DNA zipper-based tweezers

Here we report the design and development of DNA zippers and tweezers. Essentially a zipper system consists of a normal strand (N), a weak strand (W), and an opening strand (O). N strand is made up of normal DNA bases, while W is engineered to have inosine substituting for guanine. By altering the number and order of inosine, W is engineered to provide less than natural bonding affinities to N in forming the [N:W] helix. When O is introduced (a natural complement of N), it competitively displaces W from [N:W] and forms [N:O]. This principle is incorporated in the development of a molecular device that can perform the functions of tweezers (sense, hold, and release). Tweezers were constructed by holding N and W together using a hinge at one end. Thus, when the tweezers open, N and W remain in the same vicinity. This allows the tweezers to cycle among open and close positions by their opening and closing strands. Control over their opening and closing kinetics is demonstrated. In contrast to the previously reported DNA tweezers, the zipper mechanism makes it possible to operate them with opening strands that do not contain single-stranded DNA overhangs. Our approach yields a robust, compact, and regenerative tweezer system that could potentially be integrated into complex nanomachines.     

Spontaneous and catalytic fusion of supramolecules

Using principles of completive and integrative self-sorting, a clean supramolecule-to-supramolecule transformation is realised that involves fusion of a 3-component rectangle and a 2-component equilateral triangle into a 5-component scalene triangle. While the spontaneous process takes 15 h at 25 °C, the catalytic transformation is completed within 1 h.     

Silica‐Supported Perchloric Acid (HClO4–SiO2): An Efficient Catalyst for One‐Pot Synthesis of Functionalized Tetrahydropyrimidine Derivatives

HClO₄–SiO₂ has been found to be a highly efficient catalyst for the synthesis of substituted tetrahydropyrimidine and bis‐tertahydropyrimidine derivatives in good to excellent yields involving the reaction of dimethyl acetylenedicarboxylate, amines/diamines, and formaldehyde. One‐pot, atom economy, high‐bond forming efficiency, environmentally benign, good yields, and mild reaction conditions are some of the salient features of this multicomponent reaction.     

A protocol for stripping and reprobing of Western blots originally developed with colorimetric substrate TMB

Western blotting is a widely used analytical technique for detection of specific protein(s) in a given sample of tissue/cell homogenate or extract. Both chemiluminescence (CL) and colorimetric detections can be used for imaging Western blots. Colorimetric substrates offer background free, sensitive, and clean imaging results directly on the blotted membrane and provides more accurate profile with respect to prestained marker. However, blots stained with colorimetric substrates cannot be reused since no stripping protocols have been reported for such blots, thus limiting their reuse for detection of another protein. In the present study, for the first time, we report a novel method of stripping Western blots developed with the colorimetric substrate TMB for detection of a low‐abundant protein and reprobing of these blots after stripping for detection of a more abundant protein through CL procedure. The stripping procedure utilizes a stripping buffer consisting of β‐mercaptoethanol, SDS, and Tris‐HCl and a washing buffer consisting of PBS added with 0.1% Tween‐20 involves a series of steps and facilitates accurate detection of the second protein (i.e., more abundant protein) in the stripped blot through CL. The protocol is reproducible and facilitates saving of precious clinical samples, in addition to saving cost and time as compared to the existing procedures.     

Cisplatin nanoliposomes for cancer therapy: AFM and fluorescence imaging of cisplatin encapsulation, stability, cellular uptake, and toxicity

Cisplatin is the most effective cytotoxic agent against many cancers. Its usage, however, is limited due to inefficient uptake by the target cells. A liposomal formulation of cisplatin is reported to partly overcome this limitation. Physicochemical characteristics of the liposome-cisplatin preparation, including its size, stability, encapsulation efficiency, and cytoplasmic internalization efficiency, play a significant role in an effective usage of liposomal formulations. We have used atomic force microscopy (AFM) to determine physicochemical characteristics of cisplatin-encapsulated liposomes, AFM and fluorescence microscopy to examine their cytoplasmic internalization, and Live/Dead assay to examine their cell toxicity. Nonencapsulated cisplatin is globular and 10-50 nm in size. AFM force-dissection and stiffness measurements show that cisplatin-encapsulated liposomes are significantly stiffer ( approximately 100%) and more stable than liposomes without encapsulated cisplatin. Cisplatin-encapsulated liposomes of approximately 250 nm diameter (nanoliposomes) are most efficiently internalized and induce cell toxicity in a time-dependent manner. Liposomes without cisplatin of similar dimensions, although internalized in the cell cytoplasm, do not induce cell toxicity.     

Bromodimethylsulfonium bromide (BDMS)-catalyzed multicomponent synthesis of 3-aminoalkylated indoles

Bromodimethylsulfonium bromide (BDMS)-catalyzed three-component coupling reaction between indoles, aldehydes, and N-alkylanilines is reported to access substituted 3-aminoalkylated indoles at room temperature in high yields (82-96%) within 1.5-3.5 h. The salient features of this protocol are the simplicity of the procedure, the ready accessibility of the catalyst, its cost effectiveness, and higher yields in relatively short reaction times.     

Structural and polarization properties of polyimide/TiO2 nanocomposites

Polyimide (PI)/titanium dioxide (TiO₂) nanocomposite films were prepared by a solution mixing method with different contents of TiO₂ nanoparticles. The structural and thermal properties of pure PI and PI/TiO₂ nanocomposite films were studied by several techniques such as scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermally stimulated depolarization current (TSDC). The SEM and AFM measurements show the uniform dispersion of TiO₂ nanoparticles in PI matrix, and it is also observed that the value of average roughness increases with increasing the contents of TiO₂ nanoparticles. The XRD pattern shows the presence of TiO₂ nanoparticles in PI matrix. It has been observed that the average crystallite size and percentage of crystallinity increase with content of the TiO₂ nanoparticles. FTIR spectra depict the position of different bonds in PI and nanocomposite samples. The TSDC results represent the modification of polarization phenomenon after filling of PI by titania nanoparticles.     

A total reflection X‐ray fluorescence method for the determination of chlorine at trace levels in nuclear materials without sample dissolution

A total reflection X‐ray fluorescence (TXRF) method for the determination of chlorine at trace levels in nuclear fuel samples is described. Chlorine present in trace concentrations in nuclear fuel materials such as U₃O₈, (U,Pu)C, PuO₂ and Pu‐alloys was first separated from the solid matrix by pyrohydrolysis as HCl and was collected in 5 mM NaOH solution. This solution was analyzed for chlorine by TXRF spectrometry using Cl Kα analytical line excited by W Lα. Cobalt was used as internal standard. The precision for such chlorine determination was found to be within 27% (n = 4) when the analysis was carried out in air atmosphere. This could be improved to 8% by making TXRF measurement in flowing helium atmosphere. The results obtained from TXRF determinations were also compared with those obtained from ion chromatography (IC) and were in good agreement. The collection of distillate during pyrohydrolysis in NaOH helped in counterchecking loss of chlorine during TXRF sample preparation. The average deviation of TXRF‐determined values in helium‐purged TXRF measurements with IC determined values (as chloride) was 15% at a chlorine concentration level in the range of 1–70 µg/mL. Copyright © 2012 John Wiley & Sons, Ltd.     

Extraction and Fractionation of Prokinetic Phytochemicals from Chrozophora tinctoria and Their Bioactivities

Chrozophora tinctoria is an annual plant of the family Euphorbiaceae, traditionally used as a laxative, a cathartic and an emetic. A methanolic extract of Chrozophora tinctoria (MEC) whole plant and an n-butanol fraction of Chrozophora tinctoria (NBFC) were analyzed by gas chromatography–mass spectrometry (GC-MS) to detect the phytochemicals. MEC and NBFC were tested for in vitro anti acetylcholinesterase (AChE) potential. The effect of both samples on intestinal propulsive movement and spasmolytic activity in the gastrointestinal tract (GIT) was also studied. About twelve compounds in MEC and three compounds in NBFC were tentatively identified through GC-MS. Some of them are compounds with known therapeutic activity, such as toluene; imipramine; undecane; 14-methyl-pentadecanoic acid methyl ester; and hexadecanoic acid. Both NBFC and MEC samples were checked for acute toxicity and were found to be highly toxic in a dose-dependent manner, causing diarrhea and emesis at 1 g/kg concentration in pigeons, with the highest lethargy and mortality above 3 g/kg. Both the samples of Chrozophora tinctoria revealed significant (p ≤ 0.01) laxative activity against metronidazole (7 mg/kg) and loperamide hydrochloride (4 mg/kg)-induced constipation. NBFC (81.18 ± 2.5%) and MEC (68.28 ± 2.4%) significantly increased charcoal meal intestinal transit compared to distal water (41.15 ± 4.3%). NBFC exhibited a significant relaxant effect (EC₅₀ = 3.40 ± 0.20 mg/mL) in spontaneous rabbit jejunum as compared to MEC (EC₅₀ = 4.34 ± 0.68 mg/kg). Similarly, the impact of NBFC on KCl-induced contraction was more significant than that of MEC (EC₅₀ values of 7.22 ± 0.06 mg/mL and 7.47 ± 0.57 mg/mL, respectively). The present study scientifically validates the folk use of Chrozophora tinctoria in the management of gastrointestinal diseases such as constipation. Further work is needed to isolate the phytochemicals that act as diarrheal agents in Chrozophora tinctoria.