Alkynes in Reactive groups
Terminal alkynes react with azides in a copper catalyzed process called copper catalyzed alkyne azide cycloaddition (CuAAc). The reaction is a useful method for the conjugation and fluorescent labeling of biomolecules.
Lumiprobe offers a range of terminal alkyne derivatives, including fluorescent dye alkynes, and linkers with alkyne group.
1-Ethynyl pyrene
Pyrene is polyaromatic hydrocarbon containing four fused rings. This reagent contains terminal alkyne group for Click Chemistry and other reactions, such as Sonogashira coupling.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| 515B0 | 50 mg | $30.00 | in stock | |
| 615B0 | 100 mg | $50.00 | in stock |
3-Ethynyl perylene
Alkyne derivative of ultra-bright and photostable perylene fluorophore.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| 555B0 | 50 mg | $50.00 | in stock | |
| 655B0 | 100 mg | $80.00 | in stock |
AF430 alkyne
AF430 is a dye emitting in blue range. A dye is useful for flow cytometry.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A08B0 | 1 mg | $110.00 | in stock | |
| B08B0 | 5 mg | $290.00 | in stock | |
| C08B0 | 10 mg |
$470.00
|
in stock | |
| D08B0 | 25 mg |
$690.00
|
in stock | |
| E08B0 | 50 mg |
$1270.00
|
in stock | |
| F08B0 | 100 mg |
$1990.00
|
in stock |
Alkyne Amidite, hydroxyprolinol
Acetylenic amidite for the incorporation of acetylene groups into oligos.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| 21360 | 250 mg | $90.00 | in stock | |
| 41360 | 1 g | $190.00 | in stock |
Alkyne CPG modifier 500
Solid support for the synthesis of 3'-modified oligonucleotides with alkyne group for Click Chemistry.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| 12860 | 100 mg | $60.00 | in stock | |
| 22860 | 250 mg | $120.00 | in stock | |
| 32860 | 500 mg | $230.00 | in stock | |
| 42860 | 1 g | $380.00 | in stock | |
| 52860 | 5 g |
$1450.00
|
in stock |
Alkyne hydrazide
Bifunctional reagent containing alkyne group and hydrazide function. It reacts with aldehydes and ketones. Alkyne group can then be coupled with various azides via CuAAC reaction.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| 41770 | 25 mg | $95.00 | in stock | |
| 51770 | 50 mg | $195.00 | in stock | |
| 61770 | 100 mg | $290.00 | in stock |
Alkyne maleimide
Maleimide reagent for the attachment of alkyne functional group to proteins, peptides, and other molecules bearing SH (thiol) groups, including cysteine residues.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| 41780 | 25 mg | $95.00 | in stock | |
| 51780 | 50 mg | $195.00 | in stock | |
| 61780 | 100 mg | $290.00 | in stock |
Alkyne NHS ester (hexynoic acid NHS ester)
Alkyne NHS ester for the labeling of biomolecules with alkyne group for Copper catalyzed Click chemistry.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| 41720 | 25 mg | $95.00 | 7 days | |
| 51720 | 50 mg | $180.00 | in stock | |
| 61720 | 100 mg | $290.00 | in stock | |
| 91720 | 1 g |
please inquire
|
in stock |
Alkyne Phosphoramidite, 5'-terminal
Alkyne phosphoramidite for the synthesis of oligonucleotides ready for Click chemistry.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| 22260 | 250 mg | $90.00 | in stock | |
| 32260 | 500 mg | $140.00 | in stock | |
| 42260 | 1 g | $190.00 | in stock | |
| 62260 | 5 g |
$690.00
|
in stock | |
| 82260 | 10 g |
$1190.00
|
21 days |
Alkyne-PEG2-Amine
Diethyleneglycol (PEG2) based bifunctional linker, containing amine and alkyne functional groups.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| 2065-1g | 1 g | $120.00 | in stock | |
| 2065-5g | 5 g | $350.00 | in stock | |
| 2065-25g | 25 g |
please inquire
|
in stock |
Alkyne-PEG3-Amine
Alkyne PEG3 amine is a medium length heterobifunctional linker for the conjugation.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| 425-1g | 1 g | $195.00 | in stock | |
| 425-5g | 5 g |
$580.00
|
10 days |
Alkyne-PEG3-COOH
Bifunctional linker with terminal alkyne function, and carboxylic acid moiety, CAS# 1415800-32-6.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| 1743-1g | 1 g |
$490.00
|
in stock | |
| 1743-5g | 5 g |
$980.00
|
in stock | |
| 1743-25g | 25 g |
please inquire
|
in stock |
Alkyne-PEG3-iodide
PEG3 with alkyne and iodide functional groups, a reactive and hydrophilic linker for alkylation and Click chemistry.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| 2193-1g | 1 g |
$490.00
|
in stock | |
| 2193-5g | 5 g |
$1150.00
|
in stock | |
| 2193-25g | 25 g |
please inquire
|
in stock |
Alkyne-PEG3-NHS ester
Bifunctional hyrophilic linker with NHS ester and terminal alkyne functional group based on triethyleneglycol (PEG3).
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| 2298-1g | 1 g |
$490.00
|
7 days | |
| 2298-5g | 5 g |
$980.00
|
21 days | |
| 2298-25g | 25 g |
please inquire
|
21 days |
Alkyne-PEG3-OH
Alkyne-PEG3-OH is a triethyleneglycol based bifunctional linker with a hydroxyl group and an alkyne fragment.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| 418-1g | 1 g | $95.00 | in stock | |
| 418-5g | 5 g | $280.00 | in stock | |
| 418-25g | 25 g |
please inquire
|
in stock |
Alkyne-PEG4-amine
A bifunctional linker molecule containing both terminal alkyne moiety for Click chemistry, and amine group. Contains a long hydrophilic PEG4 arm.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| 2025-100mg | 100 mg | $95.00 | in stock | |
| 2025-1g | 1 g | $390.00 | in stock |
Alkyne-PEG4-maleimide
Water soluble, heterobifunctional hydrophilic linker with a length of 14 Å, containing maleimide for thiol labeling, and alkyne for Click chemistry. An ideal reagent to attach an alkyne moiety to a protein.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| 2002-100mg | 100 mg | $150.00 | in stock | |
| 2002-1g | 1 g |
$590.00
|
in stock |
BDP 558/568 alkyne
BDP 558/568 is a borondipyrromethene dye for Cyanine3 channel. This is a terminal alkyne derivative.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A74B0 | 1 mg | $110.00 | in stock | |
| B74B0 | 5 mg | $210.00 | in stock | |
| C74B0 | 10 mg | $310.00 | in stock | |
| D74B0 | 25 mg |
$410.00
|
in stock | |
| E74B0 | 50 mg |
$695.00
|
in stock | |
| F74B0 | 100 mg |
$1190.00
|
in stock |
BDP 581/591 alkyne
BDP 581/591 is a borondipyrromethene fluorophore which is useful for fluorescence polarization assays, microscopy, and two photon experiments. This alkyne is a derivative for copper-catalyzed Click chemistry.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A64B0 | 1 mg | $110.00 | in stock | |
| B64B0 | 5 mg | $210.00 | in stock | |
| C64B0 | 10 mg | $310.00 | in stock | |
| D64B0 | 25 mg |
$410.00
|
in stock | |
| E64B0 | 50 mg |
$695.00
|
in stock | |
| F64B0 | 100 mg |
$1190.00
|
in stock |
BDP 650/665 alkyne
BDP 650/665 alkyne is a red emitting BODIPY dye derivative carrying a terminal alkyne group for a copper catalyzed conjugation with azides. Absorption and emission spectra of BDP 650/665 are designed to fit Cy5 channel of various instruments.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A84B0 | 1 mg | $110.00 | in stock | |
| B84B0 | 5 mg | $210.00 | in stock | |
| C84B0 | 10 mg | $310.00 | in stock | |
| D84B0 | 25 mg |
$410.00
|
in stock | |
| E84B0 | 50 mg |
$695.00
|
in stock | |
| F84B0 | 100 mg |
$1190.00
|
in stock |
BDP FL alkyne
Borondipyrromethene dye alkyne for Click Chemistry. Bright and photostable dye for FAM channel.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A14B0 | 1 mg | $110.00 | in stock | |
| B14B0 | 5 mg | $210.00 | in stock | |
| C14B0 | 10 mg | $310.00 | in stock | |
| D14B0 | 25 mg |
$410.00
|
in stock | |
| E14B0 | 50 mg |
$695.00
|
in stock | |
| F14B0 | 100 mg |
$1190.00
|
in stock |
BDP R6G alkyne
Terminal alkyne derivative of BDP R6G dye for Click chemistry. BDP R6G is a borondipyrromethene dye whose absorption and emission spectra are similar to R6G (rhodamine 6G).
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A44B0 | 1 mg | $110.00 | in stock | |
| B44B0 | 5 mg | $210.00 | in stock | |
| C44B0 | 10 mg | $310.00 | in stock | |
| D44B0 | 25 mg |
$410.00
|
in stock | |
| E44B0 | 50 mg |
$695.00
|
in stock | |
| F44B0 | 100 mg |
$1190.00
|
in stock |
BDP TMR alkyne
Borondipyrromethene dye for TAMRA channel, with alkyne group for copper-catalyzed Click Chemistry.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A24B0 | 1 mg | $110.00 | in stock | |
| B24B0 | 5 mg | $210.00 | in stock | |
| C24B0 | 10 mg | $310.00 | in stock | |
| D24B0 | 25 mg |
$410.00
|
in stock | |
| E24B0 | 50 mg |
$695.00
|
in stock | |
| F24B0 | 100 mg |
$1190.00
|
in stock |
BDP TR alkyne
BDP TR is a fluorophore for Texas Red (ROX) channel. This borondipyrromethene dye is very bright, and resistant to oxidation.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A34B0 | 1 mg | $110.00 | in stock | |
| B34B0 | 5 mg | $210.00 | in stock | |
| C34B0 | 10 mg | $310.00 | in stock | |
| D34B0 | 25 mg |
$410.00
|
in stock | |
| E34B0 | 50 mg |
$695.00
|
in stock | |
| F34B0 | 100 mg |
$1190.00
|
in stock |
Biotin alkyne
Biotin alkyne is a reactive affinity label which can be attached to biomolecules via Click Chemistry.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| C37B0 | 10 mg | $90.00 | in stock | |
| D37B0 | 25 mg | $160.00 | in stock | |
| E37B0 | 50 mg | $270.00 | 5 days | |
| F37B0 | 100 mg |
$420.00
|
in stock |
Cyanine3 alkyne
Cyanine3 alkyne is a fluorescent dye alkyne for Click Chemistry.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A10B0 | 1 mg | $110.00 | in stock | |
| B10B0 | 5 mg | $210.00 | in stock | |
| C10B0 | 10 mg | $310.00 | in stock | |
| D10B0 | 25 mg |
$410.00
|
in stock | |
| E10B0 | 50 mg |
$695.00
|
in stock | |
| F10B0 | 100 mg |
$1190.00
|
in stock |
Cyanine5 alkyne
Cyanine5 alkyne is an alkyne dye for Click Chemistry.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A30B0 | 1 mg | $110.00 | in stock | |
| B30B0 | 5 mg | $210.00 | in stock | |
| C30B0 | 10 mg | $310.00 | in stock | |
| D30B0 | 25 mg |
$410.00
|
in stock | |
| E30B0 | 50 mg |
$695.00
|
in stock | |
| F30B0 | 100 mg |
$1190.00
|
in stock |
Cyanine5.5 alkyne
Cyanine5.5 alkyne is a NIR (near infrared) dye azide for both copper-catalyzed, and copper-free Click Chemistry.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A70B0 | 1 mg | $110.00 | in stock | |
| B70B0 | 5 mg | $210.00 | in stock | |
| C70B0 | 10 mg | $310.00 | in stock | |
| D70B0 | 25 mg |
$410.00
|
in stock | |
| E70B0 | 50 mg |
$695.00
|
in stock | |
| F70B0 | 100 mg |
$1190.00
|
in stock |
Cyanine7 alkyne
Cyanine7 alkyne is a near infrared (NIR) dye alkyne for Click chemistry.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A50B0 | 1 mg | $110.00 | in stock | |
| B50B0 | 5 mg | $210.00 | in stock | |
| C50B0 | 10 mg | $310.00 | in stock | |
| D50B0 | 25 mg |
$410.00
|
in stock | |
| E50B0 | 50 mg |
$695.00
|
in stock | |
| F50B0 | 100 mg |
$1190.00
|
in stock |
Cyanine7.5 alkyne
Reactive near infrared (NIR) dye for Click Chemistry containing a terminal alkyne group.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A60B0 | 1 mg | $110.00 | in stock | |
| B60B0 | 5 mg | $210.00 | in stock | |
| C60B0 | 10 mg | $310.00 | in stock | |
| D60B0 | 25 mg |
$410.00
|
in stock | |
| E60B0 | 50 mg |
$695.00
|
in stock | |
| F60B0 | 100 mg |
$1190.00
|
in stock |
DBCO NHS ester
Azodibenzocyclooctyne (DBCO, ADIBO) reagent for strain promoted copper free Click chemistry (spAAC). The reagent contains an NHS ester function for the attachment of the cyclooctyne to various molecules.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| 34720 | 10 mg | $60.00 | in stock | |
| 44720 | 25 mg | $95.00 | in stock | |
| 54720 | 50 mg | $145.00 | in stock | |
| 64720 | 100 mg | $210.00 | in stock | |
| 94720 | 1 g |
$1190.00
|
in stock | |
| K4720 | 5 g |
$3570.00
|
21 days | |
| N4720 | 25 g |
please inquire
|
21 days |
FAM alkyne, 5-isomer
FAM alkyne, 5-isomer - an alkyne derivative of fluorescein dye for Click Chemistry.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A41B0 | 1 mg | $80.00 | in stock | |
| B41B0 | 5 mg | $100.00 | in stock | |
| C41B0 | 10 mg | $150.00 | in stock | |
| D41B0 | 25 mg | $295.00 | in stock | |
| E41B0 | 50 mg |
$450.00
|
in stock | |
| F41B0 | 100 mg |
$780.00
|
in stock |
FAM alkyne, 6-isomer
Fluorescein dye alkyne for Click Chemistry, pure 6-isomer.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A51B0 | 1 mg | $80.00 | in stock | |
| B51B0 | 5 mg | $100.00 | in stock | |
| C51B0 | 10 mg | $150.00 | in stock | |
| D51B0 | 25 mg | $295.00 | in stock | |
| E51B0 | 50 mg |
$450.00
|
in stock | |
| F51B0 | 100 mg |
$780.00
|
in stock |
JOE alkyne, 6-isomer
JOE dye alkyne derivative for copper catalyzed Click chemistry reaction with azides. JOE dye is often used for nucleic acid labeling.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A21B0 | 1 mg | $110.00 | in stock | |
| B21B0 | 5 mg | $210.00 | in stock | |
| C21B0 | 10 mg | $310.00 | in stock | |
| D21B0 | 25 mg |
$410.00
|
in stock | |
| E21B0 | 50 mg |
$695.00
|
in stock | |
| F21B0 | 100 mg |
$1190.00
|
in stock |
R6G alkyne, 6-isomer
R6G (rhodamine 6G) terminal alkyne for copper catalyzed Click chemistry reaction with azides. Pure 6-isomer of the dye.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A52B0 | 1 mg | $110.00 | in stock | |
| B52B0 | 5 mg | $210.00 | in stock | |
| C52B0 | 10 mg | $310.00 | in stock | |
| D52B0 | 25 mg |
$410.00
|
in stock | |
| E52B0 | 50 mg |
$695.00
|
in stock | |
| F52B0 | 100 mg |
$1190.00
|
in stock |
ROX alkyne, 5-isomer
Rhodamine X (ROX, Rhodamine 101) alkyne derivative for copper catalyzed Click chemistry. ROX is a bright red-emitting dye.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A12B0 | 1 mg | $110.00 | in stock | |
| B12B0 | 5 mg | $210.00 | in stock | |
| C12B0 | 10 mg | $310.00 | in stock | |
| D12B0 | 25 mg |
$410.00
|
in stock | |
| E12B0 | 50 mg |
$695.00
|
in stock | |
| F12B0 | 100 mg |
$1190.00
|
in stock |
Sulfo-Cyanine3 alkyne
A water soluble dye alkyne for copper-catalyzed Click Chemistry. The fluorophore Sulfo-Cyanine3 is a bright and photostable dye for the Cy3® channel.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A13B0 | 1 mg | $110.00 | in stock | |
| B13B0 | 5 mg | $290.00 | in stock | |
| C13B0 | 10 mg |
$470.00
|
in stock | |
| D13B0 | 25 mg |
$690.00
|
in stock | |
| E13B0 | 50 mg |
$1270.00
|
in stock | |
| F13B0 | 100 mg |
$1990.00
|
in stock |
Sulfo-Cyanine5 alkyne
Sulfo-Cyanine5 is a water-soluble Cyanine5 dye alkyne for Click chemistry.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A33B0 | 1 mg | $110.00 | in stock | |
| B33B0 | 5 mg | $290.00 | in stock | |
| C33B0 | 10 mg |
$470.00
|
in stock | |
| D33B0 | 25 mg |
$690.00
|
in stock | |
| E33B0 | 50 mg |
$1270.00
|
in stock | |
| F33B0 | 100 mg |
$1990.00
|
in stock |
Sulfo-Cyanine5.5 alkyne
Alkyne functionalized, water soluble far red/near infrared emitting fluorophore sulfo-Cyanine5.5.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A73B0 | 1 mg | $110.00 | in stock | |
| B73B0 | 5 mg | $290.00 | in stock | |
| C73B0 | 10 mg |
$470.00
|
in stock | |
| D73B0 | 25 mg |
$690.00
|
in stock | |
| E73B0 | 50 mg |
$1270.00
|
in stock | |
| F73B0 | 100 mg |
$1990.00
|
in stock |
Sulfo-Cyanine7 alkyne
A sulfonated near infrared dye alkyne for copper-catalyzed cycloaddition with azides (CuAAC).
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A53B0 | 1 mg | $110.00 | in stock | |
| B53B0 | 5 mg | $290.00 | in stock | |
| C53B0 | 10 mg |
$470.00
|
in stock | |
| D53B0 | 25 mg |
$690.00
|
in stock | |
| E53B0 | 50 mg |
$1270.00
|
in stock | |
| F53B0 | 100 mg |
$1990.00
|
in stock |
Sulfo-Cyanine7.5 alkyne
Sulfo-Cyanine7.5 is a near infrared fluorophore similar to indocyanine green (ICG), but possessing higher fluorescence quantum yield. The dye is very hydrophilic and water soluble. The reagent is very useful for the labeling of biomolecules for in vivo imaging. This is an alkyne for copper catalyzed Click chemistry.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A63B0 | 1 mg | $110.00 | in stock | |
| B63B0 | 5 mg | $290.00 | in stock | |
| C63B0 | 10 mg |
$470.00
|
in stock | |
| D63B0 | 25 mg |
$690.00
|
in stock | |
| E63B0 | 50 mg |
$1270.00
|
in stock | |
| F63B0 | 100 mg |
$1990.00
|
in stock |
TAMRA alkyne, 5-isomer
Alkyne derivative of TAMRA dye, pure 5-isomer for CuAAC.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A71B0 | 1 mg | $110.00 | in stock | |
| B71B0 | 5 mg | $210.00 | in stock | |
| C71B0 | 10 mg | $310.00 | in stock | |
| D71B0 | 25 mg |
$410.00
|
in stock | |
| E71B0 | 50 mg |
$695.00
|
in stock |
TAMRA alkyne, 6-isomer
Terminal alkyne for copper-catalyzed Click chemistry. Tetramethylrhodamine (TAMRA) is a rhodamine dye which is popular in qPCR and other applications. TAMRA is a also a FRET acceptor for FAM.
Show pricing
| Cat. # | Quantity | Price | Lead time | Buy this product |
|---|---|---|---|---|
| A81B0 | 1 mg | $110.00 | in stock | |
| B81B0 | 5 mg | $210.00 | in stock | |
| C81B0 | 10 mg | $310.00 | in stock | |
| D81B0 | 25 mg |
$410.00
|
in stock | |
| E81B0 | 50 mg |
$695.00
|
in stock |
The count of items is incorrect.
Your cart is empty
$ 
