Metal Nitride Cluster Fullerene M3N@C80 (M=Y,Sc) Based Dyads: Synthesis,and Electrochemical,Theoretical and Photophysical Studies

The first pyrrolidine and cyclopropane derivatives of the trimetallic nitride templated (TNT) endohedral metallofullerenes I_h‐Sc₃N@C₈₀ and I_h‐Y₃N@C₈₀ connected to an electron‐donor unit (i.e., tetrathiafulvalene, phthalocyanine or ferrocene) were successfully prepared by 1,3‐dipolar cycloaddition reactions of azomethine ylides and Bingel–Hirsch‐type reactions. Electrochemical studies confirmed the formation of the [6,6] regioisomers for the Y₃N@C₈₀‐based dyads and the [5,6] regioisomers in the case of Sc₃N@C₈₀‐based dyads. Similar to other TNT endohedral metallofullerene systems previously synthesized, irreversible reductive behavior was observed for the [6,6]‐Y₃N@C₈₀‐based dyads, whereas the [5,6]‐Sc₃N@C₈₀‐based dyads exhibited reversible reductive electrochemistry. Density functional calculations were also carried out on these dyads confirming the importance of these structures as electron transfer model systems. Furthermore, photophysical investigations on a ferrocenyl–Sc₃N@C₈₀‐fulleropyrrolidine dyad demonstrated the existence of a photoinduced electron‐transfer process that yields a radical ion pair with a lifetime three times longer than that obtained for the analogous C₆₀ dyad.     

Sr doping effects on the transport and magnetic properties of GdBaCo2O5+δ

Studies on some new members of the cobalt perovskite Gd_1−xSr_xBaCo₂O_5+δ with low strontium concentrations (0<x<0.1) have been carried out with the aim of investigating possible metallization of the GdBaCo₂O_5+δ system by hole doping. Low temperature electrical resistivity, magnetic susceptibility and thermopower of the above system have been studied. The pristine compound with x=0 and δ∼0.5 exhibits a semiconductor-like behavior and two magnetic transitions below room temperature. Upon Sr²⁺ substitution, there is a fall in resistivity by 2-3 orders of magnitude at low temperature and also a dramatic reduction in the ferromagnetic to antiferromagnetic transition temperature. These changes can be explained on the basis of hole doping (and increase in the Co⁴⁺content). Evidence for an increase in Co⁴⁺ with Sr²⁺ substitution is provided by iodometric analysis.     

Cyclooctenyl complexes of palladium(II) with multidentate N-heterocycles

[Pd(cod)(cotl)]ClO₄ (cod = 1,5-cyclooctadiene, cotl = cyclooctenyl, C₈H₁₃ ^–) undergoes substitutions with multidentate N-heterocycles: 1,3-bis(benzimidazolyl)benzene (L¹), 1,3-bis(1-methylbenzimidazol-2-yl)benzene (L²), 2,6-bis(benzimidazolyl)pyridine (L³) and 2,6-bis(1-methylbenzimidazol-2-yl)pyridine (L⁴) to yield mono/binuclear complexes: [Pd(cotl)(L¹)(OClO₃)], [Pd(cotl)(L)]ClO₄ (L = L² or L³) and [Pd(cotl)₂(L⁴)](ClO₄)₂. Dihalobridged binuclear complexes [PdX(cotl)]₂ (X = Cl or Br) undergo halogen bridge cleavages with the multidentate N-heterocycles to form binuclear complexes of the type [PdX(cotl)₂L] (X = Cl or Br; L = L¹, L², L³ or L⁴). The complexes were characterized by elemental analyses, ¹H-, ¹³C-n.m.r., i.r., far-i.r. and FAB-mass spectral studies.     

Structure and dynamics in solvent-polarity-induced aggregates from a c60 fullerene-based dyad

A novel methanofullerene dyad based on a hydrophobic (acceptor C60 moiety)-hydrophilic (bridge with benzene and ester functionalities)-hydrophobic (donor didodecyloxybenzene) network is designed and synthesized. Electronic absorption spectral features revealed the molecule to exhibit a strong tendency to self-aggregate in binary solvent mixtures at room temperature, where the dielectric constant exceeds a critical value, approximately 30. The dynamic structure factors of these spherical aggregates revealed stretched exponential decay with sizes varying between 110 and 250 nm with an increasing concentration, estimated from the dynamic light scattering experiments. However, a loss of shape selectivity of these aggregates was noted at lower water volume fractions in the binary solvent mixtures. The water-extracted spherical clusters were identified to be fractals with a dimension of 1.85, leading to diffusion-limited cluster aggregation as the mechanistic route for clusterization.     

The stereoselective total synthesis of xestodecalactone C and epi-sporostatin via the Prins cyclisation

Syntheses of xestodecalactone C and epi-sporostatin are described utilising Prins cyclisations, Mitsunobu reaction and intramolecular Friedel-Crafts acylation. The approach is convergent and highly stereoselective.     

Bis(3,5-diiodo-2,4,6-trihydroxyphenyl)squaraine: a novel candidate in photodynamic therapy for skin cancer models in vivo

Photodynamic therapy (PDT) is based on the light-induced activation of a photosensitizer generating highly reactive oxygen species that induce tissue destruction in malignant tissues. The present study was carried out to assess the photosensitizing potential of bis(3,5-diiodo-2,4,6-trihydroxyphenyl)squaraine in PDT trials in vivo. Male Swiss albino mice were divided into five groups. Skin tumor was induced using 7,12-dimethylbenz(a)anthracene - DMBA in the animals of Groups II, III, IV and V, while animals of Group I served as the control. At the completion of 20 weeks of induction, the tumor bearing mice from Group III, IV and V were given an intraperitoneal injection with the squaraine dye (12.5mg/kg body weight). After 24h, in the Group IV and V animals, the tumor area was exposed to visible light from a 1000W halogen lamp. The mice from groups I to IV were sacrificed two weeks after the PDT treatment and the marker enzymes (myeloperoxidase [MPO], beta-d-glucuronidase, rhodanese, lactate dehydrogenase [LDH], hexokinase, sialic acid and caspase) were assayed in tumor and normal tissues. Animals from Group V were sacrificed after 90 days of PDT treatment and the above parameters were recorded. Reduction in tumor volume and reversal of biochemical markers to near normal levels were observed in the treatment groups. The study assumes importance as it is the first report on PDT-a novel modality, using a squaraine dye for skin cancer therapy in vivo. The uniqueness of the mode of treatment lies in the selective uptake of squaraine dye by the cancer cells and their selective destruction using PDT without affecting the neighbouring normal cells, which is much advantageous over radiation therapy now frequently used. Also in skin cancer models, the progression/cure can be visualized by the naked eye which is another point of advantage, while seeking new modalities for the treatment of cancer.     

Bioinspired Water-soluble Polymers with Grafted Polyamine Chains: Synthesis and Complexation with Oligonucleotides

The siliceous frustules of diatom algae contain complex proteins known as silaffins, which consist of a peptide chain with grafted polyamine chains. These polyamines contain twenty or more nitrogen atoms with trimethylene groups between the nitrogens. We synthesized a set of polymers containing grafted long-chain polyamine fragments by using acryloyl chloride(ACh) polymers and activated acrylic acid copolymers as the starting materials. The new polymers contained 0.05 mol%-3.2 mol% of polyamine chains, which corresponded to 0.06-3.56 mmol·g~(-1) amine groups. The new amine-containing polymers formed complexes with short(19-21-mer)deoxyribonucleic acid(DNA) and ribonucleic acid(RNA) strands, and these complexes penetrated into model yeast cells and A549 lung cancer cell. This study demonstrates the potential of these species based on long-chain polyamines to serve as novel gene delivery systems.     

Engineering bio-mimicking functional vesicles with multiple compartments for quantifying molecular transport

Controlled design of giant unilamellar vesicles under defined conditions has vast applications in the field of membrane and synthetic biology. Here, we bio-engineer bacterial-membrane mimicking models of controlled size under defined salt conditions over a range of pH. A complex bacterial lipid extract is used for construction of physiologically relevant Gram-negative membrane mimicking vesicles whereas a ternary mixture of charged lipids (DOPG, cardiolipin and lysyl-PG) is used for building Gram-positive bacterial-membrane vesicles. Furthermore, we construct stable multi-compartment biomimicking vesicles using the gel-assisted swelling method. Importantly, we validate the bio-application of the bacterial vesicle models by quantifying diffusion of chemically synthetic amphoteric antibiotics. The transport rate is pH-responsive and depends on the lipid composition, based on which a permeation model is proposed. The permeability properties of antimicrobial peptides reveal pH dependent pore-forming activity in the model vesicles. Finally, we demonstrate the functionality of the vesicles by quantifying the uptake of membrane-impermeable molecules facilitated by embedded pore-forming proteins. We suggest that the bacterial vesicle models developed here can be used to understand fundamental biological processes like the peptide assembly mechanism or bacterial cell division and will have a multitude of applications in the bottom-up assembly of a protocell.

Giant vesicle functional models mimicking a bacterial membrane under physiological conditions are constructed.     

Imaging elastic property of surfaces at nanoscale using atomic force microscope

We present a simple technique to characterize and image the distribution of local elastic property using ultrasonic atomic force microscope (UAFM). We interpret the UAFM images using simple arguments. We have demonstrated the capability of the UAFM technique to image the distribution of the local elastic property of the sample surface and semi-quantitatively map the local stiffness of the sample surface using a few selected samples. The local stiffness of the sample surface was obtained by measuring the changes in the frequency of contact resonance peak values and could verify the same using force-distance measurement at the same regions on the sample surface.