Chemoselective N-acylation via condensations of N-(benzoyloxy)amines and alpha-ketophosphonic acids under aqueous conditions

A new amide-forming reaction with N-benzoyloxyamines and alpha-ketophosphonic acids was investigated. A mixed solvent of t-BuOH/water (1:1) at 40 degrees C provided the desired amide in high yield (71-96%). Both phosphonic acids ( 9, 12, or 13) and their disodium salts (e.g., 10) were shown to react with the respective N-benzoyloxyamines ( 1b and 4) in excellent yields. The phosphonic acid methyl ester monosodium salt 11 did not react under these conditions. However, compound 11 did provide the desired amide in 22% yield upon addition of 2 equiv of TFA. The N-acylation reaction is highly chemoselective for N-benzoyloxyamines as both aliphatic amines and N-hydroxylamines were shown not to react productively with the alpha-ketophosphonic acids under the conditions tested. Moreover, the alpha-ketophosphonic acids are more selective than the related alpha-ketocarboxylic acid systems, which react with both the N-hydroxylamines and N-benzoyloxyamines. In this regard, this novel phosphonic acid methodology provides a new high-yielding, chemoselective acylating reagent for further study.     

Near-IR region absorbing 1,4-diaminoanthracene-9,10-dione motif based ratiometric chemosensors for Cu

1,4-Bis[2-aminoethylamino]anthracene-9,10-diones selectively bind with Cu²⁺ to form complexes with unusual selectivity under basic conditions. The deprotonation of the aryl amine NH in the case of these chemosensors causes a bathochromic shift in the absorption band from 585 nm and 635 nm to 725 nm and enables ratiometric estimation of Cu²⁺ between pH 8 and 12.     

Evaporation From Confined Porous Media Due to Controlled IR Heating From Above

We report an experimental study of evaporation due to controlled infrared (IR) heating from above from an initially saturated confined porous medium consisting of nearly ‘mono-disperse’ particles which has been rarely used earlier. We have used three diagnostic tools simultaneously, evaporation rate measurements using a precision weighing balance, surface temperature measurements using IR imaging, and fluorescein dye mixed with water to visualize the drying front and the evaporation sites. IR images show that the first stage, so-called constant rate period (CRP), was maintained due to films of water reaching the top surface from the saturated region below. Gradually reducing evaporation rate in stage 1 is shown to be related to ‘shrinking evaporating patches’ on the top surface, clearly revealed as lower-temperature regions in the IR images. End of CRP coincides with disappearance of the low-temperature patches. We give end of CRP in terms of the average depth (L_cap) of the liquid level from the top surface at that time. L_cap and duration of CRP are strong functions of the porous medium bead size, transition to stage 2 happening earlier for coarser spheres. The obtained L_cap values deviated from the predictions of Lehmann et al. (Phys Rev E 77(5):056309, 2008) which we show is due to a small range of pore sizes in the current experiments. For both water and highly volatile n-pentane, we show that L_cap normalized by a length scale derived from gravity-surface tension force balance goes like Bo^0.20, for Bo varying from 2.0E ? 04 to 1.0E ? 01; Bo is the Bond number. Fluorescein dye imaging shows a different view of the evaporation stages. During CRP, highly concentrated deposits of the fluorescein dye particles, orange in colour, are seen in the top few bead layers. These orange deposits represent the sites on the beads surfaces where the evaporation has taken place. Even with external heating, evaporation from such a porous medium is limited to a finite depth from the evaporating end, similar to the observation by Lehmann et al. (2008) for isothermal evaporation in Hele-Shaw cell.     

A novel naphthoquinone from <Emphasis Type="Italic">Plumbago zeylanica</Emphasis> roots

A novel naphthoquinone (1) was isolated from the methanol extract of P. zeylanica roots in addition to a known compound plumbagin (2). Their structures were determined by UV, IR, MS, ¹H, and ¹³C NMR spectroscopic analysis, including 2D NMR.     

Fluorescent Recognition of Potassium and Calcium Ions Using Functionalised CdSe / ZnS Quantum Dots

Schiff base receptor 1a has been synthesised and attached to the surface of preformed CdSe/ZnS Quantum Dots (QDs) to form QD-conjugate 2a. While 1a was determined to be selective for Mg²⁺, 2a demonstrated selectivity for both K⁺ and Ca²⁺ when tested against a range of physiologically and environmentally relevant cations by changes in the fluorescence spectra. Thus, the nanoparticle surface functions as a scaffold for the organisation of receptors enabling semi-selective binding. The fluorescence response was shown to be linear between 15–50?μM for K⁺ and 2–35?μM for Ca²⁺. It was also demonstrated that 2a could measure both K⁺ and / or Ca²⁺ in solutions containing both ions.     

Surface plasmon resonance based fiber optic sensor utilizing indium oxide

A highly sensitive surface plasmon resonance (SPR) based fiber optic sensor with indium oxide (In₂O₃) layer coated on the core of the optical fiber is presented and theoretically analyzed. The sensitivity of the SPR based fiber optic sensor has been evaluated numerically. It is shown that the proposed SPR based fiber optic sensor with In₂O₃ layer possesses high sensitivity in the near infrared region of spectrum, which needs attention to many environmental and security applications and offers more accurate and highly reproducible measurements. In addition, the sensitivity of the SPR based fiber optic sensor decreases with the increase in the thickness of In₂O₃ layer. With sensitivity as high as 4600 nm/RIU, the 170 nm thick In₂O₃ layer based fiber optic SPR sensor demonstrates better performance.     

A new antifungal eudesmanolide glycoside isolated from Sphaeranthus indicus Linn. (Family Compositae)

A new antifungal eudesmanolide glycoside 11,13-dihydro-3-O-(β-digitoxopyranose)-7α-hydroxy eudasman-6,12-olide (2) in addition to known compounds 1 and 3, has been isolated from Sphaeranthus indicus Linn. Its structure was determined by spectral analysis (UV, IR, 1D and 2D NMR and mass spectrum).     

Preparation,spectral characterization,in vitro antitumor and thermal studies of new platinum(IV) and palladium(II) thiohydrazone complexes

Pt^IV and Pd^II complexes [Pt(L)₂Cl₂] and [Pd(HL)Cl₂] [HL = salicyclaldehyde morpholine N-thiohydrazone (HL¹), benzaldehyde morpholine N-thiohydrazone (HL²), acetophenone morpholine N-thiohydrazone (HL³), p-methylacetophenone morpholine N-thiohydrazone (HL⁴), cinnamaldehyde morpholine N-thiohydrazone (HL⁵), cyclohexanone morpholine N-thiohydrazone (HL⁶), benzaldehyde aniline N-thiohydrazone (HL⁷), benzaldehyde N-(methyl, cyclohexyl)-thiohydrazone (HL⁸) and benzaldehyde N-(ethyl, cyclohexyl)-thiohydrazone (HL⁹)] were prepared in MeOH and characterized by elemental analysis, i.r., electronic, ¹H-n.m.r. and ¹³C-n.m.r. spectral data. For some of the complexes cyclic voltammetric and thermal studies were carried out. The in vitro antitumor activity of some complexes was measured.     

Synthetic Ionophores. 13. Pyridine-Diamide-Diester Receptors: Remarkable Effect of Amide Substituents on Molecular Organization and Ag(+) Selectivity

The N(Py).HN(amide) hydrogen bonding within the macrocyclic cavities in 9, 10, and 13 invokes their symmetrical electron-deficient structures ((1)H NMR) and consequently bind with water. This results in their poor ionophore characters. The steric requirement of methyl/benzyl substituents on amide N in 11 and 12 takes the substituents out of the cavity and thus positions the amide O toward the cavity ((1)H, (13)C NMR and X-ray analysis). This arrangement of two pyridine N and two amide O ((13)C NMR, IR) binding sites provides an appropriate environment for selective binding toward Ag(+) over Pb(2+), Tl(+), alkali, and alkaline earth cations. The increased spacer length in 14 leads to a lop-sided twist of pyridine rings (X-ray) and disturbs the above arrangement and leads to its poor binding character.     

Absorption and emission of light in red emissive carbon nanodots

The structure–function relationship, especially the origin of absorption and emission of light in carbon nanodots (CNDs), has baffled scientists. The multilevel complexity arises due to the large number of by-products synthesized during the bottom-up approach. By performing systematic purification and characterization, we reveal the presence of a molecular fluorophore, quinoxalino[2,3-b]phenazine-2,3-diamine (QXPDA), in a large amount (∼80% of the total mass) in red emissive CNDs synthesized from o-phenylenediamine (OPDA), which is one of the well-known precursor molecules used for CND synthesis. The recorded NMR and mass spectra tentatively confirm the structure of QXPDA. The close resemblance of the experimental vibronic progression and the mirror symmetry of the absorption and emission spectra with the theoretically simulated spectra confirm an extended conjugated structure of QXPDA. Interestingly, QXPDA dictates the complete emission characteristics of the CNDs; in particular, it showed a striking similarity of its excitation independent emission spectra with that of the original synthesized red emissive CND solution. On the other hand, the CND like structure with a typical size of ∼4 nm was observed under a transmission electron microscope for a blue emissive species, which showed both excitation dependent and independent emission spectra. Interestingly, Raman spectroscopic data showed the similarity between QXPDA and the dot structure thus suggesting the formation of the QXPDA aggregated core structure in CNDs. We further demonstrated the parallelism in trends of absorption and emission of light from a few other red emissive CNDs, which were synthesized using different experimental conditions.

Herein we unveil the presence of a molecular fluorophore quinoxalino[2,3-b]phenazine-2,3-diamine (QXPDA) in a colossal amount in red emissive CNDs synthesized from o-phenylenediamine, a well-known precursor molecule used for CND synthesis.