Metal Chelator Selection and Application Guide: From Core Concepts to Classification Dimensions, to a Research-Scenario Product Navigation (Tables 1–6)

1.Why are metal ions both “critical” and “hard to control”?

In experiments, processes, and biological systems, metal ions often play two roles at the same time:

1. A critical variable: Reaction rates, material properties, and biological processes can be strongly affected by a metal ion’s oxidation state, coordination form, and concentration (even for the same metal, behavior can be completely different under different ligation/oxidation states).

2. A hard-to-control interference: Even trace metals can produce an “amplification effect”—for example, accelerating oxidation/degradation (common for redox-active metals such as Fe/Cu), triggering precipitation or scaling (e.g., Ca/Mg forming poorly soluble salts with carbonate/phosphate), or altering color/fluorescence/electrochemical readouts. As a result, the same formulation may behave very differently across batches, water sources, or labware conditions.

In many cases, what determines system behavior is not the total metal amount, but the fraction of metal that can truly participate in reactions and interactions in that system—roughly an effective metal pool that can be thought of as “free + labile” (free species plus weakly bound, readily exchangeable species).This pool continuously shifts with pH, competing ligands (buffer salts/proteins/organic acids, etc.), ionic strength, and redox conditions—which is why it is often the hardest variable to stabilize and reproduce.

Note: Here, labile refers to the fraction of metal species that can rapidly exchange ligands on the timescale of your reaction/assay. Therefore, changing pH, ligands, ionic strength, or the redox environment can significantly change the size of the “exchangeable metal pool.”

The core value of metal chelators is not merely “removing metals,” but constraining this most difficult metal variable into a predictable, tunable, and verifiable range through designed coordination binding:

You can choose to completely mask trace-metal interference, or, in the presence of metals, maintain the active metal level at a stable setpoint. When done correctly, reproducibility and interpretability often improve markedly—metals shift from being an “uncontrollable source of interference” to a genuinely engineerable control knob.

2.Core concepts: What do chelation, denticity, and stability constants mean?

2.1 What is “chelation”? What is a “chelating agent”?

1. The key idea in the IUPAC definition of chelation is: two or more separated binding sites on the same ligand molecule form bonds or other attractive interactions with the same central atom; the resulting entity is called a chelate.

2. Accordingly, a metal chelating agent (chelating agent/chelator) can be summarized as: a molecule or functional material that uses multiple donor sites within the same molecule to bind a single metal ion at multiple points, forming a chelate. This reduces the fraction of exchangeable/reactive metal species (free + labile) in the system, and thereby rewrites the metal’s reactivity, mobility, and detectability.

3. In terms of terminology, chelate is often traced back to Morgan and Drew (1920), who used it to evoke the image of a multidentate ligand gripping a metal like a crab’s claw/pincer and forming ring-like structures.

2.2 What is the difference between “chelation” and “complexation/coordination”?

Coordination/complexation is a broader concept: as long as a ligand forms a coordination interaction with a metal, it falls under coordination/complexation.

Chelation adds two further requirements:

1. The same ligand provides two or more donor sites;

2. These sites bind simultaneously to the same central metal (typically forming one or more chelate rings).

Therefore: all chelation is a type of coordination/complexation, but not all coordination is chelation.

2.3 Denticity: how many “teeth” a ligand actually uses in this complex

IUPAC defines denticity as: in a given coordination entity, the number of donor groups by which a ligand is attached to the same central atom.

An intuitive way to think about it:

1. Monodentate = “one-point grip”;

2. Polydentate = “multi-point grip,” more likely to form chelate rings.

Key supplement: Denticity is the number of donor sites actually used in the formed complex, not the number a ligand might theoretically have. Some ligands exhibit variable denticity depending on the metal, solvent, or pH.

2.4 Stability (formation) constants: “thermodynamically, does the system favor binding or remaining free?”

In coordination and analytical chemistry, formation constants are commonly used to quantify the equilibrium tendency of complex formation. IUPAC notes that for mononuclear binary complex systems, one can distinguish:

1. Stepwise formation constants 

2. Overall (cumulative) formation constants 

3. Both are often collectively referred to as stability constants (stepwise/overall).

2.5 Conditional stability constants K′: does it work under your actual conditions?

In real systems, chelators often exist in multiple protonation states, and metals may also bind competitively with OH⁻, phosphate, citrate, proteins/buffer components, and more. As a result, the effective binding strength depends strongly on conditions such as pH, competing ligands, and ionic strength.

Analytical chemistry often uses the conditional formation/conditional stability constant K′ (also called an apparent/conditional constant) to fold these factors into a metric that is closer to real-world evaluation and selection.

2.6 Quick glossary of key terms

Term	One-sentence interpretation	Relevance to selection
Chelation	Multiple binding sites on the same ligand simultaneously bind the same metal (often forming chelate rings)	Determines whether the “exchangeable metal pool” can be compressed into the target range
Denticity	Number of donor sites a ligand actually uses to bind the metal in that complex	Higher denticity more readily yields a chelation effect, but depends on geometry/pH/metal preferences
Stability/formation constants (K_n, β_n)	How strongly complex formation is thermodynamically biased toward binding	Determines whether equilibrium favors binding vs. free species (not the same as “kinetically non-exchangeable”)
Conditional constant K′	“Effective stability” under a specific pH/competition environment	Determines whether it truly works in your system

3.Structural features: Why can chelators “capture” metals and change their behavior?

3.1 Donor atoms and donor combinations (donor set): determining “which metals you can grab” and “how resistant you are to interference”

1. O / N / S (and their combinations) influence metal preference and resistance to competition. A rough first-pass judgment can be made with HSAB: hard acids (e.g., Fe(III)) usually prefer O donors; soft acids (e.g., Hg(II), Cu(I)) prefer more polarizable donors such as S; N donors often sit in the “borderline” region and typically require considering metal oxidation state and coordination geometry together.

2. However, what is often more decisive in practice is the donor combination + spatial arrangement: even with the same O,N donor types, if the arrangement does not match the metal’s preferred coordination geometry, binding can become markedly weaker.

3.2 Geometric matching and bite parameters: determining “how securely you hold on”

1. A metal’s coordination number and geometric preferences (octahedral/tetrahedral/square planar, etc.) must match the site layout offered by the ligand.

2. Key structural parameters include chelate ring size (5- and 6-membered rings are commonly the most favorable), bite angle, and backbone rigidity vs flexibility.

3. Practical takeaway: more binding sites does not automatically mean stronger binding; the upper limit of stability comes from “enough sites + the right geometry.”

3.3 Preorganization and the macrocyclic effect: determining “easier binding” and “harder displacement”

1. Preorganization brings donor sites closer to an ideal coordination arrangement, typically reducing the energetic penalty of “getting into position,” and therefore favoring formation of stable complexes (provided size and geometry are matched).

2. Macrocycles and rigid frameworks often confer higher kinetic inertness: once a metal enters the coordination cavity, dissociation and ligand exchange are often slower—more like being “locked in.” However, complex formation can also be slower and require harsher conditions. This benefit presupposes that the cavity size and donor arrangement match the target metal’s coordination number/geometry; if the match is poor, a macrocycle may be “slow to enter, or unable to enter,” and overall performance may even be inferior to some linear ligands.

3. Selection implication: if your goal is stable encapsulation, resistance to dilution/competition, and minimal metal release, macrocycles are often a better fit; if your goal is fast reversible control or controlled release, you must carefully evaluate exchange kinetics and, when needed, introduce trigger strategies such as pH, redox, or competitive ligands.

3.4 pKa and charge states: determining “whether it is truly effective at the target pH”

1. Chelators often contain protonatable/deprotonatable sites (e.g., carboxylates, amines, phenolic OH, thiols). Under the target pH, whether donor sites are in the coordination-competent protonation/charge state directly determines effective binding strength and the usable denticity.

2. The system may also include multiple competing processes: metals can undergo hydrolysis with OH⁻ to form hydroxo species, or be sequestered by competing ligands such as phosphate/carbonate/organic acids, proteins, and buffer components—thereby redistributing metals and changing the fraction of exchangeable species.

3. Therefore, what determines application performance is not “how strong it is nominally,” but whether, under the given system conditions (pH, competing ligands, ionic strength, etc.), the chelator can constrain the exchangeable/reactive metal pool (free + labile metal pool) within a preset acceptable window (a practical manifestation of the conditional stability K′).

4.Common classification dimensions for metal chelators

Dimension	What you are selecting	Why it matters
By denticity (denticity)	Monodentate / bidentate / polydentate	Determines how readily chelate rings form and the potential upper limit of stability; also affects geometric matching and the “grip posture”
By donor atoms and donor set (donor set)	O/N/S (and their combinations and arrangements)	Determines metal preference and resistance to competition (which metals are easier to capture, and which are easier to be outcompeted)
By scaffold form and preorganization	Linear/flexible vs rigid/macrocyclic	Influences thermodynamic stability and kinetic inertness (reversible regulation vs locked encapsulation)
By acid–base behavior and charge (pKa/net charge)	Actual speciation under target pH	Determines donor-site availability, solubility/membrane permeability, and conditional constant K′K′K′ (whether it truly works in the system)
By application goal	“Masking/deactivation” vs “carrying/delivery/encapsulation”	Determines whether you aim to reduce activity, or to stably encapsulate and function at specific sites/conditions
By condition dependence and trigger mode	pH-triggered, redox-triggered, competitive-ligand-triggered, light-triggered, etc.	Determines whether you can achieve “controlled release/reversible replenishment/on-demand switching”
By target metal family	Ca/Mg; transition metals (Fe/Cu/Zn/Ni/Co…); Ln/An	Determines selectivity and anti-interference strategy: which metal must be captured, and which interferents are most problematic
By carrier form/phase	Solution-phase small molecules / soluble polymers / solid-phase resins (chelating resins, metal-capture materials)	Determines whether you regulate metal speciation in solution or physically separate/enrich/remove metals; also affects separation convenience, regenerability, and whether mobile small molecules are introduced

Notes:

1. Solid-phase chelating materials (resins/polymers) are commonly used in water treatment, engineering separations, sample pretreatment, and metal scavenging.

2. Compared with small-molecule chelators, they emphasize capacity (loading), selectivity, adsorption/desorption kinetics (mass transfer), regeneration conditions and lifetime, stability at the target pH/salinity, and whether there is functional-group leaching (cleanliness).

3. If you need to regulate the free + labile metal pool in solution → prioritize solution-phase systems. If you need to capture metals for easy separation/regeneration → prioritize solid-phase systems.

5.Three application mainlines: Where are chelators most used, and what problems do they solve?

Mainline	Typical scenarios & “pain points”	How chelators solve it	Common representatives / approaches (examples)
A Analytical & experimental: make data readable, comparable, and reproducible	Colorimetric/fluorescence/electrochemical backgrounds are skewed by trace metals; metal-catalyzed oxidation causes samples/reagents to drift over time; titration endpoints are unstable; in biochemical samples, metal-dependent enzymes/nucleases cause degradation	Use complexation to reduce the free + labile metal pool into a controllable window, lowering “unpredictable catalysis/interference”; when needed, use conditional stability K′ to evaluate the impacts of pH and competing ligands	EDTA/EGTA are commonly used to mask trace metals. If you want a true “metal buffer / set free metal activity (free metal),” you must prepare a calculable equilibrium based on known K′ and the metal–ligand ratio (not “adding a bit of EDTA equals buffering”). In complex matrices, still prioritize “effective at the target pH” (follow the K′ logic).
B Process & agriculture: make precipitation/scaling/nutrient availability manageable	Hardness ions cause scaling, precipitation, and clogging in heat exchange/irrigation; trace elements are prone to hydrolysis/precipitation and become “inactive” under alkaline conditions—especially Fe-deficiency chlorosis	Maintain metals in an available soluble form via complexation, reducing precipitation/scaling or postponing deposition risk into a more controllable condition window; in agriculture, this translates to “keeping micronutrients in an absorbable form”	Practical pH applicability of Fe chelates (commonly cited experience): Fe-EDTA is often used at lower pH (effectiveness drops noticeably above ~pH 6.5); Fe-DTPA is frequently cited as usable to ~pH 7–7.5; Fe-EDDHA can keep Fe available at higher pH (often cited to pH 9 or even higher), but is more expensive and more matrix-dependent.
C Medicine & imaging: promote clearance of harmful metals, or enable in-vivo stable encapsulation and delivery	Chelation therapy: reduce toxic metal burden such as lead (must follow guidelines and safety monitoring); imaging contrast agents: prioritize in-vivo stable coordination to minimize metal release, and incorporate risk management and disclosure for retention/deposition	Medical use emphasizes risk–benefit and evidence stratification; imaging use emphasizes stable encapsulation + minimizing release risk	Lead exposure: WHO Clinical Management of Lead Exposure guidance and CDC MMG both provide recommendations on when to consider chelation therapy under specific blood lead levels and clinical scenarios (a serious medical decision). MRI gadolinium contrast agents: EMA reviews confirmed tissue deposition; although harm to patients has not been proven, restrictions/suspensions were applied to some intravenous linear agents to reduce potential risk. FDA also issued safety communications emphasizing retention and requiring additional warnings/patient information.

Note: The pH applicability ranges in Mainline B are empirical values and can vary with water quality/matrix/competing ligands and dosage. Regulatory conclusions and implementation measures in Mainline C are time-sensitive; refer to the latest announcements from EMA/FDA and national competent authorities.

6.Boundary reminders

1. Medical boundary: chelation therapy is a serious medical intervention

“Chelation” should not be promoted as a wellness concept or generalized therapy. Any therapeutic use and decision-making should follow formal medical practice and evidence-based guidelines; be alert to exaggerated claims and health risks from unapproved products.

2. Environmental boundary: stronger chelation does not automatically mean safer

In soils/environmental media, strong chelators may increase heavy-metal solubility and mobility, raising leaching and groundwater risks. Scenario-specific trade-offs and risk controls are required for remediation/extraction/risk assessment uses.

3. Method boundary: you cannot rely on “nominal strength” alone—validation is required

Chelation performance depends strongly on the matrix and boundary conditions. Selection should first clarify the goal (masking/buffering/encapsulation/separation), and then validate—via controls (blank, metal add-back, competitive challenge, etc.)—whether the “exchangeable metal pool” is constrained within the preset window.

7.Metal Chelator Product Navigation Table｜Quickly locate Tables 1–6 by “research task / experimental scenario”

Research task / experimental need	Recommended table to check first	Why start with this table	Common follow-up links (what you’ll typically check next)
Build general DOTA-type probes: want a “broadly compatible, most literature-standard” macrocyclic chelation platform (decide later how to attach to your molecule)	Table 1 (DOTA/DOTA-GA/DOTAM/DO3A)	DOTA/DOTA-GA are the most widely used “general chassis.” This table concentrates key selection info in one place: handles (NH2/NCS/Mal/PEG/Click), activated forms (NHS/PNP/anhydride), protected forms (tBu), and SPPS building blocks	Prefer Ga rapid labeling or smaller footprint → Table 3; need DTPA series / linear chelation → Table 5; specific systems (HBED/DFO/RESCA) → Table 6
Protein/antibody labeling (random lysine labeling): attach chelator to proteins via “amine reaction” (common for antibody conjugation)	Table 1 + Table 3 + Table 5 (depending on your chelation module)	The key is to find “amine-coupling handles” such as p-SCN (isothiocyanate) or NHS activated esters; Tables 1/3/5 cover the mainstream amine-reactive handles for DOTA / NOTA-NODAGA / DTPA	For thiol site-specific labeling → see Maleimide entries in Table 1/3/5; for Zr-89 immuno-PET → Table 6 (DFO) is often linked
Site-specific protein/peptide labeling (Cys thiol): want more controllable conjugation (maleimide–thiol)	Table 1 + Table 3 + Table 5	Maleimide is the most common thiol-selective handle: Table 1 has Maleimide-DOTA/DOTA-GA; Table 3 has Maleimide-NOTA/NODAGA; Table 5 has Maleimide-DTPA	If you also need click assembly → alkyne/azide entries in Table 1/3; for materials/Au-surface anchoring → Table 1 (TA-DOTA-GA, DO3A-Thiol)
Click-assembled probes (modular build): you already have azide/alkyne substrates and want to “snap on” a chelation module like LEGO	Table 1 + Table 3	The key is to find alkyne (propargyl/butyne) or azide (N3) handles: Table 1 covers DOTA click series; Table 3 covers NOTA/NO2A/NODAGA click systems	If you want “couple first, deprotect, then chelate” → prioritize tBu protected forms (Table 1/3); if you want “ready-to-use terminal modules” → choose deprotected/directly chelatable items (e.g., Table 1 Butyne-DOTA)
Directly introduce a chelator during SPPS peptide synthesis: install a chelation module at a fixed position on the peptide	Table 1	Table 1 includes clear peptide synthesis building blocks (e.g., Fmoc-Lys-DOTA) and DOTA protected/activated forms; it matches SPPS workflows most completely	If you later want a smaller module (NOTA/NODAGA) → Table 3; if you need linear DTPA → Table 5
Ga systems (especially Ga labeling / rapid labeling): want a commonly used platform more oriented to Ga(III) (NODAGA/NOTA/NODA, etc.)	Table 3	Table 3 concentrates the cores, activated forms, handles, and protected forms of NODAGA / NODA / NOTA / NO2A (including R/S stereochemical controls)—the most common “selection pool” for Ga systems	If you are already on a DOTA workflow but want a control/switch → Table 1; if you use HBED-CC route → Table 6
Need stereochemical controls / systematic optimization: run parallel comparisons of R/S or different configurations (biodistribution/complexation kinetics/labeling efficiency)	Table 2 + Table 3	Table 2 focuses on R/S and protected forms of DOTAGA/DOTAGA2; Table 3 also includes (R)/(S)-NODA-GA, (R)/(S)-Bn-NOTA, etc.—most direct for “same scaffold, stereochemical controls”	If your core system is on the DOTA side → Table 1; if you want a more “systematic” control set → link with Table 4 (core building blocks) to build a customized series
“Customize from the core”: want to build NOTA/NODA/TRAP macrocycles yourself (route development / structure library)	Table 4 + Table 3	Table 4’s TACN protected forms / monoacetate are key core building blocks for NOTA/NODA/TRAP; Table 3 provides many corresponding finished handles and protected forms, enabling “from building block → finished product” combinations	To modify from a DOTA core → Table 1 (multiple protected intermediates available)
Need linear chelators (DTPA family) or want “controls vs DOTA/NOTA” in the same project (linear vs macrocycle comparison)	Table 5	Table 5 centers on DTPA and covers common bio-conjugation handles (Maleimide/SCN/NH2-Bn) plus tBu protected forms—suitable for linear chelation systems and comparison to macrocycles	If you also need general macrocyclic chassis → Table 1/3; for more specialized systems (DFO/HBED/RESCA) → Table 6
Zr-89 immuno-PET (or strong high-valent metal coordination systems): antibody tracing with the classic matched ligand	Table 6	Table 6 includes specialized systems such as p-SCN-Bn-deferoxamine (DFO) that are highly classic in immuno-tracing; these tasks typically do not start from DOTA/NOTA	If your antibody conjugation strategy is amine-based → you will still often cross-check p-SCN/NHS in Table 1/3/5 for controls; for other metal systems → Table 1/3
Specific methodology / specific ligand systems: HBED-CC, RESCA (including activated ester / maleimide handles)	Table 6	If your protocol explicitly specifies HBED-CC or RESCA (e.g., certain labeling strategies/literature routes), select the “same system, same handle” directly in Table 6 to avoid cross-system substitution that shifts labeling conditions and stability	If you need to attach it to proteins/peptides → link with Table 1/3/5 to compare handle strategies (NHS/SCN/Mal/Click)
Demetallize buffers/samples; suppress metal-dependent side reactions: need a “clean background” in biochemical/analytical/reaction systems	Table 6	EDTA working solutions in Table 6 are the most general “system metal control” tools: chelate trace metals, inhibit metal-dependent enzymes/side reactions, improve reproducibility	If you further need the chelation probe itself → return to Table 1/3/5 to select “conjugatable chelation modules”

Table 1｜DOTA / DOTA-GA / DOTAM / DO3A Series (Functional Handles + Activated Forms + Protected Forms)

Category	Aladdin Cat. No.	Name	CAS No.	Spec or Purity	Product features & applications
Bifunctional chelator | DOTA-GA (Maleimide, thiol coupling)	D1424098	Maleimide-DOTA-GA	1800229-46-2	≥99%	DOTA-GA macrocyclic chelation platform + maleimide: for site-specific conjugation to cysteine thiols on proteins/peptides/antibodies, enabling probes that stably chelate radiometals/paramagnetic metals (PET/SPECT imaging, targeted radiotherapy, MRI contrast precursors, etc.).
Thiol surface anchoring | TA-DOTA-GA (gold-nanomaterial labeling)	T1510709	TA-DOTA-GA	_	_	DOTA-GA bearing a disulfide ring (lipoic-acid-like) anchoring group: used for labeling/functionalizing gold nanoparticles or gold surfaces while retaining a DOTA site for metal chelation and imaging/tracing probe construction.
Bifunctional chelator | p-NCS-Bz-DOTA-GA (amine coupling, antibody/protein labeling)	P1449951	p-NCS-Bz-DOTA-GA	2194580-71-5	≥99%	para-isothiocyanate (NCS) benzyl linker + DOTA-GA: forms stable thiourea bonds with lysine amines on proteins/antibodies; a common “DOTA-functionalization” linkage strategy in radiometal (PET/SPECT) and MRI probe construction.
Bifunctional chelator | NH2-DOTA-GA (amine handle, general conjugation)	N1423930	NH2-DOTA-GA	1639843-65-4	_	Primary-amine-terminated DOTA-GA: rapidly couples with activated carboxylates/NHS esters, etc.; commonly used to install DOTA-GA onto small-molecule targeting ligands, peptides, or polymers, followed by radiometal labeling (theranostics/tracing).
Activated coupling reagent | DOTA-GA anhydride (direct amide linkage)	D1500808	DOTA-GA anhydride	1375475-53-8	Moligand™, 10 mM in DMSO	Anhydride-activated DOTA-GA: reacts directly with amine substrates to introduce the DOTA-GA chelation module; suitable for rapid conjugation to small molecules/peptides, then proceeding to metal chelation and radiolabeling workflows.
Bifunctional chelator | DOTA (p-SCN-Bn, amine coupling/protein labeling)	P774027	p-SCN-Bn-DOTA	127985-74-4	≥95%	para-isothiocyanate (SCN) benzyl-DOTA: conjugates to lysine amines on proteins/antibodies to form stable thiourea bonds; widely used to build bioconjugates that chelate radiometals/paramagnetic metals (PET/SPECT, targeted radiotherapy, MRI probe precursors).
Bifunctional chelator | DOTA (Maleimide, thiol coupling)	M649343	Maleimide-DOTA	1006711-90-5	≥99%	Maleimide-DOTA: used for thiol-selective conjugation (cysteine, thiolated oligonucleotides/peptides, etc.) to build bioconjugates for radiometal chelation; commonly used in site-specific labeling.
Bifunctional chelator | DOTA (primary amine handle, amide coupling)	A1444009	4-Aminobutyl-DOTA	753421-63-5	_	Primary-amine-terminated DOTA: amidation with NHS esters/activated carboxylic acids as a general entry to “attach DOTA onto your molecule”; widely used for DOTA-functionalization of peptides/small-molecule targeting ligands followed by radiometal labeling.
Spacer / PEGylation | NH2-PEG4-DOTA	N1423993	NH2-PEG4-DOTA	2090232-34-9	_	PEG4 spacer + terminal amine + DOTA: improves water solubility, reduces nonspecific adsorption, and relieves steric hindrance; facilitates attaching DOTA to biomolecules/nanomaterials followed by radiometal or paramagnetic metal complexation.
Activated coupling reagent | DOTA-NHS (fast amine coupling)	D647052	DOTA-NHS ester	170908-81-3	≥95%	NHS-activated DOTA: rapidly forms amide bonds with amines (peptides/proteins/small molecules), improving coupling efficiency and reproducibility; followed by metal chelation/radiolabeling.
Activated coupling reagent | DOTA-NHS (tris-tBu protected)	D649891	DOTA-mono-NHS tris (t-Bu ester)	819869-77-7	≥98%	NHS-activated DOTA (protected form): for fast amine coupling (peptides/proteins/small-molecule amines), improving coupling efficiency and reproducibility; deprotect afterward and proceed to metal chelation/radiolabeling.
Activated coupling reagent | DOTA-PNP (p-nitrophenyl ester, amine coupling)	D1510721	DOTA-PNP	474424-15-2	_	p-Nitrophenyl (PNP) ester-activated DOTA: forms amide bonds with amine substrates; similar to NHS but often convenient for monitoring reaction progress (p-nitrophenol leaving group can indicate conversion).
Click handle | DOTA (azide, copper-free / click coupling)	A1424094	Azido-mono-amide-DOTA	1227407-76-2	≥99%	Azide-handle DOTA: for SPAAC (cyclooctyne–azide, copper-free click) or CuAAC (alkyne–azide click) to attach DOTA to targeting ligands/dyes/polymers for radiometal imaging/therapy probe construction.
Click handle | Butyne-DOTA (alkyne handle, deprotected / directly chelatable)	B1424088	Butyne-DOTA	2125661-62-1	≥98%	Alkyne-handle DOTA (non-tBu protected): can be used directly for click coupling, then metal chelation/radiolabeling; suitable as a “ready-to-use terminal” DOTA-click module for rapid probe assembly.
Click-handle precursor | Propargyl-DOTA-tris(tBu)ester (terminal alkyne + protection)	P1423994	Propargyl-DOTA-tris(tBu)ester	911197-00-7	_	Terminal alkyne (propargyl) + DOTA tris-tBu protected form: for CuAAC click assembly with azide targets; deprotect afterward to obtain a metal-chelatable DOTA probe.
Click-handle precursor | Butyne-DOTA-tris(tBu)ester (alkyne + protection)	B1424038	Butyne-DOTA-tris(t-butyl ester)	2125661-54-1	_	Alkyne handle + protected DOTA: for click coupling to azide targets/materials; protected form facilitates synthesis/purification, then unified deprotection followed by metal chelation.
Click-handle precursor | N3-DOtBu3 (azide + tBu protection)	N1510701	N3-DOtBu3	1881221-43-7	_	Azide handle + protected macrocyclic chelator precursor: suitable for click coupling first, then unified deprotection followed by metal chelation/radiolabeling; commonly used in modular radiotracer assembly.
Click-handle precursor | Azido-…-DOTA (tris-tBu protection)	A1440801	Azido-mono-amide-DOTA-tris(t-Bu ester)	1402795-92-9	_	Azide handle + protected DOTA: supports the modular workflow “click first → deprotect → chelate/radiolabel”; used to rapidly generate a series of isotope/ligand control probes.
Bifunctional chelator precursor | DOTA (tris-tBu protected) + Maleimide	T679321	Maleimido-mono-amide-DOTA-tris (t-Bu ester)	1613382-10-7	≥97%	“Conjugatable maleimide + protected DOTA” all-in-one precursor: conjugate to thiol biomolecules first, then remove t-Bu protecting groups to free carboxylates for metal chelation/radiolabeling; suitable for peptide/protein site-specific DOTA labeling routes.
Bifunctional chelator precursor | 2-Aminoethyl-…-DOTA (tris-tBu protection)	A646441	2-Aminoethyl-mono-amide-DOTA-tris(t-Bu ester)	173308-19-5	≥98%	DOTA protected form with a “2-aminoethyl” linker: provides more flexible spacing and a reactive amine site for coupling with activated carboxylates/isothiocyanates, etc.; commonly used in peptide/small-molecule probe construction.
Bifunctional chelator precursor | 4-Aminobutyl-DOTA (tris-tBu protection)	T679322	4-Aminobutyl-DOTA-tris (t-butyl ester)	1402393-59-2	≥97%	4-Aminobutyl linker + protected DOTA: amine used for coupling; t-Bu protection aids synthesis and storage; fits the standard workflow “install onto ligand/material → deprotect → chelate metal.”
Amino acid / peptide synthesis building block | Fmoc-Lys-DOTA (protected form)	F1446090	Fmoc-L-Lys-mono-amide-DOTA-tris(t-Bu ester)	479081-06-6	_	SPPS lysine building block for direct DOTA installation: installs DOTA at a defined site on the peptide (often the Lys side chain), followed by deprotection and metal chelation/radiolabeling (a common route for targeted peptide probes).
Common building block for synthesis/peptide labeling | DOTA-tris (t-Bu ester)	T162093	DOTA-tris (t-Bu ester)	137076-54-1	≥97%	One of the most commonly used protected building blocks for DOTA-functionalization: easy to handle in solution/solid-phase synthesis; terminal position can be activated for coupling to amines (e.g., peptide Lys), followed by TFA deprotection and metal chelation/radiolabeling.
Synthetic intermediate | DOTA-di(tBu) (semi-protected, site-selective functionalization)	D1423986	DOTA-di(tBu)ester	913542-71-9	_	DOTA di-tBu protected form: used in stepwise routes where part of the carboxylates remain available for early coupling/modification and the rest are handled later; suitable for site-selective derivatization and probe library construction.
Synthetic intermediate | Fully protected DOTA (tBu ester)	B1022177	DOTA-tertra(tBu-ester)	585531-74-4	≥98%	Fully t-Bu protected DOTA building block: a standard intermediate for the general workflow “synthesize/couple first → unified deprotection → metal chelation”; suitable for solid-phase or solution-phase construction of radiometal probes.
Synthetic intermediate | Partially protected DOTA (mixed ester, site-selective functionalization)	T1510715	tri-tert-butyl 2,2',2''-(10-(2-ethoxy-2-oxoethyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetate	825625-07-8	_	Mixed protection DOTA precursor (three t-Bu + one ethyl ester): enables stepwise functionalization under organic/solid-phase conditions (selective deprotection/grafting), used to build customized bifunctional DOTA chelators and probe libraries.
Synthetic intermediate | Protected cyclen-polycarboxylate (DOTA/DOTAGA precursor)	T1510696	1-(tert-butyl) 5-methyl (R)-2-(1,4,7,10-tetraazacyclododecan-1-yl)pentanedioate	2735708-28-6	_	Chiral/protected macrocyclic intermediate: used to synthesize chiral or directionally substituted DOTA/DOTAGA-type bifunctional chelators (later introducing side chains/linkers/coupling groups), serving radiopharmaceutical and coordination-chemistry route development.
Synthetic intermediate | Protected cyclen-polycarboxylate (multi tBu arms)	T1510699	1-(tert-butyl) 5-methyl (R)-2-(4,7,10-tris(2-(tert-butoxy)-2-oxoethyl)-1,4,7,10-tetraazacyclododecan-1-yl)pentanedioate	2735708-29-7	_	Macrocyclic precursor with multiple carboxylate arms protected as t-Bu esters: supports stepwise functionalization and coupling under organic/solid-phase conditions, then deprotection to yield metal-chelatable polycarboxylate chelators (often used for radiometal probe construction).
Chelator–pharmacophore conjugate | DOTA–drug/inhibitor-like probe (mechanism/tracing)	P1434315	DOTA-aminomethyl-Bz-D-Ala-boroPro	2715113-34-9	_	Conjugate linking DOTA to a “boronate/boroproline”-type pharmacophore fragment: used to integrate a chelation/tracing module into a bioactive molecule for imaging/distribution tracing or “same-scaffold control probes” in mechanistic studies (specific use depends on the target system of the boroPro fragment).
Macrocyclic chelator derivative | DOTAM series (property/stability tuning core)	D1424093	DOTAM-mono-acid	913528-04-8	≥98%	A DOTA tetra-amine macrocycle derivative featuring “amide-type (DOTAM) with one acid retained”: commonly used as an intermediate for further functionalization and for tuning coordination properties; used to build more customized metal complexes (e.g., modulating complexation kinetics/charge/hydrophilicity for imaging probes or coordination chemistry studies).
Synthetic intermediate | DO3A protected form (macrocycle tri-carboxylate precursor)	T162097	DO3A-tBu-ester	122555-91-3	≥93%(N)	DO3A (a reduced version of DOTA) t-Bu protected form: a key intermediate for DOTA/DO3A bifunctional chelators, enabling selective introduction of linkers/coupling groups; after deprotection, used for metal chelation (imaging/material labeling).
Sulfur handle | DO3A-Thiol (surface/site anchoring)	D1510713	DO3A-Thiol	865470-67-3	_	DO3A (reduced DOTA) + thiol: thiol can be used for maleimide coupling or surface anchoring (e.g., gold surfaces/nanomaterial modification), while DO3A chelates metal ions; commonly used in materials labeling and imaging probe development.

Table 2｜DOTAGA / DOTAGA2 Series (Protected Forms + Stereochemical Controls + Intermediates)

Category	Aladdin Cat. No.	Name	CAS No.	Spec or Purity	Product features & applications
Synthetic intermediate | DOTAGA-tetra (t-Bu ester) (fully protected)	D1312121	DOTAGA-tetra (t-Bu ester)	306776-79-4	≥98%	Fully protected DOTAGA: a key intermediate for DOTAGA-type bifunctional chelators, enabling installation of linkers/coupling groups first, followed by deprotection and metal complexation (radiometal tracing/therapy).
Synthetic intermediate | (R)-DOTAGA-tetra (t-Bu ester) (chiral)	O679292	(R)-DOTAGA-tetra (t-Bu ester)	817562-90-6	≥97%	Chiral, fully protected DOTAGA (R): used to build chiral DOTAGA-series chelators and their metal complexes, and to compare stereochemical effects on labeling efficiency, in vivo distribution/clearance, etc. (common in imaging/therapy probe development).
Synthetic intermediate | (S)-DOTAGA-tetra (t-Bu ester) (chiral)	D1510711	(S)-DOTAGA-tetra (t-Bu ester)	1023889-20-4	_	Chiral, fully protected DOTAGA (S): paired with the R-form for stereochemical controls; commonly used to systematically evaluate how ligand stereochemistry affects complexation and in vivo behavior.
Synthetic intermediate | DOTAGA4-(OtBu)4 (fully protected)	D1510707	DOTAGA4-(OtBu)4	_	_	Fully t-Bu-protected DOTAGA derivative: a typical “synthetic building block / protected core” that supports multi-step organic synthesis and site-specific introduction of linkers; after final deprotection, used for metal complexation and radiolabeling.
Synthetic intermediate | DOTAGA protected/esterified intermediate (Ben- protection / ester intermediate)	B1510703	Ben-DOTAGA-ethyl	2100279-84-1	_	DOTAGA-series (DOTA-GLA) protected/esterified intermediate: used for subsequent selective deprotection and installation of linkers/coupling groups, ultimately yielding bifunctional chelators capable of stable complexation with radiometals (e.g., Ga, Lu, Y, In, etc.).
Synthetic intermediate | DOTAGA/DOTA partially protected acid (for stepwise modification)	B1510717	4-(4,10-bis(2-(tert-butoxy)-2-oxoethyl)-7-(2-ethoxy-2-oxoethyl) -1,4,7,10-tetraazacyclododecan-1-yl)-5-(tert-butoxy)-5-oxopentanoic acid	2100279-75-0	_	Macrocyclic precursor with mixed protection on multiple arms while retaining one free acid site: enables continued installation of linkers/coupling groups while preserving one operable site; used to build DOTAGA/DOTA bifunctional chelators and systematic control series.
Macrocyclic chelator platform | DOTAGA2 (unresolved enantiomers / general)	D1510719	DOTAGA2	1049020-11-2	_	DOTAGA2 macrocyclic chelating ligand platform: for stable complexation with various metal ions (radiometals/paramagnetic metals), serving as a core ligand or control ligand in imaging/therapy probes and coordination-chemistry studies.
Macrocyclic chelator platform | DOTAGA2 (one chiral series member)	D1510705	(S)-DOTAGA2	2861938-89-6	_	Chiral DOTAGA2 chelating ligand: used to build metal complexes with specific stereochemistry and pharmacokinetic/distribution profiles (commonly in ligand screening and controls for imaging/tracer probe R&D).
Macrocyclic chelator platform | (R)-DOTAGA2 (stereochemical control)	R1445628	(R)-DOTAGA2	914639-15-9	_	Chiral DOTAGA2 (R): paired with the S-form/racemic form to assess stereochemical impacts on complexation kinetics, in vivo distribution, clearance, and related metrics (commonly used as radiopharmaceutical/probe controls).

Table 3｜NOTA / NODA / NODAGA / NO2A Series (Bioconjugation Handles + Click + Activated Forms + Protected Forms)

Category	Aladdin Cat. No.	Name	CAS No.	Spec or Purity	Product features & applications
Bifunctional chelator | NODA-GA (p-NCS-Bn, amine coupling / protein labeling)	P1423935	p-NCS-benzyl-NODA-GA	1660127-21-8	≥98%	Isothiocyanate (NCS)–benzyl–NODAGA: conjugates to lysine amines on proteins/antibodies to form thiourea linkages; commonly used to build bioconjugate probes for radiometal labeling (e.g., Ga) and related studies.
Bifunctional chelator | NODA-GA (Maleimide, thiol coupling)	M1424061	Maleimide-NODA-GA	1440903-11-6	_	Maleimide–NODAGA: for site-specific conjugation to cysteine thiols (peptides/proteins/thiolated materials), followed by metal complexation/radiolabeling; suitable for site-specific probe construction.
Bifunctional chelator | NODA-GA (primary amine handle, general conjugation entry)	N1423998	NH2-NODA-GA	1630114-57-6	≥95%	Primary-amine-terminated NODAGA: efficiently couples with NHS esters/activated carboxylates as a general “entry point” to attach NODAGA to your molecule; after conjugation, used for radiometal labeling and in vivo distribution tracing.
Activated coupling reagent | NODA-GA-NHS (fast amine coupling)	N1424040	NODA-GA-NHS ester	1407166-70-4	_	NHS-activated ester of NODAGA: enables efficient installation of the NODAGA chelation module onto amine-containing substrates; commonly used in standard build workflows for Ga-labeled PET tracers.
Bifunctional chelator | (R)-NODAGA-NH2 (primary amine handle)	N1510723	(R)-NODAGA-NH2	2241359-94-2	_	Primary-amine-terminated (R)-NODAGA: couples with activated carboxylates/isothiocyanates, etc., as a general entry point to attach NODAGA; used afterward for metal complexation and radiolabeling.
Bifunctional chelator | NODA (NCS–aryl, amine coupling)	N1423983	NCS-MP-NODA	1374994-81-6	≥98%	NCS–aryl linker + NODA: for amine coupling to proteins/peptides/small molecules bearing amines; installs the NODA chelation module onto targeting ligands for subsequent metal complexation and tracer experiments.
Synthetic intermediate | (S)-NODA-GA protected form (common platform for Ga and related metals)	T679298	(S)-NODA-GA-tris(t-Bu ester)	438553-50-5	≥97%	(S)-NODA-GA tris-tBu protected form: NODAGA is widely used for rapid labeling and stable complexation of metals such as Ga(III); the protected form supports coupling first, then deprotection for metal complexation (a common PET tracer workflow).
Synthetic intermediate | (R)-NODA-GA protected form (stereochemical control)	R1424002	(R)-NODA-GA-tris(t-Bu ester)	1252799-47-5	_	(R)-NODA-GA tris-tBu protected form: used for stereochemical controls and systematic structure optimization; common in ligand screening and structure–property comparisons for Ga-labeling systems.
Synthetic intermediate | NODA-GA tris-tBu protected form (general)	N1451776	NODA-GA-tris(t-Bu ester)	1190101-34-8	≥98%	NODAGA tris-tBu protected form: facilitates coupling/modification first, then deprotection; commonly used for probe construction and library synthesis in Ga and related metal-labeling systems.
Macrocyclic chelator core | NOTA (basic ligand)	T405110	NOTA	56491-86-2	≥98% (HPLC)	NOTA (1,4,7-triazacyclononane-1,4,7-triacetic acid), a classic macrocyclic chelator: widely used for stable complexation with various metals (especially small-radius trivalent metals), serving as a foundational ligand for radiometal labeling, coordination chemistry, and analytical controls.
Activated coupling reagent | NOTA-NHS (fast amine coupling)	N1424108	NOTA-NHS ester	1338231-09-6	≥90%	NHS-activated NOTA: rapidly couples with amines (peptides/proteins/small molecules) to introduce the NOTA chelation module; followed by metal complexation/radiolabeling.
Activated coupling reagent | NOTA-PNP (p-nitrophenyl ester, amine coupling)	N1510734	NOTA-PNP	1402571-17-8	_	PNP-activated NOTA: forms amide bonds with amine substrates to install the NOTA chelation module; usable for probe construction and rapid coupling-condition screening.
Bifunctional chelator | p-SCN-Bn-NOTA (amine coupling / protein labeling)	P1510726	p-SCN-Bn-NOTA	147597-66-8	_	SCN–benzyl–NOTA: conjugates to lysine amines on proteins/antibodies to build NOTA-functionalized bioconjugates; used for stable complexation of radiometals/paramagnetic metals in imaging/tracing studies.
Bifunctional chelator | (R)-p-NH₂-Bn-NOTA (primary amine handle)	R1510730	(R)-p-NH₂-Bn-NOTA	1310812-52-2	_	para-Amino–benzyl–NOTA (R): terminal primary amine couples with NHS esters/activated carboxylates; the benzyl linker provides spacing, facilitating construction of protein/small-molecule probes and subsequent metal complexation/labeling.
Bifunctional chelator | NOTA (p-NH₂-Bn, primary amine handle; chiral)	P1510740	(S)-p-NH₂-Bn-NOTA	142131-37-1	_	para-Amino–benzyl–NOTA (S): terminal primary amine supports coupling with activated carboxylates/NHS esters; the benzyl linker provides spacing, commonly used to build metal-labelable targeted probes and stereochemical controls.
Bifunctional chelator | NOTA (Maleimide, thiol coupling)	M1424105	Maleimide-NOTA	1295584-83-6	≥98%	Maleimide–NOTA: for site-specific conjugation to cysteine thiols (proteins/peptides/oligonucleotides, etc.), producing NOTA-functionalized bioconjugates; followed by metal complexation/radiolabeling.
Click-handle precursor | NOTA (alkyne + di-tBu protection)	P1423985	Propargyl-NOTA(tBu)2	1924677-40-6	_	Alkyne handle + protected NOTA: used in CuAAC click coupling to attach the NOTA chelation module to azide-functional targets/peptides/polymers; deprotect afterward for metal complexation/radiometal labeling workflows.
Synthetic intermediate | NOTA-bis(tBu) (semi-protected, site-selective functionalization)	A681090	NOTA-bis(t-Bu ester)	1161415-28-6	≥97%	NOTA di-tBu protected form: supports stepwise functionalization (use the remaining reactive site for grafting/coupling first, then unified deprotection for metal complexation), suitable for systematic derivatives and structural controls.
Synthetic intermediate | NOTA-bis(tBu) (semi-protected)	N1510744	NOTA-bis(t-Bu)ester	176446-05-2	≥95%	NOTA di-tBu protected form: supports the general workflow “couple/graft first → unified deprotection → metal complexation”; commonly used for probe library construction and structural controls.
Click-handle precursor | N3-NOtBu2 (azide + protected NOTA/NO2A derivative)	N1510732	N3-NOtBu2	1881221-41-5	_	Azide handle + di-tBu protected form: for modular routes “click assemble first → deprotect → metal complexation”; suitable for rapidly generating a series of control probes.
Click handle | NO2A-Butyne (alkyne handle, compact chelation platform)	N1424065	NO2A-Butyne	2089035-56-1	≥98%	NO2A (1,4,7-triazacyclononane-1,4-diacetic acid) + alkyne: enables CuAAC click attachment of a “compact chelation module” to azide targets; often used to compare size/charge/complexation-behavior differences versus NOTA/NODAGA.
Click handle | NO2A-Azide (azide handle, compact chelation platform)	N1510736	NO2A-Azide	2125661-92-7	≥98%	NO2A + azide: for SPAAC/CuAAC click assembly to build compact chelation probes; useful as a control route for “shrinking chelator size / tuning PK.”
Click-handle precursor | NO2A-Butyne-bis(tBu) (alkyne + protected form)	N1424008	NO2A-Butyne-bis (t-Butyl ester)	2125661-91-6	_	Alkyne handle + NO2A di-tBu protected form: suited for modular routes “click first → deprotect → chelate metal”; protected form is more convenient for synthesis/purification and storage.
Synthetic intermediate | NO2A protected form (precursor for compact chelation platform)	T1279877	NO2A(tBu)	174137-97-4	_	NO2A tBu protected form: used for stepwise functionalization and linker installation; after deprotection yields NO2A-type chelators for metal complexation and probe controls (commonly used for size/charge comparisons against NOTA/NODAGA).

Table 4｜TACN / TRAP Core Scaffolds and Building Blocks (for constructing NOTA/NODA/TRAP, etc.)

Category	Aladdin Cat. No.	Name	CAS No.	Spec or Purity	Product features & applications
Synthetic building block | TACN protected form (macrocyclic core)	D1510738	DiBoc-TACN	174138-01-3	≥95%	Di-Boc-protected TACN (1,4,7-triazacyclononane): a key core intermediate for the NOTA/NODA/TRAP macrocyclic chelator family, used for subsequent installation of acetate/phosphonate arms and introduction of conjugation handles.
Synthetic building block | TACN monoacetate (protected form)	T1510742	[1,4,7]Triazonan-1-yl-acetic acid tert-butyl ester	174137-99-6	_	TACN monoacetate arm, tBu-protected building block: used to introduce the remaining acetate arms or linkers (to make NOTA/NODA, etc.), supporting site-selective modification and systematic syntheses.
Macrocyclic chelator platform | TRAP (fast-labeling ligand)	T1423933	TRAP	1242003-07-1	_	TRAP-type macrocyclic chelating ligand: known for fast labeling kinetics and suitability for rapid radiometal labeling workflows; commonly used in quick radiometal imaging-probe labeling, methodological controls, and process-window evaluation.

Table 5｜DTPA / Polyamine–Polyacetate Series (Bioconjugation Handles + Protected Forms/Precursors)

Category	Aladdin Cat. No.	Name	CAS No.	Spec or Purity	Product features & applications
Bifunctional chelator | DTPA (Maleimide, thiol coupling)	M1510746	Maleimide-DTPA	180152-82-3	≥95%	Maleimide–DTPA: for site-specific conjugation to cysteine thiols to build DTPA-functionalized bioconjugates; commonly used to chelate paramagnetic metals (e.g., Gd) or radiometals (e.g., In) for imaging/tracing.
Bifunctional chelator | DTPA (SCN, amine coupling / protein labeling)	S1510750	SCN-DTPA	117499-23-7	_	Isothiocyanate–DTPA: conjugates to lysine amines on proteins/antibodies to form thiourea bonds; commonly used to prepare protein conjugates capable of chelating metals (e.g., Gd, In) for imaging/tracing controls.
Bifunctional chelator | DTPA (p-SCN-Bn, amine coupling / protein labeling)	I983778	p-SCN-Bn-DTPA	102650-30-6	≥95%	SCN–benzyl–DTPA: conjugates to lysine amines to prepare DTPA-functionalized proteins/antibodies; commonly used for metal chelation followed by in vivo biodistribution tracing or contrast-related methodologies.
Bifunctional chelator | DTPA (p-NH2-Bn, primary amine handle)	P1510754	p-NH2-Bn-DTPA	102650-29-3	≥95%	para-Amino–benzyl–DTPA: terminal primary amine couples with activated carboxylates/NHS esters to install the DTPA chelation module onto targeting ligands/materials; followed by metal complexation for imaging/tracing.
Bifunctional chelator | DTPA (Bn-NH2 handle + partial esterification / tuning)	N1510752	NH2-Bn-DTPA-Me	126216-34-0	_	DTPA derivative bearing a benzyl primary-amine handle (as a methyl ester form): provides a conjugation site and tunes reactivity/solubility via esterification; used as a chelatable probe or intermediate for further activation/deprotection.
Synthetic intermediate | DTPA-tetra(tBu) (fully protected)	B1339795	DTPA-tetra(t-Bu erter)	174267-71-1	≥99%	Fully tBu-protected DTPA: a common synthetic intermediate for DTPA-type bifunctional chelators and contrast/tracing ligands; enables coupling first, then unified deprotection and metal complexation.
Synthetic intermediate | DTPA-tetra(tBu) (fully protected)	D1423989	DTPA-tetra(tBu)ester	180152-83-4	≥95%	Fully tBu-protected DTPA: functionally similar to the entry above (route/supply differences); used for stepwise derivatization followed by unified deprotection to proceed to metal complexation/labeling.
Bifunctional chelator precursor | Polyamine–tetraacetate (para-aminoaryl handle, tBu protected)	T1510748	tetra-tert-butyl 2,2',2”,2”'-((3-(4-aminophenyl)propane-1,2-diyl)bis(azanetriyl))tetraacetate	143106-46-1	_	“para-Aminoaryl” conjugation handle + tetraacetate arms (tBu protected): enables derivatization/grafting via the aniline site first, then deprotection to yield a polyamine–polyacetate chelator capable of metal complexation; suitable as a multidentate coordination module for materials/probes.

Table 6｜Other Chelation Systems (HBED-CC / RESCA / Deferoxamine / EDTA)

Category	Aladdin Cat. No.	Name	CAS No.	Spec or Purity	Product features & applications
Synthetic intermediate | HBED-CC protected form (ligand platform for Ga and related metals)	H1455653	HBED-CC-tris (tert-butyl ester)	2097123-80-1	≥98%	HBED-CC tris-tBu protected form: supports conjugation/derivatization with targeting ligands first, then deprotection for metal complexation; HBED-CC is very common in radiometal (especially Ga) imaging probes.
Activated coupling reagent | RESCA (TFP activated ester)	H1455723	(±)-H3RESCA-TFP	1919794-40-3	≥98%	TFP (tetrafluorophenyl) activated ester of RESCA: enables efficient coupling to amine substrates to install the RESCA chelation module; commonly used in metal complexation/labeling systems requiring mild conditions (especially in probe construction related to Al–F radiolabeling methodologies).
Chelator platform | RESCA (free acid)	H1510756	(±)-H3RESCA-OH	1919794-37-8	≥95%	RESCA free-acid ligand: used to chelate metals and serve as a core ligand for subsequent derivatization/conjugation; commonly used as the “ligand itself/control” in radiolabeling and imaging-probe methodology studies.
Chelator platform | RESCA (specific stereochemical form / control)	H1510758	(±)-(S-)H3RESCA-OH	_	_	RESCA (annotated with a specific stereochemical form): used as a control versus racemate/other stereochemical forms to assess how stereochemistry affects coupling, complexation, and in vivo behavior (commonly used in probe optimization).
Bifunctional chelator | RESCA (Maleimide, thiol coupling)	H1510760	(±)-H3RESCA-Mal	_	_	Maleimide–RESCA: for site-specific conjugation to cysteine thiols, building bioconjugate probes for metal complexation/radiolabeling (site-specific labeling scenarios).
Bifunctional chelator | RESCA (Maleimide, thiol coupling)	M1510762	Mal-RESCA	_	_	Maleimide–RESCA (same-use entry): for thiol coupling followed by metal complexation/radiolabeling; suitable for parallel comparisons of “same biomolecule, different chelation modules.”
Bifunctional chelator | Deferoxamine (p-SCN-Bn, amine coupling; commonly used for Zr labeling)	B1249216	p-SCN-Bn-deferoxamine	1222468-90-7	≥98%	SCN–benzyl–deferoxamine (DFO): conjugates to lysine amines on proteins/antibodies; DFO is a classic hydroxamate chelator, commonly used to chelate high-valent metals (a very common build route in immuno-imaging/tracing).
Basic chelator | EDTA (buffer/sample demetallization)	E196386	EDTA	60-00-4	0.5 M EDTA solution (pH 8.0)	General-purpose chelator working solution: chelates trace metals such as Ca²⁺/Mg²⁺/Fe³⁺. Common uses include inhibiting metal-dependent enzymes/nucleases, quenching metal-catalyzed side reactions, removing metal contamination, and preparing metal-free buffers and protecting samples.

For more related articles, please see below:

Chelating Agents