Relative stabilities and the spectral signatures of stacked and hydrogen-bonded dimers of serotonin

The O–H???N hydrogen-bonded dimer of serotonin is shown to be more stable than the stacked dimer in its ground electronic state, by using the Møller–Plesset second-order perturbation theory (MP2) and the 6–31g^** basis set. The vertical excitation energy for the lowest π?→?π* transition for the monomer as well as the dimer is predicted by time-dependent density functional theory. The experimentally observed red shift of excitation wavelength on oligomerisation is explained in terms of the change in the HOMO–LUMO energy gap due to complex formation. The impact of dimer formation on the proton magnetic resonance spectrum of serotonin monomer is also examined.     

MICROWAVE INDUCED DRY-MEDIA SYNTHESIS OF SPIRO[INDOLE-THIAZOLIDINONES/ THIAZINONES] AS POTENTIAL ANTIFUNGAL AND ANTITUBERCULAR AGENTS AND STUDY OF THEIR REACTIONS

A series of new spiro[3H-indole-3,2′-thiazolidine]-2,4′(1H)-diones (IV) and spiro[3H-indole-3,2′-tetrahydro-1,3-thiazine]-2,4′(1H)-diones (V) have been synthesized in 85–93% yield by the one-pot environmentally benign microwave induced technique involving the cyclocondensation of 3-arylimino-2H-indol-2-ones (III) with thioacids viz. mercapto aceticacid (a)/3-mercapto propionicacid (b) using montmorillonite KSF as inorganic solid support. Intermediates (III) were synthesized in situ by the reaction of indole-2,3-diones (I) and substituted anilines (II). The spiro compounds have been further subjected to solvent-free acetylation, aminoalkylation and thiation under microwave irradiation using solid supports. The synthesized compounds have been screened in vitro for antifungal activity against Rhizoctonia solani, Fusarium oxysporum, and Collectotrichum capsici, and antitubercular acivity against Mycobacterium tuberculosis.     

Aldol reactions of 2-thioxotetrahydropyrimidin-4(1H)-ones: stereoregulations from endo- and exocyclic chiral centres

The steric regulations imparted by the substituent at N1 in lithium mediated asymmetric aldol reactions of conformationally restricted 3-aryl-1-((S)-1-phenylethyl)-2-thioxotetrahydropyrimidin-4(1H)-ones governed the formation of anti aldol adducts, by a kinetic reaction pathway. The preferential formation of the anti aldol diastereomers was also assisted by the steric effects of the electrophile through diastereofacial selection while the electronic effects of the aryl group at N3 remained subtle. Incorporation of an endocyclic methyl group at C6 witnessed the diastereoselective formation of an anti aldol adduct by regulation of π-facial selectivity. The absolute configurations of the aldol adducts were determined by computational calculations and NMR experiments, and confirmed by single crystal X-ray analysis.     

Biocatalytic deacylation studies on tetra-O-acyl-β-D-xylofuranosyl nucleosides: synthesis of xylo-LNA monomers

A Novozyme-435 catalytic methodology has been developed for selective deacylation of one of the acyloxy functions involving a primary -OH group over the other acyloxy functions involving primary and secondary -OH groups in 4'-C-acyloxymethyl-2',3',5'-tri-O-acyl-β-D-xylofuranosyl nucleosides. Optimization of the biocatalytic reaction revealed that tetra-O-butanoyl-β-D-xylofuranosyl nucleosides are the best substrates for the enzyme. The possibility of acyl migration during enzymatic deacylation reactions has been ruled out by carrying out biocatalytic deacylation reactions on mixed esters of 4'-C-hydroxymethyl-2',3',5'-tri-O-acetyl-β-D-xylofuranosyl nucleosides. The developed methodology has been used for the efficient synthesis of xylo-LNA monomers T, U, A, and C in good yields.     

Systematic measurements of M X-ray components X-ray fluorescence cross-sections for the elements with 77 ≤ Z ≤ 92 by employing laboratory source based energy dispersive X-ray fluorescence setup

The differential X-ray fluorescence (XRF) cross-sections for (Mξ₂, Mξ₁, Mδ₁), (Mδ₂, Mα_1,2 M₅-O₃), (Mβ, M₄-O_2,3), (Mγ, Mm₂, M₃-N₄, M₅-O_2,3), (Mm₁, M₃-N_6,7, M₃-O_4,5) and (Mm_2, M₂-N₆) group of M X-rays components have been measured for the elements with 77 ≤ Z ≤ 92 following photoionization by Mn K X-rays (E_Kαβ = 5.96 keV) obtained from ⁵⁵Fe radioisotope. The measurements were performed in annular source geometry at 126° emission angle using a low-energy Ge (LEGe) detector. The measured cross-section values are compared with theoretical values calculated using available sets of M_i (i = 1–5) photoionization cross-sections, radiative emission rates (F_ij), Coster-Kronig (f_ij), and fluorescence (ω_i) yields. The measured XRF cross-sections for the (Mξ₂, Mξ₁, Mδ₁), (Mm₁, M₃-N_6,7) and (Mm₂, M₂-N₆) groups of X-rays agree with the theoretical values within the experimental errors. The (Mβ, M₄-O_2,3) group of X-rays exhibit agreement with theoretical values within experimental uncertainty for all the elements under investigation except ₇₉Au and ₈₀Hg. The XRF cross-section for the (Mδ₂, Mα_1,2) group of X-rays are in general higher by ~20% for the elements with Z = 77–83 and exhibit agreement for the ₉₀Th and ₉₂U elements. For the (Mγ, Mm₂, M₃-N₄) X-ray group, the measured values are generally higher than the theoretical values, but the deviations are within experimental uncertainties. The large deviation in measured XRF cross-section for different M X-ray components from the theoretical ones are attributed to (i) poor separation of M X-ray components (ii) contribution of self-resonant Raman scattering (RRS) process and (iii) self-fluorescence of M₅ subshell by M_i subshell X-rays (i = 1–3).     

Visible-Light-Mediated Controlled Radical Branching Polymerization in Water

Hyperbranched polymethacrylates were synthesized by green-light-induced atom transfer radical polymerization (ATRP) under biologically relevant conditions in the open air. Sodium 2-bromoacrylate (SBA) was prepared in situ from commercially available 2-bromoacrylic acid and used as a water-soluble inibramer to induce branching during the copolymerization of methacrylate monomers. As a result, well-defined branched polymethacrylates were obtained in less than 30 min with predetermined molecular weights (36 000<M_n<170 000), tunable degree of branching, and low dispersity values (1.14≤Đ≤1.33). Moreover, the use of SBA inibramer enabled the synthesis of bioconjugates with a well-controlled branched architecture.     

Experimental and theoretical investigation of superharmonic resonances in a planar oscillator under angular base excitation

This paper explores the complicated dynamic behavior of a mechanical oscillator under harmonic angular excitation. The motivation behind this work comes from the nature of the actuation produced by high-performance dither motors. A lumped-mass model, which captures the primary and the 1 : 2 superharmonic resonances observed on an analogous experimental test setup, is put forward. The equations of motion governing the dynamics of the model are derived and are found to comprise both parametric and direct forcing terms. The governing equations are solved analytically using the generalized harmonic balance method and numerical integration. The method of multiple scales is utilized to obtain closed-form expressions that relate the system parameters to the oscillation amplitudes in the vicinity of the direct and the 1 : 2 superharmonic resonances. It is found that eccentricity plays a vital role in the occurrence of the resonances. Besides, the relationship between the excitation amplitudes and the resulting oscillations for the direct and the superharmonic resonances are dissimilar. A few salient differences between classical (rectilinear) and angular base excitation mechanisms are pointed out.