among the acetylene containing marine natural products are: A group of halogenated ethers, characterized by a straight-chain C-15 carbon skeleton and a terminal enyne function which has been isolated from algae¹ and a sea hare², carotenoids³, two steroids⁴, a sesquiterpene⁵ and polyketids^6,7.A diacetylene was found in a group of several n C-22 straight-chain compounds isolated from a marine sponge⁸. One of the compounds found in the latter sponge contains, again, the enyne terminus - an end group which turns out to be quite abundant in the above and the herewith discussed compounds.In our continuing search for bioactive compounds from marine organisms we have isolated from the sponge $\text{Siphonochalina sp}$.⁹ collected at several places in the southern part of the Gulf of Eilat (the Red Sea) six n C-22 straight-chain acetylenic compounds.Extraction of the freeze-dryed sponge (petrol ether, 4% dry weight) and subsequent repeated chromatographies (LH-20 and Silica gel)^10,11 gave six closely related new compounds, named in order of polarity, Δ¹⁵-docos-1-yne ($\text{1}$; RF^12a=0.65; 0.2% based on the dry weight of the animal), octahydrosiphonochalyne ($\text{2}$; Rf^12a=0.55; 0.4%), dihydrosiphonochalyne ($\text{4}$; Rf^12a=0.44; 0.1%) siphonochalyne ($\text{3}$; Rf^12b=0.34; 0.2%), dehydrosiphonochalynol ($\text{6}$; Rf^12b=0.55; 0.1%) and siphonochalynol ($\text{5}$; Rf^12b=0.43; 0.3%).     

On the conformation of 8-substituted bicyclo [3.2.1] oct-6-en-3-ones

A series of 8-substituted bicyclo [3.2.1] oct-6-en-3-ones (of type i) possessing various R₁ and R₂ groups were prepared and characterized. The conformations of the possible isomers of 1-4 were assigned according to the following three methods: (a) NMR spectrum, (b) time averaged precise metal ion location within the Eu (dpm)₃-carbonylic compound complex, (c) UV spectra. Comparison of the chair and boat conformers by UV spectra showed that interactions between the double bonds and the carbonyl occurred in both cases, although to different extents, the ε being dependent on R₁ and R₂. The fore-mentioned interaction exists even in both series of the C₆C₇ dihydro derivatives.