• The Comet Assay (also called Single Cell Gel Electrophoresis) is used to assess DNA damage and repair in individual cells. (neb.com)
  • The assay detects single and double-stranded DNA breaks by measuring the migration of DNA from individual nuclei following alkaline treatment. (neb.com)
  • Single cell gel electrophoresis assay (comet assay) for evaluating manoparticles-induced DNA damage in cells. (cdc.gov)
  • Single cell gel electrophoresis assay (SCGE) or comet assay gained in popularity as a standard technique and is widely used for testing novel particles or chemicals for genotoxicity, monitoring environmental contamination with genotoxins, human biomonitoring and molecular epidemiology, and fundamental research in DNA damage and repair. (cdc.gov)
  • Here, we describe the method of alkaline comet assay to detect nanoparticle -induced DNA damage. (cdc.gov)
  • abstract = "The alkaline single-cell gel electrophoresis (or comet) assay was applied to evaluate the eventual DNA damage induced by the triphenolic metabolite of benzene, 1,2,4-benzenetriol (BT), in isolated human lymphocytes. (uab.cat)
  • Demonstration of chlorobenzene-induced DNA damage in mouse lymphocytes using the single cell gel electrophoresis assay. (uu.se)
  • In view of these considerations, this study was designed to evaluate the cytotoxic and genotoxic potential of geraniol, in an in vitro protocol, using two types of human cells: one without the ability to metabolize (peripheral blood mononuclear cells - PBMC), and the other with this capability (human hepatoma cell line - HepG2) through the comet assay and the micronucleus test. (geneticsmr.org)
  • Four concentrations (10, 25, 50, and 100 μg/mL) were selected for the genotoxic assessment for PBMC and three (1.25, 2.5, and 5 μg/mL) for HepG2 cells based on cytotoxicity tests (MTT assay). (geneticsmr.org)
  • This results in differing cytotoxic responses that are influenced by the nature of target cells, assay types and concentrations of ATZ. (frontiersin.org)
  • Gel electrophoresis provides a convenient assay to detect splicing and to locate the spliced regions. (brainkart.com)
  • The enzyme-linked immunosorbent spot (ELISpot ) assay enables visualization of multiple secretory products from a single responding cell. (sigmaaldrich.com)
  • This article offers 4 popular ELISA protocols: Sandwich ELISA protocol, Phosphorylation Assay Procedure, EIA Assay Procedure, & Cell-based Assay Procedure. (sigmaaldrich.com)
  • Cell DNA fragments assume a "comet with tail" formation on electrophoresis and are detected with an image analysis system. (edu.au)
  • Evaluation of potential DNA damaging effects of nitenpyram and imidacloprid in human U937-cells using a new statistical approach to analyse comet data. (uu.se)
  • One hybridoma, producing the monoclonal antibody H7, against placental alkaline phosphatase was adopted to offer CDR-containing regions for new recombinant constructs. (projectsparadise.com)
  • Protocol for the one-step, glutaraldehyde coupling method to conjugation alkaline phosphatase to antibodies and other proteins. (sigmaaldrich.com)
  • The His-tagged polyclonal antibody and alkaline phosphatase-conjugated anti-rabbit IgG were used as the primary and the secondary antibody, respectively. (chk1inhibitor.com)
  • Thermosensitive Alkaline Phosphatase catalyzes the removal of 5'- and 3'-phosphate groups from DNA, RNA, nucleotides, and proteins. (biogen.cz)
  • FastAP is a novel alkaline phosphatase, which is active in all Thermo Scientific restriction enzyme buffers as well as in PCR buffers. (biogen.cz)
  • Therefore, removal of alkaline phosphatase is not required prior to ligation. (biogen.cz)
  • Binding of FastAP Thermosensitive Alkaline Phosphatase to DNA may result in a band shift in agarose gels. (biogen.cz)
  • FastAP Thermosensitive Alkaline Phosphatase is active in all restriction enzyme buffers and may be added directly to digested DNA. (biogen.cz)
  • For Western blot analysis, protein samples (25 μg each) were separated by electrophoresis and transferred onto nitrocellulose membranes. (chk1inhibitor.com)
  • Spot 50 µl on agarose embedded cells. (neb.com)
  • The ovarian microenvironment affects the proliferation and differentiation of OGSCs, and immune cells and related cytokines are important components of the microenvironment. (biomedcentral.com)
  • It is worth noting that the proliferation and differentiation of stem cells cannot be separated from the surrounding microenvironment, and immune system related cells are an important part of the microenvironment of the OGSCs nest [ 14 ]. (biomedcentral.com)
  • On the other hand, the use of plant cell cultures for the more basic characterization of plant functions is rather limited due to the difficulties associated with functional differentiation in cell cultures. (go.jp)
  • Here, we investigate the cytotoxic effects of in vitro QD labeling on MSC proliferation and differentiation and use as a cell label in a cardiomyocyte co-culture. (biomedcentral.com)
  • The expression of osteogenesis-related gene was increased, which demonstrated that released BMP-2 could effectively induce the cell sheet osteogenic differentiation in vitro. (dovepress.com)
  • It is a complex and dynamic process to form a continuous construct via the cells' adhesion, proliferation, differentiation, and extracellular matrix (ECM) deposition on a scaffold. (dovepress.com)
  • CCN1 also induced Jag1 expression in hepatic stellate cells, whereupon they interacted with hepatic progenitor cells to promote their differentiation into cholangiocytes. (jci.org)
  • Cross-subtype neutralizing single domain antibodies against influenza present new opportunities for immunoprophylaxis and pandemic preparedness. (frontiersin.org)
  • Both single-chain variable fragments (scFv) antibodies or divalent tandem monospecific scFv [sc(Fv)2] antibodies with properties suitable for targeting were produced. (projectsparadise.com)
  • Our findings demonstrate that a single intramuscular injection in mice of AAV encoding R1a-B6 fused to Fc fragments of different isotypes equipped either, with or without antibody dependent cellular cytotoxicity (ADCC) activity, was able to drive sustained high-level expression (0.5-1.1 mg/mL) in sera with no evidence of reduction for up to 6 months. (frontiersin.org)
  • After digestions, electrophoresis on neutral gels analyzes duplexes, and electrophoresis on alka-line gels denatures and analyzes the sizes of fragments. (brainkart.com)
  • A genotoxicological technique for measuring DNA damage in an individual cell using single-cell gel electrophoresis. (edu.au)
  • Genotoxicity of plumbagin and its effects on catechol and NQNO-induced DNA damage in mouse lymphoma cells. (uu.se)
  • DNA damage in lymphocytes, as measured by alkaline single cell gel electrophoresis (pH 12.7), is greatly increased by the concurrent lysis of whole blood in both freshly isolated samples and in PHA-stimulated cultures over a period of 7 days. (elsevierpure.com)
  • This indicates that there are components in whole blood that can cause DNA damage in lymphocytes, with granulocytes and lysis of red blood cells likely candidates. (elsevierpure.com)
  • Through ionisation of molecules, IR generates toxic free radicals, which can result in single and double-strand DNA breaks, incur oxidative damage to sugar and base residues, and cause chromosomal aberrations and mutations without distinguishing between tumour and normal tissues ( 1 , 2 ). (sciendo.com)
  • Even though cancer cells are more vulnerable to IR than normal cells due to rapid cell division and inefficient DNA repair, both sustain DNA damage. (sciendo.com)
  • Earlier studies ( 7 , 10 - 12 ) have already described DNA damage and repair in human blood samples for each of the three anaesthetics and IR doses usually applied in therapy, but none has yet addressed single-dose exposure to a combination of VAs and IR, even though IR at sufficient doses has a similar mechanism of action as VA ( 13 ) and their combinations might have synergistic effects. (sciendo.com)
  • The protocol of Dr. Collins on the web site also discusses the use of lymphocytes for cells and/or UV treatment of these. (neb.com)
  • Production of a functional peripheral T cell compartment typically involves massive expansion of the bone marrow progenitors that seed the thymus. (bvsalud.org)
  • Background Multiple myeloma is an incurable malignancy of bone marrow plasma cells. (haematologica.org)
  • Multiple myeloma (MM) is an incurable hematologic malignancy characterized by the clonal proliferation of malignant plasma cells in the bone marrow. (haematologica.org)
  • 6 , 7 CXCL12 is an important mediator of several aspects of MM biology including transendothelial migration, 8 , 9 MM plasma cell migration and retention within the bone marrow, 10 , 11 angiogenesis, 7 and osteoclastic bone resorption. (haematologica.org)
  • 6 Recent animal studies involving systemic injection of labeled MM plasma cells have also demonstrated that blocking the CXCL12/CXCR4 axis leads to a 20% reduction in bone marrow tumor burden. (haematologica.org)
  • PEI-al nanocomposites carrying BMP-2 gene could efficiently transfect bone marrow mesenchymal stem cells. (dovepress.com)
  • Our results suggested that PEI-al nanocomposites efficiently deliver the BMP-2 gene to bone marrow mesenchymal stem cells and that BMP-2 gene-engineered cell sheet is an effective way for promoting bone regeneration. (dovepress.com)
  • Furthermore, we find that SET8 interacts with proliferating cell nuclear antigen through a conserved motif, and SET8 is required for DNA replication fork progression. (rupress.org)
  • Incubate 40 minutes at 4°C before beginning electrophoresis. (neb.com)
  • To avoid this, incubate samples with 6X DNA Loading Dye & SDS Solution at 65°C for 10 minutes, and chill on ice prior to electrophoresis. (biogen.cz)
  • Changes in metabolic pathway preferences are key events in the reprogramming process of somatic cells to induced pluripotent stem cells (iPSCs). (biomedcentral.com)
  • To investigate underlying disease mechanisms, induced pluripotent stem cells (iPSCs) allow the generation of patient-derived neuronal cells in a dish. (biomedcentral.com)
  • A) Schematic of the generation of OPTiKD human pluripotent stem cells (hPSCs) and of the resulting genetic circuit which allows tetracycline (TET)-dependent induction of gene knockdown both in hPSCs and hPSC-derived cells. (berterolab.com)
  • Evaluation of the potential genotoxicity of chromium picolinate in mammalian cells in vivo and in vitro. (uu.se)
  • We have previously described R1a-B6, an alpaca-derived single domain antibody (nanobody), that is capable of potent cross-subtype neutralization in vitro of H1N1, H5N1, H2N2, and H9N2 influenza viruses, through binding to a highly conserved epitope in the influenza hemagglutinin stem region. (frontiersin.org)
  • When in vitro experimental models are exposed to ATZ, they are faced with increased levels of reactive oxygen species (ROS), cytotoxicity and decreased growth rate at dosages that may vary with cell types. (frontiersin.org)
  • This review focuses on the differential responses of cell types to ATZ toxicity, testicular effects of ATZ in both in vitro and in vivo models and chemopreventive strategies, so as to highlight the current state of the art on the toxicological outcomes of ATZ exposure in several experimental model systems. (frontiersin.org)
  • The neuronal cells expressed numerous genes associated with sub-regions within the brain thus suggesting the usefulness of our in-vitro model. (biomedcentral.com)
  • Quantum Dots (QDs) offer an alternative to organic dyes and fluorescent proteins to label and track cells in vitro and in vivo . (biomedcentral.com)
  • Knowledge on P. vivax has been considerably delayed compared to P. falciparum due to its tropism for reticulocytes, which account for less than 1% of the total circulating red blood cell (RBC) count and, therefore, makes it difficult to maintain an in vitro culture of this species [ 4 ]. (biomedcentral.com)
  • To enhance the osteogenic potential of stem cell sheet, we fabricated bone morphogenetic protein 2 ( BMP-2 ) gene-engineered cell sheet using a complex of polyethylenimine-alginate (PEI-al) nanocomposites plus human BMP-2 complementary(c)DNA plasmid, and studied its osteogenesis in vitro and in vivo. (dovepress.com)
  • By comparing the gene expression profiles of somatic cells, intermediate-phase cells, and iPSCs, we found that carnitine palmitoyltransferase (Cpt)1b, a rate-limiting enzyme in fatty acid oxidation, was significantly upregulated in the early stage of the reprogramming process. (biomedcentral.com)
  • As in somatic cells, sperm intracellular cAMP concentration is regulated by the opposite action of two enzymes: the adenylyl cyclases (AC), which synthesize cAMP from ATP, and the phosphodiesterases (PDE), which break the phosphodiester bond of cAMP to form 5'-adenosine monophosphate (AMP). (plos.org)
  • However, a function for SET8 in mammalian cell proliferation has not been determined. (rupress.org)
  • 18. What is the approximate size of nucleus in a typical mammalian cell? (domocktest.com)
  • Bacterial uptake into epithelial cells is increasingly recognised as an important feature of infection. (biomedcentral.com)
  • Our recent study reported that C3 opsonisation markedly increases the ability of E. coli strain J96 to internalise into human proximal tubular epithelial cells via CD46, a complement regulatory protein expressed on host cell membrane. (biomedcentral.com)
  • In this study, we further assessed whether C3-dependent internalisation by human tubular epithelial cells is a general feature of uropathogenic E. coli and investigated features of the bacterial phenotype that may account for any heterogeneity. (biomedcentral.com)
  • Studies from our group have shown that mice deficient in C3 are resistant to ascending infection and complement can alter bacterial uptake by mouse proximal tubular epithelial cells (PTECs), a primary target of E. coli during the acute phase of pyelonephritis [ 12 ]. (biomedcentral.com)
  • Moreover, C3 opsonisation promotes E. coli invasion of human uro-epithelial cells via CD46, a complement regulatory protein expressed on host cell membranes [ 13 ]. (biomedcentral.com)
  • CD46 was not involved in the binding of E. coli to epithelial cells. (biomedcentral.com)
  • We also offer solutions for automation, site-directed mutagenesis, as well as your favorite restriction enzyme, ligase or competent cell products. (neb.com)
  • Alkaline single cell gel electrophoresis and human biomonitoring for genotoxicity: a pilot study on breast cancer patients undergoing chemotherapy including cyclophosphamide , Mutation Research, 395, 127-138. (uu.se)
  • Mechanistically, IL-36 signaling modulates neutrophils in a cell-intrinsic manner to greatly enhance not only their ability to directly kill tumor cells but also promote T and NK cell responses. (bvsalud.org)
  • 12 It is well established that hypoxia is an important selective force in the evolution of tumor cells, 13 and elevated expression of the hypoxia-inducible transcription factors HIF-1 and HIF-2 has been documented in several human cancers. (haematologica.org)
  • Place 50 µl of the enzyme solution or buffer alone onto gel surface and cover with a 22 x 22 mm cover slip. (neb.com)
  • Cells were harvested and resuspended with equilibration/wash buffer (50 mM NaH2PO4, 300 mM NaCl, pH 8.0). (chk1inhibitor.com)
  • Over-expression of hypoxia-inducible factor in multiple myeloma plasma cells strongly induced in vivo angiogenesis, and administration of a CXCL12 antagonist decreased hypoxia-inducible factor-induced angiogenesis. (haematologica.org)
  • In part, this is due to limited methods to track MSCs in vivo , precluding long-term functional studies of transplanted cells. (biomedcentral.com)
  • To further test the osteogenic potential of the cell sheet in vivo, enhanced green fluorescent protein or BMP-2-producing cell sheets were treated on the cranial bone defects. (dovepress.com)
  • In addition to pathogen virulence factors, complement C3 secreted by host cells also influences the ability of E. coli to invade cells and tissues within the urinary tract. (biomedcentral.com)
  • E. coli cells with a cloned bacterial AP gene. (biogen.cz)
  • Cytotoxin production by other bacteria (ie, Shigella dysenteriae, Vibrio parahaemolyticus, Clostridium difficile, enterohemorrhagic E coli ) results in mucosal cell destruction that leads to bloody stools with inflammatory cells. (medscape.com)
  • Atrazine (ATZ) is an environmental pollutant that interferes with several aspects of mammalian cellular processes including germ cell development, immunological, reproductive and neurological functions. (frontiersin.org)
  • It was found that ovoid cells in the epithelial layer of the ovary simultaneously expressed the germ cell specific marker MVH and the proliferation of cell marker BrdU using double-immunofluorescence staining. (biomedcentral.com)
  • Migration of DNA out of the nucleus correlates closely to the number of single and double-stranded breaks present in the DNA. (neb.com)
  • Similarly, Salmonella and Yersinia species also invade cells but do not cause cell death. (medscape.com)
  • Since S1 nuclease digests single-stranded RNA and DNA and can act endonucleolytically, it removes all single-stranded or unpaired regions from RNA and DNA. (brainkart.com)
  • Their simple modular structure and single open reading frame format are highly amenable to gene therapy-mediated delivery. (frontiersin.org)
  • One example is regulating the use of alternative splice sites to generate one or another gene product from a single gene. (brainkart.com)
  • The AD-iPSCs were differentiated into neuronal cells, in order to generate disease-specific protein association networks modeling the molecular pathology on the transcriptome level of AD, to analyse the reflection of the disease phenotype in gene expression in AD-iPS neuronal cells, in particular in the ubiquitin-proteasome system (UPS), and to address expression of typical AD proteins. (biomedcentral.com)
  • Niikura [ 5 ] and others observed germ cells expressing Stra8 (stimulated by retinoic acid gene 8) in the ovarian surface epithelium, indicating that there may be germ cells with meiotic function in the ovary. (biomedcentral.com)
  • Although a high level of PDE10A gene expression is observed in the testis, information on the identity of the isoforms or on the cell type that express the PDE10 protein is lacking. (plos.org)
  • First, a full-length functional ZIKV cDNA clone was engineered as a bacterial artificial chromosome, with each reporter gene under the cap-independent translational control of a cardiovirus-derived internal ribosome entry site inserted downstream of the single open reading frame of the viral genome. (mdpi.com)
  • Recently, stem cell- and gene-based therapy has been applied in BTE and achieved some good clinical results. (dovepress.com)
  • We detected the expression of p-tau and GSK3B, a physiological kinase of tau, in neuronal cells derived from AD-iPSCs. (biomedcentral.com)
  • Treatment of neuronal cells differentiated from AD-iPSCs with an inhibitor of γ-secretase resulted in the down-regulation of p-tau. (biomedcentral.com)
  • Plant cell cultures are widely used in the micro-propagation of clonal plants, especially virus-free plants, and in the production of useful metabolites such as paclitaxel. (go.jp)
  • I emphasize the high potential of functionally differentiated cell cultures, as well as some of the pitfalls, in the characterization of plant functions and biotechnological applications. (go.jp)
  • Anti-PvTRAMP antisera was obtained by inoculating rabbits with PvTRAMP B cell epitopes produced as synthetic peptides in order to assess its recognition in parasite lysates by Western blot and in intact parasites by indirect immunofluorescence. (biomedcentral.com)
  • The hypoxic regulation of CXCL12 was examined in multiple myeloma plasma cell lines using polymerase chain reaction and western blotting. (haematologica.org)
  • Results Strong hypoxia-inducible factor-2 protein expression was detected in CD138 + multiple myeloma plasma cells in patients' biopsy specimens. (haematologica.org)
  • Prolonged exposure to hypoxia strongly up-regulated CXCL12 expression in multiple myeloma plasma cells and hypoxia-inducible factor-2 was found to play a key role in this response. (haematologica.org)
  • Conclusions Hypoxia-inducible factor-2 is a newly identified regulator of CXCL12 expression in multiple myeloma plasma cells and a major contributor to multiple myeloma plasma cell-induced angiogenesis. (haematologica.org)
  • The moment the preferred serum titer was attained, immune spleens were removed through the mice, dissociated, and fused with SP2 o myeloma cells. (liverxreceptor.com)
  • Finally, in a cardiomyocyte co-culture QD labeled MSCs were easy to locate and formed functional cell-to-cell couplings, assessed by dye diffusion. (biomedcentral.com)
  • 14 , 15 HIF-1 and HIF-2 mediate adaptive responses to hypoxia by inducing the transcription of genes associated with erythropoiesis, glycolytic metabolism, cell survival and angiogenesis. (haematologica.org)
  • Transcriptome analysis of AD-iPS derived neuronal cells revealed significant changes in the expression of genes associated with AD and with the constitutive as well as the inducible subunits of the proteasome complex. (biomedcentral.com)
  • 3 - 5 CXCL12 is highly expressed by MM plasma cells, 6 and circulating levels of CXCL12 are higher in the peripheral blood of MM patients than in age-matched normal donors and MGUS patients. (haematologica.org)
  • The term "oncotarget" encompasses all molecules, pathways, cellular functions, cell types, and even tissues that can be viewed as targets relevant to cancer as well as other diseases. (oncotarget.com)
  • DNA replication, synthesis and subsequent cell division has been linked to each of the stages of the carcinogenesis process [ 4 , 5 ]. (walshmedicalmedia.com)
  • We show that small interfering RNA inhibition of SET8 expression leads to decreased cell proliferation and accumulation of cells in S phase. (rupress.org)
  • Mesenchymal stem cells (MSCs) are multipotent cells with the potential to differentiate into bone, cartilage, fat and muscle cells and are being investigated for their utility in cell-based transplantation therapy. (biomedcentral.com)
  • The virus provided a convenient source of DNA for hybridization reactions and RNA extracted from adeno-infected cultured cells was a rich source of viral RNA. (brainkart.com)
  • This discovery invalidated the "fixation theory of primordial follicle pool" and suggested for the first time the hypothesis that germ stem cells also exist in the ovary. (biomedcentral.com)
  • Unlike many other kinases, GSK3B is believed to be permanently active in resting cells and in neurons without extracellular stimulation and can be inactivated by Ser9 phosphorylation [ 14 ]. (biomedcentral.com)
  • According to the reports and findings, saffron plays a key role to cure different digestive system disorders via chemopreventive, inhibition of cell proliferation, induction of apoptosis, antioxidant effects and radical scavenging, genoprotective property, prevention of lipid peroxidation and anti-inflammatory processes. (ac.ir)
  • ATZ also induces morphological changes similar to apoptosis and initiates mitochondria-dependent cell death in several experimental models. (frontiersin.org)
  • In recent years, the discovery of ovarian germ stem cells (OGSCs) has provided a new research direction for the treatment of female infertility. (biomedcentral.com)
  • Traditional BTE involves three-dimensional biodegradable scaffolds, stem cells, and osteoinductive growth factors. (dovepress.com)
  • Brie﫿y, two single-stranded oligonucleotides are annealed to form a double-stranded DNA sequence containing the shRNA sequence followed by a Pol III terminator (consisting of a stretch of four or more thymidines), as well as 5'- and 3'-end "sticky" overhangs that are complementary to those generated in the targeting vector following restriction digestion with BglII and SalI (Figures 3E and 4C). (berterolab.com)
  • Nanotechnology is focused on the development of nanoscale materials and devices with use in biomedicine for drug delivery, diagnostics, imaging and cell tracking. (biomedcentral.com)
  • Bacterial virulence factors, especially fimbrial adhesins, have been conclusively shown to promote host cell invasion. (biomedcentral.com)
  • Colony counting and fluorescence-activated cell sorting (FACS) were used to calculate reprogramming efficiency. (biomedcentral.com)
  • A single colony was inoculated in a nutrient-rich bacterial growth medium super optimal broth (SOB) with ampicillin (100 μg mL−1) and grown at 37 °C overnight. (chk1inhibitor.com)
  • These proteins either arise from proteins expressed by cells at the deposition site (localized), or they precipitate systemically after production at a local site (systemic). (medscape.com)
  • Native or wild-type quaternary protein structure is usually born from a single translated protein sequence with one ordered conformation with downstream protein interactions. (medscape.com)
  • Single-electron transistors in heterostructure nanowires. (lu.se)
  • In this review, I overview our experience with functionally differentiated cultured plant cells and their characteristics, especially with regard to photoautotrophism and secondary metabolism. (go.jp)
  • Herein we investigated whether lupin proteins compared to casein modulate sterol excretion and mRNA expression of intestinal sterol transporters by use of pigs as an animal model with similar lipid metabolism as humans, and cellular cholesterol-uptake by Caco-2 cells. (biomedcentral.com)
  • There are two main phases of expansion during T cell development, following T lineage commitment of double-negative (DN) 2 cells and after successful rearrangement and selection for functional TCRß chains in DN3 thymocytes, which promotes the transition of DN4 cells to the DP stage. (bvsalud.org)
  • Thus, while poor prognostic outcomes are typically associated with neutrophil enrichment in the TME, our results highlight the pleiotropic effects of IL-36 and its therapeutic potential to modify tumor-infiltrating neutrophils into potent effector cells and engage both the innate and adaptive immune system to achieve durable antitumor responses in solid tumors. (bvsalud.org)
  • Here, we report that IL-36 cytokine can engage both innate and adaptive immunity to remodel an immune-suppressive tumor microenvironment (TME) and mediate potent antitumor immune responses via signaling in host hematopoietic cells. (bvsalud.org)
  • The ELISpot provides both qualitative (type of immune protein) and quantitative (number of responding cells) information. (sigmaaldrich.com)